Separation membrane, deaeration membrane module, deaeration device, and method for manufacturing separation membrane

Abstract

Provided is, by using poly(4-methyl-1-pentene), a separation membrane that achieves both high gas permeability and low leakage properties for a deaeration method for removing a dissolved gas from a liquid and a gas exchange method for exchanging a dissolved gas in a liquid with a gas component in a gas phase. This separation membrane contains poly(4-methyl-1-pentene) as the main component. The porosity of the entire separation membrane is 30-70%. The separation membrane has a functional layer on at least one surface side thereof. An alignment direction in which the degree of alignment is within the range of 1.5-2.5 is present in the surface of the functional layer. The degree of crystal alignment in the surface of the functional layer of the separation membrane as measured by a wide-angle X-ray diffraction method is 0.20-0.60. The crystallite size in the surface of the functional layer of the separation membrane is 10-20 nm.

Description

Separation membrane, degassing membrane module, degassing device, and method for manufacturing separation membrane

[0001] The present invention relates to a gas separation membrane, a degassing membrane module, a degassing device, and a method for producing a separation membrane.

[0002] In degassing methods for removing dissolved gases from liquids and gas exchange methods for exchanging dissolved gases in liquids with gas components in a gas phase, methods for separating gases using separation membranes as gas-permeable membranes are known. Because separation membranes are required to have high gas permeability and low leakage from the liquid being treated, poly(4-methyl-1-pentene) is sometimes used as a material for the separation membrane. Furthermore, hollow fiber membranes are sometimes used as the shape of the separation membrane.

[0003] In recent years, there has been a demand for separation membranes with higher gas permeability and lower leakage, and various methods have been proposed to obtain gas-permeable membranes with higher permeability or lower leakage. Note that lower leakage refers to the resistance to leakage of a liquid when removing dissolved gas from a liquid or when exchanging dissolved gas with a gas component in a liquid.

[0004] For example, Patent Document 1 discloses a hollow fiber membrane produced by a dry-wet solution process using a polyolefin polymer. In Patent Document 1, a polymer solution in which a polyolefin polymer is dissolved in a good solvent is extruded through a die at a temperature higher than the melting point of the polyolefin resin and brought into contact with a cooled solvent to obtain a separation membrane. This manufacturing method is called thermally induced phase separation. The resulting separation membrane has a dense layer on one surface and forms an integral asymmetric structure with pores formed inside the membrane.

[0005] Patent Document 2 discloses a hollow fiber membrane produced by a melting method. A polyolefin resin is extruded through a die at a temperature above its melting point, cooled and solidified, and then stretched to partially split and open the interior of the separation membrane. This results in a dense surface layer and a porous, non-uniform structure within the membrane.

[0006] Patent Document 3 discloses a melt spinning method for obtaining a hollow fiber microporous membrane. A polyolefin resin is extruded through a spinneret at a temperature above its melting point, cooled and solidified, and then subjected to a long-term heat treatment and stretching to cleave the interfaces of the lamellar crystals. A relaxation process is then carried out to adjust the pore size of the cleaved pores, thereby forming a porous structure with interconnected pores.

[0007] Japanese Patent Publication No. 2005-515061 Publication No. 7-155569 Publication No. 2010-269307

[0008] The separation membrane of Patent Document 1 exhibits low leakage because it has no pores on the surface, but its gas permeability is insufficient. The separation membrane of Patent Document 2 has high strength and low leakage because the porosity of the hollow fiber membrane is small, but its gas permeability is insufficient. The separation membrane of Patent Document 3 has pores with a pore size of about 20 to 60 nm on the surface of the separation membrane, so a membrane with high gas permeability can be obtained, but leakage is likely to occur and the low leakage property is not satisfactory.

[0009] In other words, when the surface layer and surface of the separation membrane exhibit low leakage, high gas permeability could not be obtained. On the other hand, when removing dissolved gas from a liquid or exchanging dissolved gas in a liquid with a gas component, holes or ruptures at the crystal interface were present on the surface of the separation membrane to improve gas permeability. The presence of holes or ruptures at the crystal interface on the surface of the separation membrane made it difficult to make the liquid less likely to leak.

[0010] In view of the above, an object of the present invention is to provide a separation membrane using poly(4-methyl-1-pentene) that satisfies both high gas permeability and low leakage.

[0011] As a result of extensive research aimed at solving the above problems, the present inventors have discovered that a separation membrane containing poly(4-methyl-1-pentene) as a main component, having a porosity within a specific range, a longitudinal orientation within a specific range on at least one surface side, and having a functional layer on at least one surface side, has high gas permeability and low leakage properties, leading to the completion of the present invention. The separation membrane of the present invention has the following configuration.

[0012] 1. A separation membrane containing poly(4-methyl-1-pentene) as a main component, the separation membrane having a porosity of 30% to 70% throughout the separation membrane, a functional layer on at least one surface side of the separation membrane, the functional layer having an orientation direction in the plane of the surface with an orientation degree of 1.5 to 2.5, the crystalline orientation degree measured by wide-angle X-ray diffraction on the surface of the functional layer of the separation membrane being 0.20 to 0.60, and the crystallite size on the surface of the functional layer of the separation membrane being 10 nm to 20 nm. 2. The separation membrane according to 1, wherein the crystallinity on the surface of the functional layer of the separation membrane is 5% to 35%. 3. The separation membrane according to 1 or 2, wherein the proportion of rigid amorphous of the separation membrane is 20% by mass to 40% by mass. 4. The separation membrane having a N ２ The separation membrane according to any one of 1 to 3, having a permeation performance of 1,000 GPU to 20,000 GPU. 5. The separation membrane according to any one of 1 to 4, wherein the separation membrane is in a hollow fiber shape, and the degree of orientation in the longitudinal direction on the surface of the functional layer is 1.5 to 2.5, the degree of crystalline orientation on the surface of the functional layer measured by wide-angle X-ray diffraction is 0.20 to 0.60, and the crystallite size on the surface of the functional layer is 10 nm to 20 nm. 6. The separation membrane according to 5, wherein the outer surface of the hollow fiber separation membrane is the functional layer. 7. A degassing membrane module comprising a case and the separation membrane according to any one of 1 to 6, wherein the separation membrane is packed in the case. 8. A degassing apparatus comprising the degassing membrane module according to 7. 9. A method for producing a liquid, in which dissolved gas is removed from a liquid to be treated using the degassing membrane module comprising the separation membrane according to any one of 1 to 6.

[0013] 10. A method for producing a hollow fiber separation membrane, comprising the following steps (1) to (4), with step (4) being carried out continuously after step (3): (1) a preparation step of melt-kneading a resin mixture containing 10% to 50% by mass of poly(4-methyl-1-pentene) and 50% to 90% by mass of a plasticizer to obtain a resin composition; (2) a spinning step of melting the resin composition, discharging it from a discharge nozzle, cooling it in a cooling bath, and winding it up at a draft ratio of 1 to 10 to obtain a resin molded product; (3) a washing step of extracting the plasticizer into a solvent while stretching the resin molded product to 1.3 to 1.9 times its original size at a stretching rate of 0.1% / second to 1.5% / second; and (4) a drying step of drying the washed resin molded product while relaxing it to 0.75 to 0.98 times its original size at a relaxation rate of 0.1% / second to 5.0% / second.

[0014] According to the present invention, the surface of a highly gas-permeable separation membrane is free of pores or ruptured pores at the crystal interface, making it difficult for liquid to leak. This makes it possible to provide a separation membrane using poly(4-methyl-1-pentene) that combines high gas permeability with low leakage. Furthermore, a degassing membrane module and a degassing device equipped with the separation membrane of the present invention can be provided, which can remove dissolved gases from a liquid to be treated with high gas permeability and low leakage.

[0015] 1 is an example of an image of a cross section cut in the thickness direction of a separation membrane captured by SEM. FIG. 2 is a schematic diagram showing a method for obtaining the thickness of a functional layer from an image obtained by binarizing the image of FIG. 1 and removing noise. FIG. 3 is an example of a process diagram for extracting a plasticizer into a solvent while stretching in a washing process. FIG. 4 is an example of a process diagram for drying while relaxing in a drying process.

[0016] The following is a detailed description of an embodiment of the present invention. The separation membrane of the present invention is a separation membrane primarily composed of poly(4-methyl-1-pentene), having a porosity of 30% to 70% throughout the separation membrane, a functional layer on at least one surface of the separation membrane, and an orientation direction in the plane of the surface having the functional layer with a degree of orientation in the range of 1.5 to 2.5. The degree of crystalline orientation measured by wide-angle X-ray diffraction at the surface of the functional layer of the separation membrane is 0.20 to 0.60, and the crystallite size at the surface of the functional layer of the separation membrane is 10 to 20 nm. Furthermore, a separation membrane is provided in which the separation membrane is hollow fiber-shaped, the degree of longitudinal orientation at the surface of the functional layer is 1.5 to 2.5, the degree of crystalline orientation measured by wide-angle X-ray diffraction at the surface of the functional layer is 0.20 to 0.60, and the crystallite size at the surface of the functional layer is 10 to 20 nm.

[0017] In this specification, a ratio based on mass (percentage, part, etc.) is the same as a ratio based on weight (percentage, part, etc.) The resin composition constituting the separation membrane will be described below.

[0018] <Resin composition constituting separation membrane> The resin composition constituting the separation membrane of the present invention mainly comprises poly(4-methyl-1-pentene) shown in (1) below. In addition to (1), the resin composition may contain the following components (2) to (3).

[0019] (1) Poly(4-methyl-1-pentene) (hereinafter referred to as "PMP") The separation membrane of the present invention must contain PMP as its main component. The "main component" here refers to a component that accounts for 70% by mass or more of all the components of the separation membrane.

[0020] PMP may be any polymer as long as it has a repeating unit 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. Specific examples of the monomer 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").

[0021] Examples of the olefin having 2 to 20 carbon atoms to be copolymerized 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, etc. The olefin having 2 to 20 carbon atoms to be copolymerized with 4-methyl-1-pentene may be one type or a combination of two or more types.

[0022] The density of the PMP raw material used as the raw material for the separation membrane of the present invention is 825 to 840 (kg / m ３ ), and 830 to 835 (kg / m ３ If the density is lower than the above range, the mechanical strength of the separation membrane may decrease, and problems such as the tendency for defects to occur may occur. On the other hand, if the density is higher than the above range, the gas permeability tends to decrease.

[0023] The melt flow rate (MFR) of PMP is not particularly limited as long as it is easily mixed with the plasticizer described below and can be co-extruded, but 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 load of 5 kg. An MFR within the above range facilitates extrusion molding to a relatively uniform film thickness. The PMP raw material may be a commercially available PMP polymer, such as TPX (registered trademark) manufactured by Mitsui Chemicals, Inc.

[0024] The content of PMP in the separation membrane is preferably 70 to 100% by mass, more preferably 80 to 100% by mass, and even more preferably 90 to 100% by mass, when the total mass of all components of the separation membrane is 100% by mass. When the content of PMP in the separation membrane is 70% by mass or more, sufficient gas permeability is achieved.

[0025] Furthermore, the content of PMP in the raw materials for producing the separation membrane is preferably 10% by mass to 50% by mass, when the total components constituting the raw materials are taken as 100% by mass. A content of 10% by mass or more improves the membrane strength of the separation membrane. On the other hand, a content of 50% by mass or less improves the permeability performance of the separation membrane. The content is more preferably 15 to 50% by mass, even more preferably 20 to 45% by mass, and particularly preferably 25 to 40% by mass.

[0026] (2) Plasticizer The resin composition constituting the separation membrane of the present invention may contain a plasticizer for PMP. From the viewpoint of increasing permeability, the content of the plasticizer 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.

[0027] 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 a combination of two or more types of plasticizers. Examples of plasticizers for PMP include palm kernel oil, dibutyl phthalate, dioctyl phthalate, butyl stearate, dibenzyl ether, coconut oil, and mixtures thereof. Among these, dibutyl phthalate and dibenzyl ether are preferred in terms of compatibility and spinnability.

[0028] The plasticizer in the PMP is preferably eluted from the separation membrane after it is formed. Furthermore, the content of the plasticizer in the raw material used to produce the separation membrane is preferably 50% by mass to 90% by mass, where the total amount of the components constituting the raw material is 100% by mass. Having a content of 90% by mass or less in the raw material results in good membrane strength for the separation membrane. Furthermore, having a content of 50% by mass or more in the raw material results in good permeability for the separation membrane. The content in the raw material is more preferably 50% by mass to 85% by mass, even more preferably 55% by mass to 80% by mass, and particularly preferably 60 to 75% by mass.

[0029] (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 the effects of the present invention are not impaired. Examples of additives include resins such as cellulose ether, polyacrylonitrile, polyolefin, polyvinyl compound, polycarbonate, poly(meth)acrylate, polysulfone, and polyethersulfone, organic lubricants, crystal nucleating agents, organic particles, inorganic particles, end-capping agents, chain extenders, ultraviolet absorbers, infrared absorbers, color inhibitors, matting agents, antibacterial agents, antistatic agents, deodorizers, flame retardants, weather resistance agents, antistatic agents, antioxidants, ion exchange agents, antifoaming agents, color pigments, fluorescent brighteners, and dyes.

[0030] <Shape and characteristics of separation membrane> The shape of the separation membrane of the present invention is preferably a hollow fiber shape separation membrane (hereinafter sometimes referred to as a "hollow fiber membrane"), but the separation membrane of the present invention is not limited to the hollow fiber shape. Hollow fiber membranes are preferred because they can be efficiently packed into a module and the effective membrane area per unit volume of the module can be made large.

[0031] The shape of the separation membrane in the present invention, i.e., the thickness of the separation membrane, the outer and inner diameters when the separation membrane is a hollow fiber membrane, and the hollowness can be determined by, for example, observing a cross section (hereinafter referred to as a "diametric cross section") obtained by applying stress to a separation membrane sufficiently cooled in liquid nitrogen and cutting it in the thickness direction of the membrane using an optical microscope or a scanning electron microscope (SEM). Specific methods are described in detail in the Examples.

[0032] The separation membrane of the present invention is composed of a dense functional layer and a porous support layer. The separation membrane obtained by the method of 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 having a functional layer and a support layer. The total thickness of the separation membrane, including the functional layer and the support layer, is preferably 10 μm to 500 μm, from the viewpoint of achieving both gas permeability and low leakage. The total thickness of the separation membrane is more preferably 30 μm or more, and even more preferably 50 μm or more. The thickness is more preferably 200 μm or less, even more preferably 150 μm or less, and particularly preferably 100 μm or less.

[0033] From the viewpoint of achieving both an effective membrane area and membrane strength when packed in 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. The outer diameter is more preferably 1000 μm or less, even more preferably 500 μm or less, and particularly preferably 450 μm or less.

[0034] In addition, considering the relationship between the pressure loss of the fluid flowing through the hollow portion 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. The outer diameter is more preferably 500 μm or less, even more preferably 300 μm or less, and particularly preferably 250 μm or less.

[0035] In addition, in view of the relationship between the pressure loss of the fluid flowing through the hollow portion and the buckling pressure, the hollow fiber membrane preferably has a hollow ratio of 15% to 70%, more preferably 20% or more, and even more preferably 25% or more, and more preferably 60% or less, even more preferably 50% or less, and particularly preferably 40% or less.

[0036] The method for adjusting the outer diameter, inner diameter, and hollowness of the hollow fibers in the hollow fiber membrane to fall within the above ranges is not particularly limited, but can be adjusted, for example, by appropriately changing the shape of the outlet holes of the spinneret used to produce the hollow fibers, or the draft ratio, which can be calculated from the take-up speed / discharge speed. As described below, the separation membrane of the present invention can be produced by forming a resin molded product from a membrane-forming solution containing a polymer, and then washing and drying the resin molded product. For convenience, the state before washing will be referred to as the "resin molded product," and the state after drying will be referred to as the "separation membrane."

[0037] The separation membrane of the present invention has a surface with a characteristic functional layer. Although the mechanism is not fully understood, the resin molded product obtained in the spinning process is subjected to a subsequent washing process in which the molded resin product is wrapped in a washing solvent to become soft and swollen. This allows the molded resin product to be gradually stretched at a low speed, achieving an orientation degree that achieves good gas permeability without generating coarse pores on the surface or large cleavage holes at the crystal interface. "Wrapping" refers to entangling the solvent with the separation membrane, making the solvent replaceable with a plasticizer. Stretching at a low speed and within a predetermined stretch ratio during washing does not result in large pores on the surface or large cleavage holes at the crystal interface, but ultra-small pores and cracks may occur. Furthermore, during washing, the plasticizer inside the molded resin product is extracted into the washing solvent. As the plasticizer passes through the stretched membrane surface, small pores on the membrane surface, approximately the size of the plasticizer molecules, may form. In the drying process following the stretching in the washing process, the swollen resin molded product is dried by relaxing it at a relaxation ratio and a relaxation rate within a specified range. This is thought to cause the tiny pores and tiny cracks at the crystal interface on the surface to shrink, resulting in the formation of a surface that is free of pores but has extremely tiny gas flow paths.

[0038] Here, relaxation is achieved, for example, by relaxing the tension applied to the separation membrane while it is running between rolls within a predetermined range. If the relaxation after stretching is too great or too small, the microscopic pores and microscopic cracks at the crystal interface will not shrink, and the desired surface pore diameter will not be obtained. In other words, a separation membrane with the desired surface pore diameter can be obtained by performing relaxation at a relaxation ratio appropriate for the stretching ratio. For example, when stretching is performed at a relatively high stretching ratio, the functional layer surface has a high degree of orientation and the molecular chains are highly constrained, so it is preferable to perform relaxation to a relatively low relaxation ratio to sufficiently cause uniform pore shrinkage. When stretching is performed at a relatively low stretching ratio, the functional layer surface has a low degree of orientation and the molecular chains are weakly constrained, so pore shrinkage due to relaxation is likely to occur. Therefore, it is preferable to perform relaxation to a relatively high relaxation ratio to limit the relaxation to a slight extent so that the microscopic pores do not become completely blocked by shrinkage. In addition, since the harmony of the relaxation and pore shrinkage rates is also important for forming an ideal membrane surface, it is preferable to perform relaxation at a relaxation rate within a predetermined range. It is also important to dry the resin molded product while relaxing it after it has been washed and swollen with the washing solvent. During the drying process of the swollen resin molded product, the evaporation of the washing solvent causes uniform shrinkage throughout the entire resin molded product, equivalent to the volume of the washing solvent. By relaxing the resin molded product at this time and releasing the tension on the resin molded product, uniform shrinkage of the micropores present on the membrane surface occurs, resulting in a uniform membrane surface with only extremely small pores. The washing / stretching and drying / relaxation steps are performed consecutively in this order. However, considering the location of the washing bath and drying furnace, it is also possible to take up the resin molded product after the washing / stretching step, and then unwind it again while it is still swollen, and then perform the drying / relaxation step.

[0039] The separation membrane of the present invention has a functional layer on the surface of at least one surface. The thickness of the functional layer is 0.1 to 2.0 μm, and the surface of the functional layer does not have openings of a size that would adversely affect low leakage. In other words, the functional layer refers to a layer of the separation membrane that does not have voids when observed at a magnification of 50,000 times using a scanning electron microscope (hereinafter referred to as SEM). The voids refer to pores with a diameter of 3 nm or more when the surface of the separation membrane is observed at a magnification of 2,000 to 50,000 times using a scanning electron microscope (SEM). When the pores are observed as described above, they may appear to be concave.

[0040] That is, in the present invention, "having a functional layer" means that when the surface of the separation membrane is observed at a magnification of 2,000 to 50,000 times using a scanning electron microscope (SEM), not a single pore, i.e., void, with a diameter of 3 nm or more is observed. Here, voids with a diameter of less than 3 nm are not easily observed with an SEM due to the resolution. Even when observed at 50,000 times, it is difficult to identify voids with a diameter of less than 3 nm, but the functional layer of the separation membrane of the present invention may have pores with a diameter of less than 3 nm, i.e., microvoids. From the viewpoint of gas permeability, it is preferable that the functional layer has microvoids, and it is even more preferable that it has many microvoids.

[0041] By having multiple micropores with a diameter of less than 3 nm on the surface of the functional layer, gas molecules can move through the pores, improving gas permeability. Furthermore, by having multiple pores, the gas permeability improves in proportion to the number of pores. On the other hand, since pores with a diameter of less than 3 nm are small compared to the molecular size of the liquid to be treated, the liquid to be treated does not pass through pores with a diameter of less than 3 nm, and this does not adversely affect the low leakage properties of the separation membrane.

[0042] The thickness of the functional layer refers to the length from any point on a surface without voids (for example, membrane surface 1 in FIG. 1) to the other surface, when a vertical line is drawn, until it first reaches a hole with a diameter of 3 nm or more, i.e., a void. A detailed explanation will be given using the drawings. The separation membrane to be observed is, for example, a separation membrane sufficiently cooled in liquid nitrogen, and stress is applied (using a razor, microtome, or broad ion beam as necessary), and a radial cross section, or a cross section parallel to the longitudinal direction of the membrane and parallel to the film thickness direction (hereinafter referred to as "longitudinal cross section") is used. A scanning electron microscope (SEM) is used to observe a longitudinal cross section including the functional layer near the surface of the separation membrane. The image obtained in this way can be used to determine the size of the voids and the thickness of the functional layer.

[0043] FIG. 1(a) is an example of a cross-sectional SEM image including a functional layer 2 near the surface of a separation membrane. FIG. 1(a) shows a membrane surface 1 and voids 3. In FIG. 1(a), the voids 3 are areas that appear darker than the surrounding area, and the symbol 3 marks the location of a representative void. The functional layer 2 is located on the membrane surface side, and an inner layer 5 is shown below the functional layer 2 as a support layer. FIG. 1(b) is a schematic diagram showing the relationship between the voids 3 and the functional layer 2. The voids 3 are holes or depressions with a diameter of 3 nm or more, and are areas that appear darker than the surrounding area in FIG. 1(a). As shown in FIG. 1(b), the shortest distance from the membrane surface 1 to each void 3 is obtained as the thickness 4 of the functional layer at each point. Although not shown, the inner layer 5 of the separation membrane is a porous layer, and even larger pores exist below the functional layer. The thickness of the functional layer is obtained as the average value of the virtual fluctuation curve 6 of the functional layer. 1(b), the virtual variation curve 6 is formed by connecting the shortest path points of each void 3. Specifically, the distance to the void 3 observed as a hole or depression with a diameter of 3 nm or more in the immediate vicinity of the film surface 1 is measured at multiple points, and the average value can be used as the thickness of the functional layer.

[0044] FIG. 2 shows an example of a method for identifying voids with a diameter of 3 nm or more. The obtained cross-sectional SEM image is binarized using the image analysis software "ImageJ", and only pores with a diameter of 3 nm or more can be extracted. In the processed image shown in FIG. 2(a), the resin part is white and the voids 3 are black. The film surface 1 is shown by a dotted line. FIG. 2(b) shows the pores with a diameter of 3 nm or more (area 7.1 nm) extracted from the processed image of FIG. 2(a). ２ The image shows the boundary lines of the voids (above) extracted. The thickness 4 of the functional layer is the average distance from the film surface 1 to the point where the shortest path, i.e., the line segment perpendicular to the line representing the film surface 1, intersects with the boundary line. The method for measuring the thickness of the surface functional layer (for example, the functional layer thickness 4 in Figure 2) will also be described in detail in the Examples.

[0045] The longitudinal direction here refers to the machine direction during production, which in the case of hollow fiber membranes is the direction perpendicular to the radial direction. The longitudinal direction can also be referred to as the fiber axis direction. The transverse direction in the case of hollow fiber membranes is the direction parallel to the radial direction, i.e., the in-plane direction of the hollow surface.

[0046] On the other hand, when the separation membrane is a flat membrane, it is difficult to determine the longitudinal direction from the appearance of the separation membrane. Therefore, in the present invention, the longitudinal direction of the flat membrane is defined as the direction in which the separation membrane is oriented. In the present invention, the existence of an orientation direction in which the in-plane orientation degree on the surface of the functional layer is in the range of 1.5 to 2.5 means that in the plane of the flat membrane, the orientation degree is at most 1.5 to 2.5 in any direction in the range of 0° to 180° parallel to the in-plane of the surface. The orientation degree in an unoriented state is 1.0.

[0047] When the thickness of the functional layer is 0.10 μm or more, low leakage properties are good, and when it is 2.0 μm or less, gas permeability is good. The thickness of the functional layer is preferably 0.10 μm or more and 1.5 μm or less. Furthermore, the thickness of the functional layer is preferably 0.10 μm or more and 1.0 μm or less, and more preferably 0.10 μm or more and 0.40 μm or less.

[0048] In the separation membrane of the present invention, the functional layer is preferably on the outer surface of the hollow fiber membrane. By having the functional layer on the outer surface, the specific surface area during operation increases, and the permeation performance is more likely to be improved.

[0049] The separation membrane of the present invention preferably has an average pore size of 100 nm or more and 1000 nm or less. The support layer of the present invention refers to a porous membrane layer that is an inner layer 5, which is closer to the functional layer on the surface of the separation membrane. The average pore size of the support layer or inner layer can be obtained, for example, by exposing the cross section of a separation membrane that has been sufficiently cooled in liquid nitrogen using a microtome, observing it using a scanning electron microscope (SEM), binarizing the obtained image using the image analysis software "ImageJ", and then extracting only pores with an average diameter greater than 100 nm. An average pore size of 100 nm or more in the support layer results in good permeability, and an average pore size of 1000 nm or less results in good strength of the separation membrane. The average pore size of the support layer is preferably 100 nm or more and 800 nm or less, more preferably 100 nm or more and 600 nm or less, even more preferably 100 nm or more and 570 nm or less, and particularly preferably 100 nm or more and 500 nm or less.

[0050] The separation membrane of the present invention has a porosity of 30% or more and 70% or less. This may also be expressed as 30% to 70%. The porosity refers to the proportion of voids when the entire membrane is 100% resin, such as PMP. A porosity of 30% or more results in good permeability, while a porosity of 70% or less results in good membrane strength. A porosity of 50% or more and 70% or less is preferred, with a porosity of 60% or more and 70% or less being particularly preferred, and a porosity of 63% or more and 68% or less being particularly preferred. To achieve a porosity within this range, structure formation using thermally induced phase separation, as described below, is preferably used. The method for measuring the porosity will be described in detail in the Examples.

[0051] The separation membrane of the present invention preferably has a longitudinal orientation degree of 1.5 or more and 2.5 or less on the surface side having the functional layer. When the longitudinal orientation degree of the surface is 1.5 or more, the order of the surface of the separation membrane is increased, making it less likely that holes will form on the surface, and improving low leakage properties. When the orientation degree is 2.5 or less, the gas permeability is improved. In other words, when the orientation degree exceeds 2.5, the crystallinity increases and the gas permeability decreases. The longitudinal orientation degree of the surface is preferably 1.7 or more, more preferably 1.8 or more. The longitudinal orientation degree of the surface is preferably 2.2 or less, more preferably 2.0 or less, and even more preferably 1.9 or less. The longitudinal orientation degree of the surface can be determined by orientation analysis using laser Raman spectroscopy. Specific methods will be described in the examples.

[0052] Generally, polymers have crystalline and amorphous regions, and the degree of orientation varies depending on whether they are crystalline or amorphous. Laser Raman spectroscopy is a method for determining the overall degree of orientation of both crystalline and amorphous regions, which is obtained as the sum of the crystalline and amorphous degrees of orientation. Laser Raman spectroscopy is a technique that irradiates the object to be measured with light, detecting and analyzing the Raman scattered light generated by the interaction between the incident light and the object. Since most of the incident light interacts with the surface of the object to be measured and generates Raman scattered light, the degree of orientation of the film surface can be selectively obtained by optimizing measurement conditions such as beam diameter, light source type, light source wavelength, diffraction grating, and slit width.

[0053] The separation membrane of the present invention preferably has a crystalline orientation of 0.20 or more and 0.60 or less. When the crystalline orientation is 0.20 or more, the order of the separation membrane is increased, surface pores are less likely to occur, and low leakage properties are good. When the crystalline orientation is 0.60 or less, gas permeability is good. The crystalline orientation is preferably 0.40 or more, more preferably 0.45 or more. The crystalline orientation is preferably 0.55 or less, more preferably 0.50 or less. The crystalline orientation can be determined by wide-angle X-ray diffraction measurement. The more perfectly oriented the crystals, the closer the crystalline orientation value is to 1. Specific methods will be explained in the examples.

[0054] As described above, the separation membrane of the present invention preferably has a longitudinal orientation degree of 1.5 or more and 2.5 or less on the surface side having the functional layer. However, as described above, since the separation membrane of the present invention is mainly composed of a polymer material, it has crystalline and amorphous regions, and the crystalline and amorphous regions each have a different orientation degree. Since the crystalline orientation degree is a value indicating the orientation degree of only the crystalline region, it is a numerical value that contributes to the orientation degree of the separation membrane of the present invention, particularly the surface orientation degree of the separation membrane. However, since the surface orientation degree calculated by the laser Raman spectroscopy and the crystalline orientation degree calculated by the wide-angle X-ray diffraction measurement are different in analytical and calculation methods, it is not possible to perform arithmetic operations on the respective measured values. That is, for example, it is not possible to calculate the contribution of the crystalline orientation degree to the surface orientation degree from the ratio of the surface orientation degree calculated by the measurement to the crystalline orientation degree calculated by the measurement, or to calculate the orientation degree of the amorphous region from the difference between the surface orientation degree and the crystalline orientation degree calculated by the measurement.

[0055] The separation membrane of the present invention preferably has a crystallite size of 10.0 nm or more and 20.0 nm or less. When the crystallite size is 10.0 nm or more, the morphological stability of the separation membrane is good, and when it is 20.0 nm or less, the gas permeability is good. The crystallite size is preferably 14.0 nm or more, more preferably 15.0 nm or more, and even more preferably 17.0 nm or more. The crystallite size is preferably 19.0 nm or less, more preferably 18.0 nm or less. The crystallite size can be determined by wide-angle X-ray diffraction measurement. Specific methods will be described in the examples.

[0056] The separation membrane of the present invention preferably has a crystallinity of 5% to 35% on the surface side having the functional layer. A crystallinity of 5% or more on the surface results in good low leakage properties, while a crystallinity of 35% or less results in good gas permeability. The crystallinity on the surface side is a value determined by infrared spectroscopy (hereinafter sometimes referred to as "IR"), and specific measurement methods will be described in the Examples. The crystallinity on the surface side is more preferably 15% to 30%, even more preferably 20% to 30%, and particularly preferably 25% to 30%.

[0057] The rigid amorphous fraction of the separation membrane of the present invention will be described. Generally, polymers have crystalline and amorphous regions. Among these, the amorphous regions can be classified into mobile amorphous, which exhibits a stepwise endothermic peak accompanied by a change in specific heat capacity at the glass transition point, and rigid amorphous, which does not undergo a change in specific heat capacity under normal conditions. Rigid amorphous may have advanced molecular orientation or may exist as so-called tie molecules connecting crystals. While molecular orientation is thought to be involved in rigid amorphous, the molecular orientation of rigid amorphous differs from the orientation of crystals, and therefore differs from the degree of crystalline orientation described above. This rigid amorphous fraction can be accurately determined from the change in specific heat capacity before and after the glass transition on the TMDSC curve of the reversible component measured by temperature-modulated differential scanning calorimetry (hereinafter referred to as "TMDSC") and the heat of fusion on the DSC curve measured by differential scanning calorimetry (hereinafter referred to as "DSC").

[0058] In the separation membrane of the present invention, the proportion of rigid amorphous poly(4-methyl-1-pentene) (hereinafter referred to as "rigid amorphous proportion") is preferably 20% by mass or more and 40% by mass or less, when the total amount of poly(4-methyl-1-pentene) in the separation membrane is taken as 100% by mass. A rigid amorphous proportion of 20% by mass or more results in good leak resistance, and a rigid amorphous proportion of 40% by mass or less results in good gas permeability. The rigid amorphous proportion is preferably 20% by mass or more and 30% by mass or less, and more preferably 23% by mass or more and 28% by mass or less.

[0059] The separation membrane of the present invention has high gas permeability and N ２ The transmission performance is preferably 1000 GPU to 20000 GPU. ２ The transmission performance is more preferably 3000 GPU or more, and even more preferably 5000 GPU or more. ２ The transmission performance is preferably 15,000 GPU or less, more preferably 10,000 GPU or less, and even more preferably 8,000 GPU or less. The calculation method will be described in detail in the Examples.

[0060] <Method for producing separation membrane> The separation membrane of the present invention is produced through four steps: (1) a preparation step, (2) a spinning step, (3) a washing step, and (4) a drying step, with step (4) being carried out consecutively after step (3). Each step will be explained below. The molded product obtained by the (2) spinning step includes not only a filament-like or hollow fiber-like molded product but also a flat membrane-like molded product.

[0061] (1) Preparation Step: This is a preparation step in which a mixture containing 10% by mass to 50% by mass of poly(4-methyl-1-pentene) and 50% by mass to 90% by mass of a plasticizer is melt-kneaded to obtain a resin composition. In the preparation step to obtain a resin composition, a mixture containing 10% by mass to 50% by mass of PMP and 50% by mass to 90% by mass of the plasticizer is melt-kneaded. The mixture preferably contains 15% by mass to 50% by mass of PMP and 50% by mass to 85% by mass of the plasticizer, more preferably 20% by mass to 45% by mass of PMP and 55% by mass to 80% by mass of the plasticizer, and particularly preferably 25% by mass to 40% by mass of PMP and 60% by mass to 75% by mass of the plasticizer.

[0062] The device used for melt-kneading the mixture may be a mixer such as a kneader, a roll mill, a Banbury mixer, or a single-screw or twin-screw extruder. Among these, a twin-screw extruder is preferred from the viewpoint of improving uniform dispersion of the plasticizer, and a twin-screw extruder with vent holes is more preferred from the viewpoint of removing volatiles such as moisture and low-molecular-weight substances. Furthermore, a twin-screw extruder equipped with a screw having a kneading disk is preferred from the viewpoint of increasing the kneading intensity and improving uniform dispersion of the plasticizer.

[0063] The resin composition obtained in the preparation step may be pelletized, remelted, and used for melt film formation, or may be directly introduced into a die and used for melt film formation. When pelletizing, it is preferable to dry the pellets and use a resin composition with a moisture content of 200 ppm (by mass) or less. By keeping the moisture content at 200 ppm (by mass) or less, deterioration of the resin can be suppressed.

[0064] (2) Spinning Process: This is a spinning process in which the resin composition obtained in the (1) preparation process is discharged from a nozzle and, immediately after passing through an air gap, introduced into a cooling bath of a solvent having a solubility parameter distance Ra for poly(4-methyl-1-pentene) in the range of 4.0 to 14.0 and a solubility parameter distance Rb for the plasticizer in the range of 3.0 to 6.0, to obtain a resin molded product. In the spinning process to obtain a resin composition, a hollow fiber membrane is obtained by utilizing phase separation from a molten mixture of the resin composition of PMP and the plasticizer. As an example, the resin composition obtained in the (1) preparation process is discharged into a gas atmosphere from a nozzle having a double annular nozzle with a gas flow path in the center, and introduced into a cooling bath to phase separate the resin composition and obtain a resin molded product.

[0065] Specifically, the resin composition in a molten state is discharged from the outer tube of a double-tube spinning nozzle, while a hollow-forming gas is discharged from the inner ring of a double-tube spinneret. It is important that the discharge gap of the nozzle is 0.05 mm to 0.30 mm. It is believed that by setting the discharge gap of the nozzle in this range, high shear is applied to the molten resin composition, which makes crystallization more likely to occur. The resin composition thus discharged is allowed to run in air, and then cooled and solidified in a cooling bath to obtain a resin molded product. It is more preferable that the discharge gap of the nozzle be 0.05 mm to 0.20 mm.

[0066] Furthermore, it is preferable that the surface of the resin composition ejected from the nozzle die, on which at least one functional layer is to be formed, be exposed to a gaseous atmosphere that promotes the evaporation of the plasticizer before cooling, i.e., an atmosphere in which the evaporation of the plasticizer can occur. 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 temperature of the nozzle die. In order to control the thickness of the functional layer, it is important that the distance from the nozzle die surface to the solvent surface be 10 mm to 30 mm. In this application, the "distance from the nozzle die surface to the solvent surface" is referred to as the "air gap." The air gap is preferably 10 mm to 20 mm, and more preferably 10 mm to 15 mm.

[0067] Here, we will explain the cooling bath that cools the resin composition discharged from the discharge nozzle. The solvent for the cooling bath is preferably selected based on its affinity with the PMP and the plasticizer. It is preferable to use a solvent for the cooling bath whose three-dimensional Hansen solubility parameter distance Ra to the PMP is in the range of 5 to 13 and whose three-dimensional Hansen solubility parameter distance Rb to the plasticizer is in the range of 4 to 10. It is more preferable to use a solvent whose Ra is in the range of 10 to 12 and whose Rb is in the range of 4 to 6. Having Ra and Rb in the above ranges allows the functional layer to be thinned and improves permeability. When Ra is in the range of 10 to 12 and Rb is in the range of 4 to 6, the functional layer can be particularly thinned, resulting in good permeability.

[0068] The affinity of PMP with a solvent can be estimated by the three-dimensional Hansen solubility parameter. The three-dimensional Hansen solubility parameter is described in Gregory R. [Ind. Eng. Chem. Res. 2011, 50, 3798-3817.] Specifically, the smaller the solubility parameter distance (Ra) in the following formula (1), the higher the affinity of the solvent with PMP.

[0069]

[0070] where δ Ａｄ , δ Ａｐ and δ Ａｈ are the dispersion term, polar term, and hydrogen bonding term of the solubility parameter of PMP, and δ Ｃｄ , δ Ｃｐ and δ Ｃｈ are the dispersion, polar and hydrogen bonding terms of the solubility parameter of the solvent.

[0071] The affinity between a plasticizer and a cooling solvent can be estimated in a similar manner. Specifically, the smaller the solubility parameter distance (Rb) in the following formula (2), the higher the affinity of the solvent for the plasticizer.

[0072]

[0073] where δ Ｂｄ , δ Ｂｐ and δＢｈ are the dispersion term, polar term, and hydrogen bonding term of the solubility parameter of PMP, and δ Ｃｄ , δ Ｃｐ and δ Ｃｈ are the dispersion term, polarity term, and hydrogen bonding term of the solubility parameter of the solvent. When the solvent is a mixed solvent, the solubility parameter of the mixed solvent (δ Ｍｉｘｔｕｒｅ ) can be calculated by the following formula (3).

[0074]

[0075] where φ ｉ , δ ｉ are the volume fraction and solubility parameter of component i, and are valid for the dispersion term, polarity term, and hydrogen bonding term, 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. The three-dimensional Hansen solubility parameter of the solvent was used if described in Gregory R. [Ind. Eng. Chem. Res. 2011, 50, 3798-3817.]. For solvent parameters not described, the values ​​contained in the software "Hansen Solubility Parameters in Practice" developed by Charles Hansen et al. were used. The three-dimensional Hansen solubility parameter of solvents and polymers not described in the above software can be calculated by the Hansen sphere method using the above software.

[0076] When dibutyl phthalate is used as the plasticizer, examples of the solvent used in the cooling bath in the spinning process include cyclohexanone, diethyl phthalate, isophorone, dihexyl phthalate, Benzoflex (registered trademark) manufactured by Eastman Co., 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 monobutyl ether, t-butyl acetate, ethyl 3-ethoxypropionate, propylene glycol monomethyl ether acetate, diacetone alcohol, isopentyl acetate, tri-n-butyl citrate, and ExxonMobil Solvesso (registered trademark) 100 manufactured by Polyethylene Glycol Co., Ltd., 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, propylene glycol monomethyl ether, triethyl citrate, methyl carbitol, ethyl lactate, ethylene glycol monobutyl ether, cyclohexane, methylcyclohexane, dimethylcyclohexane, benzyl alcohol, and dimethyl sulfoxide are preferred, and among these, triacetin is more preferred because its Ra and Rb fall within the more preferred ranges described above.

[0077] In the spinning process for producing the separation membrane of the present invention, the resin composition discharged from the nozzle is wound up by a winding device. In this case, the draft ratio calculated by (winding speed by the winding device) / (discharge speed from the nozzle) is preferably 1 to 10. The draft ratio is more preferably 3 to 6. A draft ratio of 1 or more stabilizes winding and reduces fluctuations in fiber shape. A draft ratio of 10 or less can prevent excessive stretching of the resin composition discharged from the nozzle, thereby preventing defects from occurring on the surface of the hollow fiber membrane.

[0078] (3) Washing Step: If necessary, the obtained resin molded product can be immersed in a solvent that does not dissolve the polymer but is miscible with the plasticizer to extract the plasticizer and increase the porosity. The washing step involves introducing the resin molded product into a solvent whose solubility parameter distance Ra for PMP is in the range of 8 to 35 and whose 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, thereby obtaining a separation membrane. In this process, using a solvent or mixed solvent that has appropriate affinity for both the polymer and the plasticizer ensures good solvent exchange and high washing efficiency.

[0079] When the solubility parameter distance Ra of the cleaning solvent to the PMP is 8 or more, the shape stability of the resin composition is good, and when it is 35 or less, the resin composition swells appropriately, resulting in high cleaning efficiency. The range of Ra is preferably 10 to 25, and particularly preferably 12 to 22. When the solubility parameter distance Rb of the cleaning solvent to the plasticizer is 35 or less, good solvent exchange is achieved, resulting in high cleaning efficiency. The range of Rb is preferably 10 to 25, and particularly preferably 12 to 22.

[0080] When dibutyl phthalate is used as the plasticizer, the solvent used in the washing step may be methyl isobutyl ketone, acetone, butyl glycol acetate, methyl acetate, propylene glycol monoethyl ether acetate, Benzoflex (registered trademark) manufactured by Eastman Co., 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, ethyl acetate ... Preferred are ethylene glycol monobutyl ether, dimethylcyclohexane, benzyl alcohol, dimethyl sulfoxide, propylene carbonate, cyclohexanol, glycerol diacetate, isopentyl alcohol, 2-phenoxyethanol, heptane, acetonitrile, n-amyl alcohol, methyl isobutyl carbinol, 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, and among these, methanol, ethanol, and isopropyl alcohol are more preferred because Ra and Rb are within the particularly preferred ranges described above.

[0081] The resin molded product obtained during the washing process is stretched. In this separation membrane manufacturing method, stretching during the washing process is an important step, and ultimately, a separation membrane with good gas permeability and low leakage is obtained. Generally, stretching resins such as PMP improves the degree of orientation in both the amorphous and crystalline regions. As a result, mechanical properties such as strength, dimensional stability, and transparency are improved due to the orientation, and therefore resin stretching is used in industrial fields such as fiber and film applications. It is known that stretching also improves gas barrier properties. Gas barrier properties refer to the resistance to the passage of gases such as oxygen and nitrogen; in other words, general stretching tends to reduce gas permeability.

[0082] On the other hand, it is known that gas permeability can be improved by stretching under excessive conditions. Excessive conditions refer to stretching at high temperatures, high stretch ratios, and high stretching speeds. In this case, defects such as pores are formed on the resin surface, allowing gas molecules to pass through these defects, resulting in improved gas permeability. While gas permeability is improved, pores are also formed on the surface, allowing liquid molecules to pass through the pores, resulting in reduced leakage. The inventors have discovered that in the manufacturing process of this separation membrane, stretching at a stretching speed of 0.1% / sec to 1.5% / sec and a stretching ratio of 1.3 to 1.9 times in the washing step ultimately results in a separation membrane with excellent gas permeability and low leakage, with no large pores on the membrane surface.

[0083] In the method for producing a separation membrane of the present invention, during the washing step, the resin molded product is immersed in a solvent, so that the separation membrane is covered with the solvent and in a swollen state. During the washing step, the plasticizer is extracted, and the plasticizer present inside the resin molded product diffuses from the inside of the resin molded product to the solvent via the membrane surface. It is speculated that by stretching the swollen resin molded product and causing the plasticizer to diffuse, extremely fine pores are formed on the membrane surface as the plasticizer passes through the membrane surface. Furthermore, as described below, it is speculated that relaxation in the drying step reduces the pore diameter, resulting in a separation membrane with fine pores of less than 3 nm.

[0084] Furthermore, when a swollen resin molded product is stretched to a certain magnification, the degree of orientation of the separation membrane surface increases. This is because the polymer chains in the amorphous regions of the membrane surface are stretched in the stretching direction, resulting in high orientation. On the other hand, the degree of crystalline orientation decreases in the crystalline regions. This is because stretching causes cleavage of the crystals, and the cleaved crystals lose their orientation, resulting in a decrease in the degree of crystalline orientation. At this time, the crystal cleavage reduces the crystallite size, and the starting points of the crystal cleavage can become micropores that are advantageous for gas permeability. If the film is subsequently stretched to an even higher magnification, the degree of orientation of the membrane surface further increases due to the stretching of the amorphous regions, and the crystallite size further decreases due to the crystal cleavage. However, the decreased degree of crystalline orientation begins to increase as the crystals that once lost orientation reorient in the stretching direction.

[0085] In addition, the resin molded product that has become swollen during the washing process has increased flexibility and reduced mechanical strength. Therefore, stretching a swollen resin molded product at high speed may result in irreversible destruction, such as breakage or defect formation. Furthermore, there is a risk of large holes forming when the crystals cleave. For these reasons, it is desirable to stretch the resin molded product at a low stretching speed during the washing process of the separation membrane production process. Specifically, stretching is preferably performed at a stretching speed of 0.1% / sec to 1.5% / sec. A stretching speed exceeding 1.5% / sec may result in irreversible destruction of the resin molded product during the washing process or structural destruction of the functional layer. A stretching speed of less than 0.1% increases the time required for stretching, lengthening the washing process and resulting in a disadvantage from the perspective of productivity. The stretching speed is more preferably 0.2% / sec to 1.0% / sec, and more preferably 0.3% / sec to 0.5% / sec.

[0086] The stretching ratio is preferably 1.3 to 1.9 times. If the stretching ratio is less than 1.3 times, the degree of surface orientation is insufficient, resulting in low strength and the likelihood of defects such as open pores. If the stretching ratio is 1.9 times or more, the degree of surface orientation and crystalline orientation are too high, suppressing the movement of gas molecules on the surface and reducing gas permeability. The stretching ratio is preferably 1.3 to 1.8 times, and more preferably 1.4 to 1.6 times. The temperature of the washing solvent is preferably 10 to 50°C. A temperature of 10°C or higher improves the flexibility of the resin molded product, and a temperature of 50°C or lower maintains the structure of the membrane surface. The temperature of the washing solvent is more preferably 20 to 45°C, and particularly preferably 25 to 40°C.

[0087] An example of a process diagram for the washing step in the production of hollow fiber separation membranes is shown in Figure 3. In Figure 3, a driven roll is used to transport a resin molded product into a washing bath 10 filled with a washing solvent, and the plasticizer contained in the resin molded product is extracted into the solvent. Furthermore, a difference in rotation speed is set between the rolls driven before and after two stretching support rolls 20 located in the washing bath, and stretching is performed in the stretching section shown in Figure 3 due to the difference in transport speed. However, the process of the washing step is not limited to that shown in Figure 3.

[0088] (4) Drying process: This is a process of heating the resin molded product after the washing process, and vaporizing and removing the solvent from the resin molded product that has been swollen with the solvent after the washing process. When the resin molded product is heated, a shrinkage force is generated that causes the resin molded product to shrink, so the drying process is carried out while relaxing the resin molded product to release the shrinkage force.

[0089] The heat treatment may involve transporting the resin molded product on a heated roll, transporting it through a dry heat oven, or placing it in a dry heat oven in a roll wound on a bobbin or paper tube. Relaxation refers to the process of shrinking the resin molded product in the longitudinal direction while gradually relaxing the tension applied to counteract the shrinkage force of the resin molded product. The length of the resin molded product in the longitudinal direction before drying is preferably 1.0 times, and the length after shrinkage is preferably 0.75 to 0.98 times. If the relaxation ratio is less than 0.75 times, the surface orientation of the resin molded product is impaired. If the relaxation ratio exceeds 0.98 times, the release of the shrinkage force is insufficient, making the film surface more susceptible to defects. The relaxation ratio is more preferably 0.80 to 0.95 times, and even more preferably 0.85 to 0.95 times.

[0090] The relaxation rate refers to the change in the longitudinal magnification of the resin molded product per unit time during relaxation, and is preferably 0.1% / second to 5.0% / second. If the relaxation rate is less than 0.1% / second, the contraction force may not be released in time, resulting in defects such as holes on the film surface. If the relaxation rate exceeds 5.0% / second, the relaxation rate significantly exceeds the contraction rate, causing the resin molded product to relax, resulting in poor operability. Furthermore, the relaxation of the resin molded product may result in shape defects, cracks on the film surface, or impaired film surface orientation. The rate is more preferably 0.5% / second to 2.5% / second, more preferably 1.0% / second to 2.0% / second. The drying temperature is preferably 80°C to 200°C, and more preferably 90°C to 150°C. The heat treatment time is preferably 1 second to 600 seconds, more preferably 5 seconds to 300 seconds, and even more preferably 5 seconds to 60 seconds. By carrying out the above steps, the separation membrane of the present invention, which contains PMP as a main component, can be produced.

[0091] An example of a process diagram of the drying step in the production of hollow fiber separation membranes is shown in Figure 4. In Figure 4, a driven roll is used to transport the resin molded product after the washing step in a dry heat oven 11, and the washing solvent clinging to the resin molded product is evaporated and dried. A difference in rotation speed is set between the rolls driven before and after two relaxation support rolls 21 located in the dry heat oven 11, and relaxation is performed in the relaxation section in Figure 4 due to the difference in transport speed. However, the process of the washing step is not limited to that shown in Figure 4.

[0092] <Degassing Membrane Module and Degassing Apparatus> A degassing membrane module is a structural unit that separates gas from liquid. The separation membrane of the present invention obtained as described above can be packed into a case by a known method to form a degassing membrane module. For example, a hollow fiber membrane module comprises a plurality of hollow fiber membranes and a cylindrical case. After bundling a plurality of hollow fiber membranes and inserting them into a cylindrical case, the ends are fixed and sealed to the case with a thermosetting resin such as polyurethane or epoxy resin. The ends of the hollow fiber membranes cured with the thermosetting resin are cut to obtain an open surface of the hollow fiber membrane, and a module is produced.

[0093] In the degassing membrane module equipped with the separation membrane of the present application, the liquid to be treated is water, organic solvents, and mixtures 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, lactates, saturated hydrocarbons, unsaturated hydrocarbons, cyclic saturated hydrocarbons, cyclic unsaturated hydrocarbons, aromatic hydrocarbons, terpenes, ethers, cyclic imides, 3-alkyl-2-oxazolidinones, N-alkylpyrrolidones, lactones, and nitrogen-containing solvents. The liquid may be UV ink or ceramic ink.

[0094] A degassing device is a device used to separate gas from liquid, and refers to a device equipped with a degassing membrane module packed with the present separation membrane. The device configuration is not particularly limited except for the presence of a degassing membrane module packed with the present separation membrane. For example, the device may be equipped with components such as a vacuum pump, a liquid feed pump, and flow path piping.

[0095] The method for producing a liquid from which dissolved gases have been removed is not particularly limited, but is characterized by the use of a degassing apparatus equipped with a degassing membrane module packed with the separation membrane. The configuration of the degassing apparatus and the degassing conditions, such as temperature and flow rate, are not limited. The liquid from which dissolved gases are removed may be 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, lactates, saturated hydrocarbons, unsaturated hydrocarbons, cyclic saturated hydrocarbons, cyclic unsaturated hydrocarbons, aromatic hydrocarbons, terpenes, ethers, cyclic imides, 3-alkyl-2-oxazolidinones, N-alkylpyrrolidones, lactones, and nitrogen-containing solvents. The liquid may be UV ink or ceramic ink.

[0096] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. Each property value in the examples was determined by the following method. [Measurement and evaluation methods] (1) Outer diameter and inner diameter (μm) of hollow fiber membrane After freezing a hollow fiber membrane with liquid nitrogen, stress was applied (using a razor or microtome as necessary), and the exposed cross section was observed under an optical microscope. The average values ​​of the outer diameter and inner diameter at 10 randomly selected points were taken as the outer diameter and inner diameter of the hollow fiber membrane, respectively.

[0097] (2) Hollow ratio (%) of hollow fiber membrane The hollow ratio of the hollow fiber membrane was calculated from the outer diameter and inner diameter determined in (1) above using the following formula: Hollow ratio (%) = [inner diameter (μm ２ )] ２ / [Outer diameter (μm ２ )]２ ×100.

[0098] (3) Functional Layer Thickness (μm) The thickness of the surface layer corresponding to the functional layer portion of the separation membrane was measured as follows. As in (1) above, the separation membrane was frozen with liquid nitrogen, and then stress was applied (using a razor, microtome, or broad ion beam, as necessary) to fracture it so that the radial or longitudinal cross section was exposed. Subsequently, platinum sputtering was performed under the following conditions to pretreat the radial or longitudinal cross section, and then observed at 50,000x magnification using an SEM. When a line was drawn perpendicular to the outer surface from any point on the outer surface of the separation membrane toward the inner surface, the length up to the first pore exceeding 3 nm was determined as the thickness of the membrane surface layer, i.e., the thickness of the functional layer. The pores were extracted after binarizing the analysis image using the image analysis software "ImageJ." The binarization was performed by plotting the distribution of the number of pixels, with the horizontal axis representing the brightness in the analysis image and the vertical axis representing the number of pixels at the corresponding brightness. When the number of pixels at the highest brightness is defined as A, the binarization was performed by matching the lower brightness point to the number of pixels at 1 / 2A. Furthermore, the resulting binarized image was subjected to noise removal (equivalent to Despeckle in ImageJ) once, replacing all pixels with the median value of the 3 x 3 pixels surrounding that pixel. The resulting image was used as the analysis image. Holes were extracted using the Analyze Particles command in ImageJ, and the surface layer thickness was measured from the resulting image. Measurements were performed at 10 arbitrary locations, and the average value was used as the surface layer thickness. (Sputtering) Apparatus: Hitachi High-Technologies Corporation (E-1010) Deposition time: 40 seconds Current value: 20 mA (SEM) Apparatus: Hitachi High-Technologies Corporation (SU1510) Acceleration voltage: 5 kV Probe current: 30.

[0099] (4) Evaluation of the surface pore diameter (nm) and leakage property of micropores on the surface The surface of the separation membrane was pretreated by sputtering with platinum. When observed at 50,000 times magnification using an SEM, pores with a diameter of more than 3 nm, i.e., pores with an area of ​​7.1 nm ２All larger pores were extracted, and the pore diameters were calculated from their areas assuming the pores were perfect circles, and the average value was used as the surface pore diameter. The pores were extracted using the image analysis software "ImageJ" after binarizing the analysis image (Huang binarization). Furthermore, the obtained binarized image was subjected to noise removal (equivalent to Despeckle in ImageJ) once, replacing all pixels with the median value of the 3 × 3 pixels surrounding that pixel, and the image was used as the analysis image. The pores were extracted using the Analyze Particles command in ImageJ, and the surface pore diameter was calculated from the area of ​​the obtained pores. Measurements were performed at any five locations, and the average value was used as the surface pore diameter of the micropores on the membrane surface. If pores with a diameter larger than 3 nm could not be extracted, the surface pore diameter was set to less than 3 nm. The leakage resistance was evaluated as "good" when the average pore size on the surface of the separation membrane was less than 3 nm, and as "poor" when the average pore size was 3 nm or more.

[0100] (5) Surface Structure The surface structure of the separation membrane was determined from (3) the thickness of the membrane surface layer, i.e., the thickness of the functional layer, and (4) the average pore size of the micropores on the surface. If (3) the thickness of the membrane surface layer was within the range of 0.1 to 2.0 μm and (4) the average pore size of the micropores on the surface was less than 3 nm, the surface structure was judged to have a "functional layer present," and otherwise was judged to have a "functional layer absent."

[0101] (6) Porosity (%) of 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 that had been vacuum dried at 25°C for 8 hours were measured. １ was calculated from the following formula using the outer diameter (mm) and inner diameter (mm) measured in (1) above. １ =M / [π×{(outer diameter / 2) ２ - (inner diameter / 2) ２}×L] The porosity ε (%) was calculated from the following formula: ε=1−ρ １ / ρ ２ where ρ ２ is the density of the polymer.

[0102] (7) Surface Orientation The orientation of the hollow fibers was measured by laser Raman spectroscopy using a RENISHAW inVia. Measurement mode: Microscopic Raman Objective lens: ×20 Beam diameter: 5 μm Light source: Semiconductor laser 532, 785 nm Laser power: 300 mW Diffraction grating: Single -3000, 1200 gr / mm Slit: 65 μm Detector: CCD / RENISHAW 1024 × 256 In this analysis, the 845 cm- 1 and 790 cm －１ The degree of orientation of the PMP molecular chains in the fiber axis direction was calculated using the Raman band intensity ratio of the two. The higher the degree of orientation in the fiber axis direction, the larger the value of this degree of orientation, and when there is no orientation, it is 1. Orientation degree = (I845P / I790P) / (I845V / I790V) I845P: 845 cm in a polarization configuration parallel to the fiber axis direction －１ Intensity of Raman band I790P: 790 cm in polarization configuration parallel to the fiber axis direction －１ Raman band intensity I845V: 845 cm in polarization configuration perpendicular to the fiber axis －１ Raman band intensity I790V: 790 cm in polarization configuration perpendicular to the fiber axis －１ Raman band intensity.

[0103] (8) Surface Crystallinity (%) Using a BioRad DIGILAB FTIR (FTS-55A) equipped with a single-reflection ATR attachment, ATR spectrum measurement was performed on the surface of a hollow fiber membrane that had been vacuum dried at 25°C for 8 hours. A diamond prism was used as the ATR crystal, and the measurement was performed at an incident angle of 45° and an accumulation number of 64 times. From the obtained ATR spectrum, the crystallinity was calculated using the intensity ratio of a predetermined band. In the case of a PMP hollow fiber membrane, the crystallinity was calculated using the intensity ratio of a predetermined band. －１ The band intensity around 1169 cm －１ The IR intensity ratio of the surface was calculated using the band intensities around 849 cm using the following formula: －１ Band intensity around 1169 cm －１ Crystallinity (%) = 172.9 x IR intensity ratio of the surface.

[0104] (9) Ratio of Rigid Amorphous Crystals Measurement was performed on a cut-out sample of the separation membrane. A temperature-modulated differential scanning calorimeter: Q1000 manufactured by TA Instruments was used to perform TMDSC measurement of the separation membrane under the following conditions. Data processing was performed using Universal Analysis 2000 manufactured by TA Instruments. Atmosphere: Nitrogen flow (50 mL / min) Temperature and calorific value correction: High-purity indium (T ｍ =156.61℃, ΔH ｍ = 28.71 J / g) Temperature range: from about -40°C to 100°C Heating rate: 2°C / min Sample amount: about 5 mg Sample container: aluminum standard container From the TMDSC curve of the reversible component, the specific heat difference (ΔC ｐ ) was determined, and the mobile amorphous fraction (MA) was calculated based on the following formula: The following formula is described in Thermal Analysis of Polymeric Materials, Springer, 2005, p. 780.

[0105] MA (mass%) = ΔC ｐ / ΔC ｐ ０ × 100 where ΔC ｐ ０ is the specific heat difference before and after the glass transition of the completely amorphous PMP. Next, the separation membrane was subjected to DSC measurement under the following temperature conditions using a Q100 manufactured by TA Instruments, and the heat of fusion (ΔH ｍ Temperature range: about 20°C to 300°C Heating rate: 10°C / min From the DSC curve, the heat of fusion (ΔH ｍ ) was measured, and the crystallinity ratio (C) was calculated based on the following formula: C (mass%) = ΔH ｍ / ΔH ｍ ０ × 100 where ΔH ｍ ０ is the heat of fusion of completely amorphous PMP. Using the obtained mobile amorphous fraction (MA) and crystallinity fraction (C), the rigid amorphous fraction (RA) was calculated according to the following formula: RA (mass%) = 100 - (MA + C).

[0106] (10) Gas Permeability (GPU) A small module with an effective length of 100 mm was prepared, consisting of three hollow fiber membranes. Specifically, three hollow fiber membranes were bundled and inserted into a plastic pipe, which was a cylindrical case. The gaps between the membranes and the pipe at the end of the hollow fiber membrane bundle were sealed by curing a thermosetting resin. The end of the sealed hollow fiber membrane was cut to obtain an open surface of the hollow fiber membrane, and a small module for evaluation was prepared. Using this small module, the gas permeation flow rate was measured. Nitrogen alone was used as the measurement gas for evaluation, and the pressure change on the permeation side of nitrogen per unit time was measured using an external pressure system at a measurement temperature of 37°C in accordance with the pressure sensor method of JIS K7126-1 (2006). The pressure difference between the supply side and the permeation side was set to 100 kPa. The gas temperature was 37°C. A differential pressure of 100 kPa means that the pressure difference between the gas supply side and the gas permeation side of the separation membrane is 100 kPa. The gas permeation flow rate Q was calculated using the following formula and used as the gas permeation performance. Permeation rate Q (GPU) = 10 －６ [Permeation gas amount (cm ３ )] / [Membrane area (cm ２ ) × time (s) × pressure difference (cmHg)].

[0107] (11) Measurement of Crystal Orientation and Crystallite Size The crystal orientation and crystallite size were measured by wide-angle X-ray diffraction. The separation membrane was placed on a sample holder, and wide-angle X-ray diffraction was performed by irradiating X-rays. X-ray diffractometer: D8 DISCOVER μHR Hybrid manufactured by Bruker AXS. X-ray source: CuKα ray (using multilayer mirror). Wavelength λ = 0.15418 nm. Output: 50 kV, 22 mA. Slit system: 1 mm. ２ -1 mm ２ -100 μmΦ Detector: 2-dimensional detector (Vantec500) Scan: 2θ=0° Camera length: approximately 100 mm Scan speed: 1800 seconds / frame The crystallite size L (nm) was calculated from the half-width of each peak in the 2θ profile obtained by wide-angle X-ray diffraction measurement using the following Scherrer formula.

[0108] L=K λ / βCOSθ β=(β ｅ ２ -β ０ ２ )１／２ where λ is the incident X-ray wavelength (=0.15418 nm), and β e : half-width of the diffraction peak (°), β0: correction value of half-width (=0.25°), K: Scherrer constant (=0.9). From the obtained two-dimensional wide-angle X-ray diffraction image, the diffraction intensity was cut out in the circumferential direction to create an orientation profile. The minimum value of the orientation profile was used as the baseline, and the degree of crystalline orientation was evaluated from the half-width H (°) ​​of the profile on the baseline using the following formula: Crystal orientation degree = (180 - H) / 180. Examples and comparative examples are shown below.

[0109] (Example 1) The PMP raw material was TPX (registered trademark) DX845 (density: 833 kg / m) manufactured by Mitsui Chemicals, Inc. ３ , MFR: 9.0 g / 10 min). 35% by mass of PMP and 65% by mass of dibutyl phthalate as a plasticizer were fed into a twin-screw extruder, melt-kneaded at 290 ° C, and then introduced into a melt spinning pack set at a spinning temperature of 245 ° C., and spun downward from the outer annular portion of a nozzle having one nozzle hole (double cylindrical type, nozzle hole diameter 1.2 mm, discharge gap 0.20 mm). The spun hollow fiber was introduced into a triacetin cooling bath and wound with a winder so that the draft ratio was 4.7. At this time, the air gap was set to 10 mm. Here, a metal filter with a diameter of 100 μm was used as the filter in the melt spinning pack. The wound hollow fiber was washed in isopropyl alcohol while being stretched to a stretch ratio of 1.3 at a stretching rate of 0.2% / sec, and then dried in a drying oven at 100°C while being relaxed from the isopropyl alcohol-swollen state to a relaxation ratio of 0.90 at a relaxation rate of 1.3% / sec. The physical properties of the obtained hollow fiber membrane are shown in Table 1. The obtained hollow fiber membrane had a functional layer on the outer surface of the separation membrane, mainly composed of PMP, a porosity of 61%, a degree of orientation of 1.7, a degree of crystalline orientation of 0.50, a crystallite size of 19.1 nm, a surface crystallinity of 28%, a proportion of rigid amorphous of 21%, and N ２ The permeability was 2523 GPU. The average pore size on the surface of the separation membrane was less than 3 nm, showing good low leakage and high gas permeability. The results are shown in Table 1.

[0110] (Example 2) A hollow fiber membrane was obtained in the same manner as in Example 1, except that a washing step was carried out while stretching the membrane to a stretch ratio of 1.5 at a stretching speed of 0.3% / sec. The obtained hollow fiber membrane had a functional layer on the outer surface, a porosity of 65%, a degree of orientation of 1.8, a degree of crystalline orientation of 0.45, a crystallite size of 17.6 nm, a surface crystallinity of 26%, a proportion of rigid amorphous of 23%, and N ２ The permeability was 5837 GPU. The average pore size on the surface of the separation membrane was less than 3 nm, demonstrating good low leakage. The results are shown in Table 1.

[0111] (Example 3) A hollow fiber membrane was obtained in the same manner as in Example 1, except that a washing step was carried out while stretching the membrane to a stretch ratio of 1.5 at a stretching speed of 0.8% / sec. The obtained hollow fiber membrane had a functional layer on the outer surface, a porosity of 65%, a degree of orientation of 1.9, a degree of crystalline orientation of 0.46, a crystallite size of 17.6 nm, a surface crystallinity of 25%, a rigid amorphous ratio of 24%, and N ２ The permeability was 4016 GPU. The average pore size on the surface of the separation membrane was less than 3 nm, demonstrating good low leakage. The results are shown in Table 1.

[0112] (Example 4) A hollow fiber membrane was obtained in the same manner as in Example 1, except that a washing step was carried out while stretching the membrane to a stretch ratio of 1.5 at a stretching speed of 0.3% / sec, and then drying was carried out while relaxing the membrane to a relaxation ratio of 0.90 at a relaxation speed of 2.4% / sec in a drying oven at 100°C. The obtained hollow fiber membrane had a functional layer on the outer surface, a porosity of 63%, a degree of orientation of 1.8, a crystalline orientation of 0.45, a crystallite size of 17.3 nm, a surface crystallinity of 26%, a rigid amorphous ratio of 23%, and N ２ The permeability was 4621 GPU. The average pore size on the surface of the separation membrane was less than 3 nm, demonstrating good low leakage. The results are shown in Table 1.

[0113] (Example 5) A hollow fiber membrane was obtained in the same manner as in Example 1, except that a washing step was carried out while stretching the membrane to a stretch ratio of 1.5 at a stretching speed of 0.3% / sec, and then drying was carried out while relaxing the membrane in a drying oven at 100°C at a relaxation speed of 0.6% / sec to a relaxation ratio of 0.90. The obtained hollow fiber membrane had a functional layer on the outer surface, a porosity of 65%, a degree of orientation of 1.8, a crystalline orientation of 0.44, a crystallite size of 17.7 nm, a surface crystallinity of 27%, a rigid amorphous ratio of 23%, and N ２ The permeability was 4511 GPU. The average pore size on the surface of the separation membrane was less than 3 nm, demonstrating good low leakage. The results are shown in Table 1.

[0114] (Example 6) A hollow fiber membrane was obtained in the same manner as in Example 1, except that a washing step was carried out while the membrane was stretched to a stretch ratio of 1.8 at a stretching speed of 0.5% / sec. The obtained hollow fiber membrane had a functional layer on the outer surface, a porosity of 66%, a degree of orientation of 2.0, a degree of crystalline orientation of 0.54, a crystallite size of 15.1 nm, a degree of surface crystallinity of 25%, a proportion of rigid amorphous of 25%, and N ２ The permeability was 3537 GPU. The average pore size on the surface of the separation membrane was less than 3 nm, demonstrating good low leakage. The results are shown in Table 1.

[0115] (Example 7) A hollow fiber membrane was obtained in the same manner as in Example 1, except that a washing step was carried out while stretching the membrane to a stretch ratio of 1.5 at a stretching speed of 0.3% / sec, and then drying was carried out while relaxing the membrane to a relaxation ratio of 0.96 at a relaxation speed of 1.3% / sec in a drying oven at 100°C. The obtained hollow fiber membrane had a functional layer on the outer surface, a porosity of 66%, a degree of orientation of 1.9, a crystalline orientation of 0.46, a crystallite size of 17.1 nm, a surface crystallinity of 26%, a rigid amorphous ratio of 23%, and N ２ The permeability was 4343 GPU. The average pore size on the surface of the separation membrane was less than 3 nm, demonstrating good low leakage. The results are shown in Table 2.

[0116] (Example 8) A hollow fiber membrane was obtained in the same manner as in Example 1, except that a washing step was carried out while stretching the membrane to a stretch ratio of 1.5 at a stretching speed of 0.3% / sec, and then drying was carried out while relaxing the membrane to a relaxation ratio of 0.85 at a relaxation speed of 1.3% / sec in a drying oven at 100°C. The obtained hollow fiber membrane had a functional layer on the outer surface, a porosity of 64%, a degree of orientation of 1.8, a crystalline orientation of 0.45, a crystallite size of 17.6 nm, a surface crystallinity of 26%, a rigid amorphous ratio of 23%, and N ２ The permeability was 6200 GPU. The average pore size on the surface of the separation membrane was less than 3 nm, demonstrating good low leakage. The results are shown in Table 2.

[0117] (Example 9) A hollow fiber membrane was obtained in the same manner as in Example 1, except that the hollow fiber membrane was wound on a winder to a draft ratio of 3.5, and a washing step was carried out while stretching the membrane to a stretch ratio of 1.5 at a stretching speed of 0.3% / sec. The obtained hollow fiber membrane had a functional layer on the outer surface, a porosity of 60%, a degree of orientation of 1.7, a crystalline orientation of 0.48, a crystallite size of 18.7 nm, a surface crystallinity of 29%, a rigid amorphous ratio of 21%, and N ２ The permeability was 4311 GPU. The average pore size on the surface of the separation membrane was less than 3 nm, demonstrating good low leakage. The results are shown in Table 2.

[0118] (Example 10) A hollow fiber membrane was obtained in the same manner as in Example 1, except that 40% by mass of PMP and 60% by mass of dibutyl phthalate as a plasticizer were fed into a twin-screw extruder and stretched to a stretch ratio of 1.5 at a stretching speed of 0.3% / sec, while a washing step was carried out. The obtained hollow fiber membrane had a functional layer on the outer surface, a porosity of 63%, a degree of orientation of 1.9, a degree of crystalline orientation of 0.48, a crystallite size of 17.0 nm, a surface crystallinity of 29%, a proportion of rigid amorphous of 27%, and N ２ The permeability was 5110 GPU. The average pore size on the surface of the separation membrane was less than 3 nm, demonstrating good low leakage. The results are shown in Table 2.

[0119] (Example 11) A hollow fiber membrane was obtained in the same manner as in Example 1, except that the membrane was wound on a winder to a draft ratio of 5.0, and was stretched to a stretch ratio of 1.5 at a stretching speed of 0.3% / sec while undergoing a washing process, and then was dried in a drying oven at 100°C while relaxing to a relaxation ratio of 0.96 at a relaxation speed of 1.3% / sec. The obtained hollow fiber membrane had a functional layer on the outer surface, a porosity of 63%, a degree of orientation of 2.0, a crystalline orientation of 0.49, a crystallite size of 16.9 nm, a surface crystallinity of 25%, a rigid amorphous ratio of 24%, and N ２ The permeability was 4343 GPU. The average pore size on the surface of the separation membrane was less than 3 nm, demonstrating good low leakage. The results are shown in Table 2.

[0120] (Example 12) A hollow fiber membrane was obtained in the same manner as in Example 1, except that the membrane was wound on a winder to a draft ratio of 3.5, and was stretched to a stretch ratio of 1.3 at a stretching rate of 0.2% / sec while undergoing a washing process, and then was dried in a drying oven at 100°C while relaxing to a relaxation ratio of 0.90 at a relaxation rate of 1.3% / sec. The obtained hollow fiber membrane had a functional layer on the outer surface, a porosity of 58%, a degree of orientation of 1.6, a crystalline orientation of 0.51, a crystallite size of 19.3 nm, a surface crystallinity of 31%, a proportion of rigid amorphous of 19%, and N ２ The permeability was 1912 GPU. The average pore size on the surface of the separation membrane was less than 3 nm, demonstrating good low leakage. The results are shown in Table 2.

[0121] (Comparative Example 1) A hollow fiber membrane was obtained in the same manner as in Example 1, except that no stretching was performed during the washing process, i.e., the washing process was performed at a stretching ratio of 1.0, and then no relaxation was performed during the drying process, i.e., the drying process was performed at a relaxation ratio of 1.0. The obtained hollow fiber membrane had pores with an average pore size of 18 nm on the outer surface and did not have a functional layer. In addition, the porosity was 51%, the degree of orientation was 1.4, the degree of crystalline orientation was 0.55, the crystallite size was 20.1 nm, the degree of surface crystallinity was 32%, and the proportion of rigid amorphous was 20%. ２ The permeability was 411 GPU. Because the average pore size on the surface of the separation membrane was 3 nm or more, the low leakage property was poor and the gas permeability was also insufficient. The results are shown in Table 3.

[0122] Comparative Example 2 A hollow fiber membrane was obtained in the same manner as in Example 1, except that stretching was not performed during the washing step, i.e., the washing step was performed at a stretch ratio of 1.0. The obtained hollow fiber membrane had a functional layer on the outer surface, a porosity of 50%, an orientation degree of 1.4, a crystalline orientation degree of 0.57, a crystallite size of 20.2 nm, a surface crystallinity of 32%, and a rigid amorphous ratio of 20%. ２ The permeability was 120 GPU. The gas permeability was insufficient. The results are shown in Table 3.

[0123] (Comparative Example 3) A hollow fiber membrane was obtained in the same manner as in Example 1, except that a washing step was carried out while stretching the membrane to a stretch ratio of 1.1 at a stretching speed of 0.2% / sec. The obtained hollow fiber membrane had pores with an average pore size of 32 nm on the outer surface and did not have a functional layer. In addition, the porosity was 55%, the degree of orientation was 1.5, the degree of crystalline orientation was 0.53, the crystallite size was 20.1 nm, the degree of surface crystallinity was 29%, and the proportion of rigid amorphous was 21%. ２ The permeability was 5085 GPU. Because the average pore size on the surface of the separation membrane was 3 nm or more, the low leakage property was poor and the gas permeability was also insufficient. The results are shown in Table 3.

[0124] Comparative Example 4 A hollow fiber membrane was obtained in the same manner as in Example 1, except that a washing step was carried out while the membrane was stretched to a stretch ratio of 2.0 at a stretching speed of 0.5% / sec. The obtained hollow fiber membrane had a functional layer on the outer surface, a porosity of 67%, a degree of orientation of 2.3, a degree of crystalline orientation of 0.63, a crystallite size of 13.4 nm, a surface crystallinity of 25%, and a rigid amorphous ratio of 27%. ２ The permeability was 238 GPU. The gas permeability was insufficient. The results are shown in Table 3.

[0125] (Comparative Example 5) After the same procedure as in Example 1, the hollow fiber membrane was stretched in the washing step at a stretching speed of 2.0% / sec to a stretch ratio of 1.5. However, the hollow fiber-shaped resin molding broke during stretching, and no hollow fiber membrane was obtained. The results are shown in Table 3.

[0126] (Comparative Example 6) A hollow fiber membrane was obtained in the same manner as in Example 1, except that relaxation was not performed during the drying process, i.e., the drying process was performed at a relaxation ratio of 1.0. The obtained hollow fiber membrane had pores with an average pore size of 26 nm on the outer surface of the separation membrane and did not have a functional layer. In addition, the porosity was 62%, the degree of orientation was 1.7, the degree of crystalline orientation was 0.48, the crystallite size was 19.7 nm, the degree of surface crystallinity was 29%, and the proportion of rigid amorphous was 21%. ２ The permeability was 3521 GPU. Since the average pore size on the surface of the separation membrane was 3 nm or more, the low leakage performance was poor. The results are shown in Table 3.

[0127] (Comparative Example 7) A hollow fiber membrane was obtained in the same manner as in Example 1, except that the draft ratio in the resin spinning step was set to 231, the washing step was performed at a draw ratio of 1.0, and the drying step was performed at a relaxation ratio of 1.0. The obtained hollow fiber membrane had a functional layer on the outer surface of the separation membrane, a porosity of 51%, a degree of orientation of 1.8, a degree of crystalline orientation of 0.51, a crystallite size of 20.1 nm, a surface crystallinity of 29%, a proportion of rigid amorphous of 23%, and N ２ The permeability was 30 GPU. The gas permeability was insufficient. The results are shown in Table 4.

[0128] Comparative Example 8: 100% by mass of PMP was fed into a twin-screw extruder, melt-kneaded at 290°C, and then introduced into a melt spinning pack set at a spinning temperature of 245°C. The hollow fiber was spun downward from the outer annular portion of the nozzle having one nozzle hole (double cylindrical type, nozzle hole diameter 1.2 mm, nozzle gap 0.20 mm). The spun hollow fiber was introduced into a triacetin cooling bath and wound with a winder to a draft ratio of 750. The air gap 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 fiber was stretched in air at a stretching rate of 0.5% / sec to a stretch ratio of 2.0, while undergoing a washing process. Subsequently, it was dried in a drying oven at 100°C while relaxing at a relaxation rate of 1.3% / sec to a relaxation ratio of 0.90. The obtained hollow fiber membrane had pores with an average pore diameter of 42 nm on the outer surface and did not have a functional layer. The porosity was 18%, the degree of orientation was 3.2, the degree of crystalline orientation was 0.82, the crystallite size was 9.4 nm, the degree of surface crystallinity was 25%, and the proportion of rigid amorphous was 42%. ２ The permeability was 3111 GPU. Since the average pore size on the surface of the separation membrane was 3 nm or more, the low leakage performance was poor. The results are shown in Table 4.

[0129] (Comparative Example 9) A hollow fiber membrane was obtained in the same manner as in Example 1, except that the draft ratio in the resin spinning step was set to 5.0 and the washing step was performed at a draw ratio of 1.0. The obtained hollow fiber membrane had a functional layer on the outer surface of the separation membrane, a porosity of 53%, an orientation degree of 1.7, a crystalline orientation degree of 0.64, a crystallite size of 21.5 nm, a surface crystallinity of 30%, and a rigid amorphous ratio of 21%. ２ The permeability was 321 GPU. The gas permeability was insufficient. The results are shown in Table 4.

[0130] (Comparative Example 10) A hollow fiber membrane was obtained in the same manner as in Example 1, except that a washing step was carried out while stretching the membrane to a stretch ratio of 1.3 at a stretching speed of 2.0% / sec. The obtained hollow fiber membrane had pores with an average pore size of 25 nm on the outer surface and did not have a functional layer. In addition, the porosity was 62%, the degree of orientation was 1.7, the degree of crystalline orientation was 0.49, the crystallite size was 19.6 nm, the degree of surface crystallinity was 29%, and the proportion of rigid amorphous was 21%. ２The permeation performance was 2567 GPU. Since the average pore size on the surface of the separation membrane was 3 nm or more, the low leakage performance was poor. The results are shown in Table 4.

[0131] (Comparative Example 11) The same procedure as in Example 1 was carried out, except that the relaxation rate was 6.0% / sec. During the drying process, relaxation occurred in the resin molded product, but the drying process was completed despite the relaxation, and a hollow fiber membrane was obtained. The obtained hollow fiber membrane had pores with an average pore size of 12 nm on the outer surface and did not have a functional layer. In addition, the porosity was 62%, the degree of orientation was 1.4, the degree of crystalline orientation was 0.52, the crystallite size was 19.7 nm, the degree of surface crystallinity was 28%, and the proportion of rigid amorphous was 21%. ２ The permeability was 380 GPU. Since the average pore size on the surface of the separation membrane was 3 nm or more, the low leakage performance was poor. The results are shown in Table 4.

[0132] (Comparative Example 12) A hollow fiber membrane was obtained in the same manner as in Example 1, except that the relaxation rate was 0.05% / sec. The obtained hollow fiber membrane had pores with an average pore size of 16 nm on the outer surface and did not have a functional layer. In addition, the porosity was 61%, the degree of orientation was 1.7, the degree of crystalline orientation was 0.48, the crystallite size was 19.7 nm, the degree of surface crystallinity was 28%, and the proportion of rigid amorphous was 21%. ２ The permeability was 398 GPU. Since the average pore size on the surface of the separation membrane was 3 nm or more, the low leakage performance was poor. The results are shown in Table 4.

[0133]

[0134]

[0135]

[0136]

[0137] The separation membrane of the present invention can be suitably used for separating gas from liquid or adding gas to liquid. For example, it can be suitably used as a degassing membrane for reducing the amount of dissolved gas in water, aqueous solutions, organic solvents, and resist solutions in semiconductor production lines, liquid crystal color filter production lines, and inkjet printer ink production, and as a gas exchange membrane in medical applications such as an artificial lung. In particular, as a degassing membrane, it is very useful for degassing photoresist solutions and developers used in lithography in semiconductor production lines.

[0138] REFERENCE SIGNS LIST 1 membrane surface 2 functional layer 3 void portion 4 thickness of functional layer 5 inner layer 6 virtual fluctuation curve of functional layer 10 cleaning bath 11 dry heat oven 20 stretching support roll 21 relaxation support roll

Claims

1. A separation membrane whose main component is poly(4-methyl-1-pentene), wherein the porosity of the entire separation membrane is 30% to 70%, and the separation membrane has a functional layer on at least one surface side, wherein an orientation direction exists within the surface plane of the functional layer such that the orientation degree is in the range of 1.5 to 2.5, and the crystalline orientation degree measured by wide-angle X-ray diffraction on the surface of the functional layer of the separation membrane is 0.20 to 0.60, and the crystallite size on the surface of the functional layer of the separation membrane is 10 nm to 20 nm.

2. The separation membrane according to claim 1, wherein the degree of crystallinity on the surface of the functional layer of the separation membrane is 5% to 35%.

3. The separation membrane according to claim 1 or 2, wherein the rigid amorphous content of the separation membrane is 20% by mass to 40% by mass.

4. N at 100 kPa of the separation membrane ２ The separation membrane according to any one of claims 1 to 3, having a permeability of 1,000 GPU to 20,000 GPU.

5. A separation membrane described in any one of claims 1 to 4, wherein the separation membrane is hollow fiber shaped, the longitudinal orientation degree on the surface of the functional layer is 1.5 or more and 2.5 or less, the crystalline orientation degree on the surface of the functional layer measured by wide-angle X-ray diffraction is 0.20 or more and 0.60 or less, and the crystallite size on the surface of the functional layer is 10 nm or more and 20 nm or less.

6. The separation membrane according to claim 5, wherein the outer surface of the hollow fiber separation membrane is the functional layer.

7. A degassing membrane module comprising a case and the separation membrane according to any one of claims 1 to 6, wherein the separation membrane is packed in the case.

8. A degassing device comprising the degassing membrane module according to claim 7.

9. A method for producing a liquid, which comprises removing dissolved gases from a liquid to be treated using a degassing membrane module equipped with the separation membrane according to any one of claims 1 to 6.

10. A method for producing a hollow fiber separation membrane, comprising the following steps (1) to (4), with step (4) being carried out continuously after step (3): (1) a preparation step of melt-kneading a resin mixture containing 10% to 50% by mass of poly(4-methyl-1-pentene) and 50% to 90% by mass of a plasticizer to obtain a resin composition; (2) a spinning step of melting the resin composition, discharging it from a discharge nozzle, cooling it in a cooling bath, and winding it up at a draft ratio of 1 to 10 to obtain a resin molded product; and (3) a washing step of stretching the resin molded product in a washing bath to 1.3 to 1.9 times its original size at a stretching speed of 0.1% / sec to 1.5% / sec, while extracting the plasticizer into a solvent. (4) A drying step in which the washed resin molded product is dried while being relaxed to 0.75 to 0.98 times its original size at a relaxation rate of 0.1% / second to 5.0% / second when heated.

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