JP2009252913A - Method of manufacturing solid electrolytic capacitor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of manufacturing a solid electrolytic capacitor by which the solid electrolytic capacitor with good electrical characteristic can be manufactured by controlling a polymerization speed of oxidant and monomer. <P>SOLUTION: The method of manufacturing the solid electrolytic capacitor comprises the steps of forming a capacitive element with a positive electrode, in which an anode oxidation coating is formed on a front surface thereof (S1 to S4); impregnating the oxidant and the monomer into the capacitive element in a cooling atmosphere, in the order (S5, S6); and forming a solid electrolyte consisting of a conductive polymer on the anode oxidation coating, by carrying out a chemical polymerization of the oxidant and the monomer (S7). <P>COPYRIGHT: (C)2010,JPO&INPIT

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 having a solid electrolyte made of a conductive polymer.

A capacitor element of an electrolytic capacitor is made of a valve metal such as aluminum, tantalum, or niobium, and has an anode body (anode foil or sintered body) having a large number of etching pits and fine holes formed on the surface. Furthermore, an oxide film serving as a dielectric, that is, an anodic oxide film is formed on the surface of the anode body, and electrodes are drawn from the anodic oxide film by lead wires or the like. In addition, an electrolyte is in contact with the anodic oxide film, and this electrolyte functions as a true cathode for drawing an electrode from the anodic oxide film.
Here, since the electrolyte as the true cathode has a great influence on the electrical characteristics of the electrolytic capacitor, electrolytic capacitors employing various types of electrolytes have been proposed conventionally.

  Among the above-described electrolytic capacitors, there is a solid electrolytic capacitor using a solid electrolyte having excellent electronic conductivity instead of a liquid electrolyte having ionic conductivity having poor impedance characteristics in a high frequency region. In order to form the solid electrolyte of the solid electrolytic capacitor, there is an impregnation step in which the capacitor element is impregnated with an oxidizing agent and a monomer. For example, as in the solid electrolytic capacitor manufacturing methods described in Patent Documents 1 to 4, this impregnation method involves preparing a liquid mixture of an oxidant and a monomer in advance and immersing the capacitor element in the prepared liquid mixture. For example, a method of impregnating a capacitor element with an oxidant and then impregnating with a monomer, and a method of impregnating a capacitor element with a monomer and then impregnating with an oxidant are known.

  Furthermore, it is known that the amount of oxidant and monomer impregnated in the capacitor element has a great influence on the electrical characteristics of the capacitor product. In the method of manufacturing a solid electrolytic capacitor described in Patent Document 5, the capacitor element The solid electrolytic capacitor having good electrical characteristics is manufactured by adjusting the amount of the oxidant impregnated.

JP 2003-272953 A Japanese Patent Laid-Open No. 10-340830 Japanese Patent Laid-Open No. 10-12497 Japanese Patent Laid-Open No. 6-314639 JP 2001-102254 A

  However, in the method for producing a solid electrolytic capacitor described in Patent Documents 1 to 5, the impregnation step is performed at room temperature, for example, at room temperature (25 ° C.). However, since the polymerization reaction proceeds even at room temperature, The polymerization reaction rate between the oxidant impregnated in the capacitor element and the monomer increases rapidly, and the polymerization rate of each part cannot be controlled. Therefore, for example, when a part of the polymerization reaction proceeds rapidly on the surface of the foil in the capacitor element, that is, near the entrance of the etching pit, a sufficient solid electrolyte layer can be formed to the details of the etching pit. Can not. As a result, there is a problem that the solid electrolyte layer cannot sufficiently fulfill the role as a true cathode for extracting the characteristics of the anodic oxide film, and a solid electrolytic capacitor having good electrical characteristics cannot be manufactured.

  Accordingly, an object of the present invention is to control the polymerization rate of the oxidant and the monomer, and in particular, by forming the solid electrolyte layer in the details of the etching pit and then forming the solid electrolyte layer outside the capacitor element, The object is to provide a method for producing a solid electrolytic capacitor having good characteristics.

  According to a first aspect of the present invention for achieving the above object, there is provided a method for producing a solid electrolytic capacitor, comprising impregnating a capacitor element having an anode body having an anodized film formed on the surface thereof with an oxidizing agent, and then in a cooling atmosphere A solid electrolyte made of a conductive polymer is formed on the anodized film by impregnating with a drop and chemically polymerizing the solid electrolytic capacitor.

  According to the first invention, the capacitor element after impregnation with the oxidizing agent is impregnated with the monomer in a cooling atmosphere. At this time, the monomer is dropped and impregnated into the capacitor element, and then heated to complete the polymerization, so that the monomer slowly enters the details of the etching pits of the foil in the capacitor element. After forming a uniform solid electrolyte, the polymerization reaction can be completed. As a result, it is possible to produce a solid electrolytic capacitor having better electrical characteristics (capacitance, equivalent series resistance, etc.) than impregnation at room temperature (25 ° C.) and then polymerization by heating.

  Furthermore, the cooling atmosphere of the impregnation step in the method for producing a solid electrolytic capacitor according to the second invention is −80 to 0 ° C.

  According to the second invention, when impregnation is performed in a cooling atmosphere of −80 to 0 ° C., a solid electrolytic capacitor having good electrical characteristics can be manufactured.

  Further, the oxidizing agent in the method for producing a solid electrolytic capacitor according to the third invention includes p-toluenesulfonic acid ferric salt, naphthalenesulfonic acid ferric salt, triisopropylnaphthalenesulfonic acid ferric salt, and dodecylbenzenesulfone. Any one or a mixture of two or more of ferric acid salts may be used.

  Further, the monomer in the method for producing a solid electrolytic capacitor according to the fourth invention may be any one of aniline, pyrrole, thiophene and derivatives thereof.

  Furthermore, when the monomer in the method for producing a solid electrolytic capacitor according to the fifth invention is thiophene, the thiophene derivative may be ethylenedioxythiophene.

  When the substances according to the third to fifth inventions are used as materials, a solid electrolytic capacitor having better electrical characteristics can be manufactured.

  According to the present invention, it is possible to produce a solid electrolytic capacitor having better electrical characteristics (capacitance, equivalent series resistance, etc.) than impregnation at room temperature (25 ° C.) and then polymerization by heating. .

  Embodiments of the present invention will be described below with reference to FIGS. 1 to 3 and Tables 1 and 2.

[Structure of solid electrolytic capacitor]
A solid electrolytic capacitor 1 manufactured by the manufacturing method in the present embodiment will be described with reference to FIG. FIG. 1 is an exploded perspective view of a capacitor element 6 included in the solid electrolytic capacitor 1. The capacitor element 6 includes an anode foil 2, a cathode foil 3, and a separator 4. Further, lead tabs (not shown) are connected from the anode foil 2 and the cathode foil 3, and lead wires 5 are drawn from the anode foil 2 and the cathode foil 3 through the lead tabs, respectively.

  The capacitor element 6 is formed by winding the anode foil 2 and the cathode foil 3 with the separator 4 interposed therebetween. Capacitor element 6 is impregnated with an oxidant and a monomer in order, and the oxidant and the monomer are chemically polymerized in a cooling atmosphere, so that a solid made of a conductive polymer is formed on an anodic oxide film 2a described later. The electrolyte is uniformly formed.

  FIG. 2 is a schematic diagram of the laminated structure of the solid electrolytic capacitor 1. The anode foil 2 is formed of a valve metal such as aluminum. As shown in FIG. 2, the surface of the anode foil 2 is roughened (etching pit formation) by an etching process, and an anodized film 2a is formed by anodic oxidation (chemical conversion).

  The cathode foil 3 is formed of a valve metal such as aluminum like the anode foil 2, and the surface of the cathode foil 3 is roughened (etching pits formed) and a natural oxide film 3a is formed. .

  The separator 4 has a strip shape having insulating properties, and a solid electrolyte 7 made of a conductive polymer is held on both surfaces of the separator 4. That is, the solid electrolyte 7 is sandwiched between the anodic oxide film 2 a of the anode foil 2 and the natural oxide film 3 a of the cathode foil 3 and the separator 4. In addition, polyaniline, polypyrrole, polyethylenedioxythiophene (PEDOT), etc. are used for the conductive polymer which comprises the solid electrolyte 7, These are produced | generated by the chemical polymerization of an oxidizing agent and a monomer.

[Method of manufacturing solid electrolytic capacitor]
Next, the manufacturing method of the solid electrolytic capacitor 1 is demonstrated using FIG. FIG. 3 is a process flow diagram showing a method for manufacturing the solid electrolytic capacitor 1. First, in order to increase the effective surface area of the electrode, the anode foil 2 and the cathode foil 3 are etched to roughen the surface (S1). Further, the surface of the roughened anode foil 2 is subjected to chemical conversion treatment to form an anodic oxide film 2a, and the natural oxide film 3a is formed on the roughened surface of the cathode foil 3 (S2).
Note that titanium, titanium nitride, titanium carbide, carbon, or the like may be formed on the surface of the cathode foil 3 by vapor deposition or coating.
Next, the anode foil 2 on which the anodic oxide film 2a is formed and the cathode foil 3 on which the natural oxide film 3a is formed are cut into predetermined dimensions, and lead wires 5 are connected to the anode foil 2 through lead tabs, respectively. The foil 2 and the cathode foil 3 are wound through the separator 4 (S3). Thereafter, in the ammonium adipate aqueous solution, a voltage is applied to perform element formation (cut formation), and the separator 4 is carbonized to produce a cylindrical capacitor element 6 (S4).

  In S4, when the capacitor element 6 is manufactured, the capacitor element 6 is impregnated with the oxidizing agent by immersing the manufactured capacitor element 6 in the oxidizing agent (S5). Next, the capacitor element 6 impregnated with the oxidizing agent is dropped and impregnated with the monomer solution in a cooling atmosphere of −80 to 0 ° C. (S6). Here, the steps S5 and S6 are referred to as an impregnation step. In this impregnation step, the capacitor element 6 is impregnated with an oxidant, and then a monomer is dropped in a cooling atmosphere at the above temperature, whereby a foil in the capacitor element is obtained. It becomes possible to form a polymer that is sufficiently and uniform up to the details of the etching pits.

  Next, the impregnation step of S5 and S6 described above is performed, and the oxidant and the monomer are further chemically polymerized by heating the capacitor element 6, and the anodic oxide film 2a of the anode foil 2 and the natural oxide film 3a of the cathode foil 3 A solid electrolyte 7 made of a conductive polymer is formed between the separator 4 (S7). Next, the cylindrical capacitor element 6 is housed in a bottomed cylindrical outer case (not shown), and the opening is sealed with a sealing rubber (not shown) and assembled into the shape of the solid electrolytic capacitor 1 (S8). Finally, an aging process is performed (S9), and the solid electrolytic capacitor 1 is completed.

  Table 1 shows how the electrical characteristics of the solid electrolytic capacitor 1 change when the temperature of the cooling atmosphere when the monomer solution is dropped and impregnated in the impregnation step in the method for manufacturing the solid electrolytic capacitor 1 is changed. This will be described with reference to Table 2. Note that Examples 1 to 7 and Comparative Examples described below differ only in the temperature of the cooling atmosphere when the monomer solution is dropped and impregnated, and the other steps are the same.

[Example 1]
In Example 1, in the impregnation step, the capacitor element 6 was impregnated with a solution prepared by dissolving ferric salt of p-toluenesulfonic acid as a oxidant in a solvent, and then pulled up, and the monomer solution was dropped in a cooling atmosphere at −60 ° C. did. Furthermore, the capacitor element 6 was heated at 60 ° C. for 60 minutes to produce PEDOT as a conductive polymer by chemical polymerization, and the solid electrolyte 7 was formed. (Hereinafter, the solid electrolytic capacitor 1 manufactured by the manufacturing method of Example 1 is simply referred to as the solid electrolytic capacitor 1 of Example 1.)

[Comparative example]
Next, in the impregnation process, the comparative example impregnated the capacitor element 6 with a solution in which p-toluenesulfonic acid ferric salt was dissolved in a solvent as an oxidizing agent in the impregnation step as in Example 1. Thereafter, in the comparative example, the monomer solution was dropped at room temperature (25 ° C.) in room temperature. Next, the capacitor element 6 was heated at 60 ° C. for 60 minutes in the same manner as in Example 1 to produce PEDOT as a conductive polymer by chemical polymerization, and the solid electrolyte 7 was formed. (Hereinafter, the solid electrolytic capacitor 1 manufactured by the manufacturing method of the comparative example is simply referred to as the solid electrolytic capacitor 1 of the comparative example.)

Table 1 shows a list comparing the results of measuring the electrical characteristics (capacitance, equivalent series resistance, and leakage current) of the solid electrolytic capacitor 1 according to Example 1 and the comparative example. Here, the capacitance (Cap) is a capacitance in which the capacitor can store electric charge, and the larger the value, the better. The equivalent series resistance (ESR) represents the equivalent series resistance value of loss resistance and reactance when an AC signal is passed through the capacitor, and the equivalent series resistance (ESR) of the ideal capacitor is 0Ω.
Therefore, the equivalent series resistance (ESR) is better as the value is smaller. Leakage current (LC) refers to the current that flows when a voltage is applied to an insulator. If a current flows through an insulated part, the power consumption increases, the amount of heat generation increases, and the capacitor burns out. Or damage the circuit. Therefore, the ideal leakage current (LC) of the capacitor is 0A, and the smaller this value, the better. Note that the standard value of the leakage current (LC) of the solid electrolytic capacitor 1 of the present embodiment has an upper limit of 960 μA.

As shown in Table 1, the capacitance (Cap) of the solid electrolytic capacitor 1 according to Example 1 is 1350 μF, which is larger than 1200 μF of the capacitance (Cap) of the solid electrolytic capacitor 1 according to the comparative example. . The equivalent series resistance (ESR) of the solid electrolytic capacitor 1 according to Example 1 is 7.5 mΩ, which is smaller than the equivalent series resistance (ESR) of the solid electrolytic capacitor 1 according to the comparative example.
Thereby, like the solid electrolytic capacitor 1 according to Example 1, when the monomer solution was dropped in a cooling atmosphere of −60 ° C. in the impregnation step, the capacitance (Cap) was increased and the equivalent series resistance (ESR) was increased. It can be seen that a solid electrolytic capacitor that can be made smaller and has better electrical characteristics can be manufactured. The leakage current (LC) is a value much smaller than the standard upper limit value of 960 μA in both the solid electrolytic capacitor 1 according to Example 1 and the comparative example, and thus there is no problem.

[Examples 2 to 7]
Next, Table 2 shows a list comparing the results of measuring the electrical characteristics (capacitance, equivalent series resistance and leakage current) when the monomer solution was dropped while the cooling atmosphere in the impregnation step was changed to the upper and lower limits. . Here, in Examples 2 to 7, the monomer dropping temperature was −85 ° C., −80 ° C., −40 ° C., −20 ° C., 0 ° C., and 5 ° C., respectively, and other conditions were the same as in Example 1 described above. It is.

As shown in Table 2, the solid electrolytic capacitor 1 manufactured by the manufacturing method of the example shows improved electrical characteristics as compared with the normal temperature (25 ° C.) of the comparative example. Furthermore, the solid electrolytic capacitor 1 manufactured by the manufacturing method of Example 1 and Examples 3 to 6 in which the monomer dropping temperature is between −80 to 0 ° C. is more electrostatic than the solid electrolytic capacitor 1 according to the comparative example. The capacity (Cap) is large and the equivalent series resistance (ESR) is small. In the impregnation step (S6 in FIG. 3), when a monomer is dropped in a cooling atmosphere of −80 to 0 ° C., a sufficient and uniform polymer can be formed up to the details of the etching pits of the foil in the capacitor element. Therefore, it is considered that a solid electrolytic capacitor having better electrical characteristics can be manufactured.
On the other hand, in the impregnation step (S6 in FIG. 3), when the monomer is dropped at room temperature (25 ° C.) as in the comparative example, it is dropped into the oxidizer and the capacitor element in the subsequent heating step (S7 in FIG. 3). The polymerization rate of each part becomes uncontrollable and the polymerization rate of each part becomes uncontrollable.For example, a part of the polymerization reaction occurs rapidly on the surface of the foil in the capacitor element, that is, near the entrance of the etching pit. If it has progressed, it becomes impossible to form a solid electrolyte layer sufficient for the details of the etching pits. As a result, it is considered that it is difficult to obtain the solid electrolytic capacitor 1 having better electrical characteristics as the solid electrolytic capacitor 1 manufactured by the manufacturing method of Example 1 and Examples 3 to 6.

Note that the leakage current (LC) of the solid electrolytic capacitor 1 manufactured by the manufacturing methods of Examples 2 to 7 is a value much smaller than the standard upper limit value of 960 μA in all cases, so there is no problem.
From the above results, the monomer dropping temperature in the impregnation step is preferably performed in a cooling atmosphere of −80 to 0 ° C., and more preferably in a cooling atmosphere of −60 to −20 ° C. It was confirmed that there was.

  As mentioned above, although this invention was demonstrated based on suitable embodiment, this invention is not limited to this, The manufacturing method of the solid electrolytic capacitor 1 adds the following content to the above-mentioned embodiment. Alternatively, it may be duplicated or replaced.

  In the present embodiment, a solution of ferric p-toluenesulfonate is used as the oxidizing agent, but it is not necessary to be limited to this, and any known sulfonic acid-based metal salt other than the iron p-toluenesulfonate solution ( For example, naphthalenesulfonic acid ferric salt, triisopropylnaphthalenesulfonic acid ferric salt and dodecylbenzenesulfonic acid ferric salt) may be used as the oxidizing agent. Moreover, you may use these 2 or more types of mixtures.

  Furthermore, in the present embodiment, ethylenedioxythiophene is used as a monomer, but it is not necessary to limit to this, and a known solution other than ethylenedioxythiophene (for example, aniline, pyrrole, and derivatives thereof) is used. It may be used as a monomer.

In the present embodiment, after impregnating the capacitor element 6 produced in S4 with an oxidant in the impregnation step (S5, S6) of the process flow diagram showing the method for manufacturing the solid electrolytic capacitor 1 of FIG. 3 (S5) Although the monomer is dropped in the cooling atmosphere (S6), the oxidant may be dropped in the cooling atmosphere after impregnating the monomer without being particular about this.
That is, by impregnating one of the oxidant and the monomer first and the other afterwards and sequentially in a cooling atmosphere, the oxidant and the monomer can be dropped at the same time, and the oxidant and the monomer can be polymerized. It is possible to control the polymerization rate.

  Further, in the present embodiment, the solid electrolytic capacitor 1 having a winding type capacitor element has been described. However, without particular attention to this, a laminated capacitor element of aluminum foil, a capacitor made of a sintered body of tantalum or niobium The present invention can also be applied to a solid electrolytic capacitor having an element.

It is a disassembled perspective view of the capacitor | condenser element which a solid electrolytic capacitor has. It is the schematic of the laminated structure of a solid electrolytic capacitor. It is a process flow figure showing a manufacturing method of a solid electrolytic capacitor.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Solid electrolytic capacitor 2 Anode foil 2a Anodized film 3 Cathode foil 3a Natural oxide film 4 Separator 5 Lead wire 6 Capacitor element 7 Solid electrolyte

Claims (5)

  A capacitor element having an anode body with an anodized film formed on the surface is impregnated with an oxidant and then impregnated with a monomer dropwise in a cooling atmosphere, followed by chemical polymerization. A method for producing a solid electrolytic capacitor, comprising forming a solid electrolyte composed of molecules.   The method for producing a solid electrolytic capacitor according to claim 1, wherein a cooling atmosphere in the impregnation step is −80 to 0 ° C.   The oxidizing agent is one or more of p-toluenesulfonic acid ferric salt, naphthalenesulfonic acid ferric salt, triisopropylnaphthalenesulfonic acid ferric salt and dodecylbenzenesulfonic acid ferric salt. The method for producing a solid electrolytic capacitor according to claim 1, wherein the solid electrolytic capacitor is a mixture of   The method for producing a solid electrolytic capacitor according to any one of claims 1 to 3, wherein the monomer is any one of aniline, pyrrole, thiophene, and derivatives thereof.   The method for producing a solid electrolytic capacitor according to claim 4, wherein the derivative of thiophene is ethylenedioxythiophene.

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