JP2009088277A - Electrolytic capacitor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrolytic capacitor which can be used at a high temperature above 150°C for a long time. <P>SOLUTION: The electrolytic capacitor constituted by impregnating a capacitor element formed by winding a two poles foil having a lead wire and a separator with an electrolyte, putting the capacitor element in a packaged case, running the lead wire through a through hole of a sealing element, and sealing an opening part with the sealing element is characterized in that a polyimide layer is formed on an end surface of a capacitor body where the lead wire is led out by applying and drying a polyimide precursor solution. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an electrolytic capacitor, and more particularly to an electrolytic capacitor that can withstand use at a high temperature of 150 ° C. or higher.

  Conventionally used electrolytic capacitors have a bottomed cylinder in which a capacitor element is formed by winding an electrode foil provided with a lead wire as an electrode drawing means through a separator to form a capacitor element, and impregnating a driving electrolyte. In an outer case. And a sealing body is mounted | worn with the opening part of this exterior case, and an opening part is sealed by caulking after that, and an electrolytic capacitor is formed (patent document 1).

Normally, a sealing rubber made of butyl rubber or ethylene propylene rubber is used as the electrolytic capacitor sealing body. Moreover, as an electrolytic solution impregnated in a capacitor element of a small, low impedance, 100 WV class electrolytic capacitor, conventionally, γ-butyrolactone is used as a main solvent, and tertiary salts such as phthalic acid and maleic acid are used as solutes. Etc. are known.
Japanese Patent Laid-Open No. 9-7901

  In recent years, the environmental temperature of electrolytic capacitors used for automobile electrical components and inverter lighting has increased to 150 ° C. or higher, but high temperature use of conventional electrolytic capacitors as described above is limited to 125 ° C., Conventional electrolytic capacitors could not withstand long-term use at 150 ° C. or higher.

  Thus, it has been found that the reason why the conventional electrolytic capacitor cannot be used at a high temperature of 150 ° C. or higher for a long time is the heat resistance of the conventional sealing rubber. In other words, when used at a high temperature of 150 ° C. or higher, the conventional sealing rubber undergoes thermal oxidative degradation, resulting in degradation of rubber properties, resulting in decreased rubber strength and airtightness. As a result, the characteristics of the electrolytic capacitor deteriorate. Furthermore, the vapor pressure of the electrolyte solvent inside the electrolytic capacitor increases, the amount of permeation from the sealing rubber increases, and the characteristics of the electrolytic capacitor deteriorate.

  The present invention has been proposed in order to solve the above-described problems of the prior art, and an object of the present invention is to provide an electrolytic capacitor that can withstand long-term use at a high temperature of 150 ° C. or higher. .

  In order to achieve the above object, the present inventor has conducted extensive studies on means capable of preventing thermal oxidation deterioration of the sealing rubber even when used at a high temperature of 150 ° C. or higher for a long time. Has been completed. That is, it has been found that the above problem can be solved by forming an insulating layer made of polyimide on the surface of the sealing rubber by applying and drying a polyimide precursor solution.

(Polyimide)
Polyimide resins have their high thermal and chemical stability, low dielectric constant, and excellent planarization ability. As the polyimide precursor solution for coating the surface of the sealing rubber, a solution in which a polyimide precursor (polyamic acid) is dissolved in a predetermined solvent by 5 wt% or more, preferably 5 to 50 wt%, more preferably 10 to 25 wt% is used. If this range is exceeded, the fluidity of the polyimide precursor solution will be reduced, making it difficult to form a uniform layer, and if it is less than this range, the effect of the present invention will be reduced. In addition, as this polyimide precursor solution, the photosensitive thing which introduce | transduced the non-photosensitive thing and the photopolymerizable photosensitive group is mentioned. As a solvent for the polyimide precursor solution, a ketone solvent is preferable, and among them, cyclohexane and N-methyl-2pyrrolidone are preferable.

(Formation method of polyimide layer)
The capacitor element impregnated with the electrolytic solution is housed in an outer case, a sealing rubber is disposed in the opening, and sealing is performed by drawing, and then re-forming is performed to create an electrolytic capacitor. The non-photosensitive polyimide precursor solution is dropped and applied onto the upper surface of the sealing rubber of the electrolytic capacitor (the end surface of the capacitor body from which the lead wire is drawn) with a dispenser, and then dried and imidized to form a polyimide layer. Form. The polyimide precursor solution may be applied with an applicator or the like. When a photosensitive polyimide precursor solution is used, this solution is dropped and applied to the upper surface of the sealing capacitor sealing rubber with a dispenser or the like, and then photopolymerized by irradiating light such as ultraviolet rays, and then dried and exposed to light. A polyimide layer is formed by removing the base component. When this photosensitive polyimide precursor solution is used, the drying time can be shortened, the thermal stress on the electrolytic capacitor can be reduced, and the polyimide precursor solution is sealed when cured by the ultraviolet irradiation when applied with a dispenser. It is preferable without dripping from the upper surface of the rubber. The drying temperature is preferably 50 to 200 ° C, and more preferably 70 to 150 ° C. The drying time is preferably 0.5 to 3 hours. In addition, the electrolytic capacitor re-forming step may be performed before or after the formation of the polyimide layer.

  In addition, a polyimide layer can be formed on the end surface of the capacitor body of the surface-mount type electrolytic capacitor in which an insulating plate that is installed by penetrating the lead wire is installed on the end surface of the capacitor body from which the lead wire is drawn. Furthermore, when a polyimide layer is formed in the gap between the through hole of the insulating plate and the lead wire inserted into the through hole, the stress on the joint between the lead wire and the electrode foil is alleviated during bending of the lead wire, The effect of improving the leakage current characteristic is also obtained. In addition, when the polyimide layer is formed on the end face of the capacitor body so as to cover the interface between the drawn portion of the outer case and the sealing body, there is a gap between the sealing body contracted due to thermal oxidation deterioration and the drawn portion of the outer case. Although it is easy to occur, since the polyimide layer is formed covering this part, permeation | transmission of electrolyte solution can be suppressed.

(Sealing rubber)
Examples of the sealing rubber include ethylene propylene terpolymer (EPDM), isobutylene isoprene rubber (IIR: commonly called butyl rubber), and butadiene styrene rubber (SBR). Butyl rubber having excellent electrolyte permeability is preferable. Mica, talc (flat shape is preferable), calcined clay, hydrous silicon, anhydrous silicon, carbon black, and the like are added to the elastic rubber.

(Electrolyte solvent)
When a sulfolane solvent such as sulfolane, 3-methylsulfolane, 2,4-dimethylsulfolane, etc. is used as the solvent for the electrolytic solution, the vapor pressure is low, so the permeation amount of the electrolytic solution is small and the high temperature characteristics are further improved. In addition, it is more preferable to use a lactone solvent such as γ-butyrolactone as a secondary solvent because impedance characteristics are improved. The electrolytic capacitor of the present invention has a polyimide layer having a high heat resistance and a low permeability of the electrolyte solvent on the upper surface of the sealing rubber, so that even when used at a high temperature of 150 ° C. or higher for a long time, Rubber deterioration can be prevented. As a result, the diffusion of the electrolytic solution is suppressed, and the permeation amount of the solvent of the electrolytic solution from the rubber is suppressed, so that it can withstand use at a high temperature of 150 ° C. or higher for a long time.

  That is, the deterioration of the sealing rubber under high temperature is due to the progress of thermal oxidation from the surface. Therefore, when a polyimide layer having high heat resistance is formed on the rubber surface, the thermal oxidation from the surface is suppressed and the rubber characteristics are deteriorated. It is suppressed. Further, when the decrease in the solvent of the electrolytic solution is suppressed, it is possible to suppress the decrease in the capacitance and the increase in tan δ due to the decrease in the retained amount of the electrolytic solution. Also, since polyimide has good adhesion to rubber and metal, even after a polyimide layer is formed on the top surface of the sealing rubber, the adhesion between this polyimide layer and rubber and the end face of the case that has been drawn is good. Therefore, it does not peel off from the sealing rubber and is excellent in reliability.

  As described above, according to the present invention, it is possible to provide an electrolytic capacitor that can withstand use at a high temperature of 150 ° C. or higher for a long time.

  The effects of the present invention will be specifically described below with reference to the drawings and examples.

(Example 1)
As shown in FIG. 1, a capacitor element 4 in which an anode foil and a cathode foil are wound through a separator is impregnated with an electrolytic solution, and the capacitor element 4 is housed in an outer case 2 made of aluminum, and is derived from the capacitor element. The sealing rubber 3 provided with a through-hole through which the lead wire 5 penetrated was installed in the opening of the outer case 2 and sealed by drawing, and then re-formed to produce the electrolytic capacitor 1. As an electrolytic solution, a mixed solution of sulfolane 50 wt%, γ-butyrolactone 25 wt%, 1-ethyl-2,3-dimethylimidazolinium phthalate 25 wt% was used. An N-methyl-2-pyrrolidone solution of polyamic acid 20 wt% (non-photosensitive) is dispensed as a polyimide precursor solution on the end face of the electrolytic capacitor 1 (including the upper surface of the sealing rubber and the crimped caulking portion 6). Then, the polyimide layer 7 was formed on the end face of the capacitor body. Butyl rubber was used as the sealing rubber.

(Example 2)
In place of butyl rubber, EPDM was used as the sealing rubber in Example 1 above.

(Conventional example 1)
An electrolytic capacitor was prepared in the same manner as in Example 1, and no polyimide layer was formed on the end face of the capacitor body.

(Conventional example 2)
An electrolytic capacitor was prepared in the same manner as in Example 2, and no polyimide layer was formed on the end face of the capacitor body.

[Comparison result]
The electrolytic capacitors of Examples 1 and 2 and Conventional Examples 1 and 2 produced as described above were allowed to stand at 150 ° C. for 500 hours and 1000 hours, and the amount of electrolyte permeated and the electrical characteristics were measured. The results shown were obtained.

  As is clear from FIG. 2, after 1000 hours, the permeation amount of the electrolytic solution in both Examples 1 and 2 is greatly improved as compared with Conventional Examples 1 and 2. In addition, CAP, tan δ, and impedance characteristics are also greatly improved compared to the conventional examples 1 and 2. By forming a polyimide layer on the surface of the sealing rubber of the example, thermal oxidation from the surface of the sealing rubber is suppressed. It was shown that. Moreover, in general, it is known that when the amount of electrolyte retained decreases in an electrolytic capacitor, the capacitance decreases and tan δ increases, but in the examples, the decrease in electrolyte is greatly suppressed. It is thought that deterioration of electrical characteristics can be suppressed.

Sectional view showing the structure of the electrolytic capacitor It is a table | surface which shows the permeation | transmission amount of the electrolyte solution of Example 1 and 2, and the prior art examples 1 and 2, and an electrical property result.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Electrolytic capacitor 2 ... Exterior case 3 ... Sealing rubber 4 ... Capacitor element 5 ... Lead wire 6 ... Drawing crimping part 7 ... Polyimide layer

Claims (6)

A capacitor element formed by winding a bipolar foil with a lead wire and a separator is impregnated with an electrolytic solution, and the capacitor element is housed in an outer case, and the lead wire is passed through the through hole of the sealing body to open an opening. In an electrolytic capacitor that is sealed with a sealing body,
An electrolytic capacitor, wherein a polyimide layer is formed on an end face of a capacitor body from which the lead wire is drawn by applying and drying a polyimide precursor solution. 2. The electrolytic capacitor according to claim 1, wherein the electrolytic capacitor is provided with an insulating plate that is installed by penetrating the lead wire through an end face of the capacitor body from which the lead wire is drawn. The electrolytic capacitor according to claim 1, wherein the polyimide precursor solution is a polyamic acid solution.   The electrolytic capacitor according to claim 1, wherein the drying temperature is 50 ° C. to 200 ° C.   5. The electrolytic capacitor according to claim 1, wherein the polyimide layer is formed so as to cover an interface between the outer case and the sealing body in the end face of the capacitor main body.   6. The electrolytic capacitor according to claim 1, wherein the sealing body is one or more elastic rubbers selected from ethylene propylene terpolymer, isobutylene isoprene rubber and butadiene styrene rubber.

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