JP2005109080A - Method for manufacturing solid electrolytic capacitor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing method of a solid electrolytic capacitor capable of reducing ESR. <P>SOLUTION: Anode foil, on which an oxide film layer is formed and cathode foil are wound via a separator for forming a capacitor element and repairing formation, is formed on the capacitor element. Subsequently, a polymerizable monomer solution, whose concentration is prepared to 25-32wt%, is impregnated into the capacitor element for setting the porosity of the capacitor element to 80-85%. Then, an oxidizing solution, whose concentration is prepared to 45-55wt%, is impregnated for generating the polymerization reaction of a conductive polymer in the capacitor element to form a solid electrolytic layer. After that, the capacitor element is inserted into a packaged case, sealing rubber is fitted to the edge of an opening, caulking machining is made for sealing, and aging is conducted, forming the solid electrolytic capacitor. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  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 that has been improved to reduce the equivalent series resistance (hereinafter referred to as ESR) of the solid electrolytic capacitor.

  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). Similar to the anode foil, the cathode foil is made of a valve 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 mixed solution of the two. 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

  By the way, in recent years, electronic information devices have been digitized, and 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 thereof is to provide a method for manufacturing a solid electrolytic capacitor capable of further reducing ESR.

  In order to solve the above-mentioned problems, the present inventor has intensively studied a method for producing a solid electrolytic capacitor capable of further reducing ESR as compared with the prior art, and has completed the present invention. That is, the present inventors have found that good results can be obtained by setting the porosity of the capacitor element impregnated with the monomer solution to 80 to 85% and the concentration of the oxidant solution to 45 to 55 wt%. It is.

(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 having a concentration adjusted to 25 to 32 wt%, so that the porosity of the capacitor element was 80 to 85%. Thereafter, an oxidant solution adjusted to a concentration of 45 to 55 wt% 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.

(Porosity)
The porosity of the capacitor element impregnated with the monomer solution is preferably 80 to 85%. If the porosity is greater than 85%, the amount of monomer impregnated is too small and the amount of conductive polymer formed decreases, resulting in a decrease in capacitance and an increase in ESR. On the other hand, when the porosity is less than 80%, the amount of the oxidant to be impregnated is small, and the conductivity of the formed conductive polymer is lowered, so that the ESR is increased.

  The method for adjusting the porosity to the above range is performed by adjusting the concentration of the monomer solution. This is because, when the concentration of the monomer solution is low, the volatile components increase, so that the porosity can be increased. The concentration of the monomer solution is preferably 25 to 32 wt%. This is because a desired porosity can be obtained when the concentration of the monomer solution is 25 to 32 wt%.

(EDT)
When EDT is used as the polymerizable monomer, it is preferable to use an EDT solution impregnated in the capacitor element in which EDT is dissolved in a volatile solvent so that its concentration is 25 to 32 wt%.
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 ferric paratoluenesulfonate, 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)
As the polymerizable monomer used in the present invention, 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, 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 reason why good results were obtained by setting the porosity of the capacitor element impregnated with the monomer solution to 80 to 85% and the concentration of the oxidant solution to 45 to 55 wt. This is probably because the impregnation property and permeability are improved, the progress of polymerization is improved, and a good conductive polymer is formed.

  ADVANTAGE OF THE INVENTION According to this invention, the manufacturing method of the solid electrolytic capacitor which can further reduce ESR 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. The element porosity at this time was 80%. Next, a 45 wt% ferric paratoluenesulfonic acid ethanol solution is poured into a predetermined container, the capacitor element is immersed, impregnated with an oxidant solution, heated at 120 ° C. for 60 minutes, and then the capacitor element The polymerization reaction of PEDT was generated in the inside to form a solid electrolyte layer.
And this capacitor | condenser element was inserted in the bottomed cylindrical outer case, the sealing rubber | gum 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 element porosity was 80%, and the concentration of the oxidant solution was 50 wt%. Other conditions and steps are the same as in Example 1.
(Example 3)
The concentration of the EDT solution was 25 wt%, and the element porosity was 85%. Other conditions and steps are the same as in Example 1.
Example 4
The concentration of the EDT solution was 25 wt%, the element porosity was 85%, and the concentration of the oxidant solution was 55 wt%. Other conditions and steps are the same as in Example 1.

(Comparative Example 1)
The concentration of the EDT solution was 38 wt%, the element porosity was 75%, and the concentration of the oxidant solution was 55 wt%. Other conditions and steps are the same as in Example 1.
(Comparative Example 2)
The concentration of the EDT solution was 10 wt%, the element porosity was 95%, and the concentration of the oxidant solution was 55 wt%. Other conditions and steps are the same as in Example 1.

[Comparison result]
When the ESR was examined for the examples and comparative examples obtained by the above method, the results shown in Table 1 were obtained.

  As is clear from Table 1, in all of Examples 1 to 4 in which the porosity was 80 to 85%, ESR was reduced as compared with Comparative Examples 1 and 2. In particular, when Example 4 in which the concentration of the oxidant solution is the same as 55 wt% is compared with Comparative Examples 1 and 2, the ESR of Example 4 is about 76% of Comparative Example 1 and 55% of Comparative Example 2. Reduced.

Next, when Example 1 and Example 2 in which the porosity is the same as 80% are compared, Example 2 having a higher concentration of the oxidant solution has better ESR characteristics. Further, when Example 3 and Example 4 having the same porosity of 85% were compared, Example 4 having a higher concentration of the oxidant solution had better ESR characteristics.
Further, comparing Example 1 and Example 3 in which the concentration of the oxidant solution is the same as 45 wt%, Example 3 having a larger porosity has better ESR characteristics.

Claims (4)

A solid electrolytic capacitor in which 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 impregnated with an oxidant solution to form a solid electrolyte layer made of a conductive polymer. In the manufacturing method,
A method for manufacturing a solid electrolytic capacitor, wherein a porosity of a capacitor element impregnated with the polymerizable monomer solution is 80 to 85%, and a concentration of the oxidant solution is 45 to 55 wt%.   The method for producing a solid electrolytic capacitor according to claim 1, wherein the concentration of the polymerizable monomer solution is 25 to 32 wt%.   The method for producing a solid electrolytic capacitor according to claim 1, wherein the polymerizable monomer is a thiophene derivative.   The method for producing a solid electrolytic capacitor according to claim 3, wherein the thiophene derivative is 3,4-ethylenedioxythiophene.