JP4958478B2 - Method for producing aluminum electrode foil for electrolytic capacitor - Google Patents

Description

  The present invention relates to an aluminum electrode foil for electrolytic capacitors. Furthermore, this invention relates to the aluminum electrode foil for electrolytic capacitors which can achieve a high electrostatic capacitance and easy workability.

  The aluminum foil can be etched to form an etching pit (also referred to as an etch pit, a tunnel pit, or a corrosion hole), thereby increasing the surface area. And the surface is anodized to form an oxide film, which functions as a dielectric. For this reason, various aluminum electrode foils for electrolytic capacitors suitable for the application can be manufactured by etching the aluminum foil and forming dielectric films on the surface with various voltages according to the operating voltage.

  The etching pit formed by the etching process is processed into a shape corresponding to the anodic oxidation voltage.

  Specifically, it is necessary to form a thick oxide film for a medium-high voltage capacitor application. For this reason, in order to prevent the etching pits from being filled with such a thick oxide film, the aluminum pits for medium- and high-pressure anodes are mainly formed by direct-current etching so that the etching pit shape is a tunnel type and processed to a thickness corresponding to the voltage. Is done.

  On the other hand, for low-voltage capacitor applications, fine etching pits are required, and spongy etching pits are formed mainly by AC etching.

  In order to improve the capacity of the capacitor, it is effective to increase the surface area per unit area, and various etching treatments and various aluminum foils for etching treatment are manufactured.

  However, the electrode foil with the dielectric film formed on the surface area per unit area as described above becomes very fragile, resulting in poor bonding when the lead terminal is fixed to the electrode, or when winding in a small shape. May break.

  As a method for solving these problems, for example, Patent Documents 1 to 3 propose a method for securing strength by forming a dense region where an etching process is not performed on a part of an aluminum foil. However, these methods require a step of removing a part of the etched region or resist ink portion after etching, or a step of irradiating the surface of the aluminum foil with laser light having an appropriate energy and wavelength. There is a problem that it becomes complicated.

  Patent Document 4 proposes a method for securing strength by forming a dense region with a small etching pit density in a part of an aluminum foil. However, this method is effective for medium- and high-pressure anode aluminum foils whose tunnel pit shape is mainly formed by DC etching, but AC etching in which the etching pit density is not affected by the texture. It cannot be applied to low pressure anode or cathode aluminum foil.

Further, Patent Document 5 discloses a method of simultaneously reducing the capacitance and improving the strength by reducing the entire surface of the etched foil. However, although this method can improve the overall strength, it cannot be said that the desired strength of a specific part is sufficient.
JP-A-2-222517 JP-A-60-31217 JP-A 62-198112 JP 2005-290469 A Japanese Patent Laid-Open No. 10-189398

  Thus, any aluminum electrode foil according to the prior art is sufficient in terms of reducing the bonding failure when fixing the lead terminal and the failure failure when winding to a small shape while maintaining its capacitance. However, there is room for further improvement including ease of processing.

  Accordingly, a main object of the present invention is to provide an aluminum electrode foil for electrolytic capacitors that has both a good electrostatic capacity and excellent workability.

  As a result of intensive studies to solve the problems of the prior art, the present inventor has found that the above object can be achieved by producing an aluminum foil under specific conditions, and has completed the present invention.

That is, the present invention relates to the following method for producing an aluminum electrode foil for electrolytic capacitors.
1. A method for producing an aluminum electrode foil for electrolytic capacitors,
1) A first step of obtaining an aluminum ingot from molten aluminum,
2) A second step of homogenizing the aluminum ingot,
3) a third step of obtaining an aluminum foil by rolling the homogenized aluminum;
4) a fourth step of forming an etching pit region by etching the obtained aluminum foil;
5) A method for producing an aluminum electrode foil for electrolytic capacitors, comprising a fifth step of forming a striped or network-like dense region by compressing part of an etched aluminum foil.

  The aluminum electrode foil for electrolytic capacitors of the present invention provides an electrode foil excellent in workability while maintaining the same capacitance as the electrode foil obtained by the conventional method by controlling the density of the dense region. Can do.

  Moreover, in the manufacturing method of this invention, since a partial densification process can be performed by a comparatively simple method, the aluminum electrode foil for electrolytic capacitors of this invention can be produced efficiently.

1. Aluminum electrode foil for electrolytic capacitor Aluminum electrode foil for electrolytic capacitor of the present invention is
(1) The aluminum electrode foil has an etching pit region and a dense region,
(2) The dense region has a relative density of 1.2 times to 1.6 times that of the etching pit region, and an absolute density of 2.0 g / cm ³ or more.
It is characterized by that.

A) Composition of Etched Aluminum Electrode Foil for Electrolytic Capacitor The composition of the aluminum electrode foil for electrolytic capacitor is not limited, but in particular, the aluminum purity is 99 measured according to the method described in “JIS H2111”. The thing of the mass% or more is preferable. As such an aluminum foil, at least one significant or unavoidable impurity element of Pb, Si, Fe, Cu, Mn, Mg, Cr, Zn, Ti, V, Ga, Ni and B is blended within a necessary range. Or regulated aluminum foil is also included.

  The thickness of the aluminum foil before being etched is not limited, but is usually about 20 to 300 μm, and preferably 50 to 200 μm. The aluminum foil may be appropriately annealed in the course of production or in the final step, and the production method is not particularly limited regardless of whether it is a hard foil or a soft foil.

B) Etching pit region and dense region The etching pit region and the dense region may be formed at desired positions of the aluminum electrode foil for electrolytic capacitors. These regions may be formed on at least one surface of the aluminum electrode foil for electrolytic capacitors.

  The etching pit region is a region having a structure (corrosion structure formed by etching) called an etching pit (tunnel pit). This region is a region formed by an etching process. The area on the plane is the area denoted by reference numeral 1 shown in FIG. Further, the depth of the etching pit (depth from the foil surface) can be appropriately set according to the application, desired characteristics, and the like.

  In the aluminum electrode foil for electrolytic capacitors of the present invention, the surface portion is preferably composed of an etching pit region and a dense region. That is, it is usually preferable that the region other than the dense region is substantially composed of an etching pit region. Thereby, a high capacitance can be exhibited while maintaining a desired strength. Therefore, the following description will be made on the premise of an aluminum electrode foil for electrolytic capacitors comprising an etching pit region and a dense region.

  It is desirable that the dense region is formed as a portion that requires strength when anodized to form an electrode foil. Examples of the portion where strength is required include a portion that becomes a winding core portion, a lead terminal fixing portion, and the like.

  The shape of the dense region (planar projection shape) is not limited, and may be any of a polygon, a rectangle, a circle, an ellipse, an indefinite shape, and the like. Further, the dense region can be formed in a stripe shape or a mesh shape. In this case, the strength of the entire aluminum electrode foil for electrolytic capacitors can be increased.

  The total area of the dense region (planar total projected area) is generally preferably 30% or less, particularly 10% or less, of the aluminum electrode foil for electrolytic capacitors. That is, when the surface portion is composed of an etching pit region and a dense region, the dense region is preferably 30% or less and the etching pit region is 70% or more. If the total area exceeds 30% of the aluminum electrode foil for electrolytic capacitors, the electrostatic capacity of the resulting etching foil may be reduced. The lower limit value of the total area is not limited, but is usually 0.5% or more.

Further, the lower limit value of the area of one dense region is not particularly limited as long as it can be formed, but it may be generally 5 mm ² or more. The upper limit value may be 200 mm ² or less.

The absolute density (average value) of the dense region is 2.0 g / cm ³ or more. If the average value of the absolute density is smaller than 2.0 g / cm ³ , the dense region may not have sufficient strength. Moreover, the upper limit of the absolute density of the dense region is 2.7 g / cm ³ .

  The relative density (average value) of the dense region is 1.2 times to 1.6 times, preferably 1.4 times to 1.6 times that of the etching pit region. If the average value of the relative density is smaller than 1.2 times the surrounding area, the dense region does not have sufficient strength and, for example, the contact resistance may increase when the lead terminal is fixed.

2. Manufacturing method of aluminum electrode foil for electrolytic capacitors The manufacturing method of the aluminum electrode foil for electrolytic capacitors of the present invention is not limited as long as desired etching pit regions and dense regions can be formed. For example, there is a method in which the entire surface is first etched to form an etching pit region, and then a part thereof is made into a dense region by mechanical processing.

  In particular, in the present invention, the method 1) can be more suitably employed. More specifically, for example, 1) a first step of obtaining an aluminum ingot from molten aluminum, 2) a second step of homogenizing the aluminum ingot, and 3) rolling the homogenized aluminum into aluminum. Third step for obtaining foil, 4) Fourth step for forming an etching pit region by etching the obtained aluminum foil, and 5) Second step for forming a dense region by compressing a part of the etched aluminum foil. By the method including five steps, an etched aluminum electrode foil for electrolytic capacitors can be suitably obtained.

1) First Step In the first step, an aluminum ingot is obtained from molten aluminum. The molten aluminum is the same as in 1. A molten metal having the composition described in (1) may be prepared. For example, an aluminum ingot can be produced by a known method such as semi-continuous casting using a molten metal having such a composition.

2) Second step In the second step, the aluminum ingot is homogenized. The temperature of the homogenization treatment is not limited, but it may be usually about 450 to 660 ° C. The time for the homogenization process may be set as appropriate according to the temperature of the homogenization process, the size of the aluminum ingot, and the like.

3) Third Step In the third step, an aluminum foil is obtained by rolling the homogenized aluminum. The rolling conditions can be appropriately set according to, for example, desired characteristics, aluminum composition, and the like. For example, an aluminum foil having a thickness of 50 to 200 μm can be obtained by making the thickness about 2 to 10 mm by hot rolling and then performing cold rolling. Moreover, you may obtain by annealing about 250-600 degreeC in the middle or after cold rolling as needed.

4) Fourth Step In the fourth step, an etching pit region is formed by etching the obtained aluminum foil. Thereby, an etching pit region is formed on the entire surface of the aluminum foil (etched aluminum foil).

  The etching method is not particularly limited, and may be performed according to a known method. For example, primary etching, secondary etching, and tertiary etching may be performed. Each processing condition may be as follows, for example, but is not limited thereto.

Primary etching The etching solution used in the primary etching process is not limited, and a known etching solution such as an acid aqueous solution containing hydrochloric acid, sulfuric acid, phosphoric acid, nitric acid, or the like can be used. The concentration of the etching solution is not particularly limited, but is usually set to 1 to 10 mol / L, preferably 3 to 8 mol / L. The temperature of the etching solution is not particularly limited, but a preferable solution temperature is 30 to 70 ° C. If the liquid temperature is high, the reaction is promoted, which is preferable. However, if the temperature is too high, the reaction is too fast, and the foil surface is so melted that it becomes difficult to form uniform initial pits.

The primary etching is generally performed by alternating current (AC). In that case, the current density is generally preferably about 0.3 to 1 A / cm ² . The treatment time is usually about 2 to 20 minutes.

Secondary etching The secondary etching process mainly adjusts etching pits (etching pit diameter, etc.). For example, normal chemical etching may be performed using the etching solution listed in the primary etching. The immersion time can be appropriately set within a range of usually about 30 seconds to 10 minutes.

Tertiary Etching Tertiary etching is mainly performed for the growth of etching pits toward the center of the foil.

  The etching solution used in the tertiary etching process is not limited. For example, a known etching solution such as an acid aqueous solution containing hydrochloric acid, sulfuric acid, phosphoric acid, nitric acid, or the like can be used. The concentration of the etching solution is not particularly limited, but is usually set to 1 to 10 mol / L, preferably 3 to 8 mol / L. The temperature of the etching solution is not particularly limited, but a preferable solution temperature is 20 to 60 ° C. If the liquid temperature becomes high, the reaction is promoted, which is preferable. However, if the temperature is too high, the reaction becomes too fast and it becomes difficult to maintain a uniform etching pit diameter.

The tertiary etching is generally performed by alternating current (AC). In that case, the current density is generally preferably about 0.05 to 0.5 A / cm ² . The treatment time is usually about 2 to 20 minutes.

5) Fifth Step In the fifth step, a dense region is formed by compressing a part of the etched aluminum foil obtained in the fourth step. As a method for forming the dense region, it is sufficient to provide a dense region with a predetermined density by compressing a part of the aluminum electrode foil for an electrolytic capacitor by performing a mechanical treatment at any stage after the etching process. . The dense region may be formed either before or after the anodizing treatment. When the dense region is formed after the anodizing treatment, the anodization may be performed again after the dense region is formed.

  Further, the density of the dense region may not be uniform. In particular, in the present invention, a method of forming a dense region by machining is preferable. The method of machining is not particularly limited, and is not particularly limited as long as it can be processed with desired dimensional accuracy such as rolling, pressing, or the like. More specifically, a method of partially compressing the aluminum electrode foil for electrolytic capacitors after the etching treatment through a rolling mill incorporating a patterned roll is preferable.

  In the case of manufacturing by such a method, an etching pit structure may remain in the dense region as long as the above physical properties are satisfied.

  Such an aluminum electrode foil for electrolytic capacitors has a high electrostatic capacity, and when subjected to anodization to form an electrode foil, the strength of the dense region can be made higher than that of the surrounding area. For this reason, in this invention, you may perform an anodizing process further as needed. In the anodizing process, a dielectric film is formed on an aluminum foil whose surface area is increased by forming pits by an etching process. Specifically, an anodizing process using an aluminum foil as an anode is performed to form a dielectric film.

  The anodizing treatment may be performed under known conditions. For example, a buffer solution such as ammonium borate, ammonium phosphate, or organic acid ammonium (for example, ammonium adipate) is used as the electrolytic solution, and a voltage of about 3 to 150 V is applied in one or more stages depending on the use of the capacitor. A film can be formed.

  Examples, comparative examples and conventional examples are shown below to further clarify the features of the present invention. However, the scope of the present invention is not limited to these examples.

Preparation of Aluminum Foil for Etching In each example etc., an aluminum foil for etching was first prepared as follows. A molten aluminum (Si: 50 ppm, Fe: 50 ppm, Cu: 40 ppm, balance: Al and inevitable impurities) was semi-continuously cast to obtain an ingot having a thickness of 500 mm. This ingot is homogenized at 550 ° C., then hot rolled to 5 mm, followed by intermediate annealing and cold rolling to 100 μm, and final annealing at 300 ° C. for 5 hours in a nitrogen gas atmosphere. The aluminum foil for an etching was obtained by performing.

The obtained aluminum foil for etching was etched under the following conditions.
<Etching treatment conditions>
Primary etching etching solution: Mixed solution of hydrochloric acid and sulfuric acid (hydrochloric acid concentration: 20 wt%, sulfuric acid concentration: 2 wt%, 60 ° C.)
Electrolysis: AC 0.6 A / cm ² × 30 seconds
Secondary etching etching solution: Mixed solution of hydrochloric acid and sulfuric acid (hydrochloric acid concentration: 20 wt%, sulfuric acid concentration: 2 wt%, 60 ° C)
Immersion (chemical etching): 3 minutes
Tertiary etching etching solution: Mixed solution of hydrochloric acid and sulfuric acid (hydrochloric acid concentration: 20 wt%, sulfuric acid concentration: 2 wt%, 40 ° C)
Electrolysis: AC 0.2 A / cm ² × 10 minutes (conventional example 1)
The obtained etched aluminum foil was used as an aluminum electrode foil.
(Conventional example 2)
The entire surface of the obtained etched aluminum foil was reduced by 20% to obtain an aluminum electrode foil. The rolling reduction is expressed by the following equation.

Reduction ratio (%) = (foil thickness before rolling−foil thickness after rolling) / foil thickness before rolling × 100
Example 1
With respect to the obtained etched aluminum foil, a rolling roll having 5 mmφ convex portions at a vertical pitch of 50 mm and a horizontal 20 mm pitch has a reduction rate of 20% at the portion corresponding to the convex portions, and a reduction rate of other portions at 0%. % To form a dense region (diameter of about 5 mm), and an aluminum electrode foil as shown in FIG. 1 was obtained. As shown in FIG. 1, the obtained aluminum electrode foil includes an etching pit region 1 and a dense region 2. The dense region 2 has a circular shape, and a plurality of the dense regions 2 are formed on the aluminum electrode foil.
(Example 2)
In the same manner as in Example 1, a dense region is formed by rolling so that the rolling reduction of the portion corresponding to the convex portion is 30% and the rolling reduction of the other portion is 0%, and an aluminum electrode foil is formed. Obtained.
(Example 3)
In the same manner as in Example 1, a dense region is formed by rolling so that the rolling reduction of the portion corresponding to the convex portion is 35% and the rolling reduction of the other portion is 0%, and an aluminum electrode foil is formed. Obtained.
(Test Example 1)
About the obtained aluminum electrode foil, the characteristic was measured as follows. The results are shown in Table 1.

<Capacitance>
After a 50 V chemical conversion treatment in an aqueous solution of ammonium adipate (150 g / L), the measurement was carried out with an aqueous ammonium borate solution (8 g / L) using an LCR meter. Each measurement area was 10 cm ^2, and the ratio of the dense region in the measurement area was made substantially equal to the ratio of the dense region in the total area of the aluminum foil. The relative value when the conventional example is 100 is shown.

<Lead terminal fixing strength>
After a 50 V chemical conversion treatment in an aqueous solution of ammonium adipate (150 g / L), the dense region was made to be a fixed part, and a thickness of 150 μm, a width of 2 mm, a fixed length of 7 mm, Spot welding was performed at two locations using a flat rectangular aluminum wire having a total length of 20 mm as a lead terminal. Ten samples were prepared, and the lead terminal fixing state was visually observed and evaluated by the following AC.

A: All lead terminals are crimped and the aluminum electrode foil is not damaged B: All lead terminals are crimped, but the aluminum electrode foil is cracked C: The lead terminal or the aluminum electrode foil has a drop-off portion <Dense Region density>
The cross section of the aluminum electrode foil was observed with an optical microscope, and the average thickness t ₁ (cm) of any ten dense regions was measured. Further, arbitrary 10 dense regions were punched with a 5 mmφ punch, and the total weight m ₁ (g) was measured. From the thickness t ₁ and the weight m ₁ , the absolute density of the dense region was calculated by the following formula.

Absolute density of dense region (g / cm ³ ) = m ₁ /0.625πt ₁
Furthermore, observing the cross section of the aluminum electrode foil with an optical microscope to measure the average of the portion except for the dense region thickness t _{2 (cm).} Further, a portion excluding any 10 dense regions was punched with a 5 mmφ punch, and the total weight m ₂ (g) was measured. From the thicknesses t ₁ and t ₂ and the weights m ₁ and m ₂ , the relative density of the dense region was calculated by the following formula.

Relative density of dense region = absolute density of dense region / absolute density of portion excluding dense region
= (M1 × t2) / (m2 × t1)

  As is clear from the results in Table 1, it can be seen that Examples 1 to 3 can exhibit excellent strength together with high capacitance.

It is a top view of the electrode foil produced in the Example.

Claims (1)

A method for producing an aluminum electrode foil for electrolytic capacitors,
1) A first step of obtaining an aluminum ingot from molten aluminum,
2) A second step of homogenizing the aluminum ingot,
3) a third step of obtaining an aluminum foil by rolling the homogenized aluminum;
4) a fourth step of forming an etching pit region by etching the obtained aluminum foil;
5) A method for producing an aluminum electrode foil for electrolytic capacitors, comprising a fifth step of forming a striped or network-like dense region by compressing part of an etched aluminum foil.

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