JP2010031160A - Oxidizer for producing conductive polymer, solid electrolytic condenser using the same, and production method thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a conductive polymer excellent in conductivity and thermal resistance, and an oxidizer for producing a conductive polymer excellent in storing stability, and a method for producing a solid electrolytic condenser exhibiting a low ESR and a high capacity, and being excellent in thermal resistance with the use of the oxidizer for preparing the conductive polymer. <P>SOLUTION: The oxidizer for producing a conductive polymer comprises a ferric salt of a benzene sulfonic acid derivative represented by formula (1) (wherein R represents a branched alkyl group). There are also provided the solid electrolytic condenser for forming a conductive polymer layer by using the oxidizer for producing a conductive polymer, and production method thereof. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an oxidizing agent for producing a conductive polymer, and more specifically, is used when forming a conductive polymer layer suitable as a solid electrolyte of a solid electrolytic capacitor, and has a high capacity and low equivalent series resistance (hereinafter referred to as “ESR”). And an oxidizing agent for producing a conductive polymer that contributes to the production of a solid electrolytic capacitor having excellent heat resistance. Furthermore, it is related with the solid electrolytic capacitor which uses this oxidizing agent, and its manufacturing method.

  Since the conductive polymer has high conductivity, it is useful as a solid electrolyte such as an aluminum electrolytic capacitor and a tantalum electrolytic capacitor.

  As the conductive polymer, for example, those obtained by chemical oxidative polymerization or electrolytic oxidative polymerization of pyrrole or a derivative thereof or thiophene or a derivative thereof are known.

  An organic sulfonic acid is mainly used as a dopant in the chemical oxidative polymerization of the pyrrole or its derivative or thiophene or its derivative, and among them, it is known to use an aromatic sulfonic acid. Further, transition metal salts of these aromatic sulfonic acids are used as the oxidizing agent for polymerization, and among these, it is known to use a ferric salt.

  Patent Document 1 discloses a capacitor using a conductive polymer layer polymerized by using p-toluenesulfonic acid ferric salt, which is an aromatic sulfonic acid ferric salt, as an oxidant, as a solid electrolyte.

  However, a solid electrolytic capacitor using p-toluenesulfonic acid ferric salt and having a conductive polymer layer formed tends to cause a decrease in capacitance and an increase in ESR when exposed to high temperatures for a long period of time. There is a problem of lack of heat resistance, and further improvement in heat resistance is required.

Patent Document 2 discloses a method for manufacturing a solid electrolytic capacitor in which the equivalent series resistance is reduced by using a high concentration and low viscosity oxidizing agent.
According to this document, it is described that the polymerization efficiency of a conductive polymer can be improved by using a high-concentration oxidant solution, the electrical conductivity of the conductive polymer layer can be increased, and the ESR of the solid electrolytic capacitor can be decreased. Has been.
However, when the oxidant concentration of a conventionally known oxidant solution is increased, the viscosity of the oxidant solution is also rapidly increased, which makes it difficult to handle the oxidant solution in the conductive polymer layer forming process. Has been pointed out.
In view of such a problem, this document discloses a technique for improving the handleability of an oxidizing agent while changing the solvent of the oxidizing agent to a low viscosity one and maintaining the oxidizing agent concentration at a high concentration.

According to Patent Document 2, a solid electrolytic capacitor having excellent initial characteristics can be obtained by using the oxidant solution having the above structure, but the stability of the capacitor characteristics in long-term use is insufficient, and further reliability, heat resistance There is a need for improvement in performance.
Furthermore, since propyl alcohol or ethyl alcohol specifically disclosed as a solvent for the oxidant solution in the document has a relatively low boiling point, an oxidant solution that causes a rapid and local polymerization reaction during heat polymerization. It has been pointed out that there is a risk of disturbing the storage stability of the food.

Japanese Patent Laid-Open No. 02-015611 JP 2003-272953 A

  In general, in the process of forming a conductive polymer layer on a capacitor element using a chemical polymerization method, an oxidant solution containing an organic sulfonic acid metal salt or the like as an oxidant and a thiophene monomer or the like are mixed and mixed. After the liquid is prepared and the mixed solution is impregnated into the capacitor element, the capacitor element is dried to form a conductive polymer layer on the capacitor element, or the capacitor element is immersed in the monomer solution and the oxidant solution and dried. By repeating this process, the conductive polymer layer is formed on the capacitor element.

  However, conventionally known oxidants rapidly increase in viscosity of the oxidant solution as the concentration of the oxidant solution increases. Therefore, when an oxidant solution having a concentration of more than 50% by weight is used, Since the impregnation property is deteriorated and the polymerization rate is improved, it is difficult for the polymerization solution to enter the porous capacitor element having fine voids, which causes a problem in handling.

An object of the present invention is to provide a novel oxidizer for producing a conductive polymer that contributes to the production of a solid electrolytic capacitor having a conductive polymer in the solid electrolyte. It is to provide an excellent oxidizing agent.
Another object of the present invention is to provide a solid electrolytic capacitor using such an oxidizing agent, having excellent electrical characteristics such as high capacitance and low ESR, and excellent heat resistance, and a method for producing the same.

The present inventors diligently studied and found that a solid electrolytic capacitor having remarkably excellent heat resistance can be obtained by using a ferric salt of a benzenesulfonic acid derivative having a branched alkyl group.
Furthermore, surprisingly, the oxidizer solution in which the ferric salt of the benzenesulfonic acid derivative is dissolved at a high concentration has a low viscosity and the polymerization rate is controlled even though the concentration is 50% by weight or more. The present inventors have found that a solid electrolytic capacitor having a high capacity and low ESR can be obtained by using such an oxidant solution, and the present invention has been completed.

  That is, the present invention is as follows.

  The first invention is a general formula (1),

（式中、Ｒは分岐鎖状アルキル基を示す。）
で示されるベンゼンスルホン酸誘導体の第二鉄塩を含む導電性高分子製造用酸化剤である。

(In the formula, R represents a branched alkyl group.)
It is an oxidizing agent for electroconductive polymer manufacture containing the ferric salt of the benzenesulfonic acid derivative shown by these.

  In the second invention, R is 1-methylethyl group, 1,1-dimethylethyl group, 1-methylpropyl group, 2-methylpropyl group, 1-methylbutyl group, 2-methylbutyl group, 3-methylbutyl group, Or it is 2-ethylbutyl group, It is an oxidizing agent for electroconductive polymer manufacture as described in 1st invention characterized by the above-mentioned.

  The third invention is an oxidation for producing a conductive polymer, characterized in that the oxidizing agent for producing a conductive polymer according to the first or second invention is dissolved in n-butanol by 50% by weight or more. Agent solution.

  A fourth invention is an oxidant solution for producing a conductive polymer, characterized in that the water content of the oxidant solution for producing a conductive polymer described in the third invention is less than 3.0% by weight. is there.

  A fifth invention is a solid electrolytic capacitor characterized in that a conductive polymer polymerized using the oxidant solution for producing a conductive polymer described in the third or fourth invention is used as a solid electrolyte.

According to a sixth aspect of the invention, by impregnating a capacitor element with a mixed liquid of a conductive polymer monomer and an oxidizing agent solution, or impregnating a capacitor element with a conductive polymer monomer solution and an oxidizing agent solution,
In the method for producing a solid electrolytic capacitor comprising a step of polymerizing a monomer and an oxidizing agent to form a conductive polymer layer on a capacitor element, the oxidation for producing a conductive polymer according to the third invention or the fourth invention A method for producing a solid electrolytic capacitor, wherein a conductive polymer polymerized using an agent solution is used as a solid electrolyte.

  The oxidizing agent for producing a conductive polymer of the present invention can give a conductive polymer excellent in conductivity and heat resistance.

  In addition, a solid electrolytic capacitor in which a conductive polymer layer is formed using the oxidant for producing a conductive polymer of the present invention exhibits a low ESR and a high capacity, and becomes a solid electrolytic capacitor excellent in heat resistance.

  As the oxidizing agent for producing the conductive polymer of the present invention, a metal salt of a benzenesulfonic acid derivative is used, and the benzenesulfonic acid derivative is represented by the following general formula (1).

  R in the general formula (1) represents a branched alkyl group.

The benzenesulfonic acid derivative having a branched alkyl group in the general formula (1) gives a highly conductive conductive polymer by being incorporated as a dopant in the conductive polymer, and the conductive having the dopant. The functional polymer is less likely to desorb the dopant and is extremely excellent in heat resistance.
Moreover, since the metal salt of the benzenesulfonic acid derivative in the general formula (1) is excellent in solubility in a solvent, a high-concentration oxidant solution can be easily prepared.

  Specific examples of the branched alkyl group in the general formula (1) are preferably 1-methylethyl group (iso-propyl group), 1,1-dimethylethyl group (t-butyl group), 1- Methylpropyl group (sec-butyl group), 1,1-dimethylpropyl group, 2-methylpropyl group (iso-butyl group), 1,2-dimethylpropyl group, 2,2-dimethylpropyl group, 1-methylbutyl group 2-methylbutyl group, 3-methylbutyl group (iso-amyl group), 1,1-dimethylbutyl group, 2,2-dimethylbutyl group, 3,3-dimethylbutyl group, 1,2-dimethylbutyl group And a branched alkyl group selected from the group.

  Among these, from 1-methylethyl group, 1,1-dimethylethyl group, 1-methylpropyl group, 2-methylpropyl group, 1-methylbutyl group, 2-methylbutyl group, 3-methylbutyl group and 2-ethylbutyl group A branched alkyl group selected from the group consisting of is preferably from the viewpoint of viscosity or solubility when used as an oxidizing agent solution, and more preferably a 1-methylethyl group.

  The metal that forms a metal salt with the benzenesulfonic acid derivative in the general formula (1) is preferably a transition metal, specifically iron (III), copper (II), chromium (VI), cerium. (IV), manganese (IV), manganese (VII), ruthenium (III), and zinc (II) are mentioned, More preferably, it is iron (III).

The oxidizing agent of the present invention is preferably used as an oxidizing agent solution dissolved in an organic solvent. As the organic solvent, alcohol can be preferably used from the viewpoint of the solubility of the benzenesulfonic acid derivative metal salt. Examples of the alcohol include lower alcohols having 1 to 5 carbon atoms such as methanol, ethanol, n-propanol, isopropanol, n-butanol, and amyl alcohol. These alcohols can be used alone, but two or more of them can be used in combination as a mixed solvent.
Among these, those having n-butanol as the main solvent are particularly preferable from the viewpoint of storage stability of the oxidant solution when adjusted to a high concentration.

  The concentration of the oxidizing agent dissolved in the solvent is at least 50% by weight or more, more preferably in the range of 50 to 65% by weight. The oxidizing agent of the present invention can maintain stability even at a high concentration of 50% by weight or more even in n-butanol, and exhibits low viscosity even at a concentration exceeding 50% by weight.

When used as an oxidant solution, it may be one to which a secondary solvent is added to such an extent that the storage stability is not impaired.
As the auxiliary solvent, ethers such as diethyl ether, dipropyl ether and dibutyl ether, ketones such as acetone and methyl ethyl ketone, glycols such as ethylene glycol and propylene glycol, and the like can be added.

The oxidizing agent of the present invention is preferably an oxidizing agent solution characterized by containing a small amount of moisture. By containing moisture, the polymerization rate can be appropriately controlled, and the polymerization efficiency can be improved.
The water content is preferably less than 3.0% by weight, more preferably 0.01 to 2.0% by weight. When the water content is less than 0.01% by weight, the polymerization rate is too high and the polymerization reaction starts before the polymerization solution is impregnated into the fine porous pores, resulting in a decrease in the volume appearance rate or ESR. There is a case. On the other hand, when the water content exceeds 2.0% by weight, the polymerization efficiency may decrease and ESR may increase.

Next, the manufacturing method of the oxidizing agent of the present invention will be described by taking an iron salt as an example.
Iron oxide is added to the aqueous solution of the benzenesulfonic acid derivative represented by the general formula (1), and after stirring, the unreacted iron oxide and impurities are removed by filtration, and then the water is removed to remove the target benzenesulfonic acid derivative. A ferric salt is obtained.

The aqueous solution concentration of the benzenesulfonic acid derivative used for the reaction can be 40 to 80%.
The amount of iron oxide to be added is approximately equivalent to the benzenesulfonic acid derivative.
Usually, the reaction can be carried out at 100 to 120 ° C. for 5 to 72 hours to produce the desired ferric salt of a benzenesulfonic acid derivative.
After completion of the reaction, the resulting reaction solution is filtered, and the filtrate is concentrated and dehydrated.
The amount of water in the oxidizing agent solution can be appropriately controlled in this concentration step.
Further, an oxidizing agent solution having a predetermined oxidizing agent concentration can be obtained by adding n-butanol or the like as a solvent for the oxidizing agent during the dehydration step and concentrating. Furthermore, during the dehydration step, a low-boiling solvent such as an ether compound may be added and dehydrated while azeotropically forming water, alcohol, or ether compound.
By repeating this dehydration step a plurality of times, the desired water content can be adjusted.

Next, the manufacturing method of the solid electrolytic capacitor using the oxidizing agent of this invention is demonstrated. First, the case of a wound capacitor will be described as an example.
First, an anode foil in which an oxide film is formed on the surface of a valve metal made of aluminum, tantalum, niobium, titanium, or the like and a metal cathode foil that serves as a counter cathode are prepared. An element provided with a winding part prepared by winding a strip-shaped anode foil and a cathode foil through a strip-shaped insulating separator is prepared.
The conductive polymer layer is formed on the element by impregnating the wound portion of the element with the mixed solution of the oxidant solution and the conductive polymer monomer of the present invention, drying, and polymerizing reaction in the element. by.
For impregnation of the polymerization liquid into the element portion, the conductive polymer monomer solution and the oxidant solution may be impregnated separately instead of being mixed.
This impregnation and drying process may be repeated.

As the conductive polymer monomer, a thiophene-based conductive polymer material, a pyrrole-based or aniline-based conductive polymer material is used, and 3,4-ethylenedioxythiophene is more preferable.
As the oxidizing agent, a ferric salt of a benzenesulfonic acid derivative represented by the above general formula (1) is used.

  The concentration of the oxidizing agent used is 50% by weight or more, preferably 50 to 65% by weight. This is because when the concentration of the oxidizing agent used is 50 to 65% by weight, the viscosity is low and an appropriate polymerization rate is obtained. The preferred viscosity is 500 mPa · s or less, more preferably 150 mPa · s or less, and the preferred polymerization rate is 70 to 160 seconds. Moreover, the weight blending ratio of the monomer and the oxidizing agent solution in the polymerization reaction is preferably 1: 1 to 1:10.

The polymerization reaction is usually carried out at 45 to 150 ° C., and the reaction time is 0.5 to 5 hours.
After the polymerization, washing may be performed in order to remove the polymerization residue, excess monomer, and oxidant solution. Then, it encloses in a metal case and performs a process such as aging as necessary to complete a wound capacitor.

The case of a chip capacitor will be described as an example.
A plate-like foil or sintered body of valve action metal such as aluminum, tantalum, niobium or titanium is prepared, and an anode body is prepared by oxidizing the surface of the anode body to form a dielectric oxide film. A solid electrolyte layer made of a conductive polymer, a carbon layer containing conductive carbon, and a cathode lead layer made of silver paste or the like are sequentially formed on the anode body to constitute a capacitor element.
The anode terminal is connected to the anode lead member planted on one end face of the anode body, the cathode terminal is connected to the cathode lead layer, and the capacitor element is covered and sealed with an exterior resin such as an epoxy resin to complete a chip type capacitor. To do.

  Also in the case of a chip type capacitor, the formation of the solid electrolyte layer (conductive polymer layer) can be performed in the same manner as in the case of the wound type capacitor.

  Hereinafter, the present invention will be described in more detail based on examples. In addition, this invention is not limited at all by this Example.

(Oxidizing agents 1-7)
30 g of water was added to 30.7 g of 98% by weight of 1-methylethylbenzenesulfonic acid (manufactured by Huntsman), 4 g of iron oxide (manufactured by Titanium Industry Co., Ltd.) was mixed with stirring, and refluxed at a temperature of 100 ° C. for 24 hours.
After the reaction, water was distilled off, 20 ml of n-butanol was added and azeotroped with water, this operation was repeated 5 times, and water was distilled off. Thereafter, n-butanol was added to obtain a ferric 1-methylethylbenzenesulfonate / n-butanol solution.

The concentration of the 1-methylethylbenzenesulfonic acid ferric acid / n-butanol solution obtained above was titrated with a 0.1N sodium thiosulfate aqueous solution to obtain the concentration.
Then, the n-butanol solution was added so that it might become a predetermined density | concentration (each 30, 40, 50, 55, 60, 65, and 70 weight%), and the oxidizing agent solutions 1-7 were completed.
The water content in each oxidant solution was measured by the Karl Fischer method and was 0.5% by weight, respectively.

(Oxidizing agent 8-10)
It was prepared in the same manner except that 1-methylethylbenzenesulfonic acid of the oxidizing agents 1 to 7 was replaced with p-toluenesulfonic acid.

[Evaluation of oxidizing agent solution]
The oxidizer solution adjusted to each predetermined concentration in the above steps was prepared, and the viscosity and polymerization rate were evaluated. The viscosity was measured using a vibration viscometer (manufactured by CBC Materials, VM-100A). For the polymerization rate, each oxidizing agent and 3,4-ethylenedioxythiophene (hereinafter abbreviated as “EDOT”) were placed in a screw tube and held on a 20 ° C. thermoplate for 10 minutes or more. The oxidizing agent and EDOT were mixed 5: 1 (weight ratio) and stirred for 10 seconds. Then, the time until a polymer lump having a diameter of 1 mm or more was deposited was measured and used as a polymerization rate.
It has been empirically found that the polymerization rate obtained by this polymerization rate measurement method is generally 70 to 160 seconds, which is suitable for forming a conductive polymer layer in a solid electrolytic capacitor. The measurement results are shown in Table 1.

  From Table 1, the oxidizer solution of the present invention has a low viscosity and an appropriate polymerization rate despite the concentration being 50% by weight or more.

[Evaluation of solid electrolytic capacitors]
Add the oxidizer solution prepared above and 3,4-ethylenedioxythiophene, which is a conductive polymer monomer, so that the weight ratio is 6: 1, and stir on an 18 ° C. thermoplate to prepare a polymerization solution. did.

  The polymer solution was impregnated with a wound aluminum solid electrolytic capacitor element (diameter 7 mm, height 6 mm) for 1 minute. Thereafter, polymerization was carried out at 45 ° C. for 1 hour, then at 105 ° C. for 15 minutes, and further dried at 105 ° C. for 30 minutes and at 125 ° C. for 1 hour, and a conductive polymer layer was formed on the wound capacitor to complete a solid electrolytic capacitor. . After drying, it was stored in a desiccator for 30 minutes or more, and the capacitance (μF) and ESR (mΩ) were measured with an LCR meter (model name: 4284A, manufactured by Agilent Technology). The measurement results are shown in Tables 2 and 3.

As shown in Table 2, a solid electrolytic capacitor exhibiting high capacity and low ESR was obtained by using the oxidant solution of the present invention.
ESR tends to decrease as the concentration of the oxidizing agent increases. However, regarding 70%, since the viscosity is high and the polymerization rate is high, the polymer is polymerized before being impregnated in the capacitor, so that the ESR is considered to be slightly higher.

＊酸化剤４−１〜４−８：１−メチルエチルベンゼンスルホン酸第二鉄塩／ｎ−ＢｕＯＨ溶液（５５重量％）
＊酸化剤５−１〜５−７：１−メチルエチルベンゼンスルホン酸第二鉄塩／ｎ−ＢｕＯＨ溶液（６０重量％）

* Oxidizing agents 4-1 to 4-8: 1-methylethylbenzenesulfonic acid ferric salt / n-BuOH solution (55% by weight)
* Oxidizing agent 5-1 to 5-7: 1-methylethylbenzenesulfonic acid ferric salt / n-BuOH solution (60 wt%)

  As shown in Table 3, the lower the moisture content, the lower the ESR. This is probably because the polymerization rate decreases and the amount of unreacted EDOT increases as the water content increases. However, at 0.01% by weight or less, ESR is higher than 0.01 to 2.0% by weight. This is presumably because the polymerization rate is significantly increased due to the low moisture content, and the polymerization solution is polymerized before impregnating the capacitor. As mentioned above, in the high concentration oxidizing agent, the water content is preferably 0.01 to 2.0% by weight.

[Evaluation of heat resistance test]
A conductive polymer layer is formed on a wound capacitor in the same manner as described above, and a heat resistance test is performed at a load voltage of 4.0 V for 500 hours in a constant temperature bath of 125 ° C., and an LCR meter (model name: 4284A, Agilent Technology) Product), capacitance (μF @ 120 Hz), resistance loss: tan δ (%), ESR (mΩ @ 100 kHz) were measured. Table 4 shows the measurement results.

  As shown in Table 4, the oxidizing agent 4 to 6 using ferric 1-methylethylbenzenesulfonate / n-BuOH has stable capacitance, tan δ, and ESR, while p-toluenesulfonic acid. Oxidants 8 to 10 using ferric / n-BuOH are significantly deteriorated. This indicates that a solid electrolytic capacitor having a solid electrolyte layer containing a benzenesulfonic acid substituted with a branched alkyl group as a dopant is excellent in thermal stability.

The solid electrolytic capacitor manufactured using the oxidant for manufacturing a conductive polymer of the present invention has excellent electrical characteristics and can be applied to various digital devices used in a high frequency region.
In addition, the oxidant for producing a conductive polymer of the present invention provides a conductive polymer excellent in conductivity and durability, so that not only a solid electrolytic capacitor but also a conductive polymer for antistatic treatment use can be produced. Can be suitably used.

Claims (6)

Formula (1),

(In the formula, R represents a branched alkyl group.)
An oxidizing agent for producing a conductive polymer comprising a ferric salt of a benzenesulfonic acid derivative represented by   R is 1-methylethyl group, 1,1-dimethylethyl group, 1-methylpropyl group, 2-methylpropyl group, 1-methylbutyl group, 2-methylbutyl group, 3-methylbutyl group, or 2-ethylbutyl group. The oxidizing agent for producing a conductive polymer according to claim 1, wherein the oxidizing agent is used.   An oxidizing agent solution for producing a conductive polymer, wherein the oxidizing agent for producing a conductive polymer according to claim 1 or 2 is dissolved in n-butanol by 50% by weight or more.   The water content of the oxidant solution for producing a conductive polymer according to claim 3 is less than 3.0% by weight.   A solid electrolytic capacitor, wherein a conductive polymer polymerized using the oxidant solution for producing a conductive polymer according to claim 3 or 4 is used as a solid electrolyte. By impregnating a capacitor element with a mixed liquid of a conductive polymer monomer and an oxidizing agent solution, or impregnating a capacitor element with a conductive polymer monomer solution and an oxidizing agent solution,
In the manufacturing method of the solid electrolytic capacitor including the process of carrying out the polymerization reaction of a monomer and an oxidizing agent and forming a conductive polymer layer in a capacitor element, using the oxidizing agent solution for conductive polymer manufacture according to claim 3 or 4 A method for producing a solid electrolytic capacitor comprising using a polymerized conductive polymer as a solid electrolyte.