JPS5832772B2 - Electrolytic capacitor and its manufacturing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a small electrolytic capacitor with good characteristics without the need for a spacer.

A conventional dry foil type electrolytic capacitor has a pair of electrode foils made of a valve metal such as aluminum tantalum, titanium, or niobium, each connected to a lead-out terminal also made of a valve metal. After the coil is wound with a spacer interposed therebetween, it is impregnated with a paste electrolyte, and then stored in a container and sealed.

In general, the main role of a spacer is to insulate and isolate a pair of electrode foils from each other and to hold the paste electrolyte.In order to reduce the internal resistance of an electrolytic capacitor, it is desirable to use kraft paper with as low density as possible and as thin as possible. has a density of 0.4 to 0.9
Kraft paper with a density of 15 to 90 μg/crtl is used, and kraft paper with a density of less than 0.4 g/crtl is not put into practical use.

Therefore, even when using kraft paper with a density of 0.4 g/crA, the density of pure cellulose is 1.2 g/cfl
Therefore, the porosity is about 66.6%.

Raft paper with a higher porosity is not in practical use.

In addition, in order to avoid short circuits and drops in terminal voltage caused by minute defects such as conductive particles contained in the paper-making process of kraft paper, it is necessary to overlap multiple sheets of kraft paper, or if it is a single sheet, it is thick. Since kraft paper must be used, the actual porosity is smaller than the calculated porosity.

Furthermore, since the kraft paper itself is made of crossed cellulose, the gap is in a bent state, and the actual distance between the two electrodes becomes correspondingly longer.

For this reason, it is difficult to move charge carriers, resulting in large losses in the electrolytic capacitor, and the occupancy rate of the kraft paper constituting the capacitor element is equal to or higher than that of the electrode foil.

Manila paper (density 0.
3g/cyd), Manila fibers are more flexible and strong than kraft fibers, and have longer fiber lengths, so even if the density is lowered, the physical strength after papermaking can be maintained to a certain extent, so Manila fibers are used as spacers for electrolytic capacitors. Some methods have been adopted to improve loss by making it easier for charge carriers to move using paper, but Manila paper costs 60% more than kraft paper.
~8 times higher, and in order to keep the strength after papermaking above a certain value that can withstand the capacitor manufacturing process, the paper thickness must be 30 μm.
There is a drawback that only relatively thick products can be obtained because it cannot be made smaller than the following.

There have also been proposals to use porous plastic films or rayon-mixed paper as spacers for electrolytic capacitors, but it is difficult to find a spacer that satisfies all the various conditions, and these have not been put to practical use.

Furthermore, proposals have been made to coat an organic semipermeable membrane or a microporous membrane directly on the surface of the electrode foil as a substitute for a spacer, but in the case of an organic semipermeable membrane, there are many pores with pore diameters of several tens of λ or less. If the membrane is made thicker, its ionic conductivity will deteriorate significantly, and unless it is an extremely thin membrane of 0.5μ or less, the conductivity will be poor and it cannot be used for practical use. In some cases, it is extremely difficult to manufacture the membrane itself, and since both membranes are thin, scratches easily occur when winding the electrode foil, and even a slight scratch can short-circuit both electrodes. It has the fatal disadvantages of dissolving the membrane and causing short circuits, and that it can only be used in a low voltage range of about 50 V at most, so it cannot be put to practical use at all.

The present invention has been made in view of the above-mentioned drawbacks, and involves forming a pulp fiber layer on each surface of a pair of electrode foils made of a valve metal such as aluminum, tantalum, titanium, or niobium. It is an object of the present invention to provide a method for manufacturing an electrolytic capacitor that isolates electrodes, has good electrical characteristics without using any spacers, and can be significantly reduced in size and weight.

Hereinafter, one embodiment of the present invention will be described in detail.

That is, the present invention constructs an electrolytic capacitor without using any craft paper or porous plastic film as a spacer. First, as shown in Figures 1 and 2, aluminum, tantalum, titanium, niobium, etc. The surface of one electrode foil (hereinafter referred to as anode foil) 1 made of a valve metal is roughened by an electrical, chemical or electrochemical method in a corrosive aqueous solution such as hydrochloric acid, common salt, or caustic soda. 2 and expand the substantial surface area of the anode foil 1 from several times to several tens of times, and then add boric acid, tartaric acid, citric acid, succinic acid, etc., or their sodium salts, potassium salts, and ammonium salts. The anodic oxide film 3 is produced by performing anodization treatment in an aqueous solution of these alone or in a mixed solution.

Next, the anode foil 1 on which the anodic oxide film 3 has been formed is dipped in a pulp fiber suspension or coated with a roller to adhere pulp fibers to the surface of the anodic oxide film 3, and then dried to form the pulp fiber layer 4. Formed by laminating.

Additionally, as shown in Figures 3 and 4, aluminum,
The surface of the other electrode foil (hereinafter referred to as cathode foil) 5 made of a valve metal such as tantalum, titanium, or niobium is electrically and chemically treated in a corrosive aqueous solution such as hydrochloric acid, common salt, or caustic soda in the same manner as the anode foil 1. Or a cathode foil whose surface is roughened by an electrochemical method to form a roughened bit 6 to enlarge its surface area, and then dipped in a pulp fiber suspension or coated with a roller to enlarge its surface area in the same manner as above. Pulp fibers are attached to the surface of the cathode foil 5 and dried, and a pulp fiber layer 7 is also integrally laminated on the surface of the cathode foil 5.

The pulp fiber has a length of 0.1 to 100 mm and a width of 1 to 100 mm.
Single fibers such as micro-sized kraft pulp, sulfide pulp, manila pulp, flax pulp, hemp pulp, esparto pulp, jute pulp, reed pulp, bagasse pulp, soda pulp, chemical pulp, groundwood pulp, paper mulberry, mitsumata, etc., or several types thereof Depending on the thickness and porosity of the fiber layer, a mixture of ratio) is made into a suspension and applied to the anode foil 1 and cathode foil 5.
Drying at a temperature below the cooking temperature of pulp fibers.

The thickness of the pulp fiber layer 4゜7 formed each time is about 0.1 to 25 μm, so in the case of extremely low voltage applications, it is necessary to perform the operation of dipping in the above-mentioned pulp fiber suspension or applying with a roller → drying. However, in the case of normal use, the above operation is repeated about 2 to 15 times to form the pulp fiber layers 4 and 7 to a thickness of 1 to 150 μm.

In this way, the anode foil 1 whose surface area has been expanded to generate an anodic oxide film 3 and a pulp fiber layer 4 formed thereon, and the cathode foil 5 whose surface area has been expanded and whose pulp fiber layer 7 has been formed are directly connected without using a spacer. A capacitor element is formed by winding the capacitor elements facing each other, and this is impregnated with a paste electrolyte to obtain an electrolytic capacitor.

As described above, since the pulp fiber layers 4 and 7 are directly formed on the surfaces of the anode foil 1 and the cathode foil 5, it is possible to achieve extremely low density and thin films without requiring the strength of paper as in the past. In addition, since no spacers are used, the winding operation is extremely simple, and the automatic winding machine can be simplified.

In the above embodiment, the pulp fiber layer 7 was formed after roughening the cathode foil 5, but the pulp fiber layer 7 may be formed directly on the original surface without roughening.

Further, the pulp fiber layers 4 and 7 may be formed on only one side of the electrode foils 1 and 5, or may be formed on the entire both sides.

Further, the electrode foil 1゜5 forming the pulp fiber layers 4, 7 may be formed by forming the pulp fiber layers 4, 7 on a wide foil and then cutting it into a predetermined size width, or by cutting it into a predetermined size width in advance. After that, the pulp fiber layers 4 and 7 may be formed.

In this case, the pulp fibers adhere to the cut cross section, thereby increasing the insulation effect.

Next, an example of comparison between an embodiment of the present invention and a conventional reference example will be shown.

Example rated 25V, DC-100μ electrolytic capacitor A
※※ Roughen the surface of aluminum foil in an aqueous hydrochloric acid solution to increase the surface area Llc
(D) An anode foil with an anodized film formed in an aqueous solution of ammonium diborate and a cathode foil with an aluminum base roughened in an aqueous solution of hydrochloric acid to increase the surface area.
Apply a 5% kraft pulp fiber suspension with a roller and
The product was dried at a temperature of °C, and this coating and drying process was repeated four times to form a pulp fiber layer with a thickness of 20μ on each of the surfaces of the anode foil and cathode foil, which were directly stacked and wound.

Reference example Electrolytic capacitor B with a rating of 35 V and DC-100 μF An anode foil whose surface was roughened in an aqueous hydrochloric acid solution and an anodized film formed in an aqueous ammonium borate solution, and an anode foil whose surface was roughened in an aqueous hydrochloric acid solution. This product is made by overlapping and winding a 40μ thick kraft paper spacer with a 40 μm thick kraft paper.

As is clear from Table 1, the electrolytic capacitor of Example A according to the present invention has a volume of about 315% compared to the conventional Reference Example B.
It can be made smaller.

Furthermore, by eliminating the spacer, which acts as a series resistance valve and causes an increase in tan δ of the capacitor, tan δ can be drastically reduced to about 1/2.

Further, the electrolytic capacitors of Example A and Reference Example B were each applied with a rated voltage in a high temperature atmosphere of 85°C.
Figures 5 to 7 show the high temperature load characteristics when left for 000 hours.
As shown in the figure.

That is, Fig. 5 shows the rate of change in capacitance, Fig. 6 shows the change in leakage current, and Fig. 7 shows the change in tan δ, all of which are measured every 500 hours in addition to the initial value at 85°C. It was measured using

From these results, it can be seen that Example A has no change in any of the characteristics compared to Reference Example B, and its absolute value is also small and stable even when used for a long time.

As detailed above, according to the present invention, a pulp fiber layer is formed on each surface of a pair of electrode foils made of a valve metal such as aluminum, tantalum, titanium, or niobium, and the two electrodes are isolated by the pulp fiber layer. As a result, a pulp fiber layer is directly formed on the surface of the electrode foil, which eliminates the need for the strength of conventional paper, making it possible to achieve extremely low density and thin films, and improve electrical properties, especially without using any spacers. t
It is possible to provide a method for manufacturing an electrolytic capacitor that has good an δ characteristics, can be significantly reduced in size and weight, and can also simplify the winding machine.

[Brief explanation of the drawing]

FIG. 1 is an enlarged sectional view showing an anode foil with a pulp fiber layer formed thereon used in an electrolytic capacitor according to an embodiment of the present invention;
FIG. 2 is a perspective view of the anode foil in FIG. 1, FIG. 3 is an enlarged sectional view showing the cathode foil with a pulp fiber layer formed thereon, FIG. 4 is a perspective view of the cathode foil in FIG. 3, and FIGS. FIG. 7 is an embodiment A of the present invention.
Figure 5 is a curve diagram showing the capacitance change rate, Figure 6 is a curve diagram showing changes in leakage current, and Figure 7 is a curve diagram showing tan δ. FIG. 1... Anode foil, 2, 6... Roughened bit, 3... Anodized film, 4, 7...
Pulp fiber layer, 5... Cathode foil, A...
Example of the present invention, B...Conventional reference example.

Claims (1)

[Claims] 1. A means for roughening an anode foil made of a valve metal to form a roughened bit, a means for performing an anodizing treatment after the means to form an anodized film, and a means for forming an anodized film on a pulp fiber suspension after the means. means for attaching pulp fibers to the surface of the anodic oxide film by dipping or roller coating; means for drying the pulp fibers at a temperature below the cooking temperature of the pulp fibers to form a pulp fiber layer; and valve action. A means for attaching pulp fibers to the surface of a cathode foil made of metal by immersing it in a pulp suspension or coating it with a roller, and drying it at a temperature below the cooking temperature of the pulp fibers to form a pulp fiber layer on the surface of the cathode foil. and a means for configuring a wound capacitor element by directly facing the anode foil and the cathode foil via the pulp fiber layer formed by the means and the pulp fiber layer formed on the anode foil, and 1. A method for manufacturing an electrolytic capacitor, comprising means for impregnating a paste electrolyte into a capacitor element.