JP6767141B2 - Polyvinylidene fluoride porous membrane and its manufacturing method - Google Patents

Description

The present invention relates to a polyvinylidene fluoride porous membrane and a method for producing the same. Specifically, the present invention relates to a porous membrane composed of a polyvinylidene fluoride resin as a base material, a hydrophilic polymer composed of a hydrophilic unit and a hydrophobic unit, and a method for producing the same.

In recent years, porous membranes such as ultrafiltration membranes and microfiltration membranes have been used for recovery of electrodeposition paints, removal of fine particles from ultrapure water, production of pyrogen-free water, concentration of enzymes, sterilization and clarification of fermented liquids, etc. It is used in a wide range of fields such as water, sewage, and wastewater treatment. The separation method using a porous membrane separates the substances to be separated in the liquid to be treated by the principle of sieving, which separates the substances to be separated according to the size of the pores, so that the separation accuracy is high and no phase change is involved. It is an energy-saving separation method.

When various liquids to be treated are filtered using a porous membrane such as an ultrafiltration membrane or a microfiltration membrane, some of the inorganic substances and / or organic substances contained in the liquid to be treated may be inside the membrane pores or It is adsorbed, blocked or deposited on the membrane surface to form a so-called concentration polarization layer or cake layer. As a result, a so-called fouling phenomenon occurs, and the filtration performance of the porous membrane is reduced from a fraction to a few tenths as compared with the permeation flux when pure water is filtered. When the filtration performance deteriorates due to such a fouling phenomenon, a larger membrane area is required and the membrane filtration equipment becomes large, so that the equipment introduction cost and the operation cost increase, which is a big problem.

In order to suppress such a fouling phenomenon, when the liquid to be treated is usually filtered using a porous membrane, chemical cleaning with chemicals such as alkali, acid and oxidant, and physical cleaning such as backflow cleaning and air bubbling are performed. Washing is also used. Therefore, as a material for a porous membrane, chemical durability and mechanical durability are required, and polyvinylidene fluoride resin is widely used because it has excellent durability.
On the other hand, since the polyvinylidene fluoride resin is a hydrophobic material, there is a problem that membrane fouling is likely to occur.

In response to this problem, studies have been conducted to impart hydrophilicity to polyvinylidene fluoride resin by various methods. Patent Documents 1 and 2 disclose that the surface of a porous membrane made of polyvinylidene fluoride is modified by using an agent such as an alkali or an oxidizing agent.

Further, Patent Document 3 discloses a method of imparting hydrophilicity by coating the surface of a porous membrane made of polyvinylidene fluoride with a hydrophilic polymer such as polyvinylpyrrolidone.
Further, Patent Document 4 discloses a method for producing a porous membrane by a phase separation method after pre-blending polyvinylpyrrolidone and polyvinylidene fluoride.

Japanese Unexamined Patent Publication No. 63-172745 Japanese Unexamined Patent Publication No. 2004-230280 JP-A-11-302438 Japanese Unexamined Patent Publication No. 60-216804

However, the method of modifying the surface of the porous membrane using the chemicals disclosed in Patent Documents 1 and 2 has a problem that the polyvinylidene fluoride resin itself, which is the base material, deteriorates. Further, in the method of coating the surface of the porous membrane made of polyvinylidene fluoride with the hydrophilic polymer disclosed in Patent Document 3, there is a problem that the coating layer closes the pores and the permeation flux is lowered, and the coating layer. Has the problem of peeling off during filtration.

Further, in the method of pre-blending the hydrophilic polymer and the polyvinylidene fluoride resin, the compatibility between the hydrophilic polymer and the polyvinylidene fluoride resin which is a hydrophobic polymer is low, so that the hydrophilic polymer can remain in the porous film. It is difficult, and there is a problem that it is eluted from the porous film during filtration or chemical cleaning.

The problem to be solved by the present invention is to obtain a porous membrane having excellent hydrophilicity and durability, which is suitable as an ultrafiltration membrane or a microfiltration membrane, which suppresses fouling and can achieve high filtration performance, and a method for producing the same. Is to provide.

As a result of diligent studies to solve the above problems, the present inventors have synthesized a hydrophilic polymer having a hydrophobic unit and a hydrophilic unit having high compatibility with polyvinylidene fluoride resin, and this hydrophilic polymer. By blending and polyvinylidene fluoride resin to form a porous film, we succeeded in immobilizing a hydrophilic polymer on the polyvinylidene fluoride resin, and further, the obtained porous film has a high fouling suppressing effect. The heading led to the present invention.
That is, the porous film of the present invention is a porous film composed of a polyvinylidene fluoride resin as a base material and a hydrophilic polymer, and the hydrophilic polymer is composed of a hydrophobic unit and a hydrophilic unit, and is hydrophobic. The repeating unit of the sex unit is methyl methacrylate, and the repeating unit of the hydrophilic unit is poly (ethylene glycol) methyl ether methacrylate.
The abundance ratio O / C of oxygen O and carbon C on the surface of the porous membrane is preferably 0.14 to 0.25.
In addition, the method for producing a porous film of the present invention is a method for producing a porous film by a non-solvent-induced phase separation method from a film-forming stock solution in which a polyvinylidene fluoride resin as a base material polymer and a hydrophilic polymer are dissolved in a good solvent for both. In the membrane method, the hydrophilic polymer consists of a hydrophobic unit and a hydrophilic unit, the repeating unit of the hydrophobic unit is methyl methacrylate, and the repeating unit of the hydrophilic unit is poly (ethylene glycol) methyl ether methacrylate. A hydrophilic polymer is used, and the film-forming stock solution is exposed to air at a relative humidity of 10% or more for 1 second or longer before the film-forming stock solution is coagulated.
The mass ratio of the polyvinylidene fluoride resin to the hydrophilic polymer is preferably 10/1 to 2/1.
The number average molecular weight of the hydrophilic polymer is preferably 10,000 to 55,000.
In the hydrophilic polymer, the molar ratio of the hydrophobic unit to the hydrophilic unit is preferably 95/5 to 85/15.
The number average molecular weight in the hydrophilic unit is preferably 300 to 900.

According to the present invention, it is possible to inexpensively provide a porous membrane having excellent hydrophilicity and durability that can effectively suppress fouling and achieve high filtration performance.

It is a figure which shows the structure of the hydrophilic polymer of this invention. It is an image figure which shows the relationship between the filtration time and the permeation flux obtained when the protein aqueous solution is filtered using the porous membrane of this invention. It is a figure which showed the result of having measured the abundance ratio O / C of oxygen O and carbon C on the surface of the porous membrane of an Example. It is a figure which showed the relationship between the filtration time and the permeation flux when the protein aqueous solution was filtered using the porous membrane of an Example. It is a figure which showed the relationship between the permeation flux retention rate and the abundance ratio O / C of oxygen O and carbon C on the surface of a porous membrane when the protein aqueous solution was filtered using the porous membrane of an Example. It is a figure which showed the relationship between the backflow washing recovery property when the protein aqueous solution was filtered using the porous membrane of an Example, and the abundance ratio O / C of oxygen O and carbon C on the surface of a porous membrane.

Hereinafter, a mode for carrying out the present invention (hereinafter, referred to as the present embodiment) will be described in detail. The present invention is not limited to the following embodiments, and can be used in various modifications within the scope of the gist thereof.

The porous membrane of the present embodiment is composed of polyvinylidene fluoride resin (PVDF), which is a base material polymer, and a hydrophilic polymer. The structure of the hydrophilic polymer that can be used for the porous membrane of this embodiment is shown in FIG. The hydrophilic polymer is composed of a hydrophobic unit a and a hydrophilic unit b. The repeating unit of the hydrophobic unit a is methyl methacrylate (MMA), and the repeating unit of the hydrophilic unit b is poly (ethylene glycol) methyl. It is ether methacrylate (PEGMA), and the hydrophilic polymer is a copolymer (P (MMA-PEGMA)) composed of these. By selecting a hydrophobic unit that is highly compatible with the polyvinylidene fluoride resin, this hydrophobic unit acts as an anchor effect, so that the hydrophilic polymer easily remains in the polyvinylidene fluoride resin during film formation and is firmly fixed. It becomes possible to make it. As a result, the hydrophilic polymer does not easily desorb from the porous membrane during filtration or chemical cleaning, and a porous membrane exhibiting high hydrophilicity over a long period of time can be obtained.

Further, by using polyethylene glycol (PEG) as the hydrophilic side chain c in the hydrophilic unit b, it is a causative substance that deteriorates the water permeability of the porous membrane such as proteins, polysaccharides and humic substances contained in the water to be treated. Contamination (fouling) on the porous membrane can be suppressed.

The porous membrane of the embodiment of the present invention is a porous membrane made of polyvinylidene fluoride resin as a base material. The polyvinylidene fluoride resin is suitable as a material for the porous film of the present invention because it has excellent film-forming properties and excellent mechanical and chemical durability. As the polyvinylidene fluoride resin that can be used in the present invention, a homopolymer or a copolymer of polyvinylidene fluoride can be used. Examples of the copolymer include a polyvinylidene fluoride-hexafluoropropylene copolymer and a polyvinylidene fluoride-chlorotrifluoroethylene copolymer. As the molecular weight of the polyvinylidene fluoride resin, a polymer having a weight average molecular weight of 10,000 to 1,000,000,000 can be used.

In the porous membrane of the embodiment of the present invention, the abundance ratio O / C of oxygen O and carbon C on the surface of the porous membrane is preferably 0.14 to 0.25. When the abundance ratio O / C is 0.14 or more, sufficient hydrophilicity is imparted to the porous membrane, and a high fouling suppressing effect can be obtained. On the other hand, by setting the abundance ratio O / C to 0.25 or less, the porous membrane does not swell excessively with water, and it is possible to prevent the invasion of chemicals and the like into the porous membrane matrick, and it is stable for a long period of time. It becomes possible to use.

The pore size of the porous membrane of the present embodiment is preferably 1 nm to 10 μm, more preferably 2 nm to 1 μm. When the pore diameter is 1 nm or more, the filtration resistance of the porous membrane is low and sufficient water permeability can be obtained, and when the pore diameter is 10 μm or less, a porous membrane having excellent separation performance can be obtained.

In the present embodiment, the pore diameter can be measured by filtering an index substance having a known particle size and setting the size of the index substance having a blocking rate of 90% or more as the pore diameter.
Specifically, by using monodisperse polystyrene particles as an index substance, it is possible to measure a film having a pore diameter of 20 nm or more, and by using a protein as an index substance, fine particles of 20 nm or less can be measured. It is possible to measure a film having a pore size.

The shape of the porous membrane according to the embodiment of the present invention can be applied to either a flat membrane shape or a hollow thread shape. In the case of forming a flat membrane-like porous membrane, the porous membrane of the present invention can be used alone, or a substrate such as a non-woven fabric is used as a support layer, and the porous membrane of the present invention is separated on the substrate. It can also be used as a layered form.

Similarly, in the case of a hollow filament-like porous membrane, the porous membrane of the present invention can be used as a single substance, or the porous membrane layer of the present invention is formed on a substrate such as a non-woven fabric or braid. It is also possible. When used as a hollow filament-like porous membrane, the inner diameter (corresponding to the hollow portion) is preferably 10 μm to 2 mm. If the inner diameter is 10 μm or more, the pressure loss generated when the liquid to be treated or the filtered water flows through the hollow portion can be suppressed low, and if it is 2 mm or less, the membrane packing density per unit volume is high. It is possible to make it compact. Further, the film thickness is preferably 10 μm to 1 mm. When the film thickness is 10 μm or more, sufficient strength can be obtained against the pressure from inside and outside of the hollow filament-shaped porous membrane, and when the film thickness is 1 mm or less, the membrane packing density per unit volume is increased. It is possible to make it compact.

The porous membrane of the embodiment of the present invention is not particularly limited in the membrane-forming method if a film-forming raw material made of polyvinylidene fluoride resin and P (MMA-PEGMA) as a hydrophilic polymer is used. For example, a phase separation method, A porous film can be formed by a stretching opening method, a track etching method, or the like. Above all, phase separation makes it easy to control the pore size and cross-sectional structure of the porous membrane, and is suitable as the method for producing the porous membrane of the present invention.

For example, as a phase separation method, a polyvinylidene fluoride resin and a hydrophilic polymer are dissolved in a solvent capable of dissolving both of them, and then a film-forming stock solution is discharged from a slit-type or double-tube type base to contact with a non-solvent. A non-solvent-induced phase separation method that induces phase separation, or a slit-type or double-tube type mouthpiece after dissolving the polyvinylidene fluoride resin in a latent solvent that does not dissolve at room temperature but dissolves at high temperature together with the hydrophilic polymer. Examples thereof include a heat-induced phase separation method in which a film-forming stock solution is discharged and cooled by contacting with air or water to induce phase separation.

Above all, the non-solvent-induced phase separation method makes it easy to control the pore diameter and cross-sectional structure of the obtained porous membrane, and can segregate more hydrophilic units in the hydrophilic polymer on the surface of the porous membrane. As a result, a porous membrane exhibiting higher hydrophilicity can be obtained, which is preferable.

Further, in the non-solvent-induced phase separation method, it is preferable that the membrane-forming stock solution is exposed to air having a relative humidity of 10% or more for 1 second or more before coagulating in a coagulation bath. At this time, the solvent vapor may be contained in the air. By exposing the membrane-forming stock solution to water-containing air, phase separation proceeds in the membrane-forming stock solution, and more hydrophilic polymers can be segregated on the obtained porous membrane surface, effectively imparting hydrophilicity. It becomes possible to do.

When forming the porous membrane of the present invention using the non-solvent phase separation method, an inorganic or organic additive is further added to the membrane-forming stock solution in which the polyvinylidene fluoride resin and the hydrophilic polymer are dissolved in a solvent. Spinning stability, pore size and film structure of the obtained porous film can be adjusted.

In the method for producing a porous film of the present embodiment, the good solvent that can be used as the solvent for the non-solvent-induced phase separation method is a polyvinylidene fluoride resin or a solvent capable of dissolving 1% by mass or more of a hydrophilic polymer at room temperature. Point to. For example, acetone, tetrahydrofuran, methyl ethyl ketone, N-methyl-2-pyrrolidone, N, N-dimethylformamide, N, N-dimethylacetamide, dimethyl sulfoxide, trimethyl phosphate and the like can be used.

In the method for producing a porous film of the present embodiment, the mass ratio of the polyvinylidene fluoride resin to the hydrophilic polymer (polyvinylidene fluoride resin / hydrophilic polymer) is preferably 10/1 to 2/1. When the ratio of the hydrophilic polymer is 10/1 or more, the obtained porous membrane is imparted with sufficient hydrophilicity and has a high fouling suppressing effect. On the other hand, when the ratio of the hydrophilic polymer is 2/1 or less, the permeation of water and chemicals into the obtained multimembrane can be suppressed, and high durability is exhibited.

Next, regarding the hydrophilic polymer used in the method for producing a porous film of the present embodiment, the molecular weight of the polymer, the molar ratio of the hydrophobic unit to the hydrophilic unit, and the molecular chain length of PEG in the hydrophilic unit will be described.

In the method for producing a porous membrane of the present embodiment, the number average molecular weight of the hydrophilic polymer used is preferably 10,000 to 55,000. When the number average molecular weight is 10,000 or more, most of the hydrophilic polymer remains in the porous membrane after film formation, and does not desorb from the porous membrane during filtration or chemical washing, and maintains high hydrophilicity for a long time. can do. On the other hand, when the number average molecular weight is 55,000 or less, high hydrophilicity can be exhibited without impairing the durability of the polyvinyl fluoride resin which is the base material.

Next, the ratio of the hydrophobic unit to the hydrophilic unit (hydrophobic unit / hydrophilic unit) in the hydrophilic polymer is preferably MMA / PEGMA = 95/5 to 85/15 as the molar ratio of MMA to PEGMA. When the ratio of hydrophilic units in the hydrophilic polymer is 5 or more, that is, the ratio of hydrophobic units to hydrophilic units is 95/5 or more, the porous membrane obtained after film formation has sufficient hydrophilicity and fouling resistance. Has. On the other hand, if the ratio of hydrophilic units in the hydrophilic polymer is 15 or more, that is, the ratio of hydrophobic units to hydrophilic units is 85/15 or less, the hydrophilic polymer is a polyvinylidene fluoride resin due to the anchor effect of the hydrophobic polymer. It is firmly immobilized on the surface, and the porous film can exhibit hydrophilicity for a long period of time.

Further, the number average molecular weight of PEGMA constituting the hydrophilic unit in the hydrophilic polymer is preferably 300 to 900. Here, the number average molecular weight of PEGMA depends on the molecular chain length of PEG in PEGMA, and a large molecular weight of PEGMA means that the molecular chain length of PEG is long. When the number average molecular weight is 300 or more, the molecular chain of PEG exists on the surface of the porous film after the film formation, and it is possible to impart hydrophilicity to the porous film. On the other hand, when the number average molecular weight is 900 or less, the molecular chain of PEG does not block the inside of the pores, and the porous membrane can maintain high water permeability.

In the case of a hollow filament, the porous membrane of the present embodiment is used as a cylindrical or rectangular membrane module in which hundreds to thousands of membranes are bundled and both ends are bonded to a case or the like with epoxy resin or urethane resin. Can be done. On the other hand, in the case of a flat film, it can be used as a film module in which the porous film of the present embodiment is immobilized with an epoxy resin or a urethane resin on a rectangular frame made of resin or metal.

The membrane module made of the porous membrane of the present embodiment can be used for filtering a liquid to be treated containing an inorganic substance or an organic substance. The water to be treated is not particularly limited as long as it is a liquid to which the membrane separation method can be applied. For example, river water, groundwater, lake water, dam water, seawater, sewage, secondary sewage treated water, various factory effluents, pool water. , Bath water, fermented liquid, culture liquid and the like. The liquid to be treated contains inorganic substances and organic substances of various sizes, shapes, and concentrations depending on its use. In river water and the like, examples of organic substances include low molecular weight and high molecular weight humic substances, polysaccharides, proteins and colloidal substances thereof, and examples of inorganic substances include ionic iron, manganese and calcium. Examples thereof include magnesium, aluminum, silica, colloidal substances thereof, and fine particles such as kaolin and bentonite.

The method of filtering the liquid to be treated using the membrane module made of the porous membrane of the present embodiment is not particularly limited, and for example, a method of filtering from the inner surface side to the outer surface side of the porous membrane, and vice versa. There is a method of filtering from the outer surface side to the inner surface side. Further, a filtration method in which the primary side is pressurized and a filtration method in which the secondary side is sucked can be mentioned. Further, the liquid to be treated may be subjected to pretreatment such as coagulation precipitation, pressurized flotation filtration, centrifugation, biological treatment, addition of chemicals, etc. before filtering with the hollow fiber porous membrane.

Further, every time the water to be treated is filtered for a certain period of time, it is possible to perform backflow cleaning with clear water that does not contaminate the porous film such as membrane filtered water or tap water, or air cleaning of the surface of the porous film with a gas such as air. Since the porous membrane of the present embodiment forms a hydrated layer in the vicinity of the membrane surface, it suppresses the adsorption of substances that contaminate the porous membrane of inorganic substances and organic substances in the liquid to be treated to the membrane surface, and the membrane surface during filtration. Even if it is deposited on the membrane, it can be easily peeled off from the membrane surface by backflow cleaning or air cleaning, and the porous membrane can exhibit high water permeability.

Hereinafter, the present embodiment will be described in more detail with reference to Examples and Comparative Examples, but the present embodiment is not limited to these Examples. The measurement method used in this embodiment is as follows. All of the following measurements were performed at 25 ° C.

(1) Polymerization of hydrophilic polymer P (MMA-PEGMA) Methyl methacrylate (MMA, manufactured by Sigma-Aldrich Japan) and poly (ethylene glycol) methyl ether methacrylate (PEGMA, Sigma-Aldrich Japan) at predetermined concentrations shown in Table 1 Was added to ethyl acetate (manufactured by Wako Pure Chemical Industries, Ltd.) to replace the inside of the system with nitrogen. Then, azobisisobutyronitrile (AIBN, manufactured by Wako Pure Chemical Industries, Ltd.) dissolved in ethyl acetate was added, and a polymerization reaction was carried out at 60 ° C. for 5 hours. The obtained polymer was added dropwise to hexane 10 times or more the polymerization solution, the precipitate was filtered, washed with water, and vacuum dried at 60 ° C. for 24 hours. The dried precipitate was dissolved in tetrahydrofuran, added dropwise to hexane having a volume of 10 times or more, the precipitate was filtered, washed with water, and vacuum dried at 60 ° C. for 24 hours. This work was repeated to sufficiently remove impurities. The molecular weight of the obtained hydrophilic polymer was measured by gel permeation chromatography. Using an HPLC device manufactured by Shimadzu Corporation (liquid feed pump: LC-9A, column oven: CTO-20A, detector: RID-10A, degassing unit: DGU-20A3), Showa Denko GPC column: KD- Measurements were made using 804. Here, chloroform was used as the eluent, and the liquid was passed at a flux of 1.0 ml / min. The calibration curve was prepared using a polystyrene standard sample. As a result of the measurement, a hydrophilic polymer P (MMA-PEGMA) having a number average molecular weight of 10,000 to 55,000 was obtained.

(2) Analysis of surface composition of porous membrane: Calculation of abundance ratio O / C The abundance ratio O / C of oxygen O and carbon C on the surface of the porous membrane was determined by X-ray photoelectron spectroscopy (XPS). The porous membrane was fixed to the sample table with double-sided tape, and the measurement was performed under the following conditions.
XPS measuring device: PHI X-tool manufactured by ULVAC-PHI
Excitation source: ALKα, 15kV × 50W
Photoelectron escape angle: 45 °
Path energy: 280 eV
Using the measured spectrum, the relative element concentration of each element was obtained from the area intensities of F1S, O1S, and C1S, and the abundance ratio O / C was calculated.

(3) Measurement of pure water permeation flux A flat membrane-like porous membrane with a membrane area of 6.1 × 10 ^-3 m ² was set in a flat membrane test cell CT10-T manufactured by Nitto Denko, and a cross-flow flow rate of 160 ml / I went on the condition of minutes. First, after filtering for 15 minutes under the condition of the intermembrane differential pressure of 1 bar, the amount of permeated water was measured under the condition of the intermembrane differential pressure of 0.5 bar. From the obtained permeated water amount, the pure water permeated flux J ₀ was determined by the following formula.

(4) flux after the measurement of pure water permeation flux _{J 0} of retention of measurement (3), of 50ppm raw water BSA (Bovine Serum Albumin) protein solution (buffer solution of hydrogen ion concentration pH = 7 using The filtration was performed under the condition of an intermembrane differential pressure of 0.5 bar. Using the permeated flux J 60 minutes after filtration and the pure water permeated flux J ₀ obtained in (3) above, the permeated flux retention rate J / J ₀ was calculated from the following formula.

(5) Measurement of backflow washing recoverability nRF After filtering the 50 ppm BSA protein aqueous solution of (4) above for 60 minutes, pure water is filtered from the secondary side of the porous membrane at 0.1 bar for 2 minutes, and then again on the primary side. A 50 ppm BSA protein aqueous solution was filtered under the condition of an intermembrane differential pressure of 0.5 bar. At this time, the flux of BSA protein solution immediately before backwashing and J _bb, the permeation flux of BSA protein solution immediately after backwashing was set to J _ab. Pure water flux _{J 0,} J _bb, using _{J ab,} by the following equation was calculated backwashing recovery NRf.
FIG. 2 is an image diagram showing the relationship between the filtration time and the permeation flux when the BSA protein aqueous solution is filtered using the porous membrane of the present invention. The relationship between the J0, Jbb, and Jab parameters in the above equation is as shown in this figure.

[Examples 1 to 4, Comparative Example 1]
Kynar741 (manufactured by Alchema) as a polyvinylidene fluoride resin (PVDF) and poly (ethylene glycol) methyl ether methacrylate (PEGMA) as a hydrophilic polymer have a number average molecular weight of 475 and an MMA / PEGMA molar ratio of 90/10. Using a certain P (MMA-PEGMA) (listed in No. 2 of Table 1), the mass ratio of PVDF / P (MMA-PEGMA) of these polymers is 100/0, 10/1, 8/1, 4 In addition to the solvent dimethylacetamide (DMAC), it was dissolved at 60 ° C. for 24 hours so as to be 1/1 and 2/1, and the results were compared with Comparative Example 1, Example 1, Example 2, and Example 3, respectively. The polymer solution of Example 4 was obtained. Then, the obtained polymer solution was degassed under vacuum for 24 hours to prepare a membrane-forming stock solution. The composition of each membrane-forming stock solution is shown in Table 2. The obtained undiluted film-forming solution is applied to a non-woven fabric placed on a glass plate to a thickness of 200 micrometers, left in air at a relative humidity of 30% for 10 seconds, and then immersed in deionized water for 10 minutes. Then, the undiluted membrane-forming solution was solidified to obtain a porous membrane. The obtained porous membrane was subsequently subjected to deionized water to remove DMAC remaining in the porous membrane.

The composition of the elements on the surface of the porous film thus formed was measured by XPS. The abundance ratio O / C of oxygen O and carbon C obtained as a measurement result is shown in FIG. As the ratio of the hydrophilic polymer in the membrane-forming stock solution increases, the abundance ratio O / C of the porous membrane surface also increases, indicating that the porous membrane surface is modified with the hydrophilic polymer. Further, FIG. 4 shows the relationship between the filtration time and the permeation flux obtained when a 50 ppm BSA protein aqueous solution was filtered with an intermembrane differential pressure of 0.5 bar using the obtained porous membrane. When the ratio of the hydrophilic polymer in the membrane-forming stock solution was high, the permeation flux after filtration for 60 minutes was also high, and the recovery by the backflow washing performed thereafter was also high.

The relationship between the abundance ratio O / C of the porous surface, the permeation flux retention rate J / J ₀ × 100 when the protein aqueous solution is filtered, and the backflow washing recovery nRF is shown in FIGS. 5 and 6, respectively. It is shown (see the symbol “◯” in FIGS. 5 and 6). From the figure, it can be seen that the higher the abundance ratio O / C, the higher the permeation flux retention rate and the backflow cleaning recovery property, and by adding the hydrophilic polymer of the present invention to the polyvinylidene fluoride resin, the surface of the porous membrane is surfaced. It was confirmed that the abundance ratio O / C was increased, and as a result, the fouling resistance of the porous membrane was improved.
From the above results, by using the porous membrane of the present invention, a highly hydrophilic porous membrane can be obtained, and further, the obtained porous membrane suppresses fouling, and has high filtration flux and backflow washing recovery. Was shown to have.

[Examples 5 and 6]
Similar to Examples 1 to 4 except that P (MMA-PEGMA) having an MMA / PEGMA molar ratio of 95/5 and 85/15 was used as the hydrophilic polymer (listed in Nos. 1 and 3 of Table 1). The porous membranes of Examples 5 and 6 were prepared by the method of. The abundance ratio O / C of the obtained porous membrane surface, the permeation flux retention rate J / J ₀ × 100 when the BSA protein aqueous solution was filtered, and the backflow washing recovery nRF are shown in FIGS. 5 and 6, respectively. (See reference numerals “□” in FIGS. 5 and 6). As the molar ratio of PEGMA, which is a hydrophilic unit in the hydrophilic polymer, increases, the abundance ratio O / C of the porous membrane surface also increases, and as a result, the permeation flux retention rate J / J ₀ × 100 and the backflow washing recovery nRF It turns out that it also becomes higher.

[Examples 7 and 8]
Examples 1 to 4 except that P (MMA-PEGMA) having a number average molecular weight of 300 and 900 of PEGMA constituting the hydrophilic unit was used as the hydrophilic polymer (described in Nos. 4 and 5 in Table 1). A porous membrane was prepared in the same manner as in the above. The abundance ratio O / C of the obtained porous membrane surface, the permeation flux retention rate J / J ₀ × 100 when the BSA protein aqueous solution was filtered, and the backflow washing recovery nRF are shown in FIGS. 5 and 6, respectively. (See reference numeral “Δ” in FIGS. 5 and 6). As the number average molecular weight of PEGMA constituting the hydrophilic unit in the hydrophilic polymer increases, the abundance ratio O / C of the porous membrane surface also increases, and as a result, the permeation flux retention rate J / J ₀ × 100 and backflow washing recovery It can be seen that the sex nRF also increases.

According to the present invention, there is provided a porous membrane having excellent hydrophilicity and durability, which suppresses membrane fouling and can achieve high filtration performance, which is suitable as an ultrafiltration membrane or a microfiltration membrane, and a method for producing the same. can do.
The present invention has industrial applicability in a wide range of fields to which ultrafiltration membranes and microfiltration membranes are applied, such as water treatment fields and food and pharmaceutical manufacturing.

a Hydrophobic unit b Hydrophilic unit c Hydrophilic side chain

Claims (6)

It is a porous film composed of a polyvinylidene fluoride resin which is a base material polymer and a hydrophilic polymer, and the hydrophilic polymer is composed of a hydrophobic unit and a hydrophilic unit, and the repeating unit of the hydrophobic unit is methyl methacrylate, wherein the repeating units of the hydrophilic units poly (ethylene glycol) Ri methyl ether methacrylate der abundance ratio O / C of oxygen O and carbon C of the porous membrane surface 0.14 to 0.25 der Porous membrane. This is a film-forming method for producing a porous film by a non-solvent-induced phase separation method from a film-forming stock solution prepared by dissolving a polyvinylidene fluoride resin as a base material polymer and a hydrophilic polymer in both good solvents, and the hydrophilic polymer is hydrophobic. A hydrophilic polymer composed of a sex unit and a hydrophilic unit, wherein the repeating unit of the hydrophobic unit is methyl methacrylate and the repeating unit of the hydrophilic unit is poly (ethylene glycol) methyl ether methacrylate is used, and further, the above-mentioned A method for producing a porous film, in which the undiluted film-forming solution is exposed to air at a relative humidity of 10% or more for 1 second or longer before the undiluted film-forming solution is coagulated. The method for producing a porous membrane according to claim 2 , wherein the mass ratio of the polyvinylidene fluoride resin to the hydrophilic polymer is 10/1 to 2/1. The method for producing a porous membrane according to claim 2 or 3 , wherein the hydrophilic polymer has a number average molecular weight of 10,000 to 55,000. The method for producing a porous membrane according to any one of claims 2 to 4 , wherein in the hydrophilic polymer, the molar ratio of the hydrophobic unit to the hydrophilic unit is 95/5 to 85/15. The method for producing a porous membrane according to any one of claims 2 to 5, wherein the number average molecular weight of the hydrophilic units is 300 to 900.