JP4909246B2 - Manufacturing method of solid electrolytic capacitor - Google Patents

Description

  The present invention relates to a method for manufacturing a solid electrolytic capacitor using a conductive polymer as an electrolyte.

The capacitor element of the electrolytic capacitor is made of a valve metal such as aluminum, tantalum, or niobium, and has a porous anode body (anode foil or sintered body) having a large number of etching pits and fine holes formed on the surface.
Further, an oxide film serving as a dielectric is formed on the surface of the anode body, and electrodes are drawn from the oxide film. An electrolyte is in contact with the oxide film, and this electrolyte functions as a true cathode for extracting an electrode from the 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 them, the solid electrolytic capacitor uses a solid electrolyte having electronic conductivity instead of a liquid electrolyte having inferior impedance characteristics in a high frequency region because of its ionic conductivity.

As a method for forming a conductive polymer layer as an electrolyte of a solid electrolytic capacitor, there is a chemical polymerization method in which a monomer and an oxidizing agent are brought into contact with each other to cause a polymerization reaction to form a conductive polymer layer.
In the process of forming the conductive polymer layer on the capacitor element using the chemical polymerization method,
A step of preparing a liquid mixture of a monomer and an oxidizing agent in advance, impregnating the liquid into the capacitor element, and then causing the polymerization reaction by heating the capacitor element;
A step of impregnating a capacitor element with a solution in which an oxidizing agent is dissolved in a solvent, then drying the capacitor element, and then impregnating the capacitor element with a monomer solution, followed by a polymerization reaction by heating the capacitor;
On the contrary, a step of impregnating the capacitor element with the monomer solution, then drying the capacitor element, then impregnating the capacitor element with a solution in which an oxidant is dissolved in a solvent, and then causing a polymerization reaction by heating the capacitor, etc. It is known (see Patent Documents 1 to 3).

Japanese Patent Laid-Open No. 10-340830 JP 2003-272953 A Japanese Patent Publication No. 06-052696

  Among the above steps, “a solution in which an oxidizing agent is dissolved in a solvent is impregnated into a capacitor element, then the capacitor element is dried, and then a monomer solution is impregnated with the capacitor element, and then the capacitor is heated to cause a polymerization reaction. In examining the “process”, the inventors of the present invention do not sufficiently evaporate the solvent impregnated in the capacitor element in the step of drying the capacitor element in which the capacitor element is impregnated with the oxidant solution. I found out that it wouldn't be.

  In order to sufficiently dry the capacitor element, either the capacitor element is heated at a low temperature for a long time, or the capacitor element is heated at a high temperature for a short time. Industrially, high temperature heat treatment for a short time is preferable in order to increase productivity.

  However, when the above-described capacitor element is subjected to heat treatment at a high temperature for a short time, there is a problem that the electrical characteristics of the capacitor deteriorate. As a result of investigating the cause, the present inventors have suddenly boiled the solvent present in the element, and the oxidant solution is scattered, making it difficult to retain sufficient oxidant in the capacitor element. I found out that

  On the other hand, if the capacitor element is heated at a low temperature for a long time, the low temperature heating can suppress the bumping of the solvent present in the capacitor element, but it requires a long time heating, and the production There is a problem that the performance is lowered.

  An object of the present invention is to provide a production method capable of producing a solid electrolytic capacitor having good electrical characteristics without reducing productivity.

A method for producing a solid electrolytic capacitor according to a first invention is a method for producing a solid electrolytic capacitor in which a conductive polymer is formed on a capacitor element having a porous anode body on which an oxide film is formed,
An oxidizing agent impregnation step of impregnating the capacitor element with an oxidizing agent solution comprising an oxidizing agent and a solvent in which the oxidizing agent is dissolved;
After the oxidant impregnation step, a drying step for vaporizing the solvent impregnated in the capacitor element;
A monomer impregnation step of impregnating the capacitor element with the monomer solution after the drying step;
A solid electrolyte forming step of forming a solid electrolyte made of a conductive polymer on the oxide film by chemically polymerizing the oxidant impregnated in the capacitor element and the monomer;
The drying step includes a first step of heating at a temperature lower than the boiling point of the solvent, Ri Do and a second step of heating at a temperature higher than the first step,
Temperature of the first step is 40 ° C. to 100 ° C., the temperature of the second step is characterized by 100 ° C. to 220 ° C. der Rukoto.

A method for producing a solid electrolytic capacitor according to a second invention is the method for producing a solid electrolytic capacitor according to the first invention, wherein the oxidizing agent is p-toluenesulfonic acid ferric salt, naphthalenesulfonic acid ferric salt. Any one or more of ferric salt of triisopropylnaphthalenesulfonic acid and ferric salt of dodecylbenzenesulfonic acid may be used.

The method for producing a solid electrolytic capacitor according to a third invention is the method for producing a solid electrolytic capacitor according to the first or second invention, wherein the monomer is any one of aniline, pyrrole, thiophene and derivatives thereof. There may be.

The solid electrolytic capacitor manufacturing method according to a fourth aspect of the present invention is the solid electrolytic capacitor manufacturing method according to any one of the first to third aspects of the invention, wherein the thiophene derivative may be ethylenedioxythiophene.

According to the first invention, in the drying step, the capacitor element is heated at a temperature lower than the boiling point of the solvent, and the solvent is vaporized to the amount of the solvent that does not bump (first step). Thereafter, the capacitor element is heated and dried at a temperature higher than that in the first step (second step).
By heating at a temperature lower than the boiling point of the solvent as in the first step, the bumping of the solvent can be suppressed and sufficient oxidant can be retained in the capacitor element. Can be manufactured.

According to the second to fourth inventions, it is possible to manufacture a capacitor having good electrical characteristics without reducing productivity in the first and second steps.

  An embodiment of the present invention will be described with reference to FIGS.

[Structure of solid electrolytic capacitor]
First, the structure of the solid electrolytic capacitor 1 manufactured by the manufacturing method of this embodiment is demonstrated using FIG.

  The capacitor element 6 includes an anode foil 2, a cathode foil 3, and a separator 4. The capacitor element 6 is a laminated body in which the anode foil 2 and the cathode foil 3 are opposed to each other with the separator 4 interposed therebetween. Have.

The anode foil 2 is made of a valve metal such as aluminum. FIG. 2 is a cross-sectional view of the anode foil 2, the cathode stay 3, and the separator 4.
As shown in FIG. 2, since the anode foil 2 is roughened (etching pit formation) by performing an electrochemical etching process using direct current or alternating current in an aqueous chloride solution, the surface area of the anode foil 2 is It has been expanded. In addition, an anodic oxide film 2a is formed on the anode foil 2 that has been subjected to an anodic oxidation treatment (chemical conversion) by applying a DC voltage (chemical conversion voltage) in an aqueous solution of ammonium adipate or the like.

  Similarly to the anode foil 2, the cathode foil 3 is made of a valve metal such as aluminum, and a natural oxide film 3a is formed on the surface of the cathode foil 3 by roughening (etching pit formation). Yes.

A solid electrolyte 7 made of a conductive polymer is held on both sides of the separator 4.
A solid electrolyte 7 is sandwiched between the anode foil 2 and the cathode foil 3 and the separator 4.
As the conductive polymer constituting the solid electrolyte 7, polyaniline, polypyrrole, polyethylenedioxythiophene (PEDOT) or the like can be used, and these conductive polymers are generated by chemical polymerization of an oxidizing agent and a monomer.

  As shown in FIG. 1, lead tabs are connected from the anode foil 2 and the cathode foil 3, respectively, and lead wires 5 are drawn from the anode foil 2 and the cathode foil 3 through the lead tabs.

[Method of manufacturing solid electrolytic capacitor]
Next, a method for manufacturing the solid electrolytic capacitor 1 will be described with reference to FIG.

First, as a capacitor element forming step, in order to increase the effective surface area of the electrode, an etching process is performed to roughen the surfaces of the anode foil 2 and the cathode foil 3 (A1).
Next, the surface of the roughened anode foil 2 is subjected to chemical conversion treatment to form an anodized film 2a, and the cathode foil 3 is subjected to water resistance treatment and / or heat treatment to form a natural oxide film 3a ( A2).
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 then the lead wires 5a and 5b are connected to each via a lead tab. At the same time, the anode foil 2 and the cathode foil 3 are wound through the separator 4 (A3).
Next, element formation (cut formation) is performed by applying a voltage in an aqueous solution of ammonium adipate, and then carbonization treatment of the separator 4 is performed (A4), and the cylindrical capacitor element 6 is manufactured. In addition, when there is little cellulose in the separator 4, or when a cellulose does not exist, you may abbreviate | omit the said carbonization process.

  Next, as the oxidant impregnation step, the capacitor element 6 is immersed in the oxidant solution in which the oxidant is dissolved in the solvent, thereby impregnating the capacitor element 6 with the oxidant (A5).

  Next, as a drying step, the capacitor element 6 is heated at a predetermined temperature for a predetermined time, and the solvent in the capacitor element is dried (A6).

  Next, as a monomer impregnation step, the capacitor element 6 is immersed in the monomer solution to impregnate the capacitor element 6 with the monomer solution (monomer) (A7).

  Next, as the solid electrolyte formation step, the impregnated oxidant and the monomer are chemically polymerized by heating at a predetermined temperature in the polymerization tank for a certain time, and between the anode foil 2 and the separator 4 and the cathode foil 3. A solid electrolyte 7 made of a conductive polymer is formed between the separator 4 and the separator 4 (A8).

  Next, the solid electrolytic capacitor 1 is assembled. That is, the cylindrical capacitor element 6 obtained by the above process is housed in a bottomed cylindrical outer case, and the opening is sealed with a sealing rubber or the like (A9).

  Next, aging is performed (A10), and for example, a solid electrolytic capacitor having a rating of 16V-39 μF is manufactured.

  Next, specific examples of the production method of the present invention will be described together with comparative examples. In Examples 1 to 10 and Comparative Examples described below, in the method for producing a solid electrolytic capacitor, the process of heating and drying the capacitor element 6 impregnated with the oxidizing agent (drying process) is different. The steps are all the same.

[Example 1]
In Example 1, as the oxidant impregnation step, the capacitor element 6 was impregnated with a solution of p-toluenesulfonic acid ferric salt dissolved in 1-butanol.
Next, as a drying step, the temperature of the capacitor element 6 was set to 80 ° C. (first step) and heated for 5 minutes, and then heated at 200 ° C. (second step) for 10 minutes to be dried.
Next, ethylene dioxythiophene was used as a monomer, and the capacitor element 6 was impregnated with a monomer solution as a monomer impregnation step.
Next, as a solid electrolyte forming step, the capacitor element 6 was heated at 100 ° C. for 60 minutes to form polyethylenedioxythiophene (PEDOT), which is a conductive polymer, by chemical polymerization, thereby forming the solid electrolyte 7.

(Comparative Example 1)
In Comparative Example 1, PEDOT was performed in the same manner as in Example 1 except that the drying step was not divided from the first step and the second step as in the Examples, and drying was continuously performed at 200 ° C. for 15 minutes. And solid electrolyte 7 was formed.

  The electrical characteristics (capacitance, equivalent series resistance, and leakage current) of the solid electrolytic capacitors obtained by the manufacturing methods of Example 1 and the comparative example were measured. The results are shown in Table 1.

  As shown in Table 1, the equivalent series resistance of the solid electrolytic capacitor according to the manufacturing method of Example 1 is 22.8 mΩ, and in the case of Comparative Example 1, it is 28.6 mΩ. The equivalent series resistance of Example 1 is smaller than the equivalent series resistance of Comparative Example 1 and is good.

  This result shows that the heating of the first step is performed below the boiling point of 1-butanol (117.3 ° C.), so that the solvent is evaporated to the amount of the solvent at which the oxidant solution does not bump when the second step is heated. This is considered to be because the oxidant solution can be prevented from bumping and a sufficient oxidant can be held in the capacitor element.

  Thus, in the drying step, it was confirmed that the equivalent series resistance can be reduced by heating at a temperature lower than the boiling point of the solvent and then heating at a temperature (200 ° C.) higher than the boiling point of the solvent. .

[Comparative Example 2]
In Comparative Example 2, PEDOT was formed in the same manner as in Example 1 except that the drying step was heated at 200 ° C. (first step) for 5 minutes and then dried at 80 ° C. (second step) for 10 minutes. As a result, the solid electrolyte 7 was formed.

  The electrical characteristics (capacitance, equivalent series resistance, and leakage current) of the solid electrolytic capacitors obtained by the manufacturing methods of Example 1 and Comparative Example 2 were measured. The results are shown in Table 2.

  As shown in Table 2, the equivalent series resistance of the solid electrolytic capacitor according to the manufacturing method of Example 1 is 22.8 mΩ, and in the case of Comparative Example 2 where the temperature in the second step is higher than the solvent temperature of the oxidizing agent, 30.2 mΩ. It is. The equivalent series resistance of Example 1 is smaller than the equivalent series resistance of Comparative Example 2 and is good.

  This result is thought to be because if the drying is first performed at a temperature higher than the boiling point of the solvent, the bumping of the solvent present in the capacitor element cannot be suppressed, and sufficient oxidant cannot be retained in the capacitor element. It is done.

  Thus, in the drying process, it was confirmed that it is preferable to heat at a temperature lower than the boiling point first, rather than heating at a drying temperature at which the capacitor element is first dried.

[Examples 2 to 4, Comparative Example 3]
In Examples 2 to 4, as the drying step, the first heating temperature was set to 30 to 100 ° C. and the mixture was heated for 5 minutes, and then heated at 200 ° C. (second heating temperature) for 10 minutes and dried. Further, as Comparative Example 3, a case where the first heating temperature was 120 ° C. higher than the boiling point of the solvent was also examined. Solid electrolytic capacitors were produced in the same manner as in Example 1 except for this drying step.

  The electrical characteristics (capacitance, equivalent series resistance and leakage current) of the solid electrolytic capacitors obtained by the production methods of Examples 1 and 2 to 4 were measured. The results are shown in Table 3.

As shown in Table 3, the equivalent series resistances of the solid electrolytic capacitors manufactured by the manufacturing methods of Examples 1, 3, and 4 were 22.8 mΩ, 22.7 mΩ, and 23.0 mΩ in this order, and Example 2 and the comparison The equivalent series resistance of the solid electrolytic capacitor manufactured by the manufacturing method of Example 3 is 29.8 mΩ and 28.8 mΩ in this order.
The equivalent series resistances of Examples 1, 3 and 4 are smaller than the equivalent series resistances of Example 2 and Comparative Example 3, which is good.

  As a result, when the heating temperature in the first step is as low as 30 ° C., 1-butanol, which is a solvent for the oxidant, does not sufficiently vaporize and bumps when heated at the second heating temperature (drying temperature). This is probably because the amount of the minute solvent remains in the capacitor element. On the other hand, when the heating temperature in the first step is 120 ° C., which is higher than the boiling point of the solvent, 1-butanol, which is the solvent in which the oxidant is dissolved, bumps up, and the equivalent series resistance is considered to increase.

  Thus, it was confirmed that the temperature (first step) lower than the boiling point of the solvent is preferably 40 ° C to 100 ° C. Moreover, when heating at a temperature lower than the boiling point of the solvent, it was confirmed that it was preferable to vaporize the solvent up to the amount of the solvent that would not cause sudden boiling when heated in the second step.

[Examples 5 to 8]
In Examples 5-8, as a drying process, after heating for 5 minutes with the heating temperature of the 1st process as 80 degreeC, the heating temperature of the 2nd process was heated for 10 minutes at 90-240 degreeC, and was dried. Solid electrolytic capacitors were produced in the same manner as in Example 1 except for this drying step.

  The electrical characteristics (capacitance, equivalent series resistance and leakage current) of the solid electrolytic capacitors obtained by the production methods of Example 1 and 5 to 8 were measured. The results are shown in Table 4.

  As shown in Table 4, the equivalent series resistances of the solid electrolytic capacitors produced by the production methods of Examples 1, 6, and 7 were 22.8 mΩ, 23.1 mΩ, and 24.2 mΩ in this order, and Examples 5 and 8 The equivalent series resistance of the solid electrolytic capacitor manufactured by this manufacturing method is 29.0 mΩ and 32.4 mΩ in this order. The equivalent series resistances of Examples 1, 6 and 7 are smaller than those of Examples 5 and 8 and are good.

  As a result, when the heating temperature in the second step is as low as 90 ° C., the equivalent series resistance increases because 1-butanol, which is a solvent for the oxidizing agent, does not volatilize sufficiently. On the other hand, when the second heating temperature is as high as 240 ° C., the equivalent series resistance increases because the p-toluenesulfonic acid ferric salt in the oxidant solution is decomposed.

  Thus, it was confirmed that 100 to 220 ° C. is preferable at the second heating temperature. Moreover, it was confirmed that the second heating temperature (drying temperature) is preferably lower than the thermal decomposition temperature (about 300 ° C.) of the oxidizing agent (p-toluenesulfonic acid ferric salt) in the oxidizing solvent.

In the present embodiment, the drying step is heated at two different temperatures. However, the present invention is not particularly limited to this. For example, heating at three or more different temperatures is also included because the effects of the present invention can be obtained.
In the present embodiment, when heating is performed at three different temperatures, the heating temperature in the first step is lower than the boiling point of the solvent of the oxidant solution, the heating temperature in the third step is lower than the decomposition temperature of the oxidant, The heating temperature in the second step is set to be higher than the heating temperature in the first step and lower than the heating temperature in the third step.
For example, the heating temperature in the first step is 40 to 100 ° C., the heating temperature in the second step is 60 to 120 ° C., the heating temperature in the third step is 100 to 200 ° C., and the first step <second step <third step It is preferable that

In this embodiment, 1-butanol is used as the solvent of the oxidant solution. However, in the present invention, the optimization is not particularly limited as long as optimization is performed within the temperature range of the present invention. For example, methanol (boiling point 64.7 ° C), ethanol (boiling point 78.3 ° C), 1-propanol (boiling point 97.2 ° C), or a mixed solvent thereof is also included.
The optimization means that the optimum value is determined by examining the collected data of the solvent species, the solute concentration, the amount of solvent decrease in the element, and the like.

  Moreover, in this Embodiment, the solution of p-toluenesulfonic acid ferric acid was used as an oxidizing agent, However, In this invention, it is not specifically limited to this. For example, naphthalenesulfonic acid ferric salt (decomposition point about 400 ° C), triisopropyl naphthalenesulfonic acid ferric salt (decomposition point about 400 ° C), and dodecylbenzenesulfonic acid ferric salt (decomposition point about 415 ° C). Also included are sulfonic acid metal salts such as Moreover, the mixture of these 2 or more types is also included.

  In the present embodiment, ethylenedioxythiophene is used as a monomer, but the present invention is not particularly limited to this. For example, solutions of aniline, pyrrole, thiophene and derivatives thereof are also included.

  In the present embodiment, the solid electrolytic capacitor having a wound capacitor element has been described. However, the present invention is not particularly limited thereto. For example, the present invention can also be applied to a laminated capacitor element of aluminum foil and a solid electrolytic capacitor having a sintered body of tantalum or niobium.

It is a disassembled perspective view of the capacitor | condenser element manufactured by this invention. It is sectional drawing which shows roughly the laminated structure of the solid electrolytic capacitor manufactured by this invention. It is a flowchart which shows the manufacturing process of the solid electrolytic capacitor of this invention.

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 5a Lead wire (anode)
5b Lead wire (cathode)
6 Capacitor element 7 Solid electrolyte

Claims (4)

A capacitor element having a porous anode body on which an oxide film is formed, a method for producing a solid electrolytic capacitor formed by forming a conductive polymer,
An oxidizing agent impregnation step of impregnating the capacitor element with an oxidizing agent solution comprising an oxidizing agent and a solvent in which the oxidizing agent is dissolved;
After the oxidant impregnation step, a drying step for vaporizing the solvent impregnated in the capacitor element;
A monomer impregnation step of impregnating the capacitor element with the monomer solution after the drying step;
A solid electrolyte forming step of forming a solid electrolyte made of a conductive polymer on the oxide film by chemically polymerizing the oxidant impregnated in the capacitor element and the monomer;
The drying step includes a first step of heating at a temperature lower than the boiling point of the solvent, Ri Do and a second step of heating at a temperature higher than the first step,
Wherein the temperature of the first step is 40 ° C. to 100 ° C., the manufacturing method of the temperature of the second step is a solid electrolytic capacitor according to claim 100 ° C. to 220 ° C. der Rukoto. The oxidizing agent is at least one 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. The method for producing a solid electrolytic capacitor according to claim 1 , wherein the monomer is any one of aniline, pyrrole, thiophene, and derivatives thereof . The method for producing a solid electrolytic capacitor according to claim 1 , wherein the thiophene derivative is ethylenedioxythiophene .

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