JP5262238B2 - Manufacturing method of solid electrolytic capacitor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a solid-state electrolytic capacitor excellent in humidity resistance property, suppressing damage on dielectric oxide film and conductive high polymer frame caused by free dopant. <P>SOLUTION: The method for manufacturing the solid-state electrolytic capacitor includes: a step for forming a conductive high polymer layer in an element by carrying out a chemical oxidation polymerization reaction of a polymerizable monomer and an oxidant containing dopant at a temperature at which the dopant in the oxidant does not carry out heat fixing into the element; and a step for applying a heat treatment to the element at a temperature which promotes the heat fixing of the dopant in the element after removing the dopant remained in the element by washing the element, wherein the dopant remaining after washing is made to be heat-fixed in the element by the step for applying the heat treatment, the rate of content of the free dopant in the conductive high polymer layer is adjusted. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

 The present invention relates to a solid electrolytic capacitor using a conductive polymer, and more particularly to a method of manufacturing a solid electrolytic capacitor having excellent moisture resistance.

  The anode electrode of an electrolytic capacitor is made of a valve metal such as aluminum, tantalum, or niobium. This anode electrode has etching pits and fine holes, and forms an oxide film layer as a dielectric on the anode electrode surface. An electrolyte layer is formed on the coating layer, and the electrode is drawn out. This electrolyte layer plays a role as a true cathode in the electrolytic capacitor, and greatly affects the electrical characteristics of the electrolytic capacitor.

  In recent years, with the downsizing and high performance of electronic devices, there has been a demand for solid electrolytic capacitors having a large capacitance per product volume and low ESR. In consideration of the above, a solid electrolytic capacitor using a conductive polymer such as polypyrrole, polythiophene, polyfuran, polyaniline as a solid electrolyte has been developed. These conductive polymers have high conductivity and high heat stability compared to manganese dioxide, TCNQ complex salt, etc., which are electrolytes used in conventional solid electrolytic capacitors. It greatly contributes to ESR and high reliability.

  Various methods for generating this conductive polymer have been proposed. A method of preparing a mixed liquid of a polymerizable monomer and an oxidizing agent in advance and immersing a capacitor element in this mixed liquid, or a capacitor element Is produced by chemical oxidative polymerization such as immersing each in an oxidizing agent and a polymerizable monomer (see, for example, Patent Document 1 and Patent Document 2).

  In these chemical oxidative polymerizations, the oxidant generally contains a substance that becomes a conductive polymer dopant. In particular, a sulfonic acid compound ion such as aromatic sulfonic acid is incorporated into the molecule as a dopant. The conductive polymer has high conductivity and is widely used as a solid electrolyte of a solid electrolytic capacitor (see, for example, Patent Document 3).

On the other hand, although the chemical oxidative polymerization reaction itself between the polymerizable monomer and the oxidizing agent is known to proceed even at room temperature, for example, Patent Document 4 and Patent Document 5 describe 3,4-ethylenedioxythiophene. Since the polymerization reaction takes a long time, the chemical oxidative polymerization reaction was promoted industrially by performing a heat treatment at 100 ° C. or more (see, for example, Patent Document 6, Patent Document 7, and Patent Document 8).
JP 2001-196279 A Japanese Patent Laid-Open No. 10-50559 Japanese Patent Laid-Open No. 10-32145 Japanese Patent No. 2721700 Japanese Patent No. 3040113 JP-A-10-340831 Japanese Patent No. 3296724 Japanese Patent No. 3454733

However, solid electrolytic capacitors using a conductive polymer layer doped with a dopant such as sulfonic acid compound ions as a solid electrolyte are still not sufficient in terms of moisture resistance and long-term stability. Even if promoted, it became clear that the dopant in the monomer or oxidizing agent remained in the device, and in particular, the dopant such as free sulfonate ions remaining in the conductive polymer layer had an adverse effect. .

  That is, when the element of the conventional solid electrolytic capacitor was boiled and the sulfonic acid ion as the dopant was measured, the sulfonic acid ion exceeding 4000 ppm was detected even with a small amount. From this result, there are sulfonate ions that are eluted at the boiling level, that is, sulfonate ions that remain in the device and are released. It was considered that the polymer skeleton was damaged, and as a result, the electrical characteristics, particularly the moisture resistance, were degraded.

  An object of the present invention is to provide a solid electrolytic capacitor having excellent moisture resistance characteristics by suppressing damage to the dielectric oxide film and the conductive polymer skeleton caused by the free dopant.

The present invention relates to a method for producing a solid electrolytic capacitor, wherein a polymerizable monomer and an oxidant containing a dopant are subjected to a chemical oxidative polymerization reaction at a temperature at which the dopant in the oxidant is not thermally fixed in the element. A step of forming a polymer layer, and a step of washing the device to remove the dopant remaining in the device and then subjecting the device to heat treatment at a temperature that promotes thermal fixation of the dopant in the device. The dopant remaining after washing is thermally fixed in the device by the heat treatment step, and the free dopant content in the conductive polymer layer is adjusted to 3000 ppm or less . Also, it is preferable that the dopant is a temperature that does not thermally fixed in the device at 120 ° C. or less in the chemical oxidative polymerization reaction, also, the temperature that facilitates dopant is thermally fixed in the element is to be at 0.99 ° C. or higher Although preferred, these free dopant contents and temperatures have also been found to vary with various conditions such as device structure and device shape.

  According to such a manufacturing method, a conductive polymer layer is formed by a chemical oxidative polymerization reaction at a temperature at which the dopant in the oxidant is not thermally fixed in the device, whereby the oxidative polymerization reaction by the polymerizable monomer and the oxidant is performed. In this case, dopants such as sulfonate ions in the remaining oxidizing agent are prevented from being thermally fixed in the device. The device is then cleaned to remove any free dopant remaining in the device, and then subjected to a heat treatment at a temperature that promotes the thermal fixation of the dopant into the device, so that the device still remains after cleaning. The content of the free dopant in the conductive polymer layer that causes damage to the dielectric oxide film and the conductive polymer skeleton can be adjusted by thermally fixing the released free dopant in the device, and so on.

  In addition, if the content rate of free dopants, such as a sulfonate ion in a conductive polymer layer, is 3000 ppm or less, compared with the conventional solid electrolytic capacitor, a damage to a dielectric oxide film or a conductive polymer skeleton will be suppressed. I can expect that.

  According to the present invention, it becomes easy to adjust the content of the free dopant in the conductive polymer layer, and damage to the dielectric oxide film and the conductive polymer skeleton is suppressed. A solid electrolytic capacitor that maintains stable characteristics over a long period of time can be obtained.

  In the embodiment for carrying out the present invention, a polymerizable monomer and an oxidizing agent containing a dopant are subjected to a chemical oxidative polymerization reaction at a temperature at which the dopant in the oxidizing agent is not thermally fixed in the device, and a conductive polymer in the device. Cleaning the device, and cleaning the device to remove the dopant remaining in the device and then subjecting the device to heat treatment at a temperature that promotes thermal fixation of the dopant in the device. This is a method for producing a solid electrolytic capacitor in which the dopant remaining after the heat treatment is thermally fixed in the device by the heat treatment step. The influence on the polymer skeleton can be suppressed. Therefore, it can be expected to realize a solid electrolytic capacitor having excellent moisture resistance and stable characteristics over a long period of time.

  Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a manufacturing process diagram showing a method of manufacturing a solid electrolytic capacitor according to an embodiment of the present invention.

  First, a metal foil made of a valve metal such as aluminum is prepared, and the surface is subjected to an etching process to enlarge the surface. Next, this metal foil is formed in an aqueous solution of ammonium adipate at 5 V for 30 minutes to form a dielectric oxide film on the surface.

  Next, as a production process of the conductive polymer layer, the metal foil is changed into 3,4-ethylenedioxythiophene (butanol solution) that is a polymerizable monomer and an oxidizing agent (ferric iron p-toluenesulfonate). After dipping and pulling up, chemical oxidation polymerization is performed by heating at about 60 ° C. to 100 ° C. for about 30 minutes to form a conductive polymer layer on the dielectric oxide film to obtain an element.

  Subsequently, the device was washed with running water and then heat-treated at 200 ° C. for 10 minutes, and a carbon layer and a silver paste layer were applied on the conductive polymer layer to obtain a solid electrolytic capacitor.

  As another embodiment of the present invention, a so-called wound element may be used, and the embodiment in that case is as follows. That is, the metal foil having a dielectric oxide film formed on the surface thereof is used as an anode electrode foil, and another metal foil subjected to etching treatment is used as a cathode electrode foil. These electrode foils are mainly composed of synthetic resin, for example. After being rolled up through a separator made of a non-woven fabric, and then immersed (impregnated) in a polymerizable monomer and an oxidizing agent and pulled up, as in the above embodiment, the temperature is about 60 ° C. to 100 ° C. Chemical oxidation polymerization is performed by heating for about 30 minutes to form a conductive polymer layer. Subsequent cleaning and heat treatment are performed in the same manner as in the above embodiment to obtain an element.

  In addition, to the bipolar electrode foil, a lead wire for drawing out the electrode is electrically connected by means such as stitching or ultrasonic welding, and the element according to this embodiment has a bottom made of aluminum or the like. The metal case opening is housed in a cylindrical metal case, and the metal case opening is sealed with a sealing member made of elastic rubber or the like.

Example 1
Etching is applied to a 10 × 10 mm flat aluminum foil, and a dielectric oxide film is formed on the surface of the aluminum foil by chemical conversion in an aqueous solution of ammonium adipate at 5 V for 30 minutes. After that, it is immersed in an oxidizing agent (ferric iron p-toluenesulfonate) and 3,4-ethylenedioxythiophene (butanol solution), pulled up, heated at 60 ° C. for 30 minutes to perform chemical oxidative polymerization, and dielectric. A conductive polymer layer was formed on the body oxide film to form a device. Next, this element was washed with running water and then subjected to a heat treatment at 200 ° C. for 10 minutes to apply a carbon layer and a silver paste layer on the conductive polymer layer.
(Example 2)
A solid electrolytic capacitor was obtained in the same manner as in Example 1 except that the element on which the conductive polymer layer was formed was washed and then heat-treated at 150 ° C. for 10 minutes.
(Example 3)
A solid electrolytic capacitor was obtained in the same manner as in Example 1 except that chemical oxidation polymerization was performed by heating the metal foil at 120 ° C. for 10 minutes.
Example 4
A solid electrolytic capacitor was obtained in the same manner as in Example 3 except that the element on which the conductive polymer layer was formed was washed and then heat-treated at 150 ° C. for 10 minutes.
(Comparative Example 1)
A solid electrolytic capacitor was obtained in the same manner as in Example 1 except that the metal foil was heated at 30 ° C. for 90 minutes to perform chemical oxidation polymerization.
(Comparative Example 2)
A solid electrolytic capacitor was obtained in the same manner as in Example 1 except that the element on which the conductive polymer layer was formed was washed and then heat-treated at 100 ° C. for 10 minutes.
(Comparative Example 3)
After washing the element on which the conductive polymer layer was formed as in Example 1, a solid electrolytic capacitor was obtained without performing heat treatment.
(Comparative Example 4)
A solid electrolytic capacitor was obtained in the same manner as in Comparative Example 2 except that the metal foil was heated at 120 ° C. for 10 minutes for chemical oxidation polymerization.
(Comparative Example 5)
A solid electrolytic capacitor was obtained in the same manner as in Example 1 except that the capacitor element on which the conductive polymer layer was formed was heat-treated at 150 ° C. for 10 minutes without washing.
(Conventional example 1)
Etching is applied to a 10 × 10 mm flat aluminum foil, and a dielectric oxide film is formed on the surface of the aluminum foil by chemical conversion in an aqueous solution of ammonium adipate at 5 V for 30 minutes. After that, it is immersed in an oxidizing agent (ferric iron p-toluenesulfonate) and 3,4-ethylenedioxythiophene (butanol solution), pulled up, heated at 150 ° C. for 10 minutes to perform chemical oxidative polymerization, and dielectric. A conductive polymer layer was formed on the body oxide film to form a device. Next, this element was washed with running water and then subjected to heat treatment at 150 ° C. for 10 minutes, and a carbon layer and a silver paste layer were applied on the conductive polymer layer.
(Conventional example 2)
After washing the element on which the conductive polymer layer was formed as in Conventional Example 1, a solid electrolytic capacitor was obtained without performing heat treatment.
(Conventional example 3)
A solid electrolytic capacitor was obtained without washing and heat-treating the element on which the conductive polymer layer was formed as in Conventional Example 1.

  ESR after the moisture resistance load test under the conditions of initial ESR characteristics (100 kHz: mΩ), LC (2.5 V applied: μA) and 60 ° C. 95% RH, 2.5 V applied in each example, comparative example, and conventional example. The characteristics and leakage current characteristics (LC) are shown in Table 1 as average values of 20 samples.

  In all of the examples of the present invention, the change after the moisture resistance load test is small, but in all of the conventional examples, both the ESR characteristic and the leakage current characteristic (LC) after the moisture resistance load test are greatly increased, and paratoluene sulfone is a free dopant Degradation of the film and the conductive polymer layer due to the acid was confirmed. In particular, even if the device in which the conductive polymer layer is formed as in Conventional Example 1 is cleaned and the device is heat-treated at a temperature that promotes thermal fixing of the dopant in the device, A sufficient cleaning effect could not be obtained unless the chemical oxidative polymerization reaction was performed at a temperature at which the dopant was not thermally fixed in the device.

  Of the comparative examples, although Comparative Example 1 is satisfactory as a result, it is not optimal because the polymerization time is long. In Comparative Examples 2 to 5, all the results better than the conventional examples were obtained, but in comparison with the Examples, an increase in ESR characteristics after the moisture resistance load test was observed. For example, Comparative Example 2 As in Comparative Example 4, a polymerizable monomer and an oxidizing agent containing a dopant are subjected to a chemical oxidative polymerization reaction at a temperature at which the dopant in the oxidizing agent is not thermally fixed in the device, and the device is washed to obtain a device. Even if the dopant remaining therein is removed, a desired result cannot be obtained unless the dopant is sufficiently heat-fixed in the device thereafter, and the dopant is heat-fixed in the device as in Comparative Example 5. Even if the heat treatment is performed, it has become clear that good results cannot be obtained unless cleaning is performed prior to the heat treatment.

In this example, the method for measuring free dopant (sulfonate ion) is as follows. “PTS” represents free p-toluenesulfonic acid. The PTS concentration was measured by liquid chromatography using an eluate sampled from a certain amount.
(1) Polymer weight (a) = post-polymerization element weight-pre-polymerization element weight (2) boiling post-polymerization element in boiling water for 30 minutes (eluent)
(3) PTS amount in device (b) = total weight of eluate × PTS concentration (4) free sulfonate ion content = b / a

Manufacturing process diagram showing a method of manufacturing a solid electrolytic capacitor according to an embodiment of the present invention

Claims (3)

A step of chemical oxidation polymerization reaction of a polymerizable monomer and an oxidant containing a dopant at a temperature at which the dopant in the oxidant is not thermally fixed in the device to form a conductive polymer layer in the device;
Cleaning the element to remove the dopant remaining in the element, and then subjecting the element to heat treatment at a temperature that promotes thermal fixing of the dopant in the element.
The manufacturing method of the solid electrolytic capacitor which heat-fixes the dopant which remains after washing | cleaning in an element by the process of performing the said heat processing, and adjusts the free dopant content rate in a conductive polymer layer to 3000 ppm or less .   The method for producing a solid electrolytic capacitor according to claim 1, wherein the temperature at which the dopant is not thermally fixed in the device is 120 ° C. or less.   The method for producing a solid electrolytic capacitor according to claim 1, wherein a temperature at which the dopant promotes thermal fixing in the device is 150 ° C. or higher.