JP5328584B2 - Fiber assembly - Google Patents

Description

  The present invention relates to a fiber assembly. In particular, the present invention relates to a fiber assembly that can be used as a separator for an electric double layer capacitor and a substrate for an ion conductive film.

  When a fiber assembly such as a nonwoven fabric containing fibers obtained by dry spinning a spinning solution dissolved in an organic solvent is brought into contact with an organic solvent, the fibers are dissolved and the shape of the fiber assembly cannot be maintained. There was a problem that was limited.

  For example, even if an attempt is made to use the fiber assembly as described above as a separator for an electric double layer capacitor, the electrolyte solution of the electric double layer capacitor is composed of an organic solvent, so the fiber assembly is dissolved in the organic solvent, and the separator There was a case that did not work as.

  Therefore, the applicant of the present application has proposed to insolubilize the fiber assembly (Patent Document 1). Specifically, heat treatment, electron beam irradiation, gamma ray irradiation and the like are exemplified as the insolubilization treatment. However, it has been found that such insolubilization treatment cannot be sufficiently insolubilized and may be dissolved by an organic solvent. For example, since an electric double layer capacitor using an organic solvent as an electrolytic solution does not like the presence of moisture, the electrode group in which electrodes and separators are laminated is immersed in the electrolytic solution, or the separator of the electrode group is impregnated with the electrolytic solution. In some cases, a heating process is performed to remove moisture by heating in a state, but it has been found that the separator is dissolved in this heating process and does not function as a separator.

  In addition to the case where the separator is used for the electric double layer capacitor as described above, the same problem occurs when the fiber aggregate is impregnated with a resin dissolved in an organic solvent and then dried to remove the organic solvent. It was. For example, a base material (fiber assembly) for reinforcing an ion conductive membrane is impregnated with an ion conductive resin dissolved in an organic solvent, and then dried by heating to remove the organic solvent, and the ion conductive material reinforced with the fiber assembly. When a membrane is manufactured, the fiber assembly is dissolved, and there is a case where the reinforcing action is not performed.

JP 2007-266511 A (claims, paragraph numbers 0022, 0035, etc.)

  Therefore, the inventors of the present application thought that the above-described problem does not occur if the fiber assembly is composed of fibers made of a polymer insoluble in an organic solvent. For example, it was considered that the above-described problems would not occur if the fiber aggregate was composed of carboxymethyl cellulose or polyvinyl alcohol insoluble in an organic solvent. However, it cannot be made into fiber from carboxymethylcellulose itself, and a spinning aid is necessary for making it into fiber, and it is not practical because the productivity is very poor. Further, although it is possible to fiberize polyvinyl alcohol, since the fiber is easily dissolved during spinning, the productivity is poor and it is not practical.

  The present invention has been made to solve such problems, and provides a fiber assembly that can exhibit performance without being dissolved even when an organic solvent is heated. Objective.

The invention according to claim 1 of the present invention is “ a fiber assembly in which polyacrylonitrile or polyethersulfone is coated with carboxymethylcellulose or polyvinyl alcohol , and is used for a separator for an electric double layer capacitor or an ion conductive membrane” A fiber assembly used as a base material .

The invention according to claim 2 of the present invention is characterized in that “ carboxymethyl cellulose or polyvinyl alcohol is insoluble in water, and“ insoluble in water ”means that the carboxymethyl cellulose or polyvinyl alcohol is the carboxymethyl cellulose or The fiber assembly according to claim 1 , which means that when it is put into water 100 times the mass of polyvinyl alcohol and kept heated at 90 ° C for 60 minutes, the mass remains 70% or more . Is.
The invention according to claim 3 of the present invention is as follows: "Carboxymethylcellulose is carboxymethylcellulose obtained by heating ammonium salt of carboxymethylcellulose, and polyvinyl alcohol is polyvinyl alcohol crosslinked with a maleic anhydride copolymer. The fiber assembly according to claim 2, characterized by:
Furthermore, the invention according to claim 4 of the present invention is as follows: "The fiber assembly according to claim 3, wherein the polyvinyl alcohol is a polyvinyl alcohol obtained by crosslinking completely saponified polyvinyl alcohol with a maleic anhydride copolymer. . "

In the invention according to claim 1, since polyacrylonitrile or polyethersulfone is coated with carboxymethylcellulose or polyvinyl alcohol , even when the organic solvent is heated, the form is maintained without dissolving, and the fiber assembly The body's performance can be demonstrated.
Therefore, it is a fiber assembly that can be used as a separator for an electric double layer capacitor or a substrate for an ion conductive membrane.

The inventions according to claims 2 to 4 have high water resistance since carboxymethyl cellulose or polyvinyl alcohol is insoluble in water.

  The fiber constituting the fiber assembly of the present invention is insoluble in an organic solvent so that the first polymer soluble in the organic solvent can maintain its form without dissolving even when the organic solvent is heated. Covered with a second polymer.

  This first polymer is soluble in an organic solvent so that fibers can be obtained by dry spinning a spinning solution dissolved in an organic solvent. Such a first polymer is not particularly limited as long as it is soluble in an organic solvent. For example, polyester, acrylic resin (for example, polyacrylonitrile, acrylonitrile copolymer, etc.), polymethacrylic acid, polymethacrylic acid, etc. Methyl acid, polycarbonate, polystyrene, polyamide, polyimide, polyolefin resin (eg, polyethylene, polypropylene, etc.), polyethersulfone, polysulfone, fluororesin (eg, polyvinylidene fluoride, polyvinylidene fluoride copolymer, etc.), polyurethane, para Or a meta-aramid etc. can be mentioned. In addition, the 1st polymer does not need to be 1 type, and 2 or more types may be mixed.

  The organic solvent varies depending on the type of the first polymer, and it is not particularly limited as long as the first polymer is soluble. For example, acetone, methanol, ethanol, propanol, isopropanol, tetrahydrofuran, dimethyl sulfoxide, 1, 4 -Dioxane, pyridine, N, N-dimethylformamide, N, N-dimethylacetamide, N-methyl-2-pyrrolidone, acetonitrile, formic acid, toluene, benzene, cyclohexane, cyclohexanone, carbon tetrachloride, methylene chloride, chloroform, trichloroethane, Examples thereof include ethylene carbonate, diethyl carbonate, propylene carbonate, and methyl ethyl ketone. In addition, the organic solvent does not need to be 1 type, and 2 or more types of mixed solvents may be sufficient.

  In the present invention, the term “soluble in an organic solvent” means that the polymer is charged into an organic solvent 100 times the mass of the polymer, and in the case of an organic solvent having a boiling point of 100 ° C. or less, (boiling point−10) ° C. In the case of an organic solvent having a boiling point exceeding 0 ° C., it means that the mass is reduced by 70% or more when heating is continued at 100 ° C. for 60 minutes.

  In the present invention, the first polymer is soluble even when the organic solvent is heated by being made of a fiber coated with a second polymer insoluble in the organic solvent in which the first polymer is soluble. The fiber form can be maintained.

  Such a second polymer is not particularly limited as long as it is insoluble in an organic solvent, and examples thereof include carboxymethyl cellulose (CMC) and polyvinyl alcohol (PVA). In addition, the 2nd polymer does not need to be 1 type, and 2 or more types may be mixed.

  The second polymer is preferably insoluble in water so that the second polymer not only has excellent organic solvent resistance but also water resistance. Since CMC and PVA as described above are water-soluble, it is preferable to treat them so as to be insoluble in water. For example, in the case of CMC, an ammonium salt of carboxymethyl cellulose is preferable. This is because the ammonium salt of carboxymethyl cellulose is insoluble in water due to the release of ammonia by heating. On the other hand, in the case of PVA, it is preferably cross-linked by a cross-linking agent and insoluble in water. The PVA crosslinking agent is not particularly limited, and examples thereof include maleic anhydride copolymers. In addition, as PVA, it is preferable that it is PVA fully saponified so that it may become insoluble easily.

  In the present invention, “insoluble in an organic solvent” means that a polymer is introduced into an organic solvent 100 times the mass of the polymer, and in the case of an organic solvent having a boiling point of 100 ° C. or lower (boiling point−10) ° C., 100 ° C. In the case of an organic solvent having a boiling point of more than 1, it means that the mass remains at 70% or more when heating is continued at 100 ° C. for 60 minutes. Further, “insoluble in water” means that when a polymer is poured into water 100 times the mass of the polymer and heated at 90 ° C. for 60 minutes, the mass remains at 70% or more.

  The fibers constituting the fiber assembly of the present invention are in a state in which the first polymer is covered with the second polymer, but even if the first polymer is completely covered with the second polymer, the fibers are partially covered with the second polymer. It may be covered. However, it is preferred that the first polymer is completely coated so that it is not dissolved by the organic solvent and that the first polymer is not exposed on the surface. In addition, like sea island fiber, two or more first polymers may be covered with one second polymer.

  The average fiber diameter of the fibers constituting the fiber assembly of the present invention is not particularly limited, but when the average fiber diameter is small, separation performance, liquid retention performance, wiping performance, hiding performance, insulation performance, flexibility, etc. Since it is excellent in various performances, it is preferably 10 nm to 2 μm. “Average fiber diameter” refers to an arithmetic average value of fiber diameters at 50 points, and “fiber diameter” refers to a value calculated based on an electron micrograph of a fiber assembly.

  The fiber assembly of the present invention is composed of the fibers as described above, but the aggregate state is not particularly limited because it varies depending on the intended use of the fiber assembly. For example, it can be a two-dimensional aggregate state such as a nonwoven fabric, or a three-dimensional aggregate state such as a cylinder or a hollow cylinder.

  The method for producing the fiber assembly of the present invention is not particularly limited. For example, for a fiber assembly composed of fibers obtained by dry spinning a spinning solution in which the first polymer is dissolved in an organic solvent, It can be produced by applying a coating solution in which the second polymer is dissolved and coating the fibers made of the first polymer with the second polymer. Thus, since the fiber assembly obtained by dry spinning is covered with the second polymer, it is a practical fiber assembly that can be manufactured with high productivity.

  A known electrospinning method can be employed as a dry spinning method capable of spinning fine fibers that are suitable. In other words, this electrostatic spinning method is a method of fiberizing a spinning solution by applying an electric field to the spinning solution in which the first polymer is dissolved in an organic solvent, which is supplied from the spinning solution supply unit to the spinning space. is there. The spinning solution can be supplied to the spinning space with, for example, one or more nozzles, and the nozzles are preferably reciprocated so that the fibers are uniformly dispersed. In particular, when the nozzle is circularly moved in an oval shape, the moving speed of the nozzle can be made constant, so that the fibers can be uniformly dispersed (for example, the method disclosed in Japanese Patent Application Laid-Open No. 2006-112023).

  The electric field is applied to the spinning solution supply unit side (for example, the spinning solution supply unit itself, the supply path of the spinning solution to the spinning solution supply unit) and the collector side (for example, the capturing solution) that faces the spinning solution supply unit. It can be made to act by providing a potential difference between the collector itself and the counter electrode located on the back surface side of the collector. Moreover, if a flat thing is used as a collection body, the nonwoven fabric which consists of a 1st polymer fiber can be formed, and if a solid thing is used as a collection body, the hollow part equivalent to the shape of a collection body will be used. A fiber assembly made of the first polymer fibers can be formed. Furthermore, if it collects by arbitrary collectors, if it shape | molds by compressing etc., the fiber assembly which consists of a 1st polymer fiber which has a desired shape can be formed.

  In addition, although the coating liquid which melt | dissolved the 2nd polymer is provided with respect to the aggregate | assembly of the fiber which consists of a 1st polymer, the 1st polymer does not melt | dissolve with the solvent of a coating liquid. As described above, CMC and PVA are preferable as the second polymer, and since these second polymers are soluble in water, the first polymer is preferably insoluble in water.

  A coating solution in which the second polymer is dissolved is applied to the fiber assembly made of the first polymer thus formed, and a fiber assembly in which the fiber made of the first polymer is coated with the second polymer is manufactured. can do.

If the viscosity of the coating solution is high, a film of the second polymer is likely to be formed, so that the porosity of the fiber assembly tends to be impaired. The viscosity of the coating liquid is preferably 1 to 500 mPa · s, and more preferably 1 to 100 mPa · s. This “viscosity” refers to the viscosity at a shear rate of 100 (s ⁻¹ ) measured using a viscoelasticity measuring device (Rheo Stress 6000 manufactured by HAAKE).

  The application amount of the coating solution in which the second polymer is dissolved is not particularly limited, but is preferably 5 to 50% with respect to the mass of the fiber made of the first polymer. If it is less than 5%, the first polymer fiber cannot be sufficiently covered with the second polymer and tends to be easily dissolved by an organic solvent. If it exceeds 50%, the voids in the aggregate of the first polymer fiber This is because it tends to be difficult to form a porous fiber aggregate, and more preferably 10% to 30%.

  CMC and PVA, which are suitable as the second polymer, are water-soluble, and water is often used as the solvent, but the wettability of the fibers made of the first polymer is poor, and the fibers made of the first polymer are sufficiently If there is a possibility that the second polymer cannot be coated, alcohol (for example, methanol, ethanol, isopropyl alcohol, etc.) is used as a solvent for dissolving the second polymer in order to improve the wettability of the fiber made of the first polymer. It is preferable to add. Since the first polymer may easily swell with alcohol, the amount of alcohol added is appropriately adjusted depending on the type of the first polymer. For example, when the first polymer is polyethersulfone, the alcohol is likely to swell with alcohol, and therefore the amount of alcohol added is preferably 15 to 30 vol% of the total solvent.

  The method for applying the coating liquid to the aggregate of fibers made of the first polymer is not particularly limited. For example, the method of immersing the aggregate of fibers made of the first polymer in the coating liquid, or the first polymer. The method of apply | coating or spraying a coating liquid to the aggregate | assembly of a fiber can be mentioned.

  In addition, it is preferable to insolubilize so that the 2nd polymer which comprises a coating liquid may become insoluble in water. Examples of the insolubilization treatment include heat treatment, electron beam irradiation, and gamma ray irradiation. When a crosslinking agent (eg, maleic anhydride copolymer) is added to the ammonium salt of carboxymethyl cellulose and PVA as described above, Can be easily insolubilized.

  Examples of the present invention will be described below, but the present invention is not limited to the following examples.

Example 1
Polyacrylonitrile having a molecular weight of 500,000 (manufactured by Aldrich, first polymer) was dissolved in dimethylformamide (DMF) to prepare a spinning solution having a polymer concentration of 10 mass%.

Next, using this spinning solution, spinning is performed by an electrostatic spinning method, followed by heat treatment for 30 minutes in an oven at 150 ° C., and a nonwoven fabric made of polyacrylonitrile fibers (weight: 5 g / m ² , average fiber diameter: 320 nm, thickness: 23 μm). Electrospinning was performed under the following conditions using a single metal nozzle as the spinning solution supply unit and a metal plate as the collector.

Discharge rate: 1 g / hr
Distance between nozzle and collector surface: 10 cm
Applied voltage: + 8kV
Spinning space atmosphere: temperature 25 ° C, relative humidity 25%

  Separately, an ammonium salt of carboxymethyl cellulose (Daicel Chemical Industries, DN-10L) was dissolved in water to prepare a 1 mass% aqueous solution (viscosity: 20 mPa · s).

  Subsequently, after the polyacrylonitrile fiber nonwoven fabric is impregnated with the CMC aqueous solution, heat treatment is performed at 160 ° C. for 15 minutes to insolubilize the CMC, and the nonwoven fabric composed of fibers in which the polyacrylonitrile is completely covered with the CMC (average) Fiber diameter: 350 nm, thickness: 20 μm) was obtained. The ratio of CMC mass to polyacrylonitrile mass was 15%.

(Evaluation of organic solvent resistance)
The nonwoven fabric was cut into a circular shape with a diameter of 25 mm, and a sample was collected. (1) Capacitor electrolyte, tetraethylammonium tetrafluoroborate dissolved in propylene carbonate (LIPASTE-P, manufactured by Toyama Pharmaceutical Co., Ltd.) / EAFIN), heat treated for 10 minutes at 150 ° C., (2) heat treated for 10 minutes at 80 ° C., immersed in N, N-dimethylformamide, or (3) immersed in N-methylpyrrolidone In this state, heat treatment was performed at 80 ° C. for 10 minutes. At this time, the organic solvent resistance was evaluated from the change in the size of the sample before immersion in the electrolytic solution and after the heat treatment. As a result, the nonwoven fabric was excellent in organic solvent resistance with no change in size before immersion and after heat treatment in any of cases (1) to (3).

(Evaluation of water resistance)
The nonwoven fabric was cut into a 10 mm square and a sample was collected, and then held in an atmosphere at a temperature of 25 ° C. and a relative humidity of 50% for 15 hours, and then the mass (M1) was measured. Subsequently, after drying in an oven at 100 ° C. for 30 minutes, the mass (M2) was measured. And when the moisture content (= (ΔM / M1) × 100, unit:%) was determined from the mass change before and after drying (ΔM = M1−M2), the moisture content was 0.93%.

(Example 2)
In the same manner as in Example 1, a non-woven fabric (weight per unit area: 5 g / m ² , average fiber diameter: 320 nm, thickness: 23 μm) made of polyacrylonitrile fiber was produced.

  Separately, a 1 mass% aqueous solution (viscosity) containing a fully saponified polyvinyl alcohol (polymerization degree 1000, manufactured by Wako Pure Chemical Industries) and methyl vinyl ether / maleic anhydride copolymer (ISP-AN-119) in a mass ratio of 4: 1. : 2 mPa · s) was prepared.

  Subsequently, after the polyacrylonitrile fiber nonwoven fabric is impregnated with the PVA aqueous solution, heat treatment is performed at 160 ° C. for 30 minutes to insolubilize the PVA, and the nonwoven fabric made of fibers in which the polyacrylonitrile is completely covered with PVA (average) Fiber diameter: 340 nm, thickness: 20 μm) was obtained. The ratio of PVA mass to polyacrylonitrile mass was 10%.

  In addition, when the organic solvent resistance of this nonwoven fabric was evaluated in the same manner as in Example 1, the nonwoven fabric was changed in size before immersion and after heat treatment in any case of (1) to (3). The organic solvent resistance was excellent.

  Moreover, when the water resistance of this nonwoven fabric was evaluated similarly to Example 1, the moisture content was 0.48%.

(Example 3)
Polyethersulfone having a molecular weight of 50,000 (manufactured by Sumitomo Chemical Co., Ltd., first polymer) was dissolved in dimethylformamide (DMF) to prepare a spinning solution having a polymer concentration of 25 mass%.

Next, using this spinning solution, spinning is performed by an electrostatic spinning method, followed by heat treatment for 30 minutes in an oven at 180 ° C., and a nonwoven fabric made of polyethersulfone fibers (weight: 5 g / m ² , average fiber diameter) : 520 nm, thickness: 17 μm). Electrospinning was performed under the following conditions using a single metal nozzle as the spinning solution supply unit and a metal plate as the collector.

Discharge rate: 1 g / hr
Distance between nozzle and collector surface: 10 cm
Applied voltage: + 12kV
Spinning space atmosphere: temperature 25 ° C, relative humidity 20%

  Separately, a carboxymethyl cellulose ammonium salt (Daicel Chemical Industries, DN-10L) was dissolved in a mixed solvent of water: isopropanol = 8: 2 (volume ratio) to prepare a 1 mass% solution (viscosity: 21 mPa · s). .

  Subsequently, after impregnating the polyethersulfone fiber non-woven fabric with the CMC solution, heat treatment is performed at 160 ° C. for 15 minutes to insolubilize the CMC, and the non-woven fabric is made of fibers in which the polyether sulfone is completely covered with the CMC. (Average fiber diameter: 550 nm, thickness: 16 μm) was obtained. The ratio of CMC mass to polyethersulfone mass was 14%.

  In addition, when the organic solvent resistance of this nonwoven fabric was evaluated in the same manner as in Example 1, the nonwoven fabric was changed in size before immersion and after heat treatment in any case of (1) to (3). The organic solvent resistance was excellent.

  Moreover, when the water resistance of this nonwoven fabric was evaluated similarly to Example 1, the moisture content was 0.82%.

Example 4
In the same manner as in Example 3, a nonwoven fabric made of polyethersulfone fibers (weight: 5 g / m ² , average fiber diameter: 520 nm, thickness: 17 μm) was produced.

  Separately, a completely saponified polyvinyl alcohol (polymerization degree 1000, manufactured by Wako Pure Chemical Industries) and a methyl vinyl ether / maleic anhydride copolymer (ISP-AN-119) at a mass ratio of 4: 1 and having a concentration of 1 mass%. (The solvent was water: isopropanol = 8: 2 (volume ratio), viscosity: 2 mPa · s).

  Subsequently, after impregnating the polyethersulfone fiber non-woven fabric with the PVA solution, heat treatment is performed at 160 ° C. for 30 minutes to insolubilize the PVA, and the non-woven fabric is made of fibers in which the polyether sulfone is completely covered with PVA. (Average fiber diameter: 550 nm, thickness: 16 μm) was obtained. The ratio of PVA mass to polyethersulfone mass was 12%.

  In addition, when the organic solvent resistance of this nonwoven fabric was evaluated in the same manner as in Example 1, the nonwoven fabric was changed in size before immersion and after heat treatment in any case of (1) to (3). The organic solvent resistance was excellent.

  Moreover, when the water resistance of this nonwoven fabric was evaluated similarly to Example 1, the moisture content was 0.77%.

(Comparative Example 1)
When the organic solvent resistance of a non-woven fabric made of polyacrylonitrile fiber produced in the same manner as in Example 1 (basis weight: 5 g / m ² , average fiber diameter: 320 nm, thickness: 23 μm) was evaluated in the same manner as in Example 1, In any of the cases (1) to (3), the nonwoven fabric was dissolved after the heat treatment and did not remain in its original form.

(Comparative Example 2)
When the organic solvent resistance of a nonwoven fabric (weighing weight: 5 g / m ² , average fiber diameter: 520 nm, thickness: 17 μm) made of polyethersulfone fibers produced in the same manner as in Example 3 was evaluated in the same manner as in Example 1, In all cases (1) to (3), the non-woven fabric was dissolved after the heat treatment, and the original shape was not maintained.

(Comparative Example 3)
A non-woven fabric made of polyacrylonitrile fiber prepared in the same manner as in Example 1 (basis weight: 5 g / m ² , average fiber diameter: 320 nm, thickness: 23 μm) was heat-treated at 210 ° C. for 1 minute to insolubilize it. It was. When the organic solvent resistance of the nonwoven fabric subjected to the insolubilization treatment was evaluated in the same manner as in Example 1, the nonwoven fabric was dissolved after the heat treatment in any of the cases (1) to (3) and remained in its original form. There wasn't.

  The fiber assembly of the present invention can be used for applications requiring resistance to organic solvents. In particular, it can be suitably used as a separator for an electric double layer capacitor and a substrate for an ion conductive film.

Claims (4)

A fiber assembly comprising a fiber in which polyacrylonitrile or polyethersulfone is coated with carboxymethyl cellulose or polyvinyl alcohol , and used as a separator for an electric double layer capacitor or a substrate for an ion conductive film. It is characterized in that carboxymethylcellulose or polyvinyl alcohol is insoluble in water ,
“Insoluble in water” means that the carboxymethyl cellulose or polyvinyl alcohol is added to 100 times the amount of water of the carboxymethyl cellulose or polyvinyl alcohol, and when heated at 90 ° C. for 60 minutes, the mass remains at 70% or more. That means
The fiber assembly according to claim 1. Carboxymethyl cellulose is carboxymethyl cellulose formed by heating an ammonium salt of carboxymethyl cellulose,
The fiber assembly according to claim 2, wherein the polyvinyl alcohol is polyvinyl alcohol crosslinked with a maleic anhydride copolymer. 4. The fiber assembly according to claim 3, wherein the polyvinyl alcohol is polyvinyl alcohol obtained by crosslinking fully saponified polyvinyl alcohol with a maleic anhydride copolymer.