Hollow fiber membrane and dehumidifier using the same

Abstract

To provide a hollow fiber membrane capable of obtaining compressed-air at a low dew point with a small purge air quantity, and a dehumidifier.SOLUTION: A hollow fiber membrane is composed of a hollow yarn and a hydrophilic polymer. The hollow yarn includes hydrophobic polymer, has at least fine holes, and includes the hydrophilic polymer at least in part of the surface on a hollow part side of the hollow yarn. The hydrophilic polymer has a hydrophilic unit. The hollow yarn has a plurality of finger voids. In all of the finger voids, length of the finger void in a film thickness direction of the hollow yarn accounts to 20 to 50% of film thickness of the hollow yarn.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] This invention relates to a hollow fiber membrane and a dehumidifier for removing moisture from compressed air using the same. [Background technology]

[0002] Dehumidifiers using hollow fiber membranes are used to prevent corrosion of air-driven equipment such as industrial robots, trucks, buses, trains, and medical devices due to moisture in compressed air. In these hollow fiber membrane dehumidifiers, 10-20% of the dehumidified compressed air is purged as purge air over the outer surface of the hollow fiber membrane, creating a partial pressure difference of water vapor between the hollow side surface and the outer surface. This promotes the permeation (diffusion) of moisture in the compressed air from the hollow side surface to the outer surface, thereby dehumidifying the compressed air. Increasing the amount of purge air can yield drier air with a lower dew point, but this also worsens the yield of dehumidified air. Therefore, there is a need for hollow fiber membranes that can produce air with a low dew point with a small amount of purge air.

[0003] Methods for obtaining such hollow fiber membranes include, for example, impregnating hollow fibers made of polyetherimide with a polyvinylpyrrolidone coating or a humectant, and impregnating porous hollow fiber membranes with a surface pore size of 5 nm or less with polyglycerol monofatty acid esters with an HLB of 12 or higher (see, for example, Patent Documents 1 and 2).

[0004] Furthermore, a method of dehumidification without using purge air has been proposed by increasing the air leak from the hollow fibers (see, for example, Patent Document 3). [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 11-76778 [Patent Document 2] Japanese Patent Publication No. 2005-9022

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0006] However, the hollow fiber membranes described in Patent Document 1 and Patent Document 2 have a problem in that since the outer surface of the hollow fiber membrane is coated with a hydrophilic polymer, the water vapor permeation rate is slow, and compressed air with a low dew point cannot be obtained unless the purge air volume is increased.

[0007] Further, in Patent Document 3, a silane coupling treatment is performed on the inner wall of a hollow fiber membrane in which the quantitative ratio of polyvinylpyrrolidone to polysulfone is large on the inner wall side of the hollow and decreases toward the outer wall side of the fiber, and the gas permeability is 2×10 , , 2 , -4 , , , , ,

[0009] , , , 3 , , -4 ,

[0008] , , , ,

[0010] , ~10×10 -4 cm 3 / cm 2 ·sec·cmHg, and a method using such a hollow fiber membrane has been proposed. However, since there is always a large amount of leakage from the hollow fiber, there is a problem in that the yield of compressed air after dehumidification is low even when such a low dew point is not required.

[0008] The present invention has been made in view of the above problems, and an object thereof is to provide a hollow fiber membrane capable of obtaining compressed air with a low dew point with a small amount of purge air and a dehumidifier.

Means for Solving the Problems

[0009] That is, the present invention is as follows.

[0010] A hollow fiber membrane comprising a hollow fiber and a hydrophilic polymer, wherein the hollow fiber contains a hydrophobic polymer and has at least fine pores, at least a part of the surface on the hollow portion side of the hollow fiber contains the hydrophilic polymer, the hydrophilic polymer is a polymer having a hydrophilic unit, the hollow fiber has a plurality of finger voids A hollow fiber membrane characterized in that, in all of the finger voids, the length of the finger void in the direction of the thickness of the hollow fiber is 20 to 50% of the thickness of the hollow fiber. [Effects of the Invention]

[0011] The present invention provides a hollow fiber membrane with excellent water vapor permeability and low air leakage, which can be effectively used as a dehumidifying membrane. For example, it can provide excellent effects such as obtaining compressed air with a low dew point using a small amount of purged air. [Brief explanation of the drawing]

[0012] [Figure 1] This figure shows an example of measuring the length of finger voids in the film thickness direction of a hollow fiber. [Figure 2] This figure shows a module filled with hollow fibers and hollow fiber membranes. [Figure 3] This is a diagram showing a dehumidifier case. [Figure 4] This is a method for measuring the rate of air permeation. [Figure 5] This is a method for measuring the dew point of dehumidified air. [Modes for carrying out the invention]

[0013] The hollow fiber membrane of the present invention is a hollow fiber membrane comprising a hollow fiber and a hydrophilic polymer, wherein the hollow fiber contains a hydrophobic polymer and has at least micropores, and the hydrophilic polymer is contained in at least a portion of the surface on the hollow side of the hollow fiber, the hydrophilic polymer is a polymer having hydrophilic units, the hollow fiber has a plurality of finger voids, and in all of the finger voids, the length of the finger void in the film thickness direction of the hollow fiber is 20 to 50% of the film thickness of the hollow fiber.

[0014] In the present invention, a hollow fiber membrane consists of a hollow fiber and a hydrophilic polymer, but more specifically, it refers to a hollow fiber having at least micropores, in which a hydrophilic polymer is included in at least a portion of the surface on the hollow side of the hollow fiber.

[0015] In this invention, the micropores of the hollow fiber refer to holes with a diameter of 10 to 100 nm that are present when the surface on the hollow side of the hollow fiber is observed at a magnification of 100,000 times. The presence of micropores in the hollow fiber allows for both water vapor permeability from the hollow side surface to the outer surface and air barrier properties. The diameter of the micropores is preferably 20 to 80 nm, and more preferably 20 to 60 nm. If the hollow fiber has no micropores or the diameter is less than 10 nm, water vapor permeability decreases, making it impossible to obtain low-dew-point air when used as a dehumidifying film. If it exceeds 100 nm, air barrier properties decrease and air leaks increase, thus failing to achieve the objectives of this invention. Furthermore, even if the micropores are elliptical or have other shapes, the objectives of this invention can be achieved as long as they are within the area range calculated from a circle with a diameter of 10 to 100 nm.

[0016] In this invention, the hollow fiber contains a hydrophobic polymer. Here, a hydrophobic polymer in this invention is defined as a polymer consisting of repeating units that are sparingly soluble or insoluble in water as a single polymer (number average molecular weight of 30,000 or more and 50,000 or less). Here, sparingly soluble or insoluble in water means that the solubility in 100g of pure water at 20°C is 1g or less.

[0017] In the present invention, the hydrophobic polymer contained in the hollow fiber is not particularly limited, but examples of hydrophobic polymers include polysulfone polymers, polystyrene, polyurethane, polyethylene, polypropylene, polycarbonate, polyvinylidene fluoride, polyacrylonitrile, polymethyl methacrylate, polyvinyl chloride, and polyester. Among these, polysulfone polymers and polymethyl methacrylate can be suitably used as hydrophobic polymers because they readily form hollow fiber membranes.

[0018] While the content of hydrophobic polymers in hollow fibers is not particularly limited as long as they contain them, it is preferable that the main raw material of the hollow fibers be a hydrophobic polymer, and more preferably that the hydrophobic polymer is a polysulfone polymer. Here, a polysulfone polymer is a polymer having an aromatic ring, a sulfonyl group, and an ether group in its main chain, and examples include polysulfone, polyphenylsulfone, polyethersulfone, and polyallyl ethersulfone. Furthermore, the main raw material of the hollow fibers refers to a raw material that is present in an amount of 90% by weight or more relative to 100% by weight of the total hollow fibers.

[0019] As the hydrophobic polymer that serves as the main raw material for the hollow fibers in the present invention, for example, a polysulfone polymer represented by the chemical formulas (1) and / or (2) is preferably used, but is not limited to these. In the formula, n is an integer of 1 or more, preferably 50 to 80. If n has a distribution, the average value of n is taken as n.

[0020] [ka]

[0021] The polysulfone polymer that can be used as the hydrophobic polymer in the hollow fiber of the present invention is preferably a polymer consisting only of repeating units represented by formula (1) and / or (2), but copolymers or modified products with other monomers are also acceptable as long as they do not hinder the effects of the present invention. When copolymerized with other monomers, the copolymerization ratio of the other monomers is preferably 10% by weight or less of the total polysulfone polymer.

[0022] Specific examples of polysulfone polymers that can be used as hydrophobic polymers in the hollow fibers of the present invention include Udel Polysulfone P-1700, P-3500 (manufactured by Solvay), Ultrasone S3010, P3010, S6010 (manufactured by BASF), Victrex (manufactured by Sumitomo Chemical Co., Ltd.), Radel A (manufactured by Solvay), and Ultrasone E (manufactured by BASF).

[0023] In the present invention, a hydrophilic polymer is included in at least a portion of the surface on the hollow side of the hollow fiber. In the present invention, a hydrophilic polymer is a polymer having hydrophilic units. Here, a unit refers to a repeating unit in a polymer obtained by polymerizing monomers. Therefore, a hydrophilic unit refers to a repeating unit in a polymer obtained by polymerizing hydrophilic monomers.

[0024] In this invention, a hydrophilic unit is defined as a repeating unit of a polymer (number-average molecular weight of 30,000 or more and 50,000 or less) that is readily soluble in water. Here, readily soluble in water means that the solubility in 100g of pure water at 20°C is greater than 1g.

[0025] The hydrophilic units of the hydrophilic polymer are not particularly limited, but examples include repeating units provided by monomers such as methacrylic acid, acrylic acid, 2-hydroxyethyl methacrylate, 2-hydroxyethyl acrylate, vinylpyrrolidone, vinyl alcohol, ethylene glycol, and vinyl sulfate. Among these, repeating units provided by acrylic acid and vinyl sulfate are preferred as hydrophilic units of the hydrophilic polymer because they result in good water vapor adsorption and permeability of the hollow fiber membrane.

[0026] Furthermore, since a hydrophilic polymer is a polymer having hydrophilic units, as long as it has hydrophilic units, it may also have hydrophobic units; in other words, a hydrophilic polymer may be a copolymer consisting of hydrophilic units and hydrophobic units.

[0027] Here, a hydrophobic unit is defined as a repeating unit that, as a polymer on its own (with a number-average molecular weight of 30,000 to 50,000), is sparingly soluble or insoluble in water. Here, sparingly soluble or insoluble in water means that its solubility in 100g of pure water at 20°C is 1g or less.

[0028] Copolymers consisting of hydrophilic and hydrophobic units, suitable as hydrophilic polymers, can achieve both water vapor permeability and air barrier properties in hollow fiber membranes. From this viewpoint, it is preferable that the copolymer contains at least one repeating unit provided by vinylpyrrolidone as the hydrophilic unit and at least one repeating unit provided by vinyl carboxylate as the hydrophobic unit. The number of carbon atoms at the end of the side chain of vinyl carboxylate is preferably a combination of 1 to 7. Here, the number of carbon atoms at the end of the side chain refers to the number of carbon atoms of the terminal hydrocarbon group bonded to the carbonyl carbon atom of the side chain ester bond of vinyl carboxylate. For example, a carbon number of 1 refers to vinyl acetate, and a carbon number of 2 refers to vinyl propanoate. The terminal hydrocarbon group may include not only a linear structure but also branched structures such as isopropyl groups and tert-butyl groups, cyclic structures such as cyclohexyl groups and phenyl groups, and even heteroatoms such as nitrogen atoms and oxygen atoms. The number of carbon atoms at the end of the side chain is preferably 1 to 7, more preferably 2 to 6, and more preferably 2 to 4. This allows for control over the adsorption of the copolymer to the surface of the humidifying hollow fiber membrane and the mobility of the adsorbed water, making it easier to achieve both water vapor permeability and air barrier properties of the humidifying hollow fiber membrane at high temperatures. If the number of carbon atoms at the side chain ends of the repeating units provided by the vinyl carboxylate is too high, the overall hydrophobicity of the copolymer increases, making it more prone to repelling water. Furthermore, if the number of carbon atoms at the side chain ends is 0, vinyl carboxylates that are difficult to introduce to the surface of the humidifying hollow fiber membrane are more preferable, such as vinyl acetate (1 carbon atom), vinyl propanoate (2 carbon atoms), vinyl butyrate (3 carbon atoms), vinyl pentanoate (4 carbon atoms), and vinyl pivalate (4 carbon atoms).

[0029] The hollow fibers in the hollow fiber membrane of the present invention contain a hydrophilic polymer on at least a portion of the surface on the hollow side. This presence of a hydrophilic polymer on at least a portion of the surface on the hollow side of the hollow fiber can be confirmed, for example, when the hydrophilic unit contains a carboxylic acid, ester, alcohol, etc., by the following method: The hollow fiber membrane is cut into a semi-cylindrical shape using a microtome, and measurements are taken on the surface on the hollow side of the hollow fiber using FT-IR with a field of view (aperture) of 100 μm × 100 μm, and 30 integrations per point. The obtained IR spectrum is measured at 1590 cm⁻¹. -1 The peak area Ac=c originates from the benzene ring double bond of the nearby polysulfone, and the range is 1700-1720 cm². -1 The ratio of the peak area to Ac=o, derived from nearby carboxylic acids, is Ac=o / Ac=c or 1710-1750 cm². -1 The ratio of the peak area derived from nearby ester bonds (Ac=o / Ac=c) to Ac=o is 3200-3550 cm². -1 The ratio of the peak area Ao-H derived from nearby alcohols to the peak area Ao-H / Ac=c peak area is calculated. For a single module of hollow fiber membrane, three measurements are taken on the surface on the hollow side of the hollow fiber. If the average value of Ac=o / Ac=c or Ao-H / Ac=c is 0.04 or higher, it is assumed that at least a portion of the hollow fiber contains a hydrophilic polymer. As mentioned above, the above method is an example for cases where the hydrophilic unit of the hydrophilic polymer contains structures such as carboxylic acids, esters, and alcohols. When using a hydrophilic polymer that contains other structures such as sulfonic acid groups, ketones, or amines as hydrophilic units, the determination can be made by calculating the ratio to the corresponding peak area in the same manner as above.

[0030] The hollow fibers used in the hollow fiber membrane of the present invention preferably have an inner diameter of 300 μm or more and 1000 μm or less. By setting the inner diameter of the hollow fibers within this range, pressure loss when passing a hydrophilic polymer aqueous solution through the hollow portion of the hollow fibers (described later) can be suppressed, the size of the module can be reduced, and the unevenness of the airflow on the outside of the hollow fibers tends to be small, making it less likely to cause unevenness in the water vapor permeation rate from the hollow fiber side surface to the outer surface of the hollow fiber.

[0031] Furthermore, the thickness of the hollow fiber membrane is preferably between 60 μm and 200 μm. If the thickness of the hollow fiber membrane is less than 60 μm, the rupture strength of the hollow fiber membrane decreases, and the hollow fiber membrane may break under high-pressure air. Also, if the thickness of the hollow fiber membrane exceeds 200 μm, the structural control stability during the manufacturing of the hollow fiber is lacking, and the reproducibility of the hollow fiber void portion may be poor.

[0032] The hollow fibers in the hollow fiber membrane of the present invention have multiple finger voids. More specifically, when the hollow fibers used in the hollow fiber membrane of the present invention are observed using an electron microscope at a magnification of 1000x perpendicular to the longitudinal direction of the hollow fiber, they have multiple finger voids. In the present invention, a finger void refers to a hole that has a length of 10 μm or more in the direction of the thickness of the hollow fiber, similar to the impression left by a person's thumbprint.

[0033] When the cross-sectional structure of a hollow fiber perpendicular to its longitudinal direction is an asymmetric structure with micropores whose diameter increases sequentially from the surface on the hollow side to the outer surface, or from the outer surface to the surface on the hollow side, the resistance to water vapor permeation increases, and water vapor permeability tends to decrease. Furthermore, for symmetric structures (homogeneous films) with micropores of the same diameter from the surface on the hollow side to the outer surface, selective permeability (air barrier properties) is low, and it tends to be difficult to achieve both water vapor permeability and air barrier properties. In order to achieve both water vapor permeability and air barrier properties, it is preferable that the hollow fiber used in the hollow fiber membrane of the present invention has a smaller pore diameter in the outermost surface portion on the hollow side and the outermost surface portion compared to the finger void portion, and has a finger void structure in the central portion.

[0034] In the present invention, in all finger voids in the hollow fiber, the length of the finger void in the film thickness direction of the hollow fiber is 20 to 50% of the film thickness of the hollow fiber. Here, all finger voids in the present invention refer to finger voids present when observing a cross section perpendicular to the longitudinal direction of the hollow fiber at a magnification of 1000 times. Further, the length of the finger void refers to the length of a straight line where the distance from the surface on the hollow portion side of the hollow fiber to the outer surface is maximum. When the length of the finger void in the film thickness direction of the hollow fiber is less than 20% of the film thickness of the hollow fiber, the permeation resistance of water vapor increases, and the water vapor permeability may decrease. When it exceeds 50%, the pressure resistance and air barrier property of the hollow fiber membrane may decrease, and there is a possibility that a hollow fiber membrane excellent in water vapor permeability and having a small air leak amount, which is the object of the present invention, cannot be obtained. In terms of improving the water vapor permeability, it is preferable that the length of all finger voids in the film thickness direction of the hollow fiber is 30 to 50% of the film thickness of the hollow fiber.

[0035] Further, the number of finger voids in a cross section perpendicular to the longitudinal direction of the hollow fiber is preferably 3 or more per 12000 μm 2 in the observation field when observed at a magnification of 1000 times with an electron microscope, and more preferably 5 or more. When the number of finger voids is less than 3, it may be impossible to expect an improvement in water vapor permeability, which is a characteristic of the finger void structure during the formation of the hollow fiber membrane. Also, when the number of finger voids is too large, the pressure resistance and air barrier property of the hollow fiber membrane may decrease, so it is preferably 20 or less, and more preferably 15 or less.

[0036] In the hollow fiber membrane of the present invention, the air permeation rate from the surface on the hollow portion side to the outer surface is 3.00×10 -3 ~2.00×10 -1 mL / min / cm 2 / MPa, which is preferable. In terms of easily achieving both the water vapor permeability and air barrier property of the hollow fiber membrane, the air permeation rate from the surface on the hollow portion side to the outer surface is 4.00×10 -3 ~1.00×10 -1 mL / min / cm 2It is more preferable that the pressure is 2.00 × 10⁻¹⁰. In dehumidifiers using hollow fiber membranes, higher pressure air is used compared to humidifiers, so the air permeation velocity is 2.00 × 10⁻¹⁰. -1 mL / min / cm 2 When the pressure exceeds MPa, the air barrier properties of the hollow fiber membrane are low, resulting in significant air leakage, a low yield of dehumidified air, and making it uneconomical. On the other hand, 3.00 × 10 -3 mL / min / cm 2 If the value is less than / MPa, the water vapor permeability will be low, and the air may not be sufficiently dehumidified. Here, the air permeation rate from the hollow side surface to the outer surface of the hollow fiber membrane refers to the permeation rate when air is flowed from the hollow side surface to the outer surface of the hollow fiber membrane.

[0037] On the other hand, in the hollow fiber membrane of the present invention, in order to obtain high water vapor permeability, the air permeation rate from the hollow side surface to the outer surface of the hollow fiber used in the hollow fiber membrane is 170 to 500 mL / min / cm². 2 It is preferable to use hollow fibers with a pressure of / MPa, and a flow rate of 250-500 mL / min / cm². 2 It is more preferable that the pressure is / MPa. Here, the air permeation rate from the hollow side surface of the hollow fiber to the outer surface refers to the permeation rate when air is flowed from the hollow side surface of the hollow fiber to the outer surface, with respect to a hollow fiber membrane that does not have a hydrophilic polymer.

[0038] However, since hollow fibers as they are leak a lot of air, the present invention improves air barrier properties by attaching a hydrophilic polymer to at least a portion of the surface on the hollow side of the hollow fiber, and adjusts the air permeation rate of the hollow fiber membrane to be within the above range. In addition, the hollow fiber membrane of the present invention contains a hydrophilic polymer on at least a portion of the surface on the hollow side of the hollow fiber, but a more preferred embodiment of the hollow fiber membrane is one in which a hydrophilic polymer is included on at least a portion of the surface on the hollow side, but the outer surface does not contain a hydrophilic polymer.

[0039] In the present invention, the method for attaching the hydrophilic polymer to at least a portion of the surface on the hollow side of the hollow fiber is not particularly limited. For example, the hydrophilic polymer can be attached to the micropores on the surface on the hollow side of the hollow fiber by passing an aqueous solution of the hydrophilic polymer through the hollow portion of the hollow fiber while pressurizing the hollow portion or depressurizing the outside of the hollow fiber. By attaching the hydrophilic polymer to the micropores on the surface on the hollow side, the water vapor adsorption is improved, the air barrier properties of the hollow fiber can be enhanced, and air leakage from the surface on the hollow side to the outer surface can be significantly reduced. Furthermore, since the water vapor permeability tends to decrease when the hydrophilic polymer is attached to the micropores on the outer surface of the hollow fiber membrane, it is preferable that the hydrophilic polymer is not present on the outer surface. In order to ensure that the outer surface is free of hydrophilic polymer, it is preferable to use an aqueous solution with a hydrophilic polymer concentration of 1.0% by weight or more by appropriately adjusting the concentration of the aqueous solution of the hydrophilic polymer when attaching the hydrophilic polymer. Furthermore, when pressurizing the hollow portion or reducing the pressure on the outside of the hollow fibers to allow the hydrophilic polymer to pass through, the pressure can be adjusted as appropriate within a range that does not cause the hollow fibers to tear or collapse, and it is preferable to pressurize to 20 kPa or higher.

[0040] Furthermore, if the hydrophilic polymer is a copolymer consisting of hydrophilic and hydrophobic units and is poorly soluble or insoluble in water, the copolymer may be dissolved in an organic solvent that does not dissolve the hollow fiber membrane, or in a mixed solvent of an organic solvent that is compatible with water and does not dissolve the hollow fiber membrane, and water. Specific examples of organic solvents that can be used as the organic solvent or mixed solvent include, but are not limited to, alcohol-based solvents such as methanol, ethanol, and propanol.

[0041] Furthermore, in order to prevent the hydrophilic polymer attached to the hollow side surface of the hollow fiber from leaching out during use, it is preferable to insolubilize the hydrophilic polymer by irradiating it with radiation or heat treatment after it has been attached. Alpha rays, beta rays, gamma rays, X-rays, ultraviolet rays, electron beams, etc., can be used for the radiation irradiation.

[0042] The hollow fiber membrane of the present invention can be suitably used as a dehumidifier by filling it into a module case such as a cylindrical or rectangular shape to form a module, and then assembling the module into a dehumidifier case. In other words, the hollow fiber membrane of the present invention is preferably used for dehumidification purposes, and the dehumidifier of the present invention includes the hollow fiber membrane of the present invention in the dehumidifier case. The shape of the dehumidifier case is not particularly limited, but in order to effectively utilize the water vapor permeability of the hollow fiber membrane, it is preferable that it has at least a supply port for supplying air to be dehumidified to the hollow part of the hollow fiber membrane, an outlet for discharging the dehumidified air, a purge air supply port for supplying a portion of the dehumidified air as purge air at a lower pressure than the air flowing through the hollow part of the hollow fiber membrane to the outer surface of the hollow fiber membrane, and a purge air outlet for discharging the purge air to the outside of the dehumidifier case.

[0043] In the present invention, the hollow fiber membrane preferably has a packing ratio (hereinafter referred to as "filling ratio") of 40% to 65% of the total volume of the hollow fiber membrane based on its outer diameter relative to 100% of the internal volume of the module case. A packing ratio of 40% or more reduces the gap between the bundle of hollow fiber membranes and the module case wall, making it less likely for the purge air flowing around the outside of the hollow fiber membranes to short-circuit, thus improving dehumidification efficiency. Furthermore, a packing ratio of 65% or less improves the operability when inserting the bundle of hollow fiber membranes into the module case and reduces the likelihood of damage to the bundle. Here, the sum of volumes based on the outer diameter of the hollow fiber membranes refers to the value obtained by multiplying the cross-sectional area using the outer diameter of the hollow fiber membrane by the length of the bundle to calculate the volume, and then summing the volumes of all the hollow fiber membranes.

[0044] The dehumidifier using the hollow fiber membrane of the present invention can fully exhibit its dehumidifying effect by flowing the air to be dehumidified and the purged air in a counter-flow manner.

[0045] The amount of purged air can be adjusted as appropriate depending on the dew point of the air after dehumidification, and it is preferable to set it to 10% to 30% of the supply amount of air to be dehumidified.

[0046] The present invention includes, for example, the following method for manufacturing hollow fiber membranes. In order to control the polysulfone that serves as the aggregate for the hollow fiber, the pore size of the micropores on the hollow side surface and the outer surface of the hollow fiber, and the shape of the finger voids, a stock solution (preferably 10-30% by weight, more preferably 15-25% by weight) is prepared by dissolving polyvinylpyrrolidone, which has a weight-average molecular weight of approximately 10,000 (equivalent to K-15) to 1,200,000 (equivalent to K-90), in a weight ratio of 20:1 to 1:1 (preferably 20:1 to 2:1) in a mixed solution of a good solvent for polysulfone (preferably N,N-dimethylacetamide, dimethyl sulfoxide, dimethylformamide, N-methylpyrrolidone, dioxane, etc.) and a poor solvent. When this stock solution is discharged from a double annular nozzle, the core liquid is allowed to flow inward and the nozzle is allowed to run through the dry section. In this process, the humidity of the dry section has an effect. By supplying moisture from the outer surface of the film during the dry section's operation, it is possible to accelerate the phase separation behavior near the outer surface, enlarge the pore size, and consequently reduce the water vapor permeation resistance. However, if the relative humidity is too high, solidification of the raw solution at the outer surface becomes dominant, which conversely reduces the pore size and tends to increase the water vapor permeation resistance. Therefore, a relative humidity of 60-90% is preferable. Furthermore, for process suitability, the composition of the core solution is preferably such that the ratio of good solvents in the raw solution is low. As for the concentration of the core solution, for example, when dimethylacetamide is used, an aqueous solution of 25-70% by weight, and more preferably 30-60% by weight, is used.

[0047] Subsequently, the hollow fibers are introduced into water at 10-60°C to solidify, then washed and extracted with warm water at 50-90°C to remove the solvent and polyvinylpyrrolidone. After drying with hot air at 50-100°C, hollow fibers with an air permeability rate of 170-500 mL / min / cm2 / MPa from the hollow side surface to the outer surface are obtained. The required number of these hollow fibers are bundled together and cut, and the hollow fibers are inserted into a module case. Then, potting agent is injected into both ends of the module case to seal it, and after the potting agent has solidified, both ends are cut so that the ends of the hollow fibers are open, thereby obtaining a hollow fiber module. An aqueous solution of hydrophilic polymer containing 0.5-3% by weight of polyacrylic acid is flowed under pressure into the hollow part of the hollow fibers of this module to adhere the hydrophilic polymer to the surface of the hollow part. Subsequently, to improve the durability of the hydrophilic polymer, gamma rays are irradiated while the hydrophilic polymer aqueous solution remains inside the hollow fibers to crosslink the hydrophilic polymer. After irradiation, the hollow portion is washed with 80°C hot water and dried at 50-100°C to produce the hollow fiber membrane of the present invention. [Examples]

[0048] Next, the present invention will be described with reference to examples.

[0049] (1) Dimensional measurement of hollow fibers The outer diameter, inner diameter, and film thickness of 10 hollow fibers were measured at a magnification of 200x using a digital microscope (HiROX RH-2000) perpendicular to the longitudinal direction, and the average values ​​of the 10 fibers were used as the outer diameter, inner diameter, and film thickness of the hollow fibers.

[0050] (2) Micropores on the hollow side surface The surface of the hollow portion of the hollow fiber was observed with an electron microscope at a magnification of 100,000x to confirm whether or not pores with a diameter of 10 to 100 nm were present.

[0051] (3) Length of finger voids in the film thickness direction of the hollow fiber The entire circumference of a cross-section perpendicular to the longitudinal direction of the hollow fiber was observed with an electron microscope at a magnification of 1000x. The length of the straight line that maximized the distance from the hollow side surface to the outer surface of the hollow fiber in all finger voids was measured and defined as the length of the finger void. The ratio of the length of the hollow fiber to the film thickness was determined from the length of the finger void and the film thickness obtained from the above dimensional measurements of the hollow fiber. Figure 1 shows an example of finger void length measurement.

[0052] (4) Air permeability Modules 7 filled with hollow fibers or hollow fiber membranes as shown in Figure 2 were dried in a 50°C dryer for more than 24 hours. Then, they were connected as shown in Figure 4, the purge air inlet 10 on the side of the module was closed with a stopper 14, and the flow rate adjustment valve 16 was closed. In this state, 20°C air was pressurized to a pressure of 100 kPa and flowed through the gas inlet, and the amount of air leakage from the hollow side surface to the outer surface of the hollow fiber (or hollow fiber membrane) was measured with a flow meter 17. From the membrane area of ​​the module and the amount of air leakage, a value was calculated converted to the air permeability per 1 MPa, and this was defined as the air permeability velocity of the hollow fiber or hollow fiber membrane.

[0053] (5)Dehumidification performance Module 7, filled with hollow fibers or hollow fiber membranes as shown in Figure 2, was inserted into a dehumidifier case equipped with a valve 13 that can adjust the flow rate of purge air as shown in Figure 3, and connected as shown in Figure 5. 20°C air was supplied to the humidifier from the gas inlet at a pressure of 0.5 MPa and a flow rate of 180 L / min to create saturated air, which was then introduced into the gas inlet. The amount of purge air flowing outside the hollow fiber membrane was adjusted using the purge air flow rate adjustment valve 13 so that the flow rate of the flow meter 17 was 36 L / min, and the dew point of the air exiting the gas outlet was measured using a dew point meter 21.

[0054] (6) Confirmation of hydrophilic polymer The hollow fiber membrane was cut into a semi-cylindrical shape using a microtome and fixed to the sample stage. Measurements were performed using FT-IR with a field of view (aperture) of 100 μm × 100 μm, and 30 integrations were performed for each point.

[0055] In this embodiment, since the hydrophilic unit of the hydrophilic polymer is acrylic acid, 1590 cm² -1 The peak area Ac=c originates from the benzene ring double bond of the nearby polysulfone, and 1730 cm². -1 The determination was made by calculating the ratio Ac=o / Ac=c to the nearby peak area Ac=o. In other words, for a single module of hollow fiber membrane, measurements were taken at three locations: the surface on the hollow side of the hollow fiber and the outer surface. If the average value of Ac=o / Ac=c was 0.04 or higher, it was considered that a hydrophilic polymer was attached.

[0056] (Example 1) A film-forming stock solution was prepared by heating and dissolving 26% by weight of polysulfone (Solvay's "Udel" P-3500) and 8 parts by weight of polyvinylpyrrolidone (BASF's K-30) in 65% by weight of N,N-dimethylacetamide and 1% by weight of water. A core solution was prepared using 31% by weight of N,N-dimethylacetamide and 69% by weight of water.

[0057] The film-forming solution was sent to the spinneret section and discharged from the outer tube of the orifice-type double-tube spinneret, while the core solution was discharged from the inner tube. The discharged film-forming solution passed through a dry zone atmosphere with a dew point of 30°C, then solidified in a 100% water coagulation bath, and underwent a water washing process at 80°C for 2 minutes. The resulting wet hollow fibers were wound up and cut into bundles of 286 hollow fibers. These bundles were washed in an 80°C water bath for 1 hour, and then dried in a dry heat dryer at 50°C for 24 hours to obtain hollow fibers. The inner diameter of the obtained hollow fibers was 640 μm and the film thickness was 88 μm.

[0058] When the hollow surface of this hollow fiber was observed with an electron microscope at a magnification of 100,000x, it was confirmed that there were multiple micropores in the range of 10 to 100 nm in diameter. Furthermore, when a cross-section perpendicular to the longitudinal direction of the hollow fiber was observed with an electron microscope at a magnification of 1,000x, an area of ​​12,000 μm² was observed. 2 Six finger void structures were observed in the vicinity. Furthermore, the average length of the finger voids present around the entire circumference of the hollow fiber was 40% of the fiber's thickness.

[0059] A bundle of 286 hollow fibers was filled into a cylindrical module case with an inner diameter of 19 mm, as shown in Figure 2. The hollow fibers were fixed by potting both ends of the module case so that the effective length of the hollow fibers was 19 cm. By cutting a portion of the potted area at both ends of the module case, the hollow ends of the hollow fibers were opened, and caps were attached to both ends of the module case to create the module.

[0060] To measure the air permeation rate from the hollow side surface to the outer surface of the hollow fiber, this module was dried in a 50°C dryer for more than 24 hours, and then connected as shown in Figure 4. Air at 20°C was pressurized to 100 kPa and flowed through the gas inlet, and the leak rate was measured. The air permeation rate through the hollow fiber was calculated to be 446 mL / min / cm². 2 The pressure was / MPa. In the hollow portion of the module's hollow fibers, an aqueous solution containing 1.5% by weight of polyacrylic acid with a molecular weight of 1 million was flowed for 30 minutes so that the inside of the hollow fibers was pressurized to 20 kPa, causing the polyacrylic acid to adhere to the surface on the hollow side. Next, with the aqueous solution of the hydrophilic polymer remaining in the hollow portion of the hollow fibers, the module was irradiated with gamma rays at an irradiation dose of 25 kGy. After irradiation, the inside of the hollow portion was washed with 80°C hot water and dried in a 50°C dryer for more than 24 hours to obtain a module filled with hollow fiber membranes.

[0061] To measure the air permeability rate of a hollow fiber membrane coated with a hydrophilic polymer, the connection was made as shown in Figure 4, and the air permeability rate was calculated from the amount of leakage. The result showed an air permeability rate of 1.27 × 10⁻⁶. -1 mL / min / cm 2 Significant improvements were observed in both MPa and air leakage.

[0062] Next, this module was inserted into the dehumidifier case and connected as shown in Figure 5. Saturated air at 20°C was introduced into the gas inlet at a pressure of 0.5 MPa and a flow rate of 180 L / min. The purge air flow rate control valve was adjusted so that the flow rate of purge air flowing outside the hollow fiber membrane was 36 L / min. The dew point of the air coming out of the gas outlet was measured with a dew point meter, and the result showed that the dew point at atmospheric pressure was -14.8°C.

[0063] After dew point evaluation, the hollow fiber membrane was removed from the module, cut into a semi-cylindrical shape using a microtome, and FT-IR was used to analyze the 1590 cm² surface of the hollow portion and the outer surface of the hollow fiber. -1 The peak area Ac=c originates from the benzene ring double bond of the nearby polysulfone, and 1730 cm². -1 By calculating the ratio of the peak area Ac=o (derived from nearby ester bonds) to Ac=c (Ac=o / Ac=c), the adhesion of the hydrophilic polymer was determined, and it was found that the hydrophilic polymer was attached only to the surface on the hollow side.

[0064] (Example 2) 26% by weight of polysulfone (Solvay's "Udel" P-3500) and 9 parts by weight of polyvinylpyrrolidone (BASF's K-30) were heated and dissolved in 64% by weight of N,N-dimethylacetamide and 1% by weight of water to prepare a film-forming stock solution. A solution of 31% by weight of N,N-dimethylacetamide and 69% by weight of water was used as the core solution, and spinning was carried out in the same manner as in Example 1 to obtain hollow fibers. The inner diameter of the obtained hollow fibers was 640 μm, and the film thickness was 88 μm.

[0065] When the hollow surface of this hollow fiber was observed with an electron microscope at a magnification of 100,000x, it was confirmed that there were multiple micropores in the range of 10 to 100 nm in diameter. Furthermore, when a cross-section perpendicular to the longitudinal direction of the hollow fiber was observed with an electron microscope at a magnification of 1,000x, an area of ​​12,000 μm² was observed. 2 Six finger void structures were observed in the vicinity. Furthermore, the average length of the finger voids present around the entire circumference of the hollow fiber was 40% of the hollow fiber's film thickness. A module was fabricated from a bundle of 286 of these hollow fibers using the same procedure as in Example 1. After drying, the bundles were connected as shown in Figure 4. The air permeability of the hollow fibers was measured, and the result was 324 mL / min / cm². 2 The pressure was / MPa. Polyacrylic acid was applied to the hollow side surface of the hollow fibers of this module and γ-ray irradiation was performed using the same procedure as in Example 1 to create a module filled with hollow fiber membranes. To measure the air permeation rate of the hollow fiber membrane, the connection was made as shown in Figure 4, and the air permeation rate was measured using the same procedure as in Example 1. The result showed that the air permeation rate was 5.67 × 10⁻⁶. -2 mL / min / cm 2 It was a small amount, / MPa.

[0066] This module was inserted into the dehumidifier case and connected as shown in Figure 5. The dew point of the air coming out of the gas outlet was measured in the same manner as in Example 1, and the dew point at atmospheric pressure was found to be -14.1°C.

[0067] After evaluating the dew point, the adhesion of the hydrophilic polymer was determined using the same method as in Example 1, and it was found that the hydrophilic polymer was attached only to the surface on the hollow side.

[0068] (Example 3) 27% by weight of polysulfone (Solvay's "Udel" P-3500) and 8 parts by weight of polyvinylpyrrolidone (BASF's K-30) were heated and dissolved in 64% by weight of N,N-dimethylacetamide and 1% by weight of water to prepare a film-forming stock solution. A solution of 31% by weight of N,N-dimethylacetamide and 69% by weight of water was used as the core solution, and spinning was carried out in the same manner as in Example 1 to obtain hollow fibers. The inner diameter of the obtained hollow fibers was 640 μm, and the film thickness was 88 μm.

[0069] When the hollow surface of this hollow fiber was observed with an electron microscope at a magnification of 100,000x, it was confirmed that there were multiple micropores in the range of 10 to 100 nm in diameter. Furthermore, when a cross-section perpendicular to the longitudinal direction of the hollow fiber was observed with an electron microscope at a magnification of 1,000x, an area of ​​12,000 μm² was observed. 2 Six finger void structures were observed in the vicinity. Furthermore, the average length of the finger voids present around the entire circumference of the hollow fiber was 36% of the hollow fiber's film thickness. A module was fabricated from a bundle of 286 of these hollow fibers using the same procedure as in Example 1. After drying, the bundles were connected as shown in Figure 4. The air permeability of the hollow fibers was measured, and the result was 182 mL / min / cm². 2 The pressure was / MPa. Polyacrylic acid was applied to the hollow side surface of the hollow fibers of this module and irradiated with gamma rays using the same procedure as in Example 1, resulting in a module filled with hollow fiber membranes. To measure the air permeation rate of the hollow fiber membrane, the connection was made as shown in Figure 4, and the air permeation rate was measured using the same procedure as in Example 1. The air permeation rate was found to be 7.95 × 10⁻⁶. -3 mL / min / cm 2 / MP was a small thing. This module was inserted into the dehumidifier case and connected as shown in Figure 5. The dew point of the air coming out of the gas outlet was measured in the same manner as in Example 1, and the dew point at atmospheric pressure was found to be -12.2°C.

[0070] After evaluating the dew point, the adhesion of the hydrophilic polymer was determined using the same method as in Example 1, and it was found that the hydrophilic polymer was attached only to the surface on the hollow side.

[0071] (Example 4) 26% by weight of polysulfone (Solvay's "Udel" P-3500) and 8 parts by weight of polyvinylpyrrolidone (BASF's K-30) were heated and dissolved in 65% by weight of N,N-dimethylacetamide and 1% by weight of water to prepare a film-forming stock solution. A solution of 30% by weight of N,N-dimethylacetamide and 70% by weight of water was used as the core solution, and spinning was carried out in the same manner as in Example 1 to obtain hollow fibers. The inner diameter of the obtained hollow fibers was 640 μm, and the film thickness was 90 μm.

[0072] When the hollow surface of this hollow fiber was observed with an electron microscope at a magnification of 100,000x, it was confirmed that there were multiple micropores in the range of 10 to 100 nm in diameter. Furthermore, when a cross-section perpendicular to the longitudinal direction of the hollow fiber was observed with an electron microscope at a magnification of 1,000x, an area of ​​12,000 μm² was observed. 2 Five finger void structures were observed in the vicinity. Furthermore, the average length of the finger voids present around the entire circumference of the hollow fiber was 28% of the hollow fiber's film thickness. A module was fabricated from a bundle of 286 of these hollow fibers using the same procedure as in Example 1. After drying, the bundles were connected as shown in Figure 4. The air permeability of the hollow fibers was measured, and the result was 90 mL / min / cm². 2 The pressure was / MPa. Polyacrylic acid was applied to the hollow side surface of the hollow fibers of this module and irradiated with gamma rays using the same procedure as in Example 1, resulting in a module filled with hollow fiber membranes. To measure the air permeation rate of the hollow fiber membrane, the connection was made as shown in Figure 4, and the air permeation rate was measured using the same procedure as in Example 1. The result showed an air permeation rate of 3.11 × 10⁻⁶. -3 mL / min / cm 2 It was / MPa.

[0073] This module was inserted into the dehumidifier case and connected as shown in Figure 5. The dew point of the air coming out of the gas outlet was measured in the same manner as in Example 1, and the dew point at atmospheric pressure was found to be -12.2°C.

[0074] After evaluating the dew point, the adhesion of the hydrophilic polymer was determined using the same method as in Example 1, and it was found that the hydrophilic polymer was attached only to the surface on the hollow side.

[0075] (Example 5) In Example 3, a module filled with hollow fibers was prepared, and the same module was used. An aqueous solution of 1.5% by weight of polyacrylic acid with a molecular weight of 1 million was dissolved in it as a hydrophilic polymer. This solution was then flowed onto both the hollow and outer sides of the hollow fibers under pressure of 20 kPa for 30 minutes, causing the polyacrylic acid to adhere to both the hollow and outer surfaces. Next, with the hydrophilic polymer aqueous solution remaining on the hollow and outer sides of the hollow fibers, the module was irradiated with gamma rays at a dose of 25 kGy. After irradiation, the hollow and outer sides of the hollow fibers were washed with 80°C hot water and dried in a 50°C dryer for 24 hours or more to obtain a module filled with hollow fiber membranes.

[0076] To measure the air permeation rate of the hollow fiber membrane, the connection was made as shown in Figure 4, and the air permeation rate was measured using the same procedure as in Example 1. The result was 4.08 × 10⁻⁶. -3 mL / min / cm 2 It was / MPa.

[0077] This module was inserted into the dehumidifier case and connected as shown in Figure 5. The dew point of the air coming out of the gas outlet was measured in the same manner as in Example 1, and the dew point at atmospheric pressure was found to be -13.2°C.

[0078] After evaluating the dew point, the presence of hydrophilic polymer was determined using the same method as in Example 1, and it was found that hydrophilic polymer was attached to both the surface on the hollow side and the outer surface.

[0079] (Comparative Example 1) A film-forming stock solution was prepared by heating and dissolving 27% by weight of polysulfone (Solvay's "Udel" P-3500) and 13.5 parts by weight of polyvinylpyrrolidone (BASF's K-30) in 58.5% by weight of N,N-dimethylacetamide and 1% by weight of water. A core solution was prepared using 30.5% by weight of N,N-dimethylacetamide and 69.5% by weight of water.

[0080] The film-forming solution was sent to the spinneret section and discharged from the outer tube of the orifice-type double-tube spinneret, while the core solution was discharged from the inner tube. The discharged film-forming solution passed through a dry zone atmosphere with a dew point of 30°C, then solidified in a 100% water coagulation bath, and underwent a water washing process at 80°C for 2 minutes. The resulting wet hollow fibers were wound up and cut into bundles of 286 hollow fibers. These bundles were washed in an 80°C water bath for 1 hour, and then dried in a dry heat dryer at 50°C for 24 hours to obtain hollow fibers. The inner diameter of the obtained hollow fibers was 640 μm, and the film thickness was 105 μm.

[0081] When the hollow surface of this hollow fiber was observed with an electron microscope at a magnification of 100,000x, it was confirmed that there were multiple micropores in the range of 10 to 100 nm in diameter. Furthermore, when the cross section perpendicular to the longitudinal direction of the hollow fiber was observed with an electron microscope, an area of ​​12,000 μm² was found. 2 Four finger void structures were observed in the area. The average length of the finger voids present around the entire circumference of the hollow fiber was 14% of the fiber's thickness.

[0082] A module was fabricated from this bundle of hollow fibers using the same procedure as in Example 1, and after drying, it was connected as shown in Figure 4. The air permeation rate of the hollow fibers was measured, and the air permeation rate was found to be 2.75 × 10⁻⁶. -3 mL / min / cm 2 The dew point was small even without the attachment of hydrophilic polymer at / MPa. When this module was inserted into the dehumidifier case and connected as shown in Figure 5, the dew point of the air coming out of the gas outlet was measured in the same manner as in Example 1, and the dew point at atmospheric pressure was -9.8°C.

[0083] After evaluating the dew point, the presence of hydrophilic polymer was determined using the same method as in Example 1, and it was found that no hydrophilic polymer was attached to the hollow fibers.

[0084] (Comparative Example 2) A film-forming stock solution was prepared by heating and dissolving 18% by weight of polysulfone (Solvay's "Udel" P-3500) and 7 parts by weight of polyvinylpyrrolidone (BASF's K-30) in 74% by weight of N,N-dimethylacetamide and 1% by weight of water. A solution of 34% by weight of N,N-dimethylacetamide and 66% by weight of water was used as the core solution.

[0085] The film-forming solution was sent to the spinneret section and discharged from the outer tube of the orifice-type double-tube spinneret, while the core solution was discharged from the inner tube. The discharged film-forming solution passed through a dry zone atmosphere with a dew point of 30°C, then solidified in a 100% water coagulation bath, and underwent a water washing process at 80°C for 2 minutes. The resulting wet hollow fibers were wound up and cut into bundles of 286 hollow fibers. These bundles were washed in an 80°C water bath for 1 hour, and then dried in a dry heat dryer at 50°C for 24 hours to obtain hollow fibers. The inner diameter of the obtained hollow fibers was 640 μm and the film thickness was 95 μm.

[0086] When the hollow surface of this hollow fiber was observed with an electron microscope at a magnification of 100,000x, it was confirmed that there were multiple micropores in the range of 10 to 100 nm in diameter. Furthermore, when the cross section perpendicular to the longitudinal direction of the hollow fiber was observed with an electron microscope, an area of ​​12,000 μm² was found. 2 Nine finger void structures were observed in the vicinity. Furthermore, the average length of the finger voids present around the entire circumference of the hollow fiber was 65% of the thickness of the hollow fiber, indicating a high ratio of finger void length to thickness.

[0087] A module was fabricated from this bundle of hollow fibers using the same procedure as in Example 1, dried, and then connected as shown in Figure 4. The air permeation rate of the hollow fibers was measured, and the result was 629 mL / min / cm². 2 The pressure was / MPa. Polyacrylic acid was applied to the hollow side surface of the hollow fibers of this module and irradiated with gamma rays using the same procedure as in Example 1, resulting in a module filled with hollow fiber membranes. To measure the air permeation rate of the hollow fiber membrane, it was connected as shown in Figure 4, and the air permeation rate was measured using the same procedure as in Example 1. The air permeation rate was found to be 9.33 mL / min / cm². 2The pressure was high at / MPa, indicating a significant amount of air leakage.

[0088] This module was inserted into the dehumidifier case and connected as shown in Figure 5. The dew point of the air coming out of the gas outlet was measured in the same manner as in Example 1, and the dew point at atmospheric pressure was found to be -11.6°C.

[0089] After evaluating the dew point, the adhesion of the hydrophilic polymer was determined using the same method as in Example 1, and it was found that the hydrophilic polymer was attached only to the surface on the hollow side.

[0090] [Table 1]

[0091] [Table 2] [Explanation of Symbols]

[0092] 1: Finger Void 2: Finger void length 3: Hollow fibers, hollow fiber membranes 4: Potting Department 5: Cylindrical module case 6: Cap 7: Modules 8: Gas inlet 9: Gas outlet 10: Purge air inlet 11: Purge air outlet 12: Dehumidifier Case 13: Purge air flow control valve 14: Stopcock 15, 22: Pressure gauge 16: Flow control valve 17, 18, 19: Flowmeter 20, 21: Dew point meter

Claims

1. A hollow fiber membrane made of hollow fibers and a hydrophilic polymer, The hollow fiber contains a hydrophobic polymer and has at least micropores. The surface of the hollow portion of the hollow fiber contains the hydrophilic polymer, The hydrophilic polymer is a polymer having at least one of acrylic acid, vinyl sulfate, and vinylpyrrolidone as a hydrophilic unit, The hollow fiber has a plurality of finger voids, A hollow fiber membrane characterized in that, in all of the finger voids, the length of the finger void in the film thickness direction of the hollow fiber is 20 to 50% of the film thickness of the hollow fiber.

2. The air permeation rate from the hollow side surface to the outer surface of the hollow fiber membrane is 3.00 × 10⁻⁶ －３ ~2.00 x 10 －１ mL / min / cm ２ The hollow fiber membrane according to claim 1, characterized in that it is / MPa.

3. The hollow fiber membrane according to any one of claims 1 to 2, characterized in that the outer surface of the hollow fiber does not contain the hydrophilic polymer.

4. The air permeation rate from the hollow side surface to the outer surface of the hollow fiber is 170–500 mL / min / cm². ２ A hollow fiber membrane according to any one of claims 1 to 3, characterized in that it is / MPa.

5. A hollow fiber membrane according to any one of claims 1 to 4, characterized in that it is used for dehumidification purposes.

6. A dehumidifier comprising the hollow fiber membrane described in claim 5 in a dehumidifier case.

7. A dehumidifier comprising a hollow fiber membrane in a dehumidifier case, The dehumidifier case has a supply port for supplying the air to be dehumidified to the hollow part of the hollow fiber membrane, The dehumidifier case has an outlet for discharging the dehumidified air, The dehumidifier according to claim 6, wherein the dehumidifier case has a purge air supply port for supplying a portion of the dehumidified air to the outer surface of the hollow fiber membrane as purge air at a lower pressure than the air flowing through the hollow portion of the hollow fiber membrane, and a purge air outlet for discharging the purge air to the outside of the case.

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