Porous membranes and purification methods

Abstract

A porous membrane having a non-uniform structure in the thickness direction, the porous membrane having a sparse first surface and a dense second surface, the porous membrane having a first capture layer (20nm colloidal gold capture layer) and a second capture layer (20nm colloidal gold capture layer), the first trapping layer traps colloidal gold having an average particle diameter of 20 nm when the colloidal gold having the average particle diameter of 20 nm is made to permeate from the first surface side to the second surface side of the porous membrane, and the thickness of the first trapping layer is 16.5 [mu] m or more.

Description

Technical Field

[0001] The present invention relates to a porous membrane and a purification method. Background Art

[0002] For example, in the production of antibody drugs, in the process of purifying an antibody (such as IgG) by removing inclusions from cultured cells, a porous membrane is used to remove viruses. For this porous membrane, a structure that can fractionally remove viruses and allow antibodies to pass through is required.

[0003] For example, Japanese Patent No. 5403444 (Japanese Unexamined Patent Application Publication No. 2014-097465 (Patent Document 1)) discloses a porous membrane for removing viruses from biological materials such as blood.

[0004] The porous membrane (porous hollow fiber membrane) disclosed in Patent Document 1 contains a polysulfone-based polymer and a copolymer of vinylpyrrolidone and vinyl acetate, and its surface and porous part are coated with a cellulose-based polymer (polysaccharide or polysaccharide derivative).

[0005] Prior Art Documents

[0006] Patent Documents

[0007] Patent Document 1: Japanese Patent No. 5403444 (Japanese Unexamined Patent Application Publication No. 2014-097465) Summary of the Invention

[0008] Problems to be Solved by the Invention

[0009] Before the virus removal treatment, virus inactivation treatment is usually performed. In this virus inactivation treatment, for example, the virus is inactivated by lowering the pH of the liquid containing the biological material. It is known that the virus removal performance of the porous membrane is reduced for a liquid with a low pH containing the biological material.

[0010] Therefore, conventionally, after neutralizing the liquid with a low pH containing the biological material after the virus inactivation treatment to increase the pH, the virus removal treatment is performed using a porous membrane.

[0011] However, from the viewpoint of manufacturing efficiency, it is preferable not to perform the above neutralization treatment but directly perform the virus removal treatment on the liquid with a low pH containing the biological material.

[0012] Therefore, an object of the present invention is to provide a porous membrane that can directly perform virus removal treatment on a liquid with a low pH containing a biological material, has high virus blocking ability, and maintains a high filtration flow rate for a long time.

[0013] Means for Solving the Problems

[0014] (1) A porous membrane, which is a porous membrane having a non-uniform structure in the thickness direction with a sparse first surface and a dense second surface,

[0015] The above-mentioned porous membrane has a first capture layer (20nm colloidal gold capture layer),

[0016] The above-mentioned first capture layer is a layer that captures colloidal gold with an average particle size of 20nm when the colloidal gold with an average particle size of 20nm permeates from the first surface side to the second surface side of the above-mentioned porous membrane,

[0017] The thickness of the above-mentioned first capture layer is 16.5μm or more.

[0018] (2) The porous membrane according to (1), wherein the above-mentioned porous membrane has a second capture layer,

[0019] The above-mentioned second capture layer is a layer that captures colloidal gold with an average particle size of 30nm when the colloidal gold with an average particle size of 30nm permeates from the first surface side to the second surface side of the above-mentioned porous membrane,

[0020] The above-mentioned porous membrane satisfies the relationship that a / b is 1.5 or more,

[0021] The above-mentioned a is the distance from the first surface to the position closest to the second surface side of the first capture layer,

[0022] The above-mentioned b is the distance from the first surface to the position closest to the second surface side of the second capture layer.

[0023] (3) The porous membrane according to (1) or (2), wherein the above-mentioned porous membrane contains a hydrophobic polymer and a first hydrophilic polymer,

[0024] The surface of the above-mentioned porous membrane is coated with a second hydrophilic polymer.

[0025] (4) The porous membrane according to (3), wherein the above-mentioned hydrophobic polymer is a polysulfone-based polymer.

[0026] (5) The porous membrane according to (3) or (4), wherein the above-mentioned first hydrophilic polymer is at least one of polyvinylpyrrolidone and a copolymer of vinylpyrrolidone and vinyl acetate.

[0027] (6) The porous membrane according to any one of (3) to (5), wherein the above-mentioned second hydrophilic polymer is a cellulose-based polymer.

[0028] (7) The porous membrane according to any one of (1) to (6), which has a shape of a hollow fiber membrane, wherein the inner surface of the hollow fiber membrane is the first surface, and the outer surface of the hollow fiber membrane is the second surface.

[0029] (8) The porous membrane according to any one of (1) to (7), which is used for removing viruses.

[0030] (9) A purification method using the porous membrane according to any one of (1) to (8).

[0031] Effects of the Invention

[0032] According to the present invention, it is possible to provide a porous membrane that can directly perform virus removal treatment on a low-pH liquid containing a material derived from a living organism, has a high virus blocking ability, and maintains a high filtration flow rate for a long period of time.

[0033] One of the reasons why the virus removal performance of the porous membrane is reduced for a liquid with a low pH value is that the higher-order structure of the virus is destroyed in the liquid with a low pH value, and the virus becomes linear, thereby becoming easy to pass through the pores of the porous membrane. In the porous membrane of the present invention, it is believed that by making the thickness of the first capture layer (20 nm colloidal gold capture layer) as the portion with a smaller pore size be 16.5 μm or more, even viruses that become easy to pass through like this can be captured, and therefore the virus removal treatment can be directly performed on the liquid with a low pH value. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 This is a schematic diagram for explaining an example of a method for producing a porous film.

[0035] Figure 2 is a schematic diagram for explaining depth filtration.

[0036] Figure 3 This is a diagram for explaining surface filtration (Japanese: 表層翾過).

[0037] Figure 4 It is a schematic diagram for explaining dead-end filtration in each measurement method.

[0038] Figure 5A This is a SEM image of a cross section of the porous membrane of Example 1.

[0039] Figure 5B This is a 20 nm colloidal gold binary image of a cross section of the porous membrane of Example 1.

[0040] Figure 6 This is a SEM image of a cross section of the porous membrane of Example 4. DETAILED DESCRIPTION

[0041] Hereinafter, embodiments of the present invention will be described, but the present invention is not limited to these embodiments.

[0042] <Porous membrane>

[0043] 〔Constituent materials of the porous membrane〕

[0044] The porous membrane of this embodiment contains a hydrophobic polymer and a first hydrophilic polymer.

[0045] The surface of the porous membrane (including the inner surface of the pores) is coated with a second hydrophilic polymer.

[0046] The porous membrane can be produced, for example, by adsorbing (attaching) a second hydrophilic polymer different in type from the first hydrophilic polymer to the surface (including the inner surface of the pores) of a base membrane containing a hydrophobic polymer and a first hydrophilic polymer and immobilizing it. For example, the base membrane is formed of a blend polymer of a hydrophobic polymer and a first hydrophilic polymer that are compatible with each other, and can be manufactured from a solution obtained by using a common solvent for the two polymers.

[0047] (Hydrophobic polymer)

[0048] Examples of the hydrophobic polymer include: polysulfone-based polymers such as polysulfone and polyethersulfone, cellulose-based polymers such as cellulose acetate and cellulose derivatives, and polyolefin-based polymers such as polyethylene.

[0049] Polyethersulfone is a compound containing a structural unit represented by the following formula (1).

[0050] [Chemical formula 1]

[0051]

[0052] Specific examples of polyethersulfone include Ultrason (registered trademark) E2020P, E6020P manufactured by BASF Corporation, or Sumikaexcel (registered trademark) 3600P, 4100P, 4800P, 5200P, 7600P manufactured by Sumitomo Chemical Company, etc., and E6020P, 4800P or 5200P are preferred. They can be used alone or in combination.

[0053] Polysulfone-based polymers are advantageous for obtaining highly water-permeable membranes and are excellent raw materials in the processing of uniform membranes, asymmetric membranes, etc. The polysulfone-based polymers can contain substituents such as functional groups and alkyl groups, and the hydrogen atoms of the hydrocarbon skeleton can be replaced by other atoms or substituents such as halogens. In addition, they are preferably used alone, and substances with a higher molecular weight are preferably used.

[0054] The content rate of the hydrophobic polymer in the entire porous membrane is preferably 60 to 90% by mass.

[0055] (First hydrophilic polymer)

[0056] Examples of the first hydrophilic polymer include: polyvinyl alcohol, polyethylene glycol, vinyl pyrrolidone polymers (such as polyvinyl pyrrolidone, copolymers of vinyl pyrrolidone and vinyl acetate, etc.), polyacrylic acid, cellulose, methyl cellulose, chitosan, etc. Vinyl pyrrolidone polymers refer to polymers of monomers containing at least N-vinyl pyrrolidone.

[0057] The vinyl pyrrolidone polymer preferably contains a structural unit represented by the following formula (2).

[0058] [Chemical formula 2]

[0059]

[0060] Examples of the vinyl pyrrolidone polymer include: Kollidon (registered trademark) 30, 90 or Luvitec (registered trademark) K30, K80, K85, K90, VA64 commercially available from BASF.

[0061] As the copolymer of vinyl pyrrolidone and vinyl acetate, a copolymer using vinyl pyrrolidone as a hydrophobic unit and vinyl acetate as a hydrophilic unit (hereinafter sometimes abbreviated as VA copolymer) can be used. As the VA copolymer, from the aspects of imparting hydrophilicity to the polysulfone membrane and excellent compatibility with polysulfone polymers, a copolymer with a weight ratio of vinyl pyrrolidone to vinyl acetate of 6:4 (hereinafter sometimes abbreviated as VA6 / 4), and VA65 / 35 with a weight ratio of vinyl pyrrolidone to vinyl acetate of 65:35 are preferred.

[0062] The content rate of the first hydrophilic polymer in the porous membrane is preferably 5 to 15% by mass, more preferably 6 to 10% by mass.

[0063] If the content rate of the first hydrophilic polymer in the membrane exceeds the above upper limit, the swelling in the membrane becomes larger, resulting in destabilization of the pore diameter and a decrease in pressure resistance, and sometimes the influence on virus blocking and protein permeability cannot be ignored. In addition, if the content rate of the first hydrophilic polymer in the membrane is too high, adverse conditions such as the dissolution of the first hydrophilic polymer during use and its mixing into the recovery liquid may occur. If the content rate is lower than the above lower limit, the contribution to membrane structure control may be insufficient, and thus the virus removal ability may sometimes decrease.

[0064] The content rates of the first hydrophilic polymer and the second hydrophilic polymer can be measured using nuclear magnetic resonance (hereinafter sometimes abbreviated as NMR). In addition, the content rate within the range limited to the vicinity of the membrane surface can be measured by surface infrared spectroscopy (hereinafter sometimes abbreviated as IR).

[0065] (Second hydrophilic polymer)

[0066] The second hydrophilic polymer is a polysaccharide or a polysaccharide derivative. The second hydrophilic polymer is preferably a cellulose-based polymer.

[0067] The cellulose-based polymer is preferably hydroxyalkyl cellulose. Examples of hydroxyalkyl cellulose include hydroxyethyl cellulose and hydroxypropyl cellulose (HPC).

[0068] Examples of polysaccharides other than cellulose-based include starch, dextran, and gellan gum.

[0069] From the viewpoints of avoiding an increase in solution viscosity and the penetration efficiency into the membrane interior, the weight-average molecular weight of the second hydrophilic polymer is preferably 140,000 or less. It is also preferable to appropriately reduce the molecular weight according to the pore diameter of the target membrane.

[0070] In the present embodiment, it is preferable that after manufacturing a base film containing a hydrophobic polymer and a first hydrophilic polymer, a treatment such as immersing the base film in a solution or dispersion containing the second hydrophilic polymer is performed to attach the second hydrophilic polymer to the surface of the base film. At this time, it is preferable to wash and remove the excess first hydrophilic polymer from the polysulfone-based membrane containing the first hydrophilic polymer, and then attach the second hydrophilic polymer to the membrane surface and the pore surface.

[0071] If the second hydrophilic polymer is coated on the polysulfone-based membrane containing the first hydrophilic polymer, it has the effects of maintaining stable and high hydrophilicity and suppressing the elution of the first hydrophilic polymer.

[0072] The weight ratio (IR / NMR) of the content rate (IR) of the second hydrophilic polymer present near the outer surface measured by IR to the content rate (NMR) of the second hydrophilic polymer present in the entire membrane measured by NMR is preferably 0.90 or more and 1.10 or less, and more preferably 0.93 or more and 1.05 or less.

[0073] It should be noted that the content rate of the second hydrophilic polymer in the entire porous membrane is preferably 0.5 to 2.5% by mass, and more preferably 0.7 to 2.2% by mass.

[0074] If the content rate of the second hydrophilic polymer (such as a cellulose-based polymer) in the porous membrane exceeds the above upper limit, it is saturated in terms of imparting hydrophilicity to the membrane, resulting in an excessive imparting amount. The presence of an excess sometimes clogs the pores due to swelling in the pores, reducing the water permeability and protein permeability. Additionally, if it is below the above lower limit, adsorption of the hydrophilicity-imparting protein may occur, significantly reducing the treatment amount of the protein solution. The coating of the second hydrophilic polymer also has the effect of suppressing the elution of the first hydrophilic polymer. Here, the content rate of the cellulose-based polymer as the second hydrophilic polymer can be measured by NMR in the form of the content rate of the entire membrane.

[0075] 〔Structure of the porous membrane, etc.〕

[0076] The porous membrane of this embodiment has an uneven structure (asymmetric structure) in the thickness direction. It should be noted that examples of the porous membrane having an asymmetric structure include porous membranes with different densities, porosity, cross-sectional opening ratio, average pore diameter, etc. in the thickness direction.

[0077] The porous membrane with an asymmetric structure of this embodiment can be in the shape of a flat membrane or a hollow fiber membrane. A structure is preferably such that the first surface side of the cross-section (cross-section: the cross-section in the thickness direction) of the porous membrane is sparse and the second surface side is dense.

[0078] For example, the porous membrane of this embodiment has an asymmetric structure such that the upstream side (the first surface side) is sparser than the downstream side (the second surface side) during use (filtration) such as virus removal treatment. That is, preferably, the liquid to be treated is passed through the side with the sparse structure (the first surface side), and the filtration treatment is carried out toward the side with the dense structure (the second surface side).

[0079] When the porous membrane is a hollow fiber membrane, it can be either a structure where the inner surface side is sparse and the outer surface side is dense (having a dense layer on the outer surface side) or a structure where the inner surface side is dense (having a dense layer on the inner surface side) and the outer surface side is sparse. A structure where the inner surface side is sparse and the outer surface side is dense (having a dense layer on the outer surface side) is preferred.

[0080] For example, when the inner surface (the first surface) side of the hollow fiber membrane is used as the filtration upstream side and filtration is carried out from the inside to the outside, it is preferred that the inner surface side of the hollow fiber membrane is sparse and the outer surface side is dense.

[0081] Such a structure functions to moderately disrupt the flow of the filtrate, and has the effect of making it difficult for components that affect clogging, such as aggregates, to adsorb onto the membrane surface. Therefore, it is possible to mitigate the decrease in the filtration rate caused by clogging of the inner surface of the membrane, and to shorten the processing time for target liquids such as high-concentration protein solutions.

[0082] Here, the filtration effect brought about by the porous membrane having an asymmetric structure of the present embodiment will be described.

[0083] Refer to Figure 3 , in the filtration using the porous membrane 3, smaller components 5 such as antibodies (IgG) in the cell culture solution pass through (permeate) the pores of the porous membrane 3 from the extrusion side ( Figure 3 the upper side: the first surface side of the porous membrane: the inner surface side in the case of a hollow fiber membrane) and are separated to the second surface side of the porous membrane ( Figure 2 the lower side: the outer surface side in the case of a hollow fiber membrane). On the other hand, among the components contained in the cell culture solution, components 4 (such as viruses) larger than component 5 cannot pass through the pores of the porous membrane and are removed from the filtrate.

[0084] In the case of filtration (surface filtration: screen filtration) using the Figure 3 shown (conventional) porous membrane 3 having a uniform structure in the thickness direction, the larger-sized components 4 tend to concentrate and accumulate near the outermost surface of the extrusion side ( Figure 3 the upper side: the first surface side of the porous membrane (the inner surface side of the hollow fiber membrane)), and thus clogging is likely to occur.

[0085] In contrast, as Figure 2 shown, in the case of filtration (depth filtration: deep filtration) using the (porous membrane 3 of the present embodiment) having an asymmetric structure, the larger-sized components 4 are dispersed in the thickness direction of the porous membrane 3 and are captured (clogged sequentially in the membrane thickness direction). Therefore, clogging is less likely to occur.

[0086] It should be noted that the hollow fiber membrane preferably has an asymmetric structure in which the densest part (dense layer) is present in the cross-sectional direction on the outside. The structure of the membrane can be easily confirmed, for example, by observation with an electron microscope.

[0087] The purpose of the hollow fiber membrane is to highly remove minute substances such as viruses, and therefore it is necessary to reliably capture such minute substances at any part of the membrane thickness. Substances to be captured such as viruses are captured in the middle of passing through the pore paths present in the membrane thickness (referred to as depth filtration), and due to the presence of the smallest pore part of the dense layer at the outlet, almost 100% exclusion can be ensured.

[0088] It should be noted that if a dense layer exists at the inlet, capture can also be performed at this part (called screen filtration), but in this case, since capture is performed locally at the inlet, as filtration proceeds, the permeability of the solute to be passed is reduced due to the narrowing of the pore size and the accumulation of the capture material, or the amount of permeated liquid is reduced due to clogging. Therefore, it is not preferred that a dense layer exists at the inlet.

[0089] (Thickness of the first capture layer)

[0090] In the porous membrane of the present embodiment, the layer that captures the colloidal gold with an average particle size of 20 nm when the colloidal gold with an average particle size of 20 nm is passed through from the first surface side (inner surface side) to the second surface side (outer surface side) of the porous membrane is defined as the first capture layer. That is, the porous membrane has the first capture layer. It should be noted that, similarly, the layer that captures the colloidal gold with an average particle size of 30 nm is defined as the second capture layer (30 nm colloidal gold capture layer). The porous membrane preferably has the second capture layer.

[0091] The thickness of the first capture layer (20 nm colloidal gold capture layer) is 16.5 μm or more, preferably 17 μm or more. This can achieve the above-mentioned effects of the present invention.

[0092] The ratio of the thickness of the first capture layer to the thickness of the entire porous membrane is preferably 10 to 55%, and more preferably 25 to 45%.

[0093] In the porous membrane of the present invention, the LRV (logarithmic reduction value) indicating virus blocking performance (removal performance) is preferably 3.5 or more, more preferably 4.0 or more (removal rate 99.99% or more), and further preferably 4.7 or more.

[0094] For example, "LRV ≥ 5" means that in the 5 When filtering a liquid containing 100,000 viruses, the number of viruses leaking to the filtrate side is less than 1. Thus, the higher the LRV of the porous membrane, the higher the blocking performance (removal performance) of the porous membrane for the filtration object (viruses, etc.).

[0095] Generally, it can be said that an LRV of about 4 is preferred in terms of safety (reference: Masahiro Oda et al., "Study on Issues and Case Studies of Virus Clearance Tests", PDA Journal of GMP and Validation in Japan, Vol. 7, No. 1, 2005). It is believed that hollow fiber membrane modules with an LRV of 4.7 or more have good virus removal performance.

[0096] It should be noted that the smallest virus existing in nature is the parvovirus, and the diameter of the parvovirus is about 20 nm. Therefore, the permeability of the above-mentioned 20-nm colloidal gold can be used as a reference index for the virus permeability (blocking property).

[0097] The average particle size of the above-mentioned colloidal gold refers to the average particle size described in the instruction manual of the colloidal gold product, etc.

[0098] (Ratio a / b)

[0099] When the distance from the first surface of the porous membrane to the position closest to the second surface side of the first capture layer (20-nm colloidal gold capture layer) is set as a, and the distance from the first surface of the porous membrane to the position closest to the second surface side of the second capture layer (30-nm colloidal gold capture layer) is set as b, the ratio a / b is preferably 1.5 or more, more preferably 1.6 or more, and further preferably 2.0 or more. That is, the porous membrane preferably satisfies the relationship that a / b is 1.5 or more. The above-mentioned a is the distance from the above-mentioned first surface to the position closest to the second surface side of the above-mentioned first capture layer. The above-mentioned b is the distance from the above-mentioned first surface to the position closest to the second surface side of the above-mentioned second capture layer.

[0100] In this case, the time-dependent decrease in the filtration flow rate of the porous membrane is suppressed. It is considered that the reason is that the farther the position of the 30-nm colloidal gold capture layer (the outermost layer side position) is from the position of the 20-nm colloidal gold capture layer (the outermost layer side position) (the larger a / b is), the greater the thickness of the layer that is blocked, and it takes time for the inclusions to fill the pores of the porous membrane. Therefore, the time-dependent decrease in the filtration flow rate is suppressed. Thereby, it is possible to suppress the decrease in the throughput (original Japanese: スループット) of the virus removal treatment and increase the processing amount until blocking.

[0101] The thickness (membrane thickness) of the porous membrane is preferably 30 to 200 μm, more preferably 40 to 100 μm. It should be noted that the membrane thickness of the hollow fiber membrane can be calculated by "(outer diameter - inner diameter) / 2".

[0102] It should be noted that in the case of the hollow fiber membrane, the inner diameter is preferably 150 μm or more and 400 μm or less, more preferably 200 μm or more and 350 μm or less.

[0103] In the case of the hollow fiber membrane, its porosity is preferably 15 to 60%, more preferably 20 to 50%. It should be noted that the porosity is the ratio of the area of the hollow part in the cross-section of the hollow fiber membrane, and is expressed by "hollow part cross-sectional area / (membrane part cross-sectional area + hollow part cross-sectional area)×100 (%)". By setting the porosity within the above range, it is possible to balance the filtration performance and the strength against the filtration pressure.

[0104] The porosity of the porous membrane is preferably 70% or more and 95% or less, more preferably 85% or more and 95% or less, and further preferably 90% or more and 95% or less. By setting the porosity to 70% or more, the recovery rate of antibodies (such as IgG) can be increased. On the other hand, if the porosity is too high, the strength of the porous membrane may be insufficient. By setting the porosity within the above range, both the filtration performance and the strength against the filtration pressure can be taken into account. The porosity of the porous membrane can be calculated, for example, from the mass of water in the void portion of the porous membrane when the void portion contains water and the mass of the dried porous membrane.

[0105] The pure water permeation rate of the porous membrane at 25 °C (hereinafter simply referred to as pure water Flux) is preferably 50 to 500 L / (m 2 ·h·bar). If the pure water Flux is less than the above value, it is difficult to perform efficient treatment due to problems such as a long filtration time and a large membrane area required. If the pure water Flux is greater than the above value, the pore size becomes too large, and problems such as difficulty in highly separating and removing substances such as viruses or a decrease in membrane strength and operability may occur. The pure water Flux is more preferably 80 to 400 L / (m 2 ·h·bar), and further preferably 100 to 350 L / (m 2 ·h·bar).

[0106] (Use)

[0107] The porous membrane of the present embodiment can be used, for example, for the purification of a target liquid based on virus removal (purification method). That is, the porous membrane of the present embodiment is used to remove viruses. Regarding the porous membrane of the present embodiment, for example, when manufacturing an antibody drug, in the process of purifying an antibody (such as IgG) by removing inclusions from a cell culture solution, it is suitable for removing viruses and the like contained in the cell culture solution.

[0108] It should be noted that from the aspect of the durability of the hollow fiber membrane against the pressure applied during filtration, it is preferable to use the inner surface side of the hollow fiber membrane as the filtration upstream side and perform filtration from the inside to the outside. In addition, for ease of operation and simplicity, the dead-end filtration is preferably used as the filtration method.

[0109] <Manufacturing method of the porous membrane (hollow fiber membrane)>

[0110] Hereinafter, the manufacturing method of the hollow fiber membrane as an example of the above porous membrane will be described.

[0111] The manufacturing method of the hollow fiber membrane of the present embodiment sequentially includes:

[0112] Spinning process: The spinning dope and the inner liquid are ejected from a double-layered tubular nozzle through an air travel section into a coagulation liquid, causing the spinning dope to solidify in the coagulation liquid, and pulling out the solidified product of the spinning dope from the coagulation liquid to obtain a hollow fiber membrane; and

[0113] Coating process: The surface (including the inner surface of the porous part) of the hollow fiber membrane (porous membrane) is coated with a second hydrophilic polymer.

[0114] 〔Spinning process〕

[0115] Refer to Figure 1 In the spinning process, as shown in, the spinning dope 10a and the inner liquid 10b are ejected from a double-layered tubular nozzle 11 through an air travel section (air gap) 20 into a coagulation liquid 21, causing the spinning dope to solidify in the coagulation liquid 21, and pulling out the solidified product of the spinning dope from the coagulation liquid 21 to obtain a hollow fiber membrane. The pulling out of the hollow fiber membrane, etc. is carried out, for example, by liquid guides 12, 13 and rollers 14, 15, 16. It should be noted that the hollow fiber membrane pulled out from the coagulation liquid 21 is, for example, immersed in a water washing bath 22 and then wound up by a winder 23.

[0116] The nozzle 11 is double-layered tubular, having an outer tube and an inner tube provided inside the outer tube. The spinning dope is ejected from the gap (slit) between the outer tube and the inner tube, and the inner liquid is ejected from the inside of the inner tube. The inner diameter of the outer tube is preferably 500 - 1500 μm, more preferably 600 - 1200 μm. The outer diameter of the inner tube is preferably 150 - 700 μm, more preferably 150 - 600 μm. It should be noted that the outer diameter of the inner tube is preferably about the same as the inner diameter of the hollow fiber membrane.

[0117] The linear distance of the air travel section 20 (the distance between the front end of the nozzle 11 and the liquid surface of the coagulation liquid 21), that is, the air gap length (AG length) is preferably 10 - 100 mm, more preferably 10 - 80 mm.

[0118] It should be noted that the hollow fiber membrane obtained through the spinning process can be further subjected to a cleaning process (water washing process) using pure water. The flow of water in the water washing process is preferably a flow in the opposite direction to the moving direction of the hollow fiber membrane (countercurrent), but it can also be a flow in the same direction as the moving direction of the hollow fiber membrane (cocurrent).

[0119] (Spinning dope)

[0120] The spinning dope 10a contains, for example: a resin raw material containing the above-mentioned polysulfone-based polymer and vinylpyrrolidone-based polymer, a solvent, and a non-solvent.

[0121] The spinning dope (film-forming solution) is obtained by mixing, stirring, and dissolving the above components. Heating can be performed for dissolution. However, excessive heating may cause decomposition of the polymer and high-temperature phase separation of the spinning solution unique to the present invention. Therefore, the heating temperature is preferably 30 to 80°C. In addition, the preparation of the spinning dope is preferably carried out under an inert gas enclosure.

[0122] The ejection temperature (nozzle temperature) of the spinning dope in the nozzle 11 is preferably 40 to 80°C, more preferably 45 to 60°C. If the temperature of the nozzle is low, solidification is likely to occur, the membrane structure becomes too dense, and the permeability decreases. In addition, if the temperature of the nozzle is high, the progress of phase separation is overly inhibited, large-diameter pores are likely to be generated, and the separation characteristics and strength are likely to decrease.

[0123] The concentration of the polysulfone-based polymer in the spinning dope is preferably 20 to 40% by mass, more preferably 25 to 35% by mass. To obtain high permeability, the lower the concentration of the polysulfone-based polymer, the more preferable. However, if it is too low, the strength may decrease and the separation characteristics may deteriorate. On the other hand, in order to reliably capture minute substances such as viruses, it is necessary to reduce the porosity of the dense layer as much as possible to make the capture more reliable. Therefore, the higher the concentration of the polysulfone-based polymer, the more preferable. However, if the concentration of the polysulfone-based polymer is increased, sometimes no matter how the film-forming conditions are controlled, the entire membrane becomes too dense. In addition, if the concentration of the polysulfone-based polymer is too high, the viscosity of the spinning dope becomes too high, and it may be difficult to perform spinning.

[0124] The concentration of the vinylpyrrolidone-based polymer in the spinning dope is preferably 0.5 to 20% by mass, more preferably 1 to 15% by mass. If the concentration is low, the control of the membrane structure and the residual amount in the membrane become insufficient, and the performance decreases. In addition, if the concentration is high, the phase separation (solidification) of the spinning dope is likely to proceed excessively, the operability (filtration of the spinning dope through a filter, filament breakage) during the production of the hollow fiber membrane deteriorates, and in addition, the diffusion of the polymer during phase separation is greatly reduced, so it may not be possible to form the desired membrane structure.

[0125] The solvent is a liquid capable of dissolving the polysulfone-based polymer. The solvent is preferably a polar solvent and is preferably soluble in water. The polar solvent is preferably an aprotic polar solvent. Examples of the aprotic polar solvent include N-methyl-2-pyrrolidone (NMP), N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMA), dimethyl sulfoxide (DMSO), acetonitrile, ε-caprolactam, etc. Particularly preferred are NMP, DMF, DMAc, etc., and further preferred is NMP.

[0126] The non-solvent is a liquid (excluding water) that does not dissolve the polysulfone-based polymer. Examples of the non-solvent include glycol esters, glycerol, alcohols, etc., and glycol esters are preferred. Examples of the glycol ester include ethylene glycol (EG), diethylene glycol (DEG), triethylene glycol (TEG), polyethylene glycol (PEG: polyethylene glycol 200, polyethylene glycol 400, etc.), propylene glycol (PG), glycerol, water, etc.

[0127] When using a polysulfone-based polymer and a vinylpyrrolidone-based polymer, ether polyols such as DEG, TEG, PEG, etc. are preferred, and TEG is more preferred. It should be noted that in this specification, ether polyol refers to a substance having at least one ether bond and two or more hydroxyl groups in the structure.

[0128] In the spinning dope, the ratio of the mass of the solvent (S) to the mass of the non-solvent (NS) (S / NS ratio) is preferably 25 / 75 to 55 / 45, more preferably 40 / 60 to 50 / 50. If the content of the solvent is less than this range, solidification is likely to occur, the membrane structure becomes too dense, and the permeability decreases, making it impossible to obtain the desired Flux and protein permeability. On the other hand, if the solvent content is more than this range, the progress of phase separation is overly inhibited, large-pore voids are likely to be generated, and the separation characteristics and strength are likely to decrease, which is not preferred.

[0129] There are no particular limitations on the addition order and mixing method of the resin raw material, solvent, and non-solvent that will form the hollow fiber membrane when they are mixed.

[0130] (Inner liquid)

[0131] As the composition of the inner liquid, a liquid mainly composed of the solvent and / or non-solvent contained in the spinning dope is preferably used. However, when only the solvent contained in the spinning dope is used, solidification at the inner cavity wall surface is overly inhibited, so a preferred surface structure cannot be obtained. Therefore, it is preferred to use any one of a mixed liquid of a solvent and a non-solvent, only a non-solvent, a mixed liquid of a solvent and water, a mixed liquid of a non-solvent and water, and a mixed liquid of a solvent, a non-solvent, and water.

[0132] When the inner liquid (core liquid) contains water, the water content rate in the inner liquid is preferably 5 to 30% by mass, more preferably 10 to 25% by mass. If the amount of the organic component is small, solidification is likely to occur, and the structure inside the membrane becomes too dense, resulting in a decrease in permeability.

[0133] The inner liquid may contain a solvent, a non-solvent, etc. Examples of the non-solvent include ethylene glycol, triethylene glycol (TEG), polyethylene glycol 200 or 400, glycerol, propylene glycol, etc. Examples of the solvent include N-methylpyrrolidone (NMP), dimethylacetamide, dimethylformamide, dimethyl sulfoxide, etc.

[0134] If the water content rate of the inner liquid is low and the content rates of the respective solvents are high, the solidification rate on the inner side of the hollow fiber membrane becomes slow, the phase separation time is prolonged, and a sparse structure is formed on the inner side of the hollow fiber membrane. Further, if the water content rate is high and the solvent content rate is low, the solidification rate on the inner side of the hollow fiber membrane becomes fast, the phase separation time is shortened, and a dense structure is formed on the inner side of the hollow fiber membrane.

[0135] In order to obtain the hollow fiber membrane of the present embodiment in which a sparse structure is exhibited on the inner side of the membrane, it is preferable to increase the concentration of components other than water (solvents, non-solvents, etc.) contained in the inner liquid (inner liquid concentration). The inner liquid concentration is preferably 70 to 95% by mass, more preferably 75 to 90% by mass. The ratio of the solvent to the mass of the non-solvent in the inner liquid (solvent / non-solvent) is, for example, 40 / 60 to 50 / 50.

[0136] When the spinning dope 10a and the inner liquid 10b are ejected from the double-layer tubular nozzle 11, a temperature difference can be provided between the spinning dope and the inner liquid.

[0137] (Coagulating liquid)

[0138] The coagulating liquid preferably contains a solvent and a non-solvent. It should be noted that the solvent and the non-solvent may each be one type or a mixture of multiple types. If the content rate of each solvent is too high, the solidification rate on the outer side of the hollow fiber membrane becomes slow, the phase separation time is prolonged, and a sparse structure is formed on the outer side of the hollow fiber membrane. Further, if the solvent content rate is too low, the solidification rate on the outer side of the hollow fiber membrane becomes fast, the phase separation time is shortened, and a dense structure is formed on the outer side of the hollow fiber membrane. In order to obtain the hollow fiber membrane of the present embodiment with a dense outer side of the membrane, the ratio of the total amount of the solvent and the non-solvent in the coagulating liquid (concentration of the coagulating liquid) is preferably 20 to 60% by mass, more preferably 30 to 45% by mass. The ratio of the solvent to the mass of the non-solvent in the coagulating liquid (solvent / non-solvent) is, for example, 40 / 60 to 50 / 50.

[0139] In addition, the temperature of the coagulating liquid also has a great influence on the solidification time of the membrane. If the temperature of the coagulating liquid is high, the solidification rate on the outer side of the hollow fiber membrane becomes slow, the phase separation time is prolonged, and a sparse structure is formed on the outer side of the hollow fiber membrane. Further, if the temperature of the coagulating liquid is low, the solidification rate on the outer side of the hollow fiber membrane becomes fast, the phase separation time is shortened, and a dense structure is formed on the outer side of the hollow fiber membrane. In order to obtain the hollow fiber membrane of the present embodiment with a dense outer side of the membrane, the temperature of the coagulating liquid is preferably 30 to 70°C, more preferably 40 to 60°C.

[0140] If the coagulation rate of the outer side of the hollow fiber membrane based on the concentration and temperature of the coagulation liquid is faster than the coagulation rate of the inner side of the hollow fiber membrane based on the concentration of the inner liquid, the inner surface side becomes sparse and the outer surface side becomes dense. If the coagulation rate of the outer side of the membrane is too fast relative to the inner side, the outer side of the membrane becomes too dense, which sometimes excessively inhibits the permeation of useful components such as IgG, or the thickness of the blocking layer (Japanese original: mesh まり層) becomes smaller, which easily causes a decrease in the amount of filtration over time. On the contrary, if it is slow, the pore size of the outer side of the membrane becomes larger, or the thickness of the virus capture layer becomes smaller, so that the virus and other inclusions that are to be prevented are permeated. If it is too slow, the inner surface side becomes dense, the outer surface side becomes sparse, and the liquid does not penetrate from the inner surface side of the membrane to the inside of the membrane. Therefore, in order to obtain the hollow fiber membrane of the present embodiment having an asymmetric structure that is sparse on the inner surface side and dense on the outer surface side, and that allows useful components to pass through and blocks inclusions, the balance between the inner liquid concentration and the coagulation liquid concentration and temperature is important.

[0141] After membrane formation, the hollow fiber membrane obtained by washing is cut into appropriate lengths and bundled into a bundle. The bundle is left standing for 30 minutes to 2 hours for the purpose of removing the internal liquid present in the hollow part.

[0142] As a further cleaning step, the bundle from which the internal liquid has been removed is subjected to repeated washing steps by injecting warm water from below while the bundle is in an upright state to immerse the bundle and then draining the water, thereby completely washing the solvent and non-solvent from the inside and outside of the hollow portion and the inside of the hollow fiber membrane. The temperature of the warm water is preferably 70°C to 95°C, more preferably 75°C to 90°C.

[0143] The hollow fiber membrane is preferably treated with high-pressure hot water after the above-mentioned cleaning treatment. Specifically, it is preferably placed in a high-pressure steam sterilizer in a water-immersed state and treated under normal high-pressure steam sterilization conditions, namely, a treatment temperature of 120 to 150° C. and a treatment time of 20 to 120 minutes.

[0144] The hollow fiber membrane treated with high-pressure hot water is dried and sent to the next cellulose-based polymer coating treatment step.

[0145] The drying method can be widely used by commonly used drying methods such as air drying, reduced pressure drying, hot air drying, microwave drying, etc. The temperature of the hot air during hot air drying is preferably lower than the temperature of the hot water heating treatment.

[0146] 〔Coating process〕

[0147] In the coating step, the surface (including the inner surface of the porous portion) of the hollow fiber membrane (porous membrane) is coated with the second hydrophilic polymer.

[0148] For example, the hollow fiber membrane obtained as described above is then immersed in a coating solution formed from an aqueous solution of a lower alcohol in which a cellulose-based polymer as a second hydrophilic polymer is dissolved, so that the cellulose-based polymer adheres to the membrane surface including the pore surface. Examples of the lower alcohol include ethanol and 2-propanol. The aqueous solution of the lower alcohol also helps to clean the hollow fiber membrane and can remove the vinylpyrrolidone-based polymer that cannot be completely removed by the above high-pressure hot water treatment. That is, by using the aqueous solution of the lower alcohol, there is an advantage that the removal of the remaining vinylpyrrolidone-based polymer and the coating treatment can be carried out simultaneously.

[0149] As the coating solution, preferably, it contains 0.1 to 1.0% by mass, more preferably 0.3 to 0.7% by mass of the cellulose-based polymer and 10 to 30% by mass, more preferably 15 to 25% by mass of 2-propanol in an aqueous solution. If the concentration of the cellulose-based polymer is below the above range, the imparting of hydrophilicity to the hollow fiber membrane becomes insufficient. On the other hand, if it is higher than the above range, the viscosity of the aqueous solution becomes high, and thus there is a problem that the entire membrane cannot be uniformly hydrophilized. In addition, by adjusting the concentration of the lower alcohol to the above range, excessive detachment of the VA copolymer caused by the coating solution can be suppressed. In addition, as the treatment time, it is sufficient to immerse the hollow fiber membrane in the above aqueous solution for about 30 minutes.

[0150] The hollow fiber membrane that has completed the above treatment is taken out and immersed in warm water for heat treatment. At this time, by carrying out under a reduced pressure condition of normal pressure -0.06 to -0.08 MPa, the warm water can penetrate into the interior of the pores. By this treatment, stabilization of the coating of the cellulose-based polymer can be carried out. In an aqueous solution at normal temperature, the hydroxyl groups in the cellulose of the cellulose-based polymer form hydrogen bonds between water molecules and cellulose molecules, and the interaction with the substrate to be coated is weak. Therefore, by hot water treatment, these hydrogen bonds are temporarily cut off, causing a conformational change that enhances the interaction with the hydrophobic substrate and the first hydrophilic polymer, causing reconfiguration, and thus a stable coating can be formed. The temperature of the warm water is preferably 60°C to 95°C, more preferably 80°C to 95°C. The immersion time is preferably 10 minutes to 90 minutes, more preferably 30 minutes to 60 minutes. For the hollow fiber membrane thus obtained, by carrying out the drying treatment again under the above conditions, the hollow fiber membrane of the present embodiment can be obtained.

[0151] Examples

[0152] Hereinafter, the present invention will be described in more detail by way of examples, but the present invention is not limited to these.

[0153] [Example 1]

[0154] The hollow fiber membrane (porous membrane) of Example 1 was manufactured by a method substantially the same as the manufacturing method of the hollow fiber membrane described in the embodiment. The specific manufacturing conditions and the like are as follows.

[0155] (Preparation of spinning dope)

[0156] 28.5 mass% of polyethersulfone (PES: Ultrason (registered trademark) 6020P manufactured by BASF), 9 mass% of polyvinylpyrrolidone (PVP, KOLLIDON VA64 manufactured by BASF), 28.125 mass% of N-methyl-2-pyrrolidone (NMP, manufactured by Mitsubishi Chemical Corporation), and 34.375 mass% of triethylene glycol (TEG, manufactured by Mitsubishi Chemical Corporation) were mixed and heated to dissolve uniformly, thereby preparing a spinning dope. The spinning dope was degassed by vacuum sealing.

[0157] (Preparation of inner liquid)

[0158] An inner liquid was prepared by mixing 42.75 mass% of NMP (solvent), 52.25 mass% of TEG (non-solvent), and 5 mass% of water (RO water: reverse osmosis treated water).

[0159] (Preparation of coagulation liquid)

[0160] A coagulation liquid was prepared by mixing 26 mass% of NMP (solvent), 31 mass% of TEG (non-solvent), and 43 mass% of water (RO water).

[0161] (Coating liquid)

[0162] A coating liquid was prepared by mixing 7.5 mass% of 2-propanol (manufactured by Nacalai Tesque), 0.5 mass% of hydroxypropyl cellulose (HPC, weight average molecular weight: 50000, manufactured by Nippon Soda Co., Ltd.), and 92 mass% of water (RO water).

[0163] <Spinning process>

[0164] The above-mentioned spinning dope (film-forming solution) was ejected from the annular part of a double-tube nozzle (tubular orifice nozzle), and the above-mentioned inner liquid (core liquid) was ejected from the central part of the double-tube nozzle. After the two liquids passed through a dry part (air traveling part 20: air gap) isolated from the external gas, they were drawn at a prescribed speed (spinning speed: drawing speed) in such a manner as to pass through the coagulation liquid 21 and the water washing bath 22.

[0165] At this time, the nozzle temperature (extrusion temperature) was set to 50° C. The distance of the air travel portion (air gap length) was 10 mm. The spinning speed was 19 m / min. It should be noted that the spinning speed is the take-up speed (original Japanese: 引き取り速度).

[0166] The temperature of the coagulation liquid was set to 30°C.

[0167] The temperature of the water bath was set at 55°C.

[0168] The filament (hollow fiber membrane) pulled out from the coagulation liquid is washed in a water washing bath and then wound up at a predetermined speed (winding-up speed) by a winder 23. The ejection amounts of the dope and the inner liquid from the nozzle are adjusted so that the inner diameter of the hollow fiber membrane after the spinning step becomes 205 μm and the membrane thickness becomes 65 μm.

[0169] The wound filament (hollow fiber membrane) was cut into a length of 40 cm, and a bundle of 5,000 cut hollow fiber membranes was made. For the purpose of removing the internal liquid, the bundle was placed in an upright state for 30 minutes. Then, the bundle was immersed in 85°C warm water in an upright state, thereby cleaning the bundle. The warm water was replaced 5 times and the cleaning process was repeated. Then, the bundle kept moist was quickly submerged in a high-pressure steam sterilizer added with 40°C warm water, and high-pressure hot water treatment was performed at 140°C × 20 minutes. Then, microwave drying was performed at a temperature of 35°C in the warehouse. The high-pressure steam treatment and drying were repeated 3 times in total.

[0170] <Coating step using the second hydrophilic molecule>

[0171] Hydroxypropyl cellulose (HPC, manufactured by Nippon Soda Co., Ltd.) was used as the second hydrophilic polymer to coat the surface (including the inner surface of the pores) of the hollow fiber membrane.

[0172] Specifically, the bundle of hollow fiber membranes obtained above was immersed in the above-mentioned coating solution in a container at 25°C. After the container was sealed, the pressure was quickly reduced to -0.07MPa and allowed to stand for 20 minutes. Then, after returning to normal pressure, the bundle was taken out and placed in an upright state for 5 minutes for the purpose of removing the treatment liquid. Then, the bundle was immersed in RO water at 80°C in an upright state to perform a gelation (insolubilization) treatment of HPC for 1 hour. Then, microwave drying was performed at a temperature of 35°C in the warehouse.

[0173] In this way, a bundle of hollow fiber membranes whose surfaces were coated with HPC was obtained. Table 2 shows the measured values of the inner diameter, outer diameter, and membrane thickness of the hollow fiber membranes before drying (after spinning) and after drying after the gelation treatment.

[0174] [Examples 2 to 5 and Comparative Examples 1 to 3]

[0175] In Examples 2 to 5 and Comparative Examples 1 to 3, as shown in Tables 1 and 2, at least any one of the nozzle temperature, the composition ratio of the coagulating liquid, and the film thickness of the hollow fiber membrane after the spinning process was changed with respect to Example 1. “%” in Table 1 means “mass %”. For example, in Example 2 and Comparative Example 1, only the film thickness of the hollow fiber membrane after the spinning process was changed compared with Example 1. Except for this, the hollow fiber membranes of Examples 2 to 5 and Comparative Examples 1 to 3 were manufactured by operating in the same manner as in Example 1.

[0176] It should be noted that Comparative Examples 2 and 3 correspond to Examples 1 and 2 of Patent Document 1, respectively. In Comparative Examples 2 and 3, as the vinylpyrrolidone-based polymer the same as that in Examples 1 and 2 of Patent Document 1, Luvitec VA64 (manufactured by BASF) was used.

[0177]

[0178] For each of the porous membranes (hollow fiber membranes) of the above Examples and Comparative Examples, the following items were measured and so on. The measurement results are shown in Table 2.

[0179] <Inner diameter, outer diameter, and film thickness of the hollow fiber membrane>

[0180] The inner diameter (ID), outer diameter (OD), and film thickness (Δd) of the hollow fiber membranes (after drying) of the above Examples and Comparative Examples were measured by the following method.

[0181] With the hollow fiber membranes not falling off, an appropriate number of hollow fiber membranes were passed through a 3 mm diameter hole opened in the center of a glass slide, and the hollow fiber membranes were cut with a razor along the upper and lower surfaces of the glass slide to obtain a hollow fiber membrane cross-section sample. For the obtained hollow fiber membrane cross-section sample, a projector (Nikon PROFILE PROJECTOR V-12) was used to measure the inner diameter and outer diameter of the hollow fiber membrane.

[0182] Specifically, for each hollow fiber membrane cross-section, the dimensions in the X-X direction and Y-Y direction (two orthogonal directions on the cross-section) of the outer surface of the hollow fiber membrane were measured, and the arithmetic mean of these values was taken as the outer diameter of one hollow fiber membrane cross-section. In addition, for each hollow fiber membrane cross-section, the dimensions in the X-X direction and Y-Y direction (two orthogonal directions on the cross-section) of the hollow part were measured, and the arithmetic mean was taken as the inner diameter of one hollow fiber membrane cross-section. It should be noted that the measurement was carried out in the same manner for 10 cross-sections, and the average value was taken as the inner diameter and outer diameter.

[0183] The film thickness (average value) was calculated by the formula "(outer diameter - inner diameter) / 2" based on the measurement results (average value) of the inner diameter and outer diameter of the hollow fiber membrane.

[0184] <SEM Image>

[0185] The SEM image of the cross-section of the hollow fiber membrane was obtained according to the following steps.

[0186] (1)The hollow fiber membrane was gently washed with water, and the sample was frozen with liquid nitrogen and cut.

[0187] (2)The obtained sample was fixed to the specimen stage in a manner that the cut surface could be observed, and carbon evaporation coating was performed by sputtering.

[0188] (3)The sample after carbon evaporation coating was observed using a scanning electron microscope (Hitachi S-2500) at an acceleration voltage of 10 kV to obtain the SEM image.

[0189] In Figure 5A the SEM image of the cross-section of the porous membrane (hollow fiber membrane) of Example 1 is shown. In addition, in Figure 6 the SEM image of the cross-section of the porous membrane (hollow fiber membrane) of Example 4 is shown. According to Figure 5A and Figure 6 it can be confirmed that the hollow fiber membranes of Example 1 and Example 4 have an asymmetric structure and a structure that is sparse on the inner surface side and dense on the outer surface side.

[0190] <Fabrication of Hollow Fiber Membrane Module>

[0191] The hollow fiber membrane bundle was inserted into a cylindrical container, and both ends were fixed with an adhesive. The ends were cut to obtain a module of the hollow fiber membrane bundle with both ends of the hollow fiber membrane open. The number of hollow fiber membranes was appropriately set. It should be noted that inlets and outlets (ports in Japanese) were provided at two places on the cylindrical surface of the cylindrical container so that the fluid could perfuse both the outer surface and the inner surface of the hollow fiber membrane.

[0192] <Colloidal Gold Filtration Test>

[0193] (Preparation of Colloidal Gold Dispersion)

[0194] After mixing 6 mL of a 20 nm colloidal gold homogenate (Gold Colloid manufactured by BBI Solutions) with 3 mL of a 2.0 mass % bovine serum albumin (Albumin, Bovine Serum, FV, pH 5.2 manufactured by Nacalai Tesque), 3 mL of a 0.4 mass % glutathione (reduced form) aqueous solution (manufactured by Nacalai Tesque) was further added to prepare a 20 nm colloidal gold dispersion. In addition, a 30 nm colloidal gold dispersion was also prepared in the same manner.

[0195] (Filtration test)

[0196] Using the hollow fiber membrane module prepared above, the colloidal gold dispersion (20 nm colloidal gold dispersion or 30 nm colloidal gold dispersion) was dead-end filtered at a pressure of 1000 hPa for 5 minutes (refer to Figure 4 ).

[0197] (Measurement of the thickness of the 20nm colloidal gold capture layer)

[0198] For the hollow fiber membrane after the filtration test, the thickness of the layer (capturing layer) capturing 20 nm colloidal gold (or 30 nm colloidal gold) was measured as follows.

[0199] (1) The hollow fiber membrane (sample) after filtration was adjusted under a microscope at a magnification of 100×1000 so that the thickness portion (cross section) of the membrane from the inner surface to the outer surface side was visible, and an image of the cross section was taken with an image size of 1600 pixels×1200 pixels. It should be noted that for Example 1, the cross-sectional image taken under a microscope is shown in Figure 5B .

[0200] (2) Use binarization software (WinROOF 2013) to binarize the captured image according to the following steps to determine the thickness of the colloidal gold capture layer.

[0201] a. Import the image into binarization software and select "Monochrome Image" in the image processing to convert the captured cross-sectional image into black and white.

[0202] b. Select a rectangular area from the inner surface to the outer surface of the thickness portion of the film, with one side being greater than the film thickness and the other side being 1 μm.

[0203] c. Perform “automatic binarization”, which is represented by a histogram with the horizontal axis representing the concentration value and the vertical axis representing the number of pixels.

[0204] d. Select "discriminant analysis method" to divide the binary image (the above histogram) of the cross-section captured by the microscope into the peaks of the parts stained with colloidal gold and the peaks of the non-stained parts.

[0205] e. In the above histogram, divide the interval between the peak of the part stained with colloidal gold and the peak of the non-stained part into three equal parts, and set the concentration value at the position of 1 / 3 from the stained part as the binarization threshold.

[0206] f. Take the parts where the pixels colored and displayed by binarization in the membrane cross-section are continuous at two or more adjacent points as the parts where colloidal gold is captured.

[0207] g. Measure the distance in the membrane thickness direction between the innermost surface side part and the outermost surface side part where colloidal gold is captured as the thickness of the colloidal gold capture layer.

[0208] It should be noted that in Figure 5B , the thickness of the colloidal gold capture layer is the length of the arrow in the figure.

[0209] (Measurement of ratio a / b)

[0210] For the hollow fiber membrane after the above filtration test, in the same way as the binarization of the captured image of the cross-section of the hollow fiber membrane, a [the distance from the inner surface of the hollow fiber membrane to the outermost surface side position of the first capture layer (20 nm colloidal gold capture layer)] and b [the distance from the inner surface of the hollow fiber membrane to the outermost surface side position of the second capture layer (30 nm colloidal gold capture layer)] described in the embodiment were measured.

[0211] Calculate the ratio a / b based on the measured values of a and b.

[0212] <Virus removal performance: LRV at low pH>

[0213] According to the following steps, the LRV was measured for the virus removal performance of the hollow fiber membrane for a liquid with low pH (pH: 5.2).

[0214] (Preparation of the liquid for measurement)

[0215] The liquid for measurement was prepared by adjusting the pH of the aqueous solution containing phage to 5.2.

[0216] (Steps)

[0217] (1) Using the above hollow fiber membrane module, perform dead-end filtration on the above liquid for measurement (refer to Figure 4 ), and collect the filtrate.

[0218] (2) Culture Pseudomonas aeruginosa in a medium supplemented with the collected filtrate. Here, if the filtrate contains phages, the number of phage plaques of Pseudomonas aeruginosa increases.

[0219] (3) After culturing for a specified time, measure the number of phage plaques. Determine the titer of the bacteria from the number of phage plaques, and calculate the logarithmic reduction value (LRV) using the following formula.

[0220] LRV = log 10 (1 - titer of the filtrate / titer of the test solution)

[0221] <Filtration flux: throughput>

[0222] Measure the filtration flux (throughput) per unit membrane area of the above hollow fiber membrane module according to the following steps.

[0223] (Preparation of the test solution)

[0224] Prepare an aqueous solution containing 0.5% by mass of IVIG (a plasma fraction preparation of antibodies) and phages as the test solution.

[0225] (Calculation of the membrane area)

[0226] Based on the inner diameter of the hollow fiber membrane, calculate the total surface area (membrane area) of the above hollow fiber membrane module using the following formula.

[0227] Membrane area = n × π × ID × L

[0228] Here, n is the number of hollow fiber membranes in the module, π is the pi, ID is the inner diameter of the hollow fiber membrane [m], and L is the effective length of the hollow fiber membrane in the module [m].

[0229] (Steps)

[0230] (1) Use the above hollow fiber membrane module to perform dead-end filtration on the above test solution (refer to Figure 4 ), and continuously collect the filtrate.

[0231] (2) Continuously measure (monitor) the total weight of the continuously collected filtrate.

[0232] (3) Based on the difference in the total weight of the filtrate at the moment 59 minutes after the start and the moment 60 minutes after the start, and the above membrane area, calculate the filtration flux (throughput) per unit membrane area at 60 minutes using the following formula.

[0233] Filtration flux = (total weight of the filtrate at 60 minutes - total weight of the filtrate at 59 minutes) / membrane area

[0234] The inner diameter, outer diameter, and film thickness of the hollow fiber membrane, the thickness of the 20-nm colloidal gold capture layer, the ratio a / b, the LRV at low pH, and the filtration flux after 60 minutes, measured as described above, are shown in Table 2.

[0235]

[0236] From the results shown in Table 2, it can be seen that by making the thickness of the 20-nm colloidal gold capture layer 16.5 μm or more, the LRV of the hollow fiber membrane module increases significantly. In addition, it is considered that if the thickness of the 20-nm colloidal gold capture layer is 20 μm or more, an LRV of 4.7 or more, which is desired for virus removal performance, can be achieved.

[0237] In addition, from the values of a / b and the filtration flux shown in Table 2, when the value of a / b is 1.5 or more, the decrease in throughput over time is suppressed, and more liquid volume can be processed until clogging.

[0238] Explanation of reference numerals

[0239] 10a: spinning dope, 10b: inner liquid, 11: nozzle, 12, 13: in-liquid guides, 14, 15, 16: rollers, 20: air travel section, 21: coagulating liquid, 22: water washing bath, 23: winder, 3: porous membrane (hollow fiber membrane), 4: large component, 5: small component.

Claims

1. A porous membrane, which is a porous membrane having a non-uniform structure in the thickness direction with a sparse first surface and a dense second surface, The porous membrane has a first capture layer, namely a 20-nm colloidal gold capture layer, The first capture layer is a layer that captures colloidal gold having an average particle size of 20 nm when the colloidal gold having an average particle size of 20 nm permeates from the first surface side to the second surface side of the porous membrane, The thickness of the first capture layer is 16.5 μm or more.

2. The porous membrane according to claim 1, wherein The porous membrane has a second capture layer, The second capture layer is a layer that captures colloidal gold having an average particle size of 30 nm when the colloidal gold having an average particle size of 30 nm permeates from the first surface side to the second surface side, The porous membrane satisfies the relationship that a / b is 1.5 or more, The a is the distance from the first surface to the position closest to the second surface side of the first capture layer, The b is the distance from the first surface to the position closest to the second surface side of the second capture layer.

3. The porous membrane according to claim 1 or 2, wherein The porous membrane contains a hydrophobic polymer and a first hydrophilic polymer, The surface of the porous membrane is coated with a second hydrophilic polymer.

4. The porous membrane according to claim 3, wherein, The hydrophobic polymer is a polysulfone-based polymer.

5. The porous membrane according to claim 3 or 4, wherein The first hydrophilic polymer is at least one of polyvinylpyrrolidone and a copolymer of vinylpyrrolidone and vinyl acetate.

6. The porous membrane according to any one of claims 3 to 5, wherein, The second hydrophilic polymer is a cellulose-based polymer.

7. The porous membrane according to any one of claims 1 to 6, which has the shape of a hollow fiber membrane, the inner surface of the hollow fiber membrane is the first surface, and the outer surface of the hollow fiber membrane is the second surface.

8. The porous membrane according to any one of claims 1 to 7, which is used for removing viruses.

9. A purification method, which uses the porous membrane according to any one of claims 1 to 8.

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