JPH031815B2 - - 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 of polyvinyl formal in place of the capacitor paper interposed between the anode and cathode foils to improve the tanδ characteristics and to significantly reduce the size of the electrolyte. It provides capacitors. [Summary of the Invention] The electrolytic capacitor of the present invention is provided by forming a porous thin film of polyvinyl formal with a degree of formalization of 50% or more on an anode foil and/or a cathode foil, and winding the anode foil and cathode foil to form a capacitor element. The capacitor element is characterized in that the capacitor element is impregnated with a driving electrolyte. [Embodiments of the Invention] First, polyvinyl alcohol having a saponification degree of 98 to 99% (completely saponified product) and an average degree of polymerization of 1500 is dissolved in water by heating to obtain an aqueous solution with a concentration of about 20%, and the polyvinyl alcohol and the polyvinyl alcohol are added to the aqueous solution. Dissolve approximately equal amounts of soluble starch. The aqueous solution thus prepared is coated onto the cathode foil to a thickness of 20 μm (wet thickness) using a roll coater, bar coater, doctor blade method, or the like. Next, the coating film is formalized by 50% or more with an aqueous formaldehyde solution in the presence of an acid to insolubilize it, and then immersed in water for extraction to form a porous polyvinyl formal thin film with a thickness of about 5 μm and having open cells on the cathode foil. . 100-120℃ to stabilize this porous polyvinyl formal thin film.
A heat treatment is performed in which the material is left for 2 to 5 minutes. The cathode foil thus created and the anode foil on which the dielectric oxide film was formed are overlapped and wound to form a capacitor element, and the capacitor element is impregnated with an ethylene glycol-ammonium adipate electrolyte. The table below compares the capacitor elements, dimensions, and characteristics of electrolytic capacitors (2 types, rated 10V-100μF and 50V-22μF) sealed in an aluminum case with conventional examples. Figure 1 shows the tan δ characteristics of a -100μF electrolytic capacitor in a load life test with 10V applied at 105°C, and Figure 2 shows the capacitance change rate. Note that the present invention uses curve A, conventional example 1
Curve B indicates that capacitor paper is interposed between the anode foil and cathode foil, and Conventional Example 2 is indicated by curve C, in which a porous polyvinylidene fluoride coating film is formed on the cathode foil using a selective extraction method using a mixed solvent. be.

[Table] As is clear from this result, in the present invention, since a porous thin film of polyvinyl formal is formed directly on the cathode foil, it can be made 1/5 to 1/10 the size of conventional capacitor paper, and thus the volume can be reduced. The volume of the rotated capacitor element can be reduced to about 75% of that of Conventional Example 1. Also
tan δ can also be reduced to about 1/2. Furthermore, when compared with Conventional Example 2, it is clear that the high temperature load life characteristics are excellent. In the above example, soluble starch was dissolved in an aqueous polyvinyl alcohol solution, applied to a cathode foil, and extracted by immersion in water. Similar effects can be obtained by decomposing, extracting, and making it porous. Further, in the embodiment, a case has been described in which a porous thin film of polyvinyl formal is formed on the cathode foil, but 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 of polyvinyl formal on the anode foil and/or the cathode foil, it is possible to obtain an electrolytic capacitor that is compact and has an excellent tan δ.

[Brief explanation of the drawing]

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 A porous thin film of polyvinyl formal with a degree of formalization of 50% or more is formed on an anode foil and/or a cathode foil, the anode foil and the cathode foil are wound to form a capacitor element, and the capacitor element is impregnated with a driving electrolyte. An electrolytic capacitor characterized by: