JP2016174106A - Separator for electric double layer capacitor, and electric double layer capacitor arranged by use thereof - Google Patents

Abstract

A separator for an electric double layer capacitor having excellent ion permeability, electrolyte wettability, and electrical insulation, as well as high capacitance, low internal resistance, low leakage current, and reliability Providing high electric double layer capacitors.
The following formulas (1) to (4):
Dmax ≦ 20 μm (1)
0.1 μm ≦ Dmin (2)
Dmax / Dave <3.50 (3)
Dmax / Dmin <5.00 (4)
{In the formula, Dmax is the maximum pore size (μm), Dave is the average pore size (μm), and Dmin is the minimum pore size (μm). }. The separator for electric double layer capacitors comprised from the nonwoven fabric which has the hole diameter distribution which satisfy | fills}.
[Selection figure] None

Description

  The present invention relates to a separator for an electric double layer capacitor and an electric double layer capacitor using the same.

In recent years, with the diversification of electronic devices, high performance of various power storage devices is required. In particular, an electric double layer capacitor having a large capacity and a long life and rapid charge / discharge characteristics is required.
As a separator which exists between the positive electrode and negative electrode of an electric double layer capacitor, a nonwoven fabric, for example, a cellulose-based wet nonwoven fabric, a glass fiber nonwoven fabric and the like are known. The separator functions include, for example, electrical insulation, preventing physical contact between the electrodes to prevent short circuit, excellent wettability to the electrolyte, and chemical stability to the electrolyte. And having an appropriate strength.

  In Patent Document 1 below, in an electric double layer capacitor in which a separator is disposed between a positive electrode and a negative electrode made of a carbonaceous electrode and impregnated with a non-aqueous electrolyte, the separator beats the regenerated cellulose fiber. An electric double layer capacitor characterized in that it is a paper made by containing 50% by weight or more of the above-mentioned fibers is disclosed.

  Patent Document 2 below discloses that, in an electric double layer capacitor having an electrolyte solution in which a supporting salt is dissolved in a nonaqueous solvent and a pair of polarizable electrodes facing each other through a separator, the separator has an average fiber diameter of 0. Disclosed is an electric double layer capacitor comprising a glass fiber sheet of 4 to 4 μm and containing 25 to 75% by weight of glass fiber having a fiber diameter of 1 μm or less, and the glass fiber is made of borosilicate glass ” Yes.

JP-A-11-168033 JP 2008-205084 A

  However, the electric double layer capacitor described in Patent Document 1 is a paper that is made by containing 50% by weight or more of fibers formed by beating regenerated cellulose fibers. As a result of studies by the inventors of the present application, it is difficult to increase the withstand voltage when leakage current is increased. It has also been found that beating the regenerated cellulose fiber weakens the fiber strength, and as a result, the strength of the separator is weak and the process defect rate may increase.

  Moreover, in the electric double layer capacitor described in Patent Document 2, since a glass fiber nonwoven fabric is used, chemical stability to the electrolytic solution is high. In Patent Document 2, the average fiber diameter of glass fibers is 0.4 to 4 μm, and glass fiber separators using such small-diameter glass fibers tend to be mechanically weak. In order to maintain the strength, 2 to 15% by weight or more of glass fiber of 7 μm or more is mixed. However, in the electric double layer capacitor described in Patent Document 2, short circuit (SH) defects and leakage current increase, and it is difficult to obtain sufficient performance as a separator. It became clear by examination.

  With recent diversification of electronic devices, electric double layer capacitors with low resistance and high capacity are required. In addition, with the miniaturization of electronic devices, a thin and high performance separator for an electric double layer capacitor is required. However, if the separator for the electric double layer capacitor is made thin, it is directly connected to a decrease in the strength of the base fabric, so that it is difficult to maintain high productivity as in the prior art. There is also a need to reduce the thickness while maintaining the contradictory performance of ion permeability and electrical insulation.

  Under such circumstances, the problem to be solved by the present invention is a separator for an electric double layer capacitor having excellent ion permeability, wettability of electrolytic solution, and electrical insulation, as well as high capacitance and low internal resistance. An object of the present invention is to provide an electric double layer capacitor that is low, has low leakage current, and is highly reliable.

As a result of intensive studies and repeated experiments, the inventors of the present application have unexpectedly completed the present invention described below.
That is, the present invention is as follows.
[1] The following formulas (1) to (4):
Dmax ≦ 20 μm (1)
0.1 μm ≦ Dmin (2)
Dmax / Dave <3.50 (3)
Dmax / Dmin <5.00 (4)
{In the formula, Dmax is the maximum pore size (μm), Dave is the average pore size (μm), and Dmin is the minimum pore size (μm). }. The separator for electric double layer capacitors comprised from the nonwoven fabric which has the hole diameter distribution which satisfy | fills}.
[2] The separator for an electric double layer capacitor according to [1], wherein the nonwoven fabric is composed of ultrafine fibers having an average fiber diameter of 0.1 μm or more and 5.0 μm or less.
[3] The separator for an electric double layer capacitor according to [1] or [2], wherein the nonwoven fabric has an average pore diameter (Dave) of 10 μm or less.
[4] The separator for an electric double layer capacitor according to any one of [1] to [3], wherein the nonwoven fabric has a minimum pore diameter (Dmin) of 5 μm or less.
[5] The separator for an electric double layer capacitor according to any one of [1] to [4], wherein the nonwoven fabric is a nonwoven fabric composed of thermoplastic resin fibers.
[6] The separator for an electric double layer capacitor according to any one of [1] to [5], wherein the nonwoven fabric is a nonwoven fabric that has been hydrophilized.
[7] The separator for an electric double layer capacitor according to any one of [1] to [6], wherein the nonwoven fabric has a thickness of 10 to 300 μm and a basis weight of 5 to 100 g / m ² .
[8] The separator for an electric double layer capacitor according to any one of [1] to [7], wherein the nonwoven fabric has a porosity of 30 to 95%.
[9] The separator for an electric double layer capacitor according to any one of [1] to [8], wherein the nonwoven fabric is composed of ultrafine fibers having a fiber length of 150 mm or more.
[10] The separator for an electric double layer capacitor according to any one of [1] to [9], wherein the nonwoven fabric is a laminated nonwoven fabric having at least two nonwoven fabric layers.
[11] The separator for an electric double layer capacitor according to any one of [1] to [10], wherein the nonwoven fabric is a calendered nonwoven fabric.
[12] An electric double layer capacitor having the electric double layer capacitor separator according to any one of [1] to [11].

Since the separator for electric double layer capacitors of the present invention has a highly controlled pore size distribution, it has excellent ion permeability, electrical insulation and chemical stability. In addition, the electric double layer capacitor of the present invention can be produced at a low production cost with a stable production process, a good yield, a high capacitance, and a low internal capacity by using the separator for the electric double layer capacitor of the present invention. Low resistance, low leakage current, and high reliability.
The above description does not disclose all embodiments of the present invention and all advantages related to the present invention.

  Hereinafter, the present invention will be described in more detail for the purpose of illustrating representative embodiments of the present invention, but the present invention is not limited to these embodiments.

The electric double layer capacitor separator of the present embodiment has the following formulas (1) to (4):
Dmax ≦ 20 μm (1)
0.1 μm ≦ Dmin (2)
Dmax / Dave <3.50 (3)
Dmax / Dmin <5.00 (4)
{In the formula, Dmax is the maximum pore size (μm), Dave is the average pore size (μm), and Dmin is the minimum pore size (μm). } Is a separator for an electric double layer capacitor composed of a non-woven fabric having a pore size distribution satisfying.

  The maximum pore diameter (Dmax) of the nonwoven fabric constituting the separator for the electric double layer capacitor of this embodiment is 20 μm or less. If the maximum pore diameter is 20 μm or less, the possibility of short circuiting can be reduced. The upper limit of the maximum pore diameter (Dmax) may be 20 μm or less, and is preferably 18 μm or less, more preferably 15 μm or less, still more preferably 10 μm or less, and particularly preferably 5 μm or less from the viewpoint of reducing the possibility of short circuit. can do. The lower limit value of the maximum pore diameter (Dmax) is not limited, but may be, for example, 1 μm or more, 2 μm or more, or 3 μm or more from the viewpoint of electrolyte impregnation property and ion permeability. The range of the maximum pore diameter (Dmax) is, for example, 1 μm or more and 20 μm or less, preferably 2 μm or more and 18 μm or less, and more preferably 3 μm or more and 15 μm or less.

  The minimum pore diameter (Dmin) of the nonwoven fabric constituting the separator for the electric double layer capacitor of this embodiment is 0.1 μm or more. When the minimum pore diameter is 0.1 μm or more, the ion permeability is good and the internal resistance is low. The lower limit of the minimum pore diameter (Dmin) may be 0.1 μm or more, and is preferably 0.3 μm or more, more preferably 0.5 μm or more, and even more preferably 1 from the viewpoint of electrolyte impregnation and ion permeability. 0.0 μm or more. The upper limit value of the minimum pore diameter (Dmin) is not limited, but can be set to, for example, 5 μm or less, 4 μm or less, 3 μm or less, or 2 μm or less from the viewpoint of reducing the possibility of a short circuit. The range of the minimum pore diameter (Dmin) can be, for example, 0.1 μm to 5 μm, preferably 0.3 μm to 4 μm, and more preferably 1 μm to 3 μm.

  It is preferable that the average pore diameter (Dave) of the nonwoven fabric which comprises the separator for electric double layer capacitors of this embodiment is 10 micrometers or less. The possibility of a short circuit can be reduced as it is 10 micrometers or less. The upper limit value of the average pore diameter (Dave) may be 10 μm or less, and is, for example, 8 μm or less, 5 μm or less, 4 μm or less, 3 μm or less, or 2 μm or less from the viewpoint of more effectively reducing the possibility of short circuit. be able to. The lower limit value of the average pore diameter (Dave) is not limited, but is, for example, 0.1 μm or more, 0.5 μm or more, 1.0 μm or more, 1.5 μm or more, or 2 from the viewpoint of electrolyte impregnation property and ion permeability. 0.0 μm or more.

  The ratio (Dmax / Dave) of the maximum pore diameter (Dmax) to the average pore diameter (Dave) of the nonwoven fabric constituting the separator for the electric double layer capacitor of this embodiment is less than 3.50. When Dmax / Dave is less than 3.50, the pore size distribution becomes uniform, the ion permeability in the separator becomes uniform, the leakage current (LC) can be kept low, and the possibility of a short circuit is reduced. Can do. The upper limit value of Dmax / Dave may be less than 3.50, and may be less than 3.00, less than 2.75, or less than 2.50 from the viewpoint of more effectively reducing the possibility of a short circuit. it can.

  The ratio (Dmax / Dmin) of the maximum pore diameter (Dmax) to the minimum pore diameter (Dmin) of the nonwoven fabric constituting the separator for the electric double layer capacitor of this embodiment is less than 5.00. If it is less than 5.00, the pore size distribution becomes uniform, the capacitance increases, and the possibility of short-circuiting can be reduced. The upper limit value of Dmax / Dmin may be less than 5.00, and from the viewpoint of more effectively reducing the capacity retention rate or the possibility of a short circuit, less than 4.90, less than 4.50, and 4. It can be less than 25, less than 4.00, or less than 3.75.

  In the separator for an electric double layer capacitor of the present invention, the nonwoven fabric is preferably composed of ultrafine fibers having an average fiber diameter of 0.1 μm or more and 5.0 μm or less. When the thickness is 0.1 μm or more, the strength of the nonwoven fabric is increased and the nonwoven fabric does not become too dense. Therefore, the permeability and ion permeability of the electrolytic solution are good, and the internal resistance can be lowered. On the other hand, when it is 5.0 μm or less, variation in local denseness can be reduced, excellent electrical insulation can be achieved, and the possibility of a short circuit can be reduced. The average fiber diameter of the ultrafine fibers can be, for example, 0.2 μm to 3 μm, 0.3 μm to 2 μm, 0.3 μm to 2.5 μm, or 0.3 μm to 2.0 μm.

  In the separator for the electric double layer capacitor of the present embodiment, it is preferable that the nonwoven fabric is composed of ultrafine fibers having a fiber length of 150 mm or more. When the fiber length of the ultrafine fiber is 150 mm or more, the strength and processability of the nonwoven fabric are improved. Preferably, the fiber length of the ultrafine fiber is 200 mm or more.

  As for the separator for electric double layer capacitors of this embodiment, it is preferable that the nonwoven fabric is comprised from the continuous long fiber. In the specification of the present application, the continuous long fiber refers to a fiber defined by JIS-L0222. In the electric double layer capacitor separator of the present embodiment, it is more preferable that the nonwoven fabric is composed of continuous continuous fibers of ultrafine fibers.

  As for the separator for electric double layer capacitors of this embodiment, it is preferable that the nonwoven fabric is comprised from the thermoplastic resin fiber. Examples of the thermoplastic resin include, but are not limited to, polyolefin resin, polyester resin, polyamide resin, polyphenylene sulfide resin, polyvinyl chloride, polyimide, ethylene / vinyl acetate copolymer, polyacrylonitrile, polycarbonate, polystyrene, ionomer, Polyphenylene sulfide (PPS) and mixtures thereof are mentioned. Examples of polyolefin resins include homopolymers or copolymers of α-olefins such as ethylene, propylene, 1-butene, 1-hexene, 4-methyl-1-pentene, 1-octene, Density polyethylene, linear low density polyethylene (LLDPE), high density polyethylene, polypropylene (propylene homopolymer), polypropylene random copolymer, poly 1-butene, poly 4-methyl-1-pentene, ethylene / propylene random copolymer Examples thereof include a copolymer, an ethylene-1-butene random copolymer, and a propylene-1-butene random copolymer. Examples of the polyester resin include polyethylene terephthalate (PET), polybutylene terephthalate, and polyethylene naphthalate. Examples of the polyamide-based resin include nylon-6 (Ny), nylon-66, polymetaxylene adipamide, and the like.

  The thermoplastic resin fiber is preferably a group consisting of polyethylene terephthalate (PET), nylon-6 (Ny), and polypropylene (PP) from the viewpoints of electrolyte permeability, chemical stability, electrical insulation, and the like. Is at least one selected from. Especially, it is preferable that a thermoplastic resin fiber is a polyethylene terephthalate (PET) from a heat resistant viewpoint.

  In the separator for the electric double layer capacitor of the present embodiment, it is preferable that the nonwoven fabric is subjected to a hydrophilic treatment. When the nonwoven fabric is hydrophilized, it becomes easy to impregnate the electrolyte in the voids of the nonwoven fabric, so that more electrolyte can be taken into the separator and the electric double layer capacitor has excellent ion permeability. This is preferable because a separator for a battery can be provided and a high-performance electric double layer capacitor can be provided using the separator. Hydrophilic treatment methods include physical processing methods such as hydrophilization by corona treatment or plasma treatment; chemical processing methods such as introduction of surface functional groups such as oxidization treatment, Introducing acid groups, etc .; water-soluble polymers such as PVA, polystyrene sulfonic acid or polyglutamic acid, and / or surfactants such as nonionic surfactants, anionic surfactants, cationic Processing with a treatment agent such as a surfactant or an amphoteric surfactant can be employed. A person skilled in the art can select an appropriate hydrophilization processing method and conditions, for example, the amount of treatment agent used, the amount of functional groups introduced, and the like in consideration of the affinity with the electrolytic solution.

  As for the separator for electric double layer capacitors of this embodiment, it is preferred that the thickness of a nonwoven fabric is 10-300 micrometers. It is preferable for the thickness of the nonwoven fabric to be within this range because the strength, handling properties, and electrical resistance value of the nonwoven fabric can be further reduced. The thickness of a nonwoven fabric can be 10-200 micrometers, 10-150 micrometers, 10-100 micrometers, 10-50 micrometers, or 20-50 micrometers, for example.

The separator for an electric double layer capacitor of the present embodiment preferably has a nonwoven fabric basis weight of 5 to 100 g / m ² . When the fabric weight of the nonwoven fabric is within this range, it is preferable from the viewpoint of the strength, electrical resistance value, ion permeability, etc. of the nonwoven fabric. The basis weight of the nonwoven fabric can be, for example, 7 to 90 g / m ² , 10 to 80 g / m ² , or 10 to 50 g / m ² .

  As for the separator for electric double layer capacitors of this embodiment, it is preferred that the porosity of a nonwoven fabric is 30 to 95%. When the porosity of the nonwoven fabric is within this range, it is preferable from the viewpoints of electrolyte permeability, ion permeability, prevention of short circuit, and the like. The porosity of a nonwoven fabric can be 40-90%, 45-85%, 50-80%, for example.

  The separator for the electric double layer capacitor of this embodiment preferably has a tensile strength of the nonwoven fabric of 3 N / 15 mm or more from the viewpoints of handling properties, reduction of defective rate, and the like. The tensile strength of the nonwoven fabric can be, for example, 5 N / 15 mm or more, 6 N / 15 mm or more, 7 N / 15 mm or more, or 10 N / 15 mm or more.

In the separator for the electric double layer capacitor of this embodiment, the volume resistance of the nonwoven fabric is preferably 1.0 × 10 ⁹ Ω · cm or more from the viewpoint of preventing short circuit. The volume resistance of the nonwoven fabric is, for example, 1.0 × 10 ¹⁰ Ω · cm or more, 1.0 × 10 ¹⁴ Ω · cm or more, 1.0 × 10 ¹⁵ Ω · cm or more, or 1.0 × 10 ¹⁶ Ω · cm or more. cm or more.

  As for the separator for electric double layer capacitors of this embodiment, it is preferred that the nonwoven fabric is formed by the melt blow method. In general, the melt blow method is a method in which a molten thermoplastic resin is sent to a melt blown nozzle and discharged from nozzle nozzle holes in which a plurality of nozzle holes are arranged in one or more rows. The fiber is thinned by being pulled by a high-speed and high-speed spinning gas ejected from an air gap provided so as to sandwich the wire. Next, an ultrafine and uniform melt-blown nonwoven fabric can be produced by accumulating the thinned fibers on a collector net having a suction fan at the bottom. By adopting the melt blow method, it becomes easy to achieve a highly controlled pore distribution in the separator for the electric double layer capacitor of the present embodiment.

  The separator for an electric double layer capacitor of the present embodiment may be a laminated nonwoven fabric composed of two or more layers of nonwoven fabric. As the structure of the laminated nonwoven fabric, a laminate in which a meltblown nonwoven fabric is laminated on a spunbond nonwoven fabric (hereinafter also referred to as SM), and a laminate in which a meltblown nonwoven fabric is sandwiched between two spunbond nonwoven fabric layers (hereinafter referred to as SMS). And the like)). By laminating the nonwoven fabric, the dispersibility and uniformity of the nonwoven fabric can be improved, and the strength can be reinforced. The laminated nonwoven fabrics other than SM and SMS are, for example, laminated nonwoven fabrics with knitted fabrics, woven fabrics, films, inorganic composite material layers, etc .; as nonwoven fabrics, wet nonwoven fabrics, dry nonwoven fabrics, dry pulp nonwoven fabrics, flash The structure which laminated | stacked the spinning nonwoven fabric, the spread nonwoven fabric, etc. is mentioned. Lamination methods include thermal embossing, thermal fusion methods such as ultrasonic fusion, mechanical entanglement methods such as needle punch and water jet, hot melt adhesives, methods such as urethane adhesives, extrusion Various known methods such as laminating can be employed.

  It is preferable that the nonwoven fabric which comprises the separator for electric double layer capacitors of this embodiment is the nonwoven fabric by which the calendar process was given. A nonwoven fabric can be satisfactorily formed by thermally bonding fibers in the nonwoven fabric layer by calendering. Examples of the calendering include a method in which the nonwoven fabric layer is pressure-bonded with a hot roll. This method can be carried out in a continuous integrated production line, and is therefore suitable for the purpose of obtaining a uniform nonwoven fabric with a low basis weight. . The heat bonding step can be performed, for example, at a temperature lower by 50 ° C. to 120 ° C. and a linear pressure of 100 to 1000 N / cm based on the melting point of the thermoplastic resin. When the linear pressure in the calendering is in the above range, it is preferable from the viewpoint of the strength of the nonwoven fabric, the reduction of the deformation of the fiber, the reduction of the apparent density, etc., and the highly controlled pores in the separator for the electric double layer capacitor of this embodiment Distribution is easier to achieve.

  The heat roll used in calendering may be a roll with irregularities on the surface, such as embossing or satin pattern, or a smooth flat roll. The surface pattern of the roll having irregularities on the surface is not limited as long as the fibers can be bonded together by heat, such as an embossed pattern, a satin pattern, a rectangular pattern, and a line pattern.

  The separator for an electric double layer capacitor of this embodiment may have an inorganic composite material layer on a nonwoven fabric. When the inorganic composite material layer is provided on the nonwoven fabric, the possibility of a short circuit can be further reduced. The inorganic composite material layer may contain inorganic particles. As the inorganic composite material layer, a porous layer containing a material capable of closing the pores of the inorganic composite material layer by melting at a predetermined temperature can be used. The porous layer can be provided as a porous planar structure on a nonwoven fabric, for example. Examples of the method of combining the inorganic material with the nonwoven fabric include a method of impregnating the nonwoven fabric with a slurry containing inorganic particles and coating such as transfer.

Examples of inorganic particles include oxide particles of Al, Si, and / or Zr elements having an average particle size of 0.5 to 10 μm. Specifically, for example, iron oxide, SiO ₂ (silica), Al Oxide fine particles such as ₂ O ₃ (alumina), TiO ₂ , BaTiO ₂ , ZrO; nitride fine particles such as aluminum nitride and silicon nitride; sparingly soluble ionic crystal fine particles such as calcium fluoride, barium fluoride and barium sulfate; Covalent crystalline fine particles such as silicon and diamond; clay fine particles such as talc and montmorillonite; materials derived from mineral resources such as boehmite, zeolite, apatite, kaolin, mullite, spinel, olivine, sericite, bentonite, mica, or artificial products thereof Can be used alone or in combination. . Examples of the inorganic particles include metal fine particles; oxide fine particles such as SnO ₂ and tin-indium oxide (ITO); carbonaceous fine particles such as carbon black and graphite; Fine particles having electrical insulation properties by coating with a material having a property (for example, a material constituting the above non-electrically conductive inorganic fine particles) may be used.

  Formation of the inorganic composite material layer can be performed by preparing a slurry in which inorganic particles, a binder, heat-meltable fine particles, etc. are dispersed / dissolved in a solvent, and applying and drying the obtained slurry on a nonwoven fabric. . Any solvent may be used as long as it can uniformly disperse inorganic fine particles, heat-meltable fine particles, and the like, and can dissolve or disperse the binder uniformly. For example, aromatic hydrocarbon such as toluene, methyl ethyl ketone, methyl isobutyl ketone, etc. Organic solvents such as ketones may be used. When the binder is water-soluble, when used as an emulsion, water may be used as a solvent. Note that the interfacial tension may be controlled by adding alcohols, propylene oxide glycol ether, or the like to these solvents.

  The separator for electric double layer capacitors of this embodiment can be used as a separator for electric double layer capacitors. Examples of the shape of the electric double layer capacitor include a cylindrical type in which an electrode body and a separator are wound and impregnated with an electrolytic solution, a coin type in which a rectangular electrode body and a separator are stacked, and a square type.

  EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated concretely, this invention is not limited to these Examples at all. Hereinafter, unless otherwise specified, the length direction of the nonwoven fabric is the MD direction (machine direction), and the width direction is a direction perpendicular to the length direction.

[Example 1]
A nonwoven fabric was produced by the following melt blow method (MB). Polyethylene terephthalate (PET) resin was used as the fiber material. Polyethylene terephthalate (PET) resin melted by an extruder was extruded from a nozzle having a nozzle diameter of 0.30 mm. Continuous selection of polyethylene terephthalate (PET) ultrafine fibers by appropriately selecting the melting temperature of polyethylene terephthalate (PET) resin, spinning gas temperature, single-hole discharge amount of molten resin, etc. A meltblown nonwoven fabric (PET-MB) composed of long fibers was produced. Further, the thickness and the apparent density were adjusted with an embossing roll so as to obtain a desired thickness, and the separator of Example 1 was produced.

[Examples 2 to 13]
As shown in Table 1, by changing the fiber material, nonwoven fabric configuration, etc., and selecting the single hole discharge rate, line speed, and spinning gas conditions as appropriate, it has various basis weights, apparent density, etc. The separator of Examples 2-13 comprised from the continuous continuous fiber of a fiber was produced.

  In Examples 4 and 7, the web was laminated directly on the continuous long-fiber non-woven fabric (fiber diameter 15 μm) produced by the spunbond method by the same melt blow method as described above to obtain a PET-SM structure. Furthermore, while integrating with an embossing roll, thickness and apparent density were adjusted so that it might become desired thickness, and the laminated nonwoven fabric was obtained.

  In Examples 5, 9, 10, and 13, the web was laminated directly on the continuous long-fiber nonwoven fabric (fiber diameter 15 μm) produced by the spunbond method by the same melt blow method as described above, and further on the spunbond method. The produced continuous long-fiber nonwoven fabric (fiber diameter: 15 μm) was laminated to obtain a PET-SMS structure or a PP-SMS structure. Furthermore, while integrating with an embossing roll, thickness and an apparent density were adjusted so that it might become desired thickness, and each laminated nonwoven fabric was obtained.

  In Example 9, after producing a PET-SMS nonwoven fabric, hydrophilization was performed by plasma processing. The plasma processing was performed while reducing the pressure in the plasma processing apparatus to 10 to 5 Torr and then supplying oxygen gas at a flow rate of 10 cc / min.

  In Example 10, after producing a PET-SMS nonwoven fabric, the slurry produced by the following method was applied to the obtained nonwoven fabric and dried at 100 ° C., thereby having an inorganic composite material layer on the nonwoven fabric. Ten separators were produced. In the slurry, 1000 g of water, 1000 g of spherical silica as inorganic particles, and SBR latex as a binder are placed in a container so that the SBR solid content is 3 parts by mass with respect to 100 parts by mass of spherical silica, and stirred with a three-one motor for 1 hour. Obtained by dispersing. The slurry was applied by pulling up the nonwoven fabric through the slurry.

[Comparative Example 1]
Using polyethylene terephthalate (PET), the spunbond method (SB), the spinning temperature of 300 ° C., the filament filaments are extruded onto a moving collection net and spun at a spinning speed of 4500 m / min. Charging to about 3 μC / g was performed to sufficiently open the fiber, and a PET-SB long fiber web was formed on the collection net. After heat-bonding the obtained PET-SB long fiber web with a flat roll, corona discharge machining is performed, with a calender roll, the thickness is adjusted to the desired thickness and the apparent density is adjusted, A separator of Comparative Example 1 was produced.

[Comparative Example 2]
A short fiber of rayon fibers (fiber diameter 5.3 μm, fiber length 5 mm) was beaten and collected on a net so as to have a basis weight of 16 g / m ² by a paper making method to obtain a web. This web was dehydrated and dried, and then thermocompression bonded with a calender roll to produce a separator of Comparative Example 2.

[Comparative Example 3]
Using a short glass fiber having a fiber diameter of 7.0 μm, a wet nonwoven fabric having a basis weight of 40 g / m ² was produced and used as a separator of Comparative Example 3.

(1) Measurement of average fiber diameter (μm) of ultrafine fibers The nonwoven fabric was cut into 10 cm × 10 cm, pressed on an iron plate at 60 ° C. up and down at a pressure of 0.30 MPa for 90 seconds, and then the nonwoven fabric was vapor-deposited with platinum. Using an SEM device (JSM-6510, manufactured by JEOL Ltd.), images were taken under conditions of an acceleration voltage of 15 kV and a working distance of 21 mm. The photographing magnification was 10,000 times for yarns having an average fiber diameter of less than 0.5 μm, 6000 times for yarns having an average fiber diameter of 0.5 μm or more and less than 1.5 μm, and 4000 times for yarns having an average fiber diameter of 1.5 μm or more. The field of view at each magnification was 12.7 μm × 9.3 μm at 10,000 ×, 21.1 μm × 15.9 μm at 6000 ×, and 31.7 μm × 23.9 μm at 4000 ×. Photograph 100 or more fibers at random, measure all fiber diameters, and use the following formula:
Dw = ΣWi · Di = Σ (Ni · Di ² ) / (Ni · Di)
{In the formula, Wi = weight fraction of fiber diameter Di = Ni · Di / ΣNi · Di. } Was determined as the average fiber diameter (μm). However, the fibers fused in the yarn length direction were excluded from the measurement target.

  Fabricate a single-hole nozzle with only one hole, and use a single-hole nozzle to photograph the behavior of yarn during spinning in the region of the present invention with a high-speed camera. It was confirmed that the constituent fibers were continuous long fibers. In the conventional melt blown method, it is considered that the fineness by fiber splitting and the fineness by stretching were mixed. However, according to the above spinning conditions, one fiber was not stretched but stretched. It turned out that it could be made finer. Although it is very difficult to control the fiber diameter and fiber diameter distribution in the case of fiber separation, if a single yarn is made fine, a non-woven fabric composed of fibers having high uniformity and a desired average fiber diameter is obtained. Therefore, it is easy to achieve a highly controlled pore distribution in the electric double layer capacitor separator of the present embodiment.

(2) Measurement of basis weight (g / m ² ) According to the method defined in JIS L-1906, test pieces of 20 cm in length and 25 cm in width were placed at 3 locations per 1 m in the width direction of the sample and 3 locations per 1 m in the length direction. Nine locations per 1 m × 1 m in total were collected and measured for mass, and the average value was calculated by converting to mass per unit area.

(3) Measurement of thickness (μm) According to the method specified in JIS L-1906, the thickness of 10 locations per 1 m width was measured, and the average value was obtained.

(4) Measurement of apparent density (g / cm ³ ) Using the basis weight (g / m ² ) measured in the above (2) and the thickness (μm) measured in the above (3), the apparent density (g / cm ³ ) was calculated by the following formula. .
Apparent density = (weight per unit area) / (thickness)

(5) Measurement of porosity (%) It calculated from the following formula | equation using the apparent density (g / cm < ³ >) calculated in said (4).
Porosity = {1- (apparent density) / (resin density)} / 100

(6) Measurement of maximum pore diameter (Dmax), minimum pore diameter (Dmin), and average pore diameter (Dave) of nonwoven fabric A palm porometer (model: CFP-1200AEX) manufactured by PMI was used as a measuring device. This measuring device uses a non-woven fabric as a sample, immerses the non-woven fabric in an immersion liquid with a known surface tension in advance, and applies pressure to the non-woven fabric after covering all the pores of the non-woven fabric with the immersion liquid film. The pore diameter calculated from the pressure at which the liquid is destroyed and the surface tension of the immersion liquid is measured. After using Sylwick made by PMI as the immersion liquid, the nonwoven fabric was immersed in the immersion liquid and sufficiently deaerated, then the following formula:
d = C · r / P
{Wherein d (unit: μm) is the pore diameter of the filter, r (unit: N / m) is the surface tension of the immersion liquid, and P (unit: Pa) is the liquid film having the pore diameter destroyed. Pressure, and C is a constant determined by the wetting tension, contact angle, etc. of the immersion liquid. } Was used to determine the pore diameter.

  The flow rate (wetting flow rate, unit: L / min) when the pressure P applied to the filter immersed in the immersion liquid was continuously changed from low pressure to high pressure was measured. At the initial pressure, even the liquid film with the largest pores is not broken, so the flow rate is 0 L / min. As the pressure is increased, the liquid film with the largest pores is destroyed and a flow rate is generated (bubble point). The pore diameter (μm) obtained by substituting the pressure at the bubble point into the above formula was defined as the maximum pore diameter (Dmax). When the pressure was further increased, the flow rate increased according to the pressure. The flow rate at the pressure when the liquid film with the smallest pores is destroyed matches the flow rate (dry flow rate) in the dry state of the nonwoven fabric. Therefore, the pore diameter (μm) obtained by substituting the value of the pressure when matched with the dry flow rate was defined as the minimum pore diameter (Dmin). In this measurement method, the value obtained by dividing the wetting flow rate at a certain pressure P by the dry flow rate at the same pressure is called the cumulative filter flow rate (unit:%). The pore size of the liquid film that is broken at a pressure at which the cumulative filter flow rate is 50% is referred to as the average flow pore size (μm). This average flow pore size (μm) was defined as the average pore size (Dave).

(7) Ventilation Resistance Ventilation resistance (kPa · s / m) was measured from a differential pressure at an air permeability of 4 cm ³ / cm ² · s using a KES-F8-AP1 ventilation resistance tester manufactured by Kato Tech Co., Ltd.

(8) Measurement of tensile strength (N / 15 mm) Except for 10 cm of each end of the nonwoven fabric, five test pieces each having a width of 15 mm and a length of 200 mm were sampled per 1 m in the width direction of the nonwoven fabric. A load was applied until the test piece broke, and an average value of the strength at the maximum load of the test piece in the MD direction was determined.

(9) Measurement of volume resistance (Ω · cm) Measuring apparatus: Digital Super Megameter manufactured by HIOKI, and electrode for flat plate sample SME-8311 manufactured by HIOKI were used. A 100 mm × 100 mm test piece (nonwoven fabric) was prepared, and the volume resistance value (Ω · cm) was measured under measurement conditions of a voltage of 10 V and a measurement time of 60 seconds.

(Production of element)
A pair of electrodes (40 mm wide strips) in which carbon black, activated carbon and the like were held on an aluminum foil were spirally wound through a separator to produce an element.

[Manufacture of electric double layer capacitors]
The element obtained as described above was dried at 150 ° C. for 24 hours under vacuum conditions, and then impregnated with an electrolytic solution (solvent: propylene carbonate, solute: Et4NB4 quaternary salt) and stored in a case. By sealing, an electric double layer capacitor having a rated voltage of 2.5 V and a rated capacity of 200 F was produced.

(10) Measurement of defective rate (%) When producing a capacitor, it was judged that the electrode was electrically connected by the burr at the end of the electrode, and the one that was short-circuited due to the separator penetrating and breaking, etc. The ratio of defects per 1000 pieces was defined as a defect rate (%).

(11) Measurement of capacitance (F), internal resistance (mΩ), and leakage current (μA) The initial characteristics of the electric double layer capacitor are capacitance (F), internal resistance (mΩ), leakage current ( μA) was measured by a method based on JIS-C51560.

  The separator for an electric double layer according to the present invention is excellent in ion permeability, insulative properties, and excellent wettability of an electrolytic solution. Therefore, by using this separator, an electric double layer having a large capacity, low resistance, and high reliability can be obtained. A multilayer capacitor can be manufactured. Therefore, the present invention can be suitably used in a wide range of fields such as in-vehicle use and industrial use other than the memory backup use.

Claims (12)

The following formulas (1) to (4):
Dmax ≦ 20 μm (1)
0.1 μm ≦ Dmin (2)
Dmax / Dave <3.50 (3)
Dmax / Dmin <5.00 (4)
{In the formula, Dmax is the maximum pore size (μm), Dave is the average pore size (μm), and Dmin is the minimum pore size (μm). }. The separator for electric double layer capacitors comprised from the nonwoven fabric which has the hole diameter distribution which satisfy | fills}.   The separator for an electric double layer capacitor according to claim 1, wherein the nonwoven fabric is composed of ultrafine fibers having an average fiber diameter of 0.1 μm or more and 5.0 μm or less.   The separator for electric double layer capacitors according to claim 1 or 2, wherein the nonwoven fabric has an average pore diameter (Dave) of 10 µm or less.   The separator for electric double layer capacitors according to any one of claims 1 to 3, wherein the nonwoven fabric has a minimum pore diameter (Dmin) of 5 µm or less.   The separator for an electric double layer capacitor according to any one of claims 1 to 4, wherein the nonwoven fabric is a nonwoven fabric composed of thermoplastic resin fibers.   The separator for an electric double layer capacitor according to any one of claims 1 to 5, wherein the nonwoven fabric is a nonwoven fabric subjected to a hydrophilic treatment. The separator for an electric double layer capacitor according to any one of claims 1 to 6, wherein the nonwoven fabric has a thickness of 10 to 300 µm and a basis weight of 5 to 100 g / m ² .   The separator for an electric double layer capacitor according to any one of claims 1 to 7, wherein the non-woven fabric has a porosity of 30 to 95%.   The separator for an electric double layer capacitor according to any one of claims 1 to 8, wherein the nonwoven fabric is composed of ultrafine fibers having a fiber length of 150 mm or more.   The separator for an electric double layer capacitor according to any one of claims 1 to 9, wherein the nonwoven fabric is a laminated nonwoven fabric having at least two nonwoven fabric layers.   The separator for an electric double layer capacitor according to any one of claims 1 to 10, wherein the nonwoven fabric is a calendered nonwoven fabric.   The electric double layer capacitor which has the separator for electric double layer capacitors of any one of Claims 1-11.