Separation membrane and method for manufacturing the same, as well as membrane separation element and wastewater treatment method using the same

Abstract

The present invention is a separation membrane in which a polymer film having a separation function is formed on a separation membrane support, wherein the maximum pore diameter of the surface of the separation membrane is 10-120 nm. The separation membrane has a porosity of 40-80% when a region within 15 μm from the surface of the separation membrane is measured by a confocal laser microscope, and exhibits fouling resistance and high water permeability as a separation membrane for sewage treatment applied to a membrane separation activated sludge method.

Description

[Technical Field]

[0001] The present invention provides a separation membrane that achieves both water permeability and fouling resistance when manufacturing a separation membrane used in water treatment. [Background technology]

[0002] In recent years, water treatment has made extensive use of membrane technology, which removes impurities from water using filtration membranes with micropores. For example, microfiltration membranes and ultrafiltration membranes are used in water treatment plants, and reverse osmosis membranes are used in seawater desalination. In addition, reverse osmosis membranes and nanofiltration membranes are used for treating water for semiconductor manufacturing, boiler water, medical water, and laboratory pure water. For wastewater treatment, membrane separation activated sludge methods using microfiltration membranes and ultrafiltration membranes are also applied.

[0003] Filtration membranes (separation membranes) used in water treatment are broadly classified into flat membranes and hollow fiber membranes based on their shape. Flat membranes, formed from synthetic polymers, have poor mechanical strength as standalone membranes with separation functions, and are therefore generally used in conjunction with a support such as a nonwoven or woven fabric. As such a support, nonwoven fabrics offer excellent productivity and processability because they can be obtained as a sheet without going through the weaving process, and spunbond nonwoven fabrics made from long fibers, in particular, provide sufficient support strength.

[0004] The method for forming a flat film on a support involves casting a polymer solution containing a separation film-forming component onto the support and allowing it to adhere. While strong adhesion between the flat film and the support is achieved if the polymer solution penetrates deep into the support, excessive penetration of the polymer solution to the back surface of the support can contaminate the film-forming equipment and cause defects in the subsequent separation film. Furthermore, when manufacturing a membrane separation element using the separation film, insufficient adhesion between the support plate (flow channel material) and the separation film can reduce the durability of the membrane separation element. Therefore, it is crucial that the support has adequate adhesion to the separation film-forming component.

[0005] In addition, since the separation membrane for lower wastewater treatment used in the membrane separation activated sludge process (hereinafter referred to as MBR) is used for a long time in a state where the separation membrane is immersed in activated sludge, the secretion substances and the dead bodies themselves discharged by the activated sludge, and the adhesion and deposition of impurities contained in the sludge to the membrane (hereinafter, the adhesion and deposition of sludge components to the membrane are referred to as "fouling") cause the membrane pores to be blocked and the water permeability performance to decrease. Although the attached substances and deposits can be removed by membrane cleaning using chemicals, there are many problems in terms of economy and environment such as the suspension of the filtration operation during cleaning and the waste liquid treatment of the chemicals. Therefore, it is important for the separation membrane to have fouling resistance.

[0006] Furthermore, in the separation membrane, it is required to increase the water permeability while maintaining the pore diameter corresponding to the filtration target. However, if an attempt is made to increase the water permeability, the pore diameter becomes too large, and cracks may occur on the surface, resulting in a decrease in the above-mentioned fouling resistance. That is, it is important to balance the fouling resistance and the water permeability.

[0007] Separation membrane supports having excellent film-forming properties and dimensional stability and high adhesion strength to the membrane have been proposed when manufacturing microfiltration membranes, ultrafiltration membranes, nanofiltration membranes, reverse osmosis membranes, etc. (see Patent Document 1). In addition, separation membrane supports having excellent film-forming properties and high mechanical strength and furthermore excellent water permeability have been proposed (see Patent Document 2). Furthermore, separation membranes having high fouling resistance (exclusion rate of sludge components) by controlling the composition of the polymer solution containing the separation membrane-forming components have been proposed (see Patent Document 3). And MBR separation membranes having high water permeability and fouling resistance by hydrophilizing the separation membrane have been proposed (see Patent Document 4).

Prior Art Documents

Patent Documents

[0008]

Patent Document 1

Patent Document 2

[0009] The technique described in Patent Document 1 is a separation membrane support composed of polyethylene terephthalate fibers with controlled high-density and low-density parts by partial thermocompression bonding. Since the affinity with the separation membrane forming component is poor, the adhesion between the separation membrane and the separation membrane support is low. In addition, since the porosity inside the separation membrane is not controlled, there is a problem of poor water permeability.

[0010] The technique described in Patent Document 2 is to impart an affinity with the separation membrane forming component by applying a hydrophilic agent to the separation membrane support, so the adhesion between the separation membrane and the separation membrane support is improved. However, since the hydrophilicity inside the separation membrane support remains low, the porosity inside the separation membrane is low and there is a problem of poor water permeability.

[0011] The technique described in Patent Document 3 is a separation membrane formed by adding polyethylene glycol as a pore-forming agent during film formation. By uniformizing and miniaturizing the surface pore diameter, fouling resistance is imparted. However, it is a separation membrane support composed of polyethylene terephthalate fibers, and since the affinity with the separation membrane forming component is poor, the adhesion between the separation membrane and the separation membrane support is low, the porosity inside the separation membrane is also low, and there is a problem of poor water permeability.

[0012] The technique described in Patent Document 4 is a separation membrane with particulate hydroxybutyl cellulose fixed on the surface as a hydrophilic agent, and fouling resistance can be imparted. However, the separation membrane support is composed of polyethylene terephthalate fibers, and since the affinity with the separation membrane forming component is poor, the adhesion between the separation membrane and the separation membrane support is low, and the porosity inside the separation membrane is also low, so there is a problem of poor water permeability.

[0013] Therefore, the present invention aims to provide a separation membrane for use in MBRs, such as for lower wastewater treatment, that exhibits excellent adhesion between the separation membrane and the separation membrane support, and achieves both fouling resistance and water permeability, by controlling the pore size on the separation membrane surface and the void ratio inside the separation membrane. [Means for solving the problem]

[0014] The present invention aims to solve the above-mentioned problems, and according to the present invention, the following invention is provided. [1] A separation membrane having a polymer membrane having a separation function formed on a separation membrane support, The separation membrane support contains polyethylene glycol in an amount of 0.4% by mass or more and 3.0% by mass or less. The maximum pore diameter on the surface of the separation membrane is 10 nm to 120 nm, and the porosity when measured with a confocal laser microscope in a region within 15 μm from the surface of the separation membrane is 57 A separation membrane with a viscosity of % or more and 80% or less. [2] The void ratio 60 The separation membrane described in [1] above, wherein the concentration is between % and 80%. [3] The separation membrane according to [1] or [2], wherein the standard deviation of the average pore size on the surface of the separation membrane is 30 nm or less. [4] The separation membrane according to any one of [1] to [3] above, wherein the water absorption of the separation membrane support is such that the height of the rising water, as evaluated by the JIS-L1907 (2010) Baylek method, is 100 mm or more and 180 mm or less. [5 ] The polyethylene glycol contained in the separation membrane support has a molecular weight of 1000 or more and 35000 or less. 1]~[4 ] either The separation membrane described above. [ 6 The polymer membrane having the separation function is composed of polyvinylidene fluoride, as described in [1]~[ 5 ] either The separation membrane described above. [ 7 A method for producing a separation membrane, comprising the steps of: a) casting a polymer solution containing a component for forming a polymer membrane having a separation function onto one side of the separation membrane support; and b) forming a separation membrane by solidifying the polymer solution in a coagulation solution. The polymer solution contains polyoxyalkylenes as a poro-opening agent,In step b), within 3 seconds after immersing the polymer solution in the coagulation solution, the flow of the coagulation solution is formed in the direction of the polymer solution being cast from the separation membrane support, [1] or [2] A method for producing the separation membrane described above. [ 8 [1]~[ 6 ] either A membrane separation element characterized by containing the separation membrane described above. [ 9 ]the aforementioned[ 8 A wastewater treatment method that applies the membrane separation element described in [ ] to the membrane separation activated sludge method. [Effects of the Invention]

[0015] According to the present invention, by controlling the maximum pore diameter on the surface of the separation membrane and maintaining the porosity inside the separation membrane within a certain range, fouling resistance and high water permeability can be obtained. [Modes for carrying out the invention]

[0016] [Separation membrane] The separation membrane of the present invention is a separation membrane in which a polymer membrane having a separation function is formed on a separation membrane support.

[0017] The maximum pore diameter on the surface of the separation membrane of the present invention is 10 nm or more and 120 nm or less. By setting the maximum pore diameter to 10 nm or more, preferably 30 nm or more, and more preferably 50 nm or more, the suction pressure per pore can be reduced, and water permeability can be obtained. On the other hand, by setting the maximum pore diameter to 120 nm or less, preferably 100 nm or less, fouling resistance is improved, and water permeability can be maintained over a long period of time.

[0018] The standard deviation of the average pore size on the surface of the separation membrane of the present invention is preferably 30 nm or less. More preferably, the standard deviation of the average pore size is 25 nm or less, and even more preferably 20 nm or less, resulting in a uniform pore size, which suppresses localized adhesion and accumulation of sludge components on the membrane and allows for long-term maintenance of water permeability.

[0019] The porosity of the separation membrane of the present invention, measured using a confocal laser microscope within 15 μm of the surface, is 40% to 80%. A porosity of 40% or more, preferably 57% or more, more preferably 60% or more, and even more preferably 70% or more, allows for the formation of water channels within the separation membrane, improving water permeability. On the other hand, a porosity of 80% or less, preferably 75% or less, maintains the strength of the separation membrane.

[0020] The porosity of the separation membrane can be measured and calculated using a confocal laser microscope. Specifically, it is as follows: (1) Stain the separation membrane with a fluorescent substance (3,3,3',3'-tetramethyl-1,1'-bis(4-sulfobutyl)indocarbocyanine sodium). (2) Using a confocal laser microscope, the laser beam is positioned so that the axis of the laser beam is perpendicular to the surface of the separation membrane, and a 200 μm × 200 μm area is observed parallel to the surface, and areas perpendicular to the surface up to 20 μm are observed at 0.1 μm intervals. (3) From the three-dimensional image obtained by stitching together the images, a cross-sectional image perpendicular to the surface of the separation membrane is extracted, and the area S1 from the surface to 15 μm is calculated. (4) The observed cross-sectional image is binarized to separate the structural portion consisting of the separation membrane forming component from the pore portion, and the pore area S2 is calculated within 15 μm from the separation membrane surface. (5) Using the area values ​​obtained in (3) and (4) above, the void ratio (%) is calculated from the following formula. Porosity=S2 / S1×100 The separation membrane of the present invention is preferably formed by casting and fixing a polymer solution containing a separation membrane-forming component onto at least one surface of a separation membrane support.

[0021] The separation membrane-forming component is preferably a solution of polyaryl ethersulfones such as polysulfones and polyethersulfones, polyimide, polyvinylidene fluoride, and cellulose acetate, which have separation function when formed into a separation membrane.

[0022] Among these, solutions containing polysulfone, polyaryl ethersulfone, or polyvinylidene fluoride are more preferred in terms of chemical, mechanical, and thermal stability, and polyvinylidene fluoride solutions are particularly preferred.

[0023] The thickness of the polymer membrane in the separation membrane of the present invention is preferably 50 μm or more and 500 μm or less. A polymer membrane thickness of 50 μm or more is preferable, more preferably 80 μm or more, and even more preferably 100 μm or more, which prevents exposure of the separation membrane support, exhibits fouling resistance, and suppresses the increase in filtration pressure. On the other hand, a polymer membrane thickness of 500 μm or less is preferable, more preferably 300 μm or less, and even more preferably 200 μm or less, which suppresses a decrease in water permeability, allows for an increase in the number of separation membrane layers per membrane separation element, and improves filtration performance.

[0024] The adhesive strength between the separation membrane and the separation membrane support of the present invention is preferably 1070 gf / 25 mm or more. By having an adhesive strength of 1070 gf / 25 mm or more, more preferably 1150 gf / 25 mm or more, and even more preferably 1250 gf / 25 mm or more, the separation membrane and the separation membrane support adhere firmly, suppressing the peeling of the separation membrane from the separation membrane support during long-term use or cleaning operations.

[0025] [Separation membrane support] A spunbond nonwoven fabric is preferred as the support for the separation membrane of the present invention. Spunbond nonwoven fabrics are long-fiber nonwoven fabrics composed of thermoplastic fibers. When used as a support for separation membranes, they can suppress non-uniformity and membrane defects caused by fluffing, which are common when using short-fiber nonwoven fabrics, during the casting of polymer solutions. Furthermore, spunbond nonwoven fabrics have excellent mechanical strength, allowing for the creation of highly durable separation membranes when used as a support.

[0026] The thermoplastic polymer constituting the separation membrane support of the present invention can be formed from, for example, polyester polymers, polyamide polymers, polyolefin polymers, or mixtures or copolymers thereof. Among these, polyester polymers can be used to obtain a separation membrane support with superior mechanical strength, heat resistance, water resistance, and chemical resistance.

[0027] Polyester polymers are polyesters composed of a dicarboxylic acid component and a diol component. Examples of dicarboxylic acid components include aromatic dicarboxylic acid compounds such as terephthalic acid, isophthalic acid, and sodium 5-sulfoisophthalate; aliphatic dicarboxylic acid compounds such as adipic acid and sebacic acid; and alicyclic dicarboxylic acid compounds such as cyclohexanedicarboxylic acid. Ester-forming derivatives of these compounds, particularly dimethyl derivatives, are preferred. For the purpose of improving mechanical strength, it is preferable to use terephthalic acid or its dimethyl derivative and isophthalic acid or its dimethyl derivative. As the diol component, 1,4-butanediol, 1,3-propanediol, ethylene glycol, or a combination thereof can be used. Ethylene glycol is preferred due to its excellent dimensional stability.

[0028] Examples of polyester polymers include polyethylene terephthalate, polybutylene terephthalate, polytrimethylene terephthalate, polyethylene naphthalate, polylactic acid, and polybutylene succinate, as well as copolymers thereof. Polyethylene terephthalate is preferably used due to its superior strength.

[0029] The thermoplastic fibers constituting the separation membrane support of the present invention may be single-component fibers, composite fibers composed of multiple components, or so-called blended fibers made by mixing multiple types of fibers. As a composite fiber, a composite fiber is preferred in which a high-melting-point polymer is used as the core component or island component, and a low-melting-point polymer having a melting point lower than that of the high-melting-point polymer is arranged as the sheath component or sea component. By using a composite fiber, the fibers are strongly bonded to each other by heat-pressing during the manufacture of the nonwoven fabric, so when used as a separation membrane support, non-uniformity during casting of the polymer solution due to fluffing and membrane defects can be suppressed. Although the adhesion between fibers is also good in blended fibers made by mixing fibers made only of high-melting-point polymers and fibers made only of low-melting-point polymers, composite fibers have a larger number of bonding points, and the improvement in mechanical strength when used as a separation membrane support is particularly good.

[0030] Examples of composite fiber configurations that efficiently provide thermal bonding points between fibers include concentric core sheath type, eccentric core sheath type, and sea-island type. Examples of fiber cross-sectional shapes include circular, flat, polygonal, multi-lobed, and hollow cross-sections. A concentric core sheath configuration and circular or flat cross-sectional fiber cross-sections are preferable because they strengthen the bonding between fibers by thermal compression, reduce the thickness of the resulting separation membrane support, and save space when used as a membrane separation element.

[0031] The components of the composite fiber preferably consist of a high-melting-point polymer for the core component and a low-melting-point polymer for the sheath component, with a melting point difference of 15°C or more and 45°C or less. That is, it is preferable that the melting point of the sheath component be between [melting point of core component - 45]°C and [melting point of core component - 15]°C. By setting the melting point difference to 15°C or more (the melting point of the sheath component being between [melting point of core component - 15]°C), preferably 20°C or more, only the low-melting-point polymer of the sheath component can be bonded in the heat-sealing process, and the strength of the high-melting-point polymer placed in the core can be maintained. This improves the mechanical strength of the separation membrane support. In addition, the basis weight of the nonwoven fabric can be controlled by heat-sealing, improving the permeability of the separation membrane forming component and improving the adhesion between the separation membrane and the separation membrane support.

[0032] On the other hand, by setting the melting point difference to 45°C or less (the melting point of the sheath component being [the melting point of the core component - 45]°C or higher), preferably 40°C or less, excessive adhesion of the low-melting-point polymer of the sheath component can be suppressed during heat-pressing. This allows for control of the basis weight of the nonwoven fabric, suppression of reduced permeability of the separation membrane-forming component to the nonwoven fabric, and improvement of adhesion between the separation membrane and the separation membrane support. Furthermore, the decomposition of the low-melting-point polymer of the sheath component during spinning can be suppressed, thereby suppressing yarn breakage and improving the mechanical strength of the separation membrane support.

[0033] The melting point difference of polymers can be controlled to a desired range by the copolymerization amount of the polymer. As a melting point control substance in low-melting-point polymers of sheath components, dicarboxylic acid components are preferred considering copolymerization to polyester, with isophthalic acid, cyclohexanedicarboxylic acid, naphthalenedicarboxylic acid, adipic acid, and sebacic acid being more preferred, and isophthalic acid being even more preferred due to its good polymerizability during copolymerization. These dicarboxylic acid components are preferably present in an amount of 5 mol% to 25 mol% relative to the total acid components from the viewpoint of controlling the melting point. The dicarboxylic acid component is preferably 5 mol% or more, more preferably more than 8 mol%, and even more preferably more than 11 mol%. On the other hand, by setting the dicarboxylic acid component to 25 mol% or less, more preferably less than 22 mol%, the melting point difference between high-melting-point polymers and low-melting-point polymers can be controlled to a desired range.

[0034] The melting point of the core component high-melting-point polymer is preferably 160°C to 320°C. When used as a separation membrane support composed of composite fibers, it provides good film-forming properties and a separation membrane with excellent durability. A more preferable melting point for the high-melting-point polymer is 170°C or higher, and even more preferably 180°C or higher. Even after passing through the heating process during the manufacture of the separation membrane or membrane separation element, a separation membrane with excellent mechanical strength, dimensional stability, and durability can be obtained. On the other hand, by setting the melting point of the core component high-melting-point polymer to more preferably 300°C or lower, and even more preferably 280°C or lower, the spinning temperature can be suppressed, particularly by inhibiting the decomposition of the sheath component low-melting-point polymer. This suppression of polymer decomposition reduces yarn breakage during spinning and provides mechanical strength for the separation membrane support.

[0035] The method for measuring and calculating the melting points of the core and sheath components from the composite thermoplastic fibers constituting the separation membrane support shall be as follows. (1) After peeling off the separation membrane with tape or the like, take 5 mg of the measurement sample from the separation membrane support and, as a pretreatment, melt it at 290°C for 5 minutes under a nitrogen atmosphere, then rapidly cool it to room temperature at 50°C / min. (2) Using a differential scanning calorimeter (DSC, for example, TA Instruments' "Q-2000"), measure the melting point under the following conditions. • Heating rate: 2°C / min • Measuring temperature: -20°C to 300°C (3) The melting points (°C) of the core component and sheath component obtained in (2) above are rounded to the first decimal place. (4) A sample is taken again from the separation membrane support, treated with alkali, and the sheath component is eluted to obtain a thread consisting only of the core component. (5) Take a 5 mg sample obtained in (4) and pre-process it in the same manner as in (1). (6) The sample pre-treated in (5) above is subjected to DSC measurement in the same manner as described in (2) to determine the melting point of the core component. (7) Determine the melting point of the sheath component from the melting points obtained in (3) and (6) above.

[0036] When the thermoplastic fibers constituting the separation membrane support of the present invention are core-sheath composite fibers, the composite mass ratio (core:sheath) is preferably 50% to 95% by mass for the core component (composite mass ratio (core:sheath) is 50:50 to 95:5). By setting the core component to 50% by mass or more, more preferably 60% by mass or more, and even more preferably 70% by mass or more, excessive adhesion of the low-melting-point polymer of the sheath component can be suppressed during heat-pressing when manufacturing the nonwoven fabric. This allows for control of the thickness of the nonwoven fabric and suppresses a decrease in the permeability of the coagulation liquid from the support side when using spunbond nonwoven fabric as a separation membrane support. Suppressing the decrease in the permeability of the coagulation liquid improves the porosity of the separation membrane surface, thereby improving the water permeability of the formed separation membrane. On the other hand, by setting the composite mass ratio of the core component to 95% by mass or less, more preferably 90% by mass or less, and even more preferably 80% by mass or less, the low-melting-point polymer of the sheath component adheres more easily, the thickness of the nonwoven fabric can be controlled, and consequently the mechanical strength of the separation membrane support can be improved.

[0037] The separation membrane support of the present invention is preferably hydrophilic. By using a hydrophilic spunbond nonwoven fabric as the separation membrane support, a separation membrane with high water permeability can be obtained. The mechanism is hypothesized to be as follows. In other words, separation membranes are often formed by casting and fixing a polymer solution containing separation membrane-forming components onto a separation membrane support. However, a widely used method involves immersing the cast polymer solution, along with the support, in a coagulation solution, the main component of which is water. In this case, by using a hydrophilic spunbond nonwoven fabric as the separation membrane support, the coagulation solution efficiently penetrates into the support from the opposite side of where the polymer solution is cast, and the coagulation solution efficiently contacts and coagulates the polymer solution from all directions, allowing the separation membrane to form rapidly. From this, it is thought that highly permeable voids can be formed within the separation membrane, and the porosity of the separation membrane surface can also be improved.

[0038] Furthermore, when immersing the polymer solution in the coagulation solution to fix it, pushing the coagulation solution from the opposite side of where the polymer solution was cast allows a water permeable channel to be formed up to the surface of the membrane. This increases the permeability within the separation membrane, resulting in a separation membrane with high water permeability. Moreover, the penetration of the coagulation solution from the opposite side of where the polymer solution was cast suppresses the seepage of the separation membrane-forming component to the back surface due to excessive penetration. This reduces contamination of the membrane-forming equipment and the decrease in adhesion to the channel material, thereby improving productivity and maintaining the durability of the membrane separation element.

[0039] The water absorption (hydrophilicity) of the separation membrane support of the present invention is preferably such that the height of the rising water, as evaluated by the Bylec method (after immersion in water for 10 minutes), is 100 mm or more and 180 mm or less. The height of the rising water is preferably 100 mm or more, more preferably 120 mm or more, and even more preferably 150 mm or more. The spunbond nonwoven fabric has high hydrophilicity, and when used as a separation membrane support, the coagulation bath penetrates quickly, forming highly permeable voids within the separation membrane, thereby improving the water permeability of the formed separation membrane.

[0040] The present invention can impart water absorption to the separation membrane support by hydrophilizing the constituent polymer of the thermoplastic fibers of the spunbond nonwoven fabric or by applying a hydrophilic agent. However, hydrophilizing the constituent polymer of the thermoplastic fibers constituting the separation membrane support is preferred because it provides a high hydrophilic effect and uniformly hydrophilizes the interior of the separation membrane support.

[0041] Hydrophilization of the constituent polymer of the thermoplastic fiber can be achieved by copolymerization with metal sulfonate group-containing isophthalic acid components or polyethylene glycol, but copolymerization with polyethylene glycol is preferable from the viewpoint of suppressing viscosity increase during copolymerization and achieving hydrophilization effect.

[0042] The copolymerization rate of polyethylene glycol to the separation membrane support of the present invention is preferably 0.4% by mass or more and 3.0% by mass or less. By setting the copolymerization rate to 0.4% by mass or more, more preferably 0.8% by mass or more, and even more preferably 1.6% by mass or more, the hydrophilicity of the separation membrane support is improved, and when used as a separation membrane support, the coagulation bath penetrates rapidly from the support side, promoting the formation of highly permeable voids within the separation membrane and improving the porosity of the separation membrane surface, thereby improving the water permeability of the formed separation membrane. On the other hand, by setting the copolymerization rate to preferably 2.8% by mass or less, yarn breakage due to thickness during spinning can be suppressed, and consequently the strength of the separation membrane support can be increased.

[0043] In a preferred embodiment, the polyethylene glycol is copolymerized with the sheath component of the fibers constituting the nonwoven fabric. By copolymerizing with the sheath component, the surface of the separation membrane support can be made hydrophilic, and consequently, when used as a separation membrane support, the coagulation bath can quickly penetrate from the support side, promoting the formation of highly permeable voids within the separation membrane and improving the porosity of the separation membrane surface, thereby improving the water permeability of the formed separation membrane.

[0044] Furthermore, the copolymerization rate of polyethylene glycol in nonwoven fabrics, and the copolymerization rate of polyethylene glycol in the sheath component of the composite fibers constituting the nonwoven fabrics, can be measured and calculated using nuclear magnetic resonance (NMR) spectroscopy. Specifically, the methods are as follows: (1) After peeling off the separation membrane with tape or the like, take 50 mg of the measurement sample from the separation membrane support and dissolve it in 1 mL of deuterated hexafluoroisopropanol (HFIP). (2) As the measuring device, for example, use the "AL-400" manufactured by JEOL Ltd., and the measurement conditions are as follows: 1 NMR measurements were performed using H-NMR with 128 cumulative measurements. (3) The copolymerization rate (mass%) of polyethylene glycol in the separation membrane support is calculated from the integral value of the CH2 peak in polyethylene glycol obtained by NMR measurement and the integral value of (H) of the benzene ring in the polyester polymer. (4) A sample is taken again from the separation membrane support, treated with alkali, and the sheath component is eluted to obtain a thread consisting only of the core component. (5) Dissolve 50 mg of the sample obtained in (4) in 1 mL of deuterated hexafluoroisopropanol (HFIP). (6) Perform the NMR measurement described in (2) above, and calculate the polyethylene glycol copolymerization rate (mass%) in the core component from the integral value of the CH2 peak in polyethylene glycol and the integral value of (H) of the benzene ring in the polyester polymer. (7) The copolymerization rate of polyethylene glycol in the nonwoven fabric is calculated by subtracting the copolymerization rate of polyethylene glycol in the core component (mass%) from the copolymerization rate of polyethylene glycol in the nonwoven fabric (mass%), and then dividing by the sheath ratio. The sheath ratio is calculated by observing the cross-section of the nonwoven fabric yarn.

[0045] In the separation membrane support of the present invention, when the copolymer component of the thermoplastic fiber constituent polymer is polyethylene glycol, it is preferable that the number average molecular weight of polyethylene glycol is 1,000 or more and 35,000 or less. By setting the number average molecular weight of polyethylene glycol to 1,000 or more, more preferably 3,000 or more, even more preferably 4,000 or more, and particularly preferably 7,000 or more, the hydrophilicity of the separation membrane support is improved. When used as a separation membrane support, the coagulation bath penetrates rapidly from the support side, promoting the formation of highly permeable voids within the separation membrane and improving the porosity of the separation membrane surface, thereby improving the water permeability of the formed separation membrane. On the other hand, by setting the number average molecular weight to 35,000 or less, more preferably 20,000 or less, a decrease in reactivity during copolymerization can be suppressed, and when a nonwoven fabric is used as a separation membrane support, the elution of internal materials of the support into water can be suppressed. Furthermore, yarn breakage due to thickness during spinning can be suppressed, and consequently, the strength of the separation membrane support can be increased.

[0046] The number-average molecular weight of polyethylene glycol contained in the separation membrane support can be measured and calculated using gel permeation chromatography (GPC). Specifically, it is as follows: (1) After peeling off the separation membrane with tape or the like, take 50 mg of the measurement sample from the separation membrane support into a sealable vial, add 1 mL of 28% by mass aqueous ammonia, and heat at 120°C for 5 hours to dissolve the sample. (2) After cooling, add 1.5 mL of 6 mol / L hydrochloric acid and dilute to 5 mL with purified water. After centrifugation, filter through a 0.45 μm filter to obtain the filtrate. (3) As a measuring device, for example, a differential refractive index detector RID-20A manufactured by Shimadzu Corporation is used to perform GPC measurement of the filtrate. (4) The molecular weight of polyethylene glycol in the nonwoven fabric is calculated using a molecular weight calibration curve prepared using standard samples of known molecular weights.

[0047] The single filament fineness of the thermoplastic fibers in the separation membrane support of the present invention is preferably 0.1 dtex to 3.0 dtex, more preferably 0.3 dtex to 2.5 dtex, and even more preferably 0.5 dtex to 2.0 dtex. If the single filament fineness of the thermoplastic fibers constituting the separation membrane support is 0.1 dtex or higher, the spinnability does not decrease significantly during nonwoven fabric manufacturing, and when used as a separation membrane support, it maintains breathability, allowing the polymer solution cast during film formation to quickly penetrate into the interior of the separation membrane support, resulting in a nonwoven fabric with good adhesion to the separation membrane. On the other hand, if the single filament fineness of the thermoplastic fibers constituting the separation membrane support is 3.0 dtex or lower, when used as a separation membrane support, it can be made denser, resulting in less over-penetration during polymer solution casting and a good nonwoven fabric. Fibers with different finenesses may be blended.

[0048] The average single fiber diameter of the thermoplastic fibers constituting the separation membrane support is preferably 3 μm to 30 μm, more preferably 5 μm to 25 μm, and even more preferably 7 μm to 20 μm. If the average single fiber diameter of the thermoplastic fibers constituting the separation membrane support is 3 μm or more, the spinnability is less likely to decrease during the production of the nonwoven fabric. Also, when used as the separation membrane support, the air permeability can be maintained, so that the polymer solution cast during film formation quickly penetrates into the separation membrane support, and a nonwoven fabric with good adhesion of the separation membrane can be obtained. On the other hand, if the average single fiber diameter of the thermoplastic fibers constituting the separation membrane support is 30 μm or less, when used as the separation membrane support, it can be densified, so that there is less overpenetration during the casting of the polymer solution, and a good nonwoven fabric can be obtained. Note that fibers with different average single fiber diameters may be mixed.

[0049] The basis weight of the separation membrane support of the present invention is preferably 20 g / m 2 or more and 200 g / m 2 or less. If the basis weight of the separation membrane support is 20 g / m 2 or more, more preferably 70 g / m 2 or more, and even more preferably 120 g / m 2 or more, it has high mechanical strength and excellent dimensional stability. On the other hand, if the basis weight of the separation membrane support is 200 g / m 2 or less, more preferably less than 150 g / m 2 , the thickness of the separation membrane can be reduced, the number of laminations of the separation membrane per membrane separation element can be increased, and the filtration performance can be improved.

[0050] Regarding the basis weight of each nonwoven fabric when laminated to form the separation membrane support, as long as the basis weight of the final separation membrane support is in the range of 20 g / m 2 or more and 200 g / m 2 or less, there is no particular limitation. For example, it can be appropriately determined according to the product design, such as laminating 3 sheets with a basis weight of 10 g / m 2 or laminating 2 sheets with a basis weight of 30 g / m 2 .

[0051] The thickness of the separation membrane support of the present invention is determined appropriately according to the application and product design, but is preferably 0.05 mm or more and 0.50 mm or less. A separation membrane support thickness of 0.05 mm or more, more preferably 0.15 mm or more, and even more preferably 0.20 mm or more, provides excellent mechanical strength and durability. On the other hand, a separation membrane support thickness of 0.50 mm or less, more preferably 0.40 mm or less, allows for an increase in the number of separation membrane layers per membrane separation element, thereby improving filtration performance.

[0052] [Method for manufacturing separation membranes] The present invention provides a method for producing a separation membrane, comprising the steps of: a) casting a polymer solution containing a component for forming a polymer membrane having separation function onto at least one side of a separation membrane support; and b) forming a separation membrane by solidifying the polymer solution in a solidification solution.

[0053] The polymer solution of the present invention preferably contains a component that forms a polymer membrane having separation function (hereinafter referred to as the separation membrane forming component), a porotropizing agent, and a solvent.

[0054] The separation membrane of the present invention is preferably formed by casting and fixing a polymer solution containing a separation membrane forming component, a porotropic agent, and a solvent onto a separation membrane support made of a nonwoven fabric. In fixing the polymer solution, it is preferable to immerse the cast polymer solution, along with the support, in a non-solvent coagulation solution to fix it.

[0055] The separation membrane-forming component contained in the polymer solution of the present invention is preferably a resin that has separation function when it forms a separation membrane. Suitable separation membrane-forming components include polyethylene, polypropylene, polyvinyl chloride, polyvinylidene fluoride, polysulfone, polyethersulfone, polyimide, polyetherimide, and cellulose acetate. Among these, polyvinyl chloride, polyvinylidene fluoride, polysulfone, and polyethersulfone are more preferred, and polyvinylidene fluoride is even more preferred, as they are easy to form films in solution and exhibit excellent physical durability and chemical resistance. A mixture of the above resins is also acceptable. However, it is preferable to mix the above resins at a concentration of 50% by weight or more, and more preferably at a concentration of 60% by weight or more.

[0056] The porosity-opening agent contained in the polymer solution of the present invention is preferably one that is extracted when immersed in the coagulation solution and has the effect of making the resin layer porous. The porosity-opening agent is preferably one that has high solubility in the coagulation solution, and inorganic salts such as calcium chloride and calcium carbonate can be used. Alternatively, polyoxyalkylenes such as polyethylene glycol and polypropylene glycol, water-soluble polymers such as polyvinyl alcohol, polyvinyl butyral and polyacrylic acid, and glycerin can be used. The porosity-opening agent can be arbitrarily selected depending on the resin, but for example, when using a resin containing polyvinylidene fluoride, polyethylene glycol is preferred, and among them, polyethylene glycol with a weight-average molecular weight of 10,000 or more is particularly preferred from the viewpoint of balancing surface pore size, pore size distribution and water permeability.

[0057] The solvent contained in the polymer solution of the present invention is preferably one that dissolves the separation membrane-forming component. The solvent acts on the separation membrane-forming component and the porotropic agent to promote the formation of a separation membrane. Suitable solvents include N-methylpyrrolidinone (NMP), N,N-dimethylacetamide (DMAc), N,N-dimethylformamide (DMF), dimethyl sulfoxide (DMSO), acetone, and methyl ethyl ketone. Among these, NMP, DMAc, DMF, and DMSO, which have high solubility for the separation membrane-forming component, are preferably used.

[0058] The non-solvent used in the coagulation solution in the present invention is preferably a liquid that does not dissolve the separation membrane-forming component. The non-solvent preferably acts to control the rate of coagulation of the separation membrane-forming component and thereby control the size of pores and macrovoids. For example, water or alcohols such as methanol and ethanol can be used. Among these, water and methanol are preferred in terms of ease of wastewater treatment and cost, and mixtures containing these may also be used.

[0059] The content of the separation membrane-forming component in the polymer solution of the present invention is preferably 5% by weight or more and 30% by weight or less. More preferably, the content of the separation membrane-forming component is 8% by weight or more and 20% by weight or less, which allows the strength of the separation membrane to be maintained and water permeability to be obtained.

[0060] The content of the pore-opening agent in the polymer solution of the present invention is preferably 8% by weight or more and 11% by weight or less. More preferably, the content of the pore-opening agent is 9% by weight or more and 10% by weight or less, which allows control of the standard deviation of the maximum pore diameter and the average pore diameter, and also allows for obtaining the strength of the separation membrane and stable water permeability.

[0061] The solvent content in the polymer solution of the present invention is preferably 40% by weight or more and 94.9% by weight or less. More preferably, the solvent content is 60% by weight or more and 90% by weight or less, which suppresses gelation of the polymer solution and maintains the strength of the separation membrane.

[0062] In the present invention, the non-solvent is preferable not only for use in the coagulation solution but also for addition to the polymer solution, as it facilitates the homogenization of the pore size on the separation membrane surface and allows for control of the size of voids within the separation membrane. The non-solvent content in the polymer solution is preferably 0.1% to 20% by weight. More preferably, the non-solvent content is 0.5% to 15% by weight (solvent content is 40% to 94.4% by weight), which suppresses the gelation of the polymer solution.

[0063] The coagulation solution can be a non-solvent or a mixture containing both a non-solvent and a solvent. In the coagulation solution, when a non-solvent is used in the polymer solution, it is preferable that the non-solvent content be 80% by weight or more. By having a non-solvent content of 80% by weight or more in the coagulation solution, the coagulation rate of the separation membrane forming component can be maintained, the pore size on the separation membrane surface can be stably formed, and voids in the separation membrane can be stably formed. The non-solvent content in the coagulation solution is more preferably 85% by weight or more and 100% by weight or less.

[0064] On the other hand, when no solvent is used in the polymer solution, it is preferable that the non-solvent content in the coagulation solution be 60% by weight or more. This allows for appropriate coagulation of the separation membrane forming components, stable pore formation on the separation membrane surface, and control of voids within the separation membrane. When no solvent is used in the polymer solution, it is more preferable to have a non-solvent content in the coagulation solution of 60% by weight or more and 99% by weight or less, which allows for control of the pore size on the separation membrane surface and the void ratio within the separation membrane.

[0065] In the present invention, the temperature of the coagulation solution is preferably 15°C to 80°C. More preferably, the temperature of the coagulation solution is 20°C to 60°C, which allows control of the coagulation rate, and consequently, control of the porosity in the separation membrane, thereby achieving water permeability.

[0066] Furthermore, in step b), it is preferable to form a flow of solidified liquid in the direction of the polymer solution being cast from the separation membrane support during the initial stage of solidification. The initial stage of solidification refers to the period from immersion of the polymer solution in the solidification bath until solidification is complete, preferably within 3 seconds, more preferably within 2 seconds, and even more preferably within 1 second. Forming a flow of solidified liquid during the initial stage of solidification can increase the porosity within the separation membrane. Specifically, a means of "forming a flow" is to push the solidified liquid toward the polymer solution being cast from the separation membrane support (i.e., from the back side of the separation membrane support). The pushing pressure for forming the flow is preferably 1 to 3 kPa. The pushing time is preferably 3 to 10 seconds.

[0067] In the separation membrane of the present invention, the water permeability of the separation membrane with controlled maximum pore size and porosity is calculated as the water permeability per second (cubic meters) per square meter of membrane surface at an evaluation temperature of 25°C, a pressure of 1 kPa, and is 60 × 10⁻⁶. -9 m 3 / m 2 It is greater than / second / Pa. More preferably, 65 × 10 -9 m 3 / m 2 / sec / Pa or higher, more preferably 70 × 10 -9 m 3 / m 2 Achieving a pressure of / sec / Pa or higher means high water permeability, which improves the amount of water that can be permeated per membrane separation element and thus improves filtration performance.

[0068] The membrane separation element of the present invention integrates the above-mentioned separation membrane with a flow channel material and other components in a laminated form for easier handling. Examples of such forms include a flat membrane plate frame type, a pleated type, and a spiral type. Among these, a flat membrane plate frame type is preferably used, in which a flow channel material is sandwiched and integrated between two separation membrane sheets with the sides on which the separation membrane is formed facing outwards. Multiple membrane separation elements can be connected in series or in parallel to form a separation membrane unit.

[0069] The separation membrane element of the present invention is preferably used for water treatment of seawater, brackish water, river water, wastewater, etc. In particular, it is more preferably used for wastewater treatment applied to membrane separation activated sludge processes. [Examples]

[0070] The separation membrane of the present invention will be described in detail below based on examples. These are illustrative examples, and the present invention is not limited to these. The physical properties of the separation membrane and separation membrane support, the nonwoven fabric constituting the separation membrane support, and the fibers constituting the nonwoven fabric, as well as the physical properties in the examples, were measured by the following method.

[0071] (1) Melting point of polymer (°C) The melting point of the polymer was measured using a differential scanning calorimeter (DSC). Equipment: TA Instruments "Q-2000" Heating rate: 2°C / min Measurement temperature range: -20°C to 300°C.

[0072] (2) Molecular weight of polyethylene glycol (PEG) in the separation membrane support The molecular weight of polyethylene glycol was measured and calculated using gel permeation chromatography (GPC) (such as the "Differential Refractive Index Detector RID-20A" manufactured by Shimadzu Corporation) according to the method described in the specification.

[0073] (3) Copolymerization rate (mass%) of PEG in the separation membrane support, and copolymerization rate (mass%) of PEG in the composite fibers constituting the nonwoven fabric. The copolymerization rate of PEG was measured and calculated using the "AL-400" measuring device manufactured by JEOL Ltd., according to the method described in the specification.

[0074] (4) Single yarn fineness (dtex) The single filament fineness was determined by peeling off the separation membrane with tape or the like, randomly taking 10 small sample pieces from the separation membrane support, taking 500-3000x magnification images with a scanning electron microscope (Keyence Corporation "VHX-2000"), measuring the diameter of 10 single fibers from each sample (a total of 100 fibers), correcting for the polymer density, and rounding to two decimal places.

[0075] (5) Average single fiber diameter (μm) The average single fiber diameter was calculated by peeling off the separation membrane with tape or the like, randomly taking 10 small sample pieces from the separation membrane support, taking 500-3000x magnification images with a scanning electron microscope (Keyence Corporation "VHX-2000"), measuring the diameter of 10 single fibers from each sample (a total of 100 fibers), and rounding the average value of these measurements to the first decimal place.

[0076] (6) Basis weight of separation membrane support (g / m²) 2 ) For the basis weight, after peeling off the separation membrane with tape or the like, three 30cm x 50cm separation membrane supports were taken, the weight of each sample was measured, the average of the obtained values ​​was converted to a unit area, and the result was rounded to the first decimal place.

[0077] (7) Thickness of the separation membrane support (mm) The thickness of the separation membrane support was determined by randomly selecting 10 small sample pieces after peeling off the separation membrane with tape or the like. Using a micrometer manufactured by Mitutoyo Corporation, the separation membrane support was clamped between a 6 mm diameter anvil and spindle, and two points within the sample were measured at equal intervals to the nearest 0.01 mm. The average of the 20 points was rounded to the third decimal place.

[0078] (8) Density of the separation membrane support (g / cm³) 3 ) The basis weight of the separation membrane support was divided by the thickness of the separation membrane support, and the result was rounded to the third decimal place.

[0079] (9) Water absorption of the separation membrane support (mm) The water rise height (mm) of spunbond nonwoven fabric was measured according to the JIS-L-1907 Baylek method (2010). Five 200mm x 25mm spunbond nonwoven fabric samples were taken, and the long end of each sample was immersed 20mm into a water tank. After 10 minutes, the water rise height was measured. The average of the obtained measurements was calculated to determine the water rise height, which was rounded to the first decimal place. A higher water rise height indicates improved water absorption of the nonwoven fabric. Higher water absorption improves the permeability of the coagulation solution from the separation membrane support side during membrane formation, thus improving the porosity inside the separation membrane. In Tables 1-3, the measurement results for the water rise height (mm) of spunbond nonwoven fabric are simply abbreviated as "Water Absorption (mm)".

[0080] (10) Thickness of polymer film (μm) The thickness of the polymer membrane was measured by taking 10 small sample pieces of the separation membrane, clamping the separation membrane between a 6 mm diameter anvil and spindle using a micrometer manufactured by Mitutoyo Corporation, and measuring two points within the sample at equal intervals in 0.01 mm units. The average value of the 20 points was rounded to the third decimal place. The thickness of the polymer membrane was calculated by subtracting the thickness of the separation membrane support described in (7) above from the obtained thickness.

[0081] (11) Maximum pore diameter of separation membrane surface (nm) The maximum pore size of the separation membrane was determined by measuring the pore sizes of 100 pores using a scanning electron microscope (SEM) and taking the maximum value. Equipment: HITACHI SU8100 Magnification: ×10000 Vapor deposition: Pt-Pd (platinum-palladium) x 10 seconds (12) Standard deviation of the average pore size on the separation membrane surface (nm) The standard deviation of the surface pore size of the separation membrane was calculated by measuring the pore size of 100 pores using scanning electron microscopy (SEM) observation and then determining the standard deviation.

[0082] (13) Porosity of the separation membrane (%) The porosity of the separation membrane was measured using a confocal laser microscope (Olympus Corporation; FV3000) as the measuring device, according to the method described in the specification. A total of five images were measured, and the average value was rounded to the first decimal place.

[0083] (14) Tensile strength (kgf) and tensile elongation (%) of the separation membrane The prepared separation membrane was cut into strips measuring 5 mm x 40 mm. The strength and elongation were measured at three points in the longitudinal direction under a tensile speed of 20 mm / min. The strength and elongation at the time of fracture were read, and the average value was rounded to two decimal places. Equipment: Tensilon UCT-100 Initial length: 10mm Tensile speed: 20 mm / min (15) Adhesion strength of the separation membrane (gf / 25mm) The adhesive strength of the separation membrane was determined by following the method for "adhesives - peel adhesion strength" in the JIS K6854-1 standard (2014). A 40mm x 100mm separation membrane was taken, and aluminum tape (NW-10, Nichiban Co., Ltd.) was attached to the membrane surface. A stainless steel plate (80mm x 100mm) for 180° peeling was attached to the bottom of the chuck of a Tensilon (RTG-1210, A&D Co., Ltd.). After peeling the adhesive area between the membrane sample and the aluminum tape by hand by about 5mm beforehand, the sample was set in the Tensilon with the aluminum tape on top and the sample on the bottom, and measured at a peeling speed of 50mm / min. The average load value between 10mm and 60mm from the initial load point after the start of the test was defined as the adhesive strength.

[0084] (16) Permeability of the separation membrane (×10 -9 m 3 / m 2 / sec / Pa) Using the fabricated separation membrane, a 5cm diameter circle was cut and set in a cylindrical filtration holder. Distilled water was then pre-permeated for 5 minutes at 25°C with a water head height of 1m (equivalent to a water pressure of 9800Pa). Subsequently, the membrane was permeated again while maintaining a water head height of 1m, and the permeate was collected for 3 minutes to determine the permeate rate per unit time and unit area. This was then divided by the water pressure acting on the permeate surface to determine the pure water permeability coefficient per 1Pa.

[0085] (17) Separation performance of the separation membrane (particulate rejection rate) The separation performance of the fabricated separation membrane was evaluated by its particulate rejection rate. The particulate rejection rate was calculated by filtering an evaluation stock solution, which was prepared by dispersing polystyrene latex microparticles with an average particle size of 0.09 μm at a concentration of 20 ppm in purified water using a reverse osmosis membrane. The absorbance of ultraviolet light at a wavelength of 250 nm was measured for both the evaluation stock solution and the obtained filtration permeate using a spectrophotometer (such as Hitachi U-3200), and the particulate rejection rate was calculated using the following formula. Particle rejection rate = [(Absorbance of undiluted solution - Absorbance of permeate) / Absorbance of undiluted solution] × 100 The results were evaluated on a four-point scale from S to C according to the obtained particulate rejection rate. S: The particulate filter efficiency is 95% or higher, and it is within a range where clogging due to sludge components and an increase in filtration differential pressure do not occur, making it suitable for use in MBR membrane applications. A: The particulate filter efficiency is 90% or higher, which is within a range that does not affect clogging due to sludge components or increase in filtration differential pressure, making it suitable for use in MBR membrane applications. B: The particulate filter efficiency is 85% or higher, and while it may slightly affect clogging due to sludge components and the increase in filtration differential pressure, the impact is not significant, making it suitable for MBR membrane applications. C: The particulate filter efficiency is lower than 85%, raising concerns about clogging due to sludge components and increased filtration differential pressure, making it difficult to use in MBR membrane applications.

[0086] [ reference Example 1] (separation membrane support) Polyethylene terephthalate (PET) with a melting point of 255°C and containing 0.3% by mass of titanium dioxide was used as the core component. 11.5 mol% of isophthalic acid and 2% by mass of polyethylene glycol (PE-G) (PEG20000, manufactured by Sanyo Chemical Industries, Ltd.) with a number average molecular weight of 20000 were copolymerized, and copolymerized polyethylene terephthalate (PET / I-PEG) with a melting point of 230°C and containing 0.2% by mass of titanium dioxide was used as the sheath component.

[0087] The core and sheath components were melted at temperatures of 295°C and 270°C, respectively. After spinning them out of the pores at a die temperature of 300°C and a core:sheath mass ratio of 80:20, the fibers were spun using an ejector at a spinning speed of 4400 m / min to produce concentric core-sheath filaments (circular cross-section) with the entire surface covered with PET / I-PEG. These filaments were then collected as a fiber web on a moving net conveyor.

[0088] The collected fiber web was passed between a metal textured roll, which had circular protrusions uniformly arranged in a houndstooth pattern as the upper roll, and a flat roll as the lower roll. Partial heat compression was then performed with a surface temperature of 170°C and a linear pressure of 588 N / cm on both the upper and lower rolls.

[0089] Furthermore, the partially heat-sealed sheet is passed continuously between a pair of flat rolls and fully heat-sealed at a surface temperature of 120°C and a linear pressure of 686 N / cm on both the upper and lower rolls, resulting in a PEG copolymerization rate of 0.4% by mass, a fiber diameter of 14 μm, and a basis weight of 120 g / m². 2 Thickness 350 μm, density 0.34 g / m² 2 Then, 32 circular recesses with a diameter of 0.8 mm are created per cm. 2 A separation membrane support was obtained, composed of a spunbond nonwoven fabric having a number density of [number density]. The water rise height indicating water absorption of this separation membrane support was 100 mm.

[0090] (separation membrane) A film-forming stock solution was obtained by mixing 17% by mass of polyvinylidene fluoride (PVDF) (KF#850, manufactured by Kureha Chemical Industries, Ltd.) as a membrane-forming component, 9% by mass of polyethylene glycol (PEG) (PEG, manufactured by Sanyo Chemical Industries, Ltd.) with a number average molecular weight of 20,000 as a pore-opening agent, 70% by mass of N,N-dimethylformamide (DMF) as a solvent, and 4% by mass of pure water as a non-solvent. The mixture was thoroughly stirred at a temperature of 90°C.

[0091] The obtained film-forming stock solution was cooled to 25°C, then applied to a separation membrane support. Immediately after application, it was immersed in pure water at 25°C for 5 minutes, and then immersed in hot water at 80°C to wash away the DMF and PEG, thereby obtaining a separation membrane. The porosity of this separation membrane was 41%, the maximum pore diameter on the membrane surface was 80 nm, and the standard deviation of the average pore diameter was 20 nm. The water permeability of the separation membrane was 60 × 10⁻⁶. -9 m 3 / m 2 The pressure was / sec / Pa, and the adhesive strength was 1090 gf / 25mm. The results are shown in Table 1.

[0092] [ reference [Example 2-4] The copolymerization rate of PEG (PEG20000, manufactured by Sanyo Chemical Industries, Ltd.) with a number-average molecular weight of 20000 in the sheath component was changed as shown in Table 1, except that the copolymerization rate of PEG in the separation membrane support was changed. reference The procedure was carried out in the same manner as in Example 1 to obtain a separation membrane. The results are shown in Table 1.

[0093] The PEG copolymerization rate in the separation membrane support is 0.4% by mass. reference Example 1) 2.8 mass% ( reference In Example 4), increasing the amount resulted in an increase in the water rise height, which indicates the water absorption of the separation membrane support, to 160 mm. The maximum pore diameter and the standard deviation of the average pore diameter on the separation membrane surface remained unchanged, the porosity increased to 52%, and the water permeability increased to 66 × 10⁻⁶. -9 m 3 / m 2 The pressure tended to increase to / sec / Pa. Additionally, the adhesion strength of the separation membrane to the separation membrane support also tended to increase to 1280gf / 25mm.

[0094] [Table 1]

[0095] [ reference [Examples 5-7] Except for using PEG with a number-average molecular weight of 7000 (PEG6000S manufactured by Sanyo Chemical Industries, Ltd.) as the PEG in the sheath component, and varying the copolymerization rate as shown in Table 1, the only other variation was the change in the PEG copolymerization rate in the separation membrane support. reference The procedure was carried out in the same manner as in Example 1 to obtain a separation membrane. The results are shown in Table 1.

[0096] The number-average molecular weight of PEG in the separation membrane support is set to 20000. reference Example 4) From 7000 ( reference By reducing the parameters to those in Example 7), the water rise height indicating water absorption of the separation membrane support decreased to 150 mm, the porosity decreased to 46%, and the water permeability increased to 64 × 10⁻⁶. -9 m 3 / m 2 The pressure tended to decrease to / sec / Pa. Furthermore, the adhesion strength of the separation membrane to the separation membrane support also tended to decrease to 1240gf / 25mm.

[0097] [ reference [Examples 8-10] Except for using PEG with a number average molecular weight of 1000 (PEG1000 manufactured by Sanyo Chemical Industries, Ltd.), PEG with a number average molecular weight of 3400 (PEG4000S manufactured by Sanyo Chemical Industries, Ltd.), and PEG with a number average molecular weight of 35000 (PEG35000 manufactured by Sigma-Aldrich), the following were used: reference The separation membrane was obtained using the same method as in Example 4. The results are shown in Table 1.

[0098] The number-average molecular weight of PEG in the separation membrane support is set to 20000. reference Example 4) From 1000 ( reference Example 8), 3400 ( reference By reducing the parameters to the level shown in Example 9), the water rise height indicating water absorption of the separation membrane support decreases to 100 mm, the porosity decreases to 40%, and the water permeability increases to 60 × 10⁻⁶. -9 m 3 / m 2 The pressure tended to decrease to / second / Pa. Additionally, the adhesion strength of the separation membrane to the separation membrane support also tended to decrease.

[0099] On the other hand, the number average amount of PEG in the separation membrane support was set to 35000. reference By increasing the amount to Example 10), the water rise height indicating water absorption of the separation membrane support remained unchanged at 160 mm, but the porosity decreased to 42%, the maximum pore size increased to 120 nm, and the water permeability increased to 65 × 10⁻⁶. -9 m 3 / m 2 The pressure tended to decrease to / second / Pa. Furthermore, the adhesion strength of the separation membrane to the separation membrane support also decreased, and the particulate filter efficiency also tended to decrease.

[0100] [ reference [Examples 11-13] Except for changing the content of the porosity-opening agent during membrane formation to 8% by weight, 10% by weight, and 11% by weight, the other changes were made. reference The separation membrane was obtained using the same method as in Example 4. The results are shown in Table 2.

[0101] The content of the pore-opening agent in the separation membrane manufacturing solution is 9% by weight. reference Example 4) From 8% by weight ( referenceBy reducing the amount to Example 11), the porosity decreased, and the standard deviation between the maximum pore diameter and the average pore diameter tended to increase. Furthermore, water permeability also tended to decrease, as did the particulate rejection rate. On the other hand, when the content of the pore-opening agent was reduced to 10% by weight ( reference Example 12), 11% by weight ( reference Increasing the density as in Example 13) increased the porosity, but the standard deviation between the maximum pore size and the average pore size tended to increase. Also, while the water permeability increased, the particulate filter efficiency tended to decrease.

[0102] [Table 2]

[0103] [ reference [Examples 14-17] Except for the copolymerization rates of isophthalic acid in the sheath component being 25 mol%, 22 mol%, 8 mol%, and 5 mol%, reference The separation membrane was obtained using the same method as in Example 4. The results are shown in Table 2.

[0104] The copolymerization rate of isophthalic acid is 11.5 mol%. reference Example 4) shows 25 mol% ( reference Example 14), 22 mol% ( reference Increasing the amount to Example 15) reduced the thickness of the separation membrane support, suppressed the penetration of the coagulation liquid from the support side, and tended to decrease the porosity and water permeability. On the other hand, increasing the copolymerization rate of isophthalic acid to 8 mol% ( reference Example 16), 5mol%( reference By reducing the level to that of Example 17), the thickness of the separation membrane support increased, and the water permeability tended to decrease due to the separation membrane forming components seeping through to the back.

[0105] [ reference [Examples 18-22] Except for the mass ratio of the core component polymer to the sheath component polymer of the core-sheath composite fiber constituting the separation membrane support, which was set to core:sheath = 50:50, 60:40, 70:30, 90:10, and 95:5, reference The separation membrane was obtained using the same method as in Example 4. The results are shown in Table 3.

[0106] The mass ratio of the core polymer to the sheath polymer is core:sheath = 80:20. reference Example 4) From 50:50 ( reference Example 18), 60:40 ( reference Example 19), 70:30 ( reference By changing the composition to Example 20), the thickness of the separation membrane support was reduced, the penetration of the coagulation liquid from the support side was suppressed, and the porosity and water permeability tended to decrease. On the other hand, when the mass ratio of the core component polymer to the sheath component polymer was changed to core:sheath = 90:10 ( reference Example 21), 95:5( reference By changing to Example 22), the thickness of the separation membrane support increased, and the water permeability tended to decrease due to the separation membrane forming components seeping through to the back.

[0107] [Table 3]

[0108] [ reference [Examples 23-26] The basis weight of the separation membrane support is 20 g / m². 2 70g / m 2 150g / m 2 200g / m 2 Other than the change to this, reference The separation membrane was obtained using the same method as in Example 4. The results are shown in Table 3.

[0109] The basis weight of the separation membrane support is 120 g / m². 2 ( reference Example 4) From 20g / m 2 ( reference Example 23), 70g / m 2 ( reference By reducing the amount to Example 24), the thickness of the separation membrane support was reduced, the penetration of the coagulation solution from the support side was suppressed, and the porosity and water permeability tended to decrease. On the other hand, when the basis weight was 150 g / m² 2 ( reference Example 25), 200g / m 2 ( reference Increasing the amount as in Example 26) increased the thickness of the separation membrane support, which tended to reduce water permeability due to the separation membrane forming components seeping through to the back.

[0110] [Example 27] Aside from applying the film-forming solution to the separation membrane support, and then immersing it in 25°C pure water for 1 second, pure water was applied from the separation membrane support side at a pressure of 1 kPa for about 3 seconds, the other procedure was as follows: reference The procedure was carried out in the same manner as in Example 4 to obtain a separation membrane. The results are shown in Table 4.

[0111] Because pure water was applied to the separation membrane support side within 3 seconds of immersion in pure water, there was no change in the maximum pore size or the standard deviation of the average pore size on the separation membrane surface, the porosity increased to 63%, and the water permeability increased to 75 × 10⁻⁶. -9 m 3 / m 2 The values ​​tended to increase to / second / Pa.

[0112] [Table 4]

[0113] [Examples 28-30] Separation membranes were obtained using the same method as in Example 27, except that the content of the poro-opening agent in the membrane-forming stock solution was changed to 8% by weight, 10% by weight, and 11% by weight. The results are shown in Table 4.

[0114] When the content of the porosity-opening agent in the membrane preparation solution was reduced from 9% by weight (Example 27) to 8% by weight (Example 28), the porosity decreased, and the standard deviation between the maximum pore diameter and the average pore diameter tended to increase. Furthermore, water permeability also tended to decrease, as did the particulate filter efficiency. On the other hand, when the content of the porosity-opening agent was increased to 10% by weight (Example 29) and 11% by weight (Example 30), the porosity increased, but the standard deviation between the maximum pore diameter and the average pore diameter tended to increase. Furthermore, water permeability increased, but the particulate filter efficiency tended to decrease.

[0115] [Comparative Examples 1 and 2] Except for not copolymerizing PEG in the separation membrane support (Comparative Example 1) and changing the PEG copolymerization rate in the separation membrane support to 4.0% by mass (Comparative Example 2), the other differences are as follows: reference The procedure was carried out in the same manner as in Example 4 to obtain a separation membrane. The results are shown in Table 5.

[0116] The separation membrane obtained in Comparative Example 1 used a separation membrane support that was not copolymerized with PEG, resulting in low porosity and poor water permeability.

[0117] The separation membrane obtained in Comparative Example 2 had poor water permeability due to excessive PEG copolymerization, which caused the film-forming solution to over-permeate the separation membrane support, resulting in an increase in the amount of separation membrane-forming components inside the support and leakage of the separation membrane-forming components to the back of the support.

[0118] [Table 5]

[0119] [Comparative Example 3-5] Except for the following variations, the only differences were that no poro-opening agent was added to the membrane preparation solution (Comparative Example 3), the content of the poro-opening agent was changed to 5% by weight (Comparative Example 4), and the content of the poro-opening agent was changed to 15% by weight (Comparative Example 5). reference The procedure was carried out in the same manner as in Example 4 to obtain a separation membrane. The results are shown in Table 5.

[0120] The separation membrane obtained in Comparative Example 3 had low porosity and poor water permeability because no porosity-opening agent was added.

[0121] The separation membrane obtained in Comparative Example 4 had a low content of pore-opening agent, while the separation membrane obtained in Comparative Example 5 had an excessive content of pore-opening agent. As a result, the standard deviation of the maximum pore diameter and average pore diameter on the separation membrane surface increased, leading to a poor particle rejection rate.

[0122] [Comparative Example 6] The procedure was carried out in the same manner as in Example 27, except that PEG was not copolymerized in the separation membrane support, to obtain a separation membrane. The results are shown in Table 6.

[0123] Because the separation membrane support used was not copolymerized with PEG, it had low porosity and poor water permeability.

[0124] [Table 6]

[0125] [Comparative Example 7-9] Separation membranes were obtained in the same manner as in Example 27, except that no poro-opening agent was added to the membrane preparation solution (Comparative Example 7), the content of the poro-opening agent was changed to 5% by weight (Comparative Example 8), and the content of the poro-opening agent was changed to 15% by weight (Comparative Example 9). The results are shown in Table 6.

[0126] The separation membrane obtained in Comparative Example 7 had low porosity and poor water permeability because no porosity-opening agent was added.

[0127] The separation membrane obtained in Comparative Example 8 had a low content of pore-opening agent, while the separation membrane obtained in Comparative Example 9 had an excessive content of pore-opening agent. As a result, the standard deviation of the maximum pore diameter and average pore diameter on the separation membrane surface increased, leading to a poor particle rejection rate.

[0128] [Comparative Example 10] A separation membrane was obtained in the same manner as in Comparative Example 6, except that the support was immersed in an aqueous surfactant solution for 20 hours. A 1.8 wt% polyoxyethylene sorbitan monostearate aqueous solution was used as the aqueous surfactant solution. The results are shown in Table 7. The separation membrane obtained in Comparative Example 10 had a lower porosity and inferior adhesive strength compared to the example.

[0129] [Table 7]

Claims

1. A separation membrane in which a polymer membrane having a separation function is formed on a separation membrane support, The separation membrane support contains 0.4% by mass or more and 3.0% by mass or less of polyethylene glycol. The maximum pore diameter on the surface of the separation membrane is 10 nm or more and 120 nm or less. A separation membrane having a porosity of 57% or more and 80% or less when measured with a confocal laser microscope in a region within 15 μm from the surface of the separation membrane.

2. The separation membrane according to claim 1, wherein the porosity is 60% or more and 80% or less.

3. The separation membrane according to claim 1 or 2, wherein the standard deviation of the average pore diameter on the surface of the separation membrane is 30 nm or less.

4. The separation membrane according to claim 1 or 2, wherein the water absorption of the separation membrane support is evaluated by the JIS-L1907 (2010) Baylec method, and the height of the rising water is 100 mm or more and 180 mm or less.

5. The separation membrane according to claim 1 or 2, wherein the molecular weight of the polyethylene glycol contained in the separation membrane support is 1,000 or more and 35,000 or less.

6. The separation membrane according to claim 1 or 2, wherein the component of the polymer membrane having the separation function is polyvinylidene fluoride.

7. A method for producing a separation membrane, comprising the steps of: a) casting a polymer solution containing a component for forming a polymer membrane having a separation function onto one side of the separation membrane support; and b) forming a separation membrane by solidifying the polymer solution in a coagulation solution. The polymer solution contains polyoxyalkylenes as a poro-opening agent, In step b) above, within 3 seconds after immersing the polymer solution in the coagulation solution, A method for producing a separation membrane according to claim 1 or 2, comprising forming a flow of the coagulation liquid in the direction of the polymer solution being cast from the separation membrane support.

8. A membrane separation element characterized by comprising the separation membrane described in claim 1 or 2.

9. A wastewater treatment method applying the membrane separation element described in claim 8 to a membrane separation activated sludge process.

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