JP5434079B2 - Ultrafine fiber, ion conductive composite polymer membrane, and method for producing the same - Google Patents

Description

  The present invention relates to an ultrafine fiber having a fiber diameter of 1 μm or less, and more particularly to an ultrafine fiber in which a plurality of fibers having a fiber diameter of 1 μm or less are included in a single fiber having a fiber diameter of 1 μm or less. The present invention also relates to an ion conductive polymer membrane suitable for a solid polymer fuel cell using ultrafine fibers and a method for producing the same.

  Conventionally, development of a cross-sectional shape of a fiber and performance improvement by using an ultrafine yarn has been actively performed. As one of the investigations, ultra-fine yarn using sea-island composite spinning was produced, suede-like artificial leather, high-grade clothing, life like wiping cloth, industrial materials, polishing cloth for surface polishing of hard disks ( Patent Documents 1, 2) have been developed. However, in the sea-island composite spinning, at present, the limit of the fiber diameter of the island component is 2 μm. The demand for improved performance with thinner fibers could not be fully met.

  In recent years, nanofibers have been actively developed as thinner fibers. A nanofiber is a fiber having a nano-order diameter, and has characteristics (nanofiber effect) different from those of conventional fibers having a micron-order diameter. As the nanofiber effect, there is a size effect that is embodied as an increase in specific surface area, a significant increase in reactivity and selectivity due to a decrease in volume, etc., and a uniform function in which molecules are regularly arranged and self-organized. Examples thereof include a supramolecular arrangement effect that is expressed, a cell biomaterial recognition effect that cells recognize and bind, and a hierarchical structure effect that is expressed by a nano-hierarchical structure from the polymer chain level.

  Development of a composite fiber containing a fiber having a smaller fiber diameter inside a single fiber is in progress. For example, many examples of using composite spinning using two polymers having different solubility have been reported so far. For example, a polymer alloy fiber (Patent Document 3) in which the island component is made of a hardly soluble polymer, the sea component is made of an easily soluble polymer, and the island domain has a diameter of 1 to 150 nm. However, the fiber including a large number of nanofibers used so far using composite spinning has a fiber diameter of several μm to several tens of μm. Therefore, in order to express the effect of nanofiber, it is necessary to dissolve the sea component polymer in a solvent, which is uneconomical. In this method, it is very difficult to mix two or more types of nanofibers because of the manufacturing method, and the chemical and physical properties of the fibers are limited to only one type of polymer used for the island component. There is a problem that it depends.

  Among the fibers in which the fiber diameter of the sea component is made nano level, there are those using charged spinning as nano fibers having a fiber diameter smaller than that. Polyvinyl pyrrolidone (PVP) as a core and polylactic acid (PLA) as a shell, nanofiber (500 nm / 250 nm) in nanofiber with a fiber diameter of several hundred nm (Non-patent Document 1), gelatin as a core, polylactic acid There is a nanofiber (230 nm to 460 nm / 60 to 100 nm) (Non-patent Document 2) in a fiber diameter of several hundred nm using (PLA) as a shell. However, these core-shell type fibers have one core fiber in one matrix fiber, and when the core fiber is interrupted due to fluctuation during spinning production, the function of the core fiber is expressed. Can not do. Moreover, it is produced by applying a high voltage to a nozzle using a double tube, and there is a problem that the nozzle cost is increased.

While there is a background related to ultrafine fibers as described above, fuel cells have been actively developed in recent years.
A fuel cell is a power generation device with low emissions, high energy efficiency, and low environmental burden, and is therefore in the spotlight again in recent years due to the increase in global environmental protection. Compared to conventional large-scale power generation facilities, this is a power generation device expected in the future as a relatively small-scale distributed power generation facility, and as a power generation device for mobile objects such as automobiles and ships. It is also attracting attention as a power source for small mobile devices and portable devices, and is expected to be installed in mobile phones and personal computers in place of secondary batteries such as nickel metal hydride batteries and lithium ion batteries.

Among them, a polymer electrolyte fuel cell that is attracting attention is generally composed of basic units called membrane electrode assemblies (MEA), and in MEA, an ion conductive polymer membrane (PEM) is sandwiched between a cathode and an anode, The ions formed at the anode are transported to the cathode and a current is passed through an external circuit connected to the electrode. PEMs must not only have adequate ionic conductivity, but must have the mechanical and chemical strengths required under the operating conditions of the power plant.
As such PEM materials, fluoropolymers containing super strong acid groups are known. However, since these PEM materials are fluoropolymers, they are very expensive and have a low glass transition temperature. When the temperature is around 100 ° C., the water retention is not sufficient, so that high ionic conductivity cannot be fully utilized, and the ionic conductivity is drastically lowered, which makes it impossible to function as a battery.

In order to overcome such drawbacks, various PEMs in which sulfonic acid groups are introduced into non-fluorinated aromatic ring-containing polymers have been studied. In view of heat resistance and chemical stability, aromatic polyarylene ether compounds such as aromatic polyarylene ether ketones and aromatic polyarylene ether sulfones are attracting attention as polymer skeletons. (For example, refer nonpatent literature 3), what sulfonated polyether ether ketone (for example, patent document 4), etc. are reported.
However, those having sulfonic acid groups introduced into these polymers have the disadvantage that the dimensional change during swelling increases with an increase in the amount of sulfonic acid groups introduced, and membrane breakage is likely to occur under operating conditions such as fuel cells. . In order to remedy this drawback, attempts have been reported to introduce structural units capable of forming crosslinks between polymer chains to suppress dimensional changes (for example, Patent Documents 5 to 7). It was not possible to sufficiently suppress the dimensional change.
In addition, attempts to improve performance by blending non-ion exchange group-containing polymers (for example, Patent Documents 8 and 9) and impregnating an ion conductive polymer into a porous inert film to form a composite film An attempt (for example, Patent Document 10) has been reported. However, those that were compatible by blending did not achieve both dimensional stability and proton conductivity, and those that were phase separated showed a decrease in film strength due to delamination. The composite membrane by impregnation has a problem that its production method is not simple.
In addition, a method of dispersing ion conductive polymer particles or the like in the matrix polymer is also conceivable. However, if the particle size of the ion conductive polymer to be dispersed is large, a sufficient ion conduction path is not formed, and the membrane Tend to be brittle. Therefore, it is necessary to disperse the ion conductive polymer at the nano level.

Japanese Patent Laid-Open No. 2001-1252 JP 2002-102332 A JP 2004-169261 A JP-A-6-93114 JP 2003-217342 A JP 2003-217343 A JP 2003-292609 A JP 2003-502828 A JP 2003-109624 A JP 2005-209361 A Journal of Applied Polymer Science, Vol.102, 39-45 (2006) Journal of Polymer Science: Part B PolymerPhysics, Vol43, 28 52-2861 (2005) Journal of membranescience, (Netherlands) 1993, 83, P.211-220

  The present invention has been made against the background of the problems of the prior art, and provides a fiber having both a nanofiber effect and a polymer alloy effect, and has an ion exchange group having excellent chemical stability and high proton conductivity. By using a polymer and an ion exchange group-free polymer with excellent mechanical and chemical stability, it has excellent heat resistance, processability, and ion conductivity, as well as dimensional stability, mechanical durability, and chemical durability. Another object is to obtain an excellent ion conductive polymer membrane.

As a result of intensive studies to solve the above problems, the present inventors have finally completed the present invention. That is, the present invention has the following configuration.
(1) An ultrafine fiber having a single fiber (matrix fiber) diameter of 1 μm or less, and a plurality of fibers (core fibers) having a diameter equal to or less than the fiber diameter are included in the single fiber.
(2) The ultrafine fiber according to (1), wherein the single fiber is made of an alloyed polymer, constitutes a matrix part and a core part, and the core part constitutes the internal fiber.
(3) It is produced by preparing a solution in which each polymer constituting the matrix part and the core part is blended, applying a voltage to the solution, and discharging the solution to a collecting part to which ground or a reverse voltage is applied. The ultrafine fiber according to (1) or (2).
(4) The ultrafine fiber according to any one of (1) to (3), wherein the internal fiber is a polymer having an ion exchange group.
(5) The ultrafine fiber according to any one of (1) to (4), wherein the matrix portion is a heat-meltable polymer.
(6) A nanofiber having a short axis diameter of 1 to 100 nm made of polymer A having an ion exchange group is contained in the range of 10 to 70% by mass in heat-meltable polymer B that is incompatible with polymer A. An ion conductive composite polymer film characterized by comprising:
(7) Ionic conductivity and area change rate (%) satisfy the following formula (a), and water absorption rate (mass%) and area change rate (%) satisfy the following formula (b) (6 The ion conductive composite polymer membrane described in the above).
Area change rate (%) / ion conductivity (S / cm) ≦ 200 (a)
Area change rate (%) / water absorption rate (% by mass) ≦ 0.5 (b)
(8) The ion conductive composite polymer membrane according to claim 6 or 7, wherein the heat-meltable polymer B can be melt-molded at a glass transition temperature of 300 ° C or lower.
(9) Any of (6) to (8), wherein the polymer A having an ion exchange group is a polyarylene ether-based compound containing the structural component represented by the general formula (2) together with the general formula (1) The ion conductive composite polymer membrane according to claim 1.
Here, Ar represents a divalent aromatic group, Y represents a sulfone group or a ketone group, R represents H, a sulfonic acid group, a phosphonic acid group, or a salt thereof.
However, Ar ′ represents a divalent aromatic group.
(10) Any of (6) to (8), wherein the polymer A having an ion exchange group is a polyarylene ether-based compound containing the structural component represented by the general formula (4) together with the general formula (3) The ion conductive composite polymer membrane according to claim 1.
X represents H or a monovalent cation species.
(11) A single fiber by dissolving a polymer A having an ion exchange group and a heat-meltable polymer B that is incompatible with the polymer A having an ion exchange group in a solvent, and spinning the mixed solution An assembly of fibers containing nanofibers of polymer A having a plurality of minor axis diameters of 1 to 100 nm inside is obtained, and then the hot-melt polymer B in the fibers is melted to obtain the fiber assembly. A method for producing an ion-conductive composite polymer membrane, characterized by forming a membrane, then treating the membrane in an acidic aqueous solution and washing with water.
(12) The ion conduction according to claim 11, wherein the fiber assembly comprising the polymer A having an ion exchange group and the heat-meltable polymer B is an ultrafine fiber assembly spun by an electrostatic spinning method. For producing a conductive composite polymer membrane.

  According to the ultrafine fiber of the present invention, the nanofiber effect can be obtained without the need for removal by a solvent, and since the nanofiber is composed of two or more polymers, the shortage of one polymer is replaced with the other polymer. It becomes possible to complement and to differentiate the function into each polymer, and a fiber having effects specific to nanofibers and effects specific to polymer alloys can be obtained. For example, when the matrix part is made of a heat-meltable polymer, the adhesion between fibers is increased by heating, and a high-strength nanofiber nonwoven fabric is obtained. Further, it is possible to provide an unprecedented one in which a plurality of nanofibers are further present in one nanofiber without using a special nozzle. In addition, the ion conductive polymer membrane of the present invention includes an ion exchange group-containing polymer A having excellent chemical stability and high proton conductivity, and a heat-meltable polymer B that is incompatible with the ion exchange group-containing polymer A. And the ion exchange group-containing polymer A component having an average fiber diameter of 1 to 100 nm is dispersed in the heat-meltable polymer B at the nano level, so that the nanofiber effect of the polymer A having ion exchange groups, Dimensional stability, workability, mechanical strength despite the high ionic conductivity and water absorption, because the reinforcing effect, ionic conduction effect and water absorption effect of the polymer A nanofibers with ion exchange groups are expressed. It possesses a contradictory characteristic that it excels. For this reason, it is a film | membrane suitable as polymer electrolyte membranes, such as a fuel cell. The ion conductive composite polymer membrane of the present invention is also characterized by low methanol permeability and is useful as a polymer electrolyte membrane for direct methanol fuel cells.

Hereinafter, the present invention will be described in detail.
The ultrafine fiber of the present invention preferably has a single fiber diameter of 1 μm or less, and a plurality of fibers (hereinafter referred to as core fibers) having a diameter equal to or less than the fiber diameter are contained inside the single fiber (hereinafter referred to as matrix fiber). . When the core fiber is contained, if the core fiber is interrupted due to fluctuations in discharge during the production of spinning, the function of the core fiber cannot be expressed. In terms of appearance, it is difficult to distinguish, and depending on the application, a big problem occurs. When electrical conductivity is imparted to the core fiber, it causes disconnection. In addition, when the core part is removed with a solvent to produce a hollow fiber and the hollow part is used for microreactors or separation applications, if the diameter of the single fiber is the same, the specific surface area is dramatically increased by having multiple ultrafine cavities. The contact point (reaction point) with the medium can be increased.
That is, if the fiber diameter of the matrix fiber is 1 μm or less, the probability that a plurality of core fibers are in contact with each other in the matrix fiber is greatly improved. It is possible to effectively elute to the inside of the direction, or the effect of increasing electrical conductivity is exhibited.
The fiber diameter of the contained fiber is not limited, and a plurality of fibers may be present in a single fiber. It is important to have multiple.

  Further, as the fiber structure in the present invention, the core portion does not necessarily have a circular cross section. For example, a co-continuum (the core phase and the matrix phase cannot be distinguished from each other) Those having a volume observed in the vicinity of the same volume) can obtain the same effect, and are one of the preferred forms. The composition ratio (mass / mass) of the polymer forming the core portion and the matrix portion is 10/90 to 70/30. This is because within this range, the fiber diameter of the core fiber can be reduced, while the probability of the core fibers contacting each other is high. A more preferred composition ratio is 20/80 to 60/40, still more preferably 30/70 to 50/50.

  The polymer compound used in the core part and the matrix part in the ultrafine fiber of the present invention is not particularly limited, for example, polyacrylonitrile, polyethylene, polypropylene, polyethylene oxide, polyethylene glycol, polyethylene terephthalate, polybutylene terephthalate, Polyethylene naphthalate, poly-m-phenylene terephthalate, poly-p-phenylene isophthalate, polymethacrylic acid, polymethyl methacrylate, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyvinyl chloride, polyvinylidene chloride -Acrylate copolymer, polytetrafluoroethylene, polyvinyl alcohol, polyarylate, polyacetal, polycarbonate, polystyrene, polyphenyl Polysulfide, polyamide, polyimide, polyamideimide, aramid, polyimide benzazole, polybenzimidazole, polyglycolic acid, polylactic acid, polyurethane, cellulose compound, polypeptide, polynucleoside, polynucleotide, protein, enzyme, etc. it can. Polymer compounds other than these can also be used. It is preferable that the polymer compound used for the core portion and the matrix portion have different characteristics.

The core fiber in the ultrafine fiber of the present invention is also preferably made of a polymer having an ion exchange group. This is because the ultrafine fiber of the present invention can be applied to a fuel cell described later.

The matrix portion in the ultrafine fiber of the present invention is preferably made of a heat-meltable polymer. In addition to being able to apply the ultrafine fiber of the present invention to a fuel cell, which will be described later, when it is made into a nonwoven fabric, only the matrix part is fused, and a nanofiber nonwoven fabric with excellent inter-fiber adhesion and high strength can be obtained. This is because application is possible.

  In order to express the fiber structure in the present invention, it is necessary that the polymer characteristics are different. Examples of the polymer characteristics mentioned here include viscosity, surface energy, viscoelasticity, SP value, and the like. Moreover, when a polymer is dissolved in a solvent, the viscosity, surface energy, viscoelasticity, etc. as a polymer solution are also mentioned.

  From the point of application, it is also important that the chemical, physical, optical and electrical properties of each polymer differ. For example, it is possible to obtain a high-strength sheet in which rigid nanofibers are dispersed by obtaining the form of the present invention by combining a rigid polymer and a thermoplastic polymer, and further melting the thermoplastic polymer with a heat press or the like. It is also possible to obtain an electrolyte membrane or nano-level wiring by combining a polymer having conductivity with respect to ions and electricity and a polymer having high insulating properties. In addition, a core portion is easily dissolved in a certain solvent and a matrix portion is a combination of a hardly soluble polymer to obtain the form of the present invention. Nanofibers having channels can be obtained, and can be used, for example, as microreactors, gas and liquid separation, and adsorption materials.

  The fine fiber of the present invention is produced by preparing a solution in which each polymer constituting the matrix part and the core part is blended, applying a voltage to the solution, and discharging the solution to a collecting part to which ground or a reverse voltage is applied. It is preferable. That is, it is preferable to produce by a method generally called charged spinning.

  The charged spinning method is a kind of solution spinning, and is generally a technique in which a positive high voltage is applied to a polymer solution and fiberization is caused in the process of being sprayed to a grounded or negatively charged surface. An example of the charge spinning apparatus is shown in FIG. In the figure, a charged spinning device 1 is provided with a spinning nozzle 2 that discharges a polymer that is a raw material of a fiber, and a counter electrode 5 that faces the spinning nozzle 2. The counter electrode 5 is grounded. The polymer solution charged with a high voltage jumps out from the spinning nozzle 2 toward the counter electrode 5. At that time, it is fiberized. A solution in which a polymer is dissolved in an organic solvent is discharged into an electrostatic field formed between electrodes, the solution is spun toward a counter electrode, and the fibrous material that is formed is accumulated on a collection substrate to form a nonwoven fabric. Can be obtained. The term “nonwoven fabric” as used herein refers not only to the state where the solvent of the solution has already been distilled off to form a nonwoven fabric, but also to the state containing the solvent of the solution.

In the charged spinning method, fiber is formed by volatilization of the solvent. Although phase separation is induced by solvent volatilization, it is presumed that since the solvent volatilization rate is very large, the core is fixed in a finely separated state and further finer by stretching.
In addition, when charged spinning is used, fiber formation is possible even when two or more polymers having different solubility parameters are used.

  In the case of a nonwoven fabric containing a solvent, the solvent is removed after the charged spinning. Examples of the method for removing the solvent include a method of immersing in a poor solvent and extracting the solvent, a method of evaporating the residual solvent by heat treatment, and the like.

  The material of the solution tank 3 is not particularly limited as long as it is resistant to the organic solvent used. Further, the solution in the solution tank 3 can be discharged into the electric field by a mechanical push-out system, a pump-out system, or the like.

  The spinning nozzle 2 preferably has an inner diameter of about 0.1 to 3 mm. The nozzle material may be made of metal or non-metal. If the nozzle is made of metal, the nozzle can be used as one electrode. If the nozzle 2 is made of non-metal, an electric field is applied to the extruded solution by installing an electrode inside the nozzle. Can be made. In consideration of production efficiency, it is possible to use a plurality of nozzles. In general, a nozzle having a circular cross section is used, but a nozzle having an irregular cross section can be used depending on the type of polymer and intended use.

  As the counter electrode 5, various shapes of electrodes can be used depending on the application, such as a roll-shaped electrode, a flat plate-shaped, or a belt-shaped metal electrode shown in FIG. 1.

  Moreover, although the description so far is a case where an electrode also serves as a substrate that collects fibers, a polymer fiber may be collected there by installing an object to be a substrate that collects between the electrodes. . In this case, for example, continuous production is possible by installing a belt-like substrate between the electrodes.

  Moreover, although it is common to form with a pair of electrodes, it is also possible to introduce a different electrode. It is also possible to perform spinning with a pair of electrodes, and to control the spinning state by controlling the electric field state with electrodes having different potentials introduced.

  Although the voltage application apparatus 4 is not specifically limited, A direct current high voltage generator can be used and a Van de Graf electromotive machine can also be used. The applied voltage is not particularly limited, but is generally 3 to 100 kV, preferably 5 to 70 kV, and more preferably 5 to 50 kV. Note that the polarity of the applied voltage may be either positive or negative.

  The distance between the electrodes depends on the charge amount, the nozzle size, the spinning solution flow rate, the spinning solution concentration, and the like, but a distance of 5 to 20 cm was appropriate at 5 to 50 kV.

  Examples of the solvent for the polymer include acetone, chloroform, ethanol, isopropanol, methanol, toluene, tetrahydrofuran, water, benzene, benzyl alcohol, 1,4-dioxane, propanol, carbon tetrachloride, cyclohexane, cyclohexanone, methylene chloride, phenol, Highly volatile solvents such as pyridine, trichloroethane, acetic acid, N, N-dimethylformamide (DMF), dimethyl sulfoxide (DMSO), N, N-dimethylacetamide (DMAc), 1-methyl-2-pyrrolidone (NMP) , Ethylene carbonate, propylene carbonate, dimethyl carbonate, acetonitrile, N-methylmorpholine-N-oxide, butylene carbonate, γ-butyrolactone, diethyl carbonate, diethyl Ether, 1,2-dimethoxyethane, 1,3-dimethyl-2-imidazolidinone, 1,3-dioxolane, ethyl methyl carbonate, methyl formate, 3-methyl oxazolidine-2-one, methyl propionate, 2 -A solvent having relatively low volatility such as methyltetrahydrofuran and sulfolane. Alternatively, it is possible to use a mixture of two or more of the above solvents.

  The spinning atmosphere is generally performed in the air, but by performing charge spinning in a gas having a higher discharge starting voltage than air such as carbon dioxide, spinning at a low voltage is possible, such as corona discharge. It is also possible to prevent abnormal discharge. Further, when water is a poor solvent for the polymer, polymer precipitation may occur near the spinning nozzle. Therefore, in order to reduce the moisture in the air, it is preferable to carry out in the air that has passed through the drying unit.

  Next, the step of obtaining the nonwoven fabric accumulated on the collection substrate will be described. In the present invention, while spinning the solution toward the collection substrate, the solvent evaporates depending on conditions to form a fibrous material. At normal room temperature, the solvent completely evaporates until it is collected on the collection substrate. However, if the solvent evaporation is insufficient, the solvent may be drawn under reduced pressure. The fibers of the present invention are formed at the latest when collected on the collection substrate. Further, the temperature at which the spinning is performed depends on the evaporation behavior of the solvent and the viscosity of the spinning solution, but is usually 0 to 50 ° C. And a porous fiber is further accumulated on a collection board, and a nonwoven fabric is manufactured.

  The basis weight when the ultrafine fiber of the present invention is a non-woven fabric is determined according to the intended use and is not particularly limited. However, it is preferably 0.05 to 50 g / m2 for the air filter. . The basis weight here is in accordance with JIS-L1085. If it is 0.05 g / m 2 or less, the filter collection efficiency is unfavorably low, and if it is 50 g / m 2 or more, the filter ventilation resistance becomes too high, which is not preferable.

  The thickness when the ultrafine fiber of the present invention is a non-woven fabric is determined according to the intended use and is not particularly limited, but is preferably 1 to 100 μm. The thickness here is measured with a micrometer.

  When the ultrafine fiber of the present invention is a non-woven fabric, if necessary, post-treatment can be performed so as to suit various applications. For example, a calendar process, a hydrophilic process, a water repellent process, a surfactant adhesion process, a pure water washing process, etc. for densification or adjusting the thickness accuracy can be performed.

  When the ultrafine fiber of the present invention is obtained as a non-woven fabric, it may be used alone, but may be used in combination with other members depending on handleability and use. For example, a cloth (nonwoven fabric, woven fabric, knitted fabric) that can serve as a support substrate as a collection substrate, a film, a drum, a net, a flat plate, a belt, a conductive material made of metal or carbon, a non-polymer made of an organic polymer, etc. Conductive materials can be used. By forming a non-woven fabric thereon, a member in which the support base material and the non-woven fabric are combined can be created.

  Next, the ion conductive composite polymer membrane of the present invention will be described. The ion conductive composite polymer membrane of the present invention is composed of a polymer A nanofiber having an ion exchange group and a heat-meltable polymer B having no ion exchange group. The polymer A and the heat-meltable polymer B that form the nanofiber are preferably dissolved in the same solvent.

The ion exchange group of the ion conductive polymer in the ion conductive composite polymer membrane of the present invention is not particularly limited as long as it is an atomic group having a negative charge, but preferably has proton exchange ability. As such a functional group, a sulfonic acid group, a sulfonimide group, a sulfuric acid group, a phosphonic acid group, a phosphoric acid group, and a carboxylic acid group are preferably used. Here, the sulfonic acid group is —SO ₂ (OH), the sulfonimide group is —SO ₂ NHSO ₂ R (where R means an organic group), and the sulfuric acid group is —OSO ₂ (OH), A phosphonic acid group means —PO (OH) ₂ , a phosphoric acid group means —OPO (OH) ₂ , a carboxylic acid group means —CO (OH), and salts thereof. Two or more kinds of these ion exchange groups can be contained in the polymer solid electrolyte, and it may be preferable to combine them. The combination is appropriately determined depending on the structure of the polymer. Among them, it is more preferable to have at least a sulfonic acid group, a sulfonimide group, and a sulfuric acid group from the viewpoint of high proton conductivity, and most preferable to have at least a sulfonic acid group from the viewpoint of hydrolysis resistance. Examples of ion exchange groups include proton acid groups such as sulfonic acid groups, phosphonic acid groups, and sulfonimide groups. Of these, sulfonic acid groups are preferred.

  As the polymer A having an ion exchange group in the ion conductive composite polymer membrane of the present invention, an aromatic polymer is preferable as the polymer skeleton from the viewpoint that a polymer having sufficient mechanical strength and high ion exchange group density can be easily synthesized. Specifically, polyphenylene oxide, polyether ketone, polyether ether ketone, polyether sulfone, polyether ether sulfone, polyphenylene sulfide, polyimide, polyether imide, polyimidazole, polyoxazole, polyphenylene, polystyrene and their skeleton components Can be mentioned as a copolymerized structure.

Among these polymers, it is preferable that the polymer A having an ion exchange group is a polyarylene ether-based compound including the structural component represented by the general formula (2) together with the general formula (1).
Here, Ar represents a divalent aromatic group, Y represents a sulfone group or a ketone group, R represents H, a sulfonic acid group, a phosphonic acid group, or a salt thereof.
However, Ar ′ represents a divalent aromatic group.
Furthermore, it is preferable that the polymer A having an ion exchange group is a polyarylene ether-based compound containing a constituent represented by the general formula (4) together with the general formula (3).

X represents H or a monovalent cation species.

The molecular weight (Mw) of these polymers is not particularly limited as long as it is solid at room temperature, but is 1000 or more and 1 × 10 ⁷ from the viewpoint of film strength and solubility in a solvent.
The following is preferred.

  The ion exchange capacity (IEC) of the polymer A having an ion exchange group used in the ion conductive composite polymer membrane of the present invention is 1.0 to 4.0 meq / g, preferably 1.0 to 3. 0 meq / g. If it is less than 1.0 meq / g, the proton conductivity tends to be low, and if it exceeds 4.0 meq / g, the water absorption rate tends to be high and the mechanical strength of the membrane tends to be weak.

The heat-meltable polymer B used in the ion conductive polymer membrane of the present invention is incompatible with the polymer A having an ion exchange group, but can be dissolved in the same solvent as the polymer A and can be melted. As long as the glass transition temperature is 300 ° C. or lower, it is not particularly limited whether it is an aromatic polymer or a non-aromatic polymer. Specific examples include polyarylene ether, polyether sulfone, polyether ether sulfone, Polyether ketone, polyether ether ketone, polyether ketone ketone, polysulfone, polyparaphenylene, polyphenylene sulfide, polyphenylene sulfoxide, polyphenylene sulfide sulfone, polyphenylene sulfone, polybenzoxazole, polybenzimidazole, polybenzthiazole, polyi , Polyetherimide, polyamideimide, polyamide, polyester, polyether, polystyrene, polyethylene, polypropylene, polymethylpentene, polyvinyl fluoride, polyvinylidene fluoride, polychlorotrifluoroethylene, tetrafluoroethylene-ethylene copolymer, Examples thereof include a tetrafluoroethylene-hexafluoropropylene copolymer, a tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer, and polytetrafluoroethylene. The polymer B may be a single type, a mixture of two or more types, or a copolymer. Furthermore, it is preferable that it is soluble in the same solvent as the polymer A having an ion exchange group.
If the glass transition temperature of these polymers is higher than 300 ° C., the sulfonic acid group of polymer A having an ion exchange group may be eliminated during melt molding.

The ion conductive composite polymer membrane of the present invention is a polymer A having a short axis diameter of 1 to 100 nm and having an ion exchange group having an ion exchange group, that is, a nanofiber and a polymer having an ion exchange group in the present invention. A composite film that is incompatible with A and is made of the heat-meltable polymer B.
When the nanofiber minor axis diameter is out of the range of 1 to 100 nm, the nanofiber effect is hardly expressed.
The length of the nanofiber is not particularly limited as long as the reinforcing effect, ion conduction effect, and water absorption effect of the polymer A nanofiber of the ion exchange group are exhibited, but the aspect ratio of the nanofiber (fiber length / fiber diameter) Is preferably 2 or more because the probability that the nanofibers come into contact with each other in the film is increased.

Examples of a method for containing and dispersing nanofibers, which are polymers A having a fibrous ion exchange group having a short axis diameter of 1 to 100 nm, at a nano level in a membrane include, for example, polymer A having ion exchange groups and heat-meltable polymer B Is formed into a fiber by spinning in a solvent in which both are dissolved, and a sheet-like fiber assembly containing a plurality of nanofibers of polymer A having a plurality of ion-exchange groups having a minor axis diameter of 1 to 100 nm inside the single fiber A method is preferred in which a body is obtained, and then the fiber aggregate is heated to melt the heat-meltable polymer B in the fiber to form a film. As a method of spinning a fiber containing polymer A nanofibers having an ion exchange group having a minor axis diameter of 1 to 100 nm in the matrix using the heat-meltable polymer B, dry spinning, wet spinning, static Although not particularly limited, such as an electrospinning method, spinning by an electrostatic spinning method is most preferable in that a plurality of polymer A nanofibers having a diameter equal to or smaller than the fiber diameter can be easily formed inside the fiber. Moreover, it is preferable that the average fiber diameter of a single fiber is an ultrafine fiber of 1 micrometer or less.
In the case of electrostatic spinning, for example, a mixed solution of polymer A having an ion exchange group and heat-meltable polymer B is filled in a container provided with a nozzle, and a high voltage in the range of about 3 to 100 kV is applied to the nozzle portion. It is possible to employ a method of applying and discharging the mixed solution from a nozzle toward a ground or a collecting part to which a voltage opposite to the nozzle part is applied.
The dispersion state of the polymer A nanofibers in the film can be confirmed by observing the nanofibers with a TEM observation photograph of the cross section of the film. The nano-level dispersion as used in the present invention refers to a state in which a cross section having a short axis diameter of 1 to 100 nm of the polymer A having an ion exchange group can be clearly confirmed in a TEM observation photograph of the cross section of the film.

  The solvent used for spinning in the present invention is not particularly limited as long as it is a solvent in which both the polymer A having an ion exchange group and the hot-melt polymer B are soluble. However, N- from the viewpoint of solubility, handleability, cost, and the like. Organic polar solvents such as methyl-2-pyrrolidone, N, N-dimethylacetamide, N, N-dimethylformamide, tetramethylurea, dimethylimidazolidinone, dimethyl sulfoxide, hexamethylphosphonamide are desirable, and mixtures thereof are also preferred. May be. There is no particular limitation on the dissolution temperature, and it may be at room temperature or under heating.

  The composition ratio (mass / mass) of the polymer A having ion exchange groups / the polymer B made by heat melting is 10/90 to 70/30. If the ratio of the polymer A having an ion exchange group is too small, proton conductivity tends to deteriorate, and if it is too large, the effect of blending cannot be expected. A more preferred composition ratio is 20/80 to 65/35, still more preferably 30/70 to 40/60.

In the ion conductive polymer membrane of the present invention, the ion conductivity and the area change rate (%) preferably satisfy the following formula (1), and the water absorption rate and the area change rate (%) satisfy the following formula (2). .
Area change rate (%) / ion conductivity (S / cm) ≦ 200 (1)
Area change rate (%) / water absorption rate (% by mass) ≦ 0.5 (2)
Furthermore, it is preferable that the area change rate (%) / ion conductivity (S / cm) ≦ 100 and the area change rate (%) / water absorption rate (mass%) ≦ 0.3 are satisfied.
That is, the ion-conducting polymer membrane of the present invention has a characteristic that the dimensional stability of the membrane is superior to that of the prior art, despite the high ion conductivity and water absorption of the polymer A having an ion exchange group. It is a feature.

The ion conductive composite polymer membrane of the present invention can be produced through the following main steps.
That is, a mixed solvent solution of a polymer A having an ion exchange group and a heat-meltable polymer B is spun by an electrostatic spinning method or the like, and a plurality of fibers having a diameter equal to or smaller than the fiber diameter is contained inside a single fiber having the heat-meltable polymer B as a matrix A process for obtaining a fiber aggregate (sheet) containing fibers (nanofibers) of polymer A, and a process for melting the heat-meltable polymer B component of the obtained fiber aggregate (sheet) to form a film That is, a step of hot pressing the fiber assembly (sheet), or a step of forming the fiber assembly (sheet) by melt extrusion using an extruder equipped with a T die, etc. It can be manufactured through a process in which the film is treated and a process in which the treated film is washed with pure water. According to the production method, the mixed solution of the polymer A having an ion exchange group and the hot-melt polymer B is stably discharged in a uniformly dissolved state, and then the solvent is removed during or after forming into a fiber shape. As the process proceeds, phase separation proceeds, and there are ultrafine fibers made of polymer A having ion-exchange groups in the fiber, and it is made of polymer A having ion-exchange groups stably without requiring a complicated process. Extra fine fibers are obtained. And the composite containing the ultrafine fiber in which a space | gap is hardly seen between a nanofiber and a matrix (heat-meltable polymer B) by melting the heat-meltable polymer B in the obtained fiber into a film. A polymer membrane is obtained. In addition, the obtained membrane is treated in an acidic aqueous solution, and the treated membrane is washed with pure water to obtain a polymer electrolyte membrane in which the acidic group of the polymer A having an ion exchange group is protonated. Can be obtained.

  The ion conductive composite membrane of the present invention can have any film thickness depending on the purpose, but is desirably as thin as possible from the viewpoint of ion conductivity. Specifically, the thickness is preferably 5 to 250 μm, and more preferably 5 to 100 μm. If the thickness of the ion conductive composite membrane is less than 5 μm, it is difficult to handle the ion conductive membrane and a short circuit or the like tends to occur when a fuel cell is formed. However, the power generation performance of the fuel cell tends to decrease.

  The present invention will be specifically described below with reference to examples. However, the present invention is not limited by the following examples, but should be implemented with appropriate modifications within a range that can meet the gist of the preceding and following descriptions. Of course, these are also possible and all fall within the technical scope of the present invention.

Various measurements were performed as follows.
1. Reduced viscosity The polymer powder dried under reduced pressure at 80 ° C. overnight was dissolved in N-methylpyrrolidone (NMP) at a concentration of 0.5 g / dl, and the viscosity was measured using an Ubbelohde viscometer in a constant temperature bath at 25 ° C. The reduced viscosity ηsp / c = [(t−t ₀ ) / t ₀ ] / c was evaluated. [T ₀ : dropping time of solvent only (s), t: dropping time of sample solution (s), c: concentration of sample solution (g / dl)]

2. Average fiber diameter of ultrafine single fiber A platinum-palladium alloy was vapor-deposited on a fiber assembly, photographed with a scanning electron microscope (SEM manufactured by SEM Hitachi, S-800), and a large number of SEM images displayed at 5000 or 10,000 times. Twenty fibers were randomly selected from the fibers and the fiber diameter was measured. The average value of the measured 20 fiber diameters was calculated and used as the average fiber diameter of the ultrafine fibers.

3. TEM observation of nanofiber A sample is embedded in an epoxy resin, and an ultrathin section is prepared with a microtome. The prepared section was dyed in ruthenium tetroxide (RuO ₄ ) vapor for 30 minutes, subjected to carbon deposition, and a TEM observation sampling was prepared and observed by TEM. The acceleration voltage in TEM observation was 200 kV, and the observation magnification was 50000 times and 100000 times.

4). Ion exchange capacity 50 mg of the polymer dried under reduced pressure at 80 ° C. overnight was weighed and stirred in 60 ml of 0.01 M NaOH aqueous solution for 1 hour. Thereafter, 50 ml of the solution was taken out and titrated with an aqueous 0.02M HCl solution using an automatic titrator (HIRANUMA TITSTATION TS-980). The ion exchange capacity (IEC) was calculated from the following equation.
IEC = (blank average dripping amount (ml) −sample dripping amount (ml)) × 1.2 × 0.02 / sample mass (g)

5. Ion conductivity A platinum wire (diameter: 0.2 mm) is pressed against the surface of a strip-shaped membrane sample having a width of 1 cm on a probe for measurement (made of PTFE), and the sample is placed in a constant temperature and humidity chamber at 80 ° C. and a relative humidity of 95%. The AC impedance at 10 kHz between the platinum wires is 1250FREQUENCY by SOLARTRON
Measured with RESPONSE ANALYSER. Measured by changing the distance between the electrodes from 1 cm to 4 cm at intervals of 1 cm, and canceling the contact resistance between the film and the platinum wire from the linear slope Dr [Ω / cm] plotting the distance between the electrodes and the measured resistance value And calculated.
σ [S / cm] = 1 / (film width [cm] × film thickness [cm] × Dr [Ω / cm])

6). Saturated water absorption 5 cm square sample was vacuum dried overnight at 80 ° C., and then dry mass was measured. The dried sample was kept in water at 80 ° C. for 1 day or longer, and the mass after saturated water absorption (the mass when the mass change disappeared after the start of measurement) was determined to calculate the water absorption [%] of the sample from the following formula.
Saturated water absorption [%] = [(mass after saturated water absorption / dry mass) -1] × 100

7). Area change rate A sample of 5 cm square was vacuum-dried at 80 ° C. overnight, and then the area after drying was measured. The dry sample was kept in water at 80 ° C. for 1 day or longer, and the area after saturated water absorption (the area when the area change disappeared after the start of measurement) was determined, and the area change rate [%] of the sample was calculated from the following formula.
Area change rate [%] = [(area after saturated water absorption / area after drying) -1] × 100

Synthesis Example 1: Sodium 3,3′-disulfonate-4,4′-dichlorodiphenylsulfone (abbreviation: S-DCDPS) 97.857 g (0.1992 mol), 2,6-dichlorobenzonitrile (abbreviation: DCBN) 18 .457 g (0.1073 mol), 4,4′-biphenol (abbreviation: BP) 57.072 g (0.3065 mol), potassium carbonate 46.596 g (0.3371 g), N-methyl-2-pyrrolidone (abbreviation: NMP) ) 453.135 g was weighed into a 1000 ml four-necked flask and flushed with nitrogen. Heating was performed while stirring, and the reaction solution was allowed to react for 15 hours so that the temperature of the reaction solution was 190 to 200 ° C. Then, it cooled to room temperature and poured the reaction solution into water, and precipitated in strand form. The obtained polymer was washed twice with water at room temperature and twice in boiling water, and then dried at 100 ° C. to obtain a polymer.

Example 1
The ion conductive polymer polymerized in Synthesis Example 1 and polyvinylidene fluoride (Aldrich Mw: 275,000) were dissolved in N, N-dimethylacetamide (special grade by Nacalai Tesque) at a ratio of 30/70 by weight. . The polymer concentration was 20 wt%. This blend solution was filled in a container provided with a nozzle having an inner diameter of 0.9 mm, and a voltage was applied to the nozzle portion via a high voltage power source. The solution was ejected from the tip of the nozzle, flew while evaporating the solvent, and a fiber assembly was produced in the grounded collection part. The applied voltage was 17 kV, and the distance from the nozzle tip to the collecting part was 10.5 cm. The average fiber diameter of the fiber assembly was 260 nm. It was confirmed from the TEM observation that there were a plurality of fibrous island components. The TEM observation result is shown in FIG.

(Example 2)
The same procedure as in Example 1 was conducted except that the ion conductive polymer and polyvinylidene fluoride polymerized in Synthesis Example 1 were dissolved in N, N-dimethylacetamide at a weight ratio of 40/60. The applied voltage was 18 kV, and the distance from the nozzle tip to the collecting part was 10.5 cm. The average fiber diameter of the fiber assembly was 210 nm. It was confirmed from the TEM observation that there were a plurality of fibrous island components. The TEM observation results are shown in FIG.

(Example 3)
The same procedure as in Example 1 was conducted except that the ion conductive polymer and polyvinylidene fluoride polymerized in Synthesis Example 1 were dissolved in N, N-dimethylacetamide at a weight ratio of 50/50. The applied voltage was 20 kV, and the distance from the nozzle tip to the collecting part was 10.5 cm. The average fiber diameter of the fiber assembly was 260 nm. It was confirmed from the TEM observation that there were a plurality of fibrous island components. The TEM observation result is shown in FIG.

Example 4
The same procedure as in Example 1 was conducted except that the ion conductive polymer and polyvinylidene fluoride polymerized in Synthesis Example 1 were dissolved in N, N-dimethylacetamide at a weight ratio of 70/30. The applied voltage was 25 kV, and the distance from the nozzle tip to the collecting part was 10.5 cm. The average fiber diameter of the fiber assembly was 140 nm. It was confirmed from the TEM observation that there were a plurality of fibrous island components. The TEM observation results are shown in the figure.
By heating the webs obtained in Examples 1 to 4 to melt polyvinylidene fluoride, a nanofiber nonwoven fabric having excellent adhesion between fibers was obtained.

(Synthesis Example 2: Synthesis of ion-conductive aromatic polymer A1)
3,3′-disulfo-4,4′-dichlorodiphenylsulfone disodium salt (abbreviation: S-DCDPS) 15.0 g [0.03026 mol], 2,6-dichlorobenzonitrile (abbreviation: DCBN) 2.81 g [0.01629 mol], 8.6747 g [0.04655 mol] of 4,4′-biphenol and 7.0775 g of potassium carbonate were weighed in a 200 ml four-necked flask and flushed with nitrogen. After adding 89.1 ml of NMP and stirring at 150 ° C. for 1 hour, the reaction was continued by raising the reaction temperature to 195-200 ° C. and sufficiently increasing the viscosity of the system (about 6 hours). Thereafter, the mixture was allowed to cool and precipitated into strands in water. The obtained polymer was washed in water and then dried. The reduced viscosity of the polymer was 1.93 (dl / g), and the IEC was 2.3 (meq / g).

(Example 5)
The ion conductive aromatic polymer A1 obtained in Synthesis Example 2 and polyvinylidene fluoride (PVDF: Aldrich Mw = 275,000) are added to N, N-dimethylacetamide (special grade by Nacalai Tesque) at a mass ratio of 30/70. It melt | dissolved in the ratio. The polymer concentration was 20 wt%. This blend solution was filled in a container provided with a nozzle having an inner diameter of 0.9 mm, and a voltage was applied to the nozzle portion via a high voltage power source. The solution was ejected from the tip of the nozzle, flew while evaporating the solvent, and a fiber assembly was produced in the grounded collection part. The applied voltage was 17 kV, and the distance from the nozzle tip to the collecting part was 10.5 cm. The average fiber diameter of the ultrafine fibers of the ultrafine fiber assembly was 260 nm. From the TEM observation of the ultrafine fibers, it was confirmed that there were a plurality of fibrous island components (nanofibers) having a minor axis diameter of 100 nm or less.
Next, the obtained ultrafine fiber assembly was formed into a film shape by hot pressing under vacuum conditions of 230 ° C. × 8 MPa × 5 min. Then, the obtained film was treated with a 2N H ₂ SO ₄ aqueous solution for 12 hours, and further treated with pure water to obtain a composite film. Table 1 summarizes the characteristics of the obtained composite membrane 1 such as IEC, ion conductivity, water absorption, and area change rate. From the TEM observation photograph of the composite membrane cross section, it was confirmed that a large number of nanofibers having a short axis diameter of 100 nm or less were dispersed in the composite membrane. Examples of TEM observation photographs of the composite membrane cross section are shown in FIGS.

(Example 6)
The same procedure as in Example 5 was performed except that the ion conductive polymer A1 and polyvinylidene fluoride were dissolved in N, N-dimethylacetamide at a mass ratio of 40/60. The applied voltage was 18 kV, and the distance from the nozzle tip to the collecting part was 10.5 cm. The average fiber diameter of the ultrafine fibers of the obtained ultrafine fiber assembly was 210 nm. From the TEM observation of the ultrafine fibers, it was confirmed that there were a plurality of fibrous island components (nanofibers) (TEM observation results are shown in FIG. 3). The obtained ultrafine fiber aggregate was molded into a membrane by the same method as in Example 5 and evaluated. The results are summarized in Table 1. Further, in the same manner as in Example 5, it was confirmed from the TEM observation photograph of the cross section of the composite film that a large number of nanofibers having a short axis diameter of 100 nm or less were dispersed in the composite film.

(Example 7)
The same procedure as in Example 5 was performed except that Ultem 1000, which is an ion conductive polymer A1 and a known polyetherimide (PEI), was dissolved in N, N-dimethylacetamide at a mass ratio of 40/60. The applied voltage was 18 kV, and the distance from the nozzle tip to the collecting part was 10.5 cm. The average fiber diameter of the ultrafine fibers of the obtained ultrafine fiber assembly was 270 nm. It was confirmed from the TEM observation of the ultrafine fibers that there were a plurality of fibrous island components (nanofibers). The obtained ultrafine fiber assembly was formed into a film by hot pressing under vacuum conditions of 290 ° C. × 8 MPa × 5 min. Evaluation was performed in the same manner as in Example 5. The results are summarized in Table 1. Further, in the same manner as in Example 5, it was confirmed from the TEM observation photograph of the cross section of the composite film that a large number of nanofibers having a short axis diameter of 100 nm or less were dispersed in the composite film.

(Comparative Example 1)
The ion conductive aromatic polymer A1 was dissolved in NMP to make a 10% by mass solution, this solution was cast on a glass plate and dried at 100 ° C. for 6 hours to obtain a single membrane of the aromatic polymer A. Evaluation similar to Example 5 was performed about this film | membrane.
(Comparative Example 2)
The same evaluation as in Example 5 was performed on a single membrane using Nafion (registered trademark; DuPont) 112, and the characteristics are summarized in Table 1.

From the above results, it can be seen that the ion conductive composite polymer membrane of the present invention is excellent in dimensional stability against water absorption despite high ion conductivity and high water absorption.

  According to the ultrafine fiber of the present invention, it is possible to provide an unprecedented one having a plurality of nanofibers in one nanofiber without using a special nozzle. The nanofiber effect can be obtained without the need for solvent removal, and since the nanofiber consists of two or more polymers, the shortage of one polymer can be supplemented with the other polymer and each polymer can function. In addition, the ion conductive composite polymer membrane of the present invention has outstanding performance as a polymer electrolyte membrane such as a fuel cell excellent in processability and dimensional stability as well as ion conductivity. In addition, it is also useful as a polymer electrolyte membrane for a direct methanol fuel cell, and has a feature of low methanol permeability, contributing greatly to the industry.

An example of the schematic diagram of the manufacturing apparatus in this invention. 4 is an ultrafine fiber TEM photograph described in Example 1. 4 is an ultrafine fiber TEM photograph described in Example 2. 4 is an ultrafine fiber TEM photograph described in Example 3. 4 is an ultrafine fiber TEM photograph described in Example 4. 4 is a TEM observation photograph of a cross section of the ion conductive polymer film obtained in Example 5. FIG. TEM observation photograph (enlarged) of a cross section of the ion conductive polymer film obtained in Example 5.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Charge spinning apparatus 2 Spinning nozzle 3 Solution tank 4 High voltage power supply 5 Counter electrode (collection board)
6 Nanofiber 7 Hot melt polymer B

Claims (3)

A single fiber (matrix fiber) having a diameter of 1 μm or less, made of a polymer in which the single fiber is alloyed, constitutes a matrix part and a core part , and a plurality of fibers having a diameter equal to or less than the fiber diameter inside the single fiber ( Core fiber) is included, and a solution is prepared by blending the matrix portion and each polymer constituting the core portion, a voltage is applied to the solution, and the solution is discharged to a collecting portion to which ground or a reverse voltage is applied. Ultrafine fiber characterized by being manufactured by The ultrafine fiber according to claim 1, wherein the internal fiber is a polymer having an ion exchange group. The ultrafine fiber according to claim 1 , wherein the matrix portion is a heat-meltable polymer.