Semipermeable membrane support

Abstract

To provide a semipermeable membrane supporter which has less pinholes and bleed through when providing itself with a semipermeable membrane, can form a uniform semipermeable membrane, and by which a bond strength between the semipermeable membrane and itself is high.SOLUTION: A semipermeable membrane supporter, which comprises a wet type non-woven fabric containing polyester fibers, contains an anionic surfactant.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a semipermeable membrane support. [Background technology]

[0002] Semipermeable membranes are widely used in fields such as seawater desalination, water purifiers, food concentration, wastewater treatment, medical applications such as hemofiltration, and the production of ultrapure water for semiconductor cleaning. Semipermeable membranes are composed of synthetic resins such as cellulose-based resins, polysulfone-based resins, polyacrylonitrile-based resins, fluorine-based resins, polyester-based resins, polyamide-based resins, and polyimide-based resins. However, since semipermeable membranes alone have poor mechanical strength, they are used as "filtration membranes" in which a semipermeable membrane is provided on one side of a semipermeable membrane support made of a fibrous substrate such as a nonwoven fabric or woven fabric. The "side of the semipermeable membrane support on which the semipermeable membrane is provided" is sometimes referred to as the "semipermeable membrane-forming side." Furthermore, the "side opposite to the semipermeable membrane-forming side" is sometimes referred to as the "non-semipermeable membrane-forming side."

[0003] A widely used method for producing a filtration membrane is to dissolve a synthetic resin such as the above-mentioned polysulfone-based resin in an organic solvent to prepare a semipermeable membrane liquid (dope), then coat one side (coating surface) of a semipermeable membrane support, gel it in a coagulation bath, and wash it with water to form a microporous membrane. Then, to perform efficient filtration, a spiral-type semipermeable membrane element is formed, and further, a semipermeable membrane module is assembled (Patent Document 1).

[0004] To obtain a high filtration flux and filtration performance, it is necessary that the semipermeable membrane surface has few irregularities, that lateral curvature or wrinkles do not occur during semipermeable membrane formation, that the semipermeable membrane is provided on the semipermeable membrane support with a uniform thickness, and that the occurrence of membrane defects (pinholes) is suppressed. To provide a semipermeable membrane with a uniform thickness, the semipermeable membrane-forming surface of the semipermeable membrane support needs to have excellent smoothness, and the dope needs to have uniform permeability. Furthermore, to obtain good filtration performance, the adhesiveness between the semipermeable membrane and the semipermeable membrane support needs to be excellent. Furthermore, since the assembly of a semipermeable membrane module involves a step of bonding non-semipermeable membrane-forming surfaces together using an adhesive, excellent adhesiveness between these non-semipermeable membrane-forming surfaces is also required. Furthermore, it is required that the semipermeable membrane liquid does not bleed through to the non-semipermeable membrane-forming surface. If bleed-through occurs, problems such as uneven semipermeable membrane thickness and reduced adhesiveness between non-semipermeable membrane-forming surfaces occur.

[0005] A semipermeable membrane support has been proposed in which nonwoven fabrics with different aspect ratios of tensile strength are laminated and the support is curved convexly to suppress shrinkage curl of the semipermeable membrane liquid (Patent Document 2). However, with this method, when heat-pressure bonding is performed, the number of fiber bonding points between the layers is reduced because layers with different aspect ratios of tensile strength are laminated, which may result in a decrease in interlayer strength and the risk of interlayer delamination. Furthermore, the aspect ratio of tensile strength is correlated with fiber orientation, which is greatly influenced by the water temperature and the viscosity of the slurry in which the fibers are dispersed during wet papermaking (papermaking). This makes it difficult to control fiber orientation, and stable productivity is difficult depending on the papermaking method.

[0006] A semipermeable membrane support has been proposed in which, when colored N,N-dimethylformamide is dropped onto the surface on which the semipermeable membrane is to be provided, the length of the longest direction of the wetted trace is 1.3 times or less than the length of the shortest direction, thereby ensuring uniform coating liquid permeability when the semipermeable membrane is formed through a coating process and used, and thus suppressing the occurrence of pinholes that lead to a decrease in the salt rejection rate of the semipermeable membrane (Patent Document 3). However, this method has the problem that it is not possible to completely prevent pinholes caused by the dispersion state of the fibers or undisintegrated fibers. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2008-238147 [Patent Document 2] Patent No. 5739154 [Patent Document 3] Patent Publication No. 2021-053595 Summary of the Invention [Problem to be solved by the invention]

[0008] An object of the present invention is to provide a semipermeable membrane support that, when a semipermeable membrane is provided on a semipermeable membrane support, can form a uniform semipermeable membrane with few pinholes and strike-through, and has high adhesive strength between the semipermeable membrane and the semipermeable membrane support. [Means for solving the problem]

[0009] The above problem was solved by the following means.

[0010] A semipermeable membrane supporting material comprising a nonwoven fabric containing polyester fibers, characterized in that the semipermeable membrane supporting material contains a specific surfactant.

[0011] in particular, (1) A semipermeable membrane supporting material made of a wet-laid nonwoven fabric containing polyester fibers, characterized in that the semipermeable membrane supporting material contains an anionic surfactant. [Effects of the Invention]

[0012] In the present invention, since the semipermeable membrane support contains an anionic surfactant, when a semipermeable membrane is provided on the semipermeable membrane support, pinholes and strike-through in the semipermeable membrane are reduced, making it possible to form a uniform semipermeable membrane, and the adhesive strength between the semipermeable membrane and the semipermeable membrane support is high, which are advantageously achieved. DETAILED DESCRIPTION OF THE INVENTION

[0013] The semiconductor membrane support of the present invention will be described in detail below. In this specification, the "adhesion strength between the semipermeable membrane and the semipermeable membrane support" may be abbreviated as "membrane adhesion strength".

[0014] The semipermeable membrane support of the present invention is made of a wet-laid nonwoven fabric containing polyester fibers and contains an anionic surfactant. When the semipermeable membrane support contains an anionic surfactant, when a semipermeable membrane is provided on the semipermeable membrane support, pinholes, which are membrane defects, are reduced and membrane adhesion strength is increased. Generally, when the penetration of the dope into the semipermeable membrane support is uneven, air bubbles in the semipermeable membrane support are difficult to remove, resulting in pinholes. Furthermore, air bubbles generated during fiber dispersion are mixed into the semipermeable membrane support during papermaking, causing uneven formation, which in turn causes pinholes. When the semipermeable membrane support contains an anionic surfactant, fiber dispersion is uniform, eliminating uneven formation. Furthermore, uniform penetration of the dope into the semipermeable membrane support suppresses pinholes. Furthermore, the leveling of the dope to the fibers is improved, and the semipermeable membrane is bound to the fibers so as to cover the fiber surface, increasing the bonding area between the semipermeable membrane and the fibers, thereby achieving high membrane adhesion strength even when the dope penetration rate is low. By suppressing the permeability of the dope, a dense semipermeable membrane with high membrane density can be formed.

[0015] Examples of anionic surfactants include alkyl sulfate salts, polyoxyethylene alkyl ether sulfate salts, alkylbenzenesulfonates, dialkyl sulfosuccinates, alkyldiphenylether disulfonates, alkanesulfonates, long-chain fatty acid salts, sodium salts of β-naphthalenesulfonic acid formalin condensates, sodium salts of aromatic sulfonic acid formalin condensates, polycarboxylic acid type polymer surfactants, alkyl phosphate salts, polyoxyethylene alkyl ether phosphate salts, polyoxyethylene alkylphenyl ether phosphate salts, etc. One type of anionic surfactant may be used alone, or two or more types may be used in combination.

[0016] A preferred example of the anionic surfactant is at least one selected from the group consisting of polyoxyethylene alkyl ether sulfates and polyoxyethylene alkyl ether phosphates. The alkyl group preferably has 8 to 14 carbon atoms, and particularly preferably 10 to 12. That is, preferred examples of the polyoxyethylene alkyl ether sulfates include polyoxyethylene decyl ether sulfate and polyoxyethylene dodecyl ether sulfate. Preferred examples of the polyoxyethylene alkyl ether phosphates include polyoxyethylene decyl ether phosphate and polyoxyethylene dodecyl ether phosphate.

[0017] In the present invention, the anionic surfactant is contained in the semipermeable membrane supporting material in a state where it is attached to the polyester fiber. That is, when the semipermeable membrane supporting material is produced, the anionic surfactant that has been attached to the polyester fiber in advance remains in the semipermeable membrane supporting material produced by the wet papermaking method (papermaking method). This remaining surfactant ensures uniform application and penetration of the dope. To achieve the effects of the present invention, the attachment rate of the anionic surfactant to the polyester fiber is preferably 0.01% by mass or more and 0.5% by mass or less, more preferably 0.05% by mass or more and 0.4% by mass or less, and even more preferably 0.1% by mass or more and 0.3% by mass or less.

[0018] In the present invention, the adhesion rate of an (anionic) surfactant to a polyester fiber is the amount of surfactant adhered to bone-dried polyester fiber, expressed as a percentage, and can be measured, for example, by the following method: 10 g of polyester fiber is subjected to Soxhlet extraction for 3 hours using 500 mL of a methanol / hexane mixed solvent (volume ratio 1 / 1), the solvent is distilled off, the mass of the remaining surfactant is measured, and the mass of the remaining surfactant relative to the mass of bone-dried fiber after surfactant extraction is expressed as a percentage (%).

[0019] In the present invention, the semipermeable membrane supporting material contains polyester fibers, and the polyester fibers preferably contain subject fibers and binder fibers. The subject fibers are fibers that form the skeleton of the semipermeable membrane supporting material, and are resistant to softening or melting even at temperatures at which the binder fibers soften or melt, and although the cross-sectional shape may change, the subject fibers do not lose their shape as fibers.

[0020] In the semipermeable membrane supporting material of the present invention, the number of constituent main fibers is not particularly limited, but it is preferable that the material contains two or more types of fibers with different fiber diameters. The fiber network formed by the entanglement of two or more types of main fibers with different fiber diameters creates complex, fine irregularities on the semipermeable membrane forming surface, thereby improving the membrane adhesive strength. Furthermore, this fiber network can also improve the smoothness of the semipermeable membrane forming surface, allowing for the production of a uniform semipermeable membrane.

[0021] The average fiber diameter of the main fiber is not particularly limited, but is preferably 7 to 20 μm, and more preferably 8 to 16 μm. Furthermore, when the fiber diameter of at least one main fiber is 13 μm or less, the smoothness of the semipermeable membrane-forming surface can be further improved, making it easier to obtain a semipermeable membrane with a uniform thickness, which is even more preferable. When the average fiber diameter of the main fiber is less than 7 μm, the membrane adhesive strength may decrease, or the adhesiveness between non-semipermeable membrane-forming surfaces may deteriorate. When the average fiber diameter of the main fiber is more than 20 μm, the smoothness of the semipermeable membrane-forming surface may be lost, making it difficult to obtain a semipermeable membrane with a uniform thickness. Furthermore, the Frazier (FG) air permeability may become too high, which may cause strike-through during application of the semipermeable membrane liquid.

[0022] The fiber length of the main fiber is not particularly limited, but is preferably 1 to 12 mm, more preferably 3 to 10 mm, and even more preferably 4 to 6 mm. If the fiber length is less than 1 mm, a three-dimensional fiber network is unlikely to form during the papermaking process, which may result in poor peelability from the papermaking wire. On the other hand, if the fiber length exceeds 12 mm, entanglement or tangling of the fibers may occur, which may adversely affect the uniformity of the semipermeable membrane support and the smoothness of the semipermeable membrane. The cross-sectional shape of the main fiber is preferably circular, but fibers with irregular cross sections such as T-shaped, Y-shaped, or triangular can also be included to prevent breakthrough and ensure the smoothness of the semipermeable membrane forming surface, within a range that does not impair other properties.

[0023] The semipermeable membrane supporting material of the present invention contains binder fibers, and by incorporating a step of raising the temperature to a temperature close to the softening or melting point of the binder fibers into the manufacturing process of the semipermeable membrane supporting material, the binder fibers can improve the mechanical strength of the semipermeable membrane supporting material. For example, the semipermeable membrane supporting material can be manufactured by a wet papermaking method, and the binder fibers can be softened or melted in the subsequent drying step or heat and pressure processing.

[0024] Examples of binder fibers include composite fibers such as core-sheath fibers (core-shell type), parallel fibers (side-by-side type), and radially split fibers, as well as unstretched fibers. Composite fibers are less likely to form a membrane, and therefore can improve the mechanical strength of the semipermeable membrane support. More specifically, examples include a combination of polypropylene (core) and polyethylene (sheath), a combination of polypropylene (core) and ethylene vinyl alcohol (sheath), a combination of a high-melting-point polyester (core) and a low-melting-point polyester (sheath), a combination of polyester (core) and polyethylene (sheath), and unstretched fibers of polyester, etc. Furthermore, monofilaments (all-melt type) composed solely of low-melting-point resins such as polyethylene and polypropylene, and hot-water-soluble binders such as polyvinyl alcohol-based binders, tend to form a membrane during the drying process of the semipermeable membrane support, but can be used within a range that does not impair the properties. In the present invention, a combination of polyester-based fibers, such as a high-melting-point polyester (core) and a low-melting-point polyester (sheath), and unstretched polyester fibers are preferably used.

[0025] The fiber diameter of the binder fiber is preferably different from that of the subject fiber, but is not particularly limited thereto. When the fiber diameters of the subject fiber and the binder fiber are different, the binder fiber not only improves the mechanical strength of the semipermeable membrane supporting material but also plays a role in forming a uniform three-dimensional network together with the subject fiber, and further, in a process of raising the temperature to a temperature close to that at which the binder fiber softens or melts, such as a drying process or a heat-pressure processing process, the binder fiber can also improve the smoothness of the semipermeable membrane forming surface.

[0026] The fiber length of the binder fiber is not particularly limited, but if the fiber length exceeds 20 mm, the formation tends to deteriorate. The cross-sectional shape of the binder fiber may be circular or may include fibers having modified cross sections such as T-shaped, Y-shaped, or triangular.

[0027] The semipermeable membrane supporting material of the present invention may contain, in addition to polyester fibers, synthetic fibers such as polyolefins, polyamides, polyacrylics, vinylon, vinylidene, polyvinyl chloride, benzoates, polychlors, and phenols; semisynthetic fibers such as acetate, triacetate, and promix; and regenerated fibers such as rayon, cupra, and lyocell fibers, to the extent that the performance is not impaired.

[0028] The semipermeable membrane support of the present invention is a wetlaid nonwoven fabric (wetlaid nonwoven fabric) produced by a wet papermaking method (papermaking method), which is a nonwoven fabric made by dispersing fibers in water, accumulating them into a sheet, and bonding them by one or more bonding methods (JIS L 0222: 2001 "Nonwoven Fabric Terminology" No. 104). In the present invention, it is preferable that the wetlaid nonwoven fabric has been subjected to a heat and pressure processing treatment using a heated roll.

[0029] In the wet papermaking process, fibers are first uniformly dispersed in water, then passed through a screening process (to remove foreign matter and lumps), and the resulting slurry is adjusted to a final fiber concentration of 0.01 to 0.50% by mass. This slurry is then papered in a papermaking machine to produce a wet paper. Chemicals such as dispersants, antifoaming agents, hydrophilic agents, antistatic agents, polymeric adhesives, release agents, antibacterial agents, and disinfectants may also be added during this process.

[0030] Examples of papermaking methods that can be used include Fourdrinier, cylinder, and inclined wire methods. A papermaking machine using one of these methods may be used, or a combination papermaking machine in which two or more of the same or different papermaking methods are installed online may be used. Furthermore, when the semipermeable membrane support has a multilayer structure of two or more layers, it can be manufactured by a "combined papermaking method" in which wet papers made by each papermaking method are stacked, or a "casting method" in which, after one layer is formed, a slurry in which fibers are dispersed is cast onto the layer. In the casting method, the first layer formed may be in a wet paper state or in a dry state. Furthermore, two or more dry layers may be heat-sealed to form a multilayer structure.

[0031] Wet paper produced in a paper machine is dried using a Yankee dryer, air dryer, cylinder dryer, suction drum dryer, infrared dryer, or the like to obtain a wetlaid nonwoven fabric. When drying the wet paper, the wet paper is placed in close contact with a heated roll such as a Yankee dryer and dried under heat and pressure, thereby improving the smoothness of the contacted surface. Heat and pressure drying refers to drying the wet paper by pressing it against a heated roll using a touch roll or the like. The surface temperature of the heated roll is preferably 100 to 180°C, more preferably 100 to 170°C, and even more preferably 100 to 160°C. If the surface temperature of the heated roll is below 100°C, the moisture in the wet paper produced in the paper machine may not evaporate sufficiently, resulting in an uneven thickness of the semipermeable membrane support. If the surface temperature of the heated roll is above 180°C, the wet paper produced in the paper machine may stick to the heated roll, resulting in poor formation of the semipermeable membrane support. The pressure is preferably 5 to 100 kN / m, more preferably 10 to 80 kN / m. If the pressure is less than 5 kN / m, the moisture in the wet paper produced by the paper machine may not be sufficiently removed, resulting in a non-uniform thickness of the semipermeable membrane supporting material, and if the pressure exceeds 100 kN / m, the wet paper produced by the paper machine may stick to the heat roll, resulting in poor formation of the semipermeable membrane supporting material.

[0032] In the heat and pressure processing, the wetlaid nonwoven fabric is passed between the heat rolls of the heat and pressure processing device while being nipped between them. The combination of heat rolls can be two metal rolls, a metal roll and a resin roll, or a metal roll and a cotton roll, and one or both of the heat rolls are heated. Furthermore, if necessary, the nonwoven fabric can be turned over and passed through the nip two or more times.

[0033] The surface temperature of the heated roll used in the heat and pressure processing is lower than the melting point of the main fiber (melting temperature, JIS K 7121-1987) measured by differential thermal analysis, and is preferably −70 to −20°C, more preferably −60 to −30°C, relative to the melting point of the binder fiber. If the surface temperature of the heated roll is lowered by more than 70°C below the melting point of the binder fiber, fluffing may occur, making it difficult to obtain a semipermeable membrane with a uniform thickness. On the other hand, if the surface temperature of the heated roll is increased by more than 20°C below the melting point, the molten fiber may adhere to the heated roll, causing the semipermeable membrane support to become non-uniform, making it difficult to obtain a semipermeable membrane with a uniform thickness.

[0034] The semipermeable membrane support of the present invention may have a single-layer structure or a multilayer structure. In the case of a wetlaid nonwoven fabric with a multilayer structure, the basis weight of each layer is reduced, which allows the fiber concentration of the papermaking slurry to be reduced, improving the formation of the semipermeable membrane support, and as a result, improving the smoothness and uniformity of the semipermeable membrane formation surface. Furthermore, even if the formation of each layer is uneven, this can be compensated for by stacking them. Furthermore, the papermaking speed can be increased, improving operability.

[0035] The basis weight of the semipermeable membrane support is not particularly limited, but is preferably 20 to 150 g / m 2 is preferable, and more preferably 50 to 100 g / m 2 The basis weight is 20 g / m 2 If the basis weight is less than 150 g / m, sufficient tensile strength may not be obtained. 2 If the thickness exceeds this limit, the resistance to fluid flow may increase, or the thickness may increase, making it impossible to accommodate the specified amount of semipermeable membrane within the unit or module.

[0036] The density of the semipermeable membrane support is 0.5 to 1.2 g / cm 3 is preferably 0.6 to 1.0 g / cm 3 The density of the semipermeable membrane support is 0.5 g / cm 3If the density is less than 1.2 g / cm, the thickness will be too large, which will reduce the area of ​​the semipermeable membrane that can be incorporated into the unit, and as a result, the life of the semipermeable membrane may be shortened. 3 If it exceeds this value, the liquid permeability may decrease and the life of the semipermeable membrane may be shortened.

[0037] The thickness of the semipermeable membrane support is preferably 60 to 150 μm, more preferably 70 to 130 μm, and even more preferably 80 to 120 μm. If the thickness of the semipermeable membrane support exceeds 150 μm, the area of ​​the semipermeable membrane that can be incorporated into the unit will be small, which may result in a shortened life of the semipermeable membrane. On the other hand, if the thickness is less than 60 μm, sufficient tensile strength may not be obtained or liquid permeability may be reduced, resulting in a shortened life of the semipermeable membrane.

[0038] The FG air permeability of the semipermeable membrane support is 0.5 to 5.0 cm 3 / cm 2 sec is preferable, and 1.0 to 4.5 cm 3 / cm 2 sec is more preferable, and 1.5 to 4.0 cm 3 / cm 2 It is more preferable that the FG air permeability is 0.5 cm 3 / cm 2 If it is less than 5.0 cm, the film adhesive strength may be poor. 3 / cm 2 If the time is greater than 1 / sec, strike-through may occur easily when the semipermeable membrane solution is applied, and the smoothness of the semipermeable membrane forming surface may decrease. [Example]

[0039] The present invention will be described in more detail with reference to examples. Unless otherwise specified, parts and ratios described in the examples are based on mass.

[0040] Example 1 The main fibers were 35 parts of oriented, crystallized (stretched) polyethylene terephthalate (PET) fibers with an average fiber diameter of 7 μm and fiber length of 5 mm, 35 parts of oriented, crystallized PET fibers with an average fiber diameter of 13 μm and fiber length of 5 mm, and 30 parts of unstretched polyethylene terephthalate (PET) fibers with an average fiber diameter of 11 μm and fiber length of 5 mm. The binder fibers were mixed together and disintegrated in water in a pulper. A uniform papermaking slurry (1% concentration) was prepared by agitation with an agitator and stored in two stock tanks equipped with agitators. An anionic surfactant (polyoxyethylene dodecyl ether sodium sulfate) was applied to the polyester fibers at a deposition rate of 0.50% by mass. A combination machine consisting of an inclined wire and cylinder papermaking machine was used to produce the layer on the semipermeable membrane-forming side, and the layer on the non-semipermeable membrane-forming side, with a thickness of 36 g / m. 2 After forming the combined wet paper, it was dried under heat and pressure in a Yankee dryer at a surface temperature of 130°C with the semipermeable membrane side in contact with the Yankee dryer, and the basis weight was 72 g / m. 2 A wet-laid nonwoven fabric of this size was obtained.

[0041] The obtained wetlaid nonwoven fabric was processed using a heat and pressure processing device in which first and second roll nips consisting of a metal roll (heated) and a resin roll (unheated) were installed in succession, under conditions of a metal roll surface temperature of 220°C at the first roll nip and 225°C at the second roll nip, a nip pressure of 100 kN / m, and a processing speed of 20 m / min to obtain a semipermeable membrane support. The heat and pressure processing was performed so that the semipermeable membrane-forming surface was in contact with the metal roll at the first roll nip and the non-semipermeable membrane-forming surface was in contact with the metal roll at the second roll nip, to obtain a semipermeable membrane support.

[0042] (Examples 2 to 9, Comparative Examples 1 and 2) A semipermeable membrane supporting material was obtained in the same manner as in Example 1, except that the surfactant attached to the polyester fiber and the attachment rate were changed as shown in Table 1.

[0043] <Preparation of semipermeable membrane> Using a constant speed coating device with a certain clearance (product name: Automatic Film Applicator, manufactured by Yasuda Seiki Co., Ltd.), a semipermeable membrane liquid, which was an N,N-dimethylformamide (DMF) solution (concentration: 18% by mass) of polysulfone (manufactured by SIGMA-ALDRICH Corporation, mass average molecular weight Mw<35,000, number average molecular weight Mn<16,000, product number 428302), was coated on the semipermeable membrane forming surface of the semipermeable membrane support of Examples 1 to 9 and Comparative Examples 1 and 2, followed by washing with water and drying, thereby forming a semipermeable membrane made of polysulfone with a thickness of 50 μm on the semipermeable membrane forming surface of the semipermeable membrane support, thereby obtaining a filtration membrane.

[0044] Measurement 1 (basis weight) The basis weight was measured in accordance with JIS P8124:2011.

[0045] Measurement 2 (thickness) The thickness was measured in accordance with JIS P8118:2014.

[0046] Measurement 3 (breathability) The air permeability (FG air permeability) was measured in accordance with the Frazier method of JIS L1096:2010.

[0047] Evaluation 4 (film defect (pinhole) evaluation) The semipermeable membranes obtained in the examples and comparative examples were observed with transmitted light, and pinholes present within an area of ​​15 cm x 15 cm were evaluated according to the following criteria.

[0048] ○: The number of visible pinholes is within 0 to 5. This is a level at which a high salt rejection rate can be expected. △: The number of visible pinholes is within 6 to 30. This is likely to cause a decrease in salt rejection. This is at the lower limit for practical use, but is not a problem. ×: The number of visible pinholes is 31 or more. There is a high possibility that the salt rejection rate will decrease significantly, and this is at a level that is not practical.

[0049] Rating 5 (dope penetration rate) The semipermeable membrane obtained in the examples and comparative examples was dried and cut into a width of 100 mm x length of 100 mm. After measuring the mass A (g) of the filtration membrane, the porous layer of the semipermeable membrane (non-permeable membrane supporting part) was peeled off from the filtration membrane with tape (manufactured by Nitoms Corporation, trade name: transparent packaging tape No. 3303, product number: J6030), and the mass B (g) of the semipermeable membrane supporting body was measured. Next, the semipermeable membrane supporting body was immersed in DMF, and the semipermeable membrane that had penetrated into the inside of the semipermeable membrane supporting body was dissolved. Thereafter, the semipermeable membrane supporting body was removed from the DMF, dried, and the mass C (g) of the semipermeable membrane supporting body was measured.

[0050] The mass D (g) of the porous layer of the semipermeable membrane (the portion that does not permeate into the semipermeable membrane support) was calculated using the following formula. Mass D = Mass A - Mass B

[0051] The mass E (g) of the semipermeable membrane that had permeated into the semipermeable membrane supporting body was calculated using the following formula. Mass E = Mass B - Mass C

[0052] The dope penetration rate (%) was calculated by the following formula. Dope penetration rate=[mass E / (mass D+mass E)]×100

[0053] Rating 6 (Dope Backflow) A dope was prepared by dissolving 19 parts by mass of polysulfone (trade name: P-3500LCD MB-7, manufactured by Solvay) as a solvent in 81 parts by mass of DMF (special grade reagent, manufactured by Junsei Chemical Co., Ltd.) at room temperature. After mixing the dope with black oil-based ink, the dope was applied to the coating surface of a semipermeable membrane support using a constant speed coating device with a certain clearance (trade name: TQC fully automatic film applicator, manufactured by Cortec Co., Ltd.). When the dope was applied to the coating surface of a semipermeable membrane support, a backing paper was placed under the semipermeable membrane support, and the state of the dope that had penetrated the semipermeable membrane support and soaked into the backing paper was observed, and the dope strike-through was evaluated.

[0054] 1: No bleed-through at all. Very good level. 2: Small dots with very slight bleed-through. Good level. 3: Small dots of ink have bleed-through to the other side. This does not pose a problem for use. 4: Large dots with many bleed-through spots.

[0055] Rating 7 (film adhesion strength) Using a constant-speed coating device with a constant clearance (product name: TQC Fully Automatic Film Applicator, manufactured by Cortec Co., Ltd.), a polysulfone resin DMF solution (concentration: 19%) was coated on the coated surface of the semipermeable membrane support, followed by washing with water and drying. A semipermeable membrane made of polysulfone resin was formed on the coated surface of the semipermeable membrane support, and a filtration membrane was prepared. One day after preparation of the filtration membrane, the prepared filtration membrane was cut into a width of 25 mm (crosswise to the coating direction) x length of 100 mm (coating direction) to prepare a sample. Double-sided tape (manufactured by Nichiban Co., Ltd., product name: Nicetack (registered trademark) NW-25) cut to a width of 25 mm and a length of 100 mm was attached to the entire semipermeable membrane surface of the cut filtration membrane. Only a 30 mm length was peeled off at the interface between the semipermeable membrane support and the semipermeable membrane where the double-sided tape was attached, leaving the remaining 70 mm length unpeeled to prepare the sample (at this time, the release paper of the double-sided tape was left unpeeled).

[0056] Using a tabletop material testing machine (product name: STA-1150, manufactured by A&D Co., Ltd.), the semipermeable membrane support of the peeled portion of the sample and the double-sided tape (including release paper) to which the semipermeable membrane was attached were each fixed to a chuck, and the load at which the portion that had not yet peeled peeled was measured continuously over a movement of 60 mm under conditions of a gripping length of 25 mm each and a pulling speed of 100 mm / min, and the average load [N / 25 mm] measured twice during this period was taken as the adhesive strength between the semipermeable membrane support and the semipermeable membrane.

[0057] [Table 1]

[0058] In each Example in which the semipermeable membrane supporting material contained an anionic surfactant, evaluation results at or above a practically acceptable level were obtained. On the other hand, in Comparative Examples 1 and 2 in which the semipermeable membrane supporting material did not contain an anionic surfactant, pinholes increased, membrane adhesive strength was low, dope permeability was high, and in Comparative Example 1, strike-through also occurred frequently. [Industrial Applicability]

[0059] The semipermeable membrane supporting material of the present invention can be used in fields such as seawater desalination, water purifiers, food concentration, wastewater treatment, medical applications such as blood filtration, and the production of ultrapure water for semiconductor cleaning.

Claims

1. A semipermeable membrane supporting material comprising a wetlaid nonwoven fabric containing polyester fibers, wherein the semipermeable membrane supporting material contains an anionic surfactant, and the anionic surfactant is one or more anionic surfactants selected from the group consisting of polyoxyethylene alkyl ether sulfate salts, dialkyl sulfosuccinate salts, alkyl diphenyl ether disulfonate salts, long-chain fatty acid salts, sodium salts of β-naphthalenesulfonic acid formalin condensates, sodium salts of aromatic sulfonic acid formalin condensates, polycarboxylic acid type polymer surfactants, alkyl phosphate salts, polyoxyethylene alkyl ether phosphate salts, and polyoxyethylene alkyl phenyl ether phosphate salts.

2. A semipermeable membrane support as described in claim 1, wherein the adhesion rate of the anionic surfactant to the polyester fiber is 0.01 mass% or more and 0.5 mass% or less.

3. A semipermeable membrane support as described in claim 1 or claim 2, wherein the semipermeable membrane support contains two or more types of main fibers with different fiber diameters as the polyester-based fibers, and binder fibers.

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