JP3381657B2 - Electrolytic foil having tunnel-like pits of uniform depth, electrolytic capacitor using the same as an electrode, and method for producing the foil - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an aluminum electrolytic foil used as an electrode foil of an electrolytic capacitor, a method for producing the same, and an electrolytic capacitor having the foil as an electrode foil. More specifically, the present invention relates to an aluminum electrolytic foil having tunnel-shaped pits of uniform depth on both surfaces of an aluminum foil and a non-penetrating layer at the center, a method for producing the same by direct current electrolysis in an aqueous solution, and an electrolytic capacitor used as an electrode foil. .

[0002]

2. Description of the Related Art With the recent miniaturization of electronic devices, aluminum electrolytic capacitors are required to have smaller sizes. In this aluminum electrolytic capacitor, aluminum electrolytic foil has been conventionally used as an electrode foil, and in the production of electrolytic foil for medium and high voltage electrolytic capacitors,
In order to increase the capacitance per unit area, the aluminum original foil having a high-density cubic crystal structure is etched by an aqueous solution such as an acidic electrolyte solution containing chlorine ions by direct current electrolysis to obtain a crystal orientation in the (100) direction. It forms a tunnel-shaped pit.

In the formation of this tunnel-shaped pit,
The number of pits at the starting point of corrosion is related to the magnitude of the current density applied to it, and the amount of dissolved foil is almost proportional to the amount of electricity, and as a result, in order to increase the capacitance of the aluminum foil, Was designed to increase the surface area of the foil by setting the electrolytic current density to a high level to form tunnel-shaped pits with high density and increasing the amount of electricity applied to increase the amount of dissolution.

Regarding the process of forming the tunnel-shaped pits, the formation of the pits does not occur at a high density of pits simultaneously over the entire surface of the aluminum foil.
Initially, it has been observed that pits are coarsely generated in the foil and grow, and when the growth stops, another pit starts to grow and gradually tunnel-like pits are formed on the entire surface of the foil.

For this electrolytic foil, one having a predetermined strength and a larger capacitance is desirable because of its high performance, and for that purpose, the thinnest possible unetched portion for keeping the strength in the central portion is required. It has been conventionally thought that it is necessary to leave the tunnel-shaped pits and to form the tunnel-shaped pits with high density and deeply. Regarding the formation of the tunnel-shaped pits, in the conventional method, a direct current was applied to the foil under the condition of a constant current density with respect to time as shown in FIG. 1 (a).

[0006]

According to this conventional method,
When trying to obtain an electrolytic foil having a larger electrostatic capacity, corrosion due to etching becomes excessive so as to increase the amount of applied electricity as much as possible. As a result, an electrolytic foil having a reduced mechanical strength of the foil is formed, which is difficult to avoid. Further, a technique for manufacturing an electrolytic foil has been proposed to improve this, for example, a method of gradually decreasing the electrolytic current density from the maximum value as shown in FIGS. 249550). In this method, the maximum current density is 1000 mA
/ Cm ² and the current application time is about 80 seconds as in the conventional method.

Even if this method is used to obtain a material having a large electrostatic capacity, the same disadvantages as those of the conventional method described above are exhibited, and it is difficult to avoid it completely. Fig. 2 (b) shows the result of cutting with a microscope and observing it with an electron microscope. From this figure, the tunnel-shaped pits of the electrolytic foil with reduced strength have uneven depths and zigzags on the inner end. It can be seen that in some places tunnel-shaped pits extending from both end faces penetrate the aluminum foil and there is no non-penetrating layer in the central portion.

As described above, the present invention provides an invention of an electrolytic foil, a method for producing the same, and an aluminum electrolytic capacitor using the foil, which does not have such a problem. That is, an electrolytic foil formed with tunnel-like pits capable of increasing the capacitance as much as possible without the presence of through-tunnel-like pits for reducing the mechanical strength of the aluminum electrolytic foil, its manufacturing method, and the same. It is an object of the invention to provide each invention of an electrolytic capacitor using a foil as an electrode foil, and it is an object.

[0009]

The means adopted by the present invention to achieve the above object are aluminum direct current electrolytic foil,
Each of the inventions is a method for producing the same and an electrolytic capacitor using the foil as an electrode foil. Among them, the aluminum direct current electrolytic foil has a total number of pits having a depth of 30% or more on both surfaces of the aluminum foil. Of a foil having a uniform depth, that is, a tunnel pit having a uniform depth, and having a pit non-penetrating layer having a layer thickness of 5 to 25% of the foil thickness in the center thereof. Is 70 to 150 μm. The electrolytic capacitor uses the aluminum direct current electrolytic foil as an electrode foil.

The method for producing an aluminum electrolytic foil is such that the initial current density is set to a maximum current density of 1500 mA / cm ² or more, and then rapidly reduced to 100 mA / cm ² or less by direct current electrolysis in an aqueous solution to obtain a foil thickness of 7
There is a tunnel-shaped pit with a uniform depth on both surfaces of the aluminum foil of 0 to 150 μm, and the layer thickness is 5 at the center of the pit.
It is assumed to have a pit non-penetrating layer of ˜25%.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION According to the present invention, by adopting the above-mentioned means, particularly the manufacturing method, the etching time during DC electrolysis is extremely shortened as compared with the conventional method, and at the same time, the initial current density is excessively large. Density, and suddenly 10
It is intended to provide an electrolytic foil having a novel structure in which it is reduced to 0 mA / cm ² or less, thereby exhibiting excellent characteristics. The resulting electrolytic foil with a novel structure is shown in FIG.
As shown in (a) (electrolytic foil of Example 1), it has tunnel-shaped pits having a uniform depth, that is, a uniform depth, and there is no tunnel-shaped pit at the center of the foil in the thickness direction. It has a structure with a penetration layer.

The aluminum foil used may be the same as the conventional electrolytic foil material, and the purity thereof is preferably 99.9% or more. The thickness of the foil may be the same as that of the conventional electrolytic foil, which is 70 to 150 μm.
And preferably 80 to 120 μm. And the layer thickness of the non-penetrating layer of the produced electrolytic foil needs to be 5 to 25% of the foil thickness, and preferably 5 to 15%.
Further, the thickness of the non-penetrating layer is specifically required to be 5 to 25 μm, preferably 5 to 15 μm. As the aqueous solution used for etching this electrolytic foil, hydrochloric acid, sulfuric acid containing chlorine ions, nitric acid, phosphoric acid, or the like can be used alone or in combination, and conventional ones can be used without limitation.

Regarding the current density at the time of etching, it is necessary to make the initial current density the maximum current density as described above, and then rapidly reduce it to 100 mA / cm ² . In that case, in order to obtain an electrolytic foil having a novel structure having the above excellent properties, the initial current density is 1500 to 7000.
mA / cm ² is necessary, and preferably 30
It is preferable to set it to 00 to 6000 mA / cm ² . The initial current density is set to 7,000 mA / cm ² or less in order to prevent the corrosion surface of the foil from falling off if the initial current density is exceeded. Further, if the initial current density is 1500 mA or less, the number of pits will be insufficient and the capacitance will be extremely reduced. The initial current density here is the current density at the time when electrolysis is started by applying a current to the original foil in the etching tank.

The time required to drastically reduce it to 100 mA / cm ² or less is 10 to 30 seconds, preferably 15 to 20 seconds. The reason why the current density is drastically reduced to 100 mA / cm ² or less at the end of etching is that short pits are easily formed unless this is done. The reason for setting the electrolysis time to the above range is that if it exceeds 30 seconds, long pits that form the through holes are likely to be formed, and the mechanical strength of the electrolytic foil decreases.

Further, regarding the form of attenuation of the applied current density, the maximum current density at the initial stage is suddenly increased to 100 mA / c.
There is no particular limitation as long as it is reduced to m ² or less. The form of the current density applied in the conventional etching for producing the electrolytic foil is the constant current density shown in FIG. 1A, which is very different from that applied in the present invention. Further, the time required for etching at that time is about 80 seconds, which is much longer than that of the present invention.

The adjustment of the current application time in the production of the electrolytic foil of the present invention is carried out while the foil is etched in an aqueous solution while passing between opposing electrodes. Therefore, the length of the electrode or the passage of the foil is passed. It is possible to set the time within 10 to 30 seconds by adjusting the speed and the like. Further, the current density can be adjusted by adjusting the surface area and distance of the facing electrodes, since the etching is performed while the foil is present between the facing electrodes. There are no particular restrictions on the method for adjusting the surface area of the electrode, and various methods can be adopted, and for example, there is a method of punching out a part of the electrode to change the surface area of the opposing electrode or changing the electrode surface shape. .

[0017]

EXAMPLES Examples and comparative examples of the present invention will be described below to specifically show the characteristic points and outstanding effects of the present invention. However, the present invention is not limited to these examples and patents Needless to say, it is understood based on the description of the claims.

(Example 1 and conventional example) Purity 99.98%
And 106 μm thick aluminum foil with hydrochloric acid concentration of 1
Etching was performed in a solution having a mol / L and a sulfuric acid concentration of 3 mol / L under the conditions shown in Table 1. That is, in Example 1 corresponding to the present invention, the initial current density was 4000 mA / c.
Electrolysis was performed at m ² , final current density of 100 mA / cm ² , and etching time of 20 seconds. In the conventional example corresponding to the conventional technique, electrolysis was performed at an initial current density of 350 mA / cm ² and an etching time of 80 seconds.

The properties and sectional structure of the obtained electrolytic foil are shown in Table 1 and FIG. 2 (a). It is as shown in (b).
From these results, in the present invention, the tunnel-like pits formed as compared with the prior art have a deep and uniform depth, and a thin pit non-penetrating layer is formed in the center of the foil, which means that the mechanical strength is high. You can see that it is also expensive. Further, it can be seen that the electrolytic foil of the example is superior in capacitance to the electrolytic foil of the conventional example.

The detailed distribution state of the pit depth of the obtained electrolytic foil is as shown in Table 3. From this table, in the conventional example, the pit depth is 0 to 50 μm.
It can be seen that it is distributed over a wide range beyond. On the other hand, in Example 1, 88% is present in the range of 40 to 50 μm, and most is present in the extremely limited range, and most of the pits are deep and have the same depth. I understand.

Regarding the method of measuring the depth distribution, an electrolytic foil sample embedded in an epoxy resin was measured with an ultramicrotome (manufactured by RMC) on the surface of the electrolytic foil in a depth direction of μm.
Grinding with a diamond knife in units, the surface of the ground surface at that time is taken by SEM, and the tunnel density is calculated by applying it to an image analyzer (V10 manufactured by Toyobo Co., Ltd.). Then, the distribution of the tunnel depth is calculated from the relationship between the grinding depth from the foil surface and the tunnel density.

[0022]

[Table 1]

(Example 2 and Comparative Example) Purity 99.98%
And 106 μm thick aluminum foil with hydrochloric acid concentration of 1
mol / L and sulfuric acid concentration 3 mol / L
Current density 4000mA / cm ², Final current density 100m
A / cm²Then, change the electrolysis time as shown in Table 2.
Then, etching was performed in the same manner as in Example 1. Obtained electricity
The characteristics and cross-sectional structure of the unwrapping foil are shown in Table 3 and FIGS.
It is a cage. From this result, etching time is 20 seconds or less
It can be seen that particularly excellent characteristics are exhibited. See you again
If the ching time exceeds 30 seconds, the pit depth will increase,
The pits on both sides are connected and there is no non-penetrating layer
Therefore, the mechanical strength of the electrolytic foil decreases.

The detailed distribution state of the pit depth of the obtained electrolytic foil is shown in Table 3 as in Example 1, and in Example 2, the pit depth was 20 to 30 μm.
m and the range of 30 to 40 μm each have about 45% of pits, and about 90% of the pits exist in both ranges. On the other hand, in the comparative example, 50% or more of pits having a depth of 50 μm or more were present and the pits were too deep, which is consistent with the result shown in FIG. 4 in which the non-penetrating layer does not exist.

[0025]

[Table 2]

[0026]

[Table 3]

(Example 3) Purity 99.98% and thickness 1
A raw aluminum foil having a thickness of 06 μm is formed with a hydrochloric acid concentration of 1 mol /
l in a solution with sulfuric acid concentration of 3 mol / l as illustrated in FIG.
Etching was performed in the same manner as in Example 1 with various initial current densities.
It was The capacitance of the obtained electrolytic foil during formation of 385 V is shown in FIG.
, And the initial current density is 3000 to 600.
0 mA / cm ²In the range of
It turns out that you can get it.

[0028]

According to the present invention, the tunnel-like pits in the electrolytic foil are formed to have a high density even deep inside and uniform depths. Therefore, in the center of the foil, non-existence of tunnel-like pits is observed. A penetration layer can be present. As a result, in the present invention, it is possible to provide an excellent effect that an electrolytic foil having a high capacitance can be provided without reducing mechanical strength.

[Brief description of drawings]

FIG. 1 is a diagram showing a relationship between a current density and an application time during etching in a conventional technique and an improved prior art.

FIG. 2 is an electron micrograph of a cross section of an electrolytic foil according to the present invention, where (a) is the electrolytic foil of Example 1 and (b) is the electrolytic foil of the conventional example.

FIG. 3 is an electron micrograph of a cross section of an electrolytic foil obtained in Example 2.

FIG. 4 is an electron micrograph of a cross section of an electrolytic foil obtained in a comparative example.

FIG. 5 is a diagram showing the results of experiments of Example 3;

Continuation of the front page (56) Reference JP-A-7-249550 (JP, A) JP-A-61-244013 (JP, A) JP-A-55-76100 (JP, A) JP-A-57-131399 (JP , A) JP 57-66616 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) H01G 9/04 304 C25F 3/00 C25F 3/04

Claims (6)

(57) [Claims] 1. A pit having a depth of 30% or more of the foil thickness on both surfaces of an aluminum foil has a tunnel-like pit having a uniform depth of 80% or more of the total number of pits, and a layer thickness at the center thereof. An aluminum direct current electrolytic foil having a pit non-penetrating layer having a thickness of 5 to 25% of the foil thickness of 70 to 150 μm. 2. The direct current electrolytic foil according to claim 1, wherein the foil thickness is 80 to 120 μm, and the layer thickness of the pit non-penetrating layer is 5 to 15% of the foil thickness. 3. The electrolytic foil according to claim 1, wherein the pit non-penetrating layer has a layer thickness of 5 to 25 μm. 4. A pit having a depth of 30% or more of the foil thickness on both surfaces of the aluminum foil has a tunnel-like pit having a uniform depth of 80% or more of the total number of pits, and a layer thickness at the center thereof. Having an pit non-penetrating layer having a thickness of 5 to 25% of the foil thickness is an electrolytic capacitor having an electrode foil made of an aluminum direct current electrolytic foil having a thickness of 70 to 150 μm. 5. The electrolytic capacitor according to claim 4, wherein the foil thickness is 80 to 120 μm, and the layer thickness of the pit non-penetrating layer is 5 to 15% of the foil thickness. 6. The initial current density is set to a maximum current density of 1500 mA / cm ² or more and then 100 m in 10 to 30 seconds.
All the pits with a depth of 30% or more on both surfaces of an aluminum foil having a foil thickness of 70 to 150 μm are formed by direct current electrolysis in an aqueous solution that reduces the A / cm ² or less.
A method for producing an aluminum direct current electrolytic foil having a tunnel-shaped pit having a uniform depth of 80% or more of the number and a pit non-penetrating layer having a layer thickness of 5 to 25% of the foil thickness in a central portion thereof.