JP4809417B2 - 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 electrolytic capacitor includes an anode made of a valve metal such as aluminum, tantalum, or niobium, and etching pits and fine holes are formed on the surface of the anode. An oxide film serving as a dielectric is formed on the surface of the anode.
Here, electrical extraction on the cathode side is performed by an electrolyte layer having conductivity, and this electrolyte layer serves as a true cathode in the electrolytic capacitor. Since the electrolyte layer functioning as a true cathode has a great influence on the electrical characteristics of the electrolytic capacitor, a number of methods for forming the electrolyte layer have been proposed.

  Among such electrolytic capacitors, the solid electrolytic capacitor uses a solid electrolyte having conductivity, and polyethylenedioxythiophene (PEDT) which is a conductive polymer is used (for example, Patent Document 1). reference).

In recent years, digitalization has progressed in various electronic devices, and solid electrolytic capacitors are required to have low impedance, large capacity, and small size in a high frequency region.
Various efforts have been made to satisfy such demands. For example, an anode foil and a cathode foil are wound through a separator, and a conductive polymer is held in the separator to form a wound aluminum solid electrolyte. Capacitors are being considered. Such a winding type has an advantage that a wide electrode area can be secured.
JP 2001-189242 A

In addition, solid electrolytic capacitors have been developed for vehicles and the like, and the demand for higher withstand voltage is increasing accordingly. In general, in order to improve the withstand voltage, a method of increasing the formation voltage with respect to the anode is used.
On the other hand, to reduce the impedance, it has been studied to reduce the density by performing a heat treatment on the separator. However, when such a reduction in density is achieved, loosening of the element occurs.
For this reason, even if the formation voltage is increased, there is a problem that the occurrence rate of short puncture in the aging process is increased and the yield is lowered.

  Here, in order to increase the withstand voltage, it is possible to use a separator made of acrylic fiber with little change in the shape of the fiber due to heat treatment, but in the case of a separator made of acrylic fiber, the density is reduced even if heat treatment is performed. Therefore, there is a problem that ESR (equivalent series resistance) is high as compared with the case where a separator made of cellulose fiber is used.

  Further, in the solid electrolytic capacitor, since the conductive polymer itself has no chemical conversion ability, there is a problem that the leakage current increases as the operating voltage increases.

  In view of the above problems, an object of the present invention is to provide a method for producing a solid electrolytic capacitor having good withstand voltage characteristics, low ESR, and low leakage current.

In order to solve the above problems, in the present invention, an element forming step of winding a formed anode foil and a cathode foil through a separator, and a conductive polymer forming step of holding a conductive polymer in the separator The separator is a non-woven fabric including cellulose fibers, 20 to 40 wt% acrylic fibers, and 10 to 30 wt% binder, and the binder has chemical conversion ability. It is made of an oxygen-containing compound, and is characterized in that heat treatment is performed by heating the capacitor element under a condition that the temperature exceeds 200 ° C. after the element forming step and before the conductive polymer forming step.

In the solid electrolytic capacitor according to the present invention, since a separator in which cellulose fibers and synthetic fibers are mixed is used, a high withstand voltage can be ensured even when a low ESR is achieved by heat treatment.
That is, when heat treatment at a temperature exceeding 200 ° C. is performed on the capacitor element, the fiber diameter of the cellulose fibers is reduced, and as a result, the separator gap is widened, resulting in a decrease in the resistance value of the separator itself.
Further, when the gap of the separator is widened by the heat treatment, the amount of conductive polymer retained increases, so that the ESR of the solid electrolytic capacitor can be reduced.
Further, synthetic fibers are mixed in the separator, and the synthetic fibers have a small shape change due to heat treatment. For this reason, even when the gap of the separator is expanded by the heat treatment, the synthetic fiber maintains the shape of the separator, so that the withstand voltage of the solid electrolytic capacitor is high.
Furthermore, since the binder used for the separator is made of an oxygen-containing compound having chemical conversion ability, the oxide film formed as a dielectric on the anode foil can be repaired, so that the leakage current is low.

In the present invention, before Symbol binder, such as polyvinyl alcohol or polyethylene glycol. In the present invention, the binder is preferably polyvinyl alcohol.

  In the present invention, polyaniline or a derivative thereof, polypyrrole or a derivative thereof, or polythiophene or a derivative thereof (polymerized film) can be used as the conductive polymer.

In the solid electrolytic capacitor according to the present invention, since a separator in which cellulose fibers and synthetic fibers are mixed is used, a high withstand voltage can be ensured even when a low ESR is achieved by heat treatment.
That is, if the capacitor element is heat-treated at a temperature exceeding 200 ° C., the fiber diameter of the cellulose fiber becomes thin, and the resistance value of the separator itself decreases.
Further, when the gap of the separator is widened by the heat treatment, the amount of conductive polymer retained increases, so that the ESR of the solid electrolytic capacitor can be reduced.
In addition, even when the gap of the separator is widened by the heat treatment, the synthetic fiber maintains the shape of the separator, so that the withstand voltage of the solid electrolytic capacitor is high.
Furthermore, since the binder used for the separator is made of an oxygen-containing compound having chemical conversion ability, the oxide film formed as a dielectric on the anode foil can be repaired, so that the leakage current is low.

  Hereinafter, the structure of the solid electrolytic capacitor according to the present invention will be described with reference to FIG. 1 while explaining the method of manufacturing the solid electrolytic capacitor to which the present invention is applied.

FIG. 1 is an explanatory diagram of a capacitor element used in a solid electrolytic capacitor to which the present invention is applied. In order to manufacture the solid electrolytic capacitor according to the present invention, first, a capacitor element 4 as shown in FIG. 1 is prepared in an element forming step.
The capacitor element 4 has a structure in which an anode foil 1 and a cathode foil 3 are wound via a separator 2.
From the anode foil 1 and the cathode foil 3, the anode lead wire 5 and the cathode lead wire 6 are led out from the end face of the capacitor element 4 through the resin-coated anode lead tab and cathode lead tab, respectively.
The anode foil 1 is formed by roughening a foil made of a valve metal such as aluminum by etching and then forming an oxide film by chemical conversion.

In this embodiment, the separator 2 is a nonwoven fabric provided with cellulose fibers, 20 to 40 wt% synthetic fibers, and 10 to 30 wt% binder. In this embodiment, acrylic fiber, nylon fiber, or polyester fiber is used as the synthetic fiber.
Moreover, the binder has connected the cellulose fiber and the synthetic fiber by melting and solidifying. In this embodiment, an oxygen-containing compound having a chemical conversion ability, such as polyvinyl alcohol or polyethylene glycol, is used as the binder.

Next, the capacitor element 4 is cut and cleaned. Thereby, a dielectric oxide film is formed on the cut end face of the anode foil 1. In addition, the cut formation may be performed after the heat treatment step, or may be performed both before and after the heat treatment step.
The temperature of the chemical conversion liquid is desirably 80 ° C. or lower so that the separator binder does not elute into the chemical conversion liquid.

  Next, in the heat treatment step, the capacitor element 4 is heat treated under a temperature condition exceeding 200 ° C. Here, the temperature condition is preferably a condition exceeding 300 ° C.

Next, in the conductive polymer forming step, a conductive polymer is formed on the capacitor element 4. In order to form such a conductive polymer, polythiophene or a derivative thereof, polyaniline or a derivative thereof, or polypyrrole or a derivative thereof is chemically polymerized.
As the polythiophene derivative, a thiophene derivative having at least one of a hydroxyl group, an acetyl group, a carboxyl group, an alkyl group, and an alkoxy group as a substituent at the 3-position, 3-position and 4-position, or S-position of the thiophene skeleton, or 3, 4-Alkylenedioxythiophene can be mentioned.
Examples of the polyaniline derivative include an aniline derivative having an aniline skeleton and having at least one of a alkyl group, a phenyl group, an alkoxy group, an ester group, and a thioether group as a substituent.
Examples of the polypyrrole derivative include a pyrrole derivative having at least one of a hydroxyl group, an acetyl group, a carboxyl group, an alkyl group, and an alkoxy group as a substituent at the 3-position, 3-position, 4-position or N-position of the pyrrole skeleton. it can.

  Here, when polythiophene or a derivative thereof, polyaniline or a derivative thereof, polypyrrole or a derivative thereof is chemically polymerized by a method described below, a conductive polymer is formed. In forming a conductive polymer, electrolytic polymerization may be combined.

  First, in the one-component method, a capacitor element is impregnated with a solution in which a monomer, a dopant and an oxidizing agent are mixed, or a solution in which a monomer and a dopant having an oxidizing action are mixed, and chemical polymerization is performed in this state.

Next, in the two-component method, a capacitor solution is impregnated in a capacitor element, and subsequently, a mixed solution of a dopant and an oxidizing agent is impregnated in the capacitor element and chemically polymerized.
Alternatively, the capacitor element may be impregnated with a solution in which a monomer and a dopant are mixed, and then the capacitor element may be impregnated with a mixed solution of a monomer and an oxidant and chemically polymerized.
Furthermore, the capacitor element may be impregnated with the monomer solution, and then the capacitor element may be impregnated with a liquid obtained by mixing the dopant and the oxidizing agent and chemically polymerized.
Furthermore, the capacitor element may be impregnated with a solution in which a dopant and an oxidizing agent are mixed, and then the monomer solution may be impregnated with the capacitor element and chemically polymerized.

  Next, in the three-component method, a capacitor element is impregnated with a liquid containing a dopant, subsequently, a monomer liquid is impregnated into the capacitor element, and finally, a liquid containing an oxidizing agent is impregnated into the capacitor element, and chemical polymerization is performed. Let it be done.

  In the present invention, the dopant is not particularly limited, but a sulfonic acid compound is preferable in order to obtain a solid electrolytic capacitor having good characteristics. For example, 1,5-naphthalenedisulfonic acid, 1,6-naphthalenedisulfonic acid, 1-octanesulfonic acid, 1-naphthalenesulfonic acid, 2-naphthalenesulfonic acid, 2,6-naphthalenedisulfonic acid, 2,7-naphthalenedisulfonic acid Acid, 2-methyl-5-isopropylbenzenesulfonic acid, 4-octylbenzenesulfonic acid, 4-nitrotoluene-2-sulfonic acid, m-nitrobenzenesulfonic acid, n-octylsulfonic acid, n-butanesulfonic acid, n-hexane Sulfonic acid, o-nitrobenzenesulfonic acid, p-ethylbenzenesulfonic acid, p-chlorobenzenesulfonic acid, p-decylbenzenesulfonic acid, p-dodecylbenzenesulfonic acid, p-toluenesulfonic acid, p-nitrobenzenesulfonic acid, p-pentyl Benzenesulfonic acid Ethanesulfonic acid, camphorsulfonic acid, dinonylnaphthalenesulfonic acid, acetylsulfonic acid, dodecylsulfonic acid, trichlorobenzenesulfonic acid, trifluoromethanesulfonic acid, hydroxybenzenesulfonic acid, butylnaphthalenesulfonic acid, benzenesulfonic acid, polyvinylsulfonic acid , Methanesulfonic acid, etc., and the salts include lithium salt, potassium salt, sodium salt, silver salt, copper salt, iron salt, aluminum salt, cerium salt, tungsten salt, chromium salt, manganese salt, tin salt, methyl Ammonium salt, dimethylammonium salt, trimethylammonium salt, tetramethylammonium salt, ethylammonium salt, diethylammonium salt, triethylammonium salt, tetraethylammonium salt, ethylmethylan Nium salt, diethylmethylammonium salt, dimethylethylammonium salt, triethylmethylammonium salt, trimethylethylammonium salt, diethyldimethylammonium salt, propylammonium salt, dipropylammonium salt, isopropylammonium salt, diisopropylammonium salt, butylammonium salt, dibutyl Ammonium salt, methylpropylammonium salt, ethylpropylammonium salt, methylisopropylammonium salt, ethylisopropylammonium salt, methylbutylammonium salt, ethylbutylammonium salt, tetramethylolammonium salt, tetra-n-butylammonium salt, tetra-sec- Butyl ammonium salt, tetra-t-butyl ammonium salt, piperidinium salt, pyrrolidi Umum salts, monoforinium salts, piperazinium salts, pyridinium salts, α-picolinium salts, β-picolinium salts, γ-picolinium salts, quinolinium salts, isoquinolinium salts, pyrrolinium salts, ammonium salts, and the like.

  Thereafter, the capacitor element 4 is housed in a bottomed cylindrical outer case, the opening is sealed with a sealing rubber or the like, and then subjected to aging, whereby a solid electrolytic capacitor is obtained. In aging, for example, a rated voltage is applied for 60 minutes under the condition of a temperature of 50 ° C.

[Example]
In the solid electrolytic capacitor (aluminum solid electrolytic capacitor) according to the example of the present invention, a density of 0.35 g / cm ³ obtained by mixing 50 wt% of Manila fiber (cellulose fiber), 30 wt% of acrylic fiber and 20 wt% of polyvinyl alcohol (binder), Using the separator 2 having a thickness of 30 μm, a solid electrolytic capacitor was produced as follows.

First, in an element formation step, an anode foil 1 for an electrolytic capacitor whose surface is etched and formed and a cathode foil 3 for an electrolytic capacitor whose surface is etched are wound through a separator 2 to form a capacitor element 4. Form.
In this capacitor element 4, the anode lead wire 5 and the cathode lead wire 6 are drawn from the end face of the capacitor element 4 from the anode foil 1 and the cathode foil 3 through the resin-coated anode lead tab and cathode lead tab, respectively. It is in.
Here, in Examples and Comparative Examples 1 and 2 to be described later, the anode foil and the cathode foil used for producing the capacitor element all have the same width and length, and the width is 2.4 mm and the length is 195 mm. is there.

  Next, the capacitor element 4 is cut and formed using, for example, a 10 wt% ammonium adipate aqueous solution adjusted to pH 6.0 and a temperature of 40 ° C. as a chemical conversion solution. In addition, the cut formation may be performed after the heat treatment step, or may be performed both before and after the heat treatment step.

  Next, in the heating step, the capacitor element 4 is heat-treated for 30 minutes at a temperature of 330.degree.

  Next, in the conductive polymer formation step, a solution (monomer) of 3,4-ethylenedioxythiophene as a monomer and iron (III) p-toluenesulfonate as an oxidizing agent / dopant dissolved in i-propanol After immersing the capacitor element in a molar ratio of 1: 1 to the oxidizing agent, the capacitor element is held at a temperature of 100 ° C. for 60 minutes to form polyethylenedioxythiophene (PEDT) as a conductive polymer by chemical polymerization.

  After the capacitor element 4 thus obtained is stored in a bottomed cylindrical outer case, the opening is sealed with a sealing rubber and aged at 50 ° C. and a rated voltage for 60 minutes. Table 1 shows the measurement results of the electrical characteristics of the solid electrolytic capacitor configured as described above.

(Comparative Example 1)
In Comparative Example 1, a solid electrolytic capacitor was manufactured as follows using a separator made of Manila paper having a density of 0.30 g / cm ³ and a thickness of 30 μm. In that case, it was set as the same as the Example except the structure of the separator. Table 1 shows the measurement results of the electrical characteristics of the solid electrolytic capacitor configured as described above.

(Comparative Example 2)
In Comparative Example 2, a solid electrolytic capacitor was produced using a separator made of a nonwoven fabric of acrylic fibers and having a density of 0.35 g / cm ³ and a thickness of 35 μm. In that case, it was set as the same as the Example except the structure of the separator. Table 1 shows the measurement results of the electrical characteristics of the solid electrolytic capacitor configured as described above.

(Evaluation results)
As is clear from Table 1, the solid electrolytic capacitors according to the examples of the present invention have a higher yield than Comparative Examples 1 and 2. Compared with Comparative Examples 1 and 2, the solid electrolytic capacitor according to the example of the present invention has low ESR and low leakage current.

(Other examples)
In the above examples, polyvinyl alcohol was used as the oxygen-containing compound (binder) having chemical conversion ability, but it was confirmed that the same effect can be obtained when polyethylene glycol is used instead of polyvinyl alcohol. .
In the examples, acrylic fiber was used as the synthetic fiber, but it was confirmed that the same effect could be obtained even when nylon fiber or polyester fiber was used.

  In the above-described embodiments, PEDT is used as the conductive polymer. However, when a known conductive polymer other than PEDT (for example, polyaniline or polypyrrole) is used as the conductive polymer, the same effect can be obtained. It was confirmed that it was obtained.

  In addition, when the heat processing temperature before superposition | polymerization is 200 degrees C or less, since there is little shape change of the cellulose fiber by heat processing, the effect of low ESR reduction is few. Therefore, a temperature exceeding 200 ° C. is preferred. In particular, when the temperature is 300 ° C. or higher, the cellulose fibers become carbon fibers, which is more preferable.

It is explanatory drawing of the capacitor | condenser element used for the solid electrolytic capacitor of this invention.

Explanation of symbols

1 Anode foil 2 Separator 3 Cathode foil 4 Capacitor element 5 Anode lead bar 6 Cathode lead bar

Claims (3)

In a method for producing a solid electrolytic capacitor, comprising an element forming step of winding a formed anode foil and a cathode foil through a separator, and a conductive polymer forming step of holding a conductive polymer in the separator,
The separator is a nonwoven fabric containing cellulose fibers, 20 to 40 wt% acrylic fibers, and 10 to 30 wt% binder, and the binder is made of an oxygen-containing compound having chemical conversion ability,
A method for manufacturing a solid electrolytic capacitor, comprising performing heat treatment for heating the capacitor element under a condition that the temperature exceeds 200 ° C. after the element forming step and before the conductive polymer forming step.   The method for manufacturing a solid electrolytic capacitor according to claim 1, wherein the binder is polyvinyl alcohol or polyethylene glycol.   The method for producing a solid electrolytic capacitor according to claim 1, wherein the conductive polymer is polyaniline or a derivative thereof, polypyrrole or a derivative thereof, or polythiophene or a derivative thereof.

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