JPH031816B2 - - Google Patents

Description

[Detailed description of the invention]

[Technical Field of the Invention] The present invention relates to an electrolytic capacitor that eliminates the need for capacitor paper by forming a porous thin film on an anode foil and/or a cathode foil. [Technical background of the invention and its problems] Conventionally, aluminum foil type dry electrolytic capacitors have a capacitor made of kraft paper or the like between the anode foil, which has a roughened surface and a dielectric oxide film, and the roughened cathode foil. The structure was such that a capacitor element was constructed by winding the capacitor with paper interposed therebetween, impregnating the capacitor element with a driving electrolyte, and enclosing and sealing the capacitor element in a case. The capacitor paper has two functions: isolating the anode and cathode foils and retaining the driving electrolyte. However, in terms of paper making technology and capacitor manufacturing process, for example, when cutting the anode and cathode foils to the required size, Due to the occurrence of burrs etc., the thickness of the anode and cathode foils must be equal to or greater than that of the anode and cathode foils.
This was a factor that hindered the increase in size and miniaturization.
In order to eliminate these drawbacks, as an alternative to capacitor paper, a single thin film of plastic with a high pore density is interposed between the anode foil and the cathode foil, or a porous thin film of plastic is deposited on the surfaces of the anode and cathode foils. Alternatively, a method has been proposed in which an ion-permeable thin film is formed to eliminate the need for capacitor paper. However, a single thin film of porous plastic is not practical due to its low tensile strength, and electrode foils made of water-soluble polymers such as polyvinyl alcohol, methyl cellulose, and gelatin are stable because they dissolve in the water in the electrolyte. However, if an ionic semipermeable membrane containing a water-insoluble polymer and an ion exchanger is coated, sufficient conductivity cannot be obtained, resulting in a significant increase in tanδ and decrease in capacitance. There are drawbacks to this. Furthermore, a porous membrane is formed by dissolving the polymer in a mixed solvent and applying it to the electrode, using the difference in the boiling point of the solvent or the difference in the rate of diffusion into water.
There is a problem that it redissolves or swells in the electrolyte at high temperatures. [Purpose of the Invention] This invention uses a porous thin film formed by adding a decomposable foaming agent to a completely saponified polyvinyl alcohol aqueous solution and heating and foaming it after application, instead of the capacitor paper interposed between the anode and cathode foils. In other words
The present invention provides an electrolytic capacitor that has improved tanδ characteristics and can be significantly downsized. [Summary of the invention] The electrolytic capacitor of this invention has a saponification degree of 98%.
A decomposable foaming agent is added to the above fully saponified polyvinyl alcohol aqueous solution, and this is coated on an anode foil and/or anode foil, heated to form a porous thin film, and the anode foil and cathode foil are wound to form a capacitor element. , the capacitor element is impregnated with a driving electrolyte. [Embodiment of the invention] In a 30% aqueous solution of completely saponified polyvinyl alcohol,
Add and dissolve NN′-dinitrosopentamethylenetetramine. The amount of NN'-dinitrosopentamethylenetetramine was 20 ^wt % of the polyvinyl alcohol. This aqueous solution is uniformly applied onto the cathode foil using a roll coater or bar coater, dried at 105°C, and then reheated at 160°C to crystallize the polyvinyl alcohol and decompose the blowing agent, forming a porous thin film. This cathode foil and the anode foil on which a dielectric oxide film has been formed are overlapped and wound to form a capacitor element, and the capacitor element is impregnated with an ethylene glycol-ammonium adipate electrolyte and then housed in an aluminum case. −Hermetically sealed electrolytic capacitor (rated 10V−
The table below shows the results of a comparison of capacitor element dimensions and characteristics with conventional examples for two types (100μF and 50V-22μF), and the tan δ of a load life test with 10V applied at 105℃ for electrolytic capacitors with a rating of 10V-100μF. The characteristics are shown in FIG. 1, and the capacitance change rate is shown in FIG. 2. The present invention is curve A, the conventional example 1 is curve B, in which capacitor paper is interposed between the anode foil and the cathode foil, and the conventional example 2 is curve C, in which porous holes are formed in the cathode foil by selective extraction of a mixed solvent. A thin film is formed.

[Table] As is clear from this result, in the present invention, since a porous polyvinyl alcohol thin film is formed directly on the cathode foil, the thickness is 1/5 to 1/1 of the thickness of conventional capacitor paper.
Therefore, the volume of the wound capacitor element can be reduced to approximately 75% of that of Conventional Example 1. Furthermore, tan δ can also be reduced to about 1/2.
Furthermore, when compared with Conventional Example 2, it is clear from FIGS. 1 and 2 that the high temperature load life characteristics are excellent. In addition, in the above examples, as a decomposable blowing agent,
Although we have described the case where NN'-dinitrosopentamethylenetetramine is used, any inorganic compound such as sodium bicarbonate, azodicarbonamide, benzene 1.3 disulfohydrazide, an azo compound, a sulfohydrazide compound, a nitroso compound, etc. can be used. However, those with a decomposition temperature of 140 to 150°C or higher are suitable. In addition, in the example, a case was described in which a porous thin film of polyvinyl alcohol was formed on the cathode foil.
It may be formed on the anode foil or on both the anode and cathode foils. However, when forming only on the anode foil, it is desirable to form it on the cut surface of the anode foil due to voltage resistance characteristics. [Effect of the invention] Eliminates the need for capacitor paper as a separator,
By forming a porous thin film on the anode foil and/or the cathode foil using polyvinyl alcohol to which a decomposable foaming agent has been added, an electrolytic capacitor that is compact and has an excellent tan δ can be obtained.

[Brief explanation of drawings]

The drawings show the high temperature load life characteristics; FIG. 1 is a curve diagram showing the tan δ characteristics, and FIG. 2 is a curve diagram showing the capacitance change rate. Curve A: Present invention, Curve B: Conventional example 1, Curve C: Conventional example 2.

Claims (1)

[Claims] 1 Add a decomposable foaming agent to a fully saponified polyvinyl alcohol aqueous solution with a degree of saponification of 98% or more, apply this to an anode foil and/or a cathode foil, heat it to form a porous thin film, and wrap the anode foil and cathode foil. 1. An electrolytic capacitor characterized in that the capacitor element is turned into a capacitor element, and the capacitor element is impregnated with a driving electrolyte.