Porous structure and method for producing porous structure

Abstract

The purpose of the present invention is to provide a porous structure that has high transparency and that contains a polyamide polymer, which is a fluorine-free compound, as the main component. This porous structure is composed of linked spherical bodies that have a polyamide polymer as the main component.

Description

Porous structure and method for manufacturing the same

[0001] The present invention relates to a porous structure containing a polyamide polymer as a main component and a method for producing the same.

[0002] Porous structures are used as adsorbents and porous separation membranes such as microfiltration membranes and ultrafiltration membranes for purposes such as clarification, concentration, and separation in water treatment, food, and pharmaceutical applications. In recent years, as the range of applications of porous structures has expanded, there has been an increasing demand for porous structures with higher performance (e.g., adsorption, permeability, separation, durability, etc.).

[0003] When a porous structure is used as a porous separation membrane for water treatment applications such as water purification, maintaining high permeability is required from an economical standpoint. However, as continuous filtration progresses, the porous separation membrane becomes clogged with the substances to be removed, reducing permeability and necessitating periodic cleaning. Methods for cleaning clogged porous separation membranes include physical cleaning (air scrubbing), in which air bubbles are blown onto the membrane surface while the porous separation membrane is vibrated, and chemical cleaning, in which the substances to be removed that have clogged the pores of the porous separation membrane are decomposed using chemicals such as acids or alkalis. Therefore, the porous separation membrane is required to have high mechanical and chemical durability.

[0004] In recent years, porous separation membranes using fluorine-based polymers such as polyvinylidene fluoride, which have chemical durability, have been widely used. Patent Document 1 discloses a technology that achieves high permeability and mechanical durability by processing polyvinylidene fluoride into a porous body with connected spherical structures. However, there are concerns about the burden of organic fluorine compounds on the human body and the environment, and safety confirmation and restrictions on their use are being considered. Polyamide-based polymers are one type of polymer that has a small environmental burden and high chemical durability.

[0005] Polyamide polymers have excellent heat resistance, mechanical durability, acid and alkali resistance, solvent resistance, and hydrophilicity, and are widely used in home appliances, office equipment, automotive, and other fields. Furthermore, polyamide polymers are characterized by a low environmental impact during the polymer manufacturing process because they are made from halogen-free raw materials. Furthermore, in recent years, active development of recycling technologies is also underway, and further reductions in environmental impact are expected.

[0006] On the other hand, polyamide-based polymers have the property of being difficult to dissolve in organic solvents, and therefore there are many limitations on the organic solvents that can be used during processing, making it difficult to control the structure of the porous body. Patent Document 2 discloses a method for forming a porous separation membrane made of a polyamide-based polymer by dissolving the polyamide-based polymer in a specific organic solvent and forming a porous membrane with a sponge-like structure by a thermally induced phase separation method.

[0007] International Publication No. 2003 / 106545 Japanese Patent Application Laid-Open No. 2010-104983

[0008] The porous membrane described in Patent Document 1 has high permeability, but is an organic fluorine compound, and restrictions on its use are being considered in some areas. The porous membrane described in Patent Document 2 has a sponge-like structure and is insufficient in permeability.

[0009] Therefore, an object of the present invention is to provide a porous structure having high permeability and containing, as a main component, a polyamide-based polymer, which is a non-fluorinated compound.

[0010] As a result of intensive research to solve the above-mentioned problems, the inventors discovered that the above-mentioned problems can be solved by having a structure in which spheres are linked together in a porous structure mainly composed of a polyamide-based polymer, and thus completed the present invention.

[0011] That is, the present invention encompasses the following configurations [1] to

[15] . [1] A porous structure having a structure in which spheres composed mainly of a polyamide polymer are linked together. [2] The porous structure according to [1] above, wherein the polyamide polymer is an aliphatic polyamide polymer. [3] The porous structure according to [1] or [2] above, wherein the porosity is 40% or more and 90% or less. [4] The porous structure according to any one of [1] to [3] above, wherein, in a cross-sectional image of the porous structure, the average diameter of the spheres is 0.1 μm or more and 10 μm or less. [5] In a cross-sectional image of the porous structure, the value obtained by dividing the total peripheral length of pores by the total area of ​​the pores is 1.2 μm. －１ 5.0 μm or more －１The porous structure according to any one of [1] to [4] above, wherein the aliphatic polyamide-based polymer has a value obtained by dividing the number of methylene groups by the number of amide groups of 10 or more. [7] The porous structure according to any one of [1] to [6] above, which is fibrous. [8] The porous structure according to [7] above, which is a hollow fiber membrane. [9] A method for separating fluids using the porous structure according to any one of [1] to [7] above.

[10] A fluid separation device using the porous structure according to any one of [1] to [7] above.

[11] An adsorbent using the porous structure according to any one of [1] to [7] above.

[12] A method for producing a porous structure, comprising obtaining a porous structure having a structure in which spheres are connected by a solid-liquid thermally induced phase separation method comprising a cooling step of cooling a polymer solution containing a polyamide-based polymer and a good solvent for the polyamide-based polymer.

[13] The method for producing a porous structure according to

[12] above, wherein the cooling step comprises immersing the polymer solution in a cooling solution containing 60% by mass or more and less than 100% by mass of a good solvent for the polyamide-based polymer, wherein the crystallization onset temperature Tc (°C) of the polymer solution and the temperature Tb (°C) of the cooling solution satisfy the relationship -65<Tb-Tc≦60.

[14] The method for producing a porous structure according to

[12] or

[13] above, wherein the cooling step comprises, before the cooling step, maintaining the polymer solution at a maintenance temperature Ta (°C), wherein the maintenance temperature Ta and the crystallization onset temperature Tc (°C) of the polymer solution satisfy the relationship 0<Ta-Tc≦40. ​​

[15] The method for producing a porous structure according to

[14] above, wherein the time for maintaining the polymer solution at the maintenance temperature Ta (°C) is 15 seconds or more and 50 seconds or less.

[16] The method for producing a porous structure according to

[14] above, wherein the HSP distance between the polyamide-based polymer and the good solvent is 7 MPa or less. １／２ The method for producing a porous structure according to any one of the above

[12] to

[15] , which is as follows:

[0012] According to the present invention, a porous structure having a high permeability and containing a polyamide polymer as a main component can be obtained.

[0013] FIG. 1 is a perspective schematic diagram of a structure in which spheres are connected according to one embodiment of the present invention. In FIG. 2, (2-a) is a schematic diagram showing the pressure loss at the pore inlet when the wall end is a square end, and (2-b), (2-c), and (2-d) are schematic diagrams showing the pressure loss at the pore inlet when the wall end is a circle. FIG. 3 is an electron microscope image of the cross section of the porous separation membrane obtained in Example 1. FIG. 4 is an electron microscope image of the cross section of the porous separation membrane obtained in Example 2. FIG. 5 is an electron microscope image of the cross section of the porous separation membrane obtained in Comparative Example 4.

[0014] The following describes in detail the form of a porous separation membrane as an embodiment of the porous structure of the present invention, but the present invention is not limited thereto. The term "porous structure" refers to a structure having a large number of pores, and porous structures in the form used in membrane separation processes, such as flat membranes and hollow fibers, are referred to as porous separation membranes. In this specification, "polymer" is synonymous with "resin."

[0015] <Polyamide-based polymer> The porous structure of one embodiment of the present invention (hereinafter also referred to as "this embodiment") has a structure in which spheres composed mainly of a polyamide-based polymer are linked together. "Polyamide-based polymer" refers to a polymer containing polyamide (hereinafter "PA") having an amide group (NHCO) in the main chain. The PA-based polymer may be copolymerized with other monomers or may contain other functional groups as long as the effects of the present invention are not impaired. Furthermore, the PA-based polymer used to form the porous structure may be one type, or two or more types of PA-based polymers may be mixed together.

[0016] The number average molecular weight of the PA polymer is preferably from 5,000 to 500,000. Within this range, the viscosity of the membrane-forming solution becomes sufficient, and a porous separation membrane having formability and sufficient strength can be produced.

[0017] The term "major component" refers to a component that accounts for 50% by mass or more of the constituent components. For example, in a porous separation membrane, a component that accounts for 50% by mass or more is the major component of the porous separation membrane.

[0018] From the viewpoint of further improving the mechanical durability and chemical durability of the porous separation membrane and optimizing the membrane performance, a polymer blend of the above-mentioned PA-based polymer with various polymers known to be compatible with PA-based polymers may be used as the raw material of the porous separation membrane. When a polymer blend is used, the ratio of the PA-based polymer is preferably 50% by mass or more. Furthermore, the PA-based polymer may contain a filler.

[0019] The proportion of the PA polymer constituting the porous separation membrane according to this embodiment is 50% by mass or more, preferably 60% by mass or more, and more preferably 80% by mass or more. Within this range, the characteristics of the PA polymer, such as high mechanical durability and high chemical durability, are maintained, making it suitable as a porous separation membrane.

[0020] The fact that the PA polymer is the main component can be identified by a general analytical method, for example, by nuclear magnetic resonance measurement or infrared spectroscopy.

[0021] The PA-based polymer constituting the porous separation membrane according to this embodiment is preferably an aliphatic polyamide-based polymer (hereinafter also referred to as "aliphatic PA-based polymer"). "Aliphatic polyamide-based polymer" refers to a polyamide-based polymer containing an aliphatic skeleton in the main chain. Aliphatic PA-based polymers are less susceptible to steric hindrance than aromatic PA-based polymers, which are polyamides containing aromatic rings in the main chain, and therefore are more likely to form spheres.

[0022] The term "aliphatic skeleton" refers to a structure in which carbon atoms are linked in a chain. In particular, from the viewpoint of reducing steric hindrance, the aliphatic skeleton is preferably a saturated aliphatic hydrocarbon, and more preferably a methylene group without a substituent. Examples of aliphatic polyamide polymers having a methylene skeleton include polyamide 6 (hereinafter referred to as "PA6"), polyamide 66 (hereinafter referred to as "PA66"), polyamide 610 (hereinafter referred to as "PA610"), and polyamide 12 (hereinafter referred to as "PA12"), etc.

[0023] Aliphatic PA polymers contain methylene groups (CH ２It is preferable that the value obtained by dividing the number of methylene groups by the number of amide groups (NHCO) is 10 or more. Amide groups may interfere with the movement of the polymer forming the spheres because strong hydrogen bonds act between the amide groups. When the value obtained by dividing the number of methylene groups by the number of amide groups is 10 or more, the strength of the hydrogen bonds becomes appropriate, making it easy to form spheres. Furthermore, from the viewpoint of solubility in organic solvents, it is more preferable that the value obtained by dividing the number of methylene groups by the number of amide groups is 12 or less.

[0024] The number of methylene groups and the number of amide groups can be calculated by identifying the aliphatic PA polymer by pyrolysis GC-MS. Furthermore, analysis can also be performed in combination with differential scanning calorimetry (DSC) and Fourier transform infrared spectroscopy (FT-IR). When the aliphatic PA polymer is a copolymer of two or more types or a blend of two or more types, the number of methylene groups for each aliphatic PA polymer is divided by the number of amide groups, and this value is multiplied by the molar ratio of each aliphatic PA polymer calculated from the above measurement results. The sum of these values ​​is used as the value obtained by dividing the number of methylene groups by the number of amide groups.

[0025] <Connected sphere structure> The porous separation membrane according to this embodiment has a structure in which spheres are connected (hereinafter also referred to as a "connected sphere structure"). The "connected sphere structure" refers to a structure in which spheres are partially connected in a three-dimensional manner. The spheres may be approximately spherical or approximately ellipsoidal, and the connection state is not particularly limited, and two or more adjacent spheres may be connected. A specific method for measuring the average diameter of the spheres will be described later.

[0026] A large number of such connected sphere structures, in which spheres are partially connected three-dimensionally, are gathered together, and voids form between the connected sphere structures, which are the solid parts, to form a porous structure having a structure of connected spheres (connected sphere structure). The formed voids are supported by the partially connected spheres, so they are less likely to shrink and are more likely to form larger voids than a network structure. As a result, a porous separation membrane having a connected sphere structure can maintain higher water permeability than a porous separation membrane having a network structure.

[0027] FIG. 1 shows a schematic diagram of a portion of a sphere-connected structure. In the sphere-connected structure 1 of FIG. 1, multiple spheres 10 are connected. The spheres 10 are approximately spherical or ellipsoidal. As shown in FIG. 1, because the spheres 10 are connected to other spheres 10, the entire spherical or ellipsoidal surface cannot be observed. However, the spherical shape of each sphere can be extrapolated from the shape of the outer shape of each sphere. The spheres may be connected by direct adhesion between the spheres, or by non-spherical portions between the spheres, such as constrictions 11 between the spheres. The voids 12 between the sphere-connected structures are the voids between the sphere-connected structures described above, i.e., the pores of the porous structure. In FIG. 1, the voids 12 between the sphere-connected structures are not completely enclosed, but the pores of the porous structure may be spaces surrounded by the sphere-connected structures.

[0028] The average diameter of the spheres in the cross-sectional image of the porous separation membrane according to this embodiment is preferably 0.1 μm to 10 μm, more preferably 0.5 μm to 5 μm, and even more preferably 0.8 μm to 3 μm. If the average diameter of the spheres is within the above range, the porous separation membrane is likely to have high permeability and fractionation.

[0029] The average diameter of the spheres constituting the linked sphere structure is determined by taking an electron microscope image of the cross section of the porous structure using a scanning electron microscope or the like at a magnification that allows the linked sphere structure to be clearly observed, measuring the diameters of 10 randomly selected spheres per cross section, and then performing the same measurement at five randomly selected cross sections to calculate the arithmetic mean of the obtained diameters to determine the average diameter.

[0030] When calculating the diameter of each sphere, for spheres connected by a constriction 11 (spheres with a visible outline), a straight line is drawn in the direction of the major axis and the minor axis, and the average of the major axis and the minor axis is taken as the diameter of the sphere. For connected spheres, as shown in Figure 1, a line 13 passing through the center of the sphere in the direction of the major axis and a line 14 passing through the center of the sphere in the direction of the minor axis are drawn so as to exclude the connecting portions of the spheres, and the average of the major axis and the minor axis is taken as the diameter of the sphere. In this case, there are two points on the outline of the sphere where the line drawn in the radial direction intersects, and the tangents at each intersection are approximately parallel and opposite to each other. For connected spheres, if the center of a sphere overlaps with an adjacent sphere, i.e., if the outlines are not approximately parallel and opposite to each other (corresponding to X1 in Figure 1), the sphere is excluded from the measurement. In other words, X1 in Figure 1 is a sphere for which the average diameter is not measured.

[0031] Furthermore, if two spheres appear to overlap in the depth direction of the electron microscope image, the sphere at the back (corresponding to X2 in Figure 1) is excluded from the measurement target. That is, X2 in Figure 1 is a sphere for which the average diameter is not measured. Then, the outline of the sphere at the front is used as the boundary between the two spheres at the back and front, and only the diameter of the sphere at the front is measured and calculated.

[0032] If the spheres are cut off at the edge of the electron microscope image used for measurement, the spheres at that edge are excluded from the measurement target.

[0033] A more detailed method for measuring the average diameter of the spheres constituting the linked sphere structure is as described in the Examples below.

[0034] The larger the average diameter of the spheres, the larger the sphere-connected structure, and the larger the gaps 12 between the sphere-connected structure, i.e., the larger the pores of the porous structure.

[0035] The density of the spheres of the porous separation membrane according to this embodiment is 10 ３ pieces / mm ２ 10 above ８ pieces / mm ２ The following is preferred: ３ pieces / mm ２ 10 above ６ pieces / mm ２ More preferably, 10 or less３ pieces / mm ２ 10 above ５ pieces / mm ２ More preferably, the following is true: ３ pieces / mm ２ 10 above ４ pieces / mm ２ The following is particularly preferred: The density of the spheres is 10 ３ pieces / mm ２ If it is more than 10, high strength and pressure resistance can be realized. ８ pieces / mm ２ If the thickness is less than this, high water permeability can be obtained.

[0036] The average diameter and density of the spheres can be controlled, for example, by the polymer concentration, temperature, and pressure in the polymer solution before molding into the porous separation membrane, and the temperature gradient during molding (solidification), etc. The detailed method for measuring the density of the spheres is as described in the Examples below.

[0037] In the cross-sectional image of the porous separation membrane according to this embodiment, the value obtained by dividing the total perimeter of the pores by the total area of ​​the pores is 1.2 μm －１ 5.0 μm or more －１ The following is preferred. The degree of connectivity between the connected sphere structures that form the porous structure can be expressed as the value obtained by dividing the total perimeter of pores, which are voids surrounded by the connected sphere structures, by the total area of ​​the pores in an electron microscope image of a cross section perpendicular to the surface of the porous structure. In other words, if the perimeter of a certain pore is small relative to the area of ​​the pore, this means that there are few irregularities at the interface between the pore and the connected sphere structures, and the pores and the connected sphere structures are present together. In other words, this means that the connectivity of the connected sphere structures is high. If the surface of the connected sphere structures is smooth and the connected sphere structures are present together, the pores are less likely to shrink, and high permeability and high mechanical strength are likely to be achieved. From the above perspective, the value obtained by dividing the total perimeter of pores by the total area of ​​the pores is 1.2 μm －１ 2.0 μm or more －１ More preferably, 1.2 μm or less －１ More than 1.8 μm －１ The following is more preferred: The method for measuring the perimeter and area of ​​the pores is as described in the Examples below.

[0038] Spherical bodies are formed when a portion of the PA polymer chains crystallizes while forming a regular folded structure. During the crystallization process of the polymer chains, the folded structure attempts to form spheres in order to reduce the crystal interface. At this time, if the polymer chains are mobile, they are more likely to approach the folded structure and form spheres. Therefore, it is preferable that the PA polymer is an aliphatic PA polymer, since the polymer chains are more mobile and spheres are more likely to form. Furthermore, it is preferable that the aliphatic PA polymer has a value obtained by dividing the number of methylene groups by the number of amide groups of 10 or more, since the polymer chains are more likely to move and spheres are more likely to form.

[0039] The present inventors have intensively investigated methods for improving the connectivity of the spherical-body interconnection structure, and as a result have found that one way to incorporate a polymer into the interconnections and promote growth is to gradually promote crystal growth during cooling of the polymer solution in the method for producing a porous structure described below. Specifically, it is preferable that the crystallization onset temperature Tc (°C) of the polymer solution and the temperature Tb (°C) of the cooled solution satisfy the relationship -65<Tb-Tc≦60. This allows the PA-based polymer to crystallize and form spheres preferentially over solidification, making it easier to incorporate the PA-based polymer into the interconnections of the spheres.

[0040] It is also preferable to include a step of maintaining the polymer solution at a maintenance temperature Ta (°C) before immersing the polymer solution in a cooling solution, which is the cooling step, and the maintenance temperature Ta and the crystallization onset temperature Tc of the polymer solution satisfy the relationship 0 < Ta - Tc ≦ 40. Maintaining the polymer solution at a temperature within the above range makes it easy to induce the formation of spheres before cooling and solidifying, and the time required to form the spheres is long, making it easy to form connected spheres.

[0041] <Pressure loss reduction effect due to linked sphere structure> The porous separation membrane according to this embodiment is characterized by having a structure in which linked sphere structures, the main component of which is a PA polymer, are linked. Considering the case where liquid flows from the surface of the separation membrane to the inside during liquid filtration through a porous separation membrane, the flow path narrows suddenly at the pore portion on the surface of the separation membrane, which is the inlet portion, causing a pressure loss at the inlet portion and hindering the flow. In other words, the spherical shape of each sphere constituting the linked sphere structure and the shape of the pores between the linked sphere structures form the shape of the inlet portion of the pore portion. The pressure loss at this inlet portion is expressed by the following formula (1), and is known to depend on the loss coefficient (ζ) of the inlet portion. ΔP = ζ × (V ２ ) ２ / 2g Formula (1) where ΔP: pressure loss at the inlet, ζ: loss coefficient at the inlet, V ２ : flow velocity in the pore, g: gravitational acceleration.

[0042] As shown in Figure 2, the loss coefficient (ζ) is a value determined by the shape of the flow path. In Figure 2, (2-a) to (2-d) show the inlet holes 20 of the pores and the porous structure 21. (2-a) shows the primary flow velocity V １ and the flow velocity in the pores V ２ Similarly, (2-b) to (2-d) show the primary flow velocity V １ and the flow velocity in the pores V ２ However, as shown in (2-a), when the wall surface of the inlet section is a corner end (90°), ζ = 0.5, but when the wall surface end 22 has a small radius R as in (2-b), ζ = 0.25, when the wall surface end 23 has a large radius R as in (2-c), ζ = 0.1 to 0.2, and when the wall surface end has a very large radius R as in (2-d), ζ = 0.01 to 0.05. In this way, the loss coefficient decreases as the wall surface end is circular and its radius R increases (2-b to 2-d).

[0043] In other words, the porous separation membrane according to this embodiment has a spherical structure in which spheres are connected together, and the wall edges are spherical, resulting in a structure in which pressure loss at the inlet is small and there is little obstruction to the flow of liquid. A porous separation membrane having such spheres and a spherical structure allows liquid to easily flow into the porous separation membrane, and can exhibit high permeability.

[0044] Furthermore, the greater the curvature of each sphere, i.e., the larger the average diameter of the spheres, the larger the pores, which are the gaps between the connected sphere structures, and the higher the water permeability of the porous separation membrane. On the other hand, the fractionation performance of the porous separation membrane decreases. Furthermore, if the average diameter of the spheres is small, the pores, which are the gaps between the connected sphere structures, become smaller, and the water permeability of the porous separation membrane decreases. Therefore, from the viewpoint of obtaining high water permeability and appropriate fractionation performance, the pore diameter of the porous structure is preferably 0.1 μm or more and 10 μm or less, more preferably 0.3 μm or more and 7 μm or less, and even more preferably 0.5 μm or more and 5 μm or less. The pore diameter of the porous structure can be calculated by measuring the diameters of 50 randomly selected pores in an image of the surface of the porous structure photographed using a scanning electron microscope at, for example, 1,000x or 10,000x magnification, and calculating the arithmetic average. If the number of pores in one image is less than 50, calculation is performed using multiple images so that the number of pores becomes 50.

[0045] <Thickness of membrane> The porous separation membrane according to this embodiment preferably has a membrane thickness of 40 μm or more and 300 μm or less, more preferably 40 μm or more and 250 μm or less, from the viewpoint of obtaining high water permeability and suppressing deformation such as breakage, folding, and crushing of the porous separation membrane during use. The method for measuring the membrane thickness of the porous membrane is as described in the examples below. When the porous separation membrane has a homogeneous structure throughout the membrane thickness, the pure water permeability is inversely proportional to the membrane thickness.

[0046] <Porosity> From the viewpoint of obtaining high water permeability and suppressing deformation of the porous separation membrane during use, such as breakage, folding, or crushing, the porous separation membrane according to this embodiment preferably has a porosity of 40% or more and 90% or less, more preferably 50% or more and 80% or less, and even more preferably 50% or more and 70% or less.

[0047] The pore diameter and porosity of the porous structure, like the average diameter and density described above, can be controlled, for example, by the polymer concentration, temperature, and pressure in the polymer solution before molding into the porous separation membrane, the temperature gradient during molding (solidification), and the magnification and temperature during stretching, which will be described later.

[0048] The porosity can be calculated by measuring the volume of a test piece of a porous separation membrane using Archimedes' principle and using the following formula (2). In this case, liquid A, which wets the porous separation membrane, and liquid B, which is used to measure buoyancy using Archimedes' principle, must be incompatible with each other, and liquid B must not dissolve the polymer that forms the porous separation membrane. Porosity (%) = {1 - (volume of test piece in bone-dry state / volume of test piece in wet state)} × 100 ... formula (2). A more detailed method for measuring porosity is as described in the examples below.

[0049] <Fractional particle size> The fractional particle size of the porous separation membrane according to this embodiment is preferably 0.05 μm or more and 2.0 μm or less, preferably 0.10 μm or more and 1.5 μm or less, and more preferably 0.15 μm or more and 1.0 μm or less. If the fractional particle size is 0.05 μm or more, the permeation resistance of the membrane pores is reduced, and a porous separation membrane with high permeability suitable for practical use is obtained. On the other hand, if the fractional particle size is 2.0 μm or less, the possibility of components such as turbidity leaking into the treated water is reduced.

[0050] The fractional particle size can be controlled, similarly to the average diameter and density described above, by the polymer concentration, temperature, and pressure in the polymer solution before molding into the porous separation membrane, the temperature gradient during molding (solidification), and the magnification and temperature during stretching, which will be described later.

[0051] <Pure Water Permeability, Breaking Strength, and Breaking Elongation> The porous separation membrane according to this embodiment has a pure water permeability of 0.5 m / s at 25° C. under a pressure of 100 kPa. ３ / m ２ / hr or more 5.0m ３ / m ２ / hr or less, and ３ / m ２ / hr or more 4.0m ３ / m ２ / hr or less is more preferable, and 1.0 m ３ / m ２ / hr or more 4.0m ３ / m ２ The pure water permeability can be measured by the method described later in the examples.

[0052] The porous separation membrane according to this embodiment preferably has substantially no macrovoids. "Macrovoids" refers to pores with a major axis of 50 μm or more observed in the cross section of the porous separation membrane. "Substantially no macrovoids" means that the number of macrovoids present in the cross section of the porous separation membrane is 10 / mm. ２ This means that the number of macrovoids present in the cross section of the porous separation membrane is 5 / mm or less. ２ The following is preferred, and most preferably none at all:

[0053] The breaking strength of the porous separation membrane according to this embodiment is 2.0 N / mm ２ 30.0N / mm or more ２ Preferably, 4.0 N / mm or less ２ 25.0N / mm or more ２ More preferably, 6.0 N / mm or less ２ 20.0N / mm or more ２ The following is even more preferred:

[0054] The breaking elongation of the porous separation membrane according to this embodiment is preferably 5% or more and 100% or less, more preferably 10% or more and 90% or less, and even more preferably 15% or more and 80% or less.

[0055] If the breaking strength and breaking elongation are within the above ranges, sufficient water permeability can be exhibited under normal conditions of use, and breakage of the porous separation membrane can be suppressed. The breaking strength and breaking elongation can be controlled by controlling the polymer concentration, temperature, pressure, and temperature gradient during molding (solidification) of the polymer solution before molding into the porous separation membrane, as well as the average diameter and density of the spheres, and can also be controlled by the stretching ratio and temperature described below.

[0056] <Method for producing porous separation membrane> A method for obtaining a porous separation membrane having a structure in which spheres containing a PA-based polymer as a main component according to this embodiment are linked together will be described, but the present invention is not limited to these examples of production methods.

[0057] The porous structure having a structure in which spheres containing a PA-based polymer as a main component are linked (linked sphere structure), as discovered by the present inventors, can be obtained by a solid-liquid thermally induced phase separation method including a cooling step of cooling a polymer solution containing a PA-based polymer and a good solvent for the PA-based polymer.

[0058] Methods for producing a porous separation membrane from a PA-based polymer include, for example, thermally induced phase separation, non-solvent induced phase separation, melt extraction, and stretching method. Among these, in this embodiment, it is preferable to use a solid-liquid thermally induced phase separation method.

[0059] The "thermally induced phase separation method" is a phase separation method in which a polymer solution dissolved at a high temperature is solidified by cooling. When a porous separation membrane is produced using the thermally induced phase separation method, the solvent for the PA polymer is preferably a good solvent that can dissolve the PA polymer at 60°C or higher, and examples thereof include polar solvents such as polyhydric alcohols such as ethylene glycol (hereinafter referred to as "EG") and glycerin, and N-methylpyrrolidone (hereinafter referred to as "NMP").

[0060] Furthermore, there are two main types of phase separation mechanisms in thermally induced phase separation. One is a liquid-liquid phase separation method in which a polymer solution uniformly dissolved at high temperatures separates into a polymer-rich phase and a polymer-dilute phase as the temperature decreases due to a decrease in the dissolving ability of the solution. The other is a solid-liquid phase separation method in which a polymer solution uniformly dissolved at high temperatures separates into a polymer solid phase and a polymer-dilute solution phase as the temperature decreases due to polymer crystallization. The former method primarily forms a three-dimensional network structure, while the latter method forms a sphere or a sphere-connected structure. Patent Document 2 uses a liquid-liquid phase separation method to produce a porous membrane of a PA-based polymer, forming a porous membrane with a sponge-like three-dimensional network structure. On the other hand, the likelihood of solid-liquid phase separation varies depending on the combination of polymer and good solvent, and it is preferable to select an appropriate solvent for the polymer. For example, if the main component of the polymer is PA6, EG is preferably the main component of the good solvent, and if the main component of the polymer is PA12, NMP is preferably the main component of the good solvent.

[0061] In the method for producing a porous separation membrane according to this embodiment, spheres and a structure of connected spheres are formed by the latter solid-liquid phase separation method. Compared to the three-dimensional network structure formed by the liquid-liquid phase separation method, the structure of connected spheres formed by the solid-liquid phase separation method has a bulky solid portion and the connected portions tend to be large. This is therefore preferable because the voids between the solid portions are less likely to shrink and high permeability can be easily maintained. For this reason, it is preferable to select a polymer concentration and solvent that induces solid-liquid phase separation.

[0062] It has been known that a structure in which spheres are linked (a structure in which spheres are linked) can be formed by utilizing a solid-liquid thermally induced phase separation method in a polyvinylidene fluoride (hereinafter, "PVDF")-based polymer, as in Patent Document 1. For example, Patent Document 1 discloses that spheres can be formed by discharging a PVDF-based polymer at 95 to 155°C and cooling it to 10 to 30°C. On the other hand, the PA-based polymer, which is the main component of the porous structure of the present embodiment, has a higher crystallization onset temperature and a faster crystallization rate than the PVDF-based polymer. Therefore, it was not possible to form spheres by simply applying the conditions of the discharging temperature and cooling temperature used in the solid-liquid thermally induced phase separation method for the PVDF-based polymer. As will be described later, the present inventors have succeeded in creating a porous structure having a structure in which spheres are linked, primarily composed of a PA-based polymer, by controlling the film formation temperature while focusing on the crystallization onset temperature Tc of the PA-based polymer and by selecting the solvent used in the polymer solution.

[0063] In the method for producing a porous separation membrane according to this embodiment, the discharge temperature of the PA polymer solution (hereinafter also simply referred to as "polymer solution") is preferably 100°C or higher and 200°C or lower, more preferably 110°C or higher and 190°C or lower. By setting the temperature of the polymer solution to 100°C or higher, precipitation of the polymer can be suppressed, making it easier to control the connectivity of the spherical body linked structure. On the other hand, the temperature of the polymer solution may be below the boiling point of the good solvent, but setting it to 200°C or lower is preferable because it makes it possible to make the viscosity of the membrane-forming solution easy to form and also suppresses evaporation of the solvent in the polymer solution.

[0064] The cooling step in the method for producing a porous separation membrane according to this embodiment preferably includes a step of immersing the polymer solution in a cooling solution containing 60% by mass or more but less than 100% by mass of a good solvent for the PA polymer. When the cooling solution contains 60% by mass or more but less than 100% by mass of the good solvent, the formation of a three-dimensional network structure or a skin layer due to non-solvent-induced phase separation when the polymer solution comes into contact with a poor solvent or a non-solvent is suppressed, and spheres are easily formed.

[0065] When a PA-based polymer solution is cooled, phase separation due to crystallization and solidification occur in competition. PA-based polymers are known to be crystalline polymers, and polymer solutions containing PA-based polymers as the main component have a crystallization onset temperature Tc (°C). Here, the "crystallization onset temperature Tc" is defined as follows: Using a differential scanning calorimetry (DSC) measurement device, a polymer solution containing a PA-based polymer and a solvent is sealed in a sealed DSC container, heated to the dissolution temperature at a heating rate of 10°C / min, and held for 30 minutes to dissolve uniformly. Thereafter, the temperature at which the crystallization peak rises, observed during the cooling process at a cooling rate of 10°C / min, is taken as the crystallization onset temperature Tc.

[0066] In the cooling step in the method for producing a porous separation membrane according to this embodiment, it is preferable that the crystallization onset temperature Tc (°C) of the polymer solution and the temperature Tb (°C) of the cooling solution satisfy -65<Tb-Tc≦60. This allows the PA polymer to preferentially form spheres by crystallization over solidification, making it easier to form spheres. It is more preferable that the crystallization onset temperature Tc (°C) of the polymer solution and the temperature Tb (°C) of the cooling solution satisfy -65<Tb-Tc≦50, and even more preferable that they satisfy -65<Tb-Tc≦45.

[0067] The method for producing a porous separation membrane according to this embodiment preferably includes a step of maintaining the polymer solution at a maintenance temperature Ta (°C) before the cooling step, and the maintenance temperature Ta and the crystallization onset temperature Tc (°C) of the polymer solution satisfy the relationship 0<Ta-Tc≦40. ​​Maintaining the polymer solution at a maintenance temperature Ta within the above range is preferred because it is easy to induce the formation of spheres before cooling and solidifying, and it is easy to form the spheres.

[0068] Furthermore, the time for which the polymer solution is maintained at a maintenance temperature Ta within the above temperature range is preferably 5 seconds to 100 seconds, and more preferably 15 seconds to 50 seconds, from the viewpoint of easily inducing the formation of spheres before cooling and solidifying, and facilitating the formation of spheres. Among these, a maintenance time at the maintenance temperature Ta is particularly preferably 15 seconds to 50 seconds, since this can suppress the progress of liquid-liquid thermally induced phase separation and promote the progress of solid-liquid thermally induced phase separation, and thus easily induces the formation of spheres before cooling and solidifying at the cooling solution temperature Tb (°C). When the maintenance time is 15 seconds to 50 seconds, the cooling solution temperature Tb (°C) does not necessarily need to satisfy the above range (-65<Tb-Tc≦60). By suppressing liquid-liquid thermally induced phase separation, which occurs in competition with the desired solid-liquid thermally induced phase separation, while the polymer solution is maintained at the maintenance temperature Ta (°C), a highly connected spherical structure is more likely to be formed. To suppress liquid-liquid thermally induced phase separation, it is preferable that the HSP distance between the PA polymer and the good solvent, which will be described later, is small. This makes it easier to control the water permeability and mechanical strength of the porous separation membrane. The preferred maintenance temperature Ta depends on the crystallization onset temperature Tc of the polymer solution, and a specific example of the maintenance temperature Ta is preferably 100°C or higher and 200°C or lower, and more preferably 110°C or higher and 190°C or lower.

[0069] The maintenance time of the polymer solution is the value obtained by dividing the length (m) of the pipe or the like through which the polymer solution passes at the maintenance temperature Ta±1 (°C) by the linear velocity (m / s) of the polymer solution inside the pipe or the like.

[0070] When maintaining the polymer solution at a temperature within the above range, applying pressure to the polymer solution is preferable, as this facilitates the formation of spheres. The pressure applied to the polymer solution is preferably 0.3 MPa to 30 MPa, more preferably 0.5 MPa to 25 MPa. The time for maintaining the polymer solution at the above pressure is preferably 5 seconds to 100 seconds, more preferably 15 seconds to 50 seconds. Specifically, a retention section for retaining the polymer solution is provided at a location in the liquid feed line that sends the polymer solution to the nozzle or slit die, and a pressurizing means for pressurizing the retained polymer solution and a temperature adjustment means (e.g., heating means) for adjusting the temperature of the retained polymer solution are provided, thereby maintaining the polymer solution at a constant pressure and temperature. The pressurizing means is not particularly limited, but by installing two or more pumps in the liquid feed line, pressurization can be performed at any location between them. Examples of pumps include piston pumps, plunger pumps, diaphragm pumps, wing pumps, gear pumps, rotary pumps, and screw pumps. Two or more types of pumps may be used.

[0071] The above steps form many cores of spherical bodies, facilitating the formation of a highly connected spherical body structure.

[0072] In the method for producing a porous separation membrane according to this embodiment, it is preferable to use a cooling solution in which the polymer solution is immersed, with a sufficient volume of at least 100 times the amount of the polymer solution added. The specific temperature Tb of the cooling solution is preferably 55°C or higher and 130°C or lower, and more preferably 70°C or higher and 100°C or lower.

[0073] The porous separation membrane according to this embodiment may be in the form of a fiber, a film, a sponge, or the like, and is preferably in the form of a fiber from the viewpoint of ensuring a specific surface area and liquid permeability.

[0074] The shape of the porous separation membrane according to this embodiment is not particularly limited, but a flat membrane or a hollow fiber membrane is preferred. Both of these membranes can be formed by methods conventionally known to those skilled in the art. For example, a flat membrane can be produced by casting a polymer solution on a substrate and immersing the substrate in a coagulation bath containing a cooling solution. A hollow fiber membrane can be produced by extruding a polymer solution from the outer circumferential slit of a double-tubular nozzle so as to form a hollow cylinder, and extruding a fluid selected from a non-solvent, a poor solvent, a good solvent, a mixed solvent thereof, or a liquid incompatible with the polymer solution, or a gas such as nitrogen or air, together with the polymer solution from the inner nozzle bore, and then immersing the resulting membrane in a coagulation bath containing a cooling solution.

[0075] The concentration of the PA-based polymer in the polymer solution is preferably 5% by mass or more and 60% by mass or less, more preferably 10% by mass or more and 50% by mass or less, from the viewpoint of ensuring sufficient mechanical strength while optimizing the water permeability and fractionation performance of the porous separation membrane.

[0076] The porous separation membrane according to this embodiment may be stretched to enlarge the pores and improve the water permeability.

[0077] In the method for producing a porous separation membrane according to this embodiment, the HSP distance between the PA polymer and the good solvent is 7 MPa. １／２ This improves the affinity between the PA polymer and the good solvent, and the dissolution temperature and the maintenance temperature Ta can be controlled in a wider temperature range, which makes it easier to control the formation of spherical bodies and makes it easier to optimize membrane performance such as water permeability and mechanical strength. The HSP distance between the PA polymer and the good solvent is 6 MPa or less. １／２ More preferably, 5 MPa or less １／２ It is even more preferable that the following be satisfied:

[0078] "HSP" refers to the Hansen Solubility Parameter, which is based on the idea that two substances with similar intermolecular interactions are more likely to dissolve in each other. HSP is composed of energy (δd) derived from intermolecular dispersion forces, energy (δp) derived from intermolecular dipole interactions, and energy (δh) derived from intermolecular hydrogen bonds. These three parameters can be regarded as coordinates in a three-dimensional space (Hansen space). The HSP values ​​(δd, δp, δh) of each substance can be calculated, for example, using computer software Hansen Solubility Parameters in Practice (HSPiP). Here, the HSP value (δd) of the PA polymer used in the film-forming solution is calculated as follows: １ , δp １ , δh １ ), and the HSP value of the good solvent is (δd ２ , δp ２ , δh ２ ), the distance of the HSP value between the PA polymer and the good solvent (hereinafter referred to as "HSP distance") can be calculated by the following formula (3): HSP distance (MPa １／２ ) = {4 × (δd １ -δd ２ ) ２ +(δp １ -δp ２ ) ２ + (δh １ -δh ２ ) ２} １／２ ...Formula (3).

[0079] A separation device using the porous structure according to this embodiment obtained as described above can separate various fluids (e.g., separation of liquids, separation of gases, separation of solids from liquids, separation of gases from liquids, etc.). The high permeability of the porous structure having a structure in which spheres are connected according to this embodiment is particularly suitable for use in liquid separation. Examples of liquid separation devices include, but are not limited to, a raw liquid tank, a booster pump, a module filled with the porous structure, a treatment liquid tank, and a cleaning pump.

[0080] The term "module" refers to a porous structure housed in a container so that the treatment liquid can be collected by separation. Typical examples include, but are not limited to, a structure in which a plurality of hollow fiber-shaped porous structures are packed into a cylindrical housing and fixed at one or both ends with polyurethane, epoxy polymer, or the like so that the treatment liquid can be collected, or a structure in which a flat porous structure is attached to a support plate and the ends are sealed so that the treatment liquid can be collected.

[0081] Examples of liquid separation methods include, but are not limited to, a method in which raw liquid such as factory wastewater, fermentation liquid, or culture liquid is treated using a separation device equipped with a porous structure at an operating pressure of 10 kPa or more and 1 MPa or less to remove organic matter and the like contained in the raw liquid.

[0082] The porous structure of the present embodiment can also be suitably used as an adsorbent having excellent durability, such as a gas adsorbent, an adsorbent for water purification, or an adsorbent for wastewater purification.

[0083] The present invention will be specifically explained below by way of examples, but the present invention is not limited to these examples in any way.

[0084] (1) Pure water permeability When the porous separation membrane is a flat membrane, the flat membrane is cut into a circle with a diameter of 50 mm, and set in a cylindrical filter holder. Distilled water is fed from the surface side having the spherical body connected structure under the conditions of a temperature of 25°C and a filtration differential pressure of 10 kPa. The amount of permeated water (m ３ ) and the obtained value is expressed as a unit time (h) and a unit effective membrane area (m ２ When the porous separation membrane was a hollow fiber membrane, a module having a length of 200 mm and consisting of three hollow fiber membranes was prepared and the measurement was carried out.

[0085] (2) Porosity The porosity was calculated by measuring the volume of a porous separation membrane test piece using Archimedes' principle. A specific gravity measurement kit (AD-165, manufactured by A&D Co., Ltd.) was used for the measurement, following the steps (a) to (e) below. A 2 cm x 2 cm flat membrane or a 2 cm long hollow fiber membrane was used as the test piece. (a) A wet test piece was placed on the weighing dish of the specific gravity measurement kit in air, and the zero point was adjusted. A wet test piece was prepared by immersing it in ethanol for 30 minutes or more, followed by immersion in water for 1 hour or more. (b) A liquid with a known density was used, and the wet test piece was placed on the weighing dish of the specific gravity measurement kit in the liquid, and the buoyancy (A) was measured. Here, (A) is an absolute value. (c) The volume (B) of the wet test piece was calculated by dividing (A) by the liquid density. (d) The wet test piece is dried to measure its bone-dry mass, and the bone-dry volume (C) is calculated from the density of the polymer used in the porous separation membrane. (e) The porosity is calculated using {1-((C) / (B))} x 100. Here, water was selected as the liquid for wetting the test piece, and decane was selected as the liquid for measuring buoyancy.

[0086] (3) Average diameter of spheres The porous separation membrane was cut in a direction perpendicular to the surface of the porous separation membrane by freeze-fracturing, and the cross section perpendicular to the exposed surface of the porous separation membrane was photographed at 3000x magnification using a scanning electron microscope (SU1510, manufactured by Hitachi High-Technologies Corporation). From the photographed image, 10 spheres forming a sphere-connected structure present in the region from the surface to 20 μm in the thickness direction were randomly selected, and the major and minor diameters of each were measured. The above photographs were taken at five locations, and the major and minor diameters of 10 randomly selected spherical structures in each photographed image were determined, resulting in a total of 50 major diameters and 50 minor diameters. The average value of the diameters obtained for the total of 100 was calculated and used as the average diameter of the spheres. The spheres to be measured were as described above. Note that the significant figures were two digits.

[0087] (4) Density of spheres As in the above "(3) Average diameter of spheres", a cross section perpendicular to the surface of the porous separation membrane was photographed at 3000x magnification using a scanning electron microscope (SU1510, manufactured by Hitachi High-Technologies Corporation) at 10 random locations, including a region from the surface to 20 μm in the thickness direction. In the obtained cross-sectional image, the spherical shape of each sphere was extrapolated from the shape appearing in the outer shape of each sphere, and the number of spheres per unit area of ​​the image was counted. The average density of the 10 images obtained was calculated and used as the density of the spheres. Note that the significant digits were two.

[0088] (5) Perimeter and area of ​​pores As in the above "(3) Average diameter of spheres", a cross section perpendicular to the surface of the porous separation membrane was taken at 3000x magnification using a scanning electron microscope (Hitachi High-Technologies Corporation, SU1510), and images including a region from the surface to 20 μm in the thickness direction were taken at 10 random locations. The obtained cross-sectional image was separated into a polymer structure and void pores by binarization processing under MaxEntropy conditions using image analysis software ImageJ. The total perimeter and area of ​​the obtained pores were calculated by image analysis. At this time, if the pores were interrupted at the edge of the cross-sectional image, they were excluded from the analysis. The perimeter and area of ​​the pores were calculated using the above 10 images, and the average value was used.

[0089] (6) HSP Distance The HSP distance was calculated using the HSP values ​​described in "Hansen Solubility Parameters: A User's Handbook 2nd Ed."

[0090] (7) Breaking Strength and Breaking Elongation Using a tensile tester (TENSILON (registered trademark) / RTM-100, manufactured by Toyo Baldwin Co., Ltd.), a sample having a measurement length of 50 mm was measured at a pulling rate of 50 mm / min in an atmosphere of 25° C. The measurement was carried out five times for different samples, and the average values ​​obtained were calculated to be the breaking strength and breaking elongation.

[0091] (8) Thickness of Membrane As in the above "(3) Average Diameter of Spherical Bodies," the porous separation membrane was cut in a direction perpendicular to its surface by freeze-fracturing, and the exposed cross section perpendicular to the surface of the porous separation membrane was observed at 1000x magnification using an optical microscope to determine the thickness of the membrane. Measurements were taken at 10 different cross sections, and the average value was used as the thickness of the membrane.

[0092] [Example 1] 35% by mass of PA12 polymer (Rilsamid (registered trademark) AESNO MED, manufactured by Arkema) and 65% by mass of NMP (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) were dissolved at 150°C to obtain a homogeneous polymer solution. The obtained polymer solution was allowed to stand at 150°C, degassed, and then cooled to 140°C in a pipe and maintained for 15 seconds. Density: 0.42 g / cm ３ The prepared polymer solution was discharged onto the surface of a polyester fiber nonwoven fabric support and quickly and uniformly coated at 10 m / min using a bar coater (film thickness 7 mil). The support coated with the polymer solution was quickly immersed in a cooling solution, NMP, at 70°C for 60 seconds to solidify. The obtained porous separation membrane was a flat membrane with a membrane thickness of 160 μm and had a sphere-connected structure. The evaluation results and performance of the obtained porous membrane, such as its structure, are shown in Table 1. An electron microscope image of the cross section of the porous separation membrane is also shown in Figure 3.

[0093] Example 2 20% by mass of PA6 polymer A (CM1041-LO, manufactured by Toray Industries, Inc.) and 80% by mass of EG (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) were dissolved at 170°C to obtain a homogeneous polymer solution. The obtained polymer solution was allowed to stand at 170°C, degassed, and then cooled to 151°C in a pipe and maintained for 10 seconds. The obtained polymer solution was applied to a support in the same manner as in Example 1. The support to which the polymer solution had been applied was immediately immersed in a cooling solution, a 90% by mass aqueous EG solution at 71°C, for 60 seconds to solidify. The obtained porous separation membrane was a flat membrane with a membrane thickness of 50 μm and had a sphere-linked structure. The evaluation results and performance of the obtained porous membrane, such as its structure, are shown in Table 1. An electron microscope image of a cross section of the porous separation membrane is also shown in FIG. 4.

[0094] Example 3 30% by mass of PA6 polymer A and 70% by mass of EG were dissolved at 170°C to obtain a homogeneous polymer solution. The obtained polymer solution was left to stand at 170°C, degassed, and then cooled to 156°C in a pipe and maintained for 10 seconds. The obtained polymer solution was applied to a support in the same manner as in Example 1. The support to which the polymer solution had been applied was immediately immersed in a cooling solution, a 90% by mass aqueous EG solution at 76°C, for 60 seconds to solidify. The obtained porous separation membrane was a flat membrane with a thickness of 50 μm and had a sphere-linked structure. The evaluation results and performance of the obtained porous membrane, such as its structure, are shown in Table 1.

[0095] Reference Example 1 38% by mass of PVDF polymer (Solev6013, manufactured by Solvay) and 62% by mass of γ-butyrolactone (manufactured by Mitsubishi Chemical Corporation, hereinafter referred to as "GBL") were dissolved at 170°C to obtain a homogeneous polymer solution. The obtained polymer solution was allowed to stand at 150°C, degassed, and then cooled to 150°C in a pipe and maintained for 15 seconds. The polymer solution was applied to a support in the same manner as in Example 1, except that the support to which the polymer solution was applied was immediately immersed in a cooling solution of 80% by mass aqueous GBL solution at 30°C for 60 seconds to solidify. The obtained porous separation membrane had a structure in which spheres were connected. The evaluation results of the structure and performance of the obtained porous separation membrane are shown in Table 1.

[0096] [Comparative Example 1] 35% by mass of PA12 polymer and 65% by mass of GBL were dissolved at 190°C to obtain a homogeneous polymer solution. The obtained polymer solution was allowed to stand at 190°C, degassed, and then coated onto a support in the same manner as in Example 1, except that the temperature was not lowered in the pipe and no maintenance time was provided. The support coated with the polymer solution was immediately immersed in a cooling solution of GBL at 68°C for 60 seconds to solidify. The obtained porous separation membrane had a cellular structure. The evaluation results and performance of the obtained porous separation membrane, such as its structure, are shown in Table 1.

[0097] Comparative Example 2 20% by mass of PA12 polymer and 80% by mass of GBL were dissolved at 190°C to obtain a homogeneous polymer solution. The obtained polymer solution was applied to a support in the same manner as in Comparative Example 1. The support to which the polymer solution was applied was immediately immersed in water at 0°C, which was a cooling solution, for 60 seconds to solidify it. The obtained porous separation membrane had a cellular structure. The evaluation results of the structure and performance of the obtained porous separation membrane are shown in Table 1.

[0098] [Comparative Example 3] A polymer solution was prepared in the same manner as in Comparative Example 1, except that sulfolane (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was used as the good solvent and sulfolane at 20°C was used as the cooling solution, and the polymer solution was applied to a support membrane. However, the polymer solution solidified quickly, making it difficult to produce a uniform flat membrane, and evaluation of pure water permeability was not possible. The resulting porous separation membrane had a cellular structure. The evaluation results of the structure of the resulting porous separation membrane are shown in Table 2.

[0099] [Comparative Example 4] 20% by mass of PA6 polymer B (CM1061-X01, manufactured by Toray Industries, Inc.) and 80% by mass of EG were dissolved at 170°C to obtain a uniform polymer solution. The obtained polymer solution was left to stand at 170°C and degassed, but was applied to a support in the same manner as in Comparative Example 1. The support to which the polymer solution was applied was immediately immersed in a 90% by mass aqueous EG solution at 40°C, which was a cooling solution, for 60 seconds to solidify. The obtained porous separation membrane had a three-dimensional network structure. The evaluation results and performance of the obtained porous separation membrane, such as the structure, are shown in Table 2. An electron microscope image of a cross section of the porous separation membrane is also shown in Figure 5.

[0100] [Comparative Example 5] 35% by mass of PA6 polymer A and 65% by mass of EG were dissolved at 170 ° C to obtain a uniform polymer solution. The obtained polymer solution was applied to a support in the same manner as in Comparative Example 1, except that it was left to stand at 170 ° C and degassed. The support to which the polymer solution was applied was immediately immersed in a 90% by mass aqueous EG solution at 21 ° C, which was a cooling solution, for 60 seconds to solidify. The obtained porous separation membrane had a three-dimensional network structure. The evaluation results and performance of the obtained porous separation membrane, such as the structure, are shown in Table 2.

[0101] [Comparative Example 6] 30% by mass of PA6 polymer A and 70% by mass of EG were dissolved at 170 ° C to obtain a homogeneous polymer solution. The obtained polymer solution was left to stand at 170 ° C, degassed, and then cooled to 153 ° C in a pipe and maintained for 10 seconds. The substrate was coated in the same manner as in Example 1, except that the polymer solution was immediately immersed in a 90% by mass EG aqueous solution at 66 ° C, which was a cooling solution, for 60 seconds to solidify. The obtained porous separation membrane had a three-dimensional network structure. The evaluation results and performance of the obtained porous separation membrane, such as the structure, are shown in Table 2.

[0102] Example 4: 38% by mass of PA12 polymer and 62% by mass of NMP were dissolved at 170°C to obtain a homogeneous polymer solution. This polymer solution was allowed to stand at 150°C, degassed, and then cooled to 140°C in a pipe and maintained there for 15 seconds. The solution was discharged from the outer tube of a double-tubular spinneret for hollow fiber molding at a discharge outlet temperature of 140°C, and NMP was further injected into the hollow portion from the inner tube of the double-tubular spinneret. The solution was solidified in a cooling solution of NMP at 28°C over a dry length of 10 cm. The obtained porous separation membrane was a hollow fiber membrane with an outer diameter of 940 μm, an inner diameter of 530 μm, and a membrane thickness of 205 μm, and had a sphere-linked structure. Table 3 shows the evaluation results and performance of the obtained porous separation membrane, including its structure.

[0103] Reference Example 2 38% by mass of PVDF (Solev6013, manufactured by Solvay) and 62% by mass of GBL were dissolved at 170°C to obtain a homogeneous polymer solution. This polymer solution was allowed to stand at 150°C, degassed, and then cooled to 95°C in the pipe and maintained for 15 seconds. The solution was discharged from the outer tube of a double-tubular spinneret for hollow fiber molding at a discharge outlet temperature of 95°C, and GBL was further injected into the hollow portion from the inner tube of the double-tubular spinneret. The solution was solidified in a cooling solution of an 80% by mass aqueous GBL solution at 28°C with a dry length of 10 cm. The obtained porous separation membrane was a hollow fiber membrane with an outer diameter of 950 μm, an inner diameter of 560 μm, and a membrane thickness of 195 μm, and had a sphere-linked structure. Table 3 shows the evaluation results and performance of the obtained porous separation membrane, such as its structure.

[0104] In the table, "-" means that measurement was not possible, and "nd" means that measurement was not performed.

[0105]

[0106]

[0107]

[0108] It is clear that a person skilled in the art can conceive of various modifications and alterations within the scope of the claims, and it is understood that these also naturally fall within the technical scope of the present invention. Furthermore, the components in the above-described embodiments may be combined in any manner without departing from the spirit of the invention.

[0109] This application is based on a Japanese patent application filed on March 4, 2024 (Patent Application No. 2024-031808) and a Japanese patent application filed on September 27, 2024 (Patent Application No. 2024-168166), the contents of which are incorporated by reference into this application.

[0110] 1 Sphere-connected structure 10 Sphere 11 Neck of sphere 12 Void between sphere-connected structures 13 Line passing through the center in the long axis direction of the sphere 14 Line passing through the center in the short axis direction of the sphere 20 Inlet hole of pore 21 Porous structure 22 Wall end with small radius R 23 Wall end with large radius R 24 Wall end with very large radius R V1 Primary flow velocity V2 Flow velocity in pore X1 Sphere without measuring average diameter X2 Sphere without measuring average diameter

Claims

1. A porous structure consisting of interconnected spheres whose main component is polyamide polymer.

2. The porous structure according to claim 1, wherein the polyamide-based polymer is an aliphatic polyamide-based polymer.

3. The porous structure according to claim 1 or 2, having a porosity of 40% or more and 90% or less.

4. A porous structure according to claim 1 or 2, wherein the average diameter of the spheres in a cross-sectional image of the porous structure is 0.1 μm or more and 10 μm or less.

5. In the cross-sectional image of the porous structure, the value obtained by dividing the total perimeter of the pores by the total area of ​​the pores is 1.2 μm －１ 5.0 μm or more －１ 3. The porous structure according to claim 1, wherein:

6. The porous structure according to claim 2, wherein the aliphatic polyamide polymer has a value of 10 or more when the number of methylene groups is divided by the number of amide groups.

7. The porous structure according to claim 1 or 2, which is fibrous.

8. The porous structure according to claim 7, which is a hollow fiber membrane.

9. A method for separating fluids using the porous structure according to claim 1 or 2.

10. A fluid separation device using the porous structure according to claim 1 or 2.

11. An adsorbent using the porous structure according to claim 1 or 2.

12. A method for producing a porous structure, comprising obtaining a porous structure having a structure in which spheres are connected by a solid-liquid thermally induced phase separation method including a cooling step of cooling a polymer solution containing a polyamide-based polymer and a good solvent for the polyamide-based polymer.

13. A method for producing a porous structure according to claim 12, wherein the cooling step comprises immersing the polymer solution in a cooling solution containing 60% by mass or more but less than 100% by mass of a good solvent for the polyamide-based polymer, and wherein the crystallization onset temperature Tc (°C) of the polymer solution and the temperature Tb (°C) of the cooling solution satisfy the relationship -65<Tb-Tc≦60.

14. A method for producing a porous structure according to claim 12 or 13, further comprising a step of maintaining the polymer solution at a maintenance temperature Ta (°C) prior to the cooling step, wherein the maintenance temperature Ta (°C) and the crystallization onset temperature Tc (°C) of the polymer solution satisfy the relationship 0<Ta-Tc≦40.

15. The method for producing a porous structure according to claim 14, wherein the time for which the polymer solution is maintained at the maintenance temperature Ta (°C) is 15 seconds or more and 50 seconds or less.

16. The HSP distance between the polyamide polymer and the good solvent is 7 MPa. １／２ The method for producing a porous structure according to claim 12 or 13, wherein:

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