JP5023940B2 - Solid electrolytic capacitor - Google Patents

Description

  The present invention relates to a solid electrolytic capacitor using a conductive polymer compound as a solid electrolyte, and more particularly to a solid electrolytic capacitor that has been improved to improve withstand voltage characteristics.

  An electrolytic capacitor using a metal having a valve action such as aluminum can obtain a small size and a large capacity by expanding the surface of the dielectric by making the valve action metal as an anode electrode into the shape of an etching foil or the like. It is widely used because it can. 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 and high functionality of electronic equipment.

  As the solid electrolyte used for the solid electrolytic capacitor, a conductive polymer having high conductivity and excellent adhesion to the oxide film layer of the anode electrode is used as the solid electrolyte. As this conductive polymer, for example, polyaniline, polythiophene, polyethylenedioxythiophene and the like are known.

  Among these, polyethylenedioxythiophene (hereinafter referred to as PEDOT) has attracted attention as a conductive polymer that can achieve a high breakdown voltage because the withstand voltage can be increased with respect to the thickness of the oxide film. In the capacitor using PEDOT, chemical oxidative polymerization is used, and it is manufactured as follows.

  That is, an anode foil and a cathode foil are wound through a separator to form a capacitor element, this capacitor element is impregnated with EDOT and an oxidant solution, and heated to form a PEDOT polymer layer between both electrodes. A solid electrolytic capacitor is formed (see Patent Document 1).

Such a solid electrolytic capacitor is used for in-vehicle use and inverter use, but the working voltage increases from 20 WV to 35 WV, and in order to cope with these, the capacitor element is composed of a compound having a vinyl group and a boric acid compound. It is disclosed that the withstand voltage is increased by containing a conjugate (see Patent Document 2).
Japanese Patent Laid-Open No. 9-293639 JP 2003-100560 A

  However, even with such a technique, a high withstand voltage is not sufficient, and the development of a solid electrolytic capacitor having further high withstand voltage characteristics has been desired.

  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 having high withstand voltage characteristics.

  In order to solve the above-mentioned problems, the present inventors have made extensive studies on a solid electrolytic capacitor having a high withstand voltage characteristic, and form a solid electrolyte layer made of an oxidatively polymerizable conductive polymer on a dielectric oxide film. Before trying to immerse the dielectric oxide film in a pH buffer and investigating its effect, it was found that better electrical properties can be obtained than forming without including a pH buffer. is there.

  The manufacturing method of the solid electrolytic capacitor according to the present invention is as follows. Restoration and chemical conversion are performed by immersing an aqueous solution of ammonium adipate or the like into a capacitor element produced by winding a cathode foil and an anode foil on which a dielectric oxide film layer is formed with a separator interposed therebetween. And the pH buffer agent is made to exist on the said dielectric oxide film by immersing the capacitor element produced in this way in the phosphate buffer solution used as a pH buffer agent.

  Subsequently, the capacitor element is immersed in a mixed solution of a polymerizable monomer and an oxidizing agent, and a polymerization reaction of a conductive polymer is generated in the capacitor element to form a solid electrolyte layer. And this capacitor | condenser element is accommodated in an exterior case, an opening edge part is sealed with sealing rubber | gum, and a solid electrolytic capacitor is formed.

  The capacitor element is impregnated with a polymerizable monomer and an oxidizing agent. The capacitor element is immersed in a mixture of a monomer and an oxidizing agent. The capacitor element is immersed in a monomer solution and then immersed in an oxidizing agent solution. A method of discharging the oxidant solution after discharging the monomer solution to the capacitor element can be used.

  Moreover, the manufacturing method of the flat type solid electrolytic capacitor based on this invention is as follows. That is, an anodized film layer is formed on the surface of a strip-shaped aluminum foil roughened by etching or the like, and the strip-shaped aluminum foil on which the anodized film is formed is immersed in a phosphate buffer that is a pH buffering agent. A pH buffering agent is present on the oxide film.

  Then, after forming an insulating resin band for separating the anode lead portion and the cathode portion in a predetermined portion, a conductive polymer compound film is formed in the predetermined portion, and the conductive polymer compound film is formed on the conductive polymer compound film. A cathode layer is formed by sequentially forming a graphite layer and a silver paste layer. Further, the cathode lead portion and the external cathode terminal are connected with silver paste.

  In addition, since the predetermined anode lead portion divided by the insulating resin band is an aluminum foil that cannot be soldered, a solderable metal plate is subjected to ultrasonic welding, electrical resistance welding, laser welding, etc. Make electrical connections.

(PH buffer)
As described above, by immersing the capacitor element in the pH buffering agent, the pH buffering agent is present on the dielectric film. This is because the oxidizing agent is subsequently immersed in the mixture of the polymerizable monomer and the oxidizing agent. This is performed in order to increase the pH of the film and to suppress damage to the formed oxide film. Here, a phosphate buffer is used as the pH buffering agent, and a combination of phosphoric acid (H ₃ PO ₄ ), potassium hydrogen phosphate (KH ₂ PO ₄ ), and sodium hydrogen phosphate (Na ₂ HPO ₄ ) is combined. What was adjusted to pH = 2.0-6.0 using the prepared liquid mixture is used.

Specifically, in order to adjust the pH to less than 2.0 to 4.0, phosphoric acid (H ₃ PO ₄ ) and potassium hydrogen phosphate (KH ₂ PO ₄ ) are mixed at a predetermined distribution, and pH is adjusted. In order to adjust to 4.0 to 6.0, potassium hydrogen phosphate (KH ₂ PO ₄ and sodium hydrogen phosphate (Na ₂ HPO ₄ ) are mixed at a predetermined ratio. Among ˜6.0, preferably, a phosphate buffer of 2.0 to 4.0 is used.

  In particular, the pH is limited to 2.0 to 4.0, and if it is less than 2.0, the coating is damaged by the strongly acidic polymerization liquid, and the effect is reduced by increasing the leakage current. If it exceeds 4.0, the pH is too high, the polymerization reaction becomes insufficient, the capacitance decreases, and the ESR increases. On the other hand, if it exceeds 6.0, the oxidative polymerization is further delayed to deteriorate these properties.

(Polymerizable monomer)
When 3,4-ethylenedioxythiophene (hereinafter referred to as EDOT) is used as the polymerizable monomer, an EDOT monomer can be used as the EDOT impregnated in the capacitor element substrate. A mixed monomer solution can also be used.

  Examples of the volatile solvent include hydrocarbons such as pentane and hexane, ethers such as tetrahydrofuran and dipropyl ether, esters such as ethyl formate and ethyl acetate, ketones such as acetone and methyl ethyl ketone, methanol, ethanol, and propanol. Alcohols, nitrogen compounds such as acetonitrile can be used, and methanol, ethanol, acetone and the like are particularly preferable.

(Oxidant)
As the oxidizing agent, an organic sulfonic acid metal salt such as ferric paratoluene sulfonate, periodic acid or iodic acid can be used.

(Chemical solution for restoration conversion)
As the chemical solution for restoration conversion, in addition to the adipic acid type such as ammonium adipate used above, phosphoric acid type chemical conversion solution such as ammonium dihydrogen phosphate and diammonium hydrogen phosphate, boric acid such as ammonium borate, etc. A chemical conversion solution of the system can be used.

(Other polymerizable monomers)
As the polymerizable monomer used in the present invention, in addition to the EDOT, a thiophene derivative other than EDOT, aniline, pyrrole, furan, acetylene, or a derivative thereof, which is oxidized and polymerized with a predetermined oxidizing agent, is a conductive polymer. As long as it forms, it can be applied.

(Function and effect)
The effects of the present invention are as follows.
The conventional solid electrolytic capacitor has a problem that the dielectric oxide film is damaged by the oxidizing action of the oxidizing agent used for the polymerization reaction, and the withstand voltage characteristic of the oxide film is lowered.

  On the other hand, in the present invention, a pH buffering agent having a pH of 2.0 to 6.0, preferably 2.0 to 4.0 is present on the dielectric oxide film, thereby oxidizing the coating thereafter. Since the pH of the agent can be increased, damage to the oxide film is suppressed, and the leakage current characteristics of the solid electrolytic capacitor are improved. Here, in the present invention, since a pH buffering agent is present on the dielectric oxide film, it is preferably polymerized with a mixed solution of a monomer and an oxidizing agent. That is, the polymerization is not delayed because the oxide film is protected by the pH buffer while the polymerization proceeds in a mixed solution state. When either the oxidizing agent or the monomer solution is first immersed, it is considered that the polymerization is delayed because the pH buffering agent is mixed with the reaction solution and acts on the polymerization state.

  According to the present invention, it is possible to provide a solid electrolytic capacitor having high withstand voltage characteristics.

  Hereinafter, the present invention will be described in more detail based on examples. In addition, the samples of Examples, Comparative Examples 1 and 2 and the conventional example were prepared as follows, and the electrical characteristics were evaluated.

(Example)
After roughening the surface of the aluminum foil with an etching solution to increase the surface area, the anode foil having a dielectric oxide film formed thereon was similarly applied to the cathode foil having the surface of the aluminum foil roughened with an etching solution to increase the surface area. A capacitor element wound with an intervening layer is formed. Note that a lead terminal is connected to both the anode foil and the cathode foil.

Then, the capacitor element is re-formed with an aqueous solution of ammonium adipate or the like to repair the dielectric oxide film generated in the winding process. In this embodiment, the capacitor element is immersed in an aqueous solution of phosphoric acid (H ₃ PO ₄ ) and potassium hydrogen phosphate (KH ₂ PO ₄ (pH = 3.4) to provide a pH buffer on the dielectric oxide film. Agent was present.

  Thereafter, the capacitor element was impregnated with a mixed solution of a monomer solution of 3,4-ethylenedioxythiophene and an oxidizing agent, and polyethylenedioxythiophene was chemically oxidatively polymerized in the capacitor element to form a solid electrolyte layer. Next, the capacitor element in which the solid electrolytic reforming layer is formed is housed in an exterior case, and after sealing the opening of the exterior case with a sealing rubber, an aging treatment is performed by applying a rated voltage. A solid electrolytic capacitor of 16 WV-33 μF was produced.

(Comparative Example 1)
The sample of Comparative Example 1 is a sample manufacturing method of the above example, in which the capacitor element is made into an aqueous solution (pH = 3.4) of phosphoric acid (H ₃ PO ₄ ) and potassium hydrogen phosphate (KH ₂ PO ₄ ). It produced without going through the process of immersing. The capacitor element is impregnated by mixing ammonia in addition to the mixed solution of 3,4-ethylenedioxythiophene monomer solution and oxidizing agent. Polyethylenedioxythiophene was chemically oxidatively polymerized in the capacitor element to form a solid electrolyte layer. Since other steps are the same as those in the first embodiment, description thereof will be omitted.

(Comparative Example 2)
The sample of Comparative Example 2 was used as a capacitor element in the sample manufacturing method of the above example, and phosphoric acid (H ₃ PO ₄ ) and potassium hydrogen phosphate (KH ₂ PO ₄ aqueous solution (pH = 3.4)). The immersion step was performed after the formation of the solid electrolyte layer, that is, the sample of Comparative Example 2 was impregnated with a mixed solution of 3,4-ethylenedioxythiophene monomer solution and oxidizing agent in the capacitor element, After chemically oxidizing and polymerizing polyethylenedioxythiophene in the capacitor element, it is immersed in an aqueous solution (pH = 3.4) of phosphoric acid (H ₃ PO ₄ ) and potassium hydrogen phosphate (KH ₂ PO ₄ ), In addition, the step of mixing ammonia in addition to the monomer solution of 3,4-ethylenedioxythiophene and the oxidant in the capacitor element as in Comparative Example 1 is excluded.

(Conventional example)
In the sample of the conventional example, the capacitor element is immersed in an aqueous solution (pH = 3.4) of phosphoric acid (H ₃ PO ₄ ) and potassium hydrogen phosphate (KH ₂ PO ₄ ) in the sample manufacturing method of the above example. In addition, the step of mixing ammonia in addition to the monomer solution of 3,4 ethylenedioxythiophene and the oxidizing agent in the capacitor element as in Comparative Example 1 is also excluded.

(Comparison result)
The results of evaluating the electrical characteristics (capacitance, tan δ, leakage current, ESR) of the samples of Examples, Comparative Examples 1 and 2 and the conventional example produced as described above are as shown in FIG. become.

  As shown in FIG. 1 and Table 1, an example in which a pH buffering agent was present on a dielectric oxide film and a solid electrolyte was formed thereafter was Comparative Example 2 in which the pH buffering agent was immersed in the pH buffering agent after oxidative polymerization. It can be seen that the leakage current is reduced and the damage to the oxide film is suppressed as compared with the conventional example and the comparative example 1 in which no is present.

  Specifically, with respect to the leakage current, the conventional example is 5.65 μA, the comparative example 1 is 5.07 μA, and the comparative example 2 is 3542.91 μA, whereas the example is 1.94 μA, and the leakage current is remarkably high. The withstand voltage characteristic is low and the effect of the present application can be seen.

Comparison of electrical characteristics of Examples, Comparative Examples 1 and 2 and Conventional Example in the embodiment of the present invention

Claims (5)

on the pH of the dielectric oxide film to a pH buffering agent was present which is 2.0 to 4.0, oxidative polymerization of the formed of a conductive polymer solid electrolyte layer a solid body electrolyte you characterized in that the formation Capacitor. The solid electrolytic capacitor according to claim 1, wherein the pH buffer is a phosphate buffer. The solid electrolytic capacitor, the solid electrolytic capacitor according to claim 1 or 2, characterized in that a winding type. In the solid electrolytic capacitor, an anodized film layer is formed on the surface of a foil or plate-shaped valve metal, and a solid electrolyte layer made of a conductive polymer is formed thereon. A graphite layer, silver the solid electrolytic capacitor according to claim 1 or 2, characterized in that the paste layer are sequentially formed is a flat plate type forming a cathode portion. The solid electrolytic capacitor according to any one of claims 1 to 4 , wherein the solid electrolyte layer made of the conductive polymer is poly 3,4-ethylenedioxythiophene.

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