Hollow fiber membrane, hollow fiber membrane module, cartridge for water purifier, and water purifier

Abstract

A hollow fiber membrane of the present invention comprises a dense layer. The dense layer is disposed on the outer surface side or the inner surface side of the hollow fiber membrane. The membrane thickness of the hollow fiber membrane is 40-120 µm, and when the hollow fiber membrane is divided into three equal parts in the thickness direction, and a layer including the dense layer is defined as a layer A, a layer at the center portion in the thickness direction is defined as a layer B, and a layer including the surface on the side opposite the surface side on which the dense layer is disposed is defined as a layer C, a ratio (PD / WT) of the average pore diameter (PD) of pores present in the layer C to the membrane thickness (WT) of the hollow fiber membrane is 0.0110-0.0180.

Description

Hollow fiber membrane, hollow fiber membrane module, cartridge for water purifier, and water purifier

[0001] The present invention relates to a hollow fiber membrane, a hollow fiber membrane module, a cartridge for a water purifier, and a water purifier.

[0002] Hollow fiber membranes have been widely used in fields ranging from reverse osmosis to microfiltration, including medical applications such as blood purifiers for patients with renal failure and water treatment applications such as water purifiers.

[0003] Hydrophobic polymers such as polyethylene, polysulfone, and polyethersulfone are known as materials for hollow fiber membranes, and hollow fiber membranes made from these materials are known to be subjected to hydrophilization treatment before use. Hydrophilization treatments include coating the hollow fiber membrane with a hydrophilic polymer after its production, and discharging an injection solution containing a hydrophilic polymer through a double-ring nozzle together with the hollow fiber membrane spinning solution to impart hydrophilicity. Such hydrophilization treatments increase the water permeability of the hollow fiber membrane.

[0004] Furthermore, the properties required for cartridges for water purifiers include resistance to high water pressure, high water permeability, high substance removal properties, and a long cartridge life. To this end, hollow fiber membranes for water purifiers have been developed that are strong enough to withstand water pressure, yet have high water permeability and sharp substance separation properties.

[0005] For example, Patent Document 1 discloses a method for controlling the ratio of the thickness of a hollow fiber membrane having an outer diameter of 350 μm or less to the thickness of a dense layer in a solution spinning method in order to improve resistance to high water pressure.

[0006] Patent Document 2 discloses a method for producing a hollow fiber membrane containing a vinylidene fluoride resin, which comprises controlling a preparation step of preparing a membrane-forming stock solution, an extrusion step of extruding the membrane-forming stock solution into a hollow fiber shape, and a step of contacting the extruded hollow fiber-shaped membrane-forming stock solution with an external coagulation liquid to form a hollow fiber membrane, thereby producing a hollow fiber membrane with excellent water permeability and fractionation characteristics.

[0007] Patent Document 3 discloses a method for improving fatigue durability while maintaining permeability in a porous membrane having an asymmetric hollow fiber shape by controlling the distribution of polymer trunk thickness on the cross section and surface of the porous membrane and the non-solvent vapor during phase separation.

[0008] Japanese Patent No. 6973071 Japanese Patent No. 6419917 Japanese Patent No. 7157790

[0009] However, according to the studies of the present inventors, the hollow fiber membranes disclosed in Patent Documents 1 and 2 have resistance to high water pressure, but their water permeability is not sufficiently high, and further improvement of the water permeability is considered necessary. Also, the hollow fiber membranes and porous membranes disclosed in Patent Documents 2 and 3 are thick and have excellent durability, but when the membrane area of ​​the hollow fiber membrane provided in the water purifier cartridge (hereinafter sometimes referred to as cartridge) is increased in order to extend the product life of the cartridge, there is a problem that the cartridge becomes large.

[0010] Therefore, in order to prevent the cartridge from becoming larger while increasing the membrane area of ​​the hollow fiber membrane, it is conceivable to reduce the diameter of the hollow fiber membrane, but in this case, the hollow fiber membrane tends to have poor water permeability. Note that if the outer diameter of the hollow fiber membrane is fixed and the inner diameter of the hollow fiber membrane is enlarged in order to control the membrane area and water permeability of the hollow fiber membrane provided in the cartridge, the hollow fiber membrane tends to have poor resistance to high water pressure.

[0011] In view of the above problems, the present invention aims to provide a hollow fiber membrane that combines high water permeability with fractionation characteristics, and further to achieve a smaller size and longer life for a water purifier cartridge equipped with the hollow fiber membrane.

[0012] In order to solve the above problems, the present invention is characterized by the following (1) to (13): (1) A hollow fiber membrane having a dense layer, the dense layer being disposed on the outer surface side or the inner surface side of the hollow fiber membrane, the membrane thickness of the hollow fiber membrane being 40 μm to 120 μm, and when the membrane thickness of the hollow fiber membrane is divided into three equal parts in the thickness direction, with the layer including the dense layer being Layer A, the central layer in the thickness direction being Layer B, and the layer including the surface opposite to the surface on which the dense layer is disposed being Layer C, the ratio (PD / WT) of the average pore diameter (PD) of pores present in Layer C to the membrane thickness (WT) of the hollow fiber membrane is 0.0110 to 0.0180. (2) The hollow fiber membrane according to (1) above, wherein the surface opposite to the surface on which the dense layer is disposed is 10% to 35%. (3) The hollow fiber membrane according to (1) or (2) above, wherein the dense layer is disposed on the outer surface side of the hollow fiber membrane. (4) The hollow fiber membrane according to (1) above, wherein the surface of the hollow fiber membrane on which the dense layer is disposed has a porosity of 15% or more and 45% or less. (5) The hollow fiber membrane according to (1) above, comprising a polysulfone-based polymer and polyvinylpyrrolidone. (6) The hollow fiber membrane according to (5) above, wherein the polyvinylpyrrolidone content is 2% by mass or more and 9.5% by mass or less. (7) A hollow fiber membrane module, wherein the hollow fiber membranes according to (1) or (2) above are packed in a cylindrical case, and the open ends of the hollow fiber membranes are fixed to the cylindrical case. (8) The hollow fiber membrane module according to (7) above, wherein (2N×L) / S is 3.0 or more and 13.0 or less, where S is the cross-sectional area of ​​the smallest point of a cross section perpendicular to the axial direction of the cylindrical case, L is the circumferential length of the hollow fiber membrane, and N is the number of the hollow fiber membranes packed in the cylindrical case. (9) The hollow fiber membrane module according to (7) or (8) above, wherein the removal rate of particles having a diameter of 0.3 μm or more is 99.9% or more. (10) The hollow fiber membrane module according to (7) above, wherein the ratio of the inner diameter of the hollow fiber membrane to the outer diameter of the hollow fiber membrane (inner diameter / outer diameter) is 0.57 or more and 0.67 or less. (11) The hollow fiber membrane module according to (7) above, wherein the filling rate of the hollow fiber membranes with respect to the inner space of the cylindrical case is 40% or more and 60% or less. (12) A cartridge for a water purifier equipped with the hollow fiber membrane module described in (7) or (8) above.(13) A water purifier equipped with the water purifier cartridge described in (12) above.

[0013] According to the present invention, a hollow fiber membrane is provided that combines high water permeability with fractionation properties, and furthermore, it is possible to achieve a high flow rate for a hollow fiber membrane module equipped with the hollow fiber membrane, and a compact, long-life cartridge for a water purifier.

[0014] FIG. 1 is a partially enlarged view of a cross section in a direction perpendicular to the longitudinal direction of a hollow fiber membrane using one embodiment of the hollow fiber membrane of the present invention.

[0015] A preferred embodiment of the present invention (hereinafter also referred to as "the present embodiment") will be described in detail below. In this specification, all percentages and parts expressed by mass are the same as percentages and parts expressed by weight. Figure 1 is a partially enlarged view of a cross section of a hollow fiber membrane of this embodiment in a direction perpendicular to the longitudinal direction.

[0016] In conventional technology, when the diameter of a hollow fiber membrane having a dense layer is reduced in order to increase the membrane area of ​​the hollow fiber membrane while preventing the cartridge from becoming larger, sufficient water permeability tends to be unavailable.

[0017] The present inventors have found that the membrane thickness and cross-sectional structure of a hollow fiber membrane have a significant effect on the water permeability of the hollow fiber membrane, and have created a hollow fiber membrane of the present embodiment that is provided with a dense layer, the dense layer being disposed on either the outer surface side or the inner surface side of the hollow fiber membrane, the membrane thickness of the hollow fiber membrane being 40 μm or more and 120 μm or less, and, as shown in FIG. 1 for example, when the membrane thickness of the hollow fiber membrane is divided into three equal parts in the thickness direction, with the layer including the dense layer being Layer A (A), the central layer in the thickness direction being Layer B (B), and the layer including the surface opposite to the surface on which the dense layer is disposed being Layer C, the ratio (PD / WT) of the average pore diameter (PD) of the pores present in Layer C (C) to the membrane thickness (WT) of the hollow fiber membrane is 0.0110 or more and 0.0180 or less.

[0018] The hollow fiber membrane of this embodiment has a dense layer, which is disposed on the outer or inner surface side of the hollow fiber membrane. Here, the dense layer refers to a layer in the hollow fiber membrane where extremely small pores are densely located, and is the portion that determines the fractionation characteristics of the hollow fiber membrane. Furthermore, it is preferable that the hollow fiber membrane of this embodiment does not have macrovoids or finger voids formed in the membrane cross section.

[0019] Furthermore, it is important that the hollow fiber membrane of this embodiment has a membrane thickness (WT) of 40 μm or more and 120 μm or less, and from the viewpoint of improving the strength of the hollow fiber membrane, the lower limit is preferably 45 μm or more, and more preferably 50 μm or more. On the other hand, from the viewpoint of improving the water permeability of the hollow fiber membrane and the product life of the water purifier cartridge, the upper limit is preferably 100 μm or less, and more preferably 90 μm or less.

[0020] Furthermore, the hollow fiber membrane of this embodiment has a ratio (PD / WT) of the average pore size (PD) of the pores present in the C layer to the membrane thickness (WT) of the hollow fiber membrane of 0.0110 or more, thereby improving the water permeability of the hollow fiber membrane. Furthermore, the ratio (PD / WT) of the average pore size (PD) of the pores present in the C layer to the membrane thickness (WT) of the hollow fiber membrane of 0.0180 or less allows the hollow fiber membrane to maintain sufficient strength, thereby providing not only high water pressure resistance but also excellent processability and handleability required for modularization. From the above perspectives, the ratio (PD / WT) of the average pore size (PD) of the pores present in the C layer to the membrane thickness (WT) of the hollow fiber membrane is more preferably 0.0120 or more and 0.0170 or less, and even more preferably 0.0130 or more and 0.0160 or less. The average pore size (PD) of the pores present in the C layer can be measured by the method described in the Examples. Note that "average pore size" refers to the average diameter of the pores. The ratio (PD / WT) of the average pore diameter (PD) of the pores present in layer C to the membrane thickness (WT) of the hollow fiber membrane may be 0.011 or more and 0.018 or less, 0.012 or more and 0.017 or less, or 0.013 or more and 0.016 or less.

[0021] Furthermore, in the hollow fiber membrane of this embodiment, the porosity of the surface (2) opposite the surface on which the dense layer is disposed is preferably 10% or more and 35% or less. A porosity of 10% or more on the surface of the hollow fiber membrane opposite the surface on which the dense layer is disposed is preferable because the water permeability of the hollow fiber membrane can be further improved. On the other hand, a porosity of 35% or less on the surface of the hollow fiber membrane opposite the surface on which the dense layer is disposed can further maintain its strength. From the above viewpoint, the lower limit of the porosity is more preferably 13% or more, and even more preferably 16% or more. The upper limit of the porosity is more preferably 32% or less, and even more preferably 29% or less. Furthermore, by controlling the porosity of the surface on which the dense layer is disposed within the above range, fouling is less likely to occur even when filtration is performed from the surface on which the dense layer is disposed. This makes the membrane more suitable for medical applications such as plasma separation membranes and cell separation and purification membranes for the production of biopharmaceuticals.

[0022] Furthermore, examples of means for adjusting the porosity of the surface opposite to the surface on which the dense layer of the hollow fiber membrane is disposed within the above-mentioned range include, in the method for producing a hollow fiber membrane, adjusting the content of a hydrophilic polymer in the membrane-forming solution to control the rate of phase separation of the polymer, and adjusting the viscosity and content of a good solvent in the injected liquid to control the coagulation property and diffusibility.

[0023] Furthermore, it is preferable to arrange the dense layer of the hollow fiber membrane on the surface that comes into contact with the water to be treated. For example, when the water to be treated is to be passed from the outer surface side to the inner surface side of the hollow fiber membrane, it is preferable to arrange the dense layer on the outer surface side of the hollow fiber membrane. The reason for this is that this can prevent turbid matters contained in the water to be treated from penetrating into the hollow fiber membrane, thereby suppressing deterioration of filtration resistance due to clogging of pores and suppressing a decrease in membrane permeability.

[0024] Furthermore, the hollow fiber membrane of this embodiment preferably has a porosity of 15% or more and 45% or less on the surface (1) on the side where the dense layer is disposed. A porosity of 15% or more on the surface on the dense layer side of the hollow fiber membrane is preferable because it improves water permeability. On the other hand, a porosity of 45% or less on the outer surface on the dense layer side of the hollow fiber membrane can better maintain its strength and removal performance. From the above perspective, the lower limit of the porosity is more preferably 18% or more, and even more preferably 21% or more. The upper limit of the porosity is more preferably 42% or less, and even more preferably 39% or less. Examples of means for adjusting the porosity of the surface on the dense layer side of the hollow fiber membrane within the above range include adjusting the content of hydrophilic polymer in the membrane-forming solution or the atmosphere in the dry section to control the polymer phase separation rate in the hollow fiber membrane manufacturing method. The porosity of the surface of the hollow fiber membrane can be measured by the method described in the Examples.

[0025] Furthermore, the hollow fiber membrane of this embodiment preferably contains a hydrophilic polymer. This is because imparting hydrophilicity to the membrane surface improves water permeability and suppresses adhesion of turbidity to the membrane. On the other hand, if the hydrophilic polymer content is high, the hydrophilic polymer itself may retain water, thereby causing permeation resistance and potentially reducing water permeability. Therefore, the content of the hydrophilic polymer is preferably 4 parts by mass or more and 20 parts by mass or less. The upper limit of the hydrophilic polymer content is preferably 20 parts by mass or less, more preferably 15 parts by mass or less, relative to the total mass of the hollow fiber membrane. On the other hand, the lower limit is preferably 4 parts by mass or more, more preferably 6 parts by mass or more. Furthermore, when a large amount of crosslinked hydrophilic polymer is present on the membrane surface of the hollow fiber membrane, a decrease in water permeability tends to be observed. Therefore, the mass ratio of hydrophilic polymer to hydrophobic polymer (hydrophilic polymer / hydrophobic polymer) on the surface of the hollow fiber membrane where the dense layer is present is preferably 0.80 or less, more preferably 0.70 or less. Furthermore, from the above viewpoint, the mass ratio of hydrophilic polymer to hydrophobic polymer (hydrophilic polymer / hydrophobic polymer) on the surface opposite to the surface of the hollow fiber membrane on which the dense layer is present is also preferably 0.80 or less, and more preferably 0.70 or less.

[0026] Here, the term "hydrophilic polymer" refers to a water-soluble polymeric compound or a water-insoluble polymeric compound that interacts with water molecules through electrostatic interactions or hydrogen bonds. Specific examples include nonionic hydrophilic polymers such as polyalkylene oxides (e.g., polyethylene oxide and polypropylene oxide), polyvinyl alcohol, polyvinylpyrrolidone (hereinafter sometimes referred to as PVP), polyvinyl acetate, polydimethyl methoxyacrylate, polydimethylacrylamide, copolymers of vinylpyrrolidone and acrylic acid, and copolymers of vinyl acetate and vinylpyrrolidone; anionic hydrophilic polymers such as polyacrylic acid, polyvinyl sulfate, and carboxymethyl cellulose; cationic hydrophilic polymers such as polyallylamine, polylysine, chitosan, and poly[2(dimethylamino)ethyl methacrylate]; and zwitterionic hydrophilic polymers such as polymethacryloyloxyethyl phosphorylcholine and polymethacryloyloxyethyl dimethylammoniopropionate. The hollow fiber membrane may contain two or more types of hydrophilic polymers. In particular, from the viewpoint of inhibiting adhesion of suspended matter, nonionic hydrophilic polymers and zwitterionic hydrophilic polymers are preferably used.

[0027] The material (component) constituting the substrate of the hollow fiber membrane is preferably a hydrophobic polymer. Examples of suitable hydrophobic polymers include polysulfone-based polymers, fluororesins such as polyvinylidene fluoride, cellulose-based resins such as polystyrene, polyethylene, cellulose triacetate, and cellulose diacetate, polymethyl methacrylate, polyacrylonitrile, and polyamides. Among these, polysulfone-based polymers are preferred from the viewpoint of the strength and water permeability of the hollow fiber membrane. Here, polysulfone-based polymers are polymers having an aromatic ring, a sulfonyl group, and an ether group in the main chain, such as polysulfone, polyphenylsulfone, polyethersulfone, and polyarylethersulfone. These polysulfone-based polymers may be used alone, or two or more polysulfone-based polymers may be blended in a certain ratio. Adding PVP to a spinning solution made of a polysulfone-based polymer is particularly preferred from the viewpoint of controlling the membrane structure of this embodiment.

[0028] The composition ratio of the hollow fiber membrane is preferably such that the polysulfone polymer accounts for 5 to 20% by mass (%) of all the constituent components of the hollow fiber membrane.

[0029] In this embodiment, the main component of the hollow fiber membrane is preferably, for example, a polysulfone-based polymer represented by the following chemical formula (1) and / or (2), but is not limited thereto. In the formula, n is an integer of 1 or more, preferably 50 to 80. When n has a distribution, the average value is taken as n. When the polysulfone-based polymer has the chemical formulas (1) and (2), n in formula (1) and n in formula (2) may be the same value or different values.

[0030]

[0031] The polysulfone-based polymer that can be used in the hollow fiber membrane of this embodiment is preferably a polymer consisting only of repeating units represented by the above formula (1) and / or (2), but may be copolymerized with other monomers or may be a modified product within the range that does not impair the effects of the present invention. When copolymerized with other monomers, the copolymerization ratio of the other monomers is preferably 10 mass % or less based on the total mass of the polysulfone-based polymer.

[0032] Specific examples of polysulfone-based polymers that can be used in the hollow fiber membrane of this embodiment include polysulfone-based polymers such as Udel (registered trademark) polysulfone P-1700 and P-3500 (manufactured by Solvay), Ultrason (registered trademark) S3010, P3010, and S6010 (manufactured by BASF), Victrex (registered trademark) (manufactured by Sumitomo Chemical Co., Ltd.), Radel polyphenylsulfone R-5000NT (manufactured by Solvay), Veradel polyethersulfone 3000MP (manufactured by Solvay), and Ultrason (registered trademark) E (manufactured by BASF).

[0033] In addition, the hollow fiber membrane preferably contains polyvinylpyrrolidone in addition to the polysulfone-based polymer. Polyvinylpyrrolidone of various molecular weights can be used, but it is convenient to use commercially available products such as K90 (trade name, manufactured by BASF, weight average molecular weight 1.2 million), K78 / 81 (manufactured by Ashland Japan), K60 (trade name, manufactured by Tokyo Chemical Industry Co., Ltd., weight average molecular weight 160,000), K30 (trade name, manufactured by BASF, weight average molecular weight 40,000), and K17 (trade name, manufactured by BASF, weight average molecular weight 10,000). A mixture of these or a polymer of a molecular weight range other than those mentioned above may also be used. By mixing and using the above polyvinylpyrrolidones, it is possible to adjust the viscosity of the membrane-forming solution.

[0034] In the process of producing hollow fiber membranes, the components of the hollow fiber membrane, such as polysulfone polymers and PVP, are dissolved in a solvent to prepare a spinning solution. Here, high-boiling polar solvents such as dimethylacetamide (hereinafter abbreviated as DMAc) and N-methylpyrrolidone are preferred as the solvent, but other combinations can also be used as long as they can be dissolved uniformly.

[0035] In the hollow fiber membrane of this embodiment, the polyvinylpyrrolidone content is preferably 2% by mass or more and 9.5% by mass or less based on 100% by mass of the hollow fiber membrane. When the polyvinylpyrrolidone content is 2% by mass or more, the polyvinylpyrrolidone can impart hydrophilicity to the hollow fiber membrane, thereby improving water permeability. On the other hand, when the polyvinylpyrrolidone content is 9.5% by mass or less, the swelling property of polyvinylpyrrolidone can be prevented from causing a decrease in water permeability. From the above perspective, the lower limit of the polyvinylpyrrolidone content is more preferably 3.0% by mass or more, and even more preferably 4.0% by mass or more. The upper limit of the polyvinylpyrrolidone content is more preferably 8.5% by mass or less, and even more preferably 7.5% by mass or less. The polyvinylpyrrolidone content in the hollow fiber membrane is measured as described in the Examples below.

[0036] The fractionation performance of the hollow fiber membrane is preferably 80% or more, more preferably 90% or more, of particles with a particle diameter of 0.3 μm or more. When bacteria need to be removed from raw water, the removal rate of particles with a particle diameter of 0.3 μm or more is preferably 99.9% or more, more preferably 99.99% or more.

[0037] The hollow fiber membrane of this embodiment can be obtained by controlling the composition of the spinning dope and the composition of the injectate, the linear discharge speed when the spinning dope is discharged from the spinneret and the linear discharge speed of the injectate, the dew point and temperature of the cold air in the dry section after discharge, the cold air speed, the draft ratio when the spinning dope is discharged, the coagulation bath temperature, the water washing conditions, and the like.

[0038] Next, a method for producing the hollow fiber membrane of this embodiment will be described. Although not particularly limited, the hollow fiber membrane of this embodiment can be produced by using an orifice-type double-ring spinneret, in which a spinning dope containing a polymer serving as a material for the hollow fiber membrane is discharged from an outer ring slit and an injection liquid is discharged from an inner central pipe, and the dope is passed through a dry section, coagulated in a coagulation solution, and then washed with warm water, thereby producing a hollow fiber membrane having an asymmetric structure.

[0039] The spinning draft ratio when producing the hollow fiber membrane of this embodiment is the ratio of the linear extrusion velocity of the membrane-forming composition from the outer circumferential slit of the double-ring spinneret to the winding velocity of the hollow fiber membrane, and is the value obtained by dividing the winding velocity by the linear extrusion velocity of the membrane-forming composition. The linear extrusion velocity is the linear velocity at which the membrane-forming composition is extruded from the outer circumferential slit of the double-ring spinneret, and is the value obtained by dividing the extrusion flow rate by the cross-sectional area of ​​the outer circumferential slit.

[0040] By setting the spinning draft ratio to a predetermined value or higher, the water permeability of the hollow fiber membrane is improved, whereas by setting the spinning draft ratio to a predetermined value or lower, the spinning stability is improved and the frequency of fiber breakage can be reduced.

[0041] When a double-ring spinneret such as an orifice-type double-ring spinneret is used to spin a hollow fiber membrane, the viscosity of the spinning dope at 37°C is preferably 2 Pa·s or more and 11 Pa·s or less. By making the viscosity of the spinning dope at 37°C 2 Pa·s or more, the spinnability of the hollow fiber membrane is improved. On the other hand, by making the viscosity of the spinning dope at 37°C 11 Pa·s or less, the pressure at the double-ring spinneret can be suppressed, and a stable discharge state of the spinning dope can be maintained. Furthermore, if the viscosity of the spinning dope at 37°C is too low, the phase separation rate of the polymer may increase, and the thickness of the dense layer may become too thin, resulting in a deterioration in fractionation characteristics. For this reason, the viscosity of the spinning dope at 37°C is preferably 2 Pa·s or more.

[0042] On the other hand, the liquid injected into the central pipe of the double-ring nozzle can be selected as either coagulable or non-coagulable depending on the desired shape of the hollow fiber membrane. The coagulation value is an indicator of the coagulation property of the injected liquid. This coagulation value represents the mass of the injected liquid added when the system becomes cloudy after adding the injected liquid little by little to 50 g of a 1% by mass solution of the main polymer that constitutes the membrane. The smaller the value of this coagulation value, the higher the coagulation property of the injected liquid. Based on past experience, if the coagulation value is 40 g or more (more than 80% of the original liquid volume), the particle structure of the aggregated polymer is no longer visible on the membrane surface where the dense layer is formed, and therefore it is determined to be non-coagulable.

[0043] When a coagulable liquid is used as the injected liquid, coagulation begins from the inner surface, forming a dense layer on the inner surface side of the hollow fiber membrane. On the other hand, when a non-coagulable liquid is used, coagulation begins from the outer surface in a coagulation bath provided downstream, forming a dense layer on the outer surface side of the hollow fiber membrane. Therefore, a non-coagulable liquid is particularly suitable for use in water purifiers, where the flow is filtrated from the outer surface side to the inner surface side of the hollow fiber membrane.

[0044] One method is to add a thickener to the injection liquid, and a higher viscosity of the injection liquid can improve the metering ability of the injection liquid when delivered to the double-ring nozzle. Examples of thickeners include polyvinylpyrrolidone, polyethylene glycol, polyvinyl alcohol, glycerin, and glucose.

[0045] Furthermore, adding polyethylene glycol, glycerin, or the like to the injection liquid allows the hollow fiber membrane to be opened while maintaining a smooth inner surface, which is preferable from the viewpoint of increasing the breaking strength of the hollow fiber membrane.Furthermore, since the smooth surface is also preferable when the hollow fiber membrane is used for medical purposes such as plasma separation, the activity of the substance to be separated can be suppressed.

[0046] When phase separation of the hollow fiber membrane is induced by heat during the spinning process of the hollow fiber membrane, the hollow fiber membrane is cooled in a dry section and then rapidly cooled in a coagulation bath to solidify. When phase separation of the hollow fiber membrane is induced by a poor solvent during the spinning process of the hollow fiber membrane, the spinning dope is contacted with a coagulation liquid containing a poor solvent, discharged, and solidified in a coagulation bath containing the poor solvent. Furthermore, in the method of inducing phase separation of the hollow fiber membrane using a poor solvent, the poor solvent is supplied to the interior of the hollow fiber membrane by diffusion, so the amount of poor solvent supplied varies across the membrane thickness. Therefore, the pore size in the cross section of the membrane thickness direction increases from one surface to the other. Therefore, it is preferable to contact the coagulation liquid containing a poor solvent with the spinning dope immediately after discharge. Adjusting the concentration of the coagulation liquid as a mixture of a poor solvent and a good solvent changes the coagulation properties, allowing the minor diameter of the pores on the surface in contact with the coagulation liquid and the thickness of the dense layer to be controlled.

[0047] Furthermore, on the side where the coagulation liquid and the spinning dope come into contact, phase separation is induced, and solidification progresses rapidly, resulting in a dense structure with small pore diameters. Furthermore, the pore diameter continuously increases in the direction opposite to the side where the coagulation liquid and the spinning dope come into contact. Here, if the passage time through the dry section is sufficiently long, the pore diameter on the side not in contact with the coagulation liquid will grow large. Therefore, by shortening the passage time through the dry section and quickly immersing the material in the coagulation bath, solidification on the side not in contact with the coagulation liquid will progress due to contact with the poor solvent of the coagulation bath, and a dense structure with small pore diameters can be formed.

[0048] Although it depends on conditions that affect the progress of phase separation, such as the composition and temperature of the spinning dope, the time required for passing through the dry zone is preferably 0.02 seconds or more and 0.40 seconds or less. That is, it is preferably 0.02 seconds or more, and more preferably 0.14 seconds or more. On the other hand, it is preferably 0.40 seconds or less, and more preferably 0.35 seconds or less.

[0049] The concentration of the poor solvent in the coagulation bath is preferably 30% by mass or more, more preferably 50% by mass or more, and even more preferably 80% by mass or more, based on the total coagulation liquid.

[0050] The temperature of the coagulation bath is preferably 40°C or higher, more preferably 50°C or higher, and even more preferably 60°C or higher, because a high temperature of the coagulation bath facilitates solvent exchange in the coagulation bath and can reduce the amount of solvent remaining in the hollow fiber membrane.

[0051] If the temperature of the coagulation bath is high, condensation may form on the surface of the spinneret, which may cause yarn breakage. Therefore, the discharge temperature of the spinning dope is preferably 25°C or higher, since this can prevent condensation on the surface of the spinneret. Furthermore, if the discharge temperature of the spinning dope is too high, the spinnability tends to become unstable, so the discharge temperature of the spinning dope is preferably 70°C or lower, more preferably 55°C or lower.

[0052] The concentration of the coagulation bath changes over time due to the supply of solvent from the spinning dope and the coagulation liquid. Therefore, it is preferable to suppress the concentration change by increasing the amount of the coagulation bath or to monitor the concentration and adjust it as needed.

[0053] In the dry section, providing a running section in which the temperature and humidity are more actively controlled is also effective in controlling the pore opening of the hollow fiber membrane, and is preferable because it can reduce variation in the performance of the resulting hollow fiber membrane. Furthermore, in the dry section, although not particularly limited, in order to more actively control the humidity of the dry section atmosphere, it is possible to provide cooling air tubes on both sides of the spinning dope discharged from the double ring spinneret or to surround the spinning dope discharged from the double ring spinneret with an annular cooling air tube. When providing cooling air tubes on both sides of the spinning dope discharged from the double ring spinneret, a method in which cold air is supplied from one side of the cooling air tube and exhausted from the other side, or a method in which cold air is supplied from both sides, is preferable because it can more actively control the humidity of the dry section atmosphere. In addition, surrounding the spinning dope discharged from the double ring spinneret with an annular cooling air tube is also preferable because it makes the dry section less susceptible to the influence of outside air and reduces variation in the performance of the resulting hollow fiber membrane.

[0054] In the dry section, the higher the dew point and wind speed of the cold air, the greater the supply amount of moisture, which is a poor solvent, and this is effective when it is desired to increase the pore size of the holes on the outer surface and increase the aperture ratio. The dew point of the dry section is preferably 18°C ​​or higher, more preferably 21°C or higher. The wind speed of the cold air in the dry section is preferably 0.1 m / s or higher. On the other hand, since lowering the wind speed of the cold air can suppress turbulence of the surface of the spinning dope during discharge and shaking during discharge, the wind speed in the dry section is preferably 10 m / s or lower. That is, the wind speed in the dry section is preferably 0.1 m / s or higher and 10 m / s or lower.

[0055] The length of the dry section is preferably 10 mm or more and 200 mm or less in order to obtain a suitable pore diameter on the surface of the hollow fiber membrane and to prevent the fibers from shaking during membrane production.

[0056] A poor solvent is a solvent that does not dissolve the polymer that mainly forms the structure of the hollow fiber membrane at the membrane-forming temperature. The poor solvent may be selected appropriately depending on the type of polymer, but water is preferably used. The good solvent may be selected appropriately depending on the type of polymer, but when the polymer that forms the structure of the hollow fiber membrane is a polysulfone-based polymer, N,N-dimethylacetamide is preferably used.

[0057] According to the above manufacturing method, the hollow fiber membrane is obtained in a wet state. However, the water permeability of the hollow fiber membrane is unstable if left in this state, so drying of the water and crosslinking of the hydrophilic polymer (e.g., PVP) are necessary. As mentioned above, the inclusion of a hydrophilic polymer (e.g., PVP) can impart hydrophilic properties to the hollow fiber membrane, improving water permeability and suppressing adhesion of turbidity to the membrane. However, a small amount of the hydrophilic polymer remaining in the membrane may be eluted. This is undesirable for medical and food industry applications. For the crosslinking reaction to insolubilize the membrane, gamma-ray irradiation is effective for vinyl-based hydrophilic polymers. Furthermore, crosslinking can also be achieved by heating, particularly when the hydrophilic polymer is polyvinylpyrrolidone. A drying temperature of 100°C or higher is preferred to evaporate water.

[0058] When drying the hollow fiber membrane, if the hollow fiber membrane contains a large amount of hydrophilic polymer, the hydrophilic polymer may be unevenly distributed on the surface of the hollow fiber membrane, which may result in a decrease in the water permeability of the hollow fiber membrane and a decrease in the filtration flow rate when modularized. Therefore, as a pretreatment, it is preferable to wash the inside of the obtained hollow fiber membrane with warm water. The temperature of the warm water is preferably 60°C or higher, more preferably 70°C or higher, and even more preferably 80°C or higher. It is also preferable that the temperature be 99°C or lower.

[0059] The hollow fiber membrane of this embodiment can be suitably used in a hollow fiber membrane module. A specific embodiment of the hollow fiber membrane module includes a bundle of U-shaped hollow fiber membranes housed in a cylindrical case, and an end of the bundle of hollow fiber membranes where the hollow fiber membranes have openings is fixed to one end of the cylindrical case with a sealing material.

[0060] A hollow fiber membrane module for a water purifier must be able to remove suspended matter the size of bacteria or larger. Therefore, the hollow fiber membrane module of this embodiment preferably has a particle removal rate of 99.9% or more, and more preferably 99.99% or more, for particles with a particle diameter of 0.3 μm or larger. Furthermore, in order to achieve a particle removal rate of 99.9% or more for particles with a particle diameter of 0.3 μm or larger, it is important that breakage of the hollow fiber membranes used in the hollow fiber membrane module is extremely suppressed.

[0061] Furthermore, when the bundle of hollow fiber membranes is folded into a U-shape and inserted into a cylindrical case, if the membrane thickness is small, i.e., if the inner diameter / outer diameter ratio of the hollow fiber membranes is large, the hollow portion may be crushed during the U-shape, damaging the hollow fiber membranes and causing leakage of suspended solids, bacteria, etc. that should be removed into the purified water. For this reason, the inner diameter / outer diameter ratio of the hollow fiber membranes is preferably 0.57 to 0.67, more preferably 0.57 to 0.65, and even more preferably 0.57 to 0.63.

[0062] To extend the product life of a hollow fiber membrane module using a cylindrical case for a given capacity, it is preferable to increase the filling rate of hollow fiber membranes in the inner space of the cylindrical case. On the other hand, a filling rate of 40% to 60% is preferable because it prevents raw water from permeating the entire hollow fiber membrane bundle, preventing the hollow fiber membranes at the innermost part of the hollow fiber membrane bundle from being effectively utilized. Furthermore, a filling rate of 60% or less is also preferable from the viewpoint of improving operability when inserting the U-shaped fiber bundle into the cylindrical case. From the above viewpoint, a filling rate of 45% to 57% is more preferable. Here, the filling rate is calculated using the smallest cross-section of the cylindrical case. Cylindrical cases may be used whose inner diameter expands or contracts along their longitudinal direction. Therefore, in this embodiment, the filling rate of hollow fiber membranes is calculated using the cross-sectional area (S) of the smallest point in a cross section perpendicular to the axial direction of the inner cylindrical case. The packing rate is expressed by equation (5), which is the product of the cross-sectional area (A) of the hollow fiber membrane calculated by equation (4) and twice the number of hollow fiber membranes, divided by the cross-sectional area (S) of the cylindrical case. The cross-sectional area of ​​the hollow fiber membrane is calculated including the hollow portion of the hollow fiber membrane. Cross-sectional area of ​​the hollow fiber membrane (A) = (outer diameter of the hollow fiber membrane) ２ ×π / 4 (4) Filling rate (%) = 100 × [number of threads × 2] × A / S (5)

[0063] Increasing the membrane area of ​​the hollow fiber membranes within the cylindrical case, i.e., housing a hollow fiber membrane bundle with high-density hollow fiber membranes within the cylindrical case to form a hollow fiber membrane module, is important from the perspective of extending the product life of a water purifier cartridge using this hollow fiber membrane module. The membrane area is expressed as the product of the circumferential length of the hollow fiber membranes, the number of hollow fiber membranes, and the effective length of the hollow fiber membranes within the hollow fiber membrane module. However, since the effective length depends on the size of the cylindrical case, it is important to maximize the product of the circumferential length of the hollow fiber membranes (L) and the number of hollow fiber membranes (N) x 2 per unit cross-sectional area of ​​the cylindrical case in order to extend the product life. As mentioned above, the cross-sectional area of ​​the cylindrical case is the cross-sectional area at the point where the cross-sectional area of ​​the cylindrical case perpendicular to the axial direction is smallest. In this embodiment, (2N×L) / S is preferably 3.0 or more and 13.0 or less, more preferably 4.0 or more and 12.0 or less, even more preferably 5.0 or more and 11.0 or less, and particularly preferably 6.0 or more and 10.0 or less. The circumferential length (L) of the hollow fiber membrane is calculated by the measurement method described in the Examples.

[0064] Furthermore, the hollow fiber membrane module using the hollow fiber membrane of this embodiment can be suitably used in a cartridge for a water purifier. Specific examples of the cartridge for a water purifier include one equipped with an adsorbent such as activated carbon in addition to the hollow fiber membrane module. Conventional methods can be used to manufacture a cartridge for a water purifier equipped with a hollow fiber membrane.

[0065] Furthermore, from the viewpoint of improving the water permeability and product life of a water purifier cartridge by forming a hollow fiber membrane module in which a sufficient number of hollow fiber membranes are packed in a case of a certain volume, it is preferable that the hollow fiber membrane have a small outer diameter, a large inner diameter, and a thin membrane thickness. Furthermore, from the viewpoint of improving the strength of the hollow fiber membrane, it is preferable that the hollow fiber membrane have a large outer diameter, a small inner diameter, and a thick membrane thickness. To achieve both of these contradictory conditions, it is important to control the cross-sectional structure of the hollow fiber membrane. The cross-sectional structure of the hollow fiber membrane significantly affects the membrane's strength retention and water permeability. For these reasons, it is preferable that the hollow fiber membrane have an outer diameter of 250 μm or more and 700 μm or less, and an inner diameter of 150 μm or more and 450 μm or less. From the viewpoint of obtaining a larger membrane area of ​​the hollow fiber membrane within a cylindrical case of the same volume, the outer diameter of the hollow fiber membrane is more preferably 500 μm or less, even more preferably 400 μm or less, and most preferably 350 μm or less.

[0066] Furthermore, the water purifier cartridge can be suitably used in a water purifier that includes a flow path switcher in addition to the water purifier cartridge.

[0067] The present invention will be specifically described below with reference to examples, but the present invention is not limited thereto. Evaluation methods in the examples will be explained in the following (1) to (12).

[0068] (Analysis and Evaluation Methods) (1) Viscosity Measurement of Spinning Dope Measurement was carried out using a Brookfield viscometer as specified in JIS K7117 (1999), and the average value of n=3 was taken as the measured value.

[0069] (2) Measurement of Water Permeability A hollow fiber membrane was inserted into a case equipped with reflux holes at both ends, and both ends were potted with Konishi Co., Ltd.'s epoxy resin adhesive "Quick Mender" (registered trademark). The hollow fiber membrane and potting agent protruding from both ends of the case were then cut off to produce a small module with an effective length of 12 cm. The water permeability was measured by applying water pressure to the inside of the hollow fiber membrane in a thermostatic water bath maintained at 37°C. The water permeability was calculated from the amount of water passing through the hollow fiber membrane to the outside of the hollow fiber membrane within a certain period of time ((permeable) filtration rate), the transmembrane pressure difference, and the effective membrane area of ​​the hollow fiber membrane (based on the inner diameter of the hollow fiber membrane). That is, the water permeability (UFRS) of the hollow fiber membrane was calculated using the following formula: The effective membrane area (based on the inner diameter of the hollow fiber membrane) is expressed as the product of the inner circumference of the hollow fiber membrane, the number of hollow fiber membranes, and the effective length of the hollow fiber membranes in the hollow fiber membrane module. The inner periphery of the hollow fiber membrane was calculated by multiplying the inner diameter (average value) by π. ２ ) = Qw / T / P / A Qw: (passage) filtration volume (mL) T: outflow time (hr) P: transmembrane pressure difference (Pa) A: effective membrane area of ​​hollow fiber membrane (m ２ )

[0070] (3) Measurement of the pore size on the surface of the hollow fiber membrane A 5000x magnification image (the observation magnification may be changed depending on the pore size) of the hollow fiber membrane surface was taken using an SEM (S-5500, manufactured by Hitachi High-Technologies Corporation) and imported into a computer. Next, analysis was performed using image processing software. The SEM image was binarized to obtain an image in which the pores were displayed in black and the structural polymers in white. If the structural parts could not be distinguished from the other parts due to differences in contrast within the image, the image was cut into parts with the same contrast, binarized separately, and then joined together to restore a single image. Alternatively, image analysis may be performed by filling in the parts other than the structural parts with black. If double pores were observed in the depth direction, the measurement was performed on the shallower pore. The total area S of the pores was read, and the pore size (%) per image was calculated using the following formula. The above operation was performed on 20 different hollow fiber membranes, and the calculated average of the 20 images was used as the result. Pore size (%) = {S (μm ２ ) / image size (μm ２ ) x 100

[0071] (4) Measurement of the Inner Diameter and Thickness of the Hollow Fiber Membrane The hollow fiber membrane was cut in the membrane thickness direction with a single-edged blade and set in a microwatcher (Keyence Corporation, VH-Z100). If the cross section of the hollow fiber membrane was crushed by cutting, the cutting was repeated until it became approximately a perfect circle. The cross section of the hollow fiber membrane was observed with a 1000x lens, and the membrane thickness width of the hollow fiber membrane was specified on the monitor screen on which the cross section was projected, and the numerical value displayed on the monitor screen was read. The membrane thickness width was measured at five locations per hollow fiber membrane. This series of measurements was performed on five arbitrary hollow fiber membranes, and the average of a total of 25 measurement data was calculated and used as the membrane thickness (WT) of the hollow fiber membrane. In addition, the inner diameter of the hollow fiber membrane was measured by specifying the hollow width range, and the numerical value was displayed on the monitor screen. The hollow width was measured at two locations per hollow fiber membrane. The above series of measurements was carried out on any five hollow fiber membranes, and the average value of a total of 10 measurement data was calculated to be the inner diameter (ID) of the hollow fiber membrane.

[0072] (5) Preparation of samples for SEM observation of hollow fiber membrane cross sections. The hollow fiber membranes obtained by membrane production were immersed in water for at least 1 hour to wet them, then frozen in liquid nitrogen and quickly folded to prepare samples for hollow fiber membrane cross section observation. If the hollow portions of the hollow fiber membrane or the voids in the membrane thickness were blocked, the sample preparation was redone. Blockage of the hollow portions may occur when the hollow fiber membrane is deformed in the direction of stress during the cutting process. When SEM images of the membrane cross sections were used in each of the following methods, the samples for observation were prepared using the method described herein and the images were obtained.

[0073] (6) Measurement of the average pore diameter (PD) of pores present in layer C Using the sample for observation obtained by the method in (5) above, a cross section perpendicular to the longitudinal direction was observed with an SEM (S-5500, manufactured by Hitachi High-Technologies Corporation). Images were taken consecutively in the film thickness direction at a magnification at which pores could be confirmed, with the surface side where the structure portion was dense on the left side of the image and the surface side where the structure portion was coarse on the right side of the image, and these images were joined to obtain a continuous photograph in the cross-sectional film thickness direction.

[0074] A line was drawn perpendicular to the film thickness on the obtained continuous photograph, and the line was further divided into thirds to obtain three layers. Of the three layers, the layer including the dense layer, which is a layer densely populated with extremely small pores, was designated Layer A (A), the central layer in the thickness direction was designated Layer B (B), and the layer including the surface opposite to the surface on which the dense layer was disposed was designated Layer C (C).

[0075] In the region of layer C, binarization processing was performed using image processing software, and an image was obtained in which the holes were black and the structural parts were white. The number of pixels of the scale bar showing a known length in the image was counted, and the length per pixel was calculated. The number of pixels in the dark brightness part was counted, and multiplied by the length per pixel to obtain the total area S (μm ２ ), and the number of black holes (hereinafter referred to as the total number of open holes) were read, and the average hole area (μm ２ ) was calculated. ２ The average pore size (μm) was calculated from the average pore area (μm). The calculation was performed assuming that the pore shape was a perfect circle. The hollow fiber membranes in the examples and comparative examples were observed at a magnification of 2500 or 3000 times. ２ ) = S (μm ２ ) / total number of pores Average pore size (μm)=2×√(average pore area / π) The above procedure was carried out in the same manner using 20 cross-sectional SEM images of different hollow fiber membranes, and the arithmetic mean was taken as the result.

[0076] (7) Removal rate of particles with a particle diameter of 0.3 μm or more A module was prepared by folding a bundle of hollow fiber membranes into a U-shape, inserting it into a cylindrical case, and adhesively fixing the open ends of the hollow fiber membranes. Using a particle counter (Hach A2400), air was suctioned from the open end of the hollow fiber membrane module at a flow rate of 28.3 L / min. The measurement environment was adjusted so that the number of particles in the air when suctioned at 28.3 L / min was 10,000 or more, with the measurement particle diameter set to 0.3 μm or more. The number of particles discharged from the open end was counted, and the removal rate was calculated.

[0077] (8) Ratio (PD / WT) of Average Pore Diameter (PD) of Layer C to Membrane Thickness (WT) The ratio (PD / WT) of the average pore diameter (PD) of Layer C to the membrane thickness (WT) of the hollow fiber membrane was calculated from the average pore diameter (PD) of the pores present in Layer C calculated in (6) above and the membrane thickness (WT) of the hollow fiber membrane calculated in (4) above.

[0078] (9) Measurement of the outer diameter and circumferential length of the hollow fiber membrane A hollow fiber membrane cut to a length of 30 cm in the longitudinal direction was set in an outer diameter measuring instrument (manufactured by KEYENCE Corporation, controller: LS-5500, sensor head: LS-5040), and the outer diameter of the hollow fiber membrane was measured at positions 10 cm from both ends. The same measurement was performed on 20 hollow fiber membranes, and the average value of a total of 40 measurement data was calculated to determine the outer diameter (OD) of the hollow fiber membrane. The circumferential length L of the hollow fiber membrane was calculated by multiplying the outer diameter (average value) by π.

[0079] (10) Measurement of Polyvinylpyrrolidone (PVP) Content in Hollow Fiber Membrane. A hollow fiber membrane dried at 120°C for 5 hours in a dryer was cut into a length of approximately 5 mm. After weighing, the nitrogen content of the hollow fiber membrane in its dry state was measured using an NC analyzer. When the main component of the hollow fiber membrane is polysulfone and PVP is contained as a hydrophilic polymer, the PVP content (X) of the hollow fiber membrane in its dry state was calculated from the nitrogen content (N), since no nitrogen-derived substances are contained other than PVP. Furthermore, the PVP content (Y) of the hollow fiber membrane in its dry state can also be calculated from the obtained PVP content (X). X: PVP content (%, based on the hollow fiber membrane in its dry state) = (N × 111 / 14) × 100. Y: PVP content (%, based on the polysulfone) = [X / (100-X)] × 100.

[0080] (11) Filtration flow rate of hollow fiber membrane module A tube was connected to the non-opening side of the hollow fiber membrane module so as to enable raw water to be supplied, and water at 20°C was supplied at 0.1 MPa. The amount of water that permeated the hollow fiber membrane and flowed out per unit time was measured, and the filtration flow rate (L / min) of the hollow fiber membrane module per unit time was calculated.

[0081] (12) Turbidity filtration capacity of water purifier cartridge Activated carbon was placed on the upstream side of the prepared hollow fiber membrane module to form a cartridge, and then the test was carried out according to the method specified in JIS S 3201:2004 (Test method for household water purifiers). The initial flow rate was set to 2.0 L / min.

[0082] Example 1 A spinning dope was prepared by dissolving and stirring 15 parts by mass of a hydrophobic polymer (PSF (Udel® polysulfone P-3500 manufactured by Solvay)), 4 parts by mass of a hydrophilic polymer (PVP (K90 manufactured by BASF)), 78.5 parts by mass of N,N-dimethylacetamide (DMAc), and 2.5 parts by mass of water under a nitrogen atmosphere. The viscosity of this spinning dope at 37°C was 2.7 Pa s. This spinning dope was discharged from the annular slit of a double-ring spinneret. As an injection liquid, a non-coagulable liquid consisting of 55 parts by mass of DMAc, 30 parts by mass of polyvinylpyrrolidone (K30 manufactured by BASF, weight-average molecular weight 40,000), and 15 parts by mass of glycerin was discharged from the central pipe. The spinneret was kept at 37°C. A cold air tube for humidity control was installed in the dry section, and cold air was blown from both sides of the spinning dope while it was passed through a predetermined dry length. The dew point temperature in the dry section during spinning was as shown in Table 1. The spinning solution that had passed through the dry section was immersed in a coagulation bath at 80 ° C containing a mixed solution consisting of 90 parts by mass of water and 10 parts by mass of DMAc to coagulate, and then washed with hot water in a hot bath at 80 ° C before being wound on a reel to obtain a wet hollow fiber membrane. The wound hollow fiber membrane had an outer diameter of 430 μm, an inner diameter of 310 μm, and a membrane thickness of 60 μm. The obtained hollow fiber membrane was cut into 30 cm lengths and washed with hot water at 90 ° C for 3 hours. The hollow fiber membrane was dried in a dry heat dryer and heat-treated at 160 ° C or higher to obtain a dry hollow fiber membrane. 827 of the above-mentioned dried hollow fiber membranes were folded into a U-shape and inserted into a cylindrical case (inner diameter 24.2 mm, length 56 mm), and the opening was fixed with polyurethane resin to form a hollow fiber membrane module. The filling rate was 52.2%, and the membrane area of ​​the obtained hollow fiber membrane was 0.068 m ２ The water permeability of the hollow fiber membrane, the filtration flow rate of the hollow fiber membrane module, and the removal rate of particles having a particle diameter of 0.3 μm or more are shown in Table 2.

[0083] (Example 2) A wet hollow fiber membrane was obtained in the same manner as in Example 1, except that the discharge rates of the spinning dope and the injection liquid were adjusted. The wound hollow fiber membrane had an outer diameter of 535 μm, an inner diameter of 380 μm, and a membrane thickness of 77.5 μm. The obtained hollow fiber membrane was cut into 30 cm lengths in the longitudinal direction and washed with hot water at 90°C for 3 hours. The hollow fiber membrane was dried in a dry heat dryer and heat-treated at 160°C or higher to obtain a dry hollow fiber membrane. 534 of the above dry hollow fiber membranes were folded into a U-shape and inserted into a cylindrical case (inner diameter 24.2 mm, length 56 mm), and the opening was fixed with polyurethane resin to form a hollow fiber membrane module. The filling rate was 52.2%, and the membrane area of ​​the obtained hollow fiber membrane was 0.055 m ２ The water permeability of the hollow fiber membrane, the filtration flow rate of the hollow fiber membrane module, and the removal rate of particles having a particle diameter of 0.3 μm or more are shown in Table 2.

[0084] (Example 3) A wet hollow fiber membrane was obtained in the same manner as in Example 1, except that the discharge rates of the spinning dope and the injection liquid were adjusted. The wound hollow fiber membrane had an outer diameter of 460 μm, an inner diameter of 300 μm, and a membrane thickness of 80 μm. The obtained hollow fiber membrane was cut into 30 cm lengths in the longitudinal direction and washed with hot water at 90°C for 3 hours. The hollow fiber membrane was dried in a dry heat dryer and heat-treated at 160°C or higher to obtain a dry hollow fiber membrane. 722 of the above dry hollow fiber membranes were folded into a U-shape and inserted into a cylindrical case (inner diameter 24.2 mm, length 56 mm), and the opening was fixed with polyurethane resin to form a hollow fiber membrane module. The packing ratio was 52.2%, and the membrane area of ​​the obtained hollow fiber membrane was 0.064 m ２ The water permeability of the hollow fiber membrane, the filtration flow rate of the hollow fiber membrane module, and the removal rate of particles having a particle diameter of 0.3 μm or more are shown in Table 2.

[0085] Example 4 A wet hollow fiber membrane was obtained in the same manner as in Example 1, except that the discharge rates of the spinning dope and the injection liquid were adjusted to a dry section dew point of 20°C during spinning. The wound hollow fiber membrane had an outer diameter of 460 μm, an inner diameter of 300 μm, and a membrane thickness of 80 μm. The obtained hollow fiber membrane was cut into 30 cm lengths in the longitudinal direction and washed with hot water at 90°C for 3 hours. The hollow fiber membrane was dried in a dry heat dryer and heat-treated at 160°C or higher to obtain a dry hollow fiber membrane. 722 of the above dry hollow fiber membranes were folded into a U-shape and inserted into a cylindrical case (inner diameter 24.2 mm, length 56 mm), and the opening was fixed with polyurethane resin to form a hollow fiber membrane module. The packing ratio was 52.2%, and the membrane area of ​​the obtained hollow fiber membrane was 0.064 m ２ The water permeability of the hollow fiber membrane, the filtration flow rate of the hollow fiber membrane module, and the removal rate of particles having a particle diameter of 0.3 μm or more are shown in Table 2.

[0086] (Example 5) A wet hollow fiber membrane was obtained in the same manner as in Example 1, except that the discharge rates of the spinning dope and the injection liquid were adjusted. The wound hollow fiber membrane had an outer diameter of 360 μm, an inner diameter of 220 μm, and a membrane thickness of 70 μm. The obtained hollow fiber membrane was cut into 30 cm lengths in the longitudinal direction and washed with hot water at 90°C for 3 hours. The hollow fiber membrane was dried in a dry heat dryer and heat-treated at 160°C or higher to obtain a dry hollow fiber membrane. 1,179 of the above dry hollow fiber membranes were folded into a U-shape and inserted into a cylindrical case (inner diameter 24.2 mm, length 56 mm), and the opening was fixed with polyurethane resin to form a hollow fiber membrane module. The filling rate was 52.2%, and the membrane area of ​​the obtained hollow fiber membrane was 0.081 m ２ The water permeability of the hollow fiber membrane, the filtration flow rate of the hollow fiber membrane module, the removal rate of particles with a particle diameter of 0.3 μm or more, and the turbidity filtration capacity of the water purifier cartridge are shown in Table 2.

[0087] (Example 6) A wet hollow fiber membrane was obtained in the same manner as in Example 1, except that the discharge rates of the spinning dope and the injection liquid were adjusted. The wound hollow fiber membrane had an outer diameter of 290 μm, an inner diameter of 180 μm, and a membrane thickness of 55 μm. The obtained hollow fiber membrane was cut into 30 cm lengths in the longitudinal direction and washed with hot water at 90°C for 3 hours. The hollow fiber membrane was dried in a dry heat dryer and heat-treated at 160°C or higher to obtain a dry hollow fiber membrane. 1,818 of the above dry hollow fiber membranes were folded into a U-shape and inserted into a cylindrical case (inner diameter 24.2 mm, length 56 mm), and the opening was fixed with polyurethane resin to form a hollow fiber membrane module. The packing ratio was 52.2%, and the membrane area of ​​the obtained hollow fiber membrane was 0.101 m ２ The water permeability of the hollow fiber membrane, the filtration flow rate of the hollow fiber membrane module, the removal rate of particles with a particle diameter of 0.3 μm or more, and the turbidity filtration capacity of the water purifier cartridge are shown in Table 2.

[0088] Example 7 A spinning dope was prepared by dissolving and stirring 15 parts by mass of a hydrophobic polymer (PSF (Udel® polysulfone P-3500 manufactured by Solvay)), 7 parts by mass of a hydrophilic polymer (PVP (K78 / 81 manufactured by Ashland)), 75.5 parts by mass of N,N-dimethylacetamide (DMAc), and 2.5 parts by mass of water under a nitrogen atmosphere. The viscosity of this spinning dope at 37°C was 4.5 Pa s. This spinning dope was discharged from the annular slit of a double-ring spinneret. As an injection liquid, a non-coagulable liquid consisting of 55 parts by mass of DMAc, 30 parts by mass of polyvinylpyrrolidone (K30 manufactured by BASF, weight-average molecular weight 40,000), and 15 parts by mass of glycerin was discharged from the central pipe. The spinneret was kept at 37°C. A cold air tube for humidity control was installed in the dry section, and cold air was blown from both sides of the spinning dope while it was passed through a predetermined dry length. The dew point temperature in the dry section during spinning was as shown in Table 1. The spinning solution that had passed through the dry section was immersed in a coagulation bath at 80 ° C containing a mixed solution consisting of 90 parts by mass of water and 10 parts by mass of DMAc to coagulate, and then washed with hot water in a hot bath at 80 ° C before being wound on a reel to obtain a wet hollow fiber membrane. The wound hollow fiber membrane had an outer diameter of 360 μm, an inner diameter of 220 μm, and a membrane thickness of 70 μm. The obtained hollow fiber membrane was cut into 30 cm lengths and washed with hot water at 90 ° C for 3 hours. The hollow fiber membrane was dried in a dry heat dryer and heat-treated at 160 ° C or higher to obtain a dry hollow fiber membrane. 1,179 of the above-mentioned dried hollow fiber membranes were folded into a U-shape and inserted into a cylindrical case (inner diameter 24.2 mm, length 56 mm), and the opening was fixed with polyurethane resin to form a hollow fiber membrane module. The filling rate was 52.2%, and the membrane area of ​​the obtained hollow fiber membrane was 0.081 m ２ The water permeability of the hollow fiber membrane, the filtration flow rate of the hollow fiber membrane module, and the removal rate of particles having a particle diameter of 0.3 μm or more are shown in Table 2.

[0089] (Example 8) A wet hollow fiber membrane was obtained in the same manner as in Example 7, except that the discharge rates of the spinning dope and the injection liquid were adjusted. The wound hollow fiber membrane had an outer diameter of 290 μm, an inner diameter of 180 μm, and a membrane thickness of 55 μm. The obtained hollow fiber membrane was cut into 30 cm lengths in the longitudinal direction and washed with hot water at 90°C for 3 hours. The hollow fiber membrane was dried in a dry heat dryer and heat-treated at 160°C or higher to obtain a dry hollow fiber membrane. 1,818 of the above dry hollow fiber membranes were folded into a U-shape and inserted into a cylindrical case (inner diameter 24.2 mm, length 56 mm), and the opening was fixed with polyurethane resin to form a hollow fiber membrane module. The packing ratio was 52.2%, and the membrane area of ​​the obtained hollow fiber membrane was 0.101 m ２ The water permeability of the hollow fiber membrane, the filtration flow rate of the hollow fiber membrane module, and the removal rate of particles having a particle diameter of 0.3 μm or more are shown in Table 2.

[0090] Example 9 A spinning dope was prepared by dissolving and stirring 15 parts by mass of a hydrophobic polymer (PSF (Udel® polysulfone P-3500 manufactured by Solvay)), 5 parts by mass of a hydrophilic polymer (PVP (K90 manufactured by BASF)), 2 parts by mass of a hydrophilic polymer (PVP (K30 manufactured by BASF)), 75.5 parts by mass of N,N-dimethylacetamide (DMAc), and 2.5 parts by mass of water under a nitrogen atmosphere. The viscosity of this spinning dope at 37°C was 3.8 Pa s. This spinning dope was discharged from the annular slit of a double-ring spinneret. A non-coagulable liquid consisting of 55 parts by mass of DMAc, 30 parts by mass of polyvinylpyrrolidone (K30 manufactured by BASF, weight-average molecular weight 40,000), and 15 parts by mass of glycerin was discharged from the central pipe as an injection liquid. The spinneret was kept at 37°C. A cold air tube for humidity control was installed in the dry section, and the spinning dope was passed through a predetermined dry length while cold air was flowing from both sides. The dew point temperature in the dry section during spinning was as shown in Table 1. The spinning dope that had passed through the dry section was immersed in a coagulation bath at 80 ° C containing a mixed solution consisting of 90 parts by mass of water and 10 parts by mass of DMAc to coagulate, and then washed with hot water in a hot bath at 80 ° C before being wound up on a reel frame to obtain a wet hollow fiber membrane. The wound hollow fiber membrane had an outer diameter of 360 μm, an inner diameter of 220 μm, and a membrane thickness of 70 μm. The obtained hollow fiber membrane was cut into 30 cm lengths in the longitudinal direction and washed with hot water at 90 ° C for 3 hours. The hollow fiber membrane was dried in a dry heat dryer and heat-treated at 160 ° C or higher to obtain a dry hollow fiber membrane. 1,179 pieces of the above hollow fiber membranes in a dry state were folded into a U-shape and inserted into a cylindrical case (inner diameter 24.2 mm, length 56 mm). The opening was fixed with polyurethane resin to form a hollow fiber membrane module. The packing ratio was 52.2%, and the membrane area of ​​the obtained hollow fiber membranes was 0.081 m. ２ The water permeability of the hollow fiber membrane, the filtration flow rate of the hollow fiber membrane module, the removal rate of particles with a particle diameter of 0.3 μm or more, and the turbidity filtration capacity of the water purifier cartridge are shown in Table 2.

[0091] (Example 10) A wet hollow fiber membrane was obtained in the same manner as in Example 9, except that the discharge rates of the spinning dope and the injection liquid were adjusted. The wound hollow fiber membrane had an outer diameter of 290 μm, an inner diameter of 180 μm, and a membrane thickness of 55 μm. The obtained hollow fiber membrane was cut into 30 cm lengths in the longitudinal direction and washed with hot water at 90°C for 3 hours. The hollow fiber membrane was dried in a dry heat dryer and heat-treated at 160°C or higher to obtain a dry hollow fiber membrane. 1,818 of the above dry hollow fiber membranes were folded into a U-shape and inserted into a cylindrical case (inner diameter 24.2 mm, length 56 mm), and the opening was fixed with polyurethane resin to form a hollow fiber membrane module. The packing ratio was 52.2%, and the membrane area of ​​the obtained hollow fiber membrane was 0.101 m ２ The water permeability of the hollow fiber membrane, the filtration flow rate of the hollow fiber membrane module, the removal rate of particles with a particle diameter of 0.3 μm or more, and the turbidity filtration capacity of the water purifier cartridge are shown in Table 2.

[0092] (Example 11) A wet hollow fiber membrane was obtained by the same method as in Example 9, except that the discharge rates of the spinning dope and the injection liquid were adjusted. The wound hollow fiber membrane had an outer diameter of 290 μm, an inner diameter of 180 μm, and a membrane thickness of 55 μm. The obtained hollow fiber membrane was cut into 30 cm lengths in the longitudinal direction and washed with hot water at 90°C for 3 hours. The hollow fiber membrane was dried in a dry heat dryer and heat-treated at 160°C or higher to obtain a dry hollow fiber membrane. 1,918 of the above dry hollow fiber membranes were folded into a U-shape and inserted into a cylindrical case (inner diameter 24.2 mm, length 56 mm), and the opening was fixed with polyurethane resin to form a hollow fiber membrane module. The filling rate was 55.1%, and the membrane area of ​​the obtained hollow fiber membrane was 0.107 m ２ The water permeability of the hollow fiber membrane, the filtration flow rate of the hollow fiber membrane module, and the removal rate of particles having a particle diameter of 0.3 μm or more are shown in Table 2.

[0093] Example 12 A non-coagulating liquid consisting of 76 parts by mass of DMAc, 9 parts by mass of polyvinylpyrrolidone (BASF K90), and 15 parts by mass of glycerin was used as the injection liquid, and a wet hollow fiber membrane was obtained in the same manner as in Example 9, except that the discharge rates of the spinning dope and injection liquid were adjusted. The wound hollow fiber membrane had an outer diameter of 290 μm, an inner diameter of 180 μm, and a membrane thickness of 55 μm. The obtained hollow fiber membrane was cut into 30 cm lengths in the longitudinal direction and washed with hot water at 90 ° C. for 3 hours. The hollow fiber membrane was dried in a dry heat dryer and heat-treated at 160 ° C. or higher to obtain a dry hollow fiber membrane. 1,818 of the above dry hollow fiber membranes were folded into a U-shape and inserted into a cylindrical case (inner diameter 24.2 mm, length 56 mm). The opening was fixed with polyurethane resin to form a hollow fiber membrane module. The filling rate was 52.2%, and the membrane area of ​​the obtained hollow fiber membrane was 0.101 m ２ The water permeability of the hollow fiber membrane, the filtration flow rate of the hollow fiber membrane module, the removal rate of particles with a particle diameter of 0.3 μm or more, and the turbidity filtration capacity of the water purifier cartridge are shown in Table 2.

[0094] Example 13 Wet hollow fiber membranes were obtained in the same manner as in Example 9, except that a non-coagulating liquid consisting of 73 parts by mass of DMAc, 6 parts by mass of polyvinylpyrrolidone (BASF K90), 13 parts by mass of polyvinylpyrrolidone (BASF K30, weight-average molecular weight 40,000), and 8 parts by mass of glycerin was used as the injection liquid. The wound hollow fiber membrane had an outer diameter of 360 μm, an inner diameter of 220 μm, and a membrane thickness of 70 μm. The obtained hollow fiber membrane was cut into 30 cm lengths in the longitudinal direction and washed with hot water at 90°C for 3 hours. The hollow fiber membrane was dried in a dry heat dryer and heat-treated at 160°C or higher to obtain a dried hollow fiber membrane. 1,818 of the dried hollow fiber membranes were folded into a U-shape and inserted into a cylindrical case (inner diameter 24.2 mm, length 56 mm). The opening was fixed with polyurethane resin to form a hollow fiber membrane module. The filling rate was 52.2%, and the membrane area of ​​the obtained hollow fiber membrane was 0.081 m ２ The water permeability of the hollow fiber membrane, the filtration flow rate of the hollow fiber membrane module, and the removal rate of particles having a particle diameter of 0.3 μm or more are shown in Table 2.

[0095] Comparative Example 1 A spinning dope was prepared by dissolving and stirring 15 parts by mass of a hydrophobic polymer (PSF ("Udel" (registered trademark) polysulfone P-3500 manufactured by Solvay)), 7 parts by mass of a hydrophilic polymer (PVP (K90 manufactured by BASF)), 75.5 parts by mass of N,N-dimethylacetamide (DMAc), and 2.5 parts by mass of water under a nitrogen atmosphere. The viscosity of this spinning dope at 37°C was 7.5 Pa s. This spinning dope was discharged from the annular slit of a double-ring spinneret. As an injection liquid, a non-coagulable liquid consisting of 55 parts by mass of DMAc, 30 parts by mass of polyvinylpyrrolidone (K30 manufactured by BASF, weight-average molecular weight 40,000), and 15 parts by mass of glycerin was discharged from the central pipe. The spinneret was kept at 37°C. A cold air tube for humidity control was installed in the dry section, and cold air was blown from both sides of the spinning dope while it was passed through a predetermined dry length. The dew point temperature in the dry section during spinning was as shown in Table 1. The spinning solution that had passed through the dry section was immersed in a coagulation bath at 80 ° C containing a mixed solution consisting of 90 parts by mass of water and 10 parts by mass of DMAc to coagulate, and then washed with hot water in a hot bath at 80 ° C before being wound on a reel to obtain a wet hollow fiber membrane. The wound hollow fiber membrane had an outer diameter of 460 μm, an inner diameter of 300 μm, and a membrane thickness of 80 μm. The obtained hollow fiber membrane was cut into 30 cm lengths and washed with hot water at 90 ° C for 3 hours. The hollow fiber membrane was dried in a dry heat dryer and heat-treated at 160 ° C or higher to obtain a dry hollow fiber membrane. 722 of the above-mentioned hollow fiber membranes in the dry state were folded into a U-shape and inserted into a cylindrical case (inner diameter 24.2 mm, length 56 mm), and the opening was fixed with polyurethane resin to form a hollow fiber membrane module. The filling rate was 52.2%, and the membrane area of ​​the obtained hollow fiber membrane was 0.064 m ２ The water permeability of the hollow fiber membrane, the filtration flow rate of the hollow fiber membrane module, and the removal rate of particles having a particle diameter of 0.3 μm or more are shown in Table 2.

[0096] (Comparative Example 2) A wet hollow fiber membrane was obtained in the same manner as in Comparative Example 1, except that the discharge rates of the spinning dope and the injection liquid were adjusted. The wound hollow fiber membrane had an outer diameter of 360 μm, an inner diameter of 220 μm, and a membrane thickness of 70 μm. The obtained hollow fiber membrane was cut into 30 cm lengths in the longitudinal direction and washed with hot water at 90°C for 3 hours. The hollow fiber membrane was dried in a dry heat dryer and heat-treated at 160°C or higher to obtain a dry hollow fiber membrane. 1,179 of the above dry hollow fiber membranes were folded into a U-shape and inserted into a cylindrical case (inner diameter 24.2 mm, length 56 mm), and the opening was fixed with polyurethane resin to form a hollow fiber membrane module. The packing ratio was 52.2%, and the membrane area of ​​the obtained hollow fiber membrane was 0.081 m ２ The water permeability of the hollow fiber membrane, the filtration flow rate of the hollow fiber membrane module, the removal rate of particles with a particle diameter of 0.3 μm or more, and the turbidity filtration capacity of the water purifier cartridge are shown in Table 2.

[0097] (Comparative Example 3) A wet hollow fiber membrane was obtained in the same manner as in Comparative Example 1, except that the discharge rates of the spinning dope and the injection liquid were adjusted. The wound hollow fiber membrane had an outer diameter of 290 μm, an inner diameter of 180 μm, and a membrane thickness of 55 μm. The obtained hollow fiber membrane was cut into 30 cm lengths in the longitudinal direction and washed with hot water at 90°C for 3 hours. The hollow fiber membrane was dried in a dry heat dryer and heat-treated at 160°C or higher to obtain a dry hollow fiber membrane. 1,818 of the above dry hollow fiber membranes were folded into a U-shape and inserted into a cylindrical case (inner diameter 24.2 mm, length 56 mm), and the opening was fixed with polyurethane resin to form a hollow fiber membrane module. The packing ratio was 52.2%, and the membrane area of ​​the obtained hollow fiber membrane was 0.101 m ２ The water permeability of the hollow fiber membrane, the filtration flow rate of the hollow fiber membrane module, the removal rate of particles with a particle diameter of 0.3 μm or more, and the turbidity filtration capacity of the water purifier cartridge are shown in Table 2.

[0098] Comparative Example 4: A wet hollow fiber membrane was obtained using the same method as in Example 1, except for adjusting the discharge rates of the spinning dope and the injection liquid. The wound hollow fiber membrane had an outer diameter of 570 μm, an inner diameter of 300 μm, and a membrane thickness of 135 μm. The obtained hollow fiber membrane was cut into 30 cm lengths in the longitudinal direction and washed with hot water at 90°C for 3 hours. The hollow fiber membrane was dried in a dry heat dryer and heat-treated at 160°C or higher to obtain a dry hollow fiber membrane. 470 of the above dry hollow fiber membranes were folded into a U-shape and inserted into a cylindrical case (inner diameter 24.2 mm, length 56 mm), and the opening was fixed with polyurethane resin to form a hollow fiber membrane module. The packing ratio was 52.2%, but the filtration flow rate was a low 3.0 L / min. The configurations of the obtained hollow fiber membrane and hollow fiber membrane module are shown in Tables 1 and 2.

[0099] Comparative Example 5: A wet hollow fiber membrane was obtained using the same method as in Example 1, except that the discharge rates of the spinning dope and the injection liquid were adjusted. The wound hollow fiber membrane had an outer diameter of 240 μm, an inner diameter of 180 μm, and a membrane thickness of 30 μm. The obtained hollow fiber membrane was cut into 30 cm lengths in the longitudinal direction and washed with hot water at 90°C for 3 hours. The hollow fiber membrane was dried in a dry heat dryer and heat-treated at 160°C or higher to obtain a dry hollow fiber membrane. 2,654 of the above dry hollow fiber membranes were folded into a U-shape and inserted into a cylindrical case (inner diameter 24.2 mm, length 56 mm). The opening was fixed with polyurethane resin to form a hollow fiber membrane module. The packing ratio was 52.2%, but the apex of the U-shape of the hollow fiber membrane bundle was broken, resulting in a hollow fiber membrane module with a particle removal rate of 88% for particles with a particle diameter of 0.3 μm or more. The structures of the obtained hollow fiber membranes and hollow fiber membrane modules are shown in Tables 1 and 2.

[0100]

[0101]

[0102] The present invention can be used in the field of water treatment as a hollow fiber membrane and a hollow fiber membrane module applicable to a cartridge for a water purifier or a water purifier. In addition to water purifiers, the present invention can also be suitably used for medical applications such as plasma separation membranes and cell separation and purification membranes for the production of biopharmaceuticals.

[0103] It is clear that a person skilled in the art can conceive of various modifications and alterations within the scope of the claims, and it is understood that these also naturally fall within the technical scope of the present invention. Furthermore, the components in the above-described embodiments may be combined in any manner without departing from the spirit of the invention.

[0104] This application is based on a Japanese patent application (Patent Application No. 2024-044551) filed on March 21, 2024, the contents of which are incorporated herein by reference.

[0105] 1. Surface on which the dense layer is disposed 2. Surface opposite to the surface on which the dense layer is disposed

Claims

1. A hollow fiber membrane having a dense layer, the dense layer being disposed on the outer surface side or the inner surface side of the hollow fiber membrane, the membrane thickness of the hollow fiber membrane being 40 μm or more and 120 μm or less, when the membrane thickness of the hollow fiber membrane is divided into three equal parts in the thickness direction, with the layer including the dense layer being layer A, the central layer in the thickness direction being layer B, and the layer including the surface opposite to the surface on which the dense layer is disposed being layer C, the ratio (PD / WT) of the average pore diameter (PD) of the pores present in layer C to the membrane thickness (WT) of the hollow fiber membrane being 0.0110 or more and 0.0180 or less.

2. The hollow fiber membrane according to claim 1, wherein the surface opposite to the surface on which the dense layer is disposed has a porosity of 10% or more and 35% or less.

3. The hollow fiber membrane according to claim 1 or 2, wherein the dense layer is disposed on the outer surface side of the hollow fiber membrane.

4. The hollow fiber membrane according to claim 1, wherein the surface of the hollow fiber membrane on which the dense layer is disposed has a porosity of 15% or more and 45% or less.

5. The hollow fiber membrane of claim 1, comprising a polysulfone-based polymer and polyvinylpyrrolidone.

6. The hollow fiber membrane according to claim 5, wherein the polyvinylpyrrolidone content is 2% by mass or more and 9.5% by mass or less.

7. A hollow fiber membrane module comprising a cylindrical case filled with the hollow fiber membranes according to claim 1 or 2, and the open ends of the hollow fiber membranes fixed to the cylindrical case.

8. The hollow fiber membrane module according to claim 7, wherein (2N × L) / S is 3.0 or more and 13.0 or less, where S is the cross-sectional area of ​​the smallest point of the cross section perpendicular to the axial direction of the cylindrical case, L is the circumferential length of the hollow fiber membrane, and N is the number of the hollow fiber membranes packed in the cylindrical case.

9. A hollow fiber membrane module according to claim 7 or 8, which has a removal rate of 99.9% or more of particles having a particle diameter of 0.3 μm or more.

10. The hollow fiber membrane module according to claim 7, wherein the ratio of the inner diameter of the hollow fiber membrane to the outer diameter of the hollow fiber membrane (inner diameter / outer diameter) is 0.57 or more and 0.67 or less.

11. The hollow fiber membrane module according to claim 7, wherein the filling rate of the hollow fiber membranes in the inner space of the cylindrical case is 40% or more and 60% or less.

12. A cartridge for a water purifier, equipped with the hollow fiber membrane module according to claim 7 or 8.

13. A water purifier comprising the water purifier cartridge according to claim 12.

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