JP2006278636A - Capacitor separator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a capacitor separator which is highly reliable to show superior mechanical strength even if containing an electrolyte. <P>SOLUTION: The capacitor separator is made of a wet nonwoven fabric containing core/sheath-type composite fibers which consist of a core made of a polyethylene telephthalate, and a sheath made of a polyester copolymer made by copolymerizing a terephthalic acid, an ethylene glycol, and 1,4-butanediol. <P>COPYRIGHT: (C)2007,JPO&amp;INPIT

Description

  The present invention relates to a separator that realizes a capacitor having high mechanical strength and excellent reliability even in a state containing an electrolytic solution.

There has been proposed a capacitor separator having a heat-resistant polymer fiber having a melting point or a thermal decomposition temperature of 250 ° C. or more as a main component and excellent in heat resistance (see Patent Document 1), and such heat-resistant polymer fiber. Since the separator made of is weak in the adhesive strength between the fibers, it is necessary to include a heat-sealable fiber in order to obtain a sufficient mechanical strength, and a core-sheath type composite fiber is particularly preferable. However, the polyester core-sheath type composite fibers contained in these separators for capacitors have poor chemical resistance with respect to propylene carbonate, which is a solvent of a general electrolytic solution for capacitors, in which the sheath part, which is a heat-sealing component. In the state containing the liquid, the strength decreases, and the separator may be damaged due to the expansion of the activated carbon electrode that occurs during charging.
JP 2003-257790 A

  The present invention solves the above problems found in the prior art. That is, an object of the present invention is to provide a capacitor separator having high mechanical strength and excellent reliability even in a state containing an electrolytic solution.

  As a result of intensive studies to solve this problem, the present inventors have found that a capacitor separator that does not decrease mechanical strength even in a state containing an electrolytic solution and has excellent reliability can be realized. It has come.

  That is, the present invention relates to a core-sheath type composite fiber (hereinafter referred to as “core-sheath type”) which is a polyester copolymer in which a core part is polyethylene terephthalate and a sheath part is copolymerized with terephthalic acid / ethylene glycol / 1,4-butanediol. It is a capacitor separator characterized by being made of a wet nonwoven fabric containing a composite fiber).

  The polyester copolymer in the sheath part of the core-sheath type composite fiber contained in the separator for capacitors of the present invention is terephthalic acid / ethylene glycol / 1,4-butanediol = 100/20 to 80/20 to 80 in molar ratio. The polyester copolymer is preferably used.

  The polyester copolymer in the sheath part of the sheath type composite fiber of the present invention is a polyester copolymer obtained by copolymerizing terephthalic acid / ethylene glycol / 1,4-butanediol with an aliphatic polylactone. It is preferable that

  In the capacitor separator of the present invention, the content of the core-sheath composite fiber is preferably 3 to 70% by mass.

  The capacitor separator of the present invention is preferably heat-sealed at a temperature equal to or higher than the melting point of the sheath portion of the core-sheath composite fiber.

  According to the present invention, it is possible to obtain a capacitor separator having high mechanical strength and excellent reliability even when an electrolyte is included.

  Hereinafter, the capacitor separator of the present invention (hereinafter referred to as “separator”) will be described in detail.

  The capacitor in the present invention has a power storage function constituted by sandwiching a dielectric or electric double layer between two opposing electrodes. Examples of using a dielectric include an aluminum electrolytic capacitor and a tantalum electrolytic capacitor, and examples of using an electric double layer include an electric double layer capacitor. The electrode of the electric double layer capacitor may be a pair of electric double layer capacitive electrodes, one of which is an electric double layer capacitive electrode and the other is a combination of a redox electrode.

  The electrolytic solution of the capacitor may be any one of an aqueous solution system, an organic solvent system, and a conductive polymer. Examples of the organic solvent electrolyte include dimethyl carbonate, diethyl carbonate, ethylene carbonate, propylene carbonate, acetonitrile, propionitrile, γ-butyrolactone, α-methyl-γ-butyrolactone, β-methyl-γ-butyrolactone, γ- Ion dissociation in organic solvents such as valerolactone, 3-methyl-γ-valerolactone, dimethyl sulfoxide, diethyl sulfoxide, dimethylformamide, diethylformamide, tetrahydrofuran, dimethoxyethane, dimethylsulfolane, sulfolane, ethylene glycol, propylene glycol, methyl cellosolve Examples include, but are not limited to, ionic liquids (solid molten salts) and the like. Examples of the conductive polymer include polypyrrole, polythiophene, polyaniline, polyacetylene, and derivatives thereof.

  For example, polyester-based binder fibers used for wet nonwoven fabrics include core-sheath type composite fibers in which the core part is made of polyethylene terephthalate and the sheath part is made of a copolymer of polyethylene terephthalate and an isophthalic acid component. The polyester core-sheath type composite fiber in which the temperature of the heat sealing treatment of the sheath (the temperature at which the sheath is heat-sealed) is lowered by copolymerizing the sheath is carbonic acid, which is a general electrolyte solvent for capacitors. Since the chemical resistance against propylene is weak, separators containing these polyester-based core-sheath composite fibers have a reduced mechanical strength when they contain an electrolyte, and are damaged due to expansion of the activated carbon electrode that occurs during charging. There was a fear.

  On the other hand, the sheath-core type composite fiber used in the present invention has a sheath part, which is a heat fusion component, made of a copolymer of terephthalic acid / ethylene glycol / 1,4-butanediol, and has high chemical resistance to propylene carbonate. For this reason, the separator containing the same has a small decrease in mechanical strength even in a state of containing the electrolytic solution, and has a low probability of breakage due to expansion of the electrode.

  It is preferable that the melting | fusing point of the sheath part of the core-sheath-type composite fiber used for this invention is 200 degrees C or less. When the melting point exceeds 200 ° C., the heat fusion treatment temperature of the sheath portion becomes high, and the polyethylene terephthalate in the core portion may be softened during the heat fusion treatment, and the dimensional stability may be impaired.

  The sheath of the core-sheath type composite fiber used in the present invention is preferably a polyester copolymer of terephthalic acid / ethylene glycol / 1,4-butanediol = 100/20 to 80/20 to 80 in molar ratio. When copolymerized outside the above range, the melting point of the sheath may exceed 200 ° C., and a high heat-sealing temperature may be required.

  The sheath part of the sheath type composite fiber of the present invention is preferably a polyester copolymer obtained by copolymerizing terephthalic acid / ethylene glycol / 1,4-butanediol with an aliphatic polylactone. . By copolymerizing the aliphatic polylactone, the melting point of the polyester copolymer in the sheath can be lowered without impairing the chemical resistance to propylene carbonate. As the aliphatic polylactone to be copolymerized, a homopolymer of a lactone having 4 to 11 carbon atoms or two or more types of copolymers are preferable, and ε-caprolactone is particularly preferable. The copolymerization rate of the aliphatic polylactone is preferably 20 mol% or less. If the copolymerization ratio exceeds 20 mol%, adhesion during spinning may occur and the spinning performance may be impaired.

  The sheath part of the core-sheath type composite fiber used in the present invention is within a range of 20 mol% or less, such as isophthalic acid, phthalic acid, adipic acid, sebacic acid, diethylene glycol, triethylene glycol, etc., as long as the object of the present invention is not impaired. It may be a copolymer obtained by copolymerizing. If it exceeds 20 mol%, chemical resistance against propylene carbonate may be impaired.

  The composite ratio of the core part to the sheath part of the core-sheath composite fiber used in the present invention is preferably 2/3 to 3/2 in volume ratio, but is not particularly limited, in order to exhibit the functions of the two components. May be selected as appropriate.

  The core of the core-sheath type composite fiber used in the present invention is preferably polyethylene terephthalate. Polyalkylene terephthalate having a larger number of methylene groups than polyethylene terephthalate has a lower melting point, which is not preferable because it may be softened during the heat-sealing treatment of the sheath and impair dimensional stability.

  The core-sheath type composite fiber used in the present invention is not particularly limited, but in order to prevent a short circuit due to physical contact between electrodes and to obtain a separator excellent in self-discharge characteristics, the fineness is 4.4 dtex or less. The average fiber length is preferably 30 mm or less in order to obtain a separator excellent in uniformity with little thickness unevenness.

  In order to improve the mechanical strength of the separator, the content of the core-sheath type composite fiber in the wet nonwoven fabric used in the present invention is preferably 3% by mass or more. Moreover, since there exists a possibility that ion permeability may be inhibited when the membrane | film | coat part formed by heat sealing increases too much, it is preferable that content of a core-sheath composite type fiber shall be 70 mass% or less.

  The separator of the present invention includes natural cellulose fibers, solvent-spun cellulose fibers, acrylics, polyolefins, polyesters, wholly aromatic polyesters, wholly aromatic polyester amides, polyamides, wholly aromatic polyamides, wholly aromatic polymers, as well as core-sheath type composite fibers. Ether, wholly aromatic polycarbonate, wholly aromatic polyazomedin, polyimide, polyamideimide (PAI), polyetheretherketone (PEEK), polyphenylene sulfide (PPS), poly-p-phenylenebenzobisoxazole (PBO), polybenzimidazole ( PBI), polytetrafluoroethylene (PTFE), polyvinyl alcohol, single fibers and composite fibers made of resins such as ethylene-vinyl alcohol copolymer, fibrillated ones and bacterial cellulose May contain an appropriate amount alone, it may contain a combination of two or more. Moreover, you may contain what divided | segmented various split type composite fibers. The content is preferably 30% by mass or more and 97% by mass or less in relation to the content of the core-sheath type composite fiber.

  Among these, in order to improve the heat resistance of the separator, it is preferable to contain fibers having a softening point, a melting point, and a thermal decomposition temperature of 250 ° C. or higher, such as wholly aromatic polyesters and wholly aromatic polyamides. Moreover, in order to make the pores of the separator have a dense structure and a separator having excellent self-discharge characteristics, the average fiber diameter of these fibers is preferably 20 μm or less, and when the thickness of the separator is 100 μm or less. Preferably contains a fibrillated fiber to form a finer pore separator.

  The fibrillated fiber in the present invention refers to a fiber having a fiber shape having a portion finely divided mainly in a direction parallel to the fiber axis, and at least a part of which has a fiber diameter of 1 μm or less. Different from the fibrids as specified in US Pat. No. 5,833,807 and US Pat. No. 5,026,456. The fibrils in the present invention are preferably those in which the aspect ratio of length and width (fiber diameter) is distributed in the range of 20: 1 to 100,000: 1 and the Canadian standard freeness is in the range of 0 ml to 500 ml. Furthermore, the thing whose weight average fiber length exists in the range of 0.1 mm-2 mm is preferable.

  The fibrillated fiber is produced using a high-pressure homogenizer, a high-speed homogenizer, a rotary blade type homogenizer, an ultrasonic crusher, a refiner, a beater, a mill, a milling device, or the like.

  The high-pressure homogenizer here refers to an object having a shearing force generated by applying a pressure of at least 1 MPa or more, preferably 20 to 100 MPa, more preferably 40 to 100 MPa to the object, passing through the orifice, and rapidly depressurizing and decelerating. An apparatus that can fibrillate an object. In the case of a polymer, the shearing force causes tearing mainly in a direction parallel to the fiber axis, and gradually fibrillates as a loosening force. Specifically, a material obtained by cutting a polymer fiber or pellet into a length of 5 mm or less, preferably 3 mm or less, or a pulp-like material in advance, is dispersed in water to obtain a suspension. The concentration of the suspension is a maximum of 25% by mass, preferably 1 to 10%, more preferably 1 to 2%. This suspension is introduced into a high-pressure homogenizer, a pressure of at least 1 MPa, preferably 20 to 100 MPa, more preferably 40 to 100 MPa is applied, and this operation is repeated several times to several tens of times. In some cases, chemicals such as surfactants may be added and processed.

  The bacterial cellulose in the present invention refers to bacterial cellulose produced by a microorganism. This bacterial cellulose includes cellulose and a heteropolysaccharide having cellulose as a main chain, and a glucan such as β-1,3, β-1,2, and the like. Constituent components other than cellulose in the case of heteropolysaccharides are hexoses such as mannose, fructose, galactose, xylose, arabinose, rhamnose, glucuronic acid, pentose sugars and organic acid sugars. These polysaccharides may be composed of a single substance, but two or more kinds of polysaccharides may be composed of hydrogen bonds or the like, and any of them can be used.

  The separator of the present invention may contain an appropriate amount of inorganic fibers or inorganic whiskers in addition to organic fibers. Examples of the inorganic fibers include glass fibers, micro glass fibers, rock wool, alumina fibers, alumina / silica fibers, ceramic fibers, and boron fibers.

  The separator of the present invention is preferably heat-sealed at a temperature equal to or higher than the melting point of the sheath portion of the core-sheath composite fiber.

  The separator of the present invention is subjected to calendering, heat treatment, hot pressing, and the like according to purposes such as thickness adjustment, strength improvement, impurity removal, and heat resistant dimensional stability.

  The separator of the present invention may be a single layer or may be formed of multiple layers. Specifically, wet paper making is performed using a long paper machine, a short paper machine, a circular paper machine, an inclined paper machine, or a combination machine that combines two or more of the same or different types of paper machines. Manufactured by combining one layer or multiple layers. In the case of multiple layers, a relative density difference may be provided for each layer. In the present invention, a fine wire of 80 mesh or more is used for the paper making wire of the paper machine. The water used for wet papermaking is preferably ion-exchanged water or distilled water, and dispersion aids, other additive chemicals, release agents, etc. are preferably nonionic, so long as they do not affect the capacitor characteristics. For example, an appropriate amount of ionic substances may be used.

  The separator of the present invention may be used alone, or two or more separators may be used.

Although there is no restriction | limiting in particular in the basic weight of the separator of this invention, 5-100 g / m < ² > is preferable and 10-50 g / m < ² > is more preferable.

  Although there is no restriction | limiting in particular in the thickness of the separator of this invention, 9 micrometers-300 micrometers are preferable and 50 micrometers-150 micrometers are more preferable. If the thickness of the separator is less than 9 μm, a short circuit is likely to occur due to physical contact between the electrodes. On the other hand, if the thickness is greater than 300 μm, the electrode area that can be accommodated in the capacitor is reduced, and the capacity of the capacitor tends to be insufficient.

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

<Preparation of core-sheath type composite fiber 1>
Polyethylene terephthalate pellets having a relative viscosity of 1.38 and a melting point of 256 ° C. as the core component, and copolymerized polyester pellets copolymerized with terephthalic acid / ethylene glycol / 1,4-butadiol = 100/50/50 (molar ratio) as the sheath component Got. Each of these was dried under reduced pressure, using a normal two-component composite melt spinning apparatus, at a composite ratio (volume ratio) of 1: 1, spinning at 270 ° C., discharge rate of 120 g / min, base plate hole number of 225 holes, spinning speed of 700 m Spinned at / min. The spun yarn was cooled with cold air (18 ° C.) and taken out to obtain an undrawn yarn. The obtained unstretched yarn is bundled, and the tow of 110,000 dtex is stretched at a stretch ratio of 3.3 times and stretched at a stretching temperature of 60 ° C., subjected to a tension heat treatment at 130 ° C., and after adding an oil agent, A polyester core-sheath composite fiber having a single yarn fineness of 2.2 dtex and a sheath melting point of 180 ° C. was prepared by cutting to 5 mm. This is expressed as core-sheath type composite fiber 1 or B1.

<Preparation of core-sheath type composite fiber 2>
Polyethylene terephthalate pellets having a relative viscosity of 1.38 and a melting point of 256 ° C. as the core component, and copolymerized with terephthalic acid / ethylene glycol / 1,4-butadiol = 100/40/60 (molar ratio) as the sheath component, Copolyester pellets obtained by copolymerizing 7 mol% of ε-caprolactone were obtained. Using these pellets, polyester core-sheath type composite fibers having a fineness of 2.2 dtex and a sheath part melting point of 160 ° C. were produced in the same manner as the core-sheath type composite fiber fiber 1. This is expressed as core-sheath type composite fiber 2 or B2.

<Production of fibrillated fiber>
Para-type wholly aromatic polyamide fiber (fineness: 2.5 dtex, fiber length: 3 mm) was dispersed in ion-exchanged water so as to have an initial concentration of 5% by mass, and after beating repeatedly 15 times using a double disc refiner, A fibrillated para-type wholly aromatic polyamide having a weight average fiber diameter of 0.3 μm and a weight average fiber length of 0.45 mm was prepared by repeating the treatment 30 times using a high pressure homogenizer at 50 MPa. Hereinafter, this is referred to as heat-resistant fibril fiber 1 or F1.

  The raw material slurry for producing the wet nonwoven fabric was dispersed using a pulper as shown in Table 1 and the mixing ratio. “B3” in Table 1 is a polyester-based copolymer in which ε-caprolactone is copolymerized with polyethylene terephthalate as the core and terephthalic acid / ethylene glycol / 1,4-butanediol as the sheath. “Cass Ben 7080” (fineness: 2.2 dtex, fiber length: 5 mm) manufactured by Unitika Fiber Co., Ltd., “B4” is a Teijin fiber made of polyester terephthalate in the core and polyethylene terephthalate and polyethylene isophthalate in the sheath. “Teijin Tetoron Tepyrus TJ04CN” (fineness 2.2 dtex, fiber length 5 mm), “P1” means Teijin Fibers polyethylene terephthalate fiber “Teijin Tetron Tepyrus TM04PN” (fineness 0.1 dtex, fiber length 3 mm) .

<Production of capacitor separator>

Example 1
Slurry 1 is subjected to wet paper making using a circular paper machine and dried at 130 ° C. to prepare a wet nonwoven fabric. The wet nonwoven fabric is then heated with a heat roll (diameter: 1.2 m) at 220 ° C. to form a core-sheath type composite fiber. The sheath part was heat-sealed (no pressure, 20 m / min) to obtain a capacitor separator 1 having a basis weight of 30 g / m ² and a thickness of 120 μm.

Example 2
Slurry 2 is wet-papered using a long paper machine and dried at 130 ° C. to prepare a wet nonwoven fabric. Then, the wet nonwoven fabric is sheathed with a core-sheath-type composite fiber by heat fusion treatment similar to that in Example 1. The parts were heat-sealed to obtain a capacitor separator 2 having a basis weight of 20 g / m ² and a thickness of 80 μm.

Example 3
Slurry 3 is wet-paper-made using a long paper machine and dried at 130 ° C. to prepare a wet nonwoven fabric. Then, the wet nonwoven fabric is sheathed with a core-sheath-type composite fiber by heat fusion treatment similar to that in Example 1. The parts were heat-sealed to obtain a capacitor separator 3 having a basis weight of 18 g / m ² and a thickness of 80 μm.

(Comparative Example 1)
The slurry 4 is wet-paper-made using a circular paper machine and dried at 130 ° C. to prepare a wet nonwoven fabric. Then, the wet nonwoven fabric is sheathed with a core-sheath-type composite fiber by heat fusion treatment similar to that in Example 1. The parts were heat-sealed to obtain a capacitor separator 4 having a basis weight of 30 g / m ² and a thickness of 120 μm.

(Comparative Example 2)
Slurry 5 is wet-papered using a long paper machine and dried at 130 ° C. to prepare a wet nonwoven fabric. Then, the wet nonwoven fabric is sheathed with a core-sheath type composite fiber by heat fusion treatment similar to that in Example 1. The parts were heat-sealed to obtain a capacitor separator 5 having a basis weight of 20 g / m ² and a thickness of 80 μm.

(Comparative Example 3)
Slurry 6 is wet-paper-made using a long paper machine and dried at 130 ° C. to prepare a wet nonwoven fabric. The wet nonwoven fabric is then subjected to a heat-sealing process similar to that in Example 1 to provide a sheath of core-sheath type composite fibers. The parts were heat-sealed to obtain a capacitor separator 6 having a basis weight of 18 g / m ² and a thickness of 80 μm.

  The capacitor separators 1 to 6 and the electric double layer capacitors 1 to 6 were measured by the following test method, and the results are shown in Table 2.

<Electrolytic solution puncture strength retention>
Capacitor separators 1 to 6 are cut into strips of 200 mm length and 50 mm width, and a 1 mm diameter metal needle with a rounded end (R) is attached to a desktop material tester (Orientec Corp., STA-1150) It was lowered until it penetrated at a constant speed of 50 mm / min perpendicular to the sample surface. The maximum load (g) at this time was measured at five locations, and the average value was defined as the puncture strength. Next, the sample for which the puncture strength was measured was immersed in an electrolytic solution (a solution obtained by dissolving (C ₂ H ₅ ) ₃ (CH ₃ ) NBF ₄ in propylene carbonate at a concentration of 1.5 mol / l) for 10 minutes. At this time, the entire sample is immersed in the electrolyte. After 10 minutes, the corner of the sample taken out from the electrolyte was sandwiched between clips and hung vertically, allowed to stand for 15 minutes, and then the puncture strength was measured in the same manner as before immersion in the electrolyte. The change rate of the puncture strength before and after the electrolytic solution impregnation was expressed as 100 minutes, and this was shown in Table 2 as the electrolytic solution puncture strength retention rate (%). The higher the value of the electrolyte puncture strength retention rate, the smaller the decrease in strength even when the electrolyte is contained, indicating that the separator is a highly reliable separator that does not break due to electrode expansion during capacitor charging. .

<Defect rate>
Using activated carbon electrodes that expand about 5% in volume as the positive and negative electrodes, stacking separators between the positive and negative electrodes, and winding them in a spiral shape using a winding machine to produce a spiral element did. The spiral element was housed in an aluminum case, and the positive electrode lead and the negative electrode lead were welded to the positive electrode terminal and the negative electrode terminal attached to the case, and then the case was sealed leaving the electrolyte solution injection port. The entire case was heated to 200 ° C. for 5 hours to remove moisture contained in the electrodes and separator. After allowing this to cool to room temperature in a vacuum, an electrolytic solution was injected into the case, and the injection port was sealed to prepare 100 electric double layer capacitors 1 to 6 each. The electrolyte used was the same as that used in the above <Electrolytic solution puncture strength retention>. The electric double layer capacitors 1 to 6 were charged up to 2.7 V, and the ratio of the internal short circuit due to breakage due to the volume expansion of the electrodes was examined.

Rating:
As shown in Table 2, containing core-sheath type composite fibers of Examples 1 to 3, wherein the core part is a polyester copolymer of polyethylene terephthalate and the sheath part is terephthalic acid / ethylene glycol / 1,4-butanediol. Capacitor separators 1 to 3 made of a wet non-woven fabric have a small decrease in strength even when containing an electrolytic solution, and electric double layer capacitors 1 to 3 comprising these capacitor separators have a low defect rate and excellent reliability. Showed that.

  On the other hand, capacitor separators 4 to 6 made of wet nonwoven fabric containing core-sheath type composite fibers whose sheath portions are made of a copolymer of polyethylene terephthalate and an isophthalic acid component in Comparative Examples 1 to 3 include an electrolyte. The electrical double layer capacitors 4 to 6 comprising these capacitor separators showed a high defect rate.

  As described above, according to the present invention, it is possible to obtain a capacitor separator having high mechanical strength and excellent reliability even in a state containing an electrolytic solution.

Claims (5)

  It is characterized by comprising a wet non-woven fabric containing a core-sheath type composite fiber, in which the core part is a polyester copolymer obtained by copolymerizing polyethylene terephthalate and the sheath part terephthalic acid / ethylene glycol / 1,4-butanediol. Capacitor separator.   2. The capacitor separator according to claim 1, wherein the polyester copolymer has a molar ratio of terephthalic acid / ethylene glycol / 1,4-butanediol = 100/20 to 80/20 to 80.   2. The polyester copolymer is a polyester copolymer obtained by copolymerizing an aliphatic polylactone with a copolymer of terephthalic acid / ethylene glycol / 1,4-butanediol. Or the separator for capacitors of 2.   Content of core-sheath-type composite fiber with respect to a wet nonwoven fabric is 3-70 mass%, The separator for capacitors in any one of Claims 1-3 characterized by the above-mentioned.   The capacitor separator according to any one of claims 1 to 4, wherein the heat-sealing treatment is performed at a temperature equal to or higher than a melting point of the sheath portion of the core-sheath composite fiber.