JPH0255924B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD The present invention relates to an electrolytic capacitor constructed by interposing a separator between an anode foil and a cathode foil using aluminum foil or the like. By making the electrolytic paper used as a separator thinner, the aim is to achieve smaller size and higher performance. Conventional technology and its disadvantages Generally, electrolytic capacitors, especially aluminum electrolytic capacitors, are formed by wrapping an anode aluminum foil and a cathode aluminum foil with a separator such as electrolytic paper interposed between them, and then impregnating them with liquid electrolyte and sealing them. Manufactured by The electrolyte is manufactured by using a medium in which boric acid, adipic acid, etc. are dissolved in ethylene glycol or dimethylformamide, and permeating it from both ends of the capacitor element. The disadvantage of the conventional aluminum electrolytic capacitors as described above is that the impedance characteristics of the capacitor are poor because the electrolytic paper is impregnated with an electrolytic solution, and the advantage is that they can be made smaller and have a larger capacity.
In order to obtain a small device with a large capacity, it is necessary to increase the etching ratio of the aluminum foil and to reduce the thickness of the aluminum foil and the electrolytic paper. However, when the etching magnification of aluminum foil is increased, the foil inevitably becomes thicker and more brittle. Therefore, in order to reduce the size, it is desirable that the separator used be thinner as the etching ratio of the aluminum foil is increased. However, when electrolytic paper is used as a separator, the thinner the electrolytic paper is, the higher the density of the electrolytic paper will be, otherwise the defective rate will increase when it is wound around a capacitor element, and the number of defective capacitor elements that have not been shot will increase. Even after products are commercialized and put on the market, the defective rate is increasing. That is, in order to reduce the shot defect rate, it is necessary to increase the thickness and density of electrolytic paper. Therefore, when forming electrolytic paper thinly in order to realize a smaller size and larger capacity electrolytic capacitor as described above, it is necessary to increase the density of the electrolytic paper in order to prevent shot defects. on the other hand,
The effect of these items on impedance characteristics is that when the electrolytic paper is made thicker, the impedance characteristics deteriorate in a linear manner, and when the density is increased, the impedance characteristics deteriorate in a quadratic manner, and this impedance characteristic can be improved. In order to achieve this, it is necessary to make the electrolytic paper thinner and lower its density. Currently, the thickness of electrolytic paper is 40mm even for low voltage capacitors.
Most of the paper has a thickness of 60 μm and a density of 0.40 to 0.55 g/cm ³ , but if these papers were made thin as they were, they would have many pinholes and many shot defects, making them unusable. In addition, if you use a paper with a thickness of 15 to 20 μm, it will be a homogeneous paper made with a Fourdrinier machine.
In addition, the density must be 0.70g/ ^cm3 or higher. but,
This paper has poor impedance characteristics because its density is too high and its texture is film-like. In order to further reduce the thickness of the electrolytic paper, it is necessary to apply calendar processing to the electrolytic paper and crush it in the thickness direction, but as a result, the density of the electrolytic paper inevitably becomes too high, and as mentioned above, Impedance characteristics deteriorate. At the same time, the absolute amount of electrolyte decreases, resulting in a shortened lifespan. In other words, in reality it is 10 μm.
No electrolytic paper has yet been provided that is practical in terms of shot defect rate and impedance with the thickness below. In addition, according to Japanese Patent Publication No. 53-20105 or Japanese Patent Application Laid-Open No. 53-122759, which are prior applications, instead of conventional electrolytic paper, a solution containing thermoplastic resin and a solvent that dissolves this resin as the main components is applied as a separator. or by forming porous and insulating alumite on the surface of the anode foil and laminating it on this alumite layer by roller coating, etc. A means for depositing pulp fibers, etc. is shown. However, these methods simply coat fibrillated papermaking raw materials, and with this raw material, no matter what kind of coating machine is used,
It is not possible to apply uniformly to a thickness of 10 μm or less. However, the original form of the pulp fiber remains, and the original form of the pulp fiber alone is over 10 μm.
Even if the fibrillated areas are not evenly distributed, the pulp fibers will become entangled with each other during coating, resulting in a so-called thixotropic state, which will dry unevenly on the aluminum foil, making it impossible to create a homogeneous separator. It cannot be done.
Therefore, with any of the above methods, it has not been possible to obtain a capacitor element that is small, has a large capacity, has good impedance characteristics, and is free from shot defects during winding. Problems to be Solved by the Invention As mentioned above, in the case of conventional capacitors using electrolytic paper, it is theoretically possible to obtain paper that is thin, has low density, and has almost no pinholes by paper-making means. Moreover, even when resin or pulp fiber other than electrolytic paper is used as a separator, it is not always possible to obtain a satisfactory capacitor element for the reasons mentioned above, and in the end, it is difficult to obtain a satisfactory capacitor element due to the above-mentioned reasons. An electrolytic capacitor that achieves both of these characteristics while also achieving small size, large capacity, and high performance has not yet been provided. Means for Solving the Problems Therefore, the present invention solves the problems of the conventional electrolytic capacitors described above, and achieves a reduction in shot defect rate and low impedance characteristics, while
A capacitor element that has achieved small size and high performance by forming thin electrolytic paper as a separator.
More specifically, the purpose is to obtain electrolytic paper with a thickness of 10 μm or less and a density of 0.70 g/cm ³ or less. It is characterized in that it is formed by applying a microfibrillated cellulose suspension to one or both sides of an anode foil or a cathode foil. Effect With the above configuration, a thin and homogeneous separator can be formed on the anode foil or the cathode foil, and the characteristics of the obtained capacitor element can be greatly improved. . During production, the cellulose suspension is completely fibrillated, so it can be applied homogeneously and thinly using any coating machine, ensuring a high level of product quality and uniformity. It is something that brings about an effect. Embodiment The configuration of the present invention will be explained below based on one embodiment thereof. First, aluminum foil is prepared as an electrode metal and used as an anode foil and a cathode foil. By applying a cellulose suspension to either or both sides of the anode foil or cathode foil and drying with hot air,
A capacitor is manufactured by forming a coating layer with a thickness of 10 μm or less to serve as a separator, and laminating the anode foil and cathode foil with the separator interposed therebetween and impregnating them with an electrolyte. The cellulose suspension is made by suspending cellulose fibers cut to an average fiber length of 1 mm or less in water to make a suspension with a cellulose content of 2 to 6%, and then rapidly applying this suspension to a high pressure of 500 kg/cm ² or more. Cellulose fibrils are decomposed into microfibril units by applying reduced pressure.
Microfibrillated cellulose (hereinafter abbreviated as MFC) is processed using a processing machine usually called a homogenizer.
Create. This MFC is a very viscous cellulose suspension with excellent solution retention ability, ability to inhibit evaporation, and ability to retain inorganic substances. For example, MFC manufactured by Daicel Chemical Industries, Ltd. has a viscosity of about 4,000 to 10,000 CPS, a liquid specific gravity of 1.0, a microfibril length of several tens to hundreds of μm and a width of <0.1 μm, a high water retention rate, and stability with no sedimentation. A cellulose suspension with a high concentration is obtained. This is because the length and width of ordinary wood craft pulp fibers are extremely small compared to 3 mm in length and 40 μm in width, and they still retain the properties of natural pulp.
It is possible to produce paper-like sheets. However, in general paper machines, it has the property of not being able to pass through the mesh and make paper. Therefore, in the present invention, a homogeneous separator with a thickness of 10 μm or less and a density of 0.70 g/cm ³ or less is formed by directly coating the MFC on aluminum foil, which is the electrode of an aluminum electrolytic capacitor. It is characterized by the fact that According to the above method, no matter what kind of coating machine is used, for example, a pipe doctor knife type coating machine can be used to coat a 30 μm cathode foil at a coating speed of 2.5 m/min, and hot air at 110°C is used. The separator described above can be formed by simply drying it. In the above example, even if the cathode foil is coated on both sides and then rolled up with the anode foil, MFC is coated only on one side of either the anode foil or the cathode foil, and the other side is not coated. Ordinary electrolytic paper may be used instead, or alternatively, it may be coated on one side of both the anode foil and the cathode foil, and these may be combined and wound or laminated. Below, an aluminum electrolytic capacitor was manufactured using the present invention, and various characteristics were measured along with a conventional electrolytic capacitor. The results are shown in Table 1. The electrolyte is
A comparison was made of a product manufactured with a rating of 1.8KΩcm (-40℃), 25WV, and 350μF. The thickness of the anode aluminum foil is 70μm, 210mm, and the thickness of the cathode aluminum foil is 30μm,
It is 245mm.

[Table] As is clear from Table 1, the thickness T of the separator is
Even when the thickness is 10 μm or less, the density does not increase, the basis weight decreases, and the impedance Z can be significantly lowered without worsening the shot defect rate C. Furthermore, the outer diameter of the element winding is also smaller than that of the conventional example, realizing a smaller size and larger capacity of the element. Effects of the Invention According to the present invention described in detail above, the following great effects can be brought about. In other words, since the separator is made by applying MFC instead of conventional electrolytic paper, there are no pinholes and the density does not increase even if the thickness of the separator is made thinner, and both shot defect rate and impedance characteristics are maintained well. It is possible to realize a smaller size and larger capacity of the element. In addition, in the case of conventional capacitors using electrolytic paper, if the thickness of the paper is made thinner, the tensile strength of the paper becomes weaker, and there is a drawback that it cannot be wound up into an element winding, but according to the present invention, aluminum foil can be used. Because it is coated, the aluminum foil has sufficient strength, so there is no risk of damage during winding. Furthermore, since it is gradually dried with hot air, there is no need to apply press rolls to dry it suddenly, which is the case when using a paper machine.
Density can be kept low. On the other hand, if a fibrillated pulp raw material for electrolytic paper is used to coat the electrodes in the same way as in the present invention, the base pulp fibers will remain in their original form in the solution, so the coating will not be possible. On the other hand, these pulp fibers become entangled in the separator, creating a thixotropic state and causing uneven coating, making it impossible to obtain a homogeneous separator.
Since MFC is microfibrillated, it is possible to form a thin and homogeneous coating layer. Furthermore, it has the advantage that the content of the electrolyte can be increased when impregnated with the electrolyte, thereby extending the life of the capacitor itself. That is, the life of an electrolytic capacitor is almost determined by the absolute amount of electrolyte that is impregnated, but when the density of the electrolyte is high, there are few gaps in which it can be impregnated, so the absolute amount of liquid is insufficient. However, according to the present invention, the separator can be formed thinly and the density can be kept low, so the amount of electrolyte impregnated can be increased, and the life of the capacitor element can be significantly extended. Ori,
It is useful when manufacturing electrolytic capacitors using aluminum foil or other metal materials as electrodes.

Claims (1)

[Scope of Claims] 1. In an electrolytic capacitor comprising a separator interposed between an anode foil and a cathode foil, the separator is a cellulose suspension obtained by microfibrillating a microfibrous cellulose suspension. An electrolytic capacitor characterized in that it is formed by coating one or both sides of a foil or a cathode foil. 2. The above-mentioned microfibrous cellulose suspension is obtained by cutting natural cellulose raw material into average fiber length of 1 mm, suspending it in water, and repeating high pressure and reduced pressure to form microfibrillation. The electrolytic capacitor according to item 1. 3. The electrolytic capacitor according to claim 1, wherein the separator has a coating layer having a thickness of 10 μm or less and a density of 0.70 g/cm ³ or less.