Polyamide hollow fiber membrane, hollow fiber membrane module, and method for producing a polyamide hollow fiber membrane

Abstract

The present invention aims to provide a polyamide hollow fiber membrane, a hollow fiber membrane module, and a method for producing a polyamide hollow fiber membrane, which maintain their filtration performance even after long-term storage in a preservation solution. [Solution] The polyamide hollow fiber membrane of the present invention is formed from a polyamide resin and satisfies at least one of the following features (1) to (5). (1) Fe content is 4.30 ppm or less (2) Cr content is less than 1.00 ppm (3) Cu content is less than 0.20 ppm (4) Mg content is less than 0.60 ppm (5) Zn content is less than 0.30 ppm

Description

[Technical Field]

[0001] The present invention relates to a polyamide hollow fiber membrane with excellent storage stability, a hollow fiber membrane module, and a method for producing a polyamide hollow fiber membrane. [Background technology]

[0002] Polyamide hollow fiber membranes are commonly used as hollow fiber membrane modules housed in module cases. These hollow fiber membrane modules offer excellent liquid filtration capabilities and are used in a variety of filtration applications, including the filtration of raw materials, intermediates, and chemical solutions used in pharmaceuticals and semiconductors.

[0003] For example, Patent Document 1 describes a bubble point test in which air pressure was applied to a liquid formed from polyamide resin with a surface tension of 12 mN / m at 20°C, the initial bubble point was 0.40 MPa or higher, and the burst bubble point was 0.55 MPa or higher, and the internal pressure permeability using pure water at 25°C was 50 L / (m³). 2 Polyamide hollow fiber membranes with a capacitance of ≥ ∫(atm·h) have been proposed. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2016-68005 [Overview of the project] [Problems that the invention aims to solve]

[0005] The common method for storing hollow fiber membrane modules after use in various applications is to immerse them in a storage solution such as water, an organic solvent, or a mixture thereof. However, the inventors have newly discovered that storing hollow fiber membrane modules in a storage solution for a long period of time results in a significant change in the filtration performance of the polyamide hollow fiber membrane.

[0006] The present invention aims to solve the above-mentioned conventional problems and to provide a polyamide hollow fiber membrane, a hollow fiber membrane module, and a method for manufacturing a polyamide hollow fiber membrane, which do not change in filtration performance even when stored for a long period of time in a preservation solution. [Means for solving the problem]

[0007] The inventors of this invention conducted thorough research to solve the above problems and found that the change in filtration performance when polyamide hollow fiber membranes are stored in a preservation solution for a long period of time is due to specific metal elements contained in the polyamide hollow fiber membranes. The present invention was completed by further research based on this finding.

[0008] In other words, the present invention provides inventions in the following embodiments. <1> A polyamide hollow fiber membrane formed from polyamide resin, A polyamide hollow fiber membrane that satisfies at least one of the following characteristics (1) to (5). (1) Fe content is 4.30 ppm or less (2) Cr content is less than 1.00 ppm (3) Cu content is less than 0.20 ppm (4) Mg content is less than 0.60 ppm (5) Zn content is less than 0.30 ppm <2> The relative viscosity is 2.0 to 6.5. <1> The polyamide hollow fiber membrane described above. <3> In structural analysis using X-ray diffraction, the proportion of γ crystals to the total amount of α crystals is 0-37%. <1> or <2> The polyamide hollow fiber membrane described above. <4> A polyamide hollow fiber membrane having a dense layer on the inner surface and / or outer surface, <1> ~ <3> A polyamide hollow fiber membrane as described in any of the following. <5> The blocking rate for particles with a diameter of 50 nm is 90% or higher. <1> ~ <4> A polyamide hollow fiber membrane as described in any of the following. <6> The polyamide hollow fiber membrane according to any one of <1> to <5>, wherein the retention rate of the blocking rate of particles with a particle size of 5 nm calculated by the following formula is 90% or more. Retention rate (%) = (Blocking rate of particles with a particle size of 5 nm after storage / Blocking rate of particles with a particle size of 5 nm before storage) × 100 Storage conditions: Immerse the polyamide hollow fiber membrane in propylene glycol monomethyl ether acetate and store it at 23 °C for 2 years without applying pressure. <7> The polyamide hollow fiber membrane according to any one of <1> to <6>, wherein the external pressure water permeability is 50 to 2000 L / (m 2 ·atm·h). <8> The polyamide hollow fiber membrane according to any one of <1> to <7>, wherein the retention rate of the external pressure water permeability calculated by the following formula is 90 to 110%. Retention rate (%) = (External pressure water permeability after storage / External pressure water permeability before storage) × 100 Storage conditions: Immerse the polyamide hollow fiber membrane in propylene glycol monomethyl ether acetate and store it at 23 °C for 2 years without applying pressure. <9> The polyamide hollow fiber membrane according to any one of <1> to <8>, wherein in the bubble point test with air pressure applied in 2-propanol at 20 °C, the initial bubble point is 0.20 MPa or more and the burst bubble point is 0.30 MPa or more. <10> In the bubble point test with air pressure applied in 2-propanol at 20 °C, The polyamide hollow fiber membrane according to any one of <1> to <9>, wherein the retention rate of the initial bubble point and the burst bubble point calculated by the following formula is 90 to 110%. Retention rate (%) = (Initial bubble point or burst bubble point after storage / Initial bubble point or burst bubble point before storage) × 100 Storage conditions: Immerse the polyamide hollow fiber membrane in propylene glycol monomethyl ether acetate and store it at 23 °C for 2 years without applying pressure. <11> In the module case, <1> ~ <10> A hollow fiber membrane module containing a polyamide hollow fiber membrane as described in any of the above. <12> The first step involves using a multi-screw extruder to prepare a film-forming stock solution by mixing at least a polyamide resin and sulfones. A second step involves using a double-tube nozzle for hollow fiber manufacturing, in which the film-forming raw material is discharged from the outer annular nozzle and the internal liquid is discharged from the inner nozzle, and the resulting film is immersed in a coagulation bath containing water and / or polyhydric alcohol to form a hollow fiber film, and The third step includes removing the organic solvent from the hollow fiber membrane formed in the second step, The sulfones are those which, when dissolved in water to form a 5% by mass aqueous solution, have a pH of 5.2 to 6.8 at 25°C, in a method for producing polyamide hollow fiber membranes. <13> The aforementioned sulfones are dimethyl sulfone and / or sulfolane. <12> A method for producing a polyamide hollow fiber membrane as described above. <14> The process further includes a fourth step, after the third step, in which the hollow fiber membrane is washed with an organic solvent to remove at least one metal element selected from the group consisting of Fe, Cr, Cu, Mg, and Zn. <12> or <13> A method for producing a polyamide hollow fiber membrane as described above. [Effects of the Invention]

[0009] Because the polyamide hollow fiber membrane of the present invention has a reduced content of specific metal elements, its filtration performance does not change easily even when stored for a long period of time in a storage solution, and it has excellent storage stability. [Brief explanation of the drawing]

[0010] [Figure 1] This is a schematic diagram of a device for measuring the water permeability under external pressure in a polyamide hollow fiber membrane. [Figure 2] This is a schematic diagram of an apparatus for measuring bubble points in polyamide hollow fiber membranes. [Modes for carrying out the invention]

[0011] 1. Polyamide hollow fiber membrane The polyamide hollow fiber membrane of the present invention is formed from a polyamide resin and satisfies at least one of the following characteristics (1) to (5). The polyamide hollow fiber membrane of the present invention will be described in detail below. (1) Fe content is 4.30 ppm or less (2) Cr content is less than 1.00 ppm (3) Cu content is less than 0.20 ppm (4) Mg content is less than 0.60 ppm (5) Zn content is less than 0.30 ppm

[0012] <Polyamide resin> The type of polyamide resin used to form the polyamide hollow fiber membrane of the present invention is not particularly limited, but examples include polyamide homopolymers, polyamide copolymers, or mixtures thereof. Specific examples of polyamide homopolymers include polyamide 6, polyamide 66, polyamide 46, polyamide 610, polyamide 612, polyamide 11, polyamide 12, polyamide MXD6, polyamide 4T, polyamide 6T, polyamide 9T, and polyamide 10T. Specific examples of polyamide copolymers include copolymers of polyamide with polyethers such as polytetramethylene glycol or polyethylene glycol. The ratio of the polyamide component in the polyamide copolymer is not particularly limited, but for example, the proportion of the polyamide component is preferably 70 mol% or more, more preferably 80 mol% or more, even more preferably 90 mol% or more, and particularly preferably 95 mol% or more. By satisfying the above range for the ratio of the polyamide component in the polyamide copolymer, excellent durability can be achieved. Polyamide resins may be used individually or in combination of two or more types.

[0013] The polyamide resin used in this invention may or may not be crosslinked, as long as it can be molded into a fibrous shape. From the viewpoint of cost reduction, a non-crosslinked polyamide resin is preferred.

[0014] <Polyamide hollow fiber membrane> The polyamide hollow fiber membrane of the present invention has a reduced content of at least one metal element selected from the group consisting of Fe, Cr, Cu, Mg, and Zn (hereinafter, these metal elements are also referred to as "specific metal elements").

[0015] Certain metal elements are substances that cause significant changes in filtration performance, such as the rejection rate and water permeability under external pressure, when polyamide hollow fiber membranes are stored in a preservation solution for extended periods. The reason why the filtration performance of polyamide hollow fiber membranes changes significantly due to certain metal elements when stored in a preservation solution for extended periods is not clear, but it is presumed that the polyamide resin constituting the polyamide hollow fiber membrane deteriorates due to the cutting or other processes caused by the specific metal elements, or that chemical reactions occur between the specific metal elements and other impurities in the polyamide hollow fiber membrane, resulting in changes to the porous structure of the polyamide hollow fiber membrane.

[0016] In order to obtain a polyamide hollow fiber membrane whose filtration performance does not change easily even when stored for a long period of time in a storage solution, the Fe content among the specific metal elements is 4.30 ppm or less, preferably 3.50 ppm or less, more preferably 3.00 ppm or less, even more preferably 2.50 ppm or less, even more preferably 2.00 ppm or less, even more preferably 1.50 ppm or less, and particularly preferably 1.20 ppm or less. Examples of the Fe content include 0.00 to 4.30 ppm, 0.10 to 3.50 ppm, 0.20 to 3.00 ppm, 0.50 to 2.50 ppm, 0.60 to 2.00 ppm, 0.70 to 1.50 ppm, or 0.80 to 1.20 ppm.

[0017] In order to obtain a polyamide hollow fiber membrane whose filtration performance does not change easily even when stored for a long period of time in a storage solution, the Cr content among the specific metal elements is less than 1.00 ppm, preferably 0.70 ppm or less, more preferably 0.60 ppm or less, even more preferably 0.50 ppm or less, even more preferably 0.40 ppm or less, and particularly preferably 0.30 ppm or less. Examples of the Cr content include 0.00 to 0.99 ppm, 0.00 to 0.70 ppm, 0.05 to 0.60 ppm, 0.05 to 0.50 ppm, 0.10 to 0.40 ppm, or 0.10 to 0.30 ppm.

[0018] In order to obtain a polyamide hollow fiber membrane whose filtration performance does not change easily even when stored for a long period of time in a storage solution, the Cu content among the specific metal elements is less than 0.20 ppm, preferably 0.17 ppm or less, more preferably 0.15 ppm or less, even more preferably 0.14 ppm or less, even more preferably 0.13 ppm or less, and particularly preferably 0.10 ppm or less. Examples of Cu content include 0.00 to 0.19 ppm, 0.00 to 0.17 ppm, 0.02 to 0.15 ppm, 0.02 to 0.14 ppm, 0.05 to 0.13 ppm, or 0.05 to 0.10 ppm.

[0019] In order to obtain a polyamide hollow fiber membrane whose filtration performance does not change easily even when stored for a long period of time in a storage solution, the Mg content among the specific metal elements is less than 0.60 ppm, preferably 0.50 ppm or less, more preferably 0.40 ppm or less, even more preferably 0.30 ppm or less, even more preferably 0.20 ppm or less, and particularly preferably 0.10 ppm or less. Examples of the Mg content include 0.00 to 0.59 ppm, 0.00 to 0.50 ppm, 0.02 to 0.40 ppm, 0.02 to 0.30 ppm, 0.05 to 0.20 ppm, or 0.05 to 0.10 ppm.

[0020] In order to obtain a polyamide hollow fiber membrane whose filtration performance does not change easily even when stored for a long period of time in a storage solution, the Zn content among the specific metal elements is less than 0.30 ppm, preferably 0.25 ppm or less, more preferably 0.20 ppm or less, even more preferably 0.17 ppm or less, even more preferably 0.13 ppm or less, and particularly preferably 0.10 ppm or less. Examples of the Zn content include 0.00 to 0.29 ppm, 0.00 to 0.25 ppm, 0.02 to 0.20 ppm, 0.02 to 0.17 ppm, 0.05 to 0.13 ppm, or 0.05 to 0.10 ppm.

[0021] From the viewpoint of more effectively suppressing changes in filtration performance even when the polyamide hollow fiber membrane of the present invention is stored in a storage solution for a long period of time, preferably the content of any two of the specified metal elements is within the numerical range, more preferably the content of any three of the specified metal elements is within the numerical range, even more preferably the content of any four of the specified metal elements is within the numerical range, and particularly preferably the content of all (five) of the specified metal elements is within the numerical range.

[0022] Examples of embodiments of the polyamide hollow fiber membrane of the present invention include those satisfying features (1) and (2); features (1) and (3); features (1) and (4); features (1) and (5); features (2) and (3); features (2) and (4); features (2) and (5); features (3) and (4); features (3) and (5); or features (4) and (5).

[0023] Furthermore, other embodiments of the polyamide hollow fiber membrane of the present invention include, specifically, embodiments that satisfy features (1), (2), and (3); features (1), (2), and (4); features (1), (2), and (5); features (1), (3), and (4); features (1), (3), and (5); features (1), (4), and (5); features (2), (3), and (4); features (2), (3), and (5); features (2), (4), and (5); or features (3), (4), and (5).

[0024] Furthermore, other embodiments of the polyamide hollow fiber membrane of the present invention include, specifically, embodiments that satisfy features (1), (2), (3), and (4); features (1), (2), (3), and (5); features (1), (2), (4), and (5); features (1), (3), (4), and (5); or features (2), (3), (4), and (5).

[0025] Furthermore, other embodiments of the polyamide hollow fiber membrane of the present invention include, specifically, those that satisfy features (1), (2), (3), (4), and (5).

[0026] In this invention, the content of metal elements in the polyamide hollow fiber membrane is determined by preparing a sample by decomposing and / or dissolving a dried polyamide hollow fiber membrane in nitric acid, and then measuring the prepared sample by inductively coupled plasma (ICP) emission spectroscopy.

[0027] The relative viscosity of the polyamide hollow fiber membrane of the present invention is, for example, 2.0 to 6.5. In polyamide hollow fiber membranes with reduced content of specific metal elements, from the viewpoint of ensuring good external pressure permeability before long-term storage, the relative viscosity is preferably 2.5 to 5.5, more preferably 3.0 to 5.0, even more preferably 3.5 to 4.5, and particularly preferably 4.0 to 4.3. The relative viscosity of the polyamide hollow fiber membrane can be adjusted by appropriately selecting the relative viscosity of the polyamide resin constituting the polyamide hollow fiber membrane.

[0028] In this invention, the relative viscosity of the polyamide hollow fiber membrane is measured by preparing a sample by dissolving the polyamide hollow fiber membrane in 96% by mass sulfuric acid to a concentration of 1 g / dL, and then measuring the prepared sample using an Ubbelohbe viscometer at 25°C.

[0029] In the polyamide hollow fiber membrane of the present invention, in crystal structure analysis by X-ray diffraction, the ratio of γ crystals to the total amount of α crystals and γ crystals is, for example, 0 to 37%, and in the polyamide hollow fiber membrane with reduced content of specific metal elements, from the viewpoint of ensuring good external pressure permeability before long-term storage, it is preferably 5 to 30%, more preferably 10 to 26%, and even more preferably 15 to 25%. The ratio of γ crystals to the total amount of α crystals and γ crystals in the polyamide hollow fiber membrane can be adjusted to the desired range by adjusting the relative viscosity of the polyamide hollow fiber membrane. For example, if the polyamide resin forming the polyamide hollow fiber membrane is polyamide 6, the ratio of γ crystals can be adjusted to the above preferred range by adjusting the relative viscosity of the polyamide hollow fiber membrane to the preferred range described above.

[0030] In this invention, the ratio of γ crystals to the total amount of α crystals is determined by calculating the peak areas of α and γ crystals by crystal structure analysis using X-ray diffraction, and then calculating the ratio of the peak area of ​​γ crystals to the sum of the peak areas of α and γ crystals. Specifically, the ratio of γ crystals to the total amount of α and γ crystals is a value measured using an X-ray diffractometer under the following conditions and method. • Pre-treatment: Cut a polyamide hollow fiber membrane perpendicular to its length and fix it to the pole sample plate with double-sided tape. Position the pole sample plate so that the length of the sample is parallel to the optical axis when 2θ = 0°. • Measurement method: WAXD reflection method 2θ / θ method is used. Measurement conditions: X-ray Cu-Kα rays (1.54 Å), 50 kV 300 mA, thin film, standard multi-purpose sample stage / pole sample plate, parallel beam method, receiving side solar slit = long slit used, slits: DS / SS / RS = 1.0 mm / 1.0 mm / 1.0 mm, vertical limiting slit = 10 mm, scan range: 2θ = 2°~60°, scan speed: 2° / min, step set to 0.02°. • Analysis method: Multiple peak separation (profile fitting using pseudo-Voigt function) is performed in the 2θ = 5° to 36° region. The specific analysis conditions are as follows. 1) The background is defined as the area under the straight line connecting the corrected intensity at 2θ=8° (calculated as the average intensity from 2θ=7.5° to 8.5°) and the corrected intensity at 2θ=36° (calculated as the average intensity from 2θ=35.5° to 36.5°). 2) The halo pattern due to the amorphous component is assigned as a Gaussian function so as to be tangent to the peak shapes at 2θ = 15° to 17° and 2θ = 27° to 29°. In this case, the center of the halo pattern should be at 2θ = 19° to 21°, and the full width at half maximum should be about 10. 3) For diffraction lines due to crystalline components, assign a symmetric pseudo-Voigt function to match the peak top and waveform. Perform profile fitting after fixing the parameters of the halo pattern. The 2θ position of the peak, full width at half maximum, height, and contribution ratio of the Gaussian and Lorentz functions are set during fitting. Jade+9.8 is used for fitting. 4) Using the multiple peak separation method described above, the peak area of ​​the crystalline portion, the peak area of ​​the α-crystal, and the peak area of ​​the γ-crystal are determined, and the ratio of γ-crystal to the total amount of α-crystal and γ-crystal is calculated from the following formula 1. <Expression 1> The ratio of γ crystals to the total amount of α crystals (%) = {peak area of ​​γ crystals / (peak area of ​​γ crystals + peak area of ​​α crystals)} × 100

[0031] The polyamide hollow fiber membrane of the present invention may have a dense layer on the luminal surface and / or outer surface in order to improve the blocking rate of fine particles. In the present invention, "dense layer" refers to a region where, when observing a cross-section of the polyamide hollow fiber membrane, the porous structure of a specific region adjacent to the luminal surface or outer surface of the polyamide hollow fiber membrane is denser and has a concentration of fine pores than the porous structure of other regions (for example, a region near the midpoint between the luminal surface and the outer surface), and this dense region with a concentration of fine pores determines the fractionation characteristics of the polyamide hollow fiber membrane, and includes cases where the presence of pores is substantially not observed (cases where the presence of pores is not observed in a scanning electron microscope (SEM) image at a magnification of 10,000x). The dense layer can be observed in a scanning electron microscope (SEM) image. In the polyamide hollow fiber membrane of the present invention, the thickness of the dense layer is not particularly limited, but is, for example, 0.01 to 2.0 μm, and preferably 0.1 to 1.5 μm. The polyamide hollow fiber membrane exhibits good blocking properties for fine particles due to the presence of a dense layer.

[0032] The polyamide hollow fiber membrane of the present invention has a membrane separation performance or filtration performance such that the rejection rate for particles with a particle size of 50 nm is preferably 90% or higher, more preferably 95% or higher, even more preferably 98% or higher, and particularly preferably 99% or higher. The rejection rate for fine particles varies depending on the application and purpose of use when used as a module, but as a preferred example of filtration performance, the rejection rates for particles with a particle size of 20 nm, 10 nm, and 5 nm are also preferably 90% or higher, more preferably 95% or higher, even more preferably 98% or higher, and particularly preferably 99% or higher, respectively. Thus, the polyamide hollow fiber membrane of the present invention has a pore structure that can separate fine particles with a high rejection rate and has excellent fine particle removal performance.

[0033] In this invention, the rejection rate of particles of each particle size is calculated from the proportion of gold colloid particles removed when a filtration test is performed using gold colloid particles having a predetermined average particle size. Because gold colloid particles have a very narrow particle size distribution, a filtration test using gold colloid can accurately reflect the particle rejection rate of the hollow fiber membrane. Specifically, the filtration test using gold colloid particles involves adding 2 mmol / l of tris(hydroxymethyl)aminomethane to an aqueous dispersion containing 10 ppm of gold colloid having a predetermined average particle size, performing constant-pressure dead-end filtration under conditions of a filtration pressure of 0.3 MPa and a filtration temperature of 25°C, and filtration the filtrate with a cumulative filtration volume of 0.005 m³. 3 / m 2 The solution is separated into portions, and the absorbance of the second portion at a wavelength of 524 nm is measured. The rejection rate of each particle size is then calculated using Equation 2 below. <Expression 2> Particle rejection rate (%) = {(Absorbance of unfiltered solution - Absorbance of filtrate) / Absorbance of unfiltered solution} × 100

[0034] The polyamide hollow fiber membrane of the present invention is characterized by its excellent storage stability, as its filtration performance does not change easily even when stored for a long period of time in a storage solution. Polyamide hollow fiber membranes are generally used as hollow fiber membrane modules housed in module cases, and the common method of storage after using hollow fiber membrane modules for various purposes is to immerse them in a storage solution. In the present invention, "use" of the polyamide hollow fiber membrane or hollow fiber membrane module means filtering by passing the filtration stock (stock before filtration) from one side of the polyamide hollow fiber membrane's lumen side to the other, and the type and amount of the filtration stock, the type and amount of the components to be classified, and the filtration performance are not limited. Also, in the present invention, the type of "storage solution" is not limited, and examples include water and / or organic solvents. The storage solution may contain additives such as preservatives as needed to improve its shelf life. Also, in the present invention, "storage" means keeping it immersed in the storage solution until the next use, and it is preferable to store it standing without passing the solution through it. The storage temperature is not particularly limited, but is preferably 20 to 40°C. The storage period is not particularly limited, but is usually one month or more. From the viewpoint of significantly exhibiting the effects of the present invention, it is preferably six months or more, more preferably one year or more, even more preferably two years or more, and particularly preferably three years or more.

[0035] The polyamide hollow fiber membrane of the present invention has a retention rate of the rejection rate of particles with a particle size of 5 nm, calculated by the following formula 3, preferably 90% or more, more preferably 95% or more, even more preferably 97% or more, even more preferably 98% or more, and particularly preferably 99% or more. <Expression 3> Retention rate of blocking rate (%) = (Blocking rate of 5nm particles after storage / Blocking rate of 5nm particles before storage) × 100 Storage conditions: Immerse the polyamide hollow fiber membrane in propylene glycol monomethyl ether acetate and store at 23°C for 2 years without pressurization.

[0036] One of the filtration properties of the polyamide hollow fiber membrane of the present invention is that the water permeability under external pressure is preferably 50 to 2000 L / (m³). 2·atm·h), more preferably 100 - 1500 L / (m 2 ·atm·h), still more preferably 150 - 1000 L / (m 2 ·atm·h), even more preferably 200 - 800 L / (m 2 ·atm·h), yet more preferably 250 - 800 L / (m 2 ·atm·h), particularly preferably 300 - 800 L / (m 2 ·atm·h). However, the preferred external pressure water permeation rate varies depending on the application and purpose of use when made into a module, and also varies depending on the rejection rate, which is the filtration performance of the polyamide hollow fiber membrane.

[0037] In a polyamide hollow fiber membrane having the performance of blocking 90% or more of particles with a particle size of 5 nm, the external pressure water permeation rate is preferably 50 - 1000 L / (m 2 ·atm·h), more preferably 100 - 800 L / (m 2 ·atm·h), still more preferably 150 - 600 L / (m 2 ·atm·h), even more preferably 200 - 600 L / (m 2 ·atm·h), particularly preferably 250 - 400 L / (m 2 ·atm·h).

[0038] In a polyamide hollow fiber membrane having the performance of allowing 10% or more of particles with a particle size of 5 nm to pass through but blocking 90% or more of particles with a particle size of 10 nm, the external pressure water permeation rate is preferably 100 - 1500 L / (m 2 ·atm·h), more preferably 150 - 1000 L / (m 2 ·atm·h), still more preferably 200 - 800 L / (m 2 ·atm·h), even more preferably 250 - 600 L / (m 2 ·atm·h), particularly preferably 300 - 500 L / (m 2 ·atm·h).

[0039] In a polyamide hollow fiber membrane having the performance of allowing 10% or more of particles with a particle size of 10 nm to pass through but blocking 90% or more of particles with a particle size of 20 nm, the external pressure water permeation rate is preferably 200 - 2000 L / (m2 ·atm·h), more preferably 250~1750L / (m 2 ·atm·h), more preferably 300~1500L / (m 2 ·atm·h), more preferably 500~1250L / (m 2 ·atm·h), particularly preferably 600~1000L / (m 2 ·atm·h) is

[0040] In a polyamide hollow fiber membrane having the ability to transmit more than 10% of particles with a particle size of 20 nm but block more than 90% of particles with a particle size of 50 nm, the external pressure permeability is preferably 500 to 2000 L / (m³). 2 ·atm·h), more preferably 600~1750L / (m 2 ·atm·h), more preferably 800~1500L / (m 2 ·atm·h), more preferably 1000~1500L / (m 2 ·atm·h), particularly preferably 1250~1500L / (m 2 ·atm·h) is

[0041] Thus, because the polyamide hollow fiber membrane of the present invention has high external pressure permeability, the flow rate of the treatment liquid can be set high, and the filtration efficiency can be improved.

[0042] In the present invention, the external pressure permeability of the polyamide hollow fiber membrane is a value measured by external pressure filtration, specifically, a value measured by the method described in the examples below.

[0043] The polyamide hollow fiber membrane of the present invention has a retention rate of external pressure permeability calculated by the following formula 4, preferably 90-110%, more preferably 95-105%, even more preferably 97-103%, even more preferably 98-102%, and particularly preferably 99-101%. <Expression 4> Retention rate of external pressure permeability (%) = (External pressure permeability after storage / External pressure permeability before storage) × 100 Storage conditions: Immerse the polyamide hollow fiber membrane in propylene glycol monomethyl ether acetate and store at 23°C for 2 years without pressurization.

[0044] The polyamide hollow fiber membrane of the present invention preferably exhibits, as one aspect of its filtration performance, an initial bubble point of 0.20 MPa or higher and a burst bubble point of 0.30 MPa or higher in a bubble point test conducted by applying air pressure in 2-propanol with a surface tension of 21 mN / m at 20°C. While the initial bubble point and burst bubble point vary depending on the application and intended use of the module, a more preferable example of filtration performance is an initial bubble point of 0.30 MPa or higher and a burst bubble point of 0.40 MPa or higher; an even more preferable initial bubble point of 0.35 MPa or higher and a burst bubble point of 0.45 MPa or higher; an even more preferable initial bubble point of 0.40 MPa or higher and a burst bubble point of 0.55 MPa or higher; and a particularly preferable initial bubble point of 0.45 MPa or higher and a burst bubble point of 0.65 MPa or higher. Furthermore, the initial bubble point is preferably 0.20 to 1.20 MPa, more preferably 0.30 to 1.10 MPa, even more preferably 0.35 to 1.00 MPa, even more preferably 0.40 to 0.90 MPa, and particularly preferably 0.45 to 0.80 MPa. The burst bubble point is preferably 0.30 to 1.20 MPa, more preferably 0.40 to 1.10 MPa, even more preferably 0.45 to 1.00 MPa, even more preferably 0.55 to 0.90 MPa, and particularly preferably 0.65 to 0.80 MPa. The presence of these bubble points indicates that the polyamide hollow fiber membrane has an appropriate pore size for high filtration accuracy.

[0045] In this invention, the bubble point test is a commonly used measurement method for determining the maximum pore diameter. Because it is simple and quick to perform, it is widely used to estimate pore diameter. The principle and method of the bubble point test are described in JIS standard K3832. The initial bubble point is the pressure at which air permeates from the membrane surface and bubbles begin to form when air pressure is applied to the hollow fiber membrane, and the burst bubble point is the pressure at which bubbles begin to form from approximately the entire membrane. Specifically, the initial bubble point and the burst bubble point are values ​​measured by the method described in the examples below.

[0046] In the bubble point test described above, the polyamide hollow fiber membrane of the present invention has a retention rate of the initial bubble point (hereinafter sometimes referred to as "IBP") and burst bubble point (hereinafter sometimes referred to as "BBP") calculated by the following formula 5, preferably 90 to 110%, more preferably 95 to 105%, even more preferably 97 to 103%, even more preferably 98 to 102%, and particularly preferably 99 to 101%. <Formula 5> IBP or BBP retention rate (%) = (IBP or BBP after storage / IBP or BBP before storage) × 100 Storage conditions: Immerse the polyamide hollow fiber membrane in propylene glycol monomethyl ether acetate and store at 23°C for 2 years without pressurization.

[0047] The inner and outer diameters of the polyamide hollow fiber membrane of the present invention are not particularly limited and can be set as appropriate depending on the intended use. The inner diameter is, for example, 100 to 3000 μm, preferably 150 to 1500 μm, more preferably 200 to 1000 μm, and even more preferably 350 to 800 μm. The outer diameter is, for example, 250 to 5000 μm, preferably 300 to 3000 μm, more preferably 400 to 2000 μm, and even more preferably 450 to 600 μm.

[0048] The inner and outer diameters of a polyamide hollow fiber membrane can be measured by observing a cross-section of the polyamide hollow fiber membrane under an optical microscope at 200x magnification.

[0049] From the viewpoint of improving processability when the polyamide hollow fiber membrane of the present invention is housed in a module case to form a hollow fiber membrane module, it is preferable that the values ​​of the breaking strength, breaking elongation, and tensile modulus are within the ranges described below. In the present invention, the breaking strength, breaking elongation, and tensile modulus are the average values ​​measured in accordance with JIS L-1013, with a chuck distance of 50 mm, a tensile speed of 50 mm / min, and a number of measurements of 5.

[0050] The tensile strength of the polyamide hollow fiber membrane is preferably 1.5 to 30 MPa, more preferably 2.5 to 25 MPa, even more preferably 3.5 to 15 MPa, and even more preferably 4 to 10 MPa.

[0051] The elongation at break of the polyamide hollow fiber membrane is preferably 10-500%, more preferably 20-350%, even more preferably 40-320%, and even more preferably 100-300%.

[0052] The tensile modulus of the polyamide hollow fiber membrane is preferably 10 to 100 MPa, more preferably 15 to 80 MPa, even more preferably 20 to 70 MPa, and even more preferably 20 to 60 MPa.

[0053] The polyamide hollow fiber membrane of the present invention is a hollow fiber membrane formed mainly of polyamide resin, but may contain other resin components, softeners, curing agents, crosslinking agents, antioxidants, stabilizers, dispersants, lubricants, flame retardants, anti-aging agents, antistatic agents, and other additives as needed, as long as they do not impair the effects of the present invention. These may be used individually or in combination of two or more. The total content of these components is preferably 10% by mass or less of the total polyamide hollow fiber membrane.

[0054] The polyamide hollow fiber membrane of the present invention may have coating layers, such as an organic coating layer and an inorganic coating layer, on the inner surface and / or outer surface. The thickness of the coating layer is not particularly limited, but is, for example, 0.001 to 100 μm.

[0055] 2. Method for producing polyamide hollow fiber membranes The polyamide hollow fiber membrane of the present invention can be manufactured by employing specific manufacturing conditions using the thermally induced phase separation method (TIPS method).

[0056] Specifically, the method for producing the polyamide hollow fiber membrane of the present invention is carried out through the following three steps. Step 1: Using a multi-screw extruder, a film-forming stock solution is prepared by mixing at least a polyamide resin and sulfones. The sulfones are those which, when dissolved in water to form a 5% by mass aqueous solution, have a pH of 5.2 to 6.8 at 25°C. Step 2: Using a double-tube nozzle for hollow fiber manufacturing, the film-forming raw material is discharged from the outer annular nozzle and the internal liquid is discharged from the inner nozzle, and the resulting material is immersed in a coagulation bath containing water and / or polyhydric alcohol to form a hollow fiber film. Step 3: Remove the organic solvent from the hollow fiber membrane formed in Step 2.

[0057] The method for producing the polyamide hollow fiber membrane of the present invention will be described in detail below, step by step.

[0058] <1st process> In the first step, a film-forming stock solution is prepared by mixing at least a polyamide resin and sulfones using a multi-screw extruder.

[0059] A common method for preparing a film-forming stock solution involves adding raw materials such as polyamide resin and organic solvents to a tank equipped with a heater and stirrer, and preparing the stock solution in a batch process. However, conventional batch-process methods for preparing film-forming stock solutions cannot reduce the content of specific metal elements in the polyamide hollow fiber membrane to the desired range.

[0060] Therefore, in this invention, in order to reduce the content of specific metal elements in the polyamide hollow fiber membrane to a desired range, a method is employed in which at least polyamide resin and sulfones are quantitatively fed into a multi-screw extruder to prepare a film-forming stock solution in a continuous manner. Furthermore, in this invention, in order to reduce the content of specific metal elements in the polyamide hollow fiber membrane to a desired range, the sulfones used are those whose pH at 25°C is 5.2 to 6.8 when dissolved in water to make a 5% by mass aqueous solution.

[0061] The reason why the content of specific metal elements in polyamide hollow fiber membranes can be reduced to a desired range by employing a method of continuously preparing a film-forming stock solution using a multi-screw extruder and sulfones whose pH at 25°C is 5.2 to 6.8 when dissolved in water to form a 5% by mass aqueous solution is not clear, but it is presumed to be due to the following reasons. The first reason is that the continuous method using a multi-screw extruder has a higher solubility of the polyamide resin in the sulfones than the batch method using tanks, so the time required for dissolution can be shortened, and as a result the residence time (contact time with metal) of the film-forming stock solution in the manufacturing equipment can be shortened, and it is presumed that this can suppress the contamination of the film-forming stock solution with specific metal elements originating from the manufacturing equipment. The second reason is that the sulfones have higher compatibility with polyamide resins compared to conventional organic solvents used when preparing the film-forming stock solution. This allows for a further reduction in the time required for dissolution, thereby further shortening the residence time (contact time with metal) of the film-forming stock solution in the manufacturing equipment. Consequently, it is presumed that this will further suppress the contamination of the film-forming stock solution with specific metal elements originating from the manufacturing equipment.

[0062] A multi-screw extruder is not particularly limited as long as it has multiple screws, but a twin-screw extruder is preferred from the viewpoint of versatility. The outer diameter and L / D ratio of the screws are not particularly limited and can be appropriately designed according to the desired production volume, but the outer diameter is preferably φ30 or more, and the L / D ratio is preferably 25 or more. The screw configuration is also not particularly limited, but the arrangement of the full flight and kneading discs should be appropriately designed to ensure stable production of the film-forming stock. The rotational speed of the screws is also not particularly limited and can be appropriately designed, but is preferably 30 rpm or more. The set temperature of the multi-screw extruder can be appropriately designed, but is preferably 150 to 300°C. Furthermore, it is preferable that the multi-screw extruder be equipped with a device for quantitatively feeding polyamide resin and sulfones.

[0063] Examples of sulfones include dimethyl sulfone, sulfolane, diethyl sulfone, diphenyl sulfone, 1,3-propane sulfone, 1,4-butane sulfone, busulfan, sulfolene, ethylmethyl sulfone, and methylphenyl sulfone. These may be used individually or in combination of two or more. Of these, dimethyl sulfone and / or sulfolane are preferred from the viewpoint of further reducing the content of specific metal elements in the polyamide hollow fiber membrane.

[0064] When dimethyl sulfone is used as the sulfone, the pH at 25°C of a 5% by mass aqueous solution (5% by mass of dimethyl sulfone, 95% by mass of water) is preferably 5.2 to 6.5. When sulfolane is used as the sulfone, the pH at 25°C of a 5% by mass aqueous solution (5% by mass of sulfolane, 95% by mass of water) is preferably 6.3 to 6.8. When dimethyl sulfone and sulfolane are used in combination as the sulfone, it is preferable that the pH of the 5% by mass aqueous solution of either or both is within the above preferred range. The pH of the 5% by mass aqueous solution of sulfones can be adjusted to the desired pH, for example, by adjusting the amount of oxidizing agent or reducing agent used when synthesizing the sulfones.

[0065] In the film-forming stock solution, the mass ratio of polyamide resin to sulfones (polyamide resin:sulfones) is preferably 5:95 to 50:50, more preferably 20:80 to 40:60, and even more preferably 26:74 to 30:70. By satisfying the above mass ratio, it becomes easier to adjust the particle rejection rate, initial bubble point, burst bubble point, and external pressure permeability within the aforementioned ranges.

[0066] <Second process> In the second step, a double-tube nozzle for hollow fiber production is used to discharge the film-forming raw material from the outer annular nozzle and the internal liquid from the inner nozzle, and the resulting material is immersed in a coagulation bath containing water and / or polyhydric alcohol to form a hollow fiber film.

[0067] Here, as the double-tubular nozzle for hollow fiber production, a nozzle having a double annular structure, similar to those used in melt spinning to produce core-sheath type composite fibers, can be used. The diameters of the outer annular nozzle and the inner nozzle of the double-tubular nozzle for hollow fiber production can be appropriately set according to the inner and outer diameters of the polyamide hollow fiber membrane.

[0068] Furthermore, in the second step, the internal liquid discharged from the inner nozzle of the double-tubular nozzle for hollow fiber production can be either a liquid or a gas, provided it is inert to the polyamide resin. However, liquids are preferred because they allow spinning even under conditions where the viscosity of the film-forming stock solution is low and filament formation is difficult. The liquid used as the internal liquid is not particularly limited, provided it is inert to the polyamide resin. However, a good solvent with high affinity for the polyamide resin can be used when it is desired to create relatively large pores on the inner surface of the polyamide hollow fiber, while a poor solvent can be used when it is desired to create relatively small pores on the inner surface of the polyamide hollow fiber. Specific examples of such good solvents include glycerin, diethylene glycol, triethylene glycol, tetraethylene glycol, polyethylene glycol 200, γ-butyrolactone, ε-caprolactone, propylene glycol, benzyl alcohol, 1,3-butanediol, and sulfolane. Specific examples of such poor solvents include polyethylene glycol with an average molecular weight of 300 to 1000, polypropylene glycol with an average molecular weight of 400 to 1000, higher fatty acids, and liquid paraffin. These solvents may be used individually or in combination of two or more. Furthermore, if the film-forming stock solution has high viscosity and excellent stringability, a method of introducing a gas such as an inert gas may be used.

[0069] Among these internal liquids, glycerin, 1,3-butanediol, triethylene glycol, tetraethylene glycol, polyethylene glycol 200, and sulfolane are preferably used.

[0070] In the second step, a coagulation bath containing water and / or a polyhydric alcohol is used. By employing such a coagulation bath, a polyamide hollow fiber membrane with the aforementioned properties can be formed. Specific examples of polyhydric alcohols used in the coagulation bath include glycerin, ethylene glycol, propylene glycol, butylene glycol, diethylene glycol, dipropylene glycol, diglycerin, triethylene glycol, tetraethylene glycol, polyethylene glycol (200-400), and 1,3-butanediol. Among these polyhydric alcohols, glycerin, ethylene glycol, diethylene glycol, propylene glycol, 1,3-butanediol, and polyethylene glycol 200 are preferred. These polyhydric alcohols may be used individually or in combination of two or more.

[0071] Furthermore, when using a coagulation bath containing water and polyhydric alcohol, there are no particular restrictions on the composition ratio of these components, but the mass ratio of polyhydric alcohol to water is preferably 25-80:75-20, and more preferably 40-70:60-30.

[0072] An example of an internal liquid and coagulation bath for obtaining a polyamide hollow fiber membrane comprising a dense layer formed on the luminal surface and a porous layer having relatively large pores that support the dense layer is, for example, an internal liquid which may be at least one selected from the group consisting of glycerin, polyethylene glycol with an average molecular weight of 300 to 1000, polypropylene glycol with an average molecular weight of 400 to 1000, and triethylene glycol, and a coagulation bath which may be at least one selected from the group consisting of diethylene glycol, tetraethylene glycol, and propylene glycol, or an aqueous solution containing at least one of these in a proportion of 40 to 80% by mass (preferably 40 to 60% by mass).

[0073] The temperature of the solidification bath is not particularly limited, but is usually -20 to 100°C, preferably -10 to 80°C, and more preferably 0 to 40°C. By changing the temperature of the solidification bath, the crystallization rate can be changed, thereby changing the pore size, water permeability, and strength. Generally, a lower temperature of the solidification bath tends to result in smaller pore size, lower water permeability, and improved strength, while a higher temperature tends to result in larger pore size, higher water permeability, and decreased strength. However, this can also vary depending on the solubility of the solvent in the film-forming solution and the internal liquid, as well as the crystallization rate of the resin itself. To keep the external pressure water permeability and particle rejection rate of the polyamide hollow fiber membrane within the aforementioned ranges, a low temperature of the solidification bath is preferable, but it is not always necessary to have a low temperature depending on the conditions. If the temperature of the solidification bath is within the above range, the strength of the membrane can be increased while also reducing the energy required for temperature control.

[0074] Furthermore, the flow rate when discharging the film-forming stock solution from the annular nozzle on the outside of the double-tubular nozzle for hollow fiber production is not particularly limited, but for example, it can be 2 to 20 g / min, preferably 3 to 15 g / min, and more preferably 4 to 10 g / min. The flow rate of the internal liquid is set appropriately considering the diameter of the inner nozzle of the double-tubular nozzle for hollow fiber production, the type of internal liquid used, the flow rate of the film-forming stock solution, etc., but for example, it can be 0.1 to 2 times, preferably 0.2 to 1 time, and more preferably 0.4 to 0.7 times the flow rate of the film-forming stock solution.

[0075] Thus, by carrying out the second step, the film-forming raw material discharged from the double-tubular nozzle for hollow fiber production solidifies in the coagulation bath to form a polyamide hollow fiber film.

[0076] <3rd process> In the third step, organic solvents are removed from the hollow fiber membrane formed in the second step. The method for removing organic solvents from the hollow fiber membrane is not particularly limited and includes methods such as immersion in a washing solution consisting of water or an aqueous solution, or winding the hollow fiber membrane onto a bobbin, fence, or winding machine and exposing the wound hollow fiber membrane to running water consisting of the washing solution. By such methods, organic solvents such as sulfones, components of the coagulation bath, and components of the internal liquid contained in the hollow fiber membrane can be removed. As the washing solution, it is preferable to use a solution that is inexpensive, has a low boiling point, and can be easily separated after washing by the difference in boiling point, and water is preferred. If the washing effect is insufficient with water alone, an aqueous solution in which a component that promotes washing effect is dissolved in water may be used. The component that promotes washing effect is not particularly limited, but examples include solvents such as methanol, ethanol, isopropanol, acetone, diethyl ether, and petroleum ether, and surfactants. The washing time is not particularly limited, but for example, it is 0.2 hours to 2 months, preferably 0.5 hours to 1 month, and more preferably 2 hours to 10 days. To effectively remove organic solvents remaining on the polyamide hollow fiber membrane, the composition of the washing solution may be changed, the washing solution may be stirred, or the flow rate of the washing solution may be changed.

[0077] Thus, by carrying out the third step, the polyamide hollow fiber membrane of the present invention is manufactured.

[0078] <4th process> Although the polyamide hollow fiber membrane obtained through steps 1 to 3 has a reduced content of specific metal elements, a fourth step may be added after step 3 in which the polyamide hollow fiber membrane is washed with an organic solvent in order to further reduce the content of specific metal elements.

[0079] A preferred method for cleaning polyamide hollow fiber membranes is to immerse the inner surface and / or outer surface of the polyamide hollow fiber membrane in an organic solvent, which is a cleaning solvent, and more preferably, to immerse both the inner and outer surfaces in the organic solvent. Furthermore, during immersion, it is preferable to pass the cleaning solvent from one of the inner or outer surfaces of the hollow fiber membrane to the other. In cleaning, the polyamide hollow fiber membrane may be cleaned directly, or a hollow fiber membrane module may be prepared by housing the polyamide hollow fiber membrane in a module case, and the hollow fiber membrane module may be filled with the cleaning solvent for cleaning. From the viewpoint of operability of cleaning, the method of filling the hollow fiber membrane module with the cleaning solvent for cleaning is preferred.

[0080] The immersion time is preferably one day or longer, more preferably three days or longer, even more preferably one week or longer, and particularly preferably one month or longer. There is no particular upper limit to the immersion time, but it is usually less than one year. The temperature of the washing solvent during the immersion treatment is preferably room temperature (23°C) or higher, and more preferably 35°C or higher. There is no particular upper limit to the temperature of the washing solvent, but it is usually below the boiling point of the washing solvent used.

[0081] Furthermore, the polyamide hollow fiber membrane may be subjected to ultrasonic treatment continuously or temporarily during immersion. For example, when cleaning by filling the hollow fiber membrane module with a cleaning solvent, the ultrasonic output is preferably 50 kW or more, more preferably 80 kW or more, and even more preferably 100 kW or more per inch of module. There is no particular upper limit to the ultrasonic output, but it is usually 200 kW. The ultrasonic treatment time is preferably 5 minutes or more, more preferably 15 minutes or more, even more preferably 1 hour or more, and particularly preferably 3 hours or more. There is no particular upper limit to the ultrasonic treatment time, but it is usually less than 10 hours.

[0082] During these immersion processes, to improve cleaning efficiency, new cleaning solvent may be added during immersion, or some or all of the cleaning solvent may be replaced with new cleaning solvent multiple times.

[0083] Furthermore, when passing a cleaning solvent from one of the inner or outer surfaces of a hollow fiber membrane to the other during cleaning, it is preferable to deliver the cleaning solvent from one of the liquid passage ports in either the inner or outer storage space of the hollow fiber membrane module, pass it through the inner wall of the hollow fiber membrane, and discharge the cleaning solvent from the other liquid passage port. It is preferable not to reuse cleaning solvent that has passed through the hollow fiber membrane once. The direction of liquid passage may be changed midway to improve cleaning performance.

[0084] When a cleaning solvent is passed from one side of the hollow fiber membrane's inner or outer surface to the other, the amount of solvent passed through is preferably 10 kg or more, more preferably 50 kg or more, even more preferably 300 kg or more, and particularly preferably 500 kg or more per inch of the module, for example, when filling a hollow fiber membrane module with cleaning solvent for cleaning. The temperature of the cleaning solvent is preferably room temperature (23°C) or higher, and more preferably 35°C or higher. There is no particular upper limit to the temperature of the cleaning solvent, but it is usually below the boiling point of the cleaning solvent used.

[0085] The flow rate of the liquid is not particularly limited, but for example, the volume of cleaning solvent per hour can be in the range of 0.1 to 1000 times the internal volume of the module, with 1 to 100 times being preferable. Furthermore, the flow rate may be intentionally changed to enhance the cleaning effect.

[0086] The organic solvent used as the washing solvent is not particularly limited, and any known organic solvent can be used. Examples of organic solvents include alkylene glycol monoalkyl ether carboxylate, alkylene glycol monoalkyl ether, alkyl lactate, alkyl alkoxypropionate, cyclic lactone (preferably with 4 to 10 carbon atoms), monoketone compounds which may contain a ring (preferably with 4 to 10 carbon atoms), alkylene carbonate, alkyl alkoxyacetate, alkyl pyruvate, dialkyl sulfoxide, cyclic sulfone, dialkyl ether, monohydric alcohol, glycol, alkyl acetate, and N-alkylpyrrolidone. These may be used individually or in combination of two or more.

[0087] The organic solvents used as washing solvents include propylene glycol monomethyl ether acetate (hereinafter sometimes referred to as "PGMEA"), isopropanol, propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol monopropyl ether, ethyl lactate, methyl methoxypropionate, cyclopentanone, cyclohexanone, γ-butyrolactone, diisoamyl ether (isoamyl ether), butyl acetate, isoamyl acetate, 4-methyl-2-pentanol, N-methylpyrrolidone, and diethylene glycol. Preferably, it is one or more selected from the group consisting of ethylene glycol, dipropylene glycol, propylene glycol, ethylene carbonate, propylene carbonate, cycloheptanone, 2-heptanone, butyl butyrate, isobutyl isobutyrate, undecane, pentyl propionate, isopentyl propionate, ethylcyclohexane, mesitylene, decane, 3,7-dimethyl-3-octanol, 2-ethyl-1-hexanol, 1-octanol, 2-octanol, ethyl acetoethyl acetate, dimethyl malonate, methyl pyruvate, and dimethyl oxalate.

[0088] Since cleaning solvents composed of these organic solvents exhibit better cleaning performance when they have a low water content, it is preferable not to add water other than water unintentionally contained due to moisture absorption of the organic solvent. The water content in the cleaning solvent is preferably 1% by mass or less per 100% by mass of the cleaning solvent.

[0089] Thus, by carrying out the fourth step, a polyamide hollow fiber membrane with a further reduced content of specific metal elements can be produced. However, since specific metal elements in polyamide hollow fiber membranes cannot be removed even by thorough washing with water or organic solvents, washing treatment using water or organic solvents alone is not sufficient to sufficiently reduce the content of specific metal elements. Therefore, in order to obtain the polyamide hollow fiber membrane of the present invention in which the content of specific metal elements is reduced to or below a specific value, it is necessary to manufacture it by a method including the above steps 1 to 3.

[0090] 3. Hollow fiber membrane module The polyamide hollow fiber membrane of the present invention can be housed in a module case and used as a hollow fiber membrane module. The size of the module case is not particularly limited and can be appropriately designed to suit each application. Known methods can be used to process the hollow fiber membrane module. Specifically, after housing the polyamide hollow fiber membrane bundle in a cylindrical module case, the end inside the module case is sealed together with the bundle of hollow fiber membranes using a potting material. At this time, either double-ended potting or single-ended potting may be used. Next, the potted portion where the hollow fiber membrane bundle is sufficiently sealed is cut, opening the space on the lumen side of the hollow fiber membrane. It is necessary that the space on the lumen side of the hollow fiber membrane inside the module and the space on the outside of the hollow fiber membrane are reliably separated and free from leaks. It is preferable to attach a cap with a liquid passage port to the module end where the space on the lumen side of the hollow fiber membrane is opened, so that liquid can pass through the space on the lumen side. It is also preferable to provide a liquid passage port in the module case so that liquid can pass through the space on the outside of the hollow fiber membrane inside the module case. The shape of the liquid passage port should be one that is appropriate for each application.

[0091] The potting material can be any known potting material, specifically polyurethane resin, epoxy resin, or polyolefin resin. Of these, epoxy resin and polyolefin resin are preferred from the viewpoint of improving resistance to organic solvents, and among polyolefin resins, polyethylene and polypropylene are preferred, with polyethylene being more preferred.

[0092] The polyamide hollow fiber membrane and hollow fiber membrane module of the present invention have excellent filtration performance and are characterized by their ability to maintain their filtration performance even after long-term storage in a storage solution, making them suitable for various applications. Specifically, they can be used for filtering raw materials and intermediates used in pharmaceutical manufacturing, for final filtration, for filtering chemical solutions used for cleaning pharmaceutical manufacturing equipment, and for filtering chemical solutions used in semiconductor manufacturing. More specifically, they can be used for filtering chemical solutions used after the completion of each step or before moving to the next step in semiconductor device manufacturing processes, including lithography, etching, ion implantation, and stripping steps. More specifically, they can be used for filtering chemical solutions such as developers, rinses, wafer cleaning solutions, line cleaning solutions (e.g., pipe cleaning solutions), pre-wetting solutions, wafer rinses, resists, underlayer forming solutions, upper layer forming solutions, hard coat forming solutions, aqueous developers, aqueous rinses, stripping solutions, removers, etching solutions, acidic cleaning solutions, phosphoric acid, and phosphoric acid-hydrogen peroxide mixtures. Other applications include filtering chemicals such as developers and rinse solutions for polyimides, sensor resists, and lens resists. [Examples]

[0093] The present invention will be specifically described below with reference to examples, but the present invention is not limited thereto.

[0094] Various characteristics were measured or evaluated using the following methods.

[0095] [Relative viscosity of polyamide hollow fiber membranes] Each polyamide hollow fiber membrane obtained in the Examples, Comparative Examples, and Reference Examples was dissolved in 96% by mass sulfuric acid to a concentration of 1 g / dL, and its viscometer was measured at 25°C using an Ubellobe viscometer.

[0096] [Metal element content of polyamide hollow fiber membranes] (1) Metal element content of hollow fiber membrane before organic solvent washing (step 4) 0.5 g of each polyamide hollow fiber membrane obtained in the Examples, Comparative Examples, and Reference Examples was mixed with 5 mL of nitric acid. The mixture was heated to 100°C over 10 minutes and held at 100°C for 5 minutes, then heated to 140°C over 3 minutes and held at 140°C for 5 minutes, and finally heated to 180°C over 5 minutes and held at 180°C for 10 minutes to decompose and / or dissolve the polyamide hollow fiber membrane in nitric acid. The mixture was then diluted to 50 mL with ultrapure water. The metal element content (ppm) of this sample was measured using a Thermo Fisher Scientific iCAP6500Duo ICP emission spectrometer. The measured value was obtained by subtracting the average value of the operational blank, which was measured simultaneously with the measurement of the above sample with n=10 samples. Furthermore, if the determined metal element content value was within the range of 3σ of the standard deviation obtained from the operational blank with n=10 samples, the content was considered to be 0.00 ppm. (2) Metal element content of hollow fiber membrane after organic solvent washing (step 4) Each polyamide hollow fiber membrane obtained in the Examples, Comparative Examples, and Reference Examples was placed in a 10-inch module case at a 25% occupancy rate (occupancy rate (%) = total cross-sectional area of ​​the hollow fiber membrane bundles to be accommodated / cross-sectional area of ​​the inner tube of the module case × 100), and potting was performed to fabricate a hollow fiber membrane module. The inside of this module was filled with PGMEA (immersing either the inner or outer side of the hollow fiber membrane), and held at 35°C for one week. Next, it was sonicated at an output of 800 kW for one hour. After that, 10,000 kg of PGMEA was delivered to the module through the liquid passage port in the inner space of the hollow fiber membrane, allowing the PGMEA to pass through the hollow fiber membrane. After all the PGMEA had passed through, the module was disassembled, the contained hollow fiber membrane was removed, and the PGMEA was dried off. The metal element content (ppm) of the obtained polyamide hollow fiber membrane was measured using the method (1) described above.

[0097] [Ratio of γ crystals to the total amount of α and γ crystals in a polyamide hollow fiber membrane] The ratio of γ crystals to the total amount of α and γ crystals in each polyamide hollow fiber membrane obtained in the examples, comparative examples, and reference examples was measured using the method described above with a RIGAK RINT-TTR III (CBO) X-ray analyzer.

[0098] [Water permeability under external pressure of polyamide hollow fiber membrane] Each polyamide hollow fiber membrane obtained in the Examples, Comparative Examples, and Reference Examples was cut to a length of 9-12 cm. An injection needle with a diameter matching the inner diameter was inserted into the hollow portion at both ends. One injection needle was sealed with a cap, and the other injection needle was connected to the outlet. The membrane was then set in the apparatus shown in Figure 1. Subsequently, while pure water at 25°C was passed through the membrane using the liquid transfer pump 1 for a predetermined time (h), the valve of the outlet valve 5 was adjusted to maintain a constant pressure of 0.05 MPa. The volume (L) of water that permeated through the membrane and accumulated in the receiving tray 6 was measured as the permeate volume, and the external pressure permeability was calculated using the following formula 6. The inlet pressure was measured using the inlet pressure gauge 2 shown in Figure 1, and the outlet pressure was measured using the outlet pressure gauge 4 shown in Figure 1. <Formula 6> External pressure permeability (L / (m) 2 (atm·h) = Permeation rate (L) / [Outer diameter (m) × 3.14 × Length (m) × {(Inlet pressure (atm) + Outlet pressure (atm)) / 2} × Time (h)]

[0099] [Refusal rate of fine particles in polyamide hollow fiber membranes] (1) Rejection rate of 50nm particles The rejection rate of 50 nm particle size (Gold colloid-50 nm, manufactured by British BioCell International) was measured using the method described above. (2) Blocking rate of 20nm particles The blocking rate of 20 nm particle size (Gold colloid-20 nm, manufactured by British BioCell International) was measured using the method described above. (3) Blocking rate of 10 nm particles The blocking rate of 10 nm particles (Gold colloid-10 nm, manufactured by British BioCell International) was measured using the method described above. (4) Blocking rate of 5nm particles The blocking rate of 5 nm particles (Gold colloid-5 nm, manufactured by British BioCell International) was measured using the method described above.

[0100] [Bubble points in polyamide hollow fiber membranes] Using the apparatus shown in Figure 2, the bubble points of each polyamide hollow fiber membrane obtained in the examples, comparative examples, and reference examples were measured by the following method. Ten 20cm long polyamide hollow fiber membranes were prepared, bent into a U-shape, and the end of each membrane near the opening was heat-sealed for about 1cm to seal the hollow portion. Next, a 5cm long flexible nylon tube for air piping (outer diameter 8mm, inner diameter 6mm) was prepared, one end was sealed with a silicone stopper, and about 4cm of potting agent (polyurethane resin) was introduced. Then, the bundle of hollow fiber membranes was inserted into the potting agent from the heat-sealed end and left to stand until the potting agent hardened. After the potting agent hardened, the nylon tube and potting section were cut above the heat-sealed portion of the hollow fiber membrane, opening the inner lumen of the hollow fiber membrane. At this time, it was visually confirmed whether the potting agent had entered the hollow portion and whether the potting agent filled the space between the hollow fiber membranes. If the hollow space was maintained without any problems, this was used as the bubble point measurement sample. Next, in the bubble point test, it is necessary to fill the pores of the hollow fiber membrane with liquid. Therefore, 2-propanol (surface tension of 21 mN / m at 20°C) was introduced into the glass container 13, the bubble point measurement sample 12 was immersed in it, and the pressure was reduced for several seconds to fill the pores with liquid. A bubble point measurement sample 12, immersed in 2-propanol, was set up as shown in Figure 2, and air was introduced into the lumen of the hollow fiber membrane at a rate of 0.4 MPa / min to increase the pressure. The pressure at which bubbles first emerged from the hollow fiber membrane was confirmed and this was defined as the initial bubble point (IBP). The pressure was then increased, and the pressure at which bubbles emerged from approximately the entire membrane was confirmed and this was defined as the burst bubble point (BBP).

[0101] [Breaking strength, elongation at breaking, and tensile modulus of polyamide hollow fiber membranes] The breaking strength, breaking elongation, and tensile modulus of each polyamide hollow fiber membrane obtained in the examples, comparative examples, and reference examples were measured in accordance with JIS L-1013 using a Shimadzu Corporation tensile testing machine (Autograph AG-H) under the conditions of a chuck distance of 50 mm, a tensile speed of 50 mm / min, and a number of measurements of 5. The average value of the 5 measured values ​​was adopted.

[0102] [Storage test of polyamide hollow fiber membrane] Each polyamide hollow fiber membrane obtained in the Examples, Comparative Examples, and Reference Examples was placed in a 5-inch module case at a 20% occupancy rate, and potting was performed to produce two hollow fiber membrane modules for each example. 30 L of PGMEA was supplied through the liquid passage port in the outer space of the hollow fiber membrane of the prepared hollow fiber membrane module, and the filtrate was discharged through the liquid passage port in the inner space of the hollow fiber membrane. The hollow fiber membrane module (polyamide hollow fiber membrane contained in the module) was used for filtering PGMEA. The same procedure was performed for each of the two hollow fiber membrane modules. One of the two hollow fiber membrane modules was disassembled, the contained polyamide hollow fiber membrane was removed, and the PGMEA was dried off. The filtration performance (fine particle rejection rate, external pressure permeability, IBP, BBP) of the obtained polyamide hollow fiber membrane was then measured. The measured values ​​obtained here were exactly the same as the filtration performance of each polyamide hollow fiber membrane obtained in the Examples, Comparative Examples, and Reference Examples. In other words, there was no change in the filtration performance of the polyamide hollow fiber membrane due to its use. Next, 10 L of new PGMEA was passed through the liquid passage port in the inner space of the hollow fiber membrane of another used hollow fiber membrane module, immersing both the inner and outer surfaces of the hollow fiber membrane within the module. At this time, the pressure inside the module was 0 MPa. In this state, all liquid passage ports of the module were sealed, and it was stored at room temperature (23°C) for two years. After storage, the module was disassembled, the contained hollow fiber membrane was removed, and the PGMEA was dried off. The filtration performance of each of the resulting polyamide hollow fiber membranes was then measured using the method described above. Then, the retention rates (%) for each were calculated using the following formulas 3-5. <Expression 3> Retention rate of rejection (%) = (Rejection rate of particles of each particle size after storage / Rejection rate of particles of each particle size before storage) × 100 <Expression 4> Retention rate of external pressure permeability (%) = (External pressure permeability after storage / External pressure permeability before storage) × 100 <Formula 5> IBP or BBP retention rate (%) = (IBP or BBP after storage / IBP or BBP before storage) × 100

[0103] The raw materials used in the examples, comparative examples, and reference examples are shown below. <Polyamide resin> • PA1: Polyamide 6 A1030BRT manufactured by Unitika Corporation • PA2: Polyamide 6 A1030BRF-BA manufactured by Unitika Corporation • Polyamide 6 obtained by solid-phase polymerization of PA3:A1030BRT under an N2 airflow at 170°C for 15 hours. • Polyamide 6 obtained by solid-phase polymerization of PA4:A1030BRT under an N2 airflow at 170°C for 50 hours. • Polyamide 6 obtained by solid-phase polymerization of PA5:A1030BRT under an N2 airflow at 170°C for 70 hours. PA6: Polyamide 66 obtained by solid-phase polymerization of Unitika's Polyamide 66 A125 under an N2 gas stream at 170°C for 30 hours. PA7: Polyamide 610 CM2001 manufactured by Toray Industries, Inc. • PA8: A polyamide 6 uniformly driven blend of PA3 with 0.05% by mass of sodium hydroxide. • PA9: A polyamide 6 obtained by uniformly driving-blending 0.05% by mass of potassium hydroxide into PA3.

[0104] <Sulfones> Manufacturing Example 1 15.7 parts by mass of dimethyl sulfoxide was dissolved in 24.3 parts by mass of a 27.5% by mass aqueous solution of hydrogen peroxide (an aqueous solution consisting of 27.5 parts by mass of hydrogen peroxide and 72.5 parts by mass of water). The resulting solution was gradually heated under a nitrogen atmosphere and held at 85°C for 1.5 hours. The entire volume of the solution was then concentrated 1.25 times, and the solution was allowed to stand at room temperature for 48 hours to precipitate crystals. These crystals were filtered and collected, and dried to obtain dimethyl sulfone. The pH of a 5% by mass aqueous solution of the obtained dimethyl sulfone was 4.8. This dimethyl sulfone is referred to as "DMS-1".

[0105] Manufacturing Example 2 Dimethyl sulfone was obtained using the same procedure as in Production Example 1, except that a 25.0% by mass aqueous solution of hydrogen peroxide was used instead of a 27.5% by mass aqueous solution of hydrogen peroxide. The pH of a 5% by mass aqueous solution of the obtained dimethyl sulfone was 5.2. This dimethyl sulfone is referred to as "DMS-2".

[0106] Manufacturing Example 3 Dimethyl sulfone was obtained using the same procedure as in Production Example 1, except that a 22.5% by mass aqueous solution of hydrogen peroxide was used instead of a 27.5% by mass aqueous solution of hydrogen peroxide. The pH of a 5% by mass aqueous solution of the obtained dimethyl sulfone was 5.8. This dimethyl sulfone is referred to as "DMS-3".

[0107] Manufacturing Example 4 Dimethyl sulfone was obtained using the same procedure as in Production Example 1, except that a 20.0% by mass aqueous solution of hydrogen peroxide was used instead of a 27.5% by mass aqueous solution of hydrogen peroxide. The pH of a 5% by mass aqueous solution of the obtained dimethyl sulfone was 6.5. This dimethyl sulfone is referred to as "DMS-4".

[0108] Manufacturing Example 5 Dimethyl sulfone was obtained using the same procedure as in Production Example 1, except that a 17.5% by mass aqueous solution of hydrogen peroxide was used instead of a 27.5% by mass aqueous solution of hydrogen peroxide. The pH of a 5% by mass aqueous solution of the obtained dimethyl sulfone was 6.9. This dimethyl sulfone is referred to as "DMS-5".

[0109] Manufacturing Example 6 0.45 parts by mass of tert-butylcatechol and 230 parts by mass of sulfur dioxide were added to a sealed reactor, and the temperature was raised to 100°C. Then, 162 parts by mass of 1,3-butadiene was injected at a flow rate of 0.38 parts by mass / min, and the mixture was stirred at 100°C for 1 hour. After releasing the pressure in the reactor, 720 parts by mass of water were added, and after cooling to 60°C, the contents were filtered to obtain an aqueous solution of 3-sulfolene. 1000 g of the obtained aqueous solution of 3-sulfolene (2.70 mol of 3-sulfolene) was charged into a sealed reactor together with 4.80 parts by mass of Raney nickel catalyst (50% by mass, water-containing). Next, the temperature was maintained at 30-40°C, hydrogen was introduced into the sealed reactor to pressurize it to 1.0 MPa, and the mixture was stirred for 3 hours while maintaining the pressure. After filtration, an aqueous solution of sulfolane was obtained. The obtained aqueous solution of sulfolane was heated and the water was removed by distillation to obtain crude sulfolane. Next, 100 parts by mass of crude sulfolane and 0.5 parts by mass of a 20.0% by mass aqueous solution of hydrogen peroxide (an aqueous solution consisting of 20.0 parts by mass of hydrogen peroxide and 80.0 parts by mass of water) were charged into a nitrogen-purged reactor. After stirring at low speed at 60°C for 24 hours, water and impurities were removed by heating and reducing pressure to obtain sulfolane. The pH of a 5% by mass aqueous solution of the obtained sulfolane was 6.3. This sulfolane is referred to as "SFL-1".

[0110] Manufacturing example 7 Sulfolane was obtained using the same procedure as in Production Example 6, except that a 22.5% by mass hydrogen peroxide aqueous solution was used instead of a 20.0% by mass hydrogen peroxide aqueous solution. The pH of a 5% by mass aqueous solution of the obtained sulfolane was 6.6. This sulfolane is referred to as "SFL-2".

[0111] Manufacturing Example 8 Sulfolane was obtained using the same procedure as in Production Example 6, except that a 25.0% by mass aqueous solution of hydrogen peroxide was used instead of a 20.0% by mass aqueous solution of hydrogen peroxide. The pH of a 5% by mass aqueous solution of the obtained sulfolane was 6.8. This sulfolane is referred to as "SFL-3".

[0112] Manufacturing Example 9 Sulfolane was obtained using the same procedure as in Production Example 6, except that a 27.5% by mass hydrogen peroxide aqueous solution was used instead of a 20.0% by mass hydrogen peroxide aqueous solution. The pH of a 5% by mass aqueous solution of the obtained sulfolane was 7.0. This sulfolane is referred to as "SFL-4".

[0113] The pH of the 5% aqueous solution of dimethyl sulfone or sulfolane was measured at 25°C using a "D-51" measuring device manufactured by Horiba, Ltd.

[0114] Example 1 A twin-screw extruder (PCM30, manufactured by Ikegai Co., Ltd.) equipped with a polyamide quantitative dispensing device and a powder quantitative dispensing device as auxiliary equipment was used. PA1 was used as the polyamide resin raw material, and DMS-3 was used as the medium. The twin-screw extruder was operated under conditions of screw rotation of 100 rpm and all cylinder temperatures of 200°C. PA1 was quantitatively dispensed into the twin-screw extruder at a rate of 28 parts by mass / h from the polyamide quantitative dispensing device, and DMS-3 was quantitatively dispensed at a rate of 72 parts by mass / h from the powder quantitative dispensing device (i.e., the composition ratio of the resulting film-forming stock solution was PA1 / DMS-3 = 28 / 72). Discharge of a film-forming stock solution in which the polyamide resin and DMS-3 were uniformly dissolved was confirmed from the tip of the twin-screw extruder (first step). Once the discharge of the film-forming solution stabilized, a spinning device was attached to the discharge port of the film-forming solution at the tip of the twin-screw extruder. This device was connected to a spinning nozzle (a double-tube nozzle for hollow fiber production with a double-tube structure (outer diameter 1.5 mm, inner diameter 0.6 mm)) via a metering pump, and the film-forming solution was extruded at 5 g / min from the outer annular nozzle. The spinning device was set to 200°C. Simultaneously, an internal liquid consisting of glycerin was discharged at 2.0 g / min from the inner nozzle. The extruded spinning solution and internal liquid were immersed in a solidification bath consisting of a 50% by mass aqueous solution of propylene glycol at 5°C via a 10 mm air gap to cool and solidify, forming a hollow fiber film. This film was then wound onto a bobbin at a winding speed of 20 m / min (second step). The residence time of the raw materials, from the time each raw material was fed from the feeding device to the twin-screw extruder until the film-forming solution was extruded from the nozzle, was a maximum of 15 minutes. The obtained hollow fiber membrane was immersed in water for 24 hours to extract (wash) the solvent and other substances, and then dried in a hot air dryer at 50°C for 1 hour to obtain a polyamide hollow fiber membrane (step 3). The obtained polyamide hollow fiber membrane had an outer diameter of 550 μm and an inner diameter of 300 μm. Furthermore, SEM observation confirmed the formation of a dense layer on the inner surface of the polyamide hollow fiber membrane.

[0115] Examples 2, 3, 7, 8, 12-15, Comparative Examples 1, 2, Reference Examples 1, 2 Polyamide hollow fiber membranes were obtained using the same procedure as in Example 1, except that the polyamide resin and medium were changed to those shown in Table 1. All of the obtained polyamide hollow fiber membranes had an outer diameter of 550 μm and an inner diameter of 300 μm, and the formation of a dense layer on the inner surface of the hollow fiber membrane was confirmed by SEM observation.

[0116] Examples 4-6 Polyamide hollow fiber membranes were obtained using the same procedure as in Example 3, except that the rate at which raw materials were quantitatively fed into the twin-screw extruder was changed to alter the composition ratio of the film-forming stock solution shown in Table 1. All of the obtained polyamide hollow fiber membranes had an outer diameter of 550 μm and an inner diameter of 300 μm, and the formation of a dense layer on the inner surface of the hollow fiber membranes was confirmed by SEM observation.

[0117] Examples 9-11, Comparative Example 3 Polyamide hollow fiber membranes were obtained using the same procedure as in Example 3, except that the auxiliary equipment for the twin-screw extruder was changed from a powder quantitative feeding device to a liquid quantitative feeding device, and the medium was changed from DMS-3 to those shown in Table 1. All of the obtained polyamide hollow fiber membranes had an outer diameter of 550 μm and an inner diameter of 300 μm, and the formation of a dense layer on the inner surface of the hollow fiber membrane was confirmed by SEM observation.

[0118] Comparative Examples 4-6 Polyamide hollow fiber membranes were obtained using the same procedure as in Example 9, except that the medium was changed from SFL-2 to γ-butyllactone (pH of the 5% aqueous solution measured by the above method was 5.5) in Comparative Example 4, to ε-caprolactone (pH of the 5% aqueous solution measured by the above method was 6.5) in Comparative Example 5, and to propylene carbonate (pH of the 5% aqueous solution measured by the above method was 7.0) in Comparative Example 6. All obtained polyamide hollow fiber membranes had an outer diameter of 550 μm and an inner diameter of 300 μm, and the formation of a dense layer on the luminal surface of the hollow fiber membrane was confirmed by SEM observation.

[0119] Comparative Example 7 A 2L tank equipped with a stirrer, capable of heating and sealing, was used. 504g of PA3 was used as the polyamide resin, and 1296g of DMS-3 was used as the medium. PA3 and DMS-3 were added to the tank, which was adjusted to a stirrer speed of 20 rpm and an overall temperature of 200°C. The mixture was stirred at 200°C and 20 rpm for 60 minutes to ensure uniform dissolution of PA3 and DMS-3. Next, a metering pump equipped at the discharge port of the film-forming stock solution in the tank and a spinneret (a double-tube nozzle for hollow fiber production with a double-tube structure (the hole diameter of the spinneret is 1.5 mm outer diameter and 0.6 mm inner diameter)) equipped via the metering pump extruded the film-forming stock solution at a rate of 5 g / min from the outer annular nozzle. The temperature of the metering pump and the double-tube nozzle for hollow fiber production was set to 200°C. In parallel, an internal liquid consisting of glycerin was discharged from the inner nozzle at a rate of 2.0 g / min. The extruded spinneret stock solution and internal liquid were immersed in a solidification bath consisting of a 50% by mass aqueous solution of propylene glycol at 5°C via a 10 mm air gap to cool and solidify, forming a hollow fiber film, which was then wound onto a bobbin at a winding speed of 20 m / min. This process was designated as "Process A". The winding of the hollow fiber film onto the bobbin was carried out for 2.5 hours. In this case, the residence time from the time the raw material was introduced into the apparatus until the film-forming solution was extruded from the nozzle ranged from a minimum of 85 minutes to a maximum of 225 minutes. The obtained hollow fiber membranes were immersed in water for 24 hours to extract the solvent (wash), and then dried in a hot air dryer at 50°C for 1 hour to obtain polyamide hollow fiber membranes. The obtained polyamide hollow fiber membranes had an outer diameter of 550 μm and an inner diameter of 300 μm, and SEM observation confirmed the formation of a dense layer on the inner surface of the hollow fiber membranes.

[0120] Comparative Example 8 A hollow fiber membrane was obtained by winding it onto a bobbin using the same procedure as in Step A of Comparative Example 7. Next, the obtained hollow fiber membrane was washed by immersion in water. During immersion, the water was stirred, and fresh water was continuously added at a flow rate of 0.5 L / min, allowing the solvent to be extracted (washed) for two months while the water was overflowing. After that, the membrane was dried in a hot air dryer at 50°C for one hour to obtain a polyamide hollow fiber membrane. The obtained polyamide hollow fiber membrane had an outer diameter of 550 μm and an inner diameter of 300 μm, and SEM observation confirmed the formation of a dense layer on the inner surface of the hollow fiber membrane.

[0121] Table 1 shows the manufacturing conditions for the polyamide hollow fiber membranes obtained in Examples 1-15, Comparative Examples 1-8, and Reference Examples 1 and 2, as well as the measurement results of the metal element content before and after organic solvent washing. Table 2 shows the results of the membrane evaluation of the polyamide hollow fiber membranes obtained in Examples 1-15, Comparative Examples 1-8, and Reference Examples 1 and 2. However, only for Comparative Example 1, the "filtration performance before storage" and "retention rate (%) in the storage test" were evaluated using a polyamide hollow fiber membrane washed with an organic solvent using the method described in "(2) Metal element content of hollow fiber membrane after organic solvent washing (step 4)" above. There was no change in the filtration performance of the polyamide hollow fiber membrane before storage due to organic solvent washing and use.

[0122] [Table 1]

[0123] [Table 2]

[0124] Tables 1 and 2 show that the polyamide hollow fiber membranes of Examples 1 to 15 have low content of specific metal elements, resulting in less change in filtration performance even after long-term storage in a preservation solution, and thus exhibiting excellent storage stability. Furthermore, in Examples 1 to 15, specific metal elements were removed to some extent when the polyamide hollow fiber membranes were washed with organic solvents, resulting in the acquisition of more hygienic polyamide hollow fiber membranes. On the other hand, the polyamide hollow fiber membranes of Comparative Examples 1 to 8 had a high content of specific metal elements, and their filtration performance changed significantly when stored in the storage solution for a long period of time. Furthermore, in Comparative Examples 1 to 8, the specific metal elements could hardly be removed when the polyamide hollow fiber membranes were washed with an organic solvent.

[0125] The polyamide hollow fiber membranes of Examples 3 to 11 had a lower content of specific metal elements, and furthermore, the ratio of γ crystals to the total amount of α crystals was in the range of 15 to 25%, resulting in superior water permeability under external pressure before storage compared to the other examples.

[0126] In Comparative Examples 1-3, the polyamide hollow fiber membranes used a 5% aqueous solution of sulfones with a pH outside the range of 5.2-6.8 as the medium. As a result, they contained a high amount of specific metal elements, and their filtration performance changed significantly when stored for a long period in the storage solution.

[0127] The polyamide hollow fiber membranes of Comparative Examples 4-6 used materials other than sulfones as a medium, resulting in high levels of specific metal elements. Therefore, their filtration performance changed significantly after long-term storage in the storage solution.

[0128] The polyamide hollow fiber membranes of Comparative Examples 7 and 8 were prepared using a batch-type film-forming method with tanks, resulting in high levels of specific metal elements. Consequently, their filtration performance changed significantly after long-term storage in the storage solution.

[0129] In Reference Examples 1 and 2, sodium or potassium components were intentionally added to the raw materials to produce polyamide hollow fiber membranes containing high levels of sodium or potassium, which were then evaluated. The results showed that the produced polyamide hollow fiber membranes exhibited excellent storage stability, with minimal change in filtration performance even after long-term storage in a preservation solution. This indicates that not all metal elements affect the storage stability of polyamide hollow fiber membranes; rather, the content of specific metal elements influences their storage stability. [Explanation of symbols]

[0130] 1: Liquid transfer pump 2: Inlet pressure gauge 3: Hollow fiber membrane 4: Outlet pressure gauge 5: Outlet valve 6: Drip tray 7: Air inlet 8: Regulator 9: Booster tank 10: Speed ​​Controller 11: Pressure sensor 12: Bubble point measurement sample 13: Glass container 14:2-Propanol 15: Digital pressure display 16: Two-way valve

Claims

1. A polyamide hollow fiber membrane formed from polyamide resin, A polyamide hollow fiber membrane that satisfies at least one of the following characteristics (1) to (5). (1) Fe content is 4.30 ppm or less (2) Cr content is less than 1.00 ppm (3) Cu content is less than 0.20 ppm (4) Mg content is less than 0.60 ppm (5) Zn content is less than 0.30 ppm

2. The polyamide hollow fiber membrane according to claim 1, wherein the relative viscosity is 2.0 to 6.

5.

3. The polyamide hollow fiber membrane according to claim 1, wherein, in structural analysis by X-ray diffraction, the ratio of γ crystals to the total amount of α crystals is 0 to 37%.

4. The polyamide hollow fiber membrane according to claim 1, wherein the polyamide hollow fiber membrane has a dense layer on the luminal surface and / or the outer surface.

5. The polyamide hollow fiber membrane according to claim 1, wherein the rejection rate of particles with a particle size of 50 nm is 90% or more.

6. The polyamide hollow fiber membrane according to claim 1, wherein the retention rate of the rejection rate of particles with a particle size of 5 nm, calculated by the following formula, is 90% or more. Retention rate (%) = (Rejection rate of 5 nm particles after storage / Rejection rate of 5 nm particles before storage) × 100 Storage conditions: Immerse the polyamide hollow fiber membrane in propylene glycol monomethyl ether acetate and store at 23°C for 2 years without pressurization.

7. External pressure permeability is 50-2000 L / (m 2 A polyamide hollow fiber membrane according to claim 1, wherein the properties are ・atm・h.

8. The polyamide hollow fiber membrane according to claim 1, wherein the retention rate of the external pressure permeability calculated by the following formula is 90 to 110%. Retention rate (%) = (Water permeability under external pressure after storage / Water permeability under external pressure before storage) × 100 Storage conditions: Immerse the polyamide hollow fiber membrane in propylene glycol monomethyl ether acetate and store at 23°C for 2 years without pressurization.

9. The polyamide hollow fiber membrane according to claim 1, wherein in a bubble point test conducted by applying air pressure in 2-propanol at 20°C, the initial bubble point is 0.20 MPa or higher and the burst bubble point is 0.30 MPa or higher.

10. In a bubble point test using 2-propanol under air pressure at 20°C, The polyamide hollow fiber membrane according to claim 1, wherein the retention rate of the initial bubble point and burst bubble point calculated by the following formula is 90 to 110%. Retention rate (%) = (Initial bubble point or burst bubble point after storage / Initial bubble point or burst bubble point before storage) × 100 Storage conditions: Immerse the polyamide hollow fiber membrane in propylene glycol monomethyl ether acetate and store at 23°C for 2 years without pressurization.

11. A hollow fiber membrane module in which a polyamide hollow fiber membrane according to any one of claims 1 to 10 is housed in a module case.

12. The first step involves using a multi-screw extruder to mix at least a polyamide resin and sulfones to prepare a film-forming stock solution. A second step involves using a double-tube nozzle for hollow fiber manufacturing, in which the film-forming raw material is discharged from the outer annular nozzle and the internal liquid is discharged from the inner nozzle, and the resulting film is immersed in a coagulation bath containing water and / or polyhydric alcohol to form a hollow fiber film, and The third step includes removing the organic solvent from the hollow fiber membrane formed in the second step, The sulfones are those which, when dissolved in water to form a 5% by mass aqueous solution, have a pH of 5.2 to 6.8 at 25°C, in a method for producing polyamide hollow fiber membranes.

13. The method for producing a polyamide hollow fiber membrane according to claim 12, wherein the sulfones are dimethyl sulfone and / or sulfolane.

14. A method for producing a polyamide hollow fiber membrane according to claim 12 or 13, further comprising a fourth step of washing the hollow fiber membrane with an organic solvent after the third step to remove at least one metal element selected from the group consisting of Fe, Cr, Cu, Mg, and Zn.

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