JP2005054120A - Porous membrane and method and apparatus for its production - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polybenzazole type polymer porous membrane having high mechanical strength and excellent heat resistance, a polybenzazole type polymer porous membrane which has porosity excellent enough to permit sufficient impregnation of solution of polymers in production of a compound material with other ingredient polymers using the membrane as a support membrane by setting the fibril diameter appropriately as the structural parameter for judge of the degree of impregnation, and a method of producing the membranes. <P>SOLUTION: The membranes are produced by dissolving a polybenzazole type polymer in a good solvent, flow-expanding the resultant isotropic solution of the polymer having a polymer concentration of ≤3 wt.% over a board and coagulating the polymer by bringing it contact with a poor solvent to obtain a membrane having a three-dimensional fibril network and a fibril diameter d between 0.01 and 1 μm. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a polymer porous membrane and a polymer solid electrolyte membrane using the porous membrane as a support.

  Polybenzazole polymers such as polybenzoxazole (PBO) and polybenzimidazole (PBI) are superior in terms of high heat resistance, high strength, and high elastic modulus. It is expected to be suitable as a reinforcing material when producing a composite with the above. As a technique for forming and processing a polybenzazole polymer solution into a film, film formation by a casting method using an applicator is a well-known technique. In a porous film made of a polybenzazole polymer obtained by casting on a certain substrate, the surface structure on the side in contact with the substrate and the surface structure on the side not in contact with the substrate are different and form an asymmetric structure. . The surface on the side in contact with the substrate forms a dense structure, whereas the surface on the side not in contact with the substrate forms a porous structure. When a porous film made of a polybenzazole-based polymer having such an asymmetric structure is impregnated with another component polymer solution, there is a problem that it cannot be sufficiently impregnated in a portion where a dense structure is formed.

  On the other hand, there is a fuel cell that has been attracting attention as a new power generation technology that is excellent in energy efficiency and environmental performance in recent years. In particular, polymer electrolyte fuel cells that use polymer electrolyte membranes have high energy efficiency, and have low operating temperatures compared to other types of fuel cells, making them easy to start and stop. It is expected to be applied to electric vehicles and distributed power generation. Proton-conducting ion exchange resin membranes are usually used for polymer solid electrolyte membranes. In addition to proton conductivity, features such as fuel permeation deterrence and mechanical strength that prevent permeation of fuel such as hydrogen and methanol. is required. As such a polymer solid electrolyte membrane, for example, a perfluorocarbon sulfonic acid polymer membrane into which a sulfonic acid group is introduced as represented by Nafion (trade name) manufactured by DuPont, USA is known.

  In order to increase the output and efficiency of a polymer electrolyte fuel cell, it is effective to reduce the ionic conduction resistance of the polymer solid electrolyte membrane, and one of the measures is to reduce the film thickness. Yes. However, with the polymer solid electrolyte membrane alone as described above, the mechanical strength is also reduced as the film thickness is reduced. As a result, when the polymer solid electrolyte membrane and the electrode are integrally manufactured, the membrane is caused by fluctuations in heat and moisture content. At the time of power generation accompanied by fluctuations in the size of the polymer, the polymer solid electrolyte membrane and the electrode were peeled off, resulting in a problem that the power generation characteristics were degraded. Furthermore, reducing the film thickness has a problem in that the fuel permeation deterrence is reduced, leading to a reduction in electromotive force and a decrease in fuel utilization efficiency.

  Therefore, as a method for improving the mechanical strength of the solid polymer electrolyte membrane and suppressing the dimensional change, a composite material using a porous substrate has been actively studied. Stable production of this porous substrate is indispensable for making composite membranes for polymer electrolyte fuel cells

When a polybenzazole-based polymer solution is processed into a fiber or a film, it is molded from a high-concentration liquid crystal dope as described in Patent Document 1 and Patent Document 2. Patent Document 3 describes a polymer solid electrolyte membrane in which a PBO porous membrane and various ion exchange resins are combined. However, the surface of the PBO porous film obtained by the method of directly solidifying a PBO solution film formed from a dope exhibiting liquid crystallinity described in this in a water bath has a dense layer with few openings on both sides. When the ion exchange resin is compounded, the ion exchange resin solution is not easily impregnated inside the membrane, the content of the ion exchange resin in the composite membrane is reduced, and the ion conductivity inherent in the ion exchange resin is reduced. There was a problem that the characteristics were greatly deteriorated. In a composite using a polybenzazole-based polymer network as a reinforcing material, when a polybenzazole-based polymer porous film is made from such a high concentration of liquid crystal dope, the gap of the polymer network becomes small. Uniform impregnation becomes difficult.

Patent Document 4 discloses a method for obtaining a polybenzazole-based polymer film by forming an optically anisotropic polybenzazole-based polymer solution and then solidifying it through an isotropic process by moisture absorption. The polybenzazole-based polymer film obtained by the method described therein is a transparent and highly dense film, and is not suitable for the purpose of impregnating the other component polymer solution to produce a composite.
US Pat. No. 5,552,221 US Pat. No. 5,367,042 International Patent Publication WO00 / 22684 JP 2000-273214 A

  The present invention provides a polybenzazole-based polymer porous membrane having high mechanical strength and excellent heat resistance. Furthermore, the present invention provides the definition of the fibril diameter, which is a structural parameter for judging the impregnation property when the porous membrane is used as a support membrane, and a method for producing the porous membrane.

  That is, according to the present invention, in a polybenzazole polymer porous membrane having micropores, the fibril diameter d (μm) of the porous membrane satisfies 0.001 ≦ d ≦ 1, and the porosity of both surfaces of the porous membrane The polybenzazole-based polymer porous membrane is characterized in that both are 20% or more. Further, the present invention is an isotropic solution having a polymer concentration of 3% by weight or less of a polymer solution obtained by dissolving the polybenzazole polymer in a good solvent, and casting the solution on a substrate. Provided is a method for producing the polybenzazole-based polymer porous film, which is obtained by solidifying by contacting with a poor solvent of a benzazole-based polymer.

  The present invention provides a polybenzazole-based polymer porous membrane that can be sufficiently impregnated with another component polymer solution, has high mechanical strength, and is excellent in heat resistance when producing a composite with another component polymer. And the manufacturing method is provided.

  Hereinafter, the polybenzazole polymer porous membrane of the present invention will be described in detail. A porous membrane made of the polybenzazole polymer of the present invention is formed from a solution of a polybenzazole polymer exhibiting an isotropic phase, and is washed by contacting with a poor solvent to solidify the membrane. It is a film obtained. A polybenzazole polymer film formed from a polybenzazole polymer solution exhibiting optical anisotropy yields a porous polybenzazole polymer film having a three-dimensional fibril network structure that can be sufficiently impregnated with other component polymers. Since it is not possible, it is not preferable.

  The polybenzazole-based polymer in the present invention refers to a polymer having a structure containing an oxazole ring, a thiazole ring, and an imidazole ring in the polymer chain, and includes a repeating unit represented by the following general formula in the polymer chain.

Here, Ar ₁ , Ar ₂ , Ar ₃ represent an aromatic unit and have a substituent such as various aliphatic groups, aromatic groups, halogen groups, hydroxyl groups, nitro groups, cyano groups, and trifluoromethyl groups. May be. These aromatic units are monocyclic units such as benzene rings, condensed ring units such as naphthalene, anthracene, and pyrene, and polycyclic aromatic units in which two or more of these aromatic units are connected via an arbitrary bond. But it ’s okay.

Moreover, the position of N and X in an aromatic unit will not be specifically limited if it is the arrangement | positioning which can form a benzazole ring. Furthermore, these may be not only hydrocarbon aromatic units but also heterocyclic aromatic units containing N, O, S, etc. in the aromatic ring. X represents O, S, NH.
The Ar ₁ is preferably represented by the following general formula.

Here, Y ₁ and Y ₂ represent CH or N, Z represents a direct bond, —O—, —S—, —SO ₂ —, —C (CH ₃ ) ₂ —, —C (CF ₃ ) ₂ —. , -CO-.
Ar ₂ is preferably represented by the following general formula.

Here, W is _{-O -, - S -, -} SO 2 -, - C (CH 3) 2 -, - C (CH 3) 2 -, - shows a CO-.
Ar ₃ is preferably represented by the following general formula.

  These polybenzazole-based polymers may be homopolymers having the above-mentioned repeating units, but may be random, alternating or block copolymers in which the above structural units are combined. For example, Patent Documents A to F, etc. Examples described in the above are also exemplified.

Patent Document A: US Pat. No. 4,703,103 Patent Document B: US Pat. No. 4,533,692 Patent Document C: US Pat. No. 4,533,724 Patent Document D: US Pat. No. 4,533,693 Patent Document E: US Patent Patent No. 4,359,567 Patent Document F: US Pat. No. 4,578,432

  Specific examples of these polybenzazole-based structural units include those represented by the following structural formulas.

Furthermore, not only these polybenzazole-based structural units, but also random, alternating or block copolymers with other polymer structural units may be used. At this time, the other polymer constituent unit is preferably selected from aromatic polymer constituent units having excellent heat resistance. Specifically, polyimide structural unit, polyamide structural unit, polyamideimide structural unit, polyoxydiazole structural unit, polyazomethine structural unit, polybenzazoleimide structural unit, polyether ketone structural unit, Examples thereof include polyethersulfone structural units.
As an example of a polyimide-type structural unit, what is represented by the following general formula is mentioned.

Here, Ar ₄ is represented by a tetravalent aromatic unit, but is preferably represented by the following structure.

Ar ₅ is a divalent aromatic unit and is preferably represented by the following structure. Various substituents such as a methyl group, a methoxy group, a halogen group, a trifluoromethyl group, a hydroxyl group, a nitro group, and a cyano group may be present on the aromatic ring shown here.

  Specific examples of these polyimide-based structural units include those represented by the following structural formulas.

  Examples of polyamide-based structural units include those represented by the following structural formula.

Here, it is preferable that Ar ₆ , Ar ₇ and Ar ₈ are each independently selected from the following structures. Various substituents such as a methyl group, a methoxy group, a halogen group, a trifluoromethyl group, a hydroxyl group, a nitro group, and a cyano group may be present on the aromatic ring shown here.

  Specific examples of these polyamide-based structural units include those represented by the following structural formulas.

  Examples of the polyamideimide-based structural unit include those represented by the following structure.

Here, Ar ₉ is preferably selected from the structures shown as specific examples of Ar ₅ above.
Specific examples of these polyamideimide structural units include those represented by the following structural formulas.

  Examples of the polyoxydiazole-based structural unit include those represented by the following structural formula.

Here, Ar ₁₀ is preferably selected from the structures shown as specific examples of Ar ₅ .
Specific examples of these polyoxydiazole structural units include those represented by the following structural formulas.

  Examples of polyazomethine structural units include those represented by the following structure.

Here, Ar ₁₁ and Ar ₁₂ are preferably selected from structures shown as specific examples of Ar ₆ .
Specific examples of these polyazomethine-based structural units include those represented by the following structural formulas.

  Examples of the polybenzazole imide-based structural unit include those represented by the following structural formula.

Here, Ar ₁₃ and Ar ₁₄ are preferably selected from the structures shown as specific examples of Ar ₄ .
Specific examples of these polybenzazole imide-based structural units include those represented by the following structural formulas.

  The polyether ketone structural unit and the polyether sulfone structural unit generally have a structure in which aromatic units are connected together with an ether bond by a ketone bond or a sulfone bond, and include a structural component selected from the following structural formula.

Here, Ar _{15 to} Ar ₂₃ are preferably each independently represented by the following structure. Various substituents such as a methyl group, a methoxy group, a halogen group, a trifluoromethyl group, a hydroxyl group, a nitro group, and a cyano group may be present on the aromatic ring shown here.

  Specific examples of these polyetherketone structural units include those represented by the following structural formula.

  The aromatic polymer structural unit that can be copolymerized with these polybenzazole-based polymer structural units does not strictly indicate a repeating unit in the polymer chain, but can be present together with the polybenzazole-based structural units in the polymer main chain. Indicates the unit. These copolymerizable aromatic polymer structural units can be copolymerized not only alone but also in combination of two or more. In order to synthesize such a copolymer, an amino group, a carboxyl group, a hydroxyl group, a halogen group, etc. are introduced at the end of a unit consisting of a polybenzazole polymer constituent unit, and the reaction in the synthesis of these aromatic polymers. It may be polymerized as a component, or may be polymerized as a reaction component in the synthesis of a polybenzazole-based polymer by introducing a carboxyl group into the terminal of a unit containing these aromatic polymer constituent units.

  The polybenzazole-based polymer is subjected to condensation polymerization in a polyphosphoric acid solvent to obtain a polymer. The degree of polymerization of the polymer is expressed in terms of intrinsic viscosity, and is 15 dL / g or more and 35 dL / g or less, preferably 20 dL / g or more and 26 dL / g or less. If it is below this range, the strength of the polybenzazole polymer film obtained is low, and if it is above this range, the concentration range of the polybenzazole polymer solution from which an isotropic solution is obtained is limited, etc. This is not preferable because it is difficult to form a film under anisotropic conditions.

  It is important that the polybenzazole polymer solution used in the present invention is formed with a composition under isotropic conditions in order to obtain a polybenzazole polymer porous membrane having a uniform and large gap. Therefore, the preferable concentration range of the polybenzazole-based polymer solution is 3% or less, more preferably 2% or less. If the concentration is higher than this range, a polybenzazole polymer film having a large gap cannot be obtained, and the solution exhibits anisotropy depending on the polymer composition and degree of polymerization of the polybenzazole polymer, which is not preferable.

For confirmation of isotropic and anisotropy of the polybenzazole-based polymer solution, a method that is carried out by observation with a polarizing microscope is simple. In addition, there is a method for measuring fluid viscosity (for example, J. Materials Science, H. FISCHER JAODELL A. KELLER M. MURRAY et al., Vol. 29, page 1025). In the polarization microscope observation, the sample is observed while being crushed to a thickness of about 50 μm or less between the slide glasses.

  In order to adjust the concentration of the polybenzazole polymer solution to the range shown above, the following method can be used. That is, a method in which a polymer solid is once separated from a polymerized polybenzazole-based polymer solution, and the concentration is adjusted by adding a solvent again and dissolving. Furthermore, the method of adjusting the concentration by adding a solvent to the polymer solution and diluting the polymer solution without separating the polymer solid from the polymer solution that has been subjected to condensation polymerization in polyphosphoric acid. Furthermore, there is a method of directly obtaining a polymer solution in the above concentration range by adjusting the polymerization composition of the polymer.

  Preferred solvents for use in adjusting the concentration of the polymer solution include methanesulfonic acid, dimethylsulfuric acid, polyphosphoric acid, sulfuric acid, trifluoroacetic acid, and the like, or a mixed solvent combining these solvents can also be used. Of these, methanesulfonic acid and polyphosphoric acid are particularly preferable.

  As a method for forming a polybenzazole polymer solution, in addition to a film forming method in which a polymer solution called a casting method is cast on a substrate using a glass rod, a bar coater, or a doctor blade, a linear shape is used. Any method for forming a solution into a film, such as a method of extruding from a slit die, a method of blow-extruding from a circumferential slit die, a method of roller pressing a polymer solution sandwiched between two films, or a spin coating method can be used.

  When casting a polybenzazole-based polymer solution onto a substrate, the thickness of the polybenzazole-based polymer solution on the substrate may be any thickness that can be cast, preferably 1 to 1500 μm, more preferably 20 to 1000 μm. A range is preferred.

  As a means for realizing the porous structure of the polybenzazole-based polymer film, a method is used in which an isotropic polybenzazole-based polymer solution cast on a film-forming substrate is solidified by contacting with a poor solvent. The poor solvent is a solvent miscible with the solvent of the polymer solution, and may be in a liquid phase state or a gas phase state. Further, a combination of coagulation with a poor solvent in a gas phase and coagulation with a poor solvent in a liquid phase can be preferably used. As a poor solvent used for coagulation, water, acid aqueous solution, inorganic salt aqueous solution, alcohols, glycols, organic solvents such as glycerin, etc. can be used, but the combination with polybenzazole polymer solution to be used Depending on the type, the surface porosity and porosity of the polybenzazole polymer film may be reduced, and discontinuous cavities may be formed inside the polybenzazole polymer film. Special care must be taken in selecting the solvent.

  In the coagulation of the isotropic polybenzazole polymer solution in the present invention, the poor solvent and coagulation conditions are selected from water vapor, methanesulfonic acid aqueous solution, phosphoric acid aqueous solution, glycerin aqueous solution, inorganic salt aqueous solution such as magnesium chloride, etc. As a result, the surface and internal structure of the polybenzazole polymer film and the gaps were controlled. Particularly preferred solidification means are a method of solidifying by contacting with water vapor, a method of solidifying by contacting water vapor for a short time in the initial stage of solidification, then a method of solidifying by contacting with water, a method of solidifying by contacting with an aqueous methanesulfonic acid solution, etc. is there.

The polybenzazole-based polymer film obtained by such a method differs in the surface structure on the side in contact with the substrate and the surface structure on the side not in contact with the substrate, and forms an asymmetric structure. A dense structure is formed on the surface in contact with the substrate, and a porous structure is formed on the surface not in contact with the substrate. When a porous film made of a polybenzazole polymer with such an asymmetric structure is impregnated with another component polymer solution, the formation of a dense structure on the surface in contact with the substrate is sufficiently impregnated with the other component polymer solution. Not preferable to cause the problem of not being able to.

  In response to this problem, the inventors have intensively studied the formation of a structure capable of sufficiently impregnating other component polymer solution into a porous film made of a polybenzazole-based polymer, and as a result, the fibril diameter existing on the surface of the formed porous film. If d (μm) satisfies 0.001 ≦ d ≦ 1 and the porosity of both surfaces of the porous membrane is 20% or more, the polybenzazole polymer porous membrane is sufficiently impregnated with the other component polymer solution. It was found that a polybenzazole-based polymer porous film having excellent porosity can be obtained. That is, the fibril diameter d (μm) existing on the surface of the porous film solidified by casting a polybenzazole-based polymer solution on the substrate satisfies 0.001 ≦ d ≦ 1, and It is important to select and use a film forming method and a solidification method that can satisfy both of the opening ratios of 20% or more.

  The film forming method is not particularly limited as long as the material used for the film forming substrate is such that the contact angle between the substrate and the polymer solvent is 30 ° or less. For example, a glass plate, a polymer film, stainless steel, or Hastelloy An alloy metal plate or the like can be used. It is also an effective method to modify the surface of the material used for the substrate, for example, using a glass plate that has been subjected to surface polishing, a metal plate that has been subjected to a mirror finish, a polymer film that has been subjected to corona treatment or plasma treatment, etc. You can also

  The polybenzazole-based polymer porous membrane obtained by the above method is desirably sufficiently washed for the purpose of accelerating the decomposition of the polymer by the residual solvent and avoiding problems such as the outflow of the residual solvent during use. Cleaning can be performed by immersing the membrane in a cleaning solution. A particularly preferred cleaning solution is water. Washing with water is preferably carried out until the pH of the washing solution when the membrane is immersed in water is in the range of 5 to 8, more preferably in the range of 6.5 to 7.5.

  Using a polybenzazole-based polymer isotropic solution in the specific concentration range described above, the contact angle between the polymer solvent and the substrate as a suitable coagulation means and film-forming substrate selected from the methods described above is By selecting a material having a temperature of 30 ° or less, a polybenzazole polymer porous membrane having excellent porosity and a fibril diameter that can be sufficiently impregnated with another component polymer solution can be produced.

  Applications of the polybenzazole polymer porous membrane obtained by the above method include separation membranes such as microfiltration membranes, ultrafiltration membranes and nanofiltration membranes, and medical polymer membranes such as dialysis membranes used as medical materials Is mentioned. Furthermore, it can also be used for electrical and electronic materials such as battery separators and electrically insulating porous membranes.

  Examples are shown below to describe the present invention more specifically, but the present invention is not limited to these Examples.

<Structural observation by scanning electron microscope>
Structure observation with a scanning electron microscope (SEM) was performed by the following method. First, water in the porous membrane washed with water was substituted with ethanol and further sufficiently substituted with isoamyl acetate, and then CO ₂ critical point drying was performed using a Hitachi critical point dryer (HCP-1). The porous film thus dried at the critical point was coated with a platinum coating having a thickness of 150 Å, and observed using an SEM (S-800) manufactured by Hitachi at an acceleration voltage of 10 kV and a sample tilt angle of 30 degrees.

<Fiber diameter>
The fibril diameter was measured by the following method. Obtained by observing the surface of the formed porous film with a scanning electron microscope (SEM), enlarging a photograph baked 10,000 times to 200 times, and measuring 150 fibrils on the enlarged photograph. It was.

<Surface open area ratio of porous film>
The surface porosity of the porous film was measured by the following method. After selecting a field of view corresponding to a 5 μm square on a photograph of the surface of the porous film taken with a scanning electron microscope (SEM), the polymer part corresponding to the outer surface of the film is colored white, and the other part is black. The image was taken into a computer using a scanner, and the ratio of the black portion in the image was measured using image analysis software Scion Image manufactured by Scion, USA. This operation was performed for three non-overlapping fields for one sample, and the average was defined as the surface area ratio.

<Contact angle>
The contact angle was measured by the following method. The value of the contact angle is a value at a temperature of 20 ° C. and a relative humidity of 65% RH by a droplet method. A CA-X type manufactured by Kyowa Interface Science Co., Ltd. was used as an apparatus for measuring the contact angle. The droplets are adjusted by filling a polymer solvent with a syringe set with a polytetrafluoroethylene injection needle whose tip is parallel to the substrate and extruding it. The droplet is inflated to a diameter of 1.8 mm and stopped, and in this state, the substrate is brought into contact with the droplet. When the substrate is brought into contact with the liquid droplet, the substrate is moved downward and the liquid droplet is separated from the injection needle. When the liquid droplet is separated from the injection needle, the movement is stopped, and in the state of the liquid droplet 10 seconds after that state. The contact angle was measured. This measurement is performed 10 times, and the average value is set as the value of the contact angle. About the board | substrate to measure, after washing | cleaning sufficiently using the organic solvent, neutral detergent, etc. before the measurement, it ultrasonically cleaned using distilled water. Then, after fully drying, it was stored in a desiccator kept in a dry atmosphere. The measurement was carried out promptly so that it was taken out from the dry atmosphere and finished within 30 minutes.

<Intrinsic viscosity>
Using methanesulfonic acid as a solvent, the viscosity of the polymer solution adjusted to a concentration of 0.5 g / L was measured and calculated using a Ubbelohde viscometer in a 25 ° C. constant temperature bath.

<Impregnation rate>
The impregnation rate when the other polymer was impregnated into the membrane using the polybenzazole-based porous membrane as a support was measured by the following method. The basis weight Dc [g / m ² ] of the composite membrane was measured, and the basis weight Ds [g] of the dried support membrane measured by drying the composite membrane without drying the other component polymer on the same support membrane. / M ² ], the impregnation rate of the other component polymer was determined by the following calculation.
Impregnation rate of other components [wt%] = (Dc−Ds) / Dc × 100

<Proton conductivity>
The proton conductivity σ was measured as follows. A platinum wire (diameter: 0.2 mm) is pressed against the surface of a strip-shaped film sample having a width of 10 mm on a self-made measuring probe (made of polytetrafluoroethylene) and placed in a constant temperature and humidity chamber at 80 ° C. and a relative humidity of 95%. The sample was held, and the AC impedance at 10 kHz between the platinum wires was measured by SOLARTRON 1250 FREQUENCY RESPONSE ANALYSER. The contact distance between the membrane and the platinum wire is measured by the following formula from the slope Dr [Ω / cm] of the straight line in which the distance between the electrodes is changed from 10 mm to 40 mm at intervals of 10 mm and the distance between the electrodes and the measured resistance value are plotted. Canceled and calculated.
σ [S / cm] = 1 / (film width × film thickness [cm] × Dr)

<Example 1>
A solution containing 14% by weight of polyparaphenylene cis benzobisoxazole polymer with IV = 24 dL / g in polyphosphoric acid is diluted by adding methane sulfonic acid to obtain a solution having a polyparaphenylene cis bisbisoxazole concentration of 0.5% by weight. Was prepared. The resulting solution was sandwiched between glass slides and observed with a polarizing microscope (Nikon ECLIPSE E600 POL) in a crossed Nicols field to confirm that the solution was isotropic. This solution was formed on a glass plate adjusted to 25 ° C. using an applicator having a clearance of 300 μm at a film forming speed of 5 mm / second. The dope film formed on the glass substrate in this way was 1 on a glass plate used for film formation in a constant temperature and humidity chamber (manufactured by Nagano Scientific Machinery Co., Ltd .: LH21-14P) at 25 ° C. and a relative humidity of 80%. After solidifying for a period of time, the membrane was formed by washing with water until the washing solution showed pH 7 ± 0.5. Moreover, as a result of measuring the contact angle of the glass plate used as the film-forming substrate and methanesulfonic acid used as a good solvent for the polybenzazole polymer, the contact angle was 26.0 °. When the obtained film was subjected to structural analysis by a scanning electron microscope, it was confirmed that the film was a porous film having openings on both sides. A scanning electron micrograph of the surface not in contact with the substrate is shown in FIG. 1, and a scanning electron micrograph of the surface in contact with the substrate is shown in FIG. On the surface not in contact with the substrate shown in FIG. 1, fibrils having a diameter d (μm) satisfying 0.003 ≦ d ≦ 0.3 form a three-dimensional network structure, and the surface open area ratio is 40. %Met. On the other hand, on the surface in contact with the substrate shown in FIG. 2, formation of a three-dimensional network structure of fibrils having a diameter d (μm) satisfying 0.01 ≦ d ≦ 0.3 and a surface open area ratio of 28% are satisfied. The formation of the structure was realized. That is, it is possible to form a structure in which both surfaces of the porous membrane have a fibril diameter d (μm) satisfying 0.001 ≦ d ≦ 1 and a surface opening ratio satisfying 20% or more, and having excellent porosity. Membranes can be manufactured.

  The membrane thus obtained was fixed to a stainless steel frame in water, and the water inside the porous membrane was replaced with a 20% Nafion (trade name) solution (product number: SE-20192) manufactured by DuPont, which is an ion exchange resin solution. It was replaced by immersion in a mixed solvent of water: ethanol: 1-propanol = 26: 26: 48 (weight ratio) almost the same as the solvent composition of. This porous membrane was immersed in a 20% Nafion (trade name) solution at room temperature for 30 minutes and then removed from the solution. The solvent of the Nafion (trade name) solution impregnated inside the membrane and adhered to the membrane surface was volatilized by air drying and dried. It was. The dried film was preheated in an oven at 60 ° C. for 1 hour to remove residual solvent, and then heat treated at 130 ° C. for 1 hour in a nitrogen atmosphere to evaluate the impregnation property in Example 1. Adjusted. The impregnation ratio of the ion exchange resin in the composite membrane thus adjusted was 90% by weight or more.

<Example 2>
Methanesulfonic acid was added to a dope containing 14% by weight of a polyparaphenylenecisbenzobisoxazole polymer with IV = 23.8 dL / g in polyphosphoric acid, and diluted to obtain a polyparaphenylenecisbenzobisoxazole concentration of 1.5% by weight. A solution of was prepared. The resulting solution was confirmed to be an isotropic solution by the same method as shown in Example 1. This solution was formed on a glass plate heated to 90 ° C. at a rate of 5 mm / sec using an applicator with a clearance of 300 μm. The dope film thus formed on the glass plate was placed in a constant temperature and humidity chamber at 25 ° C. and 80% relative humidity to solidify for 1 hour, and the resulting film had a pH of 7 ± 0.5. The membrane was prepared by washing with water. Moreover, as a result of measuring the contact angle of the glass plate used as the film-forming substrate and methanesulfonic acid used as a good solvent for the polybenzazole polymer, the contact angle was 28 °. The obtained film was observed with a scanning electron microscope. As a result, the surface on the side not in contact with the substrate had the same form as in FIG. In addition, on the surface on the side in contact with the substrate shown in FIG. 3, the formation of a three-dimensional network structure of fibrils having a diameter d (μm) satisfying 0.03 ≦ d ≦ 0.7 and the surface open area ratio is 23%. The formation of the structure satisfying the above has been realized. That is, as in Example 1, both surfaces of the porous membrane can form fibrils having a diameter d (μm) satisfying 0.001 ≦ d ≦ 1, and a structure satisfying a porosity of 20% or more on both surfaces can be formed. It is possible to produce a polybenzazole polymer porous membrane excellent in the above. The porous membrane thus obtained was prepared as a composite membrane of Example 2 for evaluating the impregnation property by the same method as shown in Example 1. The impregnation rate of the ion exchange resin of the composite membrane thus adjusted was 75% or more.

<Comparative Example 1>
A solution containing 14% by weight of polyparaphenylene cis benzobisoxazole polymer with IV = 24.1 dL / g in polyphosphoric acid is diluted by adding methanesulfonic acid to obtain a solution having a polyparaphenylene cis bisbisoxazole concentration of 1% by weight. Was prepared. The resulting solution was confirmed to be an isotropic solution by the same method as shown in Example 1. The solution was formed into a film by coagulation, coagulation, and washing with water in the same manner as shown in Example 2. Moreover, as a result of measuring the contact angle of the glass plate used as the film forming substrate and methanesulfonic acid used as a good solvent for the polybenzazole polymer, the contact angle was 36.3 °. The obtained film was observed with a scanning electron microscope. As a result, the surface on the side not in contact with the substrate had the same form as in FIG. On the other hand, a scanning electron micrograph of the surface in contact with the substrate is shown in FIG. As can be seen from the figure, a dense structure is formed on the surface in contact with the substrate, and the formation of fibrils with a diameter d (μm) satisfying 0.001 ≦ d ≦ 1 and the surface porosity are In both cases, formation of a structure satisfying 20% or more could not be realized. That is, it is impossible to form fibrils having a diameter d (μm) of 0.001 ≦ d ≦ 1 on both surfaces of the porous membrane and a structure satisfying a porosity of 20% or more on both surfaces. A sol polymer porous membrane could not be produced. The porous membrane thus obtained was prepared as a composite membrane of Comparative Example 1 in which the impregnation property was evaluated by the same method as shown in Example 1. The impregnation rate of the ion exchange resin of the composite membrane thus adjusted was 60% or less.

<Comparative example 2>
A dope containing 6% by weight of polyparaphenylenecisbenzobisoxazole polymer in polyphosphoric acid with IV = 24 dL / g was polymerized in a 2 L flask. The resulting dope was sandwiched between slide glasses, temperature-controlled with a Linkam hot stage, and observed with a polarizing microscope (Nikon ECLIPSE E600 POL) in a crossed Nicols field of view. It was confirmed that the 6% concentration solution is an optically anisotropic solution at a temperature of 140 ° C. or lower, and the anisotropic phase partially disappears at 140 ° C. to enter a mixed phase with the isotropic phase. This solution was formed on a glass plate heated to 90 ° C. using an applicator having a clearance of 300 μm at a film forming rate of 5 mm / second. The dope film thus formed on the glass plate was placed in a constant temperature and humidity chamber at 25 ° C. and 80% relative humidity to solidify for 1 hour, and the resulting film had a pH of 7 ± 0.5. The membrane was prepared by washing with water. Moreover, as a result of measuring the contact angle between the glass plate used as the substrate and polyphosphoric acid used as a good solvent for the polybenzazole polymer, the contact angle was 28.2 °. The obtained film was observed with a scanning electron microscope. As a result, both the surface not in contact with the substrate and the surface in contact with the substrate had a dense structure similar to that in FIG. Producing a polybenzazole polymer porous film having excellent porosity, in which d (μm) cannot form a fibril that satisfies 0.001 ≦ d ≦ 1, and a structure that satisfies a surface porosity of 20% or more. I couldn't. The porous membrane thus obtained was prepared as a composite membrane of Comparative Example 2 in which the impregnation property was evaluated by the same method as shown in Example 1. The impregnation rate of the ion exchange resin of the composite membrane thus adjusted was 10% or less.

  The proton conductivity of the polymer solid electrolyte membranes of Example 1, Example 2, Comparative Example 1, and Comparative Example 2 was evaluated. The results are shown in Table 1.

  As shown in Table 1, in the present invention, when the composite of the polybenzazole polymer porous membrane and the other component polymer is produced, the polybenzazole polymer porous membrane is sufficiently impregnated with the other component polymer solution. be able to.

  The present invention provides a polybenzazole-based polymer porous membrane excellent in porosity that can be sufficiently impregnated with a solution of another component polymer when producing a composite with the other component polymer, and a method for producing the same. It is. By using the present invention, a high-performance solid polymer membrane having high mechanical strength and excellent heat resistance can be produced as a polymer electrolyte membrane for a polymer electrolyte fuel cell or the like.

2 is a scanning electron micrograph of the surface on the side not in contact with the substrate of Example 1. FIG. 3 is a scanning electron micrograph of the surface in contact with the substrate of Example 1. FIG. 4 is a scanning electron micrograph of the surface in contact with the substrate of Example 2. FIG. 4 is a scanning electron micrograph of the surface in contact with the substrate of Comparative Example 1.

Claims (6)

A porous membrane having micropores, wherein the micropores have a three-dimensional fibril network structure. 2. The porous membrane according to claim 1, wherein an average diameter d (μm) of fibrils forming the three-dimensional fibril network structure is 0.01 ≦ d ≦ 0.1. 3. The porous membrane according to claim 1, wherein in the solidification step of the thin film polymer solution dissolved in the good solvent, the solidification support is solidified by contacting with the poor solvent of the polymer solution in an inclined state. Solidification molding method. 4. The method for solidifying and forming a porous film according to claim 3, wherein the solidified support is set at an inclination angle of 5 ° or more and 45 ° or less with respect to the horizontal, and is always washed after mutual replacement with a new poor solvent. . 5. The method for solidifying and forming a porous film according to claim 3, wherein a transition from the contact coagulation step of the coagulation support to a subsequent washing step is continuously performed. The porous membrane manufacturing apparatus according to claim 1, comprising a molding, coagulation, and washing steps.

Images