Hydrophobic porous hollow fiber membrane

Abstract

To provide a hydrophobic porous hollow fiber membrane which can exhibit high water permeable performance, highly accurate filtration performance and low adsorptivity to protein without using a chemical and a hydrophilic resin even from a dried state.SOLUTION: A hydrophobic porous hollow fiber membrane is composed of an organic polymer resin, wherein in a Log differential pore volume distribution graph of a pore diameter (D) and a pore volume (Vp) measured by a mercury press-in method, a Log differential pore volume (dVp / dlogD) has a peak of 0.2 cm3 / g or more with each of the pore diameter (D) of 0.01 μm or more and less than 0.2 μm, and the pore diameter of 0.2 μm or more and less than 10 μm.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to microfiltration membranes and ultrafiltration membranes used in water treatment applications such as wastewater treatment, water purification treatment, and industrial water production, as well as applications such as food and pharmaceutical production.

Background Art

[0002] Separation membranes such as microfiltration membranes and ultrafiltration membranes are used for purposes such as clarification, concentration, and separation in water treatment applications and food and pharmaceutical applications. In recent years, with the expansion of the application range of separation membranes, the application to filtration liquids with high filtration difficulty and applications requiring high-precision separation has been studied, and the demand for separation membranes that achieve both filtration performance and separation performance has been increasing even more.

[0003] When the separation membrane is used in water treatment applications such as water purification treatment, since the amount of water to be treated is large, as the separation membrane, a porous hollow fiber membrane capable of increasing the effective membrane area per unit volume is often adopted. In addition, due to its shape, the porous hollow fiber membrane has high pressure resistance, can apply a higher primary filtration pressure than flat membranes, and is also preferably adopted because a large amount of treated water can be obtained. Furthermore, if the water permeation performance of the hollow fiber membrane can be increased, the required membrane area will be reduced, the device will be compact, and the equipment cost can be saved, which is also advantageous in terms of membrane replacement cost and the installation floor area of the plant.

[0004] In addition, in the water treatment field, the requirements for cost are also strict, and these requirements extend not only to the price of separation membranes and modules but also to weight reduction during transportation. In order to reduce weight, it is necessary not to enclose liquid in the module, that is, for water permeability to be easily exhibited at the destination. This problem is usually solved by hydrophilic treatment using chemicals or hydrophilic resins.

[0005] In particular, in separation membranes made of hydrophobic organic polymer resins, water does not easily penetrate into the pores, so a treatment to efficiently replace the contents of the pores with water, i.e., a hydrophilization treatment, is usually necessary. Methods for hydrophilizing separation membranes include, for example, immersing the separation membrane in ethanol and then replacing it with water (Patent Document 1), or filling the separation membrane with an aqueous surfactant solution beforehand and then drying it to retain the surfactant on the pore walls (Patent Document 2). In addition, a method has been proposed to improve the wettability to water by mixing a hydrophilic resin with the resin material of the separation membrane (Patent Document 3).

[0006] Furthermore, separation membranes made of hydrophobic organic polymer resins generally have the problem of being more susceptible to contamination of the membrane surface due to hydrophobic interactions compared to separation membranes made of hydrophilic organic polymer resins. In particular, when used for the separation and purification of physiologically active substances such as proteins in the manufacturing processes of pharmaceuticals and food products, the adsorption of proteins and other substances to the separation membrane surface leads to a decrease in recovery rate and also easily causes a rapid decrease in filtration rate due to blockage of the pores of the separation membrane. In response to this, a method has been proposed in which hydrophilic organic polymer resins are mixed into the resin material of the separation membrane to suppress adsorption. However, because hydrophilic organic polymer resins have inferior chemical resistance compared to hydrophobic organic polymer resins, it has been difficult to suppress the adsorption of proteins and other substances and to stably perform separation and purification. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Application Publication No. 2006-63095 [Patent Document 2] Japanese Patent Publication No. 63-277251 [Patent Document 3] International Publication No. 2015 / 008668 [Overview of the Initiative] [Problems that the invention aims to solve]

[0008] Methods using chemicals such as alcohol or surfactants, as described in Patent Documents 1 and 2, may result in residual chemicals in the separation membrane contaminating the treated water, raising concerns about the safety of the treated water, especially for drinking water applications. While the method of mixing a hydrophilic resin into the separation membrane described in Patent Document 3 allows for hydrophilization without the use of chemicals, many hydrophilic resins have poor chemical resistance, leading to durability issues.

[0009] The object of the present invention is to provide a hydrophobic porous hollow fiber membrane that, even when dry, allows treated water to penetrate the porous hollow fiber membrane without the use of chemicals or hydrophilic resins, thereby exhibiting high water permeability, high-precision filtration performance, and low adsorption to proteins. [Means for solving the problem]

[0010] As a result of diligent research to solve the aforementioned problems, the inventors of the present invention have found that even hydrophobic organic polymer resins can solve the above problems by having a specific porous structure and pore state, and have completed the present invention.

[0011] In other words, the present invention has the following configuration. [1] A hydrophobic porous hollow fiber membrane made of organic polymer resin, in the log differential pore volume distribution graph of pore diameter (D) and pore volume (Vp) measured by mercury intrusion method, the pore diameter (D) is in the range of 0.01 μm or more and less than 0.2 μm, and the pore diameter is in the range of 0.2 μm or more and less than 10 μm, and the log differential pore volume (dVp / dlogD) is 0.2 cm 3 A hydrophobic porous hollow fiber membrane characterized by having peaks of 1 / g or more. [2] The hydrophobic porous hollow fiber membrane according to [1], characterized in that the permeability of pure water under a filtration pressure of 100 kPa at 25°C satisfies formula (1). (Dry permeability r / Wet permeability w) × 100 ≥ 80 (%) ... Equation (1) In equation (1), the dry permeability performance r is the pure water permeability performance (m) of a hollow fiber membrane that has been dried at 30°C for 24 hours or more. 3 / m 2 / (hr) represents the wet permeability performance w, which is the pure water permeability performance (m 3 / m 2 / (hr) after soaking in 50% ethanol for 20 minutes and then performing water permeation for 20 minutes through the wet hollow fiber membrane.

[0012] [3] The hydrophobic porous hollow fiber membrane is the hydrophobic porous hollow fiber membrane described in [1] or [2], where the contact angle between the membrane surface and water is 70° or more and 130° or less in the range of 2% to 10% by weight of water based on 100% by weight of the hollow fiber membrane. [4] The average pore diameter (d1) in the range where the pore diameter (D) is 0.01 μm or more and less than 0.2 μm is 0.02 μm or more and 0.08 μm or less, and the pore specific surface area Sp 0.01-0.2 (m 2 / g) and the pore volume Vp 0.01-0.2 (cm 3 / g) satisfy the relationship of formula (2), which is the hydrophobic porous hollow fiber membrane described in any one of [1] to [3]. Sp 0.01-0.2 / Vp 0.01-0.2 ≥ 100 ··· Formula (2) In formula (2), Sp 0.01-0.2 represents the pore specific surface area (S) in the range where the pore diameter (D) obtained by mercury intrusion porosimetry is 0.01 μm or more and less than 0.2 μm, and Vp 0.01-0.2 represents the pore volume (Vp) in the range where the pore diameter (D) obtained by mercury intrusion porosimetry is 0.01 μm or more and less than 0.2 μm. [5] The hydrophobic porous hollow fiber membrane is the hydrophobic porous hollow fiber membrane described in [1] to [4], which has a layer of spherical structures on the surface side of at least one surface. [6] The average diameter of the spherical bodies constituting the spherical structures is 1 μm or more and 15 μm or less, which is the hydrophobic porous hollow fiber membrane described in [1] to [5].

[0013] [7] The hydrophobic porous hollow fiber membrane has a dry permeability performance r of pure water at 25 °C under a filtration pressure of 100 kPa of 3.0 m 3 / m 2 / hr or more and 20.0 m 3 / m 2A hydrophobic porous hollow fiber membrane according to any one of [1] to [6], characterized in that it is less than or equal to / hr, has a porosity of 50% to 70%, and has a fractionated particle size of 0.1 μm to 1.0 μm. [8] A hydrophobic porous hollow fiber membrane according to any one of [1] to [7], characterized in that the organic polymer resin is a polyvinylidene fluoride resin. [9] A method for filtering a protein-containing solution, comprising using a hydrophobic porous hollow fiber membrane as described in any of [1] to [8]. A water purifier cartridge equipped with a method for filtering a hydrophobic porous hollow fiber membrane or protein-containing solution as described in any of

[10] [1] to [9]. [Effects of the Invention]

[0014] The hydrophobic porous hollow fiber membrane of the present invention allows for liquid passage from a dry state and exhibits high water permeability performance, without the need for a pre-hydrophilization process using agents such as alcohol or surfactants, or for prior hydrophilization treatment of separation membranes using hydrophilic resins.

[0015] Therefore, since processes and treatments related to hydrophilization are unnecessary, there are no safety issues such as chemicals used in the hydrophilization process mixing into the treated water, and concerns about a decrease in the chemical resistance of the porous hollow fiber membrane due to the hydrophilic resin are also eliminated.

[0016] Furthermore, a hydrophobic porous hollow fiber membrane capable of exhibiting low protein adsorption can be obtained, suppressing the adsorption of proteins and other substances, and enabling stable separation and purification. [Brief explanation of the drawing]

[0017] [Figure 1] This graph shows the logarithmic differential pore volume distribution of the hydrophobic porous hollow fiber membrane of the present invention. [Figure 2] This is a perspective view of a porous hollow fiber membrane according to an embodiment of the present invention. [Figure 3] This is a perspective view of a spherical structure according to an embodiment of the present invention. [Figure 4] This is a schematic diagram illustrating the pressure loss at the pore inlet. [Modes for carrying out the invention]

[0018] Embodiments of the present invention will be described in detail below with reference to the drawings, but the present invention is not limited in any way thereto. <Organic polymer resin for porous hollow fiber membranes> In embodiments of the present invention, the hydrophobic porous hollow fiber membrane is made of an organic polymer resin. Hydrophobicity means having a low affinity for water. The surface of the hydrophobic porous hollow fiber membrane of the present invention repels water easily and exhibits water repellency.

[0019] Examples of organic polymer resins include, but are not limited to, individual components such as polytetrafluoroethylene, polyvinylidene fluoride, polylactic acid, polyhydroxyacetic acid, polycaprolactone, polyethylene adipate, and other polyesters, polyurethanes, poly(meth)acrylic acid esters, polyvinyl acetals, polyamides, polystyrenes, polysulfones, cellulose derivatives, polyphenylene ethers, and polycarbonates, as well as polymer alloys or blends of two or more polymers selected from these, or copolymers of monomers that form the above polymers. Among these, fluorine-based resins such as polytetrafluoroethylene and polyvinylidene fluoride, or sulfone-based resins such as polysulfone and polyethersulfone, are used as resin components with excellent heat resistance and chemical resistance. In particular, polyvinylidene fluoride-based resins are preferred because they have high compatibility with solvents and allow for the easy production of a uniform manufacturing stock solution. A polyvinylidene fluoride resin refers to a resin containing at least one of a vinylidene fluoride homopolymer and a vinylidene fluoride copolymer. A polyvinylidene fluoride resin may contain multiple types of vinylidene fluoride copolymers.

[0020] Vinylidene fluoride copolymers are polymers having a vinylidene fluoride residue structure, and are typically copolymers of vinylidene fluoride monomer with other fluorinated monomers. Examples of such copolymers include copolymers of vinylide fluoride with one or more monomers selected from vinyl fluoride, tetrafluoroethylene, hexafluoropropylene, and trifluoroethylene chloride.

[0021] Furthermore, the weight-average molecular weight of the polyvinylidene fluoride resin can be appropriately selected depending on the required strength and water permeability of the separation membrane. However, as the weight-average molecular weight increases, water permeability decreases, and as the weight-average molecular weight decreases, strength decreases. For this reason, a weight-average molecular weight of 50,000 to 1,000,000 is preferable. In particular, for water treatment applications where the porous hollow fiber membrane is exposed to chemical washing, a weight-average molecular weight of 100,000 to 700,000 is preferable, and more preferably 150,000 to 600,000 is preferable.

[0022] The porous hollow fiber membrane preferably contains polyvinylidene fluoride resin as its main component, and the proportion of polyvinylidene fluoride resin in the hollow fiber membrane is preferably 80% by weight or more, more preferably 90% by weight or more, and even more preferably 95% by weight or more.

[0023] <Average pore diameter of porous hollow fiber membranes> The average pore diameter of a porous hollow fiber membrane is the average diameter of the voids and pores in the hollow fiber membrane. In the hydrophobic porous hollow fiber membrane of the present invention, the log differential pore volume (dVp / dlogD) of the pore volume (Vp) in the range of pore diameter (D) from 0.01 μm to less than 0.2 μm and the pore volume (Vp) in the range of pore diameter (D) from 0.2 μm to less than 10 μm, measured by the mercury intrusion method, is 0.2 cm³. 3 Characterized by having peaks of 0.01 μm or more / g, the porous hollow fiber membrane of the present invention has two types of pores that differ in size and type. Here, the average pore diameter (d1) in the range of pore diameter (D) from 0.01 μm to less than 0.2 μm is preferably 0.08 μm or less, and the average pore diameter (d2) in the range of pore diameter (D) from 0.2 μm to less than 10 μm is preferably 1.2 μm or more.

[0024] In the mercury intrusion method, pressure p is applied to the mercury so that it is injected into the pores of a porous hollow fiber membrane. The pore distribution function F(r) is then determined from equation (3) below by measuring the change in the volume of mercury in the cell, dV, in response to the pressure increment dp.

[0025]

number

[0026] Here, r represents the pore radius, σ represents the surface tension of mercury (0.484 N / m), and θ represents the contact angle of mercury on a flat porous membrane surface (141.3°).

[0027] The average pore diameter (d) can be determined by the following formula (4). The average pore diameter for the two types of pores is determined in two intervals, from 0.01 μm to 0.2 μm and from 0.2 μm to 10 μm, according to the respective pores.

[0028]

number

[0029] <Specific surface area and pore volume of porous hollow fiber membranes> As described above, the porous hollow fiber membrane of the present invention has a pore volume (Vp) in the range of pore diameter (D) of 0.01 μm or more and less than 0.2 μm, and a pore volume (Vp) in the range of pore diameter (D) of 0.2 μm or more and less than 10 μm, with a log differential pore volume (dVp / dlogD) of 0.2 cm³. 3 A characteristic feature is that each peak has a value greater than or equal to / g. Figure 1 shows a graph of the Log differential pore volume distribution of the porous hollow fiber membrane of the present invention. The Log differential pore volume (dVp / dlogD) is calculated by dividing the differential pore volume (dVp) by the difference value dlogD, which is the logarithmic difference of the pore diameter, and plotting this value against the pore diameter of each interval. 3A high value of / g indicates the presence of many pores of a specific pore diameter. In other words, the porous hollow fiber membrane of the present invention is characterized by having a large number of pores in both the small pore diameter range (D) of 0.01 μm to less than 0.2 μm and the large pore diameter range (D) of 0.2 μm to less than 10 μm.

[0030] Here, pore peaks in the range of pore diameters between 0.01 μm and less than 0.2 μm suggest that these are not gaps (pores) between the structures constituting the porous membrane, but rather micropores present on the surface of the structures. The following explanation uses pore diameter measurement data obtained by the mercury intrusion method.

[0031] In the measurement of pore diameter by mercury intrusion according to the present invention, the pore volume Vp (cm³) is measured in the range of pore diameter 0.01 μm or more and less than 10 μm. 3 ( / g) and specific surface area Sp(m²) 2 The specific surface area Sp is measured (per g). Here, it can be seen that the larger the specific surface area Sp is relative to the pore volume Vp, the smaller the pore diameter and the larger the specific surface area of ​​the structure.

[0032] Furthermore, a large specific surface area Sp / pore volume Vp ratio in the pore diameter range of 0.01 μm to less than 0.2 μm indicates the presence of micropores in the porous hollow fiber membrane structure. Since the mercury intrusion method measures only pores into which mercury can be injected, it can be said that micropores exist on the surface of the structure that comes into contact with the treated liquid, forming irregularities on the structure. The data shown in the surface roughness measurement described later, which is several μm or larger, also suggests that pores with diameters of 0.01 μm to less than 0.2 μm exist on the surface of the structure.

[0033] The porous hollow fiber membrane of the present invention has a specific surface area Sp in the range of pore diameter 0.01 μm or more and less than 0.2 μm. 0.01-0.2 (m 2 ( / g) and pore volume Vp 0.01-0.2 (cm 3 The relationship / g) is Sp 0.01-0.2 / Vp 0.01-0.2It is preferable that the specific surface area per unit volume is 100 or more in the fine region of less than 0.2 μm, and by having many fine irregularities on the surface of the structure constituting the porous hollow fiber membrane, the water repellency can be further enhanced. On the other hand, the specific surface area Sp in the range of pore diameter 0.2 μm to less than 10 μm 0.2-10 (m 2 ( / g) and pore volume Vp 0.2-10 (cm 3 The relationship between / g) is Sp 0.2-10 / Vp 0.2-10 A value of ≤ 5 is preferred. In the relatively large pore region of 0.2 μm or more, the specific surface area per unit volume is small, at 5 or less, and the structure has large voids between the structural elements, which allows for higher water permeability. In other words, it is preferable that the porous hollow fiber membrane of the present invention has large voids (pores) between the structural elements macroscopically, while having fine irregularities on the surface of the structural elements microscopically. The porous hollow fiber membrane of the present invention exhibits high hydrophobicity. However, it is known that highly water-repellent solid surfaces have fine irregularities, and the contact angle θ of the solid surface increases, particularly when it is 90° or greater, resulting in a larger contact angle and higher water repellency. Furthermore, it is known that having fine irregularities on a water-repellent surface reduces resistance to liquid flow. References include "Fractal Surface Structure and the Physics of Hydrophilicity and Hydrophobicity," Journal of The Vacuum Society of Japan, 2015, Vol. 58, No. 11, pp. 424-430, and "Study on Resistance Reduction Effect by Water-Repellent Microstructures," Transactions of the Japan Society of Mechanical Engineers (B), 2009, Vol. 75, No. 758, pp. 1960-1966.

[0034] In other words, the hydrophobic porous hollow fiber membrane of the present invention has relatively large voids (pores) of 0.2 μm to less than 10 μm, and also has fine irregularities on the surface of the structure forming the porous hollow fiber membrane, thereby enhancing water repellency and reducing contact between the membrane surface and the liquid to be filtered. This allows the membrane to exhibit high water permeability from a dry state without the need for a hydrophilization process, and also suppresses protein adsorption.

[0035] The porous hollow fiber membrane of the present invention has a log differential pore volume (dVp / dlogD) of 0.2 cm³ for both the pore volume (Vp) in the range of pore diameter (D) from 0.01 μm to less than 0.2 μm and the pore volume (Vp) in the range of pore diameter (D) from 0.2 μm to less than 10 μm. 3 While the characteristic feature is having peaks of 1 / g or more, even with a separation membrane having a broad pore size distribution that does not have specific peaks in this range, it is possible to calculate the average pore diameter (d1, d2), specific surface area (Sp), and pore volume (Vp). However, since the average pore diameter is large and the specific surface area (Sp) / pore volume (Vp) is also small, the effects of the present invention cannot be obtained.

[0036] Furthermore, the porous hollow fiber membrane of the present invention exhibits the maximum peak value in the log differential pore volume distribution where the pore diameter is in the range of 0.01 μm or more and less than 0.2 μm, at the pore diameter (Dp 0.01-0.2 ) and full width at half maximum (FWHM) 0.01-0.2 The relationship between Dp 0.01-0.2 / FWHM 0.01-0.2 Preferably ≥0.5, Dp 0.01-0.2 / FWHM 0.01-0.2 ≥0.7 is more preferable, Dp 0.01-0.2 / FWHM 0.01-0.2 A value of ≥0.9 is even more preferable. A larger value indicates a sharper pore size distribution in the fine region of less than 0.2 μm, which leads to higher water repellency on the surface of the structure, enabling stable high water permeability and adsorption suppression.

[0037] Furthermore, the porous hollow fiber membrane of the present invention exhibits the maximum peak value in the log differential pore volume distribution in the range of pore diameters from 0.2 μm to less than 10 μm, at the pore diameter (Dp 0.2-10 ) and full width at half maximum (FWHM) 0.2-10 The relationship between Dp 0.2-10 / FWHM 0.2-10 ≥1.2 is preferred, Dp 0.2-10 / FWHM 0.2-10 ≥1.6 is more preferable, Dp 0.2-10 / FWHM 0.2-10A value of ≥2.0 is even more preferable. A larger value in this category results in a sharp pore size distribution in the relatively large pore region of 0.2 μm or larger, enabling both high water permeability and fractionation performance.

[0038] <Spherical structure on the surface of a porous membrane> The hydrophobic porous hollow fiber membrane of the present invention preferably has a layer of spherical structures on the membrane surface side of the primary filtration side.

[0039] A spherical structure is a structure in which spherical bodies are connected three-dimensionally in a cross-section perpendicular to the length direction of the hollow fiber membrane (i.e., parallel to the radial direction of the hollow fiber membrane). The spherical bodies are approximately spherical or approximately elliptical in shape, and the connection state is not particularly limited; two or more adjacent spherical bodies may be connected. The shape of the cross-section parallel to the length direction of the porous hollow fiber membrane is not particularly limited and can take any shape, such as approximately circular or columnar. A columnar shape is a solid component with an aspect ratio (long side length / short side length) of 3 or more in a cross-section parallel to the length direction of the porous hollow fiber membrane, and typically has a structure in which many columnar solid components are connected by sharing a part of each other. When columnar solid components are present in the length direction of the porous hollow fiber membrane, the physical strength is higher. The specific method for measuring the average diameter of the spherical bodies will be described later.

[0040] By incorporating such a layer of spherical structures into a hydrophobic porous hollow fiber membrane, voids are formed between the spherical solid bodies, i.e., within the columnar structures. These voids are less prone to contraction, thus maintaining high water permeability. Furthermore, the formation of these spherical structures allows for higher strength compared to porous hollow fiber membranes with a mesh-like structure.

[0041] Furthermore, in the hydrophobic porous hollow fiber membrane of the present invention, it is preferable that the spherical bodies and their spherical structures contain a polyvinylidene fluoride-based resin. A portion of the porous hollow fiber membrane is illustrated in Figure 2. The primary filtration surface of the porous hollow fiber membrane refers to the outer surface 11 and the inner surface 12 in Figure 2. The porous hollow fiber membrane of the present invention has a layer of spherical structures on the surface side of the outer surface 11 and / or the inner surface 12.

[0042] The interior space between the outer surface 11 and the inner surface 12 of the porous hollow fiber membrane is not particularly limited in structure, but it should support a layer of spherical structures composed of spherical bodies. The surface structure may also extend into the interior. In this invention, the surface side of at least one of the surfaces means that a layer of spherical structures exists on at least one of the outer surface 11 and the inner surface 12 of the hollow fiber membrane, and at least on the surface side.

[0043] A portion of the spherical structure is schematically shown in Figure 3. In the spherical structure 2 of Figure 3, multiple spherical bodies 20 are connected. The spherical bodies 20 are approximately spherical or approximately elliptical in shape. As shown in Figure 3, since the spherical bodies 20 are connected to each other, it is not possible to observe the entire spherical or ellipsoidal surface. However, the spherical shape of each spherical body can be extrapolated from the shape revealed in the outer diameter of each individual spherical body.

[0044] The connections between the spherical bodies may be formed by direct adhesion between the spherical bodies, or by non-spherical portions between the spherical bodies, such as constrictions 21 of the spherical bodies.

[0045] The pores 22 between the spherical bodies are the gaps, or pores, between the solid parts of the spherical structure described above. In Figure 3, the pores between the spherical bodies are not completely closed off, but a pore is defined as any space surrounded by spherical bodies. Furthermore, the surface of each spherical body constituting the spherical structure has numerous fine bumps and dips, and these minute bumps and dips form the pores 23 on the surface of the spherical bodies.

[0046] The average diameter of the spherical body is preferably in the range of 1 to 15 μm, more preferably in the range of 1.5 to 10 μm, and even more preferably in the range of 2 to 8 μm.

[0047] The hydrophobic porous membrane of the present invention has two pore diameters, D, in the range of 0.01 μm to less than 0.2 μm and D, and a log differential pore volume (dVp / dlogD) of 0.2 cm³. 3Although there are peaks of 0 / g or more, the pores 22 between the spheres are targeted in the range of pore diameter from 0.2 μm to less than 10 μm. Furthermore, the fine irregularities on the surface of the spheres, i.e., the pores 23 on the surface of the spheres, are targeted in the range of pore diameter from 0.01 μm to less than 0.2 μm.

[0048] The diameter of the spherical bodies constituting the aforementioned spherical structure is determined by taking photographs of the cross-section of the hollow fiber membrane using a scanning electron microscope or the like at a magnification that allows the spherical structure to be clearly observed, measuring the diameter R of 10 or more, preferably 20 or more, arbitrary spherical bodies, and averaging the results.

[0049] When calculating the average diameter of the spherical bodies, for spherical bodies connected by a constriction 21 (spherical bodies whose outlines can be seen), a straight line is drawn in the direction of the major axis, and the size of this line is taken as the diameter R.

[0050] In the case of connected spheres, as shown in Figure 3, a straight line is drawn through the center in the direction of the major axis of the spheres, excluding the connecting parts between the spheres, and its size is defined as the diameter R. At this time, there are two points on the contour of the spheres where the line drawn in the direction of the major axis intersects, and the tangents at each intersection point are approximately parallel and opposite each other. In the case of connected spheres, if the center of one sphere overlaps with that of an adjacent sphere, the contours are not approximately parallel and opposite each other (corresponding to the symbol X1 in Figure 3), and the diameter of the sphere is not measured.

[0051] Furthermore, if two tissues appear to overlap in the depth direction of the electron microscope image, the diameter of the spherical body of the tissue further back (corresponding to symbol X2 in Figure 3) is not measured. Instead, the contour line of the spherical body in the foreground is used as the boundary line between the two spherical bodies, and only the diameter of the spherical body in the foreground is measured and calculated.

[0052] Furthermore, if the tissue is interrupted at the edge of the electron microscope image used for the determination, the diameter of the sphere at that edge will not be measured. The larger the average diameter of the spheres measured in this way, the larger the pores 22 between the spheres constituting the spherical structure tend to be.

[0053] The density of the spherical bodies is 10 3 ~108 pieces / mm 2 A range of 10 is preferred, and more preferably 10 4 ~10 6 pieces / mm 2 It is within the range of 10. The density of the spherical bodies is 10 3 pieces / mm 2 This allows for high strength and pressure resistance, and 10 8 pieces / mm 2 The following conditions result in high water permeability. Furthermore, the density of the spherical bodies is determined by taking photographs, similar to the diameter measurement, and extrapolating the spherical shape of each individual spherical body from the shape revealed by its outer diameter, thereby measuring the number of spherical bodies per unit area.

[0054] <Pressure loss reduction effect due to spherical structure> The hydrophobic porous hollow fiber membrane of the present invention preferably has a layer of spherical structures made of organic polymer resin on the primary side surface of the filtration. When considering the flow of liquid from the surface to the interior of the porous membrane during liquid filtration, the flow path narrows rapidly at the pore portion of the porous membrane surface, which is the inlet, resulting in a pressure loss at the inlet and obstructing the flow. In other words, the spherical shape of each spherical body constituting the spherical structure and the pore state between the spherical bodies of the spherical structure determine the shape of the inlet portion of the pores. This pressure loss at the inlet is expressed by the following equation (5) and is known to depend on the loss coefficient (ζ) of the inlet. ΔP = ζ × V 2 / 2g ··································Formula (5) Here, ΔP: pressure loss at the inlet, ζ: loss coefficient at the inlet, V: flow velocity, g: acceleration due to gravity.

[0055] As shown in Figure 4, the loss coefficient (ζ) is a value determined by the shape of the flow channel. When the wall surface of the inlet is at a corner (90°), ζ = 0.5 (Figure 4(a)), but as the wall surface end becomes circular and the radius of curvature increases, the loss coefficient decreases (Figures 4(b) to (d)).

[0056] In other words, in the hydrophobic porous hollow fiber membrane of the present invention, when spherical bodies of a spherical structure are present in the surface layer on the primary side of filtration, the pores of the spherical structure have low pressure loss at the inflow and a structure that does not obstruct the flow of liquid. By having such spherical bodies and spherical structures in the surface layer, liquid flows more easily into the porous hollow fiber membrane, and the effect of exhibiting high water permeability from a dry state without hydrophilization treatment can be further enhanced.

[0057] Regarding the relationship between the pores (gaps) between the spherical bodies of the spherical structure, the greater the curvature of each spherical body, that is, the larger the diameter of the spherical body, the larger the pores (gaps) between the spherical bodies become, and the higher the water permeability can be. However, if the diameter of the spherical bodies is too large, the pores become too large, and the fractionation performance decreases. On the other hand, if the diameter of the spherical bodies is too small, the pores become small, and the water permeability decreases. The spherical bodies and spherical structures of the present invention are preferably spherical bodies and spherical structures having a pore diameter in the range of 0.2 μm or more and less than 10 μm.

[0058] <Contact angle and roughness of the surface of porous hollow fiber membrane> The porous hollow fiber membrane of the present invention has a large contact angle with water and strong hydrophobicity. Specifically, in the porous hollow fiber membrane of the present invention, when the moisture content is in the range of 2% to 10% by weight relative to 100% by weight of the hollow fiber membrane, the contact angle between the membrane surface and water is 70° to 130°, preferably 80° to 125°, and more preferably 90° to 120°. Being within this range enhances the effects of the present invention.

[0059] The pores on the surface of a porous hollow fiber membrane can be quantified by evaluating the surface roughness. Specifically, the average length RSm in the surface roughness evaluation of the porous hollow fiber membrane serves as an indicator of the average spacing between spherical and columnar structures, and the root mean square height Rq serves as an indicator of the depth of the gaps between spherical and columnar structures. Specifically, the average length RSm is 5 μm to 20 μm, preferably 7 μm to 18 μm, and more preferably 9 μm to 16 μm, and the root mean square height Rq is 0.5 μm to 5 μm, preferably 1.0 μm to 4 μm, and more preferably 1.5 μm to 3 μm. When the surface of a hydrophobic porous hollow fiber membrane is within this range of macroscopic roughness and there is an appropriate spacing between structures, high water permeability and fractionation performance can be achieved.

[0060] In particular, when the hydrophobic porous hollow fiber membrane of the present invention has a layer of spherical structures on the primary surface of the filter, it is preferable because the spherical bodies are not too close together, and the gaps between the spherical and columnar structures extend from the surface to a deep position, thereby reducing the pressure loss at the inlet.

[0061] The average length RSm and root-square height Rq of the porous hollow fiber membrane surface can be measured, for example, by performing a line roughness measurement (JIS B 0601-2001) using a laser microscope manufactured by Keyence Corporation (Keyence Corporation, VK-7200).

[0062] <Porosity of porous hollow fiber membranes> The hydrophobic porous hollow fiber membrane of the present invention exhibits high water permeability, so a porosity of 50% to 70% is preferred, and more preferably 55% to 65%. If the porosity is too small, it is difficult to obtain sufficient water permeability, and if it is too large, the strength and pressure resistance of the membrane will decrease, and deformation (breakage, bending, crushing) of the porous hollow fiber membrane will easily occur during membrane filtration, resulting in poor durability in actual use.

[0063] The porosity is determined by the bulk density Da before mercury is injected into the communication hole using the mercury injection method, and then calculated using the following formula. Da = (m0 - m1) / ρ Here, m0 represents the weight of mercury when an empty measuring cell is filled with mercury, m1 represents the weight of mercury when the sample is placed in the cell and mercury is introduced into the cell, and ρ represents the density of mercury. Furthermore, the true density Dt can be determined from the volume change V1 before and after mercury is injected and the communication pores are completely replaced with mercury, using the following formula. Dt = W / (W / Da - V1) Here, W represents the weight of the sample. The porosity is a value calculated using equation (6). Porosity (%) = (Dt-Da) / Dt ×100...Equation (6).

[0064] <Fractional Particle Size> The fractional particle diameter of the porous hollow fiber membrane of the present invention is preferably 0.1 μm or more and 2.0 μm or less, more preferably 0.2 μm or more and 1.5 μm or less, and even more preferably 0.3 μm or more and 1.0 μm or less. If the fractional particle diameter is smaller than 0.1 μm, fine particle removal is possible, but the permeation resistance of the membrane pores increases, making it difficult to obtain a porous membrane with high permeability suitable for practical use. On the other hand, if the fractional particle diameter is larger than 2.0 μm, there is a higher possibility that components such as turbidity will leak into the treated water.

[0065] <Pure water permeation performance> The hydrophobic porous hollow fiber membrane of the present invention preferably satisfies the following formula (7) when filtering from a dry state without a hydrophilization process, in terms of the permeability of pure water at 100 kPa and 25°C. (Dry permeability r / Wet permeability w) × 100 ≥ 80 (%) ... Formula (7) In the above formula, the permeability performance r during drying is equal to the pure water permeability performance (m) of the dry hollow fiber membrane. 3 / m 2 / hr) represents the permeability performance when wet w is the pure water permeability performance (m) of the wet hollow fiber membrane. 3 / m 2 This represents ( / hr). The larger the percentage (%) in equation (7), the smaller the difference between the dry permeability performance r and the wet permeability performance w. In other words, it indicates that porous hollow fiber membranes, which are hydrophobic and repel water easily, are permeable to water easily.

[0066] The drying method for the dried hollow fiber membrane is not particularly limited, but the moisture content of the dried hollow fiber membrane should be in the range of 2% to 10% by weight relative to 100% by weight of the porous hollow fiber membrane, and is generally around 4-6% by weight. The moisture content is calculated from the weight of the dried hollow fiber membrane and the weight of the oven-dried hollow fiber membrane. The weight of the oven-dried hollow fiber membrane is taken as the weight of the hollow fiber membrane after drying in a vacuum dryer at 30°C for 24 hours or more, and the moisture content is calculated from the difference between the weight of the dried hollow fiber membrane and the oven-dried hollow fiber membrane. The moisture content (by weight) is then calculated by dividing the moisture content by the weight of the dried hollow fiber membrane and multiplying by 100.

[0067] In the present invention, a dry hollow fiber membrane refers to a hollow fiber membrane in a dry state obtained by drying a porous hollow fiber membrane at 30°C for 24 hours or more, and a wet hollow fiber membrane refers to a hollow fiber membrane in a wet state obtained by immersing it in 50% ethanol for 20 minutes followed by washing it with running water for 20 minutes.

[0068] Furthermore, it is preferable that the hydrophobic porous hollow fiber membrane of the present invention increases in the value of equation (7) above by increasing the filtration pressure. Specifically, it is preferable that the value of equation (7) for the pure water permeability performance at 200 kPa and 25°C be ≥ 85 (%), and that the value of equation (7) for the pure water permeability performance at 300 kPa and 25°C be ≥ 90 (%). This is thought to be because increasing the filtration pressure allows the internal flow channels of the hydrophobic porous hollow fiber membrane to be used more efficiently.

[0069] The hollow fiber membrane of the present invention has a pure water permeability of 3.0 m³ under a pressure of 100 kPa and at 25°C. 3 / m 2 / hr or more 20.0m 3 / m 2 Less than / hr, preferably 4.0m 3 / m 2 / hr or more 18m 3 / m 2 Less than / hr, more preferably 5.0m 3 / m 2 / hr or more 15.0m 3 / m 2 It is preferable that the range be less than or equal to / hr.

[0070] Conventionally, many hydrophobic porous hollow fiber membranes exhibit a significant decrease in water permeability after drying compared to before drying. Therefore, it was necessary to use chemicals such as alcohol or surfactants during wetting, or to mix hydrophilic resins into the porous hollow fiber membrane material. However, the porous hollow fiber membrane of the present invention eliminates the need for such treatments, resulting in advantages in terms of process reduction, cost, and chemical resistance.

[0071] The outer diameter and thickness of the hydrophobic porous hollow fiber membrane of the present invention should be determined so that the water permeability of the membrane module reaches the target value, while not impairing the durability of the membrane (breaking strength, bending resistance, and pressure resistance). In other words, a smaller outer diameter allows for an increase in the number of fibers packed, which is advantageous in terms of membrane surface area, but it has the problem of increasing pressure loss when liquid passes through the hollow section. Also, in external pressure type hollow fiber membrane modules, the hollow fiber membrane may buckle if the intermembrane pressure difference increases during filtration operation, but the larger the outer diameter / inner diameter ratio of the hollow fiber membrane, the higher the pressure resistance and the less likely buckling is to occur.

[0072] Therefore, as a rough guideline, the outer diameter of the hollow fiber membrane is preferably 0.3 to 3 mm, more preferably 0.4 to 2.5 mm, and even more preferably 0.5 to 2.0 mm. The outer diameter / inner diameter ratio is preferably 1.5 or higher, more preferably 1.8 or higher, and even more preferably 2.0 or higher.

[0073] The hydrophobic porous hollow fiber membrane of the present invention preferably has virtually no macrovoids. Here, a macrovoid is a pore with a major axis of 50 μm or more observed in the substantial portion of the membrane in the cross-section of the hollow fiber membrane. "Virtually no macrovoids" means 10 macrovoids / mm in the cross-section. 2 More preferably 5 pieces / mm 2 The following are preferable, and it is most desirable to have none at all.

[0074] The tensile strength of the hydrophobic porous hollow fiber membrane of the present invention is 0.2 to 2 kg / mm². 2 Preferably 0.3 to 1.5 kg / mm 2 More preferably 0.4 to 1 kg / mm 2It is preferable that the tensile elongation is within the range of 10-250%, preferably 20-200%, and more preferably 30-150%. Being within this range ensures that the hollow fiber membrane exhibits sufficient water permeability under normal operating conditions and is less prone to rupture.

[0075] <Protein permeability> The hydrophobic porous hollow fiber membrane of the present invention preferably has a protein permeability of 95% or more, and more preferably 98% or more, when filtering a protein-containing liquid.

[0076] Generally, hydrophobic porous hollow fiber membranes are known to have low permeability due to the easy adsorption of proteins to the membrane surface through hydrophobic interactions, resulting in fouling during filtration. However, evaluation of the filterability of a protein-containing solution using the hydrophobic porous hollow fiber membrane of the present invention revealed low protein adsorption and high permeability. This is thought to be because the hydrophobic porous hollow fiber membrane of the present invention has fine irregularities on its structural surface and exhibits high water repellency, reducing contact between the membrane surface and the protein-containing solution, thereby suppressing protein adsorption. For this reason, the hydrophobic porous hollow fiber membrane of the present invention can be suitably used in filtration processes such as foreign matter removal and sterilization in the separation and purification of protein-containing solutions.

[0077] Furthermore, as described above, when the hydrophobic porous hollow fiber membrane of the present invention has a layer of spherical structures, it can achieve higher strength compared to a porous hollow fiber membrane with a mesh-like structure, and is therefore more suitably used in a cross-flow method in which the raw liquid is circulated and filtered at a high linear velocity.

[0078] <Method for manufacturing hydrophobic porous hollow fiber membranes> Next, we will describe a method for obtaining a hollow fiber membrane from a polyvinylidene fluoride-based resin, in particular, among the hydrophobic porous hollow fiber membranes of the present invention. However, the present invention is not limited in any way by these manufacturing method examples.

[0079] Methods for producing hollow fiber membranes from polyvinylidene fluoride resins include thermally induced phase separation, non-solvent-induced phase separation, melt extraction, and stretching-to-opening methods. Of these, thermally induced phase separation or non-solvent-induced phase separation is preferred.

[0080] Thermally induced phase separation is a type of phase separation in which a resin solution dissolved at high temperature is solidified by cooling, while non-solvent-induced phase separation is a type of phase separation in which a resin solution is solidified by contacting it with a non-solvent.

[0081] When producing hollow fiber membranes using the thermally induced phase separation method, a poor solvent for the polyvinylidene fluoride resin solution is preferred, and particularly preferred are poor solvents with relatively high resin solubility, such as cyclohexanone, isophorone, γ-butyrolactone, alkyl ketones such as dimethyl sulfoxide, and esters.

[0082] Furthermore, when producing hollow fiber membranes using a non-solvent-induced phase separation method, a good solvent for the polyvinylidene fluoride resin solution is preferred. Examples of such good solvents include N-methyl-2-pyrrolidone, dimethylacetamide, dimethylformamide, methyl ethyl ketone, acetone, tetrahydrofuran and other lower alkyl ketones, esters, amides, and mixed solvents thereof. On the other hand, the non-solvent is a non-solvent for the resin and includes water, hexane, pentane, benzene, toluene, methanol, ethanol, carbon tetrachloride, o-dichlorobenzene, trichloroethylene, ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, butylene glycol, pentanediol, hexanediol, low molecular weight polyethylene glycol and other aliphatic hydrocarbons, aromatic hydrocarbons, aliphatic polyhydric alcohols, aromatic polyhydric alcohols, chlorinated hydrocarbons, or other chlorinated organic liquids and mixed solvents thereof.

[0083] In thermally induced phase separation and non-solvent-induced phase separation, by using a good solvent or poor solvent with high resin solubility, the hydrophobic resin and solvent can be mixed at the molecular level. As a result, when solidifying through phase separation, solvent molecules are more likely to interpose between the hydrophobic resin molecules, and consequently, irregularities are more easily formed on the surface of each spherical body in the structure.

[0084] Furthermore, there are mainly two types of phase separation mechanisms in thermally induced phase separation. One is a liquid-liquid phase separation method in which a uniformly dissolved resin solution at high temperatures separates into a concentrated phase and a dilute phase of the resin as the solution cools due to a decrease in its solubility. The other is a solid-liquid phase separation method in which a uniformly dissolved resin solution at high temperatures separates into a polymer solid phase and a polymer dilute solution phase as the resin crystallizes as it cools. In the former method, a sponge-like three-dimensional network structure is mainly formed, while in the latter method, a spherical structure is formed.

[0085] In this invention, it is preferable to form a spherical structure by the latter phase separation mechanism. In the case of a spherical structure, the solid portion is bulky, so the voids between the solid portions are less likely to contract, and a high pure water permeability performance can be maintained, which is another reason why this is preferable. For this reason, it is preferable to select a resin concentration and solvent that induce solid-liquid phase separation.

[0086] When cooling, it is preferable to use a cooling bath, which preferably contains the same solvent as the resin solution, or a low concentration of the non-solvent of the resin to form fine irregularities on the surface of the structure, thereby controlling the phase separation rate. In particular, to control the phase separation rate, it is preferable to add a modified version of the solvent of the resin solution to the solidification bath composition. When γ-butyrolactone is used as the solvent of the resin solution, adding its hydrolysate, γ-hydroxybutyric acid, makes it possible to control the phase separation rate more precisely without significantly changing the compatibility between the resin solution and the cooling bath, thereby promoting the formation of fine irregularities on the surface of the spherical structure. The amount of modified solvent of the resin solution added to the cooling bath is preferably 5 to 20% by weight, more preferably 6 to 17% by weight, and even more preferably 7 to 15% by weight.

[0087] Here, the hydrophobic porous hollow fiber membrane produced using the non-solvent-induced phase separation method or the thermal-induced phase separation method of the present invention is preferably stretched to expand the voids and improve water permeability. The stretching conditions are preferably a temperature range of 50 to 120°C, more preferably 60 to 100°C, and preferably a stretching ratio of 1.1 to 2 times. Below 50°C, it is difficult to stretch stably and uniformly, and above 120°C, the hollow fiber membrane may soften, causing the fine uneven structure on the surface of the structure and the hollow parts to collapse. Furthermore, stretching is preferably carried out in a liquid because temperature control is easy, but it may also be carried out in a gas such as steam. As the liquid, it is simple and preferable to use an aqueous solution of water or a resin solution solvent, but when stretching at around 90°C or above, it is also preferable to use low molecular weight polyethylene glycol or the like. [Examples]

[0088] The present invention will be described in more detail below with reference to examples, but the present invention is not limited in any way by these examples.

[0089] (1) Pure water permeability The permeability of pure water is evaluated by considering both the permeability performance r under dry conditions and the permeability performance w under wet conditions. <Dry permeability r> The porous hollow fiber membrane was left to stand in a 30°C forced-air constant-temperature dryer for more than 24 hours until the moisture content of the hollow fiber membrane was in equilibrium with the 30°C air inside the dryer. After this drying process, a porous hollow fiber membrane module with an effective length of 10 cm and an open end was fabricated.

[0090] Using distilled water as the raw water, the permeability per unit time was measured by filtering from the outside to the inside of a porous hollow fiber membrane (external pressure filtration) under conditions of a filtration pressure of 100 kPa and a temperature of 25°C. Then, the same measurements were performed at filtration pressures of 200 kPa and 300 kPa, and the values ​​converted to permeability per unit membrane area and per unit time of pure water were calculated for each filtration pressure. <Permeability when wet w> Using porous hollow fiber membranes, a porous hollow fiber membrane module with an effective length of 10 cm and an open-end design was fabricated. The module was immersed in a 50% ethanol aqueous solution for 20 minutes, followed by a 20-minute run-through rinse with distilled water to obtain a moist porous hollow fiber membrane module. Using this module, the same measurements as for the dry permeability performance r were performed, and the values ​​converted to permeability per unit membrane area and per unit time at various filtration pressures were calculated.

[0091] (2) Measurement of the contact angle between the porous separation membrane surface and water For measuring the contact angle of the porous hollow fiber membrane surface, a dry hollow fiber membrane was used, and the measurement was performed after making a cut along its length and opening it into a flat plate shape. The contact angle between the porous hollow fiber membrane surface and water was measured using an automatic contact angle meter (Kyowa Interface Science Co., Ltd., DM500) in an atmosphere of room temperature (25°C) and relative humidity (50%). The static contact angle was automatically calculated by computer image analysis using the θ / 2 method. The appropriate liquid volume was 1.0 μl, and the contact angle was measured 10 seconds after the start of droplet application of distilled water to the porous separation membrane surface.

[0092] (3) Measurement of surface roughness of porous hollow fiber membrane Surface roughness of porous hollow fiber membranes was measured using dry hollow fiber membranes. These membranes were cut lengthwise, flattened, and then subjected to linear roughness measurement (JIS B 0601-2001) using a laser microscope (Keyence Corporation, VK-7200) in an atmosphere of 25°C and 50% relative humidity. Specifically, within a 200 μm × 200 μm area of ​​the porous hollow fiber membrane surface, five linear roughness measurements of 50 μm length were taken at arbitrary locations, and the average length RSm and root-square height Rq were measured. This measurement was performed on five locations on the porous hollow fiber membrane surface, and the total measured values ​​for all 25 locations were averaged.

[0093] (4) Measurement of pore distribution by mercury intrusion method The porous hollow fiber membrane was oven-dried using the following method. The water-moistened hollow fiber membrane was freeze-dried at -20°C for approximately 50 hours, and then vacuum-dried at room temperature for approximately 8 hours. This oven-dried porous hollow fiber membrane was cut into pieces approximately 5 mm long, and the sample weight was weighed using an electronic balance (Shimadzu Corporation AW220). The pore diameter (D) distribution was measured using a Micromeritex pore sizer 9320. The test specimen was placed on the instrument's attached pore sizer approximately 5 cm long. 3 The procedure involved sealing the sample in a glass cell, injecting mercury under reduced pressure, and then increasing the pressure in a pressure-resistant vessel attached to the apparatus via oil to a range of approximately 4 kPa to 207 MPa (corresponding to pore diameters of approximately 7 nm to 350 μm). The surface tension of mercury was calculated using 484 dyn / cm, and the contact angle of mercury was calculated using 141.3°.

[0094] (5) Breaking strength, breaking elongation Using a tensile testing machine (TENSILON® / RTM-100, manufactured by Toyo Baldwin Co., Ltd.), a sample with a measurement length of 50 mm was tested at a tensile speed of 50 mm / min in a 25°C atmosphere, with the sample being changed at least five times, and the average values ​​of the breaking strength and breaking elongation were calculated.

[0095] (6) Measurement of the diameter of the spherical body For each porous hollow fiber membrane fabricated in the example, a cross-section perpendicular to its longitudinal direction was imaged at 3000x magnification using a scanning electron microscope. From the captured images, 10 arbitrary spherical structures were selected from the region from the surface to a thickness of 20 μm, and the major and minor axes of each were measured. The above imaging was performed at five locations, and the major and minor axes were determined for 10 arbitrary spherical structures at each location, resulting in a total of 50 major axes and 50 minor axes. Next, the average value of the total 100 diameters was calculated and used as the average diameter of the spherical structures. The spherical structures to be measured are as described above.

[0096] (7) Fractionated particle size Rejection rate measurements were performed for at least three types of polystyrene latex fine particle aqueous solutions of different sizes. Linear approximation was performed on the measured values ​​for each type, and the particle size at which the rejection rate reached 90% was defined as the fractionated particle size.

[0097] (8) Protein permeability The porous hollow fiber membrane was left to stand in a 30°C forced-air constant-temperature dryer for more than 24 hours until the moisture content of the hollow fiber membrane was in equilibrium with the 30°C air inside the dryer. After this drying process, a porous hollow fiber membrane module with an effective length of 10 cm and an open end was fabricated.

[0098] As raw water, a 1% by weight aqueous solution of collagen peptide (manufactured by Healthy Company, Inc., Fish Collagen) at 50°C, or a 1% by weight aqueous solution of gelatin (manufactured by Nitta Gelatin Co., Ltd., NITTA classics Silver) at 25°C was used. The solution was filtered from the outside to the inside of a porous hollow fiber membrane (external pressure filtration) under conditions of a filtration differential pressure of 30 kPa between the raw water and permeate sides and a membrane surface linear velocity of 1 m / sec on the raw water side. The transmittance (%) was calculated from the absorbance of the raw solution and permeate using the following formula. Transmittance (%) = Absorbance of filtrate / Absorbance of undiluted solution × 100 ... Equation (8) When using an aqueous collagen peptide solution, the absorbance value at a wavelength of 275 nm is used; when using an aqueous gelatin solution, the absorbance value at a wavelength of 280 nm is used. In this measurement, a high protein permeability indicates that there is little protein adsorption to the porous hollow fiber membrane.

[0099] <Example 1> A homogeneous solution was obtained by dissolving 38% by weight of vinylidene fluoride homopolymer with a weight-average molecular weight of 417,000 and 62% by weight of γ-butyrolactone at 150°C. After allowing this polymer solution to stand at 130°C and degassing, it was cooled to 107°C in a pipe and then discharged from the outer tube of a double-tubular die for hollow fiber molding at a discharge temperature of 100°C. Furthermore, an 85% by weight aqueous solution of γ-butyrolactone was injected into the hollow part from the inner tube of the double-tubular die. After solidification in a 5°C solidification bath consisting of an aqueous solution of 78% by weight of γ-butyrolactone, 12% by weight of γ-hydroxybutyric acid, and 10% by weight of water, with a dry length of 10 cm, it was washed with water and stretched 1.5 times in 90°C water to obtain a porous hollow fiber membrane.

[0100] Peaks were observed in the pore diameter (D) range of 0.01 μm to less than 0.2 μm and in the pore diameter range of 0.2 μm to less than 10 μm, indicating the presence of fine irregularities on the spherical surface of the porous structure. Water permeability was good, with a good transmittance of 99% for protein components and collagen peptides. Table 1 shows the evaluation results and performance of the obtained porous hollow fiber membrane, including its structure.

[0101] <Example 2> A homogeneous solution was obtained by dissolving 36% by weight of vinylidene fluoride homopolymer with a weight-average molecular weight of 417,000 and 61% by weight of γ-butyrolactone at 150°C. After allowing this polymer solution to stand at 120°C and degassing, it was cooled to 100°C in a pipe and then discharged from the outer tube of a double-tubular die for hollow fiber molding at a discharge temperature of 98°C. Furthermore, an 85% by weight aqueous solution of γ-butyrolactone was injected into the hollow part from the inner tube of the double-tubular die. After solidification in a solidification bath at 5°C consisting of an aqueous solution of 84% by weight of γ-butyrolactone, 6% by weight of γ-hydroxybutyric acid, and 10% by weight of water, with a dry length of 10 cm, it was washed with water and stretched 1.5 times in 90°C water to obtain a porous hollow fiber membrane. The evaluation results of the spherical structure and other properties of the obtained porous hollow fiber membrane and its performance are shown in Table 1.

[0102] <Comparative Example 1> The polymer solution from Example 1 was allowed to stand at 110°C, degassed, and then cooled to 102°C in a pipe. It was then discharged from the outer tube of a double-tube die for hollow fiber molding at a discharge temperature of 100°C, and 85% by weight of γ-butyrolactone injection solution was injected into the hollow portion from the inner tube of the double-tube die. After solidification in a 9°C solidification bath consisting of an aqueous solution of 85% by weight of γ-butyrolactone and 15% by weight of water, with a dry length of 4 cm, it was washed with water and stretched 1.5 times in 85°C water to obtain a porous hollow fiber membrane. There were no peaks in the pore diameter (D) range of 0.01 μm to less than 0.2 μm, and no fine irregularities were present on the surface of the spherical bodies of the porous structure. The water permeability was low, with a ratio of (dry permeability r / wet permeability w) of 72%, and the permeability of protein components and collagen peptides was 91%, indicating that protein components were easily adsorbed onto the porous separation membrane. Table 2 shows the evaluation results and performance of the obtained porous hollow fiber membrane, including its spherical structure.

[0103] <Comparative Example 2> A homogeneous solution was obtained by dissolving 39% by weight of vinylidene fluoride homopolymer with a weight-average molecular weight of 417,000, 40% by weight of diphenyl carbonate, 15% by weight of γ-butyrolactone, 5% by weight of 1,3-propylene glycol, and 1% by weight of lithium chloride at 200°C. This polymer solution was allowed to stand at 180°C, degassed, and then discharged from the outer tube of a double-tubular nozzle for hollow fiber molding. After solidification in a 10 cm dry length in a 0°C solidification bath of 100% by weight of 1-octanol, it was washed with ethanol to obtain a porous hollow fiber membrane. The evaluation results of the structure and performance of the obtained porous hollow fiber membrane are shown in Table 2.

[0104] [Table 1]

[0105] [Table 2] [Explanation of Symbols]

[0106] 1. Porous hollow fiber membrane 2 Spherical structure 11 Outer surface 12 Inner surface 20 Spherical bodies 21. Constriction of the spherical body 22 Pores between spherical bodies 23 Pores on the surface of spherical bodies 25 Inlet holes of pores 26 Structure of Porous Membrane V1 Primary side flow velocity V2 Flow velocity within pores X1 Spherical body whose contours are not approximately parallel to each other. X2 The spherical body hidden behind the contour in the foreground R: Diameter of the sphere

Claims

1. A hydrophobic porous hollow fiber membrane made of an organic polymer resin, in which, in a log differential pore volume distribution graph of pore diameter (D) and pore volume (Vp) measured by mercury intrusion porosimetry, there are areas in the range of pore diameter (D) of 0.01 μm or more and less than 0.2 μm and areas in the range of pore diameter (D) of 0.2 μm or more and less than 10 μm, where the log differential pore volume (dVp / dlogD) is 0.2 cm or more. ３ / g or more.

2. 2. The hydrophobic porous hollow fiber membrane according to claim 1, wherein the pure water permeability under a filtration pressure of 100 kPa at 25° C. satisfies formula (1). (dry permeability r / wet permeability w)×100≧80(%) Equation (1) In formula (1), the dry permeability r is the pure water permeability (m ３ / m ２ / hr), and the wet permeability w is the pure water permeability (m ３ / m ２ / hr).

3. 3. The hydrophobic porous hollow fiber membrane according to claim 1, wherein the membrane surface of the hydrophobic porous hollow fiber membrane has a contact angle between the membrane surface and water of 70° or more and 130° or less when the water content is in the range of 2% by weight to 10% by weight relative to 100% by weight of the hydrophobic porous hollow fiber membrane.

4. The average pore diameter (d1) in the range of the pore diameter (D) of 0.01 μm or more and less than 0.2 μm is 0.02 μm or more and 0.08 μm or less, and the pore specific surface area Sp ０．０１－０．２ (m ２ / g) and pore volume Vp ０．０１－０．２ (cm ３ 3. The hydrophobic porous hollow fiber membrane according to claim 1, wherein the relationship of (a) (i.e., σ / g) satisfies formula (2). Sp ０．０１－０．２ / Vp ０．０１－０．２ ≧ 100・・・Form (2) In formula (2), Sp ０．０１－０．２ represents the specific surface area (S) of pores having a pore diameter (D) determined by mercury intrusion porosimetry in the range of 0.01 μm or more and less than 0.2 μm, and Vp ０．０１－０．２ represents the pore volume (Vp) of pores having a pore diameter (D) determined by mercury intrusion porosimetry in the range of 0.01 μm or more and less than 0.2 μm.

5. 3. The hydrophobic porous hollow fiber membrane according to claim 1, wherein the hydrophobic porous hollow fiber membrane has a layer of spherical structures on at least one surface side.

6. 6. The hydrophobic porous hollow fiber membrane according to claim 5, wherein the average diameter of the spheres constituting the spherical structure is 1 μm or more and 15 μm or less.

7. The hydrophobic porous hollow fiber membrane has a pure water permeability r of 3.0 m when dried at 25°C under a filtration pressure of 100 kPa. ３ / m ２ / hr or more 20.0m ３ / m ２ 3. The hydrophobic porous hollow fiber membrane according to claim 1, wherein the membrane has a flow rate of 1000 s / hr or less, a porosity of 50% to 70% and a particle size fraction of 0.1 μm to 1.0 μm.

8. 3. The hydrophobic porous hollow fiber membrane according to claim 1, wherein the organic polymer resin is a polyvinylidene fluoride resin.

9. A method for filtering a protein-containing solution, comprising the step of filtering a protein using the hydrophobic porous hollow fiber membrane according to any one of claims 1 to 8.

10. A water purifier cartridge comprising the hydrophobic porous hollow fiber membrane according to any one of claims 1 to 8.

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