JP2007150122A - Electric double layer capacitor separator - Google Patents

Abstract

A separator for an electric double layer capacitor with low resistance and leakage current is provided.
A separator for an electric double layer capacitor comprising a porous sheet containing a fibrillated heat-resistant fiber, an aromatic polyamide fiber, and a fibrillated cellulose.
[Selection figure] None

Description

  The present invention relates to a separator for an electric double layer capacitor.

Conventionally, paper separators mainly composed of solvent-spun cellulose fibers and regenerated cellulose fibers have been used as separators for electric double layer capacitors. (For example, see Patent Documents 1 to 3). In recent years, electric double layer capacitors have been expected to be used in applications that require high energy and high output, such as auxiliary power supplies for automobiles and railway vehicles, as the capacitance has increased. In response to such a trend, improvement of the separator is also demanded. One of the problems of the separator is thinning. However, the conventional paper separator has a problem that it is difficult to reduce the thickness to some extent without reducing the strength and without generating a pinhole. As an electric double layer capacitor separator that can be made thin, an electric double layer capacitor separator made of a fiber sheet containing fibrillated fibers and polyester fibers is disclosed (for example, see Patent Document 4). However, this separator can be reduced in thickness, but has a problem of high resistance. Generally, when the separator is thinned, the leakage current tends to increase, and a separator with a small leakage current is desired.
JP-A-5-267103 JP-A-11-168033 JP 2000-3834 A JP 2001-244150 A

  The present invention has been made in view of the above circumstances, and relates to a separator for an electric double layer capacitor having a small resistance and leakage current.

  As a result of intensive studies to solve this problem, the present inventors have found that a separator for an electric double layer capacitor having a small resistance and leakage current can be realized by using a specific fiber, leading to the present invention. It is a thing.

  That is, the present invention is an electric double layer capacitor separator comprising a porous sheet containing at least fibrillated heat-resistant fibers, aromatic polyamide fibers, and fibrillated cellulose.

  In the present invention, the mass ratio of the fibrillated heat resistant fiber to the aromatic polyamide fiber is 1:15 to 94: 1, and the mass ratio of the aromatic polyamide fiber to the fibrillated cellulose is 1:45 to 15: 1. preferable.

  In the present invention, the fibrillated heat-resistant fiber is preferably a fibrillated para-type wholly aromatic polyamide fiber.

  In the present invention, an aromatic polyamide is synthesized from a dicarboxylic acid component containing 60 mol% or more of an aromatic dicarboxylic acid component and a diamine component containing 60 mol% or more of an aliphatic alkylene diamine having 6 to 12 carbon atoms. It is preferably a group polyamide.

  According to the present invention, a separator for an electric double layer capacitor with small resistance and leakage current can be obtained.

  The electric double layer capacitor in the present invention has a power storage function configured by sandwiching an electric double layer between two opposing electrodes. The electrode of the electric double layer capacitor may be a combination of a pair of electric double layer electrodes, one of which is an electric double layer electrode and the other is a redox electrode. Examples of the electric double layer type electrode include electrodes made of activated carbon or non-porous carbon. Here, the non-porous carbon refers to carbon having a microcrystalline carbon similar to graphite and having a different manufacturing method from activated carbon. In the case of activated carbon, ions enter and exit the pores with charge and discharge, while in the case of nonporous carbon, ions enter and exit between the layers of microcrystalline carbon. Examples of the redox electrode include polypyrrole, polythiophene, polyaniline, polyacetylene, polyacene, indole trimer, polyphenylquinoxaline, conductive polymers such as derivatives thereof, and metal oxides such as ruthenium oxide, indium oxide, and tungsten oxide. Although it is mentioned, it is not limited to these.

  The electrolytic solution of the electric double layer capacitor includes an aqueous solution in which an ion dissociable salt is dissolved, propylene carbonate (abbreviation PC), ethylene carbonate (abbreviation EC), dimethyl carbonate (abbreviation DMC), diethyl carbonate (abbreviation DEC), acetonitrile (Abbreviation AN), propionitrile, γ-butyrolactone (abbreviation BL), dimethylformamide (abbreviation DMF), tetrahydrofuran (abbreviation THF), dimethoxyethane (abbreviation DME), dimethoxymethane (abbreviation DMM), sulfolane (abbreviation SL), Examples include, but are not limited to, those obtained by dissolving an ion dissociable salt in an organic solvent such as dimethyl sulfoxide (abbreviation DMSO), ethylene glycol, propylene glycol, and methyl cellosolve, and ionic liquids (solid molten salts). Not something . In the case of an electric double layer capacitor in which both an aqueous solution system and an organic solvent system can be used, an organic solvent system is preferred because the aqueous solution system has a low withstand voltage. Instead of the electrolytic solution, a conductive polymer film such as polypyrrole, polythiophene, polyaniline, polyacetylene, polyacene, and derivatives thereof may be used.

  The heat resistant fiber in the present invention refers to a fiber having a softening point, a melting point, and a thermal decomposition temperature of 250 ° C. or more and 700 ° C. or less. Specifically, wholly aromatic polyamide, wholly aromatic polyester, wholly aromatic polyester amide, wholly aromatic polyether, wholly aromatic polycarbonate, wholly aromatic polyazomethine, polyphenylene sulfide (abbreviation PPS), poly (para-phenylene) Benzobisthiazole) (abbreviation PBZT), polybenzimidazole (abbreviation PBI), polyetheretherketone (abbreviation PEEK), polyamideimide (abbreviation PAI), polyimide, polytetrafluoroethylene (abbreviation PTFE), poly (para-phenylene- 2,6-benzobisoxazole) (abbreviation PBO) and the like may be used alone or in combination of two or more. PBZT may be either a transformer type or a cis type. Here, although the softening point and the melting point are not clear in the category of “softening point, melting point, and thermal decomposition temperature are all 250 ° C. or higher and 700 ° C. or lower”, the thermal decomposition temperature is 250 ° C. or higher and 700 ° C. or lower. Some are included. Examples are aramid and PBO. Among these fibers, preferred are wholly aromatic polyamides, particularly para-type wholly aromatic polyamides, which are easy to be uniformly fibrillated due to liquid crystallinity.

  The para-type wholly aromatic polyamide in the present invention is a polymer obtained by polycondensation of a para-oriented aromatic diamine and a para-oriented aromatic dicarboxylic acid halide. A polymer obtained by polycondensation of an aromatic diamine, meta-oriented aromatic dihalide, aliphatic diamine, aliphatic dicarboxylic acid, etc., from a repeating unit in which the amide bond is bonded at the para position of the aromatic ring or an oriented position equivalent thereto It is the polymer which becomes. Further, some hydrogen atoms of the aromatic rings of the para-oriented aromatic diamine and the para-oriented aromatic dicarboxylic acid halide may be substituted with a substituent that does not form an amide bond, and the aromatic ring may be polycyclic. Examples of the substituent that does not form an amide bond include an alkyl group, an alkoxy group, a halogen, a sulfonyl group, a nitro group, a phenyl group, and the like. Since an alkyl group and an alkoxy group tend to inhibit polycondensation when the number of carbon atoms is long, the number of carbon atoms is preferably 1 to 4. For example, as the para-oriented aromatic diamine in which a part of hydrogen atoms of the aromatic ring is substituted with an alkyl group, N, N′-dimethylparaphenylenediamine, N, N′-diethylparaphenylenediamine, 2-methyl-4 -Ethylparaphenylenediamine, 2-methyl-4-ethyl-5-propylparaphenylenediamine and the like are exemplified, but not limited thereto. For example, the para-oriented aromatic dicarboxylic acid halide in which a part of hydrogen atoms of the aromatic ring is substituted with an alkoxy group includes dimethoxyterephthalic acid chloride, diethoxyterephthalic acid chloride, 2-methoxy-4-ethoxyterephthalic acid chloride and the like. Although it is mentioned, it is not limited to these. For example, the para-oriented aromatic diamine having a polycyclic aromatic ring includes 4,4′-oxydiphenyldiamine, 4,4′-sulfonyldiphenyldiamine, 4,4′-diphenyldiamine, and 3,3′-oxydiphenyldiamine. 3,3′-sulfonyldiphenyldiamine, 3,3′-diphenyldiamine, and the like, but are not limited thereto. Further, as described above, some of the hydrogen atoms of these aromatic rings may be substituted with a substituent that does not form an amide bond. For example, as the para-oriented aromatic dicarboxylic acid halide having a polycyclic aromatic ring, 4,4′-oxydibenzoyl chloride, 4,4′-sulfonyldibenzoyl chloride, 4,4′-dibenzoyl chloride, 3,3 Examples include, but are not limited to, '-oxydibenzoyl chloride, 3,3'-sulfonyldibenzoyl chloride, 3,3'-dibenzoyl chloride. Furthermore, as described above, some of the hydrogen atoms of these aromatic rings may be substituted with a substituent that does not form an amide bond.

  As the para-type wholly aromatic polyamide in the present invention, poly (para-phenylene terephthalamide) having particularly excellent heat resistance is preferable among the above-mentioned polymers.

  The fibril in the present invention refers to a fiber that is not in a film form but has a fiber portion that is very finely divided mainly in a direction parallel to the fiber axis, and at least a part of which has a fiber diameter of 1 μm or less. The aspect ratio of length to width is distributed in the range of about 20 to about 100,000, and the Canadian freeness is preferably in the range of 0 to 500 ml or less, and more preferably in the range of 0 to 200 ml. Furthermore, what has a weight average fiber length in the range of 0.1-2 mm is preferable. A weight average fiber length can be calculated | required by using the commercially available fiber length measuring device using the polarization characteristic obtained by irradiating a fiber with a laser beam.

  Fibrilization in the present invention includes refiner, beater, mill, grinding device, rotary blade homogenizer that applies shearing force by high-speed rotary blade, cylindrical inner blade that rotates at high speed, and fixed outer blade. Double-cylindrical high-speed homogenizer that generates shearing force, ultrasonic crusher that is refined by ultrasonic impact, a pressure difference of at least 3000 psi is applied to the fiber suspension, and a small-diameter orifice is passed through to increase the speed. Is carried out using a high-pressure homogenizer or the like that applies a shearing force or a cutting force to the fiber by rapidly decelerating the fibers, and it is particularly preferable to treat with a high-pressure homogenizer because fine fibrils can be obtained.

  The fineness of the aromatic polyamide fiber used in the present invention is preferably 0.01 to 0.5 dtex, more preferably 0.01 to 0.1 dtex. The aromatic polyamide here is not a wholly aromatic polyamide but has, for example, a fatty chain in a part of the main chain. When the fineness of the aromatic polyamide fiber is less than 0.01 dtex, the stiffness and strength of the separator for an electric double layer capacitor are weakened, and handling properties tend to be poor. If it is thicker than 0.5 dtex, a pinhole may be formed when the thickness is reduced. The aromatic polyamide fiber used in the present invention is synthesized from a dicarboxylic acid component containing 60 mol% or more of an aromatic dicarboxylic acid component and a diamine component containing 60 mol% or more of an aliphatic alkylenediamine having 6 to 12 carbon atoms. A fiber made of aromatic polyamide is preferred because of its excellent heat resistance and chemical resistance.

  As the aromatic dicarboxylic acid, terephthalic acid is preferable from the viewpoint of heat resistance and electrolytic solution resistance. Isophthalic acid, 2,6-naphthalenedicarboxylic acid, 2,7-naphthalenedicarboxylic acid, 1,4-naphthalenedicarboxylic acid, 1 , 4-phenylenedioxydiacetic acid, 1,3-phenylenedioxydiacetic acid, diphenic acid, phthalic acid, 4,4'-oxydibenzoic acid, diphenylmethane-4,4'-dicarboxylic acid, diphenylsulfone-4,4 Aromatic dicarboxylic acids such as' -dicarboxylic acid and 4,4'-biphenyldicarboxylic acid can be used in combination of two or more. The content of these aromatic dicarboxylic acids is 60 mol% or more of the dicarboxylic acid component, and preferably 75 mol% or more.

  Examples of dicarboxylic acids other than the above dicarboxylic acids include malonic acid, succinic acid, 2,2-diethylsuccinic acid, glutaric acid, 2,2-dimethylglutaric acid, adipic acid, 2-methyladipic acid, trimethyladipic acid, and pimelic acid. One or more aliphatic dicarboxylic acids such as azelaic acid, sebacic acid and suberic acid, and alicyclic dicarboxylic acids such as 1,3-cyclopentanedicarboxylic acid and 1,4-cyclohexanedicarboxylic acid can be used. Furthermore, a polyvalent carboxylic acid such as trimellitic acid, trimesic acid and pyromellitic acid may be appropriately contained. The dicarboxylic acid component is preferably 100% aromatic dicarboxylic acid in terms of strength, electrolytic solution resistance, heat resistance, and the like.

  On the other hand, 60 mol% or more of the diamine component is composed of alkylene diamine having 6 to 12 carbon atoms, such as 1,6-hexanediamine, 1,8-octanediamine, 1,9-nonanediamine, 1,10- Decanediamine, 1,11-undecanediamine, 1,12-dodecanediamine, 2-methyl-1,5-pentanediamine, 3-methyl-1,5-pentanediamine, 2,2,4-trimethyl-1,6 Aliphatic having a straight chain or side chain such as hexanediamine, 2,4,4-trimethyl-1,6-hexanediamine, 2-methyl-1,8-octanediamine, 5-methyl-1,9-nonanediamine, etc. Examples include diamines. Among these, 1,9-nonanediamine, and the combined use of 1,9-nonanediamine and 2-methyl-1,8-octanediamine are preferable in terms of resistance to electrolytic solution. The content of the aliphatic alkylene diamine is 60 mol% or more of the diamine component, but 75 mol% or more, particularly 90 mol% or more is preferable from the viewpoint of heat resistance.

  Examples of diamines other than the above aliphatic alkylene diamines include aliphatic diamines such as ethylene diamine and 1,4-butane diamine, alicyclic diamines such as cyclohexane diamine, methyl cyclohexane diamine, isophorone diamine, norbornane dimethyl diamine, and tricyclodecane dimethyl diamine. P-phenylenediamine, m-phenylenediamine, xylylenediamine, xylenediamine, 4,4′-diaminodiphenylmethane, 4,4′-diaminodiphenylsulfone, 4,4′-diaminodiphenylether, or the like, or These mixtures can be mentioned, and these can be used in combination of not only one type but also two or more types.

  When 1,9-nonanediamine and 2-methyl-1,8-octanediamine are used in combination as the aliphatic alkylene diamine, 60 to 100 mol% of the diamine component is 1,9-nonanediamine and 2-methyl-1,8. It consists of octanediamine, and the molar ratio is preferably the former: the latter = 30: 70 to 99: 1, particularly the former: the latter = 40: 60 to 95: 5.

In the aromatic polyamide of the present invention, the molar ratio of [CONH / CH ₂ ] in the molecular chain is preferably 1/2 to 1/8, particularly 1/3 to 1/5. Aromatic polyamides in this range are excellent in electrolytic solution resistance and heat resistance.

  In the aromatic polyamide of the present invention, it is preferable that 10% or more of the terminal groups of the molecular chain are sealed with a terminal blocking agent, and 40% or more of the terminals are further sealed with 70% or more. It is preferable. By sealing the end of the molecular chain, the obtained capacitor separator has excellent strength, electrolytic solution resistance, heat resistance, and the like. The end capping agent is not particularly limited as long as it is a monofunctional compound having reactivity with the amino group or carboxyl group at the end of the polyamide. To monocarboxylic acid and monoamine. Monocarboxylic acids are preferred from the viewpoints of ease of handling, reactivity, and stability of the sealing end. Examples of the monocarboxylic acid include acetic acid, propionic acid, butyric acid, valeric acid, caproic acid, caprylic acid, lauric acid, tridecylic acid, myristic acid, palmitic acid, stearic acid, benzoic acid and the like. The terminal sealing rate can be determined from the integral value of the characteristic signal corresponding to each terminal by 1H-NMR.

  The method for producing the aromatic polyamide used in the present invention is not particularly limited, and any known method for producing a crystalline polyamide can be used. For example, it can be produced by a solution polymerization method or an interfacial polymerization method using acid chloride and diamine as raw materials, a solution polymerization method using dicarboxylic acid or an alkyl ester of dicarboxylic acid and diamine as raw materials, or a solid phase polymerization method.

  The aromatic polyamide used in the present invention can be fiberized using a known melt spinning apparatus, and can be either single spinning or composite spinning. 1-15 mm is preferable and, as for the fiber length of the aromatic polyamide fiber used for this invention, 2-6 mm is more preferable. If the fiber length is shorter than 1 mm, it is easy to fall off from the separator for the electric double layer capacitor, and if it is longer than 15 mm, the fiber tends to get tangled and become lumpy and uneven thickness tends to occur.

  The mass ratio of the fibrillated heat resistant fiber and the aromatic polyamide fiber in the separator for the electric double layer capacitor of the present invention is preferably from 1:15 to 94: 1. If the mass ratio of the fibrillated heat resistant fiber is less than 1:15, pinholes may be formed. When the ratio is more than 94: 1, the fibrillated heat-resistant fiber may fall off from the electric double layer capacitor separator, or may be released, resulting in holes or fluffing, and processability such as cutting properties may be deteriorated.

  Examples of the fibrillated cellulose in the present invention include solvent-spun cellulose, non-wood fibers such as wood fibers, wood pulp, linter, lint, hemp, and soft cell fibers, non-wood pulp fibrillated, and bacterial cellulose. The parenchyma fiber refers to a fiber insoluble in water, mainly composed of cellulose obtained by treating a portion mainly composed of parenchyma cells existing in plant stems, leaves, roots, fruits, etc. with alkali. .

  The mass ratio between the aromatic polyamide fiber and the fibrillated cellulose in the electric double layer capacitor separator of the present invention is preferably 1:45 to 15: 1. When the mass ratio of the aromatic polyamide fiber is less than 1:45, the resistance of the electric double layer capacitor separator may be increased. When the mass ratio is more than 15: 1, pinholes may be formed.

  The porous sheet in the present invention is a paper machine using a circular paper machine, a long paper machine, a short paper machine, an inclined paper machine, a combination paper machine in which the same or different types of paper machines are combined. Can be manufactured by a method. In addition to the fiber raw material, a dispersant, a thickener, an inorganic filler, an organic filler, an antifoaming agent, and the like are appropriately added to the raw material slurry as necessary, and a solid content of about 5% by mass to 0.001% by mass is added. Adjust slurry to concentration. This raw slurry is further diluted to a predetermined concentration to make paper. The porous sheet obtained by papermaking is subjected to calendering, thermal calendering, heat treatment and the like as necessary.

  Although there is no restriction | limiting in particular in the thickness of the separator for electric double layer capacitors of this invention, 10-70 micrometers is preferable, 15-50 micrometers is more preferable, 15-30 micrometers is further more preferable. If it is less than 10 μm, it is easy to break or have a hole during handling or processing, and if it is thicker than 100 μm, the electrode area that can be stored in the electric double layer capacitor is reduced, and the storage capacity of the electric double layer capacitor is reduced.

  EXAMPLES Hereinafter, although an Example demonstrates this invention in more detail, this invention is not limited to an Example.

<Fibrylated heat-resistant fiber 1>
Para-type wholly aromatic polyamide fiber (manufactured by Teijin Techno Products, Twaron 1080) is dispersed in ion-exchanged water so as to have an initial concentration of 5% by mass, and repeatedly beaten 15 times using a double disc refiner to obtain a weight average fiber. A fibrillated para-type wholly aromatic polyamide fiber having a length of 1.55 mm and Canadian freeness of 100 ml was produced. Hereinafter, this is referred to as fibrillated heat resistant fiber 1 or FB1.

<Fibrylated heat-resistant fiber 2>
The fibrillated heat-resistant fiber 1 was repeatedly beaten with a high-pressure homogenizer 25 times under the condition of 50 MPa to produce a fibrillated para-type wholly aromatic polyamide fiber having a weight average fiber length of 0.61 mm and Canadian freeness of 0 ml. Hereinafter, this is referred to as fibrillated heat resistant fiber 2 or FB2.

<Aromatic polyamide>
19.5 mol of terephthalic acid, 10.0 mol of 1,9-nonanediamine, 10.0 mol of 2-methyl-1,8-octanediamine, 1.0 mol of benzoic acid, sodium hypophosphite hydrate 0.06 Mole and 2.2 liters of distilled water were added to an autoclave having an internal volume of 20 liters to perform nitrogen substitution. Subsequently, it stirred for 30 minutes at 100 degreeC, and raised the internal temperature to 210 degreeC over 2 hours. At this time, the autoclave was pressurized to 2.2 MPa. The reaction was continued for 1 hour, and then the temperature was raised to 230 ° C. and maintained for 2 hours. The reaction was continued while gradually removing water vapor and maintaining the pressure at 2.2 MPa. Next, the pressure was reduced to 1.0 MPa over 30 minutes, and the reaction was further continued for 1 hour to obtain a prepolymer. The prepolymer was dried at 100 ° C. under reduced pressure for 12 hours and pulverized to a size of 2 mm or less. The pulverized product was subjected to solid phase polymerization at 230 ° C. and 10 Pa for 10 hours to obtain a polymer. The end-capping rate of the polymer was 90%.

<Aromatic polyamide fiber 1>
50% aromatic polyamide and 50% easy-reduced polyester are compounded, melt extruded with an extruder, and discharged from a round hole nozzle of 0.25mmφ × 24 holes, polyamide is an island component, easily reduced A sea-island type fiber (16 islands) in which a functional polyester constitutes a sea component was obtained. This sea-island type fiber was drawn using a water bath of 1 bath 90 ° C. and 2 baths 95 ° C. to obtain a drawn yarn (0.3 dtex, island component diameter 0.01 dtex) of about 200 dtex / 625 filaments. The obtained drawn yarn was cut into a fiber length of 2 mm. Subsequently, it was immersed in an aqueous NaOH solution at 40 ° C. and a concentration of 60 g / liter for 30 minutes to remove sea components, and an aromatic polyamide fiber having a fineness of 0.01 dtex and a fiber length of 2 mm was obtained. Hereinafter, this is referred to as aromatic polyamide fiber 1 or PA1.

<Aromatic polyamide fiber 2>
Aromatic polyamide was melt-extruded with an extruder, discharged from a nozzle and wound up to obtain a tow having a fineness of 0.06 dtex. This tow was cut into a fiber length of 3 mm to obtain an aromatic polyamide fiber. Hereinafter, this is referred to as aromatic polyamide fiber 2 or PA2.

<Aromatic polyamide fiber 3>
Aromatic polyamide was melt-extruded with an extruder, discharged from a nozzle and wound to obtain a tow having a fineness of 0.1 dtex. This tow was cut into a fiber length of 3 mm to obtain an aromatic polyamide fiber. Hereinafter, this is referred to as aromatic polyamide fiber 3 or PA3.

<Aromatic polyamide fiber 4>
Aromatic polyamide was melt-extruded with an extruder, discharged from a nozzle and wound up to obtain a tow having a fineness of 0.6 dtex. This tow was cut into a fiber length of 3 mm to obtain an aromatic polyamide fiber. Hereinafter, this is referred to as aromatic polyamide fiber 4 or PA4.

<Fibrylated cellulose 1>
Disperse the linter in ion exchange water to an initial concentration of 5% by mass and repeat the treatment 20 times at a pressure of 50 MPa using a high-pressure homogenizer to obtain fibrillated cellulose having a weight average fiber length of 0.33 mm and Canadian freeness of 0 ml. Produced. Hereinafter, this is referred to as fibrillated cellulose 1 or FBC1.

<Fibrylated cellulose 2>
Solvent-spun cellulose having a fineness of 1.7 dtex and a fiber length of 5 mm (manufactured by Lenzing Co., Ltd., Tencel) is dispersed in ion-exchanged water so as to have an initial concentration of 5% by mass, beaten using a double disc refiner, and weight average fiber length A fibrillated cellulose of 0.64 mm and Canadian freeness of 10 ml was prepared. Hereinafter, this is referred to as fibrillated cellulose 2 or FBC2.

  A papermaking slurry was prepared according to the raw materials and blending amounts shown in Table 1. Here, “PET1” in Table 1 means a polyethylene terephthalate fiber having a fineness of 0.1 dtex and a fiber length of 3 mm (manufactured by Teijin Fibers, Tepyrus TM04PN).

Examples 1-16
Slurries 1-16 were made by wet paper making to produce porous sheets 1-16. Next, both surfaces of the porous sheets 1 to 16 were brought into contact with a metal roll having a diameter of 1200 mm heated to 220 ° C. at a speed of 10 m / min, and then calendared at room temperature and a linear pressure of 490 N / cm, as shown in Table 2. Electric double layer capacitor separators 1 to 16 having a thickness and a density were produced. The paper machine used was a combination of a circular paper machine and a circular paper machine.

(Comparative Example 1)
The slurry 17 was subjected to wet paper making to prepare a porous sheet. Next, thermal calendaring was performed by passing between a pair of metal rolls under the conditions of 220 ° C. and linear pressure of 4.7 kN / cm, to produce a separator 17 for an electric double layer capacitor having the thickness and density shown in Table 2.

(Comparative Example 2)
The slurry 18 was subjected to wet paper making to prepare a porous sheet. Next, thermal calendaring was performed by passing between a pair of metal rolls under the conditions of 240 ° C. and linear pressure of 4.7 kN / cm, to produce a separator 18 for an electric double layer capacitor having the thickness and density shown in Table 2.

<Electric double layer capacitors 1-18>
An electrode made of activated carbon having a BET specific surface area of 1200 m ² / g was used as the positive electrode and the negative electrode, and a separator was stacked between the negative electrode and the positive electrode, and this was stored in an aluminum storage bag to form a stack type element. The entire device was vacuum heated to 200 ° C. for 10 hours to remove moisture contained in the electrodes and separator. This was allowed to cool to room temperature in a vacuum, and then an electrolytic solution was injected into the device, and the injection ports were sealed to prepare 100 electric double layer capacitors. As the electrolytic solution, a solution obtained by dissolving (C ₂ H ₅ ) ₃ (CH ₃ ) NBF ₄ in propylene carbonate so as to have a concentration of 1.5 mol / l was used.

  About the separators 1-18 for electric double layer capacitors, it measured with the following test method and the result was shown in Table 2-Table 3.

<Thickness>
The thicknesses of the electric double layer capacitor separators 1 to 18 were measured according to JIS C2111. The results are shown in Table 2.

<Density>
The density of the electric double layer capacitor separators 1 to 18 was measured in accordance with JIS C2111. The results are shown in Table 2.

<Cutability>
The state of the cut surface when the electric double layer capacitor separators 1 to 18 were cut with a push cutter was observed. Table 2 shows the case where no fuzz was generated and the sample was cut without any problem, the case where fuzz was generated, or the case where cutting was poor was indicated as x, and the case where cutting was slightly difficult was indicated as Δ.

<Internal resistance>
The electric double layer capacitors 1 to 18 were charged at a voltage of 2.7 V and then calculated from the voltage drop immediately after the start of discharge when a constant current was discharged at 20 A. Table 3 shows the average of 100 values.

<Leakage current>
The electric current measured when the electric double layer capacitors 1 to 18 were charged at a voltage of 2.7 V and held for 24 hours was defined as a leakage current. The smaller the leakage current, the better.

  As shown in Table 3, the separator for the electric double layer capacitor produced in Examples 1 to 16 is composed of a porous sheet containing fibrillated heat-resistant fiber, aromatic polyamide fiber, and fibrillated cellulose. Leakage current was small and excellent.

  On the other hand, since the separator for an electric double layer capacitor produced in Comparative Example 1 did not contain aromatic polyamide fiber and fibrillated cellulose, the internal resistance and leakage current were large.

  Since the separator for an electric double layer capacitor produced in Comparative Example 2 did not contain fibrillated cellulose, the internal resistance and leakage current were large.

  As an application example of the present invention, a separator for an electric double layer capacitor is suitable.

Claims (4)

  An electrical double layer capacitor separator comprising a porous sheet containing fibrillated heat-resistant fibers, aromatic polyamide fibers, and fibrillated cellulose.   2. The electric cable according to claim 1, wherein the mass ratio of the fibrillated heat-resistant fiber and the aromatic polyamide fiber is 1:15 to 94: 1, and the mass ratio of the aromatic polyamide fiber to the fibrillated cellulose is 1:45 to 15: 1. Multilayer capacitor separator.   The separator for an electric double layer capacitor according to claim 1 or 2, wherein the fibrillated heat-resistant fiber is a fibrillated para-type wholly aromatic polyamide fiber.   The aromatic polyamide is an aromatic polyamide synthesized from a dicarboxylic acid component containing 60 mol% or more of an aromatic dicarboxylic acid component and a diamine component containing 60 mol% or more of an aliphatic alkylenediamine having 6 to 12 carbon atoms. Item 4. The separator for an electric double layer capacitor according to any one of Items 1 to 3.