Capacitor

Abstract

To realize a capacitor in which hindrance hardly occurs in a seal part even in a use mode under a high-temperature environment.SOLUTION: A capacitor 1 according to the present invention, is a capacitor in which an open part 11a of a case body 11 housing a capacitor element 12 is sealed with an elastic sealing body 13. The elastic sealing body 13 is made of a hydrogenation acrylonitrile butadiene rubber of which an acrylonitrile content is 50% or less, and a glass transformation temperature is 0°C or less.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a capacitor.

Background Art

[0002] Conventionally, an electrolytic capacitor has been used, which houses a capacitor element impregnated with an electrolytic solution inside a case body made of aluminum or the like, and the opening of the case body is sealed with an elastic sealing body made of rubber or the like through which the lead terminals of the capacitor element penetrate. As the elastic sealing body, butyl rubber (IIR), ethylene-propylene copolymer rubber (EPDM), etc. are often used due to material properties such as elasticity and airtightness (see Patent Documents 1 and 2).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, when using a capacitor in a high-temperature environment, it may be immersed in oil such as mineral oil for cooling purposes, so oil resistance is required. However, the conventional butyl rubber and EPDM do not have sufficient oil resistance, so there is a problem that it is difficult to apply to products assuming the above usage modes, such as a shortened lifespan.

[0005] Also, when used in a high-temperature environment, the internal pressure rises due to thermal expansion and gas generation of the electrolytic solution, so there is a risk that the elastic sealing body may deform or the safety valve may operate, making it impossible to use.

[0006] Therefore, the present invention solves the above problems, and its objective is to realize a capacitor that does not easily deteriorate in product quality even when used in mineral oil for cooling purposes, and that does not easily experience problems at the sealing portion even when used in high-temperature environments. [Means for solving the problem]

[0007] To solve the above problems, the capacitor according to the present invention is a capacitor in which the opening of a case body housing a capacitor element is sealed with an elastic sealing body, wherein the elastic sealing body 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 18-50%, and more preferably in the range of 25-45%.

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

[0010] In the present invention, it is preferable that the elastic sealing body is installed in a manner that has an outer surface that is exposed to the outside in at least a portion of it. In this case, it is desirable that the elastic sealing body has a continuous front-back region that exists continuously from the outer surface to the inner surface facing the capacitor element.

[0011] In the present invention, it is preferable that a plate-like body with a higher rigidity modulus than the elastic sealing material is laminated onto the elastic sealing body. Examples of this plate-like material include a resin substrate made of phenolic resin, epoxy resin, etc. In this case as well, it is preferable that the plate-like body is laminated in such a manner that the exposed state of the outer surface of the elastic sealing material and the continuous front-back region are ensured. In this case, It is preferable that the plate-like body has an opening, and that the continuous front and back regions exist continuously along a path through the opening.Preferably, there is a gap between the plate-like body and the inner surface of the case body, and 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, if there is even a small gap between the plate-like body (resin substrate) and the case body, this gap will serve as a pathway, forming a continuous front-back region on the elastic sealing body that extends substantially from the outer surface to the inner surface. Here, it is desirable that the elastic sealing body is in close contact with the inner surface of the case body around its entire circumference. [Effects of the Invention]

[0012] According to the present invention, by using hydrogenated acrylonitrile butadiene rubber as the elastic sealing body, it is possible to realize a capacitor that has excellent oil resistance, ensures heat resistance, maintains sealing function based on the viscoelasticity of rubber, and furthermore, has significantly improved gas permeability compared to conventional materials, thereby preventing problems at the sealing portion even when used in high-temperature environments. [Brief explanation of the drawing]

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

[0014] Next, embodiments of the present invention will be described in detail with reference to the attached drawings. First, a first embodiment of the capacitor according to the present invention will be described with reference to Figure 1. Capacitor 1 is an example of an aluminum electrolytic capacitor and has a case body 11, a capacitor element 12 housed inside the case body 11, and an elastic sealing body 13 that is attached to the opening 11a of the case body 11 and seals the terminal portions 12a and 12b, which are lead terminals of the capacitor element 12, with the terminals exposed. The elastic sealing body 13 is fixed by crimping the outer circumference near the opening 11a of the case body 11.

[0015] In this embodiment, the elastic seal 13 is made of hydrogenated acrylonitrile butadiene rubber (HNBR). The elastic seal 13 has an outer surface 13a that is exposed to the outside of the capacitor 1 and an inner surface 13b that faces the capacitor element 12, and includes a continuous front-back region 13c that exists continuously from the outer surface 13a to the inner surface 13b. The elastic seal 13 also has the function of hermetically sealing the pair of terminal portions 12a and 12b of the capacitor element 12 with them led out from the inside to the outside.

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

[0017] As an index of cold resistance, there is a glass transition temperature (Tg). The hydrogenated acrylonitrile-butadiene rubber preferably has a glass transition temperature of 0 °C or lower. In particular, if the glass transition temperature is -20 °C or lower, it is more desirable. Thereby, the cold resistance is improved and flexibility can be maintained even in a low-temperature environment, so that the sealing property of the opening 11a of the case body 11 by the elastic sealing body 13 can be ensured, and leakage of the electrolytic solution can be prevented. Depending on the composition, some hydrogenated acrylonitrile-butadiene rubbers have high cold resistance with a glass transition temperature of -60 °C or lower. However, in the case of the present invention, since heat resistance is mainly required, the cold resistance is defined as a condition for providing viscoelasticity as a rubber. Generally, it is desirable that the glass transition temperature is within the range of -40 °C to -20 °C. The preferable range of the acrylonitrile content that can be compatible with the conditions within this glass transition temperature range is 25% - 45%. The glass transition temperature is greatly affected not only by the above acrylonitrile content but also by the iodine value or hydrogenation rate described later.

[0018] The polymer main chain of the hydrogenated acrylonitrile-butadiene rubber consists of carbon-carbon saturated bonds, acrylonitrile, and carbon-carbon unsaturated bonds (double bonds). The carbon-carbon saturated bond is a structure that provides elasticity, heat resistance, chemical stability, ozone resistance, and cold resistance. As an index of the amount of carbon-carbon saturated bonds, there is an iodine value (the weight (g) of iodine added per 100 g of the polymer) or a hydrogenation rate (the proportion of hydrogenated double bonds contained in the NBR polymer before hydrogenation). The iodine value and the hydrogenation rate have an inverse correlation. The higher the hydrogenation rate, the more the heat aging resistance, which is one of the problems of the hydrogenated acrylonitrile-butadiene rubber, is improved. The thermal decomposition temperature is also higher than that of NBR and exceeds 400 °C. In this case, it is preferable that the iodine value is 70 or lower and the hydrogenation rate is 75% or higher. In particular, it is desirable that the iodine value is 50 or lower and the hydrogenation rate is 80% or higher. Furthermore, it is more preferable that the hydrogenation rate is 90% or higher, and it is even more desirable that the hydrogenation rate is 95% or higher.

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

[0020] The carbon-carbon unsaturated bond becomes a cross-linked structure by vulcanization to impart the function of rubber. If the hydrogenation rate is about 90%, either sulfur vulcanization or peroxide vulcanization can be used for cross-linking the carbon-carbon unsaturated bond (double bond). However, when the hydrogenation rate exceeds 95%, since the number of double bonds decreases, it is necessary to use an organic peroxide.

[0021] Also, usually, among oil-resistant rubbers represented by acrylonitrile-butadiene rubber (NBR), rubbers with high heat resistance often have inferior strength characteristics. However, hydrogenated acrylonitrile-butadiene rubber is superior to other oil-resistant rubbers in terms of tensile strength (breaking strength), being 1.5 times (30 MPa) or more of NBR, and exceeding 40 MPa depending on the formulation. Therefore, the sealing body is less likely to deform even in a high-temperature environment, and thermal expansion is also suppressed. In addition, hydrogenated acrylonitrile-butadiene rubber shows a high stress at high elongation as the hydrogenation rate increases. From this point of view as well, it is desirable to be within the above range of the hydrogenation rate.

[0022] The elastic seal 13 described above has high oil resistance, heat resistance, heat aging resistance, cold resistance, and mechanical strength, and further possesses gas permeability suitable for use as a capacitor. In the capacitor 1, gas is generated from the capacitor element 12 due to temperature rise or chemical reactions, which increases the pressure inside the case body 11. This can cause deformation of the elastic seal 13 or damage due to the activation of the safety valve. To prevent this, the elastic seal 13 needs to release the pressure inside the case body 11 by allowing gas to permeate and dissipate to the outside while maintaining airtightness to the electrolyte.

[0023] Figures 3 and 4 are graphs comparing the weight change of the aluminum electrolytic capacitor of the first embodiment shown in Figure 1 when using conventional sealing rubber and when using the elastic sealing body 13 of this embodiment. Here, ZKB30 (product number, manufactured by Ozato Kikai Co., Ltd.) was used as the conventional ethylene-propylene copolymer rubber. The change in product weight of this conventional capacitor and the same capacitor using the elastic sealing body 13 made of hydrogenated acrylonitrile butadiene rubber was compared under conditions of 125°C. Figure 3 shows the data for a capacitor element 12 impregnated with an ethylene glycol-based electrolyte (mainly using ethylene glycol as the base (solvent) of the electrolyte), and Figure 4 shows the data for a capacitor element 12 impregnated with a γ-butyrolactone-based electrolyte (mainly using γ-butyrolactone as the base (solvent) of the electrolyte). The gases that permeate the elastic sealing body 13 are the vapors of the above-mentioned solvents and hydrogen gas generated during the repair of the oxide film. This shows that the elastic sealing body 13 of this embodiment has about 10 times the gas permeability compared to the sealing rubber of the conventional example. Therefore, by using the elastic sealing body 13, when the internal pressure rises to a certain extent due to the gas generated from the capacitor element 12, the gas escapes to the outside through the continuous front and back region 13c due to that pressure, thereby suppressing the rise in internal pressure and preventing deformation of the elastic sealing body 13 and activation of the safety valve.

[0024] Figure 5 is a graph showing the swelling properties of rubber when immersed in oil. It shows the relationship between the elapsed time and the change in rubber dimensions (%) when hydrogenated acrylonitrile butadiene rubber, used as an elastic sealing body in this embodiment, and 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), respectively. As shown in Figure 5, hydrogenated acrylonitrile butadiene rubber, used as an elastic sealing body in this embodiment, has extremely low swelling properties compared to conventional EPDM, and exhibits extremely high oil resistance to condenser immersion oil used for cooling condensers.

[0025] Figure 2 is a schematic cross-sectional view illustrating the structure of an electrolytic capacitor 1' of a second embodiment, which is a modified version of the electrolytic capacitor of the first embodiment described above. This second embodiment includes a case body 11, a capacitor element 12, and an elastic sealing body 13, similar to the first embodiment, but differs in that a resin substrate 14 made of phenolic resin, epoxy resin, or the like is laminated on the surface of the elastic sealing body 13. Since the resin substrate 14 has a higher rigidity modulus (elastic modulus) than the elastic sealing body 13, the strength of the sealing portion can be improved. 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, but the resin substrate 14 may be laminated on the inner surface 13b of the elastic sealing body, or the resin substrate 14 may be contained inside the elastic sealing body 13. In this example, the continuous front-back region 13c of the elastic sealing body 13 exists continuously between the inside and outside of the case body 11 through an opening 14a provided in the resin substrate 14. Furthermore, the continuous front-back region 13c does not necessarily have to be a region that extends in the thickness direction (up-down direction in the illustration) of the elastic sealing body 13 as shown in the figure. As a result, it is sufficient to 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] Figure 6 is a schematic cross-sectional view illustrating the structure of the electrolytic capacitor 2 of the third embodiment, which is a block-type capacitor different from the electrolytic capacitors of the first and second embodiments described above. In this embodiment, a resin substrate 24, which can be made of the same material as the resin substrate 14 of the first and second embodiments, is placed on the side (inside) of the housing space where the capacitor element 12 is housed within the opening 11a, and an elastic sealing body 23 made of hydrogenated acrylonitrile butadiene rubber, similar to that described above, is laminated on this resin substrate 24 by adhesion (bonding) or the like. This resin substrate 24 has higher rigidity (elastic modulus) than the elastic sealing body 23. In this embodiment, the outer surface 23a of the elastic sealing body 23 is exposed to the outside, but 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, since the elastic sealing body 23 is exposed to the outside, it can be used as an effective sealing material with heat resistance, oil resistance, and cold resistance (sealability). Here, terminal portions 22a and 22b, which have terminal pieces exposed to the outside, penetrate the elastic sealing body 23 and the resin substrate 24. In this embodiment, the elastic sealing body 23 has a planar shape corresponding to the opening 11a, and its outer periphery is in close contact with the inner surface of the case body 11 around its entire circumference within the opening 11a of the case body 11.

[0027] Figure 7 is a schematic cross-sectional view illustrating the structure of a fourth embodiment of an electrolytic capacitor, which is a screw-terminal type capacitor different from the electrolytic capacitors of the first and second embodiments described above. In this embodiment, a resin substrate 34, which can be made of the same material as the resin substrate 14 of the first and second embodiments, is placed on the side (inside) of the housing space where the capacitor element 12 is housed within the opening 11a, and an elastic sealing body 33 made of hydrogenated acrylonitrile butadiene rubber, similar to that described above, is laminated on a part of this resin substrate 34 (upper outer periphery) by adhesion (bonding) or the like. This resin substrate 34 has higher rigidity (elastic modulus) than the elastic sealing body 33. In this embodiment, the outer surface 33a of the elastic sealing body 33 is exposed to the outside, but the inner surface 33b (and inner periphery) is in contact with the resin substrate 34 and does not face the capacitor element 12 inside the case body 11. However, since the elastic sealing body 33 is exposed to the outside, it can be used as an effective sealing material with heat resistance, oil resistance, and cold resistance (sealability). Here, terminal portions 32a and 32b, which are equipped with screw terminals exposed to the outside, pass through the resin substrate 34, and a pressure valve 35 is attached to it. The pressure valve 35 is configured to release pressure to the outside when the internal pressure of the housing space of the capacitor element 12 increases. In this embodiment, the elastic sealing body 33 is configured in an annular shape in plan view, and its outer circumference is in close contact with the inner surface of the case body 11 around its entire circumference within the opening 11a of the case body 11.

[0028] As described above, according to the capacitors 1, 1', 2, and 3 of each embodiment, by using hydrogenated acrylonitrile butadiene rubber with an acrylonitrile content of 50% or less and a glass transition temperature of 0°C or less as the elastic sealing bodies 13, 23, and 33, it is possible to maintain product life even when used in a manner in which the product comes into contact with mineral oil or fuel oil in a high-temperature environment, thereby improving oil resistance while ensuring heat resistance, and maintaining a certain degree of cold resistance (sealability) while maintaining the sealing function based on the viscoelasticity of rubber. The elastic sealing bodies 13, 23, and 33 used are hydrogenated acrylonitrile butadiene rubber within the range described in this paragraph.

[0029] Furthermore, the elastic seal 13 achieves significantly improved gas permeability compared to conventional designs. Therefore, in the first and second embodiments, it is possible to prevent sealing deformation and safety valve activation due to oil immersion or internal pressure rise in high-temperature environments. The hydrogenated acrylonitrile butadiene rubber preferably has an acrylonitrile content in the range of 25%-45% and a glass transition temperature in the range of -20°C-40°C, and it is desirable that the hydrogenation rate is 90% or higher. In the case of a low acrylonitrile content, a particularly preferred range in the above embodiments is an acrylonitrile content of 25%-31% and a glass transition temperature in the range of -35°C-40°C. In the case of a high acrylonitrile content, it is preferable that the acrylonitrile content is 34%-40% and the glass transition temperature is around -28°C-33°C. It is even more desirable that the elastic seal used in each embodiment is hydrogenated acrylonitrile butadiene rubber that satisfies these conditions.

[0030] In particular, in the first and second embodiments, the outer surface 13a of the elastic sealing body 13 is exposed to the outside, and a continuous front-back region 13c exists from the outer surface 13a to the inner surface 13b facing the capacitor element 12. This allows the oil resistance and heat resistance of hydrogenated acrylonitrile butadiene rubber to be utilized, and gas generated inside can be released to the outside via the continuous front-back region 13c. This further enhances the material advantages of the elastic sealing body 13, thereby suppressing the rise in internal pressure and preventing deformation of the elastic sealing body 13 and activation of the safety valve. In relation to this, the rigidity of the sealing portion can be further improved by laminating the elastic sealing body 13 with a resin substrate that has a higher rigidity modulus.

[0031] Furthermore, in the third and fourth embodiments as well, if the opening 11a of the case body 11 is not sealed by the resin substrates 24, 34 but is instead sealed by the elastic sealing bodies 23, 33, then it can be considered that the elastic sealing bodies 23, 33 have a substantially continuous display area. For example, this is the case when there is a (slight) gap between the resin substrates 24, 34 and the inner surface of the case body 11, and this gap is sealed from the outside by the elastic sealing bodies 23, 33 (or their outer periphery) that are in close contact with the inner surface of the case body 11. In this case, the elastic sealing bodies 23, 33 have a continuous front-back area that is substantially continuous from the outer surface to the inner surface in the portion (outer periphery) that closes the gap. Here, it is desirable that the elastic sealing bodies 23, 33 are in close contact with the entire circumference of the inner surface of the case body 11. This ensures that the housing space of the case body 11, where the capacitor element 12 is normally housed, is reliably sealed despite the presence of the gap.

[0032] It should be noted that the capacitors according to the present invention are not limited to the illustrated examples described above, and various modifications can be made without departing from the spirit of the present invention. For example, in the above embodiments, lead-type capacitors 1, 1', block-type capacitor 2, and screw-terminal type capacitor 3 were exemplified, in which a capacitor element 12 equipped with terminals 12a, 12b with lead wires is housed in a case body 11. However, capacitors with various terminal structures such as surface-mount type and board-free type can be used. Also, although electrolytic capacitors were described as an example in the above embodiments, supercapacitors such as electric double-layer capacitors may also be used. Furthermore, in the elastic sealing bodies 13, 23, 33 shown in Figures 1, 6, and 7, a part of the outer surface 13a, 23a, 33a is configured to be uneven (with protrusions), but it may also be flat without unevenness or protrusions, and is not particularly limited. [Explanation of Symbols]

[0033] 1,1′,2,3…Capacitor, 11…Case body, 11a…Opening, 12…Capacitor element, 12a,12b…Terminal section, 13,23,33…Elastic sealing material, 13a,23a,33a…Outer surface, 13b,23b,33b…Inner surface, 13c…Continuous front and back 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 sealing body, and a pair of terminals of the capacitor element are led out from the inside to the outside through the elastic sealing body, The elastic sealing body 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. The elastic sealing body is installed in such a manner that it has an outer surface that is exposed to the outside in at least a portion of it. The elastic sealing body has a continuous front-to-back region that extends from the outer surface to the inner surface facing the capacitor element, A plate-like body with a higher rigidity modulus than the elastic sealing body is laminated to the elastic sealing body in such a manner that the exposed state of the outer surface of the elastic sealing body and the continuous front-back region are ensured. The plate-like body has openings in locations other than the gap between the portion through which the pair of terminals pass and the inner surface of the case body. The capacitor is characterized in that the continuous front and back regions exist continuously along a path through the opening of the plate-like body.

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

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

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

5. The plate-like body is a resin substrate. The capacitor according to any one of claims 1 to 4.

Images