Separation membrane and method for manufacturing the same

Abstract

A separation membrane is used in deaeration methods for removing a gas dissolved in a liquid, and gas exchange methods for exchanging a gas dissolved in a liquid and a gas component in a gas phase. The present invention provides a separation membrane that has solvent resistance and maintains high gas permeability performance by using poly(4-methyl-1-pentene), which excels in solvent resistance and gas permeability. The separation membrane contains poly(4-methyl-1-pentene) as a main component, and includes surface layers and an inner layer. At least one of the surface layers includes lamella crystals, and the surface layer including the lamella crystals has micropores. Defining porosity as the percentage of micropores in the membrane surface with the membrane surface being 100%, the porosity is 0.1% to 10%. The average pore diameter of the micropores is 3 nm to 30 nm.

Description

[Technical Field]

[0001] The present invention relates to a gas separation membrane and a method for producing the same. [Background technology]

[0002] Hollow fiber membranes are used as degassing methods to remove dissolved gases from liquids, and as gas exchange methods to exchange dissolved gases in liquids with gaseous components in the gas phase. Because the hollow fiber membranes used require high gas permeability and solvent resistance to the treated liquid, poly(4-methyl-1-pentene), which excels in these properties, is sometimes used as the membrane material. Among hollow fiber membranes, those with a dense surface layer are desirable because they can suppress the penetration of solvents into the membrane, thereby improving solvent resistance.

[0003] Various methods have been proposed to obtain gas permeable membranes using polyolefin polymers as materials. For example, Patent Document 1 discloses a wet method using polyolefin polymers. In Patent Document 1, a polymer solution obtained by dissolving a polyolefin polymer in a good solvent is extruded from a die at a temperature higher than the melting point of the polyolefin resin, and this polymer solution is brought into contact with a cooling solvent. The polyolefin polymer forms a dense, non-porous surface on the membrane surface and a porous interior through thermally induced phase separation, resulting in an integrated, asymmetrical structure. However, the method in Patent Document 1 had insufficient solvent resistance.

[0004] Patent Document 2 discloses a melt spinning method using polyolefin polymers. Specifically, a multi-cylinder spinning nozzle is used to melt-combine a crystalline thermoplastic polymer and a second polymer in two layers, and then the material is stretched to make only the layer consisting of the crystalline thermoplastic polymer porous. In other words, the polyolefin resin is extruded from the die at a temperature above its melting point, cooled and solidified, and then stretched to partially open the interior, forming a structure with a non-porous surface and a porous interior. The method in Patent Document 2 yields a film with high strength, but its gas permeability and solvent resistance were insufficient.

[0005] Patent Document 3 discloses a melt spinning method for obtaining a hollow fiber microporous membrane. Specifically, a polyolefin-based resin is extruded from a die at a temperature above its melting point, cooled and solidified, and after a long-time heat treatment, stretching is performed to cleave the interfaces of lamellar crystals, thereby forming a connected microporous structure. In the method of Patent Document 3, a membrane having high gas permeability can be obtained, but since a dense surface layer is not formed on the membrane surface, the intrusion of the solvent into the hollow fiber membrane is not suppressed. In addition, since the interfaces of the lamellar crystals are cleaved, the solvent resistance is insufficient.

[0006] Patent Document 4 discloses a melt spinning method for obtaining a hollow fiber heterogeneous membrane. By "heterogeneous" is meant that after a highly crystalline polyolefin-based polymer is melt-extruded under a certain take-up tension, air-cooled and stretched, a structure having no pores on the surface and fine pores in the inner layer is formed. In the method of Patent Document 4, fine pores can be provided on the membrane surface by controlling the take-up tension, but the gas permeability is low and the solvent resistance is insufficient.

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Summary of the Invention

Problems to be Solved by the Invention

[0008] According to our findings, in methods for separating dissolved gas from a liquid and gas exchange methods for exchanging dissolved gas in a liquid with gaseous components in the gas phase, high solvent resistance is not achieved by simply having a dense film surface. It is important that lamellar crystals grow densely and sufficiently to form a film surface having accumulated lamellar crystals.

[0009] The membranes obtained by the methods described in Patent Documents 1 and 4 have the problem that although their surfaces are dense, lamellar crystals are not formed and their solvent resistance is insufficient. Furthermore, the separation membrane obtained in Patent Document 2 has high strength, but its porosity is insufficient, so it does not have sufficient gas permeability, and furthermore, because sufficient lamellar crystals are not formed on the membrane surface, its solvent resistance is also insufficient. In addition, the separation membrane obtained in Patent Document 3 has high gas permeability, but it does not have a dense surface layer on the membrane surface, and furthermore, although lamellar crystals are seen on the membrane surface, they do not have accumulated lamellar crystals, so its solvent resistance is insufficient.

[0010] Thus, while poly(4-methyl-1-pentene) is a material with excellent solvent resistance, conventional technologies lacked lamellar crystals accumulated on the film surface, and therefore could not achieve both gas permeability and solvent resistance. On the other hand, while film surfaces with accumulated lamellar crystals have high solvent resistance, the surface is covered with plate-like crystals, which blocks gases and tends to worsen gas permeability.

[0011] Based on the above, the problem that the present invention aims to solve is to provide a separation membrane using poly(4-methyl-1-pentene) that has both gas permeability and superior solvent resistance. [Means for solving the problem]

[0012] As a result of diligent research to solve the above problems, the present inventors have found that a separation membrane mainly composed of poly(4-methyl-1-pentene), having lamellar crystals accumulated on its surface, and having pores on the side of the membrane surface with the accumulated lamellar crystals that have selective gas permeability, possesses both high gas permeability and solvent resistance, leading to the present invention. The separation membrane of the present invention has the following configuration.

[0013] 1. A separation membrane comprising a surface layer and an inner layer, with poly(4-methyl-1-pentene) as the main component, wherein at least one of the surface layers has lamellar crystals, and the surface layer having lamellar crystals is provided with micropores, the porosity being defined as the ratio of the micropores to the membrane surface, and the porosity being 0.1% to 10% when the membrane surface is considered 100%, and the average pore diameter of the micropores being 3 nm to 30 nm. Furthermore, the degree of crystallinity on the surface of the film having the lamellar crystals is 5% to 35%. It is a separation membrane. 2. The separation membrane described in 1 has an N2 permeability of 1000 GPU or more at a differential pressure of 100 kPa. 3 . 4 The separation membrane is as described in any of 1 to 3, wherein the area ratio occupied by the lamellar crystals on the surface of the membrane having the lamellar crystals is 10% to 60% when the area of ​​the membrane surface excluding the pores is taken as 100%.

[0014] 5. The separation membrane according to any one of 1 to 4, wherein the period of the lamellar crystals on the surface of the film having the lamellar crystals is 10 nm to 80 nm. 6. In the surface layer having the lamellar crystals, the micropores are 1 / μm 2 More than 20000 pieces / μm 2 The separation membrane is one of the following, described in 1 to 5 below. 7. The separation membrane is one of the separation membranes described in any of 1 to 6, wherein the porosity of the separation membrane is 30% to 70%. 8. The separation membrane according to any one of 1 to 7, wherein the inner layer of the separation membrane has a porosity of 25% to 60% when the cross-sectional area when cut in the thickness direction is taken as 100%. 9. The separation membrane is a hollow fiber type, as described in any of 1 to 8. 10. The separation membrane according to 9, wherein the surface layer having lamellar crystals is the outer surface of the hollow fiber-shaped separation membrane. 11. The separation membrane according to 9 or 10, wherein in a cross-section obtained by cutting the inner layer of the hollow fiber-shaped separation membrane parallel to the thickness direction of the membrane, the ratio of the length of the major axis a to the length of the minor axis b of the pores a / b is 1.0 to 5.0. 12. The separation membrane described above is one of the separation membranes described in any of 1 to 9, wherein the N2 permeability at a differential pressure of 100 kPa after immersion of the separation membrane in the organic solvent A described below for 3 seconds is 5 GPU or more. Organic solvent A: Chloroform / Isopropyl alcohol = 1 / 1 (volume / volume) This is a degassing module equipped with a separation membrane as described in any of sections 13.1 to 12.

[0015] 14. A method for manufacturing a separation membrane, comprising the steps (A1) to (A2) below. (A1) A preparation step to obtain a resin composition by melt-kneading a mixture containing 10% to 50% by mass of poly(4-methyl-1-pentene) and 50% to 90% by mass of a plasticizer. (A2) A molding step in which the resin composition is discharged from a discharge nozzle, and immediately after passing through an empty section of 10 mm to 30 mm, is introduced into a cooling bath of a solvent in which the solubility parameter distance Ra for poly(4-methyl-1-pentene) is in the range of 4.0 to 14.0 and the solubility parameter distance Rb for the plasticizer is in the range of 3.0 to 6.0 to obtain a resin molded product. 15. A method for producing a separation membrane according to 14, further comprising a washing step (A3) after the molding step to obtain the resin molded product (A2), wherein the resin molded product is subjected to a solvent in which the solubility parameter distance Ra for poly(4-methyl-1-pentene) is in the range of 8 to 35 and the solubility parameter distance Rb for the plasticizer is in the range of 5 to 35, thereby extracting the plasticizer contained in the resin molded product into the solvent. 16. The method for producing a separation membrane according to 15, wherein the resin molded product is stretched to 1.1 to 5.0 times its original size during the washing step (A3).

[0016] 17. A method for manufacturing a separation membrane, comprising the steps (B1) to (B3) below, wherein the resin molded product is stretched to 1.1 to 5.0 times its original size during the washing step (B3). (B1) A preparation step to obtain a resin composition by melt-kneading a mixture containing 10% to 50% by mass of poly(4-methyl-1-pentene) and 50% to 90% by mass of a plasticizer. (B2) A molding step in which, immediately after discharging the resin composition from the discharge nozzle, the resin composition is introduced into a cooling bath of a solvent in which the solubility parameter distance Ra for poly(4-methyl-1-pentene) is in the range of 5.0 to 18.0 and the solubility parameter distance Rb for the plasticizer is in the range of 1.0 to 2.9 or 6.5 to 10.0 to obtain a molded resin product. (B3) A washing step in which the obtained resin molded product is washed in a solvent in which the solubility parameter distance Ra for poly(4-methyl-1-pentene) is in the range of 8 to 35 and the solubility parameter distance Rb for the plasticizer is in the range of 5 to 35, thereby extracting the plasticizer contained in the resin molded product into the solvent. [Effects of the Invention]

[0017] According to the present invention, a separation membrane is provided that has lamellar crystals accumulated on the surface of the outer layer of the membrane, and has high gas permeability due to pores, i.e., micropores, that do not adversely affect solvent resistance. In other words, a superior separation membrane is provided that achieves both high gas permeability and better solvent resistance using poly(4-methyl-1-pentene). [Brief explanation of the drawing]

[0018] [Figure 1] This is a schematic diagram illustrating the membrane surface of a hollow fiber-shaped separation membrane. [Figure 2] This is an example of a SEM image of the membrane surface of a separation membrane, captured at a magnification of 60,000x. [Figure 3] This is an example of a SEM image taken at a magnification of 10,000x of a cross-section of a separation membrane cut in the thickness direction. [Figure 4] Figure 3 is a processed image of the surface cross-section after binarization and noise removal. [Figure 5] Figure 4 shows a processed image used to measure the thickness of the surface layer. [Figure 6] This is an explanatory diagram of the method for measuring the long axis length a and short axis length b of pores in the inner layer of a separation membrane. [Modes for carrying out the invention]

[0019] The separation membrane of the present invention is characterized by having poly(4-methyl-1-pentene) as the main component, having lamellar crystals accumulated on at least one dense surface layer, having pores on the surface of the surface layer having the accumulated lamellar crystals, having an porosity of 0.1% to 10% when the membrane surface is considered as 100%, and having an average pore diameter of 3 to 30 nm. Here, the porosity is the ratio of the total area of ​​micropores to the area of ​​the membrane surface. In this specification, a mass-based ratio (percentage, parts, etc.) is the same as a weight-based ratio (percentage, parts, etc.). The separation membrane of the present invention will be described below.

[0020] (Resin composition constituting the separation membrane) The resin composition constituting the separation membrane of the present invention mainly comprises poly(4-methyl-1-pentene) as shown in (1) below. In addition to (1), it may also contain the components shown in (2) to (3) below.

[0021] (1) Poly(4-methyl-1-pentene) (hereinafter referred to as "PMP") The separation membrane of the present invention must have PMP as its main component. Here, "main component" refers to a component that makes up 70% or more by mass of the total components of the separation membrane.

[0022] PMP is defined as a polymer that has repeating units derived from 4-methyl-1-pentene. PMP may be a homopolymer of 4-methyl-1-pentene or a copolymer of a monomer other than 4-methyl-1-pentene that is copolymerizable with 4-methyl-1-pentene. Specifically, monomers copolymerizable with 4-methyl-1-pentene include olefins having 2 to 20 carbon atoms other than 4-methyl-1-pentene (hereinafter referred to as "olefins having 2 to 20 carbon atoms").

[0023] Examples of olefins with 2 to 20 carbon atoms that copolymerize with 4-methyl-1-pentene include ethylene, propylene, 1-butene, 1-hexene, 1-heptene, 1-octene, 1-decene, 1-tetradecene, 1-hexadecene, 1-heptadecene, 1-octadecene, and 1-eicosene. The olefins with 2 to 20 carbon atoms copolymerized with 4-methyl-1-pentene may be one type or a combination of two or more types.

[0024] The density of the PMP raw material used as the raw material for the separation membrane of the present invention is 825-840 kg / m³. 3 Preferably, it is 830-835 (kg / m 3 It is even more preferable that the density is within the above range. If the density is lower than the above range, the mechanical strength of the separation membrane will decrease, and problems such as defects may occur. On the other hand, if the density is higher than the above range, gas permeability tends to decrease.

[0025] The melt flow rate (MFR) of PMP is not particularly specified as long as it is easily miscible with the plasticizer described later and can be co-extruded. However, it is preferably 1 to 200 g / 10 min, and more preferably 5 to 30 g / 10 min, under conditions of a temperature of 260°C and a 5 kg load. If the MFR is within the above range, it is easy to extrude to a relatively uniform film thickness. The PMP raw material may be a commercially available PMP polymer, for example, TPX (registered trademark) manufactured by Mitsui Chemicals, Inc.

[0026] The PMP content in the separation membrane is preferably 70-100% by mass, more preferably 80-100% by mass, and even more preferably 90-100% by mass, when the total components of the separation membrane are considered as 100% by mass. A PMP content of 70% by mass or more in the separation membrane ensures sufficient gas permeability.

[0027] Furthermore, the PMP content in the raw materials for manufacturing the separation membrane is preferably 10% to 50% by mass, when the total components constituting the raw materials are considered as 100% by mass. A content of 10% by mass or more results in good membrane strength of the separation membrane. On the other hand, a content of 50% by mass or less results in good permeability performance of the separation membrane. A content of 15 to 50% by mass is more preferable, 20 to 45% by mass is even more preferable, and 25 to 40% by mass is particularly preferable.

[0028] (2) Plasticizers The resin composition constituting the separation membrane of the present invention may contain a PMP plasticizer. From the viewpoint of improving permeability, the plasticizer content in the separation membrane is preferably 1000 ppm (by mass) or less, more preferably 500 ppm (by mass) or less, and particularly preferably 100 ppm (by mass) or less.

[0029] The plasticizer for PMP is not particularly limited as long as it is a compound that thermoplasticizes PMP. The plasticizer for PMP may be a single type of plasticizer, or two or more plasticizers may be used in combination. Examples of PMP plasticizers include palm kernel oil, dibutyl phthalate, dioctyl phthalate, butyl stearate, dibenzyl ether, coconut oil, or mixtures thereof. Among these, dibutyl phthalate and dibenzyl ether are preferred in terms of compatibility and stringability.

[0030] It is preferable to elute the plasticizer from the PMP after the separation membrane has been formed. Furthermore, the plasticizer content in the raw materials for manufacturing the separation membrane is preferably 50% to 90% by mass, when the total components constituting the raw materials are considered as 100% by mass. A content of 90% by mass or less in the raw materials results in good membrane strength of the separation membrane. A content of 50% by mass or more in the raw materials results in good permeability of the separation membrane. A content of 50% to 85% by mass in the raw materials is more preferable, 55% to 80% by mass is even more preferable, and 60% to 75% by mass is particularly preferable.

[0031] (3) Additives The resin composition constituting the separation membrane of the present invention may contain additives other than those described in (2), as long as they do not impair the effects of the present invention.

[0032] Examples of additives include resins such as cellulose ether, polyacrylonitrile, polyolefin, polyvinyl compound, polycarbonate, poly(meth)acrylate, polysulfone or polyethersulfone, organic lubricants, nucleating agents, organic particles, inorganic particles, chelating agents, chain extenders, ultraviolet absorbers, infrared absorbers, color inhibitors, matting agents, antibacterial agents, antistatic agents, deodorants, flame retardants, weather-resistant agents, antistatic agents, antioxidants, ion exchange agents, defoaming agents, coloring pigments, fluorescent whitening agents or dyes.

[0033] (Shape of the separation membrane) The separation membrane of the present invention is preferably a hollow fiber shape (hereinafter sometimes referred to as "hollow fiber membrane"), but the separation membrane of the present invention is not limited to a hollow fiber shape. Hollow fiber membranes are preferred because they can be efficiently packed into modules and allow for a large effective membrane area per unit volume of the module.

[0034] The shape of the separation membrane in this invention, that is, the thickness of the separation membrane, the outer and inner diameters in the case of a hollow fiber membrane, and the hollowness ratio, can be observed, for example, by applying stress to a separation membrane that has been sufficiently cooled in liquid nitrogen and then cutting it in the thickness direction of the membrane (hereinafter referred to as the "diameter cross-section") using an optical microscope or a scanning electron microscope (SEM). Specific methods will be described in detail in the examples.

[0035] The separation membrane of the present invention is composed of a dense surface layer and a porous inner layer. Note that the separation membrane obtained by the method described in Patent Document 3 is a microporous membrane in which a microporous structure is formed throughout the membrane by stretching, and is different from the separation membrane of the present invention. The total thickness of the separation membrane, including the surface and inner layers, is preferably 10 μm to 500 μm from the viewpoint of achieving both permeability and membrane strength. A total thickness of 30 μm or more is more preferable, and 50 μm or more is even more preferable. Furthermore, a thickness of 200 μm or less is more preferable, 150 μm or less is even more preferable, and 100 μm or less is particularly preferable.

[0036] From the viewpoint of achieving both effective film area and film strength when filled into a module, the outer diameter of the hollow fiber membrane is preferably 50 μm to 2500 μm. The outer diameter of the hollow fiber membrane is more preferably 100 μm or more, even more preferably 200 μm or more, and particularly preferably 300 μm or more. Furthermore, the outer diameter is more preferably 1000 μm or less, even more preferably 500 μm or less, and particularly preferably 450 μm or less.

[0037] Furthermore, considering the relationship between the pressure loss of the fluid flowing through the hollow section and the buckling pressure, the inner diameter of the hollow fiber membrane is preferably 20 μm to 1000 μm. The inner diameter of the hollow fiber membrane is more preferably 50 μm or more, even more preferably 100 μm or more, and particularly preferably 150 μm or more. In addition, the inner diameter is more preferably 500 μm or less, even more preferably 300 μm or less, and particularly preferably 250 μm or less.

[0038] Furthermore, considering the relationship between the pressure loss of the fluid flowing through the hollow portion and the buckling pressure, it is preferable that the hollow ratio of the hollow fiber membrane be 15% to 70%. A hollow ratio of 20% or more is more preferable, and 25% or more is even more preferable. Moreover, a hollow ratio of 60% or less is more preferable, 50% or less is even more preferable, and 40% or less is particularly preferable.

[0039] The method for setting the outer diameter, inner diameter, and hollowness ratio of the hollow fibers in a hollow fiber membrane to the above range is not particularly limited, but can be adjusted, for example, by appropriately changing the shape of the discharge hole of the spinneret used to manufacture the hollow fibers, or by changing the draft ratio which can be calculated from the winding speed / discharging speed.

[0040] (Observation of the film surface) The separation membrane of this embodiment comprises lamellar crystals accumulated on at least one surface layer, and the membrane surface has openings between the lamellar crystals that selectively allow gas to pass through. The surface of the surface layer is called the membrane surface, and in the case of a two-dimensional membrane surface, it is expressed as an opening, and in the case of a thick surface layer, it is expressed as a micropore. Figure 1 is a schematic diagram (enlarged view) showing the membrane surface of a hollow fiber separation membrane. In the hollow fiber membrane 8, the membrane surface 1 having accumulated lamellar crystals may be on the outer surface side of the hollow structure, on the inner surface side, or on both the outer and inner surfaces.

[0041] The accumulated lamellar crystals 6 refer to the areas where, when the membrane surface 1 of the separation membrane is observed at a magnification of 60,000x using a scanning electron microscope (hereinafter referred to as "SEM"), the proportion of lamellar crystals 6 is 10% or more when the surface area excluding micropores, i.e., openings 2, is taken as 100%. Lamellar crystals 6 refer to streaky protrusions, i.e., streaky bright areas, in the image of the surface of the separation membrane observed at a magnification of 60,000x using an SEM. Openings 2 refer to recesses with a diameter of 1 nm to 10 μm when the membrane surface 1 of the separation membrane is observed at a magnification of 60,000x using an SEM.

[0042] Figure 2 shows an example of an image of the membrane surface 1 of the separation membrane, captured by SEM at a magnification of 60,000x. In Figure 2, the lamellar crystals 6 of the present invention are formed by densely arranging numerous crystal chains, with lamellar crystals being formed adjacent to each other and accumulated. The openings 2 are located within the accumulated lamellar crystal group.

[0043] The proportion of lamellar crystals to the surface area of ​​the membrane excluding the open areas can be obtained by observing the membrane surface using a SEM and calculating the area ratio of lamellar crystals 6 and the area ratio of open areas 2, i.e., the porosity, from the obtained image. Micropores of 1 nm or more on the membrane surface, i.e., open areas 2, can be obtained by observing the surface 1 of the separation membrane using a SEM, binarizing the obtained image using the image analysis software "ImageJ", and then extracting only the pores with a diameter greater than 1 nm. The specific calculation method will be described in detail in the examples.

[0044] As shown in Figure 2, striated lamellar crystals grow on the membrane surface 1 of the separation membrane in this embodiment. Lamellar crystals are structures in which PMP molecular chains are folded into plate-like structures and accumulated, exhibiting excellent solvent resistance. For example, in Figure 2, the striated lamellar crystals represented by the bright areas are observed as convex areas, forming a lamellar structure in which many groups of lamellar crystals are closely accumulated. On the other hand, between the lamellar crystals, there are openings 2, or micropores, with an average pore diameter of 3 nm to 30 nm. Since these openings selectively permeate gases, the separation membrane has a membrane surface that achieves both high gas permeability and solvent resistance. The surface layer and membrane surface 1 with the accumulated lamellar crystals are preferably the outer surface when the separation membrane is hollow fiber shaped.

[0045] (Lamellar crystals on the film surface) In the separation membrane of the present invention, it is important that the proportion of lamellar crystals in the total surface area of ​​the membrane surface 1, excluding the openings 2, is 10% to 60%. A proportion of 10% or more lamellar crystals is preferable because it provides high solvent resistance, and a proportion of 60% or less lamellar crystals is preferable because it provides good gas permeability in areas other than the openings. A proportion of 20% to 60% lamellar crystals is more preferable, 25% to 55% is even more preferable, and 30% to 40% is particularly preferable.

[0046] Furthermore, the period of the lamellar crystals on the film surface 1 of the present invention is preferably 10 nm to 80 nm. The period of the lamellar crystals refers to the distance from one streaky protrusion to the nearest streaky protrusion in an image of the surface of the separation film observed at a magnification of 30,000 times using an SEM. The smaller the period of the lamellar crystals, the higher the degree of lamellar crystal accumulation tends to be. A period of 10 nm or more is preferable as it results in good solvent resistance. A period of 80 nm or less is preferable as it results in good gas permeability outside the openings. A period of 20 nm to 50 nm is more preferable, 25 nm to 45 nm is even more preferable, and 30 nm to 45 nm is particularly preferable. The specific method for measuring the period of the lamellar crystals will be described in detail in the examples.

[0047] (Degree of crystallinity of the film surface) The separation membrane of the present invention preferably has a crystallinity of 5% to 35% on the membrane surface 1. In the present invention, since the thickness of the membrane surface 1 is very small, the crystallinity of the membrane surface 1 is the same as that of the surface layer 3. A crystallinity of 5% or more on the membrane surface 1 results in good solvent resistance, and a crystallinity of 35% or less results in good transmission performance outside of the openings. The crystallinity of the membrane surface 1 is a value determined by infrared spectroscopy (hereinafter sometimes referred to as "IR"), and the specific measurement method will be explained in the examples. A crystallinity of 15% to 35% on the membrane surface 1 is more preferably, 20% to 35% is even more preferably, and 30% to 35% is particularly preferably.

[0048] (Pores on the membrane surface) For the separation membrane of the present invention, it is important that the average pore diameter of the two pores, i.e., micropores, on the membrane surface 1 is 3 nm to 30 nm. In FIGS. 1 and 2, the pores 2 on the membrane surface shown in the dark part exist without inhibiting the characteristics of each lamellar crystal 6 of the aggregated lamellar crystals 6. When the average pore diameter of the pores on the membrane surface 1 is 3 nm or more, it is preferable in terms of obtaining high gas permeability, and when it is 30 nm or less, the solvent resistance is good. The average pore diameter of the two pores, i.e., micropores, on the membrane surface 1 is more preferably 3 to 20 nm, even more preferably 3 to 18 nm, and particularly preferably 3 nm to 16 nm. The specific calculation method of the average pore diameter will be described in detail in the examples.

[0049] Also, it is important that the porosity on the membrane surface 1 is 0.1% to 10%. The porosity is the ratio of the total area of the micropore part in the area of the membrane surface, and is expressed as a ratio when the area projected on the membrane surface is 100%. That is, the porosity refers to the area ratio of the pores in the entire observation image when the surface of the hollow fiber membrane is observed at a magnification of 60,000 times using SEM. When the porosity on the membrane surface 1 is 0.1% or more, it is preferable in terms of obtaining high gas permeability, and when it is 10% or less, the solvent resistance is good. The porosity on the membrane surface 1 is more preferably 0.2% to 5.0%, even more preferably 0.5% to 2.0%, and particularly preferably 1.0% to 1.5%. The specific calculation method of the porosity will be described in detail in the examples.

[0050] Also, the number of pores 2 on the membrane surface 1 is 1.0 pores / μm 2 ~20000 pores / μm 2 is preferable. When the number of pores is 1.0 pores / μm 2 or more, it is preferable in terms of obtaining high gas permeability, and when it is 20000 pores / μm 2 or less, the solvent resistance is good. The number of pores is more preferably 10 pores / μm 2 ~10000 pores / μm 2 and even more preferably 50 pores / μm 2 ~5000 pores / μm2 It is even more preferable that the particles be 100 μm. 2 ~2000 pieces / μm 2 This is particularly preferable. The specific method for calculating the number of openings per unit area will be described in detail in the examples.

[0051] Furthermore, on the film surface 1, the porosity (%) is defined as the number of openings 2 per unit area (pieces / μm). 2 The value obtained by dividing by ) is D = 0.1 (%·μm 2 It is preferable that the number of holes is less than or equal to ( / piece). D is an indicator of the area occupied by each opening, i.e., the size of each opening. When D is 0.1 or less, the penetration of solvent into the film is suppressed, resulting in good solvent resistance. It is more preferable that D is 0.05 or less, even more preferable that it is 0.03 or less, and particularly preferable that it is 0.01 or less.

[0052] In the separation membrane of the present invention, it is preferable that the lamellar crystals on the membrane surface 1 are in an accumulated state with an area ratio of 10% to 60% and a period of 10 nm to 80 nm, and furthermore, that the crystallinity of the surface is 5% to 35%, which provides even higher solvent resistance. On the other hand, in order to achieve high solvent resistance, the membrane surface having accumulated lamellar crystals is covered with plate-like crystals, which blocks gas and tends to worsen gas permeability. In the separation membrane of the present invention, there are openings 2 with an average pore size of 3 nm to 30 nm between the lamellar crystals, at a rate of 1 pore / μm 2 There are more than 20,000 holes / μm², and these openings 2 exhibit gas permeability. However, the area occupied by openings 2 is 20,000 holes / μm². 2 Beyond a certain point, the penetration of solvents into the membrane becomes less effective, leading to a decrease in solvent resistance. Therefore, the separation membrane of the present invention has lamellar crystals accumulated on its surface, and the membrane surface is equipped with micropores, the average pore diameter of these micropores is 3 nm to 30 nm, the porosity is 0.1% to 10%, and the number of pores on the membrane surface is 1 pore / μm. 2 This combination results in a film surface that achieves both high gas permeability and solvent resistance.

[0053] (Observation of membrane cross-section) The separation membrane of this embodiment has a dense layer on the surface layer 3 on the side where the membrane surface 1 is located. As shown in Figure 3, the separation membrane has a surface layer 3 and an inner layer 4 below it. The surface layer 3 is the portion of the separation membrane from the point on which a straight line is drawn perpendicular to the surface when a cross section of the separation membrane cut in the thickness direction is observed at a magnification of 10,000x using a scanning electron microscope (SEM), up to the point where the straight line first reaches a pore larger than 50 nm. The inner layer 4 is the layer below the surface layer 3. That is, the surface layer 3 does not have pores larger than 50 nm and is denser than the inner layer.

[0054] The thickness of the surface layer 3 can be determined, for example, by applying stress to a separation membrane that has been sufficiently cooled in liquid nitrogen (using a razor, microtome, or broad ion beam as needed), observing a cross-section perpendicular to the longitudinal direction of the separation membrane and parallel to the thickness direction of the membrane (hereinafter referred to as the "cross-section") or a cross-section parallel to the longitudinal direction of the separation membrane and parallel to the film thickness direction (hereinafter referred to as the "longitudinal section") using a scanning electron microscope (SEM), binarizing the obtained image using the image analysis software "ImageJ", extracting only pores larger than 50 nm, and measuring the distance to those pores by drawing a straight line perpendicular to the membrane surface 1.

[0055] Note that the cross-section of the hollow fiber membrane is synonymous with the radial cross-section. Furthermore, the longitudinal direction of the hollow fiber membrane is the direction perpendicular to the transverse direction of the hollow fiber membrane. Moreover, the transverse direction of the hollow fiber membrane is the direction parallel to the radial direction of the hollow fiber membrane, and the transverse direction can be rephrased as the direction parallel to the hollow surface, that is, the in-plane direction of the hollow surface. Therefore, the longitudinal direction of the hollow fiber membrane can be rephrased as the direction perpendicular to the hollow surface. The thickness of the surface layer is the length from an arbitrary point on the surface of the separation membrane to the inner layer in the aforementioned SEM image, when a straight line is drawn perpendicular to the outer surface toward the inner layer, until the first pore exceeding 50 nm is reached. The specific measurement method will be described in detail in the examples.

[0056] Furthermore, the separation membrane of the present invention is a porous membrane and has voids in the inner layer 4. In this embodiment, it is preferable that the separation membrane has 3 or fewer voids larger than 10 μm per field of view when the diameter or longitudinal section of the separation membrane is observed at a magnification of 2,000 times using an SEM. Voids larger than 10 μm are often located in the inner layer 4. A void refers to a recess with a diameter of 10 nm or more when the diameter or longitudinal section of the separation membrane is observed at a magnification of 2,000 times using an SEM. A recess is a hole, and is roughly indicated by the diameter of a sphere. Having 3 or fewer voids larger than 10 μm in the membrane cross-section results in good strength for the separation membrane. Voids larger than 10 μm in the membrane cross-section can be obtained by observing the cross-section or longitudinal section of the separation membrane at a magnification of 2,000 times using an SEM, binarizing the obtained image using the image analysis software "ImageJ", and then extracting only the holes with an average diameter larger than 10 μm.

[0057] It is more preferable that there are two or fewer voids larger than 10 μm in the cross-section of the membrane, even more preferable that there be one or fewer, and particularly preferable that there be zero. The method for measuring voids larger than 10 μm in the cross-section of the membrane will be described in detail in the examples.

[0058] In this embodiment, the inner layer of the separation membrane preferably has an average pore diameter of 100 nm to 1000 nm when the membrane cross-section is observed using a SEM. The average pore diameter of the pores in the membrane cross-section can be obtained by observing the cross-section or longitudinal section of the separation membrane with a SEM at a magnification of 10,000 times, binarizing the obtained image using the image analysis software "ImageJ", and then extracting pores with an average diameter greater than 10 nm. An average pore diameter of 100 nm or more in the membrane cross-section results in good transmittance, and an average pore diameter of 1000 nm or less results in good strength of the separation membrane. The average pore diameter of the pores in the membrane cross-section is preferably 100 nm to 800 nm, more preferably 100 nm to 600 nm, even more preferably 100 nm to 570 nm, and particularly preferably 100 nm to 500 nm.

[0059] The above-mentioned voids may have any geometric shape, for example, they may be elongated, cylindrical, circular, or irregular in shape to varying degrees. The shape of the voids can be evaluated by cutting the separation membrane, which has been sufficiently cooled in liquid nitrogen, using a microtome, observing the exposed cross-section using a SEM, and determining the ratio a / b of the major axis length a to the minor axis length b of the voids. If the separation membrane is in the shape of a flat membrane, it should be cut in the direction in which the Young's modulus is maximum and parallel to the thickness direction of the membrane. If the separation membrane is in the shape of a hollow fiber, the direction in which the Young's modulus is maximum is parallel to the longitudinal direction of the membrane, and the longitudinal cross-section of the hollow fiber membrane should be observed. The specific method for measuring a / b will be described in detail in the examples.

[0060] In the separation membrane of this embodiment, when the separation membrane is stretched, both the surface layer and the inner layer are stretched. When stretched, the length a of the major axis also tends to increase. The ratio of a / b can be easily adjusted by balancing the resin extrusion speed and the draw tension, or by stretching. For example, to adjust the a / b ratio to be larger, it can be easily adjusted by decreasing the resin extrusion speed, increasing the draw tension, or increasing the stretching ratio. In the separation membrane of this embodiment, a / b correlates with the porosity and average pore diameter of the membrane surface.

[0061] In the separation membrane of this embodiment, the direction of the major axis length a of the pores tends to be parallel to the direction in which Young's modulus is maximized. That is, the direction of the major axis length a of the pores is approximately parallel to the direction in which Young's modulus is maximized, or, in the case of the separation membrane being hollow fiber in shape, to the longitudinal direction of the membrane. In the separation membrane of this embodiment, a / b is preferably 1.0 to 5.0. When a / b is 5.0 or less, the average pore diameter, porosity, and number of pores on the membrane surface are within a favorable range, resulting in a membrane surface that achieves both high gas permeability and solvent resistance. a / b is more preferably 1.5 to 4.0, even more preferably 2.0 to 3.5, and particularly preferably 2.5 to 3.0.

[0062] Furthermore, the separation membrane of this embodiment preferably has a porosity of 25% to 60% when the membrane cross-section is observed using a SEM. Porosity is the proportion of the membrane cross-section occupied by pores, and is expressed as the proportion of pores when the projected area of ​​the membrane cross-section is taken as 100%. In other words, it refers to the proportion of the area of ​​pores that make up air gaps in the entire observed image when the membrane cross-section of the separation membrane is observed using a SEM at a magnification of 10,000 times. A porosity of 25% or more in the membrane cross-section is preferable from the viewpoint of obtaining high gas permeability, and a porosity of 60% or less results in good membrane strength. A porosity of 30 to 55% in the membrane cross-section is more preferable, 35 to 50% is even more preferable, and 40 to 50% is particularly preferable. The specific method for calculating the porosity of the membrane cross-section will be described in detail in the examples.

[0063] (porosity) The separation membrane of the present invention has a total porosity of 30% to 70%. A porosity of 30% or more results in good permeability, and a porosity of 70% or less results in good membrane strength. A porosity of 40% to 65% is preferable, 45% to 60% is more preferable, and 53% to 60% is particularly preferable. To obtain a porosity within this range, structure formation using thermally induced phase separation, as described later, is preferably used. Note that the porosity in this application refers to the total porosity including the surface and inner layers of the separation membrane, and the specific method for measuring the porosity will be described in detail in the examples.

[0064] (Gas permeability performance) The separation membrane of the present invention preferably has an N2 permeability of 1000 GPU or more at 100 kPa and 37°C. More preferably, the N2 permeability is 3000 GPU or more, and even more preferably 50000 GPU or more. The calculation method will be explained in detail in the examples.

[0065] (Separation coefficient α(CO2 / N2)) The separation membrane of the present invention possesses both solvent resistance and high gas permeability due to having lamellar crystals and pores on its surface, and gas permeation is mainly carried out by "Knudsen diffusion" due to the size of the pores. On the other hand, in a non-porous structure, gas permeability is reduced because there are no through-pores, but gas permeation is carried out by a dissolution-diffusion mechanism. In other words, the density of the membrane surface can be evaluated by the gas separation coefficient, and in membranes with high density, the efficiency of degassing and gas exchange tends to decrease.

[0066] Generally, permeation through polymer membranes depends on the size of the pores in the membrane. In porous membranes with pores ranging in size from 3 nm to 10 μm, gas permeation occurs primarily by "Knudsen diffusion." In this case, the separation coefficient α, which represents the ratio of the permeation coefficient P or the gas permeation flow rate Q of two gases, is obtained by taking the square root of the ratio of the molecular weights of the gases. Therefore, for example, the separation coefficient α(CO2 / N2) for CO2 and N2 is √28 / √44 = 0.80.

[0067] On the other hand, in films where the diameter of the pores is at most 3 nm, gas permeates through a dissolution-diffusion mechanism. In this case, the separation coefficient α depends only on the polymer material and not on the film thickness. Therefore, α(CO2 / N2) can be expressed as P(CO2) / P(N2) or Q(CO2) / Q(N2). In commonly used polymers, an α(CO2 / N2) value of at least 1 is obtained. Since the dissolution-diffusion mechanism reduces gas permeability, an α(CO2 / N2) value of 1 or less is preferable because it results in good efficiency for degassing and gas exchange.

[0068] When a gas permeates through a non-porous membrane, the gas permeation coefficient decreases, while the gas separation coefficient increases. Therefore, the pore diameter of the pores that govern the gas permeability of the membrane of the present invention can be read by the gas separation coefficient α(CO2 / N2) measured for CO2 and N2. When the gas separation coefficient α(CO2 / N2) is greater than 1.0, this membrane has a non-porous structure. When the separation membrane has a non-porous structure, the efficiency of degassing and gas exchange decreases, making it not suitable for use. On the other hand, when the gas separation coefficient α(CO2 / N2) is 1.0 or less, this membrane has high degassing or gas exchange performance. Therefore, the gas separation coefficient α(CO2 / N2) of the membrane according to the present invention is preferably 0.8 to 1.0.

[0069] (Gas permeation performance after immersion in organic solvent) The separation membrane of the present invention preferably has an N2 permeation performance X of 5 GPU or more at a differential pressure of 100 kPa and 37 °C after immersing the separation membrane in chloroform / isopropyl alcohol = 1 / 1 (volume / volume) for 3 seconds. When the value of X is 5 GPU or more, the solvent resistance is good. The value of X is more preferably 10 GPU or more, further preferably 200 GPU or more, and particularly preferably 400 GPU or more.

[0070] (Method for manufacturing separation membrane) The separation membrane of the present invention can be manufactured by the following Method A or Method B. For each step of Method A and Method B, in the case of Method A, there are the following steps from (A1) to (A2), preferably from step (A1) to step (A3), and in the case of Method B, there are steps from step (B1) to step (B3). Each step is as follows. <Method A> (A1): Adjustment step (A2): Forming step (A3): Washing step <Method B> (B1): Adjustment step (B2): Forming step (B3): Washing step Hereinafter, each step of Method A will be described.

[0071] (A1) Preparation process This is a preparation step to obtain a resin composition by melt-kneading a mixture containing 10% to 50% by mass of poly(4-methyl-1-pentene) and 50% to 90% by mass of a plasticizer.

[0072] In the preparation step to obtain the resin composition, a mixture containing 10% to 50% by mass of PMP and 50% to 90% by mass of a plasticizer is melt-kneaded. The mixture preferably contains 15% to 50% by mass of PMP and 50% to 85% by mass of a plasticizer, more preferably 20% to 45% by mass of PMP and 55% to 80% by mass of a plasticizer, and particularly preferably 25% to 40% by mass of PMP and 60% to 75% by mass of a plasticizer.

[0073] For the melt-kneading of the mixture, a kneader, roll mill, Banbury mixer, or a single-screw or twin-screw extruder can be used. Among these, a twin-screw extruder is preferred from the viewpoint of achieving good uniform dispersion of the plasticizer, and a twin-screw extruder with vent holes is even more preferred from the viewpoint of being able to remove volatile substances such as water and low molecular weight substances. Furthermore, from the viewpoint of increasing the kneading strength and achieving good uniform dispersion of the plasticizer, it is preferable to use a twin-screw extruder equipped with a screw having a kneading disc.

[0074] The resin composition obtained in the preparation process may be pelletized and then remelted for use in melt film formation, or it may be directly introduced into the die and used in melt film formation. When pelletizing, it is preferable to use a resin composition in which the pellets have been dried to a moisture content of 200 ppm (by mass) or less. By keeping the moisture content at 200 ppm (by mass) or less, the deterioration of the resin can be suppressed.

[0075] (A2) Molding process This molding process involves extruding the resin composition obtained in A1 from an extrusion nozzle, and immediately after passing through an air-running section, introducing it into a cooling bath of a solvent in which the solubility parameter distance Ra for poly(4-methyl-1-pentene) is in the range of 4.0 to 14.0 and the solubility parameter distance Rb for the plasticizer is in the range of 3.0 to 6.0 to obtain a resin molded product. In the molding process to obtain the resin product, a hollow fiber membrane is obtained from the molten mixture of the resin composition of PMP and plasticizer by utilizing phase separation. As an example, the resin composition obtained in the preparation step (A1) is extruded into a gaseous atmosphere from, for example, an extrusion nozzle having a double annular nozzle with a gas flow path in the center, and introduced into a cooling bath to separate the phases of the resin composition to obtain a resin molded product.

[0076] The specific method involves discharging the molten resin composition from the outer tube of a double-ring nozzle for spinning, while simultaneously discharging a hollow-forming gas from the inner ring of a double-tube nozzle. It is important that the discharge gap of the nozzle is 0.05 mm to 0.30 mm. This range of discharge gap imparts high shear to the molten resin composition, which is believed to facilitate crystallization and promote the formation of lamellar crystals. The thus discharged resin composition is then passed through air and cooled and solidified in a cooling bath to obtain a molded resin product. A discharge gap of 0.05 mm to 0.20 mm is more preferable.

[0077] Furthermore, it is preferable that at least one surface of the resin composition discharged from the discharge nozzle, preferably the surface where lamellar crystals should form, is exposed to a gaseous atmosphere that promotes the evaporation of the plasticizer, i.e., an atmosphere in which the evaporation of the plasticizer can occur, before cooling. The gas used to form the gaseous atmosphere is not particularly limited, but air or nitrogen is preferably used. The gaseous atmosphere generally has a temperature lower than the discharge nozzle temperature. It is important that the distance from the nozzle surface to the solvent surface is 10 mm to 30 mm in order for the lamellar structure to accumulate and form a surface layer having openings. In this application, the "distance from the nozzle surface to the solvent surface" is referred to as the "free run distance". The free run distance is preferably 10 mm to 20 mm, and more preferably 10 mm to 15 mm.

[0078] Here, we will describe the cooling bath used to cool the resin composition discharged from the discharge nozzle. In the production of the separation membrane of this application, the structure of the membrane surface is affected by the type of solvent in the cooling bath. Therefore, it is preferable to select the solvent of the cooling bath based on its affinity for PMP and plasticizer. When manufacturing separation membranes using Method A, it is important to use a solvent in the cooling bath that has a solubility parameter distance Ra for PMP in the range of 4.0 to 14.0 and a solubility parameter distance Rb for plasticizer in the range of 3.0 to 6.0.

[0079] In a cooling bath, the resin composition undergoes structure formation through solvent exchange between the plasticizer and the cooling bath solvent. When a solvent with a small solubility parameter distance Ra for PMP, i.e., a high affinity for PMP, is used, the phase separation between PMP and the plasticizer is slow, resulting in a dense, non-porous membrane surface. Similarly, when a solvent with a large solubility parameter distance Rb for the plasticizer, i.e., a low affinity for the plasticizer, is used, the low efficiency of solvent-plasticizer exchange leads to the formation of a dense, non-porous membrane surface. Therefore, by using a solvent with a larger Ra and smaller Rb as the cooling bath solvent, the phase separation between PMP and the plasticizer proceeds rapidly, and the exchange between the solvent and plasticizer is also rapid, resulting in a membrane with an open surface.

[0080] On the other hand, the structure of the film surface is also affected by the cooling rate of the resin composition. If the resin composition is cooled slowly, lamellar crystals grow excessively, and the formation of pores in the cooling bath does not proceed. Therefore, in order to form a film surface with pores on its surface, it is important to rapidly cool the resin composition by setting the discharge gap and air travel distance within specified ranges. The inventors have found that by rapidly cooling a molten resin composition under conditions of a discharge gap of 0.05 mm to 0.30 mm and an air travel distance of 10 mm to 30 mm, and immediately introducing it into a cooling bath of a solvent in the range of Ra 4.0 to 14.0 and Rb 3.0 to 6.0, fine pores can be formed on the film surface 1 having accumulated lamellar crystals, to the extent that the solvent can prevent it from penetrating into the film.

[0081] When manufacturing a separation membrane using method A, a Ra value of 4.0 or higher ensures good spinning stability. A Ra range of 5.0 to 12.0 is more preferable, 6.0 to 10.0 is even more preferable, and 7.0 to 9.0 is particularly preferable. A Rb range of 6.0 or lower results in a membrane surface with fine pores. A Rb range of 3.0 to 5.0 is more preferable, and 3.0 to 4.0 is particularly preferable. The affinity between PMP and the solvent in the cooling bath can be estimated using the three-dimensional Hansen solubility parameter, as described in the literature (Ind.Eng.Chem.Res.2011,50,3798-3817). Specifically, a smaller solubility parameter distance (Ra) in the following formula (1) indicates a higher affinity of the solvent to PMP.

[0082]

number

[0083] Here, δ Ad , δ Ap and δ Ah These are the dispersion term, polarity term, and hydrogen bonding term of the solubility parameter of PMP, and δ Cd , δ Cp and δ Ch These are the dispersion term, polarity term, and hydrogen bonding term of the solvent solubility parameter.

[0084] The affinity between the plasticizer and the solvent in the cooling bath can be estimated in a similar manner. Specifically, a smaller solubility parameter distance (Rb) in equation (2) below indicates a higher affinity of the solvent for the plasticizer.

[0085]

number

[0086] Here, δ Bd , δ Bp and δ Bh These are the dispersion term, polarity term, and hydrogen bonding term of the solubility parameter of PMP, and δ Cd , δCp and δ Ch These are the dispersion term, polarity term, and hydrogen bonding term of the solvent solubility parameter.

[0087] If the solvent is a mixed solvent, the solubility parameter of the mixed solvent (δ Mixture The value of ) can be calculated using the following formula (3).

[0088]

number

[0089] Here, φ i , δ i The volume fraction and solubility parameter of component i are given, and these hold for the dispersion, polarity, and hydrogen bonding terms, respectively. Here, "volume fraction of component i" refers to the ratio of the volume of component i before mixing to the sum of the volumes of all components before mixing. For the three-dimensional Hansen solubility parameter of a solvent, if it is listed in the literature (Ind.Eng.Chem.Res.2011,50,3798-3817.), this value was used. For solvent parameters not listed, the values ​​contained in the software "Hansen Solubility Parameter in Practice" developed by Charles Hansen et al. were used. For solvents and polymers not listed in the above software, the three-dimensional Hansen solubility parameter can be calculated using the Hansen sphere method with the above software.

[0090] When manufacturing a separation membrane using Method A, the solvent used in the cooling bath of the molding process is, when dibutyl phthalate is used as the plasticizer, Eastman's Benzoflex (registered trademark), dioctyl phthalate, n-undecylbenzenesulfonic acid, diisononyl phthalate, butyl benzoate, tocopherol, methylene chloride, butyl benzyl phthalate, diisodecyl phthalate, dimethyl isosorbide, mono(2-ethylhexyl) phthalate, methyl ethyl ketone, methyl propyl ketone, tributyl phosphate, 1,4-dioxane, ditridecyl phthalate, methyl isoamyl ketone, 1-Nitropropane, cyclopentyl methyl ether, N-methylpyrrolidone, sorbitan monooleate, tetrahydrofuran, propylene glycol monostearate, n-butyl propionate, methyl isobutyl ketone, 1,3-dioxolane, n-propyl propanoate, acetone, benzyl benzoate, dibasic esters, glyceryl palmitostearate, methyl oleate, butyl glycol acetate, ascorbyl palmitate, methyl acetate, and ethyl acetate are preferred, and among these, dioctyl phthalate is more preferred because its Ra and Rb values ​​are within the aforementioned particularly preferred range.

[0091] In the molding process for manufacturing the separation membrane of the present invention, the resin composition discharged from the discharge nozzle is wound up by a winding device. In this case, the draft ratio value calculated by (winding speed) / (discharge speed from the discharge nozzle) is preferably 1 to 10. More preferably, the draft ratio value is 1 to 8. A draft ratio of 1 or more ensures stable winding and reduces variations in yarn shape. A draft ratio of 10 or less suppresses excessive stretching of the resin composition discharged from the nozzle, thereby suppressing the occurrence of defects on the surface of the hollow fiber membrane.

[0092] (A3) Washing process The resulting resin molded product can be immersed in a solvent that does not dissolve the polymer but is miscible with the plasticizer, thereby extracting the plasticizer and increasing the porosity. The washing step involves introducing the resin molded product into a solvent in which the solubility parameter distance Ra for PMP is in the range of 8 to 35 and the solubility parameter distance Rb for the plasticizer is in the range of 5 to 35, and extracting the plasticizer contained in the resin molded product into the solvent to obtain a separation membrane. In this process, using a solvent or mixed solvent that has an appropriate affinity for both the polymer and the plasticizer ensures good solvent exchange and increases washing efficiency.

[0093] The solubility parameter distance Ra of the washing solvent with respect to PMP is preferably 8 or higher for good dimensional stability of the resin composition, and preferably 35 or lower for moderate swelling of the resin composition, resulting in high washing efficiency. The range of Ra is preferably 10 to 25, and particularly preferably 12 to 22. The solubility parameter distance Rb of the washing solvent with respect to plasticizer is preferably 35 or lower for good solvent exchange, resulting in high washing efficiency. The range of Rb is preferably 10 to 25, and particularly preferably 12 to 22.

[0094] As solvents used in the washing process, when dibutyl phthalate is used as a plasticizer, methyl isobutyl ketone, acetone, butyl glycol acetate, methyl acetate, propylene glycol monoethyl ether acetate, Eastman's Benzoflex (registered trademark), N,N-dimethylacetamide, dipropylene glycol monobutyl ether, diethylene glycol monobutyl ether, t-butyl acetate, propylene glycol monomethyl ether acetate, diacetone alcohol, ε-caprolactone, isopropyl acetate, sec-butyl acetate, propylene glycol monobutyl ether, texanol, γ-butyrolactone, tetrahydrofurfuryl alcohol, N,N-dimethylformamide, dipropylene glycol methyl ether, propylene glycol monomethyl ether, triethyl citrate, methyl carbitol, ethyl lactate, etc. Diethylene glycol monobutyl ether, dimethylcyclohexane, benzyl alcohol, dimethyl sulfoxide, propylene carbonate, cyclohexanol, glycerol diacetate, isopentyl alcohol, 2-phenoxyethanol, heptane, acetonitrile, n-amyl alcohol, methyl isobutylcarbinol, tetramethylene sulfone, hexane, VM&P naphtha, hexylene glycol, ethylene glycol monomethyl ether, 2-butanol, t-butyl alcohol, 1-butanol, ethylene carbonate, isopropyl alcohol, isobutanol, 1-propanol, dipropylene glycol, ethanol, propylene glycol, methanol, glycerol carbonate, and ethylene glycol are preferred, and among these, methanol, ethanol, and isopropyl alcohol are more preferred because their Ra and Rb values ​​are within the aforementioned particularly preferred range.

[0095] During the washing process, the resin product can be stretched as needed to open the gaps between the lamellar structures, thereby further controlling the pore size and porosity of the film surface. To improve gas permeability through effective porosity, a stretching ratio of 1.1 times or more is preferable. On the other hand, as the area occupied by the pores increases, it becomes more difficult to suppress the penetration of solvents into the film, which tends to reduce solvent resistance. Therefore, a stretching ratio of 5.0 times or less is preferable. A stretching ratio of 1.2 to 3.0 is more preferable, and 1.5 to 2.0 is particularly preferable.

[0096] Furthermore, the temperature of the washing solvent is preferably 10 to 50°C. A temperature of 10°C or higher results in good flexibility of the resin molded product, while a temperature of 50°C or lower maintains the structure of the film surface. A temperature of 20 to 45°C is more preferable, and 25 to 40°C is particularly preferable.

[0097] Next, we will describe each step of Method B for obtaining the separation membrane of the present invention. (B1) Preparation process This is a preparation step to obtain a resin composition by melt-kneading a mixture containing 10% to 50% by mass of poly(4-methyl-1-pentene) and 50% to 90% by mass of a plasticizer. The preparation step (B1) for obtaining the resin composition can be carried out in the same manner as the preparation step (A1) of Method A.

[0098] (B2) Molding process This molding process involves extruding the resin composition obtained in B1 from the discharge nozzle, and immediately after passing through the idle section, introducing it into a cooling bath of a solvent in which the solubility parameter distance Ra for poly(4-methyl-1-pentene) is in the range of 5.0 to 18.0 and the solubility parameter distance Rb for the plasticizer is in the range of 1.0 to 2.9 or 6.5 to 10.0 to obtain a resin molded product. The (B2) molding process to obtain the resin molded product can be carried out in the same procedure as the (A2) molding process of Method A, but differs in the following points.

[0099] When manufacturing a separation membrane using method B, it is preferable that the surface of the resin molded product obtained in the (B2) molding process has a non-porous structure with lamellar crystals. Therefore, it is important to use a solvent in the cooling bath in which the solubility parameter distance Ra for PMP is in the range of 5 to 18, and the solubility parameter distance Rb for plasticizer is in the range of 1.0 to 2.9 or 6.5 to 10.0. Having Ra and Rb within these ranges results in a desirable membrane surface. It is presumed that when Ra is in the range of 5 to 18, solidification occurs before crystallization of PMP, and when Rb is in the range of 1.0 to 2.9 or 6.5 to 10.0, the exchange between the solvent and plasticizer occurs at an appropriate rate, and a non-porous structure is formed. It is more preferable to use a solvent in the cooling bath in which Ra is in the range of 5.0 to 7.0 and Rb is in the range of 6.5 to 10.0.

[0100] When manufacturing a separation membrane using method B, the solvent used in the cooling bath of the molding process (B2) may be: when dibutyl phthalate is used as the plasticizer, cyclohexanone, diethyl phthalate, isophorone, dihexyl phthalate, Benzoflex (registered trademark) manufactured by Eastman, diisoheptyl phthalate, dimethyl phthalate, fatty acid methyl ester, n-butyl acetate, n-amyl acetate, triacetin, N,N-dimethylacetamide, butyl diglycol acetate, acetyl triethyl citrate, n-propyl acetate, dipropylene glycol mono-N-butyl ether, diethylene glycol mono-butyl ether, t-butyl acetate, ethyl 3-ethoxypropionate, propylene glycol monomethyl ether acetate, diacetone alcohol, isopentyl acetate, tri-N-butyl citrate, ExxonMobil Preferred are Solvesso® 100, isobutyl isobutyrate, ε-caprolactone, propylene glycol phenyl ether, isopropyl acetate, sec-butyl acetate, propylene glycol monobutyl ether, Texanol, Solvesso 150, ethylbenzene, γ-butyrolactone, tetrahydrofurfuryl alcohol, N,N-dimethylformamide, dipropylene glycol methyl ether, dipropylene glycol methyl ether, propylene glycol monomethyl ether, triethyl citrate, methyl carbitol, ethyl lactate, ethylene glycol monobutyl ether, cyclohexane, methylcyclohexane, dimethylcyclohexane, benzyl alcohol, and dimethyl sulfoxide, among which triacetin is more preferred because its Ra and Rb values ​​are within the aforementioned more preferred range.

[0101] Furthermore, unlike the molding process (A2), the idle distance is not particularly limited, but the idle distance in the molding process (B2) is preferably 10 to 80 mm. Passing through an idle section of 10 to 80 mm results in a good surface thickness. The idle distance is preferably 10 to 60 mm, more preferably 10 to 40 mm, and particularly preferably 10 to 30 mm.

[0102] (B3) Washing process The washing step involves introducing the resin molded product obtained in B2 into a solvent in which the solubility parameter distance Ra for poly(4-methyl-1-pentene) is in the range of 8 to 35 and the solubility parameter distance Rb for the plasticizer is in the range of 5 to 35, and extracting the plasticizer contained in the resin molded product into the solvent while stretching it 1.1 to 5.0 times, thereby obtaining a separation membrane. (B3) The washing step differs from method A in that stretching is required. (B3) The washing step can be carried out using the same solvent as the washing step (A3) of method A, but it is important to stretch the product during the process. This allows for the cleavage of the lamellar structure between the lamellar structures on the non-porous membrane surface, forming a membrane surface that combines lamellar crystals and micropores.

[0103] Generally, a technique is known in which lamellar crystals are cleaved by stretching, creating a porous structure on the surface and inside of the separation membrane. However, with this method, only specific pores, i.e., areas with weak bonds, are cleaved significantly, which can lead to the formation of coarse pores or breakage during transport.

[0104] Therefore, it is expected that by stretching the polymer while it is plasticized and swollen with a plasticizer and a washing solvent, a uniform structure will be formed without the occurrence of defects, and a film with micropores formed between the lamellar crystals will be obtained. The inventors have found that by performing the stretching during the washing process, it is possible to form openings on the film surface 1 having accumulated lamellar crystals with a high porosity, sufficient to prevent the solvent from penetrating into the film.

[0105] To improve gas permeability through effective pore opening, the stretching ratio is preferably 1.1 times or higher. On the other hand, as the area occupied by the pores increases, it becomes more difficult to suppress the penetration of solvents into the film, which tends to reduce solvent resistance. Therefore, the stretching ratio is preferably 5.0 times or lower. A stretching ratio of 1.2 to 3.0 is more preferable, and 1.5 to 2.0 is particularly preferable.

[0106] Furthermore, for the same reasons as in the (A3) washing step, the temperature of the washing solvent is preferably 10 to 50°C, more preferably 20 to 45°C, and particularly preferably 25 to 40°C.

[0107] In the production of the separation membrane of the present invention, a drying step may be included after the washing step of (A3) or (B3). It is preferable to subject the resin molded product to a drying step for the purpose of removing the solvent that adhered during the washing step. It is preferable to dry at a temperature at which the above-mentioned washing solvent can be vaporized and removed, and specifically, it is preferable to carry out the drying at room temperature to 150°C. In this way, the separation membrane of the present invention, mainly composed of PMP, can be produced.

[0108] (Degassing module) A degassing module is a component unit that separates gas from a liquid. The separation membrane of the present invention obtained as described above can be made into a degassing module by filling it into a case using a known method. For example, a hollow fiber membrane module comprises a plurality of hollow fiber membranes and a cylindrical case. The plurality of hollow fiber membranes are bundled together and inserted into the cylindrical case, and then their ends are fixed and sealed to the case with a thermosetting resin such as polyurethane or epoxy resin. An open surface of the hollow fiber membrane is obtained by cutting the ends of the hollow fiber membranes that have been cured with the thermosetting resin, and a degassing module is manufactured.

[0109] In the degassing module equipped with the separation membrane of this application, the liquid to be processed is water, an organic solvent, or a mixture thereof. The liquid may contain a hydrocarbon solvent. The liquid may be at least one selected from the group consisting of glycols, glycol monoalkyl ethers, glycol dialkyl ethers, glycol monoacetates, glycol diacetates, alcohols, ketones, acetate esters, lactic acid esters, saturated hydrocarbons, unsaturated hydrocarbons, cyclic saturated hydrocarbons, cyclic unsaturated hydrocarbons, aromatic hydrocarbons, terpenes, ethers, cyclic imides, 3-alkyl-2-oxazolidinone, N-alkylpyrrolidone, lactone, and nitrogen-containing solvents. The liquid may also be a UV ink or a ceramic ink. [Examples]

[0110] The present invention will be described in more detail below with reference to examples, but the present invention is not limited in any way thereto. [Measurement and Evaluation Method] Each characteristic value in the examples is determined by the following method.

[0111] (1) Outer diameter and inner diameter (μm) of the hollow fiber membrane After freezing the hollow fiber membrane with liquid nitrogen, stress was applied (using a razor or microtome as needed), and the exposed diameter cross-section was observed with an optical microscope. The average values ​​of the outer and inner diameters at 10 randomly selected points were taken as the outer and inner diameters of the hollow fiber membrane, respectively.

[0112] (2) Hollow fraction of hollow fiber membrane (%) From the outer diameter and inner diameter obtained in (1) above, the hollowness ratio of the hollow fiber membrane was calculated using the following formula. Hollowness ratio (%) = [inner diameter (μm) 2 )] 2 / [Outer diameter (μm 2 )] 2 ×100.

[0113] (3) Gas Permeation Performance (GPU) A small module with an effective length of 100 mm consisting of three hollow fiber membranes was fabricated. Specifically, three hollow fiber membranes were bundled together and inserted into a cylindrical plastic pipe. At the ends of the bundle, the gaps between the membranes and the pipe were sealed by curing with a thermosetting resin. The ends of the sealed hollow fiber membranes were cut to obtain the open surfaces of the hollow fiber membranes, and a small module for evaluation was fabricated. The gas permeation flow rate was measured using this small module. Carbon dioxide or nitrogen were used individually as the measurement gas for evaluation, and the pressure change on the permeation side per unit time of carbon dioxide or nitrogen was measured using an external pressure method at a measurement temperature of 37°C in accordance with the pressure sensor method of JIS K7126-1 (2006). Here, the pressure difference between the supply side and the permeation side was set to 100 kPa. The gas temperature was set to 37°C. A differential pressure of 100 kPa indicates that the pressure difference between the gas supply side and the gas permeate side of the separation membrane is 100 kPa.

[0114] Next, the gas permeation flow rate Q was calculated using the following equation (4), and this value was defined as the gas permeation performance. Here, J is the gas flux, and P H and P L These are the partial pressures on the gas supply side and the gas permeate side, respectively. GPU is a common unit indicating the gas permeate flow rate Q, where 1 GPU = 3.35 × 10⁻¹⁵ -10 mol / m 2 The values ​​are s·Pa. Furthermore, the ratio of the gas permeation flow rates Q for each component was defined as the separation coefficient α.

[0115]

number

[0116] (4) Surface thickness (μm) The separation membrane was frozen with liquid nitrogen in the same manner as in (1) above, and then fractured by applying stress (using a razor, microtome, or broad ion beam as necessary) to expose the radial or longitudinal section. Subsequently, the radial or longitudinal section was pre-treated by sputtering with platinum, and when observed at 10,000x magnification using an SEM, the length of a straight line drawn perpendicular to the outer surface from an arbitrary point on the outer surface of the separation membrane toward the inner surface (inner layer) until the first pore exceeding 50 nm was reached was defined as the surface thickness.

[0117] Extracting pores in the inner layer, which determines the thickness of the surface layer, is performed using the image analysis software "ImageJ" after binarizing the analysis image. This is explained using Figures 3 to 5. Figure 3 is an example of an image observed at 10,000x magnification using an SEM. Figure 4 is a processed image of the surface cross section after binarization and noise removal from Figure 3. Binarization was performed by taking a distribution of the number of pixels, where the horizontal axis represents the brightness in the analysis image and the vertical axis represents the number of pixels at the corresponding brightness. When the number of pixels at the highest brightness is A, the binarization was performed by matching it to the point with the smaller brightness among two brightness points where the number of pixels is 1 / 2A. Furthermore, the obtained binarized image was subjected to noise reduction (equivalent to Despeckle in ImageJ), in which all pixels were replaced with the median value of the neighboring 3x3 pixels, and this image was used as the analysis image. As shown in Figure 5, a line perpendicular to the outer surface was drawn from an arbitrary point on the outer surface of the obtained image toward the inner surface, and the length until the first pore exceeding 50 nm was reached was calculated. Measurements were taken at 10 arbitrary locations, and the average value was used as the surface thickness. (Sputtering) Equipment: Hitachi High-Technologies Corporation (E-1010) Evaporation time: 40 seconds Current value: 20mA (SEM) Device: Hitachi High-Technologies Corporation (SU1510) Acceleration voltage: 5kV, Probe current: 30pA.

[0118] (5) Area percentage of lamellar crystals on the film surface (%) The surface of the side containing lamellar crystals was pre-treated by sputtering with platinum. Then, the area of ​​the lamellar crystals, i.e., the bright areas in the SEM image, was extracted using a SEM at 60,000x magnification, and the area ratio of the lamellar crystals to the entire observed image was calculated. Lamellar crystal extraction was performed using the image analysis software "ImageJ" after binarizing the analysis image (Otsu binarization). The resulting binarized image was then subjected to noise reduction five times (equivalent to Despeckle in ImageJ), replacing all pixels with the median of the neighboring 3x3 pixels. The resulting image was used as the analysis image. All bright areas were extracted using the ImageJ Analyze Particles command, and the area ratio of the lamellar crystals was calculated from the area of ​​the extracted bright areas. Measurements were performed at five arbitrary locations, and the average value was adopted as the area ratio of the lamellar crystals to the entire observed image. By determining the ratio of lamellar crystals in the observed image, the ratio of lamellar crystals on the film surface can be determined. (Sputtering) equipment: Hitachi High-Technologies Corporation (E-1010) Evaporation time: 40 seconds Current value: 20mA (SEM) Equipment: Hitachi High-Technologies Corporation (S5500) Acceleration voltage: 5kV, Probe current: 30pA.

[0119] (6) Average pore size (nm) of micropores on the film surface The surface on the side with lamellar crystals was pre-treated by sputtering with platinum under the same conditions as in (5). When observed at 60,000x magnification using an SEM, pores with a diameter greater than 1 nm, i.e., an area of ​​0.785 nm, were observed. 2All larger pores were extracted, and their area was used to calculate the pore diameter assuming each pore was a perfect circle. The average value of these pore diameters was then used as the surface pore diameter. Pore extraction was performed using the image analysis software "ImageJ" after binarizing the analysis image (Huang binarization). Furthermore, the resulting binarized image was subjected to a single noise reduction operation (equivalent to Despeckle in ImageJ), in which all pixels were replaced with the median of the neighboring 3x3 pixels. This image was then used as the analysis image. Pore extraction was performed using the Analyze Particles command in ImageJ, and the surface pore diameter was calculated from the area of ​​the extracted pores. Measurements were taken at five arbitrary locations, and the average value was used as the average pore diameter of the micropores on the film surface.

[0120] (7) Pore ratio of micropores on the film surface (%) The surface on the side with lamellar crystals was pre-treated by sputtering with platinum under the same conditions as in (5). When observed at 60,000x magnification using an SEM, pores with a diameter greater than 1 nm, i.e., an area of ​​0.785 nm, were observed. 2 All larger pores were extracted, and the area ratio of the open areas relative to the total area of ​​the observed image (set as 100%) was calculated from their number and area, and this was defined as the porosity of the membrane surface. Pore extraction was performed in the image analysis software "ImageJ" after binarizing the analysis image (Huang binarization). Furthermore, the resulting binarized image was subjected to a single noise reduction operation (equivalent to Despeckle in ImageJ), in which all pixels were replaced with the median of the neighboring 3x3 pixels. This image was then used as the analysis image. Pore extraction was performed using the Analyze Particles command in ImageJ, and the area ratio of the open areas relative to the total area of ​​the observed image was calculated from the number and area of ​​the obtained pores. Measurements were performed at five arbitrary locations, and the average value was defined as the porosity of the membrane surface.

[0121] (8) Membrane surface 1μm 2 Number of openings per unit area (pieces / μm) 2 ) The surface on the side with lamellar crystals was pre-treated by sputtering with platinum under the same conditions as in (5). When observed at 60,000x magnification using an SEM, pores with a diameter greater than 1 nm, i.e., an area of ​​0.785 nm, were observed. 2 All larger pores were extracted and recorded as the number of open areas in the observation region. Pore extraction was performed using the image analysis software "ImageJ" under the same conditions as in (7). Next, the area of ​​the observation region was determined, and the unit area (1 μm) was calculated using the following formula. 2 The number of openings per 1 μm was calculated. Measurements were taken at five arbitrary locations, and the average value was taken from the film surface. 2 This was defined as the number of openings per unit area. Membrane surface 1μm 2 Number of openings per unit area (pieces / μm) 2 ) = Number of openings in the observation area / Area of ​​the observation area (μm²) 2 ) (9) Area percentage of lamellar crystals on the film surface excluding the open areas (%) From the area ratio of lamellar crystals to the entire observation image obtained by (5) above, and the porosity obtained by (6) above, the area ratio of lamellar crystals to the surface excluding the porosity was calculated using the following formula and was taken as the area ratio of lamellar crystals on the film surface. Area percentage of lamellar crystals (%) = Area percentage of lamellar crystals in the entire observed image % / (1 - Pore ratio (%)) In cases where no pores were observed on the surface in (5) above, the area ratio of lamellar crystals to the entire observation image obtained in (5) was taken as the area ratio of lamellar crystals on the film surface.

[0122] (10) Porosity of the film cross-section (%) The separation membrane was frozen with liquid nitrogen in the same manner as in (1) above, and then stress was applied (using a razor, microtome, or broad ion beam as necessary) to cleave it so that the radial or longitudinal section was exposed. Subsequently, under the same conditions as in (4) above, the radial or longitudinal section was pre-treated by sputtering with platinum, and the area of ​​the pores, i.e., the dark areas in the SEM image, was extracted when observed at a magnification of 10,000x using an SEM, and the area ratio of the entire observed image was calculated to be the porosity of the membrane cross-section. Pore extraction was performed in the image analysis software "ImageJ" after binarizing the analysis image (Huang binarization). The resulting binarized image was subjected to noise reduction (equivalent to Despeckle in ImageJ) once, in which all pixels were replaced with the median of the neighboring 3x3 pixels, and the resulting image was used as the analysis image. Pores were extracted using the ImageJ Analyze Particles command, extracting all the dark areas. The area percentage occupied by pores was then calculated from the area of ​​the extracted dark areas. Measurements were taken at five arbitrary locations, and the average value was adopted as the average porosity in the film cross-section.

[0123] (11) Number of pores larger than 10 μm in the cross-section of the film The separation membrane was frozen with liquid nitrogen in the same manner as in (1) above, and then fractured by applying stress (using a razor, microtome, or broad ion beam as necessary) to expose the radial or longitudinal section. Subsequently, pretreatment was performed by sputtering with platinum under the same conditions as in (4) above. When observed with an SEM at 2,000x magnification, the number of pores with a diameter greater than 10 μm per field of view, i.e., an area of ​​78.5 μm², was observed. 2All larger pores were extracted, and their number was calculated. For pores at the edges of the image where the entire pore was not visible, the diameter was calculated in that state. Pore extraction was performed using the image analysis software "ImageJ" after binarizing the analysis image (Huang binarization). Furthermore, the resulting binarized image was subjected to a single denoising process (equivalent to Despeckle in ImageJ), where all pixels were replaced with the median of the neighboring 3x3 pixels. This result was then used as the analysis image. Pore extraction was performed using the Analyze Particles command in ImageJ, and the number of obtained pores was calculated. Measurements were performed at five arbitrary locations, and the average value was adopted as the number of pores larger than 10 μm in the membrane cross-section.

[0124] (12) The ratio of the major axis length a to the minor axis length b of the voids in the inner layer: a / b The separation membrane was frozen with liquid nitrogen in the same manner as in (1) above, and then cut using a microtome to expose the longitudinal section. The obtained section was pretreated by sputtering with platinum under the same conditions as in (5), and then observed at 10,000x magnification using an SEM. One void was randomly selected from the obtained observation images, and the major axis length a and minor axis length b of the void were determined. Vacuums that could not be considered approximately elliptical were excluded from the measurement. For the measurement, voids were used in which, when the major axis is connected to both ends by a straight line, more than 50% of the major axis length a is contained within the void. The following explanation will be given using Figures 6(a) to (c). In Figures 6(a) to (c), the major axis length a of the void is the length of the longest straight line 9 that can directly connect two points on the outer edge of the void. Here, line segment 9 does not necessarily have to be parallel to the longitudinal direction of the hollow fiber (see Figures 6(b) and (c)). Furthermore, the minor axis length b is the length of the longest straight line 10 that can directly connect two points on the outer edge of the void. Here, lines 9 and 10 do not necessarily have to intersect (see Figure 6(c)). From the major axis length a and minor axis length b obtained above, the ratio a / b of major axis length a to minor axis length b was calculated using the following formula. Measurements were taken at five locations, and the average value was adopted as the ratio a / b of major axis length a to minor axis length b of the void in the inner layer.

[0125] a / b = length of the major axis of the vacancy a (nm) / length of the minor axis of the vacancy b (nm).

[0126] (13) Porosity of the separation membrane (%) When the separation membrane was in the form of a hollow fiber membrane, the fiber length L (mm) and mass M (g) of the hollow fiber membrane were measured after vacuum drying at 25°C for 8 hours. The density ρ1 of the hollow fiber membrane was calculated using the following formula with the outer diameter (mm) and inner diameter (mm) values ​​measured in (1) above.

[0127] ρ1=M / [π×{(outer diameter / 2) 2 ―(inner diameter / 2) 2}×L] Furthermore, the porosity ε(%) was calculated using the following formula.

[0128] ε = 1 - ρ 1 / ρ² Here, ρ2 is the density of the polymer.

[0129] (14) Period length (nm) of lamellar crystals on the film surface The surface of the side containing the lamellar crystals was pretreated by sputtering with platinum under the same conditions as in (5), and then the period length of the lamellar crystals was calculated when observed at a magnification of 30,000x using an SEM. The calculation was performed using the image processing software ImageJ according to the following method. A. Load the SEM image into Image-J (the file size should be 512 x 512 pixels). When you run B.Process / FFT / FD Math, the autocorrelation function is output as the Result, and an image is output, so set the image type to 16-bit.

[0130] C. Use the line tool to create a line profile that passes through the high-brightness point in the center of the image and is also horizontal.

[0131] Run D.Analyze / Plot Profile and output Plot of Result. Execute the E.List button to output intensity and distance, and create a graph.

[0132] F. Measure the distance from the central brightness of the autocorrelation function (output image) to the first nearest neighbor peak, and calculate the period length.

[0133] (15) Crystallinity of the film surface (%) ATR spectra were measured on the surface of hollow fiber films that had been vacuum-dried at 25°C for 8 hours using a BioRad DIGILAB FTIR (FTS-55A) equipped with a single-reflection ATR attachment. A diamond prism was used for the ATR crystal, with an incident angle of 45° and 64 integrations. The degree of crystallinity was calculated from the obtained ATR spectra using the intensity ratio of predetermined bands. For PMP hollow fiber films, the value was 849 cm⁻¹. -1 Band strength in the vicinity, and 1169cm -1 The band strength in the vicinity was used to calculate the following formula.

[0134] IR intensity ratio of the outer surface = [849cm²] -1 [Nearby band strength] / [1169cm] -1 [Nearby band strength] Crystallinity (%) = 172.9 × ratio of IR intensity of the outer surface.

[0135] [PMP raw materials] The PMP raw material is TPX(registered trademark) DX845 manufactured by Mitsui Chemicals, Inc. (density: 833 kg / m³). 3 (MFR: 9.0g / 10min) was used.

[0136] (Example 1) 35% by mass of PMP and 65% by mass of dibutyl phthalate as a plasticizer were supplied to a twin-screw extruder and melt-kneaded at 290°C. The mixture was then introduced into a melt-spinning pack set to a spinning temperature of 245°C, and spun downwards from the outer annular portion of a discharge nozzle with one nozzle hole (double circular tube type, discharge hole diameter 1.2 mm, discharge gap 0.20 mm). The spun hollow fibers were introduced into a cooling bath of dioctyl phthalate and wound up with a winder to achieve a draft ratio of 3.5. The free-running distance was set to 10 mm. A metal filter with a diameter of 100 μm was used as the filter in the melt-spinning pack. The wound hollow fibers were immersed in isopropyl alcohol for 24 hours, and then vacuum-dried at room temperature to remove the isopropyl alcohol and obtain a hollow fiber film. No stretching was performed in the washing process, i.e., the stretching ratio was 1.0. The physical properties of the obtained hollow fiber film are shown in Table 1. On the lamellar crystal-bearing side of the obtained hollow fiber membrane, the average pore size was 16 nm, the porosity was 1.4%, the area occupied by the lamellar crystals was 35%, and the period of the lamellar crystals was 39 nm. Furthermore, the N2 permeability was 7733 GPU, and the N2 permeability after immersion in chloroform / isopropyl alcohol = 1 / 1 (volume / volume) was 494 GPU, indicating excellent permeability and high resistance to organic solvents.

[0137] (Example 2) A hollow fiber membrane was obtained in the same manner as in Example 1, except that butyl benzoate was used as the solvent for the cooling bath. As a result, as shown in Table 1, on the membrane surface on the side with lamellar crystals, the average pore size was 18 nm, the porosity was 0.8%, the area ratio occupied by lamellar crystals was 34%, and the period of the lamellar crystals was 46 nm. Furthermore, the N2 permeability was 11049 GPU, and the N2 permeability after immersion in chloroform / isopropyl alcohol = 1 / 1 (volume / volume) was 217 GPU.

[0138] (Example 3) A hollow fiber membrane was obtained in the same manner as in Example 1, except that the solvent for the cooling bath was N-methylpyrrolidone. As a result, as shown in Table 1, on the membrane surface on the side with lamellar crystals, the average pore size was 25 nm, the porosity was 0.2%, the area ratio occupied by lamellar crystals was 47%, and the period of the lamellar crystals was 26 nm. Furthermore, the N2 permeability was 14979 GPU, and the N2 permeability after immersion in chloroform / isopropyl alcohol = 1 / 1 (volume / volume) was 6 GPU.

[0139] (Example 4) A hollow fiber membrane was obtained in the same manner as in Example 1, except that the solvent for the cooling bath was benzyl benzoate. As a result, as shown in Table 1, on the membrane surface on the side with lamellar crystals, the average pore size was 20 nm, the porosity was 0.1%, the area ratio occupied by lamellar crystals was 37%, and the period of the lamellar crystals was 35 nm. Furthermore, the N2 permeability was 12623 GPU, and the N2 permeability after immersion in chloroform / isopropyl alcohol = 1 / 1 (volume / volume) was 10 GPU.

[0140] (Example 5) 35% by mass of PMP and 65% by mass of dibutyl phthalate as a plasticizer were supplied to a twin-screw extruder and melt-kneaded at 290°C. The mixture was then introduced into a melt-spinning pack set to a spinning temperature of 245°C, and spun downwards from the outer annular portion of a discharge nozzle with one nozzle hole (double circular tube type, discharge hole diameter 1.2 mm, discharge gap 0.20 mm). The spun hollow fibers were introduced into an N-methylpyrrolidone cooling bath and wound up with a winder to achieve a draft ratio of 3.5. The free-running distance was set to 10 mm. A metal filter with a diameter of 100 μm was used as the filter in the melt-spinning pack. Subsequently, in a washing process, the obtained hollow fibers were stretched to 1.2 times their original size at a stretching speed of 2% / second in isopropyl alcohol at 40°C, immersed for 24 hours, and then vacuum-dried at room temperature to remove the isopropyl alcohol, obtaining a hollow fiber film. As a result, as shown in Table 1, on the film surface on the side with lamellar crystals, the average pore size was 29 nm, the porosity was 0.5%, the area ratio occupied by lamellar crystals was 45%, and the period of the lamellar crystals was 30 nm. Furthermore, the N2 permeability was 23623 GPU, and the N2 permeability after immersion in chloroform / isopropyl alcohol = 1 / 1 (volume / volume) was 24 GPU.

[0141] (Example 6) A hollow fiber film was obtained in the same manner as in Example 1, except that triacetin was used as the solvent in the cooling bath and the stretching ratio in the washing step was set to 1.8 times. As a result, as shown in Table 1, on the film surface on the side with lamellar crystals, the average pore size was 10 nm, the porosity was 1.9%, the area ratio occupied by lamellar crystals was 46%, and the period of the lamellar crystals was 43 nm. Furthermore, the N2 permeability was 23267 GPU, and the N2 permeability after immersion in chloroform / isopropyl alcohol = 1 / 1 (volume / volume) was 1163 GPU.

[0142] (Example 7) A hollow fiber membrane was obtained in the same manner as in Example 1, except that the stretching ratio in the washing process was set to 1.2 times. As a result, as shown in Table 1, on the membrane surface on the side with lamellar crystals, the average pore size was 19 nm, the porosity was 2.0%, the area ratio occupied by lamellar crystals was 33%, and the period of the lamellar crystals was 47 nm. Furthermore, the N2 permeability was 18740 GPU, and the N2 permeability after immersion in chloroform / isopropyl alcohol = 1 / 1 (volume / volume) was 94 GPU.

[0143] (Example 8) A hollow fiber film was obtained in the same manner as in Example 1, except that the stretching ratio in the washing process was set to 1.8 times. As a result, as shown in Table 1, on the film surface on the side with lamellar crystals, the average pore size was 24 nm, the porosity was 4.9%, the area ratio occupied by lamellar crystals was 29%, and the period of the lamellar crystals was 55 nm. Furthermore, the N2 permeability was 25333 GPU, and the N2 permeability after immersion in chloroform / isopropyl alcohol = 1 / 1 (volume / volume) was 8 GPU.

[0144] (Comparative Example 1) A hollow fiber membrane was obtained in the same manner as in Example 1, except that triacetin was used as the solvent for the cooling bath. No stretching was performed in the washing step, i.e., the stretching ratio was 1.0. As a result, as shown in Table 1, no openings were observed on the membrane surface on the side with lamellar crystals, and the N2 permeability was a low value of 40 GPU. The area ratio occupied by lamellar crystals on the membrane surface was 54%, the period of the lamellar crystals was 23 nm, and the N2 permeability after immersion in chloroform / isopropyl alcohol = 1 / 1 (volume / volume) was 39 GPU.

[0145] (Comparative Example 2) A hollow fiber membrane was obtained in the same manner as in Example 1, except that dimethyl phthalate was used as the solvent in the cooling bath. No stretching was performed during the washing process, i.e., the stretching ratio was 1.0. As a result, as shown in Table 2, no openings were observed on the membrane surface on the side with lamellar crystals, and the N2 permeability was a low value of 158 GPU. The area ratio occupied by lamellar crystals on the membrane surface was 58%, the period of the lamellar crystals was 18 nm, and the N2 permeability after immersion in chloroform / isopropyl alcohol = 1 / 1 (volume / volume) was 15 GPU.

[0146] (Comparative Example 3) A hollow fiber membrane was obtained in the same manner as in Example 3, except that the free running distance was set to 35 mm. No stretching was performed during the washing process, i.e., the stretching ratio was set to 1.0. As a result, as shown in Table 2, no openings were observed on the membrane surface on the side with lamellar crystals, and the N2 permeability was a low value of 150 GPU. The area ratio occupied by lamellar crystals on the membrane surface was 55%, the period of the lamellar crystals was 40 nm, and the N2 permeability after immersion in chloroform / isopropyl alcohol = 1 / 1 (volume / volume) was 17 GPU.

[0147] (Comparative Example 4) A hollow fiber membrane was obtained in the same manner as in Example 1, except that the discharge gap was 0.35 mm, the draft ratio was 231, the free travel distance was 20 mm, and the solvent for the cooling bath was triacetin. No stretching was performed in the washing process, i.e., the stretching ratio was 1.0. As a result, as shown in Table 2, no lamellar crystals were observed on the membrane surface on the side with a dense surface layer (i.e., the area percentage occupied by lamellar crystals was 0%), and the N2 permeability after immersion in chloroform / isopropyl alcohol = 1 / 1 (volume / volume) was 0 GPU, which was a low value. In other words, the N2 permeability was less than GPU5, which was poor.

[0148] (Comparative Example 5) PMP was spun using 100% by mass and a draft ratio of 700, and air-cooled without using a cooling bath. After air-cooling, a hollow fiber membrane was obtained in the same manner as in Example 1, except that the drawing temperature was 130°C and the drawing ratio was 2.3 times. Since there was no cooling bath, the air-running distance was considered to be zero. Although no plasticizer was used in the raw materials, the wound hollow fibers were immersed in isopropyl alcohol for 24 hours, and then vacuum-dried at room temperature to remove the isopropyl alcohol and obtain a hollow fiber membrane. The hollow fiber membrane was drawn, but no further drawing was performed in the washing process. Drawing was excluded from Table 2. As a result, as shown in Table 2, the porosity was 20%, and the N2 permeability was a low value of 3 GPU. The area ratio occupied by lamellar crystals on the membrane surface was very low at 1%, and the period could not be calculated. The N2 permeability after immersion in chloroform / isopropyl alcohol = 1 / 1 (volume / volume) was a low value of 2 GPU.

[0149] (Comparative Example 6) PMP was spun using 100% by mass and a draft ratio of 750, and air-cooled without using a cooling bath. After air-cooling, the undrawn spun yarn was heat-treated at 190°C for 2 hours while still wound on the spool, and then drawn at a drawing temperature of 130°C and a drawing ratio of 2.3 times, except that the procedure was the same as in Example 1 to obtain a hollow fiber film. Since there was no cooling bath, the air travel distance was considered to be zero. Although no plasticizer was used in the raw materials, the wound hollow fibers were immersed in isopropyl alcohol for 24 hours, and then vacuum-dried at room temperature to remove the isopropyl alcohol and obtain a hollow fiber film. The hollow fiber film was drawn, but no further drawing was performed in the washing process. Drawing was excluded in Table 2. As a result, as shown in Table 2, no dense surface layer was observed, and the entire film had a microporous structure. The area ratio occupied by lamellar crystals on the film surface was low at 9%, and the period could not be calculated. After immersion in a chloroform / isopropyl alcohol solution (1 / 1 volume / volume), the N2 permeability was 0 GPU, indicating a low value.

[0150] (Comparative Example 7) PMP was used at 100% by mass, with an extrusion gap of 1.0 mm and a draft ratio of 400 for spinning, and the material was air-cooled without using a cooling bath. After air-cooling, the spun yarn was stretched to a draw ratio of 2.0, and then heat-set at 190°C for approximately 1 second while relaxing to a draw ratio of 0.8, except that the procedure was the same as in Example 1 to obtain a hollow fiber membrane. Since there was no cooling bath, the air travel distance was considered negligible. Although no plasticizer was used in the raw materials, the wound hollow fibers were immersed in isopropyl alcohol for 24 hours, and then vacuum-dried at room temperature to remove the isopropyl alcohol and obtain a hollow fiber membrane. The hollow fiber membrane was stretched, but no stretching was performed in the washing process. Stretching was excluded from Table 2. As a result, as shown in Table 2, no lamellar crystals were observed on the film surface on the side with the dense surface layer (i.e., the area percentage occupied by lamellar crystals was 0%), and the N2 permeability after immersion in chloroform / isopropyl alcohol = 1 / 1 (volume / volume) was 0 GPU, indicating a low value.

[0151] (Comparative Example 8) A hollow fiber membrane was obtained in the same manner as in Example 6, except that the stretching ratio in the washing process was set to 1.05 times. As a result, as shown in Table 2, the N2 permeability performance was 646 GPU, which was a low value.

[0152] [Table 1]

[0153] [Table 2]

[0154] The separation membranes obtained in Examples 1-8 all met the requirements of the present invention in terms of average pore size, porosity, area ratio occupied by lamellar crystals, and period of lamellar crystals on the membrane surface on the side with lamellar crystals. All of them exhibited excellent permeability and high resistance to organic solvents, with an N2 permeability of 1000 GPU or more and an N2 permeability of 5 or more after immersion in chloroform / isopropyl alcohol = 1 / 1 (volume / volume). On the other hand, the separation membranes of Comparative Examples 1-3, which did not have pores on the membrane surface, and the separation membrane of Comparative Example 8, whose membrane surface porosity did not meet the requirements of the present invention, showed low N2 permeability. Furthermore, the separation membranes of Comparative Examples 4-7, which did not have lamellar crystals accumulated on the membrane surface, also showed low N2 permeability after immersion in chloroform / isopropyl alcohol = 1 / 1 (volume / volume). In all of Examples 1-8, there were no pores larger than 10 μm in the inner layer. [Industrial applicability]

[0155] The separation membrane of the present invention can be suitably used for applications that separate gas from a liquid or add gas to a liquid. For example, it can be suitably used as a degassing membrane to reduce the amount of dissolved gas in water, aqueous solutions, organic solvents, and resist solutions in semiconductor manufacturing lines, liquid crystal color filter manufacturing lines, and inkjet printer ink manufacturing, and as a gas exchange membrane in artificial lungs for medical applications. In particular, as a degassing membrane, it is very useful for degassing photoresist solutions and developer solutions used in lithography in semiconductor manufacturing lines. [Explanation of symbols]

[0156] 1 Membrane surface 2 Opening part 3 Surface layer 4. Inner layer 5. Surface thickness 6 Lamellar crystals 7 voids (holes) 8. Hollow fiber-shaped separation membrane a. Long axis of the void b. Short axis of the void

Claims

1. A separation membrane comprising poly(4-methyl-1-pentene) as the main component, comprising a surface layer and an inner layer, wherein at least one of the surface layers has lamellar crystals. A separation membrane wherein the surface layer having the lamellar crystals is provided with micropores, the porosity is defined as the ratio of the micropores to the surface of the membrane, and when the surface of the membrane is considered as 100%, the porosity is 0.1% to 10%, the average pore size of the micropores is 3 nm to 30 nm, and the degree of crystallinity of the surface layer having the lamellar crystals on the membrane surface is 5% to 35%.

2. N at a differential pressure of 100 kPa ２ The separation membrane according to claim 1, wherein the permeability performance is 1000 GPU or more.

3. The separation membrane according to claim 1 or 2, wherein the area ratio occupied by the lamellar crystals on the surface of the membrane having the lamellar crystals is 10% to 60% when the area of ​​the membrane surface excluding the pores is taken as 100%.

4. The separation membrane according to claim 1 or 2, wherein the period of the lamellar crystals on the surface of the membrane having the lamellar crystals is 10 nm to 80 nm.

5. In the surface layer having the lamellar crystals, the micropores are 1 / μm ２ More than 20000 pieces / μm ２ The separation membrane according to claim 1 or 2, which is as follows:

6. The separation membrane according to claim 1 or 2, wherein the porosity of the separation membrane is 30% to 70%.

7. The separation membrane according to claim 1 or 2, wherein the inner layer of the separation membrane has a porosity of 25% to 60% when the cross-sectional area when cut in the thickness direction is taken as 100%.

8. The separation membrane according to claim 1 or 2, wherein the separation membrane has a hollow fiber shape.

9. The separation membrane according to claim 8, wherein the surface layer having lamellar crystals is the outer surface of the hollow fiber-shaped separation membrane.

10. The separation membrane according to claim 8, wherein in a cross-section obtained by cutting the inner layer of the hollow fiber-shaped separation membrane parallel to the longitudinal direction of the membrane and parallel to the thickness direction of the membrane, the ratio a / b of the major axis length a to the minor axis length b of the pores is 1.0 to 5.

0.

11. After immersing the separation membrane in the following organic solvent A for 3 seconds, the N2 at a differential pressure of 100 kPa was measured. ２ The separation membrane according to claim 1 or 2, wherein the permeability performance is 5 GPU or more. Organic solvent A: Chloroform / Isopropyl alcohol = 1 / 1 (volume / volume)

12. A degassing module comprising the separation membrane according to claim 1 or 2.

13. A method for producing a separation membrane, comprising the steps (A1) to (A2) below. (A1) A preparation step to obtain a resin composition by melt-kneading a mixture containing 10% to 50% by mass of poly(4-methyl-1-pentene) and 50% to 90% by mass of a plasticizer. (A2) A molding step in which the resin composition is discharged from a discharge nozzle, and immediately after passing through an empty section of 10 mm to 30 mm, is introduced into a cooling bath of a solvent in which the solubility parameter distance Ra for poly(4-methyl-1-pentene) is in the range of 4.0 to 14.0 and the solubility parameter distance Rb for the plasticizer is in the range of 3.0 to 6.0 to obtain a resin molded product.

14. A method for producing a separation membrane according to claim 13, further comprising a washing step (A3) after the molding step of obtaining the resin molded product (A2), wherein the resin molded product is subjected to a solvent in which the plasticizer contained in the resin molded product is extracted into the solvent, the solvent having a solubility parameter distance Ra for poly(4-methyl-1-pentene) in the range of 8 to 35 and a solubility parameter distance Rb for the plasticizer in the range of 5 to 35.

15. The method for producing a separation membrane according to claim 14, wherein the resin molded product is stretched to 1.1 to 5.0 times its original size during the washing step (A3).

16. A method for manufacturing a separation membrane, comprising the following steps (B1) to (B3), wherein in the washing step of step (B3), the resin molded product is stretched to 1.1 to 5.0 times its original size. (B1) A preparation step to obtain a resin composition by melt-kneading a mixture containing 10% to 50% by mass of poly(4-methyl-1-pentene) and 50% to 90% by mass of a plasticizer. (B2) A molding step in which, immediately after discharging the resin composition from the discharge nozzle, the resin composition is introduced into a cooling bath of a solvent in which the solubility parameter distance Ra for poly(4-methyl-1-pentene) is in the range of 5.0 to 18.0 and the solubility parameter distance Rb for the plasticizer is in the range of 1.0 to 2.9 or 6.5 to 10.0 to obtain a molded resin product. (B3) A washing step in which the obtained resin molded product is washed in a solvent in which the solubility parameter distance Ra for poly(4-methyl-1-pentene) is in the range of 8 to 35 and the solubility parameter distance Rb for the plasticizer is in the range of 5 to 35, thereby extracting the plasticizer contained in the resin molded product into the solvent.

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