Filtering method of cell culture

Abstract

[Problem] To provide a more stable filtration method with which it is possible to separate a culture containing cells from products including enzymes and antibodies at a low tangential flow velocity without clogging. [Solution] A filtration method comprising a filtration step in which a culture solution containing cells, a culture medium, a product, and a defoaming agent is passed through a porous membrane, and a filtrate containing the product is separated from the culture solution, the product of the porosity in the thickness from the outermost surface of the surface on the side of the liquid to be filtered to 0.12% of the film thickness and the porosity in the surface on the side of the liquid to be filtered is 1800%.% or more.

Description

This application claims the benefit of Japanese patent application No. 2023-182493, filed on October 24, 2023, the disclosure of which is incorporated herein by reference in its entirety. Technical Field

[0001] The present invention relates generally to process filtration systems and, more particularly, to a method for filtering cell cultures using hollow fiber membranes having high void and open porosity on the filtrate side surface. Background Art

[0002] Filtration is used to separate, clarify, modify and / or concentrate fluid solutions, mixtures or suspensions. It is often a necessary step in the biotechnology, pharmaceutical and medical industries during the production, processing and analytical stages of drugs, diagnostics and chemicals. For example, filtration can be used to remove desired compounds from a solution, or to remove byproducts, leaving a more concentrated medium. These processes can be appropriately modified by selecting various filter materials, pore sizes and / or other filtration variables.

[0003] When producing cell culture, it is usually necessary to remove the waste in the developing culture. The progress of biomanufacturing process now allows large-scale production of cell culture, making it possible to produce recombinant proteins, virus-like particles (VLP), gene therapy particles and vaccines, usually using processing container devices. Cell retention devices that remove metabolic waste and update the culture with additional nutrients are widely available. Usually, this retention uses tangential flow filtration, which is carried out by perfusion filtration of hollow fiber membrane processing container culture. In addition, bioprocessing operations are being extended, and continuous culture has been adopted. Such operation may be extended to several days, weeks or months. Many typical components, such as filters, are expected to be free of scaling under such a long time, or fully operate when maintenance or replacement is not required.

[0004] Hollow fiber membranes are commonly used for cell culture perfusion and separation of products, but such use may cause membrane fouling due to cell debris. Moreover, fouling may cause the expected product to remain in the membrane instead of passing through it. Hollow fiber membranes are usually made of polyethersulfone (PES), polysulfone, cellulose, polyvinylidene fluoride, polypropylene, polyethylene and other materials, and there is a continuous need for membranes that can resist fouling while allowing filtration of solutions with high solids content. Fluororesins such as polyethylene (PE) and polyvinylidene fluoride (PVDF) are hydrophobic materials that have been commonly used in industrial filtration, and it is known that certain molecules are less likely to be adsorbed. Specifically, low levels of adsorption were found for polyphenols, polysaccharides, and tannins. On the other hand, the structure of the membrane varies greatly depending on the manufacturing method, and even if the membrane is made of the same material, the fouling phenomenon of the membrane varies greatly depending on the manufacturing method.

[0005] The following patent document 1 describes the relationship between the permeate filtration rate and the medium flow rate in tangential flow filtration. It also describes the use of a porous membrane containing a dense layer. In addition, as Figure 6 As shown, tangential flow filtration, also known as cross-flow filtration, is a method in which the sample of the solution to be filtered flows back in a direction parallel to the membrane surface, exerting a certain pressure on the membrane and allowing particles smaller than the membrane pore size to pass through. In contrast, common direct flow filtration methods, such as syringe filters and centrifugal filters, pass the liquid from the top to the bottom through the membrane surface. In this case, the particles contained in the sample will be trapped on the membrane surface and inside, accumulating to cause blockage and impose excessive pressure load on the sample. In contrast, the characteristic of tangential flow filtration is that because the sample continuously flows back in a direction parallel to the membrane surface, particles and molecules larger than the membrane pore diameter remain upstream of the membrane, the deposition of particles on the membrane is suppressed, and the load on the sample is low.

[0006] The following Patent Document 2 describes a cell culture method and apparatus that can remove cell growth inhibitory substances and return at least one component of serum, which is an expensive high-molecular component, to a culture tank during high-density culture to reduce running costs.

[0007] The following Patent Document 3 describes a method for increasing the yield of a recombinant protein in a mammalian cell culture expressing a recombinant protein, comprising establishing a mammalian cell culture in a serum-free medium in a bioreactor and inducing cell growth arrest by perfusing with a serum-free perfusion medium having an L-asparagine concentration of 5 mM or less.

[0008] The following Patent Document 4 describes a study of monitoring and measuring the permeate flow rate from a filtration membrane during perfusion culture, and switching the filtration membrane when the permeate flow rate is at least 10% of the permeate flow rate at the start of tangential flow filtration.

[0009] The following Patent Document 5 describes a method for operating a tangential flow process in perfusion culture, which method can efficiently separate products. Prior art literature Patent Literature

[0010] Patent Document 1: Japanese Patent Application Publication No. 2018-76291 Patent Document 2: Japanese Patent Application Publication No. 2000-32977 Patent Document 3: Japanese Patent Application No. 2014-520534 Patent Document 4: Japanese Patent Application Publication No. 2014-024824 Patent Document 5: International Publication No. 2015 / 188009 Summary of the invention Problems to be solved by the invention

[0011] Patent documents 1-4 describe a method for recovering useful substances from a culture medium during continuous culture of cells producing useful substances, the method comprising an effusion step of discharging the culture medium from a cell culture tank and adding an amount of fresh culture medium equal to the discharged culture medium into the above-mentioned culture tank; and a filtration step of filtering the culture medium extracted from the above-mentioned culture tank using a porous membrane that does not substantially have a dense layer, wherein the filtration in the above-mentioned filtration step is tangential flow filtration. Furthermore, Patent Document 5 describes only a technique for efficiently separating a product from impurities.

[0012] However, although all of Patent Documents 1-4 disclose research on membrane usage such as the speed of the permeate in the filtration process, there is no record of the most suitable membrane for tangential flow filtration, and it is not clear what specific structure and material can achieve stable tangential flow. In the continuous filtration process, membrane clogging is bound to occur, which must be solved. In addition, in terms of separation, it is also necessary to retain cells and microorganisms on the concentration side, while the product is not blocked by the membrane and permeates to the permeate side. In addition, when the culture object is animal cells, if the shear rate is too high, it will cause defects in cell growth, so there is a problem that the linear velocity of the tangential flow cannot be increased.

[0013] In view of the above-mentioned prior art level, the problem to be solved by the present invention is to provide a more stable filtration method, which can separate the culture from the product at a lower tangential streamline velocity and will not cause clogging. Solution to the problem

[0014] In order to solve the above-mentioned problems, the inventors repeatedly conducted in-depth research experiments and unexpectedly found that the use of a hollow fiber membrane with high porosity and open porosity on the surface of the filtered liquid side has good permeability to the culture product and is not easy to be clogged even when the tangential streamline velocity is low, thereby completing the present invention.

[0015] That is, the present invention is as follows. [1] A filtration method comprising the steps of passing a culture medium containing cells, a culture medium, a product and a defoaming agent through a porous membrane, and separating a filtrate containing the product from the culture medium, wherein the product of the porosity from the outermost surface of the surface of the porous membrane on the side of the filtered liquid (the Japanese term corresponding to the "outermost surface" described herein is "outermost surface") to a thickness of 0.12% of the membrane thickness and the open porosity of the surface on the side of the filtered liquid is 1800%·% or more. [2] The filtration method according to [1] above, wherein the porosity from the outermost surface of the filtrate-side surface of the porous membrane to 0.12% of the membrane thickness is 50% or more. [3] The filtration method according to [1] or [2] above, wherein the porosity of the surface of the porous membrane on the side of the filtrate is 30% or more. [4] A filtration method according to any one of [1] to [3] above, wherein the ratio of the porosity from the outermost surface of the filtrate side surface to 0.12% of the membrane thickness to the open porosity of the filtrate side surface is 1.70 or greater. [5] A filtration method according to any one of the above [1] to [4], wherein the product of the porosity from the outermost surface of the filtered liquid side surface of the porous membrane to 0.12% of the membrane thickness and the open porosity of the filtered liquid side surface is 2800%·% or more. [6] A filtration method according to any one of the above [1] to [5], wherein the product of the porosity from the outermost surface of the filtrate side surface of the porous membrane to a thickness of 300 nm in the membrane thickness direction and the open porosity of the filtrate side surface is 860%·% or more. [7] The filtration method according to [6] above, wherein the porosity in a thickness of 300 nm in the membrane thickness direction from the outermost surface of the filtrate-side surface of the porous membrane is 35% or more. [8] The filtration method according to [7] above, wherein the porosity of the filtrate-side surface of the porous membrane is 30% or more. [9] The filtration method according to any one of [1] to [8] above, wherein the cross-sectional pore size from the outermost surface of the filtrate-side surface of the porous membrane to 0.12% of the membrane thickness is 1000 nm or less.

[10] The filtration method according to any one of [1] to [9] above, wherein the cross-sectional pore diameter from the outermost surface on the filtrate side of the porous membrane to a thickness of 300 nm in the membrane thickness direction is 300 nm or less.

[11] The filtration method according to any one of [1] to

[10] above, wherein the porous membrane has a thickness of 100 μm to 800 μm.

[12] The filtration method according to any one of [1] to

[11] above, wherein the flux of the porous membrane in the filtration step is 1 LMH or more.

[13] The filtration method according to any one of [1] to

[12] above, wherein the porous membrane is a hollow fiber membrane, and the filtration step is perfusion culture filtration.

[14] The filtration method according to any one of [1] to

[13] above, wherein the linear velocity of the tangential flow through the hollow fiber membrane during the perfusion culture is 0.3 m / s or less.

[15] The filtration method according to any one of [1] to

[14] above, wherein the resin forming the porous membrane is a thermoplastic resin.

[16] The filtration method according to

[15] above, wherein the thermoplastic resin contains a fluororesin as a main component.

[17] The filtration method according to the above

[16] , wherein the fluororesin comprises at least one selected from the group consisting of polyvinylidene fluoride resin (PVDF), chlorotrifluoroethylene resin, tetrafluoroethylene resin, ethylene-tetrafluoroethylene copolymer (ETFE), ethylene-monochlorotrifluoroethylene copolymer (ECTFE), hexafluoropropylene resin, and a mixture of these resins.

[18] The filtration method according to

[15] above, wherein the thermoplastic resin contains a polyolefin resin as a main component.

[19] The filtration method according to

[15] above, wherein the thermoplastic resin is polyethylene (PE) or polypropylene (PP).

[20] The filtration method according to any one of [1] to

[19] above, wherein the product is selected from proteins including enzymes and antibodies, amino acids, nucleic acids, and organic substances. Effects of the Invention

[0016] The method for filtering culture fluid involved in the present invention uses a membrane with good connectivity of micropores from the inner side of the membrane on the treated liquid side as a porous filtration membrane to the outer side of the membrane on the filtrate side (that is, the surface on the filtrate side has high porosity and open porosity). Therefore, it is possible to separate a culture containing cells from a product containing enzymes and antibodies at a lower tangential streamline velocity, the product has good permeability, cells are not likely to cause clogging, and the filtration performance is excellent. In addition, this method is a filtration method in which the membrane is not damaged during the filtration operation, so it is possible to efficiently separate proteins such as antibodies. BRIEF DESCRIPTION OF THE DRAWINGS

[0017]

Figure 1

Figure 2

Figure 3A

Figure 3B

Figure 4

Figure 5

Figure 6

Figure 7

[0018] The preferred embodiments of the present invention (hereinafter referred to as "embodiments") are described in detail below. It should be noted that the embodiments shown below illustrate devices and methods for implementing the technical ideas of the present invention, and the combination of components and the like of the technical ideas of the present invention are not specific to the following contents. The technical ideas of the present invention can be modified in various ways in the patent claims.

[0019] In the following description, the upper limit or lower limit recorded in a certain numerical range in the numerical range recorded in stages can be replaced by the upper limit or lower limit of the numerical range in other staged records. In the present embodiment, the upper limit or lower limit recorded in a certain numerical range can also be replaced by the value recorded in the embodiment. In addition, about the term "process" in the following description, it goes without saying that an independent process, when it cannot be clearly distinguished from other processes, is also included in this term as long as the function of the "process" can be realized.

[0020] The filtration method of the present embodiment is characterized in that the method includes a filtration step of allowing a culture solution containing cells, a culture medium, a product and a defoaming agent to pass through a porous membrane, and separating a filtrate containing the product from the culture solution, wherein the product of the porosity from the outermost surface of the filtered liquid side surface of the porous membrane to a thickness of 0.12% of the membrane thickness and the open porosity of the filtered liquid side surface is 1800%·% or more.

[0021] The filtration method of this embodiment is characterized in that it includes a filtration step of passing a culture solution containing cells, a culture medium, a product, and a defoaming agent through a porous membrane formed of a resin with a three-dimensional network structure, and separating a filtrate containing the product and a culture solution containing cells from the culture. The above-mentioned products are not particularly limited and include proteins including enzymes and antibodies, amino acids, nucleic acids, organic substances, etc., and proteins including enzymes and antibodies that should be produced by cells, such as transgenic cells (such as CHO cells) that produce useful proteins. In addition, before, after, or before or after the above-mentioned filtration step, an additional treatment step such as centrifugal separation, diatomaceous earth filtration, other membrane separation, sieving treatment, etc. may be further included. The shape of the porous membrane is not particularly limited, and examples thereof include flat membranes, tubular membranes, and hollow fiber membranes. From the viewpoint of space saving of the filtration device, that is, because the membrane area per unit volume of the membrane module can be increased, a hollow fiber membrane is preferred.

[0022] The above-mentioned product can be an antibody protein, as described in the general definition in biochemistry, and can be listed as a glycoprotein molecule (also called gamma globulin or immunoglobulin) produced by B lymphocytes as a defense mechanism against infection in vertebrates. For example, in the embodiment, the antibody purified by the porous membrane is used as a human drug, and has substantially the same structure as the antibody in the human body as the subject of administration.

[0023] The above products can be various antibody vaccines, vector viruses, plasmid DNA or industrial enzymes such as amylase and protease. Different culture objects can be selected for different products. For example, when the product is an enzyme, the culture object can be bacteria such as genetically modified Escherichia coli; when the product is a protein such as albumin, the culture object can be genetically modified Pichia pastoris.

[0024] Hereinafter, the structure, material (materials), and production method of the porous membrane used in the method for filtering a culture solution according to the present embodiment will be described in detail.

[0025] The porous membrane of the present embodiment preferably contains a fluororesin, such as a vinylidene fluoride system or a trifluorochloroethylene system as a main component, as a polymer component (such as a thermoplastic resin) constituting the membrane. Here, "containing ... as a main component" means containing 50% by mass or more in terms of the solid content of the polymer component. The above-mentioned polymer component may be only one kind or a combination of multiple kinds.

[0026] In addition, the weight average molecular weight (Mw) of vinylidene fluoride resin is not particularly limited, preferably 100,000 and above and 1,000,000 and below, more preferably 150,000 and above and 1,500,000 and below. In addition, not limited to the vinylidene fluoride resin of single molecular weight, it is also possible to mix a variety of different molecular weight vinylidene fluoride resins. In addition, in the present embodiment, about weight average molecular weight (Mw), it can be measured by gel permeation chromatography (GPC) based on a standard resin with known molecular weight.

[0027] On the other hand, the porous membrane may contain other polymer components. The other polymer components are not particularly limited, but are preferably compatible with the vinylidene fluoride resin, and for example, fluorine-based resins that exhibit high chemical resistance like the vinylidene fluoride resin can be appropriately used.

[0028] As the form of the above-mentioned porous membrane, for example, it can be a form of a membrane structure having a hollow fiber membrane. Here, the hollow fiber membrane means a membrane having a hollow ring-shaped form. Since the porous membrane has a membrane structure of a hollow fiber membrane, the membrane area per unit volume of the component can be increased compared to a planar membrane. However, the porous membrane of the present embodiment is not limited to a porous membrane having a membrane structure of a hollow fiber membrane (a hollow fiber-shaped porous membrane), and may have other membrane structures such as a flat membrane and a tubular membrane. The porous membrane of the present embodiment preferably contains the hollow fiber membrane of thermoplastic resin, and can also be the hollow fiber membrane consisting of thermoplastic resin only.The above-mentioned thermoplastic resin preferably contains fluororesin as main component, and can also be only composed of fluororesin.As the above-mentioned fluororesin, preferably containing at least one selected from the group consisting of vinylidene fluoride resin (PVDF), chlorotrifluoroethylene resin, tetrafluoroethylene resin, ethylene-tetrafluoroethylene copolymer (ETFE), ethylene-chlorotrifluoroethylene copolymer (ECTFE), hexafluoropropylene resin and a mixture of these resins, can also only be composed of at least one selected from the group consisting of vinylidene fluoride resin (PVDF), chlorotrifluoroethylene resin, tetrafluoroethylene resin, ethylene-tetrafluoroethylene copolymer (ETFE), ethylene-chlorotrifluoroethylene copolymer (ECTFE), hexafluoropropylene resin and a mixture of these resins.

[0029] The porous membrane of the present embodiment is preferably a porous membrane in which the ratio of the porosity from the outermost surface of the filtered liquid side surface to 0.12% of the membrane thickness (the portion from the outermost surface to the position of 0.12% relative to 100% of the membrane thickness in the membrane thickness direction) to the open porosity of the filtered liquid side surface is 1.70 or above. When the above ratio is 1.70 and above, the connectivity of the pores on the surface and the pores near the surface of the membrane interior is good, and the pores near the surface that are most helpful for filtration are not easy to be blocked. In addition, due to the good connectivity of the pores near the surface, dirt can be easily removed by washing or cross-flow effects such as backwashing, so high filtering performance can be shown. The above ratio is preferably 1.75 and above, more preferably 1.70 and above and 2.50 and below. When the above ratio is 2.50 and below, the polymer forming the pores on the surface is not easy to be deformed, and the blocking performance can be maintained. It is expected that the above ratio is 1.70 or more in the thickness from the outermost surface of the filtrate side surface to 0.12% of the membrane thickness, as described above. This is important for the porosity near the surface in contact with the filtrate to show high filtration performance. This is because the concentration of membrane dirt on the surface in contact with the filtrate is the highest, and pores are blocked, thereby affecting the performance of the entire membrane.

[0030] The porous membrane of the present embodiment preferably has an opening ratio of 30% or more on the surface on the filtrate side. When the porosity is 30% or more, high filtration performance can be achieved. When the porosity is high, the load of membrane dirt in each hole is small, and the number of completely blocked holes is small, so it is presumed that high filtration performance can be achieved. The above porosity is preferably 32% or more, and more preferably 35% or more. In addition, the above porosity can be 60% or less.

[0031] The porous membrane of this embodiment preferably has a porosity of 50% or more, more preferably 60% or more, from the filtrate side surface to 0.12% of the membrane thickness. When 50% or more, high filtration performance can be exhibited for a wider range of filtrate properties. When the above-mentioned porosity is 50% or more, similar to the open porosity, the amount of membrane dirt loaded in each hole is small, and there are few completely blocked holes, so it is estimated that high filtration performance can be exhibited. Preferably, it is 50% or more and 95% or less, more preferably 55% or more and 85% or less, and further preferably 60% or more and 80% or less. When the above-mentioned porosity is 95% or less, it can have sufficient strength in practical applications. The porous membrane of this embodiment preferably has an opening rate of 30% or more on the surface on the filtrate side and a porosity of 50% or more in the thickness from the outermost surface of the filtrate side to 0.12% of the membrane thickness.

[0032] The porous membrane of the present embodiment preferably has a cross-sectional pore diameter of 1000 nm or less in the thickness from the outermost surface on the filtrate side to 0.12% of the membrane thickness. The cross-sectional pore size is preferably 100 nm or more and 900 nm or less, more preferably 200 nm or more and 280 nm or less. When the cross-sectional pore size is 1000 nm or less, sufficient blocking performance can be achieved in practical applications. The porous membrane of this embodiment preferably has a product of a porosity from the surface of the filtered liquid side to a thickness of 0.12% of the membrane thickness and an open porosity of the filtered liquid side surface of 1800%·%. It is preferably 2000%·% and above, and more preferably 2700%·% and above. When the above product is 1800%·% and above, since the load of membrane dirt in each hole in the surface and thickness direction is very small, there are very few completely blocked holes, and therefore it is presumed that high filtering performance can be exhibited. In addition, it can also be 5000%·% and below.

[0033] The porous membrane of this embodiment preferably has a product of a porosity from the filtrate side surface to a thickness of 300 nm and an open porosity of the filtrate side surface of 860%·%. Preferably, it is 875%·% or more. When the above product is 860%·% or more, since the load of membrane dirt in each hole in the surface and thickness direction is very small, there are very few completely blocked holes, and therefore it is presumed that high filtration performance can be exhibited. Alternatively, it may be 5000%·% or less.

[0034] The porous membrane of this embodiment preferably has a porosity of 30% or more, more preferably 35% or more, from the filtrate side surface to a membrane thickness of 300 nm. When it is 50% or more, high filtration performance can be exhibited for a wider range of filtrate properties. When the above-mentioned porosity is 30% or more, similar to the open porosity, the amount of membrane dirt loaded in each hole is small, and the number of completely blocked holes is small, so it is estimated that high filtration performance can be exhibited. Preferably, it is 35% or more and 85% or less, and more preferably, it is 35% or more and 80% or less. When the above-mentioned porosity is 85% or less, it can have sufficient strength in practical applications.

[0035] The porous membrane of the present embodiment preferably has a cross-sectional pore diameter of 300 nm or less from the outermost surface on the filtrate side to a membrane thickness of 300 nm. The cross-sectional pore size is preferably 50 nm or more and 250 nm or less. When the cross-sectional pore size is 300 nm or less, sufficient blocking performance can be achieved in practical applications.

[0036] When the porous membrane of the present embodiment is a hollow fiber membrane, the inner diameter is preferably 0.3 mm or more and 5 mm or less. When the inner diameter is 0.3 mm or more, the pressure loss of the liquid flowing in the hollow fiber membrane will not become too large, and when the inner diameter is 5 mm or less, it is easy to show sufficient compression strength and burst strength under a relatively thin film thickness. The inner diameter is more preferably 0.4 mm or more and 3 mm or less, and more preferably 0.5 mm or more and 2 mm or less.

[0037] In addition, the film thickness is preferably 0.1 mm and above and 1 mm and below. When the film thickness is 0.1 mm and above, it is easy to show sufficient compression strength and burst strength, and when the film thickness is 1 mm and below, it is easy to show sufficient water permeability. The film thickness is preferably 100 μm and above and 800 μm and below, more preferably 0.15 mm and above and 0.8 mm and below, further preferably 0.16 mm and above and 0.6 mm and below, 0.17 mm and above and 0.5 mm and below. In addition, it is preferably 0.1 mm and above and 0.5 mm and below.

[0038] The outer diameter is preferably 0.5 mm and above and 5 mm and below. When the outer diameter is 0.5 mm and above, it can have sufficient tensile strength. When the outer diameter is 5 mm and below, the number of filling roots can be increased in the container containing the porous membrane (preferably porous hollow fiber membrane). The outer diameter is more preferably 0.6 mm and above and 4 mm and below, and more preferably 0.7 mm and above and 3 mm and below.

[0039] The pure water permeability of the porous membrane of this embodiment is preferably 1000 L / m 2 / hr and above and 20000L / m 2 / hr and below. When the pure water permeability is within this range, both filtration performance and blocking performance can be taken into account. The pure water permeability is preferably 1200L / m 2 / hr and above and 18000L / m 2 / hr and below, more preferably 3000L / m 2 / hr and above and 12000L / m 2 / hr and below.

[0040] The flux of the porous membrane of this embodiment is preferably 1 LMH or more.

[0041] The porous membrane of this embodiment preferably has a porosity of 50% or more from the viewpoint of water permeability, and preferably 90% or less from the viewpoint of strength, more preferably 55% or more and 85% or less, and even more preferably 65% ​​or more and 80% or less. The present inventors have found that factors including the porosity of the extreme surface layer (a difference cannot be detected by measuring the porosity of the entire membrane) have an influence on the filtration performance. Specifically, it has been found that the filtration performance is improved by controlling the ratio of the porosity from the outermost surface of the filtrate side surface to 0.12% of the membrane thickness to the open porosity of the filtrate side surface or the product of the porosity from the outermost surface of the filtrate side surface to 0.12% of the membrane thickness and the open porosity of the filtrate side surface.

[0042] The porous membrane (preferably a porous hollow fiber membrane) is preferably a three-dimensional network structure. The three-dimensional network structure referred to in this application refers to a structure that is Figure 1 The structure shown. For example, the thermoplastic resin a is joined to form a grid, and a void portion b is formed. In the three-dimensional network structure, the lumps of the resin of the so-called spherulite structure are almost not observed. The void portion b of the three-dimensional network structure is preferably surrounded by the thermoplastic resin a, and the various parts of the void portion b are interconnected. Since most of the thermoplastic resin used forms a three-dimensional network structure that can contribute to the strength of the porous membrane (preferably a hollow fiber membrane), a high-strength support layer can be formed. In addition, chemical resistance is also improved. Although the reason for the improvement in chemical resistance is not clear, it is believed that it may be due to the large amount of thermoplastic resin that forms a grid that contributes to strength. Therefore, even if a part of the grid is eroded by the drug, it will not have a significant impact on the strength of the entire layer. The porous membrane (preferably a porous hollow fiber membrane) may be a single-layer structure or a multi-layer structure of two or more layers. The layer having the surface on the filtrate side is referred to as layer (A), and the layer having the surface on the filtrate side is referred to as layer (B). For example, layer (A) and layer (B) share functions as follows: layer (A) is set as a so-called blocking layer, which uses a small surface pore size to prevent foreign matter contained in the treated liquid (raw water) from passing through the membrane, and layer (B) is set as a so-called supporting layer, which has the function of not reducing water permeability as much as possible while ensuring high mechanical strength. The sharing of functions between layer (A) and layer (B) is not limited to the above content. The porous membrane of this embodiment can be a surface having only one surface as the filtered liquid side surface.

[0043] Below, the case of a two-layer structure in which layer (A) is set as a blocking layer and layer (B) is set as a supporting layer is described. The thickness of layer (A) is preferably 1 / 100 or more and less than 40 / 100 of the film thickness. In this way, by making the thickness of layer (A) thicker, it can be used even if the raw water contains insoluble substances such as sand or coagulants. This is because the surface pore size does not change even if there is some wear. As long as it is within the range of this thickness, a balance between the desired blocking performance and high water permeability can be achieved. The thickness of layer (A) is more preferably 2 / 100 or more and 30 / 100 or less of the film thickness. The thickness of layer (A) is preferably 1 μm or more and 100 μm or less, more preferably 2 μm or more and 80 μm or less.

[0044] As a filtration process in the filtration method of this embodiment, for example, it can be a so-called internal pressure filtration process in which a culture broth (treated liquid) containing cells, culture medium, useful substances and defoaming agents is supplied to the hollow part (inner surface) of the porous hollow fiber membrane, passed through the membrane thickness (wall thickness) part of the porous hollow fiber membrane, and the liquid seeping out from the outer surface of the porous hollow fiber membrane is taken out as the filtrate. It can also be a so-called external pressure filtration process in which a treated liquid is supplied from the outer surface of the porous hollow fiber membrane, and the filtrate seeping out from the inner surface of the porous hollow fiber membrane is taken out through the hollow part. In this specification, the term "interior of the porous film" refers to a film thickness (wall thickness) portion where numerous micropores are formed.

[0045] A specific production method in the case of a hollow fiber membrane will be described. The method for manufacturing a porous membrane (preferably a porous hollow fiber membrane) of the present embodiment preferably includes: a step of ejecting a molten kneaded product containing a thermoplastic resin, an organic liquid, and an inorganic powder from a spinneret having an annular ejection port to form a hollow fiber-shaped molten kneaded product; and a step of extracting and removing the organic liquid and the inorganic powder after solidifying the hollow fiber-shaped molten kneaded product to prepare a porous membrane (preferably a porous hollow fiber membrane). The molten kneaded product may be composed of two components, a thermoplastic resin and a solvent, or may be composed of three components, a thermoplastic resin, an inorganic powder, and a solvent.

[0046] The thermoplastic resin used in the method for manufacturing the porous membrane (preferably a porous hollow fiber membrane) of the present embodiment is a resin that has elasticity and does not show plasticity at room temperature, but shows plasticity by appropriate heating, thereby being able to be molded. In addition, a thermoplastic resin is a resin that returns to its original elastomer when cooled and the temperature decreases, and does not undergo chemical changes such as molecular structure during this period (for example, see "Chemical Dictionary 6 Reduced Edition" edited by the Chemical Dictionary Editorial Committee, Kyoritsu Publishing, pages 860 and 867, 1963).

[0047] As examples of thermoplastic resins, resins recorded under the thermoplastics item (pages 829-882) of "12695 Chemical Goods" (Chemical Industry Daily, 1995), and resins recorded in pages 809-810 of "Chemical Handbook Application Revised 3rd Edition" (Compiled by the Chemical Society of Japan, Maruzen, 1980), etc. can be cited. As the names of specific examples of thermoplastic resins, polyolefins such as polyethylene and polypropylene, fluororesins such as polyvinylidene fluoride, ethylene-vinyl alcohol copolymers, polyamides, polyetherimides, polystyrenes, polysulfones, polyvinyl alcohol, polyphenylene ether, polyphenylene sulfide, cellulose acetate, polyacrylonitrile, etc. can be cited. Among them, from the aspect of strength performance, crystalline thermoplastic resins such as polyolefins, polyvinylidene fluoride, ethylene-vinyl alcohol copolymers, and polyvinyl alcohol can be preferably used. Further preferably, fluororesins such as polyolefins and polyvinylidene fluoride can be used, because they are hydrophobic and thus have high water resistance, and it can be expected to have durability in the filtration of common aqueous liquids. Specifically, the above-mentioned fluororesin preferably contains a single one or a combination of two or more of a mixture of these resins as the main component, and more preferably only consists of a resin composed of a single one or a combination of two or more of them. Particularly preferably, the above-mentioned fluororesin can use polyvinylidene fluoride with excellent chemical durability such as chemical resistance. As polyvinylidene fluoride, vinylidene fluoride homopolymer, vinylidene fluoride ratio 50 mol% and above vinylidene fluoride copolymer can be cited. As a vinylidene fluoride copolymer, a copolymer composed of vinylidene fluoride and one or more monomers selected from tetrafluoroethylene, hexafluoropropylene, chlorotrifluoroethylene or ethylene can be cited. As polyvinylidene fluoride, vinylidene fluoride homopolymer is particularly preferred.

[0048] The concentration of the thermoplastic resin in the melt kneaded product is preferably 30% to 48% by mass, preferably 32% to 45% by mass. If the concentration is 30% by mass or more, it is easy to ensure mechanical strength, and if the concentration is 48% by mass or less, the water permeability will not be reduced.

[0049] When the porous membrane is a two-layer structure, the concentration of the thermoplastic resin in the melt-kneaded product of the layer (B) is preferably 34 to 48% by mass, more preferably 35 to 45% by mass. The concentration of the thermoplastic resin in the melt-kneaded product of layer (A) is preferably 10% by mass or more and 35% by mass or less, and more preferably 12% by mass or more and 35% by mass or less. If the concentration is 10% by mass or more, both the pore size and the mechanical strength of the surface can be taken into account, and if the concentration is 35% by mass or less, the water permeability will not be reduced.

[0050] As the organic liquid, an organic liquid that is a potential solvent for the thermoplastic resin used in this embodiment is used. In this embodiment, the potential solvent refers to a solvent that hardly dissolves the thermoplastic resin at room temperature (25° C.) but can dissolve the thermoplastic resin at a temperature higher than room temperature. The organic liquid only needs to be liquid at the melt kneading temperature with the thermoplastic resin, and does not need to be liquid at room temperature.

[0051] When the thermoplastic resin is polyethylene or polypropylene, examples of the organic liquid include phthalate esters such as dibutyl phthalate, diheptyl phthalate, dioctyl phthalate, di(2-ethylhexyl) phthalate, diisodecyl phthalate, and tricosyl phthalate; sebacic acid esters such as dibutyl sebacate; adipic acid esters such as dioctyl adipate; trimellitic anhydride esters such as trioctyl trimellitic anhydride; phosphate esters such as tributyl phosphate and trioctyl phosphate; glycerol esters such as propylene glycol dicaprate and propylene glycol dioleate; paraffins such as liquid paraffin; and mixtures thereof.

[0052] When the thermoplastic resin is polyvinylidene fluoride, examples of the organic liquid include phthalates such as dimethyl phthalate, diethyl phthalate, dibutyl phthalate, dicyclohexyl phthalate, diheptyl phthalate, dioctyl phthalate, and di(2-ethylhexyl) phthalate; sebacic acid esters such as dibutyl sebacate; adipic acid esters such as dioctyl adipate; benzoic acid esters such as methyl benzoate and ethyl benzoate; phosphates such as triphenyl phosphate, tributyl phosphate, and tricresyl phosphate; ketones such as γ-butyrolactone, ethylene carbonate, propylene carbonate, cyclohexanone, acetophenone, and isophorone; and mixtures thereof.

[0053] When the thermoplastic resin is polyketone or ethylene vinyl alcohol, examples of the organic liquid include phthalate esters such as dimethyl phthalate, diethyl phthalate, dibutyl phthalate, dicyclohexyl phthalate, diheptyl phthalate, dioctyl phthalate, and di(2-ethylhexyl) phthalate; sebacic acid esters such as dibutyl sebacate; adipic acid esters such as dioctyl adipate; trimellitic acid; Trimellitic anhydride esters such as trioctyl anhydride; benzoic acid esters such as methyl benzoate and ethyl benzoate; phosphate esters such as triphenyl phosphate, tributyl phosphate, and tricresyl phosphate; glycerol esters such as propylene glycol dicaprate and propylene glycol dioleate; polyethers such as polyethylene glycol; paraffins such as liquid paraffin; ketones such as γ-butyrolactone, ethylene carbonate, propylene carbonate, cyclohexanone, acetophenone, and isophorone; glycerol; and mixtures thereof.

[0054] As inorganic fine powder, silicon dioxide, aluminum oxide, titanium oxide, zirconium dioxide, calcium carbonate, etc. can be cited, and silicon dioxide fine powder with an average primary particle size of 3nm and above and 500nm and below is particularly preferred. More preferably, it is 5nm and above and 100nm and below. More preferably, it is a hydrophobic silica fine powder that is not easy to condense and has good dispersibility, and further preferably, the hydrophobic silica with a MW (methanol wettability) value of 30% by volume and above. The MW value mentioned here refers to the value of the volume % of methanol that completely wets the powder. Specifically, the MW value is determined by the following: adding silicon dioxide to pure water, and when adding methanol to the liquid surface under stirring, the volume % of methanol in the aqueous solution when 50% by mass of silicon dioxide is precipitated is obtained. The above-mentioned "average primary particle size of inorganic fine powder" means the value obtained according to the analysis of electron microscope photos. That is, first, a group of inorganic fine powders are pretreated using the method of ASTMD3849. Thereafter, the diameters of 3,000 to 5,000 particles photographed on a transmission electron microscope photograph were measured, and the values ​​were arithmetic averaged to calculate the average primary particle size of the inorganic fine powder.

[0055] For the addition amount of inorganic fine powder, it is preferred that the mass ratio of inorganic fine powder in the melt kneaded product is 5 mass % or more and 50 mass % or less. More preferably, it is 10 mass % or more and 40 mass % or less. If the ratio of inorganic fine powder is 5 mass % or more, the effect of inorganic fine powder kneading can be fully demonstrated, and if it is 40 mass % or less, spinning can be stably performed.

[0056] The melt kneading can be performed using a common melt kneading method, for example, using an extruder. The following describes the case where an extruder is used, but the melt kneading method is not limited to an extruder. Figure 2 An example of a production apparatus for carrying out the production method of the present embodiment is shown.

[0057] Figure 2 The porous hollow fiber membrane manufacturing apparatus shown includes an extruder 10, a hollow fiber molding nozzle 20, a coagulation bath 30 storing a solution for coagulating a membrane-forming stock solution, and a plurality of rollers 50 for conveying and winding a porous hollow fiber membrane 40. Reference numeral 60 is a suction machine, and reference numeral 70 is a high-temperature container. Figure 2 The space S shown is an air gap portion through which the membrane-forming stock solution ejected from the hollow fiber molding nozzle 20 passes before reaching the solution in the coagulation bath 30 .

[0058] A hollow fiber forming nozzle 20 having one or more annular ejection ports arranged in a concentric circle is installed at the front end of the extruder 10, and the molten kneaded product is extruded by the extruder 10 and ejected from the hollow fiber forming nozzle 20. In the case of manufacturing a multilayer structure membrane, there are the following methods: a method of installing a hollow fiber forming nozzle 20 having two or more annular ejection ports at the front end of the extruder 10, and supplying the molten kneaded product to each annular ejection port using a different extruder 10 for extrusion; a method of coating the remaining layers after manufacturing one of the multiple layers. For example, in the former method of manufacturing using different extruders, the molten kneaded products supplied separately are merged and overlapped at the ejection port to obtain a hollow fiber extrudate having a multilayer structure. At this time, by extruding molten kneaded products of different compositions from adjacent annular ejection ports, a multilayer membrane having different pore sizes of adjacent layers can be obtained. Different compositions refer to different constituent materials of the molten kneaded products or different constituent ratios even if the constituent materials are the same. Even if they are the same thermoplastic resin, if the molecular weight and molecular weight distribution are significantly different, they are considered to be different in composition. The place where the melt-kneaded products of different compositions merge may be at the lower end surface of the hollow fiber molding nozzle 20 or may not be at the lower end surface of the hollow fiber molding nozzle 20.

[0059] When the molten kneaded material is extruded from the annular nozzle, it is preferred to expel the material in a manner such that the nozzle extrusion parameter R (1 / sec) is 10 or more and 1000 or less, because high productivity and spinning stability can be obtained, and thus a high-strength film can be obtained. Here, the nozzle extrusion parameter R is the value obtained by dividing the extrusion line velocity V (m / sec) by the slit width d (m) of the nozzle. The extrusion line velocity V (m / sec) is the extrusion capacity (m) per unit time of the molten kneaded material. 3 / second) divided by the cross-sectional area of ​​the nozzle (m 2 ) obtained. If R is 10 or more, the filament diameter of the hollow extrudate does not have problems such as pulse-like fluctuations, and the spinning can be stably spun with good productivity. In addition, if R is 1000 or less, the elongation at break, which is one of the important strengths of the obtained porous hollow fiber membrane, can be kept sufficiently high. The elongation at break is the elongation relative to the original length when stretched along the length direction of the membrane.

[0060] In the case of a porous hollow fiber membrane with a multilayer structure, the value obtained by dividing the ejection linear velocity V of the melt-kneaded product formed by the resin confluence and stacking by the slit width d of the ejection port is the spinning port ejection parameter R. The range of R is more preferably 50 or more and 1000 or less.

[0061] The hollow fiber-shaped molten kneaded product ejected from the ejection port is solidified by passing through a refrigerant such as air or water. However, depending on the porous hollow fiber membrane as the target, after passing through the air gap S constituted by an air layer, it is passed through a coagulation bath 30 containing water or the like. That is, the air gap S is a portion from the ejection port of the hollow fiber molding nozzle 20 to the water surface of the coagulation bath 30. As required, a container such as a cylinder may be used from the ejection port to the air gap S. After passing through the coagulation bath 30, it is wound up onto a reel or the like as required.

[0062] In particular, after the molten mixture passes through the ejection port, it is best to immediately pass it through a high-temperature container such as a cylindrical container for 0.015 seconds or more. If it is 0.015 seconds or more, the solvent vapor accumulated in the high-temperature container is suppressed from closing the surface, i.e., the pores, and then the resin concentration of the surface layer of the molten mixture is reduced by absorbing the solvent vapor, thereby increasing the open porosity and the porosity near the surface. In addition, it is found that due to the heat preservation effect of the high-temperature container and the solvent vapor generated by the molten mixture at high temperature in the container, the inner surface side of the hollow fiber molten mixture also has a higher open porosity and porosity near the surface. In order to control the pore size of the surface, it is preferably 1.0 seconds or less. More preferably, it is 0.018 seconds or more and 0.9 seconds or less, and further preferably 0.018 seconds or more and 0.8 seconds or less.

[0063] Generally, in the non-solvent induced phase separation method, a cylinder is sometimes used throughout the air gap in order to utilize the moisture in the air gap for phase separation. In the present invention, a new insight was found to control the surface opening rate and porosity by solvent vapor.

[0064] The set temperature of the high temperature container is preferably (T-60)°C to (T+60)°C relative to the ejection temperature T of the molten kneaded product. It is more preferably (T-50)°C to (T+50)°C. If it is (T-60)°C or higher, the effect of the solvent vapor can be fully exhibited. Although there is no particular reason, it is preferably (T+60)°C or lower for reasons such as preventing the resin kneaded product from deteriorating by excessively increasing the set temperature.

[0065] The time for the melt-kneaded product to pass through the air gap portion S is called the air gap time, and the air gap time is expected to be 0.20 seconds or more. If the air gap time is 0.20 seconds or more, the polymer molecules are oriented in the air gap portion, thereby further improving the compressive strength. The air gap time is more preferably 0.20 seconds or more and 5.0 seconds or less. If it is 5.0 seconds or less, stable manufacturing can be performed. It is expected to be 0.25 seconds or more and 4.0 seconds or less, and more preferably 0.30 seconds or more and 3.5 seconds or less.

[0066] In the air gap, it is desirable to use a suction machine or the like to blow cooling air at a speed of 0.80 m / sec or less in a direction perpendicular to the ejection direction. Although the reason is not yet clear, it is presumed that if it is 0.80 m / sec or less, the solvent vapor is appropriately retained on the surface of the molten kneaded product, thereby suppressing the solvent vapor from closing the surface, i.e., the pores, and further reducing the resin concentration of the surface layer of the molten kneaded product by absorbing the solvent vapor, thereby increasing the open porosity and the porosity near the surface.

[0067] In the solidified hollow fiber, the polymer-rich phase and the organic liquid-rich phase are finely separated. In addition, for example, when inorganic powder is added, when the inorganic powder is silica powder, the silica powder is unevenly present in the organic liquid-rich phase. By extracting and removing the organic liquid and the inorganic powder from the hollow fiber, the organic liquid-rich phase becomes pores. Therefore, a porous hollow fiber membrane can be obtained.

[0068] For the extraction removal of organic liquid and inorganic powder, if they can be extracted and removed with the same solvent, they can be carried out simultaneously. Usually, they are extracted and removed separately.

[0069] For the extraction and removal of organic liquids, a liquid is used that does not dissolve or modify the thermoplastic resin used and is suitable for mixing and extraction with the organic liquid. Specifically, it can be carried out by contacting it with a method such as impregnation. In order to facilitate removal from the hollow fiber membrane after extraction, the liquid is preferably volatile. Examples of the liquid include alcohols, dichloromethane, etc. If the organic liquid is water-soluble, water can also be used as the extraction liquid.

[0070] The extraction and removal of the inorganic fine powder is usually carried out using an aqueous liquid. For example, when the inorganic fine powder is silicon dioxide, it can be carried out by first contacting it with an alkaline solution to convert the silicon dioxide into silicate, and then contacting it with water to extract and remove the silicate.

[0071] The extraction removal of the organic liquid and the extraction removal of the inorganic powder can be performed either first. When the organic liquid is immiscible with water, it is preferred to first perform the extraction removal of the organic liquid and then perform the extraction removal of the inorganic powder. Since the organic liquid and the inorganic powder are usually mixed and coexist in the organic liquid concentrated phase, the extraction removal of the inorganic powder can be smoothly performed, which is advantageous.

[0072] In this way, by extracting and removing the organic liquid and the inorganic fine powder from the solidified porous hollow fiber membrane, a porous hollow fiber membrane can be obtained. In addition, for the hollow fiber membrane after solidification, the porous hollow fiber membrane can be stretched in the length direction within a range of 3 times the stretching ratio at any of the following stages: (i) before extracting and removing the organic liquid and the inorganic powder; (ii) after extracting and removing the organic liquid and before extracting and removing the inorganic powder; (iii) after extracting and removing the inorganic powder and before extracting and removing the organic liquid; and (iv) after extracting and removing the organic liquid and the inorganic powder. Generally, if the hollow fiber membrane is stretched in the length direction, the water permeability is improved, but since the pressure resistance (bursting strength and compressive strength) is reduced, most of them cannot become a membrane with practical strength after stretching. However, the porous hollow fiber membrane obtained by the manufacturing method of this embodiment has high mechanical strength. Therefore, stretching with a stretching ratio of 1.1 times or more and within 3.0 times can be implemented. By stretching, the water permeability of the porous hollow fiber membrane is improved. The stretching ratio mentioned here refers to the value obtained by dividing the hollow fiber length after stretching by the hollow fiber length before stretching. For example, when a porous hollow fiber membrane having a hollow fiber length of 10 cm is stretched until the hollow fiber length is extended to 20 cm, the stretching ratio is 2 times according to the following formula. 20cm÷10cm=2

[0073] It is desirable to perform stretching at a space temperature of 0°C or more and 160°C or less. When the temperature is higher than 160°C, not only the stretching spot is large, but also the elongation at break is reduced and the water permeability is reduced, which is not preferred. At 0°C or less, the possibility of stretching breakage is high, which is not practical. The space temperature in the stretching process is more preferably 10°C or more and 140°C or less, and further preferably 20°C or more and 100°C or less.

[0074] In this embodiment, it is preferred to stretch the hollow fiber membrane containing an organic liquid. Compared with the hollow fiber membrane not containing an organic liquid, the hollow fiber membrane containing an organic liquid breaks less during stretching. Furthermore, for the hollow fiber membrane containing an organic liquid, the shrinkage of the hollow fiber membrane after stretching can be increased, so the degree of freedom in setting the shrinkage rate after stretching is increased.

[0075] In addition, it is preferred to stretch the hollow fiber membrane containing inorganic fine powder. In the case of the hollow fiber membrane containing inorganic fine powder, the hollow fiber membrane has hardness due to the presence of the inorganic fine powder contained in the hollow fiber membrane, so the hollow fiber membrane becomes difficult to be flattened during stretching. In addition, it is also possible to prevent the pore size of the finally obtained hollow fiber membrane from becoming too small or the wire diameter from becoming too small. In the present embodiment, it is more desirable to stretch a hollow fiber membrane containing both an organic liquid and an inorganic fine powder.

[0076] Based on the above reasons, it is more preferable to stretch a hollow fiber membrane containing either an organic liquid or an inorganic fine powder than to stretch a hollow fiber membrane after the extraction is completed, and it is further preferable to stretch a hollow fiber membrane containing both an organic liquid and an inorganic fine powder than to stretch a hollow fiber membrane containing either an organic liquid or an inorganic fine powder.

[0077] In addition, the method of extracting the stretched hollow fiber membrane has the advantage that the surface and internal voids of the hollow fiber membrane increase due to stretching, so the extraction solvent can easily penetrate into the hollow fiber membrane. In addition, the method of extracting after the stretching and subsequent shrinking steps, as described later, has the advantage that the hollow fiber membrane has a low tensile elastic modulus and is easy to bend, so when the extraction is carried out in a liquid flow, the hollow fiber membrane is easily shaken by the liquid flow, and the stirring effect is increased, so it has the advantage that efficient extraction can be carried out in a short time.

[0078] In the present embodiment, since the process includes stretching the hollow fiber membrane and then shrinking it, a hollow fiber membrane with a low tensile modulus of elasticity can be finally obtained. Here, "low tensile modulus of elasticity" means that the fiber is easily stretched under a small force and returns to its original state when the force disappears. If the tensile modulus of elasticity is low, the hollow fiber membrane will not be flattened, it is easy to bend, and it is easy to be shaken by the water flow during filtration. Since the fiber is shaken irregularly with the bending of the water flow, the layer of pollutants attached and deposited on the surface of the membrane cannot grow and is easy to peel off, so a high level of filtered water can be maintained. Furthermore, in the case of forcibly shaking the fiber by flushing or air washing, the shaking becomes larger and the washing recovery effect becomes higher.

[0079] Regarding the extent of fiber length contraction when shrinking after stretching, it is desirable to make the fiber length contraction rate relative to the fiber length increment caused by stretching be in the range of 0.3 or more and 0.9 or less. For example, when a 10 cm fiber is stretched to 20 cm and then shrunk back to 14 cm, according to the following formula: Fiber length shrinkage rate = {(maximum fiber length when stretched) - (fiber length after shrinkage)} / [(maximum fiber length when stretched) - (fiber initial length)] = (20-14) / (20-10) = 0.6. The fiber length shrinkage rate is 0.6. When the fiber length shrinkage is 0.9 or more, the water permeability tends to decrease; when it is less than 0.3, the tensile elastic modulus tends to increase, which is not preferred. In this embodiment, the fiber length shrinkage is more preferably in the range of 0.50 or more and 0.85 or less.

[0080] Furthermore, by adopting the step of stretching the hollow fiber membrane to the maximum fiber length during stretching and then shrinking it, the finally obtained hollow fiber membrane will not break even when stretched to the maximum fiber length during stretching during use. Here, when the stretching ratio is X and the fiber length contraction rate with respect to the fiber length increase caused by the stretching is Y, the rate Z indicating the degree of guarantee of the elongation at break can be defined by the following formula. Z = (maximum fiber length during stretching - fiber length after contraction) / fiber length after contraction = (XY-Y) / (X+Y-XY) Among them, Z is preferably 0.2 or more and 1.5 or less, and more preferably 0.3 or more and 1.0 or less. If Z is too small, the degree of guarantee of elongation at break is reduced, and if Z is too large, the water permeability becomes lower compared with the high possibility of breakage during stretching.

[0081] In addition, the production method of the present embodiment includes the steps of stretching and then shrinking, so that the tensile elongation at break is extremely rare at low elongation, and the distribution of the tensile elongation at break can be narrowed.

[0082] From the viewpoint of shrinkage time and physical properties, the space temperature in the process of stretching and then shrinking is preferably in the range of 0° C. or more and 160° C. or less. If it is lower than 0° C., shrinkage takes time and is not practical, while if it exceeds 160° C., elongation at break decreases and water permeability decreases, which is not preferred.

[0083] In the present embodiment, the hollow fiber membrane is preferably curled in the shrinking step, so that a hollow fiber membrane with a high degree of curling can be obtained without being crushed or damaged.

[0084] Usually, the hollow fiber membrane is in the form of a straight tube without bending. Therefore, when it is bundled into a filtering component, the gap between the hollow fibers is eliminated, and the possibility of forming a fiber bundle with low porosity is high. In contrast, if a hollow fiber membrane with high curl is used, the hollow fiber membrane interval is evenly expanded due to the bending of each fiber, and a fiber bundle with high porosity can be formed. In addition, the filter component composed of hollow fiber membranes with low curl, especially when used under external pressure, the gap of the fiber bundle becomes less, the flow resistance increases, and the filtering pressure cannot be effectively transmitted to the central part of the fiber bundle. Furthermore, when the filtered sediment is peeled off from the hollow fiber membrane by backwashing or flushing, the washing effect inside the fiber bundle also deteriorates. The fiber bundle composed of hollow fiber membranes with high curl has a large porosity, and the gap between the hollow fiber membranes can be maintained even if external pressure filtration is performed, and it is not easy to have biased flow.

[0085] In this embodiment, the curling degree is preferably in the range of 1.5 or more and 2.5 or less. 1.5 or more is preferred for the above reasons, and if it is less than 2.5, the reduction in the filtration area per unit volume can be suppressed.

[0086] As a method for curling the hollow fiber membrane, there can be cited a method in which, in the process of stretching and then shrinking it, the hollow fiber membrane is placed between, for example, a pair of gear rollers with periodic projections and depressions or a pair of sponge-like belts with projections and depressions, and they are taken out during shrinkage.

[0087] In addition, in this embodiment, it is preferred to use a removal device composed of a pair of opposite infinite track type belts for stretching. In this case, removal devices are used on the upstream side and downstream side of the stretching, and in each removal device, the hollow fiber membrane is placed between the opposite belts, and the fiber is carried by moving the two belts in the same direction at the same speed. In addition, in this case, it is preferred to stretch the fiber carrying speed on the downstream side higher than the fiber carrying speed on the upstream side. If stretching is performed in this way, stretching tension will not be generated during stretching, and sliding will not be caused, which can prevent the fiber from being flattened.

[0088] Here, the inner side of the endless track type belt in contact with the driving roller is preferably made of a high elastic belt such as a fiber reinforced belt, and the outer surface in contact with the hollow fiber membrane is made of an elastomer. In addition, the compressive elastic modulus of the elastomer along its thickness direction is 0.1MPa or more and 2MPa or less, and more preferably the thickness of the elastomer is 2mm or more and 20mm. From the viewpoint of chemical resistance and heat resistance, it is particularly preferred that the elastomer on the outer surface is silicone rubber.

[0089] In addition, the stretched membrane can be heat treated as needed to improve the compressive strength. The heat treatment is preferably performed at 80°C or above and 160°C or below. If it is 160°C or below, the reduction in elongation at break and water permeability can be suppressed; if it is 100°C or above, the compressive strength can be improved. In addition, from the perspective of reducing the changes in fiber diameter, porosity, pore size, and water permeability, it is desirable to heat treat the hollow fiber membrane after the extraction is completed.

[0090] When PVDF (polyvinylidene fluoride) is used as a thermoplastic resin, in order to take into account both high porosity and high compressive strength, it is necessary to appropriately select a solvent for PVDF. First, as a method for increasing the porosity, there are methods for reducing the concentration of PVDF and methods for increasing the temperature of the hollow portion forming fluid as described above. In the case of a method for film making using a method of reducing the PVDF concentration, since the pore size also becomes larger, it is necessary to select a solvent that can achieve high porosity and small pore size. The following parameter P is a relationship between the three-dimensional solubility parameter of PVDF and the three-dimensional solubility parameter of the solvent, and evaluates the solubility of PVDF and the solvent. The right side of the relationship shows the solubility range of the Hansen solubility parameter in three dimensions, and quantitatively represents the distance from the three-dimensional solubility parameter (σdp, σpp, σhp) of PVDF to the three-dimensional solubility parameter (σdm, σpm, σhm) of the solvent. P=((σdm-σdp) 2 +(σpm-σpp) 2 +(σhm-σhp) 2 ) 0.5 [Wherein, σdm and σdp represent the dispersion terms of the solvent and polyvinylidene fluoride, respectively; σpm and σpp represent the dipole coupling terms of the solvent and polyvinylidene fluoride, respectively; σhm and σhp represent the hydrogen bonding terms of the solvent and polyvinylidene fluoride, respectively.] Additionally, the above concepts are not limited to PVDF.

[0091] In the case of a two-layer porous membrane, the parameter P between the solvent and PVDF used to prepare the melt-kneaded product B forming layer (B) is preferably greater than 7.88, more preferably 7.88 to 10.0. When the value is 7.88 or more, a decrease in water permeability can be suppressed.

[0092] In the preparation of the melt-kneaded product A forming the layer (A), the parameter P between the solvent and PVDF used is preferably 7.88, more preferably 0 to 7.88, and even more preferably 1.00 to 7.88. When the value is 7.88 or less, a high porosity and a small pore size can be achieved. Example

[0093] Hereinafter, the present embodiment will be described in more detail with reference to Examples and Comparative Examples, but the present embodiment is not limited to these Examples.

[0094] In addition, the measurement method used in this embodiment is as follows. Unless otherwise specified, all the following measurements were performed at 25° C. Hereinafter, the evaluation method will be described, and then the production methods and evaluation results of Examples and Comparative Examples will be described. In addition, the composition and production conditions of the membrane and various properties are shown in Tables 1 and 2.

[0095] (1) Determination of outer diameter, inner diameter and film thickness (mm) The hollow fiber membrane was thinly sliced ​​at intervals of 15 cm in a direction perpendicular to the length direction of the membrane using a razor or the like, and the long and short diameters of the inner diameter and the long and short diameters of the outer diameter of the cross section were measured using a microscope. The inner diameter and outer diameter were calculated using the following formulas (2) and (3), respectively. The inner diameter was subtracted from the calculated outer diameter, and the value obtained by dividing by 2 was used to calculate the membrane thickness. Measurements were performed at 20 points, and the average values ​​were used as the inner diameter, outer diameter, and membrane thickness under these conditions.

Number 1

Number 2

[0096] (2) Pure water permeability (L / m 2 / hr) After the hollow fiber membrane is immersed in a 50 mass % ethanol aqueous solution for 30 minutes, it is immersed in water for 30 minutes to make the hollow fiber membrane wet. One end of the wet hollow fiber membrane of about 10 cm in length is sealed, and an injection needle is inserted into the hollow part of the other end. Pure water at 25°C is injected into the hollow part from the injection needle at a pressure of 0.1 MPa, and the amount of pure water permeating to the outer surface is measured. The pure water permeation flux is determined by the following formula. Here, the effective length of the membrane refers to the net membrane length excluding the part where the injection needle is inserted. In addition, the number of measurements is set to 10 points, and the average value is used as the pure water permeability under each condition.

Number 3

[0097] (3) Breaking strength (MPa), breaking elongation (%) The tensile load and the displacement at break were measured under the following conditions. Sample: Wet hollow fiber membrane prepared by method (2) Measuring instrument: Instron tensile testing machine (manufactured by Shimadzu Corporation: AGS-X) Distance between chucks: 5 cm Stretching speed: 20cm / min The breaking strength and breaking elongation were determined by the following formula.

Number 4

Number 5

[0098] (4) Porosity of the entire membrane The porosity of the entire membrane can be determined by the following formula. Porosity (whole membrane) % = 100 × (wet membrane weight [g] - dry membrane weight [g]) / water specific gravity [g / cm 3 ] / (membrane volume [cm 3]) Here, the wet film refers to a film in a state where the pores are filled with pure water but the hollow part does not contain pure water. Specifically, the wet film can be obtained by immersing a sample film having a length of 10 to 20 cm in ethanol so that the pores are filled with ethanol, then repeating the immersion in pure water 4 to 5 times to fully replace the inside of the pores with pure water, and then holding one end of the hollow fiber by hand and shaking it fully for about 5 times, and then holding the other end by hand and shaking it fully for about 5 times to remove the water in the hollow part. In addition, a dry film can be obtained by drying in an oven, for example, at 60°C until a constant weight is reached after measuring the weight of the aforementioned wet film. The membrane volume can be calculated by the following formula: membrane volume [cm 3 ] = π × {(outer diameter [cm] / 2) ^2 - (inner diameter [cm] / 2) ^2} × membrane length [cm]. When the weight of a single film is too small and the error in weight measurement becomes large, a plurality of films may be used.

[0099] (5) Method for determining the boundary between layers in a multi-layer structure Using Hitachi electron microscope SU8000 series, the cross section of the membrane was observed at an accelerating voltage of 3kV. In the present embodiment and the comparative example, the vicinity of the boundary between the layers was photographed at 1000 times. According to the image taken, when the boundary line can be distinguished between the layers, the boundary line is used as the boundary between the layers. In the porous hollow fiber membrane in the present embodiment and the comparative example, since the boundary can be distinguished, the boundary line is used as the boundary between the layers.

[0100] In the case where the boundary between the layers cannot be distinguished by the above method, the boundary can also be determined by the following method. For example, in the case of a porous hollow fiber membrane with a two-layer structure, a method for determining the boundary between layer (A) and layer (B) is described. The following is a method for setting layer (A) as a blocking layer and layer (B) as a supporting layer. The cross section of the hollow fiber membrane was photographed by the electron microscope, and a photograph of the shape of 20 or more holes was used. In order to observe all the cross sections, multiple images were taken. In the present embodiment and the comparative example, the measurement was performed at 5000 times. The electron microscope sample of the cross section was obtained by cutting the membrane sample frozen in ethanol into discs. The commercially available image analysis software Winroof 6.1.3 was used to analyze the images. Figure 3A As shown, 100 lines L with equal distances to the surface FA are drawn at intervals that divide the entire film thickness into 101 equal parts (i.e., lines connecting points of the same film thickness), as shown in FIG. Figure 3BAs shown, the length Lh of the portion corresponding to the hole h in the cross-section image of the line L is measured. The average value of the cross-section length Lh is calculated by arithmetic mean, and the cross-sectional aperture of each film thickness portion is obtained. When the magnification of the scanning electron microscope photograph is high enough, the lines with equal distances to the surface FA can also be approximated by straight lines. Using the maximum value of the cross-sectional aperture obtained, the cross-sectional aperture of each film thickness portion is standardized, and the point that first reaches the standardized value closest to 0.7 from the surface FA is used as the boundary layer of the layer.

[0101] (6) Three-dimensional solubility parameters The three-dimensional solubility parameters are quoted from the following reference book: Hansen, Charles (2007). Hansen Solubility Parameters: A user's handbook, Second Edition. Boca Raton, Fla: CRC Press. (ISBN 978-0-8493-7248-3)

[0102] (7) Internal and external surface pore size and porosity The surface on the filtrate side was photographed using the same electron microscope as in (5). The photograph was taken at a magnification that allowed the shapes of 20 or more pores to be confirmed, and in the present example and comparative example, the photograph was taken at a magnification of 10,000. Using the captured image, as described in International Publication No. 2001 / 53213, a transparent sheet is superimposed on a copy of the image, the hole portion is blackened with a black pen, etc., and the transparent sheet is copied onto white paper to clearly distinguish the hole portion as black and the non-hole portion as white. Then, the image is binarized by discrimination analysis using commercially available image analysis software Winroof 6.1.3. By finding the occupied area of ​​the binarized image thus obtained, the open porosity of the surface FA and the surface FB is found. The pore size is determined as follows: the equivalent circle diameter is calculated for each pore existing on the surface, and the pore areas of each pore are added up in sequence, starting from the pore with the largest pore diameter, and the pore size of the pore when the sum reaches 50% of the total pore area of ​​each pore is determined as the pore size.

[0103] (8) Transmission pressure (kPa) The permeation pressure of the membrane was calculated as follows: That is, when the inlet pressure of the hollow fiber membrane module is Pi, the outlet pressure is Po, and the permeate side outlet pressure (back pressure) is Pf, the permeation pressure TMP is calculated as follows. TMP=(Pi+Po) / 2-Pf

[0104] (9) Tangential streamline velocity (m / s) The tangential streamline velocity Lv is calculated as follows. That is, when the number of hollow fibers introduced into the hollow fiber membrane module is n (fibers), the inner diameter of the hollow fiber membrane is Di (m), and the flow rate of the raw liquid supplied to the hollow fiber membrane module is V (m 3 / s), the tangential streamline velocity is calculated as follows. Lv=V / (nx(πx(Di / 2)^2))

[0105] (10) Minimum antibody permeability The minimum antibody permeability is calculated as follows. That is, after the start of the culture, the antibody concentrations in the culture fluid and the permeate are measured every day, and are set as Cm and Cf respectively, and their ratio (Cf / Cm) is the antibody permeability. The lowest value of the antibody permeability during the entire operation is taken as the minimum antibody permeability. The antibody concentration can be determined by known methods such as ELISA and LC-MS. The method in this embodiment is to use the xP workstation automated immunoassay system manufactured by Gyrolab for quantitative analysis.

[0106] (11) Porosity, polymer skeleton size, cross-sectional pore size The porous hollow fiber membrane was cut into a circular shape at a cross section perpendicular to the fiber length direction and then embedded in epoxy resin. After trimming, the sample cross section was subjected to BIB processing to make a smooth cross section, and then subjected to conductive treatment to prepare a microscope test sample. The microscope test sample was prepared at one cutting position of each sample. Electron microscope (SEM) images of the film cross-section of the prepared microscope test sample were obtained using a Hitachi electron microscope SU7000. The image acquisition conditions were as follows: for each microscope test sample, five fields of view including the outer surface or the inner surface were imaged. Image acquisition conditions Accelerating voltage: 1kV Detector: Reflected electron detector Camera magnification: 50000 times (device display magnification) Image resolution: 2560×1920 pixels

[0107] Image analysis was performed using ImageJ. First, Plugins-Bilateral Filter Fiji (10 times under the conditions of spatial radius = 3, range radius = 50) was applied to perform filtering. Threshold processing (Image-Adjust-Treshold: Maximum Entropy Method (MaxEntropy was selected) was performed on the filtered SEM image to binarize the pore part (the part where the pore was embedded by the embedding resin) and the polymer skeleton part. Taking the upper part of the binarized image as the reference, the pixel of the membrane portion closest to the upper part of the image is taken as the location where the film thickness is 0nm. Continuously cut out areas of a specified thickness (for example, a thickness of 100nm, sometimes a thickness of 50nm) in the film thickness direction, and calculate the porosity, polymer skeleton size, and cross-sectional pore size from each image by the method shown below. Here, for example, the porosity, polymer skeleton size, and cross-sectional pore size of the region of 0 to 300nm are respectively set to the arithmetic average of the porosity, polymer skeleton size, and cross-sectional pore size of the regions of 0 to 100nm, 100 to 200nm, and 200 to 300nm that are continuously cut out and calculated as above. In addition, for example, the porosity, polymer skeleton size, and cross-sectional pore size of the region of 0 to 480nm are the values ​​analyzed in the region of 0 to 480nm. In addition, since the 0-100nm region is an image of the openings on the outermost surface of the membrane, it is necessary to define the outermost surface of the membrane when calculating the porosity and cross-sectional pore size, and calculate the values ​​based on the binary image of only the pores. In order to obtain a binary image of only the pores, the pencil tool of Adobe Photoshop (registered trademark) Elements 9 was used to manually determine the boundary between the openings on the outermost surface of the membrane and the embedded resin part, and then the embedded resin part was smeared to obtain a binary image of only the pores. Specific operations such as Figure 4 As shown. For an image in which the polymer skeleton is at brightness 255 (white) and the pores and embedding resin are at brightness 0 (black), a line is drawn with a pencil tool to connect the two ends of the opening on the outermost surface of the membrane. Next, a smear tool is used to smear the embedding resin portion to brightness 0 (black), thereby obtaining a binary image of only the pores in the region of 0-100 nm. The positions of the two ends of the opening on the outermost surface of the membrane are determined by the operator's arbitrary judgment. Porosity (%): Apply Analyze-Analyze Particles to the binary image of the pores (the pores are at brightness 0 = black), and take the arithmetic average of the five fields of view of %area in Summary as the porosity. The settings of AnalyzeParticles are as follows. Size(Pixel^2):0-infinity Circularity: 0-1.00 Summarize: The checkbox is checked. Exclude on edges: The check box is unchecked Include Holes: The checkbox is unchecked Polymer skeleton size: For the binary image of the membrane (the image with brightness 0 = black for the polymer portion), use ImageJ's Plugins-BoneJ-Thickness to obtain the LocalThickness image. For the LocalThickness image, use Analyze-Histogram to obtain detailed information on the LocalThickness values. Calculate the arithmetic mean value based on the LocalThickness values ​​of the five fields of view obtained and define it as the polymer skeleton size. Cross-sectional aperture: For the binary image of the hole (equivalent to the image with brightness 0 = black in the hole part), apply Plugins-BoneJ-Thickness of ImageJ to obtain the LocalThickness image. For the LocalThickness image, apply Analyze-Histogram to obtain the detailed information of the LocalThickness value. Calculate the arithmetic average value of the LocalThickness values ​​of the 5 fields of view obtained and define it as the cross-sectional aperture.

[0108] (Example 1) As the thermoplastic resin, vinylidene fluoride homopolymer (KF-W#1000 manufactured by Kureha Corporation) was used, as the organic liquid, a mixture of di(2-ethylhexyl) phthalate (DEHP) (manufactured by CG ESTER Co., Ltd.) and dibutyl phthalate (DBP) (manufactured by CG ESTER Co., Ltd.) was used, and as the inorganic fine powder, silica fine powder (manufactured by Japan AEROSIL Co., Ltd., trade name: AEROSIL-R972, primary particle size of about 16 nm) was used, and a hollow fiber molding nozzle was used to carry out melt extrusion of the hollow fiber membrane using an extruder. A melt-kneaded product having a composition of vinylidene fluoride homopolymer: di(2-ethylhexyl) phthalate: dibutyl phthalate: silica fine powder = 40.0:30.8:6.20:23.0 (mass ratio) was used as a melt-kneaded product, and air was used as a fluid for forming a hollow portion. The products were extruded from a hollow fiber molding nozzle having an outer diameter of 3.0 mm and an inner diameter of 2.0 mm at a spraying temperature of 240°C. The hollow fiber-shaped melt kneaded product extruded at a discharge temperature of 240°C passes through a high-temperature container with a set temperature of 240°C for 0.36 seconds, and after a total of 1.50 seconds of air movement in the high-temperature container section, it is introduced into a coagulation bath with 30°C water added. Take it out at a speed of 5.0m / min. The wind speed of the air gap is set to 0.80m / sec. The obtained hollow fiber is immersed in isopropanol to extract and remove di(2-ethylhexyl)phthalate and dibutyl phthalate, and then dry it. Then, after immersing in a 50% by mass ethanol aqueous solution for 30 minutes, it is immersed in water for 30 minutes, and then immersed in a 20% by mass sodium hydroxide aqueous solution at 70°C for 1 hour, and further repeatedly washed with water to extract and remove silica powder to obtain a porous hollow fiber membrane. The obtained porous hollow fiber membrane is a porous membrane with the inner surface (inner diameter side surface) as the side surface of the filtered liquid. Table 1 shows the detailed composition and conditions. Figure 5 This is an electron micrograph of a cross section of the obtained porous hollow fiber membrane near the filtrate side.

[0109] The hollow fiber membrane was placed in a module housing with an effective length of 20 cm, so that the membrane area (converted to the inner surface) was 1.9 m 2 The two ends are sealed with epoxy resin to form a hollow fiber filter membrane micromodule with openings at both ends. like Figure 7 As shown, the hollow fiber filtration membrane micromodule and KML-100TFF perfusion system (manufactured by Repligen) were used to introduce CHO-K1 cells into a 15L (effective volume: 8.5L) glass bioreactor (manufactured by Repligen) to perform a continuous culture experiment. The basic medium containing glucose and defoaming agent was continuously added and adjusted to keep the cell concentration at 75±10×10 6 cells / mL. At this point, 3 / 4 of the effective volume is replaced within one day. The permeation flux of the hollow fiber membrane micromodule is set to: 2.0L / m 2 / h, permeating from the inner surface to the outer surface of the hollow fiber membrane, and the tangential flow velocity of the culture fluid through the hollow part was set to 0.30m / s. The culture was carried out for about 40 days, during which time the permeation pressure of the hollow fiber membrane was stabilized at about 12kPa. The antibody permeation rate in the permeated liquid was confirmed to be 83% or more in 40 days.

[0110] (Example 2) As the thermoplastic resin, vinylidene fluoride homopolymer (KF-W#1000 manufactured by Kureha Corporation) was used, as the organic liquid, a mixture of di(2-ethylhexyl) phthalate (DEHP) (manufactured by CG ESTER Co., Ltd.) and dibutyl phthalate (DBP) (manufactured by CG ESTER Co., Ltd.) was used, and as the inorganic fine powder, silica fine powder (manufactured by Japan AEROSIL Co., Ltd., trade name: AEROSIL-R972, primary particle size of about 16 nm) was used, and a hollow fiber molding nozzle was used to carry out melt extrusion of the hollow fiber membrane using an extruder. A melt-kneaded product having a composition of vinylidene fluoride homopolymer: di(2-ethylhexyl) phthalate: dibutyl phthalate: silica fine powder = 40.0:30.8:6.20:23.0 (mass ratio) was used as a melt-kneaded product, and air was used as a fluid for forming a hollow portion. The products were extruded from a hollow fiber molding nozzle having an outer diameter of 2.0 mm and an inner diameter of 0.90 mm at a spraying temperature of 240°C. The hollow fiber-shaped melt kneaded product extruded at a discharge temperature of 240°C passed through a high-temperature container set at 240°C for 0.090 seconds, moved in the air for a total of 0.60 seconds in the high-temperature container section, and then was introduced into a coagulation bath filled with 30°C water. It was taken out at a speed of 20 m / min, stretched at a speed of 40 m / min on a belt, shrunk at a speed of 30 m / min while blowing hot air at 140°C, and wound up on a reel. The wind speed in the air gap is set to 0.80m / sec. The obtained hollow fibrous material is immersed in isopropanol to extract and remove di(2-ethylhexyl)phthalate and dibutyl phthalate, and then dried. Next, after being immersed in a 50% by mass ethanol aqueous solution for 30 minutes, it is immersed in water for 30 minutes, and then, it is immersed in a 20% by mass sodium hydroxide aqueous solution at 70°C for 1 hour, and further repeatedly washed with water to extract and remove silica powder to obtain a porous hollow fiber membrane. The obtained porous hollow fiber membrane is a porous membrane with the inner surface (inner diameter side surface) as the filtered liquid side surface. Table 1 shows the detailed composition and conditions. The hollow fiber membrane was placed in a module housing with an effective length of 20 cm, so that the membrane area (converted to the inner surface) was 1.9 m 2 The two ends are sealed with epoxy resin to form a hollow fiber filter membrane micromodule with openings at both ends.

[0111] like Figure 7As shown, the hollow fiber filtration membrane micromodule and KML-100TFF perfusion system (manufactured by Repligen) were used to introduce CHO-K1 cells into a 15L (effective volume: 8.5L) glass bioreactor (manufactured by Repligen) to perform a continuous culture experiment. The basic medium containing glucose and defoaming agent was continuously added and adjusted to keep the cell concentration at 75±10×10 6 cells / mL. At this point, 3 / 4 of the effective volume is replaced within one day. The permeation flux of the hollow fiber membrane micromodule is set to: 2.0L / m 2 / h, permeating from the inner surface to the outer surface of the hollow fiber membrane, and the tangential streamline velocity of the culture fluid through the hollow part was set to 0.25m / s. The culture was carried out for about 40 days, during which time the permeation pressure of the hollow fiber membrane was stabilized at about 11kPa. It was confirmed that the antibody permeation rate in the permeated liquid was 85% or more in 40 days.

[0112] (Example 3) A porous hollow fiber membrane was obtained by the same method as in Example 1, except that polyethylene (SH800, manufactured by Asahi Kasei Corporation) was used as the thermoplastic resin, dibutyl adipate (DBA) (manufactured by Tokyo Chemical Industry Co., Ltd.) was used as the organic liquid, the composition of the molten mixture was set to polyethylene: dibutyl adipate: silica powder = 18.5:54.3:27.2 (mass ratio), the ejection temperature was set to 230°C, the air movement time was set to 3.0 seconds, and the winding speed was set to 10 m / min. Table 1 shows the detailed compositions and conditions.

[0113] The hollow fiber membrane was placed in a module housing with an effective length of 20 cm, so that the membrane area (converted to the inner surface) was 1.9 m 2 The two ends are sealed with epoxy resin to form a hollow fiber filter membrane micromodule with openings at both ends. like Figure 7 As shown, the hollow fiber filtration membrane micromodule and KML-100TFF perfusion system (manufactured by Repligen) were used to introduce CHO-K1 cells into a 15L (effective volume: 8.5L) glass bioreactor (manufactured by Repligen) to perform a continuous culture experiment. The basic medium containing glucose and defoaming agent was continuously added and adjusted to keep the cell concentration at 75±10×10 6 cells / mL. At this point, 3 / 4 of the effective volume is replaced within one day. The permeation flux of the hollow fiber membrane micromodule is set to: 1.0L / m 2 / h, permeating from the inner surface to the outer surface of the hollow fiber membrane, and the tangential flow velocity of the culture fluid through the hollow part was set to 0.25m / s. The culture was carried out for about 40 days, during which time the permeation pressure of the hollow fiber membrane was stabilized at about 13kPa. The antibody permeation rate in the permeated liquid was confirmed to be 84% or more in 40 days.

[0114] (Comparative Example 1) The composition of the melt-kneaded product was set to vinylidene fluoride homopolymer: di(2-ethylhexyl)phthalate: dibutyl phthalate: silica fine powder = 40.0:45.8:9.20:5.0 (mass ratio). A porous hollow fiber membrane was obtained in the same manner as in Example 2 except that the stretching and shrinking steps were not performed. Table 1 shows the detailed compositions and conditions. The hollow fiber membrane was placed in a module housing with an effective length of 20 cm, so that the membrane area (converted to the inner surface) was 1.9 m 2 The two ends are sealed with epoxy resin to form a hollow fiber filter membrane micromodule with openings at both ends.

[0115] like Figure 7 As shown, the hollow fiber filtration membrane micromodule and KML-100TFF perfusion system (manufactured by Repligen) were used to introduce CHO-K1 cells into a 15L (effective volume: 8.5L) glass bioreactor (manufactured by Repligen) to perform a continuous culture experiment. The basic medium containing glucose and defoaming agent was continuously added and adjusted to keep the cell concentration at 75±10×10 6 cells / mL. At this point, 3 / 4 of the effective volume is replaced within one day. The permeation flux of the hollow fiber membrane micromodule is set to: 1L / m 2 / h, permeating from the inner surface to the outer surface of the hollow fiber membrane, and the tangential flow velocity of the culture solution through the hollow part was set to 0.3m / s. After about 20 days of cultivation, the permeation pressure of the hollow fiber membrane rose to about 100kPa, and stable operation could not be achieved. It was confirmed that the permeation rate of the antibody in the permeated liquid had dropped to 50% on the 20th day.

[0116]

Table 1

Table 1

[0117]

Table 2

Table 2

Explanation of symbols

[0118] aThermoplastic resin b Gap 10 Extruder 20. Nozzle for hollow fiber molding 30 coagulation bath 40 Porous hollow fiber membrane 50 Roll 60 suction machine 70 High temperature container S Air gap space FA surface Lines with equal distances from L to the surface FA h Hole Lh L is the length of a portion that crosses the image and corresponds to the hole h.

Claims

1. A filtration method comprising the step of passing a culture solution containing cells, a culture medium, a product and a defoaming agent through a porous membrane to separate a filtrate containing the product from the culture solution, wherein: The product of the porosity from the outermost surface of the filtrate side surface of the porous membrane to 0.12% of the membrane thickness and the open porosity of the filtrate side surface is 1800%·% or more.

2. The filtering method according to claim 1, wherein: The porosity in the region from the outermost surface of the filtrate-side surface of the porous membrane to 0.12% of the membrane thickness is 50% or more. 3 . The filtering method according to claim 1 , wherein the porosity of the surface of the porous membrane on the side of the filtered liquid is 30% or more.

4. The filtration method according to claim 1 or 2, wherein the ratio of the porosity from the outermost surface of the filtrate side surface to 0.12% of the membrane thickness to the open porosity of the filtrate side surface is 1.70 or more.

5. The filtration method according to claim 1 or 2, wherein the product of the porosity from the outermost surface of the porous membrane on the filtrate side to 0.12% of the membrane thickness and the open porosity of the filtrate side surface is 2800%·% or more.

6. The filtration method according to claim 1 or 2, wherein the product of the porosity from the outermost surface of the filtrate side surface of the porous membrane to a thickness of 300 nm in the membrane thickness direction and the open porosity of the filtrate side surface is 860%·% or more. 7 . The filtration method according to claim 6 , wherein the porosity in a thickness of 300 nm in the membrane thickness direction from the outermost surface of the filtrate-side surface of the porous membrane is 35% or more. 8 . The filtering method according to claim 7 , wherein the open porosity of the filtrate-side surface of the porous membrane is 30% or more.

9. The filtration method according to claim 1 or 2, wherein the cross-sectional pore diameter from the outermost surface of the filtrate-side surface of the porous membrane to 0.12% of the membrane thickness is 1000 nm or less. 10 . The filtration method according to claim 1 , wherein a cross-sectional pore diameter from the outermost surface on the filtrate side of the porous membrane to a thickness of 300 nm in the membrane thickness direction is 300 nm or less. 11 . The filtration method according to claim 1 or 2 , wherein the porous membrane has a thickness of 100 μm or more and 800 μm or less. 12 . The filtration method according to claim 1 , wherein the flux of the porous membrane in the filtration step is 1 LMH or more. 13 . The filtration method according to claim 1 or 2 , wherein the porous membrane is a hollow fiber membrane, and the filtration step is perfusion culture filtration. 14 . The filtration method according to claim 1 or 2 , wherein the linear velocity of the tangential flow through the hollow fiber membrane during the perfusion culture is 0.3 m / s or less. 15 . The filtration method according to claim 1 , wherein the resin forming the porous membrane is a thermoplastic resin.

16. The filtering method according to claim 15, wherein the thermoplastic resin contains a fluororesin as a main component.

17. The filtering method according to claim 16, wherein the fluororesin comprises at least one selected from the group consisting of vinylidene fluoride resin (PVDF), chlorotrifluoroethylene resin, tetrafluoroethylene resin, ethylene-tetrafluoroethylene copolymer (ETFE), ethylene-monochlorotrifluoroethylene copolymer (ECTFE), hexafluoropropylene resin, and a mixture of these resins.

18. The filtering method according to claim 15, wherein the thermoplastic resin contains a polyolefin resin as a main component.

19. The filtering method according to claim 15, wherein the thermoplastic resin is polyethylene (PE) or polypropylene (PP).

20. The filtration method according to claim 1 or 2, wherein the product is selected from proteins including enzymes and antibodies, amino acids, nucleic acids and organic substances.

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