Hollow fiber membrane and module using same

Abstract

The present invention provides a hollow fiber membrane with which it is possible to achieve high gas separation accuracy and gas permeability. A hollow fiber membrane according to the present invention comprises a separation functional layer and a support which supports the separation functional layer, wherein the thickness of the separation functional layer is not more than 5 μm, and the variation coefficient of the thickness of the separation functional layer in the circumferential direction is not more than 30%.

Description

Hollow fiber membrane and module using the same

[0001] This invention relates to a hollow fiber membrane and a module using the same.

[0002] Hollow fiber membranes can be used to separate components from fluids and are applied to a wide range of applications, including medical devices, electrochemical devices, chemical processing devices, pharmaceutical equipment, and water purification and ultrapure water production equipment.

[0003] Polyolefin-based hollow fiber membranes are manufactured by phase separation methods or dry stretching methods. Dry stretching allows for the production of high-strength hollow fiber membranes without the use of solvents. However, dry stretching presents challenges in precise control of pore size and separation accuracy.

[0004] Therefore, Patent Document 1 discloses that by performing melt-compound spinning of two components using a multi-cylinder die and then stretching the material to make only one component porous, it is possible to produce a hollow fiber membrane consisting of two layers, a porous layer and a non-porous layer, with high separation accuracy.

[0005] Japanese Unexamined Patent Publication No. 7-116483

[0006] However, the hollow fiber membrane obtained in Patent Document 1 exhibits gas selectivity, but has the problem of having a thick separation functional layer, resulting in low gas permeability. On the other hand, if the separation functional layer is made thinner to improve gas permeability, the uniformity of the thickness of the separation functional layer is insufficient, leading to defects in the thin areas and a decrease in gas selectivity.

[0007] To solve the above problems, the present invention provides the following (1) to (11): (1) A hollow fiber membrane having a separation functional layer and a support that supports the separation functional layer, wherein the thickness of the separation functional layer is 5 μm or less, and the coefficient of variation of the thickness of the separation functional layer in the circumferential direction is 30% or less. (2) The hollow fiber membrane according to (1), wherein the ratio of the thickness of the separation functional layer to the film thickness is 10% or less. (3) The hollow fiber membrane according to (1) or (2), wherein the support has a structure selected from the group consisting of a structure made of only one type of thermoplastic resin, a laminated structure containing at least two types of thermoplastic resins, a sea-island composite structure containing at least two types of thermoplastic resins, and a structure in which the laminated structure and the sea-island composite structure are combined. (4) The hollow fiber membrane according to (3), wherein the laminated structure has segments containing at least one type of thermoplastic resin, and each segment containing a different thermoplastic resin is arranged in the circumferential direction, and the total number of segments is 4 or more and 40 or less. (5) The hollow fiber membrane according to (3), wherein the sea-island composite structure has 3 to 100 islands. (6) The hollow fiber membrane according to any one of (1) to (5), wherein the thermoplastic resin is polyethylene, polypropylene, polybutylene, or poly-4-methyl-1-pentene, or a copolymer thereof. (7) Nitrogen gas flux is 5.7 × 10 －６ cm ３ (STP) / cm ２ (1) to (6) above, having a carbon dioxide gas flux / nitrogen gas flux of 3.0 or higher, and a tensile strength of 0.3 cN / dtex or higher. (8) A bundle of threads using the hollow fiber membranes used in any of (1) to (7). (9) A module using the hollow fiber membranes used in any of (1) to (7). (10) A gas separation membrane module using the hollow fiber membranes used in any of (1) to (7). (11) An artificial lung using the hollow fiber membranes used in any of (1) to (7).

[0008] Furthermore, in order to solve the above problems, the present invention provides the following (12) to (19). (12) A hollow fiber membrane having a separation functional layer and a support that supports the separation functional layer, wherein the thickness of the separation functional layer is 5 μm or less, and the coefficient of variation of the thickness of the separation functional layer in the circumferential direction is 30% or less. (13) The hollow fiber membrane according to (12), wherein the support has a structure selected from the group consisting of a structure made of only one type of thermoplastic resin, a laminated structure containing at least two types of thermoplastic resins, a sea-island composite structure containing at least two types of thermoplastic resins, and a structure in which the laminated structure and the sea-island composite structure are combined. (14) The hollow fiber membrane according to (13), wherein the laminated structure has segments containing at least one type of thermoplastic resin, and each segment containing a different thermoplastic resin is arranged in the circumferential direction, and the total number of segments is 4 or more and 40 or less. (15) The hollow fiber membrane according to (13), wherein the sea-island composite structure has 3 or more and 100 or less islands. (16) The hollow fiber membrane according to any one of (12) to (15), wherein the thermoplastic resin is polyethylene, polypropylene, polybutylene, or poly-4-methyl-1-pentene or a copolymer thereof. (17) Nitrogen gas flux is 5.7 × 10 －６ cm ３ (STP) / cm ２ (12) to (16) a hollow fiber membrane having a gas flux of 3.0 or more / sec / cmHg, a carbon dioxide gas flux / nitrogen gas flux of 3.0 or more, and a tensile strength of 0.3 cN / dtex or more. (18) A gas separation membrane module using a hollow fiber membrane using a hollow fiber membrane using a hollow fiber membrane using a hollow fiber membrane using a hollow fiber membrane using a hollow fiber membrane using a hollow fiber membrane using a hollow fiber membrane using a hollow fiber membrane using a hollow fiber membrane using a hollow fiber membrane using a hollow fiber membrane using a hollow fiber membrane using a hollow fiber membrane using a hollow fiber membrane using a hollow fiber membrane using a hollow fiber membrane using a hollow fiber membrane

[0009] This invention provides a hollow fiber membrane that enables both high gas separation accuracy and gas permeability.

[0010] Cross-sectional views of hollow fiber membranes each having a support with a structure where two types of thermoplastic resins are laminated in the film thickness direction. Cross-sectional views of hollow fiber membranes each having a support with a structure where two types of thermoplastic resins are laminated in the circumferential direction. Cross-sectional views of hollow fiber membranes each having a support with a sea-island composite structure formed of two types of thermoplastic resins. A cross-sectional view of a hollow fiber membrane having a support with a structure where two types of thermoplastic resins are laminated in the circumferential direction, the cross-sectional view defining regions of a separation functional layer to be excluded. An example of a double cylindrical spinneret for producing the hollow fiber membrane of the present invention. An example of a triple cylindrical spinneret for producing the hollow fiber membrane of the present invention. An example of a spinneret for producing the hollow fiber membrane of the present invention.

[0011] Hereinafter, the hollow fiber membrane of the present invention will be described in detail.

[0012] The hollow fiber membrane of the present invention comprises a separation functional layer and a support that supports the separation functional layer, wherein the thickness of the separation functional layer is 5 µm or less, and the coefficient of variation of the thickness of the separation functional layer in the circumferential direction is 30% or less.

[0013] Here, it is preferable that the hollow fiber membrane of the present invention comprises a support having a structure selected from the group consisting of: a structure consisting of only one type of thermoplastic resin; a bonded structure containing at least two types of thermoplastic resins; a sea-island composite structure containing at least two types of thermoplastic resins; and a structure in which the bonded structure and the sea-island composite structure are combined.

[0014] Examples of the thermoplastic resin include polyolefin resins. Examples of the polyolefin resin include polyethylene, polypropylene, polybutylene, poly(4-methyl-1-pentene), and copolymers thereof.

[0015] The hollow fiber membrane of the present invention may contain a resin other than a polyolefin resin as the thermoplastic resin. Examples of resins other than polyolefin resins include polyester and polyamide. Examples of the polyester include polyethylene terephthalate, polytrimethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, and copolymers thereof. Examples of the polyamide include poly-ε-capramide (nylon 6), polyhexamethylene adipamide (nylon 66), and copolymers thereof.

[0016] The shape of the hollow fiber membrane is not particularly limited, but may have a circular or elliptical cross-section. When the cross-section of the hollow fiber membrane is circular, the inner diameter, outer diameter and membrane thickness are not particularly limited. However, since the pressure during gas or liquid feeding into the interior of the hollow fiber membrane becomes low, the inner diameter is preferably 100 µm or more, and more preferably 140 µm or more. On the other hand, in order to maintain the specific surface area within a suitable range and achieve miniaturization of the module, the inner diameter is preferably 300 µm or less, and more preferably 200 µm or less.

[0017] In addition, since the mechanical strength increases, the membrane thickness is preferably 15 µm or more, and more preferably 18 µm or more. On the other hand, in order to reduce the resistance during fluid permeation and reduce the outer diameter of the hollow fiber, the membrane thickness is preferably 60 µm or less, and more preferably 30 µm or less.

[0018] From the relationship between the above-mentioned preferred ranges of the inner diameter and the preferred range of the membrane thickness, the outer diameter is preferably in the range of 130 to 420 µm.

[0019] Furthermore, the hollow ratio calculated using the following formula 1 is preferably 30% or more. By using a hollow fiber membrane with a large hollow ratio, it is possible to reduce the thickness of the hollow fiber membrane while suppressing pressure loss when supplying fluid to the hollow portion when used as a gas separation membrane, thereby obtaining a hollow fiber membrane that can be made more compact in modules. For this reason, a hollow ratio of 50% or more is more preferable, and 60% or more is even more preferable. There is no particular upper limit to the hollow ratio, but 70% is preferable. By using a discharge nozzle with a structure that allows gas to be introduced as a core material inside, as described later, a hollow fiber membrane with a large hollow ratio can be obtained. Hollow ratio (%) = {Area of ​​hollow portion / Area of ​​the entire hollow fiber membrane (membrane and hollow portion)} × 100 ...Formula 1

[0020] If the cross-section of a hollow fiber membrane is circular, its inner diameter, outer diameter, and film thickness can be measured by observing the cross-section with an optical microscope.

[0021] When the cross-section of a hollow fiber membrane is elliptical, the inner diameter, outer diameter, and film thickness can be measured with an optical microscope. In this case, the inner diameter and outer diameter refer to the arithmetic mean of the major and minor axes of the hollow portion and the arithmetic mean of the major and minor axes of the entire cross-section, respectively.

[0022] The inner diameter, outer diameter, and film thickness can be measured by proportional calculation by comparing the respective lengths on the optical microscope image of the cross-section of the hollow fiber membrane with the distances at 0.2 mm intervals on a scale photographed with an optical microscope under the same magnification as the observation conditions described above.

[0023] The area of ​​the hollow portion can be measured using an optical microscope image of the cross-section of the hollow fiber membrane, for example, with image processing software such as ImageJ.

[0024] The hollow fiber membrane of the present invention has a support having a structure selected from the group consisting of a structure made of only one type of thermoplastic resin, a laminated structure containing at least two types of thermoplastic resins, a sea-island composite structure containing at least two types of thermoplastic resins, and a structure in which the laminated structure and the sea-island composite structure are combined, and a separation functional layer of 5 μm or less laminated thereon.

[0025] In this invention, the support is a layer adjacent to the separation functional layer, which will be described later. Here, the thermoplastic resins constituting the support and the separation functional layer may be of different types. Furthermore, the support may be positioned on the inner surface side of the hollow fiber membrane or on the outer surface side of the hollow fiber membrane than the separation functional layer.

[0026] A bonded structure, as shown in Figures 1 and 2, is a structure formed by bonding together segments made of different thermoplastic resins, with each segment consisting of only one thermoplastic resin running in the film thickness direction or circumferential direction. Figure 1 shows a cross-sectional view of a hollow fiber membrane having a support structure bonded in the film thickness direction.

[0027] The circumferential direction refers to the direction along the circumference of the surface of a hollow cylindrical hollow fiber membrane. If the cross-section of the hollow fiber membrane is elliptical, the above circumferential direction can be reinterpreted as the circumferential direction, meaning the direction along the circumference.

[0028] A segment is a continuous structure within a support containing one type of thermoplastic resin.

[0029] The total number of segments refers to the total number of segments in the support, and can be evaluated by observing the cross-section of the hollow fiber membrane with an electron microscope.

[0030] Specifically, if the support is made of one type of thermoplastic resin, the total number of segments is determined to be 1 because the support is made of one continuous piece of thermoplastic resin. If the support is made of two or more types of thermoplastic resin, first, the hollow fiber membrane stained with ruthenium tetroxide or the like is cut perpendicular to the longitudinal direction of the hollow fiber membrane using a microtome, the resulting cross-section is observed with an electron microscope, and the cross-sectional image magnified 1500 times is analyzed.

[0031] When the support is composed of two types of thermoplastic resin, boundary determination of regions with different brightness levels is performed on the cross-section of the hollow fiber membrane after dyeing using image processing software. The image analysis software converts the cross-section of the hollow fiber membrane after dyeing to 8-bit (256 gradations) grayscale, adjusts the brightness to maximize contrast, removes noise, and then performs boundary determination of layers where the contrast differs in consecutive areas within the image. By counting the number of divided regions, the total number of segments in the support can be evaluated.

[0032] If the support is composed of three or more types of thermoplastic resins, the total number of segments in the support can be evaluated by counting the number of continuous regions with different brightness levels in the cross-section of the hollow fiber film after dyeing.

[0033] For example, in the case of the cross-section shown in Figure 1, the total number of segments is 5.

[0034] Figure 2 shows a cross-sectional view of a hollow fiber membrane having a support structure in which two types of thermoplastic resins are bonded together in the circumferential direction. The cross-section in Figure 2, that is, a cross-section in which different thermoplastic resins are alternately arranged and bonded together in the circumferential direction, is preferable because it can easily reduce the resistance when fluid permeates in the film thickness direction.

[0035] For example, in the case of the cross-section shown in Figure 2, the total number of segments is 8. When three different types of thermoplastic resins (for example, let's call the three thermoplastic resins I, II, and III) are arranged in the circumferential direction, the order in which adjacent resins are arranged does not matter as long as they are not the same resin, and the arrangement of two adjacent thermoplastic resins in the circumferential direction does not matter as long as the support contains at least one I, II, and III. For example, if they are arranged in the order I→II→III→II around the entire circumference, the total number of segments is 4. Also, for example, if they are arranged in the order I→II→III→II→I→II→III→II around the entire circumference, the total number of segments is 8.

[0036] When four different types of thermoplastic resins (for example, let's call the four thermoplastic resins I, II, III, and IV) are arranged in the circumferential direction, the order in which adjacent resins are arranged does not matter as long as they are not the same resin, and the arrangement of two adjacent thermoplastic resins in the circumferential direction does not matter as long as the support contains at least one of each of I, II, III, and IV.

[0037] Similarly, when five or more different thermoplastic resins are arranged in the circumferential direction, the order in which the thermoplastic resins are arranged in the circumferential direction is not particularly limited.

[0038] In the cross-section shown in Figure 2, the strength in the direction perpendicular to the fiber axis tends to increase as the total number of segments increases; therefore, the total number of segments is preferably 4 or more, and more preferably 8 or more. On the other hand, the resistance to fluid permeation in the film thickness direction tends to increase as the total number of segments increases; therefore, the total number of segments is preferably 40 or less, and more preferably 20 or less.

[0039] A sea-island composite structure can be exemplified by a cross-section like the one shown in Figure 3, which consists of island components and sea components arranged to surround them. As the number of islands increases, the strength in the direction perpendicular to the fiber axis tends to increase, so the number of islands is preferably three or more, and more preferably ten or more. On the other hand, in order to keep the resistance when fluid permeates in the direction of film thickness within a more suitable range, the number of islands is preferably 100 or less, more preferably 70 or less, even more preferably 40 or less, and most preferably 20 or less. For this reason, it is preferable to use sea-island composite fibers having 3 to 100 islands as the support.

[0040] For example, in the case of the sea-island composite structure support made of two types of thermoplastic resins shown in Figure 3, the four island components are independent of each other and therefore form four segments, while the sea components, which surround the island components, form a continuous structure and thus form one segment. Therefore, the total number of segments is five.

[0041] Similarly, in the case of a support structure that combines a bonded structure and a sea-island composite structure, the total number of segments can be measured by counting the number of consecutive regions with different brightness levels.

[0042] When the cross-section of a hollow fiber membrane is circular or elliptical, the composite cross-sectional morphology of the support can be evaluated by observing the cross-section with an optical microscope or an electron microscope.

[0043] In this invention, the separation functional layer refers to a region located on the outer surface, inner surface, or both sides of the hollow fiber membrane, determined according to the definition below. First, a cross-section of a hollow fiber membrane stained with ruthenium tetroxide or the like is observed with an electron microscope, and the cross-sectional image, magnified 1500 times, is subjected to image analysis as described below. Using image analysis software, the cross-section of the hollow fiber membrane after staining is converted to an 8-bit (256-level) grayscale image, the brightness is adjusted to maximize the contrast, noise is removed, and boundary determination is performed by identifying areas with different contrasts in consecutive parts of the image as layer boundaries. Among the multiple divided regions, the region with the smallest thickness is designated as the separation functional layer.

[0044] Here, the separation functional layer refers to the region with the smallest thickness among the divided regions, and the thickness of the region means the length determined according to the definition below. If the region is located on the outer surface side of the hollow fiber membrane, a line segment is drawn from the centroid of the hollow part toward the outer surface of the hollow fiber membrane, and the length of the portion of this line segment that lies within the region is defined as the thickness of the region. If the region is located on the inner surface side of the hollow fiber membrane, a half-line is drawn from the centroid of the hollow part toward the inner surface of the hollow fiber membrane, and the length of the portion of this half-line that lies within the region is defined as the thickness of the region. If the region is sandwiched between another region located on the outer surface side of the hollow fiber membrane and another region located on the inner surface side, a line segment is drawn from the centroid of the hollow part toward the outer surface of the hollow fiber membrane, and the length of the portion of this line segment that lies within the region is defined as the thickness of the region.

[0045] Furthermore, if the support has a structure in which at least two types of thermoplastic resins are bonded in the circumferential direction, the region from which the separation function layer is excluded is determined as follows. First, the arc length L of the portion where the segment occupying the smallest area among the bonded thermoplastic resin segments intersects with the inner surface of the hollow fiber membrane is measured using the image analysis software "WinROOF2015" manufactured by Mitani Corporation. Next, point A is determined by moving counterclockwise along the inner surface of the hollow fiber membrane from the left end of the arc toward the cross-section at a distance of length L × 0.2, and point B is determined by moving clockwise along the inner surface of the hollow fiber membrane from the right end of the arc toward the cross-section at a distance of length L × 0.2. When the centroid of the hollow portion is O, the separation function layer located within the region enclosed by the semi-linear OA and semi-linear OB is excluded. The same operation is performed for all portions of the bonded thermoplastic resins that are made of the same thermoplastic resin as described above.

[0046] Furthermore, if the support has a sea-island composite structure containing at least two types of thermoplastic resins, the brightness of the island structure portion is excluded. If the support has a structure that combines a bonded structure and a sea-island composite polymorphic structure, the above two exclusion operations are performed.

[0047] The center of gravity of the hollow portion can be determined using electron microscope images or optical microscope images of the cross-section of the hollow fiber membrane, for example, using image processing software such as ImageJ.

[0048] The separation functional layer in the present invention preferably contains a polyolefin resin. Examples of polyolefin resins include polyethylene, polypropylene, polybutylene, and poly-4-methyl-1-pentene, as well as copolymers thereof. By including a polyolefin resin in the separation functional layer, when separating, recovering, or supplying specific components from a liquid using the hollow fiber membrane of the present invention, penetration of liquid into the hollow fiber membrane is less likely to occur, thereby suppressing performance degradation over time.

[0049] Furthermore, when the separation functional layer contains a polyolefin resin, it is preferable to use a polyolefin resin with a lower degree of crystallinity than the polyolefin resin forming the support. By using a polyolefin resin with a lower degree of crystallinity in the separation functional layer, the occurrence of defect pores in the separation functional layer is suppressed, and a hollow fiber membrane with high separation accuracy can be obtained.

[0050] The separation functional layer of the present invention is formed by co-extruding the resin forming the support and the resin forming the separation functional layer from a die.

[0051] The thickness of the separation layer can be controlled by the amount of resin discharged from the spinneret to form the separation layer and the spinning speed, and can also be controlled by the stretch ratio when stretching is performed.

[0052] The thickness of the separation functional layer in the hollow fiber membrane of the present invention is 5.0 μm or less, more preferably 2.0 μm or less, and even more preferably 1.7 μm or less. The thinner the separation functional layer, the lower the resistance during fluid permeation, making it possible to obtain a hollow fiber membrane that is advantageous for miniaturization of modules. Furthermore, the lower limit of the thickness of the separation functional layer is preferably 0.1 μm or more, more preferably 0.2 μm or more, even more preferably 0.5 μm or more, and most preferably 1.4 μm or more. Note that in the present invention, the thickness of the separation functional layer refers to the sum of the thicknesses of the separation functional layers on both surfaces when the separation functional layer is present on both surfaces of the hollow fiber membrane.

[0053] The uniformity of the thickness of the separation functional layer can be measured by observing the cross-section of a hollow fiber membrane stained with ruthenium tetroxide or the like using an electron microscope and evaluating the coefficient of variation of the circumferential thickness of the separation functional layer.

[0054] The coefficient of variation in the circumferential direction of the thickness of the separation functional layer was evaluated by the following method: A hollow fiber membrane stained with ruthenium tetroxide was cut perpendicular to the longitudinal direction of the membrane at an arbitrary point using a microtome, the cross-section was treated with a conductive coating (Pt coating), and the thickness of the separation functional layer at 20 randomly selected locations was evaluated from secondary electron images observed at 1500x magnification under an acceleration voltage of 1.0 kV using a scanning electron microscope (Hitachi High-Tech cold cathode field emission scanning electron microscope; Regulus® 8220). The standard deviation of the thickness of the separation functional layer was divided by the arithmetic mean to obtain the coefficient of variation in the circumferential direction of the thickness of the separation functional layer.

[0055] In the present invention, the coefficient of variation in the circumferential direction of the thickness of the separation functional layer is preferably 30% or less, more preferably 15% or less, even more preferably 8% or less, even more preferably 7% or less, and most preferably 5% or less. The smaller the coefficient of variation in the circumferential direction of the thickness of the separation functional layer, the fewer physical defects there are in the separation functional layer, and the more efficient the hollow fiber membrane with high gas separation efficiency can be obtained. Furthermore, the lower limit of the coefficient of variation in the circumferential direction of the thickness of the separation functional layer is preferably 2% or more, and more preferably 4% or more.

[0056] In this invention, the ratio of the thickness of the separation functional layer to the film thickness is evaluated by the following method. A hollow fiber membrane stained with ruthenium tetroxide is cut perpendicular to the longitudinal direction of the hollow fiber membrane at an arbitrary location using a microtome, the cross-section is treated with a conductive coating (Pt coating), and the thickness of 20 randomly selected locations of the membrane is measured from the secondary electron image observed at 1500x magnification under an acceleration voltage of 1.0 kV using a scanning electron microscope (Hitachi High-Tech cold cathode field emission scanning electron microscope; Regulus® 8220). The arithmetic mean is calculated and rounded to the first decimal place to obtain the film thickness. The film thickness is then divided by the thickness of the separation functional layer, and the percentage is rounded to the second decimal place to obtain the ratio of the thickness of the separation functional layer to the film thickness.

[0057] In the present invention, the ratio of the thickness of the separation functional layer to the film thickness is preferably 10% or less, more preferably 8% or less, and even more preferably 7% or less, from the viewpoint of obtaining high gas permeability. Furthermore, the lower limit of the ratio of the thickness of the separation functional layer to the film thickness is preferably 0.1% or more, more preferably 0.5% or more, and even more preferably 1.0% or more, from the viewpoint of maintaining the strength of the hollow fiber membrane.

[0058] The hollow fiber membrane of the present invention preferably has slit-shaped micropores because the pores are slit-shaped, making complete blockage of the pores by foreign matter less likely. To obtain slit-shaped micropores, it is preferable to perform stretching and pore opening during the manufacturing process of the hollow fiber membrane, as described later. By causing delamination between the laminated lamellae during the stretching process while forming pores, minute, uniform, and slit-shaped micropores can be easily obtained.

[0059] The shape of micropores can be evaluated by observing the inner wall surface of the hollow fiber membrane in a longitudinal section of the hollow fiber membrane.

[0060] In this invention, tensile strength refers to the tensile strength per unit weight against tension in the longitudinal direction of the hollow fiber membrane, and is the value obtained by dividing the load value at the time of fracture by the fineness, by determining the load-elongation curve under the conditions specified in JIS L1013:2010 (Test Method for Chemical Fiber Filament Yarn) 8.5.1. Here, fineness refers to the value calculated as the weight per 10,000 m from the average value of 10 measurements of the weight of a unit length of the hollow fiber membrane.

[0061] The tensile strength of the hollow fiber membrane of the present invention is preferably 0.3 cN / dtex or higher, more preferably 0.5 cN / dtex or higher, even more preferably 1.0 cN / dtex or higher, and even more preferably 1.4 cN / dtex or higher. The higher the tensile strength, the thinner the film thickness of the hollow fiber membrane can be made, which can contribute to miniaturization of the module. On the other hand, in order to keep the toughness within a suitable range, the tensile strength is preferably 5.0 cN / dtex or lower, and more preferably 2.0 cN / dtex or lower.

[0062] The hollow fiber membrane of the present invention has gas selectivity and can also be used as a gas separation membrane. The gas flux amount refers to a gas flux evaluated by the differential pressure method in accordance with JIS K7126-1:2006 (Plastics — Films and sheets — Gas permeability test method — Part 1: Differential pressure method).

[0063] Gas selectivity refers to the ratio of gas fluxes evaluated by the differential pressure method in accordance with JIS K7126-1:2006 (Plastics — Films and sheets — Gas permeability test method — Part 1: Differential pressure method).

[0064] Gases separable by the hollow fiber membrane of the present invention are not particularly limited, and examples thereof include nitrogen and carbon dioxide, and nitrogen and oxygen.

[0065] The nitrogen gas flux of the hollow fiber membrane of the present invention is 5.7×10 －６ cm ３ (STP) / cm ２ / sec / cmHg or more, preferably 6.5×10 －６ cm ３ (STP) / cm ２ / sec / cmHg or more, more preferably 7.0×10 －６ cm ３ (STP) / cm ２ / sec / cmHg or more is even more preferable. A larger nitrogen gas flux means lower gas permeation resistance, enables highly efficient gas transport inside and outside the membrane, and can contribute to miniaturization of the module when used as a gas separation module.

[0066] The gas selectivity of carbon dioxide to nitrogen (carbon dioxide flux / nitrogen flux) of the hollow fiber membrane of the present invention is preferably 3.0 to 30.0, more preferably 5.0 to 25.0, and still more preferably 6.0 to 20.0. A larger gas selectivity value means superior gas separation efficiency, and can contribute to miniaturization of the module when used as a gas separation module.

[0067] Next, the method for producing the hollow fiber membrane of the present invention will be described below.

[0068] As shown in Figure 5, the hollow fiber membrane can be manufactured using a nozzle having a gas discharge hole 10 and a polymer discharge hole 11.

[0069] A gas discharge port is a cylindrical gap through which gas is discharged. Typically, the gas discharged from the gas discharge port forms a cavity in the hollow fiber membrane.

[0070] Polymer discharge pores are gaps for discharging polymer and are positioned to surround gas discharge pores. Typically, the polymer discharged from these pores forms a hollow fiber membrane.

[0071] Furthermore, as shown in Figure 6, hollow fiber membranes can also be manufactured using a triple-cylinder nozzle having a gas outlet 13 and two types of polymer outlets 14 and 15. Using a triple-cylinder nozzle makes it possible to discharge the polymer constituting the separation functional layer only to the outside of the hollow fiber membrane, which is preferable for obtaining a hollow fiber membrane with high uniformity of thickness in the circumferential direction of the separation functional layer.

[0072] However, when attempting to use a triple-cylindrical nozzle to form a thin separation functional layer of 5.0 μm or less, as in the present invention, it was difficult to manufacture a nozzle with a narrow slit width for discharging the sheath component because the discharge weights of the core component and the sheath component differed significantly. Therefore, it was difficult to obtain a hollow fiber membrane with a thin separation functional layer and high uniformity of circumferential thickness of the separation functional layer using a triple-cylindrical nozzle.

[0073] As shown in Figure 7, the hollow fiber membrane of the present invention can be manufactured using a die in which a plurality of polymer discharge holes 17 and 18 are arranged inside an annular polymer discharge hole 16. By using such a die, a sophisticated design of the composite cross-section is possible, and a hollow fiber membrane with a thin separation functional layer and high uniformity of the circumferential thickness of the separation functional layer can be easily obtained.

[0074] One example of a method for producing the hollow fiber membrane of the present invention is a method in which a polymer containing a polyolefin is melt-spun, and then heat-treated and stretched as necessary.

[0075] The melt viscosity of the polymer is 1216 s at 280°C. －１In this case, it is preferable that the melt viscosity is 30 Pa·s or higher. A higher melt viscosity improves the spinning stability and the mechanical properties of the resulting hollow fiber membrane, so it is more preferable that the melt viscosity of the polymer be 50 Pa·s or higher. On the other hand, from the viewpoint of preventing yarn breakage, it is preferable that the melt viscosity be 500 Pa·s or less, and more preferable that be 200 Pa·s or less.

[0076] The gas discharged from the gas discharge port is not particularly limited, but from the viewpoint of suppressing oxidative degradation of the polymer discharged from the polymer discharge port, it is preferable that it be an inert gas such as nitrogen.

[0077] The method for manufacturing the hollow fiber membrane in the present invention is not particularly limited, but it is preferable to use the manufacturing method that utilizes the discharge nozzle described above.

[0078] The method for producing a hollow fiber membrane in the present invention preferably comprises a spinning step, a heat treatment step, and a stretching step. The spinning step is a step of extruding molten polymer from an extrusion nozzle and forming it into a hollow fiber shape. The heat treatment step is a step of heat treating the polymer formed into a hollow fiber shape in order to improve the orderliness of the crystalline structure. The stretching step is a step of uniformly stretching the polymer formed into a hollow fiber shape.

[0079] The uniformity of the thickness of the separation functional layer of a hollow fiber membrane can be influenced not only by the extrusion nozzle, but also by the spinning temperature, the cooling conditions of the extruded polymer, the heat treatment of the undrawn yarn obtained by spinning, and the drawing conditions. To ensure that the uniformity of the thickness of the separation functional layer of the hollow fiber membrane is within a suitable range, polymers containing polyolefins are preferably manufactured under the following spinning temperatures and cooling conditions.

[0080] The spinning temperature is the temperature at which the polymer is melted during the spinning process. From the viewpoint of suppressing polymer decomposition, the spinning temperature is preferably 310°C or lower. Furthermore, to improve fluidity and further prevent uneven discharge at the discharge nozzle, the spinning temperature is preferably 240°C or higher. A spinning temperature of 250°C to 305°C is more preferable.

[0081] In the spinning process, a heat-insulating tube may be provided directly below the discharge nozzle. By using a heat-insulating tube, the ambient temperature directly below the discharge nozzle can be stabilized, and by raising the ambient temperature directly below the discharge nozzle, the molten material extruded from the discharge nozzle can be cooled slowly, suppressing the concentration of strain stress when the molten material undergoes high deformation directly below the discharge nozzle. The length of the heat-insulating tube is preferably around 50 mm.

[0082] Furthermore, in the spinning process, a cooling compartment may be provided directly below the discharge nozzle or directly below the heat-insulating cylinder located directly below the discharge nozzle to cool the discharged polymer with cooling air. From the viewpoint of suppressing the delay in solidification of the discharged polymer, the temperature of the cooling air used to cool the discharged polymer is preferably 80°C or lower. In addition, to further prevent yarn breakage, the temperature of the cooling air is preferably 10°C or higher.

[0083] In the heat treatment process, the heat treatment temperature is preferably above the glass transition temperature of the polymer constituting the hollow fiber film and below its melting point, more preferably 80 to 220°C, and even more preferably 100 to 200°C. The heat treatment time is preferably 1 minute to 24 hours, and more preferably 5 minutes to 12 hours.

[0084] The stretching process may involve a two-stage stretching process consisting of cold stretching and hot stretching.

[0085] The cold drawing temperature is preferably near or below the glass transition temperature of the polymer constituting the hollow fiber membrane, more preferably -30 to 80°C, even more preferably -10 to 60°C, and most preferably 0 to 50°C.

[0086] In cold stretching, a low stretching ratio is preferred, more preferably 1.05 to 1.6 times, even more preferably 1.1 to 1.5 times, and most preferably 1.2 to 1.4 times, from the viewpoint of causing delamination between the laminated lamellae while forming small and uniform pores.

[0087] The thermal stretching temperature is preferably above the glass transition temperature of the polymer constituting the hollow fiber film and below its melting point, more preferably 80 to 200°C, even more preferably 100 to 180°C, and most preferably 120 to 150°C.

[0088] The stretching ratio in hot stretching is preferably 1.05 to 2.0 times, more preferably 1.1 to 1.8 times, and even more preferably 1.2 to 1.7 times, from the viewpoint of expanding the holes formed by cold stretching while making the hole size minute and uniform.

[0089] The hollow fiber membrane of the present invention has properties suitable for gas separation membrane modules, and examples of its application include degassing membranes in ultrapure water production equipment and artificial lungs.

[0090] When incorporating the hollow fiber membrane of the present invention into a gas separation membrane module, the hollow fiber membrane may be incorporated in bundles, or, if necessary, the hollow fiber membrane may be arranged in a sheet-like manner so that the spacing between the hollow fiber membranes is uniform.

[0091] Furthermore, the gas separation membrane module of the present invention is preferably in a form in which the hollow fiber membrane is housed in a case. There are no particular limitations on the method of housing the hollow fiber membrane in the case, but one example is to cut the hollow fiber membrane to the required length, bundle the required number of pieces together and place them in a cylindrical case, add a potting agent while rotating the module in a centrifuge, and after the potting agent has solidified, cut both ends of the hollow fiber membrane so that both ends are open and attach a header.

[0092] The present invention will be specifically described below with reference to examples, but the present invention is not limited thereto.

[0093] (Evaluation Method) A. Evaluation of the Thickness of the Separation Functional Layer A hollow fiber membrane stained with ruthenium tetroxide was cut perpendicular to the longitudinal direction of the hollow fiber membrane using a microtome method, and the cross-section was treated with a conductive coating (Pt coating). Using a scanning electron microscope (Hitachi High-Tech cold cathode field emission scanning electron microscope; Regulus® 8220), the thickness of the separation functional layer was evaluated from the secondary electron image observed at 1500x magnification under an acceleration voltage of 1.0 kV, and the arithmetic mean was calculated and the value was rounded to the second decimal place.

[0094] In determining the separation functional layer of the hollow fiber membrane stained with ruthenium tetroxide in this embodiment, the cross-section of the hollow fiber membrane after staining was converted to an 8-bit (256-level) grayscale image using the image analysis software ImageJ. After adjusting the brightness to maximize the contrast, noise with a brightness of 250 or higher was removed, and when determining the boundary between regions with different brightness levels, the threshold was set to 150 to determine the boundary between the separation functional layer and the support.

[0095] B. Evaluation of the coefficient of variation of the thickness of the separation functional layer in the circumferential direction. A hollow fiber membrane stained with ruthenium tetroxide was cut perpendicular to the longitudinal direction of the hollow fiber membrane at an arbitrary point using a microtome. The cross-section was treated with a conductive coating (Pt coating), and the thickness of the separation functional layer was evaluated at 20 randomly selected locations from secondary electron images observed at 1500x magnification under an acceleration voltage of 1.0 kV using a scanning electron microscope (Hitachi High-Tech cold cathode field emission scanning electron microscope; Regulus® 8220). The standard deviation of these values ​​was divided by the arithmetic mean and rounded to the first decimal place. The threshold used for measuring the thickness of the separation functional layer was the same threshold used for evaluating the thickness of the separation functional layer.

[0096] C. Evaluation of the ratio of the thickness of the separation functional layer to the film thickness A hollow fiber membrane stained with ruthenium tetroxide was cut perpendicular to the longitudinal direction of the hollow fiber membrane at an arbitrary point using a microtome, and the cross-section was treated with a conductive coating (Pt coating). Using a scanning electron microscope (Hitachi High-Tech cold cathode field emission scanning electron microscope; Regulus® 8220), the thickness of 20 randomly selected film locations was measured from secondary electron images observed at 1500x magnification under an acceleration voltage of 1.0 kV, the arithmetic mean was calculated, and the value rounded to the first decimal place was taken as the film thickness. The film thickness was divided by the thickness of the separation functional layer calculated by the method in A above, and the percentage was rounded to the second decimal place and used as the ratio of the thickness of the separation functional layer to the film thickness.

[0097] D. The fineness of the hollow fiber membrane to be evaluated was calculated by measuring the weight of 1 m of the membrane and multiplying it by 10,000. This was repeated 10 times, and the arithmetic mean was calculated and rounded to two decimal places.

[0098] E. Tensile Strength Tensile strength was evaluated using Orientec's Tensilon under the conditions of a sample length of 200 mm and a tensile speed of 200 mm / min, in accordance with JIS L1013:2010 (Test Methods for Chemical Fiber Filaments) 8.5.1. Tensile strength was defined as the value obtained by dividing the load value at fracture in the tensile strength-elongation curve by the fineness. Ten measurements were taken, and the arithmetic mean of the measured values ​​was calculated and rounded to two decimal places.

[0099] F. Gas Selectivity The fluxes of carbon dioxide and nitrogen gases in the hollow fiber membrane were evaluated in accordance with JIS K7126-1:2006 (Plastics - Films and Sheets - Gas Permeability Test Methods - Part 1: Differential Pressure Method), and their ratio (carbon dioxide flux / nitrogen gas flux) was determined. Five measurements were performed, and the arithmetic mean of the measured values ​​was calculated and rounded to two decimal places.

[0100] G. Approximately 5 mg of the melting point sample was weighed and measured using a differential scanning calorimeter, DSCQ2000, manufactured by TA Instruments. The sample was heated under nitrogen conditions, with a heating rate of 10°C / min and a measurement temperature range of 30°C to 290°C, and then cooled at a cooling rate of 10°C / min and a measurement temperature range of 290°C to 0°C. The melting point Tm (°C) of the sample was determined from the peak top temperature of the endothermic peak during the heating process in the obtained measurement result (DSC curve).

[0101] (Example 1) Poly-4-methyl-1-pentene (manufactured by Mitsui Chemicals, RT18, Tm: 238°C) and poly-4-methyl-1-pentene (manufactured by Mitsui Chemicals, MX002, Tm: 228°C) were used as core components, and poly-4-methyl-1-pentene (manufactured by Mitsui Chemicals, MX002) was used as the sheath component. Compound melt spinning was performed at 305°C using the extrusion nozzle shown in Figure 7.

[0102] In the composite melt spinning process, the yarn was melt-extruded using a twin-screw extruder, and while being weighed with a gear pump, the ratio of the extruded weights was set to RT18:MX002 = 90:10, and the yarn was extruded from the discharge nozzle. The running yarn extruded from the discharge nozzle was passed through a 50 mm heat-insulating cylinder installed directly below the discharge nozzle, and then wound at a spinning speed of 300 m / min to obtain undrawn yarn.

[0103] In the cooling compartment located directly below the insulation cylinder, the running yarn was cooled using cooling air at 23°C and 50% relative humidity at a wind speed of 0.15 m / sec.

[0104] The obtained undrawn yarn was heat-treated in an atmosphere of 185°C for 2 hours, then drawn to 1.2 times its original size at 30°C, and then further drawn to 1.2 times its original size at 125°C to obtain the hollow fiber film of Example 1.

[0105] Table 1 shows the evaluation results of the hollow fiber membrane in Example 1. The cross-section of the hollow fiber membrane was a composite cross-section in which four microporous segments formed of RT18 and four non-microporous segments formed of MX002 were alternately arranged in the circumferential direction on the support.

[0106] In determining the separation functional layer of the hollow fiber membrane stained with ruthenium tetroxide in this embodiment, the cross-section of the hollow fiber membrane after staining was converted to an 8-bit (256-level) grayscale image using the image analysis software ImageJ. After adjusting the brightness to maximize contrast, noise with a brightness of 250 or higher was removed, and when determining the boundary between regions with different brightness levels, a threshold of 150 was set to determine the boundary between the separation functional layer and the support layer. Subsequently, the region on the outer surface side of the hollow fiber membrane with a brightness of 0 to 149 was determined to be the separation functional layer, and the region on the inner surface side of the hollow fiber membrane, including the portion with a brightness of 150 or higher, was determined to be the support. The thickness of the separation functional layer was measured by drawing a line segment from the centroid point of the hollow portion toward the outer surface of the hollow fiber membrane and measuring the length of the portion of the line segment that falls within the region.

[0107] The thickness of the separation functional layer and the thickness of the hollow fiber membrane were determined using the methods described in A. Evaluation of the thickness of the separation functional layer and C. Evaluation of the ratio of the thickness of the separation functional layer to the total film thickness, and the ratio of the thickness of the separation functional layer to the total film thickness was calculated.

[0108] The hollow fiber membrane of Example 1 had a separation functional layer thickness of 1.6 μm, and the coefficient of variation of the separation functional layer thickness in the circumferential direction was small at 7.2%. Furthermore, the ratio of the separation functional layer thickness to the total film thickness was small at 7.2%. In addition, the tensile strength was 1.0 cN / dtex, and the nitrogen gas flux was 8.5 × 10⁻⁶. －６ cm ３ (STP) / cm ２With a pH of / sec / cmHg and a gas selectivity (carbon dioxide gas flux / nitrogen gas flux) of 7.0, it possessed sufficient performance for use as a gas separation membrane.

[0109] (Example 2) After heat treatment, the hollow fiber membrane of Example 2 was prepared in the same manner as in Example 1, except that it was stretched to 1.2 times its original size at 30°C and to 1.8 times its original size at 150°C.

[0110] Table 1 shows the evaluation results of the hollow fiber membrane in Example 2. The cross-section of the hollow fiber membrane was a composite cross-section in which four microporous segments formed of RT18 and four non-microporous segments formed of MX002 were alternately arranged in the circumferential direction on the support.

[0111] Furthermore, the hollow fiber membrane of Example 2 was measured using the same method as in Example 1, and the thickness of the separation functional layer was 1.4 μm, and the coefficient of variation of the circumferential thickness of the separation functional layer was small at 6.5%. In addition, the ratio of the thickness of the separation functional layer to the film thickness was small at 5.0%. Furthermore, the tensile strength was 1.5 cN / dtex, and the nitrogen gas flux was 10.0 × 10⁻⁶. －６ cm ３ (STP) / cm ２ With a pH of / sec / cmHg and a gas selectivity (carbon dioxide gas flux / nitrogen gas flux) of 7.0, it possessed sufficient performance for use as a gas separation membrane.

[0112] (Example 3) After heat treatment, the hollow fiber membrane of Example 3 was prepared in the same manner as in Example 1, except that it was stretched to 1.4 times its original size at 30°C and to 1.7 times its original size at 150°C.

[0113] Table 1 shows the evaluation results of the hollow fiber membrane in Example 3. The cross-section of the hollow fiber membrane was a composite cross-section in which four microporous segments formed of RT18 and four non-microporous segments formed of MX002 were alternately arranged in the circumferential direction on the support.

[0114] Furthermore, the hollow fiber membrane of Example 3 was measured using the same method as in Example 1, and the thickness of the separation functional layer was 1.4 μm, and the coefficient of variation of the circumferential thickness of the separation functional layer was small at 7.7%. Also, the ratio of the thickness of the separation functional layer to the film thickness was small at 7.0%. In addition, the tensile strength was 1.4 cN / dtex, and the nitrogen gas flux was 10.0 × 10⁻⁶.－６ cm ３ (STP) / cm ２ With a pH of / sec / cmHg and a gas selectivity (carbon dioxide gas flux / nitrogen gas flux) of 7.0, it possessed sufficient performance for use as a gas separation membrane.

[0115] (Example 4) The hollow fiber membrane of Example 4 was prepared in the same manner as in Example 1, except that the discharge weight ratio was RT18:MX002 = 88:12 when discharged from the discharge nozzle.

[0116] Table 1 shows the evaluation results of the hollow fiber membrane of Example 4. The cross-section of the hollow fiber membrane of Example 4 was a composite cross-section in which four microporous segments formed of RT18 and four non-microporous segments formed of MX002 were alternately arranged in the circumferential direction on the support.

[0117] Furthermore, the hollow fiber membrane of Example 4 was measured using the same method as in Example 1, and the thickness of the separation functional layer was 2.0 μm, and the coefficient of variation of the circumferential thickness of the separation functional layer was small at 7.5%. In addition, the ratio of the thickness of the separation functional layer to the film thickness was small at 7.7%. Furthermore, the tensile strength was 1.0 cN / dtex, and the nitrogen gas flux was 7.0 × 10⁻⁶. －６ cm ３ (STP) / cm ２ With a pH of / sec / cmHg and a gas selectivity (carbon dioxide gas flux / nitrogen gas flux) of 7.0, it possessed sufficient performance for use as a gas separation membrane.

[0118] (Example 5) The hollow fiber membrane of Example 5 was prepared in the same manner as in Example 1, except that the discharge weight ratio was RT18:MX002 = 95:5 when discharged from the discharge nozzle.

[0119] Table 1 shows the evaluation results of the hollow fiber membrane in Example 5. The cross-section of the hollow fiber membrane was a composite cross-section in which four microporous segments formed of RT18 and four non-microporous segments formed of MX002 were alternately arranged in the circumferential direction on the support.

[0120] Furthermore, the hollow fiber membrane of Example 5 was measured using the same method as in Example 1, and the thickness of the separation functional layer was 1.1 μm, and the coefficient of variation of the circumferential thickness of the separation functional layer was small at 6.5%. In addition, the ratio of the thickness of the separation functional layer to the film thickness was small at 4.6%. Furthermore, the tensile strength was 1.0 cN / dtex, and the nitrogen gas flux was 13.0 × 10⁻⁶. －６ cm ３ (STP) / cm ２ With a pH of / sec / cmHg and a gas selectivity (carbon dioxide gas flux / nitrogen gas flux) of 7.0, it possessed sufficient performance for use as a gas separation membrane.

[0121] (Example 6) The hollow fiber membrane of Example 6 was prepared in the same manner as in Example 1, except that the discharge weight ratio was RT18:MX002 = 97:3 when discharged from the discharge nozzle.

[0122] Table 2 shows the evaluation results of the hollow fiber membrane in Example 6. The cross-section of the hollow fiber membrane was a composite cross-section in which four microporous segments formed of RT18 and four non-microporous segments formed of MX002 were alternately arranged in the circumferential direction on the support.

[0123] Furthermore, the hollow fiber membrane of Example 6 was measured using the same method as in Example 1, and the thickness of the separation functional layer was 0.5 μm, and the coefficient of variation of the circumferential thickness of the separation functional layer was a relatively small 15.2%. Also, the ratio of the thickness of the separation functional layer to the film thickness was small at 2.0%. In addition, the tensile strength was 1.0 cN / dtex, and the nitrogen gas flux was 23.0 × 10⁻⁶. －６ cm ３ (STP) / cm ２ With a pH of / sec / cmHg and a gas selectivity (carbon dioxide gas flux / nitrogen gas flux) of 8.0, it possessed sufficient performance for use as a gas separation membrane.

[0124] (Example 7) Poly-4-methyl-1-pentene (manufactured by Mitsui Chemicals, RT18, Tm: 238°C) and poly-4-methyl-1-pentene (manufactured by Mitsui Chemicals, MX002, Tm: 228°C) were used as the core component, and poly-4-methyl-1-pentene (manufactured by Mitsui Chemicals, MX002, Tm: 228°C) was used as the sheath component. Compound melt spinning was performed at 305°C using the extrusion nozzle shown in Figure 7.

[0125] In the composite melt spinning process, the yarn was melt-extruded using a twin-screw extruder, and while being weighed with a gear pump, the ratio of the extruded weights was set to RT18:MX002 = 90:10, and the yarn was extruded from the discharge nozzle. The running yarn extruded from the discharge nozzle was passed through a 50 mm heat-insulating cylinder installed directly below the discharge nozzle, and then wound at a spinning speed of 300 m / min to obtain undrawn yarn.

[0126] In the cooling compartment located directly below the insulation cylinder, the running yarn was cooled using cooling air at 23°C and 50% relative humidity at a wind speed of 0.15 m / sec.

[0127] The obtained undrawn yarn was heat-treated in an atmosphere of 185°C for 2 hours, then drawn to 1.2 times its original size at 30°C, and then further drawn to 1.2 times its original size at 125°C to obtain the hollow fiber film of Example 7.

[0128] Table 2 shows the evaluation results of the hollow fiber membrane in Example 7. The cross-section of the hollow fiber membrane was a composite cross-section in which microporous segments formed of RT18 and non-microporous segments formed of MX002 were alternately arranged at 16 locations in the circumferential direction on the support.

[0129] Furthermore, the hollow fiber membrane of Example 7 was measured using the same method as in Example 1, and the thickness of the separation functional layer was 1.7 μm, and the coefficient of variation of the circumferential thickness of the separation functional layer was small at 5.9%. In addition, the ratio of the thickness of the separation functional layer to the film thickness was small at 7.1%. Furthermore, the tensile strength was 1.0 cN / dtex, and the nitrogen gas flux was 8.5 × 10⁻⁶. －６ cm ３ (STP) / cm ２ With a pH of / sec / cmHg and a gas selectivity (carbon dioxide gas flux / nitrogen gas flux) of 7.0, it possessed sufficient performance for use as a gas separation membrane.

[0130] (Example 8) The hollow fiber membrane of Example 8 was fabricated in the same manner as in Example 1, except that the discharge nozzle shown in Figure 7, which has a sea-island composite structure as the support, was used.

[0131] Table 2 shows the evaluation results of the hollow fiber membrane in Example 8. The cross-section of the hollow fiber membrane was a composite cross-section in which non-microporous segments formed of MX002 with 6 islands were arranged within microporous segments formed of RT18 on the support.

[0132] Furthermore, the hollow fiber membrane of Example 8 was measured using the same method as in Example 1, and the thickness of the separation functional layer was 1.7 μm, and the coefficient of variation of the circumferential thickness of the separation functional layer was small at 3.9%. In addition, the ratio of the thickness of the separation functional layer to the film thickness was small at 7.2%. Furthermore, the tensile strength was 1.0 cN / dtex, and the nitrogen gas flux was 8.5 × 10⁻⁶. －６ cm ３ (STP) / cm ２ With a pH of / sec / cmHg and a gas selectivity (carbon dioxide gas flux / nitrogen gas flux) of 7.0, it possessed sufficient performance for use as a gas separation membrane.

[0133] (Example 9) The hollow fiber membrane of Example 9 was fabricated in the same manner as in Example 1, except that the discharge nozzle shown in Figure 7, which has a sea-island composite structure as the support, was used.

[0134] Table 2 shows the evaluation results of the hollow fiber membrane of Example 9. The cross-section of the obtained hollow fiber membrane was a composite cross-section in which non-microporous segments formed of MX002 with 18 islands were arranged in a microporous segment formed of RT18 on the support.

[0135] Furthermore, the hollow fiber membrane of Example 9 was measured using the same method as in Example 1, and the thickness of the separation functional layer was 2.0 μm, and the coefficient of variation of the circumferential thickness of the separation functional layer was small at 4.0%. Also, the ratio of the thickness of the separation functional layer to the film thickness was small at 9.1%. In addition, the tensile strength was 1.0 cN / dtex, and the nitrogen gas flux was 7.0 × 10⁻⁶. －６ cm ３ (STP) / cm ２ With a pH of / sec / cmHg and a gas selectivity (carbon dioxide gas flux / nitrogen gas flux) of 7.0, it possessed sufficient performance for use as a gas separation membrane.

[0136] (Example 10) The hollow fiber membrane of Example 10 was prepared in the same manner as in Example 1, except that poly-4-methyl-1-pentene (manufactured by Mitsui Chemicals, RT18, Tm: 238°C) was used as the core component and poly-4-methyl-1-pentene (manufactured by Mitsui Chemicals, MX002, Tm: 228°C) was used as the sheath component.

[0137] Table 2 shows the evaluation results of the hollow fiber membrane in Example 10. The cross-section of the hollow fiber membrane was a composite cross-section consisting only of microporous segments formed of RT18 on the support.

[0138] Furthermore, the hollow fiber membrane of Example 10 was measured using the same method as in Example 1, and the thickness of the separation functional layer was 0.6 μm, and the coefficient of variation of the circumferential thickness of the separation functional layer was small at 8.7%. Also, the ratio of the thickness of the separation functional layer to the film thickness was small at 3.1%. In addition, the tensile strength was 1.0 cN / dtex, and the nitrogen gas flux was 22.0 × 10⁻⁶. －６ cm ３ (STP) / cm ２ With a pressure of / sec / cmHg and a gas selectivity (carbon dioxide gas flux / nitrogen gas flux) of 7.5, it possessed sufficient performance for use as a gas separation membrane.

[0139] (Comparative Example 1) A hollow fiber membrane for Comparative Example 1 was prepared in the same manner as in Example 1, except that a double-cylindrical discharge nozzle as shown in Figure 5 was used and poly-4-methyl-1-pentene (manufactured by Mitsui Chemicals, RT18, Tm: 238°C) was used.

[0140] Table 3 shows the evaluation results for the hollow fiber membrane of Comparative Example 1. The cross-section of the hollow fiber membrane was entirely composed of microporous segments. Furthermore, the tensile strength was 1.0 cN / dtex, and the nitrogen gas flux was 95.0 × 10⁻⁶. －６ cm ３ (STP) / cm ２ With a gas density of / sec / cmHg and a gas selectivity (carbon dioxide gas flux / nitrogen gas flux) of 1.3, it did not possess sufficient performance for use as a gas separation membrane.

[0141] (Comparative Example 2) A hollow fiber membrane for Comparative Example 2 was prepared in the same manner as in Example 1, except that a triple-cylindrical discharge nozzle as shown in Figure 6 was used, poly-4-methyl-1-pentene (manufactured by Mitsui Chemicals, RT18, Tm: 238°C) was used as the core component and poly-4-methyl-1-pentene (manufactured by Mitsui Chemicals, MX002, Tm: 228°C) was used as the sheath component, and the discharged materials were extruded from the discharge nozzle in a ratio of RT18:MX002 = 95:5.

[0142] Table 3 shows the evaluation results of the hollow fiber membrane in Comparative Example 2. The cross-section of the obtained hollow fiber membrane was a composite cross-section consisting only of microporous segments formed by RT18 on the support.

[0143] Furthermore, the hollow fiber membrane of Comparative Example 2 was measured using the same method as in Example 1, and the thickness of the separation functional layer was 1.6 μm, and the coefficient of variation of the circumferential thickness of the separation functional layer was large at 30.2%. In addition, the ratio of the thickness of the separation functional layer to the film thickness was small at 4.0%. Furthermore, the tensile strength was 1.0 cN / dtex, and the nitrogen gas flux was 25.0 × 10⁻⁶. －６ cm ３ (STP) / cm ２ With a value of / sec / cmHg and a gas selectivity (carbon dioxide gas flux / nitrogen gas flux) of 3.0, it did not possess sufficient performance for use as a gas separation membrane.

[0144] (Comparative Example 3) The hollow fiber membrane of Comparative Example 3 was prepared in the same manner as in Example 1, except that the discharge weight ratio was RT18:MX002 = 70:30 when discharged from the discharge nozzle.

[0145] Table 3 shows the evaluation results of the hollow fiber membrane in Comparative Example 3. The cross-section of the hollow fiber membrane was a composite cross-section in which microporous segments formed of RT18 and non-microporous segments formed of MX002 were alternately arranged in four locations in the circumferential direction on the support.

[0146] Furthermore, the hollow fiber membrane of Comparative Example 3 was measured using the same method as in Example 1, and the thickness of the separation functional layer was 5.2 μm, which is thick, and the coefficient of variation of the separation functional layer thickness in the circumferential direction was 6.6%. Also, the ratio of the thickness of the separation functional layer to the film thickness was 17.3%, which is somewhat large. In addition, the tensile strength was 1.0 cN / dtex, and the gas selectivity (carbon dioxide gas flux / nitrogen gas flux) was 7.0, while the nitrogen gas flux was 2.8 × 10⁻⁶. －６ cm ３ (STP) / cm ２ The reading was somewhat low at / sec / cmHg, and it did not have sufficient performance to be used as a gas separation membrane.

[0147] (Example 11) A hollow fiber membrane for Example 11 was prepared in the same manner as in Example 1, except that poly-4-methyl-1-pentene (manufactured by Mitsui Chemicals, RT18, Tm: 238°C) was used as the core component and poly-4-methyl-1-pentene (manufactured by Mitsui Chemicals, MX002, Tm: 228°C) was used as the sheath component, and the materials were extruded from the discharge nozzle in a ratio of RT18:MX002 = 99:1 in terms of the extruded weight.

[0148] Table 4 shows the evaluation results of the hollow fiber membrane in Example 11. The cross-section of the hollow fiber membrane was a composite cross-section consisting only of microporous segments formed of RT18 on the support.

[0149] Furthermore, the hollow fiber membrane of Example 11 was measured using the same method as in Example 1, and the thickness of the separation functional layer was 0.2 μm, and the coefficient of variation of the circumferential thickness of the separation functional layer was small at 9.0%. Also, the ratio of the thickness of the separation functional layer to the film thickness was small at 1.0%. In addition, the tensile strength was 1.0 cN / dtex, and the nitrogen gas flux was 70.0 × 10⁻⁶. －６ cm ３ (STP) / cm ２ With a pressure of / sec / cmHg and a gas selectivity (carbon dioxide gas flux / nitrogen gas flux) of 7.1, it possessed sufficient performance for use as a gas separation membrane.

[0150] (Example 12) A hollow fiber membrane for Example 12 was prepared in the same manner as in Example 1, except that poly-4-methyl-1-pentene (manufactured by Mitsui Chemicals, RT18, Tm: 238°C) was used as the core component and poly-4-methyl-1-pentene (manufactured by Mitsui Chemicals, MX002, Tm: 228°C) was used as the sheath component, and the materials were extruded from the nozzle in a ratio of extrusion weight of RT18:MX002 = 99.4:0.6.

[0151] Table 4 shows the evaluation results of the hollow fiber membrane in Example 12. The cross-section of the hollow fiber membrane was a composite cross-section consisting only of microporous segments formed of RT18 on the support.

[0152] Furthermore, the hollow fiber membrane of Example 12 was measured using the same method as in Example 1, and the thickness of the separation functional layer was 0.1 μm, and the coefficient of variation of the circumferential thickness of the separation functional layer was small at 9.8%. In addition, the ratio of the thickness of the separation functional layer to the film thickness was small at 0.5%. Furthermore, the tensile strength was 1.0 cN / dtex, and the nitrogen gas flux was 90.0 × 10⁻⁶. －６ cm ３ (STP) / cm ２ With a pressure of / sec / cmHg and a gas selectivity (carbon dioxide gas flux / nitrogen gas flux) of 7.8, it possessed sufficient performance for use as a gas separation membrane.

[0153]

[0154]

[0155]

[0156]

[0157] The hollow fiber membrane of the present invention has a thin and highly uniform separation layer, making it suitable for use as a gas separation membrane.

[0158] 1...Separation function layer, 2...Thermoplastic resin A, 3...Thermoplastic resin B, 4...Separation function layer, 5...Thermoplastic resin A, 6...Thermoplastic resin B, 7...Separation function layer, 8...Thermoplastic resin A, 9...Thermoplastic resin B, 10...Gas discharge hole, 11...Polymer discharge hole, 12...Discharge surface, 13...Gas discharge hole, 14...Polymer discharge hole A, 15...Polymer discharge hole B, 16...Polymer discharge hole, 17...Polymer discharge hole A, 18...Polymer discharge hole B, O...Center of gravity of the hollow part, L...Length of the arc where the thermoplastic resin portion intersects with the inner surface of the hollow fiber membrane, A...Point obtained by moving a distance of length L × 0.2 counterclockwise along the inner surface of the hollow fiber membrane from the left end point toward the cross-section of the arc where the thermoplastic resin portion intersects with the inner surface of the hollow fiber membrane, B...Point obtained by moving a distance of length L × 0.2 clockwise along the inner surface of the hollow fiber membrane from the right end point toward the cross-section of the arc where the thermoplastic resin portion intersects with the inner surface of the hollow fiber membrane.

Claims

1. A hollow fiber membrane having a separation functional layer and a support for the separation functional layer, wherein the thickness of the separation functional layer is 5 μm or less, and the coefficient of variation of the circumferential thickness of the separation functional layer is 30% or less.

2. The hollow fiber membrane according to claim 1, wherein the ratio of the thickness of the separation functional layer to the film thickness is 10% or less.

3. The hollow fiber membrane according to claim 1 or 2, wherein the support has a structure selected from the group consisting of a structure made of only one type of thermoplastic resin, a laminated structure containing at least two types of thermoplastic resins, a sea-island composite structure containing at least two types of thermoplastic resins, and a structure in which the laminated structure and the sea-island composite structure are combined.

4. The hollow fiber membrane according to claim 3, wherein the bonded structure has segments containing at least one type of thermoplastic resin, and each segment containing a different thermoplastic resin is arranged in the circumferential direction, and the total number of segments is 4 or more and 40 or less.

5. The hollow fiber membrane according to claim 3, wherein the sea-island composite structure has 3 to 100 islands.

6. The hollow fiber membrane according to any one of claims 1 to 5, wherein the thermoplastic resin is polyethylene, polypropylene, polybutylene, or poly-4-methyl-1-pentene, or a copolymer thereof.

7. Nitrogen gas flux is 5.7 × 10 －６ cm ３ (STP) / cm ２ A hollow fiber membrane according to any one of claims 1 to 6, wherein the gas pressure is 0.2 / sec / cmHg or higher, the carbon dioxide gas flux / nitrogen gas flux ratio is 3.0 or higher, and the tensile strength is 0.3 cN / dtex or higher.

8. A bundle of threads using a hollow fiber membrane according to any one of claims 1 to 7.

9. A module using a hollow fiber membrane according to any one of claims 1 to 7.

10. A gas separation membrane module using a hollow fiber membrane according to any one of claims 1 to 7.

11. An artificial lung using a hollow fiber membrane according to any one of claims 1 to 7.

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