JP2020049399A - Semipermeable membrane support for membrane separation activated sludge treatment - Google Patents

Abstract

To provide a semipermeable membrane support capable of improving a penetration amount of a dope into the semipermeable membrane support at a dope application time, and having high bond strength between a semipermeable membrane and the semipermeable membrane support.SOLUTION: Concerning a semipermeable membrane support for membrane separation activated sludge treatment, the semipermeable membrane support for membrane separation activated sludge treatment is a nonwoven fabric constituted of two layers of a first layer and a second layer. In the semipermeable membrane support for membrane separation activated sludge treatment, an average fiber diameter of a subject synthetic fiber contained in the first layer is larger than an average fiber diameter of a subject synthetic fiber contained in the second layer, and a first layer surface is a surface coated with a dope, and a dope penetration amount into the first layer is 18-30%.SELECTED DRAWING: None

Description

  The present invention relates to a semipermeable membrane support for treating a membrane separation activated sludge.

  BACKGROUND ART Semipermeable membranes are widely used in the fields of desalination of seawater, water purifiers, food concentration, wastewater treatment, production of ultrapure water for medical treatment represented by hemofiltration, semiconductor cleaning, and the like. The separation function layer of the semipermeable membrane is made of a porous resin such as a polyamide resin, a cellulose resin, a polysulfone resin, a polyacrylonitrile resin, a fluorine resin, and a polyester resin. However, since the porous resin alone has poor mechanical strength, the filtration membrane is in the form of a composite in which a semipermeable membrane is provided on one surface of a semipermeable membrane support made of a fibrous base material such as a nonwoven fabric or a woven fabric. Is used. Hereinafter, the surface of the semipermeable membrane support on which the dope serving as the raw material of the separation functional layer is applied and the semipermeable membrane is provided is referred to as an “applied surface”.

  One of the usage forms of these semipermeable membranes and filtration membranes is a membrane separation activated sludge treatment method (Membrane Bioreactor, MBR). The membrane separation activated sludge treatment method is widely used in treating organic wastewater because the treated water quality is stable and the maintenance is easy. In the membrane separation activated sludge treatment method, after removing contaminants in the sewage, organic substances in the sewage are decomposed and removed by activated sludge in a biological treatment tank (aeration tank). The mixed solution is separated into solid and liquid by an apparatus, and the permeated filtrate is discharged as treated water. The membrane separation unit in such a membrane separation device uses inorganic substances such as sand, sludge, and other solids that collide violently during use, and supplies oxygen to activated sludge and performs aeration operation to prevent clogging. Since the air bubbles violently collide with the film surface, it is required to have sufficient strength to withstand such an impact.

  In addition, the filtration membrane is used in a modular form. Representative modules in a sheet-like filtration membrane are a flat membrane type module and a spiral type module. Typical modules in a tubular filtration membrane are a hollow fiber module and a tube / tubular module. In the flat membrane type module, a filtration membrane is adhered and fixed to a frame material made of a resin such as polypropylene, acrylonitrile, butadiene, butadiene, and styrene (Styrene) copolymer synthetic resin (ABS resin). For bonding and fixing to the frame material, heat fusion processing, ultrasonic fusion processing, and the like are generally performed.

  A typical semipermeable membrane support includes a semipermeable membrane support containing a main synthetic fiber and a binder synthetic fiber. For example, a semi-permeable membrane having a multilayer structure containing a main synthetic fiber and a binder synthetic fiber, using a thick fiber on a surface to which a dope serving as a raw material of a separation functional layer is applied, and using a thin fiber on a back side which is an uncoated surface. A support (for example, see Patent Document 1) has been proposed. However, there is no specific description about the amount of the dope penetrating into the semipermeable membrane support.

  As another semipermeable membrane support, there has been proposed a semipermeable membrane support (for example, see Patent Document 2) in which a nonwoven fabric made of a core-sheath type polyester fiber is multilayered by a heat calendering treatment. However, there is no specific description about the amount of the dope penetrating into the semipermeable membrane support.

  In forming the semipermeable membrane, the semipermeable membrane support is impregnated with a non-solvent of the membrane-forming polymer substance, the non-solvent on the surface of the semipermeable membrane support is dried and removed, and then a dope of the membrane-forming polymer substance is applied By doing so, it is described that it is possible to control the permeation amount of the dope into the semipermeable membrane support and to improve the adhesive strength between the semipermeable membrane and the semipermeable membrane support (for example, Patent Reference 3). However, there is no specific description regarding the amount of the dope penetrating into the semipermeable membrane support and the adhesive strength of the semipermeable membrane.

Japanese Patent Publication No. Hei 4-21526 JP 2012-45509 A JP-A-49-15885

  An object of the present invention is to provide a semipermeable membrane support in which the amount of dope penetrating into a semipermeable membrane support during dope application is improved, and the adhesive strength between the semipermeable membrane and the semipermeable membrane support is high. .

  As a result of intensive studies to solve the above problems, the following invention was found.

(1) In the semipermeable membrane support for membrane separation activated sludge treatment, the semipermeable membrane support for membrane separation activated sludge treatment is a nonwoven fabric composed of two layers, a first layer and a second layer. The average fiber diameter of the main synthetic fibers included is equal to or greater than the average fiber diameter of the main synthetic fibers included in the second layer, the first layer surface is the surface to which the dope is applied, and the dope permeability of the first layer is 18 to A semipermeable membrane support for treating membrane-separated activated sludge, characterized in that the content is 30%.

(2) The semipermeable membrane for membrane separation activated sludge treatment according to the above (1), wherein the density of the semipermeable membrane support for membrane separation activated sludge treatment is 0.47 to 0.52 g / cm ^3. Support.

  The semipermeable membrane support for treating a membrane separation activated sludge of the present invention has an improved dope penetration into the first layer of the semipermeable membrane support at the time of dope coating, and the adhesion between the semipermeable membrane and the semipermeable membrane support. The effect of increasing the strength can be achieved.

In the semipermeable membrane support for membrane separation activated sludge treatment, the two-layer semipermeable membrane support in which the average fiber diameter of the main synthetic fibers contained in the first layer is larger than the average fiber diameter of the main synthetic fibers contained in the second layer FIG. 2 is a schematic view showing a cross section of a body. In the semipermeable membrane support for membrane separation activated sludge treatment, a schematic diagram showing a cross section of a semipermeable membrane support having a two-layer structure in which the average fiber diameter of the main synthetic fibers contained in the first layer and the second layer is equal. It is.

  In the present invention, a filtration membrane is formed by coating a dope as a raw material of a separation functional layer on an application surface, which is one surface of a semipermeable membrane support for membrane separation activated sludge treatment, to form a semipermeable membrane for water treatment. And a composite having a semipermeable membrane provided on one side of a semipermeable membrane support. Examples of the raw material for the separation functional layer include polyvinylidene fluoride (PVDF), vinyl chloride resin (PVC), polysulfone (PSU), polyethylene (PE), cellulose acetate (CA), and polyacrylonitrile (PAN). Various polymer materials such as a polymer, a polyvinyl alcohol (PVA), and a polyimide (PI) are used. In particular, a semipermeable membrane for membrane separation activated sludge treatment often uses a PVDF system. A dope in which a polymer material as a raw material is dissolved is applied to one side (application surface) of the semipermeable membrane support, gelled in a coagulation bath, and washed with water to form a microporous membrane. Hereinafter, the process of applying the separation functional layer to the application surface of the semipermeable membrane support in this manner is referred to as “film formation”.

  The semipermeable membrane support for membrane separation activated sludge treatment of the present invention is a nonwoven fabric composed of two layers, a first layer and a second layer, and the average fiber diameter of the main synthetic fibers contained in the first layer is the second layer. It is not less than the average fiber diameter of the main synthetic fibers contained in the layer, the first layer surface is the surface to which the dope is applied, and the dope permeability of the first layer is 18 to 30%.

  The semipermeable membrane support for treating a membrane separation activated sludge of the present invention may be any of a dry nonwoven fabric such as spunbond, meltblown, and airlaid, and a wet nonwoven fabric. A wet nonwoven fabric formed by a wet papermaking method is preferred in terms of formation.

  The semipermeable membrane support for membrane separation activated sludge treatment of the present invention is a nonwoven fabric composed of two layers, a first layer and a second layer, and the average fiber diameter of the main synthetic fibers contained in the first layer is the second layer. It is not less than the average fiber diameter of the main synthetic fibers contained in the layer. Further, it is preferable that the first layer and the second layer contain a main synthetic fiber and a binder fiber.

  In the present invention, the main synthetic fiber is a fiber that forms the skeleton of the semipermeable membrane support. Examples of the main synthetic fibers include fibers of polyester type, polyolefin type, polyamide type, polyacrylic type, vinylon type, vinylidene type, polyvinyl chloride type, benzoate type, polychloral type, phenol type and the like. Polyester fibers having high heat resistance are more preferable. In addition, cellulose derivatives such as acetate and triacetate of semi-synthetic fibers, or promix, and regenerated fibers such as rayon, cupra, lyocell fiber, polylactic acid, polybutyric acid, and polysuccinic fiber derived from natural products do not impair the performance. May be contained.

  In the present invention, the average fiber diameter of the main synthetic fibers is calculated from a scanning electron microscope image of a cross section of the semipermeable membrane support for membrane separation activated sludge treatment. From the scanning electron microscope image, 100 main synthetic fibers are randomly selected from the first layer and the second layer, and the fiber diameter in the thickness direction is measured, and the average value is defined as the average fiber diameter. The reason for measuring the fiber diameter in the thickness direction of the semipermeable membrane support for treating a membrane separation activated sludge is as follows. Generally, in a semipermeable membrane support for treating a membrane separation activated sludge formed by a wet papermaking method, fibers tend to be oriented in a direction perpendicular to the thickness direction of the semipermeable membrane support. On the other hand, the orientation of the fibers in a plane perpendicular to the thickness direction of the semipermeable membrane support is undefined. Therefore, when a fiber diameter in a direction different from the thickness direction is measured, a fiber diameter significantly larger than the actual fiber diameter may be measured. Therefore, in the present invention, the fiber diameter in the thickness direction is measured.

  The average fiber diameter of the main synthetic fibers of the first layer of the semipermeable membrane support for treating a membrane separation activated sludge in the present invention is not particularly limited, but is preferably 30 μm or less. It is more preferably from 2 to 25 μm, further preferably from 5 to 20 μm, and particularly preferably from 8 to 12 μm. When the average fiber diameter of the main synthetic fiber is less than 2 μm, the dope becomes difficult to penetrate into the semipermeable membrane support, and the adhesiveness between the semipermeable membrane and the semipermeable membrane support deteriorates, May be adversely affected. When the average fiber diameter of the main synthetic fiber exceeds 30 μm, a problem that a large amount of dope is required in order to obtain a desired thickness of the semipermeable membrane occurs, or the permeability of the dope becomes excessive, Excessive penetration of the dope also into the two layers. As a result, strikethrough may occur. In addition, the main synthetic fibers tend to stand on the surface of the nonwoven fabric, and may penetrate the semipermeable membrane to deteriorate the performance of the semipermeable membrane.

  The average fiber diameter of the main synthetic fibers in the second layer of the semipermeable membrane support for treating a membrane separation activated sludge in the present invention is not particularly limited, but is preferably 20 μm or less. It is more preferably from 2 to 16 μm, further preferably from 4 to 14 μm, particularly preferably from 7 to 11 μm. When the average fiber diameter of the main synthetic fibers is less than 2 μm, the liquid permeability may be adversely affected. If the average fiber diameter of the main synthetic fibers exceeds 20 μm, the strike-through of the dope may occur.

  The fiber length of the main synthetic fibers of the first layer and the second layer is not particularly limited, but is preferably 1 to 12 mm, more preferably 3 to 10 mm, and still more preferably 4 to 7 mm. The cross-sectional shape of the main synthetic fiber is preferably circular, and the cross-sectional aspect ratio (fiber cross-sectional major axis / fiber cross-sectional minor axis) of the fiber before dispersion in water in the wet papermaking process is preferably less than 1.0 to less than 1.2. preferable. When the fiber cross-sectional aspect ratio is 1.2 or more, the fiber dispersibility may decrease, or the entanglement or entanglement of the fibers may occur, which may adversely affect the uniformity of the nonwoven fabric and the smoothness of the coated surface. However, fibers having irregular cross-sections such as T-type, Y-type, and triangular can also be contained within a range that does not hinder other properties such as fiber dispersibility for preventing strike-through and surface smoothness.

  The aspect ratio (fiber length / fiber diameter) of the main synthetic fibers of the first layer and the second layer is preferably from 200 to 2,000, more preferably from 200 to 1500, and still more preferably from 280 to 1,000. When the aspect ratio is less than 200, the dispersibility of the fiber is good, but when the fiber falls off from the papermaking wire during papermaking, or when the fiber is stabbed into the papermaking wire and the peelability from the wire deteriorates. is there. On the other hand, if it exceeds 2,000, although it contributes to the formation of a three-dimensional network of fibers, the entanglement and entanglement of the fibers may adversely affect the uniformity of the nonwoven fabric and the smoothness of the coated surface.

  The content of the main synthetic fiber in the nonwoven fabric related to the semipermeable membrane support of the present invention is preferably 52 to 90% by mass, more preferably 55 to 85% by mass, and still more preferably 60 to 80% by mass. When the content of the main synthetic fiber is less than 52% by mass, the liquid permeability may decrease. If it exceeds 90% by mass, sufficient strength may not be obtained. In addition, the content of the main synthetic fiber with respect to the first layer is preferably from 52 to 90% by mass, more preferably from 55 to 85% by mass, and still more preferably from 60 to 80% by mass. When the content of the main synthetic fiber is less than 52% by mass, there is a possibility that the liquid permeability may decrease or the dope solution may not sufficiently penetrate. If it exceeds 90% by mass, sufficient strength may not be obtained or the dope may excessively permeate the second layer. In addition, the content of the main synthetic fiber in the second layer is preferably from 52 to 90% by mass, more preferably from 55 to 85% by mass, and still more preferably from 60 to 80% by mass. When the content of the main synthetic fiber is less than 52% by mass, there is a possibility that the liquid permeability may decrease. On the other hand, when the content exceeds 90% by mass, there is a possibility that dope strikes through.

  The semipermeable membrane support for membrane separation activated sludge treatment of the present invention contains a binder synthetic fiber. By incorporating the step of raising the temperature up to or above the softening point or melting temperature (melting point) of the binder synthetic fiber into the method for producing a semipermeable membrane support, the binder synthetic fiber can improve the strength of the semipermeable membrane support. . In the step of raising the temperature, the main synthetic fiber is not easily softened or melted, and the cross-sectional shape may be changed, but the shape of the fiber is not impaired, and the main fiber is formed of the skeleton of the semipermeable membrane support. Form. For example, the binder synthetic fiber can be softened or melted during a drying step or a heat calendering after the nonwoven fabric is manufactured by the wet papermaking method.

  Examples of binder synthetic fibers include core-sheath fibers (core-shell type), side-by-side fibers (side-by-side type), composite fibers such as radial split fibers, and undrawn fibers. Since the composite fiber does not easily form a film, the mechanical strength can be improved while maintaining the space of the semipermeable membrane support. More specifically, a combination of polypropylene (core) and polyethylene (sheath), a combination of polypropylene (core) and ethylene vinyl alcohol (sheath), a combination of high-melting polyester (core) and low-melting polyester (sheath), polyester, etc. Undrawn fiber. In addition, a single fiber (all-fused type) composed only of a low melting point resin such as polyethylene or polypropylene, or a hot water-soluble binder such as a polyvinyl alcohol type easily forms a film in a drying step of a semipermeable membrane support. However, it can be used as long as the properties are not impaired. In the present invention, a combination of a high-melting polyester (core) and a low-melting polyester (sheath) and unstretched polyester fibers can be preferably used.

  In the present invention, as the unstretched polyester fiber used as the binder synthetic fiber, a polyester such as polyethylene terephthalate, polytrimethylene terephthalate, polybutylene terephthalate and a copolymer based on the same is used at a spinning speed of 800 to 1,200 m / min. Unstretched fiber spun. The unstretched polyester fibers are hot-pressed and fused by a heat calendering treatment, whereby a high-strength semipermeable membrane support can be obtained.

  The average fiber diameter of the binder synthetic fibers of the first layer and the second layer of the semipermeable membrane support for membrane separation activated sludge treatment in the present invention is not particularly limited, but is preferably 2 to 20 μm, more preferably 5 to 17 μm. And more preferably 7 to 15 μm. When a binder synthetic fiber having a fiber diameter of less than 2 μm is used, the strength of the semipermeable membrane support may be insufficient. On the other hand, when a binder fiber having a fiber diameter of more than 20 μm is used, the fiber dispersion during papermaking is poor, the formation of the semipermeable membrane support is likely to be uneven, and the film forming property of the separation function layer is impaired. There are cases. In addition to the role of improving the mechanical strength of the semipermeable membrane support, the binder synthetic fiber also plays a role of forming a uniform three-dimensional network with the main synthetic fiber. Further, in the step of raising the temperature to a temperature equal to or higher than the softening temperature or the melting temperature of the binder synthetic fiber, the smoothness of the surface of the semipermeable membrane support can also be improved. is there.

  In the present invention, the average fiber diameter of the binder synthetic fiber is calculated from a scanning electron microscope image of a cross section of the single fiber. From the scanning electron microscope image, 100 binder synthetic fibers used for the first layer and the second layer are randomly selected, the fiber diameter is measured, and the average value is defined as the average fiber diameter.

  The fiber length of the first layer and the second layer of the binder synthetic fiber is not particularly limited, but is preferably 1 to 12 mm, more preferably 3 to 10 mm, and still more preferably 4 to 7 mm. If the fiber length is less than 1 mm, the strength of the semipermeable membrane support may decrease. If the fiber length exceeds 15 mm, the fiber dispersibility tends to decrease, and the formation of the semipermeable membrane support is uneven. And the film-forming property of the separation function layer may be impaired. The cross-sectional shape of the binder synthetic fiber is preferably circular. However, fibers having irregular cross-sections such as T-type, Y-type, and triangular are also used for preventing strike-through, smoothness of the coated surface, and adhesion between the non-coated surfaces. Can be contained within a range that does not impair the characteristics of

  The aspect ratio (fiber length / fiber diameter) of the binder synthetic fibers of the first and second layers is preferably from 200 to 2,000, more preferably from 200 to 1500, and still more preferably from 300 to 1,000. When the aspect ratio is less than 200, the dispersibility of the fiber becomes good, but the fiber may fall off from the papermaking wire during papermaking, or the fiber may be stabbed into the papermaking wire and the peelability from the wire may deteriorate. is there. On the other hand, when it exceeds 2,000, although the binder synthetic fiber contributes to the formation of the three-dimensional network, the fiber may be entangled or entangled, which may adversely affect the uniformity of the nonwoven fabric and the smoothness of the coated surface. .

  The content of the binder synthetic fiber in the nonwoven fabric related to the semipermeable membrane support of the present invention is preferably 10 to 48% by mass, more preferably 15 to 45% by mass, and still more preferably 20 to 40% by mass. When the content of the binder synthetic fiber is less than 10% by mass, the semipermeable membrane support may be broken due to insufficient strength. On the other hand, when the content exceeds 48% by mass, the film formation proceeds during the heat calendering, and there is a possibility that the liquid permeability may decrease or the semipermeable membrane may be peeled from the semipermeable membrane support. The content of the binder synthetic fiber in the first layer is preferably from 10 to 48% by mass, more preferably from 15 to 45% by mass, and still more preferably from 20 to 40% by mass. When the content of the binder synthetic fiber is less than 10% by mass, sufficient strength may not be obtained. If the content exceeds 48% by mass, the water permeability may be reduced and the dope may not sufficiently penetrate. Further, the content of the binder synthetic fiber in the second layer is preferably from 10 to 48% by mass, more preferably from 15 to 45% by mass, and still more preferably from 20 to 40% by mass. When the content of the binder synthetic fiber is less than 10% by mass, there is a possibility that sufficient strength cannot be obtained or that the dope strikes through. If it exceeds 48% by mass, water permeability may be reduced.

  In the semipermeable membrane support for treating membrane separation activated sludge of the present invention, the first layer surface is a surface to which the dope is applied (coated surface), and the first layer has a dope permeability of 18 to 30%. It is preferably from 20 to 30%, and more preferably from 24 to 30%. In the semipermeable membrane support, when the permeability of the dope in the first layer is less than 18%, the amount of the dope penetrating into the semipermeable membrane support is small. In the case where the permeability of the dope in the first layer exceeds 30%, the dope excessively penetrates into the semipermeable membrane support, and the uniformity of the semipermeable membrane is impaired. . Further, the dope seeps out from the second layer side of the semipermeable membrane support, and strikethrough occurs.

  The method for measuring the dope permeability of the first layer and the second layer in the present invention is as follows.

  16 parts by mass of PVDF (trade name: Solef (registered trademark) 6010, manufactured by Solvay) is heated at 80 ° C. to 84 parts by mass of N-methyl-2-pyrrolidone (NMP) (special reagent, manufactured by Junsei Chemical Co., Ltd.) as a solvent. A melted dope was prepared, and a gap was set to 7 using a constant-speed coating apparatus having a certain clearance (trade name: TQC fully automatic film applicator, manufactured by Cotec) under an environment of a temperature of 25 ° C. and a humidity of 50% RH. A dope of 25 ° C. was applied to the application surface of the semipermeable membrane support at an application rate of 250 mm / sec by an applicator (No. 510, Baker-type film applicator, manufactured by Yasuda Seiki Seisaku-sho, Ltd.) adjusted to 0.5 mil. Rinse with ion-exchanged water having a conductivity of 1 μS / cm or less for 24 hours, and then air-dry for 24 hours to form a semipermeable membrane on the coating surface of the semipermeable membrane support. Then, a filtration membrane was prepared.

  After measuring the mass A of the dried filtration membrane, the semipermeable membrane is peeled off from the filtration membrane with a tape, and the semipermeable membrane support is further peeled between the first layer and the second layer of the semipermeable membrane support, The mass B of the first-layer semipermeable membrane support and the mass C of the second-layer semipermeable membrane support were measured. Next, the semipermeable membrane support was immersed in NMP to dissolve the semipermeable membrane permeating the inside of the semipermeable membrane support. Thereafter, the semipermeable membrane support was taken out of the NMP and dried, and the mass D of the first layer semipermeable membrane support and the mass E of the second layer semipermeable membrane support were measured.

The mass F of the coating amount of the semipermeable membrane (the sum of the non-permeable portion (separation functional layer) and the permeable portion into the semipermeable membrane support) was calculated by the following equation.
Mass F = mass A− (mass D + mass E)

The mass G of the dope permeated into the first-layer semipermeable membrane support was calculated by the following equation.
Mass G = Mass B-Mass D

The mass H of the dope permeated into the inside of the semipermeable membrane support of the second layer was calculated by the following equation.
Mass H = Mass C-Mass E

The dope penetration into the semipermeable membrane support was calculated by the following equation.
First layer: dope permeability (% by mass) = (mass G / mass F) × 100
Second layer: dope permeability (mass%) = (mass H / mass F) × 100

  As a method for adjusting the dope permeability of the first layer of the semipermeable membrane support to 18 to 30%, selection of the fiber diameter of the main synthetic fiber, adjustment of the mixing ratio of the main synthetic fiber and the binder fiber, and heat calendering conditions using a hot roll And the like. This can be achieved by adjusting the temperature of the hot roll, the nip pressure during the hot calender, the combination of the hot roll, the resin roll, and the cotton roll, and controlling the processing speed during the hot calender.

  The semipermeable membrane support for membrane separation activated sludge treatment of the present invention is a nonwoven fabric composed of two layers, a first layer and a second layer, as shown in FIGS. 1 and 2, and is included in the first layer. Since the average fiber diameter of the main synthetic fibers is equal to or larger than the average fiber diameter of the main synthetic fibers contained in the second layer, when the dope is applied to the semipermeable membrane support, the dope easily penetrates into the first layer. However, since the average fiber diameter of the second layer is equal to or smaller than that of the first layer, the dope is less likely to penetrate. Therefore, by increasing the dope penetration amount of the first layer during formation of the semipermeable membrane, an anchoring effect is obtained, and the adhesive strength between the semipermeable membrane support and the semipermeable membrane can be increased, and the second layer Excessive permeation can be suppressed, and penetration of the dope can be prevented.

  As an example of the method for producing the semipermeable membrane support for treating membrane separation activated sludge of the present invention, a wet papermaking method will be described.

  In the wet papermaking method, first, the fibers are uniformly dispersed in water, and then the final fiber concentration is adjusted to 0.01 to 0.50% by mass through a process such as a screen (removal of foreign matters and lumps). The slurry is made on a paper machine to obtain a wet paper. Chemicals such as dispersants, defoamers, hydrophilic agents, antistatic agents, polymer thickeners, release agents, antibacterial agents, and bactericides may be added during the process to make the dispersibility of the fibers uniform. is there.

  As the papermaking method, for example, a papermaking method such as a long net, a circular net, or an inclined wire type can be used. Use a paper machine having at least one papermaking system selected from the group of these papermaking systems, or a combination papermaking machine in which two papermaking systems of the same or different types selected from the group of these papermaking systems are installed online. be able to. In the case of producing a two-layer nonwoven fabric, a laminating method of laminating wet paper made by each paper machine, or forming one sheet and then dispersing fibers on the sheet. A method of casting a slurry or the like can be used. When the slurry in which the fibers are dispersed is cast, the previously formed layer may be in a wet paper state or a dry state. Further, the two layers can be heat-sealed to form a two-layer nonwoven fabric.

  The semipermeable membrane support for membrane separation activated sludge treatment of the present invention has a two-layer nonwoven fabric, and has the purpose of controlling the permeability of dope in the thickness direction in the semipermeable membrane support for membrane separation activated sludge treatment. The average fiber diameter of the main synthetic fibers contained in the first layer is equal to or larger than the average fiber diameter of the main synthetic fibers contained in the second layer. In the case of a two-layer structure, since the fiber weight of the slurry can be reduced by decreasing the basis weight of each layer, the formation of the nonwoven fabric is improved, and as a result, the smoothness and uniformity of the semipermeable membrane application surface are improved. I do. Even if the formation of each layer is not uniform, it can be compensated by laminating. Further, the paper making speed can be increased, and the operability is improved.

  The sheet is obtained by drying the wet paper web produced by the papermaking net with a Yankee dryer, an air dryer, a cylinder dryer, a suction drum dryer, an infrared dryer, or the like. When the wet paper is dried, the wet paper is brought into close contact with a hot roll such as a Yankee dryer and dried under hot pressure, whereby the smoothness of the adhered surface is improved. Hot-press drying refers to pressing wet paper against a hot roll with a touch roll or the like to dry. The surface temperature of the heat roll is preferably from 100 to 180C, more preferably from 100 to 160C, and still more preferably from 110 to 160C. The pressure is preferably 5 to 100 kN / cm, more preferably 10 to 80 kN / cm.

  Next, a heat calender using a heat roll will be described, but the present invention is not limited to the following. The heat calender is performed by passing the base paper while nipping between the rolls of the heat calender. Examples of the combination of the rolls include two metal rolls, a metal roll and a resin roll, and a metal roll and a cotton roll. The two rolls are used as hot rolls, with one or both heated. At this time, the desired length of the semipermeable membrane support is controlled by controlling the contact length between the base paper and the heat roll before heat processing, the surface temperature of the heat roll, the nip pressure between the rolls, and the processing speed. Get. The surface temperature of the hot roll is preferably 150 to 260 ° C, more preferably 180 to 245 ° C. When the temperature is lower than 150 ° C., the strength of the semipermeable membrane support is reduced, or the dope excessively penetrates into the inside of the semipermeable membrane support, and strikethrough occurs. If the temperature exceeds 260 ° C., excessive melting of the surface of the semipermeable membrane support and voids inside the semipermeable membrane support are reduced, and the dope does not penetrate into the semipermeable membrane support. There is a risk of delamination between supports.

  The nip pressure of the roll is preferably 19 to 180 kN / cm, more preferably 39 to 150 kN / cm. If it is less than 19 kN / cm, the dope excessively penetrates into the inside of the semipermeable membrane support, and there is a possibility that strikethrough occurs. On the other hand, when it exceeds 180 kN / cm, voids inside the semipermeable membrane support are reduced, and dope does not penetrate into the semipermeable membrane support, and delamination may occur between the semipermeable membrane and the semipermeable membrane support. There is. The processing speed is preferably 4 to 100 m / min, and more preferably 10 to 80 m / min. When it is less than 4 m / min, the voids inside the semipermeable membrane support decrease, and the dope does not penetrate into the semipermeable membrane support, and there is a possibility that delamination may occur between the semipermeable membrane and the semipermeable membrane support. .

  The heat calendering by a heat roll can be performed two or more times. In this case, two or more sets of the above rolls arranged in series may be used, or two rolls may be formed by using one roll combination. It may be processed more than once. If necessary, the front and back of the sheet may be reversed. The combination of the rolls is preferably a metal roll and a resin roll, a metal roll and a metal roll, or a metal roll and a cotton roll.

The basis weight of the semipermeable membrane support is not particularly limited, but is preferably ²⁰ to 150 g / m ² , and more preferably 30 to 100 g / m ² . If it is less than 20 g / m ² , the strength of the semipermeable membrane support may be insufficient. Further, when it exceeds 150 g / m ² , the liquid permeation resistance becomes high or the thickness increases, so that a predetermined amount of semipermeable membrane cannot be stored in the unit or module in some cases.

The density of the semi-permeable membrane support is preferably 0.45~0.53g / cm ^3, more preferably 0.45~0.52g / cm ^3, 0.47~0.52g / cm ³ is more preferred. When the density of the semipermeable membrane support is less than 0.45 g / cm ³ , the thickness becomes large, so that the area of the semipermeable membrane that can be incorporated in the unit becomes small, and as a result, the life of the semipermeable membrane becomes short. In some cases, the dope penetrates into the semipermeable membrane support and the uniformity of the semipermeable membrane is impaired. On the other hand, when it exceeds 0.53 g / cm ³ , the liquid permeability is reduced, and the permeability of the dope solution to the semipermeable membrane support is reduced, and the adhesive strength between the semipermeable membrane and the semipermeable membrane support is reduced. And the semipermeable membrane may peel off.

  The thickness of the semipermeable membrane support is preferably from 50 to 200 μm, more preferably from 70 to 180 μm, and still more preferably from 80 to 170 μm. When the thickness of the semipermeable membrane support exceeds 200 μm, the area of the semipermeable membrane that can be incorporated in the unit becomes small, and as a result, the life of the semipermeable membrane may be shortened. On the other hand, if it is less than 50 μm, sufficient tensile strength may not be obtained.

  Hereinafter, the present invention will be described specifically with reference to examples, but the present invention is not limited to the examples. All parts and percentages in the examples are by weight unless otherwise specified.

<Main synthetic fiber 1>
The main synthetic fiber 1 was a stretched polyester fiber made of polyethylene terephthalate and having a fiber diameter of 8 μm and a fiber length of 5 mm.

<Main synthetic fiber 2>
The main synthetic fiber 2 was a drawn polyester fiber made of polyethylene terephthalate and having a fiber diameter of 10 μm and a fiber length of 6 mm.

<Main synthetic fiber 3>
The main synthetic fiber 3 was a drawn polyester fiber made of polyethylene terephthalate and having a fiber diameter of 12 μm and a fiber length of 6 mm.

<Main synthetic fiber 4>
The main synthetic fiber 4 was a drawn polyester fiber made of polyethylene terephthalate and having a fiber diameter of 13 μm and a fiber length of 5 mm.

<Main synthetic fiber 5>
The main synthetic fiber 5 was a drawn polyester fiber made of polyethylene terephthalate and having a fiber diameter of 25 μm and a fiber length of 5 mm.

<Binder synthetic fiber 1>
An undrawn polyester fiber (melting point: 260 ° C.) of polyethylene terephthalate and having a fiber diameter of 12 μm and a fiber length of 5 mm was used as the binder fiber 1.

<Binder synthetic fiber 2>
An undrawn polyester fiber (melting point: 260 ° C.) of polyethylene terephthalate having a fiber diameter of 10 μm and a fiber length of 5 mm was used as the binder fiber 2.

  The semipermeable membrane supports for treating membrane-separated activated sludge of Examples 1 to 5 and Comparative Examples 1 to 5 were produced under the following conditions.

(Manufacture of base paper)
After introducing water dispersion tank 2m ^3, the raw material compounding ratio shown in Table 1 (%) were mixed and dispersed in water, using a gradient / round net complex expression paper machine, the wet paper of the second layer on the inclined wire After forming and forming the first layer of wet paper on the mesh wire, and laminating both wet papers before drying, the wet paper is hot-press dried with a Yankee dryer having a surface temperature of 150 ° C., as shown in Table 1. Wet nonwoven fabrics (base papers 1 to 10) having a width of 300 mm were obtained with the target of the basis weight.

(Heat calender processing)
The obtained base papers 1 to 10 were subjected to a heat calendering treatment using a metal roll-elastic roll calender unit under the conditions shown in Table 2, and the membrane separation activities of Examples 1 to 5 and Comparative Examples 1 to 5 were performed. A semipermeable membrane support for sludge treatment was obtained. In the first treatment, the second layer hit the metal roll, and in the second treatment, the first layer hit the metal roll, so that the first layer was the coated surface and the second layer was the non-coated surface.

  The following measurements and evaluations were performed on the semipermeable membrane supports for treating membrane-separated activated sludge obtained in Examples and Comparative Examples, and the results are shown in Table 3.

[Basic weight of semipermeable membrane support for membrane separation activated sludge treatment]
The grammage was measured according to JIS P8124: 2011.

[Thickness of semipermeable membrane support for membrane separation activated sludge treatment]
The thickness was measured according to JIS P8118: 2014.

[Density of semipermeable membrane support for membrane separation activated sludge treatment]
The density of the semipermeable membrane support was calculated by dividing the grammage by the thickness according to the following formula.
Density (g / cm ³ ) = basis weight (g / m ² ) / thickness (μm)

[Air permeability of semipermeable membrane support for membrane separation activated sludge treatment]
The air permeability was measured in accordance with JIS L1092: 2010 A method.

[Peeling strength of semipermeable membrane and semipermeable membrane support for membrane separation activated sludge treatment]
JAPAN TAPPI No. It was measured according to the 19-2B method.

[Dope penetration into semi-permeable membrane support]
The material of the semipermeable membrane used to evaluate the dope permeability into the inside of the semipermeable membrane support forms a semipermeable membrane such as a fluororesin, a polysulfone resin, a polyamide resin, a cellulose resin, and a polyacrylonitrile resin. Any resin may be used. In the present invention, 16 parts by mass of PVDF (trade name: Solef 6010, manufactured by Solvay) is heated at 80 ° C. to 84 parts by mass of N-methyl-2-pyrrolidone (NMP) (special reagent, manufactured by Junsei Chemical Co., Ltd.) as a solvent. A melted dope was prepared, and a gap was set to 7 using a constant speed coating apparatus having a certain clearance (trade name: TQC fully automatic film applicator, manufactured by Cotec) under an environment of a temperature of 25 ° C. and a humidity of 50% RH. A dope at 25 ° C. was applied to the application surface of the semipermeable membrane support for semipermeable membrane at an application rate of 250 mm / sec by an applicator (No. 510, Baker-type film applicator, manufactured by Yasuda Seiki Seisakusho Co., Ltd.) adjusted to 0.5 mil. Washed with ion-exchanged water having a conductivity of 1 μS / cm or less at 20 ° C. for 24 hours, then air-dried for 24 hours, and semi-permeable on the coating surface of the semipermeable membrane support. To form, to produce a filtration membrane.

  After measuring the mass A of the dried filtration membrane, the semipermeable membrane is peeled off from the filtration membrane with a tape, and the semipermeable membrane support is further peeled between the first layer and the second layer of the semipermeable membrane support, The mass B of the first-layer semipermeable membrane support and the mass C of the second-layer semipermeable membrane support were measured. Next, the semipermeable membrane support was immersed in NMP to dissolve the semipermeable membrane permeating the inside of the semipermeable membrane support. Thereafter, the semipermeable membrane support was taken out of the NMP and dried, and the mass D of the first layer semipermeable membrane support and the mass E of the second layer semipermeable membrane support were measured.

The mass F of the coating amount of the semipermeable membrane (the sum of the non-permeable portion (porous layer) and the permeated portion into the semipermeable membrane support) was calculated by the following formula.
Mass F = mass A− (mass D + mass E)

The mass G of the dope permeated into the first-layer semipermeable membrane support was calculated by the following equation.
Mass G = Mass B-Mass D

The mass H of the dope permeated into the inside of the semipermeable membrane support of the second layer was calculated by the following equation.
Mass H = Mass C-Mass E

The dope penetration into the semipermeable membrane support was calculated by the following equation.
First layer: dope permeability (% by mass) = (mass G / mass F) × 100
Second layer: dope permeability (mass%) = (mass H / mass F) × 100

[Dope strikethrough]
Using 16 parts by mass of PVDF (trade name: Solef 6010, manufactured by Solvay) as a solvent, a dope is prepared by heating and dissolving at 84 ° C. at 80 ° C. in 84 parts by mass of NMP (special grade reagent, manufactured by Junsei Chemical Co., Ltd.). When applying the dope to the application surface of the semipermeable membrane support for the semipermeable membrane using a coating apparatus (trade name: TQC fully automatic film applicator, Cotec), lay the backing under the semipermeable membrane support. The state of the dope penetrating the semi-permeable membrane support and permeating the mount was observed, and the dope strike-through was evaluated.

：: No strikethrough at all.
Δ: Slight strikethrough is observed, but there is no problem in use.
X: There is a lot of strikethrough, and there is a possibility that the inside of the system in the coating process is stained.

  As shown in Table 3, the semipermeable membrane supports for treating membrane-separated activated sludge of Examples 1 to 5 have the main synthetic fibers in which the average fiber diameter of the main synthetic fibers contained in the first layer is contained in the second layer. , The dope permeability of the first layer was 18 to 30%, the results of the evaluation of the penetration of the dope were good, and the peel strength was 160 N or more.

  On the other hand, in Comparative Example 1, the average fiber diameter of the main synthetic fibers contained in the first layer and the second layer was the same, but the dope permeability of the first layer was 14%, and the peel strength was low. Was.

  In Comparative Example 2, the average fiber diameter of the main synthetic fibers contained in the first layer and the second layer was the same, but the dope permeability of the first layer was 17%, and the result of the evaluation of the penetration of the dope was poor. Was.

  In Comparative Example 3, the average fiber diameter of the main synthetic fibers contained in the second layer was larger than the average fiber diameter of the main synthetic fibers contained in the first layer, and the dope permeability of the first layer was 17%. The result of the dope strikethrough evaluation was poor.

  In Comparative Example 4, although the average fiber diameter of the main synthetic fibers contained in the second layer was larger than the average fiber diameter of the main synthetic fibers contained in the first layer, and the strike-through evaluation of the dope was good, Has a penetration rate of 1% and a peel strength of 55 N, which may cause film peeling.

  In Comparative Example 5, the average fiber diameter of the main synthetic fibers contained in the second layer was larger than the average fiber diameter of the main synthetic fibers contained in the first layer, the permeation amount of the dope was 35%, and the semipermeable membrane was used. Excessive penetration of the dope into the support caused strike-through of the dope.

  The semipermeable membrane support for treating a membrane separation activated sludge of the present invention can be used in the field of sewage treatment by a membrane separation activated sludge treatment method.

Claims (2)

  In the semipermeable membrane support for membrane separation activated sludge treatment, the semipermeable membrane support for membrane separation activated sludge treatment is a nonwoven fabric composed of two layers of a first layer and a second layer, and the main body contained in the first layer The average fiber diameter of the synthetic fibers is equal to or greater than the average fiber diameter of the main synthetic fibers contained in the second layer, the first layer surface is the surface to which the dope is applied, and the dope permeability of the first layer is 18 to 30%. A semipermeable membrane support for treating a membrane-separated activated sludge. Membrane separation activated sludge treatment for semipermeable membrane support according to claim 1, the density of the semipermeable membrane support is characterized by a 0.47~0.52g / cm ^3.

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