Electrolytic capacitor

Disclosed is an electrolytic capacitor including: a capacitor element including a pair of electrodes; an electrolyte interposed between the pair of electrodes; a pair of leads electrically connected to the pair of electrodes, respectively; a case in which the capacitor element and the electrolyte are accommodated, and that has an opening; a sealing member that seals the opening, and has a pair of insertion holes for leading out the leads; an insulating plate having a pair of through holes for leading out the leads; and a resin member filled between the sealing member and the insulating plate, wherein the insulating plate has a resin bonding surface that abuts against the resin member, and a mounting surface opposed to the resin bonding surface, and includes at least one protrusion or recess on the resin bonding surface.

TECHNICAL FIELD

The present invention relates to an electrolytic capacitor, and particularly relates to an electrolytic capacitor including a resin member between a sealing member and a base plate. Note that the present application is based upon and claims the benefit of priority from the corresponding Japanese Patent Application Nos. 2017-167592 and 2017-167593 both filed on Aug. 31, 2017, the entire contents of which are incorporated herein by reference.

BACKGROUND ART

In general, due to their high reliability, electrolytic capacitors are being widely used, not only for consumer devices, but also as a part of vehicle-mounted circuits that are used under severe conditions. In particular, electrolytic capacitors used in an environment with high temperature and humidity, such as in an engine, are required to ensure operations, for example, at about 150° C. for the period of time on the order of several thousands of hours.

A typical electrolytic capacitor includes a capacitor element including a pair of electrodes; an electrolyte interposed therebetween; a case in which the capacitor element and the electrolyte are accommodate, and that has an opening; a sealing member that is made of butyl rubber and seals the opening; a base plate having a pair of through holes; and a pair of leads that are electrically connected to the pair of electrodes, respectively, and extend from the through holes. Voids are formed between the sealing member and the insulating plate, and the sealing member is substantially exposed to outside air (environment with high temperature and humidity).

In general, the butyl rubber contained in the sealing member is a high-molecular weight polymer, which, upon exposure to air (oxygen) or water (moisture), undergoes oxidation degradation, causing the molecular chains thereof to break down and the molecular weight thereof to decrease. In addition, the sealing member contains carbon, and, when exposed to an environment with high temperature and humidity, undergoes a reduction in volume and becomes susceptible to cracking, and the carbon molecules contained in the sealing member are bound together to increase the conductivity of the sealing member, thus generating a leakage current between the pair of electrodes, which may impair the function of the electrolytic capacitor.

For example, the electrolytic capacitor described in PTL 1 includes a base plate including, at the center thereof, a depressed portion that is depressed so as to receive a lower portion of a capacitor body; and the capacitor body in which a capacitor element including an electrolyte is stored in a tubular metal case that is closed at the top, the lower opening of metal case is sealed by a sealing member, a pair of electrode terminals that are lead out downward from the capacitor element penetrate the sealing member so as to extend downward, and the electrode terminals further penetrate the base plate, and are bent along the bottom surface of the base plate in a direction away from each other. The capacitor body is fixed to the base plate with an adhesive injected into a recess that is provided in a non-depressed portion located around the depressed portion of the base plate and that is open at least on the depressed portion side.

The adhesive described in PTL 1 is injected from the recess of the non-depressed portion located around the depressed portion of the base plate, and serves to reliably fix the base plate and the capacitor body.

Additionally, for example, the chip-type capacitor described in PTL 2 seals the opening of a packaging case by a sealing member made of an elastic rubber or the like, and the so-called curling, in which the opening of the packaging case and a side surface located near the opening are drawn in, is further performed to seal the interior of the packaging case. PTL 2 proposes that, to an end face of a capacitor including a plurality of lead wires all guided out from the end face, an insulating plate having apertures at positions corresponding to the lead wires is abutted against, and the lead wires that are passed through the apertures so as to protrude from the insulating plate are bent along an end face of the insulating plate, and a resin layer is formed in a gap between the end face of the capacitor and the insulating plate, and gaps between the lead wires of the capacitor and the corresponding apertures of the insulating plate.

The resin layer described in PTL 2 is formed in the gap between the end face of the capacitor and the insulating plate, and the gaps between the lead wires of the capacitor and the apertures of the insulating plate, and severs to prevent water or a washing solvent from entering from the spaces between the lead wires, to which stress has been applied by the bending process, and the apertures of the insulating plate, thus realizing high reliability.

CITATION LIST

Patent Literature

SUMMARY OF INVENTION

Technical Problem

However, although the adhesive described in PTL 1 is injected from the recess of the non-depressed portion located around the depressed portion of the base plate, and assists the fixing of the capacitor body to the base plate, the rubber sealing member attached to the opening of the packaging case is easily exposed, during use, to air (oxygen) and/or water (moisture) entering the packaging case via holes provided in the base plate and is very susceptible to oxidation. When oxidized, the sealing member undergoes a reduction in volume and becomes susceptible to cracking, and the molecular weight of the rubber that forms the sealing member is reduced, and the carbon molecules contained in the sealing member are bound together, so that a leakage current tends to be generated between the pair of electrode terminals.

Since the resin layer described in PTL 2 is formed in the gap between the end face of the capacitor and the insulating plate, and the gaps between the lead wires of the capacitor and the apertures of the insulating plate, it can be considered that the sealing member, which is similarly made of an elastic rubber or the like, will be protected from air (oxygen) and/or water (water vapor) entering from the outside. However, the resin layer is made of epoxy resin or silicone resin, and has a coefficient of thermal expansion significantly different from that of the sealing member made of an elastic rubber. Accordingly, the resin layer may be detached from the sealing member by heat shock as a result of a long-term use, resulting in formation of voids in the interface therebetween. When voids are formed between the resin layer and the sealing member, the sealing member made of an elastic rubber is similarly exposed to air (oxygen) and/or water (moisture) entering from the outside, then undergoes oxidation, and becomes susceptible to cracking. Furthermore, a leakage current may be generated between the pair of electrode terminals via water that has been accumulated in the voids.

Therefore, it is an object of an aspect of the present invention to provide an electrolytic capacitor that realizes high reliability over a long period of time even under severe operating conditions, by filling a resin member between a sealing member and an insulating plate (base plate) to enhance the adhesion between the resin member and the sealing member, thus reliably blocking air (oxygen) and/or water (water vapor) entering from the outside to prevent oxidation degradation of the sealing member.

Solution to Problem

An electrolytic capacitor according to an aspect of the present invention includes a capacitor element including a pair of electrodes; an electrolyte interposed between the pair of electrodes; a pair of leads electrically connected to the pair of electrodes, respectively; a case in which the capacitor element and the electrolyte are accommodated, and that has an opening; a sealing member that seals the opening, and has a pair of insertion holes for leading out the leads; an insulating plate having a pair of through holes for leading out the leads; and a resin member filled between the sealing member and the insulating plate, wherein the insulating plate has a resin bonding surface that abuts against the resin member, and a mounting surface opposed to the resin bonding surface, and includes at least one protrusion or recess on the resin bonding surface.

Advantageous Effects of Invention

With the electrolytic capacitor according to an aspect of the present invention, it is possible to realize high reliability over a long period of time even under severe operating conditions, by filling a resin member between a sealing member and an insulating plate (base plate) to enhance the adhesion between the resin member and the sealing member, thus reliably blocking air (oxygen) and/or water (water vapor) entering from the outside to prevent oxidation degradation of the sealing member.

DESCRIPTION OF EMBODIMENTS

Hereinafter, embodiments of an electrolytic capacitor according to the present invention will be described with reference to the accompanying drawings. In the description of the embodiments, terms (e.g., “upper”, “lower”, “outside”, “inside”, etc.) that are used to indicate directions in order to facilitate the understanding are merely illustrative, and these terms are not intended to limit the present invention. In the drawings, constituent parts of the electrolytic capacitor are illustrated in relative dimensions in order to clarify the shape or the characteristics thereof, and are not necessarily shown with the same scale ratio.

First Embodiment

FIG.1is a partial broken-away perspective view partially showing the interior of an electrolytic capacitor1according to a first embodiment of the present invention.FIGS.2(a) to2(c)are a plan view, a bottom view, and a side view, respectively, of the electrolytic capacitor1shown inFIG.1. As schematically shown inFIG.1, the electrolytic capacitor1according to the first embodiment includes a capacitor element10including a pair of electrodes2(only one electrode2is shown in the drawing), an electrolyte (not shown) interposed between the pair of electrodes2, a case20that accommodates the capacitor element10and the electrolyte and has an opening, a base plate50(also referred to as an “insulating plate”) having a pair of through holes51(FIG.3), a resin member40(also referred to as an “adhesive material”) filled between the sealing member30and the base plate50, and a pair of leads60connected to the pair of electrodes2of the capacitor element10and extending from the through holes51of the base plate50. In addition, the base plate50has a resin bonding surface52that abuts against the resin member40, and a mounting surface53opposed thereto, and includes at least one protrusion70on the resin bonding surface52.

Hereinafter, the capacitor element10, the case20, the sealing member30, and the leads60(electrode2) that are widely used for the electrolytic capacitor1will be described with reference to the accompanying drawings. However, the present invention is not limited to these constituent parts, and other capacitor elements, cases, sealing members, and electrodes may be used. Note that the electrolytic capacitor1according to the present invention is also applicable to electrolytic capacitors that use an electrolytic solution or a solid electrolyte such as a conductive polymer as the electrolyte, and the so-called hybrid electrolytic capacitor that uses an electrolytic solution and a solid electrolyte as the electrolyte.

Referring again toFIG.1, the capacitor element10will be described. The capacitor element10is generally formed by winding an anode foil12having a dielectric layer, a cathode foil14, and a separator16that retains an electrolyte between the anode foil12and the cathode foil14. In addition, the capacitor element10includes a pair of electrodes2(only one electrode2is shown inFIG.1) electrically connected to the anode foil12and the cathode foil14, respectively. The capacitor element10further includes a winding stop tape (not shown) with which the outermost layer thereof is fixed.

Although not by way of limitation, the anode foil12is formed by roughening the surface of a metal foil made of a valve metal such as aluminum, tantalum, or niobium, or an alloy containing these valve metals. Surface roughening of the metal foil may be performed using an etching technique such as direct-current electrolysis or alternating-current electrolysis. By roughening the surface of the metal foil, a plurality of projections and depressions can be formed on the surface of the metal foil. The dielectric layer on the anode foil12is formed along the inner wall surfaces of holes or dents (pits) on the roughened surface, so that the surface area can be increased.

The dielectric layer on the anode foil12may be formed, for example, by immersing the metal foil in a chemical formation solution such as an ammonium adipate solution, and subjecting the metal foil (with a voltage applied thereto, if necessary) to chemical formation treatment. In general, the anode foil12can be mass-produced by roughening the surface of a large-sized metal foil containing a valve metal or the like, then subjecting the surface to chemical formation treatment, and thereafter cutting the metal foil to a desired size.

Similarly, the cathode foil14is formed by roughening the surface of a metal foil made of a valve metal such as aluminum, tantalum, or niobium, or an alloy containing these valve metals. If necessary, the cathode foil14may be subjected to surface roughening and/or chemical formation treatment, as in the case of the anode foil12.

Although not by way of limitation, the separator16may be formed, for example, using a non-woven fabric or the like containing fibers of cellulose, polyethylene terephthalate, vinylon, polyamide (e.g., aliphatic polyamide, aromatic polyamide such as aramid).

The capacitor element10can be formed, for example, by stacking and winding the anode foil12on which a dielectric layer is formed, the separator16, and the cathode foil14, and causing the separator16to retain an electrolyte. The capacitor element10shown inFIG.1is formed such that ends of the pair of electrodes2(only one electrode2is shown inFIG.1) are electrically connected to the anode foil12and the cathode foil14, respectively, and the other ends thereof extend from an end face (a lower end face inFIG.1) of the capacitor element10.

As the electrolyte, it is possible to use a solid electrolyte, an electrolytic solution, and a hybrid electrolyte obtained by combining an electrolytic solution and a solid electrolyte or the like. The electrolyte may be a mixture of a non-aqueous solvent and an ionic substance (a solute, e.g., an organic salt) dissolved in the non-aqueous solvent. The non-aqueous solvent may be an organic solvent or an ionic liquid. As the non-aqueous solvent, it is possible to use, for example, ethylene glycol, propylene glycol, sulfolane, γ-butyrolactone, N-methylacetamide and the like. Examples of the organic salt include trimethylamine maleate, triethylamine borodisalicylate, ethyldimethylamine phthalate, mono 1,2,3,4-tetramethylimidazolinium phthalate, and mono 1,3-dimethyl-2-ethylimidazolinium phthalate.

The solid electrolyte contains, for example, a manganese compound or a conductive polymer. As the conductive polymer, it is possible to use, for example, polypyrrole, polythiophene, polyaniline, and derivatives thereof. The solid electrolyte containing a conductive polymer can be formed, for example, by subjecting a raw material monomer to chemical polymerization and/or electrolysis polymerization on the dielectric layer. Alternatively, the solid electrolyte can be formed by applying, to a dielectric layer, a solution in which a conductive polymer is dissolved, or a dispersion in which a conductive polymer is dispersed. Note that the capacitor element is not limited to those described above, and may have any configuration as long as it serves the function of a capacitor element

The sealing member30can be formed using any insulating material, but is preferably formed using a rubber member having high elasticity and high sealing performance. In addition, examples of a rubber member having high heat resistance include silicone rubber, fluorine rubber, ethylene propylene rubber, chlorosulfonated polyethylene rubber (Hypalon rubber, etc.), butyl rubber, and isoprene rubber.

The sealing member30has a planar shape (e.g., a circular plate-shape or a disc shape) corresponding to the shape of the opening of the case20, and is molded in advance so as to have insertion holes (not shown) for passing the tab portions19of the electrodes2therethrough.

Each of the pair of electrodes2has a tab portion19extending from the capacitor element10, and a pair of leads60are connected to the tab portions19inside the sealing member30by welding or the like. Preferably, the tab portions19are formed of, for example, a valve metal such as aluminum, and is covered with an oxide film of that metal. On the other hand, the leads60are formed of, for example, a CP wire, a Cu wire or the like that contains a transition metal such as iron, copper, nickel, and tin. Although a portion of each of the tab portions19and each of the leads60is embedded in the sealing member30, the diameter of the leads60is smaller than the diameter of the tab portions19, and, therefore, an annular space32is formed around each of the leads60in the sealing member30.

Typically, the case20has a substantially cylindrical shape, and has an opening that accommodates the capacitor element10and the sealing member30. The case20having a substantially cylindrical shape has a side portion21, and a substantially annular drawn portion23and a curled portion25that extend continuously with the side portion21. That is, the curled portion25defines the opening of the case20. The case20is formed using, for example, a metal such as aluminum, stainless steel, copper, iron, and brass, or alloys thereof. Note that the side portion21, the drawn portion23, and the curled portion25of the case20may be partially or entirely covered by a laminate film, or may not be covered thereby. The necessity for a covering of a laminate film and the material of the laminate film may be determined based on determining the adhesion compatibility with a resin member40, which will be described below.

The electrolytic capacitor1according to an embodiment of the present invention includes a resin member40filled between the sealing member30and a base plate50, which will be described below.FIG.3(a)is a cross-sectional view of the electrolytic capacitor1, taken along the line III-III inFIG.2(a). As shown inFIG.3(a), in the electrolytic capacitor1, the capacitor element10and the sealing member30are accommodated in the case20. Then, in a state in which the electrolytic capacitor1is vertically inverted from the state shown inFIG.3(a), uncured fluid resin is filled in a space defined by the surface of the sealing member30, the inner surface of the case20and the resin bonding surface52of the base plate50, and the annular spaces32formed around the leads60so as to seal these spaces in a liquid-tight manner, thereby forming a resin member40.

In general, a liquid in the electrolytic capacitor1such as the electrolytic solution may be vaporized, for example, as a result of reflowing under severe conditions or a long-term use under a high-temperature environment, and the vaporized gas may increase the internal pressure of the case20, resulting in a stress applied to the sealing member30. When the internal pressure of the case20is increased, the electrolytic solution may infiltrate (permeate) into the sealing member30, or may reach the resin member40via the space between the sealing member30and the tab portions19of the electrodes2, or minute voids formed in the interface between the sealing member30and the case20. Then, if the electrolytic solution is evaporated and diffused to the outside of the case20, the electrolytic capacitor1is no longer able to maintain its predetermined properties.

However, according to the first embodiment of the present invention, the resin member40is fixed so as to adhere to the case20and the base plate50by providing the base plate50with the protrusion70. Accordingly, even if a liquid such as an electrolytic solution is evaporated in the case20, and infiltrates (permeates) into the sealing member30or reaches the resin member40via minutes voids, the resin member40can substantially suppress or prevent evaporation and diffusion of the electrolytic solution from the inside to the outside of the case20, thus making it possible to maintain the desired reliability of the electrolytic capacitor1.

That is, as described in [Technical Problem] above, the protrusion70according to the first embodiment of the present invention enhances the adhesion (sealing performance) between the resin member40(adhesive material) and each of the case20and the sealing member30by lengthening an entry path of air or the like entering the case20from the outside and an evaporation-diffusion path of a liquid, such as the electrolytic solution in the case20, being evaporated and diffused to the outside, and making these paths intricate (circuitous), thus realizing the desired long-term reliability of the electrolytic capacitor1.

The resin member40according to the first embodiment of the present invention is filled so as to seal the annular spaces32formed around the leads60in a liquid-tight manner. Accordingly, even if the electrolytic solution reaches the interface between the sealing member30and the resin member40, or the annular space32, it is possible to prevent corrosion of the leads60formed of a material containing a transition metal.

Next, the production processes performed before and after filling the resin member40will be described more specifically. After the capacitor element10and the sealing member30have been accommodated in the case20, a portion near the opening end of the side portion21of the case20is drawn (deformed by pressure applied thereto from the circumferential direction), to form a drawn portion23, and the case20is sealed by the sealing member30. Additionally, the opening end of the case20is curled (the opening end is deformed inward in the radial direction) to form a U-shaped or L-shaped curled portion25. That is, the drawn portion23and the curled portion25of the case20are formed so as to be continuous with the side portion21.

Then, in the case20that has been subjected to curling, uncured fluid resin is potted, applied or injected onto the sealing member30, and, thereafter, the base plate50is disposed, with the leads60being passed through the through holes51. At this time, the curled portion25abuts against a portion (referred to as a “reference surface54” in the present application), on which the protrusion70is not formed, of the resin bonding surface52of the base plate50, whereby the case20is aligned with the base plate50in the vertical direction (height direction). Thereafter, the fluid resin is cured, thereby forming a resin member40filled between the sealing member30and the base plate50. Additionally, after the resin member40has been formed by curing the fluid resin, the leads60are bent so as to extend along the mounting surface53of the base plate50.

Preferably, the fluid resin is thermosetting or photo-curable. The fluid resin may contain a filler, a curing agent, a polymerization initiator, and/or a catalyst. The thermosetting fluid resin may contain, for example, epoxy resin, phenol resin, urea resin, polyimide, polyamide imide, polyurethane, diallyl phthalate, or an unsaturated polyester. The filler may contain, for example, one or more insulating compounds (oxide, etc.) such as silica and alumina, or one or more types of insulating particles of glass, a mineral material (talc, mica, clay, etc.) or the like.

The fluid resin may be, or may contain, for example, a thermoplastic resin such as polyphenylene sulfide (PPS) or polybutylene terephthalate (PBT). Additionally, the fluid resin may be injected using a molding technique such as injection molding, insert molding or compression molding.

FIG.3(b)is a plan view of the base plate50shown inFIG.3(a), as viewed from above.FIG.4(a)is a cross-sectional view of another electrolytic capacitor1according to the first embodiment, andFIG.4(b)is a plan view of the base plate50shown inFIG.4(a), as viewed from above.FIG.5is a plan view of a base plate50of yet another electrolytic capacitor1according to the first embodiment, as viewed from above. In the drawings, a set of points (i.e., a circle) at which the curled portion25of the case20abuts against the reference surface54of the base plate50is indicated by the dashed line.

As shown inFIGS.3(b) and4(b), the base plate50according to the embodiment of the present invention, in its simplest form, has a substantially square planar shape, and includes two cut-out portions55for indicating the polarities. In addition, the base plate50has a resin bonding surface52(upper surface) that abuts against the resin member40, and a mounting surface53(lower surface) opposed to a mounting substrate (not shown), and includes at least one protrusion70on the resin bonding surface52. The protrusion70may be a single protrusion formed concentrically with the center of the case as shown inFIG.3(b), or may include two protrusions70as shown inFIG.4(b). Alternatively, the protrusion70may be a combination of a protrusion70disposed near the center and protrusions70extending radially (in the radial direction), as shown inFIG.5. Further, a larger number of protrusions70may be provided, or a grid-shaped or zigzag-shaped protrusion70(not shown) may be provided.

When the electrolytic capacitor1is subjected to a significant change in ambient temperature (thermal shock) during use, the sealing member30tends to significantly expand or contract relative to the resin member40, due to the difference in coefficient of thermal expansion between the sealing member30and the resin member40. However, according to the first embodiment of the present invention, by providing the resin bonding surface52with the protrusion70, it is possible to substantially increase the adhesion strength between the sealing member30and the resin member40to reliably block air (oxygen) and/or water (water vapor) entering from the outside, and to substantially suppress or prevent evaporation and diffusion (reduction) of a liquid such as an electrolytic solution to the outside of the case20, thus ensuring the desired long-term reliability of the electrolytic capacitor1.

Although not illustrated in detail, an inclined portion or a curved portion (not shown) may be provided near each of the through holes51of the base plate50, in order to reduce the stress applied to the leads60when the leads60are bent after the resin member40has been cured. Since the through holes51of the base plate50are formed in the protrusion70, the inclined portion or the curved portion can be easily formed as compared with a case where no protrusion is formed as in the conventional techniques.

Furthermore, the resin member40according to an embodiment of the present invention preferably includes, as shown inFIG.6, peripheral fixing portions42extending from the curled portion25toward the drawn portion23, and configured to restrict or fix the case20from the outside by being bonded to at least a portion of the outer surface of the case20(the detailed description will be given later). Accordingly, the adhesion strength between the resin member40and each of the base plate50and the case20is further improved, so that it is possible to more reliably achieve the blocking of air or the like entering from the outside, and the prevention of evaporation and diffusion of an electrolytic solution or the like to the outside, thus realizing higher reliability of the electrolytic capacitor1.

As described above, the portion (FIG.6) of the resin member40that fixes the case20from the outside is referred to as a peripheral fixing portion42in the present application, for the sake of the convenience. Preferably, the peripheral fixing portion42is integrated in one piece with the resin member40filled between the sealing member30and the base plate50, or in other words, in communication (continuous) with the resin member40. The peripheral fixing portion42can be easily formed by providing a flow channel through which uncured fluid resin for forming the resin member40flows to the outside of the case20.

Next, the configuration of the base plate50or the curled portion25of the case20for forming the peripheral fixing portions42will be described with reference toFIGS.7to11.FIGS.7(a) to7(d)are plan views of a base plate50obtained by forming recessed flow channels56(groove portions) in the reference surface54of the resin bonding surface52of the base plate50shown inFIGS.3(b) and4(b). In the drawings, the recessed flow channels56are hatched, and a set of points (i.e., a dashed circle) at which the curled portion25of the case20abuts against the reference surface54of the base plate50is indicated by the dashed line, for the sake of convenience.

In each of the cases, the curled portion25of the case20abuts against the reference surface54of the resin bonding surface52of the base plate50, and therefore, the position of the case20relative to the base plate50in the vertical direction (height direction) is restricted (aligned). Uncured fluid resin having viscosity is potted or injected onto the sealing member30in a state in which the case20is vertically inverted. Thereafter, when the base plate50is pressed downward with a predetermined pressure, the fluid resin is filled in the space between the sealing member30and each of the reference surface54of the resin bonding surface52of the base plate50, the protrusion70, and the recessed flow channels56(FIG.7), and in the annular spaces32around the leads60.

At this time, the excess fluid resin is extruded to the outside of the case20via the recessed flow channels56, and flows along the outer surface of the case20. That is, the recessed flow channels56provide communication between the fluid resins located inside and outside the curled portion25. Note that it is preferable to prevent entry of air bubbles into the space between the sealing member30and the base plate50when the base plate50is pressed downward. However, the present invention does not require complete prevention of entry of air bubbles, and allows entry of air bubbles to a certain degree. When the fluid resin filled and extruded in this manner has been cured, the resin member40and the peripheral fixing portions42are formed as a single piece.

The fluid resin covers the entire circumference of the curled portion25, and the curled portion25(in particular, an end thereof) is disposed so as to be spaced apart from the sealing member30. In particular, when the curled portion25has an U-shape, the fluid resin is filled so as to abut against the upper surface and the lower surface of the curled portion25including a curved surface protruding downward, and to abut against the inner surface and the outer surface of the distal end of the curled portion25extending in a direction along the resin bonding surface52(i.e., the fluid resin is bonded so as to surround the curled portion25from above, below, the left and the right), so that the resin member40can more firmly fix the curled portion25.

It should be noted that the distal end of the curled portion of PTL 2 described above sticks into the sealing member, and the lower surface of the curled portion is merely bonded to the resin layer, without any resin layer formed on the upper surface of the curled portion. Therefore, the bonding strength between the curled portion and the resin layer is very low.

The recessed flow channels56shown inFIGS.7(a) and7(b)extend toward corner portions57of the base plate50, and the peripheral fixing portions42are formed near the corner portions57of the base plate50. The recessed flow channels56shown inFIGS.7(c) and7(d)extend toward end portions58of the base plate50, and the peripheral fixing portions42are formed near the end portions58of the base plate50. Note thatFIG.8is a cross-sectional view taken along the line VIII-VIII inFIG.7(a), showing the recessed flow channels56extending toward the corner portions57of the base plate50.

The planar dimensions of the base plate50are specified by the user specification or a standard specification, and the peripheral fixing portions42formed near the corner portion57can be formed larger than the peripheral fixing portions42formed near the end portion58. Therefore, the former is more advantageous than the latter in terms of enhancement of the adhesion between the resin member40and each of the base plate50and the case20.

Note that the number of the recessed flow channels56may be three or less, or may be five or more. The planar shape of the recessed flow channels56may be either larger or smaller than that shown in the drawings. Additionally, the recessed flow channels56are not limited to those extending toward the corner portions57or the end portions58, but may extend toward an intermediate position between the corner portion57and the end portion58, and may not necessarily be equidistantly disposed in the circumferential direction.

FIG.9is a bottom view of the curled portion25of the case20, as viewed from below, in which the position at which the base plate50is disposed is indicated by the dashed line. The curled portion25has a substantially annular planar shape, and at least one (four inFIG.9) slit26is formed therein. The slit26of the curled portion25provides communication between the fluid resins located inside and outside the curled portion25, as in the case of the recessed flow channels56of the base plate50.

The curled portion25of the case20abuts against the reference surface54of the resin bonding surface52of the base plate50at a portion where no slit26is provided, and therefore, the position of the case20relative to the base plate50in the vertical direction (height direction) is restricted (aligned). Similarly, when the base plate50is pressed downward with a predetermined pressure after the fluid resin has been potted or injected onto the sealing member30, the fluid resin covers the entire circumference of the curled portion25, and is filled in the space between the sealing member30and the resin bonding surface52of the base plate50, and in the annular spaces32around the leads60. The excess fluid resin is extruded to the outside of the case20via the slit26of the curled portion25, and flows along the outer surface of the case20by the action of gravity. When the fluid resin filled and extruded in this manner has been cured, the resin member40and the peripheral fixing portions42that are in communication (continuous) with each other are formed as a single piece.

Although not illustrated in detail, the number of the slits26of the curled portion25is not limited to four (FIG.9), and may be three or less, or five or more. The slit26is not limited to a slit extending toward the corner portion57of the base plate50, and may be a slit extending toward the end portion58, or a slit extending toward an intermediate position between the corner portion57and the end portion58, and may not necessarily be equidistantly disposed in the circumferential direction.

As described above, it is preferable to prevent entry of air bubbles into the space between the sealing member30and the base plate50when the base plate50is pressed downward with a predetermined pressure after the fluid resin has been potted or injected onto the sealing member30. Therefore, as shown inFIG.10, the base plate50may, while maintaining the reference surface54of the resin bonding surface52thereof in a flat state (seeFIGS.7(c) and7(d)), be configured to have a curved surface on which the protrusion70disposed at the center and the recessed flow channels56extend continuously. That is, the resin bonding surface52of the base plate50may be formed so as to include a curved surface protruding upward from the center thereof toward the periphery thereof, thereby discharging air bubbles, which may be contained in the fluid resin, from the center to the periphery, and further to the outside of the case20from the recessed flow channels56.

The fluid resin may be injected using a molding technique such as injection molding, insert molding or compression molding. As shown inFIG.11, the base plate50may have a resin injection hole59extending therethrough from the resin bonding surface52to the mounting surface53, for injecting uncured fluid resin into the space between the sealing member30and the base plate50. One or more resin injection holes59may be provided. It is preferable that, separately from the resin injection hole59, the base plate50has an exhaust hole (not shown) for discharging air when injecting the fluid resin, and prevents entry of air bubbles into the space between the sealing member30and the base plate50. Upon completion of filling of the fluid resin, the resin injection hole59and the exhaust hole are filled with the fluid resin, as in the case of the space between the sealing member30and the base plate50.

Note that in relation to the cross-sectional views ofFIG.3(a),FIG.4(a)and so forth, it has been described above that the resin member40is s filled so as to completely adhere to the surface of the sealing member30, the inner surface of the case20, the resin bonding surface52of the base plate50, and the leads60in the annular spaces32. However, the present invention is not limited thereto. That is, the present invention does not exclude a resin member40that is slightly spaced apart from the above-described constituent parts, as long as the desired long-term reliability of the electrolytic capacitor1is substantially ensured by providing at least one protrusion70on the resin bonding surface52, thus lengthening an entry path of air or the like entering the case20from the outside and an evaporation-diffusion path of a liquid, such as the electrolytic solution in the case20, being evaporated and diffused to the outside, and making these paths intricate, as described above.

FIGS.12(a) to12(c)andFIGS.13(a) to13(c)are plan views, bottom views, and side views, respectively, similar toFIGS.2(a) to2(c), showing electrolytic capacitors1according to modifications of the first embodiment described above. Note that the electrolytic capacitors1according to the modifications have the same configuration as that of the above-described embodiment except that the base plate50includes wall portions80extending along the case20. Therefore, descriptions of redundant configurations have been omitted.

While the base plate50of the electrolytic capacitor1according to the first embodiment described above is generally called a “flat base plate”, the base plate50of the electrolytic capacitor1according to the modification shown inFIGS.12(a) to12(c)is also referred to as an “alignment flat base plate” because it includes wall portions80extending along the curled portion25of the case20, and the wall portions80serve to align the case20with the base plate50in the horizontal direction. Additionally, the base plate50according to the modification shown inFIGS.13(a) to13(c)is also referred to as a “vibration-resistant base plate” because it includes vibration-resistant wall portions80extending along the side portion21and the drawn portion23of the case20over a longer length, and the vibration-resistant wall portions80serve to reliably fix the case20to the base plate50to enhance the vibration resistance. The “alignment flat base plate” and the “vibration-resistant base plate” both include wall portions80on the corner portions57of the base plate50. Accordingly, in the present application, these base plates will be hereinafter collectively described and referred to as a “vibration-resistant base plate50” for the sake of convenience.

Although the detailed description has been omitted, as described above in the embodiments according to the electrolytic capacitor1including the flat base plate, the recessed flow channels56(groove portions) of the base plate50and the slit26of the curled portion25that provide communication (connection) between the resin member40and the peripheral fixing portions42can be similarly applied to the electrolytic capacitor1including the vibration-resistant base plate.

FIG.14is a cross-sectional view taken along the line XIV-XIV inFIG.13(a), andFIG.15is a cross-sectional view taken along the line XV-XV inFIG.13(a). The vibration-resistant base plate50includes wall portions80at the corner portions57, and is configured such that the resin member40is filled in a gap82formed between the side portion21(alternatively, the drawn portion23or the curled portion25) of the case20and each of the wall portions80, as shown inFIG.15. The higher the wall portions80of the vibration-resistant base plate50, the larger the amount of the fluid resin filled between the case20and the wall portions80of the vibration-resistant base plate50is, so that the adhesion strength between the resin member40and each of the base plate50and the case20can be further increased. Thus, the electrolytic capacitor1including the vibration-resistant base plate50blocks air or the like entering from the outside, and prevents evaporation and diffusion of an electrolytic solution or the like to the outside, thus making it possible to realize higher reliability of the electrolytic capacitor1. As shown inFIG.14, each of the wall portions80has a portion having a small distance from the side portion21of the case20, thus allowing the alignment between the case20and the vibration-resistant base plate50to be performed more accurately.

As described above, in general, the planar dimensions of the base plate50are specified by the user specification or a standard specification. As shown inFIG.16, the diameter of the case20may be reduced, or the planar dimensions of the base plate50may be increased. Then, the wall portion80may be formed not only on the corner portions57of the vibration-resistant base plate50but also so as to surround the case20, thus allowing the fluid resin (the resin member40) to be filled in the gap82provided around the entire circumference of the case20. The fluid resin filled in the gap82provided around the entire circumference of the case20can further increase the adhesion strength between the resin member40and each of the base plate50and the case20, as compared with the fluid resin only filled in the gap82between the corner portions57of the base plate50and the case20. The electrolytic capacitor1including the vibration-resistant base plate50configured in this manner can more reliably achieve the blocking of air or the like entering from the outside and the prevention of evaporation and diffusion of an electrolytic solution or the like to the outside, thus realizing higher reliability of the electrolytic capacitor1.

Second Embodiment

An electrolytic capacitor1according to a second embodiment of the present invention will be described with reference toFIGS.17to27. The electrolytic capacitor1according to the second embodiment generally has the same configuration as that of the first embodiment, except that the base plate50includes at least one recess75on the resin bonding surface52, in place of the protrusion70, and therefore, descriptions of redundant details have been omitted.

FIG.17is a partial broken-away perspective view partially showing the interior of the electrolytic capacitor1according to the second embodiment of the present invention. A plan view, a bottom view, and a side view showing the outer shape of the electrolytic capacitor1according to the second embodiment are the same asFIGS.2(a) to2(c)according to the first embodiment.

A capacitor element10, a case20, a sealing member30, a resin member40, and leads60(electrodes2) that are used for the electrolytic capacitor1according to the second embodiment have the same configurations as those of the first embodiment, and are formed in the same manner as in the first embodiment.

FIG.18(a)is a cross-sectional view of the electrolytic capacitor1according to the second embodiment, similar toFIG.3(a), andFIG.18(b)is a plan view of the base plate shown inFIG.18(a), as viewed from above.FIG.19(a)is a cross-sectional view of another electrolytic capacitor1according to the second embodiment, andFIG.19(b)is a plan view of the base plate50shown inFIG.19(a), as viewed from above.FIG.20is a plan view of a base plate50of yet another electrolytic capacitor1according to the second embodiment, as viewed from above. In the drawings, a set of points (i.e., a circle) at which the curled portion25of the case20abuts against the reference surface54of the base plate50is indicated by the dashed line.

As described above, in the electrolytic capacitors1according to the second embodiment, the base plate50includes at least one recess75on the resin bonding surface52(in particular, seeFIGS.17,18(a) and19(a)).

That is, according to the second embodiment of the present invention, as in the case of the first embodiment, the resin member40is fixed so as to adhere to the case20and the base plate50by providing the base plate50with the recess75. Accordingly, even if a liquid such as an electrolytic solution is evaporated in the case20, and infiltrates (permeates) into the sealing member30or reaches the resin member40via minutes voids, the resin member40can substantially suppress or prevent evaporation and diffusion of the electrolytic solution from the inside to the outside of the case20. Thus, it is possible to maintain the desired reliability of the electrolytic capacitor1.

The recess75according to the second embodiment of the present invention can enhance the adhesion (sealing performance) between the resin member40(adhesive material) and each of the case20and the sealing member30and can lengthen an entry path of air or the like entering the case20from the outside and an evaporation-diffusion path of a liquid, such as the electrolytic solution in the case20, being evaporated and diffused to the outside, and make these paths intricate (circuitous). Thus, it is possible to realize the desired reliability of the electrolytic capacitor1over a longer period of time.

Furthermore, the resin member40according to the second embodiment is filled so as to seal the annular spaces32formed around the leads60in a liquid-tight manner. Accordingly, even if the electrolytic solution reaches the interface between the sealing member30and the resin member40, or the annular space32, it is possible to prevent corrosion of the leads60formed of a material containing a transition metal (seeFIGS.18(a) and19(a)).

The production processes performed before and after filing the resin member40, and the specific properties and the constituent materials of the fluid resin are the same as those of the first embodiment, and therefore, the detailed descriptions thereof have been omitted.

As shown inFIG.18(b)andFIG.19(b), the base plate50(insulating plate), in its simplest form, has a substantially square planar shape, and includes two cut-out portions55for indicating the polarities. In addition, the base plate50has a resin bonding surface52(upper surface) that abuts against the resin member40, and a mounting surface53(lower surface) opposed to a mounting substrate (not shown), and includes at least one recess75on the resin bonding surface52. The recess75may have a circular planar shape formed concentrically with the center of the case as shown inFIG.18(b), or may have a toroidal planar shape as shown inFIG.19(b). Alternatively, the recess75may be a combination of a recess75disposed near the center and recesses75extending radially (in the radial direction), as shown inFIG.20. Further, a larger number of recesses75may be provided, or a grid-shaped or zigzag-shaped recess75(not shown) may be provided.

When the electrolytic capacitor1is subjected to a significant change in ambient temperature (thermal shock) during use, the sealing member30tends to significantly expand or contract relative to the resin member40, due to the difference in coefficient of thermal expansion between the sealing member30and the resin member40. However, according to the second embodiment of the present invention, by providing the resin bonding surface52with the recess75, it is possible to substantially increase the adhesion strength between the sealing member30and the resin member40to reliably block air (oxygen) and/or water (water vapor) entering from the outside, and to substantially suppress or prevent evaporation and diffusion (reduction) of a liquid such as an electrolytic solution to the outside of the case20, thus ensuring the desired long-term reliability of the electrolytic capacitor1.

Furthermore, the resin member40according to the second embodiment of the present invention preferably includes, as shown inFIG.21, peripheral fixing portions42extending from the curled portion25toward the drawn portion23, and configured to restrict or fix the case20from the outside by being bonded to at least a portion of the outer surface of the case20. Accordingly, the adhesion strength between the resin member40and each of the base plate50and the case20is further improved, so that it is possible to more reliably achieve the blocking of air or the like entering from the outside, and the prevention of evaporation and diffusion of an electrolytic solution or the like to the outside, thus realizing higher reliability of the electrolytic capacitor1.

FIGS.22(a) to22(d)are plan views of a base plate50obtained by forming recessed flow channels56(groove portions) in the reference surface54of the resin bonding surface52of the base plate50shown inFIGS.18(b) and19(b). In the drawings, the recessed flow channels56are hatched, and a set of points (i.e., a dashed circle) at which the curled portion25of the case20abuts against the reference surface54of the base plate50is indicated by the dashed line, for the sake of convenience.

The recessed flow channels56shown inFIGS.22(a) and22(b)extend toward the corner portions57of the base plate50, and the peripheral fixing portions42are formed near the corner portions57of the base plate50. The recessed flow channels56shown inFIGS.22(c) and22(d)extend toward the end portions58of the base plate50, and the peripheral fixing portions42are formed near the end portions58of the base plate50. Note thatFIG.23is a cross-sectional view taken along the line XXIII-XXIII inFIG.22(a), showing the recessed flow channels56extending toward the corner portions57of the base plate50.

Although the recessed flow channels56shown inFIG.23are illustrated as having the same depth as the recess75formed in the base plate50on the inner side of the curled portion25, the recessed flow channels56are not limited thereto, and may be formed so as to be deeper or shallower than the recess75.

The configurations of the peripheral fixing portions42, the recessed flow channels56, and the slit26, and the method for forming the peripheral fixing portions42are similar to those described in the first embodiment, and therefore, further descriptions of redundant details have been omitted.

Note that it is preferable to prevent entry of air bubbles into the space between the sealing member30and the base plate50when the base plate50is pressed downward with a predetermined pressure after the fluid resin has been potted or injected onto the sealing member30. Since the base plate50shown inFIG.24is configured to include a curved surface protruding downward from the center thereof to the periphery thereof, air bubbles, which may be contained in the fluid resin, are discharged from the center to the periphery, and further to the outside of the case20from the recessed flow channels56.

As shown inFIG.25, the base plate50may have a resin injection hole59extending therethrough from the resin bonding surface52to the mounting surface53for injecting uncured fluid resin into the space between the sealing member30and the base plate50. One or more resin injection holes59may be provided. It is preferable that, separately from the resin injection hole59, the base plate50has an exhaust hole (not shown) for discharging air when injecting the fluid resin, and prevents entry of air bubbles into the space between the sealing member30and the base plate50. Upon completion of filling of the fluid resin, the resin injection hole59and the exhaust hole are filled with the fluid resin, as in the case of the space between the sealing member30and the base plate50.

Although not illustrated in detail here, the modifications described with reference to theFIGS.12(a) to12(c),FIGS.13(a) to13(c)andFIGS.14to16for the vibration-resistant base plate50(insulating plate) according to the first embodiment can be similarly applied to the second embodiment (the vibration-resistant base plate50including the recess75).

FIGS.26and27are cross-sectional views of an electrolytic capacitor according to the second embodiment, taken along the line XIV-XIV and the line XV-XV, respectively, inFIG.13(a). The vibration-resistant base plate50includes wall portions80at the corner portions57, and is configured such that the resin member40is filled in a gap82formed between the side portion21(alternatively, the drawn portion23or the curled portion25) of the case20and each of the wall portions80, as shown inFIG.27. The higher the wall portions80of the vibration-resistant base plate50, the larger the amount of the fluid resin filled between the case20and the wall portions80of the vibration-resistant base plate50is, so that the adhesion strength between the resin member40and each of the base plate50and the case20can be further increased. Thus, the electrolytic capacitor1including the vibration-resistant base plate50blocks air or the like entering from the outside, and prevents evaporation and diffusion of an electrolytic solution or the like to the outside, thus making it possible to realize higher reliability of the electrolytic capacitor1. As shown inFIG.26, each of the wall portions80has a portion having a small distance from the side portion21of the case20, thus allowing the alignment between the case20and the vibration-resistant base plate50to be performed more accurately.

INDUSTRIAL APPLICABILITY

The present invention is applicable to an electrolytic capacitor including a resin member filled between a sealing member and a base plate.

REFERENCE SIGNS LIST