Polyamide porous membrane and its manufacturing method

Abstract

The object of this invention is to provide a polyamide porous membrane with improved liquid permeability. The polyamide porous membrane of this invention has a dense layer formed on at least one side; the polyamide porous membrane has striped recesses extending in one direction on the surface of the aforementioned dense layer; and, in a predetermined orientation analysis, the orientation angle of the aforementioned striped recesses is 0~5.0° or 175.0~180.0°, and the orientation intensity is 1.5~2.0.

Description

Technical Field

[0001] This invention relates to a polyamide porous membrane with excellent liquid permeability and a method for manufacturing the same. Prior Technology

[0002] Porous membrane systems are used as filtration membranes in various fields. For example, nanofiltration membranes and ultrafiltration membranes have been put into practical use in various fields, such as removing bacteria / viruses / pesticides / odor components / hardness components in the water purification field; artificial dialysis in the medical field; removal of viruses or proteins in the manufacture of pharmaceuticals or medical water; separation or concentration of heat-sensitive substances such as proteins or enzymes in the industrial field; production of ultrapure water; recovery of electrodeposited coatings; wastewater treatment in fiber / pulp factories; treatment of oily wastewater; treatment of building drainage; clarification of fruit juice; production of raw wine; concentration and desalination of cheese whey; production of concentrated milk; concentration of protein; and applications in bioreactors and water treatment in nuclear power plants.

[0003] The definitions of classifications such as nanofiltration and ultrafiltration are diverse, and their extensions may not be universally definitive. However, the IUPAC definition recommends defining ultrafiltration as porous materials with pore sizes ranging from 2 to 100 nm, and nanofiltration as those with pore sizes below 2 nm. Furthermore, nanofiltration targets substances larger than those in reverse osmosis; therefore, pore sizes are sometimes defined as 1-2 nm. On the other hand, the pore sizes of nanofiltration and ultrafiltration membranes are difficult to observe and measure even under an electron microscope, and there are variations in pore size. Therefore, the representative pore size of the membrane is not sufficient to represent its separation performance; the molecular weight cutoff is primarily used as an indicator of separation performance. Additionally, the size of the substances that can be separated by ultrafiltration membranes is not clearly distinguished before or after the molecular weight cutoff, but rather exists within a certain range. Specifically, those with a molecular weight cutoff of 1000-1000000 are generally classified as ultrafiltration, and those with a molecular weight cutoff of 200-1000 are classified as nanofiltration. As will be described later, in this specification, when referred to as "ultrafiltration" or "ultrafiltration membrane," it means a filter with a molecular weight cutoff set in the range of 1,000 to 1,000,000, or a filter membrane with a molecular weight cutoff set in the range of 1,000 to 1,000,000. When referred to as "nanofiltration" or "nanofiltration membrane," it means a filter with a molecular weight cutoff set in the range of 200 to 1,000, or a filter membrane with a molecular weight cutoff set in the range of 200 to 1,000.

[0004] As described above, porous membranes can be used as filtration membranes in various industrial fields, and are therefore sometimes used to treat solutions containing organic solvents. However, the polymer materials commonly used in conventional ultrafiltration membranes, such as cellulose acetate, polyacrylonitrile, polydifluoroethylene, polyurethane, and polyether ether, are not entirely satisfactory from the perspective of resistance to organic solvents. For example, even polyacrylonitrile and polydifluoroethylene, which have relatively high resistance to organic solvents, still have the disadvantage of easily dissolving in aprotic polar solvents and other organic solvents.

[0005] Against this backdrop, a report indicates the use of a separation membrane made from a material with high resistance to organic solvents. Among these, a method for manufacturing a porous membrane using polyamide resin has been proposed because polyamide resin is highly resistant to organic solvents and readily available at a low cost. Regarding polyamide filter membranes, for example, a report indicates that a spinning solution containing 15-25% by weight of polyamide and 5-20% by weight of polyethylene glycol is extruded together with formic acid and a coagulating core solution into a precipitation solution, and then stretched and dried in a wet state to obtain asymmetric polyamide hollow fibers composed of a thin separating membrane and a heat-supporting membrane. The pH difference between the precipitation solution and the coagulating core solution is 3 or more (for example, see Patent Document 1).

[0006] Previous technical documents Patent documents Patent Document 1: Japanese Patent Application Publication No. 58-65009 Summary of the Invention

[0007] The problem the invention aims to solve The smaller the molecular weight cutoff of a porous membrane, the lower its permeability. Therefore, the required permeability varies depending on the molecular weight cutoff. However, most conventional polyamide porous membranes do not possess adequate permeability commensurate with their molecular weight cutoff. Consequently, improvements in permeability are required. In particular, in previous technologies, porous membranes with molecular weight cutoffs of around 200 to 50,000 tend to exhibit reduced permeability, making it difficult to improve permeability even with membranes meeting the aforementioned molecular weight cutoff.

[0008] Therefore, the objective of this invention is to provide a polyamide porous membrane with improved liquid permeability and a method for manufacturing the same. The means to solve the problem

[0009] In order to solve the aforementioned problem, the inventors of this case have conducted research and found that a polyamide porous membrane with the following characteristics still has improved liquid permeability even when its molecular weight cutoff is about 200 to 50,000. The polyamide porous membrane has a dense layer formed on at least one side, the dense layer has striped recesses extending in one direction, and the orientation angle of the striped recesses obtained by orientation analysis under predetermined conditions satisfies 0 to 5.0° or 175.0 to 180.0° and the orientation intensity satisfies 1.5 to 2.0. Furthermore, the inventors of this case discovered that the aforementioned polyamide porous membrane can be obtained by the following method: after forming a polyamide porous membrane from a membrane-forming solution containing polyamide resin using thermally induced phase separation (TIPS) and non-solvent-induced phase separation (NIPS), the coagulated solution in which phase separation occurs within the polyamide porous membrane is extracted and removed. Then, the polyamide porous membrane is stretched along a uniaxial direction during or after drying. This invention was completed based on the aforementioned knowledge and insights through further repeated research.

[0010] That is, the present invention can provide an invention in the manner disclosed below. Item 1. A polyamide porous membrane having a dense layer formed on at least one side; The polyamide porous membrane has stripe-like recesses extending in one direction on the surface of the aforementioned dense layer; and, In the following orientation analysis, the orientation angle of the aforementioned striped recess is 0~5.0° or 175.0~180.0°, and the orientation intensity is 1.5~2.0. [Targeted Analysis] An electron microscope image of the dense layer surface is arranged such that the X-axis is parallel to the length direction of the striped recesses observed in the dense layer, and then binarized to obtain a binarized image. An approximate ellipse of the angular distribution of the average amplitude is calculated from the power spectrum image obtained after Fourier transforming this binarized image. The orientation angle and orientation intensity are then calculated based on this approximate ellipse. Orientation angle: The angle (°) between the minor axis of an approximate ellipse and the positive X-axis. Orientation strength: the ratio of the major axis length to the minor axis length of an approximate ellipse. Item 2. The polyamide porous membrane of Item 1 has a molecular weight cutoff of 200 to 50,000. Item 3. The polyamide porous membrane as described in Item 1 or 2, wherein the polyamide resin constituting the polyamide porous membrane is an aliphatic polyamide resin having methylene and amide groups in a molar ratio of -CH 2-:-NHCO-=4:1~10:1. Item 4. The polyamide porous membrane of any of Items 1 to 3 is a hollow fiber membrane. Item 5. A filtration method comprising using a polyamide porous membrane as described in any one of items 1 to 4 to filter a liquid containing solutes or particles. Item 6. A filter membrane assembly comprising a polyamide porous membrane as described in any one of items 1 to 4 housed in an assembly housing. Item 7. A method for manufacturing a polyamide porous membrane, comprising the following steps 1 to 4: The first step is to prepare the film-forming stock solution, which is a solution in which polyamide resin is dissolved in an organic solvent at a temperature above 100°C. The organic solvent has a boiling point above 150°C and is immiscible with polyamide resin at temperatures below 100°C. Step 2 is a step in which the polyamide resin is coagulated into a film by extruding the film-forming stock solution prepared in Step 1 into a predetermined shape into a coagulation bath at a temperature below 100°C. In this step, the coagulating liquid is brought into contact with at least one side of the surface of the film-forming stock solution after extrusion into a predetermined shape to form a polyamide porous membrane. The coagulating liquid is compatible with the organic solvent used in the film-forming stock solution and has low affinity for the polyamide resin. The third step involves extracting and removing the coagulated solution that has undergone phase separation in the polyamide porous membrane formed in the second step; and, The fourth step involves extending the polyamide porous membrane along a uniaxial direction while or after drying the membrane obtained in the third step. Item 8. The manufacturing method of Item 7, wherein in the aforementioned step 4, the material is extended along a single axis at an elongation ratio of 1.2 to 5 times. Item 9. The manufacturing method as described in Item 7 or 8, wherein in the aforementioned first step, the organic solvent used to prepare the aforementioned film-forming stock solution is an aprotic polar solvent. Item 10. If any of the manufacturing methods in items 7 to 9 is requested, it is a method for manufacturing a polyamide porous membrane in the shape of a hollow fiber membrane; The aforementioned second step involves using a sleeve-shaped nozzle for manufacturing hollow fibers with a sleeve structure, where the film-forming raw solution is ejected from the outer annular nozzle while the internal coagulation solution is ejected from the inner nozzle, and the mixture is immersed in a coagulation bath. At least one of the aforementioned internal coagulation solution and coagulation bath is a coagulation solution that is compatible with the organic solvent used in the aforementioned film-forming stock solution and has low affinity for polyamide resin. Invention Effects

[0011] The polyamide porous membrane of the present invention improves the liquid permeability by having a dense layer with a specific structure. Therefore, it can have a moderate liquid permeability corresponding to the molecular weight cutoff. In particular, the liquid permeability can still be improved even at a molecular weight cutoff of about 200 to 50,000.

[0012] Furthermore, since the permeability of the invented polyamide porous membrane has been improved, it can enhance the productivity of various industrial processes, save energy, and reduce costs. In particular, the polyamide porous membrane of this invention is formed from polyamide resin, thus exhibiting excellent resistance to a wide variety of organic solvents. Even when in contact with various types of organic solvents used in industry, it can stably maintain membrane properties and provide novel industrial processes that can replace distillation. Moreover, the polyamide porous membrane of this invention has high hydrophilicity. Therefore, when applied to conventional water filtration processes, it can improve removal performance through adsorption when removing hydrophilic substances. On the other hand, by inhibiting the adsorption of hydrophobic substances, it can prevent hydrophobic substances from covering the membrane surface and reducing the processing flow rate, i.e., fouling, thereby achieving high-efficiency filtration. Simple Explanation of the Diagram

[0013] Figure 1a shows an example of a scanning electron microscope image of the dense layer surface of a polyamide porous membrane, b shows a binarized image of the scanning electron microscope image of a after using moving average, and c shows a power spectrum image of the binarized image of b after Fourier transform. Figure 2a is a schematic diagram of the components used in determining methanol permeability, and Figure 2b is a schematic diagram of the apparatus used in determining methanol permeability. Figure 3 shows scanning electron microscope images of the dense layer of polyamide hollow fiber membranes in Examples 1-4 and Comparative Example 1. Figure 4 shows the power spectrum image obtained by binarizing and Fourier transforming the scanning electron microscope image in Figure 3. Implementation

[0014] 1. Polyamide porous membrane The polyamide porous membrane of the present invention has a dense layer formed on at least one side, characterized in that: the polyamide porous membrane has stripe-shaped recesses extending in one direction on the surface of the aforementioned dense layer, and, in the orientation analysis described later, the orientation angle of the aforementioned stripe-shaped recesses is 0~5.0° or 175.0~180.0°, and the orientation intensity is 1.5~2.0. Hereinafter, the polyamide porous membrane of the present invention will be described in detail.

[0015] [Compositional Materials] The polyamide porous membrane of the present invention is formed using polyamide resin. By using polyamide resin as the constituent resin, the polyamide porous membrane of the present invention exhibits resistance to a wide range of organic solvents.

[0016] There are no particular limitations on the types of polyamide resins used as constituent resins, and examples include homopolymers of polyamide, copolymers of polyamide, or mixtures thereof. Specifically, 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. Furthermore, examples of polyamide copolymers include copolymers of polyamide with polybutadiene glycol or polyethylene glycol and other polyethers. Furthermore, there are no particular limitations on the polyamide content ratio in the polyamide copolymer. For example, the polyamide content can preferably be 70 mol% or more, more preferably 80 mol% or more, even more preferably 90 mol% or more, and 95 mol% or more is particularly preferred. By ensuring that the polyamide content ratio in the polyamide copolymer meets the above range, superior organic solvent resistance can be achieved.

[0017] From the viewpoint of further improving resistance to a wide range of organic solvents, a preferred example of a polyamide resin used as a constituent resin may be an aliphatic polyamide resin having methylene and amide groups in a molar ratio of -CH 2-:-NHCO- = 4:1 to 10:1, and even more preferably a resin composed solely of such aliphatic polyamide resin.

[0018] Polyamide resins used as constituent resins can be cross-linked or not, but from the point of view of reducing manufacturing costs, uncross-linked ones are better.

[0019] Furthermore, there are no particular limitations on the relative viscosity of the polyamide resin; for example, it can be 2.0 to 7.0, preferably 3.0 to 6.0, and more preferably 2.0 to 4.0. By possessing the aforementioned relative viscosity, the formability and phase separation control during the manufacture of polyamide porous membranes are improved, enabling the polyamide porous membranes to exhibit excellent shape stability. In addition, here, relative viscosity refers to the value measured using an Ubbelohde viscometer at 25°C using a solution containing 1 g of polyamide resin dissolved in 100 mL of 96% sulfuric acid.

[0020] In this invention, the polyamide resin used as the constituent resin can be used alone or in combination of two or more.

[0021] In addition to the aforementioned polyamide resin, the polyamide porous membrane of the present invention may also include fillers as needed, without compromising the effects of the present invention. By including fillers, the strength, elongation, and modulus of elasticity of the polyamide porous membrane can be improved. In particular, by including fillers, the polyamide porous membrane is less prone to deformation even when high pressure is applied during filtration. There are no particular restrictions on the types of fillers that can be added. Examples include: fibrous fillers such as glass fiber, carbon fiber, potassium titanate whiskers, zinc oxide whiskers, calcium carbonate whiskers, wollastonite whiskers, aluminum borate whiskers, aramid fiber, alumina fiber, silicon carbide fiber, ceramic fiber, asbestos fiber, gypsum fiber, and metal fiber; silicates such as talc, hydrotalcite, wollastonite, zeolite, sericite, mica, kaolin, clay, pyrophyllite, bentonite, asbestos, and aluminum silicate; metal compounds such as silicon oxide, magnesium oxide, aluminum oxide, zirconium oxide, titanium oxide, and iron oxide; carbonates such as calcium carbonate, magnesium carbonate, and dolomite; sulfates such as calcium sulfate and barium sulfate; metal hydroxides such as calcium hydroxide, magnesium hydroxide, and aluminum hydroxide; and inorganic materials such as glass beads, glass flakes, glass powder, ceramic beads, boron nitride, silicon carbide, carbon black, silicon dioxide, and lead black. These fillers can be used alone or in combination of two or more. Among these fillers, talc, hydrotalcite, silica, clay, and titanium dioxide are preferred, with talc and clay being the most suitable.

[0022] There is no particular limitation on the filler content. For example, for every 100 parts by weight of polyamide resin, the filler content can be 5 to 100 parts by weight, preferably 10 to 75 parts by weight, and more preferably 25 to 50 parts by weight. By including filler in the above-mentioned contents, the strength, elongation, and modulus of elasticity of polyamide porous membranes can be improved.

[0023] Furthermore, in order to control pore size or improve membrane performance, the polyamide porous membrane of the present invention may also include additives such as thickeners, antioxidants, surface modifiers, lubricants, and surfactants as needed.

[0024] [shape] The shape of the polyamide porous membrane of the present invention is not particularly limited and can be selected from any shape such as hollow fiber membrane or flat sheet membrane. However, hollow fiber membrane is quite suitable for the present invention because it has a large filtration area per unit volume of the component and can perform filtration with high efficiency.

[0025] When the polyamide porous membrane of the present invention is a hollow fiber membrane, its outer diameter can be appropriately set according to its application, the thickness of the dense layer, and the required liquid permeability. Considering the relationship with the effective membrane area after filling the module, membrane strength, pressure loss of the fluid flowing in the hollow portion, and buckling pressure, the outer diameter of the hollow fiber membrane can be, for example, 450 µm or more, preferably 450 to 4000 µm, more preferably 500 to 3500 µm, even more preferably 700 to 3000 µm, and particularly preferably 700 to 2000 µm. Furthermore, when the polyamide porous membrane of the present invention is a hollow fiber membrane, other examples of its outer diameter range include 450 to 1000 µm or 500 to 760 µm. Furthermore, when the polyamide porous membrane of the present invention is in the shape of a hollow fiber, its inner diameter is not particularly limited, and can be, for example, 100~3000µm, preferably 200~2500µm, more preferably 300~2000µm, and even more preferably 300~1500µm. Also, when the polyamide porous membrane of the present invention is a hollow fiber membrane, other examples of its inner diameter range include 200~400µm or 230~370µm. In the present invention, the outer diameter and inner diameter of the hollow fiber membrane are determined by observing five hollow fiber membranes at 200x magnification using an optical microscope, measuring the outer diameter and inner diameter of each hollow fiber membrane (taking the largest diameter), and calculating their average values.

[0026] The thickness of the polyamide porous membrane of the present invention can be appropriately set according to the application or shape of the polyamide porous membrane, the thickness of the dense layer, and the required liquid permeability, for example, 50~600µm, and preferably 100~350µm. Furthermore, other examples of the thickness range of the polyamide porous membrane of the present invention include 200~500µm or 240~390µm. When the polyamide porous membrane of the present invention is in the shape of a hollow fiber, its thickness is calculated by subtracting the inner diameter from the outer diameter and dividing the result by 2.

[0027] [Compact layer] The polyamide porous membrane of this invention has a dense layer formed on the surface of at least one side. In this invention, "dense layer" refers to a region with densely packed micropores, which represents a region where the presence of micropores cannot be substantially confirmed in a 10,000x scanning electron microscope (SEM) image. With respect to the polyamide porous membrane of this invention, the filtration performance, such as molecular weight cutoff and liquid permeability, is almost entirely responsible for the dense layer. Furthermore, regarding the observation of the dense layer using a scanning electron microscope, when the polyamide porous membrane is a flat sheet membrane, it can be observed after being cut to an appropriate size, placed on a sample stage, and then subjected to vapor deposition treatment with Pt, Au, Pd, etc. Furthermore, when the polyamide porous membrane is a hollow fiber membrane, if you want to observe the dense layer on the outer surface, you can do so in the same way as with the flat sheet membrane. After cutting it to an appropriate size and placing it on the sample stage, you can perform a vapor deposition treatment of Pt, Au, Pd, etc. and then observe it. If you want to observe the dense layer on the inner cavity side surface, you can use a sharp tool such as a scalpel to cut along the length of the hollow fiber membrane to expose the inner cavity side surface. Then, cut it to an appropriate size, place it on the sample stage, and then perform a vapor deposition treatment of Pt, Au, Pd, etc. and then observe it.

[0028] In the polyamide porous membrane of the present invention, the thickness of the dense layer is not particularly limited, and can be, for example, 10~2000 nm, preferably 100~1500 nm, and more preferably 200~1000 nm. In the present invention, the thickness of the dense layer is the following value: the value obtained by measuring the distance (thickness) of more than 10 regions where the presence of pores cannot be substantially confirmed in an SEM image of the cross-section of the hollow fiber membrane at a magnification of 10000, and calculating the average value.

[0029] The polyamide porous membrane of the present invention has a dense layer formed on at least one surface. For example, when the polyamide porous membrane of the present invention is a hollow fiber membrane, a dense layer is formed on at least one of the inner cavity side surface and the outer surface. Alternatively, when the polyamide porous membrane of the present invention is in the shape of a flat sheet membrane, a dense layer is formed on at least one of the surface side and the back side surface. From the viewpoint of balancing molecular weight cutoff and permeability, a preferred example of the polyamide porous membrane of the present invention is one where a dense layer is provided only on one side. Furthermore, when the polyamide porous membrane of the present invention is a hollow fiber membrane, a preferred example is one where a dense layer is provided on the inner cavity side surface and no dense layer is provided on the outer surface.

[0030] In the polyamide porous membrane of the present invention, the surface of the dense layer has striped recesses extending in one direction. The striped recesses on the surface of the dense layer can be confirmed by observing the surface of the dense layer using a scanning electron microscope (SEM) at 10,000x magnification. There are multiple striped recesses on the surface of the dense layer, and each striped recess extends in the same direction. That is, in the surface of the dense layer, the length directions of the multiple striped recesses are respectively arranged in a manner that are substantially parallel.

[0031] Furthermore, in the polyamide porous membrane of the present invention, the length direction of the striped recesses existing on the surface of the dense layer is approximately consistent with the extension direction of the uniaxial extension during manufacturing. That is, if the polyamide porous membrane of the present invention is a hollow fiber membrane, the length direction of the striped recesses will be approximately parallel to the length direction of the hollow fiber membrane; if the polyamide porous membrane of the present invention is a flat sheet membrane, the length direction of the striped recesses will be approximately parallel to the extension direction of the flat sheet membrane during manufacturing.

[0032] In the polyamide porous membrane of the present invention, the striped recesses on the surface of the dense layer satisfy an orientation angle of 0~5.0° or 175.0~180.0° in the orientation analysis described later, and satisfy an orientation intensity of 1.50~2.00. By forming striped recesses on the surface of the dense layer that satisfy the orientation angle and orientation intensity as described above, the liquid permeability can be improved.

[0033] From the perspective of further improving liquid permeability, the orientation angle in the directional analysis described later should preferably be 0~3.0° or 177.0~180.0°, more preferably 1.1~2.5° or 177.5~178.9°, and even more preferably 1.1~2.5° or 177.9~178.9°. Furthermore, from the perspective of further improving liquid permeability, the orientation intensity in the directional analysis described later should preferably be 1.50~1.90, and more preferably 1.56~1.77.

[0034] The aforementioned orientation angle and orientation strength can be calculated by performing orientation analysis according to the steps shown in (1) to (4) below. (1) The electron microscope image of the dense layer surface is binarized to obtain a binarized image. (2) The aforementioned binarized image is configured such that the X-axis direction is parallel to the length direction of the striped recesses observed in the dense layer, and Fourier transform is performed to obtain a power spectrum image. (3) Calculate the approximate ellipse of the angle distribution of the average amplitude from the aforementioned power spectrum image. (4) Calculate the following orientation angle and orientation strength based on the aforementioned approximate ellipse. Orientation angle: The angle (°) between the minor axis of an approximate ellipse and the positive X-axis. Orientation strength: the ratio of the major axis length to the minor axis length of an approximate ellipse.

[0035] The orientation analysis method used in steps (1) to (4) above is recorded in the literature of Toshiharu Emae et al. ("Method for determining the fiber orientation of calculation paper by using Fourier image analysis", Proceedings of the 26th Conference of the Chinese Society for the Conservation and Restoration of Cultural Properties, pp. 44-45, 2004). The method recorded in that literature can be used, and the steps (1) to (4) above above will be explained in the following supplementary explanation.

[0036] The electron microscope image used in step (1) above can be obtained by observing the image with a scanning electron microscope (SEM) at a magnification of 10,000x. The method for observing dense layers using a scanning electron microscope is as described above. Since the binarized image obtained in step (1) above will be used for Fourier transform processing, a square electron microscope image with a pixel count that is a power of 1 on each side is used in step (1). Specifically, the binarization processing in step (1) above can be performed using the moving average method.

[0037] In step (2) above, the binarized image is configured such that the X-axis direction is parallel to the length direction (the uniaxial extension direction during manufacturing) of the striped recesses observed in the dense layer, and the Y-axis direction is parallel to the width direction (short side direction; perpendicular to the uniaxial extension direction during manufacturing) of the striped recesses, and then Fourier transform processing is performed. The Fourier transform processing in step (2) above can be performed using high-speed Fourier transform (FFT) processing. In the power spectrum image obtained by Fourier transforming the binarized image obtained in step (1) above, spots will appear at the locations corresponding to the wavenumber and direction of the periodic structure.

[0038] In step (3) above, the angular distribution pattern of the average amplitude (power spectrum pattern) can be obtained by displaying the power spectrum image obtained in step (2) above using polar coordinates. The strip-shaped recesses on the dense layer surface of the polyamide porous membrane of the present invention have orientation, and the angular distribution pattern of its average amplitude will appear as an approximately elliptical shape. Therefore, in step (3) above, the approximately elliptical shape of the angular distribution pattern of the average amplitude will be calculated.

[0039] In step (4) above, the orientation angle (°) is calculated based on the approximate ellipse (major axis length, minor axis length, and angle of the minor axis direction) obtained in step (3) above, and the ratio of the major axis length to the minor axis length of the approximate ellipse is calculated as the orientation intensity. In this invention, the orientation angle and orientation intensity are calculated as the average values ​​of the resolution results of the scanning electron microscope image 10 field of view.

[0040] The orientation analysis performed in steps (1) to (4) above can be performed using known image analysis software. For example, the orientation angle and orientation intensity can be easily calculated by using the "Non-destructive Paper Surface Fiber Orientation Analysis Program FiberOri8single03.exe (V.8.03)" (which can be downloaded from http: / / www.enomae.com / FiberOri / index.htm). The procedure for calculating the orientation angle and orientation intensity using the "Non-destructive Paper Surface Fiber Orientation Analysis Program FiberOri8single03.exe (V.8.03)" is described below. First, the electron microscope image of the surface of the dense layer (Fig. 1a) is read into the aforementioned image analysis software in such a way that the X-axis direction is parallel to the length direction of the striped recesses observed in the dense layer. Next, the electron microscope image is binarized using a moving average to create a binarized image (Figure 1b). Then, the binarized image is subjected to a high-speed Fourier transform (FFT) to create a power spectrum image (Figure 1c). Subsequently, by calculating the orientation angle and orientation degree based on the power spectrum image, the values ​​of the orientation angle and orientation degree can be output.

[0041] [Porous region] In the polyamide porous membrane of this invention, the region outside the dense layer constitutes a porous structure. Hereinafter, the region outside the dense layer will sometimes be referred to as a "porous region." Specifically, a porous region refers to a region where fine pores can be substantially confirmed in a scanning electron microscope (SEM) image at 2000x magnification. The performance of the polyamide porous membrane of this invention is almost entirely determined by the dense layer; therefore, the porous region can be considered a so-called support layer. The pore size in the porous region is not particularly limited as long as it maintains the strength of the dense layer and does not significantly impede fluid permeation.

[0042] [Molecular weight cutoff and methanol permeation] The molecular weight cutoff of the polyamide porous membrane of the present invention is not particularly limited and can be appropriately set by adjusting the thickness of the dense layer and the pore size of the area outside the dense layer. The molecular weight cutoff can be, for example, 200 to 50,000, preferably 200 to 20,000, more preferably 800 to 15,000, and even more preferably 920 to 1,400. The molecular weight cutoff indicates the pore size of the membrane, which is capable of blocking more than 90% of substances with a specific molecular weight, and the molecular weight cutoff is expressed as the molecular weight of the blocked substance.

[0043] In this invention, the molecular weight cutoff is determined using the following method: A compound with a known molecular weight dissolved in pure water at 0.1% by mass is used as the stock solution. The solution is filtered at a pressure of 0.3 MPa, and the liquid after permeation through the membrane is recovered. The concentration of the aforementioned compound in the permeate is measured, and the rejection rate is calculated according to the following formula. The rejection rates are calculated for compounds with various molecular weights, and these results are plotted in a graph. This graph displays the molecular weight of the compounds used on the horizontal axis and the rejection rate of each compound on the vertical axis. The molecular weight at the intersection of the approximate curve and the 90% rejection rate is used as the molecular weight cutoff. Furthermore, when the molecular weight cutoff is in the range of 200 to 50,000, polyethylene glycol is used; when the molecular weight cutoff is greater than 50,000, polydextrose is used. [Mathematical Expression 1]

[0044] The polyamide porous membrane of the present invention improves liquid permeability by having striped recesses extending in one direction on the surface of the dense layer, wherein the orientation angle and orientation angle of the striped recesses satisfy the aforementioned range. The liquid permeability of the polyamide porous membrane of the present invention varies depending on the molecular weight cutoff or the type of polyamide resin used, and cannot be specified in general. However, for example, the methanol permeability is 0.4~50 L / (m 2·bar·h), preferably 0.6~40 L / (m 2·bar·h), more preferably 0.8~30 L / (m 2·bar·h), and even more preferably 0.8~19 L / (m 2·bar·h).

[0045] In this invention, when the polyamide porous membrane is a hollow fiber membrane, the methanol permeation rate is measured using internal pressure filtration, and is measured according to the following procedure. First, prepare 10 hollow fiber membranes cut to 30 cm lengths, then align and bundle them together. Next, prepare a rigid nylon tube with an outer diameter of 8 mm, an inner diameter of 6 mm, and a length of 50 mm, and insert a rubber plug of approximately 20 mm in length into one end opening of the tube to plug that end opening. Then, insert epoxy resin into the opening on the opposite side of the tube to fill the inner space of the tube with the epoxy resin. The epoxy resin is a two-component mixture and a room temperature curing resin. Then, bend the bundled hollow fiber membranes into an approximately U-shape, and insert both ends of the hollow fiber membrane into the epoxy resin-filled tube until the front end touches the rubber plug, and then allow the epoxy resin to harden in this state. Next, the area of ​​the hardened epoxy resin portion near the rubber plug, along with the tubing, is cut to obtain an assembly with open hollow sections at both ends of the hollow fiber membrane. A schematic diagram of this assembly is shown in Figure 2a. Next, the aforementioned assembly is installed in the device shown in Figure 2b below, and a pressure of approximately 0.3 MPa is applied to allow methanol (100% methanol) at 25°C to flow inside the hollow fiber membrane of the aforementioned assembly for a fixed time. Then, the amount of methanol that permeates to the outside of the hollow fiber membrane is calculated, and the methanol permeation rate (L / (m²·bar·h)) is calculated according to the following formula. [Mathematical Expression 2]

[0046] Furthermore, in this invention, when the polyamide porous membrane is a flat sheet membrane, the methanol permeation is measured using a cut-off filtration method, and is measured according to the following procedure. Using a flat sheet membrane sweep tester connected to a high-pressure pump (e.g., the Sepa-CF flat sheet membrane test tank manufactured by GE Water Technologies), a flat sheet polyamide porous membrane is cut to a predetermined size (19.1 cm × 14.0 cm, effective membrane area in the tank: 155 cm²) and fixed in the tank. Then, methanol at 25°C is introduced, the methanol permeated under a predetermined pressure is recovered, and the volume (L) is measured. The methanol permeation (L / (m²·bar·h)) is calculated according to the following formula.

[0047] [Mathematical Expression 3]

[0048] When the molecular weight cutoff of the polyamide porous membrane of the present invention is greater than 1000, as a preferred example that can meet the methanol permeation range for each molecular weight cutoff range, for example, the molecular weight cutoff is 1100~2000 and the methanol permeation is 5~50 L / (m 2·bar·h); preferably, the molecular weight cutoff is 1200~1500 and the methanol permeation is 5~30 L / (m 2·bar·h); more preferably, the molecular weight cutoff is 1200~1500 and the methanol permeation is 8~20 L / (m 2·bar·h); even more preferably, the molecular weight cutoff is 1200~1400 and the methanol permeation is 9.4~19 L / (m 2·bar·h).

[0049] Furthermore, when the molecular weight cutoff of the polyamide porous membrane of the present invention is 1000 or less, as a preferred example to satisfy the methanol permeation range for each molecular weight cutoff range, examples include a molecular weight cutoff of 200 to 1000 and a methanol permeation of 0.8 to 10 L / (m²·bar·h); preferably a molecular weight cutoff of 900 to 1000 and a methanol permeation of 0.8 to 5.0 L / (m²·bar·h); more preferably a molecular weight cutoff of 900 to 1000 and a methanol permeation of 0.8 to 3.0 L / (m²·bar·h); and even more preferably a molecular weight cutoff of 920 to 990 and a methanol permeation of 0.8 to 2.9 L / (m²·bar·h).

[0050] [Organic solvent resistance] The polyamide porous membrane of this invention is formed of polyamide resin, and therefore possesses the characteristic of maintaining a stable membrane structure by suppressing changes in strength and elongation even when in contact with various types of organic solvents (organic solvent resistance). More specifically, the polyamide porous membrane of this invention is resistant to organic solvents such as alcohols, aprotic polar solvents, hydrocarbons, higher fatty acids, ketones, esters, and ethers. Examples of such organic solvents include the following. Alcohols: First-level alcohols such as methanol, ethanol, n-propanol, n-butanol, and benzyl alcohol; second-level alcohols such as isopropanol and isobutanol; third-level alcohols such as tertiary butanol; and polyols such as ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, propylene glycol, 1,3-butanediol, and glycerol. Ketones: acetone, methyl ethyl ketone, cyclohexanone, diisopropanone, etc. Ethers: Tetrahydrofuran, diethyl ether, diisopropyl ether, 1,4-dimethyl ether, etc., and glycol ethers such as ethylene glycol monomethyl ether, diethylene glycol monomethyl ether, and propylene glycol monomethyl ether. Aprotic polar solvents: N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, N-methyl-2-pyrrolidone, cyclobutane, etc. Esters: ethyl acetate, isobutyl acetate, ethyl lactate, dimethyl phthalate, diethyl phthalate, ethyl carbonate, propyl carbonate, propylene glycol monomethyl ether acetate, etc. Hydrocarbons: petroleum ether, pentane, hexane, heptane, benzene, toluene, xylene, liquid paraffin, gasoline and mineral oil. Higher fatty acids: fatty acids such as oleic acid, linolenic acid, and alpha-linolenic acid, which have 4 or more carbon atoms other than the carboxyl group (preferably 4 to 30).

[0051] In particular, as a preferred example of the organic solvent resistance of the polyamide porous membrane of the present invention, it is possible to exemplify resistance to at least one of the following organic solvents, preferably resistance to all of them. Alcohols: isopropanol, benzyl alcohol, ethylene glycol, glycerol. Ketones: acetone, methyl ethyl ketone, cyclohexanone. Ethers: Tetrahydrofuran, diethyl ether, propylene glycol monomethyl ether. Aprotic polar solvents: N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, N-methyl-2-pyrrolidone. Esters: Ethyl acetate, isobutyl acetate, dimethyl phthalate. Hydrocarbons: hexane, heptane, benzene, toluene, gasoline, mineral oil. Higher fatty acids: oleic acid, linoleic acid.

[0052] Specifically, the organic solvent resistance of the polyamide porous membrane of the present invention can be exemplified by the following: after immersion in the aforementioned organic solvent at 25°C for 14 hours, the change rate of the tensile strength and elongation of the ultrafiltration membrane after immersion is less than ±30% compared to before immersion, and preferably less than ±20%. Specifically, the change rate of tensile strength and elongation is calculated according to the following formula. [Mathematical Expression 4]

[0053] Regarding the strength and elongation of polyamide porous membranes, when the polyamide porous membrane is a hollow fiber membrane, the values ​​are measured under the conditions described in the aforementioned [Tensile Strength and Elongation] column. When the polyamide porous membrane is a flat sheet membrane, the strength and elongation are measured under the conditions described in the aforementioned [Tensile Strength and Elongation] column, except when using a short, stick-shaped sample with a width of 10 mm and a length of 100 mm.

[0054] [use] The polyamide porous membrane of this invention can be used as an ultrafiltration membrane or a nanofiltration membrane in fields such as the semiconductor industry, chemical industry, food industry, pharmaceutical industry, and medical product industry. In this invention, "ultrafiltration" or "ultrafiltration membrane" refers to a filtration membrane with a molecular weight cutoff set in the range of 1,000 to 1,000,000. Furthermore, in this invention, "nanofiltration" or "nanofiltration membrane" refers to a filtration membrane with a molecular weight cutoff set in the range of 200 to 1,000.

[0055] Furthermore, the polyamide porous membrane of the present invention is resistant to various organic solvents, and therefore is suitable for use in filtration of liquids containing organic solvents.

[0056] The polyamide porous membrane of the present invention is preferably used in the filter membrane assembly described later.

[0057] Furthermore, the polyamide porous membrane of the present invention can be provided separately as a self-supporting membrane, or it can be in the form of being laminated on a support for a precision filter membrane. The material of the support should preferably be resistant to organic solvents, and specifically includes the following: polymer materials such as polyamide, polyethylene, polypropylene, polytetrafluoroethylene, polyphenylene sulfide, and polyetheretherketone; and inorganic materials such as sintered metals and ceramics.

[0058] 2. Method for manufacturing polyamide porous membranes The manufacturing method of the polyamide porous membrane of the present invention is not particularly limited as long as it can produce a striped recess with the aforementioned orientation angle and orientation intensity formed on the surface of the dense layer. As a preferred example, a manufacturing method including the following steps 1 to 4 can be described. The polyamide porous membrane of the present invention has a dense layer formed on at least one side of its surface, and the region outside the dense layer has a porous structure. It is difficult to obtain this by simply using conventional thermally induced phase separation (TIPS) or non-solvent-induced phase separation (NIPS) methods. However, in the manufacturing method including the following steps 1 to 4, the polyamide porous membrane of the present invention can be manufactured efficiently by using the principles of both TIPS and NIPS methods and performing uniaxial stretching under predetermined conditions. Step 1: Prepare the film-forming stock solution. The film-forming stock solution is made by dissolving polyamide resin in an organic solvent at a temperature above 100°C. The organic solvent has a boiling point above 150°C and is immiscible with polyamide resin at temperatures below 100°C. Step 2: This step involves extruding the aforementioned film-forming stock solution into a coagulation bath at a temperature below 100°C to coagulate the polyamide resin into a film. In this step, the coagulating liquid is brought into contact with at least one side of the surface of the aforementioned film-forming stock solution after extrusion into a predetermined shape to form a polyamide porous membrane. The coagulating liquid is compatible with the organic solvent used in the aforementioned film-forming stock solution and has low affinity for the polyamide resin. Step 3: The coagulated liquid that has undergone phase separation in the polyamide porous membrane formed in Step 2 above is extracted and removed. Step 4: While drying the polyamide porous membrane after step 3, or after drying it, extend it along the uniaxial direction.

[0059] The following will provide a detailed explanation of each step from step 1 to step 4.

[0060] [Step 1] In step 1, a film-forming stock solution is prepared. This film-forming stock solution is obtained by dissolving polyamide resin in an organic solvent at a temperature above 100°C. The organic solvent has a boiling point above 150°C and is immiscible with polyamide resin at temperatures below 100°C.

[0061] Organic solvents with boiling points above 150°C and immiscible with polyamide resins at temperatures below 100°C include, for example, aprotic polar solvents, glycerol ethers, polyols, organic acids and organic acid esters, and higher alcohols. Specific examples of aprotic polar solvents include: cyclobutane, dimethyl sulfoxide, dimethyl sulfoxide, γ-butyrolactone, δ-valerolactone, ε-caprolactone, N,N-dimethylformamide, N,N-dimethylacetamide, N-methyl-2-pyrrolidone, ethylene carbonate, and propylene carbonate. Specific examples of glycerol ethers include: diethylene glycol dimethyl ether, diethylene glycol diethyl ether, triethylene glycol dimethyl ether, diethylene glycol dibutyl ether, and tetraethylene glycol dimethyl ether. Polyols include, specifically, glycerol, ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, hexanediol, 1,3-butanediol, and polyethylene glycol (molecular weight 100-10000). Organic acids and organic acid esters include, specifically, dimethyl phthalate, diethyl phthalate, diisopropyl phthalate, dibutyl phthalate, butyl benzyl phthalate, methyl salicylate, oleic acid, palmitic acid, stearic acid, and lauric acid. From the viewpoint of obtaining polyamide porous membranes with higher strength, the preferred organic solvents are aprotic polar solvents and polyols, preferably cyclobutane, dimethyl sulfone, γ-butyrolactone, δ-valerolactone, ε-caprolactone, propylene glycol, hexanediol, 1,3-butanediol, and polyethylene glycol (molecular weight 100~600). More preferably, cyclobutane, dimethyl sulfone, γ-butyrolactone, δ-valerolactone, and ε-caprolactone are also suitable. These organic solvents can be used alone or in combination of two or more. While using a single organic solvent may yield sufficient results, mixing two or more solvents can sometimes produce more effective polyamide porous membranes due to differences in the phase separation order or structure.

[0062] There are no particular limitations on the concentration of polyamide resin in the membrane-forming solution, such as 5-50% by mass, preferably 10-40% by mass, and more preferably 12-35% by mass. By ensuring that the concentration of polyamide resin in the membrane-forming solution meets the aforementioned range, the polyamide porous membrane can possess excellent strength and liquid permeability.

[0063] Furthermore, in step 1, when dissolving the polyamide resin in the aforementioned organic solvent, the solvent temperature must be at least 100°C. Specifically, ideally, the solvent should be dissolved at a temperature 10-50°C higher than the phase separation temperature of the film-forming solution to be prepared, and preferably at a temperature 20-40°C higher than that phase separation temperature. The phase separation temperature of the film-forming solution refers to the temperature at which liquid-liquid phase separation or solid-liquid phase separation due to crystallization occurs when the mixture of polyamide resin and the aforementioned organic solvent is slowly cooled after being mixed at a sufficiently high temperature. The phase separation temperature can be measured using a microscope equipped with a high-temperature stage.

[0064] In step 1, the temperature conditions for dissolving polyamide resin in the aforementioned organic solvent can be appropriately set within the temperature range above 100°C, depending on the type of polyamide resin and organic solvent used, according to the aforementioned indicators. The preferred temperature is 120~250°C, more preferably 140~220°C, and even more preferably 160~200°C.

[0065] Furthermore, in order to control the pore size and improve the performance of polyamide porous membranes, fillers, thickeners, antioxidants, surface modifiers, lubricants, surfactants, etc., can be added to the membrane preparation solution as needed.

[0066] The film-forming stock solution prepared in step 1 is directly supplied to step 2 at the same temperature (i.e., above 100°C).

[0067] [Step 2] Step 2 is a step in which polyamide resin is coagulated into a film by extruding the film-forming stock solution prepared in Step 1 into a predetermined shape into a coagulation bath at a temperature below 100°C. In this step, the coagulating liquid is brought into contact with at least one side of the surface of the film-forming stock solution after extrusion into the predetermined shape to form a polyamide porous film. The coagulating liquid is compatible with the organic solvent used in the film-forming stock solution and has low affinity for polyamide resin (hereinafter sometimes referred to as "coagulating liquid for forming dense layer").

[0068] In this second step, the film-forming solution, extruded into the coagulation bath in a predetermined shape, forms a dense layer on the surface in contact with the coagulating liquid for dense layer formation. Near the surface where the film-forming solution contacts the coagulating liquid for dense layer formation, the non-solvent phase separation by solvent exchange is more significantly advanced than the thermally induced phase separation by cooling, resulting in a denser structure on the surface than that of the conventional TIPS method.

[0069] To form a dense layer on only one side of the polyamide porous membrane, in step 2, the dense layer can be formed by contacting one side of the film-forming solution, which has been extruded into a predetermined shape, with a coagulating liquid, and the other side can be contacted with the coagulating liquid. This coagulating liquid is compatible with the organic solvent used in the aforementioned film-forming solution and has a high affinity for the polyamide resin (hereinafter sometimes referred to as "coagulating liquid for forming porous structures"). Alternatively, to form a dense layer on both sides of the polyamide porous membrane, in step 2, the dense layer can be formed by contacting both sides of the film-forming solution, which has been extruded into a predetermined shape, with a coagulating liquid.

[0070] Specifically, the coagulant for forming the dense layer is a solvent that is miscible with the organic solvents used in the aforementioned film-forming stock solution at temperatures below 50°C, but will not dissolve the polyamide resin at temperatures below its boiling point or below 200°C. Examples of coagulants for forming the dense layer include: aqueous solvents such as water and aqueous solutions with a water content of 80% by mass or more; monovalent lower alcohols such as 1-propanol, 2-propanol, and isobutanol; glycol ethers such as polyethylene glycol with an average molecular weight of 300 or more, polypropylene glycol with an average molecular weight of 400 or more, diethylene glycol diethyl ether, triethylene glycol monomethyl ether, and propylene glycol monoethyl ether; and glycol acetates such as triacetin and propylene glycol monoethyl ether acetate. Among these, polyethylene glycol with an average molecular weight of 300-1000, polypropylene glycol with an average molecular weight of 400-1000, triacetin, and triethylene glycol monomethyl ether are preferred, with polyethylene glycol having an average molecular weight of 300-700 being more desirable, and polyethylene glycol with an average molecular weight of 400-600 being even more desirable. These solvents can be used alone or in combination of two or more. In this invention, the average molecular weight of polyethylene glycol and polypropylene glycol is the number average molecular weight calculated based on the hydroxyl value, which is the value measured according to JIS K 1557-6:2009 "Plastics - Polyurethane Raw Materials - Test Methods for Polyols - Part 6: Method for Calculating Hydroxyl Value by Near-Infrared (NIR) Spectrophotometry".

[0071] Furthermore, within the limits that allow for the formation of a dense layer, the coagulating solution for forming the dense layer may also contain solvents such as glycerol used in the coagulating solution for forming porous structures (solvents that are miscible with the organic solvents used in the aforementioned film-forming solution at temperatures below 25°C and that dissolve polyamide resin at temperatures below their boiling points). When the coagulating solution for forming the dense layer is to contain solvents used in the coagulating solution for forming porous structures, the content of such solvent may be, for example, 20% by mass or less, and preferably 10% by mass or less.

[0072] The coagulating solution for forming porous structures can be a solvent that is miscible with the organic solvent used in the aforementioned film-forming solution at temperatures below 25°C and that dissolves the polyamide resin at temperatures below its boiling point. Specific examples of coagulating solutions for forming porous structures include glycerol, ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, polyethylene glycol 200, propylene glycol, 1,3-butanediol, cyclobutane, N-methyl-2-pyrrolidone, γ-butyrolactone, δ-valerolactone, and aqueous solutions containing 20% ​​by mass or more of these. Among these, an aqueous solution selected from at least one of the group consisting of glycerol, propylene glycol, diethylene glycol and polyethylene glycol 200, and containing such solutions at a ratio of 25 to 75% by mass, is preferred. An aqueous solution selected from at least one of the group consisting of glycerol, diethylene glycol, tetraethylene glycol and propylene glycol, and containing such solutions at a ratio of 40 to 80% by mass (preferably 40 to 60% by mass) is also preferred.

[0073] In the case of forming a hollow fiber membrane as a polyamide porous membrane system, step 2 involves using a sleeve-shaped nozzle for hollow fiber manufacturing with a sleeve structure. The aforementioned membrane-forming solution is ejected from the outer annular nozzle, while an internal coagulation solution is ejected from the inner nozzle, and the membrane is immersed in a coagulation bath. In this case, it is sufficient to use a dense layer-forming coagulation solution in at least one of the internal coagulation solution and the coagulation bath. When both the internal coagulation solution and the coagulation bath use a dense layer-forming coagulation solution, a hollow fiber membrane with dense layers formed on both the inner and outer surfaces and a porous interior can be obtained. Furthermore, when a dense layer-forming coagulation solution is used as the internal coagulation solution and a porous structure-forming coagulation solution is used as the coagulation bath, a hollow fiber membrane with a dense layer formed on the inner surface and porous interior and outer surfaces can be obtained. Furthermore, when a porous structure-forming coagulation solution is used as the internal coagulation solution and a dense layer-forming coagulation solution is used as the coagulation bath, a hollow fiber membrane with a dense layer formed on the outer surface and a porous region on the inner cavity side surface and inside can be obtained. In addition, since the internal coagulation solution used in forming the hollow fiber membrane passes through a double-ring nozzle, it is preferable that it does not contain water with a boiling point below the temperature of the double-ring nozzle.

[0074] The sleeve-shaped nozzle for hollow fiber manufacturing can use a nozzle with a double-tube structure, such as that used in melt spinning to manufacture core-sheath type composite fibers. The diameter of the outer annular nozzle and the inner nozzle of the sleeve-shaped nozzle for hollow fiber membrane manufacturing can be appropriately set according to the inner and outer diameters of the hollow fiber membrane.

[0075] Furthermore, the flow rate of the film-forming solution discharged from the annular nozzle outside the sleeve-shaped nozzle used in hollow fiber manufacturing will also depend on the slit width, so there is no particular limitation. For example, it can be 2 to 30 g / min, preferably 3 to 20 g / min, and more preferably 5 to 15 g / min. In addition, regarding the flow rate of the internal coagulation liquid, it can be appropriately set by considering the diameter of the inner nozzle of the sleeve-shaped nozzle used in hollow fiber manufacturing, the type of internal liquid used, and the flow rate of the film-forming solution. For example, it can be 0.1 to 2 times the flow rate of the film-forming solution, preferably 0.2 to 1 times, and more preferably 0.4 to 0.7 times.

[0076] Furthermore, if the case is to form a flat sheet membrane as a polyamide porous membrane system, the second step is to use the aforementioned coagulation solution for forming a dense layer as a coagulation bath, and to extrude the aforementioned film-forming stock solution into a predetermined shape and immerse it in the coagulation bath.

[0077] In step 2, the coagulation bath temperature can be below 100°C, preferably -20 to 100°C, more preferably 0 to 60°C, even more preferably 2 to 20°C, and especially preferably 2 to 10°C. The optimal temperature of the coagulation bath can be varied depending on the organic solvent used in the membrane preparation solution and the composition of the coagulation solution. However, generally, the following tendency can be observed: by setting a lower temperature, thermally induced phase separation will occur preferentially, and by setting a higher temperature, non-solvent phase separation will occur preferentially. That is, if a hollow fiber membrane with a dense layer formed on the inner cavity side surface is to be manufactured, in order to increase the pore size of the dense layer on the inner cavity side surface, the coagulation bath should be set at a low temperature; in order to make the dense layer on the inner cavity side surface even denser and to make the internal structure coarser, the coagulation bath should be set at a high temperature.

[0078] Furthermore, if the hollow fiber membrane is formed as a polyamide porous membrane system, the temperature of the coagulation liquid inside only needs to be around the set temperature of the sleeve nozzle, for example, 120~250℃, and preferably 160~230℃, more preferably 180~220℃.

[0079] By implementing step 2 in the manner described above, the film-forming solution can be coagulated in a coagulation bath, and a polyamide porous membrane with a dense layer formed on at least one side surface can be formed.

[0080] [Step 3] In step 3, the coagulated liquid that has undergone phase separation in the polyamide porous membrane formed in step 2 is extracted and removed.

[0081] To extract and remove the coagulated liquid that has undergone phase separation in the polyamide porous membrane, simply immerse the polyamide porous membrane formed in the aforementioned second step in the extraction solvent, or spray the polyamide porous membrane formed in the aforementioned second step with the extraction solvent.

[0082] In step 3, the extraction solvent used for extraction removal should be inexpensive, have a low boiling point, and be easily separated after extraction by the difference in boiling points. Examples include water, glycerol, methanol, ethanol, isopropanol, acetone, diethyl ether, hexane, petroleum ether, and toluene. Among these, water, methanol, ethanol, isopropanol, and acetone are preferred, with water, methanol, and isopropanol being the most suitable. Furthermore, when extracting phthalates, fatty acids, or other water-insoluble organic solvents, isopropanol and petroleum ether are suitable choices.

[0083] When extracting and removing coagulated liquid by immersing a polyamide porous membrane in an extraction solvent, there is no particular limitation on the immersion time. For example, it can range from 0.2 hours to 2 months, preferably 0.5 hours to 1 month, and more preferably 2 hours to 10 days. Furthermore, the extraction solvent can be replaced or the membrane can be stirred to effectively extract and remove the coagulated liquid remaining in the polyamide porous membrane.

[0084] The polyamide porous membrane system, after being extracted and the coagulated liquid from which phase separation occurred, in the manner described above, is supplied to the fourth step described later.

[0085] [Step 4] In step 4, the polyamide porous membrane after step 3 is dried simultaneously or after drying, and then extended along a uniaxial direction. Although the striped recesses with the aforementioned orientation angle and orientation intensity have not yet been formed on the surface of the dense layer in the polyamide porous membrane after step 3, step 4 can form striped recesses with the aforementioned orientation angle and orientation intensity on the surface of the dense layer.

[0086] In step 4, the uniaxial extension is performed either while the polyamide porous membrane with the extraction solvent attached after step 3 is being dried, or after the polyamide porous membrane with the extraction solvent attached after step 3 is being dried. If the uniaxial extension is performed after step 3 while the membrane is still attached with the extraction solvent, and then the membrane is dried, the extended polyamide porous membrane will shrink significantly due to drying, making it impossible to form striped recesses with the aforementioned orientation angle and orientation intensity on the surface of the dense layer, and thus failing to adequately improve the liquid permeability.

[0087] To achieve uniaxial stretching while drying, drying can be performed under tension required for stretching applied to the polyamide porous membrane. As for the temperature conditions for uniaxial stretching while drying, there are no particular limitations as long as both drying and stretching are feasible; for example, 40°C or higher is acceptable, preferably 40~160°C, more preferably 50°C~140°C, and even more preferably 120~140°C.

[0088] Furthermore, when extending along a uniaxial direction after drying, the temperature conditions during drying are not particularly limited as long as the attached extraction solvent can evaporate. For example, 40°C or higher is acceptable, preferably 40~160°C, more preferably 50°C~140°C, and even more preferably 120~140°C. Additionally, when extending along a uniaxial direction after drying, the temperature conditions during extension are not particularly limited, as long as they are -10~140°C, preferably 0~120°C. From the viewpoint of further improving the liquid permeability, it is preferable to extend the temperature above the glass transition point of the polyamide resin used (preferably 50~120°C), and even more preferably 60~100°C.

[0089] Uniaxial stretching can be performed using known methods, such as continuous winding from a low-speed roller to a high-speed roller. Alternatively, the ends of a polyamide porous membrane cut to a fixed length can be held and stretched using a tensile testing machine, or manually. When the polyamide porous membrane is a hollow fiber membrane, uniaxial stretching can be performed along the length of the hollow fiber membrane. Furthermore, when the polyamide porous membrane is a flat sheet membrane, uniaxial stretching can be performed in either the longitudinal or transverse direction of the flat sheet membrane.

[0090] When stretching in one direction, the elongation ratio can be, for example, 1.2 to 5 times, and preferably 1.2 to 3 times. From the viewpoint of improving the strength of the polyamide porous membrane and giving it excellent water pressure resistance, the elongation ratio is preferably 1.2 to 2.4 times, and more preferably 1.5 to 2.0 times.

[0091] 3. Filtering components The polyamide porous membrane of the present invention is housed in a component box and used as a filter membrane component. The component box has a treated liquid inlet and a permeate outlet.

[0092] When the polyamide porous membrane of the present invention is in the shape of a hollow fiber, it can be used as a hollow fiber membrane module.

[0093] Specifically, the hollow fiber membrane module can have the following structure: the hollow fiber polyamide porous membrane of the present invention is bundled together and placed in a module box, and one or both ends of the hollow fiber polyamide porous membrane are sealed with a potting compound to fix it in place. The hollow fiber membrane module can have an opening connected to the flow path through the outer wall side of the hollow fiber polyamide porous membrane, and an opening connected to the hollow portion of the hollow fiber polyamide porous membrane, serving as the inlet for the treated liquid or the outlet for the filtrate.

[0094] There are no particular limitations on the shape of hollow fiber membrane modules; they can be either flow-blocking or flow-sweeping modules. Specifically, examples include: flow-blocking modules where hollow fiber membrane bundles are bent into a U-shape for filling, and the ends of the hollow fiber polyamide porous membrane bundles are sealed before being cut to create an opening; and flow-blocking modules where the hollow opening at one end of a hollow fiber polyamide porous membrane bundle is sealed by heat sealing or other means, and then the end of the hollow fiber polyamide porous membrane bundle on the opening side is sealed before being cut to create an opening. After the hollow fiber polyamide porous membrane bundle is filled vertically, both ends of the hollow fiber polyamide porous membrane bundle are sealed and only one end is cut off to expose the opening of the flow interception assembly; after the hollow fiber polyamide porous membrane bundle is filled vertically, both ends of the hollow fiber polyamide porous membrane bundle are sealed, and then the sealing parts at both ends of the hollow fiber polyamide porous membrane bundle are cut off, and two flow paths are made on the side of the filter box to form a sweeping flow assembly.

[0095] There are no particular limitations on the filling rate of the hollow fibrous polyamide porous membrane inserted into the module housing. For example, the volume of the hollow fibrous polyamide porous membrane, including the volume of the hollow portion, can be 30-90% of the volume of the module housing, preferably 35-75% of the volume, and more preferably 45-65% of the volume. By satisfying the above filling rate, sufficient filtration area can be ensured, and the filling operation of the hollow fibrous polyamide porous membrane into the module housing can be facilitated, and the potting compound can flow easily between the hollow fibrous polyamide porous membranes.

[0096] There are no particular restrictions on the potting compound used in the manufacture of hollow fiber membrane modules. However, when the hollow fiber membrane module is to be used to handle organic solvents, the potting compound should preferably contain organic solvents. Examples of potting compounds include: polyamide, silicone resin, epoxy resin, melamine resin, polyethylene, polypropylene, phenolic resin, polyimide, and polyurea resin. Among these potting compounds, those with low shrinkage and swelling after curing and not too hard are preferred. Preferred examples include polyamide, silicone resin, epoxy resin, and polyethylene. One potting compound can be used alone, or two or more can be used in combination.

[0097] There are no particular limitations on the material of the module box used for hollow fiber membrane modules, and examples include polyamide, polyester, polyethylene, polypropylene, polydifluoroethylene, polytetrafluoroethylene, polyvinyl chloride, polyurethane, polyether sulfide, polycarbonate, polyarylate, and polyphenylene sulfide. Among these, polyamide, polyethylene, polypropylene, polytetrafluoroethylene, polycarbonate, polyurethane, and polyether sulfide are particularly suitable, and polyamide, polyethylene, polypropylene, and polytetrafluoroethylene are even more preferred.

[0098] Furthermore, when the polyamide porous membrane of the present invention is in the shape of a flat sheet membrane, it can be used as a sheet-type assembly, a spiral assembly, a rotating flat sheet membrane assembly, etc., such as a plate-frame type or a stacked type.

[0099] The filtration membrane assembly utilizing the polyamide porous membrane of the present invention can be used in the semiconductor industry, chemical industry, food industry, pharmaceutical industry, and medical product industry for ultrafiltration or nanofiltration applications such as removing foreign matter from solvents, concentrating useful components in solvents, recovering solvents, and purifying water. Furthermore, one embodiment of the filtration membrane assembly utilizing the polyamide porous membrane of the present invention is suitable for filtration of liquids containing organic solvents.

[0100] Furthermore, one embodiment of the filter membrane assembly utilizing the polyamide porous membrane of the present invention is suitable for use in filtration of a liquid containing an organic solvent. Example

[0101] The present invention will be specifically described below using examples, but the present invention is not limited to these examples.

[0102] 1. Measurement Method [Outer and inner diameters of hollow fiber membranes, thickness of hollow fiber membranes] Five hollow fiber membranes were observed using an optical microscope at 200x magnification. The outer and inner diameters of each membrane were measured (at their maximum diameter), and the average values ​​were calculated. The thickness of the hollow fiber membrane was calculated by subtracting the inner diameter from the outer diameter and dividing by 2.

[0103] [Orientation Analysis (Orientation Angle and Orientation Strength)] Polyamide hollow fiber membranes were cut into approximately 1 cm pieces and bisected along their length to expose the dense layer on the inner cavity side surface, thus creating a sample sheet. The sample sheet was placed on a sample stage, and platinum deposition was performed on the dense layer of the sample sheet using an MSP-1S type magnetron sputtering apparatus (manufactured by VACUUM DEVICE, Inc.) at a discharge voltage of 45 mA and a deposition time of 15 seconds. Subsequently, the dense layer was observed at 1000x magnification using a scanning electron microscope (SEM), and the resulting image was obtained using ImageJ image processing software (total pixels 262,144, vertical pixels 512, horizontal pixels 512). The obtained image was configured such that the X-axis direction was parallel to the length direction of the striped recesses observed in the dense layer (the length direction of the polyamide hollow fiber membrane), and the Y-axis direction was parallel to the width (short side) direction of the striped recesses. Then, image analysis software (a non-destructive paper surface fiber orientation analysis program FiberOri8single03.exe (V.8.03); available for download from http: / / www.enomae.com / FiberOri / index.htm) was used to analyze the image.

[0104] In image analysis, specifically, after binarizing the image using a moving average method, a high-speed Fourier transform (FFT) is performed to convert it into a power spectrum image. The resulting power spectrum image is then subjected to orientation analysis to determine the orientation angle and orientation intensity. Furthermore, in the aforementioned image analysis software used in this measurement, an angular distribution map (power spectrum pattern) of the average amplitude is obtained from the power spectrum image, and an approximate ellipse of this angular distribution map is calculated. The angle of the minor axis of this approximate ellipse relative to the positive X-axis is output as the orientation angle (°), and the ratio of the major axis length to the minor axis length of this approximate ellipse is output as the orientation intensity. Additionally, the orientation angle and orientation intensity are calculated as the average value of the analysis results from 10 fields of view of the scanning electron microscope image.

[0105] [Methanol penetration] First, fabricate the component shown in Figure 2a. Specifically, first prepare 10 hollow fiber membranes cut to 30cm lengths, then align and bundle them together. Next, prepare a rigid nylon tube with an outer diameter of 8mm, an inner diameter of 6mm, and a length of 50mm. Insert a rubber plug of approximately 20mm length into one end opening of the tube to plug that end opening. Then, insert epoxy resin into the opening on the opposite side of the tube to fill the inner space of the tube. The epoxy resin is a two-component mixture and a room-temperature curing resin. Next, bend the bundled hollow fiber membranes into an approximate U-shape and insert both ends of the hollow fiber membranes into the epoxy resin-filled tube until the front ends touch the rubber plugs. Then, allow the epoxy resin to harden in this state. Next, the area of ​​the hardened epoxy resin part near the rubber plug is cut together with the tube to create an assembly with open hollow sections at both ends of the hollow fiber membrane.

[0106] Next, the aforementioned component was installed in the device shown in Figure 2b, and a pressure of about 0.3 MPa was applied to make methanol (100% methanol) at 25°C flow inside the hollow fiber membrane of the aforementioned component for a fixed time. Then, the amount of methanol that permeated to the outside of the hollow fiber membrane was calculated, and the methanol permeation amount (L / (m2·bar·h)) was calculated according to the following formula. [Mathematical Expression 5]

[0107] [Molecular weight cutoff] A stock solution containing 0.1% by mass of commercially available GPC standard polyethylene glycol (PEG, Agilent Technologies, molecular weights 600, 1000, 4000, 7000, 20000, 50000) dissolved in methanol was used. The liquid was passed through the solution at a pressure of 0.3 MPa, and the permeate was recovered. The concentration of PEG in the permeate was determined using a high-speed liquid chromatography (HPLC) instrument, and the rejection rate was calculated using the following formula. A graph was created based on the rejection rates for PEG at various molecular weights. This graph displays the molecular weight of the PEG used on the horizontal axis and the rejection rate on the vertical axis. The molecular weight at the intersection of the approximate curve and the 90% rejection rate was taken as the molecular weight cutoff. [Mathematical Expression 6]

[0108] [Water pressure resistance] Following the method described in the [Methanol Permeation] section, a module with polyamide hollow fiber membrane openings at both ends was fabricated. The resulting module was then installed in the apparatus shown in Figure 2b. With the module partially immersed in water, air was applied from the inside to pressurize it to 2 MPa, and the presence of any rupture (fracture) in the polyamide hollow fiber membrane was investigated. Five modules were fabricated for each polyamide hollow fiber membrane for testing, and the number of modules that ruptured was determined.

[0109] 2. Experimental Example 1 2-1. Manufacturing hollow fiber membranes [Comparative Example 1] 250g of polyamide 6 flakes (Unitico A1030BRT, relative viscosity 3.53) and 750g of cyclobutane (Tokyo Kasei Corporation) were dissolved by stirring at 180°C for 1.5 hours. The stirring speed was then reduced to defoam for 1 hour to prepare the film-forming stock solution. The film-forming stock solution was fed to a spinneret maintained at 210°C using a metering pump and extruded at a rate of 13.0g / min. The spinneret had an outer diameter of 1.5mm and an inner diameter of 0.6mm. The internal coagulant (coagulant for dense layer formation) was a mixture of polyethylene glycol 400 (PEG400, average molecular weight 400) and glycerol (Gly) (by weight, 90 parts by weight of PEG400 and 10 parts by weight of glycerol) fed at a rate of 5.0g / min. The extruded film-forming solution is introduced through a 10mm air gap into a coagulation bath at 5°C consisting of a 50% by mass propylene glycol (PG) aqueous solution (coagulation solution for porous structure formation), where it is cooled and solidified to form a polyamide hollow fiber membrane. The membrane is then drawn at a speed of 20 m / min. After immersing the wound polyamide hollow fiber membrane in water for 24 hours for solvent extraction (washing), it is dried in a hot air dryer (130°C) without further stretching to obtain the polyamide hollow fiber membrane.

[0110] [Examples 1-4] Up to the solvent extraction step, the operation was carried out under the same conditions as in Comparative Example 1 to form a polyamide hollow fiber membrane. Then, the wound polyamide hollow fiber membrane was immersed in water for 24 hours to extract the solvent. Next, the polyamide hollow fiber membrane was sequentially passed through a feed roller, a hot air dryer (internal temperature 130°C), and a stretching roller, with simultaneous drying and stretching. In this operation, the polyamide hollow fiber membrane was stretched between the feed roller and the stretching roller, and drying and stretching were performed simultaneously during passage through the hot air dryer. The stretching ratios for this operation were 1.5 times (Example 1), 2 times (Example 2), 2.5 times (Example 3), and 3 times (Example 4).

[0111] [Comparative Example 2] The steps up to solvent extraction were performed under the same conditions as in Comparative Example 1 to form a polyamide hollow fiber membrane. The wound polyamide hollow fiber membrane was then immersed in water for 24 hours to extract the solvent. Next, the polyamide hollow fiber membrane was passed sequentially through a feed roller, a stretching roller, a hot air dryer (internal temperature 130°C), and a traction roller, and dried after stretching. In this operation, the polyamide hollow fiber membrane was stretched between the feed roller and the stretching roller, and no further stretching was performed after the stretching roller. The stretching ratio in this operation was 2 times.

[0112] [Example 5] Up to the solvent extraction step, the operation was performed under the same conditions as in Comparative Example 1 to form a polyamide hollow fiber membrane. Then, the wound polyamide hollow fiber membrane was immersed in water for 24 hours to extract the solvent. Next, the polyamide hollow fiber membrane was passed sequentially through a feed roller, a hot air dryer (internal temperature 130°C), a traction roller, and an extension roller, and then extended after drying. In this operation, the polyamide hollow fiber membrane was set to not be extended between the feed roller and the traction roller, but only between the traction roller and the extension roller. The extension ratio of this operation was 2 times.

[0113] 2-2. Results of Physical Property Evaluation of Hollow Fiber Membranes Table 1 shows the manufacturing conditions, orientation analysis results (orientation angle, orientation intensity), methanol permeation, molecular weight cutoff, and pressure test results for each polyamide hollow fiber membrane. Figure 3 shows images of the dense layer (inner lumen side surface) of the polyamide hollow fiber membranes of Examples 1-4 and Comparative Example 1 observed at 1000x using a scanning electron microscope. Figure 4 shows a power spectrum image obtained by binarizing and performing Fourier transform on the scanning electron microscope images (1000x) of the dense layer of the polyamide hollow fiber membranes of Examples 1-4 and Comparative Example 1.

[0114] In the polyamide hollow fiber membrane of Comparative Example 1 (which was not stretched), scanning electron microscopy (1000x) confirmed the formation of a dense layer on the inner lumen side surface, where no pores were observable. The orientation analysis of the dense layer showed an orientation angle of 169° and an orientation intensity of 1.19. Furthermore, the polyamide hollow fiber membrane of Comparative Example 1 had a molecular weight cutoff of 12000 and a low methanol permeability of 3.9 L / (m²·bar·h).

[0115] In the polyamide hollow fiber membranes of Examples 1-4, which underwent simultaneous drying and stretching, a dense layer with no observable pores was maintained on the inner cavity side surface as observed by scanning electron microscopy (1000x). Furthermore, striped recesses were formed in the dense layer along a direction parallel to the length of the polyamide hollow fiber membrane. The orientation analysis results satisfied the orientation angle of 0-5.0° or 175.0-180.0° and the orientation intensity of 1.5-2.0. Additionally, in the polyamide hollow fiber membranes of Examples 1-4, although the molecular weight cutoff was the same as that of the unstretched Comparative Example 1, the methanol permeation was increased to 9.4-16 L / (m²·bar·h). In particular, Examples 1 and 2, which were stretched at a stretch ratio of 1.5-2.0, also exhibited excellent pressure resistance.

[0116] Furthermore, in the polyamide hollow fiber membrane of Example 5, which was stretched after drying, it was also confirmed, as in Examples 1-4, that striped recesses were formed in the dense layer along a direction parallel to the length direction of the polyamide hollow fiber membrane. In addition, the polyamide hollow fiber membrane of Example 5 also had the same molecular weight cutoff as the unstretched Comparative Example 1, and the methanol permeation was increased.

[0117] On the other hand, in the polyamide hollow fiber membrane of Comparative Example 2, which was stretched in a wet state and then dried, it was also confirmed that striped recesses were formed in the dense layer in a direction parallel to the length direction of the polyamide hollow fiber membrane. However, the molecular weight cutoff and methanol permeation were the same as those of Comparative Example 1, and the functionality was the same as that of Comparative Example 1 without stretching.

[0118] [Table 1]

[0119] 3. Experimental Example 2 3-1. Manufacturing hollow fiber membranes [Comparative Example 3] 300g of polyamide 6 flakes (Unitico A1030BRT, relative viscosity 3.53), 515g of dimethyl sulfoxide (Tokyo Chemical Co., Ltd.), and 185g of cyclobutane sulfoxide (Tokyo Chemical Co., Ltd.) were dissolved by stirring at 180°C for 1.5 hours. The stirring speed was then reduced to defoam for 1 hour to prepare the film-forming stock solution. The film-forming stock solution was fed into a spinneret maintained at 210°C using a metering pump and extruded at a rate of 13.0g / min. The spinneret had an outer diameter of 1.5mm and an inner diameter of 0.6mm. Polyethylene glycol 400 (PEG400, average molecular weight 400) was fed at a rate of 5.0g / min as the internal coagulant (coagulant for dense layer formation). The extruded film-forming solution is introduced through a 10mm air gap into a coagulation bath at 5°C consisting of a 50% by mass propylene glycol (PG) aqueous solution (coagulation solution for porous structure formation), where it is cooled and solidified to form a polyamide hollow fiber membrane. The membrane is then drawn at a speed of 20 m / min. After immersing the wound polyamide hollow fiber membrane in water for 24 hours for solvent extraction (washing), it is dried in a hot air dryer (130°C) without further stretching to obtain the polyamide hollow fiber membrane.

[0120] [Example 6] The steps up to solvent extraction were performed under the same conditions as in Comparative Example 3 to form a polyamide hollow fiber membrane. The wound polyamide hollow fiber membrane was then immersed in water for 24 hours to extract the solvent. Next, the polyamide hollow fiber membrane was passed sequentially through a feed roller, a hot air dryer (internal temperature 130°C), a traction roller, and an extension roller, and then extended after drying. In this operation, the polyamide hollow fiber membrane was not extended between the feed roller and the traction roller, but only after the traction roller. The extension ratio in this operation was 2 times.

[0121] [Example 7] Except for the use of polypropylene glycol 400 (PPG400, average molecular weight 400) as the internal coagulation liquid (coagulation liquid for forming dense layer), a polyamide hollow fiber membrane was manufactured under the same conditions as in Example 6.

[0122] 3-2. Results of Physical Property Evaluation of Hollow Fiber Membranes Table 2 shows the manufacturing conditions, orientation analysis results (orientation angle, orientation strength), methanol permeation, molecular weight cutoff, and pressure test results for each polyamide hollow fiber membrane.

[0123] In the polyamide hollow fiber membrane of Comparative Example 3 (which was not stretched), scanning electron microscopy (1000x) confirmed the formation of a dense layer with no observable pores on the inner lumen side surface. The orientation analysis of the dense layer showed an orientation angle of 12.9° and an orientation intensity of 1.16. Furthermore, the polyamide hollow fiber membrane of Comparative Example 3 had a molecular weight cutoff of 920 and a low methanol permeability of 0.6 L / (m²·bar·h).

[0124] In the polyamide hollow fiber membranes of Examples 6 and 7, which were stretched after drying, a dense layer with no observable pores was maintained on the inner lumen side surface through scanning electron microscopy (1000x). Striped recesses were formed in the dense layer along a direction parallel to the length of the polyamide hollow fiber membrane. The orientation analysis results satisfied the orientation angle of 175.0~180.0° and the orientation intensity of 1.5~2.0. Furthermore, the polyamide hollow fiber membranes of Examples 6 and 7 maintained the same molecular weight cutoff as the unstretched Comparative Example 3, and the methanol permeation was increased to 2.1~2.9 L / (m²·bar·h).

[0125] [Table 2]

[0126] 4. Experimental Example 3 4-1. Manufacturing hollow fiber membranes [Comparative Example 4] 150g of polyamide 11 flakes (ARKEMA Rilsan BESV0 A FDA, relative viscosity 2.50) and 850g of γ-butyrolactone (Fujifilm and Kazumitsu Pure Chemicals Co., Ltd.) were dissolved by stirring at 180°C for 1.5 hours, followed by defoaming at a reduced stirring speed for 1 hour to prepare the film-forming stock solution. The film-forming stock solution was fed to a spinneret maintained at 210°C using a metering pump and extruded at a rate of 13.0g / min. The spinneret had an outer diameter of 1.5mm and an inner diameter of 0.6mm. The internal coagulant (coagulant for dense layer formation) was a mixture of polyethylene glycol 400 (PEG400, average molecular weight 400) and glycerol (Gly) (by weight, 90 parts by weight of PEG400 and 10 parts by weight of glycerol) fed at a rate of 5.0g / min. The extruded film-forming solution is introduced through a 10mm air gap into a coagulation bath at 5°C consisting of a 50% by mass propylene glycol (PG) aqueous solution (coagulation solution for porous structure formation), where it is cooled and solidified to form a polyamide hollow fiber membrane. The membrane is then drawn at a speed of 20 m / min. After immersing the wound polyamide hollow fiber membrane in water for 24 hours for solvent extraction (washing), it is dried in a hot air dryer (130°C) without further stretching to obtain the polyamide hollow fiber membrane.

[0127] [Example 8] Up to the solvent extraction step, the operation was carried out under the same conditions as in Comparative Example 4 to form a polyamide hollow fiber membrane. Then, the wound polyamide hollow fiber membrane was immersed in water for 24 hours to extract the solvent. Next, the polyamide hollow fiber membrane was passed sequentially through a feed roller, a hot air dryer (internal temperature 130°C), a traction roller, and an extension roller, and extension was performed after drying. In this operation, the polyamide hollow fiber membrane was not extended between the feed roller and the traction roller, but only after the traction roller. The extension ratio of this operation was 2 times.

[0128] 4-2. Results of Physical Property Evaluation of Hollow Fiber Membranes Table 3 shows the manufacturing conditions, orientation analysis results (orientation angle, orientation strength), methanol permeation, molecular weight cutoff, and pressure test results for each polyamide hollow fiber membrane.

[0129] In the polyamide hollow fiber membrane of Comparative Example 4 (which was not stretched), scanning electron microscopy (1000x) confirmed the formation of a dense layer with no observable pores on the inner lumen side surface. The orientation analysis of the dense layer showed an orientation angle of 165.0° and an orientation intensity of 1.08. Furthermore, the polyamide hollow fiber membrane of Comparative Example 4 had a molecular weight cutoff of 860 and a low methanol permeability of 0.2 L / (m²·bar·h).

[0130] In the polyamide hollow fiber membrane of Example 8, which was stretched after drying, a dense layer with no observable pores was maintained on the inner lumen side surface through scanning electron microscopy (1000x). Striped recesses were formed in the dense layer along a direction parallel to the length of the polyamide hollow fiber membrane, and the orientation analysis results satisfied the orientation angle range of 0~5.0° and the orientation intensity range of 1.5~2.0. Furthermore, the polyamide hollow fiber membrane of Example 8 maintained the same molecular weight cutoff as the unstretched Comparative Example 4, and the methanol permeation was increased to four times that of Comparative Example 4.

[0131] [Table 3]

[0132] 1: Component 1a: Hollow fiber membrane 1b: Pipe fittings filled with hardened epoxy resin 2: Liquid delivery pump 3: Pressure gauge 4: Pressure relief valve 5: Drain tray 6: Methanol that permeates to the outside of the hollow fiber membrane

Claims

1. A polyamide porous membrane having a dense layer formed on at least one side; the polyamide porous membrane having striped recesses extending in one direction on the surface of the aforementioned dense layer; and, in the following orientation analysis, the orientation angle of the aforementioned striped recesses is 0~5.0° or 175.0~180.0°, and the orientation intensity is 1.5~2.0; [Orientation Analysis] An electron microscope image of the surface of the dense layer is arranged such that the X-axis direction is parallel to the length direction of the striped recesses observed in the dense layer, and binarized to obtain a binarized image; an approximate ellipse of the angle distribution of the average amplitude is calculated from the power spectrum image after Fourier transformation of the binarized image; the following orientation angle and orientation intensity are calculated based on the approximate ellipse; Orientation angle: the angle (°) of the minor axis direction of the approximate ellipse relative to the positive direction of the X-axis; Orientation intensity: the ratio of the major axis length to the minor axis length of the approximate ellipse.

2. The polyamide porous membrane of claim 1 has a molecular weight cutoff of 200 to 50,000.

3. The polyamide porous membrane as claimed in claim 1 or 2, wherein the polyamide resin constituting the polyamide porous membrane is an aliphatic polyamide resin having methylene and amide groups in a molar ratio of -CH2-:-NHCO-=4:1 to 10:

1.

4. The polyamide porous membrane, as requested in item 1 or 2, is a hollow fiber membrane.

5. A filtration method comprising using a polyamide porous membrane as described in any one of claims 1 to 4 to filter a liquid containing solutes or particles.

6. A filter membrane assembly comprising housing a polyamide porous membrane as claimed in any one of claims 1 to 4 in an assembly housing.

7. A method for manufacturing a polyamide porous membrane, comprising the following steps 1 to 4: Step 1, preparing a membrane-forming solution, wherein the membrane-forming solution is obtained by dissolving polyamide resin in an organic solvent at a temperature above 100°C, wherein the organic solvent has a boiling point above 150°C and is immiscible with polyamide resin at temperatures below 100°C; Step 2, a step of coagulating polyamide resin into a membrane by extruding the membrane-forming solution prepared in Step 1 into a predetermined shape into a coagulation bath at a temperature below 100°C, wherein in this step, the coagulated liquid is brought into contact with at least one surface of the membrane-forming solution after extrusion into a predetermined shape to form a polyamide porous membrane, wherein the coagulated liquid is miscible with the organic solvent used in the membrane-forming solution and has low affinity for polyamide resin; The third step is to extract and remove the coagulated liquid that has undergone phase separation in the polyamide porous membrane formed in the second step above; and the fourth step is to extend the polyamide porous membrane along a uniaxial direction while drying the polyamide porous membrane after the third step above, or after drying.

8. The manufacturing method of claim 7, wherein in the aforementioned step 4, the extension is performed along a single axis by an extension ratio of 1.2 to 5 times.

9. The manufacturing method of claim 7 or 8, wherein in the aforementioned first step, the organic solvent used to prepare the aforementioned film-forming stock solution is an aprotic polar solvent.

10. The manufacturing method of claim 7 or 8, which is a method for manufacturing a polyamide porous membrane in the shape of a hollow fiber membrane; wherein the aforementioned second step is a step of using a sleeve-shaped nozzle for hollow fiber manufacturing with a sleeve structure to discharge the aforementioned membrane-forming solution from an outer annular nozzle and simultaneously discharge an internal coagulation solution from an inner nozzle, and immersing the solution in a coagulation bath; wherein at least one of the aforementioned internal coagulation solution and the coagulation bath is a coagulation solution that is compatible with the organic solvent used in the aforementioned membrane-forming solution and has low affinity for polyamide resin.

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