JP2008047783A - Solid electrolytic capacitor and manufacturing method thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To restrain a leakage current in a solid electrolytic capacitor from lowering. <P>SOLUTION: A capacitor element is manufactured, which is yielded by winding an anode foil on the surface of which an anode oxidation coated film is formed and a cathode foil, via a separator containing any of chemically conversible compounds such as polyvinyl alcohol, polyethylene glycol, and starch. The compound of the separator is melted by heating the capacitor element to bring the separator and the anode foil into close contact. The capacitor element is impregnated with an oxidant and a monomer. A solid electrolyte consisting of PEDT is formed on the separator by chemical polymerization. Aging is performed by applying voltage to the anode foil and the cathode foil. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a solid electrolytic capacitor having a solid electrolyte made of a conductive polymer and a method for manufacturing the solid electrolytic capacitor.

A capacitor element of an electrolytic capacitor has an anode body (anode foil or sintered body) in which a large number of etching pits and fine holes made of a valve metal such as aluminum, tantalum, or niobium are formed. An oxide film serving as a dielectric is formed on the surface of the anode body, and electrodes are drawn from the oxide film.
Specifically, the electrolyte is in contact with the oxide film, and this electrolyte functions as a true cathode that draws 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 conventionally proposed.

  Among them, the solid electrolytic capacitor is an electrolytic capacitor in which a solid electrolyte having conductivity is used, and has excellent impedance characteristics in a high frequency region as compared with a liquid electrolyte. As the solid electrolyte, polyethylenedioxythiophene (PEDT), which is a conductive polymer, is widely used.

In addition, with the digitization, there is an increasing demand for increasing the capacity and miniaturization of capacitors. As a capacitor that can meet these requirements, there is a wound solid electrolytic capacitor.
The capacitor element of this winding type solid electrolytic capacitor has an anode foil and a cathode foil each having an anodized film formed on the surface thereof wound around a separator, and the separator holds a solid electrolyte made of a conductive polymer. Therefore, it is possible to secure a wide electrode area (for example, see Patent Document 1).

JP 2001-189242 A

The electrolytic capacitor using the conventional electrolytic solution has a high chemical conversion ability because the electrolytic solution contains a compound having a chemical conversion ability (capability of forming an oxide film on the surface of the anode foil) such as carboxylic acid. Yes. For this reason, by performing aging in a manufacturing process, an oxide film is repaired and a leakage current can be reduced.
On the other hand, the above-mentioned solid electrolytic capacitor has poor chemical conversion ability because the polymer, dopant, oxidant, etc. contained in the solid electrolyte have no chemical conversion ability, and leakage current is reduced even if aging is performed in the manufacturing process. There was a problem that the yield was worse.

Therefore, in order to solve the above problem, it is conceivable that a compound having a chemical conversion ability represented by carboxylic acid is dissolved in a solution such as an oxidant solution or a monomer solution and contained in the capacitor element.
However, in the above method, since the carboxylic acid and the alcohol that is the solvent of each solution cause an esterification reaction and oxygen necessary for the formation is lost, it is difficult to improve the formation ability.

  The objective of this invention is providing the manufacturing method of the solid electrolytic capacitor which can reduce a leakage current, and a solid electrolytic capacitor.

  The solid electrolytic capacitor of the present invention is a solid electrolytic capacitor in which a conductive polymer is formed on a capacitor element in which an anode foil and a cathode foil each having an anodized film formed on a surface thereof are wound through a separator. The separator is adhered to the anode foil by heat treatment and contains a compound having a chemical conversion ability.

  In the present invention, the compound may be an oxygen-containing compound, or any of polyvinyl alcohol, polyethylene glycol, and starch.

  Furthermore, in the present invention, the conductive polymer may be any one of polyaniline, polypyrrole, polythiophene, polyethylenedioxythiophene, and derivatives thereof.

  The method for producing a solid electrolytic capacitor of the present invention, in which a conductive polymer is formed on a capacitor element in which an anode foil and a cathode foil having an anodized film formed on a surface thereof are wound through a separator, A capacitor element manufacturing step of winding a separator containing a capable compound to manufacture a capacitor element, and a heat treatment step of melting the compound and heating the capacitor element so that the separator and the anode foil are in close contact with each other It is characterized by having.

  At this time, in the heat treatment step, the temperature at which the capacitor element is heated is preferably 200 to 330 ° C.

  According to the present invention, when the heat treatment is performed, the compound contained in the separator causes the separator and the anode foil to adhere to each other. Can be high. For this reason, when aging is performed, the oxide film is efficiently repaired, and the leakage current can be reduced.

Embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is an external view of a capacitor element included in the wound solid electrolytic capacitor of the present embodiment. FIG. 2 is a schematic cross-sectional view of the capacitor element 1.
As shown in FIG. 1, the capacitor element 1 has an anode foil 2 and a cathode foil 3, and the anode foil 2 and the cathode foil 3 are wound via a separator 4. .

The anode foil 2 is made of a valve metal such as aluminum. The surface of the anode foil 2 is roughened by a process such as etching or vapor deposition, and an oxide film 2a is formed by anodic oxidation (chemical conversion).
Similarly to the anode foil 2, the cathode foil 3 is made of aluminum or the like, and its surface is roughened and a natural oxide film 3a is formed.

The separator 4 is a cellulose separator containing polyvinyl alcohol which is a compound having chemical conversion ability, and the dissolved polyvinyl alcohol brings the separator 4 and the oxide film 2 a of the anode foil 2 into close contact with each other.
A solid electrolyte 5 made of a conductive polymer is held on both surfaces of the separator 4. That is, the solid electrolyte 5 is sandwiched between the anode foil 2 and the cathode foil 3 and the separator 4. As the conductive polymer constituting the solid electrolyte 5, polyaniline, polypyrrole, polythiophene, polyethylenedioxythiophene (PEDT) or a derivative thereof can be used, and these are generated by chemical polymerization of monomers.
Furthermore, lead tabs are connected to the anode foil 2 and the cathode foil 3, and lead wires 6 are drawn from the anode foil 2 and the cathode foil 3 through the lead tabs.

Next, a method for manufacturing a solid electrolytic capacitor will be described with reference to FIGS.
FIG. 3 is a process diagram showing a method for manufacturing a solid electrolytic capacitor.
As shown in FIG. 3, first, in order to increase the effective surface area of the electrode, the surfaces of the anode foil 2 and the cathode foil 3 are subjected to etching treatment to be roughened.
Further, the surface of the roughened anode foil 2 is subjected to chemical conversion treatment to form an oxide film 2a, and the natural oxide film 3a is formed on the surface of the cathode foil 3 by water resistance treatment and / or heat treatment. Then, after the anode foil 2 and the cathode foil 3 on which the oxide films 2a and 3a are formed are cut into predetermined dimensions, the lead wire 6 is connected to each through a lead tab, and the anode foil 2 and the cathode foil 3 are connected to each other. The cylindrical capacitor element 1 is manufactured through winding through the separator 4 and further through cut formation and, if necessary, carbonization of the separator 4 (capacitor element manufacturing process).

  And the capacitor | condenser element 1 is heated so that polyvinyl alcohol melt | dissolves and the oxide film 2a of the anode foil 2 and the separator 4 contact | adhere (heat treatment process).

Further, the capacitor element 1 is immersed in an i-propanol solution of p-toluenesulfonic acid iron (III) (hereinafter referred to as PTS), which is an oxidizing agent (molar ratio of PTS and i-propanol, 1: 1) for 30 seconds, and the oxidizing agent is added. Impregnate.
Thereafter, the mixture is heated at 150 ° C. for 10 minutes to remove i-propanol.
Further, the capacitor element 1 is immersed in an ethanol solution of 3,4-ethylenedioxythiophene as a monomer (molar ratio of 3,4-ethylenedioxythiophene and ethanol 1: 3) to impregnate the monomer.
The capacitor element 1 impregnated with the oxidizing agent and the monomer is heated at 100 ° C. for 60 minutes to perform chemical polymerization. Thereby, a solid electrolyte 5 made of a conductive polymer is formed between the anode foil 2 and the cathode foil 3 and the separator 4.

  Next, a solid electrolytic capacitor is assembled. That is, the cylindrical capacitor element 1 obtained by the process described above is housed in a bottomed cylindrical outer case and the opening is sealed with a sealing rubber or the like. Finally, aging is performed at 100 ° C. and rated voltage for 60 minutes to complete the manufacturing process.

Next, electrical characteristics of specific examples according to the present invention will be described in comparison with comparative examples.
In addition, although the Example and comparative example which are demonstrated below differ in the material of the separator 4, and the conditions of the heat treatment process for making anode foil 2 and the separator 4 contact | adhere, all other processes are the same. .
Hereinafter, only the material of the separator and the conditions of the heat treatment process in each example and each comparative example will be described in order.

[Example 1]
In the solid electrolytic capacitor of Example 1 of the present invention, a cellulose separator containing 20 wt% polyvinyl alcohol is used as the separator. Then, the capacitor element was heat-treated at 250 ° C. for 30 minutes.

[Example 2]
In the solid electrolytic capacitor of Example 2 of the present invention, a cellulose separator containing 20 wt% polyvinyl alcohol is used as the separator. And it heat-processed on 200 degreeC and the conditions for 30 minutes with respect to the capacitor | condenser element.

(Comparative Example 1)
In the solid electrolytic capacitor of Comparative Example 1, a separator made only of cellulose was used. Then, the capacitor element was heat-treated at 250 ° C. for 30 minutes.

(Comparative Example 2)
In the solid electrolytic capacitor of Comparative Example 2, a cellulose separator containing 20 wt% polyvinyl alcohol is used as the separator. Note that no heat treatment was performed on the capacitor element.

[Example 3]
In the solid electrolytic capacitor of Example 3, a cellulose separator containing 20 wt% polyvinyl alcohol is used as the separator. Then, the capacitor element was heat-treated at 190 ° C. for 30 minutes.

[Example 4]
In the solid electrolytic capacitor of Example 4, a cellulose separator containing 20 wt% polyvinyl alcohol is used as the separator. And it heat-processed on 330 degreeC and the conditions for 30 minutes with respect to the capacitor | condenser element.

[Example 5]
In the solid electrolytic capacitor of Example 5, a cellulose separator containing 20 wt% polyvinyl alcohol is used as the separator. Then, the capacitor element was heat-treated at 350 ° C. for 30 minutes.

  In the above Examples 1 to 5 and Comparative Examples 1 and 2, the anode electrode foil and the cathode electrode foil used for the capacitor element all have the same width and length, and the width is 5 mm and the length is 125 mm.

  Measure the electrical characteristics (capacitance, tan δ (tangent of loss angle), equivalent series resistance (ESR) and leakage current) of Examples 1 to 5 and Comparative Examples 1 and 2, and calculate the yield. did. The results are shown in Table 1.

As is clear from Table 1, the solid electrolytic capacitors of the present invention according to Examples 1 and 2 show a lower leakage current value than those of Comparative Examples 1 to 4. That is, the formation capacity of the solid electrolytic capacitor is high.
Moreover, it was confirmed that even if the polyvinyl alcohol contained in the separator was melted, the electrostatic capacity, tan δ, and ESR were not affected.

  In the above examples, polyvinyl alcohol was used as the compound having chemical conversion ability. However, it was confirmed that the same effect can be obtained when any of polyethylene glycol, starch, and oxygen-containing compound is used. It was.

  Furthermore, in the above embodiment, PEDT was used as a solid electrolyte, but the same applies when a known conductive polymer other than PEDT (for example, polyaniline, polypyrrole, polythiophene, or a derivative thereof) is used as the solid electrolyte. It was confirmed that the effect of can be obtained.

  As described above, according to the present invention, when the heat treatment is performed, the separator 4 and the anode foil 2 are in close contact with each other, so that the oxygen of the chemical contained in the separator 4 is surely brought into contact with the oxide film 2a. The conversion capacity of the capacitor 1 is increased. Thereby, when aging is performed, the oxide film 2a is efficiently restored, and a decrease in leakage current can be suppressed.

Moreover, the fall of a leakage current can be reliably suppressed by making the heating temperature in a heat treatment process 200-330 degreeC (Example 1, 2, 4).
When the heating temperature is 190 ° C., the effect of improving the leakage current is small (Example 3). At 350 ° C., the capacitance decreases, tan δ increases, and ESR tends to increase (Example). 5).

  In the above embodiment, the wound type solid electrolytic capacitor has been described. However, the present invention is also applicable to solid electrolytic capacitors having other shapes.

It is a schematic perspective view of the capacitor | condenser element which the solid electrolytic capacitor which concerns on embodiment of this invention has. It is sectional drawing which shows typically the laminated structure of the capacitor | condenser element shown in FIG. It is a figure which shows the manufacturing process flow of the solid electrolytic capacitor which has a capacitor | condenser element shown in FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Capacitor element 2 Anode foil 2a Oxide film 3 Cathode foil 3a Natural oxide film 4 Separator 5 Solid electrolyte 6 Lead wire

Claims (6)

In a solid electrolytic capacitor formed by forming a conductive polymer on a capacitor element in which an anode foil and a cathode foil having an anodized film formed on a surface are wound through a separator,
A solid electrolytic capacitor, wherein the separator is in close contact with the anode foil by heat treatment and contains a compound having a chemical conversion ability.   The solid electrolytic capacitor according to claim 1, wherein the compound is an oxygen-containing compound.   The solid electrolytic capacitor according to claim 1, wherein the compound is any one of polyvinyl alcohol, polyethylene glycol, and starch.   The solid electrolytic capacitor according to claim 1, wherein the conductive polymer is any one of polyaniline, polypyrrole, polythiophene, polyethylenedioxythiophene, and derivatives thereof. In a method for producing a solid electrolytic capacitor in which a conductive polymer is formed on a capacitor element in which an anode foil and a cathode foil having an anodized film formed on a surface are wound through a separator,
A capacitor element manufacturing process for winding a separator containing a compound having a chemical conversion ability to manufacture a capacitor element;
A method for producing a solid electrolytic capacitor, comprising: a heat treatment step of heating the capacitor element so that the compound is melted and the separator and the anode foil are in close contact with each other.   The method for manufacturing a solid electrolytic capacitor according to claim 5, wherein, in the heat treatment step, a temperature for heating the capacitor element is 200 to 330 ° C.

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