Separation membrane and method for producing the same

Abstract

To provide a separation membrane exhibiting high elongation and organic solvent resistance while maintaining high gas permeation performance using a highly gas-permeable poly(4-methyl-1-pentene).SOLUTION: The separation membrane is mainly made of a poly(4-methyl-1-pentene), has a dense layer on at least one surface, and is configured such that the ratio O / I of an orientation degree O of an outer surface to an orientation degree I of an inner surface through polarized infrared spectroscopy is 1.8-3.0, the ratio SA of a total area of a gap a virtual diameter of which is 200-700 nm to a total area of a gap on the diameter section of the membrane is 20-50%, and the ratio SB of a total area of a gap a virtual diameter of which is 1000-1600 nm to the total area of the gap is 10-50%.SELECTED DRAWING: None

Description

[Technical field]

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

[0002] There are methods using separation membranes as a degassing method for removing dissolved gas from liquids and a gas exchange method for exchanging dissolved gas in liquid with a gas component in a gas phase. Since high gas permeability is required for separation membranes used in these applications, poly(4-methyl-1-pentene) with excellent gas permeability is sometimes used as a membrane material. Among them, a membrane having a dense layer on the surface is desirable in that it can suppress leakage of the liquid to be treated. On the other hand, such a membrane having a dense layer often has low gas permeability compared to a membrane without a dense layer, and in order to increase the permeability, it is necessary to make the dense layer thinner, which results in the formation of through holes in the thin dense layer, and the liquid to be treated is likely to leak from the holes. In addition, in order to form a high porosity in the support layer, high-speed winding is performed, and the membrane has low elongation due to the high orientation of the support layer, and there is a risk of it breaking during use.

[0003] Furthermore, as the liquids to be treated become more diverse, they may be used to treat liquids containing organic solvents, and in order to improve their practicality, they are required to have better organic solvent resistance.

[0004] Various methods have been proposed to obtain a gas-permeable membrane with high permeability. For example, Patent Document 1 discloses a dry-wet solution method using a polyolefin polymer. Specifically, Patent Document 1 describes a method in which a polymer solution in which a polyolefin polymer is dissolved in a good solvent is extruded from a die at a temperature higher than the melting point of the polyolefin resin, and the polymer solution is brought into contact with a cooling solvent to form an asymmetric structure having a thin dense layer on one surface by thermally induced phase separation.

[0005] However, the membrane of Patent Document 1 is wound at a high speed, and has problems such as insufficient elongation.In addition, the dense layer is thin, and there is a risk of defects occurring when attempting to further increase gas permeability.

[0006] Patent Document 2 discloses a separation membrane produced by a melting method. Specifically, a polyolefin resin is extruded through a die at a temperature equal to or higher than the melting point, cooled and solidified, and then stretched to partially cleave the resin and open the interior, forming a structure with a dense surface and porous interior. This method has excellent organic solvent resistance due to the high surface orientation, but has the disadvantage that the dense layer is thick and the structure has a low porosity, resulting in insufficient gas permeability and elongation. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Special Publication No. 2005-515061 [Patent Document 2] Japanese Patent Application Publication No. 7-155569 Summary of the Invention [Problem to be solved by the invention]

[0008] It is difficult to achieve high gas permeability while maintaining practical organic solvent resistance and elongation with the separation membrane of Patent Document 1. In addition, the separation membrane obtained in Patent Document 2 has organic solvent resistance, but has insufficient porosity and does not have sufficient gas permeability and elongation.

[0009] In view of the problems with the conventional technology described above, the present inventors have an object to provide a separation membrane that uses poly(4-methyl-1-pentene), which has excellent gas permeability, and that has high elongation and organic solvent resistance while maintaining high gas permeability. [Means for solving the problem]

[0010] As a result of intensive research to solve the above problems, the inventors have found that a membrane having poly(4-methyl-1-pentene) as a main component, a ratio O / I of the degree of orientation O of the outer surface to the degree of orientation I of the inner surface as measured by polarized infrared spectroscopy of 1.8 or more and 3.0 or less, a ratio a of the total area of ​​voids having a virtual diameter of 200 nm or more and 700 nm or less to the total area of ​​voids in the radial cross section of the membrane of 20 or more and 50% or less, and a ratio b of the total area of ​​voids having a virtual diameter of 1000 nm or more and 1600 nm or less to the total area of ​​voids of 10% or more and 50% or less, can have high elongation and organic solvent resistance while maintaining high gas permeability, and have completed the present invention.

[0011] That is, the membrane is characterized in that it has poly(4-methyl-1-pentene) as its main component, the ratio O / I of the degree of orientation O of the outer surface to the degree of orientation I of the inner surface as measured by polarized infrared spectroscopy is 1.8 or more and 3.0 or less, the ratio a of the total area of ​​voids with a virtual diameter of 200 nm or more and 700 nm or less to the total area of ​​voids in the radial cross section of the membrane is 20% or more and 50% or less, and the ratio b of the total area of ​​voids with a virtual diameter of 1000 nm or more and 1600 nm or less to the total area of ​​voids is 10% or more and 50% or less. Effect of the Invention

[0012] According to the present invention, a separation membrane is provided that uses poly(4-methyl-1-pentene) having excellent gas permeability, and that has high elongation and organic solvent resistance while maintaining high gas permeability. [Brief description of the drawings]

[0013] [Figure 1] Figure 1 shows an example of a radial cross section captured with a SEM at a magnification of 10,000 times. [Diagram 2] FIG. 2 shows the image in FIG. 1 after it has been binarized and noise removed. [Diagram 3] FIG. 3 shows the contours of voids larger than 10 nm extracted from the image in FIG. 2 and the dense layer thickness. [Figure 4]Figure 4 shows an example of an image of a radially cut cross section taken with an SEM at a magnification of 5,000x. [Diagram 5] FIG. 5 is a diagram that illustrates a longitudinal section and the internal structure of a separation membrane. [Figure 6] Figure 6 is an example of an image of a cross section cut vertically, taken with an SEM at a magnification of 5,000 times. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] The separation membrane of the present invention is composed mainly of poly(4-methyl-1-pentene), and has a ratio O / I of the degree of orientation O of the outer surface to the degree of orientation I of the inner surface as measured by polarized infrared spectroscopy of 1.8 to 3.0, and a ratio S of the total area of ​​voids having a virtual diameter of 200 nm to 700 nm to the total area of ​​voids in the radial cross section of the membrane. A is 20% or more and 50% or less, and the ratio S of the total area of ​​voids with a virtual diameter of 1000 nm or more and 1600 nm or less to the total area of ​​voids B is 10% or more and 50% or less, and has a dense layer on at least one surface. In this specification, a ratio (percentage, part, etc.) based on mass is the same as a ratio (percentage, part, etc.) based on weight.

[0015] (Resin composition constituting separation membrane) The resin composition constituting the separation membrane of the present invention contains poly(4-methyl-1-pentene) shown in (1) below as a main component, and may contain the following components (2) to (6) in addition to (1).

[0016] (1) Poly(4-methyl-1-pentene) (hereinafter referred to as "PMP") The separation membrane of the present invention must contain PMP as a main component. The main component here refers to the component that is contained in the largest amount by mass among all the components of the separation membrane.

[0017] PMP may have 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").

[0018] Examples of the olefin having 2 to 20 carbon atoms to be copolymerized with 4-methyl-1-pentene include ethylene, propylene, 1-butene, 1-hexene, 1-heptene, 1-octene, 1-decene, 1-tetradecene, 1-hexadecene, 1-heptadecene, 1-octadecene, and 1-eicosene.

[0019] 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.

[0020] The density of the PMP of the present invention is 825 (kg / m 3 ) or more 840 (kg / m 3 ) or less, and 830 (kg / m 3 ) or more 835 (kg / m 3 If the density is less than the above range, the mechanical strength of the separation membrane may decrease, and defects may easily occur. On the other hand, if the density is greater than the above range, the gas permeability tends to decrease.

[0021] 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 easily mixed with the plasticizer (B) described later and can be co-extruded, but is preferably 1 g / 10 min to 200 g / 10 min, more preferably 5 g / 10 min to 30 g / 10 min. If the MFR is within the above range, it is easy to extrude to a relatively uniform film thickness.

[0022] PMP may be produced directly by polymerizing olefins, or may be produced by pyrolyzing a high molecular weight 4-methyl-1-pentene polymer. The 4-methyl-1-pentene polymer may be purified by a method such as solvent fractionation, which separates the polymer based on the difference in solubility in a solvent, or molecular distillation, which separates the polymer based on the difference in boiling point.

[0023] In addition to the PMP produced as described above, a commercially available polymer such as TPX manufactured by Mitsui Chemicals, Inc. may also be used.

[0024] 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 components of the separation membrane are taken as 100% by mass. When the content of PMP in the separation membrane is 70% by mass or more, the gas permeability is sufficient.

[0025] The content of PMP in the raw material 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 material 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.

[0026] (2) Plasticizer for PMP 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 (mass basis) or less, more preferably 500 ppm (mass basis) or less, and particularly preferably 100 ppm (mass basis) or less.

[0027] The plasticizer for PMP is not particularly limited as long as it is a compound that thermoplasticizes PMP. The plasticizer for PMP may be a single type of plasticizer or a combination of two or more types of plasticizers.

[0028] 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 preferably used from the viewpoints of compatibility and spinnability.

[0029] The plasticizer for PMP is preferably dissolved from the separation membrane after it is formed. 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 components constituting the raw material are taken as 100% by mass.

[0030] A content of 90% by mass or less leads to good membrane strength of the separation membrane. Also, a content of 50% by mass or more leads to good permeability of the separation membrane. The content is more preferably 50% by mass or more and 85% by mass or less, further 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.

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

[0032] 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-blocking agents, chain extenders, ultraviolet absorbers, infrared absorbers, color prevention agents, matting agents, antibacterial agents, antistatic agents, deodorants, flame retardants, weather resistance agents, antistatic agents, antioxidants, ion exchange agents, defoamers, color pigments, fluorescent brightening agents, and dyes.

[0033] (Separation membrane shape) 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.

[0034] 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 observed, for example, by applying stress to a hollow fiber membrane sufficiently cooled in liquid nitrogen, cutting the membrane in the thickness direction, and observing the cross section (hereinafter referred to as the "diameter cross section") using an optical microscope or a scanning electron microscope (SEM). Specific methods will be described in detail in the Examples.

[0035] 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.

[0036] From the viewpoint of achieving both the effective membrane area when packed in a module and the 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, further preferably 200 μm or more, and particularly preferably 300 μm or more. The outer diameter is more preferably 1000 μm or less, further preferably 500 μm or less, and particularly preferably 450 μm or less.

[0037] In addition, in consideration of 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.

[0038] 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.

[0039] The method for adjusting the outer diameter, inner diameter, and hollowness of the hollow fiber membrane to 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 manufacture the hollow fiber membrane, the draft ratio calculated by the take-up speed / discharge speed, or the free running distance, which is the distance from the outlet hole to the cooling bath in the forming process described below.

[0040] It is important that the separation membrane of the present invention has a dense layer. By having a dense layer, leakage of the liquid to be treated can be suppressed. The dense layer refers to a layer that does not have voids, for example, when the radial cross section of the separation membrane is observed at a magnification of 10,000 times using a scanning electron microscope (SEM) (for example, FIG. 1). Here, the term "voids" refers to, for example, a layer having an area of ​​3.57 nm 2 or less when the radial cross section of the separation membrane is observed at a magnification of 5,000 times using a scanning electron microscope (hereinafter, "SEM"). 2or more, that is, a recess with a virtual diameter of 10 nm or more. The term "recess" as used herein refers to a dark area in an image observed by SEM, and the image captured by SEM can be binarized (Huang's binarization) using image analysis software to extract its outline. Here, the term "multiple voids" refers to 10 or more voids per field of view, that is, recesses with a virtual diameter of 10 nm or more, when the radial cross section is observed at a magnification of 5,000 times using SEM. In addition, the thickness of the dense layer of the separation membrane of the present invention is preferably 0.10 μm or more and 2.00 μm or less. The dense layer thickness refers to the length from an arbitrary point on a surface without voids (for example, membrane surface 1 in FIG. 1) to the other surface, where a straight line is drawn vertically to a hole with a diameter of more than 10 nm, that is, a void. The dense layer thickness can be obtained by, for example, 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 using a scanning electron microscope (SEM), binarizing the obtained image using image analysis software "ImageJ" (for example, FIG. 2), and extracting only pores larger than 10 nm. The method for measuring the dense layer thickness (for example, dense layer thickness 2 in FIG. 3) will be described in detail in the Examples. The separation membrane of the present invention preferably has a dense layer thickness of 0.10 μm or more and 2.0 μm or less. When the dense layer thickness is 0.10 μm or more, the leakage resistance is good, and when the dense layer thickness is 2.0 μm or less, the permeability is good. The dense layer thickness is preferably 0.1 μm or more and 1.5 μm or less. In addition, the dense layer thickness is preferably 0.1 μm or more and 1.0 μm or less, and more preferably 0.1 μm or more and 0.4 μm or less.

[0041] In the separation membrane of the present invention, it is preferable to contact the dense layer with the liquid to be treated during operation. By contacting the dense layer with the liquid to be treated, it is possible to suppress the shape change of the separation membrane and prevent a significant decrease in permeation performance, which is preferable. In addition, it is preferable that the dense layer is on the outer surface of the separation membrane of the present invention. The outer surface here refers to the longer surface of the two surfaces parallel to the membrane thickness direction in the radial cross section of the separation membrane. For example, in a hollow fiber membrane, it refers to the surface on the outer diameter side. On the other hand, in the case of a flat membrane, the length of the two surfaces is equal, so for convenience in the present invention, the surface with the higher degree of orientation of the two surfaces parallel to the membrane thickness direction is referred to as the outer surface. In addition, in the radial cross section of the separation membrane, the other surface parallel to the membrane thickness direction with respect to the outer surface is referred to as the inner surface. By having the dense layer on the outer surface, the contact area of ​​the liquid to be treated can be increased compared to the case where the liquid to be treated is contacted with the inner surface, and the permeation performance is more likely to be improved. In addition, the separation membrane of the present invention preferably has a plurality of pores, in which the average area A of pores having a virtual diameter of 200 nm or more and 700 nm or less (hereinafter referred to as "small pores") and the average area B of pores having a virtual diameter of 1000 nm or more and 1600 nm or less (hereinafter referred to as "large pores") are within a specific range. A and the average area of ​​the large voids S B is a value measured at a radial cross section. An example of an image taken by SEM is shown in Figure 4.

[0042] The "average area A of small voids" is the arithmetic mean value of the areas of all recesses with a virtual diameter of 200 nm to 700 nm in the observation range when the diameter cross section is observed at a magnification of 5,000 times using a SEM. The average area A of small voids is 0.1 μm 2 More than 0.3μm 2 The average area A of the small voids is preferably 0.1 μm or less. 2 By setting the average area A of the small voids to 0.3 μm or more, the interconnectivity of the large voids can be improved, and the gas permeability can be improved. 2 The average area A of the small voids is 0.15 μm or less to maintain elongation. 2 More than 0.28μm 2More preferably, it is 0.20 μm or less. 2 More than 0.25μm 2 It is even more preferable that:

[0043] The "average area B of large voids" is the arithmetic mean value of the areas of all recesses with a virtual diameter of 1000 nm to 1600 nm in the observation range when the diameter cross section is observed at a magnification of 5,000 times using an SEM. The virtual diameter of the voids was calculated from the area of ​​the contours of the recesses extracted by binarizing the obtained SEM images (Huang's binarization) using image analysis software such as ImageJ. The average area B of large voids is 1.0 μm 2 2.0μm or more 2 It is preferable that the average area B of the large voids is 1.0 μm or less. 2 On the other hand, the average area B of the large voids is 2.0 μm or more, so that the gas permeability can be improved. 2 The average area B of the large voids is 1.2 μm or less to maintain high elongation. 2 More than 1.9μm 2 More preferably, it is 1.5 μm or less. 2 More than 1.8μm 2 It is even more preferable that:

[0044] Furthermore, the values ​​of the coefficients of variation of A and B are preferably 15% or less. The coefficient of variation of A is calculated by dividing the standard deviation of A at any 10 points in the observed area by the arithmetic mean of A and multiplying the result by 100. The coefficient of variation of B is calculated in the same manner. By keeping the coefficients of variation of A and B at 15% or less, a homogeneous structure is maintained, and therefore high permeability and elongation can be maintained. The coefficients of variation of A and B are more preferably 10% or less, and even more preferably 5% or less.

[0045] The separation membrane of the present invention has a ratio S of the total area of ​​small voids to the total area of ​​voids. B (hereinafter referred to as “S A ") and the ratio of the total area of ​​large voids to the total area of ​​voids S B (hereinafter referred to as “SB It is important that the range of S A , S B are expressed by the following equations (1) and (2), respectively.

[0046] S A = (total area of ​​small voids) / (total area of ​​voids) Equation (1) S B = (total area of ​​large voids) / (total area of ​​voids) Equation (2) The total area of ​​voids is the sum of the areas of all voids in the observation range when the radial cross section is observed at a magnification of 5,000 times using an SEM. The total area of ​​small voids is the sum of the areas of small voids in the observation range when the radial cross section is observed at a magnification of 5,000 times using an SEM, and the total area of ​​large voids is the sum of the areas of large voids in the observation range when the radial cross section is observed under the same conditions. S A It is important that the ratio is between 20% and 50%. A The gas permeability can be improved by making the S A By keeping the value at 50% or less, high elongation can be maintained. A More preferably, the ratio is 25% or more and 40% or less, and further preferably, 30 to 40%. B It is important that the ratio is between 10% and 50%. B By keeping the S content at 10% or more, high gas permeability can be maintained. B By keeping the value at 50% or less, high elongation can be maintained. B is more preferably 20% or more and 50% or less, and further preferably 30% or more and 50% or less. The method for measuring the virtual diameter will be described in detail in the Examples.

[0047] Further, the above S A , S B The coefficients of variation of S are preferably 15% or less. A The coefficient of variation of is calculated by dividing the standard deviation of A of 10 points in any area observed by the arithmetic mean of A and multiplying it by 100. BThe coefficient of variation of is calculated in the same manner. A and S B The coefficient of variation of is 15% or less, so that a homogeneous structure can be maintained, and high permeability and elongation can be maintained. A and S B The coefficient of variation of each of these is more preferably 10% or less, and further preferably 5% or less.

[0048] (average length of large voids) In the separation membrane of the present invention, among the voids having a virtual diameter of 1000 nm to 1600 nm in 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"), the average length of the voids outside the center of the membrane thickness is preferably 3500 nm or more, and the average length of the voids inside the center of the membrane thickness is preferably 1000 nm to 3000 nm. As an example, a drawing showing a schematic diagram of a longitudinal cross section and an internal structure of a separation membrane is shown in FIG. 5. The center of the membrane thickness is a point (membrane thickness / 2) μm from one surface of the membrane in the membrane thickness direction, and the average length of the large voids is the length of the longest straight line that can directly connect two points on the outer edge of the large voids when the longitudinal cross section is observed at a magnification of 5,000 times using an SEM (for example, FIG. 6). The average length of the large voids is the arithmetic average value of the lengths of 30 randomly selected large voids. When the average length of the large voids outside the center of the film thickness is 3500 nm or more, the orientation degree O of the outer surface can be increased, and the film can have organic solvent resistance. The average length of the large voids outside the center of the film thickness is more preferably 4000 nm or more, and even more preferably 4500 nm or more. On the other hand, when the average length of the large voids inside the center of the film thickness is 1000 nm or more, the film strength is good, and when it is 3000 nm or less, sufficient elongation can be maintained during operation. The average length of the large voids inside the center of the film thickness is more preferably 1000 nm or more and 2500 nm or less, and even more preferably 1000 nm or more and 2000 nm or less. The method for calculating the average length of the large voids will be described in detail in the examples.

[0049] (porosity) The separation membrane of the present invention preferably has a porosity of 30% or more and 70% or less. 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 such a range, a 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.

[0050] (Outer surface orientation degree O) The separation membrane of the present invention preferably has an outer surface orientation degree O in the longitudinal direction of 2.0 or more and 3.5 or less. The longitudinal direction here means the machine direction during production, and an outer surface orientation degree O of 2.0 or more provides good organic solvent resistance. When the outer surface orientation degree O of the separation membrane is 2.3 or more, 2.5 or more, a higher effect can be obtained.

[0051] On the other hand, when the degree of orientation O of the outer surface of the separation membrane is 3.5 or less, the flexibility of the separation membrane is good.

[0052] 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.

[0053] (Ratio of outer surface orientation to inner surface orientation) It is important that the ratio O / I of the orientation degree O of the outer surface to the orientation degree I of the inner surface of the separation membrane of the present invention is 1.8 or more and 3.0 or less. When the ratio O / I of the orientation degree O of the outer surface to the orientation degree I of the inner surface is 3.0 or less, sufficient elongation can be maintained while maintaining the organic solvent resistance of the surface. On the other hand, when the ratio O / I of the orientation degree O of the outer surface to the orientation degree I of the inner surface is 1.8 or more, the organic solvent resistance is good. The ratio O / I of the orientation degree O of the outer surface to the orientation degree I of the inner surface is preferably 2.0 or more and 3.0 or less, more preferably 2.5 or more and 3.0 or less. The measurement method of the orientation degree will be described later in the examples.

[0054] (Gas permeability) The separation membrane of the present invention preferably has an N2 permeability of 5 GPU or more at 100 kPa and 37° C. The N2 permeability is more preferably 10 GPU or more, even more preferably 50 GPU or more, particularly preferably 100 GPU or more, and even more particularly preferably 200 GPU or more. The calculation method will be described in detail in the Examples.

[0055] (Change in gas permeability before and after immersion in organic solvent) It is important that the separation membrane of the present invention has a change rate Y / X of 0.30 or more and 1.20 or less, where X is the N2 permeability of the separation membrane at a differential pressure of 100 kPa, and Y is the N2 permeability of the separation membrane at a differential pressure of 100 kPa after immersing the separation membrane in chloroform for 5 seconds. Examples of organic solvents used as degassing membranes include triacetin, N-methylpyrrolidone, and acetone, but all of them are expected to be used for a long time, so in this application, the change rate Y / X of N2 permeability at 100 kPa and 37°C after immersing in chloroform for 5 seconds was calculated as an accelerated test. The change rate Y / X of the permeability after immersing in chloroform for 5 seconds is 0.30 or more and 1.20 or less, so that the above-mentioned organic solvent can be used well when the treated liquid is used. The change rate Y / X of the permeability after immersing in chloroform for 5 seconds is preferably 0.50 or more and 1.20 or less, more preferably 0.60 or more and 1.20 or less.

[0056] (CO2 / N2 selectivity) The dense layer of the present application is non-porous, and therefore has a very long leak time, and because it is non-porous, gas permeation is performed by a dissolution-diffusion mechanism. On the other hand, in a porous structure, because it has through-holes, it has a short leak time, and gas permeates by Knudsen diffusion. That is, the denseness of the dense layer can be evaluated by the gas separation factor, and a membrane with high density tends to have a long leak time.

[0057] In general, permeation through polymer membranes depends on the pore size in the membrane. In membranes with a maximum pore size in the dense layer of 3 nm or less, gas permeates 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 the two gases, depends only on the polymer material and not on the thickness of the dense layer. Thus, for example, the gas separation factor α0(CO2 / N2) for CO2 and N2 can be expressed as P0(CO2) / P0(N2). Commonly used polymers produce α0(CO2 / N2) values ​​of at least 1.

[0058] 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, α1 (CO2 / N2) is √28 / 44 = 0.80. Knudsen diffusion may cause leakage, and α1 (CO2 / N2) of 1 or more is preferable because it reduces the risk of leakage. In particular, in the case of a thin membrane with a dense layer thickness of 0.1 μm to 3.0 μm as described above, a CO2 / N2 selectivity of 1.0 or more results in good low leakage properties.

[0059] When 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. The defects here refer to holes with a size of 3 nm or more on the surface of the dense layer. Thus, the presence or absence of holes or defects in the dense layer of the membrane of the present invention can be read by the gas separation coefficient α(CO2 / N2) measured for CO2 and N2. If the gas separation coefficient α(CO2 / N2) is less than 1, the membrane has a large number of holes or defects in the dense layer. If there are a large number of holes or defects in the dense layer, premature liquid or plasma leakage will occur and the membrane is not suitable for long-term use. Similarly, such membranes cannot be used for applications in the field of gas separation. On the other hand, if the gas separation coefficient α(CO2 / N2) is 1.0 or more, the membrane has low leakage properties. Therefore, the gas separation factor α(CO2 / N2) of the membrane according to the present invention is preferably 1.0 or more, more preferably 1.5 or more, and even more preferably 2.0 or more.

[0060] (Elongation at break) The separation membrane of the present invention preferably has a breaking elongation in the longitudinal direction of 300% or more. A breaking elongation of 300% or more can suppress breakage during use. The breaking elongation is more preferably 350% or more, further preferably 400% or more, and particularly preferably 450% or more. The method for measuring the tensile modulus of the separation membrane will be described in detail in the Examples.

[0061] (Membrane manufacturing method) A method for producing a separation membrane, comprising the following steps (1) and (2): (1) A preparation step of melt-kneading a 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 discharged from a nozzle having a gap of 0.05 mm or more and 0.30 mm or less at a nozzle temperature of 220° C. or more and 260° C. or less, and wound up at a draft ratio of 5 to 30.

[0062] Next, the method for producing a separation membrane of the present invention will be specifically described using as an example the case where the separation membrane is a hollow fiber membrane.

[0063] (Preparation process) In the preparation process for obtaining 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 a 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 a plasticizer, more preferably 20% by mass to 45% by mass of PMP and 55% by mass to 80% by mass of a plasticizer, and particularly preferably 25% by mass to 40% by mass of PMP and 60% by mass to 75% by mass of a plasticizer.

[0064] As the device used for melt-kneading the mixture, a kneader, a roll mill, a Banbury mixer, or a mixer such as a single-screw or twin-screw extruder can be used. Among them, from the viewpoint of improving the uniform dispersion of the plasticizer, it is preferable to use a twin-screw extruder, and from the viewpoint of removing volatile substances such as moisture and low molecular weight substances, it is more preferable to use a twin-screw extruder with a vent hole. In addition, from the viewpoint of increasing the mixing strength and improving the uniform dispersion of the plasticizer, it is preferable to use a twin-screw extruder equipped with a screw having a kneading disk portion.

[0065] The resin composition obtained in the preparation step may be pelletized once and then melted again for use in melt film formation, or may be directly introduced into a die for use in melt film formation. When pelletizing once, it is preferable to use a resin composition in which the pellets are dried to reduce the moisture content to 200 ppm (mass basis) or less. By reducing the moisture content to 200 ppm (mass basis) or less, deterioration of the resin can be suppressed.

[0066] (Formation process) In the hollow fiber membrane forming process, a hollow fiber membrane is obtained from a molten mixture of PMP and a plasticizer, i.e., a resin composition, by utilizing phase separation. Specifically, the resin composition obtained in the preparation process is discharged into a gas atmosphere from a discharge nozzle having a double annular nozzle with a gas flow path in the center, and introduced into a cooling bath to phase separate the resin composition, thereby obtaining a resin molded product.

[0067] As a specific method, the above-mentioned resin composition in a molten state is discharged from the outer tube of a double annular spinning nozzle, while the hollow portion forming gas is discharged from the inner ring of a double tube type spinneret. The resin composition discharged in this way is cooled and solidified in a cooling bath to obtain a resin molded product. At that time, it is important that the gap of the nozzle is 0.05 mm or more and 0.30 mm or less. By making the gap of the nozzle 0.30 mm or less, high shear is applied when the above-mentioned resin composition in a molten state is discharged from the spinneret, and the orientation degree of the resin, especially on the outer surface, is increased, and organic solvent resistance can be obtained. In addition, by making the gap of the nozzle 0.05 mm or more, the resin can be stably discharged. The gap of the nozzle is more preferably 0.05 mm or more and 0.18 mm or less, and more preferably 0.05 mm or more and 0.13 mm or less. In addition, it is important that the nozzle temperature is 220 ° C. or more and 260 ° C. or less. By setting the die temperature at 220° C. or higher and 260° C. or lower, the resin composition in a molten state starts phase separation in advance inside the die, forming the large voids described above and improving the gas permeability. The die temperature is more preferably 220° C. or higher and 250° C. or lower, even more preferably 220° C. or higher and 240° C. or lower, and particularly preferably 220° C. or higher and 230° C. or lower.

[0068] Here, the cooling bath for cooling the resin composition discharged from the nozzle is described. The solvent of the cooling bath is preferably selected based on the affinity with PMP and the plasticizer. As the solvent of the cooling bath, it is preferable to use a solvent in which the solubility parameter distance Ra to PMP is in the range of 5 to 13 and the solubility parameter distance Rb to the plasticizer is in the range of 4 to 10, and it is more preferable to use a solvent in which Ra is in the range of 10 to 12 and Rb is in the range of 4 to 6. When Ra and Rb are in the above range, the dense layer can be thinned and the permeability is good. The reason for this is that when Ra is in the range of 10 to 12, solidification occurs before crystallization of PMP, and when Rb is in the range of 4 to 6, the solvent and the plasticizer are quickly exchanged, and as a result, the layer is thinned while suppressing excessive crystallization. It is believed that this leads to good permeability.

[0069] The affinity of PMP with a solvent can be estimated by the three-dimensional Hansen solubility parameter, as described in the literature (Ind. Eng. Chem. Res. 2011, 50, 3798-3817.). Specifically, the smaller the solubility parameter distance (Ra) in the following formula (1), the higher the affinity of the solvent with PMP.

[0070]

number

[0071] Here, δ Ad , δ Ap and δ Ah are the dispersion term, polar term and hydrogen bond 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.

[0072] The affinity between the plasticizer and the cooling solvent can be estimated in a similar manner. Specifically, the smaller the solubility parameter distance (Rb) in the following formula (2), the higher the affinity of the solvent to the plasticizer.

[0073]

number

[0074] Here, δ Bd , δ Bp and δ Bh are the dispersion term, polar term and hydrogen bond 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.

[0075] When the solvent is a mixed solvent, the solubility parameter (δ Mixture ) can be calculated using the following formula (3).

[0076]

number

[0077] Here, φ i , δ i are the volume fraction and solubility parameter of component i, which are valid for the dispersion term, polarity term, and hydrogen bond 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. For the 3D Hansen solubility parameters of the solvent, the values ​​were used if they were given in the literature (Ind. Eng. Chem. Res. 2011, 50, 3798-3817.). For solvent parameters not given, the values ​​included in the software "Hansen Solubility Parameter in Practice" developed by Charles Hansen et al. were used. For the 3D Hansen solubility parameters of solvents and polymers not given in the above software, they can be calculated by the Hansen sphere method using the above software.

[0078] 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.

[0079] It is also preferred that the resin composition discharged from the nozzle is exposed to a gaseous atmosphere that promotes the evaporation of the plasticizer, i.e., an atmosphere in which the evaporation of the plasticizer can occur, before cooling by at least one of its surfaces, preferably the surface on which the dense layer is to be formed. The gas used to form the gaseous atmosphere is not particularly limited, but preferably air or nitrogen is used. The gaseous atmosphere generally has a temperature lower than the nozzle temperature. In this case, in order to evaporate a sufficient amount of the plasticizer, it is preferred to expose at least one of the surfaces of the molded body to the gaseous atmosphere for at least 0.5 milliseconds (ms).

[0080] 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 5 or more and 30 or less. The draft ratio is more preferably 10 or more and 25 or less, and even more preferably 15 or more and 20 or less. When the draft ratio is 5 or more, the orientation degree O of the resin on the outer surface that is rapidly cooled and solidified after discharge is high, and organic solvent resistance can be obtained. Specifically, the orientation of the molecular chains by draft occurs when the resin composition is stretched because the winding speed is faster than the discharge speed, but when the resin composition is stretched, if it is in a cooling bath, the outer surface side that directly contacts the cooling bath solidifies first, so that the outer surface side is stretched while solidifying, and the molecular chains are strongly oriented. On the other hand, the inner surface side of the separation membrane that does not contact the cooling bath is stretched before solidification progresses, so that orientation is difficult to apply. In this way, when the draft ratio is large, it is possible to create a difference in orientation between the outer surface side and the inner surface side of the separation membrane. This allows the outer surface side with a high degree of orientation to have organic solvent resistance while maintaining high elongation due to the effect of the inner surface side with a low degree of orientation. By setting the draft ratio to 30 or less, it is possible to prevent excessive stretching of the resin composition discharged from the die, and to prevent leakage due to defects in the dense layer.

[0081] (Cleaning process) The resin composition thus obtained is immersed in a solvent that does not dissolve the polymer but is miscible with the plasticizer, and the plasticizer is dissolved through the process, thereby increasing the porosity. In this case, by using a solvent or mixed solvent that has a suitable affinity with the plasticizer, good solvent exchange is performed and cleaning efficiency is improved. The solvent is not particularly limited as long as it does not dissolve the polymer but is miscible with the plasticizer, and specific examples of the solvent that are preferably used include methanol, ethanol, isopropanol, and acetone.

[0082] (drying process) The resin composition after the washing step is preferably subjected to a drying step for the purpose of removing the solvent attached in the washing step. Drying is preferably carried out at a temperature at which the above-mentioned solvent that does not dissolve the polymer but is miscible with the plasticizer can be vaporized and removed, specifically, drying is preferably carried out at a temperature from room temperature to 150°C.

[0083] (Heat treatment process) The separation membrane can then 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 around a bobbin or paper tube in a dry heat oven.

[0084] The heat treatment temperature is preferably from 100° C. to 200° C., more preferably from 110° C. to 180° C., and even more preferably from 120° C. to 160° C. The heat treatment time is preferably from 1 second to 600 seconds, more preferably from 5 seconds to 300 seconds, and even more preferably from 10 seconds to 60 seconds.

[0085] In this manner, the separation membrane of the present invention containing PMP as a main component can be produced. EXAMPLES

[0086] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. [Measurement and evaluation methods] The respective property values ​​in the examples were determined by the following methods. (1) Outer and inner diameters of hollow fiber membrane (μm) 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 outer and inner diameters of 10 randomly selected points were determined as the outer and inner diameters of the hollow fiber membrane, respectively. (2) Hollow ratio of hollow fiber membrane (%) From the outer diameter and inner diameter obtained in (1) above, the hollow ratio of the hollow fiber membrane was calculated according to the following formula.

[0087] Hollowness ratio (%) = 100 × [inner diameter (μm 2 )] 2 / [Outer diameter (μm 2 )] 2 (3) Gas permeability (GPU) A small module with an effective length of 100 mm was produced, consisting of a single separation membrane. The hollow fiber membrane used was vacuum dried for 3 hours before producing the small module. This small module was used to measure the gas permeation rate. Carbon dioxide or nitrogen was used alone as the measurement gas for evaluation, and the pressure change per unit time on the permeation side of carbon dioxide or nitrogen was measured using an external pressure method at a measurement temperature of 37°C in accordance with the pressure sensor method of JIS K7126-1 (2006). Here, the pressure difference between the supply side and the permeation side was set to 100 kPa.

[0088] Next, the gas permeation rate Q was calculated by the following formula. The ratio of the gas permeation rates of each component 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.

[0089] Transmission speed Q(GPU)=10 -6 [Permeation gas volume (cm 3 )] / [Membrane area (cm 2 ) × time (s) × pressure difference (cmHg)] Among the results measured by the above method, the nitrogen permeability was designated as X.

[0090] The N2 permeability Y at a differential pressure of 100 kPa after immersing the separation membrane in chloroform for 5 seconds was measured by immersing the separation membrane in chloroform with both ends raised so that only the outer surface was in contact with the membrane. A small module with an effective length of 100 mm was similarly produced using the membrane. The membrane was immersed in chloroform for 5 seconds, then immediately immersed in isopropanol to remove the chloroform, and finally immersed in water to remove the isopropanol. A small module was then produced using the membrane that had been vacuum dried for 3 hours. The nitrogen permeability was measured using this small module in the same manner as in the above measurement, and the result was adopted as the N2 permeability Y at a differential pressure of 100 kPa after immersing the membrane in chloroform for 5 seconds. (4) Dense layer thickness (μm) 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 break it so that the radial or longitudinal cross section was exposed. Next, platinum was sputtered under the following conditions to perform pretreatment on the radial or longitudinal cross section, and then the thickness of the dense layer was determined by observing the separation membrane at a magnification of 10,000 times 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 until the first pore exceeding 10 nm was reached was determined as the thickness of the dense layer. The extraction of the pores was performed after binarizing the analysis image using the image analysis software "ImageJ". The binarization was performed by binarizing the analysis image using the image analysis software "ImageJ" ... Furthermore, the binarized image obtained was subjected to a noise removal process (equivalent to Despeckle in ImageJ) in which all pixels were replaced with the median value of the 3 x 3 pixels surrounding that pixel, and the resulting 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 random locations, and the average value was used as the dense layer thickness.

[0091] (Sputtering) Equipment: Hitachi High-Technologies Corporation (E-1010) Deposition time: 40 seconds Current value: 20mA (SEM) Equipment: Hitachi High-Technologies Corporation (SU1510) Acceleration voltage: 5 kV Probe Current: 30 (5) Measurement of small and large voids The separation membrane was frozen with liquid nitrogen, and then stress was applied (using a razor or microtome as necessary) to break it so that the radial cross section was exposed. Next, the radial cross section was pretreated by sputtering with platinum under the conditions described below, and then observed at 5,000x magnification using an SEM, and 10 random areas were observed. After extracting all voids in each field of view, the average area A of small voids and the average area B of large voids were calculated. Furthermore, the ratio S of the total area of ​​small voids to the total area of ​​voids was calculated. A , the ratio of the total area of ​​large voids to the total area of ​​voids S B The virtual diameter of the void was calculated from the area of ​​the concave portion extracted by binarizing the SEM image obtained using the image analysis software ImageJ (Huang's binarization). A , S B The coefficient of variation was calculated by dividing each standard deviation by the arithmetic mean and multiplying it by 100.

[0092] (Sputtering) Equipment: Hitachi High-Technologies Corporation (E-1010) Deposition time: 40 seconds Current value: 20mA (SEM) Equipment: Hitachi High-Technologies Corporation (SU1510) Acceleration voltage: 5 kV Probe Current: 30 (6) Average length of large voids After freezing the separation membrane with liquid nitrogen, stress was applied (using a razor or microtome as necessary) to expose the longitudinal cross section, which is a cross section parallel to the longitudinal direction and film thickness direction of the separation membrane. Next, the longitudinal section was pretreated by sputtering with platinum, and the average length of the voids was measured when observed at a magnification of 5,000 times using an SEM. Observation was performed on two regions, the outside from the center of the film thickness and the inside from the center of the film thickness, and the region from the outer surface of the separation membrane to a point at (film thickness / 2) μm in the film thickness direction was defined as the outside from the center of the film thickness, and the region from the inner surface of the separation membrane to a point at (film thickness / 2) μm in the film thickness direction was defined as the inside from the center of the film thickness. The extraction of the holes is performed after binarizing the analysis image (Huang's binarization) using the image analysis software "ImageJ". The obtained binarized image was used as the analysis image after noise removal (equivalent to Despeckle in ImageJ) in which all pixels are replaced with the median value of the 3 × 3 pixels around that pixel (equivalent to Despeckle in ImageJ). The pores were extracted using the Analyze Particles command in ImageJ, with an area of ​​0.785 μm 2 More than 2.10μm 2 All the following pores, i.e., pores with a virtual diameter of 1000 nm or more and 1600 nm or less, were extracted, and the lengths of 30 pores randomly selected from each of the two regions mentioned above were calculated, and the arithmetic mean value was adopted as the average pore length.

[0093] (Sputtering) Equipment: Hitachi High-Technologies Corporation (E-1010) Deposition time: 40 seconds Current value: 20mA (SEM) Equipment: Hitachi High-Technologies Corporation (SU1510) Acceleration voltage: 5 kV Probe Current: 30 (7) Breaking elongation (%) The breaking elongation of the separation membrane was measured in an environment of 20°C and 65% humidity using a tensile tester (Orientec Co., Ltd. Tensilon UCT-100) with a sample length of 100 mm and a tensile speed of 100 mm / min, and other conditions were measured according to the method specified in "JIS L 1013:2010 Chemical fiber filament yarn test method 8.11 Elasticity". The breaking elongation (%) was calculated from the ratio of the sample length at break to the initial sample length. The measurement was performed five times, and the average value was used. (8) Porosity (%) The fiber length L (mm) and mass M (g) of the hollow fiber membrane were measured after vacuum drying at 25° C. for 8 hours. The density ρ1 of the hollow fiber membrane was calculated from the following formula using the outer diameter (mm) and inner diameter (mm) measured in (1) above.

[0094] ρ1=M / [π×{(outer diameter / 2) 2 - (inner diameter / 2) 2}×L] The porosity ε (%) was calculated from the following formula.

[0095] ε=1-ρ1 / ρ2 where ρ2 is the density of the polymer. (9) Orientation degree of outer surface O 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 separation membrane in the longitudinal direction (MD) and the direction perpendicular to the longitudinal direction (diameter) (TD) after vacuum drying at 25°C for 8 hours. A diamond prism was used as the ATR crystal, with an incidence angle of 45°, an accumulation count of 64 times, and a wire grid polarizer, and measurements were performed with S-polarized light. From the obtained ATR spectrum, a 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 separation membrane, the 918 cm -1 The intensity of the band near (-CH3 group rocking vibration) was measured in the MD and TD of 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. Orientation degree of outer surface O = [MD direction 918 cm -1 band intensity near 918 cm in the TD direction -1 band intensity near The degree of orientation is 1465 cm -1 The measurements were normalized so that the intensities of nearby bands (-CH bending vibration) were the same. (10) Inner surface orientation I After freezing the separation membrane with liquid nitrogen in the same manner as in (1) above, the membrane was cut parallel to the longitudinal direction using a razor or microtome so that the hollow part of the membrane, i.e., the inner surface, was exposed, and the orientation parameter of the hollow part, 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 the direction perpendicular to the longitudinal direction (diameter direction) (TD). Note that a diamond prism was used as the ATR crystal, the incidence angle was 45°, the number of accumulations was 64, and the polarizer was a wire grid, and the measurement was performed with S-polarized light. From the obtained ATR spectrum, a 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 separation membrane, the band intensity ratio of 918 cm -1 The intensity of the band near (-CH3 group rocking vibration) was measured in the MD and TD of 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 I = [MD direction 918 cm -1 band intensity near 918 cm in the TD direction -1 band intensity near The degree of orientation is 1465 cm -1 The measurements were normalized so that the intensities of nearby bands (-CH bending vibration) were the same. [PMP] As a PMP, I prepared the following:

[0096] PMP:TPX DX845 (density: 833kg / m 3 , MFR: 9.0g / 10min) [Other ingredients] Plasticizer: Dibutyl phthalate Example 1 35% by mass of PMP and 65% by mass of dibutyl phthalate were fed to a twin-screw extruder, melt-kneaded at 290°C, and then introduced into a melt spinning pack with a nozzle temperature of 225°C, and spun downward from the outer annular part of the nozzle having one nozzle hole (double circular tube type, nozzle hole diameter 2.0 mm, discharge gap 0.10 mm). The spun separation membrane was introduced into a cooling bath and wound up by a winder so that the draft ratio was 18. At that time, the free running distance was set to 20 mm. Here, a metal filter with a diameter of 200 μm was used as the filter in the melt spinning pack. The wound separation membrane was immersed in isopropanol for 24 hours, and further vacuum dried at room temperature to remove isopropanol, and a separation membrane was obtained. The physical properties of the obtained separation membrane are shown in Table 1. The ratio S of the total area of ​​voids with a virtual diameter of 200 nm to 700 nm in the obtained separation membrane A is 36%, and the ratio of the total area of ​​voids with a virtual diameter of 1000 nm to 1600 nm S B The orientation degree of the outer surface O was 41%, the ratio O / I of the orientation degree of the inner surface I to the orientation degree of the outer surface O was 2.8, the N2 permeability was 220 GPU, the rate of change in N2 permeability Y / X before and after immersion in chloroform was 0.72, the breaking elongation was 462%, and the CO2 / N2 separation coefficient α was 2.2, indicating that the material had high permeability and excellent elongation, as well as organic solvent resistance.

[0097] Example 2 A separation membrane was obtained in the same manner as in Example 1, except that the draft ratio was set to 23. As a result, as shown in Table 1, the ratio S of the total area of ​​voids having a virtual diameter of 200 nm to 700 nm was A is 37%, and the ratio of the total area of ​​voids with a virtual diameter of 1000 nm to 1600 nm S B The ratio O / I of the degree of orientation of the outer surface O to the degree of orientation of the inner surface I was 2.0, and the rate of change Y / X in N2 permeability before and after immersion in chloroform was 0.68.

[0098] Example 3 A separation membrane was obtained in the same manner as in Example 1, except that the draft ratio was set to 28. As a result, as shown in Table 1, the ratio S of the total area of ​​voids having a virtual diameter of 200 nm to 700 nm was A is 34%, and the ratio of the total area of ​​voids with a virtual diameter of 1000 nm to 1600 nm S B The ratio O / I of the degree of orientation O of the outer surface to the degree of orientation I of the inner surface was 2.0, and the rate of change Y / X in N2 permeability before and after immersion in chloroform was 0.66.

[0099] Example 4 A separation membrane was obtained in the same manner as in Example 1, except that the discharge gap was set to 0.15 mm. As a result, as shown in Table 1, the ratio S of the total area of ​​voids having a virtual diameter of 200 nm to 700 nm was A is 27%, and the ratio of the total area of ​​voids with a virtual diameter of 1000 nm to 1600 nm S B The ratio O / I of the degree of orientation of the outer surface O to the degree of orientation of the inner surface I was 1.9, and the rate of change Y / X in N2 permeability before and after immersion in chloroform was 0.46.

[0100] Example 5 A separation membrane was obtained in the same manner as in Example 1, except that the discharge gap was set to 0.20 mm. As a result, as shown in Table 1, the ratio S of the total area of ​​voids having a virtual diameter of 200 nm to 700 nm was A is 29%, and the ratio of the total area of ​​voids with a virtual diameter of 1000 nm to 1600 nm S B The ratio O / I of the degree of orientation of the outer surface O to the degree of orientation of the inner surface I was 1.8, and the rate of change Y / X in N2 permeability before and after immersion in chloroform was 0.39.

[0101] Example 6 A separation membrane was obtained in the same manner as in Example 1, except that the die temperature was set to 235° C. As a result, as shown in Table 1, the ratio S of the total area of ​​voids having a virtual diameter of 200 nm to 700 nm was A is 43%, and the ratio of the total area of ​​voids with a virtual diameter of 1000 nm to 1600 nm S B The orientation ratio O / I of the outer surface to the inner surface was 2.3, and the N2 gas permeability was 15 GPU.

[0102] Example 7 A separation membrane was obtained in the same manner as in Example 1, except that the die temperature was set to 245° C. As a result, as shown in Table 2, the ratio S of the total area of ​​voids having a virtual diameter of 200 nm to 700 nm was A is 46%, and the ratio of the total area of ​​voids with a virtual diameter of 1000 nm to 1600 nm S B The orientation ratio O / I of the outer surface to the inner surface was 2.2, and the N2 gas permeability was 9 GPU.

[0103] Example 8 A separation membrane was obtained in the same manner as in Example 1, except that the PMP content was 30% by mass, the dibutyl phthalate content was 70% by mass, and the coagulation bath was N-methylpyrrolidone. As a result, as shown in Table 2, the ratio S of the total area of ​​voids having a virtual diameter of 200 nm to 700 nm was obtained. A is 36%, and the ratio of the total area of ​​voids with a virtual diameter of 1000 nm to 1600 nm S B The orientation ratio O / I of the outer surface orientation O to the inner surface orientation I was 2.8, the N2 gas permeability was 232 GPU, and the rate of change Y / X in N2 permeability before and after immersion in chloroform was 0.85.

[0104] 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, the die temperature was set to 270° C., and the discharge gap was set to 0.35 mm. As a result, as shown in Table 2, the ratio S of the total area of ​​voids having a virtual diameter of 200 nm to 700 nm was A is 80%, and the ratio S of the total area of ​​voids with a virtual diameter of 1000 nm to 1600 nm B The ratio O / I of the degree of orientation of the outer surface O to the degree of orientation of the inner surface I was 1.5, and the rate of change Y / X in N2 permeability before and after immersion in chloroform was a low value of 0.00.

[0105] Comparative Example 2 A separation membrane was obtained in the same manner as in Example 1, except that the draft ratio was set to 30, the die temperature was set to 255° C., and the discharge gap was set to 0.35 mm. As a result, as shown in Table 2, the ratio S of the total area of ​​voids having a virtual diameter of 200 nm to 700 nm was A is 62%, and the ratio of the total area of ​​voids with a virtual diameter of 1000 nm to 1600 nm S B The orientation ratio O / I of the outer surface O to the inner surface I was 1.4, and the rate of change Y / X in N2 permeability before and after immersion in chloroform was a low value of 0.00.

[0106] Comparative Example 2 A separation membrane was obtained in the same manner as in Example 1, except that the PMP was 100% by mass, the nozzle temperature was 270° C., the discharge gap was 0.35 mm, and the draft ratio was 700, followed by air cooling. As a result, as shown in Table 2, the ratio S of the total area of ​​voids having a virtual diameter of 200 nm to 700 nm was obtained. A is 85%, and the ratio of the total area of ​​voids with a virtual diameter of 1000 nm to 1600 nm S B The ratio O / I of the degree of orientation of the outer surface O to the degree of orientation of the inner surface I was 1.6, and the rate of change Y / X in N2 permeability before and after immersion in chloroform was a low value of 0.19.

[0107] Comparative Example 3 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.

[0108] [Table 1]

[0109] [Table 2]

[0110] The separation membranes obtained in Examples 1 to 8 have a ratio S of the total area of ​​voids having a virtual diameter of 200 nm or more and 700 nm or less. A , the ratio of the total area of ​​voids with a virtual diameter of 1000 nm to 1600 nm S BThe requirements of the present invention were met in all items, including the ratio O / I of the degree of orientation of the outer surface to the degree of orientation of the inner surface, and the N2 permeability was 5 GPU or more, the rate of change Y / X in N2 permeability before and after immersion in chloroform was 0.5 to 2.0, and the elongation at break was 500% or more, showing high permeability and excellent elongation, as well as high organic solvent resistance. On the other hand, the proportion S of the total area of ​​voids with a virtual diameter of 200 nm to 700 nm A , the ratio of the total area of ​​voids with a virtual diameter of 1000 nm to 1600 nm S B The separation membranes of Comparative Examples 1 to 3, in which at least one of the ratios O / I of the degree of orientation O of the outer surface to the degree of orientation I of the inner surface did not satisfy the requirements of the present invention, showed low values ​​in at least one of the permeability, elongation, and organic solvent resistance. [Industrial Applicability]

[0111] 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 manufacturing lines, liquid crystal color filter manufacturing lines, and ink production for inkjet printers, and as a gas exchange membrane in an artificial lung for medical use. In particular, as a degassing membrane, it is very useful for degassing photoresist solutions and developing solutions used in lithography in semiconductor manufacturing lines.

Claims

1. A separation membrane characterized by having poly(4-methyl-1-pentene) as a main component, the ratio O / I of the degree of orientation O of the outer surface to the degree of orientation I of the inner surface by polarized infrared spectroscopy being 1.8 or more and 3.0 or less, and in the radial cross-section of the membrane, the ratio S of the total area of voids having a virtual diameter of 200 nm or more and 700 nm or less to the total area of voids Ａ being 20% or more and 50% or less, and the ratio S of the total area of voids having a virtual diameter of 1000 nm or more and 1600 nm or less to the total area of voids Ｂ being 10% or more and 50% or less, and having a dense layer on at least one surface.

2. The separation membrane according to claim 1, wherein the dense layer is in the range of 0.1 μm or more and 2.0 μm or less.

3. Among the voids having a virtual diameter of 1000 nm or more and 1600 nm or less in a cross-section parallel to the longitudinal direction of the membrane and parallel to the membrane thickness direction, the average length of the voids outside the center of the membrane thickness is 4000 nm or more, and the average length of the voids inside the center of the membrane thickness is 1000 nm or more and 3000 nm or less. The separation membrane according to any one of claims 1 or 2.

4. The separation membrane according to any one of claims 1 or 2, wherein the degree of orientation O of the outer surface by polarized infrared spectroscopy is 2.0 or more and 3.5 or less.

5. The separation membrane according to any one of claims 1 or 2, wherein the separation membrane is in a hollow fiber shape.

6. CO ２ / N ２ The separation membrane according to any one of claims 1 or 2, having a selectivity of 1 or more.

7. The N ２ permeation performance at 100 kPa is 5 GPU or more. The separation membrane according to any one of claims 1 or 2.

8. A separation membrane mainly composed of poly(4-methyl-1-pentene), wherein the N2 permeation performance of the separation membrane at a differential pressure of 100 kPa is X, and after the separation membrane is immersed in chloroform for 5 seconds, N ２ When the permeation performance is Y, the separation membrane has a change rate of permeation performance Y / X of 0.3 or more and 1.2 or less.

9. The separation membrane according to any one of claims 1 or 2, having an elongation at break in the longitudinal direction of 300% or more.

10. The separation membrane according to any one of claims 1 or 2, having a dense layer on the outer surface.

11. A method for manufacturing a separation membrane including the following steps (1) to (2). (1) A preparation step of melt-kneading a 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 step of discharging the resin composition from a die orifice having a gap of 0.05 mm or more and 0.30 mm or less at a die temperature of 220°C or more and 260°C or less and winding it up at a draft ratio of 5 or more and 30 or less.

12. In the molding step, a solvent having a solubility parameter distance Ra of 5 or more and 13 or less with respect to poly(4-methyl-1-pentene) and a solubility parameter distance Rb of 4 or more and 10 or less with respect to the plasticizer is used in a cooling bath. The method for manufacturing a separation membrane according to claim 11, characterized in that.

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