Separator for aluminum electrolytic capacitor and aluminum electrolytic capacitor

Abstract

In a separator for an aluminum electrolytic capacitor having a conductive polymer, short circuit resistance is improved. The constitution of an aluminum electrolytic capacitor separator for an aluminum electrolytic capacitor having a conductive polymer as a cathode material, which is sandwiched between a pair of electrodes, is characterized in that it contains synthetic fibers and a binder, and has a breaking strength of 40 to 180 kPa, a breaking resistance index of 3.5 to 7.5 kPa / (g / m 2 ).

Description

Technical Field

[0001] This invention relates to a separator for aluminum electrolytic capacitors and an aluminum electrolytic capacitor using the separator. Background Technology

[0002] In recent years, electronic devices and automotive electronics have been increasingly becoming more functional. This necessitates higher speeds for the computers used in these devices. The key to this computer speed increase is the increase in CPU processing speed. Due to the increased CPU processing speed, operating frequencies have further increased. Therefore, capacitors used in power supply circuits require improved characteristics at high frequencies.

[0003] In aluminum electrolytic capacitors that use electrolyte in the cathode material (hereinafter referred to as "non-solid electrolytic capacitors"), it is difficult to improve high-frequency characteristics. Therefore, aluminum electrolytic capacitors that use conductive polymers in the cathode material (hereinafter referred to as "solid electrolytic capacitors") are being marketed. Compared with non-solid electrolytic capacitors, solid electrolytic capacitors have the characteristics of low ESR (equivalent series resistance) and excellent high-frequency characteristics.

[0004] Furthermore, in recent years, aluminum electrolytic capacitors (hereinafter referred to as "hybrid electrolytic capacitors") that simultaneously use conductive polymers and electrolytes in the cathode material have been commercialized. Hybrid electrolytic capacitors possess characteristics of both non-solid electrolytic capacitors and solid electrolytic capacitors. That is, they are characterized by having the same capacitance characteristics as non-solid electrolytic capacitors, but with the same low ESR as solid electrolytic capacitors.

[0005] The conductivity mechanism of conductive polymers is electronic conduction, which exhibits high conductivity compared to electrolytes, whose conduction mechanism is ion conduction. Therefore, solid electrolytic capacitors and hybrid electrolytic capacitors using conductive polymers in the cathode material (hereinafter, solid electrolytic capacitors and hybrid electrolytic capacitors are collectively referred to as "conductive polymer capacitors") can achieve lower ESR compared to non-solid electrolytic capacitors.

[0006] Unlike non-solid electrolytic capacitors, solid electrolytic capacitors do not use electrolyte in their cathode material, and the electrolyte does not evaporate from the sealing area, thus extending their lifespan. Solid electrolytic capacitors are particularly suitable for applications requiring less frequent maintenance, and their use is expanding in applications such as radio communication base stations and servers in data centers.

[0007] Furthermore, from the perspectives of reducing the number of components, saving space, and lightweighting, hybrid electrolytic capacitors are used in various applications. In automotive applications such as electric power steering and advanced driver support systems, the safety and reliability of the components used are paramount. Therefore, it is required that the components safely reach their lifespan in the event of a failure. Because the failure mode of hybrid electrolytic capacitors is open circuit, their adoption in automotive applications is expanding.

[0008] There are two methods for forming the conductive polymer layer in a conductive polymer capacitor. One method involves impregnating a polymeric liquid (monomer and oxidant solution) of conductive polymers into an element wound together with electrode foil and separators, followed by polymerization within the element to form the conductive polymer layer (hereinafter referred to as the "polymeric liquid type"). The other method involves impregnating a dispersion of conductive polymers (a dispersion in which conductive polymers are used as the dispersion medium) into the wound element, then drying it to remove the dispersion medium, thereby forming the conductive polymer layer (hereinafter referred to as the "dispersion type").

[0009] Dispersion-type conductive polymer capacitors are said to have better voltage withstand characteristics than polymer-type conductive polymer capacitors, and are used in applications requiring rated voltages of around 50-60V. However, both polymer-type and dispersion-type capacitors have circuits where their insufficient voltage withstand prevents their application, requiring conductive polymer capacitors with higher rated voltages than previously available.

[0010] Therefore, for conductive polymer capacitors, it is required to maintain the characteristics compared to non-solid electrolytic capacitors, namely low ESR, while improving voltage withstand characteristics, i.e., suppressing the occurrence of short-circuit failures. Moreover, for the separators used, the polymer or dispersion of conductive polymers is required to have good impregnation and retention properties, and improved short-circuit withstand performance.

[0011] Cellulose separators are used as spacers in conductive polymer capacitors. Typically, cellulose separators are carbonized after element fabrication. This serves two main purposes. One is to suppress the reaction between the hydroxyl groups of cellulose and oxidizing agents through carbonization. The other purpose is to improve the permeability and retention of the conductive polymer polymer solution or dispersion by increasing the porosity between the fibers constituting the separator through carbonization.

[0012] The carbonization treatment of cellulose separators has the aforementioned effects; however, the heat applied during carbonization causes thermal decomposition of cellulose, which leads to a decrease in the mechanical strength of the separator. Furthermore, cellulose molecules are slowly decomposed under acidic conditions, so even by impregnating the element with a polymer or dispersion of acidic conductive polymers, the decrease in the mechanical strength of the separator becomes significant. To avoid this problem with cellulose separators, separators blended with synthetic fibers are used, for example, the technologies disclosed in Patent Documents 1 to 4.

[0013] Existing technical documents

[0014] Patent documents

[0015] Patent Document 1: Japanese Patent Application Publication No. 2004-235293

[0016] Patent Document 2: Japanese Patent Application Publication No. 2018-73895

[0017] Patent Document 3: Japanese Patent Application Publication No. 2019-176074

[0018] Patent Document 4: Japanese Patent Application Publication No. 2004-146137 Summary of the Invention

[0019] The problem the invention aims to solve

[0020] Patent Document 1 discloses a separator containing non-fibrillated organic fibers, fibrillated polymers with a melting point or thermal decomposition temperature of 250°C or higher, and a water absorption rate of 5 mm / min or higher, as a synthetic fiber. It is claimed that by using this separator, the formation of conductive polymers within the solid electrolytic capacitor becomes more uniform, thereby reducing the ESR of the solid electrolytic capacitor.

[0021] The separator in Patent Document 1 uses a very fine fibrillated polymer with a large aspect ratio. Therefore, by significantly increasing the number of fibers in the separator, the frequency of entanglement between the fibrillated polymers and other fibers is increased, thereby making the separator denser.

[0022] However, even with a dense separator like that in Patent Document 1, there are still issues with weak mechanical strength, such as tensile strength and tear strength, which makes it impossible to suppress short-circuit failures. When the content of fibrillated polymer is increased to improve the short-circuit resistance of the separator in Patent Document 1, the density of the separator becomes too high, the permeability of the polymer and dispersion of the conductive polymer deteriorates, and the ESR cannot be reduced.

[0023] Patent document 2 discloses a wet nonwoven fabric formed from synthetic fibers with an average pore size in the range of 0.5 to 15 μm and a wet tensile strength of 0.30 kN / m or higher after immersion in ion-exchange water at 70°C for 30 minutes. It is claimed that by controlling the average pore size within the range of 0.5 to 15 μm and ensuring a wet tensile strength of 0.3 kN / m or higher after immersion in ion-exchange water at 70°C for 30 minutes, the compactness of the separators can be ensured, and the shape of the separators can be maintained during the re-chemical synthesis process. Therefore, the occurrence of short-circuit failures in aluminum electrolytic capacitors can be suppressed.

[0024] Patent document 3 discloses a wet nonwoven fabric containing polyester main fibers, polyester binder, and polyvinyl alcohol binder. The wet nonwoven fabric has an average pore size of 5.0–20.0 μm, with pore size frequencies in the range of 5.0–15.0 μm accounting for more than 70% of all pore sizes, and pore size frequencies above 20.0 μm accounting for less than 10%. It is said that this configuration can homogenize the gaps between the fibers constituting the separator, thereby improving the short-circuit withstand capability of the separator and enhancing the permeability of the polymer and dispersion of conductive polymers. Therefore, in aluminum electrolytic capacitors using this separator, both increased capacitance and reduced short-circuit failure rate can be achieved simultaneously.

[0025] The separators described in Patent Documents 2 and 3 can suppress the occurrence of short-circuit defects by controlling the average aperture of the separator. However, even with these separators, it is difficult to suppress the deterioration of ESR and the occurrence of short-circuit defects.

[0026] The high density and homogeneity of the separators described in Patent Documents 2 and 3 can help reduce short-circuit defects in capacitors. However, there are cases where the separators have weak mechanical strength, such as tensile strength and tear strength, or where the pores are narrow when used to impregnate or retain conductive polymers or dispersions. Therefore, it has been determined that simply controlling the average pore size of the separators cannot simultaneously achieve good impregnation, retention, and short-circuit resistance in conductive polymers or dispersions.

[0027] Patent document 4 discloses a separator for an electrochemical element, which is a nonwoven fabric containing at least a portion of fibrillated polymer fibers with a fiber diameter of less than 1 μm and a weight-average fiber length ranging from 0.2 to 2 mm, and organic fibers with a fineness of less than 3.3 dtex, having a melting point or thermal decomposition temperature of 250°C or higher. The volume resistivity of the separator for the electrochemical element is 1 × 10⁻⁶. 11 The resistance is above Ω·cm. This configuration allows for the production of a dense separator with high volume resistivity. Furthermore, it has been documented that aluminum electrolytic capacitors using this separator exhibit low internal resistance and excellent high-speed charge / discharge characteristics.

[0028] However, as described in Patent Document 4, even if the separator is dense and can reduce the internal resistance of the capacitor, its mechanical strength, such as tensile strength and tear strength, is weak. Although it has a low ESR, it cannot suppress the occurrence of short circuit failure.

[0029] During the winding of an aluminum electrolytic capacitor containing conductive polymer capacitors, and inside the wound element, various forces in various directions are applied to the separators. For example, there are forces applied along the longitudinal direction of the separator (MD direction: in the case of pulping on a paper machine, the direction of the separator parallel to the direction of travel), forces extending from the center of the wound element towards the outer edge, and forces pressing against unevenness such as burrs on the tabs and electrode foil. Here, as a means to improve the withstand voltage of the aluminum electrolytic capacitor, it is known to increase the thickness of the oxide coating formed on the surface of the anode foil. If the oxide coating becomes thicker, the thickness of the anode foil itself also becomes thicker; therefore, the aforementioned forces applied to the separators become greater.

[0030] In conventional separators, applying various forces in different directions results in the following problems: the bonds between the fibers constituting the separator are severed; uneven fiber density caused by fiber movement leads to fiber loss in areas where fibers were originally present. Consequently, due to these deficiencies, the isolation between the anode and cathode foils becomes insufficient, resulting in short circuits.

[0031] To suppress the occurrence of partial loss of the separator as described above, if the separator is made denser or the bonding area between the fibers is increased, the pores between the fibers constituting the separator become narrower. Therefore, even if the occurrence of short-circuit failure in the capacitor can be suppressed, the permeability and retention of the polymer and dispersion of the conductive polymer are deteriorated, and the deterioration of ESR cannot be suppressed.

[0032] The inventors of this invention conducted in-depth research and found that, in order to balance the permeability and retention of the conductive polymer liquid and dispersion with the improvement of the short-circuit withstand capability of the separator, it is important to improve the stability of the separator under various forces applied in various directions during the winding process and inside the winding coil. In other words, by improving the stability under various forces in various directions, the occurrence of partial defects can be suppressed.

[0033] This invention was made in view of the aforementioned problems. Its object is to improve the short-circuit withstand capability of the separator by enhancing the stability of various forces applied to the separator in various directions during and after winding the element, while maintaining the permeability and retention of the conductive polymer polymer solution or dispersion. Furthermore, its object is to ensure that the ESR of the conductive polymer capacitor using this separator does not deteriorate compared to conventional conductive polymer capacitors, thus suppressing the occurrence of short-circuit failures.

[0034] Solution to the problem The separator of the present invention is made to solve the above-mentioned problem, and has, for example, the following configuration.

[0035] Specifically, the separator, sandwiched between a pair of electrodes and used as the cathode material in an aluminum electrolytic capacitor with a conductive polymer, contains synthetic fibers and a binder. The separator has a bursting strength of 40–180 kPa and a bursting strength index of 3.5–7.5 kPa / (g / m³). 2 ).

[0036] Moreover, for example, the aforementioned synthetic fiber is characterized by containing fibrillated synthetic fibers and non-fibrillated synthetic fibers.

[0037] Moreover, for example, the aforementioned separator contains 70-95% by mass of the aforementioned synthetic fiber and 5-30% by mass of the aforementioned adhesive, and the total mass of the aforementioned separator contains 20-70% by mass of the aforementioned fibrillated synthetic fiber and 10-75% by mass of the aforementioned non-fibrillated synthetic fiber.

[0038] A further characteristic, for example, is that the tensile modulus is 500 to 2000 MPa.

[0039] Furthermore, the aluminum electrolytic capacitor of the present invention is characterized by using a conductive polymer as the cathode material and using the separator of the present invention described above as the separator.

[0040] The effects of the invention

[0041] According to the present invention, by having a configuration that solves the above-mentioned problems, it is possible to obtain a separator that maintains the permeability and retention of the polymer liquid or dispersion of the conductive polymer, while having stability against various forces applied to the separator in various directions during winding and inside the element roll after winding.

[0042] The conductive polymer capacitor using the separator of the present invention has a low ESR but can suppress the occurrence of short-circuit failure. Furthermore, it can facilitate the increase of the withstand voltage of the conductive polymer capacitor. Detailed Implementation

[0043] The following describes in detail the methods for implementing the present invention.

[0044] In this invention, focusing on the partial loss of separators that occur inside the element roll during and after winding, synthetic fibers and adhesives are used to improve the stability of various forces applied to the separators in various directions inside the element roll during and after winding.

[0045] Conventional separators that improve short-circuit withstand capability by increasing the density and homogeneity of the separator have limitations in balancing low ESR with suppression of short-circuit failure. The separator of the present invention improves short-circuit withstand capability by enhancing stability against various forces applied to the separator in various directions, thereby achieving improved short-circuit withstand capability without impairing the permeability and retention of conductive polymers or dispersions.

[0046] The inventors of this invention conducted in-depth research and found that by controlling the burst strength and burst resistance index of the separator within a certain range, it is possible to maintain the permeability and retention of the conductive polymer liquid and dispersion while preventing partial loss, thereby improving short-circuit withstand performance. Furthermore, it was discovered that conductive polymer capacitors using the separator of this invention can simultaneously achieve low ESR and suppress short-circuit failure, thus completing this invention.

[0047] In the manner of carrying out the present invention, the bursting strength and the bursting strength index obtained by dividing the bursting strength by the unit area mass of the separator are used as indicators of the stability of various forces applied to the separator in various directions during and after winding the element.

[0048] Bursting strength differs from mechanical strength such as tensile strength and tear strength when force is applied in a specific direction. It can be measured to withstand forces applied simultaneously from multiple directions. Even for a separator with strong mechanical strength in a specific direction, such as tensile strength or tear strength, its bursting strength may not be strong. When forces are applied from other directions, the bonds between the fibers constituting the separator may be broken, or fibers may move from their original locations, sometimes resulting in partial loss.

[0049] In addition to bursting strength, the bursting strength index can be used as an indicator of the strength of the bonds between the fibers constituting the separator. The bursting strength index represents the bursting strength per unit area mass; therefore, by comparing bursting strength indices, the degree of interweaving and the size of the bonded area of ​​the fibers constituting the separator can be compared. If the bursting strength index is within a certain range, it indicates that the degree of interweaving and the bonded area of ​​the fibers constituting the separator are under control.

[0050] The less interlacing the fibers or the smaller the bonding area, the easier it is for the bonds between the fibers constituting the separator to be broken. Sometimes, partial loss occurs due to fibers moving from where they should be. Conversely, the more interlacing the fibers or the larger the bonding area, the less likely conductive polymers or dispersions are to penetrate into the interior of the separator.

[0051] As described above, by controlling the burst strength and burst index within a certain range, it is possible to provide a separator that maintains the permeability and retention of the polymer liquid and dispersion of conductive polymers while improving the stability of the separator under various forces applied in various directions during winding and inside the element roll after winding.

[0052] The separator used to implement the present invention is, for example, sandwiched between a pair of electrodes and used in an aluminum electrolytic capacitor in which a conductive polymer is used as the cathode material. The separator has a burst strength of 40–180 kPa and a burst strength index of 3.5–7.5 kPa / (g / m³). 2 The preferred tensile strength is 50–160 kPa, and the bursting index is 4.0–7.0 kPa / (g / m²). 2 ).

[0053] In the partition used to implement the present invention, the bursting strength is 40–180 kPa and the bursting index is 3.5–7.5 kPa / (g / m²). 2 This improves the stability of the separator under various forces applied in various directions during and after the element is wound. Furthermore, it can have pores between the fibers constituting the separator, necessary for impregnation and retention of polymeric or dispersion liquids containing conductive polymers.

[0054] Therefore, it is possible to maintain the permeability and retention of conductive polymers and dispersions, and improve their short-circuit resistance without causing partial loss of the separator.

[0055] When the tensile strength is below 40 kPa, it cannot withstand the various forces applied to the separator in different directions during and after the element is wound. The bonds between the fibers constituting the separator are broken, and the fibers move, resulting in uneven density and thus partial defects in the separator. Consequently, the isolation between the anode foil and the cathode foil becomes insufficient. For example, burrs on the electrode foil may penetrate the separator, or the tabs may compress and damage the separator, leading to short circuits.

[0056] The upper limit of the bursting strength is 180 kPa, determined by the thickness and density of the separators suitable for use in conductive polymer capacitors. If the bursting strength exceeds 180 kPa, there is a tendency for the ESR to increase.

[0057] When the bursting index is below 3.5 kPa / (g / m 2 When the bursting index is 3.5 kPa / (g / m), 2Compared to the separators described above, the fibers constituting the separator have weaker bonding. This indicates less fiber interweaving or a smaller bonding area. Consequently, it cannot withstand the various forces applied to the separator in different directions during and after element winding, causing fiber movement and disappearance from their intended locations, resulting in partial deficiencies in the separator. Consequently, the isolation between the anode and cathode foils becomes insufficient, leading to short circuits.

[0058] When the bursting index exceeds 7.5 kPa / (g / m 2 When the bursting index is 7.5 kPa / (g / m), 2 Compared to the separators below, the fibers constituting the separator are excessively bonded together. This indicates that the interweaving of the fibers is excessively dense, or the bonding area between the fibers is large. Consequently, the impregnation of the conductive polymer solution and dispersion becomes uneven, leading to a deterioration in ESR.

[0059] The separator in the embodiments of the present invention contains synthetic fibers from the viewpoint of chemical stability, and an adhesive from the viewpoint of mechanical strength.

[0060] In the embodiments of the present invention, any synthetic fiber can be selected as long as it meets the requirements for burst strength and bursting index. From the viewpoint of the permeability of polymers and dispersions with high acid resistance, oxidation resistance, and conductivity, examples of synthetic fibers that can be used include polyamide fibers, acrylonitrile fibers, polyester fibers, and vinylon fibers.

[0061] In addition, in order to improve the density and mechanical strength of the separator, and further to improve the permeability and retention of the polymer and dispersion of the conductive polymer, the synthetic fiber in the embodiments of the present invention preferably contains fibrillated synthetic fiber and non-fibrillated synthetic fiber.

[0062] Fibrous synthetic fibers refer to synthetic fibers that are produced by processing such as pulping to generate fine fibrils in a branch-like manner from the main component, or synthetic fibers that are manufactured in a branch-like state similar to pulp.

[0063] From the perspective of heat resistance and chemical resistance, fibrillated synthetic fibers are preferably fibrillated polyamide fibers. Specifically, fibrillated aromatic polyamide fibers are preferred.

[0064] Non-fibrillated synthetic fibers refer to synthetic fibers without branched or leaf-like fibrils. Non-fibrillated synthetic fibers can be fibers formed from a single component, fibers formed from multiple components, or have a composite fiber structure. Non-fibrillated synthetic fibers can use polyamide fibers, acrylonitrile fibers, polyester fibers, vinylon fibers, etc. From the viewpoint of chemical resistance and the permeability of polymers and dispersions of conductive polymers, polyamide fibers, acrylonitrile fibers, and polyester fibers are preferred. The adhesive in the embodiments of the present invention is used for bonding between the fibers constituting the separator. Any adhesive can be selected as long as it meets the requirements for burst strength and burst strength index. Furthermore, by forming a coating with the adhesive, it is less likely to cause burrs from the electrode foil to penetrate the separator, or the electrode tabs to compress the separator and cause damage, thus improving the short-circuit resistance of the separator. Here, the coating refers to a membrane-like substance formed by the adhesive under humid and hot conditions, existing at the entanglement points and between the fibers constituting the separator.

[0065] From the perspective of improving mechanical strength and easily forming a coating, polyvinyl alcohol or vinyl alcohol copolymers are preferred as adhesives.

[0066] Furthermore, as a component of the separator in an embodiment of the present invention, it preferably contains 70 to 95% by mass of synthetic fiber and 5 to 30% by mass of adhesive, and preferably contains 20 to 70% by mass of fibrillated synthetic fiber and 10 to 75% by mass of non-fibrillated synthetic fiber in the total mass of the separator.

[0067] When the synthetic fiber content is below 70% by mass and the binder content exceeds 30% by mass, the ESR of conductive polymer capacitors sometimes deteriorates. This is believed to be because the increased binder content leads to a larger film area, which excessively fills the pores between the fibers forming the separator, worsening the permeability and retention of the conductive polymer's polymer solution and dispersion.

[0068] When synthetic fibers exceed 95% by mass and binder is less than 5% by mass, the mechanical strength of the separator is low, failing to improve short-circuit withstand capability and sometimes failing to suppress short-circuit failures in conductive polymer capacitors. When fibrillated synthetic fibers are less than 20% by mass and non-fibrillated synthetic fibers exceed 75% by mass, the density of the separator tends to be low, making it difficult to effectively suppress short-circuit failures. Furthermore, due to the low density, the retention of conductive polymers also tends to decrease, making it difficult to reduce ESR.

[0069] On the other hand, when the percentage of fibrillated synthetic fibers exceeds 70% by mass and the percentage of non-fibrillated synthetic fibers is less than 10% by mass, the density of the separator tends to be high, and the impregnation of the polymer and dispersion of conductive polymers tends to become uneven, with a tendency for ESR characteristics to fluctuate.

[0070] For example, by containing 20-70% by mass of fibrillated synthetic fibers with an average fiber length in the range of 0.3-2.0 mm, 10-75% by mass of non-fibrillated synthetic fibers with a fiber length in the range of 1.5-6.5 mm, and 5-30% by mass of binder, the breaking strength and bursting index can be within a certain range, thus forming the separator of the present invention.

[0071] When the fiber length is shorter than the above value, there is a concern about insufficient tensile strength. When the fiber length is longer than the above value, there is a concern about damage to the homogeneity of the separator, such as its texture.

[0072] In this invention, tensile modulus is used as an indicator of the elasticity of the separator. Tensile modulus represents the deformability within the elastic deformation region; the lower the tensile modulus, the easier it is to stretch and deform with a weak force. Conversely, the higher the tensile modulus, the stronger the force required to achieve deformation.

[0073] The tensile modulus of the separator of the present invention is preferably 500 to 2000 MPa. If the tensile modulus is in the range of 500 to 2000 MPa, the separator has moderate elasticity, and exhibits a soft responsiveness to various forces applied to the separator in various directions during element winding and within the element roll after winding. This results in good conformability to the electrode foil, allowing the formation of a separator with high adhesion to the electrode foil. Consequently, the continuity of the formed conductive polymer can be maintained at the interface between the electrode foil and the separator, reducing the ESR of the conductive polymer capacitor.

[0074] When the tensile modulus is below 500 MPa, the separator is prone to deformation due to various forces applied to it in different directions during and after the element is wound. As a result, the electrode foil and the separator become excessively tightly fitted, and the separator acts as a sealant. Consequently, the impregnation of the conductive polymer liquid or dispersion becomes uneven, and sometimes the ESR reduction effect of the conductive polymer capacitor is not achieved.

[0075] When the tensile modulus exceeds 2000 MPa, the extensibility of the separator is low, which deteriorates the adhesion to the electrode foil. As a result, the continuity of the conductive polymer at the interface between the electrode foil and the separator is damaged, and sometimes the ESR reduction effect of the conductive polymer capacitor cannot be obtained.

[0076] The thickness and density of the separator used to implement the present invention can be adopted without particular limitation to meet the desired characteristics of the conductive polymer capacitor. Typically, separators for conductive polymer capacitors are used with a thickness of 20–100 μm and a density of 0.20–0.60 g / cm³. 3 The thickness and density of the separators on the left and right sides, but not limited to that range.

[0077] There are no particular limitations on the manufacturing method of the separators. From the viewpoint of the homogeneity of the separators, the preferred method is the papermaking method in which the fibers dispersed in water are piled up on the wire, dehydrated, dried and then rolled up.

[0078] In the embodiment of this invention, the separator is a wet nonwoven fabric formed using a papermaking process. The papermaking method for the separator is not particularly limited as long as it meets the requirements for burst strength and bursting index; methods such as long-wire papermaking, short-wire papermaking, and cylinder papermaking can be used, and multiple layers formed by these papermaking methods can be combined. Furthermore, during papermaking, additives such as dispersants, defoamers, and reinforcing agents can be added as long as the impurity content does not affect the conductivity of the separator for conductive polymer capacitors. Post-processing such as reinforcement, hydrophilic processing, calendering, and embossing can also be performed after the paper layers are formed.

[0079] By employing the above configuration, the separator used in implementing the present invention maintains good permeability and retention of the polymeric liquid and dispersion of the conductive polymer, while possessing stability against various forces applied to the separator in various directions during element winding and inside the element roll after winding. No partial loss occurs in the separator, thus improving short-circuit withstand capability. Furthermore, by using this separator in conductive polymer capacitors, short-circuit failures can be suppressed even with low ESR. Consequently, it is beneficial to increase the voltage withstand capability of conductive polymer capacitors.

[0080] [Methods for determining the properties of separators and conductive polymer capacitors]

[0081] The specific determination of the characteristics of the separator and the conductive polymer capacitor in this embodiment was carried out under the following conditions and methods.

[0082] 〔thickness〕

[0083] The thickness of the separator is determined by using the micrometer specified in "JIS C 2300-2 'Cellulose Paper for Electrical Use - Part 2: Test Methods' 5.1 Thickness" under "5.1.1 Measuring Instrument and Measurement Method a Outer Micrometer" and overlapping it to form 10 sheets as described in "5.1.3 Measuring Thickness of Overlapped Paper".

[0084] 〔density〕

[0085] The density of the separator in an oven-dry state was determined according to the method specified in Method B of "JIS C 2300-2' Electrical Cellulose Paper - Part 2: Test Methods' 7.0A Density".

[0086] [Fracture Strength]

[0087] The breaking strength of the separator was determined according to the method specified in "JIS C 2300-2 'Cellulose paper for electrical use - Part 2: Test methods' 11. Bursting strength".

[0088] [Bursting Index]

[0089] The bursting strength index is calculated by dividing the bursting strength value obtained by the above test method by the unit area mass of the separator obtained by the method specified in "JIS C 2300-2' Electrical Cellulose Paper - Part 2: Test Methods' 6. Mass per Unit Area".

[0090] [Tension Modulus]

[0091] The tensile modulus in the longitudinal direction (MD direction) of the separator was determined according to the method specified in "JIS P 8113 'Paper and paperboard - Test methods for tensile properties - Part 2: Constant speed tensile test'".

[0092] [Length-weight average fiber length of protofibrillated synthetic fibers]

[0093] The measurement was performed using the apparatus described in "JIS P 8226-2 'Pulps-Determination of Fibre length by automated optical analysis-Part 2: Unpolarized light method'" (ISO 16065-2 'Pulps-Determination of Fibre length by automated optical analysis-Part 2: Unpolarized light method'), specifically the Fiber Tester PLUS (manufactured by Lorentzen & Wettre). The length-weight average fiber length was taken as the fiber length of the fibrillated synthetic fiber.

[0094] [Fiber length of non-fibrillated synthetic fibers]

[0095] Purchase various commercially available non-fibrillated synthetic fibers and cut them to the desired length as the fiber length of the non-fibrillated synthetic fibers.

[0096] [The manufacturing process of solid electrolytic capacitors]

[0097] Using the separators shown in the following embodiments, comparative examples, and existing examples, two types of solid electrolytic capacitors were manufactured: one with a diameter of 10.0 mm and a height of 10.0 mm and a rated voltage of 35 V and a capacitance of 150 μF, and the other with a rated voltage of 80 V and a capacitance of 22 μF.

[0098] The specific production method is as follows.

[0099] A capacitor element was fabricated by interlocking and winding a 115 μm thick anode foil and a 50 μm thick cathode foil, which had undergone etching and oxide coating treatments respectively, without contacting each other. The outer periphery of the element roll was then secured with tape. The fabricated capacitor element was then dried after undergoing a re-chemical synthesis treatment.

[0100] A solid electrolytic capacitor with a rated voltage of 35V is produced by impregnating the capacitor element with a polymer solution of conductive polymer, followed by heating / polymerization to dry the solvent and form a conductive polymer layer. The conductive polymer polymer solution uses 3,4-ethylenedioxythiophene as the monomer and ferric p-toluenesulfonate solution as the oxidant solution.

[0101] A solid electrolytic capacitor with a rated voltage of 80V is impregnated with a conductive polymer dispersion in its capacitor element, followed by heating / drying to form a conductive polymer layer. The conductive polymer dispersion used is a dispersion in which PEDOT / PSS (a composite formed from poly(3,4-ethylenedioxythiophene) and polystyrene sulfonic acid) is used as the dispersion medium.

[0102] Next, capacitor elements are placed in a specified casing, the opening is sealed, and the capacitors are cured to obtain solid electrolytic capacitors.

[0103] [Manufacturing process of hybrid electrolytic capacitors]

[0104] Using the separators from the various embodiments, comparative examples, and existing examples, two types of hybrid electrolytic capacitors with a diameter of 10.0 mm and a height of 10.5 mm were manufactured: one with a rated voltage of 35 V and a capacitance of 270 μF, and the other with a rated voltage of 160 V and a capacitance of 6.8 μF.

[0105] The specific production method is as follows.

[0106] A capacitor element was fabricated by interlocking and winding a 115 μm thick anode foil and a 50 μm thick cathode foil, which had undergone etching and oxide coating treatments respectively, without contact. The outer periphery of the element roll was secured with tape. The fabricated capacitor element underwent further chemical synthesis and was then dried. A 35V rated voltage hybrid electrolytic capacitor was then impregnated with a conductive polymer solution, followed by heating / polymerization to dry the solvent and form a conductive polymer layer. The conductive polymer solution used 3,4-ethylenedioxythiophene as the monomer and ferric p-toluenesulfonate solution as the oxidant solution.

[0107] A 160V hybrid electrolytic capacitor is impregnated with a conductive polymer dispersion in its capacitor elements, followed by heating / drying to form a conductive polymer layer. The conductive polymer dispersion used is a dispersion containing PEDOT / PSS (a composite formed from poly(3,4-ethylenedioxythiophene) and polystyrene sulfonic acid) as the dispersion medium.

[0108] Then, the driving electrolyte is impregnated into the above-mentioned capacitor element, the capacitor element is placed in a specified casing, the opening is sealed, and it is aged to obtain each hybrid electrolytic capacitor.

[0109] [Evaluation methods for conductive polymer capacitors]

[0110] The specific performance evaluation of the conductive polymer capacitor in this embodiment was carried out under the following conditions and methods.

[0111] [Short circuit failure rate]

[0112] Prepare 1000 wound capacitor elements, count the number of short-circuit defects generated during the curing process, and divide the number of short-circuit defective elements by the number of capacitor elements that have undergone curing, and use the percentage as the short-circuit defect rate.

[0113] [ESR]

[0114] The ESR of the fabricated capacitor element was measured using an LCR meter at a temperature of 20°C and a frequency of 100kHz.

[0115] [Example]

[0116] Hereinafter, specific embodiments of the separator of the present invention will be described.

[0117] [Example 1]

[0118] The separator of Example 1 was obtained by using a raw material consisting of 60% by mass of fibrillated acrylonitrile fiber (length-weight average fiber length 0.8 mm), 30% by mass of aramid fiber (fiber length 2.0 mm), and 10% by mass of polyvinyl alcohol to form a cylinder paper.

[0119] The separator in the completed Example 1 has a thickness of 50 μm and a density of 0.55 g / cm³. 3 The bursting strength is 120 kPa, and the bursting index is 4.4 kPa / (g / m). 2 The tensile modulus is 2030 MPa.

[0120] [Example 2]

[0121] The separator of Example 2 was obtained by using a mixture of 45% by mass of fibrillated polyester fiber (average fiber length 0.5 mm), 50% by mass of vinylon fiber (fiber length 5.0 mm), and 5% by mass of ethylene-vinyl alcohol copolymer to form a cylinder paper.

[0122] The separator in the completed Example 2 has a thickness of 20 μm and a density of 0.45 g / cm³. 3 The bursting strength is 52 kPa and the bursting index is 5.8 kPa / (g / m). 2 Its tensile modulus is 480 MPa.

[0123] [Example 3]

[0124] The separator of Example 3 was obtained by using a mixture of 60% by mass of fibrillated aramid fiber (length-weight average fiber length 0.4 mm), 10% by mass of acrylonitrile fiber (fiber length 5.0 mm) and 30% by mass of polyvinyl alcohol to form a cylinder paper.

[0125] The separator in the completed Example 3 has a thickness of 50 μm and a density of 0.60 g / cm³. 3 The bursting strength is 178 kPa and the bursting index is 5.9 kPa / (g / m). 2 Its tensile modulus is 1320 MPa.

[0126] [Example 4]

[0127] The separator of Example 4 was obtained by using a mixture of 70% by mass of fibrillated aramid fiber (length-weight average fiber length 0.8 mm), 10% by mass of nylon fiber (fiber length 3.0 mm) and 20% by mass of polyvinyl alcohol to form a cylinder paper.

[0128] The separator in the completed Example 4 has a thickness of 40 μm and a density of 0.50 g / cm³. 3 The bursting strength is 135 kPa and the bursting index is 6.8 kPa / (g / m). 2 Its tensile modulus is 1710 MPa.

[0129] [Example 5]

[0130] The separator of Example 5 was obtained by using a raw material mixed with fibrillated acrylonitrile fiber (length-weight average fiber length 1.2 mm) 45% by mass, nylon fiber (fiber length 3.0 mm) 30% by mass and polyvinyl alcohol 25% by mass to form a cylinder paper.

[0131] The separator in the completed Example 5 has a thickness of 80 μm and a density of 0.40 g / cm³. 3The bursting strength is 155 kPa and the bursting index is 4.8 kPa / (g / m). 2 Its tensile modulus is 1620 MPa.

[0132] [Example 6]

[0133] The separator of Example 6 was obtained by using a mixture of 30% by mass of fibrillated aramid fiber (length-weight average fiber length 1.8 mm), 40% by mass of polyester fiber (fiber length 3.0 mm), and 30% by mass of polyvinyl alcohol to form a cylinder paper.

[0134] The separator in the completed Example 6 has a thickness of 100 μm and a density of 0.45 g / cm³. 3 The bursting strength is 163 kPa and the bursting index is 3.6 kPa / (g / m). 2 The tensile modulus is 870 MPa.

[0135] [Example 7]

[0136] The separator of Example 7 was obtained by using a mixture of 45% by mass of fibrillated aramid fiber (length-weight average fiber length 0.6 mm), 40% by mass of acrylonitrile fiber (fiber length 3.0 mm), and 15% by mass of polyvinyl alcohol to form a cylinder paper.

[0137] The separator in the completed Example 7 has a thickness of 50 μm and a density of 0.35 g / cm³. 3 The bursting strength is 100 kPa, and the bursting index is 5.7 kPa / (g / m). 2 Its tensile modulus is 1270 MPa.

[0138] [Example 8]

[0139] The separator of Example 8 was obtained by using a mixture of raw materials containing 20% ​​by mass of fibrillated aramid fibers (length-weight average fiber length 0.3 mm), 50% by mass of acrylonitrile fibers (fiber length 2.0 mm), and 30% by mass of ethylene-vinyl alcohol copolymer to form a cylinder paper.

[0140] The separator in the completed Example 8 has a thickness of 45 μm and a density of 0.35 g / cm³. 3 The bursting strength is 116 kPa and the bursting index is 7.4 kPa / (g / m). 2 Its tensile modulus is 1112 MPa.

[0141] [Example 9]

[0142] The separator of Example 9 was obtained by using a mixture of raw materials containing 30% by mass of fibrillated acrylonitrile fiber (length-weight average fiber length 1.4 mm), 50% by mass of aramid fiber (fiber length 4.0 mm), and 20% by mass of ethylene-vinyl alcohol copolymer to form a cylinder paper.

[0143] The separator in the completed Example 9 has a thickness of 70 μm and a density of 0.40 g / cm³. 3 The bursting strength is 117 kPa and the bursting index is 4.2 kPa / (g / m). 2 Its tensile modulus is 1960 MPa.

[0144] [Example 10]

[0145] The separator of Example 10 was obtained by using a raw material consisting of 20% by mass of fibrillated polyester fiber (length-weight average fiber length 1.6 mm), 75% by mass of acrylonitrile fiber (fiber length 6.0 mm) and 5% by mass of polyvinyl alcohol to form a cylinder paper.

[0146] The separator in the completed Example 10 has a thickness of 40 μm and a density of 0.20 g / cm³. 3 The bursting strength is 41 kPa and the bursting index is 5.1 kPa / (g / m). 2 Its tensile modulus is 533 MPa.

[0147] [Comparative Example 1]

[0148] Using a mixture of 65% by mass of fibrillated aramid fibers (length-weight average fiber length 0.4 mm), 5% by mass of acrylonitrile fibers (fiber length 5.0 mm), and 30% by mass of polyvinyl alcohol, cylinder papermaking was performed to obtain the separator of Comparative Example 1.

[0149] The separator in Comparative Example 1 had a thickness of 40 μm and a density of 0.50 g / cm³. 3 The bursting strength is 158 kPa, and the bursting index is 7.9 kPa / (g / m²). 2 Its tensile modulus is 1420 MPa.

[0150] [Comparative Example 2]

[0151] Using a mixture of 75% by mass of fibrillated aramid fibers (length-weight average fiber length 0.3 mm), 10% by mass of nylon fibers (fiber length 2.0 mm), and 15% by mass of polyvinyl alcohol, cylinder papermaking was performed to obtain the separator of Comparative Example 2.

[0152] The separator in Comparative Example 2 had a thickness of 60 μm and a density of 0.60 g / cm³. 3The bursting strength is 121 kPa and the bursting index is 3.4 kPa / (g / m). 2 Its tensile modulus is 1750 MPa.

[0153] [Comparative Example 3]

[0154] Using a raw material containing 25% by mass of fibrillated acrylonitrile fiber (length-weight average fiber length 1.9 mm), 40% by mass of polyester fiber (fiber length 3.0 mm), and 35% by mass of polyvinyl alcohol, cylinder papermaking was performed to obtain the separator of Comparative Example 3.

[0155] The separator in Comparative Example 3 had a thickness of 80 μm and a density of 0.35 g / cm³. 3 The bursting strength is 187 kPa and the bursting index is 6.7 kPa / (g / m). 2 The tensile modulus is 570 MPa.

[0156] [Comparative Example 4]

[0157] Using a mixture of 15% by mass of fibrillated aramid fibers (length-weight average fiber length 0.5 mm), 60% by mass of acrylonitrile fibers (fiber length 2.0 mm), and 25% by mass of ethylene-vinyl alcohol copolymer, cylinder papermaking was performed to obtain the separator of Comparative Example 4.

[0158] The separator in Comparative Example 4 had a thickness of 35 μm and a density of 0.35 g / cm³. 3 The bursting strength is 94 kPa and the bursting index is 7.7 kPa / (g / m). 2 Its tensile modulus is 980 MPa.

[0159] [Comparative Example 5]

[0160] Using a raw material containing 15% by mass of fibrillated acrylonitrile fiber (length-weight average fiber length 0.9 mm), 80% by mass of acrylonitrile fiber (fiber length 6.0 mm), and 5% by mass of polyvinyl alcohol, cylinder papermaking was performed to obtain the separator of Comparative Example 5.

[0161] The separator in Comparative Example 5 had a thickness of 50 μm and a density of 0.30 g / cm³. 3 The bursting strength is 43 kPa and the bursting index is 2.9 kPa / (g / m). 2 The tensile modulus is 2060 MPa.

[0162] [Comparative Example 6]

[0163] Using a mixture of 45% by mass of fibrillated polyester fiber (length-weight average fiber length 0.4 mm), 52% by mass of vinylon fiber (fiber length 3.0 mm), and 3% by mass of ethylene-vinyl alcohol copolymer, cylinder papermaking was performed to obtain the separator of Comparative Example 6.

[0164] The separator in Comparative Example 6 had a thickness of 20 μm and a density of 0.45 g / cm³. 3 The bursting strength is 35 kPa and the bursting index is 3.9 kPa / (g / m). 2 Its tensile modulus is 460 MPa.

[0165] [Existing Example 1]

[0166] A separator was manufactured using the same method as described in Example 1 of Patent Document 1, resulting in the separator of Existing Example 1.

[0167] The separator in Example 1 has a thickness of 45 μm and a density of 0.36 g / cm³. 3 The bursting strength is 46 kPa and the bursting index is 2.8 kPa / (g / m). 2 ), with a tensile modulus of 720 MPa.

[0168] [Existing Example 2]

[0169] A separator was manufactured using the same method as described in Example 1 of Patent Document 2, resulting in the separator of Existing Example 2.

[0170] The separator in Example 2 has a thickness of 30 μm and a density of 0.55 g / cm³. 3 The bursting strength is 54 kPa and the bursting index is 3.3 kPa / (g / m). 2 Its tensile modulus is 1560 MPa.

[0171] [Existing Example 3]

[0172] A separator was manufactured using the same method as described in Example 1 of Patent Document 3, resulting in the separator of Existing Example 3.

[0173] The separator in Example 3 has a thickness of 60 μm and a density of 0.20 g / cm³. 3 The bursting strength is 94 kPa and the bursting index is 7.8 kPa / (g / m). 2 Its tensile modulus is 540 MPa.

[0174] [Existing Example 4]

[0175] A separator was manufactured using the same method as described in Example 1 of Patent Document 4, resulting in the separator of Existing Example 4.

[0176] The separator in Example 4 has a thickness of 55 μm and a density of 0.33 g / cm³. 3 The bursting strength is 37 kPa and the bursting index is 2.0 kPa / (g / m). 2 Its tensile modulus is 630 MPa.

[0177] The raw materials and formulations of each separator in Examples 1-10, Comparative Examples 1-6, and Existing Examples 1-4 described above are shown in Table 1.

[0178] [Table 1]

[0179]

[0180] Table 2 shows the evaluation results of each separator in Examples 1-10, Comparative Examples 1-6, and Existing Examples 1-4 described above.

[0181] [Table 2]

[0182]

[0183] Conductive polymer capacitors fabricated using the separators from each embodiment, comparative example, and existing example will be described. Solid electrolytic capacitors with a rated voltage of 35V and a capacitance of 150μF, rated voltage of 80V and a capacitance of 22μF, and hybrid electrolytic capacitors with a rated voltage of 35V and a capacitance of 270μF, rated voltage of 160V and a capacitance of 6.8μF, were fabricated using the separators from each embodiment, comparative example, and existing example. The performance evaluation results of each capacitor are shown in Table 3.

[0184] [Table 3]

[0185]

[0186] The following describes in detail the evaluation results of conductive polymer capacitors using the separators of each embodiment, comparative example, and existing example.

[0187] The capacitors using the separators of Examples 1 and 2 have the same ESR as those using the separators of Existing Examples 1 to 4, but have a lower short-circuit failure rate.

[0188] In addition, the capacitors using the separators of Examples 3 to 10 have the same short-circuit failure rate as the capacitors using the separators of Examples 1 and 2, but have a lower ESR.

[0189] It can be assumed that the lower ESR of the separators in Examples 3 to 10 is due to the tensile modulus of the separators being 533 to 1960 MPa, which provides good adhesion to the electrode foil and maintains the continuity of the conductive polymer at the interface between the electrode foil and the separator.

[0190] Therefore, it can be seen that by having appropriate elasticity in the separator, ESR can be reduced. That is, if the tensile modulus of the separator is defined to be in the range of 500-2000 MPa, then low ESR can be achieved in conductive polymer capacitors.

[0191] The thickness, density, and breaking strength of the separator in Comparative Example 1 were at the same level as those in the embodiments, but its bursting index was higher than that of the embodiments, at 7.9 kPa / (g / m³). 2 The capacitor using the separator of Comparative Example 1 has a higher ESR than those of the embodiments.

[0192] The reason for the higher ESR of the capacitor using the separator in Comparative Example 1 is believed to be that the burst index of the separator is as high as 7.9 kPa / (g / m). 2 The fibers constituting the separator are too tightly bonded to each other. It is believed that in the separator of Comparative Example 1, since the content of non-fibrillated synthetic fibers is 5% by mass, it becomes excessively dense, the bursting index is too high, and the impregnation of the polymer and dispersion of conductive polymers becomes uneven.

[0193] This indicates that if the bursting strength index of the separator is 7.5 kPa / (g / m³), then... 2 The following parameters allow for the production of conductive polymer capacitors with low ESR. Furthermore, it is known that by ensuring the content of non-fibrillated synthetic fibers is 10% by mass or more, the impregnation properties of the polymer solution and dispersion of the conductive polymer can be maintained. The thickness, density, and burst strength of the separator in Comparative Example 2 are at the same level as those in the embodiments, but its burst strength index is lower than that of the embodiments, at 3.4 kPa / (g / m³). 2 The capacitor using the separator in Comparative Example 2 had a higher short-circuit failure rate compared to the embodiments. Additionally, its ESR was slightly higher than that of the existing examples.

[0194] The increased short-circuit failure rate of the capacitor using the separator in Comparative Example 2 is attributed to the separator's low burst strength index of 3.4 kPa / (g / m). 2 The fibers constituting the separator have weak bonding. Due to the low bursting index, it is believed that the separator cannot withstand various forces applied to it in various directions during and after winding the element, resulting in partial loss of the separator and short-circuit defects. In addition, the higher ESR of the capacitor using the separator of Comparative Example 2 can be attributed to the original fiberized aramid content of 75% by mass.

[0195] This indicates that if the bursting index is 3.5 kPa / (g / m 2 The above can suppress the occurrence of short-circuit failure in conductive polymer capacitors. Furthermore, it is known that by keeping the content of the original fibrous synthetic fiber below 70% by mass, the deterioration of ESR can be suppressed.

[0196] The separator in Comparative Example 3 had the same thickness, density, and burst strength index as the embodiments, but its burst strength was higher, at 187 kPa. The capacitor using the separator of Comparative Example 3 had a higher ESR compared to the embodiments.

[0197] The reason for the higher ESR of the capacitor using the separator in Comparative Example 3 is believed to be the high breaking strength of the separator, reaching 187 kPa. Since the separator in Comparative Example 3 contains 35% polyvinyl alcohol by mass, its breaking strength is considered excessively high. Furthermore, it fills the pores between the fibers constituting the separator. Therefore, it can be concluded that the conductivity of the polymer and dispersion of the separator in Comparative Example 3 is impaired.

[0198] Therefore, it can be seen that if the tensile strength exceeds 180 kPa, the ESR deteriorates. That is, it indicates that if the tensile strength is below 180 kPa, a separator suitable for conductive polymer capacitors can be formed, resulting in a low ESR. Furthermore, it is known that by keeping the binder content below 30% by mass, the pores between the fibers constituting the separator, necessary for impregnation and retention of the conductive polymer liquid or dispersion, can be created, thus forming a low ESR.

[0199] The separator in Comparative Example 4 had the same thickness, density, and breaking strength as the examples, but its bursting index was as high as 7.7 kPa / (g / m³). 2 The capacitor using the separator in Comparative Example 4 has a higher ESR compared to the other embodiments. Furthermore, the solid electrolytic capacitor with a rated voltage of 80V and the hybrid electrolytic capacitor with a rated voltage of 160V have high short-circuit failure rates.

[0200] The higher ESR of the capacitor using the separator in Comparative Example 4 is attributed to the high burst index of the separator, reaching 7.7 kPa / (g / m). 2 The fibers constituting the separator are too strongly bonded together. Due to the high burst index, it is understood that the bonding area between the fibers constituting the separator is large, suggesting that the impregnation of the conductive polymer solution and dispersion is uneven. Furthermore, in Comparative Example 4, the original fibrous aromatic polyamide content in the separator was 15% by mass; therefore, the separator's density is considered low, leading to a higher short-circuit failure rate in capacitors with high rated voltages.

[0201] In addition to the evaluation of the capacitor using the separator of Comparative Example 1, the evaluation of the capacitor using the separator of Comparative Example 4 also showed that if the burst strength index of the separator is 7.5 kPa / (g / m²), it is effective. 2 Below this level, conductive polymer capacitors can achieve low ESR. Furthermore, it is known that if the content of the original fibrous synthetic fiber is 20% by mass or more, the density of the separator can be improved, thus suppressing the occurrence of short circuits.

[0202] The separator in Comparative Example 5 had the same thickness, density, and breaking strength as the examples, but its bursting index was as low as 2.9 kPa / (g / m³). 2 The capacitor using the separator in Comparative Example 5 has a higher short-circuit failure rate and ESR compared to the embodiments.

[0203] The increased short-circuit failure rate of the capacitor using the separator in Comparative Example 5 is attributed to the separator's low burst strength index of 2.9 kPa / (g / m). 2 The fibers constituting the separator have weak bonding. Furthermore, in the separator of Comparative Example 5, the content of the original fibrous aramid was 15% by mass and the content of acrylic acid was 80% by mass. Therefore, the density of the separator was considered too low, resulting in a higher short-circuit failure rate. Furthermore, the low density of the separator resulted in less retention of conductive polymers and a higher ESR. In addition to the evaluation of the capacitor using the separator of Comparative Example 2, the evaluation of the capacitor using the separator of Comparative Example 5 also showed that if the burst strength index of the separator is 3.5 kPa / (g / m²), the... 2 The above can suppress the occurrence of short-circuit failure in conductive polymer capacitors. Furthermore, it is known that if the content of protofibrillated synthetic fibers is 20% or more by mass and the content of non-protofibrillated synthetic fibers is 75% or less by mass, the density of the separator can be improved, preventing the ESR of the capacitor from deteriorating and suppressing the occurrence of short-circuit failure.

[0204] The separator in Comparative Example 6 had the same thickness, density, and burst strength index as the embodiments, but its burst strength was as low as 35 kPa. The capacitor using the separator of Comparative Example 6 had a higher short-circuit failure rate compared to the embodiments.

[0205] The increased short-circuit failure rate of the capacitor using the separator in Comparative Example 6 is attributed to the separator's low breaking strength of 35 kPa. This makes it unable to withstand the various forces applied to the separator in different directions during element winding and within the element roll, resulting in partial defects in the separator and insufficient isolation between the anode and cathode foils. Furthermore, the separator in Comparative Example 6 contains 3% by mass of ethylene-vinyl alcohol copolymer, thus contributing to its lower breaking strength.

[0206] This indicates that if the tensile strength of the separator is above 40 kPa, it can suppress the occurrence of short-circuit failure in conductive polymer capacitors. Furthermore, if the binder content is above 5% by mass, it can improve the tensile strength of the separator and enhance its short-circuit withstand capability.

[0207] The separator in Existing Example 1 is the same as the separator described in Example 1 of Patent Document 1. The bursting strength index of the separator in Existing Example 1 is as low as 2.8 kPa / (g / m³). 2 Therefore, the short-circuit failure rate is also high in the evaluation results of capacitors.

[0208] The separator in Existing Example 2 is the same as the separator described in Example 1 of Patent Document 2. The bursting strength index of the separator in Existing Example 2 is as low as 3.3 kPa / (g / m³). 2 Therefore, the short-circuit failure rate is also high in the evaluation results of capacitors.

[0209] Based on the evaluation results of capacitors using the separators in Existing Examples 1 and 2, and a comparison with the various embodiments, it is evident that simply containing 20-70% by mass of fibrillated synthetic fibers and 10-75% by mass of non-fibrillated synthetic fibers in the separator is insufficient to suppress short-circuit failure; an adhesive is necessary. Furthermore, it is clarified that if the burst strength index of the separator is 3.5 kPa / (g / m³),... 2 The above can suppress the occurrence of short circuit failure.

[0210] Furthermore, it is believed that the separator in Example 2 is a separator with controlled wet tensile strength. Although it is resistant to forces from one direction, it is weak in resistance to forces from various directions and cannot suppress the occurrence of short circuit failures. Therefore, it can be seen that by setting the breaking strength and bursting index within a certain range, the stability against forces from various directions can be improved, and the occurrence of short circuit failures can be suppressed.

[0211] The separator in Existing Example 3 is the same as the separator described in Example 1 of Patent Document 3. The bursting strength index of the separator in Existing Example 3 is as high as 7.8 kPa / (g / m³). 2 The evaluation results of the capacitors using the separators in Example 3 showed a high short-circuit failure rate and a high ESR.

[0212] The separator in Example 3 is made of non-fiberized synthetic fibers and polyvinyl alcohol. Therefore, it is believed that the separator has low density, resulting in a higher short-circuit failure rate for the capacitors. Furthermore, it is believed that the higher ESR of the capacitors using the separator in Example 3 is due to the high burst index of 7.8 kPa / (g / m³). 2Based on the evaluation results of the capacitors in Existing Examples 2 and 3, and a comparison with the various embodiments, it was found that controlling the average aperture of the separator alone was insufficient to suppress short-circuit failures in conductive polymer capacitors. It was necessary to improve the stability of the separator under various forces applied in various directions during element winding and within the element roll. In other words, it was determined that the breaking strength and burst strength index of the separator must be within a certain range. The separator in Existing Example 4 is the same as the separator described in Example 1 of Patent Document 4. Evaluation results of the capacitor using the separator in Existing Example 4 showed a high short-circuit failure rate and a high ESR.

[0213] The reason given for the increased short-circuit failure rate of the capacitor using the separator of Existing Example 4 is that the breaking strength of the separator in Existing Example 4 is as low as 37 kPa and the burst strength index is as low as 2.0 kPa / (g / m). 2 This component cannot withstand the various forces applied to the separator in different directions during element winding and within the element roll. Furthermore, the separator in Existing Example 4 has a cellulose content of 15% by mass. Therefore, it is believed that by impregnating and retaining the conductive polymer solution or dispersion, the separator's breaking strength decreases, and the short-circuit failure rate further increases. Moreover, due to the presence of cellulose, the impregnation and retention properties of the conductive polymer solution or dispersion are reduced, resulting in a higher ESR.

[0214] Based on the evaluation results of the capacitor in Example 4 and the comparison with various embodiments, it can be seen that in the separator containing cellulose, it is impossible to improve the short-circuit resistance while maintaining the permeability and retention of the polymer liquid and dispersion of conductive polymer. It must be composed only of synthetic fibers and binders.

[0215] As explained above, according to embodiments of the present invention, the bursting strength of the separator containing synthetic fibers and binder is controlled to be 40–180 kPa and the bursting index is controlled to be 3.5–7.5 kPa / (g / m²). 2 This invention improves the stability of the separator under various forces applied in various directions during and after winding the element, while maintaining the permeability and retention of the conductive polymer polymer solution and dispersion. Therefore, partial loss of the separator can be suppressed. Furthermore, the ESR of the conductive polymer capacitor using the separator of this invention is not deteriorated, and short-circuit failures can be suppressed. In addition, by setting the tensile modulus of the separator to a range of 500–2000 MPa, the adhesion between the electrode foil and the separator can be controlled, resulting in a lower ESR for the conductive polymer capacitor.

[0216] As described above, the conductive polymer capacitor using the separator of this embodiment can suppress the occurrence of short-circuit failures without deteriorating the ESR. Furthermore, it can also facilitate the increase of the withstand voltage of the conductive polymer capacitor.

Claims

1. A separator for an aluminum electrolytic capacitor, characterized in that, It is sandwiched between a pair of electrodes and used in aluminum electrolytic capacitors where the cathode material is a conductive polymer. The separator contains synthetic fibers and adhesives. The synthetic fibers include fibrillated synthetic fibers and non-fibrillated synthetic fibers. The thickness of the separator is 20–100 μm. The fibrillated synthetic fiber contains only fibers selected from polyamide fibers, acrylonitrile fibers, and polyester fibers. The non-fibrillated synthetic fiber contains only fibers selected from nylon fiber, acrylonitrile fiber, polyester fiber, and vinylon fiber. The bursting strength of the separator is 40–180 kPa, and the bursting index is 3.5–7.5 kPa / (g / m³). 2 ).

2. The separator for aluminum electrolytic capacitors according to claim 1, characterized in that, The separator contains 70-95% by mass of the synthetic fiber and 5-30% by mass of the adhesive, and the total mass of the separator contains 20-70% by mass of the fibrillated synthetic fiber and 10-75% by mass of the non-fibrillated synthetic fiber.

3. The separator for aluminum electrolytic capacitors according to any one of claims 1 to 2, characterized in that, The tensile modulus is 500–2000 MPa.

4. An aluminum electrolytic capacitor, characterized in that, It is an aluminum electrolytic capacitor that uses a conductive polymer as the cathode material. The aluminum electrolytic capacitor uses the separator as described in any one of claims 1 to 3.

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