JPH08264391A - Etching of aluminum foil for electrolytic capacitor - Google Patents

Abstract

PURPOSE: To increase the mechanical strength of aluminum foil for an electrolytic capacitor. CONSTITUTION: A method for etching aluminum foil for an electrolytic capacitor includes three processes; a first process wherein electrochemical etching is conducted with DC current being applied in an aqueous solution including chlorine ions, a second process wherein electrochemical etching is conducted in an aqueous solution including chlorine ions and solphate ions, and a third process wherein electrochemical or chemical etching is conducted in an aqueous solution including nitrate ions or chlorine ions. In the first process, a through pit is formed. And, a non-through pit is formed in the second process. In the third process, the pits formed in the first and the second process are enlarged.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for etching aluminum foil for electrolytic capacitors.

[0002]

2. Description of the Related Art Generally, an aluminum electrode foil for an electrolytic capacitor is generally subjected to electrolytic etching and chemical etching individually or in combination for the purpose of expanding the effective surface area thereof. In, a tunnel-shaped pit that penetrates the aluminum foil is formed in a direction perpendicular to the foil surface. Ion conduction is carried out to the cathode foil through the through pits, so that it can be used as a so-called double anode in which two foils are stacked. However, in the "penetration type" in which the majority of the penetration pits occupy, the bending strength is low, and there is a problem that foil breakage occurs when the electrode foil as a capacitor element is wound. On the other hand, a so-called "core-remaining type" in which a "core" portion having no pits in the thickness of 5 to 20% of the thickness is left near the center of the thickness of the aluminum foil.
Has a high mechanical strength because it has no through pit, but has a problem that it cannot be used as a double anode.
Further, in order to further increase the effective surface area for downsizing of the electrolytic capacitor, the number of tunnel-shaped pits must be increased by etching, but an increase in the number of tunnel-shaped pits increases the amount of corrosion, This leads to a decrease in the mechanical strength of the foil. In particular, when the number of pits in a tunnel shape is increased in the "penetrating type" foil, the mechanical strength is significantly reduced. On the other hand, the "core-remaining type" foil has an advantage that the effective surface area can be increased because the mechanical strength is small and the number of tunnel pits can be easily increased because the "core" portion remains. Further, in order to maintain the mechanical strength of the foil while expanding the effective surface area, conventionally, there has been proposed a method of forming non-etched linear or strip-shaped non-corroded portions on the surface of the foil.

[0003]

However, the provision of non-corroding parts in the form of lines or strips has the disadvantage that the expansion of the effective surface area is prevented accordingly. Also, when the effective surface area is increased by increasing the amount of corrosion, the mechanical strength of the foil decreases, so it becomes brittle and breaks easily when it is used in the chemical conversion process. It is necessary to increase the diameter of the core to increase the radius of curvature for winding, but when increasing the diameter of the winding core, there is a wasted space in the center of the capacitor element, and the volume of the capacitor relative to the capacitance It has the disadvantage of low efficiency, and it has been extremely difficult to solve the contradictory effects of increasing the effective surface area and maintaining mechanical strength at the same time. Then, this invention aims at solving the above-mentioned conventional difficult problems.

[0004]

In the conventional penetration type aluminum electrode foil, tunnel pits formed to increase the effective surface area are deeply extended to penetrate the foil. Not all pits formed in the foil penetrate the foil, some of which extend beyond the center of the foil thickness but are non-penetrating. Regarding the degree of penetration required for the double anode, it is not always necessary that all the pits penetrate, and if the number of penetration pits is reduced, the reduction in mechanical strength can be prevented to that extent. When the number of penetration pits is extremely reduced, the degree of penetration may deteriorate. In that case, a sufficient degree of penetration can be maintained by providing a step of selectively thickening only the penetration pits. From these things, in the etching method for manufacturing the through type aluminum electrode foil, it was devised to form the through pit and the non-through pit separately.

That is, in the method for producing an aluminum foil for an electrolytic capacitor according to the present invention, electrochemical etching is performed with a direct current in the first step in an aqueous solution containing at least chlorine ions, and then in the second step. Electrochemically at a direct current in an aqueous solution containing at least chlorine ions and sulfate ions, and then as a third step, electrochemically or chemically etching in an aqueous solution containing at least nitrate ions or chlorine ions, In the method for etching an aluminum foil for electrolytic capacitors, which includes a third step of enlarging the pits formed in the previous two steps, a through pit is provided in the first step, and a non-through pit is provided in the second step. It is characterized by.

Further, between the first step and the second step, the through pits formed in the first step are enlarged by electrochemically or chemically etching in an aqueous solution containing at least nitrate ions or chlorine ions. It is characterized by adding an intermediate step to

[0007]

EXAMPLES Examples of the present invention will be described in detail below.
In the first step, the concentration of chlorine ions in the aqueous solution was adjusted to 1
The range is 0 to 80 g / 1, the concentration of aluminum ions is 1 to 5 g / 1, and the current density is 40 to 70 mA.
/ Cm ² , the liquid temperature is 65 to 85 ° C., and the quantity of electricity is 1.2 to 3.6 C / cm ² .

In the above, the chlorine ion concentration is 1
If it is less than 0 g / 1, the required number of through pits will not be generated, and if it exceeds 80 g / 1, the number of pits generated will be excessive. Therefore, a preferable range is 10 to 80 g / l. Is less than 1 g / 1, aluminum ions in the liquid are increased by the dissolved aluminum, and the liquid components are not stable, and when it exceeds 5 g / 1, the number of pits is reduced.
g / l is suitable, and if the liquid temperature is less than 65 ° C, the pits do not form tunnels and will not penetrate.
If the temperature exceeds ℃, the number of pits will be excessive. Therefore, 65 to 85 ° C is suitable as a preferable range. If the current density is less than 40 mA / cm ² , the number of pits is small and 70 mA / cm ² If it exceeds, the pit does not penetrate. Therefore, a preferable range is 40 to 70 mA / cm ² , and if the electric quantity is less than 1.2 C / cm ² , the number of pits generated is small and the pit does not penetrate.
If it is more than 3.6 C / cm ² , the number of pits penetrating becomes excessive, so the preferable range is 1.2 to 3.6 C / cm ^2.
Is appropriate.

Next, in the second step, the concentration of chloride ions in the aqueous solution is set to 10 to 30 g / 1, the concentration of sulfate ions is set to 350 to 500 g / 1, and the concentration of aluminum ions is set to 5 to 20 g. / 1, the current density is 250 to 350 mA / cm ² , and the liquid temperature is 65 to
The temperature is 85 ° C., and the amount of electricity is 12 to 24 C / cm ² .

In the above, the chlorine ion concentration is 1
If it is less than 0 g / 1, the required number of non-penetrating pits will not be generated, and if it exceeds 30 g / 1, the dissolution of the surface will proceed at the same time as the formation of pits and the capacity will be reduced, so the preferred range is 10-30 g. / L is appropriate, and if the sulfate ion concentration is less than 350 g / 1, the pits penetrate, and if it exceeds 500 g / 1, the pit length becomes too short and a larger effective surface area is obtained. Therefore, the preferable range is 350 to 500 g / l, and if the aluminum ion is less than 5 g / 1, the dissolved aluminum increases the aluminum ion in the liquid and the liquid component is not stable, When it exceeds 20 g / 1, the number of pits is reduced, so a preferable range is 5 to 20 g / l, and when the liquid temperature is less than 65 ° C. Pits not like a tunnel, 8
If the temperature exceeds 5 ° C, the pit length becomes short and a larger effective surface area cannot be obtained.
85 ℃ is suitable, and the current density is 250mA / c
If it is less than m ² , the pit will penetrate, resulting in 350 mA.
If it exceeds / cm ² , the surface will be dissolved simultaneously with the formation of pits and the effective surface area will be reduced. Therefore, the preferable range is 250 to 350 mA / cm ² , and the electric quantity is 12 c / cm ² . If not, a sufficient number of pits cannot be obtained, and if it exceeds 24 C / cm ² , adjacent pits will overlap, leading to a decrease in effective surface area. Therefore, the preferable range is 12 to 24 C / c.
m ² is suitable.

In the third step, the concentration of nitrate ions in the aqueous solution is set to 100 to 200 g / l and the concentration of aluminum ions is set to 10 to 30 g / l. In the above, if the nitrate ion is less than 100 g / l, the pit expansion effect is small, and if it exceeds 200 g / l, the dissolution of the surface proceeds and the capacity is reduced, so a preferable range is 100 to 200 g / l. If the amount of aluminum ion is less than 10 g / l, the dissolution stability is poor, and if it exceeds 30 g / l, the pit expansion capability is reduced, so a preferable range is 10 to 30 g / l. As another method, the chlorine ion concentration in the aqueous solution is 10 to 30 g / l and the aluminum ion concentration is 5 to 20 g / l. In the above, if the chloride ion is less than 10 g / l, the pit expansion effect is small, and if it exceeds 30 g / l, the dissolution of the surface progresses and the effective surface area is reduced.
g / l is suitable, aluminum ion is 5 g / l
If the amount is less than 10 g, the stability of dissolution is poor, and if it exceeds 20 g / l, the pit expansion capability decreases, so the preferable range is 5
-20 g / l is suitable. Further, in the third step, when electrochemically performed at a liquid temperature of 60 to 85 ° C., a current density is 10 to 300 mA / cm ² , and an electric quantity is 6 to 42 C / c.
m ² and the etching time is 3 to 3 when chemically performed.
It is set to 0 minutes. In the above, the liquid temperature is 60 ° C
If it is less than 80%, the pit expansion ability is low, and if it exceeds 85 ° C., the dissolution of the surface will proceed.
A temperature of ~ 85 ° C is suitable. Further, in the case of performing electrochemically, if the current density is less than 10 mA / cm ² , the pit expansion effect is small, and if it exceeds 300 mA / cm ² , dissolution of the surface will proceed, so the preferred range is 10 to 3
00mA / cm ² is suitable, and the amount of electricity is 6C / c
If it is less than m ² , the pit expansion effect is small and 42 C / c
Because if it exceeds m ² pits which leads to decrease in the large blind pits increase the effect of the effective surface area is too enlarged, it is appropriate 6~42C / cm ² as a preferred range. Further, in the case of chemical treatment, if the time is less than 3 minutes, the pit expansion effect is small, and if it exceeds 30 minutes, the pits are excessively expanded and the non-penetrating pits, which have a large effect on increasing the effective surface area, are reduced. As 3 to 30
Minutes are appropriate.

In addition, in the intermediate step added between the first step and the second step, the concentration of nitrate ion in the aqueous solution is adjusted to 10%.
The range is 0 to 200 g / 1, and the concentration of aluminum ions is 10 to 30 g / 1.

In the above, when the nitrate ion is less than 100 g / 1, the pit expansion effect is small, and when it exceeds 200 g / 1, the dissolution of the surface progresses to reduce the effective surface area, and the preferable range is 100 to 200 g /
1 is suitable, and aluminum ion is 10 g /
If it is less than 1, the dissolution stability is poor, and if it exceeds 30 g / 1, the pit expansion capability is poor, so a preferable range is 10 to 30 g / l.

As another method in the intermediate step added between the first step and the second step, the concentration of chloride ion in the aqueous solution is 10 to 30 g / 1, and the concentration of aluminum ion is 5 to 20 g / 1. And

In the above, if the chlorine ion is less than 10 g / 1, the pit expansion effect is small, and if it exceeds 30 g / 1, the dissolution of the surface proceeds and the capacity is reduced, and the preferable range is 10 to 30 g. / L is suitable, and if the aluminum ion content is less than 5 g / 1, the dissolution stability is poor, and if it exceeds 20 g / 1, the pit expansion capability decreases, so the preferred range is 5-20 g / l.
l is suitable.

In addition, in the intermediate step added between the first step and the second step, the liquid temperature is set to 60 to 85 ° C., and when electrochemically performed, the current density is set to 10 to 300.
When the intermediate step is chemically performed, the etching time is 3 to 1 when mA / cm ² and the amount of electricity are 0.6 to 6 C / cm ^2.
0 minutes.

In the above, if the liquid temperature is lower than 60 ° C., the pit expansion ability is low, and if it exceeds 85 ° C., the dissolution of the surface is promoted. A preferable range is 60 to 85 ° C. When electrochemically performed, if the current density is less than 10 mA / cm ² , the pit-expansion effect is small, and if it exceeds 300 mA / cm ² , dissolution of the surface proceeds, so the preferred range is 10 to 30.
0 mA / cm ² is suitable. The amount of electricity is 0.6C /
If it is less than cm ² , the pit expansion effect is small and 6C / c
Since exceeds m ² too enlarged pits leads to an increase decrease in the large blind pits effect on the effective surface area is suitably 0.6~6C / cm ² as a preferred range.

In the case where the intermediate step is chemically performed, if the etching time is less than 3 minutes, the pit expansion effect is small, and if it exceeds 10 minutes, the pits are excessively expanded and the effective surface area is greatly increased. 3 to 10 minutes is suitable as a preferable range because it leads to a reduction in through pits.

Next, the etching method of the aluminum foil for electrolytic capacitors of the present invention will be described in comparison with a conventional example.

Example 1 Thickness 104 μm, O material, 4
Aluminum foil with N, (100) plane occupancy 90% is filled with chlorine ions 65.0 g / 1, aluminum ions 2.4 g /
In an aqueous solution containing 1, current density of 60 mA / cm ^2, amount of electricity 3.6C / cm ^2, after the first step of the DC etched at a liquid temperature of 75 ° C., chlorine ions 22g as the second step
/ 1, sulfate ion 435g / 1, aluminum ion 1
Current density 300 mA / c in aqueous solution containing 4 g / 1
m ² , electric quantity 18 C / cm ² , direct current etching at a liquid temperature of 72 ° C., and as a third step, nitrate ion 135 g
Chemical etching is performed for 10 minutes at a liquid temperature of 75 ° C. in an aqueous solution containing 1/1 of aluminum ion 18 g / 1.

Example 2 Thickness 104 μm, O material, 4N
Example 1 An aluminum foil having a (100) plane occupancy of 90% was used.
Current density of 60 mA / c in the same aqueous solution as the first step
After the first step in which direct current etching was performed at m ² , an electric quantity of 1.4 C / cm ² , and a liquid temperature of 75 ° C., a liquid temperature of 75 ° C. was used as an intermediate step in an aqueous solution containing 135 g / 1 of nitrate ions and 18 g / 1 of aluminum ions. Chemically etch for 5 minutes.
Then, as a second step, in a solution containing chlorine ions 22 g / 1, sulfate ions 435 g / 1, aluminum ions 14 g / 1, a current density of 300 mA / cm ² and an electric quantity of 18 C
/ DC ² , liquid temperature 72 ℃, after DC etching,
In this step, chemical etching is performed for 10 minutes at a liquid temperature of 75 ° C. in an aqueous solution containing nitrate ions of 135 g / 1 and aluminum ions of 18 g / 1.

(Embodiment 3) Thickness 104 μm, 0 material, 4N
Example 1 An aluminum foil having a (100) plane occupancy of 90% was used.
Current density 60 mA / cm ² in the same liquid as the first step of the quantity of electricity 1.8C / cm ^2, after DC etched at a liquid temperature of 75 ° C., chlorine ions 15 g / l as an intermediate step, an aluminum ion 18 g / l Current density 15 in aqueous solution containing
mA / cm ² , electricity amount 1.8 C / cm ² , liquid temperature 65 ° C.
DC etching with. Then, in a second step, a current density of 300 mA / cm 2 in an aqueous solution containing chlorine ion 22 g / l, sulfate ion 435 g / l, and aluminum 14 g / l.
² , direct current etching at a charge of 18 C / cm ² and a liquid temperature of 72 ° C., and then as a third step, in a solution containing chlorine ions of 15 g / l and aluminum ions of 18 g / l, a current density of 100 mA / cm ² and a charge of 30 C / l. cm ² , liquid temperature 6
DC etching is performed at 5 ° C. (Conventional example) An aluminum foil having a thickness of 104 m, O material, 4N, and (100) plane occupancy rate of 90% was formed with the same liquid as in the second step of Example 1 with a current density of 100 mA / cm ² , and an electric charge of 21.
Direct current etching was performed at 6 C / cm ² and a liquid temperature of 68 ° C., and the same chemical etching as in the third step of Example 1 was performed. Each of the aluminum foils etched in the above-mentioned examples and conventional examples was subjected to 350 V formation in a boric acid aqueous solution, and its capacitance and mechanical strength were bending strength, and a certain amount of air was used as the degree of penetration to form a constant amount of the formation foil. The air permeability (the smaller the value of the air permeability, the better the degree of penetration) was measured, and the results shown in Table 1 were obtained.

[Table 1]

As is clear from Table 1, the example 1 is superior in bending strength to the conventional example, while having the same capacitance and air permeability, and is also excellent in the bending strength. In Examples 3 and 4, although not as strong as Example I,
It is superior in bending strength and air permeability as compared with the conventional example, demonstrating the effect of the present invention.

[0024]

According to the present invention, penetrating pits and non-penetrating pits, in other words, pits necessary for imparting penetrability to the electrode foil and pits having a great effect on increasing the effective surface area are separately formed. In order to prevent the formation of excessive through pits, it is possible to prevent the decrease in foil strength and to produce an aluminum foil for electrolytic capacitors with high mechanical strength. Can be provided.

[Procedure amendment]

[Submission date] May 11, 1995

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be corrected] 0023

[Correction method] Change

[Correction content]

As is clear from Table 1, the example 1 is superior in bending strength to the conventional example, while having the same capacitance and air permeability, and is also excellent in the bending strength. In Examples 3 and 4, although the bending strength is not as high as in Example 1,
It is superior in bending strength and air permeability as compared with the conventional example, demonstrating the effect of the present invention.

Claims (12)

[Claims] 1. A first step of electrochemically etching at a direct current in an aqueous solution containing at least chlorine ions, and electrochemically at a direct current in an aqueous solution containing at least chlorine ions and sulfate ions. In a method for etching an aluminum foil for electrolytic capacitors, which comprises a second step of selectively etching and a third step of electrochemically or chemically etching in an aqueous solution containing nitrate ions or chlorine ions. Etching of aluminum foil for electrolytic capacitors, characterized in that through-pits are formed in the first step, non-through-pits are formed in the second step, and the pits already formed are enlarged in the third step. Method. 2. An intermediate step of enlarging the through pits by electrochemically or chemically etching in an aqueous solution containing at least nitrate ions or chlorine ions between the first step and the second step. The method for etching an aluminum foil for an electrolytic capacitor according to claim 1, further comprising: 3. In the first step, the etching current density is 40 to 70 mA / cm ² , and the quantity of electricity is 1.2 to 3.6.
The method for etching an aluminum foil for an electrolytic capacitor according to claim 1 or 2, wherein C / cm ² and a liquid temperature are 65 to 85 ° C. 4. In the second step, the etching current density is 250 to 350 mA / cm ² , and the electric quantity is 12 to 2
4. The temperature is 4 C / cm ² , and the liquid temperature is 65 to 85 ° C.
The method for etching an aluminum foil for an electrolytic capacitor as described in 2 or 3. 5. When performing the third step electrochemically, the liquid temperature is 60 to 85 ° C. and the current density is 10 to 300 mA.
/ Cm < ² >, and the amount of electricity is 6 to 42 C / cm < ² >, The etching method of the aluminum foil for electrolytic capacitors of Claim 1, 2, 3 or 4. 6. When the third step is chemically performed,
The method for etching an aluminum foil for an electrolytic capacitor according to claim 1, 2, 3, or 4, wherein the liquid temperature is in the range of 60 to 85 ° C and the enching time is in the range of 3 to 30 minutes. 7. When performing the intermediate step electrochemically, the liquid temperature is 60 to 85 ° C. and the current density is 10 to 300 m.
The method for etching an aluminum foil for an electrolytic capacitor according to claim 2, 3, 4, 5 or 6, wherein A / cm ² and an amount of electricity are in the range of 0.6 to 6 C / cm ² . 8. When the intermediate step is chemically carried out,
The method for etching an aluminum foil for electrolytic capacitors according to claim 2, 3, 4, 5, 6 or 7, wherein the liquid temperature is 60 to 85 ° C and the etching time is 3 to 10 minutes. 9. The electrolytic solution used in the first step is at least 10 to 80 g / 1 of chlorine ions and 1 of aluminum ions.
The method for etching an aluminum foil for an electrolytic capacitor according to any one of claims 1 to 8, wherein the etching range is from 5 to 5 g / 1. 10. The electrolytic solution used in the second step is at least 10 to 30 g of chloride ions / 1, 350 to sulfate ions 350.
The method for etching an aluminum foil for an electrolytic capacitor according to any one of claims 1 to 9, comprising a range of 500 g / 1 and aluminum ions 5 to 20 g / 1. 11. In the third step, the aqueous solution contains at least nitrate ion in the range of 100 to 200 g / l and aluminum ion in the range of 10 to 30 g / l, or at least chloride ion in the range of 10 to 30 g / l and aluminum ion 5 to 5. 2. The method for etching an aluminum foil for an electrolytic capacitor according to claim 1, wherein the aluminum foil contains a range of 20 g / l. 12. The aqueous solution used in the intermediate step contains at least nitrate ion in the range of 100 to 200 g / 1 and aluminum ion in the range of 10 to 30 g / 1, or at least chloride ion in the range of 10 to 30 g / 1 and aluminum ion 5.
The method for etching an aluminum foil for an electrolytic capacitor according to any one of claims 2 to 11, wherein the etching method is an aqueous solution containing a range of -20g / 1.