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 having a high-density sponge structure including pores having a size 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 having a size of 10 μm to 1,000 μm, and a method of producing the same.

Description

Technical Field

[0001] This invention relates to a hollow fiber membrane and a method for preparing the hollow fiber membrane, and more specifically, to a hollow fiber membrane preferably used in a humidification device for a fuel cell system, and a method for preparing the hollow fiber membrane. Background Technology

[0002] In recent years, humidification and dehumidification methods using water vapor permeation membranes have attracted attention. These methods offer advantages such as requiring no maintenance and no separate power supply.

[0003] Hollow fiber membranes, which are water vapor permeable membranes in a hollow form, are used for humidification of the diaphragm in fuel cell stacks and the like. In the case of fuel cells, humidification with a high airflow rate of approximately 4,000 NL / min is required for vehicle systems. Therefore, the hollow fiber membrane used for humidification needs to have high water vapor permeability and high hollow fiber membrane strength. The hollow fiber membrane used for humidification needs to have air barrier properties to prevent air leakage from the hollow fibers, and it should also have water vapor permeability. Therefore, when the hollow fiber membrane is made into a porous membrane with pores of very fine diameter, the required water vapor permeation rate can be obtained when the porous membrane is pressurized. Furthermore, the airflow rate varies significantly depending on the operating location or method. For example, a low flow rate may be sufficient when driving in urban areas; however, a high flow rate is required when driving on mountain roads or during rapid acceleration.

[0004] Various polymer-based membranes have been proposed as hollow fiber membranes for humidification. For example, hollow fiber membranes for humidification made from polyimide resin-based materials exist. These membranes are characterized by excellent heat resistance, durability, and gas barrier properties. On the other hand, they suffer from low water vapor permeability.

[0005] Furthermore, hollow fiber membranes for humidification prepared using fluorine-based ion exchange membranes exhibit higher water vapor permeability and gas barrier properties than those prepared using polyimide resin-based materials. On the other hand, hollow fiber membranes prepared using fluorine-based ion exchange membranes do not achieve the water vapor permeability required for practical use as humidification membranes, and they also have insufficient heat resistance, while the price of hollow fiber membranes themselves is very high.

[0006] Regarding the methods for membrane preparation, hollow fiber membranes are prepared by using non-solvent phase separation (NIPS) or thermal phase separation (TIPS).

[0007] According to the non-solvent phase separation method, a membrane is prepared by discharging a spinning solution in which the polymer resin is dissolved in a good solvent through a spinneret, and then contacting the discharged spinning solution with a liquid containing a non-solvent, thereby causing the spinning solution to solidify.

[0008] According to the thermally induced phase separation method, a spinning solution is prepared by forcibly dissolving a polymer resin in a poor solvent at a temperature above the phase separation temperature, discharging the spinning solution through a spinneret, and then contacting the discharged spinning solution with a cooling liquid at a temperature below the phase separation temperature to solidify the spinning solution and thus prepare a membrane.

[0009] However, hollow fiber membranes prepared by non-solvent-induced phase separation do not exhibit the spherical structure observed in membranes prepared by thermally induced phase separation. Instead, they possess a three-dimensional network structure including macropores. Therefore, these hollow fiber membranes suffer from insufficient tensile strength. Hollow fiber membranes prepared by thermally induced phase separation have a spherical structure that does not include macropores and is symmetrical along the membrane thickness direction. Consequently, while these membranes exhibit high mechanical strength, controlling the pore size is difficult, and they also suffer from poor separation characteristics.

[0010] Therefore, in order to commercialize hollow fiber membranes, physical and mechanical properties should be improved by enhancing tensile strength and high moisture diffusion performance, and for this purpose, the optimal structure of the hollow fiber membrane needs to be ensured. Summary of the Invention

[0011] Technical issues

[0012] One object of the present invention is to provide a hollow fiber membrane with excellent tensile strength and moisture diffusion characteristics.

[0013] Another object of the present invention is to provide a method for preparing the above-mentioned hollow fiber membrane.

[0014] Technical solution

[0015] One embodiment of the present invention provides a hollow fiber membrane comprising, from the center, the following layers in sequence: a first layer having a high-density sponge structure having pores with a size of less than 1 nm; a second layer having a finger-like structure; and a third layer having a low-density sponge structure having pores with a size of 10 μm to 1,000 μm.

[0016] The thickness of the first layer can be from 1 μm to 40 μm, the thickness of the second layer can be from 20 μm to 60 μm, and the thickness of the third layer can be from 20 μm to 50 μm.

[0017] The hollow fiber membrane can have a strength of 0.1 g / s / m measured at 1 bar pressure and 80°C. 2 The above refers to water vapor transmission rates.

[0018] The hollow fiber membrane can achieve a flow rate of 100 cc / min / cm at a pressure of 0.7 bar. 2 The following are the nitrogen permeability rates.

[0019] The hollow fiber membrane can achieve a flow rate of 100 cc / min / cm at a pressure of 0.7 bar. 2 The following are the oxygen permeability values.

[0020] The hollow fiber membrane can have a tensile strength of 100 gf / fiber or higher.

[0021] The first to the third layers may each independently contain one or more selected from polyethersulfone, polyphenylsulfone, polysulfone, polyvinylidene fluoride, polyimide, polyetherimide, polyamide, polyacrylonitrile, and cellulose acetate.

[0022] The hollow fiber membrane has an inner diameter of 600 μm to 1,400 μm and an outer diameter of 1,000 μm to 2,000 μm.

[0023] Another embodiment of the present invention provides a method for preparing a hollow fiber membrane, comprising: mixing a non-solvent, a poor solvent, and a polymer resin to prepare a first spinning solution; mixing a non-solvent, a good solvent, and a polymer resin to prepare a second spinning solution; spinning the first spinning solution using a thermally induced phase separation method to prepare a hollow first layer; passing the spun support through a mixture of a good solvent and a non-solvent; and discharging the first layer and the second spinning solution through a spinneret using a non-solvent-induced phase separation method to form a second layer and a third layer.

[0024] The first spinning solution may contain 45% to 70% by weight of a polymer resin, and the second spinning solution may contain 15% to 40% by weight of a polymer resin.

[0025] The polymer resin may contain one or more selected from polyethersulfone, polyphenylsulfone, polysulfone, polyvinylidene fluoride, polyimide, polyetherimide, polyamide, polyacrylonitrile, and cellulose acetate.

[0026] The non-solvent may include one or more selected from water, methanol, ethanol, isopropanol, acetone, hexane, pentane, benzene, toluene, carbon tetrachloride, o-dichlorobenzene, and polyethylene glycol.

[0027] The good solvent may contain one or more selected from N-methyl-2-pyrrolidone, dimethyl sulfoxide, dimethylacetamide, dimethylformamide, methyl ethyl ketone, tetrahydrofuran, tetramethylurea, and trimethyl phosphate.

[0028] The undesirable solvent may include one or more selected from butanol, isobutanol, octanol, pentanol, isopentanol, dimethyl phthalate, diethyl phthalate, dibutyl phthalate, dioctyl phthalate, and polyoxyethylene octylphenyl ether.

[0029] The first spinning solution and the second spinning solution may each independently contain one or more hydrophilic additives selected from polyvinylpyrrolidone, polyethylene glycol, polyethylene oxide, glycerol, diethyl glycol and triethylene glycol.

[0030] The first spinning solution and the second spinning solution may each independently contain one or more nonionic surfactants selected from polyoxyethylene alkyl ethers, fatty sorbitan esters, and alkyl monoglyceride ethers.

[0031] Beneficial effects

[0032] Since the hollow fiber membrane according to the present invention comprises each of a first layer, a second layer, and a third layer: the first layer serves as an inner support layer and has a high-density sponge structure comprising pores with a size of less than 1 nm; the second layer serves as an intermediate layer and includes a finger-like structure; and the third layer serves as an outer layer and has a low-density sponge structure comprising pores with a size of 10 μm to 1,000 μm, the hollow fiber membrane exhibits excellent moisture diffusion characteristics. Furthermore, since the hollow fiber membrane according to the present invention comprises both a first layer comprising a high-density sponge structure and a third layer comprising a low-density sponge structure on both sides of the second layer comprising the finger-like structure, it further enhances tensile strength. Attached Figure Description

[0033] Figure 1 This is a cross-sectional view of a hollow fiber membrane according to an embodiment of the present invention. Detailed Implementation

[0034] In the following, embodiments of the present invention will be described in detail so that those skilled in the art can readily implement the invention. However, the present invention can be implemented in various different forms and is not intended to be limited to the embodiments described herein.

[0035] Hollow fiber membranes according to one aspect of the present invention will now be described.

[0036] This invention relates to a hollow fiber membrane for humidification, which has the following characteristics: excellent mechanical strength, high hydrophilicity, high moisture diffusivity, and low gas permeability to nitrogen, oxygen, etc.

[0037] According to the hollow fiber membrane 100 of the present invention, from the center, it comprises: a first layer 10 having a high-density sponge structure having pores with a size of less than 1 nm; a second layer 20 having a finger-like structure; and a third layer 30 having a low-density sponge structure having pores with a size of 10 μm to 1,000 μm.

[0038] The inventors of this invention can obtain a hollow fiber membrane having the three-layer structure described above by the following steps: by using a thermally induced phase separation method to discharge a spinning solution containing a high content of polymer resin, forming a first layer 10 including a dense sponge structure as an inner support layer, immersing the first layer 10 in a mixed solvent of a non-solvent and a good solvent, and then discharging the first layer together with the spinning solution by a non-solvent induced phase separation method.

[0039] The hollow fiber membrane 100 of the present invention can possess the excellent mechanical strength required for hollow fiber membranes because the first layer 10, serving as the inner support layer, comprises a high-density sponge structure, and excellent water dispersibility can be provided by the second layer 20, serving as the intermediate layer, comprising a finger-like structure, and the third layer 30, serving as the outer layer, comprising a low-density sponge structure. Therefore, the terms "high density" for the high-density sponge structure of the first layer 10 and "low density" for the low-density sponge structure of the third layer 30 can refer to the relative density between the two layers, and the absolute values ​​of these densities are not particularly limited and can be suitably chosen by those skilled in the art, provided that the first layer 10 imparts sufficient mechanical strength to the hollow fiber membrane and the third layer 30 possesses excellent water dispersibility, allowing water molecules to easily permeate and rapidly transfer.

[0040] 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 micropores with a size of less than 1 nm. Therefore, the first layer 10 acts as an inner support layer of the hollow fiber membrane and can impart excellent mechanical strength. Here, the sponge structure can be understood as a three-dimensional network structure formed by a large number of interconnected pores.

[0041] According to embodiments, the first layer 10 in the hollow fiber membrane 100 of the present invention can be formed with a thickness of 1 μm to 40 μm, and preferably with a thickness of 10 μm to 20 μm. When the thickness of the inner support layer is less than 1 μm, it cannot impart sufficient physical and mechanical properties to the hollow fiber membrane, which may reduce the tensile strength of the hollow fiber membrane. When the thickness is greater than 40 μm, it is difficult to control the pore size, and the water dispersibility of the hollow fiber membrane may be excessively deteriorated.

[0042] Next, the second layer 20, comprising a finger-like structure, serves as an intermediate layer, providing macropores for the hollow fiber membrane 100 of the present invention. It reduces water molecule flow resistance, increases permeation flux, and thus imparts excellent water dispersion properties. The second layer 20, comprising the finger-like structure, is located between the first layer 10 and the third layer 30, which serves as the outer layer of the hollow fiber membrane 100 of the present invention. Here, the finger-like structure can be understood as an arrangement of vertical internal defects resembling a finger shape. This finger-like structure refers to the finger-like structure formed internally during the formation of the hollow fiber membrane, where the solvent and additives inside the spinning solution are rapidly phase-changed and expelled in one go. Since the finger-like structure is formed at a rapid phase-change rate, the second layer comprising the finger-like structure may also include dense regions along with the finger-like structure. According to an embodiment of the present invention, the second layer has the following advantages: due to this finger-like structure, not only is the flow resistance of water molecules reduced and the permeation flux increased, but also, due to the presence of dense regions, the nitrogen or oxygen permeation rate (excluding water vapor) can be reduced.

[0043] According to embodiments, in the hollow fiber membrane 100 of the present invention, the second layer 20 can be formed to have a thickness of 20 μm to 60 μm, and preferably, the second layer 20 can be formed to have a thickness of 35 μm to 50 μm. When the thickness of the second layer 20 is less than 20 μm, the macropores cannot be sufficiently fixed in the hollow fiber membrane, and the water dispersion characteristics may be reduced. When the thickness exceeds 60 μm, there may be a problem of deterioration of the mechanical properties of the hollow fiber membrane in the thickness direction.

[0044] The third layer 30 is the outermost layer formed next, located on the outermost side of the hollow fiber membrane of the present invention, and has a low-density sponge structure including fine pores with a size of 10 μm to 1,000 μm. Therefore, water molecules can easily permeate into the loose area outside the hollow fiber membrane, so that the third layer 30 can quickly transfer water molecules to the second layer 20, which includes the above-described finger structure, in contact with the third layer 30.

[0045] According to an embodiment, the third layer 30 in the hollow fiber membrane 100 of the present invention can be formed to have a thickness of 20 μm to 50 μm, and preferably, the third layer 30 can be formed to have a thickness of 30 μm to 50 μm.

[0046] According to an embodiment, the hollow fiber membrane 100 has a strength of 0.1 g / s / m measured at a pressure of 1 bar and a temperature of 80°C. 2 The preferred value is 0.3 g / s / m 2 The above refers to water vapor transmission rates. Water vapor transmission rate is an index representing the performance of water vapor transmission. When the water vapor transmission rate is 0.1 g / s / m... 2When the above conditions are met, the fuel cell stack can be optimally humidified, water vapor can be stably supplied, and the electrolyte membrane performance of the fuel cell stack can be fully utilized.

[0047] According to the embodiment, for the hollow fiber membrane 100, the nitrogen permeability can be 100 cc / min / cm at a pressure of 0.7 bar. 2 The following, and can be, for example, 80cc / min / cm 2 For example, 50cc / min / cm 2 For example, 30cc / min / cm 2 The following, and preferably 20cc / min / cm 2 The following is true. This is because when the nitrogen permeability exceeds 100 cc / min / cm... 2 At that time, the water vapor permeability of hollow fiber membranes may be severely degraded.

[0048] According to the embodiment, for the hollow fiber membrane 100, the oxygen permeability can be 100 cc / min / cm at a pressure of 0.7 bar. 2 The following, and can be, for example, 80cc / min / cm 2 Below, for example, 50cc / min / cm 2 For example, 30cc / min / cm 2 The following, and preferably 20cc / min / cm 2 The following is true. This is because when the oxygen permeability exceeds 100 cc / min / cm... 2 At that time, the water vapor permeability of hollow fiber membranes may be severely degraded.

[0049] According to embodiments, the tensile strength of the hollow fiber membrane 100 can be 100 gf / fiber or more, and can be, for example, 200 gf / fiber or more, for example, 250 gf / fiber or more, and preferably 300 gf / fiber or more. Because the hollow fiber membrane 100 of the present invention includes a high-density sponge structure in the inner support layer of the hollow fiber membrane, its mechanical and physical properties are improved, and it can ensure that the tensile strength meets the above-mentioned range.

[0050] According to embodiments, the first layer 10 to the third layer 30 may each independently comprise one or more selected from polyethersulfone, polyphenylsulfone, polysulfone, polyvinylidene fluoride, polyimide, polyetherimide, polyamide, polyacrylonitrile, and cellulose acetate. For example, polyethersulfone, polyphenylsulfone, polysulfone, and polyvinylidene fluoride may be used. However, the materials are not limited to these, as long as the material is a polymeric resin that can be used in hollow fiber membranes to achieve the intended effects of the present invention.

[0051] According to the embodiment, the inner diameter of the hollow fiber membrane 100 can be from 600 μm to 1,400 μm, and the outer diameter can be from 1,000 μm to 2,000 μm. When the inner and outer diameters of the hollow fiber membrane meet the above ranges, excellent moisture diffusion characteristics can be ensured as a hollow fiber membrane for humidification.

[0052] According to another aspect of the present invention, a method for preparing a hollow fiber membrane is provided, the method comprising: mixing a non-solvent, a poor solvent, and a polymer resin to prepare a first spinning solution, and mixing a non-solvent, a good solvent, and a polymer resin to prepare a second spinning solution (S1); spinning the first spinning solution by using a thermally induced phase separation method to prepare a hollow first layer 10 (S2); passing the spun support through a mixture of a good solvent and a non-solvent (S3); and discharging the first layer 10 and the second spinning solution through a spinneret by a non-solvent-induced phase separation method to form a second layer 20 and a third layer 30 (S4).

[0053] First, step (S1) is the step of preparing the spinning solution for preparing the hollow fiber membrane of the present invention. Since the hollow fiber membrane 100 of the present invention is prepared by sequentially combining thermal phase separation and non-solvent phase separation, the first spinning solution and the second spinning solution used in each step can be used separately.

[0054] The first spinning solution contains a non-solvent, a poor solvent, and a polymer resin, while the second spinning solution contains a non-solvent, a good solvent, and a polymer resin.

[0055] First, the polymer resin is dissolved in a mixture of a poor solvent and a non-solvent to prepare the first spinning solution.

[0056] According to embodiments, the polymer resin may comprise one or more selected from polyethersulfone, polyphenylsulfone, polysulfone, polyvinylidene fluoride, polyimide, polyetherimide, polyamide, polyacrylonitrile, and cellulose acetate. For example, polyethersulfone, polyphenylsulfone, polysulfone, and polyvinylidene fluoride may be used. However, the polymer resin is not limited to these, as long as it is a polymer resin that can be used in hollow fiber membranes to achieve the intended effects of the present invention.

[0057] According to embodiments, the first spinning solution may contain 45% to 70% by weight of a polymer resin, and may contain, for example, 50% to 70% by weight, preferably 60% to 70% by weight of a polymer resin. When the polymer resin content of the first spinning solution is less than 45% by weight, the mechanical strength of the hollow fiber membrane may be weak, while when the polymer resin content exceeds 70% by weight, the viscosity of the first spinning solution becomes so high that spinning may be difficult. Furthermore, forming the first layer 10 as an inner layer with small pores may be difficult, and there is a risk that the temperature of the undesirable solvent should be increased to dissolve a large amount of polymer resin.

[0058] A poor solvent is one that does not dissolve the selected polymer resin at room temperature (25°C) but can only dissolve the polymer resin when heated to a high temperature, especially above 100°C. In this invention, the poor solvent can significantly dissolve the polymer resin at a temperature of 100°C to 150°C.

[0059] According to an embodiment, the undesirable solvent is contained in the first spinning solution and may contain one or more selected from butanol, isobutanol, octanol, pentanol, isoamyl alcohol, dimethyl phthalate, diethyl phthalate, dibutyl phthalate, dioctyl phthalate, and polyoxyethylene octylphenyl ether; however, the undesirable solvent is not necessarily limited to these. Based on the total weight of the first spinning solution, the undesirable solvent may be contained in a proportion of 20% to 50% by weight. When the content of the undesirable solvent is less than 20% by weight, the viscosity of the first spinning solution may become too high, making spinning difficult, and there is a risk of raising the temperature of the undesirable solvent to dissolve a large amount of polymer resin. When the content exceeds 50% by weight, the strength of the hollow fiber membrane may be too low.

[0060] A non-solvent is a solvent that cannot dissolve the selected polymer resin across all temperature ranges. According to embodiments, the non-solvent is contained in the first and second spinning solutions and may include one or more selected from water, methanol, ethanol, isopropanol, acetone, hexane, pentane, benzene, toluene, carbon tetrachloride, o-dichlorobenzene, and polyethylene glycol; however, the non-solvent is not necessarily limited to these. Based on the total weight of the first spinning solution, the content of the non-solvent can be from 1% to 10% by weight. When the non-solvent content is less than 1% by weight, the strength of the hollow fiber membrane may decrease, while when the content is greater than 10% by weight, it may not be easy to form pores in the inner support layer of the hollow fiber membrane.

[0061] Next, the polymer resin is dissolved in a mixture of a good solvent and a non-solvent to prepare a second spinning solution.

[0062] The second spinning solution may contain 15% to 40% by weight of polymer resin, and may contain, for example, 20% to 40% by weight, preferably 20% to 30% by weight of polymer resin. When the polymer resin content of the second spinning solution is less than 15% by weight, the porosity of the hollow fiber membrane may be too low, while when the polymer resin content exceeds 40% by weight, the porosity of the first layer 10 as the inner active layer and the third layer 30 as the outer layer becomes too high, and there may be a problem of reduced overall mechanical strength of the hollow fiber membrane.

[0063] Specific examples of polymer resins are as described above. The same type of polymer resin as the polymer resin contained in the first spinning solution can be used, or different types of polymer resins can be used.

[0064] According to embodiments, a good solvent is contained in the second spinning solution and may contain one or more selected from N-methyl-2-pyrrolidone, dimethyl sulfoxide, dimethylacetamide, dimethylformamide, methyl ethyl ketone, tetrahydrofuran, tetramethylurea, and trimethyl phosphate; however, the good solvent is not necessarily limited to these. Based on the total weight of the second spinning solution, the good solvent may be contained in a proportion of 30% to 60% by weight. When the content of the good solvent is less than 30% by weight, the viscosity of the second spinning solution becomes too high, making spinning difficult, and there is a risk that the temperature of the good solvent should be increased to successfully dissolve the polymer resin. When the content exceeds 60% by weight, the viscosity of the second spinning solution may become too low, and spinnability may deteriorate.

[0065] Specific examples of non-solvents are as described above. Non-solvents of the same type as those contained in the first spinning solution can be used, or non-solvents of different types can be used.

[0066] According to the embodiments, the first spinning solution and the second spinning solution may each independently contain a hydrophilic additive, which plays a role in assisting the formation of pores in the hollow fiber membrane. For example, the spinning solution may also contain one or more hydrophilic additives selected from polyvinylpyrrolidone, polyethylene glycol, polyethylene oxide, glycerol, diethyl ethylene glycol and triethylene glycol.

[0067] Based on the total weight of each spinning solution, the hydrophilic additive can be included in a proportion of 5% to 25% by weight. When the content of the additive is less than 5% by weight, pore formation in the hollow fiber membrane may not be achieved smoothly, while when the content exceeds 25% by weight, phase separation of the spinning solution can occur rapidly, leading to fiber breakage during spinning.

[0068] According to the embodiments, the first spinning solution and the second spinning solution may each independently contain one or more nonionic surfactants selected from polyoxyethylene alkyl ethers, fatty acid sorbitan esters and alkyl monoglycerides.

[0069] There is no specific order of preparation in the preparation of the first spinning solution and the second spinning solution.

[0070] Next, step (S2) is to form a first layer 10, which includes a high-density sponge structure, as an inner support layer using a first spinning solution via thermally induced phase separation.

[0071] Specifically, in step (S2), a first layer 10 serving as an inner support layer is formed by discharging a first spinning solution obtained by mixing a non-solvent, a poor solvent, and a polymer resin through a spinneret at a spinning temperature of 100°C to 300°C. Since the first layer 10 is formed using a first spinning solution containing a high content of polymer resin through a thermally induced phase separation method, a hollow fiber membrane with excellent mechanical strength and good moisture diffusion characteristics can be formed.

[0072] The discharge rate of the first spinning solution can be adjusted from approximately 10 g / min to 60 g / min.

[0073] During the process of discharging the first spinning solution through, for example, a spinneret consisting of two tubes, the mixed liquid can be discharged into the hollow cavity of the spun product. At this time, the mixed liquid may contain both a good solvent and a non-solvent. Specific examples of good solvents and non-solvents are described above. By discharging the mixed liquid into the hollow cavity of the spun product in this manner, hollow fiber membranes can be more easily obtained.

[0074] The spun product exiting the spinneret can be cured by passing through an air gap and contacting the mixed solvent, which will be described in step (S3) below. The air gap is mainly an air layer or an inert gas layer, in which case the length of the air gap can be maintained between 0.1 cm and 15 cm.

[0075] The first layer 10 formed by step (S2) serves as the inner support layer of the hollow fiber membrane 100 of the present invention, and the hollow fiber membrane prepared by step (S2) can have an inner diameter of about 600 μm to 1,400 μm and an outer diameter of 1,000 μm to 2,000 μm.

[0076] Next, the support spun in step (S2) is cured while in contact with a mixture of a good solvent and a non-solvent (S3).

[0077] The mixed solvent can, for example, be cooled to 5°C to 25°C and serve to cure the support spun in step (S2). Specific examples of good solvents and non-solvents included in the mixed solvent are described above.

[0078] Next, step (S4) involves discharging the first layer 10, which was cured in step (S3), and the second spinning solution through a spinneret to form a hollow fiber membrane, which serves as an intermediate layer (20) and an outer layer (30).

[0079] The spinneret can be, for example, a double tube consisting of two tubes. Therefore, when the first layer 10 formed by step (S3) and the second spinning solution are respectively supplied to the spinneret consisting of the double tubes, and specifically, when the first layer 10 is supplied to the inside of the spinneret while the second spinning solution is supplied to the outside of the spinneret, the inner surface of the resulting spun product can be formed by the first layer 10, and the outer surface can be formed by the spun product of the second spinning solution.

[0080] The spun product exiting the spinneret can be cured by passing through an air gap. This air gap is mainly an air layer or an inert gas layer, and in this case, the length of the air gap can be maintained between 1 cm and 50 cm.

[0081] In step (S4), when the mixed solvent of non-solvent and good solvent deposited on the outer side of the first layer 10 in step (S3) comes into contact with the second spinning solution during spinning, a rapid phase change occurs. As a result, a second layer 20 with a finger-like structure, serving as an intermediate layer, is rapidly formed on the outer surface of the support layer. At this time, the mixed solvent acts as the pore liquid during the hollow fiber membrane spinning process. When the mixed solvent is discharged through the nozzle of the spinneret, which consists of two tubes, the solvent contained in the second spinning solution and the non-solvent contained in the mixed solvent are instantaneously exchanged during the contact process between the mixed solvent and the second spinning solution. This results in the formation of the intermediate layer with a finger-like structure through a curing process. Subsequently, as the second spinning solution discharged through the nozzle of the spinneret passes through the air gap, the non-solvent and the second spinning solution react with each other through a contact process on the outer side of the second layer 20 with the finger-like structure, leading to a phase change. Therefore, a third layer 30, which is an outer layer with a low-density sponge structure, can be formed.

[0082] In step (S4), specific examples of non-solvent and good solvents for the second spinning solution are as described above.

[0083] Example

[0084] The present invention will be specifically described below by way of examples and comparative examples. However, the following examples are only used to promote understanding of the present invention, and therefore the scope of the present invention is not limited thereto.

[0085] Examples

[0086] A first spinning solution was prepared by mixing 65 wt% polyphenylsulfone (PPSu), 20 wt% butanol, 10 wt% polyethylene glycol (PEG 200), and 5 wt% Triton X-10 as a nonionic surfactant, and stirring the mixture at 150°C for 24 hours.

[0087] A second spinning solution was prepared by mixing 28 wt% polyphenylsulfone, 25 wt% polyethylene glycol (PEG 200), 45.5 wt% solvent and 1.5 wt% Triton X-10 as a nonionic surfactant, and stirring the mixture at 150 °C for 24 hours.

[0088] The first spinning solution prepared as described above is discharged through a spinneret consisting of two tubes to obtain a spun product. At this time, a mixed liquid consisting of 80% by weight of dimethylacetamide (DMAc) and 20% by weight of polyethylene glycol (PEG) at 25°C is supplied to the inside of the spinneret consisting of two tubes and discharged therefrom, while the first spinning solution is supplied to the outside of the spinneret consisting of two tubes and discharged therefrom.

[0089] The spun product is passed through an air gap of 5 cm in length and then immersed in a curing liquid in a curing bath. The curing liquid is a mixture of N-methyl-2-pyrrolidone and water at 25°C.

[0090] The hollow fiber membrane obtained after curing in the curing bath is continuously discharged again through a spinneret consisting of two tubes.

[0091] At this point, the hollow fiber membrane thus formed is supplied to the first spinning solution of the spinneret consisting of two tubes and discharged through the first spinning solution of the spinneret consisting of two tubes, and the second spinning solution is supplied to the outside of the spinneret consisting of two tubes and discharged through the outside.

[0092] Subsequently, the discharged product was washed with pure water at 25°C, hydrothermally treated with a post-treatment liquid containing water and glycerol at 80°C, and then dried to obtain a hollow fiber membrane.

[0093] Comparative Examples

[0094] A first spinning solution was prepared by mixing 65 wt% polyphenylsulfone (PPSu), 20 wt% isobutanol, 10 wt% polyethylene glycol (PEG200), and 5 wt% Triton X-10 as a nonionic surfactant, and stirring the mixture at 150°C for 24 hours.

[0095] The spinning solution thus prepared is discharged through a spinneret consisting of two tubes to obtain the spun product. During the discharge of the spinning solution, a mixed liquid consisting of 80% by weight dimethylacetamide (DMAc) and 20% by weight polyethylene glycol (PEG) at 25°C is discharged through the interior of the hollow cavity of the spun product.

[0096] The spun product is passed through an air gap of 30 cm in length and then immersed in a curing liquid in a curing bath. Water at 50°C is used as the curing liquid.

[0097] The spun product obtained by curing in a curing bath was washed with pure water at 50°C, hydrothermally treated with a post-treatment liquid containing water and glycerol at 80°C, and then dried to obtain a hollow fiber membrane.

[0098] Evaluation Example 1 : Measurement of Water Vapor Transmission Rate

[0099] A stainless steel tube module was prepared by passing a 17-strand hollow fiber membrane obtained from the examples or comparative examples through a stainless steel tube with a diameter of 10 mm and fixing the two ends of the tube with an adhesive. Dry gas was allowed to flow from the inlet to the outlet of the stainless steel tube module through the interior of the hollow fiber membrane at a temperature of 80°C. The gas exiting the outlet was humidified using a humidifier, and the humidified gas flowed through the exterior of the hollow fiber membrane. In this manner, the gas flowed in a single-pass crossflow. The linear velocity inside the hollow fiber membrane was set to 1,000 cm / s using an air flow meter. The temperature and humidity of the gas at the dry gas inlet and outlet were measured at this time. The water vapor transmission rate was determined from these values ​​and was specified as the water vapor transmission ratio by dividing the water vapor transmission rate by the dry gas flow time, the effective area of ​​the hollow fiber membrane, and the dry gas inlet pressure. The results are shown in Table 1 below. Here, the effective area of ​​the hollow fiber membrane refers to the area determined by (the inner diameter of the hollow fiber membrane × the ratio of the circumference of the circle to its diameter × the length of the hollow fiber membrane) when the dry gas flows through the interior of the hollow fiber membrane.

[0100] Evaluation Example 2: Measurement of Nitrogen Gas Transmission Rate

[0101] A pressure regulator was installed in a nitrogen-containing cylinder, and a stainless steel tube was connected to the cylinder to allow nitrogen to flow through. Gas flow meters were installed at both ends of the tube, and the tube containing the hollow fiber membrane obtained through the examples or comparative examples was also installed. The hollow fiber membrane was placed inside a 10 mm diameter tube using an adhesive, allowing nitrogen to flow through the interior of the hollow fiber membrane. One end of the hollow fiber membrane was blocked, allowing nitrogen to flow from the inside to the outside. A pressure of 0.7 bar was then maintained, and the flow rate at both ends of the tube was measured. The nitrogen permeability was determined by dividing the average of the flow rate values ​​measured as described above by the membrane area of ​​the hollow fiber membrane. The results are shown in Table 1 below.

[0102] Evaluation Example 3: Measurement of Tensile Strength

[0103] Hollow fiber membrane samples (membrane length 100 mm) were prepared according to the examples or comparative examples. The membrane samples were then fixed to the upper and lower action fixtures using an Instron 4304. A 1 N load cell was used, and the tensile strength was measured by stretching at a crosshead speed of 50.0 mm / min. The results are shown in Table 1 below.

[0104] [Table 1]

[0105]

[0106] The comparative hollow fiber membrane has a structure consisting only of a sponge layer and lacks a second layer with a finger-like structure. Therefore, the membrane thickness is relatively thin, resulting in lower tensile strength compared to the hollow fiber membrane of the embodiment. Furthermore, while forming the second layer with a finger-like structure, dense regions are also generated due to the rapid phase transition described above. However, in the comparative example, since the second layer with a finger-like structure including such dense regions is absent, the nitrogen permeability increases rapidly.

[0107] Specific embodiments of the present invention have been described and illustrated above. However, the present invention is not intended to be limited to the described embodiments, and it will be apparent to those skilled in the art that various modifications and variations can be made without departing from the concept and scope of the present invention. Therefore, such modified embodiments and varied embodiments should not be understood separately from the technical concept or idea of ​​the present invention, and the modified embodiments should be understood to be within the scope of the claims of the present invention.

Claims

1. A hollow fiber membrane, comprising, from its center: The first layer has a high-density sponge structure including pores with a size of less than 1 nm; The second layer includes finger-like structures; and The third layer has a low-density sponge structure comprising pores ranging from 10 μm to 1,000 μm in size. The first layer has a thickness of 1 μm to 40 μm, the second layer has a thickness of 20 μm to 60 μm, and the third layer has a thickness of 20 μm to 50 μm. The terms "high density" and "low density" in the context of the high-density sponge structure of the first layer and the low-density sponge structure of the third layer refer to the relative density between the two layers.

2. The hollow fiber membrane according to claim 1, in, The hollow fiber membrane has a strength of 0.1 g / s / m measured at a pressure of 1 bar and a temperature of 80°C. 2 The above refers to water vapor transmission rates.

3. The hollow fiber membrane according to claim 1, in, The hollow fiber membrane has a strength of 100 cc / min / cm. 2 The following are the nitrogen permeability rates at a pressure of 0.7 bar.

4. The hollow fiber membrane according to claim 1, in, The hollow fiber membrane has a strength of 100 cc / min / cm. 2 The following are the oxygen permeability at a pressure of 0.7 bar.

5. The hollow fiber membrane according to claim 1, in, The hollow fiber membrane has a tensile strength of 100 gf / fiber or higher, where gf / fiber means grams per fiber.

6. The hollow fiber membrane according to claim 1, in, Each of the first to the third layers independently comprises one or more selected from polyethersulfone, polyphenylsulfone, polysulfone, polyvinylidene fluoride, polyimide, polyetherimide, polyamide, polyacrylonitrile, and cellulose acetate.

7. The hollow fiber membrane according to claim 1, in, The hollow fiber membrane has an inner diameter of 600 μm to 1,400 μm and an outer diameter of 1,000 μm to 2,000 μm.

8. A method for preparing the hollow fiber membrane according to claim 1, comprising: The steps of mixing a non-solvent, a poor solvent, and a polymer resin to prepare a first spinning solution, and mixing a non-solvent, a good solvent, and a polymer resin to prepare a second spinning solution; The step of preparing a hollow first layer by spinning the first spinning solution using a thermally induced phase separation method; The step of passing the spun support through a mixture of a good solvent and a non-solvent; and The step of forming the second and third layers by discharging the first layer and the second spinning solution through a spinneret using a non-solvent phase separation method.

9. The method according to claim 8, in, The first spinning solution contains 45% to 70% by weight of a polymer resin. The second spinning solution contains 15% to 40% by weight of a polymer resin.

10. The method according to claim 8, in, The polymer resin comprises one or more selected from polyethersulfone, polyphenylsulfone, polysulfone, polyvinylidene fluoride, polyimide, polyetherimide, polyamide, polyacrylonitrile, and cellulose acetate.

11. The method according to claim 8, in, The non-solvent comprises one or more selected from water, methanol, ethanol, isopropanol, acetone, hexane, pentane, benzene, toluene, carbon tetrachloride, o-dichlorobenzene, and polyethylene glycol.

12. The method according to claim 8, in, The good solvent comprises one or more selected from N-methyl-2-pyrrolidone, dimethyl sulfoxide, dimethylacetamide, dimethylformamide, methyl ethyl ketone, tetrahydrofuran, tetramethylurea, and trimethyl phosphate.

13. The method according to claim 8, in, The undesirable solvent comprises one or more selected from butanol, isobutanol, octanol, pentanol, isopentanol, dimethyl phthalate, diethyl phthalate, dibutyl phthalate, dioctyl phthalate, and polyoxyethylene octylphenyl ether.

14. The method according to claim 8, in, The first spinning solution and the second spinning solution each independently further contain one or more hydrophilic additives selected from polyvinylpyrrolidone, polyethylene glycol, polyethylene oxide, glycerol, diethyl ethylene glycol and triethylene glycol.

15. The method according to claim 8, in, The first spinning solution and the second spinning solution each independently further contain one or more nonionic surfactants selected from polyoxyethylene alkyl ethers, fatty acid sorbitan esters and alkyl monoglycerides.

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