JPH0384916A - Electrolytic capacitor - Google Patents

Abstract

PURPOSE:To prevent a reduction and a loss in a capacitance due to a reduction in an inside electrolyte, to prevent an impedance characteristic from being deteriorated and to obtain an electrostatic capacitor whose reliability is high and whose life is long by a method wherein a separator is formed of a nonwoven fabric or a woven fabric which includes a hollow thread having a through hole on a side face in one part or a whole part. CONSTITUTION:A hollow thread 11 composed of a polyester or the like is formed in such a way that its cross section is nearly circular and that a hollow part 12 is formed at its inside. A crack-shaped through hole 13 is formed in a side face of the hollow thread 11 so that the hollow part 12 at the inside is interlinked with the outside. Consequently, a cellulose constituting a separator 4 is composed of the hollow thread 11 having the through hole 13 in the side face. When it is impregnated with an electrolyte, the electrolyte creeps into and is held at the inside space of the hollow thread and the electrolyte can be interlinked with an outside face through the through hole at the side face. As a result, a solderability on the surface of the hollow thread is enhanced; an adhesion amount of the electrolyte to the outside of the hollow thread is increased.

Description

[Detailed description of the invention] [Industrial application field]

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

[Conventional technology]

Dry electrolytic capacitors use so-called valve metals, such as aluminum, tankard, niobium, and titanium, on which an insulating oxide film layer is formed as the anode, and the surface of this valve metal becomes a dielectric layer by anodizing or other operations. Form an insulating oxide film layer. Furthermore, a cathode is arranged opposite to this anode, and a separator made of various materials such as paper or porous resin sheet is arranged between the anode and the cathode. The separator holds an electrolytic solution and forms a capacitor element. FIG. 1 is a partially exploded view showing the structure of a capacitor element 1. FIG. As shown in the figure, a strip-shaped anode foil 2 on the surface of which a dielectric oxide film is formed by anodizing treatment, and a strip-shaped cathode foil 3 having approximately the same width as the anode foil 2, these electrode foils 2
．． The capacitor element 1 is overlapped with two separators 4 which are similarly cut into strips having a width slightly wider than the capacitor element 3, and is wound from one end to form a cylindrical capacitor element 1. In addition, a narrow anode lead 5 is connected to a predetermined position of the anode foil 2 by means such as welding or pressure welding to obtain an electrical connection with the outside.
A similar cathode foil portion 6 is connected to the cathode foil 3, and has a structure extended from the upper end surface of the capacitor element l. The capacitor element 1 is impregnated with an electrolytic solution and housed in an outer case (not shown), and the opening of the outer case is sealed with a sealing member. Electrolyte solutions are made by dissolving various inorganic acids, organic acids, or their salts in various solvents including polyhydric alcohols and acid amides, and adding additives depending on the purpose of use.
A function that directly contacts the dielectric oxide film layer on the anode surface and functions as a true cathode, and also acts on the defective or deteriorated parts of the dielectric oxide film to cause an anodic oxidation reaction and repair the oxide film. Therefore, the electrode arranged as a cathode serves as a collector rather than a cathode. Due to its nature, the electrolyte needs to come into contact with the anode and cathode electrodes in a sufficient amount in order to maintain sufficient conductivity and film repair function. However, if the electrolyte is in excess,
The electrolyte may adhere to the leads of the capacitor element, leading to an increase in leakage current, or an accident may occur in which the electrolyte leaks from a sealed container housing the capacitor element. The separator has the function of preventing the above-mentioned disadvantages, and is used to maintain a sufficient amount of electrolyte between the anode and the cathode. The separator also has the role of preventing short circuit accidents caused by direct contact between the anode and cathode. In order to meet these functions, the separator must have a large amount of electrolyte held per unit volume (or area), and a low-resistance structure with a high degree of porosity to ensure sufficient ionic conduction by the electrolyte. It is required to have the following. For this reason, if the density or voids of the separator itself are increased, short-circuit accidents between electrodes will increase, voltage resistance will be insufficient, and the amount of electrolyte retained will also decrease. Selection of constituent members and density is considerably difficult.

[Problem to be solved by the invention] 1" By the way, recent electrolytic capacitors are required to maintain stable characteristics for a long period of time. One of the main factors that determines the life characteristics of electrolytic capacitors is There is a residual amount of internal electrolyte. Electrolytic capacitors are highly sealed to retain the electrolyte in the outer container for a long period of time, but with long-term use, internal pressure increases and the sealed structure Gradual evaporation of the electrolyte is unavoidable due to deterioration of the electrolytic capacitor, and when the electrolyte decreases, deterioration such as a decrease in capacitance and an increase in loss occurs.The separator used in conventional electrolytic capacitors is Kraft Craft paper is often made from fibers of Manila hemp or Manila hemp.Kraft paper is cheap and can be made into strong paper, but the drawback is that the fibers are flat, which lengthens the current path for the electrolyte and increases resistance. Compared to kraft paper, Manila hemp paper has a smaller fiber flatness, and the current path is shorter than the former, giving it an advantage in terms of resistance, but it is more expensive.Recently, attempts have also been made to use synthetic resin fibers such as polyolefin. These synthetic resin fibers have a nearly circular bottom shape in cross section, which shortens the current path and reduces resistance.However, all of these conventional separator materials have smooth fiber surfaces, so the fibers The electrolyte is not taken into the interior, and the electrolyte does not adhere well to the fiber surface.The electrolyte is retained at the intersections of fibers and in the narrow gaps between adjacent fibers due to surface tension. The electrolyte is mainly retained.For this reason, existing separators cannot retain a sufficient amount of electrolyte to obtain a long-life electrolytic capacitor, and improvements have been desired. If the capacitor element contains a larger amount of electrolyte than the separator can hold, excess electrolyte may leak from the capacitor element into the exterior case, adhere to the terminals, increase leakage current, or leak to the outside. This may cause liquid leakage accidents.

[Means to solve the problem]

The present invention relates to an electrolytic capacitor having an improved separator suitable for obtaining long-term stable characteristics. That is, the present invention provides a capacitor element consisting of an anode electrode having a dielectric oxide film layer formed on its surface, a cathode electrode placed opposite to the anode electrode, and a separator interposed between these electrodes to hold an electrolyte. The electrolytic capacitor is characterized in that the separator is made of a nonwoven fabric or a woven fabric partially or entirely containing hollow fibers having through holes on the side surface. Hollow fibers have a structure in which the inside of the fiber is hollow, and the material used is known to be polyester fiber. The hollow fiber is produced by polymerizing polyester in the presence of a polymerization catalyst such as an antimony compound. In order to create a hollow structure, the molten polyester is
The polyester is discharged from the divided annular nozzle 10 as shown in the figure, and the polyester discharged from the 10 adjacent nozzles of the base are fused together before solidifying to form a hollow polyester thread. -m, when using hollow fibers for textile products such as clothing, if so-called hollow parts occur on the side surfaces of the hollow fibers, the texture and gloss will deteriorate, so tears, or holes may be formed on the side surfaces. In order to prevent this, the opening area of the divided end of the nozzle lO is increased to ensure that the polyester is fused at the discharge end. In order to increase the resistance and reduce the resistance, it is preferable that many through holes such as cracks be formed on the side surfaces of the hollow fibers. Therefore, the base nozzle 10 may be of the usual split form as shown in FIG. FIG. 3 is a perspective view of 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 is formed inside. Furthermore, a crack-shaped through hole 13 is formed on the side surface of the hollow fiber 11, so that the internal cavity 12 communicates with the outside. The hollow fibers that can be used in the present invention are not limited to polyester, but may be other polymers as long as they are stable at least to the electrolyte and can be formed into hollow fibers. In addition, the formation of through holes on the side surface is not due to the shape of the nozzle IO mentioned above, but is caused by physical means such as selectively dissolving and removing the hollow fiber surface or sudden heat stress during the solidification process, causing cracks on the surface. Various means such as forming a shaped through hole can also be used.

[For production]

According to this invention, since the cellulose constituting the separator is made of hollow fibers with through holes on the side surfaces, when impregnated with an electrolytic solution, the electrolytic solution enters and is retained in the internal space of the hollow fibers, and the electrolytic solution is Communication with the outside surface can be maintained through the through holes on the sides. Therefore, the wettability of the hollow fiber surface is improved, and the amount of electrolyte adhering to the outside of the hollow fiber is also increased. As a result, the amount of electrolyte held by the separator increases when viewed per unit volume (or area), and although the numerical value varies depending on the fiber diameter of the hollow fiber and the exclusive cross-sectional area of the hollow part, compared to conventional separator paper, It can hold approximately twice to several times as much electrolyte.

【Example】

The present invention will be explained below based on Examples. First, the following separators used in this invention were created. The hollow fiber shown in FIG. 3 was used as the fiber. The component of the hollow fiber is polyester, the average fiber diameter is 10 μm, and the diameter of the internal hollow part is approximately circular, and the average diameter is 6 μm.
It is m. Furthermore, since the nozzle was formed using a four-split nozzle, fissure-like through holes were discontinuously formed on the side surface of the hollow fiber. A non-woven separator having a thickness of 50 μm was prepared by using the hollow fibers for the entire material or by mixing the hollow fibers with Manila hemp fibers at a certain mixing ratio. As a comparative example, a 50 μm thick separator made of only Manila hemp fibers was prepared. The Manila hemp fibers have a flat cross section, with an average short axis of about 4 μm, an average long axis of about 8 μm, and an oblateness ratio of about 1:2. In order to compare the electrolyte retention ability of these separators, the separators were impregnated with the same electrolyte and the amount of electrolyte retained per predetermined area was investigated. To measure the retained amount, only a band-shaped separator is wound into a cylindrical shape, impregnated with an electrolyte (ethylene glycol-ammonium adipate electrolyte), and then placed in a centrifuge (rotation speed 100 times/min). The separator was centrifuged for 5 seconds, then disassembled, and the middle part of the separator was cut into a predetermined area (10 cd), weighed on a precision balance, and the weight of the separator itself, which was previously measured in a dry state, was subtracted.Preparation The composition of the separator (hollow fiber content) and the amount of electrolyte retained are as shown in Table 1. It can be seen that the amount of electrolyte retained per unit area is increased in each case compared to the fiber separator.In particular, the separator using only hollow fibers in Example 4 has an increased amount of electrolyte retained by approximately 2% compared to the comparative example. Next, these separators are cut into strips and wound together with electrode foil to create a cylindrical capacitor element, as shown in Figure 1. After being impregnated with electrolyte, it is made of metal. It is housed in an exterior case, and the opening of the exterior case is closed with a rubber sealing plate to form an electrolytic capacitor.This electrolytic capacitor has a rated voltage of 25V and a capacitance of 122V.
00μF. The initial electrical characteristics (capacitance, loss, leakage current) of each of these electrolytic capacitors were as shown in Table 2. Looking at the results in Table 1, it can be seen that there is not much difference in the initial electrical characteristics in terms of capacitance and leakage current, but in terms of loss, because the fiber cross section of the separator of this invention is almost circular, the internal resistance bone is small. It can be seen that the value is small and low. Further, a long-term high temperature load life test was conducted on these electrolytic capacitors by applying a rated voltage (50V) at 105°C. The test investigated the rate of change in capacitance value over time with respect to the initial capacitance value, and the change in loss value over time. The results are shown in FIG. Note that (a) in the same figure is a graph showing the rate of change in capacitance, and (c) in the same figure is a graph showing changes in loss value. As can be seen from these graphs, the electrolytic capacitor of the comparative example has a small amount of electrolyte retained inside, so when used for a long time, the capacitance decreases and the loss increases significantly.
The test was stopped at 00 hours. On the other hand, it can be seen that in the electrolytic capacitor of this example, the decrease in capacitance is smaller than that of the comparative example, the increase in loss is suppressed, and the electrical characteristics are maintained stably for a long period of time.

【Effect of the invention】

As described above, according to the present invention, it is possible to increase the amount of electrolyte held in the separator. Therefore, when an electrolytic capacitor is used for a long period of time, capacitance decreases and losses due to a decrease in the internal electrolyte. Deterioration of impedance characteristics is prevented, and a highly reliable and long-life electrolytic capacitor can be obtained. Furthermore, since the separator has a high electrolyte holding capacity, excess electrolyte will not flow out from the capacitor element into the exterior case, causing an increase in leakage current or a liquid leakage accident. Further, since the separator of the present invention can have a substantially circular fiber cross section, the resistance in the separator is low, and as a result, the loss and impedance characteristics of the electrolytic capacitor are improved.

[Brief explanation of drawings]

Figure 1 is a partially exploded view showing the element structure of an electrolytic capacitor.
FIG. 2 is a cross-sectional view of a nozzle used in forming hollow fibers used in the separator of the present invention;
FIG. 3 is a perspective view of hollow fibers used in the separator of the present invention, and FIG. 4 is a graph showing the results of a high-temperature load test on an electrolytic capacitor.
b) shows the change in loss value. 1... Capacitor element 3... Cathode foil 5... Anode lead 10... Base nozzle 12... Cavity 2... Anode foil 4... Separator 6... Cathode lead 11...・Hollow fiber 13...through hole

Claims (1)

[Claims] (1) It has a capacitor element consisting of an anode electrode with a dielectric oxide film layer formed on its surface, a cathode electrode placed opposite to the anode electrode, and a separator interposed between these electrodes to hold an electrolyte. An electrolytic capacitor, wherein the separator is made of a nonwoven fabric or a woven fabric partially or entirely containing hollow fibers having through holes on the side surface.