DESCRIPTION
TITLE OF THE INVENTION:
HOLLOW FIBER MEMBRANE MODULE, WATER PURIFIER CARTRIDGE, AND WATER PURIFIER
TECHNICAL FIELD [0001]
The present invention relates to a hollow fiber membrane module, a cartridge for water purifiers, and a water purifier.
BACKGROUND ART [0002]
In recent years, water purifiers for purifying tap water have been widely used at home, and water purification cartridges are used in which various filter materials for purifying the tap water are retained. Generally used as the filter materials are: activated carbon and ion exchangers for eliminating free residual chlorine, a musty odor, trihalomethanes, ions of heavy metals including lead, etc. from tap water; and hollow fiber membranes for eliminating suspended substances, bacteria, etc. from tap water. There are various types of water purifiers, including: a water purifier of the type to be attached to the cock; a water purifier of the type to be built in the shower head of a water faucet body; and a water purifier of the type to be disposed under the sink. All these types have limitations in cartridge size because of the limited kitchen space, and consumers prefer compact products. [0003]
Patent Document 1 describes a water purifier cartridge of the type to be mounted in a water faucet body, and indicates that lives regarding the removal of substances to be removed can be set with a satisfactory balance by regulating the volume ratio between the fibrous-activated-carbon part and the hollow-fiber membrane part in the cartridge. [0004]
Patent Document 2 discloses use of composited hollow fiber membranes in water purifier applications, based on the notion that it is effective to have a structure which is less apt to be clogged and has a long life. Patent Document 2 describes a

process in which a shaped polyethylene object obtained through melting is stretched to form pores therein and thereby obtain a hydrophobic hollow fiber membrane and this hollow fiber membrane is then immersed in a solution of a hydrophilic copolymer to obtain a hydrophilic hollow fiber membrane. [0005]
Patent Document 3 discloses a hollow fiber membrane module employing high-performance microfiltration membranes having an asymmetric structure, and contains a description of the removal ratio for particles having a diameter of 0.1 um or 0.2 um, said removal ratio being important in water purifier applications.
BACKGROUND ART DOCUMENTS PATENT DOCUMENTS
[0006]
Patent Document 1: JP-A-2005-768 Patent Document 2: JP-A-11-262764 Patent Document 3: JP-A-2009-285547
SUMMARY OF THE INVENTION
PROBLEMS THAT THE INVENTION IS TO SOLVE
[0007]
However, the water purifier cartridge disclosed in Patent Document 1 has a problem in that this water purifier cartridge has a short life depending on the performance of the hollow fiber membranes used therein. The composited hollow fiber membranes disclosed in Patent Document 2 have a problem in that the hollow fiber membranes have an increased membrane thickness due to the compositing thereof and hence have an increased outer diameter, making it difficult for the hollow fiber membranes to have a sufficiently large membrane area within a limited space, and the cartridge for water purifiers which employs the hollow fiber membranes hence has a short life. In addition, in producing the composited hollow fiber membranes disclosed in Patent Document 2, it is necessary, in case hydrophilizing the hydrophobic hollow fiber membranes, that the hollow fiber membranes, which itself is hydrophobic, should be coated with a hydrophilic polymer. However, the hydrophilizing agent containing the hydrophilic polymer has a high viscosity and hence there is the following unsolved problem: in cases when hollow

fiber membranes having a reduced outer diameter are employed in order to obtain a cartridge for water purifiers which has a prolonged life and when a bundle thereof that has an increased density of the hollow fiber membranes is hydrophilized, then some of the hollow fiber membranes undesirably adhere to each other due to the hydrophilization and the adhered portions of the hollow fiber membrane bundle are not effectively utilized, resulting in a decrease in the life of the water purifier cartridge employing the hollow fiber membranes. The hollow fiber membrane module disclosed in Patent document 3 has a problem in that, depending on the outer diameter, water permeability, etc. of the hollow fiber membranes employed in the hollow fiber membrane module, the cartridge for water purifiers which employs the hollow fiber membranes has a reduced life. [0008]
An object of the present invention is to provide a hollow fiber membrane module which satisfies separation performance (ability to remove particles of 0.3 um or larger) required of water purifiers and which, even when having a reduced size, has a sufficient membrane area of the hollow fiber membranes, thereby attaining a prolongation of the life of a water purifier cartridge including this hollow fiber membrane module mounted therein.
MEANS TO SOLVE THE PROBLEMS [0009]
In order to solve the above problems, the present invention is constituted by following (1)-(8).
(1) A hollow fiber membrane module including a cylindrical case and, packed
therein, a U-shaped hollow fiber membrane bundle obtained by bundling a plurality of hollow fiber membranes containing a hydrophobic polymer and a hydrophilic polymer, the hollow fiber membrane bundle having open ends, which have been fixed to an opening portion of the cylindrical case with a potting material, in which
the hollow fiber membranes have an outer diameter of 350 um or less, and the cylindrical case and the hollow fiber membranes satisfy (2N×L)/S being 6.2 or larger, where S is an area of a cross-section of the cylindrical case which is perpendicular to an axial direction of the cylindrical case and which is located at a portion of the cylindrical case where the cylindrical case has a smallest cross-sectional area, L is a circumference length of each hollow fiber membrane, and N is the number of the hollow

fiber membranes packed in the cylindrical case,
the hollow fiber membrane module has a removal ratio for particles with a particle diameter of 0.3 um or larger of 99.9% or higher.
(2) The hollow fiber membrane module according to (1), in which a ratio between an inner diameter of the hollow fiber membranes and the outer diameter of the hollow fiber membranes (inner diameter/outer diameter) is 0.67 or less.
(3) The hollow fiber membrane module according to (1) or (2), in which the hollow fiber membranes have a packing ratio of 60% or less in a space inside the cylindrical case.
(4) The hollow fiber membrane module according to any one of (1) to (3), in which the hollow fiber membranes have a water permeability of 30 mL/Pa/hr/m2 or higher.
(5) The hollow fiber membrane module according to any one of (1) to (4), in which the hydrophobic polymer is a polysulfone-based polymer.
(6) The hollow fiber membrane module according to any one of (1) to (5), in which the hydrophilic polymer comprises polyvinylpyrrolidone.
(7) A cartridge for water purifiers which comprises the hollow fiber membrane module according to any one of (1) to (6) mounted therein.
(8) A water purifier including the cartridge for water purifiers according to (7).
ADVANTAGES OF THE INVENTION
[0010]
According to the present invention, it is possible to provide a hollow fiber membrane module which satisfies separation performance (ability to remove particles of 0.3 um and larger) required of water purifiers and which, even when having a reduced size, has a sufficient membrane area of the hollow fiber membranes. It is also possible to attain a prolongation of the life of a water purifier cartridge including this hollow fiber membrane module mounted therein. The hollow fiber membrane module of the present invention can be used not only in cartridges for water purifiers but also as large-size modules for water treatment.
MODE FOR CARRYING OUT THE INVENTION
[0011]

Embodiments of the present invention will be described below.
“Mass” is synonymous with “weight” herein. [0012]
The hollow fiber membranes to be used in the hollow fiber membrane module of the present invention can be obtained, for example, by a nonsolvent-induced phase separation process in which a hollow fiber membrane having an asymmetric structure is produced by a liquid injection method using a double-ring nozzle. In this process, a membrane-forming solution is injected into the peripheral slit of the double-ring nozzle and a non-coagulating liquid or the like is injected into the center pipe of the nozzle to form the hollow shape of a hollow fiber membrane. In this process, for example, the membrane-forming solution is ejected from the double-ring nozzle together with the non-coagulating liquid or the like, runs in the air of a given zone, and is then led to a coagulating bath disposed on the downstream side. The membrane formation dope is coagulated by the coagulating bath to become a hollow fiber membrane having a hollow shape. This hollow fiber membrane is washed with water and thereafter wound up on a reel. [0013]
The hollow fiber membranes include a hydrophobic polymer, and this hydrophobic polymer constitutes the base material of the hollow fiber membranes. Suitable for use as the hydrophobic polymer are polysulfone-based polymers such as polysulfones, polyethersulfones, and polyarylates. More suitable are polysulfones. Furthermore, the following resins can also be suitably selected: fluororesins such as poly(vinylidene fluoride), cellulosic resins such as cellulose triacetate and cellulose diacetate, and resins including poly(methyl methacrylate), polyacrylonitrile, or a polyamide. [0014]
The membrane-forming solution contains, dissolved therein, components for constituting hollow fiber membranes, e.g., a polysulfone-based polymer. As a solvent for dissolving the polymer, various solvents including dimethyl sulfoxide, dimethylacetamide, dimethylformamide, N-methyl-2-pyrrolidone, and dioxane may be used. Especially desirable are dimethylacetamide, dimethyl sulfoxide, dimethylformamide, and N-methyl-2-pyrrolidone. An appropriate solvent may be suitably selected in accordance with the viscosity of the membrane-forming solution and

the coagulating properties of the injection liquid. [0015]
It is important that a hydrophilic polymer should be included in the hollow fiber membranes to be used in the hollow fiber membrane module of the invention. The reasons for this are that hydrophilicity can be imparted to the surface of hollow fiber membranes, that the water permeability thereof can be improved, and that suspended substances can be inhibited from adhering to the hollow fiber membranes and from clogging into some of the micropores of the hollow fiber membranes. From the standpoint of sufficiently obtaining these effects, the content of the hydrophilic polymer is preferably 3 parts by mass or higher, more preferably 5 parts by mass or higher, based on the mass of the whole hollow fiber membranes. Meanwhile, when the content of the hydrophilic polymer in the hollow fiber membranes is too high, the hydrophilic polymer enhances, rather than reduces, the permeation resistance because the hydrophilic polymer itself retains water, resulting in a decrease in the water permeability of the hollow fiber membranes. Consequently, the mass of the hydrophilic polymer is preferably 20 parts by mass or less, more preferably 15 parts by mass or less, based on the mass of the whole hollow fiber membranes. [0016]
The term “hydrophilic polymer” means either a water-soluble polymeric compound or a polymeric compound which is water-insoluble but interacts with water molecules by electrostatic interaction or hydrogen bonds. Specific examples thereof include nonionic hydrophilic polymers such as poly(alkylene oxide)s such as polyethylene oxide) and poly(propylene oxide), poly(vinyl alcohol), polyvinylpyrrolidone (hereinafter referred to as “PVP”), poly(vinyl acetate), poly(dimethyl methoxyacrylate), polydimethylacrylamide, copolymers of vinylpyrrolidone with acrylic acid, and copolymers of vinyl acetate with vinylpyrrolidone, anionic hydrophilic polymers such as poly(acrylic acid), poly(vinyl sulfate), and carboxymethyl cellulose, cationic hydrophilic polymers such as polyallyamine, polylysine, chitosan, and poly(2-dimethylaminoethyl methacrylate), and amphoteric hydrophilic polymers such as polymethacryloyloxyethylphosphorylcholine and poly(methacryloyloxyethyl dimethylammoniopropionate). Two or more hydrophilic polymers may be contained in the hollow fiber membranes. Especially from the standpoint of inhibiting the adhesion of suspended substances, nonionic hydrophilic polymers and amphoteric hydrophilic

polymers are suitable for use. When affinity for the polysulfone-based resin is taken into account, the hollow fiber membranes more preferably include polyvinylpyrrolidone or polyethylene glycol), especially preferably includes polyvinylpyrrolidone. In the case of use in water purifier applications, it is desirable from the standpoint of safety that elution of the hydrophilic polymer from the hollow fiber membranes is little, and use of polyvinylpyrrolidone alone is suitable. [0017]
The hollow fiber membranes to be used in the hollow fiber membrane module of the present invention are obtained by regulating the composition of the spinning solution, composition of the injection liquid, rates at which the spinning solution and the injection liquid are ejected from a spinneret, dew point and temperature of cold air and cold-air velocity in a dry zone after the ejection, draft ratio during the ejection of the spinning solution, temperature of the coagulating bath, etc. Thereafter, a plurality of hollow fiber membranes thus obtained are bundled to give a hollow fiber membrane bundle, which is water-washed and dried under controlled water-washing, dehydration, and drying conditions, thereby giving a hollow fiber membrane bundle of satisfactory quality which, when used in a hollow fiber membrane module, enables the hollow fiber membrane module to have a removal ratio for particles with a particle diameter of 0.3 um or larger of 99.9% or higher. The hollow fiber membrane bundle obtained by the process described above is bent into a U-shape, and the opening portions of the hollow fiber membrane bundle are bonded and fixed to a cylindrical case with a potting material, e.g., a polyurethane resin, thereby obtaining a hollow fiber membrane module. [0018]
It is essential that hollow fiber membrane modules for water purifiers should have the ability to remove suspended substances not smaller than the sizes of bacteria. It is hence important for the hollow fiber membrane module of the present invention to have a removal ratio for particles with a particle diameter of 0.3 um or larger of 99.9% or higher. In order to make the hollow fiber membrane module to have a removal ratio for particles with a particle diameter of 0.3 um or larger of 99.9% or higher, it is important that the hollow fiber membranes to be used in the hollow fiber membrane module should be exceedingly highly inhibited from suffering damage. [0019]
In cases when hollow fiber membranes including a hydrophilic polymer are

produced so as to have an outer diameter as extremely small as 350 μm or less and a bundle thereof is formed in which the hollow fiber membranes are present in a high density, then there are cases where the hydrophilic polymer remains in excess mainly between the hollow fiber membranes after the water washing. If the hollow fiber membrane bundle in this state is dried, there are cases where water aggregates in the vicinity of the outer surface of the hollow fiber membranes, the insolubilized hydrophilic polymer is unevenly distributed, resulting in occurrence of portions where the hollow fiber membranes have been bonded to each other to render the hollow fiber membrane bundle rigid. Rigid hollow fiber membrane bundles not only tend to have impaired processability in module fabrication but also have a tendency that that portion of the hollow fiber membranes which lies at the vertex of the U-shaped hollow fiber membrane bundle cracks due to the loss of the flexibility of the hollow fiber membrane bundle, resulting in damage to the hollow fiber membrane bundle. Upon damage of the hollow fiber membrane bundle, the removal ratio for particles with a particle diameter of 0.3 μm or larger decreases to below 99.9%. [0020]
This tendency is significant especially when the hollow fiber membranes have a reduced diameter and are included in the hollow fiber membrane bundle in an increased density. From this standpoint, the content of an insoluble hydrophilic polymer in the hollow fiber membrane bundle (hereinafter, that content is sometimes referred to as “proportion of an insolubilized hydrophilic polymer in the hollow fiber membrane bundle”) is preferably 80% or less, more preferably 60% or less, based on the mass of all the hydrophilic polymer contained in the hollow fiber membrane bundle. When the amount of the insoluble hydrophilic polymer is too small, the hollow fiber membranes have reduced water permeability. Consequently, the content of the insoluble hydrophilic polymer in the hollow fiber membrane bundle is preferably 5% or higher, more preferably 10% or higher, even more preferably 15% or higher. [0021]
The proportion of an insolubilized hydrophilic polymer can be determined in the following manner. A hollow fiber membrane bundle which has been dried is placed in N, N-dimethylacetamide (DMAc) solution as a solvent, and the contents are stirred and subj ected to suction filtration. The mass of a dry solid basis of the residue is measured as the mass of an insolubilized hydrophilic polymer (uC). The proportion of the

insolubilized hydrophilic polymer is calculated by dividing the mass of the insolubilized hydrophilic polymer (uC) by the mass of all the hydrophilic polymer (wC) contained in the hollow fiber membrane bundle, using equation (1).
Proportion of insolubilized hydrophilic polymer (%) = 100×uC/wC (1)
[0022]
Examples of means for obtaining a hollow fiber membrane bundle having a content of an insoluble hydrophilic polymer within that range include: a method in which hollow fiber membranes formed by a coagulating bath are washed in a water washing bath disposed before a winding step; and a method in which hollow fiber membranes are wound up and bundled and the hollow fiber membrane bundle is washed off-line. It is more preferred to perform the two washing operations in a suitable combination. For washing the hollow fiber membranes, it is preferred to use water or a water-soluble solvent, e.g., an alcohol. Washing with a liquid having a high temperature of 80°C or above is preferred because a satisfactory washing efficiency is attained therewith. [0023]
After the washing of the hollow fiber membranes, it is preferred to dry the hollow fiber membrane bundle, from the standpoints of quality retention during storage and handleability. The temperature for this drying is preferably 60°C or higher, and is preferably below 140°C. Drying temperatures lower than 60°C result in a reduced drying rate and hence in a poor efficiency of producing the hollow fiber membrane bundle. Drying temperatures of 140°C and higher result in too high a drying rate and hence in drying unevenness within the fiber bundle, and this may undesirably render the hollow fiber membrane bundle rigid. [0024]
Examples of means for avoiding the drying unevenness include: to centrifugally remove the liquid before high-temperature drying; and to dry the hollow fiber membrane bundle with air blowing. [0025]
The water permeability of the hollow fiber membranes of the present invention is preferably 30 mL/Pa/hr/m2 or higher, more preferably 35 mL/Pa/hr/m2 or higher, even more preferably 40 mL/Pa/hr/m2 or higher. There is no particular upper limit on the water permeability of the hollow fiber membranes. However, there is a concern that too high a water permeability may result in a decrease in separation performance, an upper

limit of the water permeability of the hollow fiber membranes is preferably less than 120
mL/Pa/hr/m2, more preferably less than 100 mL/Pa/hr/m2.
[0026]
With respect to the separation properties of the hollow fiber membranes, the removal ratio for particles with a particle diameter of 0.2 um is preferably 80% or higher, more preferably 90% or higher. From the standpoint of the necessity of removing bacteria from raw water, it is essential that the removal ratio for particles with a particle diameter of 0.3 um or larger should be 99.9% or higher. [0027]
A plurality of such hollow fiber membranes obtained are bundled and this fiber bundle is bent into a U-shape and inserted into a cylindrical case. The opening end portions of the hollow fiber membrane bundle are fixed to an opening portion of the cylindrical case with a potting material to obtain a hollow fiber membrane module. The hollow fiber membrane module is inserted into a cartridge case, and an adsorbent such as activated carbon and an ion exchanger are filled thereinto. Thus, a cartridge for water purifiers can be fabricated, the cartridge being capable of removing substances unnecessary for the human body which may be contained in general tap water. [0028]
From the standpoint of the product life of the cartridge for water purifiers, it is preferable that the hollow fiber membranes have a smaller outer diameter. Meanwhile, from the standpoint of filtration rate, it is preferable that the hollow fiber membranes have a larger inner diameter and a smaller membrane thickness. From the standpoint of fiber strength, it is preferable that the hollow fiber membranes have a larger outer diameter, a smaller inner diameter, and a larger membrane thickness. For attaining all of these, it is important that the hollow fiber membranes should have an outer diameter of 350 um or less, and the outer diameter thereof is more preferably 330 um or less, especially preferably 300 um or less. Meanwhile, from those standpoints, the outer diameter of the hollow fiber membranes is preferably 190 um or larger, more preferably 220 um or larger, especially preferably 260 um or larger. The inner diameter of the hollow fiber membranes is preferably 150 um or larger, more preferably 155 um or larger, especially preferably 160 um or larger. Meanwhile, from those standpoints, the inner diameter of the hollow fiber membranes is preferably 220 um or less, more preferably 210 um or less, especially preferably 200 um or less.

[0029]
The membrane thickness of the hollow fiber membranes is preferably 90 um or less, more preferably 85 um or less. Meanwhile, the membrane thickness of the hollow fiber membranes is preferably 30 um or larger, more preferably 50 um or larger. [0030]
In cases when small-diameter hollow fiber membranes having an outer diameter of 350 um or less have too small a membrane thickness, i.e., too large an inner diameter/outer diameter ratio, there is a problem when a bundle of such hollow fiber membranes is bent into a U-shape and inserted into a cylindrical case. Specifically, the hollows may collapse upon folding into a U-shape to damage the hollow fiber membranes, resulting in a possibility that the suspended substances, bacteria, etc. to be removed might leak out to the purified water. It is hence preferable that the hollow fiber membranes having an outer diameter of 350 um or less have an inner diameter/outer diameter ratio of 0.67 or less, more preferably 0.61 or less, even more preferably 0.6 or less. [0031]
A means for prolonging the product life of a hollow fiber membrane module in the cylindrical case with a given capacity is to simply heighten the packing ratio of the hollow fiber membranes in the space inside the cylindrical case. Meanwhile, packing ratios of 60% and lower are preferred because such packing ratios are effective in avoiding a trouble that raw water does not infiltrate into the whole hollow fiber membrane bundle so that inner hollow fiber membrane portions of the hollow fiber membrane bundle are not effectively utilized. Packing ratios of 60% and lower are preferred also from the standpoint that the efficiency of inserting the U-shaped fiber bundle into the cylindrical case is improved. The packing ratio is calculated with respect to the cross-section of the cylindrical case which has a smallest area among the cross-sections of the cylindrical case.
There are cases where a cylindrical case in which the inner diameter increases or decreases along the longitudinal direction thereof may be used. Consequently, in the present invention, the packing ratio of the hollow fiber membranes is determined with respect to the cross-sectional area (S) of a portion where the cross-section perpendicular to the axial direction of the inner cylinder case has a smallest cross-sectional area. The packing ratio, which is expressed by equation (2), is determined by dividing the integrated value of the cross-sectional area (A) of the hollow fiber membranes and a double of the number of the hollow fiber membranes by the cross-sectional area (S) of the cylindrical

case. In calculating the cross-sectional area of the hollow fiber membranes, the hollows of the hollow fiber membranes are ignored.
Packing ratio (%) = 100 × [(number of fibers) × 2] ×A/S (2)
[0032]
In a preferred configuration of the hollow fiber membranes, the cross-section has a concentric double-ring shape. However, the outer ring, in particular, need not be always circular, and the hollow fiber membranes may be ones having projections on the outer surface thereof or ones having a polygonal shape. [0033]
It is important to dispose hollow fiber membranes in a cylindrical case so as to result in a large membrane area, that is, to encase a hollow fiber membrane bundle made up of high-density hollow fiber membranes in a cylindrical case to fabricate a hollow fiber membrane module, from the standpoint of prolonging the product life of the water purifier cartridge employing this hollow fiber membrane module. The membrane area is represented by the product of the circumference length of each hollow fiber membrane, the number of the 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, for prolonging the product life, how the integrated value of [circumference length (L) of hollow fiber membrane] and [(number of hollow fiber membranes (N)) × 2] is increased. As stated above, the cross-sectional area of the cylindrical case is the cross-sectional area of a portion where the cross-section perpendicular to the axial direction of the cylindrical case has a smallest cross-sectional area. In the present invention, it is important that (2N×L)/S should be 6.2 or larger, and the value thereof is preferably 6.5 or larger, more preferably 6.8 or larger, especially preferably 7.0 or larger. There is no particular upper limit on (2N×L)/S. However, the value thereof is preferably 9.3 or less because the outer diameter of the hollow fiber membranes is preferably 260 um or larger from the standpoint of fiber strength and the packing ratio thereof is preferably 60% or less. The circumference length L of each hollow fiber membrane is calculated by the method which will be described in Examples. [0034]
For attaining a large membrane area of the hollow fiber membranes in the cylindrical case, it is important to employ hollow fiber membranes having an outer

diameter of 350 μm or less, as stated above. The outer diameter thereof is preferably 330
μm or less, more preferably 300 μm or less.
[0035]
The hollow fiber membrane module of the present invention is suitable for use in a cartridge for water purifiers which includes the hollow fiber membrane module and activated carbon. This cartridge for water purifiers is suitable for use in a water purifier including the water purifier cartridge and a channel switch.
EXAMPLES
[0036]
The present invention is explained below in detail by reference to Examples. [0037]
(1) Outer Diameter and Inner Diameter of Hollow Fiber Membranes and
Circumference length of Hollow Fiber Membranes
A hollow fiber membrane was cut with a blade perpendicularly to the longitudinal direction to expose the cross-sections. One of the exposed cross-sections was examined for outer diameter and inner diameter with Microwatcher (VH-Z100, manufactured by Keyence Corp.) using the 1,000-diametr lens. Five cross-sections were thus examined for outer diameter and inner diameter, and the measured values were averaged. The circumference length L of the hollow fiber membranes was calculated by [outer diameter (average value)] × π. [0038]
(2) Water Permeability
Hollow fiber membranes were inserted into a cylindrical case equipped at both ends with holes for circulating liquids and were bonded and fixed to both ends of the case with chemical reaction type epoxy resin adhesive “Quick Mender (registered trademark)”, manufactured by Konishi Co., Ltd. Both ends were opened by cutting, thereby producing a small hollow fiber membrane module having an effective length of 12 cm. Next, 37°C water was fed to the inside of the hollow fiber membranes while applying pressure to the water, and the amount of water which was flowing out per unit time period from the outside of the hollow fiber membranes after permeation was measured. The water permeability was calculated using the following equation.
Water permeability (mL/hr/Pa/m2) = Q / (T×P×A)

Q: amount (mL) of water flowing out from outside of the hollow fiber membranes
T: time period (hr) during which pressure was applied to water
P: pressure (Pa) to water
A: effective area (m2) of the hollow fiber membranes
[0039]
(3) Determination of Proportion of Insolubilized Hydrophilic Polymer in
Hollow Fiber Membrane Bundle
One gram of a hollow fiber membrane bundle was placed in a vial containing 50 mL of N, N-dimethylacetamide (DMAc) solution, and the contents were stirred and then subjected to suction filtration. The residue on the filter paper was vacuum-dried at 60°C for 5 hours. The mass of the dried solid was measured as the mass (uC) of an insolubilized hydrophilic polymer. The proportion of the insolubilized hydrophilic polymer was calculated using the following equation (1), in which wC is the mass of all the hydrophilic polymer contained in the hollow fiber membrane bundle.
Proportion of insolubilized hydrophilic polymer (%) = 100×uC/wC (1)
[0040]
(4) Removal Ratio for Particles having Particle Diameter of 0.3 um or larger
A hollow fiber membrane bundle was bent into the U-shape and inserted into a
cylindrical case, and the opening-side ends of the hollow fiber membranes were bonded and fixed to produce a module. Using a particle counter (A2400, manufactured by Hach Inc.), air was sucked from the opening-side end of the hollow fiber membrane module at a flow rate of 28.3 L/min. The particle counter was set so as to detect particles having a diameter of 0.3 um or larger, and the measurement environment was regulated so that the number of particles in the air during suction at 28.3 L/min was 10,000 or larger. The number of particles discharged from the opening-side end was counted to calculate the removal ratio. [0041]
(5) Filtration Rate of Hollow Fiber Membrane Module
A tube was connected to the non-opening-side end of the hollow fiber membrane module so that raw water could be fed thereto. Water having a temperature of 20°C was fed thereto at 0.1 MPa and the amount of water which was flowing out per unit time period after permeation through the hollow fiber membranes was measured. The filtration rate per unit time period (L/min) of the hollow fiber membrane module was

calculated. [0042]
(6) Turbidity-filtering Ability of Water Purifier Cartridge
Activated carbon was disposed on the upstream side of the hollow fiber membrane module produced, thereby fabricating a cartridge. Thereafter, the cartridge was examined by the method as provided for in JIS S 3201:2004 (testing methods for household water purifiers). The initial flow rate was set at 2.0 L/min. [0043]
[Example 1]
A membrane-forming solution obtained by dissolving 7 parts by mass of polyvinylpyrrolidone (PVP) (K90, manufactured by ISP Ltd.), 75 parts by mass of N,N-dimethylacetamide (DMAc), 3.0 parts by mass of water, and 15 parts by mass of a polysulfone (Udel Polysulfone (registered trademark) P-3500, manufactured by Solvay S.A.) was ejected from the annular slit of a double-ring spinneret. A liquid obtained by dissolving 55 parts by mass of DMAc, 30 parts by mass of PVP (K30, manufactured by BASF A.G.; weight-average molecular weight, 40,000), and 15 parts by mass of glycerin was ejected as an injection liquid from the center pipe. Cold-air pipes were disposed in the dry zone. The extrudate was caused to run over a given dry-zone distance while supplying cold air from both sides of the membrane-forming solution, subsequently coagulated by immersion in an 85°C coagulating bath containing a mixture solution composed of 90 parts of water and 10 parts of DMAc, thereafter subjected to a water washing step, and then wound up on a reel, thereby obtaining a hollow fiber membrane in a wet state. The hollow fiber membrane which had been wound up had an outer diameter of 300 ^im, an inner diameter of 180 um, and a membrane thickness of 60 um. [0044]
The hollow fiber membrane bundle obtained was cut in a length of 30 cm in the longitudinal direction and washed with hot water at 85°C for 1 hour. The cut fibers were dried and heat-treated in a drying/heating oven at 100°C for 10 hours, thereby obtaining a hollow fiber membrane bundle in a dry state. [0045]
One thousand, seven hundred and twenty-eight (1728) of the hollow fiber membranes were wetted with water, then bent into a U-shape, and dried again. This U-shaped hollow fiber membrane bundle in a dry state was inserted into a cylindrical case

(inner diameter, 24.4 mm; length, 56 mm), and the open portions thereof were fixed with a
polyurethane resin. Thus, a hollow fiber membrane module was produced.
[0046]
The packing ratio was 52.2%, the membrane area of the hollow fiber membranes obtained was 0.099 m2, and (2N×L)/S was 6.97. Tables 1 and 2 show the various performances including the water permeability of the hollow fiber membranes, filtration rate of the hollow fiber membrane module, removal ratio of the hollow fiber membrane module regarding the removal of particles having a particle diameter of 0.3 um or larger, and turbidity-filtering ability of the water purifier cartridge. [0047]
[Example 2]
A hollow fiber membrane having an outer diameter of 330 um and a membrane thickness of 65 um was obtained in the same manner as in Example 1 while regulating the ejection rates of the solution and inj ection liquid. The hollow fiber membrane bundle obtained was treated in the same manner as in Example 1, thereby obtaining a hollow fiber membrane bundle in a dry state. [0048]
One thousand, four hundred and twenty-eight (1428) of the hollow fiber membranes were wetted with water, then bent into a U-shape, and dried again. This U-shaped hollow fiber membrane bundle in a dry state was inserted into a cylindrical case (inner diameter, 24.4 mm; length, 56 mm), and the open portions thereof were fixed with a polyurethane resin. Thus, a hollow fiber membrane module was produced. [0049]
The packing ratio was 52.2%, the membrane area of the hollow fiber membranes obtained was 0.090 m2, and (2N×L)/S was 6.33. Tables 1 and 2 show the water permeability of the hollow fiber membranes, the removal ratio of the hollow fiber membrane module regarding the removal of particles having a particle diameter of 0.3 um or larger, and the filtration rate of the hollow fiber membrane module. [0050]
[Example 3]
A membrane-forming solution prepared in the same manner as in Example 1 was ejected from the annular slit of a double-ring spinneret. A liquid obtained by dissolving 55 parts by mass of DMAc, 30 parts by mass of polyvinylpyrrolidone (K30,

manufactured by BASF A.G.; weight-average molecular weight, 40,000), and 15 parts by mass of glycerin was ejected as an inj ection liquid from the center pipe. A cold-air pipe was disposed in the dry zone. The extrudate was caused to run over a given dry-zone distance while supplying cold air from one side of the membrane-forming solution, subsequently coagulated by immersion in a coagulating bath containing a mixture solution composed of 90 parts of water and 10 parts of DMAc, thereafter subjected to a water washing step, and then wound up on a reel, thereby obtaining a hollow fiber membrane in a wet state. The hollow fiber membrane which had been wound up had an outer diameter of 300 um and a membrane thickness of 60 um. [0051]
The hollow fiber membrane bundle obtained was cut in a length of 30 cm in the longitudinal direction and washed with hot water at 90°C for 2 hours. The cut fibers were dried and heat-treated in a drying/heating oven at 100°C for 10 hours, thereby obtaining a hollow fiber membrane bundle in a dry state. [0052]
One thousand, seven hundred and twenty-eight (1728) of the hollow fiber membranes were wetted with water, then bent into a U-shape, and dried again. This U-shaped hollow fiber membrane bundle in a dry state was inserted into a cylindrical case (inner diameter, 24.4 mm; length, 56 mm), and the open portions thereof were fixed with a polyurethane resin. Thus, a hollow fiber membrane module was produced. [0053]
The packing ratio was 52.2%, the membrane area of the hollow fiber membranes obtained was 0.099 m2, and (2N×L)/S was 6.97. Tables 1 and 2 show the water permeability of the hollow fiber membranes, the filtration rate of the hollow fiber membrane module, and the removal ratio of the hollow fiber membrane module regarding the removal of particles having a particle diameter of 0.3 um or larger. [0054]
[Example 4]
A hollow fiber membrane having an outer diameter of 300 um and a membrane thickness of 60 um was obtained in the same manner as in Example 1 while regulating the ejection rates of the solution and inj ection liquid. The hollow fiber membrane bundle obtained was treated in the same manner as in Example 1, thereby obtaining a hollow fiber membrane bundle in a dry state.

[0055]
One thousand, eight hundred and twenty-four (1824) of the hollow fiber membranes were wetted with water, then bent into a U-shape, and dried again. This U-shaped hollow fiber membrane bundle in a dry state was inserted into a cylindrical case (inner diameter, 24.4 mm; length, 56 mm), and the open portions thereof were fixed with a polyurethane resin. Thus, a hollow fiber membrane module was produced. [0056]
The packing ratio was 55.1%, the membrane area of the hollow fiber membranes obtained was 0.105 m2, and (2N×L)/S was 7.35. Tables 1 and 2 show the water permeability of the hollow fiber membranes, the filtration rate of the hollow fiber membrane module, and the removal ratio of the hollow fiber membrane module regarding the removal of particles having a particle diameter of 0.3 um or larger. [0057]
[Example 5]
A hollow fiber membrane having an outer diameter of 300 um and a membrane thickness of 52 um was obtained in the same manner as in Example 1 while regulating the ejection rates of the solution and inj ection liquid. The hollow fiber membrane bundle obtained was treated in the same manner as in Example 1, thereby obtaining a hollow fiber membrane bundle in a dry state. [0058]
One thousand, seven hundred and twenty-eight (1728) of the hollow fiber membranes were wetted with water, then bent into a U-shape, and dried again. This U-shaped hollow fiber membrane bundle in a dry state was inserted into a cylindrical case (inner diameter, 24.4 mm; length, 56 mm), and the open portions thereof were fixed with a polyurethane resin. Thus, a hollow fiber membrane module was produced. [0059]
The packing ratio was 52.2%, the membrane area of the hollow fiber membranes obtained was 0.099 m2, and (2N×L)/S was 6.97. Tables 1 and 2 show the water permeability of the hollow fiber membranes, the filtration rate of the hollow fiber membrane module, and the removal ratio of the hollow fiber membrane module regarding the removal of particles having a particle diameter of 0.3 um or larger. [0060]
[Comparative Example 1]

A hollow fiber membrane having an outer diameter of 360 um and a membrane thickness of 70 um was obtained in the same manner as in Example 1 while regulating the ejection rates of the solution and inj ection liquid. The hollow fiber membrane bundle obtained was treated in the same manner as in Example 1, thereby obtaining a hollow fiber membrane bundle in a dry state. [0061]
One thousand and two hundred (1200) of the hollow fiber membranes were wetted with water, then bent into a U-shape of the letter U, and dried again. This U-shaped hollow fiber membrane bundle in a dry state was inserted into a cylindrical case (inner diameter, 24.4 mm; length, 56 mm), and the open portions thereof were fixed with a polyurethane resin. Thus, a hollow fiber membrane module was produced. [0062]
The packing ratio was 52.2%, the membrane area of the hollow fiber membranes obtained was 0.083 m2, and (2N×L)/S was 5.80. Tables 1 and 2 show the various performances including the water permeability of the hollow fiber membranes, filtration rate of the hollow fiber membrane module, removal ratio of the hollow fiber membrane module regarding the removal of particles having a particle diameter of 0.3 um or larger, and turbidity-filtering ability of the water purifier cartridge. [0063]
[Comparative Example 2]
A hollow fiber membrane having an outer diameter of 360 um and a membrane thickness of 70 um was obtained in the same manner as in Example 1 while regulating the ejection rates of the solution and inj ection liquid. The hollow fiber membrane bundle obtained was treated in the same manner as in Example 1, thereby obtaining a hollow fiber membrane bundle in a dry state. [0064]
One thousand and four hundred (1400) of the hollow fiber membranes were wetted with water, then bent into a U-shape, and dried again. This U-shaped hollow fiber membrane bundle in a dry state was inserted into a cylindrical case (inner diameter, 24.4 mm; length, 56 mm), and the open portions thereof were fixed with a polyurethane resin. Thus, a hollow fiber membrane module was produced. [0065]
The packing ratio was 61.0%, the membrane area of the hollow fiber

membranes obtained was 0.097 m2, and (2N×L)/S was 6.77. Tables 1 and 2 show the various performances including the water permeability of the hollow fiber membranes, filtration rate of the hollow fiber membrane module, removal ratio of the hollow fiber membrane module regarding the removal of particles having a particle diameter of 0.3 um or larger, and turbidity-filtering ability of the water purifier cartridge. [0066]
[Comparative Example 3]
A hollow fiber membrane having an outer diameter of 300 um and a membrane thickness of 60 um was obtained in the same manner as in Example 1. The hollow fiber membrane obtained was cut in a length of 30 cm in the longitudinal direction and washed with hot water at 90°C for 2 hours. Thereafter, the cut fibers were dried and heat-treated in a drying/heating oven at 160°C for 5 hours, thereby obtaining a hollow fiber membrane bundle in a dry state. [0067]
One thousand, seven hundred and twenty-eight (1728) of the hollow fiber membranes were wetted with water, then bent into a U-shape, and dried again, in order to obtain a (2N×L)/S value of 6.97. It was attempted to insert this U-shaped hollow fiber membrane bundle in a dry state into a cylindrical case (inner diameter, 24.4 mm; length, 56 mm), but the hollow fiber membrane bundle was unable to be inserted because the bundle was exceedingly rigid. Namely, this Comparative Example failed to produce a hollow fiber membrane which included the U-shaped hollow fiber membrane bundle packed in the cylindrical case and which had a value of (2N×L)/S of 6.97. The water permeability of the hollow fiber membranes is shown in Table 1. [0068]
[Comparative Example 4]
A hollow fiber membrane having an outer diameter of 300 um and a membrane thickness of 60 um was obtained in the same manner as in Example 1. The hollow fiber membrane obtained was cut in a length of 30 cm in the longitudinal direction and washed with hot water at 90°C for 2 hours. Thereafter, the cut fibers were dried and heat-treated in a drying/heating oven at 160°C for 5 hours, thereby obtaining a hollow fiber membrane bundle in a dry state. [0069]
One thousand, six hundred and eighty (1680) of the hollow fiber membranes

were wetted with water, then bent into a U-shape, and dried again. This U-shaped hollow fiber membrane bundle in a dry state was inserted into a cylindrical case (inner diameter, 24.4 mm; length, 56 mm). However, some of the hollow fiber membranes were damaged at the vertex of the hollow fiber membrane bundle. The hollow fiber membrane module thus obtained had a removal ratio for particles with a particle diameter of 0.3 ^im or larger of 82%. Tables 1 and 2 show the water permeability of the hollow fiber membranes and the removal ratio of the hollow fiber membrane module regarding the removal of particles having a particle diameter of 0.3 um or larger. [0070]
[Comparative Example 5]
A membrane-forming solution obtained by dissolving, with heating, 16 parts by mass of a polysulfone (Udel Polysulfone (registered trademark) P-3500, manufactured by Solvay S.A.), 3 parts by mass of polyvinylpyrrolidone (K30, manufactured by ISP Ltd.), 3 parts by mass of polyvinylpyrrolidone (K90, manufactured by ISP Ltd.), 77 parts by mass of dimethylacetamide, and 1 part by mass of water was ejected from the annular slit of a double-ring spinneret. An injection liquid composed of 65 parts by mass of DMAc and 35 parts by mass of water was ejected from the center pipe of the double-ring spinneret. The extrudate was caused to run through a dry zone, coagulated by immersion in a 70°C coagulating bath containing a mixture solution composed of 90 parts of water and 10 parts of DMAc, thereafter subjected to a water washing step, and then wound up on a reel, thereby obtaining a hollow fiber membrane in a wet state. The hollow fiber membrane which had been wound up had an outer diameter of 280 um and a membrane thickness of 40um. [0071]
The hollow fiber membrane bundle obtained was cut in a length of 30 cm in the longitudinal direction and washed with hot water at 90°C for 2 hours. The cut fibers were dried and heat-treated in a drying/heating oven at 100°C for 10 hours, thereby obtaining a hollow fiber membrane bundle in a dry state. [0072]
One thousand, nine hundred and thirty-two (1932) of the hollow fiber membranes were wetted with water, then bent into a U-shape, and dried again. This U-shaped hollow fiber membrane bundle in a dry state was inserted into a cylindrical case (inner diameter, 24.4 mm; length, 56 mm), and the open portions thereof were fixed with a

polyurethane resin. Thus, a hollow fiber membrane module was produced. [0073]
The packing ratio was 52.2%. However, this hollow fiber membrane module had a removal ratio for particles with a particle diameter of 0.3 μm or larger of 88.5% because some of the hollow fiber membranes which lay at the vertex of the hollow fiber membrane bundle had broken. Tables 1 and 2 show the water permeability of the hollow fiber membranes and the removal ratio of the hollow fiber membrane module regarding the removal of particles having a particle diameter of 0.3 μm or larger. [0074]
[Comparative Example 6]
A hollow fiber membrane having an outer diameter of 300 μm and a membrane thickness of 60 μm was obtained in the same manner as in Example 1 while regulating the ejection rates of the solution and injection liquid. The hollow fiber membrane bundle obtained was treated in the same manner as in Example 1, thereby obtaining a hollow fiber membrane bundle in a dry state. [0075]
Two thousand and sixteen (2016) of the hollow fiber membranes were wetted with water, then bent into a U-shape, and dried again. This U-shaped hollow fiber membrane bundle in a dry state was inserted into a cylindrical case (inner diameter, 24.4 mm; length, 56 mm) in an attempt to produce a hollow fiber membrane module. However, some of the hollow fiber membranes broke upon the insertion because of the too high packing ratio. A module of satisfactory quality was unable to be produced. The water permeability of the hollow fiber membranes is shown in Table 1.

[0078]
While the invention has been described in detail and with reference to specific embodiments thereof, it will be apparent to one skilled in the art that various changes and modifications can be made therein without departing from the spirit and scope thereof.

This application is based on a Japanese patent application filed on March 22, 2016 (Application No. 2016-056696), the contents thereof being incorporated herein by reference.

WE CLAIM:
[Claim 1]
A hollow fiber membrane module comprising a cylindrical case and, packed therein, a U-shaped hollow fiber membrane bundle obtained by bundling a plurality of hollow fiber membranes comprising a hydrophobic polymer and a hydrophilic polymer, the hollow fiber membrane bundle having open ends, which have been fixed to an opening portion of the cylindrical case with a potting material, wherein
the hollow fiber membranes have an outer diameter of 350 um or less, and
the cylindrical case and the hollow fiber membranes satisfy (2N×L)/S being 6.2 or larger, where S is an area of a cross-section of the cylindrical case which is perpendicular to an axial direction of the cylindrical case and which is located at a portion of the cylindrical case where the cylindrical case has a smallest cross-sectional area, L is a circumference length of each hollow fiber membrane, and N is the number of the hollow fiber membranes packed in the cylindrical case,
the hollow fiber membrane module has a removal ratio for particles with a particle diameter of 0.3 um or larger of 99.9% or higher. [Claim 2]
The hollow fiber membrane module according to claim 1, wherein a ratio between an inner diameter of the hollow fiber membranes and the outer diameter of the hollow fiber membranes (inner diameter/outer diameter) is 0.67 or less. [Claim 3]
The hollow fiber membrane module according to claim 1 or 2, wherein the hollow fiber membranes have a packing ratio of 60% or less in a space inside the cylindrical case. [Claim 4]
The hollow fiber membrane module according to any one of claims 1 to 3, wherein the hollow fiber membranes have a water permeability of 30 mL/Pa/hr/m2 or higher. [Claim 5]
The hollow fiber membrane module according to any one of claims 1 to 4, wherein the hydrophobic polymer is a polysulfone-based polymer. [Claim 6]

The hollow fiber membrane module according to any one of claims 1 to 5, wherein the hydrophilic polymer comprises polyvinylpyrrolidone. [Claim 7]
A cartridge for water purifiers which comprises the hollow fiber membrane module according to any one of claims 1 to 6 mounted therein. [Claim 8]
A water purifier comprising the cartridge for water purifiers according to claim 7.