Capacitor

Abstract

Provided is a capacitor that does not readily experience trouble at a sealing part, even when used in high-temperature environments.　This capacitor 1 is formed by sealing an opening 11a in a case body 11 that accommodates a capacitor element 12 with an elastic sealing body 13 and is characterized in that the elastic sealing body 13 comprises a hydrogenated acrylonitrile butadiene rubber that has an acrylonitrile content of no more than 50% and has a glass transition temperature of no more than 0°C.

Description

capacitor

[0001] The present invention relates to a capacitor.

[0002] Conventionally, electrolytic capacitors have been used in which a capacitor element impregnated with an electrolyte solution is housed inside a case body made of aluminum or the like, and the opening of the case body is sealed with an elastic seal made of rubber or the like, through which the lead terminals of the capacitor element pass. Because of their material properties such as elasticity and airtightness, butyl rubber (IIR) and ethylene-propylene copolymer rubber (EPDM) are often used as the elastic seal body (see Patent Documents 1 and 2).

[0003] JP-A No. 63-18615 JP-A No. 7-249552

[0004] However, when a capacitor is used in a high-temperature environment, it may be immersed in oil such as mineral oil for cooling purposes, and therefore oil resistance is required. However, the above-mentioned conventional butyl rubber and EPDM do not have sufficient oil resistance, and therefore have a problem of being difficult to apply to products that are intended for such use, such as a shortened lifespan.

[0005] Furthermore, when used in a high-temperature environment, the internal pressure increases due to thermal expansion of the electrolyte and gas generation, which may cause the elastic sealing member to deform or the safety valve to activate, making the battery unusable.

[0006] Therefore, the present invention solves the above problems, and its object is to realize a capacitor that is resistant to deterioration in product quality even when used in mineral oil for cooling purposes, and is resistant to problems at the sealing portion even when used in a high-temperature environment.

[0007] In order to solve the above problems, the capacitor of the present invention is a capacitor in which an opening of a case body accommodating a capacitor element is sealed with an elastic seal, and is characterized in that the elastic seal is made of hydrogenated acrylonitrile butadiene rubber having an acrylonitrile content of 50% or less and a glass transition temperature of 0°C or less.

[0008] In the present invention, the hydrogenated acrylonitrile butadiene rubber preferably has an acrylonitrile content in the range of 18 to 50%, and more preferably in the range of 25 to 45%.

[0009] In the present invention, it is more desirable that the hydrogenated acrylonitrile butadiene rubber has a glass transition temperature of −20° C. or lower.

[0010] In the present invention, the elastic seal is preferably installed in a manner that has at least a portion of an outer surface exposed to the outside, and in this case, the elastic seal desirably has a front-back continuous region that extends continuously from the outer surface to the inner surface facing the capacitor element.

[0011] In the present invention, a plate-like body having a higher modulus of rigidity than the elastic sealing material is preferably laminated on the elastic sealing body. Examples of such a plate-like body include a resin substrate made of phenolic resin, epoxy resin, or the like. Even in this case, the plate-like body is preferably laminated in such a manner that the exposed outer surface of the elastic sealing material and the continuous front-back region are ensured. In this case, it is preferable that there is a gap between the plate-like body and the inner surface of the case body, and that this gap is sealed from the outside by an elastic sealing body that is in close contact with the inner surface of the case body. In this case, even if there is a small gap between the plate-like body (resin substrate) and the case body, this gap serves as a path through which a continuous front-back region that is substantially continuous from the outer surface to the inner surface of the elastic sealing body is formed. Here, it is preferable that the elastic sealing body be in close contact with the inner surface of the case body along the entire periphery.

[0012] According to the present invention, by using hydrogenated acrylonitrile butadiene rubber for the elastic sealant, it is possible to ensure excellent oil resistance and heat resistance, and furthermore, it is possible to maintain the sealing function based on the viscoelasticity of rubber. Furthermore, since the gas permeability is significantly improved compared to conventional materials, it is possible to realize a capacitor that is less likely to experience problems at the sealant even when used in a high-temperature environment.

[0013] FIG. 1 is a schematic cross-sectional view showing the cross-sectional structure of a first embodiment of a capacitor according to the present invention. FIG. 2 is a schematic cross-sectional view showing the cross-sectional structure of a second embodiment of a capacitor according to the present invention. FIG. 3 is a graph showing the gas permeability of hydrogenated acrylonitrile butadiene rubber in an aluminum electrolytic capacitor using an ethylene glycol-based electrolyte solution, compared with a conventional sealing rubber. FIG. 4 is a graph showing the gas permeability of hydrogenated acrylonitrile butadiene rubber in an aluminum electrolytic capacitor using a γ-butyrolactone-based electrolyte solution, compared with a conventional sealing rubber. FIG. 5 is a graph showing the swelling properties of hydrogenated acrylonitrile butadiene rubber and EPDM, based on the relationship between the elapsed time when the rubber is immersed in oil and the change in rubber dimensions. FIG. 6 is a schematic cross-sectional view showing the cross-sectional structure of a third embodiment of a capacitor according to the present invention. FIG. 7 is a schematic cross-sectional view showing the cross-sectional structure of a fourth embodiment of a capacitor according to the present invention.

[0014] Next, embodiments of the present invention will be described in detail with reference to the accompanying drawings. First, a first embodiment of a capacitor according to the present invention will be described with reference to Fig. 1. Capacitor 1 is an example of an aluminum electrolytic capacitor, and includes a case body 11, a capacitor element 12 housed inside this case body 11, and an elastic sealing body 13 attached to an opening 11a of case body 11 and sealing terminals 12a and 12b formed from lead terminals of capacitor element 12 while they are extended. Elastic sealing body 13 is fixed by crimping the outer periphery of case body 11 near opening 11a.

[0015] In this embodiment, elastic sealing member 13 is made of hydrogenated acrylonitrile butadiene rubber (HNBR). Elastic sealing member 13 has outer surface 13a exposed to the outside of capacitor 1 and inner surface 13b facing capacitor element 12, and includes front-to-back continuous region 13c extending continuously from outer surface 13a to inner surface 13b. Elastic sealing member 13 also functions to hermetically seal a pair of terminals 12a, 12b of capacitor element 12 while extending from the inside to the outside.

[0016] The hydrogenated acrylonitrile butadiene rubber used for the elastic sealant 13 preferably has an acrylonitrile content (bound acrylonitrile content) of 50% or less. In particular, the acrylonitrile content is preferably within the range of 18% to 50%, and more preferably within the range of 25% to 45%. This is because, generally, as the acrylonitrile content increases, oil resistance improves but cold resistance decreases. If cold resistance decreases to a certain extent, the viscoelasticity of the elastic sealant 13 as rubber decreases, which may impair its sealing function as a sealant.

[0017] The glass transition temperature (Tg) is an indicator of cold resistance. The hydrogenated acrylonitrile butadiene rubber preferably has a glass transition temperature of 0°C or lower. A glass transition temperature of -20°C or lower is particularly desirable. This improves cold resistance and allows flexibility to be maintained even in low-temperature environments, thereby ensuring the tight sealing of the opening 11a of the case body 11 by the elastic sealing member 13 and preventing leakage of the electrolyte. Some hydrogenated acrylonitrile butadiene rubbers have high cold resistance with a glass transition temperature of -60°C or lower, depending on their composition. However, in the present invention, heat resistance is primarily required, and therefore cold resistance is defined as a condition for having the viscoelasticity of rubber. Generally, the glass transition temperature is preferably within the range of -40°C to -20°C. The preferred range of acrylonitrile content that can achieve this glass transition temperature range is 25% to 45%. The glass transition temperature is significantly affected not only by the acrylonitrile content described above but also by the iodine value or hydrogenation rate, which will be described later.

[0018] The polymer backbone of hydrogenated acrylonitrile butadiene rubber consists of carbon-carbon saturated bonds, acrylonitrile, and carbon-carbon unsaturated bonds (double bonds). The carbon-carbon saturated bonds provide elasticity, heat resistance, chemical stability, ozone resistance, and cold resistance. The amount of carbon-carbon saturated bonds can be measured by the iodine value (the weight (g) of iodine added per 100 g of polymer) or the hydrogenation rate (the proportion of double bonds hydrogenated in the NBR polymer before hydrogenation). The iodine value and the hydrogenation rate have an inverse correlation. The higher the hydrogenation rate, the better the heat aging resistance, which is one of the problems of hydrogenated acrylonitrile butadiene rubber. The thermal decomposition temperature is also higher than that of NBR, exceeding 400°C. In this case, it is preferable that the iodine value is 70 or less and the hydrogenation rate is 75% or more, and it is particularly desirable that the iodine value is 50 or less and the hydrogenation rate is 80% or more. Furthermore, the hydrogenation rate is more preferably 90% or more, and even more preferably 95% or more.

[0019] Acrylonitrile has a cyano group and is structured to provide oil resistance, fuel resistance, and high strength. As the acrylonitrile content increases, oil resistance improves but cold resistance decreases. Therefore, a certain level of acrylonitrile content is necessary, but if cold resistance deteriorates too much (the glass transition temperature increases), the sealing effect due to the viscoelasticity of rubber cannot be expected, so a balance with cold resistance must be achieved. However, as mentioned above, in the region of high hydrogenation rate (for example, when the hydrogenation rate is 80% or more, preferably 90% or more), even if the acrylonitrile content is reduced, the glass transition temperature does not decrease and may even increase. Therefore, it is preferable to set the acrylonitrile content relatively high, at 36-44%.

[0020] The carbon-carbon unsaturated bonds become crosslinked by vulcanization to provide rubber functionality. If the hydrogenation rate is about 90%, either sulfur vulcanization or peroxide vulcanization can be used to crosslink the carbon-carbon unsaturated bonds (double bonds), but if the hydrogenation rate exceeds 95%, the number of double bonds decreases and an organic peroxide must be used.

[0021] Furthermore, among oil-resistant rubbers, such as acrylonitrile butadiene rubber (NBR), rubbers with high heat resistance are usually inferior in strength characteristics, but hydrogenated acrylonitrile butadiene rubber has a tensile strength (breaking strength) superior to other oil-resistant rubbers, at least 1.5 times (30 MPa) that of NBR, and exceeding 40 MPa depending on the blending. Therefore, the sealing body is less likely to deform even in a high-temperature environment, and thermal expansion is also suppressed. Note that the higher the hydrogenation rate of hydrogenated acrylonitrile butadiene rubber, the higher the stress it exhibits at high elongation. From this point of view, the above-mentioned hydrogenation rate range is desirable.

[0022] The elastic sealing member 13 has high oil resistance, heat resistance, heat aging resistance, cold resistance, and mechanical strength, and also has gas permeability suitable for a capacitor. In the capacitor 1, gas is generated from the capacitor element 12 due to a temperature rise or a chemical reaction, which increases the pressure inside the case body 11. This may cause deformation of the elastic sealing member 13 or damage due to activation of the safety valve. To prevent this, the elastic sealing member 13 must be able to permeate and dissipate the gas to the outside while maintaining its airtightness against the electrolyte, thereby releasing the pressure inside the case body 11.

[0023] 3 and 4 are graphs comparing the weight change when a conventional sealing rubber is used as the elastic seal of the aluminum electrolytic capacitor of the first embodiment shown in FIG. 1 and when the elastic seal 13 of this embodiment is used. Here, the change in product weight was compared between a capacitor using a conventional sealing rubber made of ethylene-propylene copolymer rubber and the same capacitor using an elastic seal 13 made of hydrogenated acrylonitrile butadiene rubber in an environment at a temperature of 125°C. FIG. 3 shows data for a capacitor element 12 impregnated with an ethylene glycol-based electrolyte (using ethylene glycol as the electrolyte base (solvent) primarily), and FIG. 4 shows data for a capacitor element 12 impregnated with a γ-butyrolactone-based electrolyte (using γ-butyrolactone as the electrolyte base (solvent) primarily). Gases that permeate the elastic seal 13 include vapors of the solvent and hydrogen gas generated during oxide film repair. This shows that elastic sealing member 13 of this embodiment has gas permeability about 10 times that of the conventional sealing rubber. Therefore, by using elastic sealing member 13, when the internal pressure increases to a certain extent due to gas generated from capacitor element 12, that pressure causes the gas to escape to the outside through front-to-back continuous region 13c, thereby suppressing the increase in internal pressure and preventing deformation of elastic sealing member 13 and activation of the safety valve.

[0024] 5 is a graph showing the swelling of rubber when immersed in oil. The graph shows the relationship between the elapsed time and the dimensional change (%) of the rubber when the hydrogenated acrylonitrile-butadiene rubber used as the elastic sealant in this embodiment and an ethylene-propylene copolymer rubber (EPDM) as a comparative example are immersed in non-polar oils such as mineral oil and fuel oil (gasoline, lubricating oil). As shown in FIG. 5, the hydrogenated acrylonitrile-butadiene rubber used as the elastic sealant in this embodiment has extremely low swelling compared to conventional EPDM, and is extremely high in oil resistance to condenser immersion oil used for cooling condensers.

[0025] FIG. 2 is a schematic cross-sectional view showing the structure of an electrolytic capacitor 1′ according to a second embodiment, which is a modification of the electrolytic capacitor according to the first embodiment. This second embodiment includes the same case body 11, capacitor element 12, and elastic sealing body 13 as the first embodiment, but differs in that a resin substrate 14 made of a phenolic resin, epoxy resin, or the like is laminated on the surface of the elastic sealing body 13. The resin substrate 14 has a higher modulus of rigidity (elasticity) than the elastic sealing body 13, thereby improving the strength of the sealing portion. This structure is particularly suitable for large products. In the illustrated example, the resin substrate 14 is laminated (attached) on the outer surface 13a of the elastic sealing body 13. However, the resin substrate 14 may also be laminated on the inner surface 13b of the elastic sealing body, or the resin substrate 14 may be contained within the elastic sealing body 13. In this example, the continuous region 13c of the elastic sealing body 13 is continuous between the interior and exterior of the case body 11 through an opening 14a in the resin substrate 14. The continuous front-to-back region 13c does not need to be a region that extends in the thickness direction (vertical direction in the figure) of the elastic sealing body 13 as shown, but rather it need only form a path through which gas generated inside the case body 11 can pass through the elastic sealing body 13 and escape to the outside.

[0026] FIG. 6 is a schematic cross-sectional view showing the structure of an electrolytic capacitor 2 according to a third embodiment, which is a block-type capacitor different from the electrolytic capacitors according to the first and second embodiments. In this embodiment, a resin substrate 24, which may be made of the same material as the resin substrate 14 according to the first and second embodiments, is disposed within the opening 11a on the side of the space (inside) housing the capacitor element 12. An elastic sealant 23, made of hydrogenated acrylonitrile butadiene rubber similar to that described above, is laminated on the resin substrate 24 by adhesive bonding or other methods. The resin substrate 24 has a higher rigidity (elastic modulus) than the elastic sealant 23. In this embodiment, the outer surface 23a of the elastic sealant 23 is exposed to the outside, while the inner surface 23b is in contact with the resin substrate 24 and does not face the capacitor element 12 inside the case body 11. However, because the elastic sealant 23 is exposed to the outside, it can be used as an effective sealant material with heat resistance, oil resistance, and cold resistance (hermeticity). Terminal portions 22a and 22b, each having a terminal piece exposed to the outside, penetrate elastic sealing body 23 and resin substrate 24. In this embodiment, elastic sealing body 23 has a planar shape corresponding to opening 11a, and its outer periphery is in close contact with the inner surface of case body 11 within opening 11a of case body 11.

[0027] 7 is a schematic cross-sectional view showing the structure of an electrolytic capacitor according to a fourth embodiment, which is a screw terminal type capacitor different from the electrolytic capacitors according to the first and second embodiments. In this embodiment, a resin substrate 34, which may be made of the same material as the resin substrate 14 according to the first and second embodiments, is disposed inside the opening 11a on the side of the space housing the capacitor element 12 (inside the opening 11a). An elastic sealant 33, made of hydrogenated acrylonitrile butadiene rubber similar to that described above, is laminated on a portion (the upper outer periphery) of the resin substrate 34 by adhesive bonding or the like. The resin substrate 34 has a higher rigidity (elastic modulus) than the elastic sealant 33. In this embodiment, the outer surface 33a of the elastic sealant 33 is exposed to the outside, but the inner surface 33b (and the inner periphery) is in contact with the resin substrate 34 and does not face the capacitor element 12 inside the case body 11. However, because the elastic sealant 33 is exposed to the outside, it can be used as an effective sealant material with heat resistance, oil resistance, and cold resistance (hermeticity). Here, terminal portions 32a and 32b equipped with screw terminals exposed to the outside penetrate resin substrate 34, and pressure valve 35 is attached. Pressure valve 35 is configured to release pressure to the outside when the internal pressure of the accommodation space for capacitor element 12 increases. Note that elastic sealing body 33 in this embodiment is configured in a ring shape in a plan view, and its outer periphery is in close contact with the inner surface of case body 11 along the entire periphery within opening 11a of case body 11.

[0028] As described above, in the capacitors 1, 1', 2, and 3 of each embodiment, by using hydrogenated acrylonitrile-butadiene rubber having an acrylonitrile content of 50% or less and a glass transition temperature of 0°C or less as the elastic sealant 13, 23, and 33, the product life can be maintained even when used in a high-temperature environment in contact with mineral oil or fuel oil, and oil resistance can be improved while ensuring heat resistance, and a certain degree of cold resistance (hermeticity) can be ensured to maintain the sealing function based on the viscoelasticity of rubber. The elastic sealant 13, 23, and 33 uses hydrogenated acrylonitrile-butadiene rubber within the ranges described in this paragraph.

[0029] Furthermore, since the elastic sealing member 13 can achieve gas permeability that is significantly improved over conventional sealing members, in the first and second embodiments, sealing deformation and safety valve activation due to oil immersion or increased internal pressure in high-temperature environments can be prevented. The hydrogenated acrylonitrile-butadiene rubber preferably has an acrylonitrile content in the range of 25% to 45% and a glass transition temperature in the range of −20°C to −40°C, and further desirably has a hydrogenation rate of 90% or higher. When the acrylonitrile content is in the low range, particularly preferred ranges in the above embodiments are an acrylonitrile content of 25% to 31% and a glass transition temperature in the range of −35°C to −40°C. When the acrylonitrile content is in the high range, an acrylonitrile content of 34% to 40% and a glass transition temperature of approximately −28°C to −33°C are preferred. It is even more desirable that the elastic sealing member used in each embodiment be a hydrogenated acrylonitrile-butadiene rubber that satisfies these conditions.

[0030] In particular, in the first and second embodiments, outer surface 13a of elastic sealing body 13 is exposed to the outside, and has front-to-back continuous region 13c that exists continuously from outer surface 13a to inner surface 13b facing capacitor element 12. This makes it possible to take advantage of the oil resistance and heat resistance of hydrogenated acrylonitrile butadiene rubber, and also allows gas generated inside to escape to the outside via front-to-back continuous region 13c, further enhancing the material advantages of elastic sealing body 13, thereby suppressing an increase in internal pressure and preventing deformation of elastic sealing body 13 and activation of the safety valve. In addition, in relation to this point, by configuring elastic sealing body 13 to have a structure in which it is laminated with a resin substrate having a higher rigidity, the rigidity of the sealing portion can be further improved.

[0031] Furthermore, in the third and fourth embodiments, when the opening 11a of the case body 11 is configured to be sealed not by the resin substrate 24, 34 but by the elastic sealing body 23, 33, the elastic sealing body 23, 33 can be considered to have a substantially continuous display area. For example, a (slight) gap may exist between the resin substrate 24, 34 and the inner surface of the case body 11, and this gap is sealed from the outside by (the outer periphery of) the elastic sealing body 23, 33 that is in close contact with the inner surface of the case body 11. In this case, the elastic sealing body 23, 33 has a front-back continuous area that is substantially continuous from the outer surface to the inner surface at the portion (outer periphery) that closes the gap. Here, it is desirable that the elastic sealing body 23, 33 be in close contact with the entire inner surface of the case body 11. This allows the storage space of the case body 11, in which the capacitor element 12 is normally housed, to be reliably sealed despite the presence of the gap.

[0032] The capacitor according to the present invention is not limited to the illustrated examples described above, and various modifications may be made without departing from the spirit and scope of the present invention. For example, the above embodiments illustrate lead-type capacitors 1, 1', in which a capacitor element 12 having terminals 12a, 12b with lead wires is housed in a case body 11, a block-type capacitor 2, and a screw-terminal-type capacitor 3. However, capacitors with various terminal structures, such as surface-mounted capacitors and self-supporting capacitors, may also be used. Furthermore, while the above embodiments illustrate electrolytic capacitors, supercapacitors such as electric double layer capacitors may also be used. Furthermore, although the elastic sealing bodies 13, 23, and 33 shown in FIGS. 1, 6, and 7 have portions of their outer surfaces 13a, 23a, and 33a that are uneven (have protrusions), they may also be flat without any unevenness or protrusions, and are not particularly limited.

[0033] 1, 1', 2, 3... Capacitor, 11... Case body, 11a... Opening, 12... Capacitor element, 12a, 12b... Terminal portion, 13, 23, 33... Elastic sealing material, 13a, 23a, 33a... Outer surface, 13b, 23b, 33b... Inner surface, 13c... Front and back continuous region, 14, 24, 34... Resin substrate, 14a... Opening, 35... Pressure valve

Claims

1. A capacitor in which the opening of a case body housing a capacitor element is sealed with an elastic seal, the elastic seal being made of hydrogenated acrylonitrile butadiene rubber having an acrylonitrile content of 50% or less and a glass transition temperature of 0°C or less.

2. The capacitor of claim 1, wherein the hydrogenated acrylonitrile butadiene rubber has an acrylonitrile content in the range of 18-50%.

3. The capacitor according to claim 2, wherein the hydrogenated acrylonitrile butadiene rubber has a glass transition temperature of -20°C or lower.

4. The capacitor of claim 3, wherein the hydrogenated acrylonitrile butadiene rubber has an acrylonitrile content in the range of 25-45%.

5. The capacitor according to any one of claims 1 to 4, wherein the elastic sealing body is installed in such a manner that it has an outer surface that is at least partially exposed to the outside.

6. The capacitor according to claim 5, wherein the elastic sealing body has a front-back continuous region that is continuous from the outer surface to an inner surface facing the capacitor element.

7. The capacitor according to any one of claims 1 to 4, wherein the elastic sealing body is laminated to a resin substrate having a higher modulus of rigidity than the elastic sealing body.

Images