JP4821818B2 - Solid electrolytic capacitor and manufacturing method thereof - Google Patents

Description

  The present invention relates to a solid electrolytic capacitor and a manufacturing method thereof, and more particularly to a solid electrolytic capacitor capable of reducing an equivalent series resistance (hereinafter referred to as ESR) of a solid electrolytic capacitor and a manufacturing method thereof.

  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 (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 manufactured 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. 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 to form 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 solid electrolytic capacitor capable of further reducing ESR and a method for manufacturing the same. .

  The present inventors thought that the separator may be the reason why a sufficient effect of reducing the ESR cannot be obtained by the conventional method for producing a solid electrolytic capacitor, and have intensively studied the main fibers and the binder of the separator. As a result, it has been found that ESR is further reduced by using a separator having nylon fibers as main fibers and polyvinyl alcohol (hereinafter referred to as PVA) as a binder.

(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 using nylon fiber as a main fiber and PVA as a binder to form a capacitor element. Apply. Then, it is immersed in warm water at 80 ° C. or higher and lower than 100 ° C. for 5 to 120 minutes, and heat-treated at 80 ° C. or higher and lower than 250 ° C. for 10 to 180 minutes.

Then, the capacitor element is immersed in a mixed solution prepared by mixing a polymerizable monomer and an oxidizing agent together with a predetermined solvent, and a polymerization reaction of a conductive polymer is generated in the capacitor element to form a solid electrolyte layer. Then, this 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.

(Separator)
Usually, a separator for a solid electrolytic capacitor mainly composed of synthetic fibers is composed of synthetic fibers and a binder for joining them. As this binder, synthetic resin itself is used, or synthetic resin is made into a fiber shape and melted in a separator manufacturing process to bond main fibers.

  In the present invention, good results were obtained by using a separator having nylon fibers as the main fibers and PVA as a binder. As said nylon fiber, nylon 6, nylon 66, nylon 610, nylon 612, nylon 10, and nylon 12 can be used individually or in combination of 2 or more types. Moreover, it is preferable to use PVA binder fiber for PVA used as a binder.

Then, these nylon fibers and PVA binder fibers are mixed and dispersed in water to prepare a slurry. The separator of the present invention can be obtained by making paper with this long slurry, slanted long mesh, or round mesh paper machine and drying with a dryer.
In addition, as for content of the binder with respect to a separator, 10-20 wt% is preferable. Moreover, since the separator of the present invention has good heat resistance, it has been confirmed that it can withstand lead-free reflow.

The reason why ESR is reduced by using a separator having nylon fibers as main fibers and PVA as a binder is considered as follows. That is, when a capacitor element is impregnated with a polymerizable monomer and an oxidizing agent to form a conductive polymer, nylon fibers as the main fibers are decomposed by the oxidizing agent, and the separator becomes coarse by reducing the fiber content. For this reason, it is considered that the amount of conductive polymer such as PEDT contained in the capacitor element increases, the overall conductivity is improved, and the ESR is reduced. In addition, since PVA is used as a binder, it is considered that the PVA dissolved during the restoration conversion adheres to the oxide film, thereby further enhancing the ESR reduction effect.
This was found from the fact that the nylon fiber was reduced as a result of observing the capacitor element after the conductive polymer was formed.

(Heat treatment)
In the present invention, it has been found that if the heat treatment is performed before impregnating the polymerizable monomer and the oxidizing agent, the ESR is further reduced. The reason is considered to be that the decomposition of nylon fibers is promoted. The heat treatment temperature is preferably 80 to 250 ° C., more preferably 90 to 170 ° C., and the heat treatment time is preferably 10 to 180 minutes, more preferably 30 to 120 minutes.

(Hot water immersion treatment)
Further, in the present invention, it was found that ESR is further reduced when the hot water immersion treatment is performed before impregnating the polymerizable monomer and the oxidizing agent. The reason is considered to be that the adhesion state of PVA to the oxide film is improved. In addition, the temperature of this warm water is preferably 80 to 100 ° C, more preferably 90 to 100 ° C, and the immersion time is preferably 5 to 120 minutes, more preferably 60 to 120 minutes.

(EDT and oxidizing agent)
When EDT is used as the polymerizable monomer, EDT monomer can be used as EDT impregnated in the capacitor element, but a monomer solution in which EDT and a volatile solvent are mixed at a volume ratio of 1: 0 to 1: 3. Can also be used.
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.

  Further, 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 40 to 58 wt%, and 45 to 57 wt%. % Is more preferable. 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.

  As described above, according to the present invention, a solid electrolytic capacitor capable of reducing ESR and a method for manufacturing the same can be provided.

Then, this invention is demonstrated further in detail based on Examples 1-4 and the comparative example manufactured as follows. Example 1 is a reference example of the present invention.
Example 1
A solid electrolytic capacitor was prepared as follows using a separator using nylon fiber as a main fiber and PVA as a binder (the content of the binder with respect to the separator is 15%). An electrode lead means was connected to the anode foil and cathode foil having an oxide film layer formed on the surface, and both electrode foils were wound through the separator to form a capacitor element having an element shape of 5φ × 2.8L. . And this capacitor | condenser element was immersed in ammonium dihydrogenphosphate aqueous solution for 40 minutes, and restoration | repair chemical conversion was performed. After the repair formation, the capacitor element was immersed in warm water at 90 ° C. for 60 minutes and then heat treated at 100 ° C. for 10 minutes.
On the other hand, EDT and 50% ferric paratoluenesulfonic acid ethanol solution are mixed in a predetermined container, and the capacitor element is immersed in the above mixed solution for 10 seconds, heated at 120 ° C. for 60 minutes, Then, a polymerization reaction of PEDT was generated 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 by applying a voltage of 5.2 V at 150 ° C. for 120 minutes to form a solid electrolytic capacitor. This solid electrolytic capacitor has a rated voltage of 4 WV and a rated capacity of 150 μF.

(Example 2)
After the repair conversion, the capacitor element was immersed in warm water at 90 ° C. for 10 minutes and then heat treated at 170 ° C. for 120 minutes. Other conditions and steps are the same as in Example 1.
(Example 3)
After the repair conversion, the capacitor element was immersed in warm water at 90 ° C. for 60 minutes and then heat treated at 170 ° C. for 120 minutes. Other conditions and steps are the same as in Example 1.

Example 4
After the repair conversion, the polymerization process was started without performing either hot water immersion treatment or heat treatment. Other conditions and steps are the same as in Example 1.
(Comparative example)
A separator using PET fiber as the main fiber and PET as a binder (the content of the binder with respect to the separator is 15%) was transferred to the polymerization step without performing either warm water immersion treatment or heat treatment after restoration conversion. Other conditions and steps are the same as in Example 1.

[Comparison result]
When Examples 1 to 4 and Comparative Examples obtained by the above method were examined for ESR, the results shown in Table 1 were obtained.

  As is clear from Table 1, when the comparative example is compared with Example 4 in which the transition to the polymerization process is carried out without performing either hot water immersion treatment or heat treatment after the restoration conversion, nylon fiber is used as the main fiber, and a PVA binder is used. In Example 4 using the separator, the ESR was reduced to about 84.8% compared to the comparative example using the PET fiber as the main fiber and using the separator using the PET binder.

Further, when Examples 1 to 3 in which hot water immersion treatment and heat treatment were performed after the repair conversion were compared with the comparative example, the ESR was reduced to about 61.7 to 68.3%. Further, even when Examples 1 to 3 and Example 4 differing in the presence or absence of hot water immersion treatment and heat treatment after restoration conversion, ESR was reduced to about 72.8 to 80.5%.
For this reason, the effect of reducing ESR is greater when nylon fiber is the main fiber and a separator using PVA binder is used, and the effect of reducing ESR is greater when hot water immersion treatment and heat treatment are performed after restoration formation. It turned out to be bigger.

Claims (2)

In a solid electrolytic capacitor in which an anode foil and a cathode foil are wound through a separator to form a capacitor element, and this capacitor element is impregnated with a polymerizable monomer and an oxidizing agent to form a conductive polymer.
A capacitor element using a separator polyvinyl alcohol nylon fibers and main fibers and a binder, depositing the said polyvinyl alcohol oxidized film was immersed in warm water, then between less than 80 ° C. or higher 250 ° C. 30 to 120 minutes A solid electrolytic capacitor characterized in that heat treatment is used to promote separator densification with an oxidizing agent. In a method for producing a solid electrolytic capacitor in which a capacitor element obtained by winding an anode foil and a cathode foil through a separator is impregnated with a polymerizable monomer and an oxidizing agent to form a solid electrolyte layer made of a conductive polymer,
As the separator, a separator using nylon fiber as a main fiber and polyvinyl alcohol as a binder is used, and after forming the capacitor element, it is immersed in warm water of 80 ° C. or more and less than 100 ° C. to attach the polyvinyl alcohol to the oxide film. , then, by a heat treatment between 30 to 120 minutes at less than 80 ° C. or higher 250 ° C., a manufacturing method of a solid electrolytic capacitor is characterized in that to promote density of the separator with an oxidizing agent.