JP4966698B2 - Electric double layer capacitor separator and electric double layer capacitor - Google Patents

Description

  The present invention comprises an inorganic fiber-based non-woven sheet using inorganic fibers as a skeleton material, an electric double layer capacitor separator having sufficient mechanical strength and good electrolyte wettability, and an electric double layer capacitor using the same About.

  With the rapid spread of portable electronic devices, the scope and demand for capacitors and storage batteries are expanding. In recent years, capacitors have attracted attention due to their features such as long life, rapid charge / discharge, and no maintenance required. In particular, demand for electric double layer capacitors having a large capacity is increasing.

  Electric double layer capacitors are mainly used as backup power supplies for various electronic devices. As portable electronic devices become smaller and higher in performance, electric double layer capacitors are also required to be smaller and higher in performance. ing. For this reason, the separator of the electric double layer capacitor is required to have a small thickness, a high porosity, and a high electrolyte solution retention property. Further, a separator for a cylindrical (or wound type) capacitor is required to have mechanical strength for winding.

  Conventionally, organic fiber nonwoven fabrics mainly composed of synthetic fibers such as olefin resin, polyester, and aramid have been used as separators for electric double layer capacitors. In recent years, however, in order to increase the capacity of electric double layer capacitors. In addition, an organic solvent such as propylene carbonate having a high withstand voltage is used as a solvent for the electrolytic solution, and the organic electrolytic solution using an organic solvent such as propylene carbonate having a strong hydrophilic property is composed of hydrophobic fibers. The organic fiber nonwoven fabric separator has a problem that wettability is inferior, and the electrolyte solution absorbability and the electrolyte solution retainability are deteriorated.

  On the other hand, if the inorganic fiber nonwoven fabric is made of inorganic fibers such as glass fibers and ceramic fibers, the inorganic fibers are hydrophilic, so that they have high wettability with respect to an organic electrolyte using an organic solvent such as propylene carbonate. be able to. However, since inorganic fibers are not self-adhesive, sufficient mechanical strength cannot be obtained only by entanglement of inorganic fibers. Therefore, in the conventional inorganic fiber nonwoven fabric separator, an organic resin binder liquid (emulsion, resin solution, etc.) is impregnated or applied to the inorganic fiber nonwoven fabric, or an organic resin powder or fiber is added in advance. An inorganic fiber nonwoven fabric is produced and heat-treated, and the inorganic fibers are bonded together with an organic resin to obtain a predetermined mechanical strength (for example, Patent Documents 1 and 2).

  However, if the inorganic fibers are impregnated or coated with an organic resin binder solution or the inorganic fibers are bonded by heating or melting the organic resin powder or fiber, Instead of binding only the intersections of the inorganic fibers, a film made of an organic resin is formed on the crossing portions of the inorganic fibers and other fiber surfaces, and even on the gaps between the inorganic fibers, so that the inorganic fibers are well wetted. Therefore, there has been a problem that the electrolyte penetration and the electrolyte retention of the inorganic fiber nonwoven fabric separator are reduced.

  Therefore, the present applicant previously mixed a suitable amount of fibrillated organic fibers with a finer fiber diameter into the inorganic fibers and wet-made, so that the inorganic fibers are sufficiently bonded by the entanglement of the fibrillated organic fibers. An inorganic fiber nonwoven fabric separator has been proposed in which mechanical strength is obtained and good wettability is maintained without covering the surface of the inorganic fiber with a hydrophobic organic component formed into a film (Patent Document 3).

  However, since the production facilities for electric double layer capacitors are often produced by diverting the facilities for aluminum electrolytic capacitors, the form of electric double layer capacitors is often cylindrical. In this cylindrical shape, since the separator is strongly pulled and wound at a high speed, the mechanical strength is higher, and further, the stickiness (elongation) of the separator is required. That is, when a conventional inorganic fiber nonwoven fabric separator is wound and incorporated in such a cylindrical capacitor, it is difficult to form a cylindrical shape due to insufficient mechanical strength and elongation.

JP-A-1-304719 Japanese Patent Laid-Open No. 11-14002 JP 2005-327935 A

  In view of the above-mentioned conventional problems, the present invention comprises an inorganic material-based nonwoven fabric sheet having inorganic fibers as a skeleton material, and has good mechanical strength such as tensile strength and tensile elongation, while being excellent in the inorganic material. Electrolyte double layer capacitor separator with excellent electrolyte wettability, good electrolyte penetration and electrolyte retention, and operation without interruption when installed in a cylindrical capacitor, and electricity using the same An object is to provide a double layer capacitor.

  As a result of intensive studies to solve the above-mentioned problems, the inventors of the present invention can increase the mechanical strength of the inorganic fiber nonwoven fabric separator, increase the tensile elongation, and can be assembled without being cut even when wound in a wound capacitor. To achieve this, a monofilamentous organic fiber that functions as a skeleton material having a high melting point component, which is a rigid and supple fiber material, and a low melting point component that has excellent thermal adhesiveness due to thermal melting of the low melting point component. It has been found that an appropriate amount of an organic binder composed of a heat-adhesive organic fiber or the like to be provided and a small amount of an inorganic binder may be added. Further, it was found that electrolyte permeability and electrolyte retention can be maintained high, and sheet shrinkage can be suppressed by adding organic fibers that function as the skeleton material.

  That is, since the heat-adhesive organic fiber is a thick fiber, the number of fibers interposed in the nonwoven fabric sheet is small, and the number of contact intersections of the heat-adhesive organic fiber for binding fiber materials such as inorganic fibers, that is, Cannot earn a lot of adhesion points. Adding more heat-adhesive organic fibers to increase the number of adhesion points significantly increases the pore size of the separator and significantly impairs short-circuit resistance, and decreases the amount of inorganic material added to significantly impair the electrolyte wettability of the separator. End up. Therefore, in order to increase the number of adhesion points by adding as little heat-adhesive organic fiber as possible, it was necessary to press the nonwoven sheet to reduce the thickness, that is, to increase the density. Have the inconvenience of breaking and the porosity decreasing. Further, during the production of the line, the wet paper sheet is heated and dried while being transported with tension applied in the flow direction. At this time, surface shrinkage occurs in the sheet width direction. As a result, the density of the sheet is lowered, resulting in a bulky, fluffy nonwoven fabric sheet, the sheet strength is lowered, the pore diameter is increased, and the nonwoven fabric sheet is unsuitable for the separator.

  For this reason, it was further found out that the inconvenience can be solved by adding an inorganic binder as a third component to the inorganic fiber and the organic fiber. That is, by including a small amount of an inorganic binder, it has become possible to prevent a decrease in the electrolyte wettability of the separator due to the addition of organic fibers. In addition, in order to form an inorganic binder after drying a complex porous structure having a very large specific surface area in which fine primary particles are aggregated to form secondary particles, the inorganic fibers and An inorganic binder having such a structure is interposed in the gap between the fibers having the entangled structure of the organic fibers, so that the pore structure of the separator can be refined and a complicated maze can be formed. In addition, by including an inorganic binder, it is possible to prevent the sheet due to the addition of the heat-adhesive organic fibers from being soft and fluffy, and to suppress surface shrinkage in the sheet width direction during heat drying. Became.

This invention is made | formed based on this knowledge, The separator for electric double layer capacitors of this invention is an inorganic fiber with an average fiber diameter of 1.5 micrometers or less, and a fiber diameter of 30 micrometers or less as described in Claim 1. at least including monofilament organic fibers of high melting point component as a skeleton material, the fiber material to each other is their skeletal material is made of wet papermaking sheets thus bonded to the inorganic binder and organic binder over a electric double layer separators for capacitors The inorganic binder is mainly composed of a silica-type scaly inorganic substance having a hydroxyl group amount of 20 μmol / m ² or more by a BET method, an average particle size of 2 μm or less by a laser scattering method, and an aspect ratio of 10 or more. an inorganic binder, the organic binder is heat-bondable organic fibers comprising at least a low-melting component (the motor When the filamentous organic fiber is a composite fiber having a high-melting component and a low-melting component, the monofilament-like organic fiber can also serve as the heat-bonding sheet. While the fiber materials are bonded to each other by thermal melting of the low melting point component of the organic organic fiber, the high melting point component of the monofilament organic fiber containing at least the high melting point component is not thermally melted, and the inorganic fiber and A monofilament in which the surface of the inorganic binder is not substantially formed with a film of the organic fiber and the organic binder , and the inorganic fiber is 55 to 95% by mass in the wet papermaking sheet and contains at least the high melting point component. Jo organic fiber 2 to 35 wt%, the inorganic binder contains 0.5 to 10 mass%, the wet papermaking sheet , Porosity is 80% or more, tensile strength, wherein the tensile elongation and the 5N / 25 mm width or more is 3% or more.
Also, the electric double layer capacitor of the present invention, in order to achieve the above object, as claimed in claim 2, characterized by using a separator of claim 1, wherein.

The separator for an electric double layer capacitor according to the present invention uses, as a skeleton material, an inorganic fiber having an average fiber diameter of 1.5 μm or less and a monofilament organic fiber containing at least a high melting point component having a fiber diameter of 30 μm or less. materials with each other, an inorganic binder and an organic binder over Thus an electric double layer separators for capacitors made of bonded wet papermaking sheet, the inorganic binder, BET method of hydroxyl groups per specific surface area by the 20 [mu] mol / m ² The above is an inorganic binder mainly composed of a silica-type scaly inorganic substance having an average particle diameter of 2 μm or less by an laser scattering method and an aspect ratio of 10 or more, and the organic binder includes a heat-adhesive organic fiber containing at least a low melting point component ( The monofilamentous organic fiber is a composite fiber having a high melting point component and a low melting point component The monofilament-like organic fiber may also serve as the wet-paper-sheet, and the wet-made sheet is bonded to the fiber material by thermal melting of the low-melting-point component of the thermo-adhesive organic fiber containing at least the low-melting-point component. On the other hand, the high melting point component of the monofilament-like organic fiber containing at least the high melting point component is not thermally melted, and the surface of the inorganic fiber and the inorganic binder is substantially made of the organic fiber and the organic binder. No film is formed, and in the wet papermaking sheet, the inorganic fiber is 55 to 95% by mass, the monofilament organic fiber containing at least the high melting point component is 2 to 35% by mass, and the inorganic binder is 0.5 to 0.5%. contains 10 mass%, the wet papermaking sheet is a void ratio of 80% or more, and a tensile strength of 5N / 25 mm width or higher tensile By beauty it is configured at least 3%, by having a sufficient mechanical strength such as strength tensile yet nonwoven sheet of inorganic fibers mainly easily incorporated into the capacitor of the cylindrical (wound) Thus, the addition of the inorganic binder does not hinder good electrolyte solution wettability, and the electrolyte solution permeability and the electrolyte solution retention property are improved, and the capacitor performance can be improved.

The separator for an electric double layer capacitor according to the present invention uses, as a skeleton material, an inorganic fiber having an average fiber diameter of 1.5 μm or less and a monofilament organic fiber containing at least a high melting point component having a fiber diameter of 30 μm or less. materials with each other, an inorganic binder and an organic binder over Thus an electric double layer separators for capacitors made of bonded wet papermaking sheet, the inorganic binder, BET method of hydroxyl groups per specific surface area by the 20 [mu] mol / m ² The above is an inorganic binder mainly composed of a silica-type scaly inorganic substance having an average particle diameter of 2 μm or less by an laser scattering method and an aspect ratio of 10 or more, and the organic binder includes a heat-adhesive organic fiber containing at least a low melting point component ( The monofilamentous organic fiber is a composite fiber having a high melting point component and a low melting point component The monofilament-like organic fiber may also serve as the wet-paper-sheet, and the wet-made sheet is bonded to the fiber material by thermal melting of the low-melting-point component of the thermo-adhesive organic fiber containing at least the low-melting-point component. On the other hand, the high melting point component of the monofilament-like organic fiber containing at least the high melting point component is not thermally melted, and the surface of the inorganic fiber and the inorganic binder is substantially made of the organic fiber and the organic binder. No film is formed, and in the wet papermaking sheet, the inorganic fiber is 55 to 95% by mass, the monofilament organic fiber containing at least the high melting point component is 2 to 35% by mass, and the inorganic binder is 0.5 to 0.5%. contains 10 mass%, the wet papermaking sheet is a void ratio of 80% or more, and a tensile strength of 5N / 25 mm width or higher tensile Provided that beauty is 3% or more.

Here, when the monofilament-like organic fiber that functions as a skeleton material is a composite fiber having a high-melting-point component and a low-melting-point component and can also serve as a heat-adhesive organic fiber as an organic binder, In other words, it is substantially the same as including 2% by mass or more of the monofilament-like organic fiber and 2% by mass or more of the thermoadhesive organic fiber.
The monofilament-like organic fibers are extruded from a die having a predetermined diameter and spun, so that the fiber diameters are almost uniform, that is, the fiber diameter distribution is very narrow, and therefore can be expressed as the fiber diameter. The fiber diameter of the monofilament-like organic fiber is usually expressed in decitex, expressed in grams when a 10,000 m fiber is spun, and the fiber diameter is naturally determined if the material, ie density, is determined. On the other hand, glass fibers are spun by a manufacturing method called a centrifugal method or a blow method, and the fiber diameter varies, that is, has a wide distribution, and therefore is usually expressed as an average fiber diameter.

  In addition, the inorganic fiber is 55% by mass or more and is composed of a non-woven sheet mainly composed of an inorganic material, and the fiber material serving as a skeleton material is bound as an organic binder by thermal melting of a low-melting-point component of the heat-adhesive organic fiber. Since the high melting point component of the monofilament-like organic fiber functioning as a material is not thermally melted, the separator made of the wet papermaking sheet does not form a film made of the molten organic material on the surface of the inorganic material, and the entire separator 55 The good electrolyte solution wettability of the inorganic material occupying the mass% or more is not hindered, and the electrolyte solution permeability and the electrolyte solution retainability are improved. When the content of the inorganic fiber is less than 55% by mass, the content of the hydrophilic inorganic material is decreased and the content of the hydrophobic organic material is increased. Unsuitable because of worsening of sex. For this reason, it is more preferable if the content of the inorganic fiber is 65% by mass or more, and further 75% by mass or more. Moreover, when the content of the monofilament organic fiber functioning as the skeleton material is less than 2% by mass, the function (mechanical strength, tensile elongation, etc.) of the organic fiber cannot be sufficiently exhibited, which is not suitable. For this reason, it is more preferable if the content of the monofilament organic fiber functioning as the skeleton material is 5% by mass or more, and further 10% by mass or more.

  In addition, since the inorganic fiber and the organic fiber are further added with a small amount of an inorganic binder, the separator made of the wet papermaking sheet has less surface shrinkage in the sheet width direction at the time of heating and drying, and is bulky. No decrease in strength or enlargement of pore diameter, and even if the paper sheet is pressed to increase the number of adhesion points of the heat-adhesive organic fibers, the inorganic fibers are not easily broken. The liquid-absorbing property and the electrolytic solution holding property are further improved, and the pore structure is miniaturized and a complicated labyrinth is formed, so that the short circuit resistance is improved.

  Examples of the inorganic fibers include glass fibers, silica fibers, alumina fibers, silica-alumina fibers, artificial amorphous fibers such as rock wool and slag wool, acicular crystalline materials such as potassium titanate whiskers and calcium carbonate whiskers. From inorganic fibers that are easily available industrially, such as mineral fine fibers such as fibers, sepiolite, and attapulgite, one or more types are selected and used so that the average fiber diameter is 1.5 μm or less. be able to.

  Further, since the inorganic fiber is a fine fiber having an average fiber diameter of 1.5 μm or less, the skeleton material has a large number of fibers in the wet papermaking sheet and forms a microporous structure of the wet papermaking sheet. Have a role. In addition, since the inorganic fiber has an average fiber diameter of 1.5 μm or less, the wet papermaking sheet has a large number of fibers, the wet papermaking sheet has a fine microporous structure, and has a large porosity. Further, the inorganic binder can be attached or filled in the surface of the inorganic fiber or in the gap between the fibers, and the paper making yield of the inorganic binder can be improved. When the porosity of the separator is high, the internal resistance can be reduced, the amount of electrolyte retained can be increased, and a cylindrical shape (winding type) that requires a longer time to permeate the electrolyte than a square (multilayer) capacitor The electrolytic solution absorption speed in the case of a capacitor can be increased (the porosity of the separator of the present invention is preferably 80% or more, more preferably 85% or more). Therefore, if the content of the inorganic fiber is less than 55% by mass, the porosity of the wet papermaking sheet is lowered, or the pore diameter of the wet papermaking sheet is increased to reduce short-circuit resistance. For this reason, it is more preferable if the content of the inorganic fiber is 65% by mass or more, and further 75% by mass or more. In addition, when the content of the inorganic fiber exceeds 95% by mass, the content of the organic binder such as the organic fiber or the thermoadhesive organic fiber that functions as the inorganic binder or the skeleton material decreases, and the function of the inorganic binder ( This is unsuitable because the organic fibers functioning as a skeletal material (such as prevention of surface shrinkage in the sheet width direction during heat drying) and the function of the organic fibers (such as improvement in mechanical strength and tensile elongation) cannot be sufficiently exhibited. For this reason, it is more preferable if content of an inorganic fiber is 85 mass% or less.

As the inorganic binder, a gel-like material formed from an inorganic sol such as silica sol, alumina sol, titania sol, or zirconia sol can also be used as an inorganic binder. When wet paper is impregnated, it is attached and dried, but the former can hardly be attached and the binder effect is low, and the latter can be attached almost 100%, but the sheet is hardened and wound into a roll. However, it is limited to the use of a small amount as a surface modifier for inorganic fibers and organic fibers. Therefore, as a result of intensive studies by the present inventors, scaly matter, that is, the amount of hydroxyl group per specific surface area by the BET method is 20 μmol / m ² or more, the average particle size by the laser scattering method is 2 μm or less, and the aspect ratio is 10 or more. It was found that the silica-based scale-like inorganic substance can be used favorably as an inorganic binder. Based on this finding, the inorganic binder used in the present invention is, as described above, provided that it is an inorganic binder mainly composed of the silica-based scale-like inorganic substance.

When the silica-based scaly inorganic substance is used as an inorganic binder at a content of 0.5% by mass or more, the sheet due to the addition of the heat-adhesive organic fibers that could not be prevented by the combination of inorganic fibers and organic fibers is soft and fluffy. In addition, it is possible to suppress surface shrinkage in the sheet width direction during drying by heating. In addition, when the silica-based scaly inorganic substance is used as an inorganic binder at a content of 1% by mass or more, the inorganic binder uniformly adheres to the surface of the inorganic fiber and the organic fiber, so that the electrolyte wettability of the separator and the electrolyte retention The wettability of the wet papermaking sheet can be improved, and the handling workability can be improved.
On the other hand, when the silica-based scaly inorganic substance is used as an inorganic binder at a content exceeding 10% by mass, the wet papermaking sheet becomes too dense to lower the porosity (that is, the density becomes too high) and the tensile elongation is low. Therefore, it is unsuitable. In addition, even if a large amount of the silica-based scale-like inorganic substance is used, the material cost (product cost) becomes too high for the effect of the inorganic binder, so the amount of the necessary minimum effect is limited. Is good. For this reason, it is more preferable if content of the said inorganic binder is 6 mass% or less.

  Examples of the organic fiber include a monofilament-like organic fiber that functions as a skeleton material of a wet papermaking sheet that includes at least a high melting point component, and a thermoadhesive organic fiber that includes at least a low melting point component as an organic binder. For example, cellulose fibers, polyethylene fibers, polypropylene fibers, acrylic fibers, nylon fibers, polyester fibers, polyamide fibers, polyvinyl alcohol fibers and the like single fibers or composite fibers, monofilament fibers or fibrillated fibers (pulp fibers, beating fibers 1 type or 2 types or more can be selected and used. When the monofilament organic fiber functioning as a skeleton material of the wet papermaking sheet containing at least the high melting point component is a composite fiber containing a high melting point component and a low melting point component, the low melting point component of the monofilament organic fiber is used as an organic binder. In order to function, it serves as both the function as a skeleton material of a wet papermaking sheet and the function as an organic binder.

  The monofilament-like organic fiber functioning as a skeleton material of the wet papermaking sheet containing at least the high melting point component is selected from a single fiber consisting of a high melting point component or a composite fiber having a high melting point component and a low melting point component. As a monofilament-like organic fiber composed of a single fiber having a high melting point component, for example, a high melting point polyethylene terephthalate fiber can be used. Examples of monofilament-like organic fibers comprising composite fibers having a high melting point component and a low melting point component include, for example, a core-sheath type polyester fiber having a high melting point polyethylene terephthalate as a core component and a low melting point copolymer polyester as a sheath component ( A core-sheath type PET-PET fiber) or a core-sheath type composite fiber (core-sheath type PET-PE fiber) having a high melting point polyethylene terephthalate as a core component and a low melting point polyethylene as a sheath component can be used. As the composite fiber, in addition to the core-sheath type, a composite fiber such as a sea-island type, a side-by-side type, or a split fiber type can be used.

  The heat-adhesive organic fiber containing at least a low melting point component as the organic binder may be either a single fiber made of a low melting point component or a composite fiber having a high melting point component and a low melting point component. As the heat-adhesive organic fiber composed of a single fiber having a low melting point component, for example, a low melting point polyethylene fiber or the like can be used. Examples of the heat-adhesive organic fiber composed of a composite fiber having a high melting point component and a low melting point component include, for example, a core-sheath type composite fiber (core) having a high melting point polyethylene terephthalate as a core component and a low melting point copolymer polyester as a sheath component. (Sheath type PET-PET fiber) or the like can be used.

  The heat-adhesive organic fiber is a monofilament organic fiber composed of a composite fiber having the high melting point component and the low melting point component, for example, a high melting point polyethylene terephthalate as a core component and a low melting point copolyester or polyethylene as a sheath component. The core-sheath type fiber (core-sheath type PET-PET fiber, core-sheath type PET-PE) is preferable. From the viewpoint of solvent resistance to the electrolytic solution, polyethylene is considered to be superior in molecular structure to polyester, and it is more preferable that the sheath component is polyethylene. By doing so, the function (skeleton material) of the monofilament-like organic fiber containing at least the high melting point component and the function of the thermoadhesive organic fiber (excellent thermal adhesive force does not impair the bonding force even in the capacitor. The organic binder material that firmly binds the fiber material in the non-woven sheet) can be made to function with one type of organic fiber, and the content of the organic material can be kept to a minimum amount, In order to suppress the deterioration of the electrolyte wettability as much as possible, to suppress the enlargement of the hole diameter as much as possible, and to cover the above-mentioned adverse effects (occurrence of surface shrinkage in the sheet width direction during heating and drying) due to the inclusion of organic fibers The content of the inorganic binder to be included can be reduced, and the content of the inorganic fiber can be increased accordingly.

  Examples of the organic fiber include the above-described monofilament organic fiber (skeleton material) composed of a single fiber having a high melting point component, and monofilament organic fiber (skeleton material, organic binder) composed of a composite fiber having a high melting point component and a low melting point component. Materials), organic fibers (organic binder materials) consisting of single fibers of low melting point components, and binder functions such as fibrillated cellulose fibers, fibrillated acrylic fibers, and fibrillated aramid fibers (fiber materials entangled at the intersection of fiber materials) May be used as an organic binder, and in this case, a small amount of the fibrillated organic fiber can highly supplement the binding effect of the skeletal fiber material. If a small amount of the fibrillated organic fiber is included, other organic fibers such as the heat-adhesive organic fiber can be used. The content of the binder can be reduced to more increment of the fibrillated organic fibers, it is possible to reduce the overall amount of the organic binder (content) as a result.

The separator has a tensile elongation of 3% or more . When the tensile elongation is less than 3%, there is a possibility that the separator may be suddenly cut when it is wound by winding when manufacturing a cylindrical (winding type) capacitor. However, if the tensile strength is too low even if the tensile elongation is good, the separator may be stretched and wound because the strength of the separator is low when the separator is pulled and wound. 5N / 25mm width or more .

  As described above, the separator uses the inorganic fiber and the monofilament-like organic fiber containing at least the high melting point component as a skeleton material, and the fiber materials that are the skeleton material are bonded by the inorganic binder and the organic binder. It is necessary to be configured as a wet papermaking sheet, and there is no particular limitation on the point at which the inorganic binder or the organic binder is added to obtain the wet papermaking sheet. As long as it is a method for obtaining a wet papermaking sheet having the above structure, it may be internally added (mixed paper at the time of wet papermaking) or externally added (impregnated after forming into a sheet). However, it is preferable to wet-mix the inorganic binder, the organic fiber, and the inorganic binder from the viewpoint that the inorganic binder can be easily and uniformly filled in the wet paper-making sheet. In the wet papermaking sheet, in order to efficiently attach or fill the inorganic binder to the surface of the organic fiber functioning as the inorganic fiber or the skeleton material and the gap between these fiber materials, during wet papermaking, It is preferable to use an adsorbent (polymer flocculant or the like).

Next, examples of the present invention will be described in detail together with comparative examples.
Example 1
80% by mass of C glass short fiber (# 104 manufactured by Jones Manville) having an average fiber diameter of 0.45 μm as an inorganic fiber, and scaly silica having an average particle diameter of 0.5 μm (laser scattering method) as an inorganic binder (Asahi Glass Stech) A monofilament-like organic material consisting of a single fiber having a high melting point component, Sunlabry LFS HN-050, manufactured by Suntory LFS HN-050, the amount of hydroxyl group per specific surface area by BET method is 20 to 70 μmol / m ² , and the aspect ratio is 10 to 200) Monofilament made of a composite fiber having a high melting point component and a low melting point component, 5% by mass of a polyester fiber (Teijin Tepyrus, melting point 200 ° C., modified polyethylene terephthalate) having a fineness of 0.06 dtex and a fiber length of 3 mm as a fiber (skeleton material) As organic fiber (skeleton material, organic binder material) fineness 1.2dtex, fiber length Disperse and mix 10% by mass in water with a core-sheath PET-PE fiber having a core component of mm of polyethylene terephthalate and a sheath component of polyethylene (Tepyrus manufactured by Teijin Ltd., core component melting point 250 ° C., sheath component melting point 120 ° C.), Further, an appropriate amount of a polymer flocculant is added, wet papermaking is performed with a square sheet machine for handmaking, a pressure of 0.6 MPa is applied with a press machine, and then dried at 110 ° C., at 150 ° C. Heat treatment was performed for 3 minutes to obtain an inorganic fiber sheet having a basis weight of 11.4 g / m ² and a thickness of 50 μm. When the obtained inorganic fiber sheet was observed with a microscope, a film of an organic material covering the surface of the inorganic material (that is, glass fiber and silica) in the inorganic fiber sheet was hardly confirmed. This was used as the separator for the electric double layer capacitor of Example 1.

(Example 2)
69% by mass of C glass short fibers (CMLF306 manufactured by Nippon Sheet Glass Co., Ltd.) having an average fiber diameter of 0.6 μm as inorganic fibers, and flaky silica (Laser Scattering Method) having an average particle diameter of 0.2 μm (laser scattering method) as inorganic binders Sunlably LFS HN-050, monofilament-like organic fiber composed of 1% by mass of hydroxyl group per specific surface area by BET method of 20 to 70 μmol / m ² and aspect ratio of 10 to 200) and a single fiber having a high melting point component ( Monofilamentous organic material composed of 10% by mass of a polyester fiber (Tepile manufactured by Teijin Ltd., melting point 200 ° C., modified polyethylene terephthalate) having a fineness of 0.06 dtex and a fiber length of 3 mm as a skeletal material, and a composite fiber having a high melting point component and a low melting point component Fineness 1.5dtex, fiber length 5 as fiber (framework material, organic binder material) Disperse and mix in water with 20% by mass of core-sheath PET-PET fiber (Melty manufactured by Unitika, core component melting point 250 ° C., sheath component melting point 130 ° C.) whose core component is polyethylene terephthalate and sheath component is copolymerized polyester. Further, an appropriate amount of a polymer flocculant is added, wet papermaking is performed with a square sheet machine for handmaking, a pressure of 0.6 MPa is applied with a press machine, and then dried at 110 ° C., 160 ° C. For 3 minutes to obtain an inorganic fiber sheet having a basis weight of 11.8 g / m ² and a thickness of 50 μm. When the obtained inorganic fiber sheet was observed with a microscope, a film of an organic material covering the surface of the inorganic material (that is, glass fiber and silica) in the inorganic fiber sheet was hardly confirmed. This was used as the separator for the electric double layer capacitor of Example 2.

(Example 3)
60% by mass of C short glass fibers (# 104, manufactured by Jones Manville) having an average fiber diameter of 0.45 μm as inorganic fibers, and scaly silica having an average particle diameter of 0.5 μm (laser scattering method) as an inorganic binder (Asahi Glass Stech) A monofilament-like organic material consisting of a single fiber having a high melting point component, Sunlabry LFS HN-050, manufactured by Suntory LFS HN-050, the amount of hydroxyl group per specific surface area by BET method is 20 to 70 μmol / m ² , and the aspect ratio is 10 to 200) Monofilament made of a composite fiber having 10% by mass of a polyester fiber (Tepyrus manufactured by Teijin Ltd., melting point 200 ° C., modified polyethylene terephthalate) having a fineness of 0.06 dtex and a fiber length of 3 mm as a fiber (skeleton material), and a high melting point component and a low melting point component Fine organic fiber (skeleton material, organic binder material) fineness 1.2dtex, fiber Disperse and mix in water with 25% by mass of PET-PE fiber having a core component of polyethylene terephthalate of 5 mm and a sheath component of polyethylene (Tepyrus manufactured by Teijin Ltd., core component melting point 250 ° C., sheath component melting point 120 ° C.), Further, an appropriate amount of a polymer flocculant is added, wet papermaking is performed with a square sheet machine for handmaking, a pressure of 0.6 MPa is applied with a press machine, and then dried at 110 ° C., at 150 ° C. Heat treatment was performed for 3 minutes to obtain an inorganic fiber sheet having a basis weight of 10.4 g / m ² and a thickness of 50 μm. When the obtained inorganic fiber sheet was observed with a microscope, a film of an organic material covering the surface of the inorganic material (that is, glass fiber and silica) in the inorganic fiber sheet was hardly confirmed. This was used as the separator for the electric double layer capacitor of Example 3.

Example 4
30% by mass of C glass short fibers (# 104 manufactured by Jones Manville) having an average fiber diameter of 0.45 μm as inorganic fibers and 55% by mass of C glass short fibers (CMLF 306 manufactured by Nippon Sheet Glass Co., Ltd.) having an average fiber diameter of 0.6 μm; As an inorganic binder, scaly silica having an average particle size of 0.5 μm (laser scattering method) (Sun Lovely LFS HN-050, manufactured by Asahi Glass Stech Co., Ltd.), the amount of hydroxyl group per specific surface area by BET method is 20 to 70 μmol / m ² , aspect ratio Ratio 10 to 200) 10% by mass, monofilamentous organic fiber (skeleton material, organic binder material) composed of a composite fiber having a high melting point component and a low melting point component, a core component having a fineness of 1.2 dtex and a fiber length of 5 mm is polyethylene terephthalate The sheath component is polyethylene sheath-type PET-PE fiber (Tepyrus manufactured by Teijin Ltd. 2% by mass (250 ° C., melting point of sheath component 120 ° C.) and 3% by mass of microfibrillated cellulose fiber (manufactured by Daicel Chemical Industries) with 0 ml Canadian freeness are dispersed and mixed in water, and polymer flocculant Is added in an appropriate amount, wet-made with a square sheet machine for hand-making, subjected to a pressure of 0.6 MPa with a press machine, dried at 110 ° C., and heat-treated at 150 ° C. for 3 minutes. Thus, an inorganic fiber sheet having a basis weight of 12.2 g / m ² and a thickness of 50 μm was obtained. When the obtained inorganic fiber sheet was observed with a microscope, a film of an organic material covering the surface of the inorganic material (that is, glass fiber and silica) in the inorganic fiber sheet was hardly confirmed. This was designated as the separator for the electric double layer capacitor of Example 4.

(Comparative Example 1)
In Example 1, except that the blending amount of C glass short fibers (# 104 manufactured by Jones Manville) having an average fiber diameter of 0.45 μm was changed to 85% by mass, and the blending amount of the inorganic binder was changed to 0% by mass, respectively. Obtained an inorganic fiber sheet having a basis weight of 8.8 g / m ² and a thickness of 50 μm in the same manner as in Example 1. This was used as the electric double layer capacitor separator of Comparative Example 1.

(Comparative Example 2)
In Example 2, except that the blending amount of C glass short fibers (CMLF306 manufactured by Nippon Sheet Glass Co., Ltd.) having an average fiber diameter of 0.6 μm was changed to 70% by mass, and the blending amount of the inorganic binder was changed to 0% by mass, respectively. In the same manner as in Example 2, an inorganic fiber sheet having a basis weight of 9.1 g / m ² and a thickness of 50 μm was obtained. This was used as the separator for the electric double layer capacitor of Comparative Example 2.

(Comparative Example 3)
In Example 3, the blending amount of C glass short fibers (# 104 manufactured by Jones Manville) having an average fiber diameter of 0.45 μm was changed to 65% by mass, and the blending amount of the inorganic binder was changed to 0% by mass. Obtained an inorganic fiber sheet having a basis weight of 8.9 g / m ² and a thickness of 50 μm in the same manner as in Example 3. This was used as the separator for electric double layer capacitor of Comparative Example 3.

(Comparative Example 4)
In Example 4, except that the blending amount of C glass short fiber (CMLF306 manufactured by Nippon Sheet Glass Co., Ltd.) having an average fiber diameter of 0.6 μm was changed to 65% by mass, and the blending amount of the inorganic binder was changed to 0% by mass, respectively. In the same manner as in Example 4, an inorganic fiber sheet having a basis weight of 8.3 g / m ² and a thickness of 50 μm was obtained. This was used as the electric double layer capacitor separator of Comparative Example 4.

Next, the separator characteristics of Examples 1 to 4 and Comparative Examples 1 to 4 obtained above were evaluated by the following methods. Moreover, the test cell of an electric double layer capacitor was produced with the following method using each separator of the said Examples 1-4 and Comparative Examples 1-4, and the capacitor characteristics were evaluated with the following method. The results are shown in Table 1.
[thickness]
Measurement was performed using a dial thickness gauge at a load of 19.6 kPa.
[Basis weight]
A mass (g) of 0.1 m ² was measured, and this was multiplied by 10 to obtain a basis weight (g / m ² ).
[density]
Calculated value of basis weight (g / m ² ) ÷ thickness (μm).
[Tensile strength]
Tensile strength at normal temperature (N / 25 mm width) was measured with a constant velocity tensile tester. The measurement conditions were a tensile speed of 25 mm / min and a distance between chucks of 100 mm.
[Tensile elongation]
The tensile strength at normal temperature (N / 25 mm width) was measured with a constant-speed tensile testing machine, the distance between chucks (C ₁ ) when fractured was measured, and calculated from the following formula. The measurement conditions were a tensile speed of 25 mm / min and an initial chuck distance (C ₀ ) of 100 mm.
Tensile elongation (%) = (C ₁ −C ₀ ) ÷ C ₀ × 100
[Electrolyte absorption time]
The separator was cut into a rectangular shape with a width of 25 mm and a length of 100 mm to make a sample, and one end (lower end) in the length direction was set perpendicular to the electrolyte surface so as to be immersed in the electrolyte by a length of 10 mm. It was suspended in a state, and the time (minutes) until the electrolyte was sucked up to a height of 50 mm from the electrolyte surface was measured, and was defined as the electrolyte solution absorption time. In addition, as the non-aqueous electrolyte (organic electrolyte), a non-aqueous solution in which 1 mol · dm ⁻³ of a quaternary salt of Et ₄ NBF ₄ was dissolved in a propylene carbonate (PC) solvent was used.
[Porosity]
It calculated from the following formula from the apparent density of the separator and the true density of the solid content of the constituent material.
Porosity (%) = {(true density of material solids) − (apparent density of separator)} ÷ (true density of material solids) × 100

[Production of electric double layer capacitor]
Kneaded activated carbon having a specific surface area of 1500 m ² / g, carbon black, and polytetrafluoroethylene resin to form a sheet-like material having a thickness of 0.2 mm, which is cut into 10 cm square, and the aluminum foil is adhered with a conductive adhesive. And used as both a positive electrode and a negative electrode. A separator is sandwiched between the electrodes, and an electric double layer is impregnated with a non-aqueous solution (organic electrolyte) in which 1 mol · dm ⁻³ of Et ₄ NBF ₄ quaternary salt is dissolved in a propylene carbonate (PC) solvent as an electrolyte. A capacitor test cell was fabricated.
[Leakage current ratio]
The leakage current immediately after the DC voltage of 2.5 V was applied to the test cell for 2 hours and charged to 2.5 V was measured, and the ratio when the value of the leakage current in Example 1 was 100 was used.
[Voltage holding ratio]
The initial voltage (V ₀ ) of the test cell and a voltage (V ₁ ) after charging for 500 hours after charging a DC voltage of 25 ° C. and a voltage of 2.5 V over 2 hours were measured, and the voltage holding ratio was Was calculated.
Voltage holding ratio (%) = (V ₁ / V ₀ ) × 100

From the results in Table 1, the following was found.
(1) The separators of Examples 1 to 4 of the present invention contain 55% by mass or more of inorganic fibers, have high tensile strength, and have a tensile elongation of 3% or more. In addition, the separators of Examples 1 to 4 have a relatively high porosity and good electrolyte wettability despite the fact that the density is high due to the addition effect of the inorganic binder. The time was shorter than the separators of Comparative Examples 1 to 4. Moreover, since the separator of Examples 1-4 has a more complicated micropore structure by the filling effect being obtained by adding an inorganic binder, the leakage current ratio of the capacitor can be reduced, and the voltage holding ratio can be improved. Therefore, it was confirmed that the separators of Examples 1 to 4 can contribute to the long life of the electric double layer capacitor.
(2) The separators of Comparative Examples 1 to 4 have a composition in which the inorganic binder is reduced to 0% by mass with respect to the configuration of the separators of Examples 1 to 4, and the weight loss is supplemented with inorganic fibers. Since the amount was zero, the effective binding force of the organic fibers could not be obtained and the tensile strength was lowered. Moreover, since the density was low overall and the hole structure was not miniaturized and complicated, the leakage current ratio and voltage maintenance ratio of the capacitor deteriorated.

Claims (2)

The average fiber diameter of 1.5μm or less of the inorganic fibers, including at least monofilament organic fibers of high melting point component of the following fiber diameter 30μm as a skeleton material, the fiber material to each other is their skeleton material, inorganic binder and organic binder over Thus, a separator for an electric double layer capacitor composed of a wet papermaking sheet,
The inorganic binder is mainly composed of a silica-type scaly inorganic substance having an amount of hydroxyl groups per specific surface area by the BET method of ²⁰ μmol / m ² or more, an average particle diameter of 2 μm or less by the laser scattering method, and an aspect ratio of 10 or more. And
The organic binder is a heat-adhesive organic fiber containing at least a low-melting-point component (if the monofilament-shaped organic fiber is a composite fiber having a high-melting-point component and a low-melting-point component, the monofilament-shaped organic fiber may also serve as) And
The wet papermaking sheet is formed by bonding the fiber materials to each other by thermal melting of the low melting point component of the thermoadhesive organic fiber containing at least the low melting point component, while the monofilamentous organic fiber containing at least the high melting point component is high. The melting point component is not heat-melted, and the film of the organic fiber and the organic binder is not substantially formed on the surface of the inorganic fiber and the inorganic binder,
In the wet papermaking sheet, the inorganic fiber is 55 to 95% by mass, the monofilament organic fiber containing at least the high melting point component is 2 to 35% by mass, the inorganic binder is 0.5 to 10% by mass ,
A separator for an electric double layer capacitor , wherein the wet papermaking sheet has a porosity of 80% or more, a tensile strength of 5 N / 25 mm width or more, and a tensile elongation of 3% or more . An electric double layer capacitor comprising the separator according to claim 1 .