JP2832730B2 - Electrolytic capacitor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial applications]

The present invention relates to an electrolytic capacitor using a capacitor element having a separator interposed between electrodes, and more particularly to a dry electrolytic capacitor having an improved separator.

2. Description of the Related Art A dry electrolytic capacitor uses a so-called valve metal having an insulating oxide film layer formed on its surface, such as aluminum, tantalum, niobium, and titanium, as an anode. An insulating oxide film layer serving as a dielectric layer is formed. Further, a cathode is arranged to face the anode, and a separator made of a material such as various kinds of paper and a porous resin sheet is arranged between the anode and the cathode. The separator holds the electrolyte,
A capacitor element is configured. FIG. 1 is a partial exploded view showing the structure of the capacitor element 1. FIG. As shown in the figure, a strip-shaped anode foil 2 having a surface on which a dielectric oxide film is formed by anodizing treatment, and a strip-shaped cathode foil 3 having substantially the same width as the anode foil 2 are formed by the electrolytic foils 2 and 3. It is superimposed via two separators 4 which are also cut into a strip with a slightly wide width, and wound from one end to form a cylindrical capacitor element 1. A narrow anode lead 5 for obtaining an electrical connection with the outside is connected to a predetermined position of the anode foil 2 by means such as welding or pressure welding, and a similar cathode lead 6 is connected to the cathode foil 3. And has a structure drawn out from the upper end face of the capacitor element 1. The capacitor element 1 is impregnated with an electrolytic solution, housed in an outer case (not shown), and the opening of the outer case is sealed with a sealing member. The electrolytic solution is prepared by dissolving various inorganic acids, organic acids or salts thereof in various solvents including polyhydric alcohols and acid amides, and blending additives according to the purpose of use. In addition to functioning as a true cathode by directly contacting the dielectric oxide film layer on the surface, it also acts on defective or deteriorated parts of the dielectric oxide film, causing anodizing reaction to repair the oxide film. Have both. Thus, an electrode arranged as a cathode acts as a collector rather than a cathode. Due to the nature of the electrolyte, it is necessary that a sufficient amount of the electrolyte contact the anode electrode and the cathode electrode in order to maintain a sufficient conductivity and a film repairing function. However, when the electrolyte is excessive, the electrolyte adheres to the lead portion of the capacitor element and the like,
In some cases, the leakage current may increase, or an accident may occur in which the electrolyte leaks from the sealed container housing the capacitor element. The separator has a function of preventing the above-described inconvenience, and is used to hold a sufficient amount of electrolyte between the anode and the cathode. The separator also has a role of preventing a short circuit accident due to direct contact between the anode and the cathode. In order to match such a function, the separator is
It is required to have a large electrolyte holding amount per unit volume (or area), and to have a low-resistance structure with a high degree of porosity in order to sufficiently achieve ionic conduction by the electrolyte. For this reason, if the density and voids of the separator itself are increased, a short circuit between the electrodes will increase, the pressure resistance will be insufficient, and the holding amount of the electrolyte may decrease. The choice of components and density is quite difficult.

[Problems to be solved by the invention]

Incidentally, recent electrolytic capacitors are required to maintain stable characteristics for a long period of time. One of the main factors that determine the life characteristics of an electrolytic capacitor is the remaining amount of the internal electrolytic solution. Electrolytic capacitors are highly sealed in order to retain the electrolyte in the outer container for a long time.However, in long-term use, the electrolyte gradually evaporates due to an increase in internal pressure or deterioration of the sealed structure. Inevitably, when the amount of the electrolytic solution decreases, deterioration such as a decrease in capacitance and an increase in loss occurs. As separators used in conventional electrolytic capacitors, those made of kraft or Manila hemp fibers are widely used. Kraft paper can be made of inexpensive and strong paper, but has the drawback that the current path of the electrolyte solution becomes longer due to the flatness of the fibers and the resistance increases. Manila hemp paper has a smaller fiber flatness than kraft paper, and the current path is shorter than the former, which is advantageous in terms of resistance but is expensive. Recently, attempts have been made to use fibers of synthetic resins such as polyolefins. Since these synthetic resin fibers can be formed into a substantially circular cross section, the current path is shortened and the resistance is reduced. However, since the surface of the fiber is flat in any of such conventional separator materials, the electrolyte is not taken into the fiber, and the state of adhesion of the electrolyte to the fiber surface is not sufficient. Mainly, the holding of the electrolytic solution is carried out by the surface tension at the intersection of the fibers or in the narrow gap between the adjacent fibers. For this reason, existing separators cannot hold a sufficient amount of electrolyte to obtain a long-life electrolytic capacitor, and improvements have been desired. Also, if the electrolytic solution is included in the capacitor element in an amount larger than the separator can hold, the excess electrolytic solution flows out of the capacitor element into the outer case and adheres to the terminals to increase the leakage current. Or it may cause a liquid leakage accident to the outside.

[Means for Solving the Problems]

The present invention relates to an electrolytic capacitor having an improved separator suitable for obtaining long-term stable characteristics. That is, the present invention relates to a capacitor element comprising an anode electrode having a surface formed with an inducer oxide film layer, a cathode electrode arranged opposite to the anode electrode, and a separator interposed between the electrodes while being held by an electrolytic solution. Wherein the separator is made of a nonwoven fabric or a woven fabric partially or wholly including hollow fibers having through holes on the side surfaces. The hollow fiber has a structure in which the inside of the fiber is hollow,
Known materials include polyester fibers. The hollow fiber is produced by a polymerization reaction of polyester in the presence of a polymerization catalyst such as an antimony compound.
In order to form a hollow structure, molten polyester is discharged from a divided annular nozzle 10 as shown in FIG. 2, and the polyester discharged from adjacent nozzles 10 is melted before solidification. To form a hollow polyester color. Generally, when a hollow fiber is used for a textile product such as clothing, if so-called hollow tearing occurs on the side of the hollow fiber, its feeling and gloss decrease, so that the side is torn, that is, to prevent the formation of through holes. The opening area of the divided end of the base nozzle 10 is increased to ensure the fusion of the polyester at the discharge end.However, in the case of a separator, the conductivity of the electrolytic solution is increased to reduce the resistance. In order to reduce the number of holes, it is preferable that many through holes such as cracks are formed on the side surface of the hollow fiber. Therefore, the base nozzle 10 may be of a normal divided form as shown in FIG. FIG. 3 is a perspective view showing a hollow fiber used in the present invention. The hollow fiber 11 made of polyester or the like has a substantially circular cross section and a hollow portion 12 formed therein. A crack-shaped through-hole 13 is formed on the side surface of the hollow fiber 11 so that the internal cavity 12 and the outside communicate with each other. The hollow fiber that can be used in the present invention is not limited to polyester, and is at least stable to an electrolytic solution,
Other polymers may be used as long as they can be formed into hollow fibers. Also, the formation of through holes on the side surface is not based on the shape of the nozzle 10 described above, but rather is performed by selectively dissolving and removing the surface of the hollow fiber or by cracking the surface by physical means such as rapid thermal stress during the solidification process. It is also possible to use various means such as forming a through hole in a shape.

[Action]

According to the present invention, since the fiber surface constituting the separator is formed of hollow fibers having through holes on the side surfaces, when impregnated with the electrolyte, the electrolyte penetrates and is held in the internal space of the hollow fibers, and the electrolyte is Communication can be maintained with the outer surface through the through hole in the side surface. For this reason, the wettability of the surface of the middle fiber is also improved, and the amount of the electrolytic solution attached to the outside of the hollow fiber is also increased. As a result, when viewed in unit volume (or per area), the amount of electrolyte retained in the separator increases, and the value differs depending on the fiber diameter of the hollow fiber and the occupied cross-sectional area of the hollow part. It can hold approximately twice or several times the amount of electrolyte.

【Example】

Hereinafter, the present invention will be described based on examples. First, the following was prepared as a separator used in the present invention. The hollow fiber shown in FIG. 3 was used as the fiber. The component of the hollow fiber was polyester, the average fiber diameter was 10 μm, and the diameter of the hollow portion inside was formed to be approximately circular.
μm. Also, since the hollow fiber is formed by the four-part nozzle, a through hole is formed discontinuously on the side surface of the hollow fiber. This hollow fiber was used as a whole, or a blend of manila hemp fibers was mixed with the hollow fiber at a fixed mixing ratio to prepare a 50 μm-thick nonwoven fabric separator. As a comparative example, a 50 μm-thick separator composed of only Manila hemp fiber was prepared. The cross section of the Manila hemp fiber has a flattened shape, the average of the minor axis is about 4 μm, the average of the major axis is about 8 μm, and the flattening ratio is about 1:
2 In order to compare the electrolytic solution holding capacity of these separators, the same electrolytic solution was impregnated into the separators, and the amount of retained electrolytic solution per predetermined area was examined. For the measurement of the retained amount, only the band-shaped separator was wound into a cylindrical shape, and this was impregnated with an electrolytic solution (ethylene glycol-ammonium adipate-based electrolytic solution), and this was centrifuged (rotational speed 100 times / minute). Centrifuged for 5 seconds to disassemble, cut the middle part of the separator into a predetermined area (10 cm ² ), weigh it with a precision balance,
The weight of the separator itself measured in a dry state in advance is reduced. Table 1 shows the composition (hollow fiber content) of the prepared separator and the measurement results of the retained electrolyte amount. As can be seen from this table, it can be seen that the separator of this example has an increased amount of retained electrolyte per unit area as compared with the separator of the comparative Manila hemp fiber. In particular, the separator using only the hollow fibers of Example 4 has approximately twice the amount of the electrolyte retained as compared with the comparative example. Next, those obtained by cutting these separators into strips are referred to as first.
As shown in the figure, a cylindrical capacitor element was wound by winding it together with the electrode foil, impregnated with the electrolytic solution, stored in a metal outer case, and closed by a rubber-sealed sealing plate at the outer case opening. It was a capacitor. This electrolytic capacitor has a rated voltage of 25 V and a capacitance of 2200
μF. The initial electrical characteristics (capacitance, loss, leakage current) of each electrolytic capacitor were as shown in Table 2. According to this result, the electrical characteristics at the initial stage are not so different in the capacitance and the leakage current, but the loss is small because the fiber cross section of the separator of the present invention is almost circular, and the internal resistance is small. It can be seen that the value is low. Furthermore, a long-term high-temperature load life test was performed by applying a rated voltage (50 V) to these electrolytic capacitors at 105 ° C.
The test examined the rate of change of the capacitance value over time relative to the initial capacitance value and the change of the loss value over time. The result is shown in FIG. FIG. 3A is a graph showing the change rate of the capacitance, and FIG. 3B is a graph showing the change of the loss value. As can be seen from these graphs, since the electrolytic capacitor of the comparative example has a small amount of retained electrolyte inside, the use of the capacitor for a long time significantly reduces the capacitance and increases the loss significantly.
The test was stopped at 0 hours. On the other hand, it can be seen that the electrolytic capacitor of this example has a smaller decrease in capacitance, suppresses a rise in loss, and maintains the electrical characteristics stably for a long period of time as compared with the electrolytic capacitor of the comparative example.

【The invention's effect】

As described above, according to the present invention, the electrolytic solution holding amount of the separator can be increased, and therefore, by using the electrolytic capacitor for a long period of time, a decrease in the capacitance due to a decrease in the internal electrolytic solution, a loss, The deterioration of impedance characteristics is prevented, and a long-life electrolytic capacitor with high reliability can be obtained. In addition, since the separator has a high electrolyte retention capacity, excess electrolyte flows out of the capacitor element into the outer case,
There is no increase in leakage current and no liquid leakage accident. Also, since the separator of the present invention can have a substantially circular fiber cross section, the resistance in the separator is low,
As a result, the loss and impedance characteristics of the electrolytic capacitor are improved.

[Brief description of the drawings]

FIG. 1 is a partial exploded view showing an element structure of an electrolytic capacitor.
FIG. 2 is a diagram showing a cross section of a nozzle used when forming a hollow fiber used in the separator of the present invention,
FIG. 3 is a perspective view showing a hollow fiber used for the separator of the present invention, and FIG. 4 is a graph showing a result of a high-temperature load test of an electrolytic capacitor.
(B) shows a change in the loss value. DESCRIPTION OF SYMBOLS 1 ... Capacitor element 2 ... Anode foil 3 ... Cathode foil 4 ... Separator 5 ... Anode lead, 6 ... Cathode lead 10 ... Base nozzle, 11 ... Hole thread 12 ... Cavity part, 13 ... Through-hole

Claims (1)

(57) [Claims] 1. A capacitor element comprising: an anode electrode having a dielectric oxide film layer formed on a surface thereof; a cathode electrode disposed opposite to the anode electrode; and a separator interposed between the electrodes to hold an electrolytic solution. Wherein the separator is formed of a nonwoven fabric or a woven fabric partially or wholly including a hollow fiber having a through hole on a side surface.