JP2003297686A - Method for producing solid electrolytic capacitor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing a solid electrolytic capacitor in which ESR can be reduced. <P>SOLUTION: An anode foil and a cathode foil having an oxide film layer formed on the surface are wound through a separator to form a capacitor element which is then subjected to restoration formation. Subsequently, the capacitor element is immersed into mixture liquid prepared by mixing polymerizable monomer and an oxidizing agent together with a specified solvent and impregnated with the polymerizable monomer and the oxidizing agent. Substantially, simultaneously with the end of impregnation, it is preheated at a specified temperature so that polymerization reaction of conductive polymer takes place in the capacitor element thus forming a solid electrolytic layer. Thereafter, the capacitor element is inserted into an enclosure case, a sealing rubber is fixed to the end part of opening, and the case is sealed by caulking before the entirety is subjected to aging thus forming a solid electrolytic capacitor. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a solid electrolytic capacitor, and more particularly to a method for manufacturing a solid electrolytic capacitor which has been improved to reduce the equivalent series resistance (hereinafter referred to as ESR) of the solid electrolytic capacitor. It is about.

[0002]

2. Description of the Related Art An electrolytic capacitor using a metal having a valve action, such as tantalum or aluminum, has a valve action metal as a counter electrode on the anode side formed into a sintered body, an etching foil, or the like so that the dielectric is expanded. It is widely used because it is possible to obtain a small size and a large capacity. In particular, a solid electrolytic capacitor using a solid electrolyte as an electrolyte has characteristics such as small size, large capacity, low equivalent series resistance, easy chip formation, and suitability for surface mounting. It is indispensable for downsizing, high functionality, and cost reduction of electronic devices.

In this type of solid electrolytic capacitor, for small size and large capacity use, generally, an anode foil and a cathode foil made of a valve metal such as aluminum are wound with a separator interposed therebetween to form a capacitor element. The capacitor element is impregnated with a driving electrolytic solution, and the capacitor element is housed in a case made of metal such as aluminum or a case made of synthetic resin, which is hermetically sealed. In addition, aluminum, tantalum, niobium, titanium, etc. are used as the anode material, and the same kind of metal as the anode material is used as the cathode material.

As the solid electrolyte used in the solid electrolytic capacitor, manganese dioxide, 7, 7, 8, 8-
Tetracyanoquinodimethane (TCNQ) complex is known, but in recent years, polyethylenedioxythiophene (hereinafter referred to as PEDT), etc., which has a slow reaction rate and excellent adhesion to the oxide film layer of the anode electrode, etc. There is a technique (Japanese Patent Application Laid-Open No. 2-15611, etc.) that focuses on the conductive polymer.

PE in such a winding type capacitor element
A solid electrolytic capacitor of the type in which a solid electrolyte layer made of a conductive polymer such as DT is formed is manufactured as follows. First, the surface of the anode foil made of a valve metal such as aluminum is roughened by electrochemical etching in a chloride aqueous solution to form a large number of etching pits, and then in an aqueous solution of ammonium borate or the like. A voltage is applied to form an oxide film layer serving as a dielectric. Similar to the anode foil, the cathode foil is also made of a valve metal such as aluminum, but its surface is only subjected to etching treatment.

In this way, the anode foil having the oxide film layer formed on the surface and the cathode foil having only the etching pit are wound with the separator interposed therebetween to form a capacitor element. Then, on the capacitor element that has been subjected to repair formation,
A polymerizable monomer such as 3,4-ethylenedioxythiophene (hereinafter referred to as EDT) and an oxidant solution are respectively discharged or immersed in a mixed solution of both to accelerate the polymerization reaction in the capacitor element, and to improve the PEDT. To produce a solid electrolyte layer composed of a conductive polymer such as. Then, the capacitor element is housed in a cylindrical outer case having a bottom to form a solid electrolytic capacitor.

[0007]

By the way, in recent years, electronic information devices have been digitized, and the driving frequency of the microprocessor (MPU), which is the heart of these electronic information devices, has been increasing. Along with this, the increase in power consumption has progressed, and the problem of reliability due to heat generation has become apparent. As a countermeasure against this, reduction of the drive voltage has been attempted.

In order to reduce the driving voltage, a DC-DC converter called a voltage control module is widely used as a circuit for supplying highly accurate electric power to a microprocessor, and a voltage drop occurs in its output side capacitor. In order to prevent this, many capacitors with low ESR are used. As a capacitor having such a low ESR characteristic, the solid electrolytic capacitor as described above has been put into practical use,
It is used a lot.

However, the driving frequency of the microprocessor is remarkably increased, and the power consumption is further increased accordingly. To cope with this, further increase of the power supplied from the capacitor to prevent the voltage drop is required. There is. That is, it is necessary to be able to supply a large amount of power in a short time, and for this reason, a solid electrolytic capacitor is required to have a large capacity, a small size, a low voltage, and further excellent ESR characteristics. It should be noted that such a problem similarly occurs not only when EDT is used as the polymerizable monomer, but also when other thiophene derivative, pyrrole, aniline or the like is used.

The present invention has been proposed in order to solve the above-mentioned problems of the prior art, and an object thereof is to provide a method of manufacturing a solid electrolytic capacitor which can further reduce ESR. It is in.

[0011]

In order to solve the above problems, the inventors of the present invention have made extensive studies as to a method of manufacturing a solid electrolytic capacitor capable of further reducing ESR, and as a result, It has been completed. That is, the inventors of the present invention found that there is a difference in the ESR reduction effect depending on the length of time until the heat polymerization step after the step of impregnating the capacitor element with the polymerizable monomer and the oxidizing agent is completed, The present invention has been completed.

(Method of Manufacturing Solid Electrolytic Capacitor) The method of manufacturing the solid electrolytic capacitor according to the present invention is as follows. That is, an anode foil and a cathode foil each having an oxide film layer formed on the surface thereof are wound with a separator interposed therebetween to form a capacitor element, and this capacitor element is subjected to restoration chemical conversion. Subsequently, the capacitor element is dipped in a mixed solution prepared by mixing a polymerizable monomer, an oxidizing agent and a predetermined solvent to impregnate the capacitor element with the polymerizable monomer and the oxidizing agent. Almost at the same time as the completion of impregnation, heating to a predetermined temperature causes a polymerization reaction of the conductive polymer in the capacitor element to form a solid electrolyte layer. After that, this capacitor element is inserted into an outer case, a sealing rubber is attached to the opening end, and after sealing by caulking, aging is performed to form a solid electrolytic capacitor.

As a method for impregnating the capacitor element with the polymerizable monomer and the oxidizing agent, the capacitor element is dipped in a mixed solution of the polymerizable monomer and the oxidizing agent, or the mixed solution is injected into the capacitor element by a syringe or the like. The method or the method of separately injecting the polymerizable monomer and the oxidant solution into the capacitor element can be used. As described above, in the present invention, good results were obtained by polymerizing and heating almost at the end of impregnation. Specifically, it is preferable to heat the polymerization within 15 minutes after completion of the impregnation.
It is more preferably within 10 minutes and even more preferably within 5 minutes.

The reason why good results were obtained by polymerizing and heating almost at the same time as the completion of impregnation is considered as follows. Usually, the impregnated capacitor element is configured to promote the heat polymerization reaction by a method such as putting it in a constant temperature bath. In this case, the capacitor element is usually attached to a lead frame or the like, and subjected to the impregnation step and the polymerization heating step in units of several to several tens. Therefore,
There is a state in which the impregnated capacitor element is left at room temperature until the impregnation step shifts to the polymerization heating step.

However, when the impregnated capacitor element is left for a long time, the polymerizable monomer and the solvent evaporate from the end surface of the capacitor element, and the ratio of the polymerizable monomer, the oxidizing agent and the solvent in the capacitor element becomes nonuniform. ,as a result,
It is considered that the conductive polymer formed becomes non-uniform and good results cannot be obtained.

Further, as a method of heating for polymerization almost simultaneously with the completion of impregnation, there is a method of heating immediately after the injection of the polymerizable monomer and the oxidizing agent is completed, and a method of heating immediately after the capacitor element is immersed in the mixed solution and pulled up. Etc. can be used. As the heating method, a method of applying hot air to the capacitor element immediately after the impregnation, a method of sequentially charging the capacitor elements immediately after the impregnation into a constant temperature bath at a predetermined temperature, or the like can be used. It is also possible to immerse the capacitor element in a container into which the mixed solution has been injected, heat the container, and then put it in a thermostat to accelerate the polymerization reaction.

(EDT and Oxidizing Agent) When EDT is used as the polymerizable monomer, the ED that impregnates the capacitor element
Although EDT monomer can be used as T,
It is also possible to use a monomer solution in which EDT and a volatile solvent are mixed in a volume ratio of 1: 0 to 1: 3. As the volatile solvent, hydrocarbons such as pentane, ethers such as tetrahydrofuran, esters such as ethyl formate, ketones such as acetone, alcohols such as methanol, nitrogen compounds such as acetonitrile and the like can be used. But,
Of these, methanol, ethanol, acetone and the like are preferable.

As the oxidant, an aqueous solution of ferric p-toluenesulfonate, periodate or iodic acid dissolved in butanol can be used, and the concentration of the oxidant in the solvent is preferably 40 to 58 wt%. 45-5
7 wt% is more preferable. The higher the concentration of oxidant to solvent, the lower the ESR.

(Chemical conversion solution for repair chemical conversion) As chemical conversion solution for repair chemical conversion, phosphoric acid-based chemical conversion solutions such as ammonium dihydrogen phosphate and diammonium hydrogen phosphate, boric acid-based chemical conversion solutions such as ammonium borate, Adipic acid-based chemical conversion solutions such as ammonium adipate can be used, but above all,
It is desirable to use ammonium dihydrogen phosphate. Further, it is preferable that the time for immersing the capacitor element in the chemical conversion liquid and applying the voltage to perform the repair chemical formation is 5 to 120 minutes.

(Other Polymerizable Monomer) As the polymerizable monomer used in the present invention, in addition to the above EDT, EDT
Other thiophene derivatives, aniline, pyrrole, furan, acetylene or their derivatives, which are oxidatively polymerized by a predetermined oxidant to form a conductive polymer, can be applied. As the thiophene derivative, one having the following structural formula can be used.

[Chemical 1]

[0021]

EXAMPLES Next, the present invention will be described in more detail based on Examples and Comparative Examples produced as follows. (Example 1) A capacitor element having an element shape of 5φ x 2.8 L, in which an electrode lead-out means is connected to an anode foil and a cathode foil having an oxide film layer formed on the surface and both electrode foils are wound with a separator interposed therebetween. Was formed. Then, the capacitor element is immersed in an ammonium dihydrogen phosphate aqueous solution for 40 minutes,
Repair formation was performed. On the other hand, place the EDT and
% Ferric paratoluenesulfonate butanol solution was mixed at a ratio of 1: 3, and the capacitor element was immersed in the above mixed solution for 10 seconds to impregnate the capacitor element with EDT and an oxidant. Then, the capacitor element is pulled out from the polymerization solution, left in a constant temperature bath of 60 ° C. for 1 hour within 5 minutes, and further heated in a constant temperature bath of 150 ° C. for 1 hour to allow PEDT polymerization reaction in the capacitor element. It was generated to form a solid electrolyte layer. Then, insert this capacitor element into a cylindrical outer case with a bottom, and attach a sealing rubber to the open end,
It was sealed by caulking. After that, 150 ℃, 1
Aging is performed by applying a voltage of 26 V for 20 minutes,
A solid electrolytic capacitor was formed. The solid electrolytic capacitor has a rated voltage of 20 WV and a rated capacity of 22 μF.

(Comparative Example 1) After pulling up the capacitor element from the polymerization solution, it was left at room temperature for 1 hour, then left in a constant temperature bath at 60 ° C for 1 hour, and further heated in a constant temperature bath at 150 ° C for 1 hour. Then, a polymerization reaction of PEDT was generated in the capacitor element to form a solid electrolyte layer. The other conditions and steps are the same as in Example 1.

(Comparative Example 2) After pulling up the capacitor element from the polymerization solution, it was left at room temperature for 3 hours, then left in a constant temperature bath at 60 ° C for 1 hour, and further heated in a constant temperature bath at 150 ° C for 1 hour. Then, a polymerization reaction of PEDT was generated in the capacitor element to form a solid electrolyte layer. The other conditions and steps are the same as in Example 1.

[Comparison Results] The initial characteristics of the examples and comparative examples obtained by the above method were examined.
The results shown in are obtained.

[Table 1]

As is clear from Table 1, the ESR of the example in which the polymerization heating was performed immediately after the completion of the impregnation was about 87% compared to the comparative example 1 in which the polymerization heating was performed 1 hour after the completion of the impregnation. It was reduced to 4%. Also, the ESR was about 8 as compared with Comparative Example 2 in which polymerization heating was performed 3 hours after the completion of impregnation.
It was reduced to 8.4%.

[0026]

As described above, according to the present invention, E
A method for manufacturing a solid electrolytic capacitor that can further reduce SR can be provided.

Claims (3)

[Claims] 1. A solid electrolysis in which a capacitor element in which an anode foil and a cathode foil are wound via a separator is impregnated with a polymerizable monomer and an oxidizing agent, and a solid electrolyte layer made of a conductive polymer is formed by a heat polymerization reaction. A method for producing a solid electrolytic capacitor, which comprises performing heat polymerization at substantially the same time as the completion of impregnation of the capacitor element with a polymerizable monomer and an oxidizing agent. 2. The method for producing a solid electrolytic capacitor according to claim 1, wherein the polymerizable monomer is a thiophene derivative. 3. The method for producing a solid electrolytic capacitor according to claim 2, wherein the thiophene derivative is 3,4-ethylenedioxythiophene.