Hollow fiber membrane and method for producing the same

Abstract

The present invention relates to a hollow fiber membrane comprising, in order from the center, a first layer with a high-density sponge structure containing pores of 1 nm or less, a second layer with a finger-like structure, and a third layer with a low-density sponge structure containing pores of 10 to 1,000 μm in size, and a method for producing the same.

Description

Technical Field

[0001] The present invention relates to a hollow fiber membrane and a method for manufacturing the same, and more specifically, to a hollow fiber membrane preferably used in a humidifying device of a fuel cell system and a method for manufacturing the same.

Background Art

[0002] In recent years, methods of performing humidification or dehumidification using a water vapor permeable membrane have attracted attention. The humidification and dehumidification methods using a water vapor permeable membrane have advantages such as no need for maintenance and no need for a separate power source for driving.

[0003] A hollow fiber membrane in which the water vapor permeable membrane is hollow is used for diaphragm humidification of a fuel cell stack. In the case of a fuel cell, humidification is required for a large air flow rate of about 4,000 NL / min for in-vehicle use. Therefore, the humidifying hollow fiber membrane is required to have high water vapor permeability and high hollow fiber membrane strength. The humidifying hollow fiber membrane requires gas barrier properties to prevent air leakage from the hollow fiber and also must have water vapor permeability. Therefore, the membrane of the hollow fiber is made into a porous membrane having very fine diameter voids, and by pressurizing this, a desired water vapor permeation amount can be obtained. Also, the air flow rate varies greatly depending on the driving location and driving method. For example, when driving in an urban area, a low flow rate may be sufficient, but a high flow rate is required on mountain roads or during sudden acceleration.

[0004] As the humidifying hollow fiber membrane, membranes using various types of polymers have been proposed. As an example, there is a humidifying hollow fiber membrane using a polyimide resin as a material. The characteristics of this membrane are that it is excellent in heat resistance, durability, and gas barrier properties. On the other hand, it has a drawback of low water vapor permeability.

[0005] Also, the humidifying hollow fiber membrane using a fluorine-based ion exchange membrane has higher water vapor permeability and gas barrier properties than the humidifying hollow fiber membrane using a polyimide resin as a material. On the other hand, it does not have sufficient water vapor permeability for actual use as a humidifying hollow fiber membrane, is also poor in heat resistance, and the price of the hollow fiber membrane itself is very high.

[0006] Depending on the method of manufacturing the hollow fiber membrane, it is manufactured using the non-solvent induced phase separation method (Non-solvent Induced Phase Separation: NIPS) or the thermally induced phase separation method (Thermally Induced Phase Separation: TIPS).

[0007] According to the non-solvent induced phase separation method, a spinning solution in which a polymer resin is dissolved in a good solvent is discharged through a die, and the discharged spinning solution is brought into contact with a liquid containing a non-solvent to induce solidification of the spinning solution and produce a membrane.

[0008] According to the thermally induced phase separation method, a spinning solution is produced by forcibly dissolving a polymer resin in a poor solvent at a temperature equal to or higher than the phase separation temperature. This spinning solution is discharged through a die, and the discharged spinning solution is brought into contact with a coolant at a temperature lower than the phase separation temperature to solidify the spinning solution and produce a membrane.

[0009] However, the hollow fiber membrane produced by the non-solvent induced phase separation method does not have the bead structure exhibited in the case of the thermally induced phase separation method, and has a three-dimensional network structure including macrovoids, so there is a drawback that the tensile strength is insufficient. The hollow fiber membrane produced by the thermally induced phase separation method does not contain macrovoids and has a bead structure that is symmetric in the membrane thickness direction. Therefore, the mechanical strength of the membrane is high, but it has a drawback that it is difficult to control the pore size and the separation characteristics are low.

[0010] Therefore, for the commercialization of hollow fiber membranes, it is necessary to improve the tensile strength together with high water diffusion performance to improve the physical and mechanical properties. For this purpose, it is required to ensure the optimal structure of the hollow fiber membrane. Summary of the Invention Problems to be Solved by the Invention

[0011] An object of the present invention is to provide a hollow fiber membrane having excellent tensile strength and moisture diffusion characteristics.

[0012] Another object of the present invention is to provide a method for manufacturing the hollow fiber membrane.

Means for Solving the Problems

[0013] One embodiment of the present invention provides a hollow fiber membrane including, in order from the center, a first layer having a high-density sponge structure including pores of 1 nm or less, a second layer including a finger-like structure, and a third layer having a low-density sponge structure including pores with a size of 10 to 1,000 μm.

[0014] The thickness of the first layer may be 1 to 40 μm, the thickness of the second layer may be 20 to 60 μm, and the thickness of the third layer may be 20 to 50 μm.

[0015] The hollow fiber membrane may have a water vapor permeability of 0.1 g / s / m or more measured under a pressure of 1 bar and a temperature of 80°C. 2 or more.

[0016] The hollow fiber membrane may have a nitrogen permeability of 100 cc / min / cm or less at a pressure of 0.7 bar. 2 or less.

[0017] The hollow fiber membrane may have an oxygen permeability of 100 cc / min / cm or less at a pressure of 0.7 bar. 2 or less.

[0018] The hollow fiber membrane may have a tensile strength of 100 gf / fiber or more.

[0019] Each of the first layer to the third layer may independently include one or more selected from the group consisting of polyethersulfone, polyphenylsulfone, polysulfone, polyvinylidene fluoride, polyimide, polyetherimide, polyamide, polyacrylonitrile, and cellulose acetate.

[0020] The inner diameter of the hollow fiber membrane can be 600 to 1,400 μm, and the outer diameter can be 1,000 to 2,000 μm.

[0021] Another embodiment of the present invention provides a method for manufacturing a hollow fiber membrane, including steps of mixing a non-solvent, a poor solvent and a polymer resin to produce a first spinning solution, mixing a non-solvent, a good solvent and a polymer resin to produce a second spinning solution, spinning the first spinning solution using a thermally induced phase separation method to produce a hollow first layer, passing the spun support through a mixed solvent of a good solvent and a non-solvent, and discharging the first layer and the second spinning solution through a die to form a second layer and a third layer by a non-solvent induced phase separation method.

[0022] The first spinning solution can contain 45% to 70% by weight of the polymer resin, and the second spinning solution can contain 15% to 40% by weight of the polymer resin.

[0023] The polymer resin can include one or more selected from the group consisting of polyethersulfone, polyphenylsulfone, polysulfone, polyvinylidene fluoride, polyimide, polyetherimide, polyamide, polyacrylonitrile, and cellulose acetate.

[0024] The non-solvent can include one or more selected from the group consisting of water, methanol, ethanol, isopropanol, acetone, hexane, pentane, benzene, toluene, carbon tetrachloride, o-dichlorobenzene, and polyethylene glycol.

[0025] The good solvent can include one or more selected from the group consisting of N-methyl-2-pyrrolidone, dimethyl sulfoxide, dimethylacetamide, dimethylformamide, methyl ethyl ketone, tetrahydrofuran, tetramethyl urea, and trimethyl phosphate.

[0026] The poor solvent can include one or more selected from the group consisting of butanol, isobutanol, octanol, pentanol, isopentanol, dimethyl phthalate, diethyl phthalate, dibutyl phthalate, dioctyl phthalate, and polyoxyethylene octylphenyl ether.

[0027] The first spinning solution and the second spinning solution can each independently further include one or more hydrophilic additives selected from the group consisting of polyvinylpyrrolidone, polyethylene glycol, polyethylene oxide, glycerin, diethyl glycol, and triethylene glycol.

[0028] The first spinning solution and the second spinning solution can each independently further include one or more nonionic surfactants selected from the group consisting of polyoxyethylene alkyl ether, fatty acid sorbitan ester, and alkyl monoglyceryl ether.

Advantages of the Invention

[0029] The hollow fiber membrane according to the present invention includes pores of 1 nm or less, a first layer which is an internal support layer having a high-density sponge structure, a second layer which is an intermediate layer including a finger-like structure, and pores of 10 to 1,000 μm in size, and all includes a third layer which is an outer layer having a low-density sponge structure, so it has excellent moisture diffusion characteristics. Further, the hollow fiber membrane according to the present invention has, on both side surfaces of the second layer including the finger-like structure, both the first layer including the high-density sponge structure and the third layer including the low-density sponge structure, so there is an effect that the tensile strength is further improved.

Brief Description of the Drawings

[0030]

Figure 1

Best Mode for Carrying Out the Invention

[0031] Hereinafter, embodiments of the present invention will be described in detail so that those having ordinary knowledge in the technical field to which the present invention pertains can easily implement it. However, the present invention can be embodied in various different forms and is not limited to the embodiments described herein.

[0032]

[0033] Hereinafter, a hollow fiber membrane according to an embodiment will be described.

[0034] The present invention relates to a humidifying hollow fiber membrane having excellent mechanical strength, high hydrophilicity, high water diffusivity, and low gas permeability such as nitrogen or oxygen.

[0035] The hollow fiber membrane 100 according to an embodiment of the present invention includes, in order from the center, a first layer 10 having a high-density sponge structure containing pores of 1 nm or less, a second layer 20 having a finger-like structure, and a third layer 30 having a low-density sponge structure containing pores with a size of 10 to 1,000 μm.

[0036] The inventors formed a first layer 10, which is an internal support layer having an extremely dense sponge structure, by discharging a spinning solution containing a high content of a polymer resin using a thermally induced phase separation method, supported this on a mixed solvent of a non-solvent and a good solvent, and then discharged this together with the spinning solution by a non-solvent induced phase separation method, thereby obtaining a hollow fiber membrane having the three-layer structure as described above.

[0037] The hollow fiber membrane 100 of the present invention can impart excellent mechanical strength to the hollow fiber membrane by including a high-density sponge structure in the first layer 10 which is an internal support layer, and can provide excellent water dispersion characteristics through the second layer 20 which is an intermediate layer including a finger structure and the third layer 30 which is an outer layer including a low-density sponge structure. Therefore, the "high density" and "low density" of the high-density sponge structure of the first layer 10 and the low-density sponge structure of the third layer 30 may mean the relative density between the two layers. When the first layer 10 can sufficiently impart the mechanical strength of the hollow fiber membrane and the third layer 30 has excellent water dispersion characteristics for easy entry and rapid transmission of water molecules, the absolute numerical values of these densities are not particularly limited and can be appropriately selected by those skilled in the art.

[0038] Specifically, the first layer 10 of the hollow fiber membrane 100 is located closest to the center of the hollow fiber membrane and has a high-density sponge structure including fine pores with a size of 1 nm or less. By serving as the internal support layer of the hollow fiber membrane in this way, excellent mechanical strength can be imparted. Here, the sponge structure may be understood as a three-dimensional network structure formed by connecting a large number of pores to each other.

[0039] In one embodiment, the first layer 10 can be formed in the hollow fiber membrane 100 of the present invention at 1 μm to 40 μm, preferably 10 μm to 20 μm. When the thickness of the internal support layer is less than 1 μm, sufficient physical and mechanical properties are not imparted to the hollow fiber membrane, so the tensile strength of the hollow fiber membrane may decrease. When it exceeds 40 μm, it is difficult to control the pore size and the water dispersibility of the hollow fiber membrane may excessively decrease.

[0040] Next, the second layer 20, which is an intermediate layer including a finger-like structure, provides macrovoids in the hollow fiber membrane 100 of the present invention, thereby reducing the flow path resistance of water molecules and increasing the permeation flow rate. As a result, it plays a role in imparting excellent water dispersion characteristics. The second layer 20 including the finger-like structure is located between the first layer 10 and the third layer 30 which is the outer layer in the hollow fiber membrane 100 of the present invention. Here, the finger-like structure can be understood as an array of vertical internal defects similar to the shape of a finger, and in the process of forming the hollow fiber membrane, it means a finger-like structure formed inside when the solvent and additives inside the spinning solution suddenly escape due to a rapid phase transition rate. Since the finger-like structure is formed at a rapid phase transition rate, the second layer including the finger-like structure can also include a dense region together with the finger-like structure. According to an embodiment of the present invention, the second layer, due to such a finger-like structure, not only reduces the flow path resistance of water molecules and increases the permeation flow rate, but also has the advantage that the nitrogen permeability and oxygen permeability other than water vapor can be reduced by the dense region.

[0041] In one embodiment, the second layer 20 can be formed in the hollow fiber membrane 100 of the present invention with a thickness of 20 μm to 60 μm, preferably 35 μm to 50 μm. When the thickness of the second layer 20 is less than 20 μm, macrovoids may not be sufficiently ensured in the hollow fiber membrane, so the water dispersion characteristics may decrease. When it exceeds 60 μm, there may be a problem that the mechanical properties in the thickness direction of the hollow fiber membrane decrease.

[0042] Next, the third layer 30, which is the outer layer formed next, is located on the outermost side of the hollow fiber membrane 100 of the present invention and has a low-density sponge structure including fine pores with a size of 10 μm to 1,000 μm. Thereby, it is easy for water molecules to enter the hydrophobic part on the outside of the hollow fiber membrane, and it plays a role in quickly transmitting water molecules to the second layer 20 including the finger-like structure in contact with the third layer 30.

[0043] In one embodiment, the third layer 30 can be formed in the hollow fiber membrane 100 of the present invention at 20 μm to 50 μm, preferably 30 μm to 50 μm.

[0044] In one embodiment, the hollow fiber membrane 100 has a water vapor permeability of 0.1 g / s / m 2 or more, preferably 0.3 g / s / m 2 or more, measured under a pressure of 1 bar and a temperature of 80°C. The water vapor permeability is an index indicating the water vapor permeation performance. When the water vapor permeability is 0.1 g / s / m 2 or more, optimal humidification for the fuel cell stack can be performed, so that water vapor can be stably supplied, and the electrolyte membrane performance of the fuel cell stack can be fully exerted.

[0045] In one embodiment, the hollow fiber membrane 100 has a nitrogen permeability of 100 cc / min / cm at a pressure of 0.7 bar 2 or less, for example 80 cc / min / cm 2 or less, for example 50 cc / min / cm 2 or less, for example 30 cc / min / cm 2 or less, preferably 20 cc / min / cm 2 or less. This is because when the nitrogen permeability exceeds 100 cc / min / cm 2 the water vapor permeation performance of the hollow fiber membrane may substantially decrease.

[0046] In one embodiment, the hollow fiber membrane 100 has an oxygen permeability of 100 cc / min / cm at a pressure of 0.7 bar 2 or less, for example 80 cc / min / cm 2 or less, for example 50 cc / min / cm 2 or less, for example 30 cc / min / cm 2 or less, preferably 20 cc / min / cm 2 or less. This is because when the oxygen permeability exceeds 100 cc / min / cm 2 the water vapor permeation performance of the hollow fiber membrane may substantially decrease.

[0047] In one embodiment, the hollow fiber membrane 100 may have a tensile strength of 100 gf / fiber or more, for example, 200 gf / fiber or more, for example, 250 gf / fiber or more, preferably 300 gf / fiber or more. By including a high-density sponge structure in the internal support layer of the hollow fiber membrane, the mechanical and physical properties of the hollow fiber membrane 100 of the present invention are improved, and a tensile strength satisfying the above range can be ensured.

[0048] In one embodiment, each of the first layer 10 to the third layer 30 may independently include one or more selected from the group consisting of polyethersulfone, polyphenylsulfone, polysulfone, polyvinylidene fluoride, polyimide, polyetherimide, polyamide, polyacrylonitrile, and cellulose acetate. For example, polyethersulfone, polyphenylsulfone, polysulfone, and polyvinylidene fluoride can be used. However, the present invention is not limited thereto as long as it is a polymer resin that can be used for the hollow fiber membrane to achieve the intended effects of the present invention.

[0049] In one embodiment, the inner diameter of the hollow fiber membrane 100 is 600 to 1,400 μm, and the outer diameter may be 1,000 to 2,000 μm. When the inner diameter and outer diameter of the hollow fiber membrane satisfy the above range, excellent moisture diffusion characteristics as a hollow fiber membrane for humidification can be ensured.

[0050] Another embodiment of the present invention provides a method for manufacturing a hollow fiber membrane, including steps (S1) of mixing a non-solvent, a poor solvent, and a polymer resin to produce a first spinning solution, and mixing a non-solvent, a good solvent, and a polymer resin to produce a second spinning solution; (S2) spinning the first spinning solution using a thermally induced phase separation method to produce a hollow first layer 10; (S3) passing the spun support through a mixed solvent of a good solvent and a non-solvent; and (S4) discharging the first layer 10 and the second spinning solution through a die to form a second layer 20 and a third layer 30 by a non-solvent induced phase separation method.

[0051] First, the step (S1) is a step of preparing a spinning solution for manufacturing the hollow fiber membrane of the present invention. The hollow fiber membrane 100 of the present invention can use a first spinning solution and a second spinning solution related to each process by sequentially using the thermal induced phase separation method and the non-solvent induced phase separation method in combination.

[0052] The first spinning solution contains a non-solvent, a poor solvent, and a polymer resin, and the second spinning solution contains a non-solvent, a good solvent, and a polymer resin.

[0053] First, a polymer resin is dissolved in a mixed solvent of a poor solvent and a non-solvent to produce a first spinning solution.

[0054] In one embodiment, the polymer resin can include one or more selected from the group consisting of polyethersulfone, polyphenylsulfone, polysulfone, polyvinylidene fluoride, polyimide, polyetherimide, polyamide, polyacrylonitrile, and cellulose acetate. For example, polyethersulfone, polyphenylsulfone, polysulfone, and polyvinylidene fluoride can be used. However, as long as it is a polymer resin that can be used for the hollow fiber membrane to achieve the effects targeted in the present invention, it is not limited to this.

[0055] In one embodiment, the first spinning solution can contain 45 wt% to 70 wt% of the polymer resin, for example, 50 wt% to 70 wt%, preferably 60 wt% to 70 wt%. When the polymer resin content of the first spinning solution is less than 45 wt%, the mechanical strength of the hollow fiber membrane may become weak. When it exceeds 70 wt%, not only does the viscosity of the first spinning solution become too high and spinning becomes difficult, but also the formation of the first layer 10, which is an internal support layer with a small pore size, may become difficult, and there is a burden of having to raise the temperature of the poor solvent to dissolve a large amount of the polymer resin.

[0056] The poor solvent refers to a solvent that cannot sufficiently dissolve the selected polymer resin at room temperature (25°C), and can only be dissolved when heated to a high temperature, specifically 100°C or higher. In the present invention, the polymer resin can be sufficiently dissolved at a temperature of 100°C to 150°C.

[0057] In one embodiment, the poor solvent is included in the first spinning solution and may include one or more selected from the group consisting of butanol, isobutanol, octanol, pentanol, isopentanol, dimethyl phthalate, diethyl phthalate, dibutyl phthalate, dioctyl phthalate, and polyoxyethylene octyl phenyl ether, but is not necessarily limited thereto. The poor solvent may be included at 20% to 50% by weight based on the total weight of the first spinning solution. When the content of the poor solvent is less than 20% by weight, not only is the viscosity of the first spinning solution too high and spinning becomes difficult, but there is also a burden of having to raise the temperature of the poor solvent to dissolve a large amount of the polymer resin. When it exceeds 50% by weight, the strength of the hollow fiber membrane may become too low.

[0058] The non-solvent refers to a solvent that cannot dissolve the selected polymer resin in all temperature ranges. In one embodiment, the non-solvent is included in the first spinning solution and the second spinning solution and may include one or more selected from the group consisting of water, methanol, ethanol, isopropanol, acetone, hexane, pentane, benzene, toluene, carbon tetrachloride, o-dichlorobenzene, and polyethylene glycol, but is not necessarily limited thereto. The content of the non-solvent may be 1% to 10% by weight based on the total weight of the first spinning solution. When the content of the non-solvent is less than 1% by weight, the strength of the hollow fiber membrane may decrease. When it exceeds 10% by weight, it may become difficult to form pores in the internal support layer of the hollow fiber membrane.

[0059] Next, a second spinning solution is prepared by dissolving the polymer resin in a mixed solvent of a good solvent and a non-solvent.

[0060] The second spinning solution can contain 15% to 40% by weight of the polymer resin, for example, it can contain 20% to 40% by weight, preferably 20% to 30% by weight. When the content of the polymer resin in the second spinning solution is less than 15% by weight, the porosity of the hollow fiber membrane may be too low. When it exceeds 40% by weight, the porosity of the first layer 10 which is the internal active layer and the third layer 30 which is the outer layer becomes too high, and there may arise a problem that the mechanical strength of the entire hollow fiber membrane is inhibited.

[0061] Specific examples of the polymer resin are as described above. The same type of polymer resin as that contained in the first spinning solution can be used, or different types can be used.

[0062] In one embodiment, the good solvent is contained in the second spinning solution, and may include one or more selected from the group consisting of N-methyl-2-pyrrolidone, dimethyl sulfoxide, dimethylacetamide, dimethylformamide, methyl ethyl ketone, tetrahydrofuran, tetramethyl urea, and trimethyl phosphate, but is not necessarily limited thereto. The good solvent can be contained in an amount of 30% to 60% by weight based on the total weight of the second spinning solution. When the content of the good solvent is less than 30% by weight, not only does the viscosity of the second spinning solution become too high and spinning becomes difficult, but there is also a burden of having to raise the temperature of the good solvent for smooth dissolution of the polymer resin. When it exceeds 60% by weight, the viscosity of the second spinning solution becomes too low and the spinnability may decrease.

[0063] Specific examples of the non-solvent are as described above. The same type of non-solvent as that contained in the first spinning solution can be used, or different types can be used.

[0064] In one embodiment, the first spinning solution and the second spinning solution can each independently further contain a hydrophilic additive that plays a role in forming pores in the hollow fiber membrane. For example, they can further contain one or more hydrophilic additives selected from the group consisting of polyvinylpyrrolidone, polyethylene glycol, polyethylene oxide, glycerin, diethyl glycol, and triethylene glycol.

[0065] The hydrophilic additive can be contained in an amount of 5% to 25% by weight based on the total weight of each spinning solution. If the content of the additive is less than 5% by weight, pore formation in the hollow fiber membrane may not proceed smoothly. If it exceeds 25% by weight, phase separation of the spinning solution may proceed rapidly, and yarn breakage may occur during the spinning process.

[0066] In one embodiment, the first spinning solution and the second spinning solution can each independently further contain one or more nonionic surfactants selected from the group consisting of polyoxyethylene alkyl ether, fatty acid sorbitan ester, and alkyl monoglyceryl ether.

[0067] There is no special manufacturing procedure in the manufacturing process of the first spinning solution and the second spinning solution.

[0068] Next, the step (S2) is a step of forming a first layer 10, which is an internal support layer containing a high-density sponge structure, by using the first spinning solution and the thermal-induced phase separation method.

[0069] Specifically, in the step (S2), the first layer 10, which is an internal support layer, can be formed by discharging a first spinning solution obtained by mixing a non-solvent, a poor solvent, and a polymer resin through a die at a spinning temperature of 100°C to 300°C. The first layer 10 can form a hollow fiber membrane with good water diffusivity and very excellent mechanical strength by forming a first spinning solution containing a high content of polymer resin by the thermal-induced phase separation method.

[0070] The discharge rate of the first spinning solution can be adjusted to about 10 to 60 g / min.

[0071] In the step of discharging the first spinning solution through a die composed of, for example, a double tube, a mixed solution can be discharged into the hollow interior of the spun material. At this time, the mixed solution may contain a good solvent and a non-solvent. Specific examples of the good solvent and the non-solvent are as described above. Thus, by discharging the mixed solution into the hollow interior of the spun material, the morphology of the hollow fiber membrane can be obtained more easily.

[0072] The spun material discharged through the die can be solidified by contacting a mixed solvent in step (S3) described later through an air gap. The air gap is mainly an air layer or an inert gas layer. At this time, the length of the air gap can be maintained at 0.1 to 15 cm.

[0073] The first layer 10 formed through the step (S2) serves as an internal support layer in the hollow fiber membrane 100 of the present invention. The hollow fiber membrane produced through the step (S2) may have an inner diameter of about 600 to 1,400 μm and an outer diameter of 1,000 to 2,000 μm.

[0074] Next, in step (S3), the support spun in the step (S2) is brought into contact with a mixed solvent of a good solvent and a non-solvent to be solidified.

[0075] The mixed solvent may be in a state cooled to, for example, 5°C to 25°C, and serves to solidify the support spun in the step (S2). Specific examples of the good solvent and the non-solvent contained in the mixed solvent are as described above.

[0076] Next, in step (S4), the first layer 10 solidified in the step (S3) and the second spinning solution are discharged through a die to form a second layer 20, which is an intermediate layer of the hollow fiber membrane, and a third layer 30, which is an outer layer, by a non-solvent-induced phase separation method.

[0077] The said spinneret can be composed of, for example, a double tube composed of two tubes. Therefore, the first layer 10 and the second spinning solution formed through the said step (S3) are separately supplied by being separated to the spinneret composed of the double tube. In particular, by supplying the first layer 10 to the inside of the spinneret and the second spinning solution to the outside of the spinneret, the inner surface of the obtained spun product can be composed of the first layer 10, and the outer surface can be composed of the spun product of the second spinning solution.

[0078] The spun product discharged through the said spinneret can be solidified through an air gap. The said air gap is mainly an air layer or an inert gas layer. At this time, the length of the air gap can be maintained at 1 to 50 cm.

[0079]

[0080] Through the said step (S4), the mixed solvent of the non-solvent and the good solvent adhering to the outside of the first layer 10 in the said step (S3) and the second spinning solution come into contact with each other during the spinning process, and a rapid phase transition occurs. As a result, the second layer 20, which is an intermediate layer with a finger structure, is quickly formed on the outer surface of the support layer. At this time, the said mixed solvent serves as the role of the bore liquid in the spinning process of the hollow fiber membrane. The moment it is discharged from the nozzle of the spinneret composed of a double tube, the solvent contained in the second spinning solution and the non-solvent contained in the said mixed solvent are instantaneously replaced during the process of coming into contact with the second spinning solution, and through the process of solidification, an intermediate layer with a finger structure is formed. Then, the second spinning solution discharged through the nozzle of the spinneret forms the third layer 30, which is an outer layer having a low-density sponge structure, as a result of the non-solvent and the second spinning solution reacting with each other and undergoing a phase transition during the process of coming into contact with moisture during the process of passing through the air gap.

[0081] In the said step (S4), specific examples of the non-solvent and the good solvent of the second spinning solution are as described above.

Embodiments for Carrying Out the Invention

[0082] The present invention will be specifically described through the following examples and comparative examples. However, the following examples are only for helping to understand the present invention, and the scope of rights of the present invention is not limited thereby.

[0083]

[0084] [Examples]

[0085] 65% by weight of polyphenyl sulfone (PPSu), 20% by weight of isobutanol, 10% by weight of polyethylene glycol (PEG 200), and 5% by weight of triton x-10 as a nonionic surfactant were mixed and stirred at 150 °C for 24 hours to produce a first spinning solution.

[0086] 28% by weight of polyphenyl sulfone, 25% by weight of polyethylene glycol (PEG 200), 45.5% by weight of a solvent, and 1.5% by weight of triton x-10 as a nonionic surfactant were mixed and stirred at 150 °C for 24 hours to produce a second spinning solution.

[0087] The produced first spinning solution was discharged through a spinneret composed of a double tube to obtain a spun fiber. At this time, a mixed solution at 25 °C composed of 80% by weight of dimethylacetamide (DMAc) and 20% by weight of polyethylene glycol (PEG) was supplied and discharged inside the spinneret composed of the double tube, and the spinning solution was supplied and discharged outside the spinneret composed of the double tube.

[0088] The spun fiber was passed through an air gap having a length of 5 cm and then immersed in a coagulating liquid in a coagulation bath. The coagulating liquid used a mixed solvent of N-methyl-2-pyrrolidone and water at 25 °C.

[0089] The hollow fiber membrane obtained by coagulation in the coagulation bath was continuously discharged again through a spinneret composed of a double tube.

[0090] At this time, the hollow fiber membrane formed through the first spinning solution of the spinneret composed of the double tube was supplied and discharged, and the second spinning solution was supplied and discharged outside the spinneret composed of the double tube.

[0091] After that, it was washed with pure water at 25°C, then subjected to hot water treatment using a post-treatment liquid at 80°C containing water and glycerin, and then dried to obtain a hollow fiber membrane.

[0092]

[0093] [Comparative Example]

[0094] 65 wt% of polyphenylsulfone (PPSu), 20 wt% of isobutanol, 10 wt% of polyethylene glycol (PEG 200), and 5 wt% of triton x-10 as a non-ionic surfactant were mixed and stirred at 150°C for 24 hours to produce a first spinning solution.

[0095] The spinning solution thus produced was discharged through a spinneret composed of a double tube to obtain a spun product. During the step of discharging the spinning solution, a mixed solution at 25°C composed of 80 wt% of dimethylacetamide (DMAc) and 20 wt% of polyethylene glycol (PEG) was discharged into the hollow interior of the spun product.

[0096] The spun product was passed through an air gap having a length of 30 cm and then immersed in a coagulation liquid in a coagulation bath. The coagulation liquid used was water at 50°C.

[0097] The spun product obtained by coagulation in the coagulation bath was washed with pure water at 50°C, then subjected to hot water treatment using a post-treatment liquid at 80°C containing water and glycerin, and then dried to obtain a hollow fiber membrane.

[0098]

[0099] [Evaluation Example 1] Measurement of Water Vapor Permeability

[0100] A stainless steel tube module is fabricated by passing 17 hollow fiber membranes obtained by examples and comparative examples through a stainless steel tube with a diameter of 10 mm and fixing both ends with an adhesive. Under a temperature condition of 80°C, a dry gas is made to flow inside the hollow fiber membranes from the gas inlet of the stainless steel tube module toward the gas outlet. The gas coming out from the gas outlet is humidified by a humidifying device, and the humidified wet gas is made to flow outside the hollow fiber membranes. In this way, the gas is made to flow in a one-pass cross-flow manner. The linear velocity inside the hollow fiber membranes is set to 1,000 cm / s with an air flow meter. The temperature and humidity of the gas at the dry gas inlet and the dry gas outlet at this time are measured. The water vapor permeation amount is obtained from these numerical values, and the value obtained by dividing it by the time during which the dry gas was flowed, the effective area of the hollow fiber membranes, and the air injection pressure of the dry gas is defined as the water vapor permeability, and the results are shown in Table 1 below. Here, the effective area of the hollow fiber membranes is the area obtained by multiplying the inner diameter of the hollow fiber membranes by the pi and the length of the hollow fiber membranes when the dry gas flows inside the hollow fibers.

[0101]

[0102] [Evaluation Example 2] Measurement of Nitrogen Permeability

[0103] A pressure regulator is installed on a nitrogen gas cylinder filled with nitrogen gas, and it is connected so that the nitrogen gas flows through a stainless steel pipe. Gas flow meters are installed at the front end and the rear end of the pipe, and a tube containing the hollow fiber membranes obtained by examples and comparative examples is attached. The hollow fiber membranes are positioned in a 10-mm-diameter tube using an adhesive so that nitrogen gas flows inside the hollow fiber membranes. One end of the hollow fiber membranes is blocked, and after allowing the nitrogen gas to flow from the inside to the outside, the flow rate values at the front end and the rear end of the pipe are measured while maintaining a pressure of 0.7 bar. The nitrogen permeability is a value obtained by dividing the average value of the measured flow rates by the membrane area of the hollow fiber membranes. The results are as shown in Table 1 below.

[0104]

[0105] [Evaluation Example 3] Measurement of Tensile Strength

[0106] After preparing hollow fiber membrane samples (membrane length: 100 mm) obtained from the examples and comparative examples, Instron 4304 was used. With a 1N cell, test pieces of the membrane were fixed to the upper and lower action grips, and then the tensile strength was measured by pulling at a crosshead speed of 50.0 mm / min. The results are as shown in Table 1 below.

[0107]

Table 1

[0108]

[0109] The hollow fiber membrane of the comparative example is composed only of a sponge layer and has no finger-structured second layer. Therefore, the membrane thickness is relatively thin, and the tensile strength is lower than that of the hollow fiber membrane of the example. Also, although the finger-structured second layer is formed and, as described above, dense regions are also generated together by rapid phase transition, in the comparative example, since there is no finger-structured second layer including such dense regions, the nitrogen permeability has increased rapidly.

[0110]

[0111] As described above, specific examples of the present invention have been described and illustrated. However, the present invention is not limited to the described examples, and it is obvious to those with ordinary knowledge in this technical field that various modifications and deformations are possible without departing from the spirit and scope of the present invention. Therefore, such modified examples or deformed examples should not be individually understood from the technical spirit or perspective of the present invention, and the deformed examples should be considered to belong to the scope of the claims of the present invention.

Claims

1. In order from the center, a first layer having a high-density sponge structure containing pores with an average pore diameter of 1 nm or less; a second layer containing macrovoids extending in the radial direction; and a third layer having a low-density sponge structure containing pores with an average pore diameter of 10 to 1,000 μm, wherein the thickness of the first layer is 1 to 40 μm, the thickness of the second layer is 20 to 60 μm, and the thickness of the third layer is 20 to 50 μm, a hollow fiber membrane.

2. The hollow fiber membrane has a water vapor permeability of 0.1 g / s / m or more measured under a pressure of 1 bar and a temperature of 80 °C. ２ The hollow fiber membrane according to claim 1.

3. The hollow fiber membrane has a nitrogen permeability of 100 cc / min / cm or less at a pressure of 0.7 bar. ２ The hollow fiber membrane according to claim 1.

4. The hollow fiber membrane has an oxygen permeability of 100 cc / min / cm or less at a pressure of 0.7 bar. ２ The hollow fiber membrane according to claim 1.

5. The hollow fiber membrane has a tensile strength of 100 gf / fiber or more.

6. Each of the first layer to the third layer independently contains one or more selected from the group consisting of polyethersulfone, polyphenylsulfone, polysulfone, polyvinylidene fluoride, polyimide, polyetherimide, polyamide, polyacrylonitrile, and cellulose acetate.

7. The inner diameter of the hollow fiber membrane is 600 to 1,400 μm, and the outer diameter is 1,000 to 2,000 μm.

8. Steps of manufacturing a first spinning solution by mixing a non-solvent, a poor solvent and a polymer resin, and manufacturing a second spinning solution by mixing a non-solvent, a good solvent and a polymer resin; Steps of spinning the first spinning solution using a thermal-induced phase separation method to manufacture a hollow first layer; Steps of passing the spun support through a mixed solvent of a good solvent and a non-solvent; and Steps of discharging the first layer and the second spinning solution through a die to form a second layer and a third layer by a non-solvent-induced phase separation method, wherein the thickness of the first layer is 1 to 40 μm, the thickness of the second layer is 20 to 60 μm, and the thickness of the third layer is 20 to 50 μm, A method for manufacturing a hollow fiber membrane.

9. The first spinning solution contains 45% to 70% by weight of the polymer resin, The second spinning solution contains 15% to 40% by weight of the polymer resin. The method for manufacturing a hollow fiber membrane according to claim 8.

10. The polymer resin contains one or more selected from the group consisting of polyethersulfone, polyphenylsulfone, polysulfone, polyvinylidene fluoride, polyimide, polyetherimide, polyamide, polyacrylonitrile, and cellulose acetate. The method for manufacturing a hollow fiber membrane according to claim 8.

11. The non-solvent contains one or more selected from the group consisting of water, methanol, ethanol, isopropanol, acetone, hexane, pentane, benzene, toluene, carbon tetrachloride, o-dichlorobenzene, and polyethylene glycol. The method for manufacturing a hollow fiber membrane according to claim 8.

12. The good solvent contains one or more selected from the group consisting of N-methyl-2-pyrrolidone, dimethyl sulfoxide, dimethylacetamide, dimethylformamide, methyl ethyl ketone, tetrahydrofuran, tetramethyl urea, and trimethyl phosphate. The method for manufacturing a hollow fiber membrane according to claim 8.

13. The method for producing a hollow fiber membrane according to claim 8, wherein the poor solvent contains at least one selected from the group consisting of butanol, isobutanol, octanol, pentanol, isopentanol, dimethyl phthalate, diethyl phthalate, dibutyl phthalate, dioctyl phthalate, and polyoxyethylene octyl phenyl ether.

14. The method for producing a hollow fiber membrane according to claim 8, wherein the first spinning solution and the second spinning solution each independently further contain at least one hydrophilic additive selected from the group consisting of polyvinylpyrrolidone, polyethylene glycol, polyethylene oxide, glycerin, diethyl glycol, and triethylene glycol.

15. The method for producing a hollow fiber membrane according to claim 8, wherein the first spinning solution and the second spinning solution each independently further contain at least one nonionic surfactant selected from the group consisting of polyoxyethylene alkyl ether, fatty acid sorbitan ester, and alkyl monoglyceryl ether.

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