KR101806674B1 - Anodizing solution in high voltage of aluminum foil coated with metal oxide of electrolytic capacitor, and method of manufacturing aluminium foil for electrolytic capacitor - Google Patents

Abstract

A high-voltage anodizing solution for an aluminum foil coated with a metal oxide and an aluminum foil for an electrolytic capacitor using the same, wherein the high-voltage anodizing solution comprises an aqueous solution of boric acid containing 100 g boric acid per 1 L of water, , And propylene glycol, wherein propylene glycol is contained in an amount of 10% by volume to 30% by volume based on the total volume.

Description

FIELD OF THE INVENTION [0001] The present invention relates to a high-voltage anodizing solution for an aluminum foil coated with a metal oxide, and an aluminum foil for an electrolytic capacitor using the same. BACKGROUND ART ELECTROLYTIC CAPACITOR}

The present invention relates to a high voltage anodizing solution for an aluminum foil coated with a metal oxide and an aluminum foil for an electrolytic capacitor using the same. More specifically, the present invention relates to an anodizing process for an electrolytic capacitor, A high voltage anodizing solution of an aluminum foil for an electrolytic capacitor coated with a metal oxide and a process for producing an aluminum foil for an electrolytic capacitor using the same.

BACKGROUND ART [0002] Electrolytic capacitors having a small size and large capacitance have been used in many electronic devices. In an aluminum electrolytic capacitor using an alumina layer (Al ₂ O ₃ ) formed by anodic oxidation of 99.99% or more of a high purity aluminum foil as a dielectric, theoretically, the effective surface area of the electrode is increased or the thickness of the dielectric layer is reduced Or by increasing the dielectric constant of the dielectric layer, the capacitance of the electrolytic capacitor can be increased.

However, there is a limitation in minimizing the thickness of the dielectric layer due to deterioration of the withstand voltage characteristic. Techniques for increasing the effective surface area of the electrodes have been continuously developed. However, there is a limitation in achieving the miniaturization of capacitors and improving the withstand voltage characteristics.

To solve this problem, research has been conducted on the development of a dielectric layer having a dielectric constant higher than that of alumina having a dielectric constant of about 8 to 9, which is conventionally used. An oxide layer such as zirconium oxide (ZrO ₂ ), niobium oxide (Nb ₂ O ₅ ), tantalum oxide (Ta ₂ O ₅ ) or the like is coated by a sol-gel method and used as a dielectric layer. Since the oxide layer has a high dielectric constant of 20 or more, it can contribute to the miniaturization of the capacitor compared to the alumina layer of the same thickness. The oxide films as described above may be used alone or in the form of a separately formed alumina layer.

At this time, the oxide films are easily coated on the flat thin film, but it is not easy to coat the thin film on the surface through the sol-gel method. That is, in an aluminum electrolytic capacitor, a plurality of pores or pits are formed through etching on the surface of a flat aluminum foil to increase the effective surface area. In this case, the inside diameter of the pores is generally 1 to 2 μm And has a length of 10 to 50 mu m, it is difficult to uniformly coat the oxide film on the inner wall of the pores by the sol-gel method. In addition, when the step of anodizing the aluminum foil having the oxide film formed on its surface is performed under a high voltage condition of 700 V or more, there arises a problem such that the anodic oxidation does not occur or the oxide film is peeled due to generation of a severe arc on the surface of the aluminum foil . Accordingly, there is a limit in improving the capacitance of the capacitor and it is difficult to maintain the withstand voltage.

An object of the present invention is to provide a high-voltage anodizing solution for an aluminum foil coated with a metal oxide, which can stably carry out an anodizing process under a voltage condition of 700 V or more for high-voltage electrolytic capacitors.

Another object of the present invention is to provide a method for producing an aluminum foil for an electrolytic capacitor using the high-voltage anodizing solution.

The high-voltage anodizing solution of the aluminum foil coated with a metal oxide according to an embodiment of the present invention includes an aqueous boric acid solution containing 100 g of boric acid per 1 L of water and propylene glycol Propylene glycol is contained in an amount of 10% by volume to 30% by volume based on the total volume.

In one embodiment, the high-voltage anodizing solution may comprise 70 vol% boric acid aqueous solution and 30 vol% propylene glycol based on the total volume.

In one embodiment, the high-voltage anodizing solution can be used in the process of anodizing an aluminum foil having a metal oxide sol-gel coated on the etched-pore surface at a voltage of 700 V to 1,000 V.

A method of manufacturing an aluminum foil for an electrolytic capacitor according to an embodiment of the present invention includes the steps of impregnating a porous aluminum foil containing a plurality of etching pores in a vacuum state with a metal oxide sol contained in a chamber, A step of discharging the metal oxide sol, a step of drying the aluminum foil coated with the metal oxide sol, a sintering step of sintering the dried coating film, and an anodic oxidation of the aluminum foil having the sintered coating film formed thereon, Forming a composite oxide layer comprising an aluminum oxide layer and a metal oxide layer stacked on an inner wall surface of the etch-pores, wherein the anodic oxidant solution comprises 100 g of boric acid per liter of water And an aqueous solution of boric acid and propylene glycol, wherein propylene glycol is present in an amount of from 10% by volume to 30% By volume.

In one embodiment, the manufacturing method may further include a pressing step of pressing the aluminum foil in a state impregnated with the metal foil sol, before performing the recovery step. At this time, the step of impregnating the metal oxide sol includes the steps of disposing the aluminum foil in the chamber in a non-vacuum state, making the chamber in a vacuum state in a state in which the aluminum foil is disposed and providing the metal oxide sol in the vacuum chamber Step < / RTI >

In one embodiment, the step of forming the composite oxide layer may be performed at a voltage of 700 V to 1,000 V.

According to the above-described method for producing an aluminum foil for an electrolytic capacitor coated with a metal oxide of the present invention and a method for producing an aluminum foil for electrolytic capacitors using the same, an anodic oxidation process can be stably performed at a voltage of 700 V or higher . Particularly, it can be confirmed that peeling of the metal oxide film does not occur. Accordingly, the withstand voltage and capacity of the manufactured electrolytic capacitor can be improved, and the market competitiveness of the product can be improved.

1 is a flowchart illustrating a method of manufacturing an aluminum foil according to an embodiment of the present invention.
2 is a conceptual diagram for explaining an apparatus for manufacturing an aluminum foil for performing the manufacturing method of FIG.
FIG. 3 is a graph showing changes in withstand voltage characteristics of the high-voltage anodizing solution according to changes in propylene glycol content with time.
FIG. 4 is a graph showing the specific capacitance change with voltage change after the anodic oxidation process for the metal oxide coated sample and the uncoated sample. FIG.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. The present invention is capable of various modifications and various forms, and specific embodiments are illustrated in the drawings and described in detail in the text. It is to be understood, however, that the invention is not intended to be limited to the particular forms disclosed, but on the contrary, is intended to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention. Like reference numerals are used for like elements in describing each drawing.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The singular expressions include plural expressions unless the context clearly dictates otherwise. In the present application, the term "comprises" or "having ", etc. is intended to specify that there is a feature, step, operation, element, part or combination thereof described in the specification, , &Quot; an ", " an ", " an "

Unless defined otherwise, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Terms such as those defined in commonly used dictionaries are to be interpreted as having a meaning consistent with the contextual meaning of the related art and are to be interpreted as either ideal or overly formal in the sense of the present application Do not.

FIG. 1 is a flow chart for explaining a method of manufacturing an aluminum foil according to an embodiment of the present invention, and FIG. 2 is a conceptual diagram for explaining an apparatus for manufacturing an aluminum foil for performing the manufacturing method of FIG.

Referring to FIGS. 1 and 2, an aluminum foil TG is immersed in a metal oxide sol 212 in a vacuum chamber 210 in an aluminum foil manufacturing apparatus 200 (step S110).

At this time, the aluminum foil (TG) is immersed in the metal oxide sol 212 in a state including a plurality of etch-pores formed on the surface.

Specifically, an aluminum foil (TG) is disposed in the empty non-vacuum chamber 210, and the inside of the chamber 210 is evacuated. Air in the etching-pores of the aluminum foil (TG) can be discharged to the outside while being made into a vacuum state. At this time, the chamber 210 may be evacuated using the pump 240 of the manufacturing apparatus 200, and a valve may be installed in the tube connecting the pump 240 and the chamber 210. The vacuum state pressure may be between about 759 torr and 1 millitorr. The air inside the aluminum foil pore is discharged. In the vacuum state, the aluminum foil TG is immersed in the metal oxide sol 212. Since the air inside the etching pores of the aluminum foil TG is in a vacuum state while the vacuum state is being formed, the metal oxide sol 212 is sucked into the etching pores in the soaking process, The wall surface can be uniformly coated with the metal oxide sol 212.

The metal oxide sol 212 is a coating material in the form of a sol consisting of a metal oxide such as zirconium oxide (ZrO ₂ ), titanium oxide (TiO ₂ ), niobium oxide (Nb ₂ O ₅ ) (Ta ₂ O ₅ ), barium titanate (BaTiO ₃ ), and the like. These may be used alone or in combination of two or more. The metal oxide sol 212 may be prepared using a precursor of a metal oxide. Depending on the type of the metal oxide sol 212, the kind and concentration of the precursor and the solvent, the kind of the additive, and the compounding ratio may vary.

The aluminum foil TG may be attached to the support 214 of the chamber 210 and may be immersed in the metal oxide sol 212. The front surface of the chamber 210 includes a transparent window for confirming the coating state of the chamber 210 and a pressure gauge 250 for confirming the pressure inside the chamber 210 may be installed in the chamber 210.

The metal oxide sol 212 is stored in the coating material supply unit 220 and then supplied to the chamber 210 through the supply channel after the chamber 210 is evacuated to be accommodated in the inner space of the chamber 210, TG) can be immersed. At this time, a valve is provided in the supply passage to open / close the flow of the metal oxide sol 212. That is, the valve provided in the tube connecting the pump 240 and the chamber 210 is closed, and the valve connected to the supply channel is gradually opened, so that the metal oxide sol 212 is supplied into the chamber 210 And the amount of liquid of the metal oxide sol 212 in the chamber 210 can be adjusted through the opening amount of the valve connected to the supply flow path.

After the aluminum foil TG is immersed in the metal oxide sol 212 for a predetermined period of time, the remaining metal oxide sol 212 is recovered (Step S120), and the metal oxide sol (Step S130).

The valve connected to the supply flow path is closed to stop the supply of the metal oxide sol 212 and the valve connected to the discharge flow path connected between the chamber 210 and the coating material supply unit 220 is opened to discharge the remaining metal oxide The sol 212 is returned to the coating material supply unit 220 again.

If the rate at which the metal oxide sol 212 is discharged through the discharge channel, that is, the height of the metal oxide sol 212 remaining in the chamber 210 is set to more than 10 mm / s, the dip- coating layer may increase the pulling speed of the aluminum foil TG and increase the amount of the metal oxide sol 212 coated on the surface of the aluminum foil TG so that a thick coating layer may be formed. There is a disadvantage in that the thickness is uneven and cracks can easily occur. Therefore, the rate at which the metal oxide sol 212 is discharged is preferably 10 mm / s or less, and may be about 0.2 mm / s to about 10 mm / s.

At this time, before the remaining metal oxide sol 212 is recovered, a step of applying pressure while immersing the aluminum foil TG in the metal oxide sol 212 may be further performed. This process can be performed additionally in order to more uniformly and easily proceed the coating of the metal oxide sol 212, and a pressure of about 1 to 5 atm may be applied. A pressurization process may be performed for about 10 minutes to 1 hour. If the coating is not easy due to the depth and / or shape of the etching-pores, the metal oxide sol 212 can be uniformly coated on the inner wall of the etching-pores by applying the pressure as described above. When the depth of the etching-pores is more than 10 mu m, it is preferable to perform the pressing process. As the inert gas, argon (Ar), helium (He) or the like can be used as the gas used in the pressurizing step. After applying pressure, keep the coating for a certain time (10 ~ 30 minutes). The inert gas may be supplied through the gas supply unit 230 connected to the chamber 210.

As described above, the remaining metal oxide sol 212 is recovered and dried. The drying process may be performed at about 100 ° C to 200 ° C, and may be performed for about 30 to 60 minutes. Accordingly, the metal oxide sol 212 is uniformly coated on the surface of the aluminum foil (TG), particularly the inner wall surface of the etch-pores, to form a coating film. The thickness of the coating film can be determined by adjusting the number of cycles including the immersion step (S110), the recovery step (S120), and the drying step (130). That is, the coating thickness can be determined depending on whether the immersion step (S110), the collection step (S120), and the drying step (130) are performed in one cycle and the cycle is repeated several times. At this time, a pressurizing process may be further added to the cycle.

Subsequently, a sintering process is performed on the aluminum foil (TG) on which the coating film is formed (step S140), and anodizing process is performed on the sintered aluminum foil (TG) using an anodizing solution (step S150) ≪ / RTI >

Specifically, the sintering process is a process of crystallizing the coating film, and can be performed at about 350 ° C to about 600 ° C. At this time, the sintering process can be performed for about 10 minutes to about 60 minutes. The sintering process may be performed at atmospheric pressure or under an oxygen atmosphere.

In one example, the sintering process may be performed subsequently after at least one cycle including the above-described immersion process (S110), recovery process (S120), and drying process (130) is performed. Alternatively, the sintering process may be performed subsequent to the immersion step (S110), the collecting step (S120), and the drying step (130) each time the cycle is included in the cycle.

After the sintering process as described above, the sintered aluminum foil (TG) is subjected to an anodizing process, wherein the anodizing process is performed at a voltage of 700 V or more. The current condition at this time may be 20 mA / cm ² to 50 mA / cm ² .

The anodizing solution contains an aqueous solution of boric acid and propylene glycol. The boric acid aqueous solution contains 100 g of boric acid per liter of water and propylene glycol is contained in an amount of 10% by volume to 30% by volume based on the total volume of the anolyte. The anolyte solution may be prepared by mixing propylene glycol with an aqueous solution of boric acid, and the mixture may be stirred at a temperature ranging from 30 to 70 ° C for 1 to 2 hours.

When boric acid alone is mixed with boric acid and ethylene glycol as an anodic oxidizing solution and the anodic oxidation process is performed under a voltage condition of 700 V or more, there is a problem that the coating film peels off. In addition, when the aqueous boric acid solution contains less than 10% by volume of propylene glycol, the problem of peeling due to the addition of propylene glycol can not be solved. If it exceeds 30% by weight, peeling of the coating film is prevented, There is a problem that the composite oxide layer is not properly formed. Therefore, in the case of the anodic oxidizing solution according to the present invention containing propylene glycol, it is preferable that the content of propylene glycol is 10% by volume to 30% by volume with respect to the volume of the total anodizing solution. Considering the characteristics of the composite oxide layer thus prepared, the content of propylene glycol is most preferably 30 vol% based on the total volume of the anolyte solution, and the remaining 70 vol% is occupied by the aqueous boric acid solution.

Due to the anodic oxidation process, the inner wall surface inside the etching pores of the aluminum foil TG is oxidized to a predetermined thickness and converted into aluminum oxide, and a coating film is formed on the metal oxide layer. Since the coating film has a uniform thickness and is formed on the inner wall surface of the etching pores of the aluminum foil TG, ultimately a metal oxide layer having a uniform thickness is formed on the inner wall surface, An aluminum foil including a composite oxide layer which is a mixed layer of a metal oxide layer having a high dielectric constant is formed. Such an aluminum foil can be applied to electrolytic capacitors for high voltage.

As described above, it is possible to form a metal oxide layer having a high dielectric constant uniformly in a porous aluminum foil (TG) including a plurality of etching-pores, to increase the effective surface area of the electrode through the etching- An anodic oxidation process can be stably performed by using an oxidizing solution to produce an aluminum foil having a composite oxide layer containing both aluminum oxide and a metal oxide layer. Such an aluminum foil can improve the electrostatic capacitance in the same volume by constructing an electrolytic capacitor together with an electrolyte as an electrode structure. As a result, the size of the aluminum electrolytic capacitor can be reduced, and the market competitiveness of the product can be improved. That is, in an electrolytic capacitor including two electrode structures and an electrolyte interposed therebetween, at least one electrode structure may be composed of the aluminum foil according to the present invention.

Hereinafter, concrete examples of the positive electrode electrolyte of the present invention and comparative examples will be described in more detail.

Manufacture of anodizing solution

An aqueous solution of boric acid was prepared by mixing 100 g of boric acid with 1 L of water. An aqueous solution of boric acid and propylene glycol were mixed and stirred at 50 ° C for about 1 hour to prepare anodic oxidized solutions 1 to 5. The content of propylene glycol in each of the anolyte solutions 1 to 5 was 10% by volume, 20% by volume, 30% by volume, 50% by volume and 70% by volume based on the total volume of the anolyte.

Preparation of anodic oxidation samples 1 to 6

In order to perform an anodic oxidation process using an anodic oxidizing solution and an aqueous boric acid solution, an aluminum foil having an etch-pore formed thereon was first prepared, and a zirconium oxide film was coated on the surface of the aluminum foil by the sol-gel method as follows.

A zirconia sol solution having a concentration of 0.4 mol / l was prepared by using zirconium n-butoxide (Zr [O (CH ₂ ) ₃ CH ₃ ] ₄ ] as a precursor of zirconium oxide. The solvent of the zirconia sol solution was 2-methoxyethanol, [CH ₃ OCH ₂ CH ₂ OH], and acetic acid [CH ₃ COOH] was used as an additive. In the preparation of the zirconia sol solution, the molar ratio of zirconium to acetic acid was 1: 6, and after stirring at room temperature for 60 minutes, nitric acid (HNO ₃ ) was added to prevent precipitation of zirconium oxide. (50 mTorr) in a state where the aluminum foil having the etch-pores formed therein was placed in the chamber, and the air inside the etching-pores was discharged for about 30 minutes to supply the prepared zirconia sol solution to the chamber Respectively.

The aluminum foil was immersed in the zirconia sol solution for 15 minutes, and then the pressure of 3 atm was applied with argon gas to maintain the solution for 10 minutes, and then the residual zirconia sol solution was adjusted to fall to 0.5 mm / s. Subsequently, after the chamber was opened, the aluminum foil having the coating film formed thereon was dried at 100 DEG C for 1 hour. The immersion, pressurization and drying processes were performed four times. The sintering process was performed at 500 ° C for 30 minutes to crystallize the coating film.

Characterization of anodised foil

After the samples including the aluminum foil having the surface on which the zirconium oxide film was formed were prepared as described above, a constant current of 50 mA / cm ² was applied to each of the samples using an aqueous solution of boric acid and an anolyte solutions 1 to 5, Anodic oxidation was performed, and anodized aluminum foil was cut into 50 mm x 30 mm to prepare a sample for capacity measurement. The sample was immersed in an aqueous solution at 30 캜 in which 80 g of boric acid and 1 L of pure water were mixed.

The voltage was set to 800 V and 900 V in the anodizing process in substantially the same process as the above process, and the capacity was measured.

The results are shown in Table 1 below.

Propylene glycol
Content (vol%) Capacity (㎌ / cm ² ) 700V 800V 900V 0 (boric acid aqueous solution) 0.52 0.43 0.30 10 (Anodizing solution 1) 0.53 0.46 0.35 20 (Anodizing solution 2) 0.69 0.47 0.42 30 (anodizing solution 3) 0.72 0.62 0.51 50 (Anodizing solution 4) 0.67 0.49 0.42 70 (Anodizing solution 5) 0.53 0.43 0.34

Referring to Table 1, it can be seen that as the propylene glycol is increased from 10% by volume to 30% by volume, the voltage condition of the anodization process tends to increase in capacity at 700V, 800V and 900V, respectively. Compared with the case where a pure aqueous solution of boric acid containing no propylene glycol was used, it can be confirmed that the case where propylene glycol was contained increased the capacity under the same voltage condition. It can be seen that as the content of propylene glycol increases, the arc generated on the aluminum foil surface is reduced and the composite oxide is stably produced, and the exfoliation of zirconium oxide is reduced.

On the other hand, when the content of propylene glycol is more than 30% by volume, as in the case of the anodic oxidants 4 and 5, the anodic oxidation can not be stably carried out as the viscosity of the anodized oxidant increases, You can see the result.

Evaluation of withstand voltage characteristics

When the voltage condition of the anodic oxidation process was 700V, the withstand voltage characteristics of each of the anodized thin films were evaluated with time. The results are shown in Fig.

FIG. 3 is a graph showing changes in withstand voltage characteristics of the high-voltage anodizing solution according to changes in propylene glycol content with time.

The% shown in Fig. 3 means the volume% and represents the content of propylene glycol contained in the anodizing solution.

Referring to FIG. 3, when the anodic oxidizing solution 1 (10%) or the anodic oxidizing solution 2 (20%) was used, the prepared thin film It can be confirmed that the withstand voltage characteristic is higher.

When the anodic oxidizing solution 3 (30%) is used, it can be confirmed that the voltage rising time is long, but it is increased up to 800V. In the case of using pure aqueous solution of boric acid not containing propylene glycol, the result of using an anolyte solution 3 is remarkably increased as compared with that exhibiting withstand voltage at 700V.

Evaluation of pH and Conductivity of Anodic Oxidant

PH and conductivity were measured for each of the boric acid aqueous solution and the anodic oxidized solutions 1 to 5. The results are shown in Table 2 below.

Propylene glycol content (vol%) 0%
(Boric acid aqueous solution) 10%
(Anodic oxidizing solution 1) 20%
(Anodizing solution 2) 30%
(Anodizing solution 3) 50%
(Anodizing solution 4) 70%
(Anodizing solution 5) pH 2.43 2.64 2.73 2.91 3.97 4.15 conductivity
(/ / Cm) 350 251 168 115 51.8 39.1

Referring to Table 2, it can be seen that the pH value tends to increase from 1 to 5 in the anolyte solution, and the conductivity tends to decrease. Through the reduction of conductivity, it can be seen that anodic oxidation can be efficiently performed to a high voltage as the arc generation is reduced. However, contrary to this characteristic, anodization can not be carried out up to a desired voltage due to an increase in viscosity due to an increase in the content of propylene glycol.

Therefore, from the results of Table 2 and the results of Table 1 and FIG. 3, it can be seen that when the content of propylene glycol is from 10% by volume to 30% by volume, the withstand voltage and capacity increase effect can be secured at the same time.

Evaluation of capacity increase characteristics

An uncoated sample was prepared in the state that the aluminum foil was not coated with zirconium oxide. The sample was subjected to an anodic oxidation process at 700 V, 800 V, and 900 V using an anolyte solution 3, and then the capacity was measured. The results are shown in Fig. 4 together with the results of anodization of aluminum foil coated with zirconium oxide (coating sample).

FIG. 4 is a graph showing the specific capacitance change with voltage change after the anodic oxidation process for the metal oxide coated sample and the uncoated sample. FIG.

Referring to FIG. 4, it can be seen that the capacity of the coating sample coated with zirconium oxide is at least 50% higher than the capacity of the uncoated sample. In particular, when the anodic oxidation process is performed at 900 V, the capacity increases to 71.3%.

It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the present invention as defined by the following claims. It can be understood that it is possible.

200: manufacturing apparatus 210: chamber
212: metal oxide sol 214: support
220: coating material supply unit 230: gas supply unit
240: Pump 250: Pressure gauge

Claims (7)

An aqueous solution of boric acid containing 100 g of boric acid per liter of water; And
Propylene glycol,
A high-voltage anodizing solution containing propylene glycol in an amount of 10 to 30 vol% based on the total volume and the aqueous solution of boric acid in an amount of 70 to 90 vol%
The high-voltage anodizing solution
Characterized in that an aluminum foil in which a metal oxide is sol-gel coated on an etch-pore-formed surface having a diameter of 1 to 2 占 퐉 and a depth of 10 to 50 占 퐉 is used in an anodic oxidation process at a voltage of 700 V to 1,000 V doing,
High Voltage Anodizing Solution of Aluminum foil for Electrolytic Capacitors Coated with Metal Oxide.
The method according to claim 1,
Characterized in that it comprises 70% by volume of an aqueous boric acid solution and 30% by volume of propylene glycol with respect to the total volume,
High Voltage Anodizing Solution of Aluminum foil for Electrolytic Capacitors Coated with Metal Oxide.
delete Impregnating a porous aluminum foil containing a plurality of etch-pores having a diameter of 1 to 2 占 퐉 and a depth of 10 to 50 占 퐉 in a vacuum state in a metal oxide sol contained in the chamber;
A recovery step of discharging the metal oxide sol remaining in the chamber;
Drying the aluminum foil coated with the metal oxide sol;
A sintering step of sintering the dried coating film; And
The aluminum foil on which the sintered coating film was formed was anodized using an anodic oxidation liquid at a voltage of 700 V to 1,000 to form a composite oxide layer including an aluminum oxide layer and a metal oxide layer stacked on the inner wall surface of the etching- ; And
The anodizing solution contains an aqueous solution of boric acid containing 100 g of boric acid per liter of water and propylene glycol, wherein propylene glycol is contained in an amount of 10 to 30 vol% based on the total volume Characterized in that said boric acid aqueous solution is comprised between 70% and 90% by volume,
Method for manufacturing aluminum foil for electrolytic capacitors.
5. The method of claim 4,
Characterized by further comprising a pressurizing step in which the aluminum foil is impregnated with the metal oxide sol before the recovery step is carried out,
Method for manufacturing aluminum foil for electrolytic capacitors.
6. The method of claim 5,
The step of impregnating the metal oxide sol
Disposing an aluminum foil in a chamber in a non-vacuum state;
Placing the chamber in a vacuum state with the aluminum foil disposed thereon; And
And providing a metal oxide sol into the chamber in a vacuum state.
Method for manufacturing aluminum foil for electrolytic capacitors.
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