JP2003297687A - Method for producing solid electrolytic capacitor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a solid electrolytic capacitor exhibiting excellent moisture resistance. <P>SOLUTION: A capacitor element having a dielectric oxide film formed on the surface of a valve action metal basic body becoming an anode is immersed into solution of polymerizable monomer, e.g. 3,4-ethylene dioxythiophene, and then immersed into aqueous solution of oxidizing agent in the temperature range of 0°C-20≤ for 30 min or longer thus forming a conductive polymer layer on the surface of the dielectric oxide film through chemical polymerization of the polymerizable monomer. Since the temperature of the aqueous solution of oxidizing agent is low, reaction rate of polymerization is controlled and since a compact conductive polymer layer is formed on the dielectric oxide film of the capacitor element, a low ESR solid electrolytic capacitor can be realized. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

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

[0002]

2. Description of the Related Art In recent years, solid electrolytic capacitors using a conductive polymer as a solid electrolyte have been put into practical use for the purpose of lowering ESR. Generally, as these conductive polymers, there are polythiophene, polypyrrole, polyaniline, and their derivatives. Among them, polythiophene and its derivatives have higher conductivity and higher thermal stability than polypyrrole, polyaniline, or their derivatives. Since it is particularly excellent, it has been attracting attention in recent years, and as a solid electrolytic capacitor using polythiophene as a solid electrolyte, it is disclosed in Japanese Patent Application Laid-Open No. HEI-2.
-15611 and the like.

Although polythiophene and its derivatives can be produced by chemical oxidative polymerization and electrolytic polymerization,
When electrolytic polymerization means is taken, it is necessary to attach several electrodes for polymerization to one piece, and it is difficult to mass-produce the conductive polymer because it is formed into a film on the electrode. In the case of the chemical oxidative polymerization means, there is no such problem, and a person skilled in the art can easily obtain a large amount of the conductive polymer layer as compared with electrolytic polymerization. Well known in the.

As the oxidizer for the chemical oxidative polymerization, alkali metal, persulfate such as ammonium, iron (III), copper (II), chromium (VI), cerium (IV), ruthenium (III) are used. ) And manganese (VII), but when water is used as a safe solvent, ammonium persulfate is often used as the oxidant.

When a sintered element body formed by sintering tantalum powder or the like is used as a capacitor element, the surface of the element body is smooth, so that the adhesive force is low and the formed conductive polymer layer may peel off. There is. Therefore, an oxidizing agent that allows the conductive polymer to grow in a particulate form rather than a planar form is selected, and an aqueous solution of persulfate is known as such an oxidizing agent. Oxidizing agents containing persulfate ions are preferred.

[0006]

A solid electrolytic capacitor using a conductive polymer as a solid electrolyte is superior to a solid electrolytic capacitor using a conventional electrolytic solution as an electrolyte or a solid electrolytic capacitor using manganese dioxide as a solid electrolyte. Although its equivalent series resistance (ESR) is sufficiently low, in recent years, further reduction of ESR is required.

Therefore, the present invention has been completed as a result of studying a manufacturing method capable of obtaining a solid electrolytic capacitor having a lower ESR.

[0008]

[Means for Solving the Problems] A capacitor element having a dielectric oxide film formed on the surface of a valve-acting metal substrate serving as an anode is sequentially immersed in a polymerizable monomer solution and an oxidant solution to chemically polymerize the polymerizable monomer. Thus, in the method for producing a solid electrolytic capacitor in which a conductive polymer layer is formed on the surface of the dielectric oxide film, the capacitor element is immersed in an oxidant solution at 0 ° C. or higher and 20 ° C. or lower for 30 minutes or longer, It is characterized in that a conductive polymer layer is formed by a chemical polymerization reaction in an oxidant solution.

When the conductive polymer layer is formed on the capacitor element while being immersed in the oxidant solution, if the oxidant solution is kept at 20 ° C. or lower, the E of the completed solid electrolytic capacitor will be obtained.
SR is reduced. The reason for this is not necessarily clear, but the polymerization reaction speed becomes slow, and a fine conductive polymer is formed even in the fine structure of the capacitor element, resulting in a resistance at the interface with the dielectric oxide film. It is thought to be for reduction. On the other hand, if the temperature is 0 ° C or lower, the polymerization reaction is further delayed and the production time becomes long, which is not practical.
In these temperature ranges, a polymerization time of 30 minutes or more is required to secure the electrostatic capacity of the solid electrolytic capacitor and achieve low ESR. If the time is less than 30 minutes, the electrical characteristics of the solid electrolytic capacitor deteriorate.

Further, the temperature of the polymerizable monomer solution is set to be equal to or higher than the temperature of the oxidizing agent solution.

The viscosity of the polymerizable monomer solution increases at low temperatures, and it takes time to sufficiently impregnate the inside of the capacitor element. Therefore, if the impregnation of the polymerizable monomer is performed at the temperature of the oxidizing agent solution or higher, the impregnation time can be shortened.

It is preferable that the polymerizable monomer is thiophene or a derivative thereof.

Examples of the thiophene derivative include those having the following structures. Thiophene or its derivative is
As compared with polypyrrole or polyaniline, the solid electrolytic capacitor has a high electric conductivity and particularly excellent thermal stability, and thus a solid electrolytic capacitor having low ESR and excellent heat resistance can be obtained.

[0014]

[Chemical 1] X is O or S When X is O, A is alkylene, or polyoxyalkylene When at least one of X is S, A is alkylene, polyoxyalkylene, substituted alkylene, substituted polyoxyalkylene: where the substituent is Alkyl group, alkenyl group, alkoxy group

Of the thiophene derivatives, 3,4-ethylenedioxythiophene is preferably used.

3,4-ethylenedioxythiophene is
Upon contact with an oxidant, poly- (3,4-ethylenedioxythiophene) is generated by a gradual polymerization reaction, so that a monomer solution of 3,4-ethylenedioxythiophene is used in a capacitor element having a fine structure. It is possible to polymerize while penetrating to the inside. As a result,
The conductive polymer layer can be formed even inside the capacitor element, and the capacitance of the solid electrolytic capacitor can be increased.

It is preferable that the oxidant solution is an aqueous oxidant solution containing persulfate ions.

In a solid electrolytic capacitor in which a sintered body obtained by sintering fine powder of valve metal is used as a capacitor element, an oxidizer in which a conductive polymer grows in a particle shape rather than a planar shape is preferable. An aqueous solution of persulfate can be selected as the oxidizing agent

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION Next, embodiments of the present invention will be described in more detail. FIG. 1 is a sectional view showing the internal structure of a solid electrolytic capacitor. Reference numeral 1 is a capacitor element, which is formed by molding fine tantalum powder into a predetermined shape, embedding an anode lead wire such as tantalum wire, and further sintering to obtain a tantalum sintered body, which is further dipped in a phosphoric acid aqueous solution or the like. A predetermined voltage is applied to form an anodized film as a dielectric on the surface of the tantalum fine powder. The sintered body is not limited to tantalum, and valve metal such as aluminum, niobium, or titanium can be used.

Reference numeral 2 is a conductive polymer layer formed on the anodized film. The conductive polymer layer is formed by oxidative polymerization of 3,4-ethylenedioxythiophene.

This polymerization step is a step in which the capacitor element is first dipped in a monomer solution diluted with a predetermined solvent, and then further dipped in an oxidant solution containing persulfate ions.

As the oxidizing agent containing persulfate ion, an aqueous solution in which an alkali metal salt or ammonium salt of persulfate is dissolved in water as a solvent and further sulfuric acid is dissolved can be used.

The liquid temperature of the polymerizable monomer solution of 3,4-ethylenedioxythiophene was 25 ° C., and the immersion time of the capacitor element was 30 seconds.

The oxidant aqueous solution has a liquid temperature of 0 ° C. or higher and 20
The temperature range is below ℃, and the immersion time of the capacitor element is 3
It was set to 0 minutes or more.

After forming the conductive polymer layer on the capacitor element, predetermined washing with running water and drying are performed.

After completion of the above-mentioned drying, the step of immersing in the polymerizable monomer solution and the oxidizing agent solution was performed again, and repeated until the conductive polymer layer had a desired thickness.

After the polymerization, the capacitor element is formed with the shaped carbon layer 3 on the conductive polymer layer 2 and the silver paste layer 4 on the carbon layer.

Thereafter, the anode lead wire 5 is welded to the anode lead wire of the capacitor element, and the cathode lead wire 6 is connected to the silver paste layer so as to be electrically connected to the outside.

Further, the capacitor element, except for a part of the anode lead wire and the cathode lead wire, is resin-coated by transfer molding to form an exterior resin 7.

Then, the anode lead wire and the cathode lead wire are bent along the end surface of the exterior resin 7 so that surface mounting is possible, and the solid electrolytic capacitor is completed.

[0031]

EXAMPLES Next, specific examples will be described in detail in comparison with comparative examples. (Example 1) As an anode, the size was 3.9 x 3.3 x 1.
Using a tantalum sintered body of 6 mm ^{3 and} a tantalum wire as the anode wire, the weight of the anode body of about 100 mg is 0.05 w.
It was anodized in a t% phosphoric acid aqueous solution at 90 ° C. and 40 V for 180 minutes, washed with running deionized water, and dried to obtain a capacitor element. It was noted that this state was regarded as a capacitor and the capacity in the chemical conversion liquid was measured and the result was 104 μF.

Next, this capacitor element was mixed with 50 g of 2-propanol and 50 g of 3,4-ethylenedioxythiophene.
It was immersed for 30 seconds in a monomer solution prepared by mixing with g. The temperature of this monomer solution was 25 ° C. Next, 40 g of ammonium persulfate as an oxidizing agent containing persulfate ions
And 4 g of sulfuric acid were dissolved in 100 g of pure water and immersed in an oxidizing agent solution for 60 minutes to carry out chemical oxidative polymerization. The temperature of this oxidant solution was 15 ° C. In this way, a conductive polymer layer was formed on the anodized film forming the capacitor element, washed with running water for 30 minutes, and then the capacitor element was dried. Then, until the polymer layer has a desired thickness, the number of polymerizations from dipping in a monomer solution to drying is 5
Repeated times, the amount of conductive polymer layer formed on the capacitor element (amount of attached polymer) was measured.

Next, a carbon layer is formed on the conductive polymer layer of the capacitor element, a silver paint layer serving as a cathode is formed on the carbon layer, and a cathode lead terminal is formed on the silver paint layer. Anode lead terminals were attached to the anode wires drawn out from the anode body, resin coating was performed by transfer molding, and the cathode lead terminals and the anode lead terminals were bent at predetermined positions to complete a chip-shaped solid electrolytic capacitor.

The solid electrolytic capacitor completed as described above had a rated voltage of 10 V and a rated capacitance of 100 μF.

(Example 2) A solid electrolytic capacitor was manufactured under the same conditions except that the temperature of the oxidizing agent aqueous solution in Example 1 was set to 20 ° C.

(Example 3) A solid electrolytic capacitor was manufactured under the same conditions except that the polymerization time in Example 1 was changed to 90 minutes.

Example 4 A solid electrolytic capacitor was manufactured under the same conditions except that the polymerization time in Example 1 was changed to 30 minutes.

(Comparative Example 1) A solid electrolytic capacitor was manufactured under the same conditions except that the temperature of the oxidizing agent aqueous solution in Example 1 was changed to 25 ° C.

(Comparative Example 2) A solid electrolytic capacitor was manufactured under the same conditions except that the temperature of the oxidizing agent aqueous solution in Example 1 was changed to -2 ° C.

(Comparative Example 3) The temperature of the polymerizable monomer solution of Example 1 was 10 ° C, and the temperature of the oxidizing agent aqueous solution was 15 ° C.
Other than that, a solid electrolytic capacitor was manufactured under the same conditions.

Comparative Example 4 A solid electrolytic capacitor was manufactured under the same conditions except that the immersion time of the capacitor element in the oxidant aqueous solution of Example 1 was set to 20 minutes.

The capacitance and E of the solid electrolytic capacitors manufactured by the above Examples 1 to 4 and Comparative Examples 1 to 4
When the SR was measured, the results were as shown in Table 1 below.

[0043]

[Table 1]

Comparing Examples 1 and 2 and Comparative Example 1 in which the temperature of the oxidizing agent aqueous solution is different, the ESR of each of Examples 1 and 2 in which the temperature of the oxidizing agent aqueous solution was 20 ° C. or less was 31 mΩ, While an ESR as low as 38 mΩ can be realized, in Comparative Example 1 in which the temperature of the oxidant aqueous solution is 25 ° C., the ESR is as high as 50 mΩ. As described above, since the ESR of the solid electrolytic capacitor increases as the temperature of the oxidant aqueous solution increases, it is understood that the temperature of the oxidant aqueous solution is preferably 20 ° C. or lower.

On the other hand, comparing Example 1 and Example 2 with Comparative Example 3, the electrostatic capacity of Comparative Example 3 is 85 μF, which is lower than 101 μF and 103 μF of Example 1 and Example 2. This is because the rate of the polymerization reaction slows when the temperature of the oxidant aqueous solution is lower than 0 ° C. Therefore, when the polymerization time is the same, the polymerization of the conductive polymer does not proceed sufficiently, and as a result, This is because the capacitance has decreased.
This is supported by the amount of polymer attached to the capacitor element. Therefore, it is understood that the temperature of the oxidant aqueous solution is preferably 0 ° C. or higher in order to increase the speed of the polymerization reaction and shorten the production time.

Further, comparing Example 1, Example 3, Example 4 and Comparative Example 4 having different polymerization times, the polymerization time was 2
In Comparative Example 4, which is as short as 0 minutes, it can be seen that the polymer adhesion amount and the electrostatic capacity are both small, and the polymerization reaction does not proceed sufficiently. On the other hand, comparing Example 4 and Example 3, Example 4
Although the polymerization time of 30 minutes is 30 minutes, the polymerization time in Example 3 is 90 minutes, which is long, but compared with Example 4.
Neither the amount of attached polymer nor the capacitance is so large. It is considered that this is because, after a certain amount of time, the conductive polymer is saturated inside the capacitor element and further polymerization reaction does not proceed. Therefore, it can be seen that the polymerization time of 30 minutes or more is sufficient.

Further, comparing Example 1 and Comparative Example 3 in which the temperature of the monomer solution is different, the temperature of the monomer solution is 1
In Comparative Example 3 where the temperature is 0 ° C. and the temperature is low, both the amount of attached polymer and the capacitance are small. It is considered that this is because when the temperature becomes low, the viscosity of the monomer solution increases and the capacitor element cannot be sufficiently impregnated with the monomer solution. Therefore, when the temperature of the oxidant aqueous solution is as low as 0 ° C. to 20 ° C., the temperature of the monomer solution is set higher than the temperature of the oxidant aqueous solution to impregnate the capacitor element with the monomer. It can be seen that is easy to progress.

[0048]

As described above, according to the present invention, a capacitor element in which a dielectric oxide film is formed on the surface of a valve action metal base serving as an anode is successively immersed in a polymerizable monomer solution and an oxidant solution, By the chemical polymerization of the polymerizable monomer,
In the method for producing a solid electrolytic capacitor in which a conductive polymer layer is formed on the surface of the dielectric oxide film, the ESR is obtained by chemically polymerizing for 30 minutes or more in an oxidant solution at 0 ° C or higher and 20 ° C or lower. A low solid electrolytic capacitor can be provided.

[Brief description of drawings]

FIG. 1 is a sectional view showing a basic structure of a solid electrolytic capacitor of the present invention.

[Explanation of symbols]

1 Capacitor element 2 Conductive polymer layer 3 carbon layer 4 Silver paint layer 5 Anode lead terminal 6 Cathode extraction terminal 7 Resin exterior layer

Claims (5)

[Claims] 1. A capacitor element in which a dielectric oxide film is formed on the surface of a valve action metal substrate serving as an anode is successively immersed in a polymerizable monomer solution and an oxidant solution, and the dielectric monomer is formed by chemical polymerization of the polymerizable monomer. In a method for producing a solid electrolytic capacitor in which a conductive polymer layer is formed on the surface of a body oxide film, the capacitor element is immersed in an oxidant solution at 0 ° C. or higher and 20 ° C. or lower for 30 minutes or longer, and then in an oxidant solution. A method for producing a solid electrolytic capacitor in which a conductive polymer layer is formed by a chemical polymerization reaction in step 1. 2. The method for producing a solid electrolytic capacitor according to claim 1, wherein the temperature of the polymerizable monomer solution is equal to or higher than the temperature of the oxidant solution. 3. The method for producing a solid electrolytic capacitor according to claim 1, wherein the polymerizable monomer is a monomer composed of thiophene or a derivative thereof. 4. The method for producing a solid electrolytic capacitor according to claim 3, wherein the derivative of thiophene is 3,4-ethylenedioxythiophene. 5. The method for producing a solid electrolytic capacitor according to claim 1, wherein the oxidizing agent solution is an aqueous oxidizing agent solution containing persulfate ions.