JPH02112215A - Electrolytic capacitor - Google Patents

Abstract

PURPOSE:To obtain a substantially low tandelta and impedance without increasing defects such as short-circuit by a method wherein cellulose system fibers whose raw material is cotton linter and which are manufactured by a copper-ammonia method enabling to control a fiber diameter are papered into a separator. CONSTITUTION:Cellulose system fibers whose raw material is cotton linter and which are manufactured by a copper-ammonia method enabling to control a fiber diameter are papered into an electrolytic capacitor separator. The separator is composed of the fine cellulose system fibers whose average diameter is not larger than 20mum. If Manila, craft, esparto or hemp fibers are mixed during papering, fibers entwist each other more efficiently.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to an electrolytic capacitor that achieves extremely low tan δ impedance without increasing short circuit defects.

2. Description of the Related Art Conventionally, paper separators made of kraft or manila fibers have been generally used as separators for electrolytic capacitors made of aluminum, tantalum, etc.

In recent years, efforts have been made to lower impedance and lower tanδ to improve the performance of electrolytic capacitors.
Manila paper with a low density of about 9/cA is also being considered due to its necessity.

Problems to be Solved by the Invention However, since conventional manila and kraft paper are paper made using natural fibers, the fiber diameter is fixed,
It is not possible to make fine fibers with a diameter of 0 μ or less, and if the density is continued as it is, a porous paper structure with uneven fiber parts and void parts will result, which will weaken the strength of the separator and weaken the electrolytic capacitor. There is a drawback in that short circuits between electrodes often occur due to flakes in the electrode foil, resulting in poor product yield.

On the other hand, in order to solve these problems, a separator for electrolytic capacitors (Japanese Patent Publication No. 6,113,368), which is made of an organic resin nonwoven fabric and is made by bonding spun synthetic resin fibers, was invented.

Since this separator is made of fine organic synthetic fibers with an average fiber diameter M1 of 1QII or less, the distance traveled by charge carriers can be shortened, and the separator is made of substantially continuous fibers.
In addition, most of the fibers are arranged in a certain direction and are bonded at the intersections of each fiber, so the strength is strong and the density of the nonwoven fabric can be reduced without causing short-circuits or separator breakage. , is known to effectively reduce impedance.

However, if this separator is made of non-woven fabric made of untreated organic synthetic fibers, it has poor affinity for the electrolyte and cannot achieve the desired low impedance. Since it is said that special affinity imparting treatments such as attaching surfactants to fibers are required, careful consideration must be given to these treatment methods so as not to adversely affect the capacitor function. In addition, in cellulose fibers such as manila and kraft paper, the electrolyte penetrates into the fibers, which fills a part of the area where charge carriers move and serves to lower impedance. The fiber separator improves the affinity of the surface to which the surfactant is attached and helps lower impedance, but the electrolyte does not penetrate into the underlying M machine synthetic fiber, so this region is a charge transfer region. It cannot be used as such at all.

Furthermore, this organic synthetic fiber separator has a tensile resistance of 6
Since it has an elongation of around 0%, the winding element lacks dimensional stability in the winding manufacturing process, and there is also concern about an increase in short-circuit defects.

In general, the equivalent circuit of an electrolytic capacitor is expressed by the resistance R/ of the capacitance C1 electrode film dielectric and the combined resistance Re of the electrolyte and separator, as shown in Figure 3, and the equation for the impedance derived from the equivalent circuit is is shown in Equation 1.

Z=-(RJ+Re1)2-1-(1/cuc)2=・
...Formula 1%Formula %: The resistance R of the electrode film dielectric generally decreases in proportion to the reciprocal of the frequency, 1/f, and becomes approximately equal to "0" at high frequencies. On the other hand, the combined resistance Re of the electrolyte and separator is not affected by the frequency and has a nearly constant relationship from low to high frequencies, and has a relationship as shown in equation 2 with respect to the electrode area and separator thickness. In order to achieve low impedance, it is necessary to lower Re.

Re=kd/s---
- = In Equation 2 = constant d: Separator thickness S: Electrode area However, conventional separators made of manila, kraft paper, and organic synthetic fibers do not impair workability in the manufacturing process of electrolytic capacitors, and provide stable quality. It has been difficult to lower the combined resistance Re of the electrolytic solution and the separator while maintaining the desired low impedance.

The present invention eliminates these conventional drawbacks6.
- / It has strong strength, has affinity and permeability to the electrolyte even without affinity treatment, and can achieve the desired low impedance without causing shorts between electrodes. The aim is to provide an electrolytic capacitor that enables

Means for Solving the Problems In order to achieve this object, the present invention is a separator made using cellulose fibers produced by a copper ammonia method that uses cotton linters as raw materials and can control fibers and miscellaneous functions. The average diameter of the fibers is set to 20μ or less, so that the fibers are more entangled with each other.

Function In the electrolytic capacitor configured as described above, the separator is composed of fine fibers with an average fiber diameter of 20 μm or less, so when the density is adjusted to the same as that of a conventional separator, the entanglement points of the fibers are Since the amount increases in inverse proportion to the diameter of the fibers, there is extremely little unevenness in papermaking compared to conventional separators, and the strength is increased, so shorts between electrodes are greatly improved.

Further, when the paper unevenness 1 strength is adjusted to be the same as that of conventional separators, the density can be made extremely low, and the above-mentioned Re can be made low.

Example Embodiments of the present invention will be described below with reference to the accompanying drawings.

In FIG. 1, -1 is a case made of aluminum, and a capacitor element 2 is housed in this case 1. This capacitor element 2 is constructed by winding aluminum foil with a separator 6 interposed between an anode foil 3 and a cathode foil 4 whose surface area has been expanded by etching or other methods.
The separator 6 is made of cotton linter as a raw material, and is made of fibers manufactured by a copper ammonia method that allows the fiber diameter to be controlled, and has an average diameter of 20 μm or less.

Reference numeral 6 denotes a sealing body which houses the capacitor element 2 in the case 1, impregnates it with an electrolytic solution, and then seals it at the opening of the case 1 to form an electrolytic capacitor.

The finer the fiber diameter of the separator 6, the greater the effect and the lower the impedance.
Conventional kraft and manila fibers have a diameter of 20 to 30 microns, and it is virtually impossible to reduce the thickness of the separator to less than 30 microns.

In general, the strength of the separator 6 is determined by the entanglement force between fibers or physical bonding force due to affinity, and chemical adhesive force.

Conventional manila and kraft fibers have a fiber diameter of 20 to 30μ.
Since the nonwoven fabric is thick, if the density is reduced in order to lower the impedance, the entangling force will decrease and the fabric will become noticeably uneven, resulting in poor workability and an increase in the incidence of short circuits. , a limit naturally arises.

Since the separator of the present invention is made of fine fibers with an average diameter of 20μ or less, the strength of the separator is relatively small even when the density is lowered, because there are many points where the fibers intertwine with each other. Since the miscellaneous work can be made thinner freely, even if the density is low, if the fibers are made delicate, unevenness in papermaking can be suppressed.
Low impedance can be achieved.

Furthermore, unless treated with a surfactant or the like, the nonwoven fabric made of the above-mentioned organic synthetic fibers has no affinity with the fiber itself, has poor impregnability with the electrolyte, and cannot achieve low impedance, and has poor retention of the electrolyte. This is bad, and the life of the capacitor will be extremely shortened. Furthermore, since the elongation against tension remains approximately 60% even after the stretching process, this may impair the winding precision in the winding process and induce defects such as short circuits.

On the other hand, in the present invention, since the raw material cotton cellulose itself has affinity, the electrolyte impregnating and retaining properties are good even without affinity imparting treatment. In addition, it has almost no elongation under tension and has little effect on winding accuracy, etc.

As described above, the electrolytic capacitor of the present invention can dramatically reduce impedance without causing problems such as short circuit between electrodes during the winding process.

Specific examples according to the present invention will be described below.

(Example 1) An electrolytic capacitor separator made of cotton linter as a raw material and made from cellulose 10 \-7 type fiber manufactured by the copper ammonia method that can control the fiber diameter was used. An electrolytic capacitor was produced by winding up the element, impregnating it with a solution '11, assembling it, and subjecting it to an aging treatment.

(Example 2) An electrolytic capacitor was produced in the same manner as in Example 1 except that the average fiber diameter was changed to 107 mm.

(Example 3) An electrolytic capacitor was produced in the same manner as in Example 1 except that the average fiber diameter was changed to 6μ.

(Example 4) An electrolytic capacitor was produced in the same manner as in Example 1 except that a separator was prepared by mixing 40% by weight of the fiber of the present invention with an average fiber diameter of 6μ and 60% by weight of conventional Manila fiber.

(Conventional Example 1) An electrolytic capacitor was produced in the same manner as in Example 1 using conventional manila paper of normal density (0.5 g/cj) as a separator.

(Conventional Example 2) An electrolytic capacitor was produced in the same manner as in Example 1 using conventional Manila paper adjusted to a low density (o, 3eg/d) as a separator.

Table 1 shows the physical properties of the separators used in the examples and conventional examples. Further, Table 2 shows the short circuit occurrence rate immediately after winding up of the internal capacitor elements of the embodiment and the conventional example. Table 3 shows the characteristics of an electrolytic capacitor assembled by impregnating these internal elements with an electrolyte.

Also, FIG. 2 shows the impedance change with respect to frequency at 20°C.

(Margins below) As can be seen from the above results, it is clear that Examples 1 to 4 exhibit excellent characteristics without the occurrence of short circuits in the capacitor elements compared to Conventional Example 1.

Effects of the Invention As described above, the present invention provides a high-performance, high-quality electrolytic capacitor that does not increase short-circuit defects, etc. (tan δ, and impedance is significantly lowered), and its practical effects are significant. be.

[Brief explanation of the drawing]

FIG. 1 is an exploded perspective view showing an embodiment of the electrolytic capacitor of the present invention, FIG. 2 is a temperature characteristic diagram of impedance at 20"C of capacitors obtained in the embodiment of the present invention and the conventional example,
Figure 3 is an equivalent circuit diagram of a 1F solution capacitor. 1... Case, 2... Capacitor element, 3... Anode foil, 4...・Cathode foil, 6・
... Separator, 6 ... Sealing body.

Claims (4)

[Claims] (1) A capacitor element is enclosed in a case, using cellulose fibers manufactured by the copper ammonia method, which uses cotton linter as the raw material and whose fiber diameter can be controlled, and is wound with a paper-made separator interposed between electrode foils. Electrolytic capacitor. (2) The electrolytic capacitor according to claim 1, wherein the cellulose fibers have an average diameter of 20 μm or less. (3) The electrolytic capacitor according to claim 1, wherein a cylinder method or a Fourdrinier method is used for paper making. (4) The electrolytic capacitor according to claim 1, wherein at least one type of fiber from manila, kraft, esparto, and hemp is mixed into the paper during papermaking.