Separation membrane and manufacturing method therefor

Abstract

The present invention uses poly(4-methyl-1-pentene), which is excellent in chemical resistance and gas permeability, to provide a separation membrane having high strength and low leakage while maintaining high gas permeability. Provided is a separation membrane having poly(4-methyl-1-pentene) as a main component. The poly(4-methyl-1-pentene) in the separation membrane has a rigid amorphous fraction RA of 43-60%, inclusive, the separation membrane having a porosity of 30-70%, inclusive, and a dense layer on at least one surface.

Description

Separation membrane and method for producing the same

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

[0002] Hollow fiber membranes are used as a degassing method for removing dissolved gases from liquids and as a gas exchange method for exchanging dissolved gases in liquids with gas components in the gas phase. Hollow fiber membranes used in these applications are required to have solvent resistance to the liquid being treated and high gas permeability, and poly(4-methyl-1-pentene), which has excellent properties in these areas, is sometimes used as a membrane material. Among these hollow fiber membranes, membranes having a thin, dense surface layer of 2.0 μm or less are desirable because they can increase the gas permeation flow rate across the entire membrane.

[0003] On the other hand, separation membranes having such a thin dense layer on the surface are not suitable for production by stretching because stretching causes through-holes to form in the thin dense layer, which cause leakage of the solution. Furthermore, the support layer located inside the surface layer of the separation membrane is a layer with multiple voids, and its strength is low due to its high porosity.

[0004] In recent years, there has been a demand for separation membranes with high permeability and high strength. Various methods have been proposed to obtain gas-permeable membranes that have high permeability or high strength and low leakage. Low leakage refers to the resistance to leakage of liquid when removing dissolved gas from a liquid or when exchanging dissolved gas with a gas component in a liquid.

[0005] For example, Patent Document 1 discloses a dry-wet solution method using a polyolefin polymer. Specifically, in Patent Document 1, a polymer solution obtained by dissolving a polyolefin polymer in a good solvent is extruded through a die at a temperature higher than the melting point of the polyolefin resin, and the polymer solution is brought into contact with a cooled solvent to form an asymmetric structure having a dense layer on one surface by thermally induced phase separation. However, the membrane in Patent Document 1 is not stretched, and has the problem of insufficient strength. Furthermore, in order to prevent the pores in the dense layer from becoming larger due to stretching, the stretching should not exceed 10%, and there is a disadvantage that stretching can only be performed at a low ratio.

[0006] Patent Document 2 discloses a hollow fiber membrane produced by a melting method. Specifically, a polyolefin resin is extruded through a die at a temperature above its melting point, cooled and solidified, and then stretched to partially cleave the resin and open the interior, forming a dense surface layer and a porous interior. This method produces a membrane with high strength and low leakage, but has the disadvantage of insufficient gas permeability due to the low porosity of the structure.

[0007] International Publication No. 2003 / 061812 JP 7-155569

[0008] It is difficult to achieve high strength while maintaining practical gas permeability and low leakage with the separation membrane of Patent Document 1. Furthermore, the separation membrane obtained in Patent Document 2 has high strength and low leakage, but has insufficient porosity and does not have sufficient gas permeability.

[0009] In view of the problems of the conventional technology described above, the present inventors have an object to provide a separation membrane that has high strength and low leakage while maintaining high gas permeability, by using poly(4-methyl-1-pentene), which has excellent chemical resistance and gas permeability.

[0010] As a result of intensive research to solve the above problems, the present inventors have found that a separation membrane containing poly(4-methyl-1-pentene) as a main component and having a dense layer on at least one surface, in which the rigid amorphous fraction RA of poly(4-methyl-1-pentene) in the membrane is within a specific range and the porosity is within a specific range, can maintain high gas permeability while also having high strength and low leakage, and have completed the present invention.

[0011] That is, the separation membrane is composed primarily of poly(4-methyl-1-pentene), and has a rigid amorphous fraction (RA) of 43% to 60% of the poly(4-methyl-1-pentene) in the separation membrane, as defined by Formula 1, and has a porosity of 30% to 70% of the entire separation membrane, and has a dense layer on at least one surface side of the separation membrane: RA(%)=100-(MA+C) Formula 1 where MA is the mobile amorphous fraction and C is the crystallinity.

[0012] The separation membrane is the separation membrane described above, in which the loss modulus (E") has a peak in the temperature range of 30.0°C to 50.0°C in a temperature-loss modulus (E") curve obtained by a dynamic viscoelasticity test.

[0013] According to the present invention, a separation membrane having high strength and low leakage while maintaining high gas permeability is provided by using poly(4-methyl-1-pentene), which has excellent chemical resistance and gas permeability.

[0014] 1 is an example of an image of a cross section cut in the thickness direction of a separation membrane captured by an SEM. FIG. 2 is an image obtained by binarizing the image of FIG. 1 and removing noise. FIG. 3 is a schematic diagram showing a method for obtaining the thickness of a dense layer from an image. FIG. 4 is a two-dimensional diffraction image of wide-angle X-rays of a hollow fiber membrane. FIG. 5 is a diagram showing the intensity distribution in the azimuthal angle direction at 2θ=9.7° of a hollow fiber membrane.

[0015] The separation membrane of the present invention is a separation membrane containing poly(4-methyl-1-pentene) as a main component, characterized in that the rigid amorphous fraction RA of the poly(4-methyl-1-pentene) in the separation membrane is 43% or more and 60% or less, the porosity is 30% or more and 70% or less, and the separation membrane has a dense layer on at least one surface side.

[0016] 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.

[0017] <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).

[0018] (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 the component that is contained in the largest amount by mass of all the components of the separation membrane, and is approximately 50% by weight or more.

[0019] 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 copolymerizable with 4-methyl-1-pentene other than 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").

[0020] Examples of the olefin having 2 to 20 carbon atoms that can 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.

[0021] 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 of the present invention is 825 kg / m ３ More than 840kg / m ３ Preferably, it is 830 kg / m or less. ３ More than 835kg / 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 measured at 260°C under a load of 5 kg is not particularly limited as long as it is in a range in which the plasticizer described below can be easily mixed and co-extruded, but is preferably 1 g / 10 min to 200 g / 10 min, and more preferably 5 g / 10 min to 30 g / 10 min. If the MFR is in the above range, it is easy to extrude the PMP to a relatively uniform film thickness.

[0024] PMP may be produced directly by polymerizing olefins, or by thermal decomposition of a high-molecular-weight 4-methyl-1-pentene polymer. Furthermore, the 4-methyl-1-pentene polymer may be purified by solvent fractionation, which separates the polymer based on the difference in solubility in a solvent, or by molecular distillation, which separates the polymer based on the difference in boiling point. In addition to the PMP produced by polymerizing olefins as described above, commercially available PMP such as TPX manufactured by Mitsui Chemicals, Inc. may also be used.

[0025] The content of PMP in the separation membrane is preferably 70% by mass or more and 100% by mass or less, more preferably 80% by mass or more and 100% by mass or less, and even more preferably 90% by mass or more and 100% by mass or less, 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 obtained.

[0026] Furthermore, the content of PMP in the raw materials for producing the separation membrane is preferably 10% by mass or more and 50% by mass or less, 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% by mass or more and 50% by mass or less, even more preferably 20% by mass or more and 45% by mass or less, and particularly preferably 25% by mass or more and 40% by mass or less.

[0027] (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.

[0028] 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.

[0029] Examples of plasticizers for PMP include palm kernel oil, dibutyl phthalate, dioctyl phthalate, dibenzyl ether, coconut oil, and mixtures thereof. Among these, dibutyl phthalate and dibenzyl ether are preferred in terms of compatibility and spinnability.

[0030] The plasticizer for PMP is preferably eluted from the separation membrane after it is formed. Furthermore, the content of the plasticizer for PMP in the raw material for producing the separation membrane is preferably 50% by mass or more and 90% by mass or less, when the total amount of the components constituting the raw material is taken as 100% by mass.

[0031] A content of 90% by mass or less improves the membrane strength of the separation membrane. A content of 50% by mass or more improves the permeability of the separation membrane. The content is more preferably 50% by mass or more and 85% by mass or less, even more preferably 55% by mass or more and 80% by mass or less, and particularly preferably 60% by mass or more and 75% by mass or less.

[0032] (3) Additives The resin composition constituting the separation membrane of the present invention may contain additives other than those described in (2) above, as long as the effects of the present invention are not impaired.

[0033] 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.

[0034] <Shape of Separation Membrane> The shape of the separation membrane of the present invention is preferably a hollow fiber shape separation membrane (hereinafter referred to as "hollow fiber membrane". 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.

[0035] The shape of the separation membrane in the present invention, i.e., the thickness of the separation membrane, the outer and inner diameters of the 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.

[0036] From the viewpoint of achieving both permeability and membrane strength, the thickness of the separation membrane is preferably 10 μm or more and 500 μm or less. The thickness 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.

[0037] From the viewpoint of achieving both an effective membrane area when packed in a module and membrane strength, the outer diameter of the hollow fiber membrane is preferably 50 μm or more and 2500 μm or less. 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.

[0038] 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 or more and 1000 μm or less. 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 inner diameter is more preferably 500 μm or less, even more preferably 300 μm or less, and particularly preferably 250 μm or less.

[0039] 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%. The hollow ratio is more preferably 20% or more, and even more preferably 25% or more. The hollow ratio is more preferably 60% or less, even more preferably 50% or less, and particularly preferably 40% or less.

[0040] 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 hole of the spinneret used to produce the hollow fibers, the draft ratio calculated from the take-up speed / discharge speed, or the free running distance, which is the distance from the outlet nozzle to the cooling bath in the forming process described below.

[0041] 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 stretching the resin molded product. For convenience, the state before stretching is referred to as the "resin molded product," and the state after stretching is referred to as the "separation membrane."

[0042] The separation membrane of the present invention has a dense layer thickness of 0.1 μm or more and 2.0 μm or less. The dense layer refers to a layer in the separation membrane that does not have voids when observed at a magnification of 10,000 times using a scanning electron microscope (SEM). The voids refer to, for example, pores with a diameter of 10 nm or more when the radial cross section or longitudinal cross section of the separation membrane is observed at a magnification of 2,000 times using a scanning electron microscope (hereinafter referred to as "SEM"). When the pores are observed as described above, they may appear concave. In other words, having a dense layer means that when the membrane surface is observed at a magnification of 2,000 to 10,000 times using a scanning electron microscope (SEM), no pores with a diameter of 10 nm or more, i.e., no voids, are observed. Here, pores with a diameter of less than 10 nm are not easily observed when observing with an SEM due to the resolution. Although it is difficult to identify voids with a diameter of less than 10 nm even when observed at 10,000x magnification, the dense layer of the separation membrane of the present invention may have pores with a diameter of less than 10 nm, i.e., minute voids. From the viewpoint of gas permeability, it is preferable that the voids in the dense layer have a small diameter, and it is even more preferable that the dense layer has no voids.

[0043] The dense layer thickness refers to the length of a line drawn perpendicularly from any point on a surface without voids (for example, membrane surface 1 in FIG. 1) to the other surface, until it first reaches a hole with a diameter of more than 10 nm, i.e., a void. A detailed explanation will be given using the drawings. The separation membrane to be observed is obtained, for example, by applying stress to a separation membrane sufficiently cooled in liquid nitrogen (using a razor, microtome, or broad ion beam as necessary) to obtain a radial cross section, or a cross section parallel to the longitudinal direction of the membrane and parallel to the membrane thickness direction (hereinafter referred to as "longitudinal cross section"). A scanning electron microscope (SEM) is used to observe a longitudinal cross section including the dense layer near the surface of the separation membrane. The image thus obtained can be used to determine the size of the voids and the thickness of the dense layer.

[0044] FIG. 1(a) is an example of a cross-sectional SEM image including a dense layer near the surface of a separation membrane. FIG. 1(a) shows a membrane surface 1 and voids 3. In FIG. 1(a), voids are areas that appear darker than the surrounding area, and reference numeral 3 marks the location of a typical void. A dense layer 2 is located on the membrane surface, and an inner layer 5 is shown below the dense layer 2 as a support layer. FIG. 1(b) is a schematic diagram showing the relationship between the voids 3 and the dense layer 2. The voids 3 are holes or depressions with a diameter of 10 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 dense layer at each point. Although not shown, the inner layer 5 of the separation membrane is a porous layer, and even larger voids exist below the dense layer.

[0045] The thickness of the dense layer is obtained as the average value of the hypothetical fluctuation curve 6 of the dense layer. In this case, the hypothetical fluctuation curve 6 is formed by connecting the shortest path points of each void 3, as shown in FIG. 1(b). Specifically, the distance to the void 3 observed as a hole or depression with a diameter of 10 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 dense layer. Furthermore, the coefficient of variation of the thickness of the dense layer may be determined from the fluctuation of the hypothetical fluctuation curve 6. Specifically, the distance to the void 3 observed as a hole or depression with a diameter of 10 nm or more in the immediate vicinity of the film surface 1 may be measured at multiple points and the variation may be determined. The coefficient of variation can be calculated from the results of multiple measurements of the thickness of the dense layer by dividing the standard deviation by the average value and converting it to a percentage.

[0046] 2 and 3 show an example of a method for identifying voids with a diameter of 10 nm or more. The obtained cross-sectional SEM image is binarized using the image analysis software "ImageJ", and only pores larger than 10 nm are extracted. In the image after processing shown in FIG. 2, the resin part is white and the void part 3 is black. The film surface 1 is indicated by a dotted line. FIG. 3 shows the method for identifying voids with a diameter of 10 nm or more (area 78.5 nm) from the image after processing shown in FIG. 2. ２ 3. The thickness 4 of the dense layer is the distance from the film surface 1 to the point where the shortest path, i.e., the line segment drawn perpendicularly from the line representing the film surface 1, intersects with the boundary line shown in FIG.

[0047] The longitudinal direction here refers to the machine direction during production, and in the case of hollow fiber membranes, it is the direction perpendicular to the radial direction. Furthermore, in the case of hollow fiber membranes, the transverse direction is the direction parallel to the radial direction, i.e., it can be rephrased as the in-plane direction of the hollow surface. 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 other words, in the orientation degree measurement using polarized IR described below, the direction with the highest intensity is defined as the longitudinal direction of the flat membrane. Furthermore, the method for measuring the dense layer thickness (e.g., dense layer thickness 2 in Figure 3) will also be described in detail in the Examples.

[0048] A dense layer having a thickness of 0.10 μm or more provides good leak resistance, while a dense layer having a thickness of 2.0 μm or less provides good permeability. That is, the dense layer preferably has a thickness of 0.1 μm or more and 1.5 μm or less. The dense layer preferably has a thickness of 0.1 μm or more and 1.0 μm or less, and more preferably has a thickness of 0.1 μm or more and 0.4 μm or less.

[0049] The separation membrane of the present invention preferably has a dense layer on its outer surface, which increases the specific surface area during operation and makes it easier to improve permeation performance.

[0050] In the separation membrane of the present invention, the coefficient of variation of the dense layer thickness is preferably 80% or less, more preferably 50% or less, even more preferably 30% or less, and particularly preferably 10% or less. Having the coefficient of variation within the above range makes it easier to achieve both permeation performance and separation performance. There is no particular restriction on the lower limit of the coefficient of variation of the dense layer thickness, but typically, the smaller the value, the more preferable, with 0% being most preferred. A method for adjusting the coefficient of variation of the dense layer thickness within the above range includes, for example, setting the draft ratio when discharging the resin composition from the discharge nozzle to a range of 1 to 10, but is not limited thereto.

[0051] In addition, the separation membrane of the present invention preferably has 3 or less voids larger than 10 μm per membrane area in the support layer. The support layer is a layer of the separation membrane excluding the dense layer, and has a plurality of voids. A plurality of voids refers to 10 or more voids per field of view when the support layer in a radial cross section or longitudinal cross section is observed at a magnification of 2,000 times using an SEM. When the support layer has 3 or less voids larger than 10 μm, the strength of the separation membrane is improved. For example, voids of 10 μm or more in the support layer can be obtained by applying stress to a separation membrane sufficiently cooled in liquid nitrogen (using a razor, microtome, or broad ion beam as necessary), observing the radial cross section or longitudinal section using a scanning electron microscope (hereinafter referred to as SEM), and binarizing the obtained image using the image analysis software "ImageJ", followed by extracting only pores having an average diameter larger than 10 μm. The number of voids larger than 10 μm in the support layer is more preferably 2 or less, even more preferably 1 or less, and particularly preferably 0. A method for measuring the number of voids larger than 10 μm in the support layer will be described in detail in the Examples.

[0052] The separation membrane of the present invention preferably has an average pore size of the support layer 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 inner than the dense layer on the surface of the separation membrane. The average pore size of the support layer can be obtained, for example, by exposing the diameter 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 extracting only pores with an average diameter greater than 100 nm. When the average pore size of the support layer is 100 nm or more, the permeability is good, and when it is 1000 nm or less, the strength of the separation membrane is good. 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. The method for measuring the average pore size of the support layer will be described in detail in the Examples.

[0053] <Rigid Amorphous Ratio (RA)> Generally, polymers have crystalline and amorphous regions, and the amorphous regions can be classified into mobile amorphous regions that show a stepwise endothermic peak accompanied by a change in specific heat capacity at the glass transition point, and rigid amorphous regions that do not undergo a change in specific heat capacity under normal conditions. Rigid amorphous regions may have advanced molecular orientation, or may exist as tie molecules connecting crystals.

[0054] The proportion of this rigid amorphous material can be determined with high accuracy from the change in specific heat capacity before and after the glass transition on a TMDSC curve of the reversible component measured by temperature-modulated differential scanning calorimetry (hereinafter referred to as "TMDSC") and the heat of fusion on a DSC curve measured by differential scanning calorimetry (hereinafter referred to as "DSC").

[0055] It is important that the separation membrane of the present invention has a rigid amorphous fraction RA (hereinafter referred to as "rigid amorphous fraction RA") of 43% or more and 60% or less of poly(4-methyl-1-pentene). The rigid amorphous fraction RA can be calculated by the formula RA (%) = 100 - (MA + C), where MA is the mobile amorphous fraction and C is the crystallinity.

[0056] When the rigid amorphous fraction RA is 43% or more, the strength of the separation membrane is good, and when it is 60% or less, the flexibility of the separation membrane is good. The rigid amorphous fraction RA is preferably 48% or more and 60% or less, more preferably 50% or more and 60% or less, and even more preferably 56% or more and 60% or less.

[0057] A method for making the rigid amorphous fraction RA 43% or more and 60% or less includes a method for adjusting the production conditions described in the separation membrane production method described later to fall within the preferred ranges.

[0058] Preferred production conditions for controlling the rigid amorphous fraction RA to 43% or more and 60% or less during production of a separation membrane include employing production conditions in which a resin molded product having a predetermined structure, described below, is stretched at a predetermined temperature and speed to a stretch ratio of 2.0 to 6.0 times, and the temperature range and heating time for heat setting after stretching are set within the preferred ranges described below.

[0059] <Porosity> The separation membrane of the present invention has a porosity of 30% or more and 70% or less. The porosity refers to the proportion of voids when the entire membrane is PMP. A porosity of 30% or more results in good permeability, and a porosity of 70% or less results in good membrane strength. The porosity is preferably 40% or more and 65% or less, more preferably 45% or more and 60% or less, and particularly preferably 53% or more and 60% or less. In order to obtain a porosity in this range, structure formation using thermally induced phase separation, which will be described later, is preferably used. The method for measuring the porosity will be described in detail in the Examples.

[0060] Next, the characteristics of the separation membrane of the present invention will be described. (Regarding the peak temperature of the loss modulus (E")-temperature curve) In the separation membrane of the present invention, the loss modulus (E") has a peak in the loss modulus (E")-temperature curve obtained by conducting a dynamic viscoelasticity test (temperature dependency test) in the longitudinal direction of the membrane, and it is preferable that the peak temperature is in the range of 30.0°C or higher and 50.0°C or lower. The peak in the loss modulus (E")-temperature curve in the vicinity of this temperature range (30.0°C or higher and 50.0°C or lower) is thought to correspond to the movement of amorphous chains of PMP restrained by microcrystals. The amorphous chains restrained by microcrystals hardly move at low temperatures outside this temperature range, but their mobility increases rapidly near this peak temperature.

[0061] A high peak temperature, i.e., the amorphous chains restrained by the microcrystals are less likely to move, means that the degree of restraint of the amorphous chains is high. Since the peak temperature of the loss modulus (E")-temperature curve of the separation membrane of the present invention is at a high temperature of 30.0°C or higher, it is thought that the degree of restraint of the amorphous chains by the microcrystals is high and the mobility is low, and as a result, it is thought that the strength of the membrane can be increased. A peak temperature of 50.0°C or lower is preferable in that it can suppress a decrease in permeability due to excessive restraint of the amorphous chains and provides good permeability performance.

[0062] In the loss modulus (E")-temperature curve, the peak temperature of the loss modulus (E") is preferably in the range of 31.0°C or higher and 40.0°C or lower, more preferably in the range of 32.0°C or higher and 36.0°C or lower, and even more preferably in the range of 32.5°C or higher and 35.0°C or lower. In order to improve the accuracy in measuring the peak temperature, it is preferable to determine the peak temperatures in the loss modulus (E")-temperature curve for any three or more, preferably five or more, membrane fragments of the separation membrane and use the average value thereof. The measurement method for the dynamic viscoelasticity test will be described in detail in the Examples.

[0063] In order to set the peak temperature of the loss modulus (E")-temperature curve to 30.0°C or more and 50.0°C or less, one example is to set the production conditions described in the method for producing a separation membrane described later within the preferred range, but the method is not limited to this. Preferred production conditions during production include, for example, in the method for producing a separation membrane, employing production conditions in which a resin molded product having a predetermined structure described later is stretched at a predetermined stretching temperature with a stretch ratio of 2.0 times or more and 6.0 times or less. Further, one example is to set the temperature range and heating time of the heat setting after stretching within the preferred ranges described later.

[0064] (Stress at 5% Elongation (F5 Value)) The separation membrane of the present invention preferably exhibits an F5 value of 5.0 MPa or more in the longitudinal direction of the membrane at 25°C. The longitudinal direction in the present invention refers to the machine direction during production. The conditions for measuring the stress at 5% elongation will be explained in detail in the Examples. In the separation membrane of the present invention, an F5 value in the above range means that the degree of orientation of the PMP molecular chains is high. In other words, the PMP molecular chains are highly ordered and rigid, and as a result, high membrane strength can be obtained. Examples of a method for achieving a stress of 5.0 MPa or more at 5% elongation in the longitudinal direction include a method in which the stretching conditions during stretching are set within the preferred ranges described below. The stress at 5% elongation is more preferably 7.0 MPa or more, even more preferably 8.0 MPa or more, particularly preferably 9.0 MPa or more, and most preferably 9.5 MPa or more. The stress at 5% elongation in the longitudinal direction is preferably 20.0 MPa or less, which is preferable in that a decrease in permeability due to excessive orientation of molecular chains can be suppressed and good permeability performance can be achieved. The stress at 5% elongation is more preferably 18.0 MPa or less, even more preferably 15.0 MPa or less, and particularly preferably 13.0 MPa or less.

[0065] To improve the accuracy of the measurement, it is preferable to determine the F5 values ​​for any 5 or more, preferably 10 or more membrane fragments and use the average value. The method for measuring the F5 value will be described in detail in the Examples.

[0066] (Crystalline Orientation Degree π) In the separation membrane of the present invention, the molecular chains of the polymer are preferably oriented in a certain direction. The certain direction is the longitudinal direction of the separation membrane. The crystalline orientation degree π of the molecular chains is 0.7 or more and less than 1.0. The crystalline orientation degree π is calculated from the half-width H (°) ​​obtained by wide-angle X-ray diffraction measurement based on the following formula 1: Crystalline Orientation Degree π = (180° - H) / 180° ... Formula 2 where H is the half-width (°) of the diffraction intensity distribution in the circumferential direction of the wide-angle X-ray diffraction image.

[0067] The method for measuring the porous orientation of molecular chains and the degree of crystalline orientation π is specifically described below. To calculate the degree of crystalline orientation π, the hollow fiber membrane is attached to a fiber sample stage so that the longitudinal direction of the hollow fiber membrane is vertical.

[0068] X-ray diffraction produces a circular diffraction pattern called a Debye-Scherrer ring. In a non-oriented sample, no significant change in diffraction intensity is observed along the Debye ring. However, in an oriented sample, a bias occurs in the intensity distribution along the Debye ring. Therefore, the degree of orientation can be calculated from this intensity distribution using the above formula 2.

[0069] More specifically, when the molecular chains are non-oriented, a 2θ / θ scan in the short direction (i.e., a diffraction pattern showing the diffraction intensity distribution in the radial direction of the Debye ring) reveals a peak between diffraction angles 2θ of 5° and 30°. The horizontal axis of the resulting diffraction pattern is the X-ray diffraction angle 2θ, and the vertical axis is the diffraction intensity. By fixing the diffraction angle 2θ at a peak position with high diffraction intensity in the resulting diffraction pattern, where the horizontal axis is the X-ray diffraction angle 2θ and the vertical axis is the diffraction intensity, and scanning the sample in the azimuth angle β direction, a diffraction pattern is obtained where the horizontal axis represents the azimuth angle β and the vertical axis represents the diffraction intensity. In a non-oriented sample, the diffraction intensity is nearly constant over the entire 360° circumferential direction of the Debye ring. In a diffraction pattern where the horizontal axis represents the X-ray diffraction angle 2θ and the vertical axis represents the diffraction intensity, the peak position, i.e., the value of the diffraction angle 2θ at which the peak is observed, varies depending on the type, structure, and formulation of the polymer. In the case of α-crystal PMP, a diffraction peak originating from the (200) plane, i.e., a plane parallel to the molecular chain, is observed around 2θ = 10°. In the present invention, the value of 2θ when scanning the sample in the azimuth angle β direction is the position of the diffraction peak originating from the (200) plane in the case of α-crystal PMP. The positions of the diffraction peaks originating from the (200) plane are 10° and 20°. The specific method for measuring the degree of crystal orientation π is described below.

[0070] When the molecular chains are oriented in the longitudinal direction, strong diffraction intensity is observed on the Debye ring at an azimuth angle β (i.e., on the equator) corresponding to the short-side direction of the separation membrane around 2θ = 10°, while small diffraction intensity is observed in other areas (see, for example, Figure 4). In other words, in the oriented sample, the diffraction intensity distribution in the radial direction of the Debye ring shows a diffraction peak around 2θ = 10°, similar to the non-oriented sample, while the distribution in the circumferential direction shows a diffraction peak at an azimuth angle β corresponding to the short-side direction of the separation membrane, unlike the non-oriented sample. For example, Figure 5 shows the intensity distribution in the azimuth angle β direction at 2θ = 10° for the hollow fiber membrane of Example 4, and in this figure, peaks are observed around β = 90° and 270°.

[0071] As described above, the intensity distribution in the azimuthal angle β direction is obtained by fixing the value of the diffraction angle 2θ and measuring the intensity in the azimuthal angle β direction (circumferential direction) from 0° to 360°. This intensity distribution can also be said to be the intensity distribution obtained by scanning the crystal peak in the diffraction image in the circumferential direction. Here, in the β scan, if the intensity ratio between the maximum intensity and the minimum intensity is 0.80 or less or 1.25 or more, a peak is considered to exist, and the half-width H at the position half the peak height is calculated in this azimuthal angle intensity distribution.

[0072] The degree of crystal orientation π is calculated by substituting this half-width H into the above formula 2. The degree of crystal orientation π of the separation membrane of the present invention is in the range of 0.7 or more and less than 1.0, preferably 0.8 or more and less than 1.0, and more preferably 0.9 or more and less than 1.0. A degree of crystal orientation π of 0.7 or more increases the mechanical strength of the separation membrane. Note that, when wide-angle X-ray diffraction measurement is performed at measurement points 1 cm apart in the longitudinal direction of the separation membrane, the degree of crystal orientation π is preferably 0.4 or more and less than 1.0 at 80% or more of the measurement points.

[0073] In addition, when the ratio of the maximum intensity to the minimum intensity in the intensity distribution obtained by scanning the crystal peak in the circumferential direction is in the range of more than 0.80 and less than 1.25, it is considered that no peak exists. In other words, in this case, the separation membrane is determined to be non-oriented.

[0074] The half-value width H is preferably obtained from an intensity distribution obtained by scanning a crystal peak (2θ=10°) derived from the (200) plane of the α-crystal of PMP in the circumferential direction by wide-angle X-ray diffraction measurement.

[0075] An example of a means for setting the degree of crystalline orientation π of the molecular chains within the above range is a method for producing a separation membrane, in which the draft ratio when discharging the resin composition from a discharge nozzle is set to a range of 1 to 10, and the resin composition is stretched 3 to 6 times at a temperature between the glass transition temperature of the thermoplastic resin + 10° C. and the glass transition temperature + 100° C. The degree of crystalline orientation π of the molecular chains can be increased, for example, by increasing the stretch ratio.

[0076] <Orientation degree of outer surface> The separation membrane of the present invention preferably has an orientation degree of the outer surface in the longitudinal direction of 1.3 to 3.0. The outer surface here refers to the longer of the two surfaces parallel to the membrane thickness direction in the radial cross section of the separation membrane. For example, in the case of a hollow fiber membrane, it refers to the outer diameter side surface. On the other hand, in the case of a flat membrane, the lengths of the two surfaces are equal, so for convenience in the present invention, the surface with the higher orientation degree of the two surfaces parallel to the membrane thickness direction is referred to as the outer surface. Furthermore, in the radial cross section of the separation membrane, the other surface parallel to the membrane thickness direction relative to the outer surface is referred to as the inner surface. That is, in the case of a hollow fiber membrane, it is the inner diameter side surface, and in the case of a flat membrane, it is the surface with the lower orientation degree of the two surfaces parallel to the membrane thickness direction that is referred to as the inner surface. An orientation degree of the outer surface of 1.3 or more results in good membrane strength. A separation membrane with an orientation degree of 1.4 or more, or 1.7 or more, can achieve even greater effects.

[0077] On the other hand, when the degree of orientation of the outer surface is 3.0 or less, the flexibility of the separation membrane is good. The degree of orientation of the outer surface of the separation membrane is preferably 2.8 or less, more preferably 2.5 or less.

[0078] The degree of orientation can be determined by orientation analysis using polarized infrared spectroscopy (hereinafter referred to as "polarized IR"). A specific method will be described in the examples.

[0079] (Ratio of outer surface orientation degree / inner surface orientation degree) The separation membrane of the present invention preferably has a ratio of outer surface orientation degree / inner surface orientation degree of 1.0 or more and 1.5 or less. When the ratio of outer surface orientation degree / inner surface orientation degree is 1.5 or less, ２ / N ２ The selectivity is good. On the other hand, when the ratio of the degree of orientation of the outer surface to the degree of orientation of the inner surface is 1.0 or more, the strength of the separation membrane is good. The ratio of the degree of orientation of the outer surface to the degree of orientation of the inner surface is preferably 1.0 or more and 1.4 or less, and more preferably 1.0 or more and 1.3 or less. The method for measuring the degree of orientation will be described later in the examples.

[0080] (Gas permeability) The separation membrane of the present invention has a N ２ It is preferable that the transmission performance is 5 GPU or more. ２ The transmission performance is more preferably 10 GPU or more, even more preferably 50 GPU or more, particularly preferably 100 GPU or more, and even more preferably 200 GPU or more. The calculation method will be described in detail in the Examples.

[0081] (CO ２ / N ２ Selectivity) The dense layer of the present invention is non-porous, which means that it has a very long leak time, and because it is non-porous, gas permeation occurs via a solution-diffusion mechanism. On the other hand, a porous structure has through-holes, which means that it has a short leak time, and gas permeates via Knudsen diffusion. In other words, the density of the dense layer can be evaluated by the gas separation factor, and membranes with high density tend to have long leak times.

[0082] Generally, permeation through a polymer membrane depends on the pore size in the membrane. In membranes where the maximum pore size of the dense layer is 3 nm or less, gases permeate by a solution-diffusion mechanism. In this case, the separation factor α, which indicates the ratio of the permeability coefficients or gas flow rates Q of two gases, depends only on the polymer material and not on the thickness of the dense layer. Therefore, for example, CO ２ and N ２ Gas separation factor α for ０ (CO ２ / N ２) is P ０ (CO ２ ) / P ０ (N ２ In commonly used polymers, at least one α ０ (CO ２ / N ２ ) value is generated.

[0083] On the other hand, in a porous membrane with pores of 3 nm to 10 μm in size, gas permeates mainly by "Knudsen diffusion." In this case, the gas separation coefficient α1 is obtained by the square root of the ratio of the molecular weights of the gases. Therefore, α １ (CO ２ / N ２ ) is √28 / 44 = 0.80. If it is Knudsen diffusion, there is a risk of leakage, and α １ (CO ２ / N ２ ) is preferably 1 or more, since the risk of leakage is reduced. In particular, in the case of a thin membrane having a dense layer thickness of 0.1 μm or more and 3.0 μm or less as described above, CO ２ / N ２ A selectivity of 1.0 or higher indicates good low leakage. When a gas permeates a membrane having a microporous support structure and a dense layer with defects, on the one hand the apparent permeability coefficient increases, but on the other hand the gas separation coefficient decreases.

[0084] The defects referred to here are holes of 3 nm or more in size on the surface of the dense layer. Therefore, the presence or absence of holes or defects in the dense layer of the membrane of the present invention can be determined by CO ２ and N ２ The gas separation factor α (CO ２ / N ２ ) can be read by the gas separation factor α (CO ２ / N ２ If the gas separation coefficient α(CO ２ / N ２) is 1.0 or more, the membrane has low leakage. Therefore, the gas separation coefficient α(CO ２ / N ２ ) is preferably 1.0 or more, more preferably 1.5 or more, and even more preferably 2 or more.

[0085] (Tensile modulus) The separation membrane of the present invention preferably has a tensile modulus of 100 MPa or more in the longitudinal direction. A tensile modulus of 100 MPa or more allows the membrane to maintain good strength during use. The tensile modulus is more preferably 200 MPa or more, even more preferably 250 MPa or more, and particularly preferably 300 MPa or more. The method for measuring the tensile modulus of the separation membrane will be described in detail in the Examples.

[0086] <Method for Producing Separation Membrane> The method for producing a separation membrane of the present invention comprises the following steps (1) to (3): (1) a preparation step of melt-kneading a mixture containing 10% by mass or more and 50% by mass or less of PMP and 50% by mass or more and 90% by mass or less of a plasticizer to obtain a resin composition; (2) a molding step of discharging the resin composition 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 having an outer surface orientation degree of 1.0 to 1.5 and an outer surface orientation degree / inner surface orientation degree ratio of 1.0 to 1.5; and (3) a stretching step of stretching the resin molded product by 2 to 6 times at a temperature condition of 60°C to 120°C to obtain a stretched product.

[0087] Next, the method for producing the separation membrane of the present invention will be specifically described using an example in which the separation membrane is a hollow fiber membrane. (Preparation Step) In the preparation step to obtain a resin composition for producing the separation membrane of the present invention, a mixture containing 10% by mass to 50% by mass of PMP and 50% by mass to 90% by mass of 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 plasticizer, more preferably 20% by mass to 45% by mass of PMP and 55% by mass to 80% by mass of plasticizer, and particularly preferably 25% by mass to 40% by mass of PMP and 60% by mass to 75% by mass of plasticizer.

[0088] 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 volatile substances 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.

[0089] The resin composition obtained in the preparation step may be pelletized and re-melted for melt film formation, or may be directly introduced into a die for melt film formation. When pelletizing, it is preferable to dry the pellets to use a resin composition with a moisture content of 200 ppm (by mass) or less. By reducing the moisture content to 200 ppm (by mass) or less, resin degradation can be suppressed. (Formation Step) In the separation membrane formation step, a resin molded product is obtained from a molten mixture of PMP and plasticizer, i.e., a resin composition, by utilizing phase separation. Specifically, the resin composition obtained in the preparation step is discharged into a gas atmosphere, for example, from a discharge die having a double annular nozzle with a gas flow path in the center, and then introduced into a cooling bath to phase separate the resin composition and obtain a resin molded product.

[0090] 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. The resin composition thus discharged is cooled and solidified in a cooling bath to obtain a resin molded product.

[0091] Here, the cooling bath for cooling the resin composition discharged from the nozzle will be described. 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 dense layer to be thinned, resulting in good permeability. When Ra is in the range of 10 to 12 and Rb is in the range of 4 to 6, the dense layer can be made particularly thin, resulting in good permeability. Furthermore, when the ratio of the orientation degree of the outer surface of the resin molded article to the orientation degree of the inner surface is in the range of 1.0 to 1.5 and the orientation degree of the outer surface is in the range of 1.0 to 1.5, as described below, high-magnification stretching is possible. The reason for this is believed to be that when Ra is in the range of 10 to 12, solidification occurs before crystallization of the PMP, and when Rb is in the range of 4 to 6, the solvent and plasticizer are exchanged quickly, resulting in a thin layer while suppressing excessive crystallization. This is thought to result in good permeability and enable high-magnification stretching.

[0092] 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 3, the higher the affinity of the solvent with PMP.

[0093]

[0094] 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 δＣｈ are the dispersion, polar and hydrogen bonding terms of the solubility parameter of the solvent.

[0095] 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 4, the higher the affinity of the solvent for the plasticizer.

[0096]

[0097] where δ Ｂｄ , δ Ｂｐ and δ Ｂｈ 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.

[0098] When the solvent is a mixed solvent, the solubility parameter (δ Ｍｉｘｔｕｒｅ ) can be calculated using the following formula 5.

[0099]

[0100] 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.

[0101] In the method for producing a separation membrane of the present application, when dibutyl phthalate is used as the plasticizer, the solvent used in the cooling bath in the formation step is preferably triacetin or N-methylpyrrolidone, and among these, N-methylpyrrolidone is more preferred because Ra and Rb are within the above-mentioned more preferred ranges.

[0102] Furthermore, it is preferable that at least one surface of the resin composition discharged from the nozzle die, preferably the surface on which a dense layer is to be formed, be exposed to a gaseous atmosphere that promotes evaporation of the plasticizer, i.e., an atmosphere in which evaporation of the plasticizer can occur, before cooling. The gas used to form the gaseous atmosphere is not particularly limited, but air or nitrogen is preferably used. The gaseous atmosphere generally has a temperature lower than the nozzle die temperature. In this case, in order to evaporate a sufficient amount of the plasticizer, it is preferable to expose at least one surface of the molded body to the gaseous atmosphere for at least 0.5 milliseconds (ms).

[0103] In the forming process for producing the separation membrane of the present invention, the resin composition discharged from the discharge nozzle is wound up by a winding device. In this case, it is important that the draft ratio, calculated by (winding speed by the winding device) / (discharge speed from the discharge nozzle), is 1 or more and 10 or less. The draft ratio is more preferably 1 or more and 8 or less, and even more preferably 1 or more and 6 or less. A draft ratio of 1 or more stabilizes winding and reduces fluctuations in the thread shape. By setting the draft ratio to 10 or less, excessive stretching of the resin composition discharged from the nozzle can be suppressed, and molecular chain orientation on the outer surface is suppressed, making it possible to perform high-magnification stretching in the stretching process described below.

[0104] Specifically, molecular chain orientation due to drafting occurs when the resin composition is stretched due to the take-up speed being faster than the extrusion speed. However, if the resin composition is in a cooling bath during stretching, the outer surface side that directly contacts the cooling bath solidifies first, and the outer surface side is stretched while solidifying, resulting in strong molecular chain orientation. On the other hand, the inner surface side of the separation membrane that does not contact the cooling bath is stretched before solidification progresses, and therefore orientation is difficult to achieve. Thus, when the draft ratio is high, the orientation on the outer surface side and the inner surface side of the resin molded product before stretching becomes uneven. When such a resin molded product is stretched, the outer surface side, which is already oriented, cannot withstand high-magnification stretching, causing defects.

[0105] The inventors discovered that the ratio of the orientation degree of the outer surface of a resin molded product before stretching to the orientation degree of the inner surface is in the range of 1.0 to 1.5, and that high stretching is possible when the orientation degree of the outer surface is in the range of 1.0 to 1.5, thereby achieving the present invention. The ratio of the orientation degree of the outer surface of a resin molded product before stretching to the orientation degree of the inner surface is preferably 1.0 to 1.4, more preferably 1.0 to 1.3, and even more preferably 1.0 to 1.2. When the ratio of the orientation degree of the outer surface of a resin molded product before stretching to the orientation degree of the inner surface is 1.5 or less, it is possible to both suppress the occurrence of surface defects and achieve stretching at a magnification of 2.0 or more. On the other hand, when the ratio of the orientation degree of the outer surface to the orientation degree of the inner surface is 1.0 or more, yarn deformation during stretching can be suppressed. The degree of orientation of the outer surface of the resin molded product before stretching is preferably 1.0 or more and 1.4 or less, more preferably 1.0 or more and 1.3 or less, and even more preferably 1.0 or more and 1.2 or less.

[0106] By setting the degree of orientation of the outer surface of the resin molded product before stretching to 1.5 or less, it is possible to suppress the occurrence of defects on the surface and to stretch the molded product at a stretching ratio of 2.0 or more. On the other hand, by setting the degree of orientation of the outer surface to 1.0 or more, it is possible to suppress yarn deformation during stretching. The method for measuring the degree of orientation will be described later in the Examples.

[0107] For example, attempts were made to control rigid amorphous structures by stretching a resin molded product with an outer surface orientation degree / inner surface orientation degree ratio of 1.5 or more, but it was difficult to stretch uniformly, making it impossible to control rigid amorphous structures, and CO ２ / N ２ The selectivity decreased.

[0108] In general, separation membranes having many voids, for example, separation membranes with a porosity of 30% or more, are very difficult to stretch because destruction of the structure progresses from the voids during stretching. This tendency is particularly pronounced when the separation membrane has a phase-separated structure obtained by dry-wet spinning utilizing the principles of non-solvent-induced phase separation or thermally induced phase separation, due to the presence of many fine voids and the high porosity.

[0109] In the case of a resin molded product in which the ratio of the orientation degree of the outer surface to the orientation degree of the inner surface exceeds 1.5, it is difficult to stretch the molded product by 2.0 times or more. After careful investigation into the cause, it was found that the take-up speed is as high as 72 m / min, which tends to increase the draft ratio, and as a result, the orientation of the outer and inner surfaces of the resin molded product before stretching becomes non-uniform, as described above. In other words, the ratio of the orientation degree of the outer surface to the orientation degree of the inner surface becomes large, and the surface that has already been oriented cannot withstand high-magnification stretching, resulting in the occurrence of defects (i.e., CO ２ / N ２ It was discovered that the selectivity was 1 or less, making it impossible to stretch at a high magnification.

[0110] In response to this, the present inventors discovered that a resin molded product can be uniformly stretched as a whole if the ratio of the orientation degree of the outer surface to the orientation degree of the inner surface is within a predetermined range and the orientation degree of the outer surface is 1.5 or less, making it possible to stretch at a high ratio of 2.0 or more. Such uniform and high-ratio stretching has succeeded in controlling the rigid amorphous fraction and in increasing strength while suppressing the occurrence of defects.

[0111] (Washing step) The resin composition obtained in this way is immersed in a solvent that does not dissolve the polymer but is miscible with the plasticizer, and a porous structure can be obtained by undergoing a step of eluting the plasticizer. In this case, by using a solvent or mixed solvent that has a moderate affinity with the plasticizer, good solvent exchange is achieved and cleaning efficiency is improved. There are no particular limitations on the solvent as long as it does not dissolve the polymer but is miscible with the plasticizer, but specific examples that are preferably used include methanol, ethanol, isopropanol, and acetone.

[0112] (Drying step) The resin composition after the washing step is preferably subjected to a drying step for the purpose of removing the solvent adhered in the washing step. Drying is preferably carried out at a temperature that does not dissolve the polymer but allows the solvent that is miscible with the plasticizer to evaporate and be removed, specifically, at a temperature between room temperature and 150°C.

[0113] (Stretching step) The formed resin molded product may be once wound up and then unwound again for stretching, or may be directly sent to the stretching step for stretching. The stretching step is important in controlling the rigid amorphous fraction RA within the above-mentioned range. The stretching method is not particularly limited, and may be, for example, a method in which the resin molded product is transported on heated rolls to raise the temperature at which stretching is performed and stretched using the difference in peripheral speed between the rolls, or a method in which the resin molded product is transported in a dry heat oven or a liquid bath to raise the temperature at which stretching is performed and stretched using the difference in peripheral speed between the rolls. Among these, transporting in a dry heat oven or a liquid bath is preferred in terms of suppressing collapse of the hollow portion and increasing the hollow ratio. Furthermore, stretching may be performed before or after eluting the plasticizer, but it is preferred to perform it after eluting the plasticizer in order to reduce the amount of solvent remaining in the separation membrane and increase the porosity.

[0114] The preferred range of the stretching temperature in the stretching step is 60°C or higher and 120°C or lower, more preferably 70°C or higher to 110°C or lower, and even more preferably 75°C or higher and 90°C or lower. Stable and uniform stretching can be achieved by stretching in an atmosphere of 60°C or higher. Stretching in an atmosphere of 120°C or lower can suppress yarn deformation due to softening of the PMP and reduce the hollow ratio. The stretch ratio is preferably 2.0 times or higher and 6.0 times or lower, more preferably 3.0 times or higher and 6.0 times or lower, even more preferably 3.5 times or higher and 6.0 times or lower, and particularly preferably 4.5 times or higher and 6.0 times or lower. The inventors have found that by setting the stretching temperature to 60°C or higher and the stretch ratio to 2.0 times or higher and 6.0 times or lower, the rigid amorphous fraction (RA) can be controlled within a preferred range, resulting in good membrane strength. Furthermore, setting the stretch ratio to 6.0 times or lower can suppress the generation of through-holes in the dense layer.

[0115] (Heat Treatment Step) Subsequently, the separation membrane can be heat-treated by heating at 100°C or higher and 200°C or lower. This heat treatment step can increase the crystallinity of the PMP, resulting in a separation membrane with greater strength. The heat treatment can be carried out by conveying the membrane on a heated roll, by conveying the membrane in a dry heat oven, or by placing the membrane in a roll wound on a bobbin or a paper tube in a dry heat oven.

[0116] The heat treatment temperature is preferably 100° C. or higher and 200° C. or lower, more preferably 110° C. or higher and 180° C. or lower, and even more preferably 120° C. or higher and 160° C. or lower. The heat treatment time is preferably 1 second or higher and 600 seconds or lower, more preferably 5 seconds or higher and 300 seconds or lower, and even more preferably 10 seconds or higher and 60 seconds. By including the above steps, the separation membrane of the present invention, which contains PMP as a main component, can be produced.

[0117] The present invention will be explained in more detail below with reference to examples, but the present invention is not limited to these examples. Measurement and evaluation methods are shown below.

[0118] The respective property values ​​in the examples were determined by the following methods. (1) Outer diameter and inner diameter (μm) of hollow fiber membrane: After freezing the 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. (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 (%) = 100 × [inner diameter (μm)] ２ / [Outer diameter (μm)] ２ (3) Gas Permeability (GPU) A small module with an effective length of 100 mm was prepared, consisting of a single hollow fiber membrane. This small module was used to measure the gas permeation rate. Carbon dioxide or nitrogen was used alone as the measurement gas, and the pressure change per unit time of the carbon dioxide or nitrogen permeation side was measured using an external pressure method at a measurement temperature of 37°C in accordance with the pressure sensor method of JIS K7126-1 (2006). The pressure difference between the supply side and the permeation side was set to 100 kPa.

[0119] Next, the gas permeation rate Q was calculated using the following formula: The ratio of the gas permeation rates of the individual components was defined as the separation factor α. Here, the membrane area was calculated from the outer diameter and length of the region contributing to gas permeation.

[0120] Transmission rate Q (GPU) = 10 －６ [Permeation gas amount (cm ３ )] / [Membrane area (cm ２) × time (s) × pressure difference (cmHg)] (4) Dense layer thickness (μm) As in the above (1) outer diameter and inner diameter (μm) of the hollow fiber membrane, the separation membrane was frozen with liquid nitrogen and then stressed (using a razor, microtome, or broad ion beam as necessary) to expose the radial cross section or longitudinal cross section. Subsequently, platinum sputtering was performed under the following conditions to pretreat the radial cross section or longitudinal cross section, and then observed at 10,000x magnification using an SEM. When a straight 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 10 nm was defined as the dense layer thickness. Pores were extracted after binarizing the analysis image using the image analysis software "ImageJ". The binarization was performed by plotting the brightness of the analysis image on the horizontal axis and the number of pixels at the corresponding brightness on the vertical axis. When the distribution of the number of pixels was taken, the number of pixels at the highest brightness was defined as A, and the number of pixels at 1 / 2A was determined by matching the lower brightness point to the lower brightness point. Furthermore, the obtained binarized image was subjected to noise removal (equivalent to Despeckle in ImageJ) once, in which all pixels were replaced with the median value of the 3 x 3 pixels surrounding that pixel. The image was used as the analysis image. Holes were extracted using the Analyze Particles command in ImageJ, and the dense layer thickness was measured from the obtained image. Measurements were performed at 10 arbitrary locations, and the average value was adopted as the dense layer thickness. The coefficient of variation of the dense layer thickness was calculated by dividing the standard deviation by the average value for the dense layer thickness at any 10 measured locations and converting it to a percentage.

[0121] (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 (5) Voids larger than 10 μm in the support layer The separation membrane was frozen with liquid nitrogen in the same manner as in (1) above, and then stress was applied (using a razor, microtome, or broad ion beam as necessary) to expose the radial cross section or longitudinal cross section. Subsequently, sputtering was performed with platinum under the following conditions, and after pretreatment of the radial cross section or longitudinal cross section, holes with a diameter larger than 10 μm, i.e., an area of ​​78.5 μm were observed at a magnification of 2,000 times using an SEM. ２ All larger pores were extracted, their number was calculated, and the average pore size of the support layer was determined. 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 x 3 pixels surrounding that pixel, and the resulting image was used as the analysis image. The pores were extracted using the Analyze Particles command in ImageJ, and the number of obtained pores was calculated. Measurements were performed at any five locations, and the average value was used as the voids larger than 10 μm in the support layer.

[0122] (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 (6) Average pore size of support layer After freezing the separation membrane with liquid nitrogen in the same manner as in (1) above, it was cut using a microtome so that the cross section was exposed. Subsequently, sputtering was performed with platinum under the following conditions, and the cross section was pretreated. After that, when observed at 2,000 times magnification using an SEM, the average pore size of pores with a diameter greater than 100 nm, that is, an area of ​​7854 nm ２All larger pores were extracted, and the average pore diameter was calculated from the average area to determine the average pore diameter of the support layer. The observation field was centered at a point (membrane thickness / 2) μm in the membrane thickness direction from one surface of the separation membrane, and the membrane thickness was determined by observing a similar sample at a magnification of 250 times using an SEM. The length of a straight line drawn from any point on one surface to the other surface so that it was the shortest length was determined as the membrane thickness of the separation membrane. Pore extraction is performed after binarizing the analysis image (Huang binarization) using the image analysis software "ImageJ". The obtained binarized image was subjected to noise removal (equivalent to Despeckle in ImageJ) once, in which all pixels are replaced with the median value of the 3 × 3 pixels surrounding that pixel. The image used as the analysis image was used. Pore extraction was performed using the Analyze Particles command of ImageJ, with an area of ​​7854 nm ２ All larger pores were extracted, and the average pore size of the support layer was calculated from the average area of ​​the obtained pores. Note that measurements were taken at five random locations, and the average value was used as the average pore size of the support layer.

[0123] (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 (7) Rigid amorphous fraction (RA) Measurement was carried out by cutting out a separation membrane. TMDSC measurement of the separation membrane was carried out under the following conditions using a temperature modulated differential scanning calorimeter: Q1000 manufactured by TA Instruments. Note that for data processing, Universal Analysis 2000 manufactured by TA Instruments was used. Atmosphere: nitrogen flow (50 mL / min) Temperature / calorie 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 (Δ C 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.

[0124] MA (%) = ΔC ｐ / ΔC ｐ ０ × 100 where ΔC ｐ ０ is the difference in specific heat capacity before and after the glass transition of the completely amorphous PMP.

[0125] Subsequently, the separation membrane was subjected to DSC measurement under the following conditions using a Q100 manufactured by TA Instruments. 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 20°C to 300°C Heating rate: 10°C / min Sample amount: about 5 mg Sample container: aluminum standard container From the DSC curve, the heat of fusion (ΔH ｍ ) was measured, and the percentage of crystallinity (C) was calculated based on the following formula: C (%) = ΔH ｍ / ΔH ｍ ０ × 100 where ΔH ｍ ０is the heat of fusion of completely amorphous PMP. Using the obtained mobile amorphous fraction (MA) and crystallinity (C), the rigid amorphous fraction (RA) was calculated according to the following formula 1: RA (%) = 100 - (MA + C) Formula 1 (8) Peak temperature of loss modulus (E") - temperature curve The loss modulus of the separation membrane was determined by viscoelasticity measurement. A sample of 30 mm in length was cut out of the hollow fiber membrane in the longitudinal direction. Using a dynamic viscoelasticity measuring device (Rheogel-E4000, manufactured by UBM), the temperature dependence of the loss modulus (E") was measured in a nitrogen atmosphere while heating at a temperature range of -100°C to 200°C at a heating rate of 3°C / min. The measurement length was 10 mm, the frequency was 10 Hz, and the tensile strain was 0.05%. The loss modulus (E") was plotted on the vertical axis and the temperature on the horizontal axis. The maximum value of the loss modulus (E") between 20°C and 90°C was taken as the peak, and the corresponding temperature was taken as the peak temperature (°C) of the loss modulus (E"). Measurement was performed three times using different samples, and the average value was calculated. (9) Tensile Modulus (MPa) The tensile modulus of the separation membrane was measured in an environment of 20°C and 65% humidity using a tensile tester (Tensilon UCT-100 manufactured by Orientec Co., Ltd.) under conditions of a sample length of 100 mm and a tensile speed of 100 mm / min, with the rest being in accordance with the method specified in "JIS L 1013:2010 Test Method for Chemical Fiber Filament Yarn, 8.10 Initial Tensile Resistance." The apparent Young's modulus calculated from the initial tensile resistance was used as the tensile modulus (kgf / mm ２ The measurement was carried out five times, and the average value was used. (10) Porosity (%) 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. The density ρ of the hollow fiber membrane １ was calculated from the following formula using the outer diameter (mm) and inner diameter (mm) measured in (1) above.

[0126] ρ １ =M / [π×{(outer diameter / 2) ２ - (inner diameter / 2) ２}×L] The porosity ε (%) was calculated from the following formula.

[0127] ε = 1 - ρ １ / ρ ２ where ρ ２is the density of the polymer. (11) Stress at 5% Elongation (F5 Value) The tensile modulus of the separation membrane was measured in an environment of a temperature of 25°C and a humidity of 65% using a tensile tester (Tensilon UCT-100 manufactured by Orientec Co., Ltd.) under conditions of a sample length of 100 mm and a tensile speed of 100 mm / min. The tension when the sample was stretched by 5% (when the chuck distance was 105 mm) was divided by the cross-sectional area of ​​the sample (excluding the hollow portion) before measurement, and the F5 value (MPa) was defined as the value. The measurement was performed five times, and the average value was calculated. (12) Degree of orientation of outer surface Using a BioRad DIGILAB FTIR (FTS-55A) equipped with a single-reflection ATR attachment, S-polarized ATR spectrum measurements were performed on the outer surface of the resin molded product and separation membrane in the longitudinal direction (MD) and the direction perpendicular to the longitudinal direction (diameter direction) (TD) after vacuum drying at 25 ° C. Note that a diamond prism was used as the ATR crystal, the incident angle was 45 °, the number of integration times was 64, and the polarizer was a wire grid, and the measurement was performed with S-polarized light. From the obtained ATR spectrum, one band whose band intensity changes in MD and TD was used, and the band intensity ratio was calculated as the orientation parameter. For example, in the case of a PMP resin molded product and separation membrane, 918 cm －１ Nearby bands (-CH ３ The strength of the base vibration (rolling vibration) was measured in the MD and TD of the resin molded product and the separation membrane.

[0128] Since the band intensity is strong when the vibration direction of the molecular chain and the polarization direction of the incident light are the same, the ratio of the band intensities changes in correlation with the degree of orientation, so the degree of orientation was calculated using the following formula: Orientation degree of outer surface = [918 cm in MD direction] －１ Band intensity around 918 cm in the TD direction －１ The degree of orientation is 1465 cm －１The band (-CH bending vibration) intensity near the center was normalized to the same intensity and measured. (13) Degree of Orientation of Inner Surface After freezing the resin molded product and separation membrane with liquid nitrogen in the same manner as in (1) above, they were cut parallel to the longitudinal direction using a razor or microtome to expose the hollow portion of the membrane, i.e., the inner surface, and the orientation parameter of the hollow portion, i.e., the inner surface, was measured using a BioRad DIGILAB FTIR (FTS-55A) equipped with a single-reflection ATR attachment in the same manner as in (12) above. The separation membrane sample was vacuum dried at 25°C for 8 hours, and S-polarized ATR spectrum measurement was performed on the inner surface of the separation membrane sample in the longitudinal direction (MD) and in the direction perpendicular to the longitudinal direction (diameter direction) (TD).

[0129] A diamond prism was used as the ATR crystal, the incident angle was 45°, the number of integration times was 64, and a wire grid was used as the polarizer, and the measurement was performed with S-polarized light. From the obtained ATR spectrum, one band whose band intensity changes in MD and TD was used, and the band intensity ratio was calculated as the orientation parameter. For example, in the case of a PMP resin molded product and a separation membrane, the band intensity ratio was 918 cm －１ Nearby bands (-CH ３ The intensity of the group vibration (rolling vibration) was measured in the MD and TD of the resin molded product and the separation membrane. Since the band intensity is strong when the vibration direction of the molecular chain and the polarization direction of the incident light are the same, the ratio of the band intensities changes in correlation with the degree of orientation, so the degree of orientation was calculated using the following formula. Internal orientation = [918 cm in the MD direction] －１ Band intensity around 918 cm in the TD direction －１ The degree of orientation is 1465 cm －１The measurement was normalized so that the band (-CH bending vibration) intensity near the center was the same. (14) Crystal orientation: π In the case of a hollow fiber membrane, the hollow fiber membrane was attached to a fiber sample stage so that the longitudinal direction of the separation membrane was vertical. In the case of a flat membrane, the film was attached to the sample stage so that the X-ray incidence direction was perpendicular to the film surface. X-ray diffraction measurements (2θ / θ scan, β scan) were performed using an X-ray diffractometer (Rigaku Corporation, SmartLab for polymers, CuKα radiation). First, the presence of a peak top in the 2θ / θ scan was confirmed. In the obtained diffraction pattern, where the horizontal axis is the X-ray diffraction angle 2θ and the vertical axis is the diffraction intensity, the diffraction angle 2θ was fixed at the peak position of high diffraction intensity, and the sample was scanned in the azimuthal angle β direction, resulting in a diffraction pattern where the horizontal axis represents the azimuthal angle β and the vertical axis represents the diffraction intensity. The value of 2θ fixed when scanning the sample in the azimuthal angle β direction was the position of the diffraction peak derived from the (200) plane in the case of α-crystals of PMP. In the case of the α-crystal of PMP, the diffraction peak derived from the (200) plane was located at around 10°. Next, the intensity distribution in the azimuth angle β direction was obtained by measuring the intensity from 0° to 360° in the azimuth angle β direction using a β scan, relative to the 2θ value determined by the 2θ / θ scan (Figure 5).

[0130] Here, a peak was deemed to exist when the intensity ratio between the maximum peak intensity and the minimum peak intensity was 0.80 or less or 1.25 or more. In the intensity distribution in the azimuth angle β direction, the width at half the peak height (half width H) was determined, and the degree of crystalline orientation π was calculated using the following formula (1). The straight line passing through the two minimum intensity points in the β scan was used as the baseline. Degree of crystalline orientation π = (180° - H) / 180° Formula 2 [PMP Raw Material] The following PMP was prepared.

[0131] PMP: TPX DX845 (density: 833 kg / m ３ , MFR: 9.0g / 10min) [Other raw materials] Plasticizer: dibutyl phthalate.

[0132] Example 1 35% by mass of PMP and 65% by mass of dibutyl phthalate were fed into a twin-screw extruder and melt-kneaded at 290°C. The mixture was then introduced into a melt spinning pack set at a spinning temperature of 245°C and spun downward from the outer annular portion of the nozzle having one nozzle hole (double cylindrical type, nozzle diameter 4.6 mm, slit width 0.45 mm). The spun resin molded product was introduced into a cooling bath and wound up with a winder to a draft ratio of 5. The idle running distance was set to 20 mm. A metal filter with a diameter of 200 μm was used as the filter in the melt spinning pack. The wound resin molded product was immersed in isopropanol for 24 hours and further vacuum-dried at room temperature to remove the isopropanol. The obtained resin molded product was stretched at a speed of 500 mm / min in an atmosphere of 80°C to a stretch ratio of 3 to obtain a separation membrane.

[0133] The physical properties of the obtained separation membrane are shown in Table 1. The rigid amorphous ratio RA of the obtained separation membrane was 47%, the porosity was 43%, and N ２ The permeability is 48 GPU, the tensile modulus is 370 MPa, and the CO ２ / N ２ The separation factor α was 7.3, and the membrane had high permeability, excellent strength, and low leakage.

[0134] Example 2 A separation membrane was obtained in the same manner as in Example 1, except that the stretching ratio was 4. As a result, as shown in Table 1, the rigid amorphous fraction RA was 49%, and the tensile modulus was 395 MPa.

[0135] Example 3 A separation membrane was obtained in the same manner as in Example 1, except that the stretching ratio was set to 5. As a result, as shown in Table 1, the rigid amorphous fraction RA was 54%, and the tensile modulus was 450 MPa.

[0136] Example 4 A separation membrane was obtained in the same manner as in Example 1, except that the coagulation bath was changed to N-methylpyrrolidone and the stretching ratio was set to 6 times. As a result, as shown in Table 1, the rigid amorphous fraction RA was 58%, and the tensile modulus increased to 465 MPa. Furthermore, the dense layer thickness was 0.18 μm, and the N ２ The transmission performance increased to 220 GPU.

[0137] Example 5 A separation membrane was obtained in the same manner as in Example 1, except that the stretching ratio was 5 times and the stretching temperature was 60° C. As a result, as shown in Table 1, the rigid amorphous fraction RA was 50%, and the tensile modulus increased to 410 MPa.

[0138] Example 6 A separation membrane was obtained in the same manner as in Example 1, except that the stretching ratio was 5 times and the stretching temperature was 100° C. As a result, as shown in Table 1, the rigid amorphous fraction RA was 52%, and the tensile modulus increased to 415 MPa.

[0139] Example 7 A separation membrane was obtained in the same manner as in Example 1, except that the PMP content was 40% by mass, the dibutyl phthalate content was 60% by mass, and the draft ratio was 9. As a result, as shown in Table 1, the rigid amorphous fraction RA was 46%, and the tensile modulus was reduced to 360 MPa.

[0140] Comparative Example 1 A separation membrane was obtained in the same manner as in Example 1, except that the draft ratio was set to 231 and stretching was not performed. As a result, as shown in Table 2, the rigid amorphous fraction RA was 39%, and the tensile modulus was a low value of 86 MPa.

[0141] <Comparative Example 2> Except for not performing stretching, a separation membrane was obtained in the same manner as in Example 1. As a result, as shown in Table 2, the rigid amorphous fraction RA was 36%, and the tensile modulus was a low value of 92 MPa.

[0142] Comparative Example 3 A separation membrane was obtained in the same manner as in Example 1, except that the PMP was spun at 100% by mass and a draft ratio of 700, and then air-cooled and stretched at a stretching temperature of 130°C and a stretching ratio of 2.3. As a result, as shown in Table 2, the porosity was 20% and N ２ The transmission performance showed a low value of 3 GPU.

[0143] Comparative Example 4 The same procedure as in Example 1 was carried out except that the PMP content was 8 mass % and the dibutyl phthalate content was 92 mass %, but spinning was not possible due to thread breakage.

[0144]

[0145]

[0146] The separation membranes obtained in Examples 1 to 7 satisfied the requirements of the present invention in all items of rigid amorphous ratio RA and porosity, and both were N ２ Permeability is 5 GPU or more, tensile modulus is 100 MPa or more, CO ２ / N ２ The separation coefficient α was 1 or more, and the membranes had high permeability, excellent strength, and low leakage. On the other hand, the separation membranes of Comparative Examples 1 to 4, which did not satisfy the requirements of the present invention in at least one of the rigid amorphous fraction RA and porosity, ２ Permeability, tensile modulus and CO ２ / N ２ At least one of the separation factors α showed a low value.

[0147] 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.

[0148] 1 membrane surface 2 dense layer 3 voids 4 dense layer thickness 5 inner layer of separation membrane 6 hypothetical fluctuation curve of dense layer

Claims

1. A separation membrane mainly composed of poly(4-methyl-1-pentene), wherein the ratio RA of the rigid amorphous poly(4-methyl-1-pentene) in the separation membrane, defined by the following formula 1, is 43% or more and 60% or less, and the porosity of the entire separation membrane is 30% or more and 70% or less, A separation membrane having a dense layer on at least one surface side of the separation membrane. RA (%)=100-(MA+C)...Formula 1 Here, MA is the mobile amorphous fraction and C is the crystallinity.

2. The separation membrane according to claim 1, wherein the loss modulus (E") of the separation membrane has a peak in a temperature range of 30.0°C to 50.0°C in a loss modulus (E")-temperature curve obtained by a dynamic viscoelasticity test.

3. The separation membrane according to claim 1 or 2, wherein the separation membrane has a crystal orientation degree π of 0.70 or more and less than 1.00 when measured with wide-angle X-rays, the crystal orientation degree π being calculated based on the following formula 2: Crystal orientation degree π=(180°-H) / 180°...Formula 2 H is the half-width (°) of the diffraction intensity distribution in the circumferential direction of the wide-angle X-ray diffraction image.

4. 3. The separation membrane according to claim 1, which is a gas-permeable membrane used for separating a gas from a liquid or dissolving a gas in a liquid.

5. The separation membrane according to claim 1 or 2, wherein the dense layer has a thickness from the surface side of the separation membrane in the range of 0.1 μm or more and 2.0 μm or less.

6. The separation membrane according to claim 1 or 2, wherein the dense layer has voids with a diameter of less than 10 nm.

7. The separation membrane according to claim 1 or 2, wherein the rigid amorphous ratio RA is 50% or more and 60% or less.

8. 3. The separation membrane according to claim 1, wherein in a temperature-loss modulus (E") curve obtained by a dynamic viscoelasticity test of the separation membrane, the loss modulus (E") has a peak in a temperature range of 31.0°C or higher and 40.0°C or lower.

9. 3. The separation membrane according to claim 1, wherein the stress at 5% elongation (F5 value) in the longitudinal direction of the separation membrane is 5.0 MPa or more.

10. The separation membrane according to claim 1 or 2, which is in the form of a hollow fiber.

11. 3. The separation membrane according to claim 1, wherein the ratio of the degree of orientation of the outer surface to the degree of orientation of the inner surface of the separation membrane, as measured by polarized infrared spectroscopy, is 1.0 or more and 1.5 or less.

12. 3. The separation membrane according to claim 1, wherein the degree of orientation of the outer surface of the separation membrane, as measured by polarized infrared spectroscopy, is 1.3 or more and 3.0 or less.

13. The separation membrane is ２ Permeability and N ２ Permeability ratio (CO ２ / N ２ The separation membrane according to claim 1 or 2, wherein the selectivity is 1 or more.

14. The separation membrane is N ２ The separation membrane according to claim 1 or 2, having a permeability of 5 GPU or more.

15. The separation membrane according to claim 1 or 2, wherein the separation membrane has a tensile modulus in the longitudinal direction of 100 MPa or more.

16. The separation membrane according to claim 1 or 2, wherein the dense layer is on an outer surface of the separation membrane.

17. A method for producing a separation membrane, comprising the following steps (1) to (3): (1) A preparation step of melt-kneading a resin mixture containing 10% by mass or more and 50% by mass or less of poly(4-methyl-1-pentene) and 50% by mass or more and 90% by mass or less of a plasticizer to obtain a resin composition. (2) A molding process in which the resin composition is melted, discharged from a discharge nozzle, cooled in a cooling bath, and wound up at a draft ratio of 1 to 10 to obtain a resin molded product having an outer surface orientation degree of 1.0 to 1.5 and an outer surface orientation degree / inner surface orientation degree ratio of 1.0 to 1.

5. (3) A stretching step in which the resin molded product is stretched at a temperature of 60° C. to 120° C. and a stretched size of 2 to 6 times to obtain a stretched product.

18. 18. The method for producing a separation membrane according to claim 17, wherein in the molding step, a solvent having a three-dimensional Hansen solubility parameter distance Ra to poly(4-methyl-1-pentene) in the range of 5 to 13 and a three-dimensional Hansen solubility parameter distance Rb to the plasticizer in the range of 4 to 10 is used as a cooling bath.