JP2005072619A - Solid electrolytic capacitor and manufacture thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a solid electrolytic capacitor, which is superior in electrical characteristics and is large in capacitance, by a method wherein a solid electrolyte layer consisting of conductive molecules, which are dense and even, is formed in the interior of a wound capacitor element, and a method of manufacturing the capacitor. <P>SOLUTION: After a capacitor element formed by winding anode electrode foils and cathode electrode foils via separators is impregnated with a mixed solution formed by mixing a 3,4-ethylene dioxy thiophene with an oxidiizng agent, a stage for leaving it for 15 hours or 2 hours at 25°C or 100°C is repeated by a predetermined number of times, and the solid electrolyte layer is formed in the interior of the capacitor element. <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 using a conductive polymer as an electrolyte.

  An electrolytic capacitor is made of a valve action metal such as tantalum or aluminum, and has a structure in which an oxide film layer serving as a dielectric is formed on the surface of an anode electrode having fine holes and etching pits, and an electrode is drawn from the oxide film layer. Become.

  And extraction of the electrode from an oxide film layer is performed by the electrolyte layer which has electroconductivity. Therefore, in the electrolytic capacitor, the electrolyte layer serves as a true cathode. For example, in an aluminum electrolytic capacitor, a liquid electrolyte is used as a true electrode, and the cathode electrode is merely responsible for electrical connection between the liquid electrolyte and an external terminal.

  The electrolyte layer that functions as a true cathode is required to have adhesiveness, denseness, and uniformity with the oxide film layer. In particular, the adhesion within the fine holes of the anode electrode and the etching pits has a great influence on the electrical characteristics, and a number of electrolyte layers have been proposed in the past.

  A solid electrolytic capacitor uses a solid electrolyte having conductivity instead of a liquid electrolyte lacking in impedance characteristics in a high frequency region because of ionic conduction. Among them, manganese dioxide, 7, 7, 8, 8- Tetracyanoquinodimethane (TCNQ) complexes are known.

  The solid electrolyte layer made of manganese dioxide is formed by immersing an anode element made of a tantalum sintered body in an aqueous manganese nitrate solution and thermally decomposing it at a temperature of about 300 ° C. to 400 ° C. In a capacitor using such a solid electrolyte layer, the oxide film layer tends to be damaged during the thermal decomposition of manganese nitrate, so that the leakage current tends to increase, and the specific resistance of manganese dioxide itself is high. It has been difficult to obtain sufficiently satisfactory impedance characteristics. In addition, since the lead wire is damaged by the heat treatment, it is necessary to separately provide an external terminal for connection as a subsequent process.

  As a solid electrolytic capacitor using a TCNQ complex, one disclosed in Japanese Patent Application Laid-Open No. 58-191414 (Patent Document 1) is known. The TCNQ complex is melted by heat, immersed in an anode electrode, and applied. Thus, a solid electrolyte layer is formed. This TCNQ complex has high conductivity, and good results in frequency characteristics and temperature characteristics can be obtained.

  However, since the TCNQ complex has the property of moving to an insulator in a short time after being melted, it is difficult to control the temperature during the capacitor manufacturing process, and the TCNQ complex itself lacks heat resistance. There is a remarkable variation in characteristics due to solder heat.

  In order to solve the disadvantages of these manganese dioxide and TCNQ complex, it has been attempted to use a conductive polymer such as polypyrrole as a solid electrolyte layer.

  Conductive polymers such as polypyrrole are produced mainly by chemical oxidative polymerization (chemical polymerization) or electrolytic oxidative polymerization (electrolytic polymerization), but chemical oxidative polymerization produces dense films with high strength. It was difficult to produce. On the other hand, in the electrolytic oxidation polymerization method, it is necessary to apply a voltage to an object that forms a film, and therefore it is difficult to apply it to an anode electrode for an electrolytic capacitor having an oxide film layer that is an insulator on the surface. A method for forming a conductive precoat layer on the surface of the oxide film layer in advance, for example, a conductive polymer film chemically polymerized using an oxidizing agent as a precoat layer, and then forming an electrolyte layer by electrolytic polymerization using the precoat layer as an electrode (Patent Document 2, Patent Document 3: Manganese dioxide is used as a precoat layer).

  However, since the precoat layer is formed in advance, the manufacturing process becomes complicated, and in the electropolymerization, a solid electrolyte layer is generated from the vicinity of the external electrode for polymerization disposed on the coating surface of the anode electrode. It was very difficult to continuously produce a conductive polymer film having a sufficient thickness.

  Therefore, a foil-like anode electrode and a cathode electrode are wound through a separator to form a so-called wound capacitor element, and chemical polymerization only is performed by immersing a monomer solution such as pyrrole and an oxidizing agent in this capacitor element. An attempt was made to form an electrolyte layer made of a conductive polymer film formed by the above method.

  Such a wound-type capacitor element is well known in aluminum electrolytic capacitors, but it avoids the complexity of electrolytic polymerization by holding the conductive polymer layer with a separator, and at the same time, it is a foil-shaped capacitor with a large surface area. It was expected to increase the capacity with the electrodes. Furthermore, by using a wound capacitor element, it was expected that the electrodes of both electrodes and the separator could be held with a constant tightening force and contributed to the adhesion between the electrodes of both electrodes and the electrolyte layer.

JP 58-191414 A JP 63-173313 A JP-A-63-158829 JP-A-2-15611

  However, when the capacitor element is impregnated with a mixed solution in which a monomer solution and an oxidizing agent are mixed, a solid electrolyte layer is not formed even inside the capacitor element, and the expected electrical characteristics cannot be obtained. found.

  Therefore, when the monomer solution and the oxidizing agent were impregnated separately, or when the polymerization temperature of the solution during the reaction was lowered, good electrical characteristics were obtained to some extent, but only the pressure resistance characteristics were insufficient. was there. The cause is that, even by these means, the solid electrolyte layer formed near the end face of the capacitor element hinders the subsequent penetration of the solution and the solution does not penetrate sufficiently into the inside, resulting in a dense It was thought that this was caused by the failure to form a uniform solid electrolyte layer.

  In addition, when performing chemical polymerization at a low temperature, strict temperature control is required, and the production apparatus becomes complicated, resulting in a problem that the product cost increases.

  On the other hand, as a result of repeated studies on various conductive polymers, attention was focused on polyethylene dioxythiophene (PEDT), which has a slow reaction rate and excellent adhesion to the oxide film layer of the anode electrode (Patent Document 4). ).

  The present invention pays attention to the slow polymerization reaction rate of polyethylenedioxythiophene, and produces a solid electrolyte layer made of a dense and uniform conductive polymer inside the wound capacitor element, and has electrical characteristics. It is an object of the present invention to provide a solid electrolytic capacitor having a large capacity and a method for producing the same.

  The method for producing a solid electrolytic capacitor of the present invention comprises impregnating a mixed solution obtained by mixing 3,4-ethylenedioxythiophene and an oxidizing agent into a capacitor element in which an anode electrode foil and a cathode electrode foil are wound through a separator. Thereafter, a step of leaving at 25 ° C. to 100 ° C. for 15 hours to 2 hours, preferably at 50 ° C. for 4 hours is performed to produce polyethylene dioxythiophene.

  Further, the blending ratio of 3,4-ethylenedioxythiophene and oxidizing agent is preferably in the range of 1: 3 to 1:15.

  As described above, in the present invention, the capacitor element obtained by winding the anode electrode foil and the cathode electrode foil through the separator is impregnated with a mixed solution obtained by mixing 3,4-ethylenedioxythiophene and an oxidizing agent. Thus, the mixed solution penetrates into the inside of the capacitor element, and polyethylene dioxythiophene, that is, a solid electrolyte, is obtained by a gentle polymerization reaction between 3,4-ethylenedioxythiophene and an oxidizing agent after the penetration and after the penetration. The layer is also generated inside the capacitor element, and the solid electrolyte layer is formed in a state where the solid electrolyte layer is held by the separator with a certain tightening force from the generation process.

  In the present invention, a capacitor element obtained by impregnating a capacitor element in which an anode electrode foil and a cathode electrode foil are wound through a separator is impregnated with a mixed solution in which 3,4-ethylenedioxythiophene and an oxidizing agent are mixed. The mixed solution penetrates into the inside of the container. Then, polyethylene dioxythiophene, that is, a solid electrolyte layer is also generated inside the capacitor element by a gentle polymerization reaction of 3,4-ethylenedioxythiophene and an oxidizing agent that occurs after the permeation process and after the permeation. The layer is held by the separator from its production process. As a result, a dense and uniform solid electrolyte layer can be formed inside the capacitor element, and as a result, the electrical characteristics of the solid electrolytic capacitor are improved. Combined with the solid electrolytic capacitor using the conventional conductive polymer for the solid electrolyte layer, the improvement is remarkable.

  In addition, since the capacitor element winds the anode electrode foil and the cathode electrode foil with a constant tightening force through the separator, the anode electrode foil, the cathode electrode foil and the separator are in close contact with each other at a certain pressure. As a result, the solid electrolyte layer held by the separator is also in close contact with the anode electrode foil at a constant pressure. Therefore, the adhesion between the oxide film layer on the anode electrode foil and the solid electrolyte layer is improved, and it becomes easy to obtain desired electrical characteristics.

  Further, in the process of producing polyethylenedioxythiophene, heat treatment in a high temperature range is not performed unlike conventional manganese dioxide and TCNQ complex, so that damage to the oxide film layer is suppressed and the reliability of the product is improved. In addition, the lead wire is not damaged by heat treatment, and can be used as it is as a terminal for external connection.

  Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 shows a solid electrolytic capacitor according to the present invention, in which an anode electrode foil 1 made of a valve metal such as aluminum and having an oxide film layer formed on a surface thereof, and a cathode electrode foil 2 are wound around a separator 3. A capacitor element is formed. Then, the capacitor element is impregnated with a mixed solution in which 3,4-ethylenedioxythiophene and an oxidizing agent are mixed, and polyethylene dioxythiophene generated by the polymerization reaction in the mixed solution that has permeated the separator 3 is solid electrolyte layer. 5 is held by the separator 3 with a constant tightening force.

  The anode electrode foil 1 is made of a valve metal such as aluminum, and as shown in FIG. 2, the surface thereof is roughened by electrochemical etching treatment in an aqueous chloride solution to form a large number of etching pits 8. doing. Further, an oxide film layer 4 serving as a dielectric is formed on the surface of the anode electrode foil 1 by applying a voltage in an aqueous solution of ammonium borate or the like.

  The cathode electrode foil 2 is made of aluminum or the like, similar to the anode electrode foil 1, and has a surface subjected only to etching treatment.

  Lead wires 6 and 7 for connecting the respective electrodes to the outside are connected to the anode electrode foil 1 and the cathode electrode foil 2 by known means such as stitching or ultrasonic welding. The lead wires 6 and 7 are made of aluminum or the like, and are formed of an external connection portion that is responsible for electrical connection between the connection portion of the anode electrode foil 1 and the cathode electrode foil 2 and the outside, and is an end face of the wound capacitor element 10. Is derived from

Separator 3 is a mixture of glass paper or glass paper and paper such as manila paper, kraft paper, etc. When using a mixed paper separator, the paper mixture ratio in weight per unit area is 80% or less for paper. It is desirable to be. The thickness of the separator 3 may be arbitrary, but when a thick separator is used, the diameter of the capacitor element 10 to be wound becomes large, so that a thickness of 80 μm to 200 μm is used. The reason for using glass separator or glass paper and paper separator 3 is that the oxidation reaction between the oxidant in the mixed solution impregnated in capacitor element 10 and separator 3 is suppressed to maintain the oxidizing ability of the oxidant. This is to improve the permeability of the mixed solution.

  The capacitor element 10 is formed by winding the anode electrode foil 1 and the cathode electrode foil 2 with the separator 3 interposed therebetween. The dimensions of the bipolar electrode foils 1 and 2 are arbitrary depending on the specifications of the solid electrolytic capacitor to be manufactured, and the separator 3 may have a slightly larger width depending on the dimensions of the bipolar electrode foils 1 and 2. .

  3,4-ethylenedioxythiophene can be obtained by a known production method disclosed in JP-A-2-15611. The oxidizing agent is ferric p-toluenesulfonate dissolved in ethylene glycol. The ratio of ethylene glycol and ferric p-toluenesulfonate in the oxidizing agent may be arbitrary, but in the present invention, 1: 1 is used. The mixing ratio of this oxidizing agent and 3,4-ethylenedioxythiophene is preferably in the range of 1: 3 to 1:15.

  As a method for impregnating the capacitor element 10 with a mixed solution obtained by mixing 3,4-ethylenedioxythiophene and an oxidizing agent, known means such as a reduced pressure impregnation method, a pressure impregnation method, or the like can be used.

  Next, the manufacturing method of the solid electrolytic capacitor in the invention and the solid electrolytic capacitor obtained thereby will be specifically described.

  (Example 1) The anode electrode foil 1 and the cathode electrode foil 2 are made of a valve metal, for example, aluminum or tantalum, and the surface thereof is enlarged by etching in advance. The anode electrode foil 1 is further subjected to chemical conversion treatment, and an oxide film layer 4 made of aluminum oxide is formed on the surface.

  The anode electrode foil 1 and the cathode electrode foil 2 are wound through a separator 3 made of glass paper having a thickness of 80 to 200 μm to obtain a capacitor element 10.

  In this embodiment, the capacitor element 10 has a diameter of 4φ and a vertical dimension of 7 mm. Lead wires 6 and 7 are electrically connected to the anode electrode foil 1 and the cathode electrode foil 2 of the capacitor element 10, respectively, and protrude from the end face of the capacitor element 10.

  The capacitor element 10 having the above configuration is impregnated with a mixed liquid of 3,4-ethylenedioxythiophene and an oxidizing agent. As the oxidizing agent, ferric p-toluenesulfonate dissolved in ethylene glycol is used, and the blending ratio of 3,4-ethylenedioxythiophene and oxidizing agent is preferably in the range of 1: 3 to 1:15. .

  In the impregnation, the capacitor element 10 is immersed in an impregnation tank in which a certain amount of the mixed solution is stored, and the pressure is reduced as necessary.

  Next, the capacitor element 10 impregnated with the mixed solution is pulled up from the impregnation tank and allowed to stand at a polymerization temperature of 25 ° C. to 100 ° C. for 15 hours to 2 hours to produce polyethylene dioxythiophene, that is, the solid electrolyte layer 5 by polymerization reaction.

  The range of the polymerization temperature and the standing time is such that the capacitance, tan δ and impedance characteristics are improved among the electrical characteristics of the manufactured solid electrolytic capacitor when the polymerization temperature is increased, but the leakage current characteristics tend to be deteriorated. As can be seen, it can be arbitrarily changed within the above range according to the specifications of the capacitor element 10 to be manufactured. It should be noted that it is appropriate to leave at a polymerization temperature of 25 ° C. for about 15 hours, at 50 ° C. for about 4 hours, and at 100 ° C. for about 2 hours, and to stand at a temperature of 50 ° C. for 4 hours. The balance between the coating state and the process time was optimal.

  Next, the capacitor element is washed with water, an organic solvent or the like for about 120 minutes and dried at 100 ° C. to 180 ° C. for about 30 minutes, and then at 40 ° C. to 60% of the withstand voltage of the anode electrode foil 1 at room temperature. A series of production steps of the solid electrolyte layer 5 is completed through a so-called aging step in which a voltage of about a level is applied. In addition, you may repeat the production | generation process of the above solid electrolyte layer 5 in multiple times as needed.

  In this way, the capacitor element 10 in which the solid electrolyte layer 5 is formed on the separator 3 interposed between the anode electrode foil 1 and the cathode electrode foil 2 is formed, for example, by covering the outer periphery with an exterior resin to form a solid electrolytic capacitor. To do.

  (Example 2) A capacitor element 10 manufactured in the same manner as in Example 1 described above, and a separator 3 in which glass paper and paper were mixed was used. The paper can be selected from Manila paper, kraft paper, etc. In this embodiment, Manila paper was used. The mixing ratio in weight per unit area was 80% or less for paper and 80 μm to 200 μm.

  Next, the electrical characteristics of the solid electrolytic capacitor according to Example 1 and the conventional solid electrolytic capacitor will be compared. As a comparative example, a capacitor element having the same configuration as that of Example 1 was used, and (Comparative Example 1) a monomer solution made of pyrrole and an oxidizing agent were impregnated into the capacitor element at room temperature to form a solid electrolyte layer. Comparative Example 2 A capacitor element was impregnated with a monomer solution composed of pyrrole and an oxidizing agent at a low temperature of about −10 ° C. to form a solid electrolyte layer. Ten samples each were manufactured, and the average value of each initial characteristic was measured. The results are shown below.

  As is clear from this result, the solid electrolytic capacitor according to Example 1 is equivalent in capacitance, tan δ, and the like as compared with Comparative Example 2 in which polypyrrole was generated in a low temperature range, and was excellent in withstand voltage characteristics. The characteristics are shown.

  Next, a solid electrolytic capacitor according to Example 2 and a solid electrolytic capacitor in which a solid electrolyte layer made of polyethylenedioxythiophene was produced by the same manufacturing method as in Example 2 as a comparative example (Comparative Example 3). Comparison is made between a paper using manila paper as a separator and (Comparative Example 4) a paper using carbonized paper obtained by carbonizing manila paper at about 350 ° C. to 400 ° C. as a separator. Similarly to the previous comparison, 10 samples were manufactured, and the average value of each initial characteristic was measured. The results are shown below.

  As is apparent from this result, in Comparative Example 3 using ordinary manila paper, an oxidation reaction occurs with the oxidant in the mixed solution impregnated in the capacitor element, and the oxidation ability of the oxidant is lowered. Adhesion with the oxide film layer of the anode electrode foil is poor, and desired characteristics cannot be obtained in terms of capacitance and impedance characteristics. Further, when the carbonized separator is used, in addition to the impedance characteristic, the leakage current characteristic is remarkably inferior.

It is a disassembled perspective view of the capacitor | condenser element used by this invention. It is the elements on larger scale of the anode electrode foil used by this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Anode electrode foil 2 Cathode electrode foil 3 Separator 4 Oxide film layer 5 Solid electrolyte layer 6, 7 Lead wire 8 Etching pit 10 Capacitor element

Claims (4)

After impregnating a mixed solution in which 3,4-ethylenedioxythiophene and an oxidizing agent are mixed into a capacitor element in which an anode electrode foil and a cathode electrode foil are wound through a separator, the mixture is used for 15 hours at 25 to 100 ° C. A method for producing a solid electrolytic capacitor, characterized in that polyethylene dioxythiophene is produced in a capacitor element by performing a step of leaving for 2 hours, and the polyethylene dioxythiophene is held in a separator with a constant tightening force . 2. The method for producing a solid electrolytic capacitor according to claim 1, wherein a mixed solvent obtained by mixing 3,4-ethylenedioxythiophene and an oxidizing agent is impregnated in the capacitor element and then left at 50 ° C. for 4 hours. The method for producing a solid electrolytic capacitor according to claim 1 or 2, wherein the mixing ratio of 3,4-ethylenedioxythiophene and the oxidizing agent is 1: 3 to 1:15. 4. The method for producing a solid electrolytic capacitor according to claim 1, wherein the oxidizing agent is ferric p-toluenesulfonate dissolved in ethylene glycol.