Porous fiber and liquid treatment column

Abstract

To provide a porous fiber capable of simultaneously and efficiently adsorbing a plurality of substances of different sizes to be removed that are present in a liquid to be treated, and a liquid treatment column incorporating the porous fiber.SOLUTION: A porous fiber has, in a fiber cross section, a region A and a region B separated by a region boundary, wherein a cross-sectional pore diameter Ap of the region A and a cross-sectional pore diameter Bp of the region B satisfy a relationship of Ap>Bp, and the region A and the region B each has a uniform structure.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to porous fibers and liquid treatment columns. [Background technology]

[0002] Many adsorbents packed into liquid treatment columns to adsorb and remove target substances contained in the liquid to be treated are porous in order to increase the surface area that contributes to adsorption. Adsorbents are generally in the form of beads or fibers. Among these, hollow fibers and solid fibers are superior in that they can ensure a sufficient flow path for the liquid to be treated when packed into a liquid treatment column. For example, Patent Document 1 discloses a porous fiber in which the cross-sectional shape in the radial direction of the fiber is modified to increase the surface area per volume of the fiber and the specific surface area of ​​the pores inside the fiber.

[0003] Patent Document 2 discloses a method for producing fibers that are made porous throughout the fiber in order to increase the porosity that contributes to the ability to adsorb substances.

[0004] Patent Document 3 discloses a porous fiber having powder particles inside for the purpose of simultaneously adsorbing a plurality of substances. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] International Publication No. 2016 / 067967 [Patent Document 2] Japanese Patent Application Publication No. 7-145512 [Patent Document 3] International Publication No. 2018 / 186210 Summary of the Invention [Problem to be solved by the invention]

[0006] However, since the porous structure inside the porous fiber described in Patent Document 1 is homogeneous, it is difficult to simultaneously adsorb and remove target substances with different molecular weights and sizes.

[0007] Patent Document 2 does not include any idea or description of simultaneously adsorbing and removing target substances with different molecular weights or sizes.

[0008] In Patent Document 3, the powder particles inside the porous fiber selectively adsorb low molecular weight compounds with a molecular weight of less than 1000, and it was difficult to simultaneously and efficiently adsorb and remove multiple target substances with molecular weights of several thousand to several million.

[0009] Therefore, an object of the present invention is to provide a porous fiber and a liquid treatment column that can simultaneously and efficiently adsorb a plurality of substances to be removed that have different molecular weights and sizes and are present in a liquid to be treated. [Means for solving the problem]

[0010] The present invention has the following configurations for solving the above problems. (1) A porous fiber having, in a fiber cross section, a region A and a region B separated by a region boundary, wherein the cross-sectional pore diameter Ap of the region A and the cross-sectional pore diameter Bp of the region B satisfy the relationship Ap>Bp, and the region A and the region B each have a uniform structure. (2) The porous fiber according to (1) above, wherein the region A is adjacent to the surface. (3) The porous fiber according to (1) or (2) above, wherein the ellipticity of the pores on the surface is 2.0 or more. (4) The porous fiber according to any one of (1) to (3) above, wherein the pore size on the surface is 1.5 times or more and less than 100 times the cross-sectional pore size in the region adjacent to the surface. (5) A porous fiber according to any one of (1) to (4) above, wherein, when the total area of ​​the fiber cross section is S, the area of ​​the region A is As, the area of ​​the region B is Bs, and the area of ​​the region boundary is Xs, the values ​​of As / S and Bs / S are 0.2 or more, and the value of Xs / S is 0.2 or less. (6) The porous fiber according to (5) above, which satisfies the following formula (1): As / S+Bs / S+Xs / S=1.0...Equation (1) (7) The porous fiber according to any one of (1) to (6) above, wherein the surface porosity is 5% or more. (8) The porous fiber according to any one of (1) to (7) above, wherein the region A and the region B form an islands-in-sea, sheath-core or multilayer composite structure. (9) The porous fiber according to any one of (1) to (8) above, which is a solid fiber. (10) The porous fiber according to any one of (1) to (9) above, wherein the Ap is 55 nm or more and 350 nm or less, and the Bp is 4 nm or more and 50 nm or less. (11) The porous fiber according to any one of (1) to (10) above, wherein the region A and the region B are made of the same material. (12) The porous fiber according to any one of (1) to (11) above, which contains an amorphous polymer compound. (13) A liquid treatment column incorporating the porous fiber according to any one of (1) to (12) above. [Effects of the Invention]

[0011] The porous fiber and liquid treatment column incorporating the porous fiber of the present invention make it possible to simultaneously and efficiently adsorb a plurality of substances to be removed that are present in the liquid to be treated and have different molecular weights and sizes. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a diagram showing an example of a scanning electron microscope image in which region 1 and region 2 are distinguished by brightness difference. [Figure 2] FIG. 2 is an enlarged view of the boundary of the virtual region in FIG. 1. [Figure 3] 3 is a schematic diagram showing a pore diameter line profile at a perpendicular to a tangent at any point on the imaginary region boundary of FIG. 2. FIG. [Figure 4]These are examples of changes in cross-sectional pore diameter at region boundaries. These are a schematic diagram of a case where the cross-sectional pore diameter changes discontinuously (Figure 4-A), a schematic diagram of a case where the cross-sectional pore diameter changes continuously (Figure 4-B), and a schematic diagram of a case where there are locally large and small cross-sectional pore diameter areas (Figure 4-C). [Figure 5] These are examples of fiber cross sections of porous fibers, including a schematic diagram showing an islands-in-sea type (Figure 5-A), a schematic diagram showing a sheath-core type (Figure 5-B), and a schematic diagram showing a multilayer type (Figure 5-C). DETAILED DESCRIPTION OF THE INVENTION

[0013] The porous fiber of the present invention has, in the fiber cross section, Region A and Region B separated by a region boundary, in which the cross-sectional pore diameter Ap of Region A and the cross-sectional pore diameter Bp of Region B satisfy the relationship Ap>Bp, and Region A and Region B each have a uniform structure, i.e., a composite porous fiber.

[0014] "Fiber cross section" means a cross section perpendicular to the longitudinal direction of the fiber.

[0015] By having regions A and B with different cross-sectional pore diameters, multiple substances to be removed that differ in molecular weight and size can be adsorbed with high efficiency in the respective pores, and the fiber can have higher mechanical strength than a fiber having only region A. Furthermore, the cross-sectional pore diameters of regions A and B can be appropriately controlled depending on the size of the substances to be removed, but to prevent clogging of the pores, it is preferable that the cross-sectional pore diameter of each region be larger than the size of the substances to be removed. The cross-sectional pore diameters of regions A and B can be controlled by the concentration of the spinning dope, the temperature of the coagulation bath during spinning, etc.

[0016] The porous fiber of the present invention has regions A and B with different cross-sectional pore sizes, and therefore can simultaneously adsorb multiple substances of different sizes to be removed, such as proteins, humic substances, sugars, or inorganic salts in water treatment and biopharmaceutical purification applications, or toxins, proteins, or drugs in medical applications. For medical applications, blood purification columns that adsorb pathogens from blood must minimize the amount of blood removed from the patient's body. Because the porous fiber of the present invention can simultaneously adsorb and remove multiple substances to be removed with high efficiency, the column volume can be reduced, making it suitable for use in blood purification columns.

[0017] Combinations of substances of different sizes (small size / large size) to be removed using blood purification columns include inflammatory cytokines / immune complexes in autoimmune diseases, inflammatory cytokines / LDL cholesterol in arteriosclerosis, inflammatory cytokines / endotoxins in sepsis, and β2 microglobulin / proteoglycans in dialysis amyloidosis.

[0018] The method for determining the region A, region B and region boundaries in the porous fiber of the present invention will be described with reference to FIGS. 1 to 3 as examples.

[0019] The cross section of the porous fiber is observed using a scanning electron microscope (e.g., S-5500, manufactured by Hitachi High-Technologies Corporation) at a magnification that allows the entire fiber cross section to be observed. In the porous fiber of the present invention, regions A and B each have a uniform structure, and regions A and B can be observed with uniform brightness. Furthermore, since brightness varies depending on the cross-sectional pore size, virtual region 1 (100) and virtual region 2 (101) can be distinguished by the brightness difference at the virtual region boundary 102, as shown in Figure 1. If regions A and B are made of the same material, the difference in cross-sectional pore size is small (e.g., approximately 10 nm), and the brightness difference between the regions is small, the contrast and brightness are appropriately adjusted to increase the brightness difference between the regions. The virtual region boundary of the distinguished regions is determined by visual inspection or image processing. When visual inspection is performed, the location where the brightness changes visually is considered to be the virtual region boundary. When processing the image, the two regions are binarized so that the brighter region is white and the darker region is black, and the boundary between them is used as the virtual region boundary. At this time, the judgment is made ignoring unevenness that occurred when preparing the cross section of the porous fiber, brightness and darkness due to scratches, or brightness and darkness due to noise. When processing the image, appropriate image processing such as smoothing or noise removal is performed depending on the situation before binarization.

[0020] After determining the virtual region boundary, the image is enlarged to a magnification sufficient to observe the porous structure, and the location where the porous structure changes is determined as the exact region boundary. The location where the porous structure changes is determined using the following image processing method. The pore diameters of the pores present on the line profile of the perpendicular line 103 to the tangent at any point on the virtual region boundary 102 (see Figure 2) are plotted as shown in Figure 3. Here, image analysis software (e.g., ImageJ) is used to fit the pores to a circle, and the diameter of the resulting circle is taken as the pore diameter, with the center of the circle taken as the position of the pore. As shown in Figure 3, the pore diameter within each region is constant within a range of variation, but changes across a certain boundary. The boundary on the virtual region 1 side is taken as the region 1 boundary 104, the boundary on the virtual region 2 side is taken as the region 2 boundary 105, and the region between the region 1 boundary 104 and the region 2 boundary 105 is taken as the region boundary 106.

[0021] The "region boundary" refers to the region separating Region 1 and Region 2. The region boundary may have a discontinuous change in cross-sectional pore size (Figure 4-A) or a continuous change (Figure 4-B). There may also be localized areas with larger or smaller cross-sectional pore sizes (Figure 4-C).

[0022] For each region determined by the above method, the region with the larger cross-sectional pore diameter determined by the method described below in "Cross-sectional pore diameter of each region" is designated Region A, and the region with the smaller cross-sectional pore diameter is designated Region B. That is, in the porous fiber of the present invention, the cross-sectional pore diameter Ap of Region A and the cross-sectional pore diameter Bp of Region B satisfy the relationship Ap > Bp. Region A and / or Region B may be present in multiple locations on the fiber cross section, and in that case, similar measurements are made for each location.

[0023] The porous fiber of the present invention may have two or more regions with different cross-sectional pore sizes in the fiber cross section. For example, if the fiber cross section has three regions, region X, region Y, and region Z, with different cross-sectional pore sizes, and the relationship Xp>Yp>Zp is satisfied when the cross-sectional pore sizes are Xp, Yp, and Zp, region A and region B may be appropriately selected so as to satisfy the relationship Ap>Bp. Specific combinations of region A and region B include region X and region Y, region X and region Z, and region Y and region Z.

[0024] The cross-sectional pore diameter can be calculated from an image of each region of the cross section of the porous fiber taken with a scanning electron microscope (e.g., S-5500 manufactured by Hitachi High-Technologies Corporation) at a magnification at which the contours of the pores can be clearly observed. Specifically, the cross-sectional pore diameter can be calculated by the method described below in "Cross-sectional pore diameter of each region."

[0025] The cross-sectional pore diameter Ap of region A and the cross-sectional pore diameter Bp of region B may be appropriately determined so as to enhance the adsorption performance of the respective target substances to be removed, as long as the relationship Ap>Bp is satisfied. For example, if the target substances to be removed in region B have molecular weights of several thousand to several tens of thousands and sizes of about 1 to 10 nm, such as cytokines or β2 microglobulin, from the viewpoint of adsorbing these substances, the cross-sectional pore diameter Bp of region B is preferably 4 nm or more, more preferably 9 nm or more, and even more preferably 14 nm or more. On the other hand, it is preferably 50 nm or less, more preferably 42 nm or less, and even more preferably 35 nm or less.

[0026] Furthermore, when the substances to be removed in region A are LDL cholesterol, immune complexes, endotoxins, or proteoglycans, which have molecular weights of hundreds of thousands to millions and sizes of about 15 to 100 nm, the pore size is preferably 55 nm or more, more preferably 65 nm or more, and even more preferably 75 nm or more, from the viewpoint of adsorbing these substances. On the other hand, the pore size is preferably 350 nm or less, more preferably 240 nm or less.

[0027] The cross-sectional pore size of the porous fiber can be controlled, for example, by the composition of the spinning dope or the temperature of the coagulation bath during spinning.

[0028] The area ratios of region A, region B, and region boundaries in the fiber cross section of the porous fiber of the present invention are not particularly limited, but from the viewpoint of ensuring sufficient adsorption performance for multiple substances to be removed, when the total area of ​​the fiber cross section is S, the area of ​​region A is As, and the area of ​​region B is Bs, the values ​​of the area ratio of region A (As / S) and the area ratio of region B (Bs / S) are preferably 0.1 or more, more preferably 0.2 or more, and even more preferably 0.3 or more.

[0029] Furthermore, when the area of ​​the region boundary is Xs, from the viewpoint of ensuring sufficient adsorption performance for multiple substances to be removed, the value of the region boundary area ratio (Xs / S) is preferably 0.20 or less, more preferably 0.10 or less, and even more preferably 0.05 or less. Note that when multiple regions A and / or regions B exist in the fiber cross section, the total area of ​​each region is used for judgment.

[0030] The porous fiber of the present invention may have regions other than region A, region B, and region boundaries, such as non-porous regions intended to improve the strength of the fiber, but from the viewpoint of improving the adsorption performance of the substances to be removed, it is preferable that the porous fiber does not include regions other than region A, region B, and region boundaries, i.e., that the following formula (1) is satisfied. As / S+Bs / S+Xs / S=1.0...Equation (1) The area of ​​each region in the cross section of the porous fiber can be controlled, for example, by adjusting the amount of spinning dope discharged corresponding to each region during spinning.

[0031] "Uniform structure" means that the region is characterized by a homogeneous porous structure throughout. Specifically, when the cross-sectional pore size is calculated at five randomly selected locations within a region not including boundaries on the fiber cross section, if the coefficient of variation is always less than 15%, the region is determined to have a uniform structure. In other words, if there is a combination of five locations within the region where the coefficient of variation of the cross-sectional pore size is 15% or more, the region is determined not to have a uniform structure. By achieving a uniform structure, the entire region becomes a porous structure suitable for adsorption of the target substance, thereby improving adsorption performance. At the same time, adsorption of substances other than the target substance can be suppressed.

[0032] In the cross section of the fiber, region A or region B may be located in one place, or may be located in a plurality of dispersed places.

[0033] In the porous fiber of the present invention, it is preferable that region A is adjacent to the surface. By having region A, which has a large cross-sectional pore diameter, adjacent to the surface that comes into contact with the liquid to be treated, both the substances to be removed in region A and region B can easily penetrate into the interior of the fiber, improving adsorption performance. Furthermore, region A and region B may have any shape in the cross section of the fiber.

[0034] The porous fiber of the present invention may be a hollow fiber having a hollow portion or a solid fiber having no hollow portion, and there are no particular limitations on the cross-sectional shape or diameter of the fiber. In particular, the composite structure of region A and region B is preferably an islands-in-sea type (FIG. 5-A), a sheath-core type (FIG. 5-B), or a multilayer type (FIG. 5-C), because these can be produced by existing manufacturing methods.

[0035] The term "islands in the sea" refers to a composite structure composed of island components and a sea component surrounding the island components. The shape, number, and arrangement of the island components are not limited and may be determined arbitrarily from the viewpoint of ease of production and performance.

[0036] The term "core-sheath type" refers to a composite structure in which island components of the sea type are combined into one. The shape and arrangement of the core can be determined arbitrarily.

[0037] The term "multilayer type" refers to a composite structure in which the fiber cross section has a hollow portion and is alternately laminated with region A and region B. There is no limitation on the number of layers, but from the perspective of ease of production, four layers or less is preferred, and three layers or less is more preferred.

[0038] When the porous fiber is a hollow fiber, the substances to be removed in the liquid to be treated can be adsorbed by contacting the liquid to be treated only with the inside or outside of the hollow fiber, or by flowing the liquid to be treated on both the inside and outside of the hollow fiber.

[0039] When the porous fiber is a solid fiber, it has a continuous structure that is not divided by hollow portions, and therefore has higher strength and elongation than hollow fibers when the fiber volume is the same as that of hollow fibers, and can be made thinner. When making an adsorbent with the same surface area, the fiber volume of solid fibers becomes smaller than that of hollow fibers by making them thinner, allowing for the fiber bundle and liquid treatment column to be made smaller. Therefore, it is preferable that the porous fiber is a solid fiber. The shape of the fiber cross section can be controlled by, for example, the arrangement of the spinning dope discharge holes in region A and region B.

[0040] The porous fiber of the present invention preferably has pores on the surface of the fiber with an ellipticity of 2.0 or more.

[0041] "Ellipticity" refers to the ratio of the major axis to the minor axis of a pore, as determined by the method described below in "Ellipticity of Surface Pores." When the porous fiber is a hollow fiber, the fiber surface refers to either the inner surface or the outer surface, or both. When the pore shape of the fiber surface is perfectly circular, increasing the pore size can widen the entrance for the target substance to penetrate into the fiber. However, at the same time, substances larger than the target substance can easily penetrate into the fiber, potentially competing with the adsorption of the target substance. On the other hand, making the surface pore shape elliptical can widen the entrance for the target substance to penetrate into the fiber while preventing substances larger than the target substance from penetrating into the fiber, thereby improving the adsorption performance of the target substance. Therefore, the ellipticity of the pores on the fiber surface is preferably 2.0 or more, more preferably 2.5 or more. On the other hand, since a too high ellipticity reduces the stability of the porous structure, the ellipticity is preferably 10 or less, more preferably 8 or less, and even more preferably 5 or less.

[0042] The ellipticity of the pores on the fiber surface can be controlled by heat treatment during spinning.

[0043] The porous fiber of the present invention preferably has a surface pore size that is 1.5 times or more but less than 100 times the cross-sectional pore size of the region adjacent to the surface. By making the pore size of the fiber surface larger than the cross-sectional pore size of the region adjacent to the surface, the substances to be removed can more easily diffuse into the interior of the fiber, improving adsorption performance. The substances to be removed in region A have a larger molecular size than the substances to be removed in region B, making them particularly difficult to penetrate into the interior of the fiber, and it is presumed that the porous structure of the fiber surface is particularly important. From the viewpoint of improving adsorption performance, the pore size of the fiber surface is more preferably 2.0 times or more, and even more preferably 3.0 times or more, the cross-sectional pore size of the region adjacent to the surface. On the other hand, from the viewpoint of maintaining the mechanical strength of the fiber, it is preferably less than 100 times, more preferably less than 50 times, and even more preferably less than 30 times. The pore size of the fiber surface can be calculated using the method described below in "Surface Pore Size."

[0044] For example, when region A is adjacent to the surface and the substances to be removed are LDL cholesterol, immune complexes, endotoxins, or proteoglycans, which have molecular weights of hundreds of thousands to millions and sizes of about 15 to 100 nm, the surface pore size is preferably 100 nm or more, more preferably 150 nm or more, and even more preferably 200 nm or more so that these substances can easily diffuse into the fiber.On the other hand, the surface pore size is preferably 500 nm or less, more preferably 400 nm or less.

[0045] The pore size on the fiber surface of a porous fiber can be controlled, for example, by the composition of the spinning solution in the region adjacent to the fiber surface, whether or not heat treatment is performed during spinning, or the speed of cold air in the free-running section.

[0046] The porous fiber of the present invention preferably has a surface porosity of 5% or more.

[0047] "Open area ratio" refers to the ratio of pores present. Increasing the open area ratio of the fiber surface can ensure the diffusion of the substance to be removed into the fiber interior. The open area ratio of the surface is more preferably 10% or more, and even more preferably 20% or more. On the other hand, from the viewpoint of preventing a decrease in fiber strength, non-selective adsorption, or the outflow of fine particles generated inside the pores to the outside of the fiber, the open area ratio of the surface is preferably 95% or less, and more preferably 85% or less. The open area ratio of the surface can be calculated by the method described below in "Surface open area ratio."

[0048] The surface porosity can be controlled by the speed of the cold air in the free-running section during spinning.

[0049] In the porous fiber of the present invention, the porosity of Region A and Region B in the fiber cross section is preferably 5% or more and 95% or less. A high porosity allows the entire region to contribute to adsorption, improving adsorption performance. Therefore, the porosity of Region A and Region B is more preferably 14% or more, even more preferably 18% or more, particularly preferably 24% or more, and most preferably 35% or more. On the other hand, from the viewpoint of maintaining the mechanical strength of the fiber, the porosity of Region A and Region B is preferably 95% or less, more preferably 90% or less, and even more preferably 85% or less. The porosity of Region A and Region B in the fiber cross section can be calculated from the ratio of the total area of ​​all pores to the area of ​​the entire image in the binarized fiber cross section image used in the "cross-sectional pore diameter of each region" described below.

[0050] The adsorption principle of the porous fiber of the present invention may be any of hydrophobic interaction, electrostatic interaction, and hydrogen bonding, or a combination of these principles. Hydrophobic interaction is particularly preferred because it has sufficient power to adsorb proteins and has minimal effect on blood cells and the like. These adsorption principles are basically determined by the fiber material, as described below. Multiple ligands that specifically interact with the target substance may be immobilized on the surface and within the pores of the porous fiber. However, it is difficult to simultaneously immobilize multiple ligands to the porous fiber, and even if immobilization is successful, competition between the ligands may reduce the amount of ligand immobilized and reduce adsorption performance. Therefore, it is preferable to immobilize only one type of ligand to the porous fiber.

[0051] From the viewpoint of achieving both blood compatibility and adsorption performance, the porous fiber of the present invention desirably has an appropriate degree of hydrophobicity on the outer surface of the fiber and on the surfaces of the pores inside the fiber. The hydrophobicity can be quantified by the dispersive component of the surface free energy, and specifically, the dispersive component of the surface free energy measured by inverse gas chromatography should be 5 to 100 mJ / m 2 It is preferable that the concentration is 10 to 80 mJ / m 2 , and more preferably 20 to 70 mJ / m 2 is.

[0052] The materials of the regions A and B of the porous fiber of the present invention may be the same or different, but from the viewpoint of preventing peeling or deformation of the porous fiber due to differences in physical or chemical properties caused by the difference in materials, it is preferable that the materials of the regions A and B are the same.

[0053] Polymers are preferably used as the material for the porous fiber of the present invention from the viewpoints of moldability and cost. Examples of polymers include polymethyl methacrylate (hereinafter referred to as "PMMA"), polyacrylonitrile (hereinafter referred to as "PAN"), polysulfone, polyethersulfone, polyarylethersulfone, polypropylene, polystyrene, polycarbonate, polylactic acid, polyethylene terephthalate, cellulose, cellulose triacetate, ethylene-vinyl alcohol copolymer, polycaprolactam, polymethylpentene, polyvinylidene fluoride, polyester-based polymer alloys, and derivatives thereof. Among these, PMMA, PAN, polysulfone, polyethersulfone, polyester-based polymer alloys, polystyrene, and cellulose triacetate, which have appropriate hydrophobic interactions, are preferably used.

[0054] The porous fiber of the present invention preferably contains an amorphous polymer, and more preferably contains an amorphous polymer as the main component.

[0055] "Mainly composed of an amorphous polymer" means that of the components constituting the porous fiber, amorphous polymers account for 50% by mass or more of the total. Amorphous polymers are particularly excellent in terms of moldability and cost. Furthermore, because they are composed only of amorphous portions, they have a uniform structure even from a microscopic perspective, which allows for the expectation of uniform adsorption reactions on the surface. Furthermore, compared to crystalline polymers, which have two domains, crystalline and amorphous, with significant differences in physical and chemical properties, amorphous polymers are easier to handle as materials. Among amorphous polymers, PMMA is particularly preferred because it has moderate hydrophobicity, excellent strength, and can withstand radiation sterilization when used in medical applications.

[0056] The amorphous polymer contained in the porous fiber of the present invention is preferably a polymer compound having a hydrophilic group, since it has excellent blood compatibility. Examples of hydrophilic groups include a hydroxyl group, a carboxyl group, an amino group, an ester group, an amide group, a sulfo group, a urethane group, and a phosphate group. Among these, a polymer containing an ester group is preferred, since it has moderate hydrophilicity and can achieve both blood compatibility and chemical stability. A polymer containing an ester group, such as PMMA, is preferred because it has excellent blood compatibility and can easily exhibit functions by modifying the terminal groups.

[0057] The porous fiber of the present invention preferably has a negative charge. A negative charge can be imparted to the porous fiber by adding a material having a functional group exhibiting a negative charge to the spinning dope. Examples of the functional group exhibiting a negative charge include a sulfo group, a carboxyl group, a phosphate group, a phosphite group, an ester group, a sulfite group, a hyposulfite group, and a sulfide group.

[0058] The amount of negative charge per 1 g of dried porous fiber is preferably 5 μeq to 130 μeq. When the porous fiber has an appropriate negative charge, for example, sialic acid present on the surface of cells or albumin, a major protein in blood that has a negative charge, repels the porous fiber, thereby suppressing fouling due to nonspecific adsorption.

[0059] The porous fiber of the present invention can be produced by either melt spinning or solution spinning, and the fiber obtained by melt spinning can be made porous by post-treatment such as drawing or extraction. Among these, solution spinning can produce a fiber having a porous structure with sufficient pore volume and porosity by uniformly dissolving the fiber material in a solvent and then removing the solvent. Furthermore, by appropriately designing the spinning dope that forms each region, multiple regions with different pore sizes can be easily formed within the porous fiber. Furthermore, since post-treatment for making the fiber porous is not required, productivity is excellent and the risk of peeling or breakage is extremely low. For these reasons, solution spinning is preferred as the method for producing the porous fiber.

[0060] Hereinafter, methods for producing porous fibers by solution spinning will be described, but the methods are not limited to these.

[0061] First, to obtain a porous fiber having multiple regions with different cross-sectional pore sizes, multiple spinning dope solutions with different compositions are simultaneously extruded from a spinneret. For example, when producing a porous fiber having Region A and Region B, spinning dope a is used to form Region A, and spinning dope b is used to form Region B. In this case, by reducing the difference in viscosity between spinning dope solutions a and b, it is easier to maintain a balance in the flow rate when the dope solutions are extruded, and Region A and Region B can be made continuous in the longitudinal direction of the fiber. In addition, the position of each region in the fiber cross section is consistent. Furthermore, the fiber shape is less likely to vary. On the other hand, if the spinning viscosities are the same, adequate solvent exchange at the interface is less likely to occur, and peeling is more likely to occur at the region boundary. Therefore, the viscosity of the spinning dope solution with the higher viscosity divided by the viscosity of the spinning dope solution with the lower viscosity is preferably 1.1 or more, more preferably 1.3 or more, and even more preferably 1.5 or more. On the other hand, it is preferably 77.0 or less, more preferably 51.0 or less, and even more preferably 29.0 or less. For the purpose of controlling viscosity, the molecular weight of the fiber-forming components may be adjusted, and a thickener, a surfactant, water, alcohol, or the like may be added to the spinning dope.

[0062] In addition, it is preferable that the solvent used in all spinning dope is the same. By using the same solvent, when removing the solvent in a coagulation bath or the like during spinning, it is not necessary to bring the dope into contact with another solvent having a different solubility, and therefore, it is possible to suppress changes in the pore structure.

[0063] After simultaneously discharging the spinning dope solutions a and b from the spinneret, it is preferable to allow them to run in an airtight state for a certain period of time and then introduce them into a coagulation bath containing a non-solvent or poor solvent for the fiber material for coagulation. It is also preferable to actively cool the fibers during this airtight state. Cooling the fibers during this airtight state quickly completes the formation of domains, continuous interfaces, and porous structures, resulting in fibers with a consistent structure in the longitudinal direction of the fibers. Therefore, it is preferable to cool the fibers with cold air in the airtight state. The cold air velocity is preferably 3.3 m / s or more, more preferably 4.6 m / s or more, and even more preferably 5.2 m / s or more. Furthermore, increasing the cold air velocity to quickly cool the fibers after discharge suppresses the aggregation of the fiber material on the fiber surface and improves the surface open area ratio. The airtight state of the fibers is preferably 0.2 seconds or more and 2 seconds or less. Limiting the airtight state to a certain period of time reduces the risk of fiber breakage. Furthermore, adjusting the airtight state can control the dense layer thickness. The shorter the idle time, the more easily the fiber-forming components are precipitated on the fiber surface, and the thicker, denser layer can be formed.

[0064] The "dense layer" refers to a region in the cross section of the fiber where no pores with a diameter of 4 nm or more exist.

[0065] The spinneret temperature during spinning is preferably 150° C. or less in order to ensure sufficient cooling of the fiber after extrusion.

[0066] The coagulation bath into which the spinning dope is immersed after being discharged from the spinneret usually contains a coagulant such as water or alcohol alone, or a mixture with the solvent that makes up the spinning dope. The porous structure on the surface and inside of the porous fiber can be controlled by adjusting the coagulation bath temperature. In general, the pore size can be increased by increasing the coagulation bath temperature. The mechanism behind this is unclear, but is presumed to be as follows. When the spinning dope is immersed in the coagulation bath, desolvent removal and coagulation shrinkage occur in competition with each other. At high temperatures, desolvent removal is faster, and the fiber solidifies and fixes before the interior shrinks, resulting in a larger average pore size for the porous fiber.

[0067] The cross-sectional pore size of Region A and Region B can be controlled by the concentration of the polymer (fiber material) in each spinning solution, the addition of a pore-forming agent, or the position of each region on the fiber cross section. For example, the cross-sectional pore size can be enlarged by decreasing the concentration of the fiber material in the spinning solution or adding a pore-forming agent. Furthermore, the closer to the outer periphery of the fiber cross section, the faster the structure formation during idle running and the solvent removal in the coagulation bath, resulting in a larger cross-sectional pore size. Therefore, it is preferable to position Region A near the outer periphery of the fiber. In addition to the concentration of the fiber material in each spinning solution and the addition of a pore-forming agent, the surface pore size can be improved by incorporating positively and / or negatively charged functional groups into a portion of the polymer (fiber material) to finely disperse the fiber material components. Examples of positively charged functional groups include amino groups, guanidyl groups, and amidine groups. Examples of negatively charged functional groups include sulfo groups, carboxyl groups, phosphate groups, phosphite groups, ester groups, sulfite groups, hyposulfite groups, and sulfide groups.

[0068] The adsorption performance of the porous fiber of the present invention can be measured by the amount of adsorption of the target substance to be removed in each of areas A and B. For example, when the target substances are the inflammatory cytokine IL-6 and LDL cholesterol, the adsorption amount of IL-6 on the porous fiber is 0.04 μg / cm 3 It is preferable that the concentration is equal to or higher than 0.06 μg / cm 3 or more, and more preferably 0.09 μg / cm 3 The adsorption capacity of LDL cholesterol on the porous fiber was 0.10 mg / cm 3 It is preferable that the concentration is equal to or higher than 0.15 mg / cm, and more preferably 0.15 mg / cm 3 More preferably, it is 0.30 mg / cm 3 That's all.

[0069] The liquid treatment column of the present invention has the porous fiber of the present invention built in. By incorporating the porous fiber of the present invention, it is possible to obtain a liquid treatment column that is easy to handle and exhibits high adsorption performance.

[0070] When incorporating porous fibers, in order to prevent the porous fibers from repelling each other due to static electricity or the like and becoming disorganized, or to prevent the individual fibers from adhering to each other, the fiber bundle may be wrapped in a film, net, mesh, nonwoven fabric, or the like, or a processed yarn called a covering yarn may be spirally wrapped around one or more fibers.

[0071] The liquid treatment column of the present invention preferably has a structure in which porous fibers are embedded in a casing having ports at both ends that communicate with the interior. Examples of the casing shape include a rectangular or hexagonal casing or a cylindrical casing with both ends open. Among these, a cylindrical casing, particularly a cylindrical casing with a perfectly circular cross section in the radial direction, is preferred. This is because the lack of corners in the casing can prevent the liquid to be treated from stagnating at the corners. Furthermore, by making both ends of the casing open, the flow of the liquid to be treated is less likely to be disturbed, minimizing pressure loss. The casing can be made of plastic or metal, with plastic being preferred from the standpoints of cost, moldability, mass, blood compatibility, and the like. When plastic is used as the casing material, a thermoplastic resin with excellent mechanical strength and thermal stability is preferred. Examples of thermoplastic resins include polycarbonate resins, cellulose resins, polyester resins, polyarylate resins, polyimide resins, cyclic polysulfone resins, polyethersulfone resins, polyolefin resins, polystyrene resins, polyvinyl alcohol resins, ABS resins, and mixtures thereof. Among these, polypropylene, polystyrene, polycarbonate, ABS resin, or derivatives thereof are preferred from the viewpoint of moldability and radiation resistance required for the casing. In particular, resins with excellent transparency, such as polystyrene and polycarbonate, are advantageous in ensuring safety because, for example, the internal state can be observed during perfusion of the liquid to be treated.

[0072] Both ends of the casing are preferably physically sealed, for example, by arranging a mesh or by fixing the casing with a resin or the like and then penetrating the partition wall to provide a through-hole that connects the inside and outside of the casing.

[0073] The "through hole" means an opening that penetrates the partition wall in the longitudinal direction of the porous fiber. That is, the through hole is a hole that exists in the partition wall and penetrates through it, and that connects the inside and outside of the casing separated by the partition wall.

[0074] The term "partition wall" refers to a portion at the end of the casing that separates the inside and outside of the casing, and examples thereof include a resin that fixes the casing and the fibers. When using a resin as a partition wall, a resin liquid such as polyurethane is injected from both ends of the casing, and the resin liquid is allowed to harden while flowing toward the end of the casing by centrifugal force, and then the unnecessary portion is removed. Among sealing methods, the method of arranging a mesh is preferred because it is easier to process than the method of forming a partition wall and easily distributes the flow of the treated liquid uniformly within the column. In addition, in order to further improve the dispersibility of the treated liquid within the column, a mesh with a large pressure loss, a baffle plate, or a plate-shaped member called a flow control plate called a straightening plate may be attached to a portion of the mesh.

[0075] The fiber form when the fibers are incorporated into the casing can be in the form of finely chopped porous fibers or in the form of advanced processing such as knitted fabric, woven fabric, or nonwoven fabric. Among these, a fiber bundle formed by bundling straight fibers is preferred, and it is preferable to insert it parallel to the longitudinal direction of the casing. A fiber bundle formed by bundling straight porous fibers easily ensures a flow path for the liquid to be treated, making it easy to evenly distribute the liquid to be treated within the casing. Furthermore, the flow is less likely to become turbulent, which is advantageous in preventing increased pressure loss. Therefore, even when highly viscous blood is used as the liquid to be treated, the risk of coagulation within the casing can be minimized. Furthermore, in the case of porous fibers having multiple regions with different pore sizes, a straight fiber bundle is preferred because it can minimize the risk of peeling at the interface between the regions due to the pressure during the delivery of the liquid to be treated. [Example]

[0076] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. First, measurement methods and evaluation methods are described below.

[0077] <Determination of Area A, Area B and Area Boundaries> A porous fiber block was prepared by placing the thoroughly moistened porous fiber in a water-filled container and freezing the container with liquid nitrogen. The block was sliced ​​to a thickness of 200 nm at -65°C using an ultramicrotome equipped with a cryosystem to produce sections exposing the porous fiber cross-section. The sections were freeze-dried in a vacuum dryer at 0.1 torr or less to sublimate the water. A platinum-palladium (Pt-Pd) thin film was then formed on the sample surface by sputtering, and the specimen was used for observation. The fiber cross-section of the specimen was observed using a scanning electron microscope (Hitachi High-Technologies Corporation S-5500) at a magnification of 400x, allowing the entire fiber cross-section to be observed. Based on the brightness difference, a virtual region boundary was visually determined, and the fiber cross-section was divided into two regions. When the brightness difference between the regions was small, the contrast and brightness were appropriately adjusted to increase the brightness difference between the regions. Next, the image was magnified to a magnification (10,000x) that allowed for sufficient visualization of pores, including the virtual region boundary, and the fiber cross section was imaged. A perpendicular line was drawn to the tangent at any point on the virtual region boundary, and the pore diameter and position of any pores present on the perpendicular line were calculated. A line profile was created showing the pore diameter transition around the virtual region boundary, with the horizontal axis representing the pore position and the vertical axis representing the pore diameter. Image analysis software (ImageJ) was used to fit the pores to a circle, and the diameter of the resulting circle was taken as the pore diameter, with the center of the circle representing the pore position. Furthermore, perpendicular lines were drawn to the virtual region boundary so that the number of pores in virtual region 1 and virtual region 2 was 50 or more. For regions where the measured pore pixel count was 5 or less, the magnification was further increased and the pore diameter was calculated. The maximum magnification was 50,000x, and any pixel count of 5 or less even at 50,000x magnification was considered noise.

[0078] Next, the cross-sectional pore diameters and coefficients of variation for regions 1 and 2 were determined using the methods described below in "Cross-sectional pore diameter of each region" and "Coefficient of variation for each region," and the 99% confidence interval for the cross-sectional pore diameter of each region was calculated. Observation was performed from the region 1 side toward the virtual region boundary on the line profile. When five consecutive pores with diameters outside the 99% confidence interval of the cross-sectional pore diameter of region 1 were found, the position of the pore closest to region 1 among the pores outside the range was determined to be the boundary of region 1. The boundary of region 2 was determined in the same manner for region 2. The region between the boundary of region 1 and the boundary of region 2 was determined to be the region boundary. The region with the larger cross-sectional pore diameter was determined to be region A, and the region with the smaller cross-sectional pore diameter was determined to be region B.

[0079] <Cross-sectional pore diameter of each region> The center of each region, identified by brightness difference, was observed and photographed using a scanning electron microscope (Hitachi High-Technologies Corporation S-5500) at a magnification of 50,000x, allowing for clear observation of the hole outlines. After photographing, the images were binarized using image analysis software (ImageJ) so that the holes appeared black and the structure appeared white, and the total area of ​​the holes was calculated. When binarization of the holes and structure was difficult due to contrast differences in the electron microscope image, a transparent sheet was placed over the printout and the holes were filled in black using a black pen. The transparent sheet was then copied onto white paper, and the image was then binarized so that the holes appeared black and the structure appeared white. Note that black areas with five or fewer consecutive pixels were treated as white, representing the structure, because it was difficult to distinguish between noise and holes. The equivalent circle diameter, which is the diameter of a circle with the same area, was calculated from the area of ​​each pore, and the resulting equivalent circle diameters were arranged in descending order. The areas of the pores were added up starting with the largest equivalent circle diameter, and the equivalent circle diameter of the pore when the sum exceeded half of the total area of ​​all the pores was taken as the cross-sectional pore diameter. Cross-sectional pore diameters were calculated in the same manner at five locations within the same region, excluding boundaries, and the average value was taken as the cross-sectional pore diameter of that region. The cross-sectional pore diameter was rounded to one decimal place.

[0080] <Coefficient of variation of cross-sectional pore diameter> The coefficient of variation was calculated from the cross-sectional pore diameters of five locations within the same region, excluding the boundaries, calculated in the above "Cross-sectional pore diameter of each region." The coefficient of variation was rounded to one decimal place.

[0081] <Area ratio of area A, area B and area boundary> The boundaries of Region 1 and Region 2 were drawn on the image of the fiber cross section, assuming that the region boundary existed around the entire circumference of the imaginary region boundary, using the width of the region boundary calculated from the line profile with the imaginary region boundary created in the "Determination of Region A, Region B, and Region Boundary" section above. The areas of Region A, Region B, and the region boundary were calculated using image processing software (ImageJ). The ratios of Region A (A / S), Region B (B / S), and Region Boundary (X / S) were calculated by dividing by the area of ​​the entire fiber cross section. The area ratios were rounded to one decimal place.

[0082] <Porosity of Region A and Region B> The porosity of each image was calculated by dividing the total area of ​​all pores calculated in the "cross-sectional pore diameter of each region" above by the area of ​​the image used for analysis. As with the cross-sectional pore diameter, the average of five different points was taken as the porosity of that region. Note that the porosity was rounded to one decimal place.

[0083] <Ovality of surface pores> Wet porous fibers were frozen with liquid nitrogen and freeze-dried in a vacuum dryer at 0.1 torr or less for 24 hours to sublimate the water, producing dried samples. A platinum-palladium (Pt-Pd) thin film was then formed on the sample surface by sputtering, creating a surface observation sample. The fiber surface of the surface observation sample was observed and photographed using a scanning electron microscope (Hitachi High-Technologies Corporation, S-5500) at magnifications (10,000–50,000x) sufficient to clearly visualize the contours of the pores on the fiber surface. After imaging, the images were binarized using image analysis software (ImageJ) to identify the surface pores, with the pores appearing black and the structured areas appearing white. If the contrast difference in the electron microscope image made it difficult to binarize the pores and structured areas, a transparent sheet was placed over the printed image and the pores were filled in black with a black pen. The transparent sheet was then copied onto blank paper, and the image was then binarized to display the pores as black and the structured areas as white. Black areas with five or fewer consecutive pixels were treated as white areas, which are structures, because it was impossible to distinguish between noise and holes. Each identified hole was fitted with an ellipse, and the minor and major diameters were measured to calculate the ratio of the major diameter to the minor diameter (hereinafter referred to as the "major diameter / minor diameter ratio"). The major diameter / minor diameter ratios were calculated for 15 or more holes per image, and the average value was used as the major diameter / minor diameter ratio. Taking into account variations, the average value of the major diameter / minor diameter ratios of holes in each image, calculated from nine or more images spaced at least 1 cm apart in the longitudinal direction of the fiber, was used as the ellipticity of the surface holes. The ellipticity of the surface holes was calculated by rounding to one decimal place.

[0084] <Surface pore size> Using the binarized images obtained in the "ellipticity of surface pores" section above, the equivalent circle diameter was calculated from the area of ​​each pore, and the equivalent circle diameters were arranged in descending order. The areas of the pores were added up, starting with the largest equivalent circle diameter. When the sum exceeded half the total area of ​​all pores, the equivalent circle diameter of the pore was taken as the surface pore diameter. Using nine or more images spaced at least 1 cm apart in the longitudinal direction of the fiber, the equivalent circle diameters were calculated in the same manner, and the average was taken as the surface pore diameter. The surface pore diameter was rounded to one decimal place.

[0085] <Surface porosity> The pore size for each image was calculated by dividing the total area of ​​all pores calculated using the "surface pore size" above by the area of ​​the entire image used for analysis. To account for variations, the surface pore size was calculated in the same way using nine or more images spaced at least 1 cm apart in the longitudinal direction of the fiber, as with the surface pore size, and the average value was used as the surface pore size. The surface pore size was calculated by rounding to one decimal place.

[0086] <Amount of negative charge> 0.02 g of the dried porous fiber was weighed and washed with 20 mL of 0.1 mol / L aqueous sodium hydroxide solution, followed by distilled water. After washing, 1% by mass phenolphthalein solution was added dropwise to the distilled water, and washing with distilled water was repeated until the color disappeared. After washing, the porous fiber was freeze-dried for 24 hours in a vacuum dryer at 0.1 torr or less. The porous fiber was then placed in a test tube, 20 mL of 0.001 mol / L aqueous sodium hydroxide solution was added, and the mixture was shaken at 30°C at 150 rpm for 24 hours. After shaking, 10 mL of the supernatant was collected and titrated with 0.001 mol / L hydrochloric acid. Two drops of 0.1% by mass methyl red were added as an indicator. The amount of negative charge was calculated using the following formula (2): Amount of negative charge (μeq / g) = {Volume of supernatant used in titration (mL) × Normality of sodium hydroxide (μeq / mL) – Titration volume (mL) × Normality of hydrochloric acid (μeq / mL)} / Dry mass of porous fiber (g) Equation (2) The negative charge amount was rounded to the nearest whole number.

[0087] <Dispersion component of surface free energy> The freeze-dried porous fiber was packed into a glass column, and the dispersive component of the surface free energy was measured and calculated using a surface free energy analyzer (iGC-SEA) manufactured by Japan Science Core Co., Ltd., following the method described in "Inverse gas chromatography applications: A review" Adv. Colloid Interface Sci., 212, 21-44 (2014). Specifically, linear alkanes with 6 to 9 carbon atoms were used as the test solvent, and the retention volume was calculated from the resulting chromatogram. The dispersive component of the surface free energy was calculated from the retention volume of each alkane.

[0088] <Adsorption performance of porous fibers> Human IL-6 was added to commercially available human plasma to an initial concentration of 25 ng / mL and stirred. 3 The resulting solution was placed in a 15 mL centrifuge tube, to which 2.6 mL of the human plasma was added. Using a seesaw shaker (Wave-SI, manufactured by TAITEC) set to 38 and at the maximum angle (one cycle per 1.7 seconds), the tube was shaken at 37°C for 2 hours. 1 mL of human plasma was sampled before and after contact with the porous fiber. IL-6 was measured by ELISA (HUMAN IL-6 QUANTIKINE QUICKKIT, manufactured by R&D), and LDL cholesterol was measured by the direct method. The IL-6 and LDL cholesterol concentrations C1 and D1 in the human plasma before contact with the porous fiber, and the IL-6 and LDL cholesterol concentrations D2 after contact were determined, and the adsorption amount per fiber volume was calculated using the following formula (3) or (4): IL-6 adsorption per fiber volume (μg / cm 3 )=(C1-C2)×2.6 / 0.19...Equation (3) Amount of LDL cholesterol adsorbed per fiber volume (mg / cm 3 )=(D1-D2)×2.6 / 0.19...Equation (4) Each adsorption amount was measured three times and averaged, and the average was rounded to two decimal places.

[0089] [Example 1] Spinning solution a for forming region A was prepared by mixing 40.9 parts by mass of syn-PMMA with a weight-average molecular weight of 1.4 million, 6.8 parts by mass of iso-PMMA with a weight-average molecular weight of 500,000, and 428 parts by mass of dimethyl sulfoxide (hereinafter referred to as "DMSO") so that the PMMA concentration was 10% by mass, and stirring the mixture at 110°C for 8 hours. The viscosity of the resulting spinning solution at 110°C was 190 poise.

[0090] Similarly, as spinning solution b for forming region B, 31.7 parts by mass of syn-PMMA having a weight average molecular weight of 400,000, 31.7 parts by mass of syn-PMMA having a weight average molecular weight of 1.4 million, 16.7 parts by mass of iso-PMMA having a weight average molecular weight of 500,000, 20 parts by mass of PMMA copolymer having a molecular weight of 300,000 containing 1.5 mol% of sodium parastyrene sulfonate having a sulfo group exhibiting a negative charge, and 376 parts by mass of DMSO were mixed and stirred at 110 ° C. for 8 hours to prepare a spinning solution. The viscosity of the obtained spinning solution at 110 ° C. was 4230 poise.

[0091] Using a concentric sheath-core spinneret, spinning solution a was simultaneously extruded into the air at a rate of 1.0 cc / min, with spinning solution b forming the core and the sheath. The spinneret temperature was 99°C. The length of the free-running section was 550 mm, and the free-running time was 0.72 seconds. The fiber was cooled with cold air at a speed of 7.5 m / sec during free-running. The fiber was then introduced into a coagulation bath containing a 20% by mass DMSO aqueous solution at 43°C. The resulting porous fiber was washed in a 40°C water bath, then introduced into a bath containing a 70% by mass glycerin aqueous solution to retain moisture. It was then passed through a heat treatment bath at 85°C to remove excess glycerin, and wound up at 46 m / min to obtain porous fiber 1.

[0092] [Example 2] The same procedure as in Example 1 was carried out, except that the 85°C heat treatment bath was omitted, to obtain porous fiber 2.

[0093] [Example 3] The same procedure as in Example 1 was carried out except that the coagulation bath temperature was set to 60°C, and porous fiber 3 was obtained.

[0094] [Example 4] The same procedure as in Example 1 was carried out except that the coagulation bath temperature was set to 70°C, to obtain porous fiber 4.

[0095] [Example 5] The same procedure as in Example 1 was carried out except that the spinning solution a was used as the core and the spinning solution b was used as the sheath, to obtain porous fiber 5. [Example 6] To obtain a PMMA concentration of 15% by mass, 31.7 parts by mass of syn-PMMA with a weight average molecular weight of 400,000, 31.7 parts by mass of syn-PMMA with a weight average molecular weight of 1.4 million, 16.7 parts by mass of iso-PMMA with a weight average molecular weight of 500,000, 20 parts by mass of PMMA copolymer with a molecular weight of 300,000 containing 1.5 mol% of sodium parastyrene sulfonate having a negatively charged sulfo group, and 567 parts by mass of DMSO were mixed and stirred at 110 ° C. for 8 hours to prepare spinning solution a3 for forming region A2. The viscosity of the resulting spinning solution c at 110 ° C. was 102 poise.

[0096] The same procedure as in Example 1 was carried out except that the spinning dope b was used as the sheath, the spinning dope c was used as the core, and the coagulation bath temperature was set to 61°C, to obtain porous fiber 6.

[0097] [Example 7] The same procedure as in Example 1 was carried out except that the discharge rates of the spinning dope a were 0.2 cc / min and the spinning dope b were 1.8 cc / min, to obtain porous fiber 7.

[0098] [Example 8] To obtain a PMMA concentration of 18% by mass, 31.7 parts by mass of syn-PMMA having a weight average molecular weight of 400,000, 31.7 parts by mass of syn-PMMA having a weight average molecular weight of 1.4 million, 16.7 parts by mass of iso-PMMA having a weight average molecular weight of 500,000, 20 parts by mass of PMMA copolymer having a molecular weight of 300,000 containing 1.5 mol% of sodium parastyrene sulfonate having a sulfo group exhibiting a negative charge, and 456 parts by mass of DMSO were mixed and stirred at 110 ° C. for 8 hours to prepare spinning solution d for forming region A2. The viscosity of the obtained spinning solution d at 110 ° C. was 590 poise.

[0099] A porous fiber 8 was obtained in the same manner as in Example 1, except that the spinning dope b was used as the core and the spinning dope d was used as the sheath.

[0100] [Comparative Example 1] Fiber 1 was obtained in the same manner as in Example 1, except that only the spinning dope b was used, a circular (single nozzle) spinneret was used, and the discharge rate was set to 2.0 cc / min.

[0101] Comparative Example 2 Fiber 2 was obtained in the same manner as in Example 1, except that only the spinning dope a was used, a circular (single nozzle) spinneret was used, and the discharge rate was set to 2.0 cc / min.

[0102] [Reference example 1] The same operation as in Example 1 was carried out, except that only the spinning solution a was used, a circular (single nozzle) spinneret was used, and the discharge rate was set to 1.0 cc / min. As a result, thread breakage occurred frequently, and fibers could not be obtained.

[0103] Using the obtained porous fibers 1 to 8, the determination of region A, region B and region boundaries, the cross-sectional pore diameter of region A and region B, the variation rate of cross-sectional pore diameter, porosity, the ratio of each region in the fiber cross section, the ellipticity of the surface pores, the surface porosity, the amount of negative charge and the adsorption performance were measured. The results are shown in Tables 1 and 2.

[0104] Using the obtained fibers 1 and 2, the cross-sectional pore size, the variation rate of the cross-sectional pore size, the porosity, the ellipticity of the surface pores, the surface open area, the amount of negative charge, and the surface free energy were measured. variance components of The results of measuring the adsorption performance are shown in Table 3.

[0105] [Table 1]

[0106] [Table 2]

[0107] [Table 3] [Explanation of symbols]

[0108] 100 Virtual Area 1 101 Virtual Area 2 102 Virtual Area Boundary 103 Perpendicular to the tangent at any point on the boundary of an imaginary region 104 Boundary of Area 1 105 Boundary of Area 2 106 Area Boundary 107 Area 1 108 Area 2 109 Sea 110 islands 111 cores 112 sheath

Claims

1. In the fiber cross section, it has a region A and a region B separated by a region boundary, The cross-sectional pore diameter Ap of the region A and the cross-sectional pore diameter Bp of the region B satisfy the relationship Ap>Bp, and A porous fiber, wherein the region A and the region B each have a uniform structure.

2. The porous fiber of claim 1 , wherein said region A is adjacent to the surface.

3. 3. The porous fiber according to claim 1, wherein the ellipticity of the pores on the surface is 2.0 or more.

4. 3. The porous fiber according to claim 1, wherein the pore size at the surface is at least 1.5 times but less than 100 times the cross-sectional pore size of the region adjacent to the surface.

5. 3. The porous fiber according to claim 1, wherein the values ​​of As / S and Bs / S are 0.2 or more, and the value of Xs / S is 0.2 or less, where S is the total area of ​​the fiber cross section, As is the area of ​​the region A, Bs is the area of ​​the region B, and Xs is the area of ​​the region boundary.

6. The porous fiber according to claim 5, which satisfies the following formula (1): As / S+Bs / S+Xs / S=1.0...Formula (1)

7. 3. The porous fiber according to claim 1, wherein the surface porosity is 5% or more.

8. 3. The porous fiber according to claim 1, wherein the region A and the region B form a composite structure of an islands-in-sea type, a core-sheath type, or a multi-layer type.

9. 3. The porous fiber of claim 1 or 2, which is a solid fiber.

10. Ap is 55 nm or more and 350 nm or less, and 3. The porous fiber according to claim 1, wherein the Bp is 4 nm or more and 50 nm or less.

11. 3. The porous fiber according to claim 1, wherein the region A and the region B are made of the same material.

12. The porous fiber according to claim 1 or 2, which contains an amorphous polymer compound.

13. A liquid treatment column incorporating the porous fiber according to claim 1 or 2.

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