JP4608865B2 - Manufacturing method of solid electrolytic capacitor - Google Patents

Description

  The present invention relates to a method of manufacturing a solid electrolytic capacitor, and more particularly to a method of manufacturing a solid electrolytic capacitor that has been improved to improve the capacitance and equivalent series resistance (hereinafter referred to as ESR) characteristics of the solid electrolytic capacitor. It is.

  An electrolytic capacitor using a metal having a valve action such as tantalum or aluminum is obtained by expanding the dielectric by making the valve action metal as the anode-side counter electrode into the shape of a sintered body or an etching foil. Since it is small and a large capacity can be obtained, it is widely used. In particular, a solid electrolytic capacitor using a solid electrolyte as an electrolyte has features such as small size, large capacity, low equivalent series resistance, easy to chip, and suitable for surface mounting. It is indispensable for miniaturization, high functionality and low cost of electronic equipment.

  In this type of solid electrolytic capacitor, as a small-sized and large-capacity application, an anode foil and a cathode foil made of a valve metal such as aluminum are generally wound with a separator interposed therebetween to form a capacitor element. It is impregnated with a driving electrolyte, and has a sealed structure in which a capacitor element is housed in a metal case such as aluminum or a case made of synthetic resin. As the anode material, aluminum, tantalum, niobium, titanium and the like are used, and as the cathode material, the same kind of metal as the anode material is used.

  As solid electrolytes used for solid electrolytic capacitors, manganese dioxide and 7,7,8,8-tetracyanoquinodimethane (TCNQ) complexes are known. There is a technique (see Patent Document 1) that focuses on a conductive polymer such as polyethylenedioxythiophene (hereinafter referred to as PEDT) having excellent adhesion to an oxide film layer of an electrode.

  A solid electrolytic capacitor of a type in which a solid electrolyte layer made of a conductive polymer such as PEDT is formed on such a wound capacitor element is produced as follows. First, the surface of the anode foil made of valve action metal such as aluminum is roughened by electrochemical etching treatment in an aqueous chloride solution to form many etching pits, and then in an aqueous solution such as ammonium borate. A voltage is applied to form an oxide film layer serving as a dielectric (chemical conversion). Like the anode foil, the cathode foil is made of a valve action metal such as aluminum, but the surface is only subjected to etching treatment.

Thus, the anode foil having the oxide film layer formed on the surface and the cathode foil having only the etching pits are wound through a separator to form a capacitor element. Subsequently, a polymerizable monomer such as 3,4-ethylenedioxythiophene (hereinafter referred to as EDT) and an oxidizer solution are respectively discharged into the capacitor element subjected to restoration conversion, or immersed in a mixture of both. The polymerization reaction is promoted in the capacitor element, and a solid electrolyte layer made of a conductive polymer such as PEDT is generated. Thereafter, the capacitor element is housed in a bottomed cylindrical outer case, and the opening of the case is sealed with a sealing rubber to produce a solid electrolytic capacitor.
JP-A-2-15611

  Incidentally, in recent years, electronic information devices have been digitized, and further, the driving frequency of a microprocessor (MPU), which is the heart of these electronic information devices, has been increased. Along with this, the power consumption has been increasing and the problem of reliability due to heat generation has become obvious. Therefore, the drive voltage has been reduced as a countermeasure.

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

However, the increase in the driving frequency of the microprocessor is remarkable, and accordingly, the power consumption further increases. In order to cope with this, further increase in the power supplied from the capacitor to prevent the voltage drop is required. That is, a large amount of power must be able to be supplied in a short time. For this reason, solid electrolytic capacitors are required to have higher ESR characteristics as well as larger capacity, smaller size, and lower voltage.
Such a problem occurs not only when EDT is used as the polymerizable monomer but also when other thiophene derivatives, pyrrole, aniline, and the like are used.

  The present invention has been proposed to solve the above-described problems of the prior art, and an object of the present invention is to provide a method of manufacturing a solid electrolytic capacitor capable of improving capacitance and ESR characteristics. There is.

  In order to solve the above-mentioned problems, the present inventor has intensively studied a method for producing a solid electrolytic capacitor capable of improving the electrostatic capacity and further reducing the ESR as compared with the prior art. It has come. That is, the present inventor adjusted the viscosity of the oxidant solution to 40 to 180 mpa. It has been found that good results can be obtained by setting s.

(Method for manufacturing solid electrolytic capacitor)
The manufacturing method of the solid electrolytic capacitor according to the present invention is as follows. That is, an anode foil and a cathode foil having an oxide film layer formed on the surface thereof are wound through a separator to form a capacitor element, and this capacitor element is subjected to restoration conversion. Subsequently, this capacitor element was impregnated with a polymerizable monomer solution, and thereafter the viscosity was 40 to 180 mpa. The s oxidizing solution is impregnated to cause a polymerization reaction of the conductive polymer in the capacitor element, thereby forming a solid electrolyte layer. Thereafter, the capacitor element is inserted into an outer case, a sealing rubber is attached to the opening end, and sealing is performed by caulking, and then aging is performed to form a solid electrolytic capacitor.

  In addition, as a method of impregnating the capacitor element with the polymerizable monomer and the oxidizing agent, after immersing the capacitor element in the polymerizable monomer solution, after immersing in the oxidizing agent solution, or after injecting the polymerizable monomer into the capacitor element, A method of injecting an oxidant solution can be used.

(Viscosity of oxidizer solution)
The viscosity of the oxidant solution is 40 to 180 mpa. s is preferred. The viscosity of the oxidant solution is 40 mpa. If it is less than s, the viscosity is too low and the oxidant scoops up the lead wire, increasing the leakage current and possibly causing a short circuit. Furthermore, since the oxidizing agent is insufficient, the ESR characteristic is deteriorated. On the other hand, the viscosity of the oxidant solution is 180 mpa. When s is exceeded, the penetration of the oxidant solution into the pits of the oxide film is insufficient, and the electrostatic capacity decreases. The viscosity of the oxidant solution is measured with a B-type viscometer.

(Preparation of viscosity)
The viscosity of the oxidant solution is 40 to 180 mpa. As a method for preparing s, a method in which a thickener is added to an oxidant solution and stirring is preferable when preparation by an oxidant concentration is difficult. As this thickener, it is preferable to use Aerosil. The amount of the thickener added to the oxidizing agent is preferably 0.5 to 1.5 wt%.

(EDT)
When EDT is used as the polymerizable monomer, it is preferable to use a monomer solution in which EDT and a volatile solvent are mixed so that the EDT concentration is 25 to 30 wt% as the EDT impregnated in the capacitor element.
Examples of the volatile solvent include 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. Of these, methanol, ethanol, acetone and the like are preferable.

(Oxidant)
As the oxidizing agent, an aqueous solution of paratoluenesulfonic acid ferric acid, periodic acid or iodic acid dissolved in ethanol can be used, and the concentration of the oxidizing agent with respect to the solvent is preferably 45 to 55 wt%, and 50 to 55 wt%. More preferred. The higher the oxidant concentration in the solvent, the lower the ESR. As the oxidant solvent, the volatile solvent used in the monomer solution can be used, and ethanol is particularly preferable. Ethanol is suitable as the oxidant solvent because it is easy to evaporate due to its low vapor pressure and the remaining amount is small.

(Chemical solution for restoration conversion)
As the chemical solution for restoration chemical conversion, phosphoric acid type chemicals such as ammonium dihydrogen phosphate and diammonium hydrogen phosphate, boric acid type chemicals such as ammonium borate, and adipic acid type chemicals such as ammonium adipate, etc. Although a liquid can be used, it is preferable to use ammonium dihydrogen phosphate. The immersion time is preferably 5 to 120 minutes.

(Other polymerizable monomers)
The polymerizable monomer used in the present invention includes, in addition to the above EDT, a thiophene derivative other than EDT, aniline, pyrrole, furan, acetylene or a derivative thereof, which is oxidatively polymerized with a predetermined oxidizing agent, and is a conductive polymer. As long as it forms, it can be applied. As the thiophene derivative, one having the following structural formula can be used.

(Action / Effect)
As described above, the viscosity of the oxidant solution is 40 to 180 mpa. The reason why a favorable result was obtained by setting s is considered as follows.
That is, the viscosity of the oxidant solution is 40 to 180 mpa. If it is within the range of s, the oxidant does not crawl up the lead wire, and a sufficient amount of oxidant is impregnated in the element, so that the ESR characteristics are improved. Further, since the oxidizing agent sufficiently penetrates into the etching pits of the electrode foil, the electrostatic capacity is also improved.

  ADVANTAGE OF THE INVENTION According to this invention, the manufacturing method of the solid electrolytic capacitor which can improve an electrostatic capacitance and an ESR characteristic can be provided.

  Subsequently, the present invention will be described in more detail based on Examples and Comparative Examples manufactured as follows.

Example 1
An electrode lead means was connected to the anode foil and the cathode foil having an oxide film layer formed on the surface, and both electrode foils were wound through a separator to form a capacitor element. And this capacitor | condenser element was immersed in ammonium dihydrogen phosphate aqueous solution for 40 minutes, and restoration | restoration conversion was performed.
On the other hand, a 30 wt% ethanol solution of EDT was poured into a predetermined container, and a capacitor element was immersed therein to impregnate the EDT solution, followed by drying. Aerosil was then added to give a viscosity of 40 mpa. The ethanol solution of paratoluenesulfonic acid ferric acid prepared in s is poured into a predetermined container, and the capacitor element is immersed therein and impregnated with an oxidant solution, and heated at 120 ° C. for 60 minutes to obtain a capacitor. A PEDT polymerization reaction was generated in the device to form a solid electrolyte layer.
And this capacitor | condenser element was inserted in the bottomed cylindrical exterior case, the sealing rubber was attached to the opening edge part, and it sealed by the crimping process. Thereafter, aging was performed to form a solid electrolytic capacitor.

(Example 2)
The viscosity of the oxidant solution is 180 mpa. s. Other conditions and steps are the same as in Example 1.

(Comparative Example 1)
The viscosity of the oxidant solution is 35 mpa. s. Other conditions and steps are the same as in Example 1.
(Comparative Example 2)
The viscosity of the oxidant solution is 250 mpa. s. Other conditions and steps are the same as in Example 1.

[Comparison result]
The capacitance and ESR of the examples and comparative examples obtained by the above methods were examined, and the results shown in Table 1 were obtained.

  As is clear from Table 1, both Examples 1 and 2 in which the viscosity of the oxidant solution was within the scope of the present invention showed lower ESR than Comparative Examples 1 and 2.

Claims (1)

A capacitor element in which an anode foil and a cathode foil are wound through a separator is impregnated with a polymerizable monomer solution and then dried, and the dried capacitor element is impregnated with an oxidant solution to form a solid made of a conductive polymer. In the method for producing a solid electrolytic capacitor for forming the electrolyte layer,
The oxidant solution has a viscosity of 40 to 180 mpa. s for producing a solid electrolytic capacitor.