JP4844973B2 - Manufacturing method of electrode foil - Google Patents

Description

  The present invention relates to a method for producing an electrode foil that is optimal for forming a metal oxide on the surface of a valve action metal foil on which a dielectric oxide film is formed.

  In order to achieve an increase in the capacity of an electrolytic capacitor, it is known to form a metal oxide film having a relatively large dielectric constant on the surface of a valve metal foil such as an aluminum foil and use this as an electrode.

  Conventionally, methods such as CVD, ion plating, and sputtering are known as methods for forming a metal oxide on the surface of this type of valve-acting metal foil (base material). However, these methods not only require special and expensive manufacturing equipment, but also form a metal oxide as a thin film on a large-area substrate or a metal on a substrate having a complicated surface shape. There is a problem that it is extremely difficult to form an oxide as a thin film.

  Therefore, in order to solve these problems, a method using a metal oxide sol formed by hydrothermal treatment has been proposed. For example, a metal oxide in which a mixed aqueous solution of zirconium salt and yttrium salt, which is a rare earth, is hydrothermally treated under saturated water vapor pressure, and the resulting mixed oxide sol is applied to the surface of the substrate, followed by drying and firing. Have been proposed (Patent Document 1, Patent Document 2).

Apart from this, the following method has been proposed (Patent Document 3). Zirconium oxychloride is suspended in ethanol, and an aqueous boric acid solution and then ammonium water are added to hydrolyze the zirconium oxychloride to obtain a hydrated zirconium sol containing a boron compound. A base material is immersed in the sol so that the sol is adhered, and this is heat-treated and dried to form a zirconium oxide film. Next, the substrate is immersed in a medium from which boron oxide can be extracted, and boron oxide is eluted and desorbed from the zirconium oxide film.
Japanese Patent Laid-Open No. 63-233088 JP-A-2-38362 JP-A-5-319953

  However, in the manufacturing methods shown in Patent Documents 1 to 3, a metal oxide is formed as a thin film on a substrate having a large area, or a metal oxide is formed as a thin film on a substrate having a complicated surface shape. The problem that it is difficult to do was not able to be solved sufficiently. Furthermore, the method that requires a high-temperature heat treatment process in the formation process of the metal oxide has a common risk that the base material may be deformed, and in any case, it is difficult to form the metal oxide as a thin film. It had a problem.

  The present invention solves such conventional problems, and provides a method for producing an electrode foil capable of easily forming a metal oxide as a thin film regardless of the size and surface shape of a substrate. With the goal.

The present invention provides an electrode foil manufacturing method in which a metal oxide is formed on the surface of a dielectric oxide film formed on the surface of a valve action metal foil, wherein the metal oxide is a fluoro metal complex compound and / or a metal in a solution. The formula that results from the presence of fluoride;
M _a F _b ^c− + dH ₂ O → M _a O _d + bF ⁻ + 2dH ⁺
(Wherein M is one selected from the group consisting of Ti, Zr, Si, Nb, Ta, Hf, In, Sn and rare earth elements; a, b, c and d are coefficients, and ma = B−c = 2d, where m is the oxidation number of the metal M and satisfies the relationship of a> 0, b> 0, c ≧ 0, and d> 0)) It relates to the manufacturing method.

As described above, the electrode foil manufacturing method according to the present invention is a method in which a metal oxide is coated on the surface of a dielectric oxide film of a valve action metal foil in a solution of a fluoro metal complex compound and / or a metal fluoride. Even if the area of the valve action metal foil that is the base material is large or the surface shape is complicated, the metal oxide thin film on the surface of the dielectric oxide film at a temperature sufficiently lower than the melting point of the valve action metal foil, Moreover, it can be formed inexpensively with a simple apparatus.
Furthermore, it is possible to intentionally select and form a metal oxide having a relative dielectric constant or insulation resistance larger than that of the dielectric oxide film on the surface of the dielectric oxide film formed on the surface of the valve action metal foil. it can.
In addition, it is possible to control the coating thickness of the metal oxide while suppressing the dissolution of the dielectric oxide film by allowing the fluoride ion scavenger to be present in the solution of the fluoro metal complex compound and / or metal fluoride. It becomes. As a result, the thickness of the metal oxide can be effectively secured, and the withstand voltage can be set high, so that an effect of obtaining an electrode foil having a high CV value can be obtained. The CV value is represented by the product of the capacity (C) and the withstand voltage (V), and the higher the value, the better the electrical characteristics.
In addition, by adjusting the pH of the solution containing the fluoride ion scavenger, the thickness of the metal oxide coating can be more easily controlled by controlling the amount of dissolution of the dielectric oxide film.

In the method for producing an electrode foil according to the present invention, when forming a metal oxide on the surface of the dielectric oxide film formed on the surface of the valve action metal foil, a fluoro metal complex compound and / or a metal fluoride is added to the solution. The formula that results from the presence;
M _a F _b ^c− + dH ₂ O → M _a O _d + bF ⁻ + 2dH ⁺
A metal oxide (M _a O _d ) is formed using the reaction of

In the formula, M is one selected from the group consisting of Ti, Zr, Si, Nb, Ta, Hf, In, Sn, and rare earth elements. The rare earth element is a generic term for the elements Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu. M is preferably Ti, Zr, Si, Nb, or Ta from the viewpoint that the electrolytic capacitor has a higher CV value.
a, b, c, and d are coefficients, and ma = b−c = 2d, where m is the oxidation number of the metal M, and a relationship of a> 0, b> 0, c ≧ 0, and d> 0 is satisfied.

  In the present invention, the valve action metal foil is used with a dielectric oxide film formed on the surface thereof. When a valve metal foil without a dielectric oxide film is used, the metal oxide referred to in the present invention cannot be generated on the valve metal surface, and as a result, the effects of the present invention are achieved. That is extremely difficult. The reaction proceeds effectively due to the presence of the film, but if the film does not exist, the reaction does not proceed and the metal oxide is not generated. In the present invention, the thickness of the dielectric oxide film of the valve metal foil is usually 1.0 nm or more.

  The dielectric oxide film can be formed by subjecting the valve action metal foil to a conventionally known oxidation treatment, for example, an anodic oxidation treatment. As the valve action metal foil, a foil made of a material capable of forming a dielectric oxide film exhibiting a valve action by oxidation treatment is used. For example, an aluminum foil, a tantalum foil, a niobium foil or the like is used. By oxidizing these foils, an aluminum oxide film, a tantalum oxide film, and a niobium oxide film are formed on the surface as dielectric oxide films, respectively. As the valve action metal foil, either a plain foil (non-etched foil) or an etched foil can be used. Etched foil is a foil that has been etched to increase the surface area of the foil.

  When the dielectric oxide film is formed by anodic oxidation, if the heat treatment step is included in this formation process, invalid dissolution of the dielectric oxide film can be suppressed when forming the metal oxide, and as a result, there is no waste. A metal oxide can be formed efficiently. That is, the defect portion of the dielectric oxide film is exposed by the heat treatment process, and the defect portion is repaired by the subsequent anodic oxidation, so that a dense dielectric oxide film can be formed. Ineffective dissolution of the dielectric oxide film during formation can be suppressed. Therefore, it is desirable to use the heat treatment step as an intermediate step of the anodizing treatment step, and perform the anodizing treatment again after the heat treatment step.

  For example, it is desirable to sequentially perform a first anodizing process, a heat treatment process, and a second anodizing process. The processing conditions in the first anodizing treatment step and the second anodizing treatment step are not particularly limited as long as the dielectric oxide film is formed and the object of the present invention is achieved. The heat treatment step is performed, for example, in the atmosphere at a temperature of 350 to 400 ° C. for 3 to 5 minutes.

  The fluoro metal complex compound and / or metal fluoride may be any metal that can precipitate the metal contained in the compound as an oxide based on the above reaction formula. Fluoro metal complex compounds and / or metal fluorides containing a metal that has a relative dielectric constant and insulation resistance larger than that of a dielectric oxide film when converted into an oxide are useful. The metal M exemplified in the above reaction formula is a metal whose relative dielectric constant is larger than that of the dielectric oxide film when it becomes an oxide. For example, when the dielectric oxide film is an aluminum oxide film, the relative dielectric constant of the film is about 9, but when a fluorometal complex compound or metal fluoride containing Ti or Zr is used as the metal M, the relative dielectric constant is obtained. Are about 40 or about 20 titanium oxide films or zirconium oxide films, respectively. As a result, the capacity (C) of the electrode foil increases and a high CV value is achieved.

Specific examples of the fluorometal complex compound include ammonium ammonium fluoride ((NH ₄ ) ₂ TiF ₆ ) and zircon ammonium fluoride ((NH ₄ ) ₂ ZrF ₆ ). These Ti and Zr are more versatile than other valve metals, and both titanium ammonium fluoride ((NH ₄ ) ₂ TiF ₆ ) and zircon ammonium fluoride ((NH ₄ ) ₂ ZrF ₆ ) are easily available. There are advantages. In particular, Ti has a high relative dielectric constant compared to other valve metals, so it has a significant effect on capacity increase. When Zr is used, the dielectric film withstand voltage is improved compared to other valve metals. Therefore, it is desirable to use ammonium titanium fluoride ((NH ₄ ) ₂ TiF ₆ ) or zircon ammonium fluoride ((NH ₄ ) ₂ ZrF ₆ ) as the fluorometal complex compound. However, the present invention is not limited to this.

For example, when ammonium titanium fluoride is used as the fluorometal complex compound, the metal oxide production reaction is represented by the following formula:
TiF ₆ ²⁻ + 2H ₂ O → TiO ₂ + 6F ⁻ + 4H ⁺
Proceed based on.
For example, when zircon ammonium fluoride is used as the fluorometal complex compound, the metal oxide production reaction is represented by the following formula:
ZrF ₆ ²⁻ + 2H ₂ O → ZrO ₂ + 6F ⁻ + 4H ⁺
Proceed based on.

Similar effects can be obtained by using a metal fluoride instead of the fluorometal complex compound, and the fluorometal complex compound and the metal fluoride can be used in combination.
Specific examples of the metal fluoride include titanium fluoride (TiF ₄ ). When titanium fluoride is used, the metal oxide formation reaction is represented by the following formula:
TiF ₄ + 2H ₂ O → TiO ₂ + 4F ⁻ + 4H ⁺
Proceed based on.

The inventors obtained new knowledge while continuing the research. That is, the effect of improving the CV value even when the concentration of the fluorometal complex compound and / or metal fluoride is extremely low is sufficiently exhibited. In other words, the metal oxide is not necessarily formed on the entire surface of the dielectric oxide film, and may be formed in an island shape (partial). Specifically, the preferable adhesion amount of the metal oxide formed on the electrode foil is 10 to 1000 μg / m ² in terms of the effective surface area of the electrode foil. If it is less than 10 μg / m ² , the effects of the present invention may not be sufficiently exhibited. On the other hand, when it exceeds 1000 μg / m ² , it is often formed on the entire surface instead of islands.

In order to form the metal oxide in an island shape, for example, the above-described ammonium titanium fluoride ((NH ₄ ) ₂ TiF ₆ ) or ammonium zircon fluoride ((NH ₄ ) ₂ ZrF ₆ ) is used as the fluorometal complex compound. In this case, the concentration may be 0.0005 mol / l or more and less than 0.01 mol / l. This is because if it is less than 0.0005 mol / l, the effect of improving the CV value may not be sufficiently obtained. On the other hand, the upper limit concentration is preferably less than 0.01 mol / l. It is because it may not become island shape at 0.01 mol / l or more. Moreover, less than 0.01 mol / l is preferable also from the complexity of work. That is, it is necessary to perform heat treatment after forming the metal oxide in order to fix the generated metal oxide to the substrate. Therefore, if the concentration is less than 0.01 mol / l, it may be air-dried, and a heat treatment step is unnecessary, and the equipment for that purpose and the energy required for the heat treatment are unnecessary. In addition, by using such a low concentration, the amount of chemicals used can be greatly reduced, and the environmental load during waste liquid treatment can also be reduced.

  The reason why the CV value is improved at such a very low concentration is unclear, but at present, it is presumed as follows. Fluoride ions dissolve the dielectric oxide film to form a metal oxide. At that time, it is considered that the weak part of the dielectric oxide film is preferentially dissolved. The weak part may be a structural defect or a recess due to a scratch. It is considered that the metal oxide is preferentially formed at the weak spot of the dielectric film by preferential dissolution. That is, it is considered that the weak part is reinforced with the metal oxide, thereby improving the withstand voltage and increasing the capacity at the part.

  It is preferable that a fluoride ion scavenger is present in the solution of the fluoro metal complex compound and / or metal fluoride (hereinafter simply referred to as “treatment solution”). The presence of the fluoride ion scavenger makes it possible to control the coating thickness of the metal oxide while suppressing dissolution of the dielectric oxide film.

  Further, as described above, a fluoride ion scavenger is also effective when the metal oxide is formed in an island shape. That is, the fluoride ion scavenger suppresses the dissolution of the dielectric oxide film, so that the weak part of the dielectric film is more preferentially dissolved than the other parts, and the metal oxide formation reaction proceeds more slowly. As a result, the formation state of the metal oxide can be easily controlled, and as a result, the metal oxide can be easily formed in an island shape.

As the fluoride ion scavenger, for example, a boron-containing compound can be used.
Specific examples of the boron-containing compound include ammonium borate, boron oxide, boric acid and the like. These compounds can be used alone or in combination. As ammonium borate, for example, ammonium tetraborate tetrahydrate _{((NH 4) 2 B 4} O 7 · 4H 2 O), pentaborate ammonium octahydrate _{((NH 4) 2 O ·} 5B 2 O ₃ · _8H 2 O) and the like.

  An electrode foil having a high CV value can be obtained by adjusting the pH of the treatment solution containing the fluoride ion scavenger. Here, in particular, an electrode foil having a higher CV value can be obtained by adjusting the pH of the solution to be higher than 7. Although this mechanism has not been clarified at the present time, it is considered to suppress a rapid reaction and promote generation of a more uniform metal oxide.

  Specific examples of the pH adjusting agent for adjusting the pH include, for example, ammonia, hydrazine, amines, basic salts, hydroxides, and the like, and at least one pH adjusting agent selected from these groups Can be used.

  The concentration of the pH adjuster in the treatment solution is not particularly limited as long as the pH of the treatment solution is adjusted within a predetermined range. Two or more kinds of pH adjusters may be used.

  Ammonium borate, boron oxide and boric acid as fluoride ion scavengers can also be used as pH adjusters, and these ammonium borate, boron oxide and boric acid can be used alone or in combination. . Thus, by using ammonium borate, boron oxide, and boric acid, there is an effect that an electrode foil having a high CV value can be obtained. In addition, it is possible to simplify the composition system of the solution by using a material having both functions of a fluoride ion scavenger and a pH adjuster, and as a result, the solution management in the manufacturing process becomes easy. It also has an effect.

  Even when ammonium borate, boron oxide, or boric acid is used alone or in combination, at least one of the above-described pH adjusters, that is, ammonia, hydrazine, amines, and basic salts may be used in combination. As described above, since there are a plurality of pH adjustment methods, there is an effect that the degree of freedom in process design increases.

  The treatment method using the treatment solution is not particularly limited as long as the contact between the surface of the valve metal foil having the dielectric oxide film formed on the surface and the treatment solution can be secured, and an immersion method is usually adopted. That is, the valve action metal foil is immersed in the treatment solution and held.

The treatment temperature and treatment time are not particularly limited as long as the object of the present invention can be achieved, but usually, the treatment solution is set at a temperature close to room temperature from the viewpoint of reducing the production cost.
For example, the treatment solution is set to 20 to 40 ° C.
The processing time is usually set to 0.5 to 4 hours. By setting the treatment time longer, an island-shaped metal oxide can be easily formed. This is because by repeating the dissolution and precipitation of the metal oxide itself by increasing the processing time, the larger metal oxide becomes larger and the particles are unevenly distributed, resulting in a more island-like shape. It is thought that.

The thickness of the formed metal oxide film can be controlled by adjusting the processing temperature and the processing time. The same applies when the metal oxide is formed in an island shape.
During the treatment, the metal oxide is deposited and formed based on the above reaction formula while the dielectric oxide film is dissolved by the fluoride ions.
It is preferable to form a metal oxide having a relative dielectric constant larger than that of the dielectric oxide film by selecting a fluorometal complex compound and / or a metal fluoride.

(Embodiment 1)
In the first embodiment, description will be made using ammonium titanium fluoride ((NH ₄ ) ₂ TiF ₆ ) as the fluorometal complex compound.
After etching the aluminum foil, an anodizing treatment, a heat treatment, and an anodizing treatment were sequentially performed to obtain a valve action metal foil having a dielectric oxide film (aluminum oxide film) on the surface. In particular, the heat treatment was performed by holding at 400 ° C. for 5 minutes in the atmosphere.

0.01 g (Example 1), 0.02 g (Example 2), and 0.04 g (Example 3) of ammonium titanium fluoride were added to 100 ml of pure water, stirred, and completely dissolved to obtain an aqueous solution. The concentrations were 0.0005 mol / l (Example 1), 0.001 mol / l (Example 2), and 0.002 mol / l (Example 3), respectively.
Further tetraborate ammonium tetrahydrate as a fluoride ion-capturing agent and pH adjusting agent to the aqueous solution _{((NH 4) 2 B 4} O 7 · 4H 2 O) 0.02g ( Example 1), 0.04 g (Example 2) and 0.08 g (Example 3) were completely dissolved to obtain an aqueous solution. The concentrations were 0.00076 mol / l (Example 1), 0.0015 mol / l (Example 2), and 0.003 mol / l (Example 3), respectively.
The obtained aqueous solutions of Examples 1 to 3 are put in a polystyrene container, and a valve action metal foil having a dielectric oxide film on the surface is immersed in this aqueous solution, and left as it is at 30 ° C. for 2 hours to prepare an electrode foil. Obtained.

  When the electrode foils obtained in Examples 1 to 3 were taken out and the cross section was observed with a transmission electron microscope, it was found that a metal oxide film (titanium oxide film) was formed on the dielectric oxide film. It was. Initially, it was thought that the film was covered with a dielectric oxide film, but subsequent detailed analysis revealed that it is very likely that it was formed in an island shape. The amount of titanium can be measured from analysis by ICP. By converting the amount of titanium to the amount of titanium oxide, the amount of metal oxide formed on the electrode foil can be known. On the other hand, the minimum amount of titanium oxide necessary for the monoatomic layer to cover the surface of the electrode foil can be calculated from the crystal structure of the titanium oxide and the effective surface area of the electrode foil. Comparing the former measured value with the latter calculated value, it was found that the former was smaller. From this result, it is considered that the metal oxide film is formed in an island shape (partial) on the dielectric oxide film.

When the CV value of the electrode foil was measured, the CV value tended to increase as the amount of ammonium ammonium fluoride increased.
The capacity was measured using a LCR meter (manufactured by Agilent Technologies; Model 4284A) in a 15 wt% ammonium adipate aqueous solution at room temperature.
The pressure resistance was measured using a potentiogalvanostat (manufactured by Hokuto Denko Co., Ltd .; model HZ3000).
The capacity of the electrode foil is usually inversely proportional to the thickness of the dielectric oxide film. However, in the first embodiment, the amount of titanium ammonium fluoride increases, and the capacity increases as the amount of titanium oxide (TiO ₂ ) increases. This is because fluoride ions contained in titanium ammonium fluoride partially dissolve the dielectric oxide film formed on the surface of the aluminum foil, so that an aluminum oxide film having a relative dielectric constant of about 9 is obtained in an amorphous state. This is considered to be because titanium oxide having a relative dielectric constant of a certain degree was replaced.

(Embodiment 2)
In the second embodiment, description will be made using ammonium titanium fluoride ((NH ₄ ) ₂ TiF ₆ ) as the fluorometal complex compound.
The aluminum foil was etched by the same method as in Embodiment 1, and then anodized to obtain a valve metal foil having a dielectric oxide film on the surface.

Titanium ammonium fluoride 0.05 g (Example 4), 0.10 g (Example 5), and 0.18 g (Example 6) were added to 100 ml of pure water, stirred, and completely dissolved to obtain an aqueous solution. The concentrations were 0.0025 mol / l (Example 4), 0.005 mol / l (Example 5), and 0.009 mol / l (Example 6), respectively.
Further, 2.6 g of ammonium pentaborate octahydrate ((NH ₄ ) ₂ O · 5B ₂ O ₃ · 8H ₂ O) as a fluoride ion scavenger and pH adjuster was added to this aqueous solution (Example 4), 5 0.2 g (Example 5) and 10.4 g (Example 6) were completely dissolved to obtain an aqueous solution. The concentrations were 0.048 mol / l (Example 4), 0.096 mol / l (Example 5), and 0.192 mol / l (Example 6), respectively.
The obtained aqueous solutions of Examples 4 to 6 are put in a polystyrene container, and a valve action metal foil having a dielectric oxide film on the surface is immersed in this aqueous solution, and left as it is at 30 ° C. for 2 hours to prepare an electrode foil. Obtained.

When the electrode foils obtained in Examples 4 to 6 were taken out and the cross section was observed with a transmission electron microscope, it was found that a metal oxide (island-like titanium oxide) was formed on the dielectric oxide film. It was. The amount of titanium can be measured from analysis by ICP. By converting the amount of titanium to the amount of titanium oxide, the amount of metal oxide formed on the electrode foil can be known. On the other hand, the minimum amount of titanium oxide necessary for the monoatomic layer to cover the surface of the electrode foil can be calculated from the crystal structure of the titanium oxide and the effective surface area of the electrode foil. Comparing the former measured value with the latter calculated value, it was found that the former was smaller. From this result, it is considered that the metal oxide film is formed in an island shape (partial) on the dielectric oxide film.
When the CV value of the electrode foil was measured, the CV value tended to increase as the amount of ammonium ammonium fluoride increased.
The capacitance and breakdown voltage were measured by the same method as in the first embodiment.
The capacity of the electrode foil is usually inversely proportional to the thickness of the dielectric oxide film. However, in the second embodiment, the amount of titanium ammonium fluoride increases and the capacity increases as the amount of titanium oxide (TiO ₂ ) increases. This is because fluoride ions contained in titanium ammonium fluoride partially dissolve the dielectric oxide film formed on the surface of the aluminum foil, so that an aluminum oxide film having a relative dielectric constant of about 9 is obtained in an amorphous state. This is considered to be because titanium oxide having a relative dielectric constant of a certain degree was replaced.

(Embodiment 3)
In the third embodiment will be described with reference to Jirukonfu' ammonium _{((NH 4) 2 ZrF 6} ) as the metal fluoro complex compound.
The aluminum foil was etched by the same method as in Embodiment 1, and then anodized to obtain a valve metal foil having a dielectric oxide film on the surface.

Zircon ammonium fluoride 0.01 g (Example 7), 0.02 g (Example 8) and 0.04 g (Example 9) were added to 100 ml of pure water and stirred, and completely dissolved to obtain an aqueous solution. The concentrations were 0.0005 mol / l (Example 7), 0.001 mol / l (Example 8), and 0.002 mol / l (Example 9), respectively.
Further tetraborate ammonium tetrahydrate as a fluoride ion scavenger and pH adjusting agent to the aqueous solution _{((NH 4) 2 B 4} O 7 · 4H 2 O) and 0.015 g (Example 7), 0. 03 g (Example 8) and 0.06 g (Example 9) were completely dissolved to obtain an aqueous solution. The concentrations were 0.0005 mol / l (Example 7), 0.001 mol / l (Example 8), and 0.002 mol / l (Example 9), respectively.
The aqueous solutions of Examples 7 to 9 thus obtained were placed in a polystyrene container, and a valve action metal foil having a dielectric oxide film on the surface was immersed in the aqueous solution, and left at 30 ° C. for 2 hours. An electrode foil was obtained.

When the electrode foils obtained in Examples 7 to 9 were taken out and the cross section was observed with a transmission electron microscope, it was found that a metal oxide film (zirconium oxide film) was formed on the dielectric oxide film. It was. Initially, it was thought that the film was covered with a dielectric oxide film, but subsequent detailed analysis revealed that it is very likely that it was formed in an island shape. The amount of zirconia can be measured from analysis by ICP. By converting the amount of zirconia to the amount of zirconium oxide, the amount of metal oxide formed on the electrode foil can be known. On the other hand, the minimum amount of zirconium oxide necessary for the monoatomic layer to cover the surface of the electrode foil can be calculated from the crystal structure of zirconium oxide and the effective surface area of the electrode foil. Comparing the former measured value with the latter calculated value, it was found that the former was smaller by two orders of magnitude or more. From this result, it is considered that the metal oxide film is formed in an island shape (partial) on the dielectric oxide film.
When the CV value of the electrode foil was measured, the CV value tended to increase as the amount of ammonium zircon fluoride increased.
The capacitance and breakdown voltage were measured by the same method as in the first embodiment.
Although the capacity of the electrode foil is inversely proportional to the thickness of the dielectric oxide film, in the third embodiment, the amount of ammonium zircon fluoride increased, and the capacity increased as the amount of zirconia oxide (ZrO ₂ ) formed increased. This is because fluoride ions contained in zircon ammonium fluoride partially dissolve the dielectric oxide film formed on the surface of the aluminum foil, so that an aluminum oxide film having a relative dielectric constant of about 9 is obtained in an amorphous state. This is considered to be because it was replaced with zirconium oxide having a relative dielectric constant of a certain degree.

(Embodiment 4)
In the fourth embodiment will be described with reference to Jirukonfu' ammonium _{((NH 4) 2 ZrF 6} ) as the metal fluoro complex compound.
The aluminum foil was etched by the same method as in Embodiment 1, and then anodized to obtain a valve metal foil having a dielectric oxide film on the surface.

Zircon ammonium fluoride 0.06 g (Example 10), 0.12 g (Example 11), and 0.21 g (Example 12) were added to 100 ml of pure water, stirred, and completely dissolved to obtain an aqueous solution. The concentrations were 0.0025 mol / l (Example 10), 0.005 mol / l (Example 11), and 0.009 mol / l (Example 12), respectively.
Further, 2.6 g of ammonium pentaborate octahydrate ((NH ₄ ) ₂ O · 5B ₂ O ₃ · 8H ₂ O) as a fluoride ion scavenger and a pH adjuster (Example 10) 5.2 g (Example 11) and 10.4 g (Example 12) were completely dissolved to obtain an aqueous solution. The concentrations were 0.048 mol / l (Example 10), 0.096 mol / l (Example 11), and 0.192 mol / l (Example 12), respectively.
The aqueous solutions of Examples 10 to 12 thus obtained were placed in a polystyrene container, and a valve action metal foil having a dielectric oxide film on the surface was immersed in the aqueous solution, and left at 30 ° C. for 2 hours. An electrode foil was obtained.

When the electrode foils obtained in Examples 10 to 12 were taken out and the cross section was observed with a transmission electron microscope, it was found that a metal oxide (island-like zirconium oxide) was formed on the dielectric oxide film. It was. The amount of zirconia can be measured from analysis by ICP. By converting the amount of zirconia to the amount of zirconium oxide, the amount of metal oxide formed on the electrode foil can be known. On the other hand, the minimum amount of zirconium oxide necessary for the monoatomic layer to cover the surface of the electrode foil can be calculated from the crystal structure of zirconium oxide and the effective surface area of the electrode foil. Comparing the former measured value with the latter calculated value, it was found that the former was smaller by two orders of magnitude or more. From this result, it is considered that the metal oxide film is formed in an island shape (partial) on the dielectric oxide film.
When the CV value of the electrode foil was measured, the CV value tended to increase as the amount of ammonium zircon fluoride increased.
The capacitance and breakdown voltage were measured by the same method as in the first embodiment.
The capacity of the electrode foil is inversely proportional to the thickness of the dielectric oxide film, but in Embodiment 4, the capacity increased as the amount of zircon ammonium fluoride increased and the amount of zirconia oxide (ZrO ₂ ) formed increased. This is because fluoride ions contained in zircon ammonium fluoride partially dissolve the dielectric oxide film formed on the surface of the aluminum foil, so that an aluminum oxide film having a relative dielectric constant of about 9 is obtained in an amorphous state. This is considered to be because it was replaced with zirconium oxide having a relative dielectric constant of a certain degree.

  The result of having measured the CV value, the capacity | capacitance, and the leakage current of the electrode foil of Examples 1-12 in Embodiment 1-4 is shown in a table | surface compared with a conventional product. The leakage current was measured by performing a potential sweep using a potentiogalvanostat (manufactured by Hokuto Denko Co., Ltd .; model HZ3000) and reading a current value of 2V.

As is apparent from Table 1, the electrode foil manufacturing method according to the present embodiment can increase the CV value up to about 1.8 times at the maximum.
Note that the conventional product is an electrode foil manufactured by etching an aluminum foil and then anodizing the same as in the first to fourth embodiments.

  The present invention is very useful as a method for producing an electrode foil for an electrolytic capacitor.

Claims (17)

In the method of manufacturing an electrode foil in which a metal oxide is formed on the surface of the dielectric oxide film formed on the surface of the valve action metal foil, the metal oxide includes a fluoro metal complex compound and / or a metal fluoride in the solution. The formula that results from
M _a F _b ^c− + dH ₂ O → M _a O _d + bF ⁻ + 2dH ⁺
(Wherein M is one selected from the group consisting of Ti, Zr, Si, Nb, Ta, Hf, In, Sn and rare earth elements; a, b, c and d are coefficients, and ma = B−c = 2d, where m is the oxidation number of the metal M and satisfies the relationship of a> 0, b> 0, c ≧ 0, and d> 0)) Manufacturing method.   The method for producing an electrode foil according to claim 1, wherein the metal oxide is formed in an island shape on the surface of the dielectric oxide film.   The method for producing an electrode foil according to claim 1 or 2, wherein any one of ammonium ammonium fluoride and ammonium zircon fluoride is used as the fluorometal complex compound.   The method for producing an electrode foil according to claim 3, wherein the concentration of ammonium titanium fluoride or ammonium zircon fluoride in the solution is 0.0005 mol / l or more and less than 0.01 mol / l.   The method for producing an electrode foil according to any one of claims 1 to 4, wherein any one of an aluminum foil, a tantalum foil, and a niobium foil is used as the valve action metal foil.   The method for producing an electrode foil according to any one of claims 1 to 5, wherein either a plain foil or an etched foil is used as the valve action metal foil.   The method for producing an electrode foil according to any one of claims 1 to 6, wherein the dielectric oxide film is formed by anodic oxidation.   The method for producing an electrode foil according to claim 7, wherein the step of forming the dielectric oxide film by anodic oxidation includes a heat treatment step.   The method for producing an electrode foil according to any one of claims 1 to 8, wherein a metal oxide having a relative dielectric constant larger than that of the dielectric oxide film is formed as the metal oxide.   The method for producing an electrode foil according to any one of claims 1 to 9, wherein the metal oxide is formed while dissolving the dielectric oxide film formed on the surface of the valve action metal foil.   The method for producing an electrode foil according to any one of claims 1 to 10, wherein a fluoride ion scavenger is present in the solution.   The method for producing an electrode foil according to claim 11, wherein a boron-containing compound is used as the fluoride ion scavenger.   The method for producing an electrode foil according to claim 12, wherein at least one of ammonium borate, boron oxide, and boric acid is used as the boron-containing compound.   The method for producing an electrode foil according to any one of claims 1 to 13, wherein the pH of the solution is adjusted.   The method for producing an electrode foil according to claim 14, wherein the pH of the solution is adjusted to be higher than 7.   The method for producing an electrode foil according to claim 14, wherein the pH of the solution is adjusted using at least one pH adjuster selected from the group consisting of ammonia, hydrazine, amines, basic salts, and hydroxides.   The solution according to any one of claims 1 to 16, wherein at least one selected from the group consisting of ammonium borate, boron oxide, and boric acid is used as a fluoride ion scavenger and a pH adjuster in the solution. Manufacturing method of electrode foil.