Separation membrane, method for manufacturing same, membrane separation element, and sewage treatment method using 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

Separation membrane and its manufacturing method, membrane separation element and sewage and wastewater treatment method using the same

[0001] The present invention provides a separation membrane that satisfies both water permeability and fouling resistance when fabricating a separation membrane for use in water treatment.

[0002] In recent years, membrane technology has been widely used in water treatment, using filtration membranes with fine pores to remove impurities from water. For example, microfiltration and ultrafiltration membranes are used for water treatment at water purification plants, and reverse osmosis membranes are used for seawater desalination. Furthermore, reverse osmosis and nanofiltration membranes are used to treat water for semiconductor manufacturing, boiler water, medical water, and pure water for laboratories. The membrane separation activated sludge process, which uses microfiltration and ultrafiltration membranes, is also used to treat sewage wastewater.

[0003] Filtration membranes (separation membranes) used in water treatment are broadly classified into flat membranes and hollow fiber membranes based on their shape, and flat membranes made of synthetic polymers are generally used by being fixed and integrated with a support such as a nonwoven fabric or woven fabric, since they have poor mechanical strength when used alone as a membrane with separation function. As the support, nonwoven fabrics are excellent in productivity and processability because they can be obtained as a sheet-like product without going through a weaving process, and spunbonded nonwoven fabrics made from long fibers in particular can provide the strength of a support.

[0004] The method for forming a flat membrane on a support involves casting a polymer solution containing separation membrane-forming components onto the support and allowing it to adhere. If the polymer solution penetrates deep into the support, the flat membrane and support will be firmly bonded. However, if the polymer solution penetrates excessively and reaches the back surface of the support, it will contaminate the membrane-forming equipment and cause defects in the separation membrane produced later. Furthermore, when a membrane separation element is manufactured using the separation membrane, the adhesive strength between the separation membrane and the support plate (flow path material) will be insufficient, resulting in a decrease in the durability of the membrane separation element. Therefore, it is important for the support to have adequate adhesiveness with the separation membrane-forming components.

[0005] Furthermore, separation membranes for wastewater treatment used in membrane bioreactors (hereinafter referred to as MBR) are used for long periods of time while immersed in activated sludge, and therefore have the problem of clogging the membrane pores and reducing water permeability due to adhesion and deposition of secretions from the activated sludge, its remains, and impurities contained in the sludge (hereinafter, adhesion and deposition of sludge components on the membrane will be referred to as "fouling"). Adherence and deposits can be removed by cleaning the membrane with chemicals, but this can cause many economic and environmental problems, such as the need to stop filtration operation during cleaning and the disposal of waste chemicals, so it is important that the separation membrane is resistant to fouling.

[0006] Furthermore, separation membranes are required to have a high water permeability while maintaining a pore size appropriate for the filter material. However, increasing the water permeability results in excessively large pore sizes, which can lead to cracks on the surface and a decrease in the aforementioned fouling resistance. In other words, it is important to achieve a good balance between fouling resistance and water permeability.

[0007] A separation membrane support has been proposed that has excellent membrane formability and dimensional stability when producing microfiltration membranes, ultrafiltration membranes, nanofiltration membranes, reverse osmosis membranes, etc., and has high adhesive strength with the membrane (see Patent Document 1). A separation membrane support has also been proposed that has excellent membrane formability, high mechanical strength, and excellent water permeability (see Patent Document 2). Furthermore, a separation membrane that has high fouling resistance (sludge component rejection rate) achieved by controlling the composition of a polymer solution containing separation membrane-forming components has been proposed (see Patent Document 3). Finally, a separation membrane for MBR that has high water permeability and fouling resistance achieved by hydrophilizing the separation membrane has been proposed (see Patent Document 4).

[0008] Japanese Patent Publication No. 2011-5455 Japanese Patent Publication No. 2012-130890 Japanese Patent Publication No. 2010-221218 Japanese Patent Publication No. 2015-110208

[0009] The technology described in Patent Document 1 has a separation membrane support made of polyethylene terephthalate fibers in which high-density and low-density areas are controlled by partial thermocompression bonding, and has poor affinity with the components that form the separation membrane, resulting in low adhesion between the separation membrane and the separation membrane support.In addition, the porosity inside the separation membrane is not controlled, which has the problem of poor water permeability.

[0010] The technology described in Patent Document 2 improves the adhesion between the separation membrane and the separation membrane support by adding a hydrophilic agent to the separation membrane support, thereby achieving affinity with the separation membrane-forming components. However, the hydrophilicity inside the separation membrane support remains low, resulting in a problem of low porosity inside the separation membrane and poor water permeability.

[0011] The technology described in Patent Document 3 involves a separation membrane produced by adding polyethylene glycol as a pore-opening agent, and imparting fouling resistance by making the surface pore size uniform and fine. However, the separation membrane support is made of polyethylene terephthalate fibers, which have poor affinity with the components forming the separation membrane, resulting in low adhesion between the separation membrane and the separation membrane support, low porosity inside the separation membrane, and poor water permeability.

[0012] The technology described in Patent Document 4 involves a separation membrane in which particulate hydroxybutyl cellulose is fixed to the surface as a hydrophilizing agent, and this can impart fouling resistance. However, the separation membrane support is made of polyethylene terephthalate fibers, which have poor affinity with the components that form the separation membrane, resulting in low adhesion between the separation membrane and the separation membrane support, and low porosity inside the separation membrane, resulting in poor water permeability.

[0013] Therefore, an object of the present invention is to provide a separation membrane for use in sewage treatment and the like that is applicable to MBR, which has excellent adhesion between the separation membrane and the separation membrane support and which combines fouling resistance and water permeability by controlling the pore size on the surface of the separation membrane and the porosity inside the separation membrane.

[0014] The present invention aims to solve the above-mentioned problems, and provides the following inventions. [1] A separation membrane comprising a polymer membrane having a separation function formed on a separation membrane support, wherein the maximum pore size on the surface of the separation membrane is 10 nm to 120 nm, and the porosity is 40% to 80% when a region within 15 μm from the surface of the separation membrane is measured with a confocal laser microscope. [2] The separation membrane according to [1], wherein the porosity is 57% to 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], wherein the water absorbency of the separation membrane support is evaluated by the Byreck method of JIS-L1907 (2010), and the height of water rises is 100 mm to 180 mm. [5] The separation membrane according to any one of [1] to [4], wherein the separation membrane support contains polyethylene glycol in an amount of 0.4% by mass or more and 3.0% by mass or less. [6] The separation membrane according to [5], wherein the molecular weight of the polyethylene glycol contained in the separation membrane support is 1,000 to 35,000. [7] The separation membrane according to any one of [1] to [6], wherein the component of the polymer membrane having separation function is polyvinylidene fluoride. [8] A method for producing a separation membrane, comprising: step a) casting a polymer solution containing components for forming a polymer membrane having separation function onto one surface of the separation membrane support; and step b) coagulating the polymer solution in a coagulation liquid to form a separation membrane, wherein step b) includes forming a flow of the coagulation liquid in the direction of the polymer solution being cast from the separation membrane support within 3 seconds after immersing the polymer solution in the coagulation liquid. [9] A membrane separation element comprising the separation membrane according to any one of [1] to [7].

[10] A sewage and wastewater treatment method in which the membrane separation element according to [9] is applied to a membrane separation activated sludge process.

[0015] According to the present invention, by controlling the maximum pore size on the surface of the separation membrane and making the porosity inside the separation membrane within a certain range, it is possible to obtain a separation membrane that is resistant to fouling and has high water permeability.

[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 size on the surface of the separation membrane of the present invention is 10 nm or more and 120 nm or less. By making the maximum pore size 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 making the maximum pore size 120 nm or less, preferably 100 nm or less, fouling resistance is improved and water permeability can be maintained for 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 25 nm or less, and even more preferably 20 nm or less, to provide uniform pore sizes, thereby preventing localized adhesion and deposition of sludge components on the membrane and maintaining water permeability for a long period of time.

[0019] The separation membrane of the present invention has a porosity of 40% or more and 80% or less when measured with a confocal laser microscope in a region within 15 μm from the surface. By setting the porosity to 40% or more, preferably 57% or more, more preferably 60% or more, and even more preferably 70% or more, water flow paths are formed in the separation membrane, improving water permeability. On the other hand, by setting the porosity to 80% or less, preferably 75% or less, the strength of the separation membrane can be maintained.

[0020] The porosity of a separation membrane can be measured and calculated using a confocal laser microscope. Specifically, the method is as follows: (1) The separation membrane is stained with a fluorescent substance (3,3,3',3'-tetramethyl-1,1'-bis(4-sulfobutyl)indocarbocyanine sodium). (2) Using a confocal laser microscope, the separation membrane surface is positioned so that the axial direction of the laser light is perpendicular to the separation membrane surface, and a 200 μm x 200 μm area is observed parallel to the surface, and an area up to 20 μm perpendicular to the surface is observed at 0.1 μm intervals. (3) From a three-dimensional image created by stitching together the obtained images, a cross-sectional image perpendicular to the separation membrane surface is extracted, and the area S1 from the surface to 15 μm is calculated. (4) The observed cross-sectional image is binarized into the structural portion consisting of the separation membrane-forming components and the pore portion, and the area S2 of the pores within 15 μm from the separation membrane surface is calculated. (5) The area values ​​obtained in (3) and (4) are used to calculate the porosity (%) according to the following formula: Porosity=S2 / S1×100 The separation membrane of the present invention is preferably produced by a method in which a polymer solution containing separation membrane-forming components is cast onto at least one surface of a separation membrane support and then fixed.

[0021] The separation membrane-forming component is preferably a solution of a material that has a separation function when formed into a separation membrane, such as polyarylethersulfone, polysulfone, polyethersulfone, polyimide, polyvinylidene fluoride, or cellulose acetate.

[0022] Among these, solutions containing polysulfone, polyaryl ether sulfone or polyvinylidene fluoride are more preferred in terms of chemical, mechanical and thermal stability, with polyvinylidene fluoride solutions being 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. By making the thickness of the polymer membrane preferably 50 μm or more, more preferably 80 μm or more, and even more preferably 100 μm or more, exposure of the separation membrane support can be prevented, anti-fouling properties can be exhibited, and an increase in filtration pressure can be suppressed. On the other hand, by making the thickness of the polymer membrane preferably 500 μm or less, more preferably 300 μm or less, and even more preferably 200 μm or less, a decrease in water permeability can be suppressed, the number of separation membranes stacked per membrane separation element can be increased, and filtration performance can be improved.

[0024] The adhesive strength between the separation membrane of the present invention and the separation membrane support is preferably 1070 gf / 25 mm or more. By setting the adhesive strength to be 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 are firmly adhered to each other, and peeling of the separation membrane from the separation membrane support during long-term use or cleaning operations can be suppressed.

[0025] [Separation membrane support] A spunbonded nonwoven fabric is preferred as the separation membrane support of the present invention. A spunbonded nonwoven fabric is a long-fiber nonwoven fabric made of thermoplastic fibers, and when used as a separation membrane support, it can suppress non-uniformity and membrane defects when a polymer solution is cast, which are caused by fluffing that is likely to occur when a short-fiber nonwoven fabric is used. In addition, a spunbonded nonwoven fabric has excellent mechanical strength, and when used as a separation membrane support, a separation membrane with excellent durability can be obtained.

[0026] The thermoplastic polymer constituting the separation membrane support of the present invention can be formed from, for example, a polyester polymer, a polyamide polymer, a polyolefin polymer, or a mixture or copolymer of these, etc. Among these, a polyester polymer can be used to obtain a separation membrane support that is more excellent in durability, such as mechanical strength, heat resistance, water resistance, and chemical resistance.

[0027] The polyester polymer is a polyester 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 5-sodium sulfoisophthalate, aliphatic dicarboxylic acid compounds such as adipic acid and sebacic acid, and alicyclic dicarboxylic acid compounds such as cyclohexanedicarboxylic acid. Their ester-forming derivatives, 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 is 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, polybutylene succinate, and copolymers thereof. Polyethylene terephthalate is preferably used because of its excellent strength.

[0029] The thermoplastic fibers constituting the separation membrane support of the present invention may be fibers made of a single component, composite fibers made of multiple components, or so-called mixed fibers in which multiple types of fibers are mixed. As composite fibers, composite fibers in which a high-melting point polymer is used as the core or island component and a low-melting point polymer having a melting point lower than that of the high-melting point polymer is used as the sheath or sea component are preferred. By using composite fibers, the fibers are firmly bonded to each other by thermocompression bonding during the production of nonwoven fabrics, thereby suppressing non-uniformity during casting of the polymer solution and membrane defects due to fluffing when used as a separation membrane support. Although mixed fibers made of a mixture of fibers made only of a high-melting point polymer and fibers made only of a low-melting point polymer also have good adhesion between the fibers, composite fibers have a larger number of bonding points and therefore provide particularly good improvement in mechanical strength when used as a separation membrane support.

[0030] The composite form of the composite fiber can be, for example, a concentric sheath-core type, an eccentric sheath-core type, or an islands-in-the-sea type, since these types allow efficient thermal bonding between the fibers. The cross-sectional shape of the fiber can be, for example, a circular cross section, a flat cross section, a polygonal cross section, a multi-lobal cross section, or a hollow cross section. A concentric sheath-core type composite form and a circular or flat cross section of the fiber are preferred, since this strengthens the bonding between the fibers by thermal compression bonding, and also reduces the thickness of the resulting separation membrane support, thereby saving space when used as a membrane separation element.

[0031] The components of the composite fiber preferably have a high-melting-point polymer core component and a low-melting-point polymer sheath component, with the melting point difference between them being 15°C or more and 45°C or less. That is, the melting point of the sheath component is preferably [melting point of core component - 45]°C or more and [melting point of core component - 15]°C or less. By making the melting point difference 15°C or more (the melting point of the sheath component is [melting point of core component - 15]°C or less), preferably 20°C or more, it is possible to bond only the low-melting-point polymer of the sheath component in the thermocompression bonding step, and the strength of the high-melting-point polymer disposed in the core portion can be maintained. This improves the mechanical strength of the separation membrane support. Furthermore, thermocompression bonding can control the basis weight of the nonwoven fabric, improving the permeability of the separation membrane-forming components 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 is at least [the melting point of the core component - 45]°C), preferably 40°C or less, excessive adhesion of the low-melting point polymer of the sheath component during thermocompression bonding can be suppressed. This makes it possible to control the basis weight of the nonwoven fabric, suppress a decrease in the permeability of the separation membrane-forming components into the nonwoven fabric, and improve the adhesion between the separation membrane and the separation membrane support. Furthermore, decomposition of the low-melting point polymer of the sheath component during spinning can be suppressed, and yarn breakage can be suppressed, thereby improving the mechanical strength of the separation membrane support.

[0033] The melting point difference between the polymers can be controlled within a desired range by the copolymerization amount of the polymer. As the melting point control substance for the low-melting point polymer of the sheath component, a dicarboxylic acid component is preferred in consideration of copolymerization into a polyester, with isophthalic acid, cyclohexanedicarboxylic acid, naphthalenedicarboxylic acid, adipic acid, and sebacic acid being more preferred, and isophthalic acid, which has good polymerizability during copolymerization, being even more preferred. From the viewpoint of controlling the melting point, these dicarboxylic acid components are preferably 5 mol% or more and 25 mol% or less relative to the total acid components. 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 the high-melting point polymer and the low-melting point polymer can be controlled within a desired range.

[0034] The melting point of the high-melting-point polymer of the core component is preferably 160°C to 320°C. When a separation membrane support composed of composite fibers is formed, a separation membrane with good membrane formability and excellent durability is obtained. The melting point of the high-melting-point polymer is more preferably 170°C or higher, and even more preferably 180°C or higher. Even after passing through a heating process during the production of a separation membrane or membrane separation element, a separation membrane with excellent mechanical strength and dimensional stability and excellent durability can be obtained. On the other hand, by making the melting point of the high-melting-point polymer of the core component more preferably 300°C or lower, and even more preferably 280°C or lower, the spinning temperature can be kept low, and decomposition of the low-melting-point polymer of the sheath component in particular can be suppressed. Suppressing polymer decomposition reduces thread breakage during spinning, and mechanical strength of the separation membrane support can be obtained.

[0035] The melting points of the core and sheath components of the composite thermoplastic fiber constituting the separation membrane support are measured and calculated as follows: (1) After peeling the separation membrane with tape or the like, a 5 mg measurement sample is taken from the separation membrane support, and as a pretreatment, the sample is melted at 290°C for 5 minutes under a nitrogen stream, and then rapidly cooled to room temperature at 50°C / min. (2) The melting point is measured using a differential scanning calorimeter (DSC, for example, the "Q-2000" manufactured by TA Instruments) under the following conditions: - Heating rate: 2°C / min - Measurement temperature: -20°C to 300°C (3) The melting points (°C) of the core and sheath components obtained in (2) above are rounded to one decimal place. (4) Another measurement sample is taken from the separation membrane support, and treated with alkali to elute the sheath component, resulting in a yarn consisting of only the core component. (5) 5 mg of the sample obtained in (4) above is collected and pretreated in the same manner as in (1) above. (6) The sample pretreated in (5) above is subjected to DSC measurement in the same manner as in (2) above to measure the melting point of the core component. (7) The melting point of the shell component is determined from the melting points obtained in (3) and (6) above.

[0036] When the thermoplastic fiber constituting the separation membrane support of the present invention is a core-sheath composite fiber, the composite mass ratio (core:sheath) is preferably 50% by mass to 95% by mass of the core component (composite mass ratio (core:sheath) of 50:50 to 95:5). By making the core component 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 during thermocompression bonding in producing a nonwoven fabric can be suppressed. This makes it possible to control the thickness of the nonwoven fabric, and when a spunbonded nonwoven fabric is used as a separation membrane support, a decrease in the permeability of the coagulation liquid from the support side can be suppressed. Suppressing a decrease in the permeability of the coagulation liquid improves the porosity of the surface of the separation membrane, 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 mass% or less, more preferably 90 mass% or less, and even more preferably 80 mass% or less, the low-melting point polymer of the sheath component becomes more easily adhered, the thickness of the nonwoven fabric can be controlled, and 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 behind this is speculated as follows. Separation membranes are often produced by casting a polymer solution containing separation membrane-forming components onto a separation membrane support and solidifying it. To solidify the polymer solution, a commonly used method involves immersing the cast polymer solution together with the support in a coagulation liquid, the main component of which is water. In this case, by using a hydrophilic spunbond nonwoven fabric as the separation membrane support, the coagulation liquid efficiently penetrates into the support from the side opposite to where the polymer solution was cast, allowing the coagulation liquid to efficiently contact and coagulate the polymer solution from all directions, resulting in rapid formation of the separation membrane. It is believed that this allows for the formation of highly liquid-permeable pores within the separation membrane, thereby improving the porosity of the separation membrane surface.

[0038] Furthermore, when the membrane is immersed in a coagulation liquid to solidify the polymer solution, the coagulation liquid can be pushed in from the side opposite to where the polymer solution was cast, forming permeable channels all the way to the membrane surface, which is believed to improve the liquid permeability within the separation membrane and result in a separation membrane with high water permeability. Furthermore, penetration of the coagulation liquid from the side opposite to where the polymer solution was cast prevents excessive penetration of the separation membrane-forming components, which would otherwise lead to exudation to the back of the support. This is believed to prevent contamination of the membrane production equipment and a 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 water rising when evaluated by the Byreck method (after immersion in water for 10 minutes) is 100 mm or more and 180 mm or less. The height of water rising is preferably 100 mm or more, more preferably 120 mm or more, and even more preferably 150 mm or more. The spunbonded nonwoven fabric has high hydrophilicity, and when used as a separation membrane support, the coagulation bath quickly penetrates the fabric, forming voids within the separation membrane that have high liquid permeability, thereby improving the water permeability of the resulting separation membrane.

[0040] The separation membrane support of the present invention can be imparted with water absorbency by hydrophilizing the constituent polymer of the thermoplastic fibers of the spunbond nonwoven fabric or by adding a hydrophilic agent, but hydrophilizing the constituent polymer of the thermoplastic fibers that make up the separation membrane support is preferred because it has a high hydrophilizing effect and can make the separation membrane support uniformly hydrophilic all the way to the inside.

[0041] The constituent polymer of the thermoplastic fiber can be made hydrophilic by copolymerizing a metal sulfonate group-containing isophthalic acid component or polyethylene glycol, but copolymerizing polyethylene glycol is preferred from the viewpoints of suppressing thickening during copolymerization and improving hydrophilicity.

[0042] The copolymerization rate of polyethylene glycol relative to the separation membrane support of the present invention is preferably 0.4% by mass or more and 3.0% by mass or less of polyethylene glycol in the separation membrane support. 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 quickly penetrates from the support side, promoting the formation of highly liquid-permeable pores in the separation membrane and an improvement in 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, thread breakage due to thickness variation during spinning can be suppressed, and thus the strength of the separation membrane support can be increased.

[0043] In a preferred embodiment, the polyethylene glycol is copolymerized into the sheath component of the fibers constituting the nonwoven fabric. By copolymerizing into the sheath component, the surface of the separation membrane support can be hydrophilized, and therefore, when used as a separation membrane support, the coagulation bath can quickly penetrate from the support side, promoting the formation of pores with high liquid permeability within the separation membrane and an improvement in the porosity of the separation membrane surface, thereby improving the water permeability of the formed separation membrane.

[0044] The copolymerization rate of polyethylene glycol in the nonwoven fabric and the copolymerization rate of polyethylene glycol in the sheath component of the composite fiber constituting the nonwoven fabric can be measured and calculated using a nuclear magnetic resonance (NMR) spectrometer. Specifically, the procedure is as follows: (1) After peeling the separation membrane with tape or the like, 50 mg of a measurement sample is collected from the separation membrane support and dissolved in 1 mL of deuterated hexafluoroisopropanol (HFIP). (2) As a measurement device, for example, "AL-400" manufactured by JEOL Ltd. or the like is used, and the measurement conditions are as follows: １ H-NMR is measured with an accumulation count of 128. (3) CH in polyethylene glycol obtained by NMR measurement ２ The copolymerization rate (mass%) of polyethylene glycol in the separation membrane support is calculated from the integral value of the peak and the integral value of (H) of the benzene ring in the polyester polymer. (4) A measurement sample is again taken from the separation membrane support and treated with alkali to elute the sheath component, resulting in a thread consisting only of the core component. (5) 50 mg of the sample obtained in (4) is dissolved in 1 mL of deuterated hexafluoroisopropanol (HFIP). (6) The NMR measurement of (2) is performed to determine the CH in the polyethylene glycol. ２ The copolymerization rate (% by mass) of polyethylene glycol in the core component is calculated from the integral value of the peak and the integral value of (H) of the benzene ring in the polyester polymer. (7) The copolymerization rate (% by mass) of polyethylene glycol in the core component is subtracted from the copolymerization rate (% by mass) of polyethylene glycol in the nonwoven fabric, and the result is divided by the sheath ratio. The sheath ratio is calculated by observing the cross section of the yarn in the nonwoven fabric.

[0045] When the copolymerization component of the constituent polymer of the thermoplastic fiber in the separation membrane support of the present invention is polyethylene glycol, the number-average molecular weight of the polyethylene glycol is preferably 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, and when used as a separation membrane support, the coagulation bath quickly penetrates from the support side, promoting the formation of highly liquid-permeable pores in 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 the nonwoven fabric is used as a separation membrane support, the elution of internal substances of the support into water can be suppressed. Furthermore, thread breakage due to thickness or thinness during spinning can be suppressed, thereby increasing the strength of the separation membrane support.

[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, the procedure is as follows: (1) After peeling the separation membrane with tape or the like, 50 mg of a measurement sample is collected from the separation membrane support in a sealable vial, 1 mL of 28% by mass ammonia water is added, and the sample is heated at 120°C for 5 hours to dissolve the sample. (2) After cooling, 1.5 mL of 6 mol / L hydrochloric acid is added, and the volume is adjusted to 5 mL with purified water. After centrifugation, the mixture is filtered through a 0.45 μm filter to obtain a filtrate. (3) GPC measurement of the filtrate is performed using a measuring device such as a Shimadzu Corporation "Differential Refractive Index Detector RID-20A." (4) The molecular weight of polyethylene glycol in the nonwoven fabric is calculated using a molecular weight calibration curve created using standard samples of known molecular weight.

[0047] The single filament fineness of the thermoplastic fiber 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 fiber constituting the separation membrane support is 0.1 dtex or more, spinnability is less likely to decrease during nonwoven fabric production, and when used as a separation membrane support, breathability is maintained, so that the polymer solution cast during membrane formation quickly penetrates into the separation membrane support, resulting in a nonwoven fabric with good separation membrane adhesion. On the other hand, if the single filament fineness of the thermoplastic fiber constituting the separation membrane support is 3.0 dtex or less, high density can be achieved when used as a separation membrane support, resulting in a good nonwoven fabric with little over-penetration during polymer solution casting. Note that fibers with different finenesses may be mixed.

[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, spinnability is less likely to decrease during nonwoven fabric production, and when used as a separation membrane support, breathability can be maintained, allowing the polymer solution cast during membrane formation to quickly penetrate into the separation membrane support, resulting in a nonwoven fabric with good separation membrane adhesion. On the other hand, if the average single fiber diameter of the thermoplastic fibers constituting the separation membrane support is 30 μm or less, high density can be achieved when used as a separation membrane support, resulting in a good nonwoven fabric with little over-penetration of the polymer solution during casting. 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 20 g / m ２ More than 200g / m ２ The basis weight of the separation membrane support is preferably 20 g / m or less. ２ More preferably, 70 g / m ２ More preferably, 120 g / m ２ By setting the weight of the separation membrane support to 200 g / m or more, high mechanical strength and excellent dimensional stability are obtained. ２or less, more preferably 150 g / m ２ By making the thickness less than 1 / 2 mm, the thickness of the separation membrane can be reduced, and the number of separation membranes stacked per membrane separation element can be increased, thereby improving the filtration performance.

[0050] When laminating the nonwoven fabrics to form a separation membrane support, the weight of each nonwoven fabric is set to 20 g / m ２ More than 200g / m ２ There are no limitations as long as the weight is within the following range. For example, ２ Three-ply laminate and 30 g / m ２ The thickness is determined appropriately depending on the product design, such as two layers of laminated laminated laminate.

[0051] The thickness of the separation membrane support of the present invention is determined appropriately depending on the application and product design, but is preferably 0.05 mm or more and 0.50 mm or less. By setting the thickness of the separation membrane support to 0.05 mm or more, more preferably 0.15 mm or more, and even more preferably 0.20 mm or more, excellent mechanical strength and durability are achieved. On the other hand, by setting the thickness of the separation membrane support to 0.50 mm or less, more preferably 0.40 mm or less, the number of separation membranes stacked per membrane separation element can be increased, thereby improving filtration performance.

[0052] [Method for manufacturing separation membrane] The method for manufacturing a separation membrane of the present invention includes step a) of casting a polymer solution containing components for forming a polymer membrane having separation function onto at least one surface of a separation membrane support, and step b) of coagulating the polymer solution in a coagulation liquid to form a separation membrane.

[0053] The polymer solution of the present invention preferably contains components that form a polymer membrane having a separation function (hereinafter referred to as separation membrane-forming components), a pore-opening agent, and a solvent.

[0054] The separation membrane of the present invention is preferably produced by a method in which a polymer solution containing a separation membrane-forming component, a pore-opening agent, and a solvent is cast onto a separation membrane support made of a nonwoven fabric, and then solidified. When solidifying the polymer solution, a method in which the cast polymer solution together with the support is immersed in a coagulation liquid, which is a non-solvent, to solidify the solution is preferred.

[0055] The separation membrane-forming component contained in the polymer solution of the present invention is preferably a resin that has separation function when formed into a separation membrane. Examples of separation membrane-forming components that can be used 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, as they are easy to form membranes from a solution and have excellent physical durability and chemical resistance, with polyvinylidene fluoride being even more preferred. A mixture of the above resins may also be used. However, the resin content is preferably 50% by weight or more, more preferably 60% by weight or more.

[0056] The pore-opening agent contained in the polymer solution of the present invention is preferably one that is extracted when immersed in a coagulation liquid and has the effect of making the resin layer porous. The pore-opening agent is preferably one that is highly soluble in the coagulation liquid, and inorganic salts such as calcium chloride and calcium carbonate can be used. Other examples include polyoxyalkylenes such as polyethylene glycol and polypropylene glycol, water-soluble polymers such as polyvinyl alcohol, polyvinyl butyral, and polyacrylic acid, and glycerin. The pore-opening agent can be selected arbitrarily depending on the resin. For example, when a resin containing polyvinylidene fluoride is used, polyethylene glycol is preferred. Among these, polyethylene glycol with a weight-average molecular weight of 10,000 or more is particularly preferred from the viewpoint of the balance between 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 components. The solvent acts on the separation membrane-forming components and the pore-opening agent to promote their formation of a separation membrane. Examples of solvents that can be used 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 in the separation membrane-forming components, are preferred.

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

[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, and more preferably 8% by weight or more and 20% by weight or less, which allows the strength of the separation membrane to be maintained and also allows 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, and more preferably 9% by weight or more and 10% by weight or less, which makes it possible to control the standard deviation of the maximum pore size and the average pore size, and also to obtain the strength and stable water permeability of the separation membrane.

[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, and more preferably 60% by weight or more and 90% by weight or less, which can suppress gelation of the polymer solution and maintain the strength of the separation membrane.

[0062] The non-solvent in the present invention is preferably added not only to the coagulation liquid but also to the polymer solution, since this facilitates the uniformization of the pore size on the surface of the separation membrane and the control of the size of the voids in the separation membrane. The content of the non-solvent in the polymer solution is preferably 0.1 wt% or more and 20 wt% or less. The content of the non-solvent is more preferably 0.5 wt% or more and 15 wt% or less (solvent amount is 40 wt% or more and 94.4 wt% or less), which can suppress gelation of the polymer solution.

[0063] The coagulation liquid can be a non-solvent or a mixture containing a non-solvent and a solvent. When a non-solvent is used in the polymer solution in the coagulation liquid, the non-solvent content is preferably 80% by weight or more. By making the non-solvent content in the coagulation liquid 80% by weight or more, the coagulation rate of the separation membrane-forming components can be maintained, the pore size on the surface of the separation membrane can be stably formed, and voids in the separation membrane can also be stably formed. The non-solvent content in the coagulation liquid is more preferably 85% by weight or more and 100% by weight or less.

[0064] On the other hand, when a non-solvent is not used in the polymer solution, the content of the non-solvent in the coagulation liquid is preferably 60% by weight or more. This allows the coagulation rate of the separation membrane-forming components to be appropriate, stabilizing the formation of pores on the surface of the separation membrane and controlling the voids in the separation membrane. When a non-solvent is not used in the polymer solution, the content of the non-solvent in the coagulation liquid is more preferably 60% by weight or more and 99% by weight or less, thereby allowing the pore size on the surface of the separation membrane and the porosity in the separation membrane to be controlled.

[0065] In the present invention, the temperature of the coagulation liquid is preferably 15° C. or higher and 80° C. or lower. The coagulation liquid temperature is more preferably 20° C. or higher and 60° C. or lower, which makes it possible to control the coagulation rate, and in turn, to control the porosity in the separation membrane and obtain water permeability.

[0066] Furthermore, in step b), it is preferable to form a flow of coagulation liquid in the direction of the polymer solution being cast from the separation membrane support at the beginning of the coagulation process. The beginning of the coagulation process refers to the period from when the polymer solution is immersed in the coagulation bath until coagulation is complete, and is preferably within 3 seconds, more preferably within 2 seconds, and even more preferably within 1 second after immersion in the coagulation bath. By forming a flow of coagulation liquid at the beginning of the coagulation process, the porosity within the separation membrane can be increased. Specific examples of means for "forming a flow" include forcing the coagulation liquid toward the polymer solution being cast from the separation membrane support (i.e., from the back side of the separation membrane support). The forcing pressure for forming the flow is preferably 1 to 3 kPa. The forcing time is preferably 3 to 10 seconds.

[0067] In the separation membrane of the present invention, the water permeability of the separation membrane in which the maximum pore size and porosity are controlled is calculated as the water permeation rate (cubic meters) per second per square meter of membrane surface at an evaluation temperature of 25°C and a pressure of 1 kPa, and is 60 x 10 －９ m ３ / m ２ / sec / Pa or more. More preferably, 65×10 －９ m ３ / m ２ / sec / Pa or more, more preferably 70×10 －９ m ３ / m ２ / sec / Pa or more means that the membrane has high water permeability, and the amount of water permeated per membrane separation element is increased, thereby improving filtration performance.

[0068] The membrane separation element of the present invention is formed by integrating the above-mentioned separation membrane with a flow path material and laminating them together for ease of handling, and examples of its configuration 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 path material is sandwiched and integrated between two separation membrane sheets with the separation membrane-formed side facing outward. A plurality of 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 treating seawater, brackish water, river water, sewage water, etc. In particular, it is more preferably used for treating sewage water by a membrane separation activated sludge process.

[0070] The separation membrane of the present invention will be specifically described below based on examples. These are merely 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 methods.

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

[0072] (2) Molecular Weight of Polyethylene Glycol (PEG) of Separation Membrane Support The molecular weight of polyethylene glycol was measured and calculated using a gel permeation chromatography (GPC) measuring device (such as a "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 separation membrane support, and copolymerization rate (mass%) of PEG in composite fiber constituting nonwoven fabric The copolymerization rate of PEG was measured and calculated using an "AL-400" measuring device manufactured by JEOL Ltd. according to the method described in the specification.

[0074] (4) Single Fiber Fineness (dtex) The single fiber fineness was determined by peeling the separation membrane with tape or the like, randomly collecting 10 small samples from the separation membrane support, taking photographs at 500 to 3000 magnifications with a scanning electron microscope ("VHX-2000" manufactured by Keyence Corporation), measuring the diameters of 10 single fibers from each sample, a total of 100 single fibers, and correcting the average value for the polymer density and rounding off to one decimal place.

[0075] (5) Average Single Fiber Diameter (μm) The average single fiber diameter was determined by peeling the separation membrane with tape or the like, then randomly collecting 10 small samples from the separation membrane support, taking photographs at 500 to 3000 magnifications with a scanning electron microscope ("VHX-2000" manufactured by Keyence Corporation), measuring the diameters of 10 single fibers from each sample, a total of 100 single fibers, and rounding the average value to one decimal place.

[0076] (6) Basis weight of separation membrane support (g / m ２ ) The basis weight was determined by peeling the separation membrane with tape or the like, then sampling three 30 cm × 50 cm separation membrane supports, measuring the weight of each sample, and converting the average of the obtained values ​​into a value per unit area, which was then rounded to the first decimal place.

[0077] (7) Thickness (mm) of the separation membrane support The thickness of the separation membrane support was measured by peeling the separation membrane with tape or the like, randomly collecting 10 small sample pieces, and using a micrometer manufactured by Mitutoyo Corporation, clamping the separation membrane support between an anvil and spindle with a diameter of 6 mm, measuring two points on the small sample pieces at equal intervals to the nearest 0.01 mm, and rounding off the average of a total of 20 points to the nearest hundredth.

[0078] (8) Density of separation membrane support (g / cm 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 two decimal places.

[0079] (9) Water Absorbency (mm) of Separation Membrane Support The water rise height (mm) of a spunbonded nonwoven fabric was measured according to JIS-L-1907 Byreck method (2010). Five 200 mm x 25 mm spunbonded nonwoven fabrics were taken, the long ends of the nonwoven fabrics were immersed 20 mm into a water tank, and the height of the water rising above the water surface 10 minutes after immersion was measured. The water rise height was calculated by averaging the obtained measurements and rounded to the nearest tenth. The higher the water rise height, the better the water absorbency of the nonwoven fabric. The higher the water absorbency, the better the permeability of the coagulation liquid from the separation membrane support side during separation membrane formation, and the higher the porosity inside the separation membrane. In Tables 1 to 3, the measurement results of the water rise height (mm) of a spunbonded nonwoven fabric are simply abbreviated as "water absorbency (mm)."

[0080] (10) Thickness of polymer membrane (μm) The thickness of the polymer membrane was measured by taking 10 small sample pieces of the separation membrane, clamping the separation membrane between an anvil and a spindle with a diameter of 6 mm using a micrometer manufactured by Mitutoyo Corporation, measuring two points on the small sample pieces at equal intervals to the nearest 0.01 mm, and rounding off the average of a total of 20 points to the nearest 1 / 2. 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 size (nm) on the surface of the separation membrane The maximum pore size of the separation membrane was determined by measuring the pore sizes of 100 pores by observation with a scanning electron microscope (SEM) and taking the maximum value. Apparatus: HITACHI SU8100 Observation magnification: ×10,000 Vapor deposition: Pt-Pd (platinum palladium) ×10 seconds (12) Standard deviation of average pore size (nm) on the surface of the separation membrane The standard deviation of the surface pore size of the separation membrane was calculated by measuring the pore sizes of 100 pores by observation with a scanning electron microscope (SEM) and then determining the standard deviation.

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

[0083] (14) Tensile strength (kgf) and tensile elongation (%) of separation membrane The prepared separation membrane was cut into a 5 mm x 40 mm strip, and the strength and elongation were measured at three points in the longitudinal direction at a tensile speed of 20 mm / min. The strength and elongation at break were read and the average value was rounded to one decimal place. Apparatus: Tensilon UCT-100 Initial length: 10 mm Tensile speed: 20 mm / min (15) Adhesive strength of separation membrane (gf / 25 mm) The adhesive strength of the separation membrane was measured with reference to the "Adhesive - Peel Adhesion Strength" method of JIS K6854-1 standard (2014). A 40 mm x 100 mm separation membrane was collected, and aluminum tape (NW-10, Nichiban Co., Ltd.) was attached to the membrane surface. A stainless steel plate (80 mm x 100 mm) for 180° peeling was attached to the bottom of the chuck of a Tensilon (RTG-1210, A&D Co., Ltd.), and the adhesive portion between the film sample and the aluminum tape was manually peeled off about 5 mm in advance. The sample was then set on the Tensilon so that the aluminum tape was on top and the sample was on the bottom, and measurements were made at a peel rate of 50 mm / min. The average load value between 10 mm and 60 mm from the initial load point after the start of the test was taken as the adhesive strength.

[0084] (16) Water permeability of separation membrane (x 10 －９ m ３ / m ２The produced separation membrane was cut into a circle with a diameter of 5 cm and set in a cylindrical filter holder. Distilled water was pre-permeated for 5 minutes at 25°C while maintaining a head height of 1 m (equivalent to a water pressure of 9,800 Pa), and then the membrane was permeated again while maintaining a head height of 1 m. The permeated water was sampled for 3 minutes to determine the permeation amount per unit time and unit area, and this was divided by the water pressure applied to the permeation surface to determine the pure water permeability coefficient per 1 Pa.

[0085] (17) Separation Performance of Separation Membrane (Particle Rejection Rate) The separation performance of the prepared separation membrane was evaluated by particle rejection rate. A stock solution for evaluation, prepared by dispersing polystyrene latex particles having an average particle size of 0.09 μm in water purified by reverse osmosis to a concentration of 20 ppm, was filtered, and the absorbance of ultraviolet light at a wavelength of 250 nm was measured for the stock solution for evaluation and the obtained filtered permeate using a spectrophotometer (such as the U-3200 manufactured by Hitachi, Ltd.), and the particle rejection rate was calculated using the following formula: Particle Rejection Rate = [(Absorbance of Stock Solution - Absorbance of Permeate Liquid) / Absorbance of Stock Solution] × 100 The obtained particle rejection rate was evaluated on a four-level scale, from S to C. S: The particle rejection rate was 95% or higher, within the range where clogging due to sludge components and the like and an increase in filtration differential pressure do not occur, and the membrane can be suitably used for MBR membrane applications. A: The particulate rejection rate is 90% or more, which is within the range that does not affect clogging due to sludge components and the like or the increase in filtration differential pressure, making it suitable for use in MBR membranes. B: The particulate rejection rate is 85% or more, which has a slight but not significant effect on clogging due to sludge components and the increase in filtration differential pressure, making it suitable for use in MBR membranes. C: The particulate rejection rate is less than 85%, which raises concerns about clogging due to sludge components and the increase in filtration differential pressure, making it difficult to use in MBR membranes.

[0086] Example 1 Separation Membrane Support Polyethylene terephthalate (PET) having a melting point of 255°C and containing 0.3% by mass of titanium oxide was used as the core component, and copolymerized polyethylene terephthalate (PET / I-PEG) having a melting point of 230°C and containing 0.2% by mass of titanium oxide was used as the sheath component, in which 11.5 mol% of isophthalic acid components relative to the total acid components and 2% by mass of polyethylene glycol (PEG) having a number-average molecular weight of 20,000 (PEG20000 manufactured by Sanyo Chemical Industries, Ltd.) were copolymerized.

[0087] The core component and sheath component were melted at temperatures of 295°C and 270°C, respectively, and spun from the orifices at a spinneret temperature of 300°C in a core:sheath mass ratio of 80:20. The resulting mixture was then spun at a spinning speed of 4,400 m / min using an ejector to spin concentric core-sheath filaments (circular in cross section) whose entire surfaces were covered with PET / I-PEG. The filaments were collected as a fiber web on a moving net conveyor.

[0088] The collected fiber web was passed between a metal uneven roll as an upper roll, in which circular convex portions were uniformly arranged in a houndstooth pattern, and a flat roll as a lower roll, and was partially thermocompression bonded at a surface temperature of the upper and lower rolls of 170°C and a linear pressure of 588 N / cm.

[0089] Furthermore, the partially thermocompression-bonded sheet was continuously passed between a pair of flat rolls, and the entire surface was thermocompression-bonded at a surface temperature of the upper and lower rolls of 120°C and a linear pressure of 686 N / cm, resulting in a PEG copolymerization rate of 0.4 mass%, a fiber diameter of 14 μm, and a basis weight of 120 g / m ２ , thickness 350 μm, density 0.34 g / m ２ 32 circular recesses with a diameter of 0.8 mm per cm ２ A separation membrane support was obtained which was made of a spunbond nonwoven fabric having a number density of 100 mm. The water rise height, which indicates the water absorbency of this separation membrane support, was 100 mm.

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

[0091] The obtained membrane forming solution was cooled to 25°C and then applied to a separation membrane support. After application, the support was immediately immersed in pure water at 25°C for 5 minutes, and then 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 size on the surface of the separation membrane was 80 nm, and the standard deviation of the average pore size was 20 nm. The water permeability of the separation membrane was 60 × 10 －９ m ３ / m２ The adhesive strength was 1090 gf / 25 mm. The results are shown in Table 1.

[0092] [Example 2-4] Separation membranes were obtained in the same manner as in Example 1, except that the copolymerization rate of PEG having a number average molecular weight of 20,000 (PEG20000 manufactured by Sanyo Chemical Industries, Ltd.) in the sheath component was changed as shown in Table 1, and the copolymerization rate of PEG in the separation membrane support was changed. The results are shown in Table 1.

[0093] By increasing the PEG copolymerization rate in the separation membrane support from 0.4% by mass (Example 1) to 2.8% by mass (Example 4), the water rise height, which indicates the water absorption of the separation membrane support, increased to 160 mm, and the porosity increased to 52% and the water permeability increased to 66 × 10 without any change in the maximum pore size or the standard deviation of the average pore size on the separation membrane surface. －９ m ３ / m ２ / sec / Pa. In addition, the adhesive strength of the separation membrane to the separation membrane support also tended to increase to 1280 gf / 25 mm.

[0094]

[0095] [Examples 5-7] Separation membranes were obtained in the same manner as in Example 1, except that PEG having a number average molecular weight of 7000 (PEG6000S manufactured by Sanyo Chemical Industries, Ltd.) was used as the PEG in the sheath component, and the copolymerization rate was changed as shown in Table 1, thereby changing the copolymerization rate of PEG in the separation membrane support. The results are shown in Table 1.

[0096] By decreasing the number average molecular weight of PEG in the separation membrane support from 20,000 (Example 4) to 7,000 (Example 7), the water rise height, which indicates the water absorption of the separation membrane support, decreased to 150 mm, the porosity decreased to 46%, and the water permeability decreased to 64 × 10 －９ m ３ / m ２ / sec / Pa. In addition, the adhesive strength of the separation membrane to the separation membrane support also tended to decrease to 1240 gf / 25 mm.

[0097] Examples 8-10 Separation membranes were obtained in the same manner as in Example 4, except that PEG having a number-average molecular weight of 1,000 (PEG1000 manufactured by Sanyo Chemical Industries, Ltd.), PEG having a number-average molecular weight of 3,400 (PEG4000S manufactured by Sanyo Chemical Industries, Ltd.), and PEG having a number-average molecular weight of 35,000 (PEG35000 manufactured by Sigma-Aldrich) were used. The results are shown in Table 1.

[0098] By decreasing the number average molecular weight of PEG in the separation membrane support from 20,000 (Example 4) to 1,000 (Example 8) or 3,400 (Example 9), the water rise height, which indicates the water absorption of the separation membrane support, decreased to 100 mm, the porosity decreased to 40%, and the water permeability decreased to 60 × 10 －９ m ３ / m ２ / sec / Pa. In addition, the adhesive strength of the separation membrane to the separation membrane support also tended to decrease.

[0099] On the other hand, by increasing the number average molecular weight of PEG in the separation membrane support to 35,000 (Example 10), the water rise height indicating the 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 －９ m ３ / m ２ / sec / Pa. Furthermore, the adhesive strength of the separation membrane to the separation membrane support also decreased, and the particle rejection rate also tended to decrease.

[0100] Examples 11 to 13 Separation membranes were obtained in the same manner as in Example 4, except that the content of the pore-opening agent during separation membrane formation was changed to 8 wt %, 10 wt %, and 11 wt %. The results are shown in Table 2.

[0101] By decreasing the content of the pore-opening agent in the separation membrane forming solution from 9 wt% (Example 4) to 8 wt% (Example 11), the porosity decreased and the standard deviation of the maximum pore size and the average pore size tended to increase. Furthermore, the water permeability also decreased and the fine particle rejection rate also tended to decrease. On the other hand, by increasing the content of the pore-opening agent to 10 wt% (Example 12) or 11 wt% (Example 13), the porosity increased, but the standard deviation of the maximum pore size and the average pore size tended to increase. Furthermore, the water permeability increased, but the fine particle rejection rate tended to decrease.

[0102]

[0103] Examples 14 to 17 Separation membranes were obtained in the same manner as in Example 4, except that the copolymerization rate of isophthalic acid in the sheath component was 25 mol %, 22 mol %, 8 mol %, or 5 mol %. The results are shown in Table 2.

[0104] By increasing the copolymerization rate of isophthalic acid from 11.5 mol% (Example 4) to 25 mol% (Example 14) and 22 mol% (Example 15), 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, by decreasing the copolymerization rate of isophthalic acid to 8 mol% (Example 16) and 5 mol% (Example 17), the thickness of the separation membrane support increased and the water permeability tended to decrease due to the breakthrough of the separation membrane-forming components.

[0105] Examples 18 to 22 Separation membranes were obtained in the same manner as in Example 4, except that the mass ratio of the core component polymer to the sheath component polymer in the core-sheath composite fibers constituting the separation membrane support was changed to core:sheath = 50:50, 60:40, 70:30, 90:10, or 95:5. The results are shown in Table 3.

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

[0107]

[0108] [Examples 23-26] The basis weight of the separation membrane support was 20 g / m ２ , 70 g / m ２ , 150 g / m ２ , 200 g / m ２ The separation membrane was obtained in the same manner as in Example 4, except that the temperature was changed to the following: The results are shown in Table 3.

[0109] The basis weight of the separation membrane support is 120 g / m ２ (Example 4) to 20 g / m ２ (Example 23), 70 g / m ２ By reducing the basis weight to 150 g / m (Example 24), 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. ２ (Example 25), 200 g / m ２ Increasing the amount of the separation membrane support to (Example 26) increased the thickness of the separation membrane support, and the permeability tended to decrease due to breakthrough of the separation membrane-forming components.

[0110] [Example 27] A separation membrane was obtained in the same manner as in Example 4, except that after the membrane forming solution was applied to the separation membrane support, it was immersed in pure water at 25°C and, within 1 second, pure water was pressed against it from the separation membrane support side at a pressure of 1 kPa for about 3 seconds. The results are shown in Table 4.

[0111] Within 3 seconds of immersion in pure water, pure water was pressed against the separation membrane support side. This resulted in no change in the maximum pore size or standard deviation of the average pore size on the separation membrane surface, but the porosity increased to 63%, and the water permeability increased to 75 × 10－９ m ３ / m ２ / sec / Pa.

[0112]

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

[0114] By reducing the content of the pore-opening agent in the separation membrane forming solution from 9 wt% (Example 27) to 8 wt% (Example 28), the porosity decreased and the standard deviation of the maximum pore size and average pore size tended to increase. Furthermore, the water permeability also decreased and the fine particle rejection rate also tended to decrease. On the other hand, by increasing the content of the pore-opening agent to 10 wt% (Example 29) or 11 wt% (Example 30), the porosity increased, but the standard deviation of the maximum pore size and average pore size tended to increase. Furthermore, the water permeability increased, but the fine particle rejection rate tended to decrease.

[0115] [Comparative Examples 1 and 2] Separation membranes were obtained in the same manner as in Example 4, except that PEG was not copolymerized in the separation membrane support (Comparative Example 1) and the PEG copolymerization rate in the separation membrane support was changed to 4.0 mass% (Comparative Example 2). The results are shown in Table 5.

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

[0117] The separation membrane obtained in Comparative Example 2 had poor water permeability due to excessive penetration of the membrane forming solution into the separation membrane support due to an excessive PEG copolymerization rate, resulting in an increase in the amount of separation membrane-forming components inside the separation membrane support and breakthrough of the separation membrane-forming components.

[0118]

[0119] [Comparative Examples 3 to 5] Separation membranes were obtained in the same manner as in Example 4, except that no pore-opening agent was added to the separation membrane forming solution (Comparative Example 3), the pore-opening agent content was changed to 5 wt% (Comparative Example 4), and the pore-opening agent content was changed to 15 wt% (Comparative Example 5). The results are shown in Table 5.

[0120] The separation membrane obtained in Comparative Example 3 had a low porosity and poor water permeability because no pore-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, which resulted in increased standard deviations of the maximum pore size and average pore size on the separation membrane surface and inferior fine particle rejection rate.

[0122] The results are shown in Table 6.

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

[0124]

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

[0126] The separation membrane obtained in Comparative Example 7 had a low porosity and poor water permeability because no pore-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, which resulted in increased standard deviations of the maximum pore size and average pore size on the separation membrane surface and inferior fine 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 the aqueous surfactant solution for 20 hours. A 1.8 wt % aqueous solution of polyoxyethylene sorbitan monostearate 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 Examples.

[0129]

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 polyethylene glycol in an amount of 0.4% by mass or more and 3.0% by mass or less, The maximum pore size 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. 3. The separation membrane according to claim 1, 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 claim 1 or 2, wherein the water absorption of the separation membrane support is evaluated by the Byreck method according to JIS-L1907 (2010) in terms of the height of water rise, and the height of water rise is 100 mm or more and 180 mm or less.

5. 3. The separation membrane according to claim 1, 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. 3. The separation membrane according to claim 1, wherein the component of the polymer membrane having a separation function is polyvinylidene fluoride.

7. A method for producing a separation membrane, comprising: step a) casting a polymer solution containing components for forming a polymer membrane having a separation function onto one surface of the separation membrane support; and step b) solidifying the polymer solution in a coagulation liquid to form a separation membrane, The polymer solution contains polyoxyalkylenes as a pore-opening agent, In the step b), within 3 seconds after the polymer solution is immersed in the coagulation liquid, 3. The method for producing a separation membrane according to claim 1, further comprising forming a flow of the coagulation liquid in the direction of the polymer solution being cast from a separation membrane support.

8. A membrane separation element comprising the separation membrane according to claim 1 or 2.

9. A sewage and wastewater treatment method, comprising applying the membrane separation element according to claim 8 to a membrane separation activated sludge process.

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