CA3207688A1 - Production method for porous membrane - Google Patents

Abstract

Provided is a porous membrane having high filtration performance and little variation in membrane performance. A production method for a porous membrane containing a thermoplastic resin comprises producing the porous membrane using particles obtained by adjusting a particle diameter of a pelletal or particulate thermoplastic resin by at least one of crushing and pulverization so as to have a particle diameter dispersity V 0.8 where the particle diameter dispersity V is defined as V = (D90 - D10)/D50.

Description

PRODUCTION METHOD FOR POROUS MEMBRANE
TECHNICAL FIELD
100011 The present disclosure relates to a production method for a porous membrane.
BACKGROUND

[0002] Tap water treatment is a process of obtaining drinking water or industrial water from natural water sources such as river water, lake and marsh water, and underground water, which are types of turbid water. Sewage treatment is a process of obtaining regenerated water for miscellaneous use or clarified water that can be discharged through treatment of domestic wastewater such as sewage. In these treatments, it is essential to remove suspended matter by performing a solid-liquid separation operation (clarification operation). In tap water treatment, suspended matter (clay, colloids, bacteria, etc.) originating from a natural water source (turbid water) are removed. In sewage treatment, suspended matter (sludge, etc.) is removed from treated water that has undergone biological treatment (secondary treatment) through suspended matter, activated sludge, or the like in sewage.

[0003] These clarification operations have conventionally been performed mainly by sedimentation, sand filtration, or coagulation sedimentation and sand filtration, but the use of membrane filtration is also becoming more common in recent years. Examples of advantages of membrane filtration include the following.
(1) High and stable clarification level of obtained water quality (high safety of obtained water) (2) Small installation space of filtration apparatus (3) Ease of automatic operation

[0004] For example, in the case of tap water treatment, membrane filtration may be used instead of coagulation sedimentation and sand filtration or may be used at a later stage than coagulation sedimentation and sand filtration, for example, as a means of further improving the water quality of treated water that has undergone coagulation sedimentation and sand filtration. The use of membrane filtration in sewage treatment is also being investigated for separation of sludge from water that has undergone secondary treatment of sewage, for example.
Ref. No. P0232569-ZZ (1/40) Date Recue/Date Received 2023-07-26 100051 Such clarification operations by membrane filtration are mainly performed by ultrafiltration membranes or microfiltration membranes (pore diameter in a range of several nanometers to several hundreds of nanometers) having a hollow fiber shape. There are two types of filtration schemes using hollow fiber filtration membranes: internal pressure filtration in which filtration is performed from an internal surface side of the membrane toward an external surface side of the membrane; and external pressure filtration in which filtration is performed from an external surface side of the membrane toward an internal surface side of the membrane. Of these filtration schemes, external pressure filtration is advantageous in terms that a larger membrane surface area can be provided at a side that is in contact with turbid source water, and thus the suspended matter load per unit membrane surface area can be reduced. Patent Literature (PTL) 1 to 3 disclose hollow fibers and production methods for these hollow fibers.
[0006] Clarification by membrane filtration has numerous advantages that conventional sedimentation and sand filtration lack as described above, and thus membrane filtration is becoming more commonly used in tap water treatment and sewage treatment as an alternative technique or complementary technique for conventional methods. However, widespread adoption of membrane filtration is being hindered by the lack of establishment of a technique for performing stable membrane filtration operation over a long period (refer to Non-Patent Literature (NPL) 1). Stable membrane filtration operation is mainly hindered by deterioration of water permeation performance of a membrane. The main cause of deterioration of water permeation performance is membrane clogging (fouling) caused by suspended matter and the like (refer to NPL 1). There are also instances in which water permeation performance is reduced due to suspended matter rubbing against and abrading the membrane surface.
[0007] Incidentally, one known production method for porous membranes is thermally induced phase separation. This production method uses a thermoplastic resin and an organic liquid. The organic liquid is a solvent that dissolves the thermoplastic resin at high temperature but does not dissolve the thermoplastic resin at room temperature (i.e., a latent solvent). Thermally induced phase separation is a method in which the thermoplastic resin and the organic liquid are kneaded at high temperature to cause dissolution of the thermoplastic resin in the organic liquid and are subsequently cooled to room Ref. No. P0232569-ZZ (2/40) Date Recue/Date Received 2023-07-26 temperature so as to induce phase separation, and then the organic liquid is removed to produce a porous product. This method has the following advantages.
(a) Even a polymer such as polyethylene for which there is no appropriate solvent that can cause dissolution at room temperature can be used to form a membrane.
(b) Particularly in a situation in which the thermoplastic resin is a crystalline resin, it is easy to promote crystallization during membrane production and obtain a membrane having high strength because membrane production is performed through dissolution at high temperature and subsequent cooling and solidification.
[0008] Due to these advantages, this method is widely used as a method for producing porous membranes (for example, refer to NPL 2 to 5).
CITATION LIST
Patent Literature [0009] PTL 1: JP S60-139815 A
PTL 2: JP 113-215535 A
PTL 3: JP H4-065505 A
PTL 4: JP 2018-507944 A
Non-Patent Literature [0010] NPL 1: Y. Watanabe, R. Bian, Membrane, 24(6), 1999, pp. 310-318 NPL 2: Editorial Committee of Dictionary of Plastic and Functional Polymeric Materials, "Dictionary of Plastic and Functional Polymeric Materials", Industrial Research Center of Japan, February 2004, pp. 672-679 NPL 3: Hideto Matsuyama, "Production of Polymeric Porous Membranes by Thermally Induced Phase Separation (TIPS)", Chemical Engineering, Kagaku Kogyo-sha Co., Ltd., June 1998, pp. 45-56 NPL 4: Akira Takizawa, "Membranes", IPC, January 1992, pp. 404-NPL 5: D. R. Lloyd, et al., Journal of Membrane Science, 64,1991, pp.

SUMMARY
100111 It has been conventionally known to produce a porous membrane by pulverizing a particulate thermoplastic resin, as described in PTL 4. However, Ref. No. P0232569-ZZ (3/40) Date Recue/Date Received 2023-07-26 such conventional techniques are insufficient as a method of stably producing porous membranes by controlling the particle diameter and particle diameter distribution after pulverization or as a means of controlling variation in the membrane performance of porous membranes.
100121 It could therefore be helpful to provide a porous membrane having high filtration performance and little variation in membrane performance. A porous membrane according to the present disclosure can suitably be used in a method of clarifying, by membrane filtration, turbid water that is natural water, domestic wastewater, or water resulting from treatment thereof, for example.
100131 We thus provide the following.
[1] A production method for a porous membrane containing a thermoplastic resin, the production method comprising producing the porous membrane using particles obtained by adjusting a particle diameter of a pelletal or particulate thermoplastic resin by at least one of crushing and pulverization so as to have a particle diameter dispersity V 0.8 where the particle diameter dispersity V is defined as V = (D90 - D10)/D50.
[2] The production method for a porous membrane according to [1], wherein a circularity of the particles is 0.5 or less.
[3] The production method for a porous membrane according to [1] or [2], wherein a linearity of the particles is 1.8 or more.
[4] The production method for a porous membrane according to any of [1] to [3], wherein the particle diameter dispersity V 1.3.

[5] The production method for a porous membrane according to any of [1] to [4], wherein a D50 particle diameter of the particles is 50 i-LM to 500 jtm.

[6] The production method for a porous membrane according to any of [1] to [5], wherein a mixture of the particles and an organic liquid or a mixture of the particles, an organic liquid, and an inorganic fine powder is melt-kneaded and extruded and thereafter the organic liquid or the organic liquid and the inorganic fine powder are extracted to produce the porous membrane.

[7] The production method for a porous membrane according to [6], wherein a ratio of a D50 particle diameter of the particles to an average primary particle diameter of the inorganic fine powder, expressed by (the D50 particle diameter of the particles)/(the average primary particle diameter of the inorganic fine powder), is 3,200 to 35,000.

[8] The production method for a porous membrane according to any of [1] to [7], wherein the porous membrane is a hollow fiber membrane.
Ref. No. P0232569-ZZ (4/40) Date Recue/Date Received 2023-07-26 [91 The production method for a porous membrane according to any of [1] to [8], wherein the thermoplastic resin is a resin containing polyvinylidene fluoride as a main component.
[10] The production method for a porous membrane according to any of [1] to [9], wherein the thermoplastic resin is a resin containing ethylene chlorotrifluoroethylene or ethylene tetrafluoroethylene as a main component.
[0014] It is thus possible to obtain a porous membrane with little variation in physical properties.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] In the accompanying drawings:
FIG. 1 is a schematic diagram of a three-dimensional (3D) network structure; and FIG. 2 is a schematic diagram of an example of an apparatus for producing a porous hollow fiber membrane.
DETAILED DESCRIPTION
[0016] An embodiment of the present disclosure will be described in detail below. The present disclosure is not limited to the following embodiment.
[0017] A porous membrane obtainable by the production method according to this embodiment will be described below.
[0018] A porous membrane obtainable by the production method according to this embodiment contains a thermoplastic resin. The porous membrane may consist only of the thermoplastic resin, or may further contain other components.
[0019] The thermoplastic resin preferably contains a fluororesin, and may consist only of a fluororesin.
The fluororesin preferably contains one or more selected from the group consisting of vinylidene fluoride resin (PVDF), chlorotrifluoroethylene resin, tetrafluoroethylene resin, ethylene-tetrafluoroethylene copolymer (ETFE), ethy len e-mon ochlorotrifluoroethyl ene copolymer (ECTFE), hexafluoropropylene resin, and mixtures of these resins, and may consist only of one or more selected from the group consisting of vinylidene fluoride resin (PVDF), chlorotrifluoroethylene resin, tetrafluoroethylene resin, ethylene-tetrafluoroethylene copolymer (ETFE), ethy lene-monochlorotrifluoroethy lene copolymer (ECTFE), hexafluoropropylene resin, and mixtures of these resins.
Ref. No. P0232569-ZZ (5/40) Date Recue/Date Received 2023-07-26 The thermoplastic resin is preferably a vinylidene fluoride-based resin or a chlorotrifluoroethylene-based resin, and more preferably a vinylidene fluoride-based resin.
The thermoplastic resin may be just one type of thermoplastic resin or may be a combination of a plurality of types of thermoplastic resins.
100201 The porous membrane preferably contains the thermoplastic resin as a main component.
The thermoplastic resin preferably contains the fluororesin as a main component, more preferably contains a vinylidene fluoride-based resin or a chlorotrifluoroethylene-based resin as a main component, and further preferably contains a vinylidene fluoride-based resin as a main component. The thermoplastic resin is preferably a resin containing ethylene chlorotrifluoroethylene or ethylene tetrafluoroethylene as a main component.
The phrase "contains as a main component" as used herein means containing 50 mass% or more (preferably 70 mass% or more, more preferably 80 mass% or more, and further preferably 90 mass% or more) in terms of solid content of the thermoplastic resin or porous membrane.
100211 The thermoplastic resin may be a fluororesin only, such as a vinylidene fluoride-based resin or a chlorotrifluoroethylene-based resin (preferably a .. vinylidene fluoride-based resin only).
[0022] The thermoplastic resin may contain a vinylidene fluoride-based resin and another thermoplastic resin. The other thermoplastic resin is preferably a thermoplastic resin that is miscible with the vinylidene fluoride-based resin.

For example, a fluororesin or the like that displays high chemical resistance of a similar level to the vinylidene fluoride-based resin can suitably be used.
[0023] As the polymerization method for the vinylidene fluoride-based resin, emulsion polymerization or suspension polymerization can suitably be used.
[0024] The weight-average molecular weight (Mw) of the thermoplastic resin (for example, vinylidene fluoride-based resin) is preferably 100,000 or more and 1,000,000 or less, and more preferably 150,000 or more and 1,500,000 or less. There is no limitation to a thermoplastic resin (for example, vinylidene fluoride-based resin) having a single molecular weight, and a plurality of vinylidene fluoride-based resins having different molecular weights may be mixed.
In this specification, the weight-average molecular weight (Mw) can be measured by gel permeation chromatography (GPC) with a standard resin Ref. No. P0232569-ZZ (6/40) Date Recue/Date Received 2023-07-26 of known molecular weight as a reference.
[0025] The form of the porous membrane may be a form having the membrane structure of a hollow fiber membrane, for example. The porous membrane is preferably a hollow fiber membrane. The term "hollow fiber membrane" as used herein refers to a membrane having a hollow ring-shaped form. Through the porous membrane having the membrane structure of a hollow fiber membrane, it is possible to increase the membrane area per unit volume of a module as compared with a flat membrane.
The porous membrane is not limited to a porous membrane having the membrane structure of a hollow fiber membrane (i.e., a hollow fiber porous membrane) and may be a porous membrane having another membrane structure such as a flat membrane or a tubular membrane. The porous membrane may have pores communicating through the inside of the porous membrane from one surface to the other surface in the thickness direction. The pure water permeability of the porous membrane, measured as described in the EXAMPLE
section below, may be 500 L/m2/hr or more, and may be 1000 L/m2/hr or more, for example.
[0026] The porous membrane is preferably a hollow fiber membrane that contains the thermoplastic resin, and may be a hollow fiber membrane that consists only of the thermoplastic resin.
[0027] It is desirable for the porous membrane (preferably porous hollow fiber membrane) to have a three-dimensional (3D) network structure. The term "three-dimensional network structure" as used herein refers to a structure such as illustrated schematically in FIG. 1. For example, thermoplastic resin a is joined to form a network and thereby foim void parts b. Lumps of resin having what is referred to as a spherulite structure are rarely observed in the three-dimensional network structure. The void parts b in the three-dimensional network structure are surrounded by the thermoplastic resin a and are preferably in communication with one another. Most of the used thermoplastic resin forms a three-dimensional network structure that is capable of contributing to the strength of the porous membrane (preferably hollow fiber membrane) and thus enables formation of a support layer having high strength.
In addition, the chemical resistance improves. Although the reason for improvement in chemical resistance is not clear, it is thought that since a large amount of thermoplastic resin forms a network that can contribute to strength, the strength of the overall layer is not significantly affected even when part of Ref. No. P0232569-ZZ (7/40) Date Recue/Date Received 2023-07-26 the network is corroded by a chemical.
00281 The porous membrane (preferably porous hollow fiber membrane) may have a single-layer structure or may have a multilayer structure including two or more layers. A layer that includes a surface at a filtration feed side is referred to as layer (A), whereas a layer that includes a surface at a filtrate side is referred to as layer (B).
For example, functions may be assigned such that the layer (A) is used as a so-called blocking layer and is caused to display a function of blocking membrane permeation by foreign matter contained in liquid to be treated (source water) through the small surface pore diameter thereof, whereas the layer (B) is used as a so-called support layer that has a function of ensuring high mechanical strength while also reducing water permeability as little as possible. Assignment of functions of the layer (A) and the layer (B) is not limited to that described above. In the porous membrane, just one surface may be the surface at the filtration feed side.
100291 The following provides a description for the case of a two-layer structure in which the layer (A) is a blocking layer and the layer (B) is a support layer.
The thickness of the layer (A) is preferably 1/100 or more and less than 40/100 of the total membrane thickness. Through the layer (A) having a comparatively large thickness in this manner, the porous membrane can be used even in a case in which the source water contains insoluble matter such as sand or aggregates. This is because the surface pore diameter does not change even when the porous membrane is worn down to a certain extent. A thickness that is within this range makes it possible to balance the desired blocking performance with high water permeation performance. The thickness of the layer (A) is more preferably 2/100 or more and 30/100 or less of the membrane thickness. The thickness of the layer (A) is preferably 1 inn or more and 100 pm or less, and more preferably 2 i..tm or more and 80 pm or less.
100301 The production method for the porous membrane (preferably porous hollow fiber membrane) according to this embodiment is a method using particles obtained by adjusting the particle diameter of a pelletal or particulate thermoplastic resin by crushing and/or pulverization so as to have a particle diameter dispersity V 0.8 where the particle diameter dispersity V is defined as V = (D90 - D10)/D50. The production method for the porous membrane according to this embodiment is more preferably a production method in which Ref. No. P0232569-ZZ (8/40) Date Recue/Date Received 2023-07-26

- 9 -a mixture of the particles and an organic liquid or a mixture of the particles, an organic liquid, and an inorganic fine powder is melt-kneaded and extruded and thereafter the organic liquid or the organic liquid and the inorganic fine powder are extracted.
In this specification, the product obtained by melt-kneading (i.e., melting and kneading) such a mixture is referred to as a melt-kneaded product.

[0031] The production method for the porous membrane according to this embodiment is preferably a method including a step of extruding a melt-kneaded product containing the particles, an organic liquid, and an inorganic fine powder from a spinneret having a circular ring-shaped discharge port so as to form a hollow fiber-shaped melt-kneaded product and a step of coagulating the hollow fiber-shaped melt-kneaded product and subsequently extracting and removing the organic liquid and the inorganic fine powder to produce a porous membrane (preferably porous hollow fiber membrane). The melt-kneaded product may be formed of two components that are the particles and a solvent or may be formed of three components that are the particles, an inorganic fine powder, and a solvent.
[0032] The thermoplastic resin that is used in the production method for the porous membrane (preferably porous hollow fiber membrane) according to this embodiment is a resin that has elasticity without displaying plasticity at normal temperature but that displays plasticity and becomes shapeable upon appropriate heating. Moreover, the thermoplastic resin is a resin that returns to its original elastic body when the temperature thereof decreases through cooling and that does not experience chemical change of molecular structure or the like during this cooling (for example, refer to Encyclopaedia Chimica 6th Reduced Edition, edited by the Editorial Committee of Encyclopedia Chimica, Kyoritsu Shuppan Co., Ltd., pp. 860 and 867, 1963).
[0033] Examples of thermoplastic resins that can be used include resins described in the "Thermoplastics" section (pp. 829-882) in "12695 Chemical Products" (The Chemical Daily Co., Ltd., 1995) and resins described in pages 809 to 810 of "Handbook of Chemistry, Applied Chemistry Section, Revised 3rd Edition" (edited by The Chemical Society of Japan, Maruzen, 1980).
Specific examples of names of thermoplastic resins that can be used include polyolefins such as polyethylene and polypropylene, fluororesins such as polyvinylidene fluoride, ethylene-vinyl alcohol copolymer, polyamide, polyether imide, polystyrene, polysulfone, polyvinyl alcohol, polyphenylene Ref. No. P0232569-ZZ (9/40) Date Recue/Date Received 2023-07-26

- 10 -ether, polyphenylene sulfide, cellulose acetate, and polyacrylonitrile. Of these examples, a crystalline thermoplastic resin such as a poly olefin, a fluororesin (polyvinylidene fluoride, etc.), an ethylene-vinyl alcohol copolymer, or a polyvinyl alcohol having crystallinity can suitably be used from a perspective of exhibiting strength. A poly olefin, a fluororesin such as polyvinylidene fluoride, or the like can more suitably be used due to having high water resistance as a result of being hydrophobic and being expected to have durability during filtration of typical water-based liquids. More specifically, the fluororesin preferably contains, as a main component, one or a combination of two or more of vinylidene fluoride resin (PVDF), chlorotrifluoroethylene resin, tetrafluoroethylene resin, ethyl ene-tetrafluoroethylene copolymer (ETFE), ethy lene-monochlorotrifluoro ethyl ene copolymer (ECTFE), hexafluoropropylene resin, and mixtures of these resins, and more preferably formed of only one of these resins or a combination of two or more of these resins. Polyvinylidene fluoride can particularly suitably be used as the fluororesin due to having excellent chemical durability in terms of chemical resistance, etc. The polyvinylidene fluoride may be a vinylidene fluoride homopolymer or may be a vinylidene fluoride copolymer in which the ratio of vinylidene fluoride is 50 mol% or more. The vinylidene fluoride copolymer may be a copolymer of vinylidene fluoride with one or more monomers selected from the group consisting of tetrafluoroethylene, hexafluoropropylene, chlorotrifluoroethylene, and ethylene. The polyvinylidene fluoride is particularly preferably a vinylidene fluoride homopolymer.
[0034] The mass ratio of the thermoplastic resin in the melt-kneaded product is preferably 30 mass% or more and 48 mass% or less, and more preferably 32 mass% or more and 45 mass% or less. It is easy to ensure mechanical strength when the mass ratio is 30 mass% or more, whereas water permeation performance is not reduced when the mass ratio is 48 mass% or less.
The mass ratio of the particles in the melt-kneaded product is preferably 30 mass% or more and 48 mass% or less, and more preferably 32 mass% or more and 45 mass% or less. It is easy to ensure mechanical strength when the mass ratio is 30 mass% or more, whereas water permeation performance is not reduced when the mass ratio is 48 mass% or less.
[0035] Moreover, in a case in which the porous membrane is a membrane having a two-layer structure, the mass ratio of the thermoplastic resin in the melt-kneaded product for the layer (B) is preferably 34 mass% or more and 48 Ref. No. P0232569-ZZ (10/40) Date Recue/Date Received 2023-07-26

- 11 -mass% or less, and more preferably 35 mass% or more and 45 mass% or less.
The mass ratio of the thermoplastic resin in the melt-kneaded product for the layer (A) is preferably 10 mass% or more and 35 mass% or less, and more preferably 12 mass% or more and less than 35 mass%. A balance of surface pore diameter and mechanical strength can be achieved when the mass ratio is 10 mass% or more, whereas reduction of water permeation performance does not occur when the mass ratio is 35 mass% or less.
The mass ratio of the particles in the melt-kneaded product for the layer (B) is preferably 34 mass% or more and 48 mass% or less, and more preferably 35 mass% or more and 45 mass% or less.
The mass ratio of the particles in the melt-kneaded product for the layer (A) is preferably 10 mass% or more and 35 mass% or less, and more preferably

12 mass% or more and less than 35 mass%. A balance of surface pore diameter and mechanical strength can be achieved when the mass ratio is 10 mass% or more, whereas reduction of water permeation performance does not occur when the mass ratio is 35 mass% or less.
[0036] The organic liquid serves as a latent solvent for the thermoplastic resin used in this embodiment. In this embodiment, the term "latent solvent" refers to a solvent that causes almost no dissolution of the thermoplastic resin at room temperature (25 C) but that can dissolve the thermoplastic resin at a higher temperature than room temperature. The organic liquid is not necessarily required to be a liquid at normal temperature so long as it is in a liquid state at a temperature at which it is melt-kneaded with the thermoplastic resin.
[0037] Examples of organic liquids that can be used in a case in which the thermoplastic resin is polyethylene include: phthalic acid esters such as dibutyl phthalate, diheptyl phthalate, dioctyl phthalate, di(2-ethylhexyl) phthalate, diisodecyl phthalate, and ditridecyl phthalate; sebacic acid esters such as dibutyl sebacate; adipic acid esters such as dioctyl adipate; trimellitic acid esters such as trioctyl trimellitate; phosphoric acid esters such as tributyl phosphate and trioctyl phosphate; glycerin esters such as propylene glycol dicaprate and propylene glycol dioleate; paraffins such as liquid paraffin;
and mixtures thereof.
[0038] Examples of organic liquids that can be used in a case in which the thermoplastic resin is polyvinylidene fluoride include: phthalic acid esters such as dimethyl phthalate, diethyl phthalate, dibutyl phthalate, dicyclohexyl phthalate, diheptyl phthalate, dioctyl phthalate, and di(2-ethylhexyl) phthalate;
Ref. No. P0232569-ZZ (11/40) Date Recue/Date Received 2023-07-26 sebacic acid esters such as dibutyl sebacate; adipic acid esters such as dioctyl adipate; benzoic acid esters such as methyl benzoate and ethyl benzoate;
phosphoric acid esters such as triphenyl phosphate, tributyl phosphate, and tricresyl phosphate; ketones such as y-butyrolactone, ethylene carbonate, propylene carbonate, cyclohexanone, acetophenone, and isophorone; and mixtures thereof.
[0039] The mass ratio of the organic liquid in the melt-kneaded product is preferably 10 mass% or more and 70 mass% or less, and more preferably 20 mass% or more and 60 mass% or less. If the mass ratio of the organic liquid is 10 mass% or more, the thermoplastic resin can be stably dissolved. If the mass ratio of the organic liquid is 70 mass% or less, stable production can be achieved because of sufficient viscosity for the spinning of the porous membrane.
[0040] Examples of inorganic fine powders that can be used include silica, alumina, titanium oxide, zirconium oxide, and calcium carbonate. Silica is preferable.
The average primary particle diameter of the inorganic fine powder is preferably 3 nm or more and 500 nm or less, and more preferably 5nm or more and 100 nm or less. In particular, fine powder silica having an average primary particle diameter of 3 nm or more and 500 nm or less is preferable.
Hydrophobic silica fine powder having low tendency to aggregate and good dispersibility is more preferable, and hydrophobic silica having an MW
(methanol wettability) value of 30 vol% or more is even more preferable.
The term "MW value" as used herein refers to a value for vol% of methanol that causes complete wetting of the powder. Specifically, the MW
value is determined by placing the silica in pure water, adding methanol below the liquid surface under stirring, and determining the vol% of methanol in the aqueous solution when 50 mass% of the silica has precipitated.
The "average primary particle diameter of the inorganic fine powder"
referred to above is a value determined through analysis of an electron micrograph. Specifically, a group of inorganic fine powder particles are first pretreated by a method in ASTM D3849. The diameters of 3,000 to 5,000 particles recorded in a transmission electron micrograph are then measured, and these diameters are arithmetically averaged so as to calculate the average primary particle diameter of the inorganic fine powder.
[0041] The mass ratio of the inorganic fine powder in the melt-kneaded Ref. No. P0232569-ZZ (12/40) Date Recue/Date Received 2023-07-26

- 13 -product is preferably 5 mass% or more and 50 mass% or less, and more preferably 10 mass% or more and 40 mass% or less. The effect of kneading the inorganic fine powder can be sufficiently displayed when the mass ratio of the inorganic fine powder is 5 mass% or more, whereas stable spinning can be performed when the mass ratio of the inorganic fine powder is 40 mass% or less.
[0042] A mixture made up of: particles obtained by adjusting the particle diameter of a pelletal or particulate thermoplastic resin such as polyvinylidene fluoride by pulverization, etc.; and an organic liquid or a mixture made up of:
particles obtained by adjusting the particle diameter of a pelletal or particulate thermoplastic resin such as polyvinylidene fluoride by pulverization, etc.; an organic liquid; and an inorganic fine powder is obtained through mixing using a Henschel mixer, a Banbury mixer, a Proshare mixer, or the like.
As for the order of mixing the three components of the particles .. obtained by adjusting the particle diameter of a thermoplastic resin such as polyvinylidene fluoride, the organic liquid, and the inorganic fine powder, rather than mixing the three components simultaneously, first mixing the inorganic fine powder and the organic liquid to cause the organic liquid to sufficiently adsorb to the inorganic fine powder and then blending and mixing the particles obtained by adjusting the particle diameter of the thermoplastic resin such as polyvinylidene fluoride is advantageous from the viewpoint of improving the melt formability and the porosity and mechanical strength of the porous membrane obtained.
Without preliminary kneading by a Henschel mixer or the like, the .. particles obtained by adjusting the particle diameter of the thermoplastic resin such as polyvinylidene fluoride and the organic liquid may be directly supplied to a melt-kneading extruder such as a twin screw extruder separately. It is also possible to, for enhancement in kneadability, perform melt-kneading after mixing to form pellets, supply the pellets to the melt-kneading extruder to be extruded into a hollow fiber shape, and perform cooling and solidification to obtain a hollow fiber.
[0043] The melt-kneading of the mixture can be performed using a typical melt-kneading means such as an extruder. Although the following describes a case in which an extruder is used, the means of melt-kneading is not limited to an extruder. One example of a production apparatus that can be used to implement the production method according to this embodiment is illustrated Ref. No. P0232569-ZZ (13/40) Date Recue/Date Received 2023-07-26

- 14 -in FIG. 2.
100441 A porous hollow fiber membrane production apparatus illustrated in FIG. 2 includes an extruder 10, a nozzle 20 for hollow fiber formation, a coagulation bath 30 that holds a solution for coagulating a membrane production stock solution, and a plurality of rollers 50 for conveying and taking up a porous hollow fiber membrane 40. A space S illustrated in FIG. 2 is a free traveling part through which the membrane production stock solution discharged from the nozzle 20 for hollow fiber formation passes before reaching the solution in the coagulation bath 30.
100451 The nozzle 20 for hollow fiber formation, which has one or more concentrically disposed circular ring-shaped discharge ports, is attached to the tip of the extruder 10. A melt-kneaded product is extruded by the extruder 10 and discharged from the nozzle 20 for hollow fiber formation. In the case of producing a membrane having a multilayer structure, a method in which a nozzle 20 for hollow fiber formation having two or more circular ring-shaped discharge ports is attached to the tips of extruders 10 and in which melt-kneaded products are supplied and extruded by different extruders 10 from the respective circular ring-shaped discharge ports or a method in which one of the multiple layers is produced and is subsequently coated with the remaining layer(s) may be adopted. For example, the fonner of these production methods using different extruders can obtain an extrudate in a hollow fiber form having a multilayer structure by merging and overlapping the supplied melt-kneaded products at the discharge ports. In this case, melt-kneaded products of different compositions can be extruded from circular ring-shaped discharge ports that are adjacent to each other to obtain a multilayer membrane having different pore diameters in layers that are adjacent to each other. The term "different compositions" refers to a case in which constituents of the melt-kneaded products are different or a case in which constituents of the melt-kneaded products are the same but the ratios thereof are different. Even in the case of the same type of thermoplastic resin, the constituents are considered to be different in a situation in which there is a clear difference in terms of molecular weight or molecular weight distribution. The merging position of the melt-kneaded products having different compositions may be a lower end face of the nozzle 20 for hollow fiber formation or may be a different position to the lower end face of the nozzle 20 for hollow fiber formation.
[0046] In extrusion of a melt-kneaded product from a circular ring-shaped Ref. No. P0232569-ZZ (14/40) Date Recue/Date Received 2023-07-26

- 15 -discharge port, it is preferable to perform discharge such that a spinneret discharge parameter R (1/sec) is a value of not less than 10 and not more than 1,000 because this results in high productivity and spinning stability, and yields an even stronger membrane. The term "spinneret discharge parameter R"
as used herein refers to a value obtained by dividing the discharge linear velocity V (m/sec) by the slit width d (m) of the discharge port. The discharge linear velocity V (m/sec) is a value obtained by dividing the discharge volume per time (m3/sec) of the melt-kneaded product by the cross-sectional area (m2) of the discharge port. When R is 10 or more, spinning is stably achieved with good productivity and without problems such as the pulsation of the thread diameter of the hollow extrudate. Moreover, when R is 1,000 or less, it is possible to maintain sufficiently high breaking elongation of the obtained porous hollow fiber membrane, which is one important aspect of strength. The breaking elongation is the ratio of elongation relative to the original length when the membrane is pulled in a longitudinal direction.
In the case of a porous hollow fiber membrane having a multilayer structure, a value obtained by dividing the discharge linear velocity V of a layered melt-kneaded product after resin merging by the slit width d of the discharge port is defined as the spinneret discharge parameter R. The range for R is more preferably not less than 50 and not more than 1,000.
[0047] The hollow fiber-shaped melt-kneaded product discharged from the discharge port is coagulated by passing through a coolant such as air or water.
Depending on the target porous hollow fiber membrane, the discharged melt-kneaded product is caused to pass through the aforementioned free traveling part S, which is formed of an air layer, and then caused to pass through the coagulation bath 30 containing water or the like. Specifically, the free traveling part S is a part from the discharge port of the nozzle 20 for hollow fiber formation to the water surface of the coagulation bath 30. A vessel such as a tube may be used in the free traveling part S from the discharge port as necessary. The melt-kneaded product that has passed through the coagulation bath 30 is then wound up into a skein or the like as necessary.
[0048] The thermoplastic resin to be fed into the extruder 10 is particles obtained by adjusting the particle diameter of a pelletal or particulate thermoplastic resin by crushing and/or pulverization. By using, as the thermoplastic resin, particles obtained by adjusting the particle diameter of a pelletal or particulate thermoplastic resin by crushing and/or pulverization, it Ref. No. P0232569-ZZ (15/40) Date Recue/Date Received 2023-07-26

- 16 -is possible to produce a porous membrane having high filtration performance and little variation in membrane performance. The D50 particle diameter of the thermoplastic resin to be fed into the extruder 10 may be 30 ttm or more, and may be 50 p.m to 500 p.m.
Non-limiting examples of the means for crushing and/or pulverizing the pelletal or particulate thermoplastic resin include a multi-stage pulverization method in which pellets are coarsely pulverized and then finely pulverized and a method in which refinement is performed in a single step. If the particles after pulverization do not reach a predetermined particle diameter with a fine pulverizer, an ultra-fine pulverizer capable of finer pulverization may be used to perform pulverization. Specific examples of pulverization means include pulverization means using a hammer mill, turbo mill, jet mill, pin mill, centrifugal mill, Rotoplex, pulverizer, wet pulverization, chopper mill, ultra rotor, etc. A normal temperature or freeze pulverization method may be used. For example, a freeze pulverization method is suitable for a vinylidene fluoride-based resin having a low glass transition point of about -35 C.
Freeze pulverization may be performed by freezing the pelletal or particulate thermoplastic resin with a low-temperature (for example, -50 C or less, or -100 C or less) liquid gas such as liquid nitrogen. Pulverization may be performed without oxygen (for example, oxygen concentration of 5 % or less, or 2 % or less). Examples of pulverization methods in freeze pulverization treatment include a pin mill, hammer mill, and jet mill.
[0049] Classification is performed using an appropriate classifier to obtain particles within a predetermined particle diameter range. In the case of obtaining particles within the predetermined particle diameter range from the classified particles, the particles may be further classified by another classifier, after which a fine powder not larger than a predetermined particle diameter is removed and the remaining particles (medium powder) are taken to be a product. Particles larger than the intended particle diameter range after classification may be re-pulverized to obtain particles within the predetermined particle diameter range. Non-limiting examples of equipment used for classification include a vibrating sieve, an inertial airflow classifier, and a rotating blade classifier.
[0050] In the case of mixing two types of polymers, each polymer may be pulverized and then mixed using a mixer. Classification may be performed after pulverization or after mixing, with there being no limitation. It is preferable Ref. No. P0232569-ZZ (16/40) Date Recue/Date Received 2023-07-26

- 17 -that all polymers to be fed into the mixer have a particle diameter dispersity V
(described later) within the below-described preferable range.
[0051] The particle diameter distribution of the particles after pulverization can be measured using a laser diffraction/scattering particle size distribution analyzer.
[0052] The particles adjusted in particle diameter by crushing and/or pulverization preferably have a volume-based median diameter (D50 particle diameter) obtained from the particle diameter distribution in the range of 50 i..tm to 500 pin. The D50 particle diameter is more preferably 70 1.1M to 400 1.1M.
If the D50 particle diameter is 50 [tm or more, for example when performing melt-kneading using an extruder or the like, the particles can be stably fed into the extruder without poor biting into the screw. If the D50 particle diameter is 500 JAM or less, the porous membrane can be produced stably without poor dissolution and the like.
In this specification, the D10 particle diameter, D50 particle diameter, and D90 particle diameter are values measured using a laser diffraction particle size analyzer.
100531 Similarly, the D10 particle diameter and D90 particle diameter are obtained from the particle diameter distribution. When particle diameter dispersity V = (D90 - D10)/D50 is defined from the obtained D10, D50, and D90 particle diameters, the particle diameter dispersity V of the particles adjusted in particle diameter by crushing and/or pulverization is preferably 0.8 or more, more preferably 1.3 or more, and further preferably 1.3 or more and 3.5 or less.
In the hollow fiber-shaped product present after coagulation, a polymer-rich partial phase and an organic liquid-rich partial phase are present as finely divided portions. Note that in a case in which an inorganic fine powder is added, for example, when fine powder silica is used as this inorganic fine powder, the fine powder silica becomes concentrated in the organic liquid-rich partial phase. When the organic liquid and the inorganic fine powder are extracted and removed from this hollow fiber-shaped product, the organic liquid-rich portion phase becomes internal pores. Accordingly, a porous hollow fiber membrane can be obtained.
If the particle diameter dispersity is 0.8 or more, the particles of the thermoplastic resin enter between the coagulated inorganic fine powder or between the particles of the inorganic fine powder, so that the miscibility of Ref. No. P0232569-ZZ (17/40) Date Recue/Date Received 2023-07-26

- 18 -the thermoplastic resin and the inorganic fine powder forming the polymer portion and pore portion of the porous membrane can be improved to obtain a more uniform structure of the porous membrane and reduce variation in membrane performance. The uniformity of the porous membrane can be evaluated by the variation in membrane performance. If the particle diameter dispersity is 1.3 or more, the bulk density stabilization time in a hopper, storage tank, or the like for temporary storage of the particles is shortened, and the transportability of the particles is stabilized. If the particle diameter dispersity is 3.5 or less, segregation in the hopper, storage tank, or the like can be prevented.
[0054] The ratio of the D50 particle diameter of the particles adjusted in particle diameter by crushing and/or pulverization to the average primary particle diameter of the inorganic fine powder ((the D50 particle diameter (nm) of the particles)/(the average primary particle diameter (nm) of the inorganic fine powder)) is preferably 3,200 or more and 35,000 or less, and more preferably 5000 to 33000. If the ratio is 3,200 or more, in the case of mixing the three components of the particles obtained by adjusting the particle diameter of the pelletal or particulate thermoplastic resin such as polyvinylidene fluoride by pulverization, etc., the organic liquid, and the inorganic fine powder and feeding the mixture into the extruder, the temperature of the extruder stabilizes more quickly. It is presumed that, although silica is likely to adhere to the polymer wall surface after mixing, if the ratio is 3,200 or more, the area of the polymer wall surface exposed without being covered with silica increases, as a result of which heat conduction to the polymer is facilitated and the stabilization of the temperature is accelerated.
Although there is no particular reason, stable mixing is achieved if the ratio is 35,000 or less.
[0055] The circularity of the particle shape of the particles adjusted in particle diameter by crushing and/or pulverization is preferably 0.5 or less, and more preferably 0.46 or less. The circularity may be 0.1 or more. When the circularity is lower, the bulk density is higher and the feeding into the extruder is more stable. The circularity is represented by the following formula (1). A

value closer to 1.0 indicates that the shape is closer to a circle.
[Math. 1]
Area ________________________________ Circularity = 47c x ... (1).
(Circumference)2 Ref. No. P0232569-ZZ (18/40) Date Recue/Date Received 2023-07-26

- 19 -[0056] The linearity of the particles adjusted in particle diameter by crushing and/or pulverization is preferably 1.8 or more, and more preferably 2.0 or more.
The linearity may be 10 or less. When the linearity is higher, in the case of mixing the three components of the particles, the organic liquid, and the inorganic fine powder, the gaps between the particles increase before the bulk density is stabilized, so that the mixability with the inorganic fine powder is improved. The linearity is represented by the following formula (2). A value closer to 1.0 indicates that the shape is closer to a perfect circle, and a larger value indicates a more elongated shape.
[Math. 21 11 (Absolute maximum length)2 Linearity ¨ 4 X ... (2).
(Area) [0057] The extraction and removal of the organic liquid and the extraction and removal of the inorganic fine powder can be performed at the same time in a case in which extraction and removal using the same solvent are feasible. In general, the organic liquid and the inorganic fine powder are extracted and removed separately to each other.
[0058] The extraction and removal of the organic liquid are performed using a liquid suitable for extraction that is miscible with the organic liquid without dissolving or denaturing the thermoplastic resin that is used. Specifically, the extraction and removal of the organic liquid can be performed through contact by an approach such as immersion. The liquid is preferably volatile because this facilitates removal of the liquid from the hollow fiber membrane after extraction. Examples of the liquid include alcohols and methylene chloride.
When the organic liquid is water-soluble, water may be used as the extractant.
[0059] The extraction and removal of the inorganic fine powder are usually performed using a water-based liquid. When the inorganic fine powder is silica, for example, the silica is first converted to a silicate by contact with an alkaline solution, and then the silicate can be extracted and removed by contact with water.
[0060] The extraction and removal of the organic liquid and the extraction and removal of the inorganic fine powder may be performed in any order. When the organic liquid is immiscible with water, it is preferable to first perform the extraction and removal of the organic liquid, followed by the extraction and removal of the inorganic fine powder. Since the organic liquid and the inorganic fine powder are normally present together in a miscible form in the Ref. No. P0232569-ZZ (19/40) Date Recue/Date Received 2023-07-26

- 20 -organic liquid-rich partial phase, this is advantageous because it enables smooth progression of the extraction and removal of the inorganic fine powder.

[0061] By extracting and removing the organic liquid and the inorganic fine powder from the coagulated porous hollow fiber membrane in this manner, it is possible to obtain a porous hollow fiber membrane.
The hollow fiber membrane after coagulation can be stretched in the longitudinal direction of the porous hollow fiber membrane with a stretch ratio in a range not exceeding 3 times at any stage (i) before the extraction and removal of the organic liquid and the inorganic fine powder, (ii) after the extraction and removal of the organic liquid and before the extraction and removal of the inorganic fine powder, (iii) after the extraction and removal of the inorganic fine powder and before the extraction and removal of the organic liquid, and (iv) after the extraction and removal of the organic liquid and the inorganic fine powder. In general, the stretching of a hollow fiber membrane in a longitudinal direction improves water permeation performance but reduces pressure resistance performance (for example, breaking strength and compressive strength), and thus often results in the membrane obtained after stretching lacking practical strength. However, the porous membrane (for example, porous hollow fiber membrane) obtained by the production method according to this embodiment has high mechanical strength. Accordingly, stretching can be performed with a stretch ratio of not less than 1.1 times and not more than 3.0 times. This stretching improves the water permeation performance of the porous membrane (for example, porous hollow fiber membrane). The term "stretch ratio" as used herein refers to a value obtained .. by dividing the hollow fiber length after stretching by the hollow fiber length before stretching. For example, in a case in which a porous hollow fiber membrane having a hollow fiber length of 10 cm is stretched to a hollow fiber length of 20 cm, the stretch ratio is 2 times according to the following formula.
20 cm 10 cm = 2.
100621 It is desirable that the stretching is performed with a space temperature of not lower than 0 C and not higher than 160 C. A space temperature of higher than 160 C is not preferable because it results in large stretching marks and reduction of breaking elongation and water permeation performance, whereas a space temperature of lower than 0 C is not practical as there is a high probability of breaking during stretching. The space temperature during the stretching step is more preferably not lower than 10 C and not higher than Ref. No. P0232569-ZZ (20/40) Date Recue/Date Received 2023-07-26

- 21 -140 C, and even more preferably not lower than 20 C and not higher than 100 C.
[0063] In this embodiment, it is preferable that the stretching is performed with respect to a hollow fiber membrane that contains the organic liquid. A
hollow fiber membrane that contains the organic liquid is less likely to break during stretching than a hollow fiber membrane that does not contain the organic liquid. Moreover, stretching of a hollow fiber membrane that contains the organic liquid makes it possible to increase contraction of the hollow fiber membrane after stretching, and thus increases the degree of freedom in design when setting the contraction ratio after stretching.
[0064] Moreover, it is preferable that stretching is performed with respect a hollow fiber membrane that contains the inorganic fine powder. A hollow fiber membrane that contains the inorganic fine powder is less likely to be squashed flat during stretching due to the hardness of the hollow fiber membrane that results from the presence of the inorganic fine powder contained in the hollow fiber membrane. Moreover, the presence of the inorganic fine powder can prevent the pore diameter in the finally obtained hollow fiber membrane becoming too small and the fiber diameter becoming too thin.
In this embodiment, it is more desirable for stretching to be performed with respect to a hollow fiber membrane that contains both the organic liquid and the inorganic fine powder.
[0065] For the reasons set forth above, stretching of a hollow fiber membrane that contains either one of the organic liquid and the inorganic fine powder is preferable compared to stretching of a hollow fiber membrane after completion of extraction, and stretching of a hollow fiber membrane that contains both the organic liquid and the inorganic fine powder is more preferable compared to stretching of a hollow fiber membrane that contains either one of the organic liquid and the inorganic fine powder.
[0066] Moreover, a method in which extraction is performed with respect to a hollow fiber membrane that has been stretched is advantageous in terms that the extraction solvent can easily infiltrate to an inner part of the hollow fiber membrane because the stretching increases voids at the surface and inside of the hollow fiber membrane. Furthermore, a method in which extraction is performed after a step of stretching and then contraction is advantageous because, as described below, a hollow fiber membrane having a low tensile modulus and high bendability is obtained, which, in a case in which extraction Ref. No. P0232569-ZZ (21/40) Date Recue/Date Received 2023-07-26

- 22 -is then performed in liquid flow, facilitates shaking of the hollow fiber membrane by the liquid flow and increases an effect of agitation, thereby enabling high efficiency extraction in a short time.
[0067] In this embodiment, it is possible to ultimately obtain a hollow fiber membrane having low tensile modulus in a case in which a step of stretching and then contracting the hollow fiber membrane is included. Note that the phrase "low tensile modulus" as used herein means that a fiber is easily extended through little force and then returns to its original state when the force is removed. A low tensile modulus means that the hollow fiber membrane is not squashed flat, easily bends, and is easily shaken by water flow during filtration. As a result of a fiber being shaken in accordance with water flow without bending thereof being fixed, a layer of contaminants that becomes attached to and deposited on the membrane surface can easily be stripped off without growing, and a high water filtration rate can be maintained.
Furthermore, when a fiber is forcefully shaken by flushing or air scouring, this increases the shaking and enhances the effect of washing recovery.
[0068] With regards to the degree of fiber length contraction in a situation in which contraction is performed after stretching, it is desirable that the fiber length contraction ratio relative to the increase of fiber length due to stretching is within a range of not less than 0.3 and not more than 0.9. For example, in a situation in which a 10 cm fiber is stretched to 20 cm and is subsequently contracted to 14 cm, the fiber length contraction ratio is 0.6 according to the following formula.
Fiber length contraction ratio = ((Maximum fiber length during stretching) ¨ (Fiber length after contraction)}/[(Maximum fiber length during stretching) ¨ (Original fiber length)] = (20 ¨ 14)/(20 ¨ 10) = 0.6.
A fiber length contraction ratio of 0.9 or more is not preferable because water permeation performance tends to decrease, whereas a fiber length contraction ratio of less than 0.3 is not preferable because the tensile modulus tends to increase. In this embodiment, the fiber length contraction ratio is more preferably within a range of not less than 0.50 and not more than 0.85.
[0069] Moreover, by adopting a step of stretching the hollow fiber membrane to the maximum fiber length during stretching and subsequently contracting the hollow fiber membrane, the hollow fiber membrane that is ultimately obtained will not break even when, during use, it is stretched up to the maximum fiber length during stretching.
Ref. No. P0232569-ZZ (22/40) Date Recue/Date Received 2023-07-26

- 23 -When the stretch ratio is taken to be X and the fiber length contraction ratio relative to the increase of fiber length due to stretching is taken to be Y, a ratio Z that represents the degree of assurance of breaking elongation 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).
Z is preferably not less than 0.2 and not more than 1.5, and more preferably not less than 0.3 and not more than 1Ø Assurance of breaking elongation decreases when Z is too small, whereas there is less water permeation performance in exchange for increased possibility of breaking during stretching when Z is too large.
[0070] Moreover, in a case in which the production method according to this embodiment includes a step of stretching and then contraction, with regards to tensile breaking elongation, breaking at low elongation is highly unlikely, and .. a narrower distribution of tensile breaking elongation can be achieved.
[0071] It is desirable in terms of contraction time and physical properties that the space temperature in the step of stretching and then contraction is within a range of not lower than 0 C and not higher than 160 C. A temperature of lower than 0 C is not preferable because contraction becomes time consuming and is not practical, whereas a temperature exceeding 160 C is not preferable because it reduces breaking elongation and lowers water permeation performance.
[0072] In this embodiment, it is preferable that crimping of the hollow fiber membrane is performed in the contraction step. This makes it possible to obtain a hollow fiber membrane having a high degree of crimping without squashing or damage thereof.
[0073] Hollow fiber membranes generally have a straight tube form without bends. Consequently, when hollow fiber membranes are bundled together as a filtration module, they are likely to form a fiber bundle having a low void ratio without gaps between the hollow fibers. In contrast, the use of hollow fiber membranes having a high degree of crimping enables the formation of a fiber bundle having a high void ratio because bending of the individual fibers widens intervals between the hollow fiber membranes, on average. Moreover, particularly during use with external pressure, a filtration module formed of hollow fiber membranes having a low degree of crimping experiences reduction of voids in the fiber bundle, increased flow resistance, and lack of Ref. No. P0232569-ZZ (23/40) Date Recue/Date Received 2023-07-26

- 24 -effective transmission of filtration pressure to the center of the fiber bundle.
Furthermore, in a situation in which backwashing or flushing is performed in order to strip filtration sediment from the hollow fiber membranes, the effect of washing is small in an inner part of the fiber bundle. In the case of a fiber bundle that is formed of hollow fiber membranes having a high degree of crimping, the void ratio is large, gaps between hollow fiber membranes are maintained even in external pressure filtration, and channeling tends not to occur.
[0074] The degree of crimping of the porous membrane (preferably hollow fiber membrane) obtained by the production method according to this embodiment is preferably within a range of not less than 1.5 and not more than 2.5. A degree of crimping of 1.5 or more is preferable for the reasons set forth above, whereas a degree of crimping of 2.5 or less can inhibit reduction of filtration area per volume.
[0075] The method of crimping of the hollow fiber membrane may be a method in which, in the step of stretching and then contraction, the hollow fiber membrane is sandwiched between a pair of gear rolls having periodic irregularities or a pair of sponge belts having irregularities, for example, and is taken up while being caused to contract.
[0076] Moreover, in the production method according to this embodiment, the stretching is preferably performed using a take up machine including a pair of continuous belts that are in opposition. In this case, take up machines are used at an upstream side and a downstream side of the stretching, and the hollow fiber membrane is sandwiched between opposing belts in each of the take up machines and is fed through movement of both belts at the same speed in the same direction. Moreover, in this case, stretching is preferably performed by adopting a higher fiber feed rate at the downstream side than at the upstream side. By performing stretching in this manner, stretching can be performed without yielding to stretching tension and without slipping during stretching, and squashing of the fiber into a flat form can be prevented.
[0077] The continuous belt is preferably a belt for which an inner side that comes into contact with a drive roll is formed of a high elasticity belt such as a fiber reinforced belt and for which a surface at an outer side that comes into contact with the hollow fiber membrane is formed of an elastic body. Moreover, it is more preferable that the compression modulus of the elastic body in a thickness direction is not less than 0.1 MPa and not more than 2 MPa and that Ref. No. P0232569-ZZ (24/40) Date Recue/Date Received 2023-07-26

- 25 -the thickness of the elastic body is not less than 2 mm and not more than 20 mm. In particular, it is preferable in terms of chemical resistance and heat resistance for the elastic body at the outer surface to be silicone rubber.
[0078] The membrane that has been stretched may be heat treated as necessary so as to increase compressive strength. It is desirable for the heat treatment to be performed at not lower than 80 C and not higher than 160 C. A temperature of 160 C or lower can inhibit reduction of breaking elongation and water permeation performance, whereas a temperature of 100 C or higher can increase compressive strength. Performing the heat treatment with respect to the hollow fiber membrane after extraction is complete is desirable in terms that this reduces change of fiber diameter, internal porosity, pore diameter, and water permeation performance.
EXAMPLES
[0079] The following provides a more specific description of this embodiment through examples and comparative examples. However, this embodiment is not limited to only the following examples.
[0080] Note that measurement methods used in this embodiment are as follows.
[0081] All of the measurements described below were performed at 25 C
unless otherwise specified. The following describes evaluation methods and then describes production methods and evaluation results for the examples and comparative examples.
[0082] Moreover, compositions, production conditions, and various aspects of performance of membranes are shown in Table 1.
[0083] (1) External diameter, internal diameter, and membrane thickness A hollow fiber membrane was perpendicularly sliced with a razor or the like at 15-cm intervals in the longitudinal direction of the membrane, and the major axis and minor axis of an internal diameter and the major axis and minor axis of an external diameter in the cross section were measured using a microscope. The internal diameter and the external diameter were calculated by the following formulae (2) and (3), and the membrane thickness was calculated as a value obtained by subtracting the calculated internal diameter from the calculated external diameter and then dividing by 2. Measurements were made at 20 points, and average values for these 20 points were taken to be the internal diameter (mm), the external diameter (mm), and the membrane thickness (mm) under those conditions.
Ref. No. P0232569-ZZ (25/40) Date Recue/Date Received 2023-07-26

- 26 -[Math. 3]
Internal major axis Internal minor axis [mm] [rin.]
Internal deter [min] = __________________________________ [Math. 4]
External major axis External minor axis [mm] HF [mm]
External diameter [mm] = _____________________________________ (3) [0084] (2) Pure water permeability (L/m2/hr) A hollow fiber membrane was immersed in 50 mass% ethanol aqueous solution for 30 minutes and was then immersed in water for 30 minutes to wet the hollow fiber membrane. One end of the wet hollow fiber membrane, which was of approximately 10 cm in length, was sealed and an injection needle was .. inserted into the hollow part at the other end. Pure water of 25 C was injected into the hollow part with a pressure of 0.1 MPa from the injection needle. The amount of pure water that permeated to the external surface was measured, and the pure water peimeation flux was determined by the following formula (4).
Note that the membrane effective length is the net membrane length exclusive of the part where the injection needle was inserted. Moreover, 10 measurements were made, and the average value thereof was taken to be the pure water permeability under each condition.
[Math. 5]
60 [minilir] x Amount of permeated water pp Pure water permeability 11./m2/hr] _________________________________ = ( 4 ) Membrane Membrane Meaeurement n x writ,' X efftallre X
time [mini diameter [m] length Its) [0085] (3) Variation coefficient of pure water permeability Each sample n = 50 was measured by the method of measuring pure water permeability in (2), and the variation coefficient = (standard deviation/average value) X 100 was calculated.
[0086] (4) Required time for stabilization of extruder temperature A mixture was fed into an extruder. From the time at which a predetermined extrusion output was reached, whether the barrel temperature, Ref. No. P0232569-ZZ (26/40) Date Recue/Date Received 2023-07-26

- 27 -after entering the range of 10 C of a set temperature, was within the range of 10 C for 10 minutes was determined. If the barrel temperature was determined to be within the range of 10 C for 10 minutes, it was determined that the temperature stabilized, and the time from when the predetermined extrusion output was reached to when the barrel temperature entered the range of 10 C was taken to be the required time for stabilization. If the barrel temperature, after entering the range of 10 C of the set temperature, deviated again from the range of 10 C, the barrel temperature was monitored for 10 minutes from when it entered the range of 10 C next time, and the required time for stabilization (minutes) was determined by the foregoing method.
[0087] (5) Feedability into extruder When feeding raw material into an extruder, if the raw material could be stably fed for 20 minutes without any feeding failure, the feedability was rated A (not problematic). If a feeding failure occurred, the feedability was rated B (problematic).
[0088] (6) Stretch failure When stretching the membrane, it was monitored for 15 minutes, and the number of stretch failures and breaks during stretching was counted through visual observation.
[0089] (7) Particle diameter distribution Measurement was performed using MS3000 (produced by Malvern Panalytical, Ltd.) as a particle diameter distribution analyzer and water as a dispersion medium, with a dispersion medium refractive index of 1.330 and a particle refractive index of 1.420. D10, D50, and D90 were calculated based on particle volume.
In the case of performing classification after pulverization, "particles after pulverization" in the table refer to particles fed into the extruder after pulverization and classification.
[0090] (8) Circularity and linearity Using electron microscope SU8000 series produced by Hitachi, Ltd., polymer particles were observed at an acceleration voltage of 3 kV. In the observation, an image was recorded at a magnification enabling confirmation of at least 20 polymer particles. When preparing each observation sample, the sample was placed on a table so as to be as thin and flat as possible so that the polymer particles would not overlap each other. A transparent sheet was placed on a copy of the recorded image, particle parts were blacked out using a black Ref. No. P0232569-ZZ (27/40) Date Recue/Date Received 2023-07-26

- 28 -pen or the like, and the transparent sheet was copied onto a blank sheet such that particle parts indicated by black were clearly discernable from other parts indicated by white. Binarization was performed by discriminant analysis using Winroof 2018 Ver 4.23.1. The circularity and linearity were calculated from shape feature value analysis of the binarized image thus obtained.
In the case of performing classification after pulverization, "particles after pulverization" in the table refer to particles fed into the extruder after pulverization and classification.
[0091] (9) Internal and external surface pore diameter and surface porosity The same electron microscope as in (8) was used to record an image of a surface at a filtration feed side. The image was recorded at a magnification enabling confirmation of the shapes of at least 20 pores. In the examples and comparative examples, the image was recorded at x10,000.
A transparent sheet was placed on a copy of the recorded image, pore parts were blacked out using a black pen or the like, and the transparent sheet was copied onto a blank sheet such that pores parts indicated by black were clearly discernable from non-pore parts indicated by white as described in WO
2001/53213 Al. Thereafter, commercially available image analysis software Winroof 2018 Ver 4.23.1 was used to perform binarization by discriminant analysis. Occupied area in the binarized image thus obtained was then determined to determine the surface porosity of the external surface.
The pore diameter was determined by calculating an equivalent circle diameter for each pore present at a surface, adding the areas of these pores in descending order of pore diameter, and determining the diameter of a pore at which the sum of the added areas reached 50 % of the total area of the pores.
[0092] (10) Segregation in hopper Particles (80 kg) obtained by pulverizing a thermoplastic resin were stored in a hopper (capacity 500 L) for temporary storage at a temperature of 25 C and a humidity of 40 %. After 8 hours from the start of the storage, particles were removed from the top and particles at the bottom were observed.
The segregation property was rated A (not problematic) if no accumulation of a fine powder was visually observed, and rated B (problematic) if such accumulation was visually observed.
[0093] (11) Bulk density stabilization time in hopper Particles (80 kg) obtained by pulverizing a thermoplastic resin were stored in a hopper (capacity 500 L) for temporary storage at a temperature of Ref. No. P0232569-ZZ (28/40) Date Recue/Date Received 2023-07-26

- 29 -25 C and a humidity of 40 %. The bulk density was measured every 10 minutes for 2 hours from the start of the storage. The stabilization time was rated C
(fast stabilization) if the bulk density was 10 % or less two consecutive times from the start of the storage, specifically, the bulk density was 10 % or less at 10 minutes and at 20 minutes from the start of the storage, and rated D (slow stabilization) if the bulk density was 10 % or less only at or after 20 minutes.
100941 (Example 1) A vinylidene fluoride homopolymer (Kynar 740 produced by Arkema K.K.) was used as a thermoplastic resin. Pelletal Kynar 740 was pulverized by a freeze pulverization method using Linrex Mill (produced by Hosokawa Micron Corporation). Classification was carried out using a vibrating sieve, and particles of 355 jtm or more in sieve opening were removed and particles of 53 [tm or more were adopted as a product. After the pulverization, the D50 particle diameter was 160 1.1M and the particle diameter dispersity V was 1.1.
The circularity was 0.43 and the linearity was 2.5.
The vinylidene fluoride homopolymer after pulverization, a mixture of di(2-ethylhexyl) phthalate (DEHP) (produced by CG Ester Corporation) and dibutyl phthalate (DBP) (produced by CG Ester Corporation) as an organic liquid, and fine powder silica (produced by Nippon Aerosil Co., Ltd.; product name: AEROSIL-R972; average primary particle diameter: approximately 16 nm) as an inorganic fine powder were used to perform melt extrusion of a hollow fiber membrane from an extruder using a nozzle for hollow fiber formation. A melt-kneaded product having a composition of vinylidene fluoride homopolymer:di(2-ethylhexyl) phthalate:dibutyl phthalate: fine powder silica = 40.0:31.7:5.30:23.0 (mass ratio) was extruded at a discharge temperature of 240 C from the nozzle for hollow fiber formation having an external diameter of 1.7 mm and an internal diameter of 0.9 mm, using air as a fluid for hollow part formation.
The hollow fiber-shaped melt-kneaded product that was extruded at a discharge temperature of 240 C was, after 0.60 seconds of free traveling, guided into a coagulating bath holding 30 C water. The hollow fiber-shaped melt-kneaded product was taken up at a rate of 30 m/min, was sandwiched between belts, and was stretched at a rate of 60 m/min. Thereafter, the hollow fiber-shaped melt-kneaded product was caused to contract at a rate of 45 m/min while being blown with hot air of 140 C in device settings, and was wound up into a skein.
Ref. No. P0232569-ZZ (29/40) Date Recue/Date Received 2023-07-26

- 30 -The resultant hollow fiber-shaped product was immersed in isopropyl alcohol so as to extract and remove di(2-ethylhexyl) phthalate and dibutyl phthalate and was subsequently dried. Next, the hollow fiber-shaped product was immersed in 50 mass% ethanol aqueous solution for 30 minutes, was then immersed in water for 30 minutes, was subsequently immersed in 20 mass%
sodium hydroxide aqueous solution at 70 C for 1 hour, and was also repeatedly washed with water so as to extract and remove the fine powder silica and thereby obtain a porous hollow fiber membrane.
Details of composition and conditions are shown in Table 1.
[0095] (Example 2) A porous hollow fiber membrane was obtained by the same method as in Example 1 with the exception that the vinylidene fluoride homopolymer after pulverization was classified in such a manner that particles of 300 [tm or more in sieve opening were removed and particles of 90 [tm or more were adopted as a product. Details of composition and conditions are shown in Table 1.
[0096] (Example 3) A porous hollow fiber membrane was obtained by the same method as in Example 1 with the exception that the vinylidene fluoride homopolymer after pulverization was not classified. Details of composition and conditions are shown in Table 1.
[0097] (Example 4) A porous hollow fiber membrane was obtained by the same method as in Example 1 with the exception that the vinylidene fluoride homopolymer after pulverization was classified in such a manner that particles of 425 1..tm or more in sieve opening were removed and particles of 53 p.m or more were adopted as a product.
[0098] (Example 5) A porous hollow fiber membrane was obtained by the same method as in Example 1 with the exception that the vinylidene fluoride homopolymer was pulverized using disk-type pulverizer Spiral Mill (produced by Seishin Enterprise Co., Ltd.). Details of composition and conditions are shown in Table 1.
[0099] (Example 6) A porous hollow fiber membrane was obtained by the same method as in Example 1 with the exception that the same disk-type pulverizer Spiral Mill Ref. No. P0232569-ZZ (30/40) Date Recue/Date Received 2023-07-26

- 31 -as in Example 5 was used and the clearance between the fixed blade and the rotary blade installed in the pulverizer was adjusted to adjust the particle diameter. Details of composition and conditions are shown in Table 1.
[0100] (Example 7) A porous hollow fiber membrane was obtained by the same method as in Example 3 with the exception that a vinylidene fluoride homopolymer (Solef 6010 produced by Solvay) was used as a thermoplastic resin. Details of composition and conditions are shown in Table 1.
[0101] (Example 8) A porous hollow fiber membrane was obtained by the same method as in Example 3 with the exception that ethylene-chlorotrifluoroethylene (Halar 901 produced by Solvay) was used as a thermoplastic resin and the composition of the melt-kneaded product was vinylidene fluoride homopolymer:di(2-ethylhexyl) phthalate: dibutyl phthalate:fine powder silica =
40.0:33.7:3.70:23.0 (mass ratio). Details of composition and conditions are shown in Table 1.
[0102] (Comparative Example 1) A porous hollow fiber membrane was obtained by the same method as in Example 1 with the exception that the vinylidene fluoride homopolymer after pulverization was classified in such a manner that particles of 250 1.1m or more in sieve opening were removed and particles of 90 pm or more were adopted as a product. Since the particle diameter dispersity was 0.70, the variation coefficient of the pure water permeability of the porous membrane was high and large variation in the structure of the porous membrane was recognized.
[0103] (Example 9) A porous hollow fiber membrane was obtained by the same method as in Example 1 with the exception that the vinylidene fluoride homopolymer after pulverization was classified in such a manner that particles of 850 1..tm or more in sieve opening were removed and particles of 355 m or more were adopted as a product. Since the ratio of the D50 particle diameter of the particles to the average primary particle diameter of the inorganic fine powder was 37,500, five stretch failures occurred in 15 minutes. An evaluation sample was collected. Details of composition and conditions are shown in Table 1.
[0104] (Example 10) A porous hollow fiber membrane was obtained by the same method as Ref. No. P0232569-ZZ (31/40) Date Recue/Date Received 2023-07-26

- 32 -in Example 1 with the exception that the vinylidene fluoride homopolymer after pulverization was classified in such a manner that particles of 300 lam or more in sieve opening were removed and particles of 53 p.m or more were adopted as a product and fine powder silica (produced by Nippon Aerosil Co., Ltd.; product name: AEROSIL-RX50; primary particle diameter:
approximately 40 nm) was used as an inorganic fine powder. Since the ratio of the D50 particle diameter of the particles to the average primary particle diameter of the inorganic fine powder was 2,750, the required time for the stabilization of the extruder temperature was 50 minutes. An evaluation sample was collected. Details of composition and conditions are shown in Table 1.
[0105] (Example 11) A porous hollow fiber membrane was obtained by the same method as in Example 1 with the exception that the vinylidene fluoride homopolymer after pulverization was classified in such a manner that particles of 106 [tm or more in sieve opening were removed and particles of 32 ra or more were adopted as a product. Since the D50 particle diameter of the particles was 50 Jim, stable feeding into the extruder was not possible, but a sample was collected when feeding could be performed intermittently for short periods of time. Details of composition and conditions are shown in Table 1.
[0106] (Example 12) A porous hollow fiber membrane was obtained by the same method as in Example 1 with the exception that Kynar 720 produced by Arkema K.K. was used as a vinylidene fluoride homopolymer after pulverization, the vinylidene fluoride homopolymer after pulverization was classified in such a manner that particles of 425 pm or more in sieve opening were removed and the remaining particles were adopted as a product, and the composition of the melt-kneaded product was vinylidene fluoride homopolymer:di(2-ethylhexyl) phthalate:dibutyl phthalate:fine powder silica = 40.0:31.3:5.70:23.0 (mass ratio).
[0107] (Example 13) A porous hollow fiber membrane was obtained by the same method as in Example 12 with the exception that the vinylidene fluoride homopolymer after pulverization was classified in such a manner that particles of 850 ptm or more in sieve opening were removed and particles of 90 p.m or more were adopted as a product.
[0108] (Example 14) Ref. No. P0232569-ZZ (32/40) Date Recue/Date Received 2023-07-26

- 33 -A porous hollow fiber membrane was obtained by the same method as in Example 13 with the exception that the vinylidene fluoride homopolymer after pulverization was classified in such a manner that particles of 850 lam or more in sieve opening were removed and particles of 106 [tm or more were adopted as a product and the composition of the melt-kneaded product was vinylidene fluoride homopolymer:di(2-ethylhexyl) phthalate:dibutyl phthalate:fine powder silica = 40.0:31.7:5.30:23.0 (mass ratio).
[0109] (Example 15) A porous hollow fiber membrane was obtained by the same method as in Example 14 with the exception that the vinylidene fluoride homopolymer after pulverization was classified in such a manner that particles of 250 tim or more in sieve opening were removed and the remaining particles were adopted as a product.
[0110] (Example 16) A porous hollow fiber membrane was obtained by the same method as in Example 13 with the exception that the vinylidene fluoride homopolymer after pulverization was classified in such a manner that particles of 850 tim or more in sieve opening were removed and particles of 90 inn or more were adopted as a product.
[0111] (Example 17) A porous hollow fiber membrane was obtained by the same method as in Example 13 with the exception that the vinylidene fluoride homopolymer after pulverization was classified in such a manner that particles of 425 t.tm or more in sieve opening were removed and the composition of the melt-kneaded product was vinylidene fluoride homopolymer:di(2-ethylhexyl) phthalate:dibutyl phthalate:fine powder silica = 45.0:28.7:5.20:21.1 (mass ratio).
[0112] (Example 18) A porous hollow fiber membrane was obtained by the same method as in Example 13 with the exception that the vinylidene fluoride homopolymer after pulverization was classified in such a manner that particles of 425 p.m or more in sieve opening were removed and the composition of the melt-kneaded product was vinylidene fluoride homopolymer:di(2-ethylhexyl) phthalate:dibutyl phthalate:fine powder silica = 34.0:34.4:6.30:25.3 (mass ratio).
[0113] (Comparative Example 2) Ref. No. P0232569-ZZ (33/40) Date Recue/Date Received 2023-07-26

- 34 -Solef 6010 (powder) was purchased as a vinylidene fluoride homopolymer, and the circularity and linearity of the particles were analyzed.

The powder product was particles after polymerization and was not subjected to pulverization. Moreover, neither crushing nor pulverization of resin as described in the examples was performed.
Ref. No. P0232569-ZZ (34/40) Date Recue/Date Received 2023-07-26

- 35 -[0114] [Table 1]
r, ci = ' . a ,, ..g O''.'4 11R E E 2 1 41r--i.':1 I .7, .4 a g 2 .el....72,,2, a :.'_. .g . LI, .; 11 '".1 .9, i 1.14 ...5 ,fõ r';', a _ 3: -:,' '-7 -.
CZ
2 . . .
7. `4 '-j F, ?"' ".I.-2',9,,F, 4 ,..--, -'44,f!'f,1* r.
E z ,F
- - - -'.-- t'22,?, _ - .. ..
R, 2r.e3-=-9gni 2 2 n i =i=-= '-',,"' `.E 7 ,:z .'..., g 2, ...,, .22, 2 f. R A 2 Ã '.:_il 2, ,.,-,r, _ ' a gi õ7,,,2,,, ,?., R., ..2,,,RR., a '_--?., 21,s.
22'-'-i ,9,1 7 R .. , . . .. , .
, te, r , ..e -'8' a ,,,!,,,5',5, 4 ''L R . i ":. i'l n a fc, L gL . , r.=
. -;., ..,.<
7.4 ,.. t III 4' i'd , E
-;3' R ''''M 212 R,1 4. C., ,, ' 4 i t ''' r' , PA IP k . 2 r, g i&r1'4 i ,:', õ:t ,,, g ,9 =,2-..R,R., 4 n 3 ' ' ' f al, E .--.1 L.
õ, g p.,.= R 2 , = .41 i 42 n :.., g i --,, I `.".' 1 7 -4 a g 2, ,,,,I,2,2, 4 f a .1 ,.; 11 1: a 1 if . . g '0, , .
,.., - - .. ..
,-Iii"' 1 rt.1:
1 --,='-' 1' 1, '54'.t, 71,, ,,,..
L't .--'-'t1 -2 /A =-3.- " R ,i' t'r 2,-0; , 01,I L- ., 1 g'.17=`,1 1; .4 41..-4.4 ,-2, Pc :A E 2j: ilfrU. C41.1,;i tp4. r.:1-.'_a_aa';2.r'-'51" 2,R-5C.14..?==!.i5-525':2,22¨tialiqjf-," '4,2 ''4% tWtH.4 il.1...,'..
g .¨a,. 2".j =F 4.;-.34 -.Q:.; 2 .-,2 - ,I.,..:: Am F.,1-F, 2 l'il 11.'3A112.1:1;'Itiiililirli1141141APAL4gAilt,i2E2ni6,LT.2,hign:
.B1 ''' 11 Fl Pli .g' e P
It Ref. No. P0232569 -ZZ (35/40) Date Recue/Date Received 2023-07-26

- 36 -[Table 1 (cont'd)]
7-1 ;2 ..,,,,..1,14 :54 ' .
.1 :='- 4 :!-.5 , ,.t 1'.;'..,T, .' @ - , =' e - 'A 1 7,,, <t lc .f!, 4' a ! _.':f, .-i¨L-A
.0 , ..4' c 74E71 õ R 2 0 ,., a -4 ! .:",-" '9-. ..', 4 "r: .4., .I
1- F.. , E 2 -, 0 ..,E ,,, ' t 4 c'F',"',IFil,4', 8 , 4 , .,.. q e .r., p .
,-õ, 4 u ,, g ..:,,f,-4=g,?õ n ff, 0.1,-, .f,-,,,,-;, g .,.-.,7:,,r.,,,,, _ : ,..., , !,,,, & ,,.;. , -2 '' 2-g ..:
L.t!
'.4 a .=..i , :', -.e i:V'-al-ri 2 ';', ,Ir: ; Fr.,' 1 R
3 ''''-',71.; p ,,";, a, c , ' , , ..
]
.4 a .'' g,,, :: 4.
I..1131 I 2 ';..; ',,- ri i -'r2 1 a 1 a ''''4"'-'41 m " :0; 9 a- :f L` 0 ..'''i td c 1, t '''.1'Ml t2`,T,A.F,,a 5 ';,,' ',' iP1'..5. 1. 2 < 0 F g <!..1.g,., 4 'f.' 4 . ,.. 5, a 4 - 41 8 P "
I P.
..., 11.
i 'i 'a I
a 2 .4 . ,A, ,i... 4 ,.! .. g ?., 4 n _4, .:4 P ,9, 5. E
.õ
, ,,,--,-,y ;,,E.ii5 0 $ , - 0 t-.a1,- .-== d - g r. g - P.. ,,72, ,t el ;?,-,, a s ,..
1,-f.
;. g , ? -E ,g c , -'474:7,t10 =:,¶' A' Igt,1'.' :11111:,-11 ,', t2g.
=j11'.1..ii.'.-12 li-El2410.5S-2>'..n ii.f,,:i'g..,,i.gi&.:A5,,p,-;-..!¨õ,.1.1,Asu'q2-9;',-8'.2:14-:','I
-'s'l m.711i4;pr",=ry.'8.3ry.44.E,M.74,2?,,e P..,i 1.1 k. g 2 Ref. No. P0232569-ZZ (36/40) Date Recue/Date Received 2023-07-26

- 37 -INDUSTRIAL APPLICABILITY
101151 It is thus possible to provide a porous membrane (preferably porous hollow fiber membrane) with high productivity and little variation in membrane performance.
Ref. No. P0232569-ZZ (37/40) Date Recue/Date Received 2023-07-26

Claims (10)

- 38 -

1. A production method for a porous membrane containing a thermoplastic resin, the production method comprising producing the porous membrane using particles obtained by adjusting a particle diameter of a pelletal or particulate thermoplastic resin by at least one of crushing and pulverization so as to have a particle diameter dispersity V 0.8 where the particle diameter dispersity V is defined as V = (D90 -D10)/D50.

2. The production method for a porous membrane according to claim 1, wherein a circularity of the particles is 0.5 or less.

3. The production method for a porous membrane according to claim 1 or 2, wherein a linearity of the particles is 1.8 or more.

4. The production method for a porous membrane according to claim 1 or 2, wherein the particle diameter dispersity V 1.3.

5. The production method for a porous membrane according to claim 1 or 2, wherein a D50 particle diameter of the particles is 50 ilm to inn.

6. The production method for a porous membrane according to claim 1 or 2, wherein a mixture of the particles and an organic liquid or a mixture of the particles, an organic liquid, and an inorganic fine powder is melt-kneaded and extruded and thereafter the organic liquid or the organic liquid and the inorganic fine powder are extracted to produce the porous membrane.

7. The production method for a porous membrane according to claim 6, wherein a ratio of a D50 particle diameter of the particles to an average primary particle diameter of the inorganic fine powder, expressed by (the D50 particle diameter of the particles)/(the average primary particle diameter of the inorganic fine powder), is 3,200 to 35,000.

8. The production method for a porous membrane according to claim 1 or 2, wherein the porous membrane is a hollow fiber membrane.

9. The production method for a porous membrane according to claim 1 or 2, wherein the thermoplastic resin is a resin containing polyvinylidene fluoride as a main component.

10. The production method for a porous membrane according to claim 1 or 2, wherein the thermoplastic resin is a resin containing ethylene chlorotrifluoroethylene or ethylene tetrafluoroethylene as a main component.