JP2008062229A - Porous polyvinylidene fluoride membrane and method for preparing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide porous polyvinylidene fluoride membrane excellent in chemical resistance and a method for preparing the same. <P>SOLUTION: The porous polyvinylidene fluoride membrane is characterized by having R<SB>1</SB>value not lower than 1.5 which is calculated from the following equation (1). R<SB>1</SB>=A<SB>763</SB>/A<SB>840</SB>(1), wherein A<SB>763</SB>represents absorbance at 763cm<SP>-1</SP>and A<SB>840</SB>represents absorbance at 840cm<SP>-1</SP>, each obtained by IR measurement. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a polyvinylidene fluoride porous membrane excellent in chemical resistance suitable for water treatment such as water purification treatment, drinking water production, industrial water production, and wastewater treatment, and a method for producing the same.

  In recent years, the technology of separation means using a separation membrane having selective permeability has been remarkably advanced. Such separation operation techniques include, for example, separation means, washing means, sterilization means, and the like in various fields such as manufacturing processes of drinking water, ultrapure water and pharmaceuticals, sterilization and finishing of brewed products, and wastewater treatment. It has been put to practical use as a purification system. In these fields of application, the use of separation membranes has become widespread because finer water (advanced treatment), improved safety, and improved accuracy are required at a high level.

  Important properties required for the separation membrane include chemical strength (chemical resistance), separation accuracy, permeation performance, and physical strength.

  Above all, chemical strength is important. For example, in the water purification treatment, a disinfectant such as sodium hypochlorite is added to the membrane module part for the purpose of sterilizing the permeated water and preventing biofouling of the membrane, and for the purpose of removing the clogging substances of the membrane, When washing with an alkali, a surfactant or the like, the film itself may be deteriorated.

  The deterioration of the membrane causes a decrease in the mechanical strength of the membrane, and the decrease in the mechanical strength causes defects such as membrane breakage, cracking, and pinholes, leading to an accident that raw water is mixed into the treated water. Accordingly, in recent years, a separation membrane using a fluorine-based resin having both chemical strength (chemical resistance) and physical strength, for example, a polyvinylidene fluoride separation membrane has been used.

  Patent Document 1 discloses a polyvinylidene fluoride resin porous film having a maximum temperature of 160 ° C. or higher among peak temperatures obtained by DSC (differential scanning calorimetry) as a film having excellent chemical strength (ozone oxidation resistance). Is disclosed. This uses information on the crystallinity of the polyvinylidene fluoride resin as an index of chemical resistance. The inventors of the present invention evaluated chemical strength (chemical resistance) using several films having the highest peak temperature obtained by DSC of 160 ° C. or higher in the same film using the polyvinylidene fluoride resin. We obtained knowledge that chemical resistance is different. As a result of further investigation on the cause, it was found that the chemical resistance of the polyvinylidene fluoride porous film not only crystallinity but also the crystal structure greatly contributed to the present invention.

Prior art documents related to the present invention include the following.
JP 2000-218267 A JP-A-2005-200563 JP-A-60-97001 JP-A-3-215535 JP 2003-138422 A JP-A-2005-146230 JP-A-2005-194461

  An object of the present invention is to provide a polyvinylidene fluoride porous membrane excellent in chemical resistance and a method for producing the same in view of the above-mentioned problems of the prior art.

The above problems are solved by the following (1) and (2).
(1) The value of R ₁ calculated by the following formula (1) from the absorbance (A ₇₆₃ ) of ₇₆₃ cm ^{−1 and} the absorbance (A ₈₄₀ ) of ₈₄₀ cm ⁻¹ obtained by IR measurement is 1.5 or more. Polyvinylidene fluoride porous membrane characterized.
R ₁ = A ₇₆₃ / A ₈₄₀ (1)
(2) The method for producing a polyvinylidene fluoride porous membrane according to claim 1, wherein the polyvinylidene fluoride resin porous membrane is heat-treated at 160 ° C. or lower in a state where the dimensions are not fixed.

  According to the polyvinylidene fluoride porous membrane having excellent chemical resistance according to the present invention, the safety at the time of water formation is improved, and the lifetime of the porous membrane can be extended.

Polyvinylidene fluoride membrane of the present invention, the value of _{R 1} is 1, which is calculated by absorbance 763cm ^-1 obtained by IR measurement _{(A 763)} and absorbance at 840 cm ^-1 following formula from _{(A 840) (1)} .5 or more.
R ₁ = A ₇₆₃ / A ₈₄₀ (1)
Here, A ₇₆₃ is the absorbance attributed to the α-type crystal structure, and A ₈₄₀ is the absorbance attributed to the β-type crystal structure (see, for example, Patent Document 2). The value of R ₁ indicates the ratio of α-type and β-type in the crystalline region of polyvinylidene fluoride. From the IR chart of the porous film as shown in FIG. 1, a line is drawn between the minimum values of the IR chart in the vicinity of 695 and 780 cm ⁻¹ , and the characteristic absorption peak height attributed to the α-type crystal structure in the vicinity of 763 cm ^−1. Read. In addition, a line is drawn between the minimum values of the IR chart in the vicinity of 810 and 925 cm ⁻¹ to read the characteristic absorption peak height attributed to the β-type crystal structure in the vicinity of 840 cm ⁻¹ to obtain R ₁ .

The α-type crystal structure of the polyvinylidene fluoride resin refers to a fluorine atom (or hydrogen atom) bonded to one main chain carbon in a polymer molecule, and a hydrogen atom (or fluorine atom) bonded to one adjacent carbon atom. Atom) is in the trans position, and the hydrogen atom (or fluorine atom) bonded to the carbon atom adjacent to the other (reverse side) is in the Gauche position (60 degree position), The molecular chain is a TG ⁺ TG ⁻ type molecular chain, and the dipole efficiency of C—F ₂ and C—H ₂ bonds is perpendicular to the molecular chain. Each has a component in the parallel direction. When performing IR analysis polyvinylidene fluoride resin having an α-type crystal structure, 1212cm ^-1, has characteristic peaks (characteristic absorptions) around 1183 cm ^-1 and 763cm ^-1, 2θ in the powder X-ray diffraction analysis = 17.7 degrees, 18.3 degrees, and 19.9 degrees have characteristic peaks.

The β-type crystal structure of the polyvinylidene fluoride resin is that the fluorine atom and the hydrogen atom bonded to the carbon atom adjacent to one main chain carbon in the polymer molecule are each in the trans configuration (TT-type structure), that is, adjacent to each other. A fluorine atom and a hydrogen atom bonded to a matching carbon atom are present at a position of 180 degrees when viewed from the direction of the carbon-carbon bond. The carbon-carbon bond in which the TT-type structure part constitutes the TT-type main chain has a planar zigzag structure, and the dipole efficiency of the C—F ₂ and C—H ₂ bonds has a component perpendicular to the molecular chain. Have. IR analysis of the β-type crystal structure has characteristic peaks (characteristic absorption) around 1274 cm −1, 1163 cm −1 and 840 cm −1. In powder X-ray diffraction analysis, the characteristic is around 2θ = 21 degrees. Has a typical peak.

  In the polyvinylidene fluoride porous membrane of the present invention, the α-type crystal structure is present at a higher ratio than the β-type crystal structure. It is considered that the chemical resistance is improved when the α-type crystal structure is present at a higher ratio than the β-type crystal structure because of the following reason. The α-type crystal structure is presumed to be caused by the fact that the hydrogen atom and the fluorine atom are delocalized compared to the β-type crystal structure and there is less charge bias. That is, the polyvinylidene fluoride porous membrane of the present invention is superior because the non-polar α-type crystal structure is present in a higher proportion than the β-type crystal structure in which hydrogen atoms and fluorine atoms are localized and polarized intramolecularly. It is estimated to have high chemical resistance.

  The manufacturing method of the polyvinylidene fluoride porous membrane of this invention is shown. A known technique can be applied to a production method other than heat treatment, and there are steps of production, coagulation, and extraction of a resin-containing solution, and heat treatment or the like may be appropriately performed. For example, a polyvinylidene fluoride porous film can be produced by the methods described in Patent Documents 3 to 7.

  In the porous membrane of the present invention, it is preferable to perform heat treatment in a free state in which the porous membrane is not fixed. For example, after the stretching treatment, it is possible to perform the heat treatment at the same time as extracting the solvent and the flocculant by winding the porous film once in a frame or a cassette and then setting the porous film in a free state. When heat treatment is performed in a fixed state, thermal shrinkage or the like occurs and distortion occurs, and the crystal structure in the microenvironment of the porous film changes. Specifically, the transition from the α-type crystal structure to the β-type crystal structure occurs, and the ratio of the β-type crystal structure in the porous film increases, and a desired effect may not be obtained.

  As a procedure for performing the heat treatment, it may be performed after the film formation and before the extraction component is removed by washing or the like, or after the removal. Moreover, the yarn bundle state in which the membranes are bundled may be performed after the drying process, or may be heat-treated after being modularized. When heat treatment is performed after modularization, it is preferable to allow for a space in advance so as to prevent shrinkage due to heat treatment.

  As a heat treatment method, a dry method using hot air, a wet method performed by immersing in a liquid, a method performed by contacting a porous film with a heat-modulated metal roll, a method performed using a gas such as steam, or a method of emitting electromagnetic waves The porous film can be either wet or dry. Among them, the method carried out in water is easy because temperature control is easy. It is also possible to preferably employ a non-solvent of polyvinylidene fluoride resin such as low molecular weight polyethylene glycol. Furthermore, heat treatment in a mixed liquid of a plurality of components such as a mixed liquid of water and polyethylene glycol or a surfactant aqueous solution can also be employed.

  Depending on the selection of the immersion liquid in the wet method, it is possible to simultaneously perform the extraction and removal of the extracted components in the film-forming stock solution and the heat treatment.

  The heat treatment temperature of the present invention is preferably in the range of 70 ° C. to 160 ° C. from the viewpoint of obtaining the effect of heat treatment and not impairing the required characteristics of the porous film other than the chemical strength.

  Although the heat processing time of this invention does not have a restriction | limiting in particular, The range of 1 to 5 hours is preferable from a viewpoint of process property. By increasing the heat treatment temperature, the treatment time can be shortened.

  After the heat treatment, it is preferably left at room temperature or the like and allowed to cool slowly.

These heat treatment methods are based on the value of R ₁ calculated by the equation (1) from the absorbance (A ₇₆₃ ) of ₇₆₃ cm ^{−1 and} the absorbance (A ₈₄₀ ) of ₈₄₀ cm ⁻¹ obtained by IR measurement of the polyvinylidene fluoride porous membrane. The heat treatment conditions are appropriately set so that the value becomes 1.5 or more. In setting the heat treatment conditions, it is preferable to determine the optimum heat treatment conditions in advance by examining the correlation between each heat treatment condition and the value of R ₁ and taking the process into consideration.

  The above-mentioned vinylidene fluoride resin porous membrane is housed in a casing having a raw solution inlet, a permeate inlet, and the like and used as a membrane module. When the membrane module is a hollow fiber membrane, the permeate can be collected by bundling a plurality of hollow fiber membranes and placing them in a cylindrical container and fixing both ends or one end with polyurethane, epoxy resin or the like. Or by fixing the hollow fiber membrane in a flat plate shape so that the permeate can be collected. When the membrane is a flat membrane, the flat membrane is wound around in an envelope shape around the collecting tube and wound into a spiral shape and placed in a cylindrical container so that the permeate can be collected. Flat membranes are arranged on both sides of the plate so that the perimeter is fixed tightly so that the permeate can be collected.

  The membrane module is used as a separation device for separating water and the like by providing a pressurizing means at least on the stock solution side or a suction means on the permeate side. A pump may be used as the pressurizing means, or a pressure due to a water level difference may be used. Moreover, what is necessary is just to utilize a pump and a siphon as a suction means.

  This separation device can be used for water purification, clean water treatment, wastewater treatment, industrial water production, etc. in the field of water treatment, and uses river water, lake water, groundwater, seawater, sewage, wastewater, etc. as treated water.

  The vinylidene fluoride-based resin porous membrane can also be used for a battery separator that separates the positive electrode and the negative electrode inside the battery. In this case, the battery performance is improved due to high ion permeability or breakage. Effects such as improved battery durability due to high strength can be expected.

  Furthermore, when a charged group (ion exchange group) is introduced into a charged membrane by introducing a charged group (ion exchange group) into a vinylidene fluoride resin porous membrane produced by the above-described production method, the ion recognition performance is improved, and the charged membrane due to high breaking strength is used. Effects such as improved durability can be expected.

  Furthermore, when the above-mentioned vinylidene fluoride resin porous membrane is impregnated with an ion exchange resin and used as a fuel cell as an ion exchange membrane, particularly when methanol is used as a fuel, swelling of the ion exchange membrane due to methanol can be suppressed. Improvement of fuel cell performance can be expected. Furthermore, improvement in the durability of the fuel cell due to high breaking strength can be expected.

  Examples of the present invention will be described below. In the following examples, each measurement was performed according to the following method.

Various measurement (analysis) methods and apparatuses (1) IR analysis (1-1) Measurement conditions Surface reflection method. A polyvinylidene fluoride hollow fiber membrane was measured as a sample.
(1-2) Measuring apparatus Fourier transform infrared spectrophotometer JIR-5500 manufactured by JEOL Ltd.

(4) Tensile strength measurement (4-1) Measurement conditions The measurement was carried out in water at 25 ° C., the distance between chucks was 20 mm, the tensile speed was 100 mm / min, and the number of specimens was 10 (values in Table 1 are shown as average values). )
(4-2) Measuring device Autograph AGS-100G manufactured by Shimadzu Corporation

  The tensile rupture strength retention in the examples was measured by the above method, and the value before immersion in hypochlorous acid aqueous solution was described as 100%.

  Hereinafter, although the example of the crystal structure control method of the polyvinylidene fluoride resin porous membrane used in this invention and the example of a sodium hypochlorite tolerance evaluation test are demonstrated, this invention is not limited by this.

  Polyvinylidene fluoride (hereinafter sometimes abbreviated as PVDF) (Solvay Solexis Co., Ltd., SOLEF6010) as a vinylidene fluoride resin, gamma-butyrolactone (Mitsubishi Chemical Co., Ltd.) as a solvent, silica (inorganic particles) Tokuyama Co., Ltd., Fine Seal X-45, average agglomerated particle size 4.0 to 5.0 μm) and glycerin (produced by Kao Corporation, purified glycerin) as the aggregating agent in a weight ratio of 30:56:23, respectively. : A mixed solution was prepared so as to have a ratio of 21.

  The above mixed solution was heated and kneaded (temperature: 150 ° C.) in a twin-screw kneading extruder, and the extruded strand was passed through a pelletizer to form chips. This chip was extruded using an extruder (150 ° C.) equipped with a double ring nozzle having an outer diameter of 1.6 mm and an inner diameter of 0.8 mm. At this time, tetraethylene glycol was injected into the hollow portion of the extrudate.

  The hollow fiber extruded from the nozzle into the air was passed through an air travel distance of 3 cm, put into a 20% sodium sulfate aqueous solution (temperature 60 ° C.) by weight percent concentration, and allowed to cool and solidify by passing through a salt water bath of about 100 cm. . Next, the obtained hollow fiber-like material was heat-treated in flowing water at 95 ° C. for 180 minutes, and the solvent (gamma-butyrolactone), the flocculant (glycerin), and the injection solution (tetraethylene glycol) were extracted and removed.

The hollow fiber thus obtained was immersed in an aqueous solution of sodium hydroxide having a weight percent concentration of 5% at 40 ° C. for 120 minutes to extract and remove inorganic particles (Fine Seal X-45). A hollow fiber membrane was obtained. R ₁ obtained by IR measurement of the produced hollow fiber membrane was 2.5.

  In order to evaluate the oxidation resistance of the obtained hollow fiber membrane, it was immersed in an aqueous sodium hypochlorite solution (effective chlorine concentration: 5000 ppm) at 60 ° C. for 7 days, and its physical property evaluation (tensile breaking strength) was measured. The results are shown in Table 1.

A hollow fiber membrane was obtained in the same manner as in Example 1, except that heat treatment was performed for 120 minutes in flowing water at 95 ° C., and the solvent, flocculant, and injection solution were extracted and removed. R ₁ obtained by IR measurement of the produced hollow fiber membrane was 2.0.

  In order to evaluate the oxidation resistance of the obtained hollow fiber membrane, it was immersed in an aqueous sodium hypochlorite solution (effective chlorine concentration: 5000 ppm) at 60 ° C. for 7 days, and its physical property evaluation (tensile breaking strength) was measured. The results are shown in Table 1.

Comparative Example 1
A hollow fiber membrane was obtained in the same manner as in Example 1 except that the heat treatment was performed in flowing water at 50 ° C. for 180 minutes and the solvent, the flocculant, and the injection solution were extracted and removed. R ₁ obtained by IR measurement of the produced hollow fiber membrane was 1.0.

  In order to evaluate the oxidation resistance of the obtained hollow fiber membrane, it was immersed in an aqueous sodium hypochlorite solution (effective chlorine concentration: 5000 ppm) at 60 ° C. for 7 days, and its physical property evaluation (tensile breaking strength) was measured. The results are shown in Table 1.

  A mixed solution was prepared so that the weight ratio of PVDF (manufactured by Kureha Co., Ltd., # 1000) and gamma-butyrolactone (manufactured by Mitsubishi Chemical Corporation) as a solvent was 40:60.

  The above mixed solution was heated and kneaded (temperature 120 ° C.) in a twin-screw kneading extruder and extruded using a double ring structure nozzle (100 ° C.) having an outer diameter of 1.5 mm and an inner diameter of 0.8 mm. At this time, a 90% by weight concentration aqueous solution of gamma-butyrolactone was injected into the hollow portion of the extrudate.

  The extruded product extruded into the air from the nozzle was put into an aqueous solution of 80% gamma-butyrolactone at a weight percent concentration (temperature 30 ° C.) through an air travel distance of 5 cm, and allowed to cool and solidify by passing through a bath of about 100 cm. . Next, the obtained hollow fiber-like material is heat treated in flowing water at 80 ° C. for 120 minutes, and the solvent (gamma-butyrolactone), the flocculant (glycerin), and the injection solution (tetraethylene glycol) are extracted and removed to obtain a hollow fiber membrane. It was.

R ₁ obtained by IR measurement of the produced hollow fiber membrane was 1.8.

  In order to evaluate the oxidation resistance of the obtained hollow fiber membrane, it was immersed in an aqueous sodium hypochlorite solution (effective chlorine concentration: 5000 ppm) at 60 ° C. for 7 days, and its physical property evaluation (tensile breaking strength) was measured. The results are shown in Table 1.

2 is an IR chart of a hollow fiber membrane manufactured by the method of Example 1. FIG.

Claims (2)

In the polyvinylidene fluoride porous membrane, the value of R ₁ calculated by the following formula (1) from the absorbance (A ₇₆₃ ) of ₇₆₃ cm ^{−1 and} the absorbance (A ₈₄₀ ) of ₈₄₀ cm ⁻¹ obtained by IR measurement is 1.5 or more. A polyvinylidene fluoride porous membrane characterized by
R ₁ = A ₇₆₃ / A ₈₄₀ (1)               2. The method for producing a polyvinylidene fluoride porous membrane according to claim 1, wherein the polyvinylidene fluoride resin porous membrane is heat-treated at a temperature of 160 [deg.] C. or less in a state in which dimensions are not fixed.

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