JP5336141B2 - Method for forming anodized film of valve metal using ionic liquid with water added - Google Patents

Description

  The present invention relates to a method for forming an anodized film of a valve metal using a mixed solution of water and an ionic liquid.

In general, the anodic oxidation method is a method of forming an oxide film on a metal surface in an acidic aqueous solution or a neutral aqueous solution using a metal as an anode. This method is often used to form an oxide film on the surface of valve metals such as aluminum, tantalum, and niobium. For example, aluminum is a thick porous type in acidic aqueous solutions such as sulfuric acid, oxalic acid, and phosphoric acid. In the neutral aqueous solution such as borate, phosphate and adipate, a thin and dense barrier type film is formed. The mechanism of film formation is not fundamentally different between the barrier type and the porous type, and which is formed depends on the film solubility of the solution, that is, the anion species and their concentration and proton concentration. The film also always contains some anions and protons, which influences the properties.
Aluminum porous oxide films are mainly used for the purposes of metal anticorrosion, friction prevention, and decoration by coloring. On the other hand, the barrier-type film is widely used as a dielectric for electrolytic capacitors, and is a main application for anodization.

  Electrolytic capacitors generally use a valve metal such as aluminum or tantalum as an anode metal, an oxide film formed on the surface thereof as a dielectric, and a cathode formed with an electrolyte layer formed on the dielectric. It has a configuration. In particular, conductive polymer electrolytic capacitors using a conductive polymer as an electrolyte are expanding the market due to their excellent impedance characteristics.

  Typically, polypyrrole or polythiophene derivatives are used as the conductive polymer, but in general, these conductive polymers make capacitors with a higher withstand voltage than electrolytic capacitors using liquid as an electrolyte. Is difficult. This is because, unlike liquids, conductive polymers do not have the ability to repair oxide films formed on valve metal surfaces that are essentially dielectrics. Therefore, in a conductive polymer electrolytic capacitor, it is important to efficiently form an excellent film by anodic oxidation.

As described above, an oxide film as a dielectric of an electrolytic capacitor is generally formed in a neutral aqueous solution such as borate, phosphate, or adipate. There existed a subject that formation efficiency was inadequate and it was difficult to obtain the oxide film which has sufficient thickness efficiently. Moreover, although it has been reported that an ionic liquid has an anodic oxidation capability, nothing is described regarding the relationship between the anodic oxidation efficiency and the water content for forming an oxide film (Patent Document 1).
International Publication WO2005 / 012599 Pamphlet

  The present invention has been made to solve the above-mentioned problems, and the object of the present invention is to form a highly efficient valve metal anodic oxide film by using an ionic liquid to which water is added in a certain concentration range. Is to provide a method.

  As a result of intensive studies in view of the above, the present inventors can efficiently form a thick oxide film with a valve metal by anodizing using an ionic liquid to which water is added in a certain concentration range. I discovered this and made the present invention.

  That is, the present invention relates to a method for forming an anodic oxide film on a valve metal using an ionic liquid to which water is added in a range of 2 wt% to 50 wt%.

  The present invention also relates to a method for manufacturing an electrolytic capacitor, characterized in that the above oxide film forming method is used as at least a part of the manufacturing process.

  An ionic liquid with water added in the range of 2 wt% to 50 wt% has a high anodizing ability and is more efficient than conventional anodizing methods using neutral aqueous solutions such as borate, phosphate and adipate. A thicker oxide film can be formed.

  First, the ionic liquid used in the present invention will be described. An ionic liquid, also called a room temperature molten salt, refers to a liquid that is liquid at room temperature despite being composed only of ions, and is composed of a combination of a cation such as imidazolium and an appropriate anion. The ionic liquid is not partially ionized and dissociated like a normal organic solvent, but is considered to be formed from only ions and 100% ionized.

  It has already been reported that ionic liquids have the ability to anodize valve metals. For example, high-voltage conductive polymer capacitors have been fabricated using the ability to repair defects in aluminum oxide films (Patent Documents). 1). The anodic oxidation ability here refers to the ability to form an oxide film on the valve metal and the ability to repair defects in the previously formed oxide film. The valve metal is also called a valve metal. The metal surface is uniformly covered with the surface of the metal oxide film by anodic oxidation, and exhibits excellent corrosion resistance. The oxide film flows in only one direction and is reversed. This means a so-called rectifying action (valve action) that is very difficult to flow in the direction. As valve metals that are covered with an oxide film by anodic oxidation and exhibit a rectifying action, aluminum, tantalum, niobium, titanium, hafnium, zinc, tungsten, bismuth, antimony, and the like are known. Among these, aluminum, Tantalum, niobium, etc. are used for electrolytic capacitors.

  The amount of water added to the ionic liquid is preferably in the range of 2 wt% to 50 wt%, particularly preferably in the range of 5 wt% to 45 wt%, by weight. When the added weight ratio of water is as low as 2 wt% or less, it is almost equivalent to anodic oxidation using only ionic liquid, and an oxide film can be formed, but a sufficiently thick oxide film can be obtained efficiently. I can't. In the case of a hydrophilic ionic liquid, it is known to absorb moisture in the atmosphere by leaving it in the air. However, the amount of water in the ionic liquid absorbed in this way is generally saturated at 2 wt% or less. Therefore, it is considered that 2 wt% or more of water is not naturally contained in the ionic liquid unless water is intentionally added. On the other hand, when the added weight ratio of water is as large as 50 wt% or more, the influence of water decomposition becomes large, a large amount of current flows, and the efficiency of forming an anodic oxide film is the conventional borate, phosphate, It becomes lower than the anodic oxidation method using a neutral aqueous solution such as adipate.

Next, the anion component of the ionic liquid used in the present invention will be described.
Examples of the anion component of the ionic liquid in the present invention include anions selected from the group consisting of sulfonate anion, carboxylate anion, sulfate anion, imide anion, halogen anion, boron anion, and phosphorus anion. It is not limited. This will be described in order below.

The sulfonate anion is described as R ³ SO ₃ ⁻ , and the sulfate anion is described as R ⁴ OSO ₃ ^— (wherein R ³ and R ⁴ represent an aliphatic hydrocarbon group, an alicyclic hydrocarbon group, an aromatic hydrocarbon group, Represent). More specifically, examples of the sulfonate anion include a methanesulfonate anion, a benzenesulfonate anion, a toluenesulfonate anion, a naphthalenesulfonate anion, an alkylnaphthalenesulfonate anion, an anthraquinonesulfonate anion, and a hydroxysulfonate anion. .

Specific examples of the sulfate anion include CH ₃ CH ₂ OCH ₂ CH ₂ OSO ₃ ⁻ , C ₆ H ₅ OCH ₂ CH ₂ OSO ₃ ⁻ , and the like. Of course, the sulfate anion suitable for the present invention is not limited to these examples.

  Examples of other anions preferably used in the present invention include imide anions, and specific examples include sulfonylimide, bis (methylsulfonyl) imide, bis (pentylsulfonyl) imide anion and the like.

  Examples of the halogen anion include a fluorine anion, a chlorine anion, a bromine anion, and an iodine anion. Of course, it is not limited to these examples suitable for the present invention.

  Examples of other anions preferably used in the present invention include boron anions. Specifically, tetrafluoroboron anions can be exemplified, but the examples are not limited to these examples.

  Examples of other anions that are preferably used in the present invention include phosphorus anions, and specific examples include hexafluorophosphorus anions, but are not limited thereto.

  In addition, as the anion component used in the present invention, a carboxylic acid anion can be preferably used in the present invention because an ionic liquid having a high anodizing ability is obtained.

  Carboxylate anion is formate anion or general formula (1);

An anion represented by can be used. In the formula (1), R ¹ and R ² are each independently a hydrogen atom, a protected or unprotected hydroxyl group, a protected or unprotected amino group, an alkoxy group, a nitro group, a cyano group, a carboxyl group, a halogen atom, C ₁ -C ₂₀ alkyl group which may form a straight chain or branched or ring and may have a substituent, may have a straight chain or branched or ring and have a substituent alkenyl group which may C ₂ -C ₂₀ optionally, linear or branched or cyclic formed to have C ₂ may have also well substituent -C ₂₀ alkynyl group, substituted C ₆ -C ₂₀ aryl group which may be substituted, C ₄ -C ₂₀ heteroaryl group which may have substituent, C ₇ -C ₂₀ aralkyl group which may have substituent, substituted A C ₄ -C ₂₀ heteroaralkyl group which may have a group; And they may be the same or different from each other, and may form a ring together.

  In the present invention, “may have a substituent” means that it may be substituted with another atom or substituent. The “substituent” is not particularly limited as long as it does not adversely affect the reaction. Specifically, the hydroxyl group, alkyl group, alkoxy group, alkylthio group, nitro group, amino group, cyano group, carboxyl group, A halogen atom etc. are mentioned.

As a more specific example of R ¹ and R ^2, the C ₁ -C ₂₀ alkyl group which may form a straight chain, a branched chain or a ring and may have a substituent is particularly limited. Although not intended, for example, methyl group, hydroxymethyl group, ethyl group, n-propyl group, isopropyl group, cyclopropyl group, n-butyl group, sec-butyl group, tert-butyl group, cyclobutyl group, n-pentyl group , A cyclopentyl group, an n-hexyl group, a cyclohexyl group, an n-octyl group, an n-decyl group, and the like, and those obtained by substituting an arbitrary number of hydrogen atoms of these alkyl groups with fluorine atoms. Can be mentioned. Examples of the alkenyl group which may form a C _{2 to} C ₂₀ straight chain or branched or ring and may have a substituent include, for example, vinyl group, propenyl group, styryl group, isopropenyl group, cyclopropenyl Group, butenyl group, cyclobutenyl group, cyclopentenyl group, hexenyl group, cyclohexenyl group and the like. Examples of the alkynyl group which may form a C _{2 to} C ₆ straight chain or branched or ring and may have a substituent include, for example, an ethynyl group, a propynyl group, a phenylethynyl group, a cyclopropylethynyl group, Examples include butynyl, pentynyl, cyclobutylethynyl group, and hexynyl group. Examples of the aryl group that may have a substituent include a phenyl group, a naphthyl group, an anthryl group, a phenanthryl group, a terphenyl group, and a 3,4,5-trifluorophenyl group. Examples of the heteroaryl group which may have a substituent include, for example, pyrrolinyl group, pyridyl group, quinolyl group, imidazolyl group, furyl group, indolyl group, thienyl group, oxazolyl group, thiazolyl group, 2-phenylthiazolyl group. , 2-anisyl thiazolyl group and the like. Examples of the aralkyl group which may have a substituent include, for example, benzyl group, chlorobenzyl group, bromobenzyl group, salicyl group, α-hydroxybenzyl group, phenethyl group, α-hydroxyphenethyl group, naphthylmethyl group, anthra Examples include senylmethyl group, 3,5-difluorobenzyl group, and trityl group. Examples of the heteroaralkyl group which may have a substituent include a pyridylmethyl group, a difluoropyridylmethyl group, a quinolylmethyl group, an indolylmethyl group, a furfuryl group, and a thienylmethyl group. In addition, when R ¹ or / and R ² has a hydroxyl group as a substituent, the hydroxyl group may be protected or unprotected, and when it is protected, the protecting group is not particularly limited. Examples of the method include various ethers, various esters, various sulfonate esters, and various carbonate esters.

These ionic liquids may be used alone or in admixture of two or more at any ratio. Moreover, when it has an asymmetric point in a molecule | numerator, an optically active body may be sufficient and a racemic body may be sufficient. From the viewpoint of anodic oxidation ability and availability, at least one of R ¹ and R ² is a hydrogen atom or a hydroxyl group, and the other is a methyl group, an ethyl group, a trifluoromethyl group, a phenyl group, a benzyl group, or a naphthyl group. A group or the like is preferable. When at least one of R ¹ and R ² is a hydroxyl group, it may be protected or unprotected, but generally unprotected is preferable because it exhibits a higher anodic oxidation ability. More specifically, at least one of R ¹ and R ² is a hydroxyl group and the other is a phenyl group, that is, mandelic acid or a derivative thereof is particularly preferable. Also preferred are those in which R ¹ and R ² together form a cyclohexyl group or a phenyl group.

  Next, the cation component of the ionic liquid will be described. Cationic components include ammonium and its derivatives, imidazolinium and its derivatives, pyridinium and its derivatives, pyrrolidinium and its derivatives, pyrrolinium and its derivatives, pyrazinium and its derivatives, pyrimidinium and its derivatives, triazonium and its derivatives, triazinium and its derivatives Derivatives, triazines and derivatives thereof, quinolinium and derivatives thereof, isoquinolinium and derivatives thereof, indolinium and derivatives thereof, quinoxalinium and derivatives thereof, piperazinium and derivatives thereof, oxazolinium and derivatives thereof, thiazolinium and derivatives thereof, morpholinium and derivatives thereof, Piperazine and its derivatives, but the resulting ionic liquid is relatively low Because they exhibit a degree, imidazolium derivatives are preferred, as the imidazolium derivatives diethyl imidazolium, ethyl butyl imidazolium, dimethyl imidazolium are preferred, particularly preferably ethyl methyl imidazolium, methyl butyl imidazolium.

  The ionic liquid of the present invention is a substance obtained by combining the above anion and the above cation, and can be synthesized by a known method. Specifically, a method such as an anion exchange method, an acid ester method, or a neutralization method can be used.

  In the present invention, a nitro compound, a phosphoric acid compound, a boric acid compound, a polyhydric alcohol, a silicon compound, an ammonium salt, an amine salt, if necessary, in order to realize an improvement in thermal stability and further improvement in anodized film formation efficiency. Additives such as quaternary ammonium salts, tertiary amines and organic acids, imidazolium salts can be added. Examples of nitro compounds include nitrophenol, nitroacetophenone, nitrobenzoic acid, nitrobenzyl alcohol, nitrocresol, nitrotoluene, nitroanisole and the like. Examples of phosphoric acid compounds include orthophosphoric acid, phosphorous acid, hypophosphorous acid, pyrophosphoric acid, polyphosphoric acid, methyl phosphate, ethyl phosphate, butyl phosphate, isopropyl phosphate, dibutyl phosphate, dioctyl phosphate, etc. Is mentioned. Examples of boric acid compounds include boric acid and its complex compounds. Examples of the polyhydric alcohols include erythritol, glycerin, threitol, ribitol, arabinitol, allitol, glucitol, mannitol, sorbitol, xylitol, iditol, galactitol, taritol, polyvinyl alcohol and the like. Examples of the silicon compound include colloidal silica, aluminosilicate, silicone compound, silane coupling agent and the like. Examples of ammonium salts include ammonium adipate, ammonium borate, ammonium phosphate, ammonium adipate, and ammonium maleate. Examples of the amine salt include triethylamine maleate, and examples of the quaternary ammonium salt include quaternary ammonium maleate and quaternary ammonium phthalate. Examples of tertiary amines and organic acids include combinations of tertiary amines such as triethylamine and diisopropylethylamine and adipic acid, phosphoric acid, boric acid, salicylic acid, malic acid, succinic acid, and the like. Examples of the imidazolium salt include 1,3-ethylmethylimidazolium-p-toluenesulfonate, 1,3-butylmethylimidazolium-p-toluenesulfonate, 1,3-ethylmethylimidazolium-p-tri Examples thereof include fluoromethylphenyl sulfonate and 1,3-butylmethylimidazolium-p-trifluoromethylphenyl sulfonate.

  The addition amount of these additives can be arbitrarily selected as long as the properties of the ionic liquid as a liquid are not lost. For example, when ammonium adipate is added to the ionic liquid, although it depends on the type of the ionic liquid, it is generally preferably in the range of 0.1 wt% or more and 50 wt% or less for improving the anodizing ability. In the case of 0.1 wt% or less, the concentration is too low to show the effect of addition. Moreover, when it is 50 wt% or more, the additive does not often dissolve in the ionic liquid, and even when dissolved, the viscosity of the ionic liquid increases, and the properties of the ionic liquid as a liquid are lost.

  Moreover, these additives may be used independently and may mix and use 2 or more types by arbitrary ratios.

Next, the anodic oxidation method in the present invention will be described.
The anodic oxidation method is widely used as a means to form an oxide film of the valve metal on the surface of the valve metal. The oxide film is formed by applying voltage or current in the electrolyte solution with the valve metal on which the oxide film is to be formed as the anode. To do. This method is the most general method for forming an oxide film on the surface of a valve metal such as aluminum, tantalum, or niobium, and the valve metal includes aluminum and / or its alloy, tantalum and / or its alloy, Niobium and / or an alloy thereof may be used.

  The present invention does not necessarily need to be performed only with a mixture of ionic liquid and water, and may contain a solvent as an optional component. The solvent used may be a known solvent and is not particularly limited. For example, methanol, ethanol, butanol, 2-propanol, acetone, diethyl ether, ethyl acetate, THF, DMF, acetonitrile, DMSO, dimethyl carbonate, ethylene Examples include carbonate, propylene carbonate, hexane, toluene, chloroform, and the like, which may be selected according to the purpose. However, attention must be paid to the electrochemical stability of the solvent and the incorporation of impurities derived from the solvent.

  Next, the manufacturing method of the electrolytic capacitor in this invention is demonstrated.

  By combining a dielectric made of an oxide film formed by the anodic oxidation method with the valve metal, an anode made of the valve metal and the dielectric oxide film can be formed and used as an anode of a capacitor.

  First, a wound aluminum electrolytic capacitor will be described. The capacitor may be configured by winding the anode foil and the cathode foil with a separator interposed therebetween, and an electrolyte made of a conductive polymer or an electrolyte between the anode foil and the cathode foil. For example, after the element is housed in a bottomed cylindrical aluminum case, the opening of the aluminum case is sealed with a sealing agent to form a wound aluminum electrolytic capacitor.

  As the cathode of the conductive polymer capacitor of the present invention, for example, carbon paste and silver paste can be formed by a conventionally known method. The anode and cathode are each connected to a terminal. In this way, an aluminum electrolytic capacitor having at least an anode, an electrolyte, and a cathode can be formed.

  Next, in the chip type tantalum capacitor, an oxide film / manganese dioxide layer / carbon layer / silver paste layer formed by the above method is sequentially formed on a sintered body produced by molding and firing tantalum powder. A tantalum wire is embedded in the sintered body or welded to the surface.

  First, powder metal tantalum is sintered into a rectangular parallelepiped shape to obtain a microporous anode body, and then a surface of the anode body (including the surface of micropores) is coated with a tantalum oxide film as a dielectric. It forms by said anodic oxidation method. Next, a manganese dioxide layer as a solid electrolyte layer is formed on the tantalum oxide film, and a cathode conductor layer is further formed thereon. For the solid electrolyte layer, for example, a conductive polymer such as pyrrole or thiophene can be used. The cathode conductor layer is composed of, for example, a graphite layer and a silver paste layer stacked in this order.

  Next, a method for producing a conductive polymer capacitor electrolyte by chemical polymerization in the present invention will be described. The conductive polymer capacitor here means a capacitor using a conductive polymer as an electrolyte. The chemical polymerization method is a method of polymerizing and synthesizing a conductive polymer monomer such as pyrrole in the presence of an appropriate oxidizing agent. Examples of the oxidizing agent include ferric paratoluenesulfonate, ferric naphthalenesulfonate, ferric n-butylnaphthalenesulfonate, ferric triisopropylnaphthalenesulfonate, persulfate, hydrogen peroxide, diazonium salt , Halogens and halides, or transition metal salts such as iron, copper, and manganese can be used. The conductive polymer synthesized by chemical polymerization can obtain a polymer having conductivity in a single step by incorporating an anion of an oxidant into the polymer as a dopant in the polymerization process. It is preferable to use ferric paratoluenesulfonate containing paratoluenesulfonate ions having high mobility as an oxidizing agent.

  The polymerization conditions may be known polymerization conditions, and the temperature range is from -100 ° C to 200 ° C, particularly preferably from -30 ° C to 150 ° C. The polymerization time is 1 minute to 120 hours, particularly preferably 1 minute to 1440 minutes. The polymerization may be repeated a plurality of times.

  In the electrolytic capacitor of the present invention using the oxide film formed by the above method, constituent elements of the capacitor not particularly mentioned are not particularly limited, and conventionally known ones can be appropriately applied.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further more concretely, this invention is not limited at all by these Examples, In the range which does not change the summary, it can change suitably.

<Ionic liquid and salt>
First, a method for synthesizing or obtaining ionic liquids and salts used as examples will be described.

1-butyl-3-methylimidazolium mandelate ([BMIm] [MA])

1-butyl-3-methylimidazolium hydrogen carbonate 50% aqueous solution (5000 mg, 12.48 mmol) was added, and the mixture was cooled to 0 ° C. Thereafter, an aqueous solution of mandelic acid (1899 mg, 12.48 mmol) was slowly added dropwise and stirred at room temperature for 1 hour. The reaction solution was concentrated as it was, the solvent was distilled off under reduced pressure, dichloromethane was added to the resulting residue, and the organic layer was dried over anhydrous sodium sulfate. The solvent was distilled off under reduced pressure to obtain 3622.3 mg of the target compound as a light brown oil. (Yield 100%)
¹ H NMR (CDCl ₃ , 300 MHz) δ 0.93 (t, 3H), 1.29-1.34 (m, 2H), 1.74-1.79 (m, 2H), 3.84 (s, 3H), 4.10 (t, 2H), 4.92 (s, 1H), 7.04 (s, 1H), 7.14-7.26 (m, 1H), 7.23-7.26 (M, 3H), 7.54 (d, 2H), 10.74 (s, 1H)

1-butyl-3-methylimidazolium caprylate ([BMIm] [CA])

1-butyl-3-methylimidazolium hydrogen carbonate 50% aqueous solution (5.0 g, 12.48 mmol) was added, and the mixture was cooled to 0 ° C. Thereafter, an aqueous solution of caprylic acid (1.8 g, 12.48 mmol) was slowly added dropwise and stirred at room temperature for 1 hour. The reaction solution was concentrated as it was, the solvent was distilled off under reduced pressure, dichloromethane was added to the resulting residue, and the organic layer was dried over anhydrous sodium sulfate. The solvent was distilled off under reduced pressure to obtain 2.2 g of the objective compound as a yellow oil. (Yield 62%)
¹ H NMR (CDCl ₃ , 300 MHz) δ 0.83-0.92 (m, 7H), 1.21-1.29 (m, 11H), 1.38 (m, 2H), 1.73-1. 78 (m, 2H), 3.85 (s, 3H), 4.17 (t, 2H), 7.72 (s, 1H), 7.79 (s, 1H), 9.39 (s, 1H) )

1-ethyl-3-methylimidazolium lactate ([EMIm] [LA])

Purchased from Aldrich.

Ammonium phosphate ([NH ₄ H ₂ PO ₄ ])
Purchased from Aldrich.

<Analyzed film thickness analysis>
An aluminum plate (manufactured by Wako Pure Chemical Industries, Ltd.) with a purity of 99.99% processed to 10 mm × 10 mm × 0.5 mm is immersed in various ionic liquids or salts using the measurement cell shown in FIG. 1, and at a rate of 100 mV / sec. After increasing the voltage to 40 V to form a film, the sample for analysis was prepared by washing with methanol and drying. For the oxide film analysis of the obtained sample, XPS (Quantum 2000 manufactured by ULVAC-PHI) was used, X-ray intensity: AlKα / 15 kV · 12.5 W, X-ray beam diameter: 50 μmΦ, sputtering rate: 0.9 nm / min ( Under a condition of (SiO ₂ conversion), the depth profile measurement was performed by an argon ion etching method. In the obtained depth profile, a sputtering time in which both Al _2P data and O _1S data values fluctuate by 5% or more compared with the immediately preceding data after passing through a steady state for a certain time is “corresponding to the oxide film thickness. It was defined as “sputtering time”. In addition, in the data using ammonium phosphate, the film thickness (nm) of the oxide film using various ionic liquids was calculated by using the result of 0.40 nm / min recognized in the film thickness and sputtering time. Asked.

<Charge efficiency>
The charge efficiency (%) was obtained from an IV curve obtained at the time of forming an oxide film as shown in FIG. 2 (example using [BMIm] [CA]).

The accumulated charge is obtained from the current value when the voltage is increased to 40 V, the film thickness theoretically formed from the charge is calculated using the following equation (1), and the charge efficiency is obtained from equation (3). .
Film thickness = Molecular weight of aluminum oxide × Integrated charge / (6 × 96486 × Aluminum oxide area × Aluminum oxide density) Formula (1)

Here, 6 means the number of electrons necessary for film formation from Equation (2), and 96486 is a Faraday constant.
_{2Al + 3H 2 O → Al 2} O 3 + 6H + + 6e - Equation (2)

The molecular weight of aluminum oxide was 102, and the density of aluminum oxide was 3.9 cm ² / g.
Charge efficiency = actually obtained film thickness / theoretically formed film thickness × 100 Formula (3)

Example 1
An oxide film analysis of [BMIm] [CA] containing 11 wt% of water by weight ratio was performed to determine the film thickness and charge efficiency of the oxide film. The film thickness obtained was 51 nm and the charge efficiency was 99%. FIG. 2 shows the obtained IV curve.

(Example 2)
An oxide film analysis of [BMIm] [MA] containing 25 wt% water by weight was performed to determine the film thickness and charge efficiency of the oxide film. The film thickness obtained was 63 nm and the charge efficiency was 97%.

(Example 3)
An oxide film analysis of [EMIm] [LA] containing 43 wt% of water was performed, and the film thickness and charge efficiency of the oxide film were determined. The film thickness obtained was 58 nm and the charge efficiency was 87%.

Example 4
The oxide film was analyzed under the same conditions except that 0.1 wt% ammonium phosphate was added to Example 3, and the film thickness and charge efficiency of the oxide film were determined. The film thickness obtained was 64 nm and the charge efficiency was 95%.

(Comparative Example 1)
An oxide film analysis of [BMIm] [CA] containing 0.9 wt% of water by weight ratio was performed to determine the film thickness and charge efficiency of the oxide film. The film thickness obtained was 32 nm and the charge efficiency was 40%.

(Comparative Example 2)
An oxide film analysis of [BMIm] [CA] containing 60 wt% water by weight was performed, but no film was formed.

(Comparative Example 3)
An oxide film analysis of [BMIm] [MA] containing 0.3 wt% of water by weight was performed, and the film thickness and charge efficiency of the oxide film were determined. The film thickness obtained was 40 nm and the charge efficiency was 73%.

(Comparative Example 4)
An oxide film analysis of [BMIm] [MA] containing 75 wt% water by weight was performed, but no film was formed.

(Comparative Example 5)
An oxide film analysis of [EMIm] [LA] containing 1.1 wt% of water by weight was performed to determine the film thickness and charge efficiency of the oxide film. The film thickness obtained was 34 nm and the charge efficiency was 80%.

(Comparative Example 6)
An oxide film analysis of [EMIm] [LA] containing 90 wt% water by weight was performed, but no film was formed.

(Comparative Example 7)
An oxide film analysis of a 0.1 wt% ammonium phosphate aqueous solution was performed to determine the film thickness and charge efficiency of the oxide film. The film thickness obtained was 50 nm and the charge efficiency was 71%.

  The results of Examples 1 to 4 and Comparative Examples 1 to 7 are summarized in Table 1.

  From Table 1, it can be seen that all of the ionic liquids shown in Examples 1 to 4 have a higher anodic oxide film ability than the ionic liquids and salts shown in Comparative Examples 1 to 7. For reference, actual data for [BMIm] [CA] is shown in FIG.

(Example 5)
The aluminum etched foil was anodized using [BMIm] [MA] containing 25 wt% of water, and 3,4-ethylenedioxythiophene (hereinafter abbreviated as EDOT) on the formed oxide film. A conductive polymer aluminum electrolytic capacitor was manufactured by forming a conductive polymer obtained by chemical polymerization of Stark-V TECH.

  That is, an aluminum etched foil having an effective area of 10 mm × 10 mm is immersed in [BMIm] [MA] containing 25 wt% of water in a weight ratio, and is first increased from 0 to 45 V at a rate of 20 mV / sec. A constant voltage of 45V was applied for 40 minutes, and a film was formed on the surface of the aluminum etched foil with [BMIm] [MA]. The foil was washed with running deionized water for 3 minutes and then dried at 120 ° C. for 1 hour. The liquid volume of the aluminum etched foil obtained at this time was 20 μF. The volume in the liquid was calculated from the slope of the graph obtained in a constant current charge / discharge test of 50 μA between 0 and 4 V using solartron, model number “1480” manufactured by Toyo Technica.

  Next, 3,4-ethylenedioxythiophene as a monomer for the conductive polymer, and iron para-toluenesulfonate (40 wt% 1-butanol solution) as the oxidant at a molar ratio of EDOT: oxidant: ionic liquid = 1: 0 The chemical polymerization composition used for electrolyte formation was prepared by mixing at a blending ratio of 0.5.

  This chemical polymerization composition was mixed in a well-dried beaker, and then the aluminum etched foil was immersed in the polymerization solution in the polymerization solution, and after being pulled up, heat treatment was performed at 120 ° C. for 1 hour. The same treatment was repeated four times so that the foil surface was uniformly covered with the electrolyte.

  The conductive polymer aluminum electrolytic capacitor thus obtained was used as a sample, and after aging at 20 V for 1 hour, the initial capacity was measured using the mercury cell shown in FIG. The device uses solartron, model number “1480” manufactured by Toyo Technica, performs a constant current charge / discharge test of 50 μA in the range of 0 to 4 V, calculates the capacity from the slope of the obtained graph, and is one of the capacitor characteristics The capacity expression rate was determined.

The volume expression rate (%) was defined as in equation (4).
Volume expression rate = (volume in liquid / initial volume) × 100 formula (4)
In addition, impedance (mΩ) and withstand voltage (V), which are capacitor characteristics, were measured. The impedance measurement was performed using the mercury cell shown in FIG. 3 after the initial capacity measurement. Electrochemical Analyzer Model 608B (ALS / [H] CH Instruments) was used as the apparatus, and measurement was performed in the range of 1 Hz to 1 MHz under the conditions of DC Potential: 0 V and AC Amplitude: 100 V. An impedance value of 10 kHz was defined as impedance.

  The withstand voltage was measured using the mercury cell shown in FIG. As a device, model number “TR6143” manufactured by Advantest Corporation was used and measured by increasing the voltage at a speed of 20 mV / sec. The withstand voltage value was defined as a voltage at which a current of 10 mA flowed.

  As for the obtained capacitor characteristics, the capacity expression rate was 58%, the impedance was 235 mΩ, and the breakdown voltage was 42V. All the results are average values of three electrodes.

(Comparative Example 8)
An experiment was performed in the same manner as in Example 5 except that the aluminum etched foil was anodized using a 0.1 wt% ammonium phosphate aqueous solution. The liquid volume obtained at this time was 25 μF. Moreover, the obtained capacitor | condenser characteristic was 53% of capacity | capacitance expression rates, the impedance was 240 mohm, and the withstand voltage was 38V.

  The results of Example 5 and Comparative Example 8 are summarized in Table 2.

  From Table 2, it can be seen that a conductive polymer aluminum electrolytic capacitor can also be produced using a foil anodized with an ionic liquid to which water is forcibly added.

Cell used for anodic oxidation of aluminum with ionic liquid [BMIm] [CA] IV curve Mercury cell for measuring electrodes

Claims (8)

  A method for forming an anodized film of a valve metal using a solution containing at least an ionic liquid and water, wherein the water is in a range of 2 wt% to 50 wt%.   The anion component of the ionic liquid has at least one anion selected from a sulfonate anion, a carboxylate anion, a sulfate anion, an imide anion, a halogen anion, a boron anion, and a phosphorus anion. 2. A method for forming an anodized film of a valve metal according to 1. The carboxylate anion according to claim 2 is a formate anion or general formula (1);
(Wherein R ¹ and R ² are each independently a hydrogen atom, a protected or unprotected hydroxyl group, a protected or unprotected amino group, an alkoxy group, a nitro group, a cyano group, a carboxyl group, a halogen atom, a straight chain or branched or alkyl group optionally C ₁ -C ₂₀ optionally may have a substituent to form a ring, may have a straight-chain or branched or may substituents may form a ring C ₂ -C ₂₀ alkenyl group, straight chain, branched or ring may be formed and optionally substituted C ₂ -C ₂₀ alkynyl group, optionally substituted C _{6 to} C ₂₀ aryl group, optionally having C _{4 to} C ₂₀ heteroaryl group, optionally having C _{7 to} C ₂₀ aralkyl group and having substituent Represents a C _{4 to} C ₂₀ heteroaralkyl group which may be The structure may be at least one selected from the group represented by the following formula: An anodized film forming method for valve metal.   The cation component of the ionic liquid is ammonium cation, imidazolium cation, pyridinium cation, pyrrolidinium cation, pyrrolium cation, pyrazinium cation, pyrimidinium cation, triazonium cation, triazinium cation, triazine cation, key From the group consisting of norinium cation, isoquinolinium cation, indolinium cation, quinoxalinium cation, piperazinium cation, oxazolinium cation, thiazolinium cation, morpholinium cation, piperazine cation and derivatives thereof The method for forming an anodic oxide film of a valve metal according to any one of claims 1 to 3, wherein the method is selected.   In addition to ionic liquid and water, group consisting of nitro compounds, phosphate compounds, boric acid compounds, polyhydric alcohols, silicon compounds, ammonium salts, amine salts, quaternary ammonium salts, tertiary amines and organic acids, imidazolium salts The method for forming an anodized film of a valve metal according to claim 1, wherein at least one selected from the above is selected and contained.   A method for producing an electrolytic capacitor, wherein the method for forming an oxide film of a valve metal according to any one of claims 1 to 5 is used as at least a part of the production process.   The manufacturing method according to claim 6, wherein the electrolytic capacitor is a conductive polymer capacitor.   8. The method for producing a conductive polymer capacitor electrolyte according to claim 7, wherein the conductive polymer capacitor electrolyte is formed by chemical polymerization.