JP2618638B2 - Method for manufacturing solid electrolytic capacitor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial applications]

The present invention relates to a method for producing a solid electrolytic capacitor having good performance using a conductive polymer compound as a solid electrolyte.

[Prior art]

A conventional solid electrolytic capacitor, for example, a solid electrolytic capacitor using aluminum as an electrode, has a dielectric aluminum oxide on a porous aluminum foil having a large specific surface area formed by etching and forming fine holes called etching pits on the surface. A solid electrolyte is used instead of a liquid electrolyte for the electrolyte layer between the dielectric layer and the cathode. The use of a solid electrolyte instead of a liquid electrolyte as described above is preferable because it does not cause problems such as liquid leakage. These solid electrolytic capacitors have a structure in which a solid electrolyte is laminated on a metal such as aluminum or tantalum having an anodized film, and the solid electrolyte of this type of solid electrolytic capacitor mainly decomposes manganese nitrate. Manganese dioxide was used. However, according to this thermal decomposition step, aluminum and the like oxidation of the NO _X gas is the dielectric material generated during the thermal decomposition, damage to the metal oxide film such as tantalum occurs, therefore the finally obtained solid electrolyte There are extremely shortcomings that degrade the dielectric properties of the capacitor, such as a decrease in withstand voltage and an increase in leakage current. In order to compensate for these drawbacks, a method of forming a solid electrolyte layer without applying high heat, that is, a method of using a highly conductive organic semiconductor material as a solid electrolyte has been attempted. Among such solid electrolytes, conductive polymer compounds have attracted attention because of their relatively low production cost and relatively good adhesion to dielectric films. Such a conductive polymer compound is disclosed in, for example,
As can be seen in Japanese Patent No. 47109, for example, after applying an aqueous solution in which an oxidizing agent is dissolved on a dielectric layer of a solid electrolytic capacitor, water as a solvent is removed, and then the oxidizing agent and a conductive polymer compound are removed. It is made by polymerizing the reacting monomers.

[Problems to be solved by the invention]

However, since the dielectric layer is formed on a porous metal foil such as aluminum or tantalum, when water is used alone as the solvent of the oxidizing agent, the etching pits on which the porous dielectric layer is formed are not formed. It is difficult to penetrate the monomer giving the conductive polymer to the inside and to cause a polymerization reaction. That is, when performing gas phase polymerization, a polymerization reaction of a monomer occurs at a contact interface between an aqueous solution in which an oxidizing agent is dissolved and the monomer, and as a result, a polymer film formed from the monomer is generated at the interface. This hinders the formation of a polymer compound inside the etching pit. The inconvenience that the conductive polymer compound cannot be generated in the etching pits results in a decrease in the capacitance of the solid electrolytic capacitor, a loss, or a decrease in the impedance value at a high frequency. Also, at least in the early stage of solid electrolyte layer formation, even if a tentative capacitance value is measured, the degree of polymerization of the conductive polymer in the etching pit is insufficient, and a certain period of time such as a life test has elapsed. Accordingly, there is a disadvantage that the capacitance is greatly reduced. For the purpose of solving such a problem, acetone and a low-viscosity solvent having a low boiling point such as acetonitrile were added to the oxidizing agent aqueous solution.In that case, when water alone was used as the oxidizing agent solvent, On the contrary, the result was that the leakage current increased. Therefore, in the present invention, with an oxidizing agent using a complex solvent obtained by adding another solvent to water, high capacitance and its stabilization, loss,
The present inventors have studied an oxidizing agent solution capable of obtaining excellent characteristics such as a reduction in high-frequency impedance and the use thereof, and have reached the present invention.

[Means for Solving the Problems]

According to the present invention, in producing a solid electrolytic capacitor using a conductive polymer compound as a solid electrolyte, organic amides, carboxylic acid esters, carbonic acid esters, and phosphoric acid are formed on the surface of the porous dielectric layer. Esters, 1,3-propanediol, tertiary butyl alcohol, ethylene glycol, propylene glycol, 2- (methoxymethoxy) ethanol, 2-isopropoxyethanol, benzyl alcohol, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, A state in which an aqueous solution of an oxidizing agent containing a polar solvent having one or more high boiling points and high viscosities selected from diethylene glycol monoethyl ether, triethylene glycol monomethyl ether, or phosphoric acid, polyphosphoric acid or a salt thereof is attached. In, it is characterized in that allowed to produce a conductive polymer compound by gas phase polymerisation in the dielectric layer. In the type of the porous dielectric used in the present invention,
Although there is no particular limitation, for example, oxides of metals such as aluminum, tantalum, niobium, titanium, and zirconium can be suitably used. These porous derivatives can be produced by making the surface of a corresponding metal plate, preferably a metal foil, which is the base thereof, porous by etching or the like, and then treating the surface layer by electrolytic oxidation or the like. According to the present invention, an oxidizing agent aqueous solution containing a polar solvent having a high boiling point and a high viscosity is applied to these porous dielectric layers by means of dipping, coating, spraying, or the like, and the solution does not dry, that is, the surface is not dried. In a wet state, a conductive polymer compound is generated on the dielectric layer by vapor phase polymerization to form a solid electrolyte layer of a solid electrolytic capacitor. The reason for selecting a solvent having a high boiling point and a high viscosity to be blended in the oxidizing agent aqueous solution is that, in the polymerization method of the present invention, water functions as a catalyst during the polymerization, but the solvent of the oxidizing agent solution is water alone. In such a case, the monomer of the conductive polymer compound does not sufficiently reach the fine etching pit, and a desired capacitance cannot be obtained. Therefore, it is necessary to sufficiently permeate the monomer into the etching pit before conducting the polymerization reaction. For this purpose, it is conceivable to improve the permeability into the etching pit by lowering the boiling point and viscosity of the solvent. However, the oxidizing agent solution does not evaporate and the immersion is insufficient, and the capacitance is rather reduced. Therefore, in the present invention, this problem is solved by blending a polar solvent having a high boiling point and a high viscosity. The high boiling point or high viscosity solvent that can be blended with the oxidizing agent solution is naturally selected from those having a boiling point or viscosity higher than that of water. However, it is not necessary that both the boiling point and the viscosity both exceed water. For example, even if the boiling point is lower than water, if the viscosity is sufficiently higher than water, the object of the present invention is satisfied. Even if the solvent has a lower viscosity than water, the solvent is compatible if the boiling point is higher than water. However, those in which either one of the boiling point and the viscosity is significantly lower than that of water should be excluded. As described above, the solvent is preferably compatible with water, and a polar solvent is more preferred. Examples of the organic amides include organic acid amides and N-substituted products thereof. Specific examples of such amides include formamide, dimethylformamide, diethylformamide, acetamide, N-methylacetamide, and N-methylacetamide. , N-diethylacetamide, N-ethylacetamide, N, N-diethylacetamide, propionamide, N-methylpropionamide, pyrrolidone, N-methylpyrrolidone, N-ethylpyrrolidone, piperidone,
There are N-methylpiperidone, N-ethylpiperidone, phosphoric acid ethylamide, phosphoric acid hexamethyltriamide, methyloxazolidinone, ethyltoxazolidinone and the like. Examples of the esters include monoesters, diesters of monocarboxylic acid, dicarboxylic acid or polycarboxylic acid, diesters and polyesters of carbonic acid, and esters of carbonic acid, triethyl phosphate and trimethyl phosphate. Esters of phosphoric acid. Furthermore,
The alcohol residue or the acid residue of such esters may be substituted with a hydrophilic group such as a hydroxyl group or a carboxyl group, and these esters form a lactone ring. There may be. Representative of such esters are 3-methoxybutyl acetate, 3-ethoxybutyl acetate,
Dimethyl maleate, diethyl maleate, ethylene glycol diacetate, propylene glycol diacetate, propylene carbonate, γ-butyrolactone,
γ-valerolactone, γ-caprolactone, γ-caprylolactone and the like. Alcohols and ethers are monovalent or divalent.
In addition to the monohydric alcohols, polyhydric alcohols, and tertiary alcohols, ethers having one or more bonds in the molecule can be used. Specific examples of such compounds include 1,3-propanediol, tertiary butyl alcohol, ethylene glycol, propylene glycol, 2- (methoxymethoxy) ethanol, 2-isopropoxyethanol, benzyl alcohol, ethylene glycol monobutyl ether, Examples thereof include diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, and triethylene glycol monomethyl ether. In the present invention, as a solvent to be mixed with water that can be used, as described above, any solvent that can achieve the object of the present invention can be used, and such a solvent can be used. And two or more of them can be used in combination. The type of the oxidizing agent used in the present invention is not particularly limited, but it is needless to say that the oxidizing agent must be soluble in water and the compounding solvent. Representative examples of the oxidizing agent include ammonium persulfate, sodium persulfate, potassium persulfate, pyridine-N-oxide, alkyl-N-pyridine oxide, quinone, alkylquinone, chloranil, hydrogen peroxide, dimethyl sulfoxide, sodium chlorate, Potassium chlorate, ammonium chlorate, sodium bromate, potassium bromate, ammonium bromate, ferric sulfate, FeCl ₃ , FeBr ₃ , Fe (NO ₃ ) ₃ , Fe ₂ (C ₂ O ₄ ) ₃ ,
_{Fe (ClO 4) 3, K} 3 Fe (CN) 6, (C 5 H 5) 2 Fe + FeCl 4 - CuCl
₂ , CuBr ₂ , CuSO ₄ , Cu (NO ₃ ) ₂ , HNO ₃ , PbO ₂ , diazonium salts, etc., particularly ammonium persulfate, Fe
Cl ₃ , quinone, FeBr ₃ , (C ₅ H ₅ ) ₂ Fe ⁺ FeCl ₄ ^{− and the} like are preferable. The oxidizing agent aqueous solution containing the polar solvent of the present invention is first added with one selected from any one or more of the above-described oxidizing agents, or alternatively, water and any combination of one or more of the solvents described above. It is prepared by dissolving one selected from one or more optional combinations of the above-mentioned oxidizing agents in a mixture obtained by mixing with one selected from the above. The amounts of the oxidizing agent and the solvent used in this case are not particularly limited, but can be appropriately determined and used so as to obtain a solid electrolytic capacitor having good properties. Examples of the formulation usually used as the oxidizing agent solution of the present invention include an aqueous solution containing 20 to 35% by weight of an oxidizing agent such as ammonium persulfate,
It is obtained by adding 5 to 20% by weight of the above-mentioned solvent. The oxidizing agent solution containing the solvent is applied to the surface of the porous dielectric by applying, spraying, or the like, or by immersing the electrode on which the porous dielectric is formed in the solution. Then, means for removing the excess solution by pulling it up may be used. The solution is not dried, that is, the gas phase polymerization is performed in a wet state. The electrically conductive polymer compound formed by the gas phase polymerization is a polymer compound having a structure represented by the following formula (1) or (2) as a repeating unit. (Wherein, R _{1 to} R ₈ may be the same or different, and hydrogen,
Chlorine, carbon, iodine, halogen such as fluorine, alkyl group, alkoxy group, amino group, alkyl-substituted amino group,
A dialkyl-substituted amino group, an aryl group such as a phenyl group, or a cyano group, or two substituents selected from R _{1 to} R ₅ and R ₆ and R ₇ are taken together and are unsubstituted or substituted May form an aliphatic or aromatic ring, wherein X is N-
R ₈ , S, O, Se or Te is shown. Representative examples of such a polymer compound include, for example, polypyrrole, poly-3-methylpyrrole, poly-N-methylpyrrole, polythiophene, poly-3-ethylthiophene, poly-3,4-dimethylthiophene, polyfuran,
Examples thereof include polyindole, polyaniline, poly-2-methylaniline, and polyethoxyaniline. Further, these conductive polymers may be used by doping a known dopant in a gas phase or a liquid phase. Examples of these dopants include NO ₂ , BF ₄ , SO ₃ , and FeCl ₃ . In addition, these dopants which serve both as the oxidizing agent and as the dopant can be added during the treatment with the oxidizing agent solution. Further, by adding a compound contained in boron tetrafluoride to the oxidizing agent solution, the effect of the dopant can be enhanced and the conductivity can be further increased. After the conductive polymer is formed, there is also a means for toping by electrolytic treatment in an electrolytic solution in which a dopant imparting agent is dissolved. In the gas phase polymerization method of the present invention, for example, a monomer solution giving a conductive polymer having a repeating unit represented by the above formula (1) or (2) is caused to accompany an inert gas such as nitrogen, argon, and helium. Introduces into the porous dielectric layer to which the oxidizing agent solution containing the high boiling point or high viscosity solvent is adhered, and polymerizes, or guides the vapor of the monomer solution to the porous dielectric layer to which the oxidizing agent solution is attached. And can be achieved by polymerization. The temperature range in the case of gas phase polymerization is not particularly limited, but generally it can be carried out at a temperature between -60 ° C and + 200 ° C, more preferably at a temperature between -15 ° C and + 25 ° C. . Regarding the temperature in the case of this gas phase polymerization, it is particularly preferable to perform the reaction at room temperature because the operation is simple in terms of operation. The time required to generate a conductive polymer by gas phase polymerization may be determined by observing the process of forming the conductive polymer or monitoring it using an appropriate measuring device. Generally, it takes about several minutes to several hours.

[Action]

According to the present invention, the oxidizing agent aqueous solution used during the gas phase polymerization of the conductive polymer to be a solid electrolyte, high boiling point, organic amides, esters, alcohols that are high viscosity solvents,
Alternatively, one or more polar solvents selected from phosphoric acid, polyphosphoric acid or a salt thereof are blended, and the polymerization reaction is performed in a wet state of the oxidizing agent solution. Is formed. Further, the formed solid electrolyte is dense, and the degree of adhesion is improved.

【Example】

Hereinafter, the present invention will be described in detail with reference to Examples, but it goes without saying that the scope of the present invention is not limited to these Examples. (Example 1) Aluminum foil 1.5 cm x 0.5 cm with a thickness of 90 m (purity 99.9
9%) as a base material and the surface of the foil is electrochemically etched by alternate use of direct current and alternating current using the aluminum foil as an anode to make the surface of the foil porous. The porous surface has an average pore diameter of 0.1 μm and a specific surface area of about 15 μm.
It was twice. Next, the etched aluminum foil is electrochemically treated in a solution of ammonium borate to form a dielectric oxide film of aluminum oxide (Al ₂ O ₃ ) on the surface. Next, ammonium persulfate ((NH ₄ ) ₂ S ₂ O ₈ ), 25% by weight
And an aqueous solution containing 5% by weight of propylene carbonate,
The aluminum foil having a dielectric oxide film of aluminum oxide obtained as described above is immersed in repeated repetition of decompression and pressurization, and then the excess solution is removed. Then, the aluminum foil was placed in a closed container containing 3-methylpyrrole with the surface wet, and subjected to gas phase polymerization to form a conductive polymer film of poly-3-methylpyrrole. This treatment of immersion in the oxidizing agent solution and gas-phase polymerization was repeated three times. Thereafter, a conductive paste "Doitite XA-167" (trade name) in which silver powder was dispersed in an acrylic solvent was applied to the surface of the conductive polymer forming layer, and dried overnight to obtain a solid electrolytic capacitor. Next, in order to examine the electrical characteristics of the obtained solid electrolytic capacitor, an anode-side lead wire was connected to the surface of the aluminum foil, and a cathode-side lead wire was connected to the surface of the silver paste layer. Was used to measure the electrical characteristics. The results are shown in Table 1 together with Examples 2 to 4 and Comparative Examples 1 to 4 described below. In addition, after applying a protective resin film to the silver paste surface of the solid electrolytic capacitors of these examples and comparative examples, put them in a thermostat, apply 10 V at 85 ° C., and perform a high-temperature load test for 1000 hours. Were also measured for the electrical characteristics. The results are shown in Table 2. (Example 2) In Example 1, instead of propylene carbonate, γ-
Butyrolactone is replaced by 3,4 instead of 3-methylpyrrole
-A solid electrolytic capacitor was manufactured under the same conditions as in Example 1 except that dimethylthiophene was used. (Example 3) A solid electrolytic capacitor was manufactured under the same conditions as in Example 1 except that ethylene glycol was used instead of propylene carbonate and indole was used instead of 3-methylpyrrole. (Example 4) A solid electrolytic capacitor under the same conditions as in Example 1 except that 10% by weight of 3-methyloxazolidinone was used instead of 5% by weight of propylene carbonate and pyrrole was used instead of 3-methylpyrrole in Example 1. Was manufactured. (Comparative Examples 1 to 4) Solid electrolytic capacitors were manufactured under the conditions corresponding to the respective numbers of Examples 1 to 4, except that the aqueous solution to which the added solvent was not added in each of Examples 1 to 4 was used. As can be seen from the results, all the solid electrolytic capacitors manufactured by forming the solid electrolyte by the method of the present invention can obtain a high capacitance value, and the decrease is small even after the high temperature load test is performed. It can also be seen that the loss, ESR, etc. can be reduced and the characteristics are stable. On the other hand, in the case of using the oxidizing agent solution without adding the solvent, the capacitance is obtained at the initial value much less than that of the example, but the capacitance value after the high calm load test is often decreased. This indicates that a dense solid electrolyte layer having good adhesion was not stably formed in the etching pit. The same applies to loss and ESR.

【The invention's effect】

As described above, according to the present invention, a solid electrolyte layer made of a conductive polymer that is dense and has good adhesion can be uniformly formed on a porous dielectric layer formed by etching pits. A solid electrolytic capacitor with a large loss and low ESR value can be obtained. In addition, since the film forming the solid electrolyte layer is dense and has good adhesion, there is little change even when used for a long time due to a high temperature load or the like, and stable characteristics can be maintained.

Claims (1)

(57) [Claims] In producing a solid electrolytic capacitor using a conductive polymer compound as a solid electrolyte, an organic amide, an ester of a carboxylic acid, an ester of a carbonic acid and an ester of a phosphoric acid are formed on the surface of a porous dielectric layer. Esters, 1,3-propanediol, tertiary butyl alcohol, ethylene glycol, propylene glycol, 2- (methoxymethoxy)
Ethanol, 2-isopropoxyethanol, benzyl alcohol, ethylene glycol monobutyl ether,
An aqueous solution of an oxidizing agent containing one or two or more polar solvents selected from diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, triethylene glycol monomethyl ether, or phosphoric acid, polyphosphoric acid or a salt thereof is attached thereto. A method for producing a solid electrolytic capacitor, comprising producing a conductive polymer compound on a dielectric layer by vapor phase polymerization.