Hollow fiber separation apparatus and method for manufacturing a hollow fiber separation apparatus

Abstract

To provide a hollow fiber separation device where the mixing of air bubbles to a sealant and the deterioration of porous hollow fibers are reduced and to provide a production method by which the hollow fiber separation device where the mixing of air bubbles to the sealant and the deterioration of porous hollow fibers are reduced can be easily produced.SOLUTION: A hollow fiber separation device is provided. The bundle of porous hollow fibers is accommodated in a housing. The end part of the porous hollow fiber is sealed with a thermoplastic sealant between the housing and the porous hollow fiber and the porous hollow fibers; and the porous hollow fiber has an extension part where an outer periphery surface does not contact with the sealant and which extends in an axial direction and a contraction part where the outer periphery surface is in contact with the sealant.SELECTED DRAWING: Figure 4

Description

Technical Field

[0001] The present invention relates to a hollow fiber separation device and a method for manufacturing the hollow fiber separation device.

Background Art

[0002] A hollow fiber separation device is manufactured, for example, by housing and sealing a bundle of porous hollow fibers in a housing. The sealing is performed by filling the voids existing between the porous hollow fibers and between the porous hollow fibers and the housing with a sealing material. As the sealing material, a two-component mixed adhesive such as polyurethane or epoxy has been used. Since the two-component mixed adhesive has a low viscosity, it can be sealed by pouring the two components into the above-mentioned voids after mixing. In addition, it is easy to remove bubbles from the sealing portion. However, the sealing portion formed by the two-component mixed adhesive has a problem of being eroded by an organic solvent. Therefore, it cannot be used for applications using an organic solvent.

[0003] Examples of sealing materials that are not eroded by organic solvents include thermoplastic resins. However, since thermoplastic resins have a high viscosity even when melted, it is difficult to remove bubbles during sealing, and there is a problem that the defective rate tends to be high.

[0004] As an example of a method for removing bubbles, there is a method of increasing the fluidity of the sealing material by adjusting the melting temperature. However, this method takes time for temperature adjustment, so the productivity is poor. In addition, when the tube diameter is thick, it takes time for heat to reach the sealing material at the center, making it difficult to seal the center. In addition, since the outer porous hollow fibers are exposed to heat for a long time, they tend to deteriorate. As a result, the defective rate tends to be high.

[0005] As another example of a method for removing bubbles, there is a method of removing bubbles by moving the sealing material by applying a force from the outside.

[0006] For example, Patent Document 1 describes a method in which one end of a large number of porous hollow fiber porous separation membranes is inserted into a heat-meltable resin, and then the heat-meltable resin is heated to a molten state while pressure is applied from the surroundings. However, this method has the disadvantage that the outer diameter becomes smaller when pressure is applied, making it difficult to obtain a uniform diameter.

[0007] Patent Document 2 describes a method in which the end of a porous hollow fiber, whose surface is formed of a heat-meltable synthetic resin, is inserted into a sheath, the space between the sheath and the porous hollow fiber is kept tight, and the sheath is heated to a temperature at which the surface of the porous hollow fiber melts while the space between the sheath and the porous hollow fiber is reduced in pressure. Such a method requires a device for reducing the pressure inside the sheath.

[0008] Another method involves pre-moltening a thermoplastic resin and attaching it to the ends of the porous hollow fibers, then drawing them into the housing. The housing has a section with a smaller inner diameter. However, this method has drawbacks: it requires a long time to adjust the viscosity of the sealing material, and it can only be applied to highly durable porous hollow fibers due to the strong external force applied to them. [Prior art documents] [Patent Documents]

[0009] [Patent Document 1] Japanese Patent Application Publication No. 5-57153 [Patent Document 2] Japanese Patent Publication No. 2004-016905 [Overview of the Initiative] [Problems that the invention aims to solve]

[0010] The object of the present invention is to provide a hollow fiber separation device that reduces the incorporation of air bubbles into the sealing material and the deterioration of porous hollow fibers, and a manufacturing method that can easily produce a hollow fiber separation device that reduces the incorporation of air bubbles into the sealing material and the deterioration of porous hollow fibers. [Means for solving the problem]

[0011] According to one aspect of the present invention, a hollow fiber separation device is provided. The hollow fiber separation device houses a bundle of porous hollow fibers within a housing. The porous hollow fibers are sealed at their ends between the housing and the porous hollow fibers and between the porous hollow fibers themselves by a thermoplastic sealant. The porous hollow fibers have an axially stretched portion whose outer surface is not in contact with the sealant and a contracted portion whose outer surface is in contact with the sealant. The porous hollow fiber contains polytetrafluoroethylene and has a microstructure that includes nodes and fibrils present between the nodes and extending in the axial direction of the porous hollow fiber. Let Dsh be the average distance between nodes in the contracted portion and Dst be the average distance between nodes in the stretched portion, satisfying equation (1) below. {(Dst-Dsh) / Dst}×100≧10(%) (1)

[0012] Another aspect of the present invention provides a method for manufacturing a hollow fiber separation device. This method includes the step of forming porous hollow fiber fibers by uniaxially stretching a porous hollow fiber precursor in the axial direction. The method also includes a heating step in which a thermoplastic sealant is placed around the porous hollow fiber at the end of the bundle of porous hollow fibers and housed in a housing, and the end of the housing in which the sealant and the bundle of porous hollow fiber are placed is heated to melt the sealant and cause the heated portion of the porous hollow fiber to shrink. Furthermore, the method includes a step of solidifying the molten sealant. [Effects of the Invention]

[0013] According to the present invention, it is possible to provide a hollow fiber separation device in which the incorporation of air bubbles into the sealing material and the deterioration of porous hollow fibers are reduced, and a manufacturing method that can easily produce a hollow fiber separation device in which the incorporation of air bubbles into the sealing material and the deterioration of porous hollow fibers are reduced. [Brief explanation of the drawing]

[0014] [Figure 1] A schematic cross-sectional view showing an example of a housing containing porous hollow fibers and sealing material. [Figure 2] A cross-sectional view along the radial direction of the porous hollow fiber in the area where the sealing material is present in Figure 1. [Figure 3] A schematic cross-sectional view showing the heating process involved in the manufacturing of an example of a hollow fiber separation device. [Figure 4]Cross-sectional view schematically showing an example of a hollow fiber separation device according to an embodiment. [Figure 5] Cross-sectional view along the radial direction of the porous hollow fiber of the portion where the sealing material exists in the hollow fiber separation device shown in FIG. 4. [Figure 6] Cross-sectional view schematically showing another example of a state in which a porous hollow fiber and a sealing material are accommodated in a housing. [Figure 7] Cross-sectional view along the radial direction of the porous hollow fiber of the portion where the sealing material exists in FIG. 6. [Figure 8] Cross-sectional view schematically showing a heating process related to the manufacture of a hollow fiber separation device of another example. [Figure 9] Cross-sectional view schematically showing another example of a hollow fiber separation device according to an embodiment. [Figure 10] Cross-sectional view along the radial direction of the porous hollow fiber of the portion where the sealing material exists in the hollow fiber separation device shown in FIG. 9. [Figure 11] Scanning electron micrograph of the stretched portion of the porous hollow fiber. [Figure 12] Scanning electron micrograph of the contracted portion of the porous hollow fiber.

Mode for Carrying Out the Invention

[0015] Hereinafter, embodiments will be described with reference to the drawings as appropriate. In the embodiments, the same reference numerals are given to common configurations, and duplicate descriptions are omitted. Also, each figure is a schematic diagram for explaining the embodiments and facilitating their understanding. Although there are parts where the shape, dimensions, ratios, etc. are different from the actual device, these can be appropriately designed and changed in consideration of the following description and known techniques.

[0016] Also, when the term "porous hollow fiber" is described in this specification, it includes a porous hollow fiber having a stretched portion axially extended whose outer peripheral surface does not contact the sealing material and a contracted portion whose outer peripheral surface contacts the sealing material, as well as a porous hollow fiber consisting only of the axially extended stretched portion. When the porous hollow fiber further includes a non-porous layer covering the surface of the porous hollow fiber body, it may be described as "porous hollow fiber" including the non-porous layer.

[0017] The hollow fiber separation device according to this embodiment houses a bundle of porous hollow fibers within a housing. The porous hollow fibers are sealed at their ends between the housing and the porous hollow fibers, and between the porous hollow fibers themselves, by a thermoplastic sealant. The porous hollow fibers have an axially stretched portion whose outer surface is not in contact with the sealant, and a contracted portion whose outer surface is in contact with the sealant.

[0018] The housing can accommodate a bundle of porous hollow fibers.

[0019] Porous hollow fibers have portions that are stretched in the axial direction. Because porous hollow fibers are formed by stretching in the axial direction, they have numerous through-holes on their sides. Therefore, for example, particles larger than the through-holes can be separated from a liquid passing through these through-holes. Thus, a hollow fiber separation device containing bundles of porous hollow fibers can be applied to applications for separating particles in liquids.

[0020] The porous hollow fibers are sealed at their ends by a thermoplastic sealant between the housing and the porous hollow fibers, and between the porous hollow fibers themselves. Therefore, the porous hollow fibers have portions where their outer surface is in contact with the sealant.

[0021] Sealing with thermoplastic sealants is performed by melting the sealant with heat, then cooling and solidifying it again. Therefore, when the sealant is melted with heat, the portion of the porous hollow fiber whose outer surface is in contact with the sealant is heated along with the sealant. When heated, the porous hollow fiber, which is stretched in the axial direction, contracts in the direction opposite to the stretching direction.

[0022] Therefore, the portion of the porous hollow fiber's outer surface that is in contact with the sealing material shrinks and becomes a contracted portion. The portion of the outer surface that is not in contact with the sealing material forms an extended portion that is stretched in the axial direction. Thus, the porous hollow fiber has both an extended portion and a contracted portion.

[0023] The sealing material in contact with the outer surface of the porous hollow fiber melts upon heating and moves in accordance with the contraction of the porous hollow fiber. As air bubbles escape from the sealing material during this movement, the sealed area formed by the solidification of the melted sealing material has reduced air bubble contamination.

[0024] Therefore, the porous hollow fiber, which has an axially extended portion whose outer surface is not in contact with the sealing material and a contracted portion whose outer surface is in contact with the sealing material, is sealed within the housing without undergoing either a long heating process or a process in which strong external force is applied to the porous hollow fiber. As a result, deterioration of the porous hollow fiber can be reduced.

[0025] Therefore, the hollow fiber separation device according to this embodiment can reduce the incorporation of air bubbles into the sealing material and the deterioration of porous hollow fibers.

[0026] Further details will be provided regarding the hollow fiber separation apparatus according to this embodiment.

[0027] (housing) The housing can accommodate a bundle of porous hollow fibers inside. The housing may be, for example, cylindrical with a substantially constant inner diameter along the axial direction. Preferably, the housing contains a fluororesin such as perfluoroalkoxyalkane (PFA).

[0028] (Porous hollow fiber) An example of a method for manufacturing porous hollow fibers is described below. Porous hollow fibers can be produced, for example, by uniaxially stretching a porous hollow fiber precursor formed from a polymer material that can be used to produce porous hollow fibers by uniaxial stretching.

[0029] Polymer materials that can be used to produce porous hollow fibers by uniaxial stretching may include, for example, polyethylene (PE), polypropylene (PP), and polytetrafluoroethylene (PTFE). It is particularly preferable to include PTFE. PTFE has a high melting point of approximately 330°C and a high thermal shrinkage rate. It also has high chemical resistance. Therefore, porous hollow fibers containing PTFE can be used even when the liquid used for separation is, for example, a resist, developer, organic solvent, strong acid, or strong alkali used in semiconductor manufacturing.

[0030] A porous hollow fiber precursor is formed from a polymer material. The porous hollow fiber precursor may be, for example, an extruded product. Regarding extrusion molding, a method for producing an extruded product using PTFE as the material is described below as an example.

[0031] As raw materials for extruded products, PTFE fine powder and extrusion aids such as lubricants can be used. By mixing PTFE fine powder with extrusion aids such as lubricants, a paste-like mixture can be obtained.

[0032] Organic solvents can be used as extrusion aids. Examples of organic solvents include petroleum hydrocarbons and fluorinated solvents. Examples of petroleum hydrocarbons include commonly used solvent naphtha (e.g., registered trademark: Isoper E, manufactured by Exxon Chemicals), white oil, and liquid paraffin with 6 to 12 carbon atoms (e.g., registered trademark: Cactus Normal Paraffin N-10, manufactured by Japan Energy Co., Ltd.).

[0033] The amount of extrusion aid added can be, for example, 15% to 30% by weight relative to the amount of PTFE fine powder added.

[0034] The mixture may be aged before being subjected to extrusion molding. Alternatively, the aged mixture may be compressed to produce a compressed molded body (billet). Compression removes air from the PTFE fine powder, improving the uniformity of the extruded product. The shape of the compressed molded body is not particularly limited, but it may be cylindrical or cylindrical, for example.

[0035] By subjecting the above mixture to extrusion molding, a tubular extruded product can be obtained. Extrusion molding can be performed, for example, by placing the mixture into the cylinder of an extruder and extruding it into a tubular shape. The inner and outer diameters of the extruded product can be adjusted by adjusting the dimensions of the die and core pin of the extruder.

[0036] As described above, a porous hollow fiber precursor is obtained.

[0037] By uniaxially stretching the porous hollow fiber precursor formed as described above, porous hollow fibers can be created. The specific method of uniaxial stretching will be described later. When uniaxial stretching is performed, polymer fibers are drawn out from the polymer material contained in the porous hollow fiber precursor and stretched in the stretching direction. In this way, a microstructure containing nodes and fibrils can be formed. Nodes refer to regions where polymer fibers are not stretched and the polymer material is aggregated. Fibrils refer to polymer fibers that exist between nodes and are oriented in the stretching direction.

[0038] Such microstructures have numerous through-pores between nodes, between fibrils, or between nodes and fibrils. Because porous hollow fibers have such microstructures, they can separate particles larger than the through-pores from particles smaller than the through-pores. Therefore, they can be used in applications such as removing particulate matter from liquids.

[0039] The porosity of porous hollow fibers can be adjusted by controlling the stretching ratio during uniaxial stretching. The relationship between the stretching ratio and the porosity of porous hollow fibers varies depending on temperature conditions, etc., but for example, if the stretching ratio during uniaxial stretching is doubled, porous hollow fibers with a porosity of approximately 50% can be produced. The porosity of porous hollow fibers can be set to any desired value, but it is preferably between 30% and 80%. To obtain a porosity within this range, it is preferable to set the stretching ratio between 1.5 and 6 times.

[0040] When the porous hollow fibers manufactured as described above are heated, the fibrils in their microstructure contract, shortening the distance between nodes. Therefore, they have the property of thermally shrinking in the direction opposite to the stretching direction.

[0041] A thermal shrinkage rate of 10% or more is preferable because it allows the sealing material to move a greater distance in response to the shrinkage of the porous hollow fiber, thus more effectively reducing the incorporation of air bubbles into the sealing material. A thermal shrinkage rate of 25% or more is even more preferable.

[0042] Porous hollow fibers may further comprise a non-porous layer covering the surface of the porous hollow fiber body. The non-porous layer is a layer that does not have through-holes. Porous hollow fibers further comprising a non-porous layer are impermeable to liquids but permeable to gases. Therefore, they can be used, for example, in applications such as gas separation from liquids, degassing, or ozonated water production.

[0043] The non-porous layer can be formed, for example, by applying a PTFE dispersion to the outer surface of the porous hollow fiber body and then firing it. A porous hollow fiber having the non-porous layer formed in this way can be heat-shrinkable.

[0044] An example of a method for forming a non-porous layer is described below.

[0045] A PTFE dispersion comprises a dispersion medium and PTFE powder in the dispersion medium. As the PTFE dispersion, materials commonly used in methods for forming resin tubes by coating, such as dip coating, can be used. For example, a PTFE dispersion is an aqueous dispersion obtained by emulsion polymerization of PTFE powder in an aqueous dispersion medium. A PTFE dispersion can also be a suspension containing PTFE powder.

[0046] The dispersion medium may be, for example, water. The composition of the PTFE dispersion is not particularly limited, and for example, dispersions or suspensions with compositions commonly used in methods such as dip coating can be used.

[0047] A dispersed PTFE coating is obtained by applying PTFE dispersion to the outer surface of the porous hollow fiber body. To apply the PTFE dispersion, for example, the porous hollow fiber body can be immersed in the PTFE dispersion. Specifically, a dip coating method is preferred. In the dip coating method, a uniform coating thickness can be formed by passing the porous hollow fiber body through the PTFE dispersion and pulling it up at a constant speed.

[0048] A PTFE dispersion is applied to a porous hollow fiber body, and the resulting dispersed PTFE coating is fired. In this way, a non-porous layer is obtained.

[0049] Alternatively, a PTFE dispersion can be applied once, followed by firing, and then another PTFE dispersion can be applied to the outer surface of the resulting non-porous layer and fired again. By repeatedly applying the dispersion and firing alternately, the thickness of the non-porous layer can be adjusted to the desired thickness.

[0050] The firing temperature for the dispersed PTFE coating on the porous hollow fiber body should be above the melting point of PTFE, and preferably above 340°C. If the firing temperature is too high, the PTFE will undergo thermal decomposition, which is undesirable. Therefore, a firing temperature of 400°C or lower is preferable. Furthermore, fixing the porous hollow fiber during firing is preferable as it prevents shrinkage of the porous hollow fiber during firing.

[0051] By housing porous hollow fibers together with a sealing material in a housing and then heating them, porous hollow fibers can be formed that have an axially stretched portion whose outer surface is not in contact with the sealing material, and a contracted portion whose outer surface is in contact with the sealing material.

[0052] It is preferable that the average distance between nodes in the contraction section (Dsh) and the average distance between nodes in the extension section (Dst) satisfy the following equation (1). {(Dst-Dsh) / Dst}×100≧10(%) (1) The left-hand side of equation (1) represents the internode shrinkage rate (%) of the porous hollow fiber. When the internode shrinkage rate is 10% or more, as shown in equation (1), the distance the sealing material moves to follow the thermal shrinkage of the porous hollow fiber becomes larger. Therefore, it is easier to obtain a hollow fiber separation device with less air bubble contamination in the sealing material. It is more preferable that the internode shrinkage rate of the porous hollow fiber be 25% or more.

[0053] (Sealing material) The encapsulant can include a thermoplastic resin. An example of a thermoplastic resin is PFA. PFA has high chemical resistance. Therefore, a hollow fiber separation apparatus equipped with PFA as the encapsulant can be used even when the liquid to be separated is, for example, resist, developer, organic solvent, strong acid, or strong alkali used in semiconductor manufacturing. The melting point of PFA is approximately 310°C.

[0054] Examples of sealing material forms include films and tubes.

[0055] In particular, it is preferable that the tube (first tube) contains PFA and shrinks radially due to heat. After inserting the end of the porous hollow fiber into the first tube, heating the first tube to the extent that it shrinks due to heat can cause the porous hollow fiber and the first tube to adhere tightly and become one unit. As a result, the amount of air bubbles between the porous hollow fiber and the sealing material can be reduced.

[0056] Preferably, the dimensions of the first tube are such that the inner diameter before heat shrinkage is larger than the outer diameter of the porous hollow fiber, and the inner diameter after heat shrinkage is smaller than the outer diameter of the porous hollow fiber. With these dimensions, the adhesion between the first tube and the porous hollow fiber can be further improved.

[0057] Furthermore, a second tube can be used in combination as a sealing material. As the second tube, for example, a tube containing PFA that shrinks radially due to heat can be used and has an inner diameter that can accommodate multiple porous hollow fibers. For example, the ends of multiple porous hollow fibers integrated with the first tube as described above are inserted together into the second tube, and the second tube is heated to cause thermal shrinkage. In this way, the packing density of the porous hollow fibers can be increased, for example, bringing it closer to a close-packed state (porosity of 26%). The packing density of the sealing material is preferably 15% or more, and more preferably in the range of 20% to 30%, before being subjected to the heating process.

[0058] (Hollow fiber separation device) An example of a hollow fiber separation device will be explained along with its manufacturing method, with reference to Figures 1-5.

[0059] Figures 1 and 2 schematically show an example of a state in which the porous hollow fiber 1, the first tube 2a, and the second tube 2b are housed in the housing 3. Figure 1 is a cross-sectional view along the axial direction of the porous hollow fiber 1. Figure 2 is a cross-sectional view along the radial direction of the porous hollow fiber 1 in the portion where the first tube 2a and the second tube 2b are located.

[0060] The conditions shown in Figures 1 and 2 can be prepared, for example, as follows.

[0061] Insert both ends of multiple porous hollow fibers 1 into a first tube 2a with a length of 2L. Bend the multiple porous hollow fibers 1 into a U-shape and gather their ends together. Insert the gathered multiple porous hollow fibers 1 and the first tube 2a into a second tube with a length of 2L to tie the multiple porous hollow fibers 1 together. In this state, arrange the porous hollow fibers 1 so as close to close packing as possible.

[0062] A porous hollow fiber 1, with a first tube 2a and a second tube 2b positioned at its ends, is housed in a housing 3. At this time, aligning the ends of the porous hollow fiber 1 and the sealing material 2 with the ends of the housing 3 is preferable, as this allows for efficient heating in the subsequent heating step.

[0063] As shown in Figure 1, multiple porous hollow fibers 1 are housed in a housing 3 in a U-shape. The first tube 2a and the second tube 2b are housed in the housing 3, positioned at their respective ends. The length of the area where the first tube 2a and the second tube 2b are located is 2L. In the housing 3, the surface defined at the end where the first tube 2a and the second tube 2b are located is defined as the bottom surface.

[0064] As shown in Figure 2, the porous hollow fiber 1 has a portion where its outer surface is in contact with the first tube 2a, and the first tube 2a has a portion where its outer surface is in contact with the second tube 2b. In this portion, the first tube 2a and the second tube 2b are arranged between the porous hollow fiber 1 and between the housing 3 and the porous hollow fiber 1.

[0065] Figure 3 is a cross-sectional view showing the end of the housing 3, which contains the porous hollow fiber 1, the first tube 2a, and the second tube 2b, covered with a heating element 4.

[0066] As shown in Figure 3, the bottom surface of the housing 3 and the side surface of the housing 3, where the first tube 2a and the second tube 2b are located inside, are covered with a heating element 4 and heated. Heating can be carried out by known methods, for example, using a salt bath or a band heater. The heating process melts the first tube 2a and the second tube 2b and causes the porous hollow fiber 1 to shrink due to heat. As a result, the molten first tube 2a and the second tube 2b can move in accordance with the thermal shrinkage of the porous hollow fiber 1. Heating from both the bottom surface and the side surface of the housing 3 is preferable as it allows for efficient sealing. The heating temperature is preferably above the melting point of the first tube 2a and the second tube 2b.

[0067] After heating is complete, the molten first tube 2a and second tube 2b are solidified again. This allows the spaces between the porous hollow fibers 1 and between the porous hollow fibers 1 and the housing 3 to be sealed with the sealing material 2. The sealing material 2 can be solidified, for example, by allowing the housing 3 inside to cool along with the heating element 4.

[0068] As described above, the hollow fiber separation device 10 can be obtained.

[0069] The resulting hollow fiber separation device will be described below with reference to Figures 4 and 5.

[0070] The hollow fiber separation device 10 comprises porous hollow fibers 1, a sealing material 2, and a housing 3.

[0071] Figure 4 is a cross-sectional view of the hollow fiber separation apparatus, taken along the axial direction of the porous hollow fiber. The ends of the porous hollow fiber 1 and the sealing material 2 are located inward from the ends of the housing 3 due to thermal shrinkage. The distance from the end of the housing 3 to the ends of the porous hollow fiber 1 and the sealing material 2 is represented by 11L.

[0072] Figure 5 is a cross-sectional view of the hollow fiber separation apparatus in the area where the sealing material is present, taken along the radial direction of the porous hollow fibers. The sealing material 2 is filled between the porous hollow fibers 1 and between the porous hollow fibers 1 and the housing 3.

[0073] In the porous hollow fiber 1 shown in Figure 4, the portion of the outer surface that is not in contact with the sealing material 2 is the stretched portion, and the portion of the outer surface that is in contact with the sealing material 2 is the contracted portion.

[0074] The stretched portion remains stretched in the axial direction and has numerous through-holes in its microstructure, which includes nodes and fibrils, between nodes, between fibrils, or between nodes and fibrils. Therefore, for example, particles larger than these through-holes can be excluded and separated from a liquid. Thus, the hollow fiber separation device described above can be applied to applications such as filtration.

[0075] Furthermore, with reference to Figures 6 to 10, other examples of hollow fiber separation devices will be described along with their manufacturing methods.

[0076] Figures 6 and 7 schematically show the porous hollow fiber 1, the first tube 2a, and the second tube 2b housed within the housing 3. The porous hollow fiber 1 has a non-porous layer 12 on the outside of its main body.

[0077] The conditions shown in Figures 6 and 7 can be prepared as follows.

[0078] A first tube 2a, 2L in length, is fixed to each end of a plurality of porous hollow fibers 1. The porous hollow fibers 1 are aligned in one direction to form a bundle, and one end of the bundle is inserted into a second tube 2b, 2L in length. The second tube 2b is then heated to shrink and fix it in place. By performing this fixing at both ends of the bundle, the first tube 2a and the second tube 2b can be positioned at both ends of the porous hollow fibers 1.

[0079] A porous hollow fiber 1, with a first tube 2a and a second tube 2b positioned at both ends, is housed in a housing 3. At this time, it is preferable that the ends of the porous hollow fiber 1, the first tube 2a and the second tube 2b, and the ends of the housing 3 are aligned with the two bottom surfaces of the housing 3, as this allows for efficient heating in the subsequent heating step.

[0080] As shown in Figure 6, the multiple porous hollow fibers 1 are housed in the housing 3, aligned in one direction. The first tube 2a and the second tube 2b are housed in the housing 3 at both ends of the porous hollow fiber 1, positioned outside the non-porous layer 12. That is, the first tube 2a and the second tube 2b are located at both ends of the housing 3. Otherwise, it is the same as described with reference to Figures 1 and 2.

[0081] Figure 8 is a cross-sectional view showing the end of a housing 3, which contains porous hollow fibers 1 with a non-porous layer 12 on the outside, a first tube 2a, and a second tube 2b, covered with a heating element 4.

[0082] As shown in Figure 8, one side of the bottom surface of the housing 3 and the side surface of the housing 3 in which the first tube 2a and the second tube 2b are located are covered with a heating element 4 and heated. The heating step and the step of solidifying the first tube 2a and the second tube 2b to obtain the sealing material 2 can be carried out in the same manner as described above. This is done for both ends of the housing 3.

[0083] As described above, the hollow fiber separation device 10 can be obtained.

[0084] The resulting hollow fiber separation device will be described below with reference to Figures 9 and 10.

[0085] The hollow fiber separation device 10 comprises a porous hollow fiber 1, a sealing material 2, and a housing 3. The porous hollow fiber 1 has a non-porous layer 12 on the outside of its main body.

[0086] Figure 9 is a cross-sectional view of the hollow fiber separation apparatus, taken along the axial direction of the porous hollow fiber. Due to thermal shrinkage, the ends of the porous hollow fiber 1 and the sealing material 2 are both located inward from the ends of the housing 3. The distance from the end of the housing 3 to the ends of the porous hollow fiber 1 and the sealing material 2 is represented by 11L, respectively.

[0087] Figure 10 is a cross-sectional view of the region where the sealing material is located in the hollow fiber separation apparatus, taken along the radial direction of the porous hollow fiber. The porous hollow fiber 1 comprises a non-porous layer 12 that covers the surface of the porous hollow fiber 1 body. The sealing material 2 is filled between the porous hollow fibers 1 and between the porous hollow fibers 1 and the housing 3.

[0088] Aside from the points mentioned above, the hollow fiber separation apparatus is the same as described below with reference to Figures 4 and 5.

[0089] The hollow fiber separation device described above has a two-layer structure with a non-porous layer 12 on the outside of the main body of the porous hollow fiber 1. The non-porous layer 12 is impermeable to liquids but permeable to gases. Therefore, the hollow fiber separation device 10 can remove dissolved gases from the liquid by flowing any liquid into the porous hollow fiber 1 and reducing the pressure inside the housing 3. Accordingly, hollow fiber separation devices according to other examples can be used, for example, for degassing applications.

[0090] <Measurement method> The following describes methods for measuring the porosity, thermal shrinkage rate, packing efficiency, SEM observation, and internode distance of porous hollow fibers.

[0091] (Porosity of porous hollow fibers) The porosity of porous hollow fibers can be measured as follows.

[0092] First, the apparent specific gravity d of the porous hollow fiber is measured by the water displacement method. The measurement of apparent specific gravity by the water displacement method can be performed according to the method described in JIS K 7112:1999. Next, assuming a PTFE specific gravity of 2.2, the porosity P (%) is calculated using the following formula. P = {(2.2-d) / 2.2} × 100.

[0093] (Thermal shrinkage rate of porous hollow fibers) The thermal shrinkage rate of porous hollow fibers can be measured as follows. Porous hollow fibers, whose length has been measured beforehand, are heated to 300°C or 350°C and held for 5 minutes. After cooling, the length of the porous hollow fibers at room temperature is measured. The thermal shrinkage rate of the porous hollow fiber is calculated as the percentage difference (%) between the length of the porous hollow fiber before heating and the length of the porous hollow fiber before heating.

[0094] (Dimensional calculation of porous hollow fibers) The calculated wall thickness of porous hollow fibers can be measured using a microscope. The measurement is performed on the radial cross-section of the porous hollow fiber. Four arbitrary points are taken within the same cross-section, and the wall thickness of the section passing through each point is measured. The average of these measurements is taken as the calculated wall thickness of the porous hollow fiber.

[0095] (Filling rate) The packing density of porous hollow fibers is calculated as the sum of the cross-sectional areas of all porous hollow fibers relative to the radial cross-sectional area inside the housing of the hollow fiber separation device in the area where the sealing material is present. The cross-sectional area of ​​the porous hollow fibers includes the pores (hollow portions) of the porous hollow fibers.

[0096] (SEM observation) Observation using a scanning electron microscope (SEM) can be performed as follows. First, the porous hollow fiber is cut in half along the stretching direction. Next, the cut cross-section is observed at 1000x magnification using a scanning electron microscope (SEM).

[0097] (Measurement of distance between nodes) The distance between nodes can be measured as follows: For the obtained SEM observation image, the length of the scale bar is measured with a metal ruler, and the scaling factor is calculated. Ten arbitrary points are taken between nodes in the image, and the distance between nodes at each point is measured in the stretching direction. Converting these metal ruler measurements using the scaling factor yields the distance between nodes.

[0098] <Examples> The hollow fiber separation apparatus used in the example was manufactured as follows.

[0099] (Example 1) Porous hollow fibers were manufactured as follows: For the PTFE fine powder used for extrusion molding, we used PTFE fine powder Polyflon (registered trademark) F106 manufactured by Daikin Industries, Ltd.

[0100] To 100 parts by mass of PTFE fine powder (F106), 21 parts by mass of naphtha (extrusion aid) were added, and the mixture was prepared by mixing at room temperature using a turbler mixer. Subsequently, the obtained mixture was formed into a cylindrical shape using a pre-molding machine. The formed mixture was then fed into an extruder equipped with a die and core pin of a size that would produce an extruded product of a predetermined size, and extruded. In this manner, a porous hollow fiber precursor was obtained.

[0101] The obtained porous hollow fiber precursor was uniaxially stretched in the axial direction while being heated at 300°C to a stretch ratio of 2. Next, it was subjected to firing at 380°C to 400°C to obtain porous hollow fibers. The firing was carried out while the extruded product was fixed in place to prevent shrinkage of the extruded product. After cooling, the obtained porous hollow fibers were wound onto a roll.

[0102] As described above, a porous hollow fiber made of PTFE was obtained with a porosity of 50%, an inner diameter of φ1.0 mm, an outer diameter of φ2.0 mm, and a heat shrinkage rate of 35%. Seven of these porous hollow fibers were prepared.

[0103] Next, 14 first tubes made of perfluoroalkoxyalkane (hereinafter referred to as PFA) were prepared as a sealing material. The first tubes were cylindrical in shape made of PFA and were heat-shrinkable.

[0104] One end of a porous hollow fiber was inserted 20 mm into the first tube, and then the tube was heated at 200°C for 1 minute to cause thermal shrinkage. This fixed the first tube to one end of the porous hollow fiber. The inner diameter of the first tube before shrinkage was φ2.2 mm and its length was 20 mm. After shrinkage, the inner diameter was φ2.0 mm and the wall thickness after shrinkage was 0.2 mm. In the same manner, the first tube was fixed to the other end of the porous hollow fiber. A porous hollow fiber with the first tube fixed to both ends was prepared in the same manner. A total of seven porous hollow fibers with the first tube fixed to both ends were prepared in the same manner.

[0105] Next, a second tube was prepared. The second tube was a cylindrical tube made of PFA and was heat-shrinkable.

[0106] Seven porous hollow fibers, each with a first tube fixed to both ends, were bent into a U-shape so that their 14 ends were aligned. The porous hollow fibers with aligned ends were then inserted 20 mm into the second tube. That is, one end of the second tube and all 14 ends of the porous hollow fibers to which the first tube was fixed were aligned.

[0107] Next, the second tube was heated and thermally shrunk. The inner diameter of the second tube before shrinkage was φ11 mm and its length was 20 mm. After shrinkage, the wall thickness was 0.3 mm and the inner diameter after shrinkage was φ9.4 mm. This aligned and fixed the porous hollow fibers and the first tube so that they approached close packing. The porous hollow fiber bundle was prepared in the manner described above.

[0108] For the housing, a tube made of PFA with an inner diameter of 10 mm and an outer diameter of 12 mm was used.

[0109] The porous hollow fiber bundle prepared as described above was inserted into the housing. At this time, the ends of the porous hollow fiber bundle were aligned with the ends of the housing.

[0110] Next, the bottom and sides of the housing, extending 20 mm from the bottom, were covered with a 330°C band heater and heated for 30 minutes. After 30 minutes, the heating element was allowed to cool, and the housing was removed from the heating element.

[0111] In this way, a hollow fiber separation device was obtained.

[0112] (Example 2) Porous hollow fibers having a non-porous layer on the outer circumference were manufactured as follows.

[0113] Porous hollow fibers with an inner diameter of φ0.95 mm and a calculated wall thickness of 100 μm were manufactured by extrusion molding using a core wire. Details are as follows:

[0114] For the PTFE fine powder used for extrusion molding, we used PTFE fine powder Polyflon (registered trademark) F201 manufactured by Daikin Industries, Ltd.

[0115] A mixture was prepared by adding 21 parts by mass of naphtha (extrusion aid) to 100 parts by mass of PTFE fine powder (F201), and then mixing it at room temperature using a turbler mixer. The resulting mixture was then formed into a cylindrical shape using a pre-molding machine. The formed mixture was fed into an extruder equipped with a die sized to produce an extruded product with a wall thickness of 100 μm. Next, a silver-plated copper wire with an outer diameter of φ0.95 mm was placed in the paste extruder to serve as the core wire. Extrusion molding was performed while inserting the core wire at a speed faster than the extrusion speed. This resulted in an extruded product with the core wire coated and uniaxially stretched. The extruded product was porous. The obtained extruded product was subjected to drying at 180°C to 200°C and firing at 380°C to 400°C to obtain porous hollow fibers. The firing was performed with the extruded product fixed to prevent shrinkage. After cooling, the obtained porous hollow fibers were wound onto a roll. After applying PTFE dispersion to the outer surface of the porous hollow fiber, it was fired to form a non-porous layer on the outside of the porous hollow fiber. The resulting porous hollow fiber had an inner diameter of φ0.95 mm and a calculated wall thickness of (100 + 10) μm, and had a two-layer structure with a non-porous layer on the outer surface of the porous hollow fiber body.

[0116] Fourteen of these porous hollow fibers were prepared.

[0117] Next, 28 first tubes made of PFA were prepared as sealing material.

[0118] In the same manner as in Example 1, the first tube described above was fixed to both ends of the porous hollow fiber. The inner diameter of the first tube before shrinkage was φ1.5 mm and its length was 20 mm. After shrinkage, the inner diameter was φ1.17 mm and the wall thickness after shrinkage was 0.2 mm. A total of 14 porous hollow fibers were prepared, with the first tube fixed to both ends.

[0119] Next, I prepared two second tubes.

[0120] Fourteen porous hollow fibers, each with a first tube fixed to both ends, were aligned in one direction so that both ends were aligned. One end of each aligned fiber was then inserted 20 mm into the second tube. In other words, one end of the second tube was aligned with all 14 ends of the porous hollow fibers to which the first tube was fixed.

[0121] Next, the second tube was heated and heat-shrunk. The second tube was a cylindrical tube made of PFA and was heat-shrinkable. The inner diameter of the second tube before shrinkage was φ11 mm and its length was 20 mm. After shrinkage, the wall thickness was 0.3 mm and the inner diameter after shrinkage was φ9.4 mm. This allowed the porous hollow fibers and the first tube to be aligned and fixed in place so that they were in the closest packing position.

[0122] Similarly, the second tube was attached to the other end of the porous hollow fiber.

[0123] As described above, a bundle of porous hollow fibers was prepared.

[0124] A cylindrical housing made of PFA was used. The porous hollow fiber bundle prepared as described above was inserted into the housing. At this time, both ends of the porous hollow fiber bundle were aligned with the bottom surface of the housing.

[0125] Next, the bottom and sides of the housing, extending 20 mm from the bottom, were covered with a 330°C band heater and heated for 30 minutes. After 30 minutes, the band heater was allowed to cool, and the housing was removed from the band heater. This process was repeated for both ends.

[0126] In this way, a hollow fiber separation device was obtained.

[0127] <Result> In the hollow fiber separation apparatus of Example 1, the filling rate of the porous hollow fibers was 56%. Furthermore, the ends of the sealing material and porous hollow fibers had moved 7 mm inward from the ends of the housing (corresponding to L11 in Figure 4). That is, the shrinkage rate relative to the length of the heated region was 35%.

[0128] In the hollow fiber separation apparatus of Example 2, the ends of the sealing material and porous hollow fibers also moved 7 mm inward from the ends of the housing (corresponding to L11 in Figure 9). That is, the shrinkage rate relative to the length of the heated area was 35%.

[0129] This is thought to be because the molten sealing material, due to heating, moved in accordance with the thermal contraction of the porous hollow fibers. Since air bubbles are removed from the sealing material by this movement, the hollow fiber separation apparatus in the example can produce a sealing material with fewer air bubbles.

[0130] In the housing of Example 1, the outer diameter of the region where the sealing material was present was between 11.83 mm and 11.93 mm. This value showed a small difference from the outer diameter of the housing before heating.

[0131] In the hollow fiber separation apparatus of the example, air bubbles are removed from the sealing material without applying external force such as pressure to the housing during the manufacturing process. Therefore, it is thought that the difference in the outer diameter of the housing before and after heating was small. Consequently, it is thought that the hollow fiber separation apparatus of the example has less air bubbles mixed into the sealing material, and the deterioration of porous hollow fibers is reduced.

[0132] Tables 1 to 3 show the dimensions of various porous hollow fibers in the hollow fiber separation apparatus of the examples before and after heat treatment. Table 1 shows the dimensions of the porous hollow fiber (porous tube Φ1 × Φ2 (coreless molding)) in the hollow fiber separation apparatus of Example 1. Table 2 shows the dimensions of the porous hollow fiber (porous tube Φ0.95 × 100 μm (microtube E porous)) before the formation of a non-porous layer on the outer surface, as described in Example 2. Table 3 shows the dimensions of the porous hollow fiber (2-layer tube Φ0.95 × (100 + 10) μm (microtube E porous + PTFE coating)) in the hollow fiber separation apparatus of Example 2.

[0133] In Tables 1-3, the post-heating change rate is shown as a positive number when the post-heating dimension increased compared to the pre-heating dimension, and as a negative number when the post-heating dimension decreased.

[0134] [Table 1]

[0135] [Table 2]

[0136] [Table 3]

[0137] As shown in Tables 1-3, the porous hollow fibers heated at 350°C for 5 minutes were shortened by more than 10% in length.

[0138] Figure 11 shows the SEM image of Example 1 before heating. Figure 12 shows the SEM image after heating. As is clear from the comparison, in Figure 12 the distance between nodes 13 is smaller and the length of the fibril length 14 is shorter compared to Figure 11.

[0139] Table 4 shows the measurement results of the internode distance before and after heating for porous hollow fibers in the hollow fiber separation apparatus of Examples 1 and 2.

[0140] [Table 4]

[0141] The results in Table 4 show that the sample heated at 350°C for 5 minutes exhibited a variation rate of 10% or more in the internode distance, calculated from the average internode distance before heating (i.e., the stretched portion) (Dst) and the average internode distance after heating (i.e., the contracted portion) (Dsh).

[0142] From the results above, the porous hollow fibers in the hollow fiber separation devices of Examples 1 and 2 all underwent thermal shrinkage. As a result, the molten sealing material moves inward from the edges of the housing, following the thermal shrinkage of the porous hollow fibers. During this movement, air bubbles escape from the sealing material. Therefore, without applying external force, the sealing material fills the spaces between the porous hollow fibers and between the porous hollow fibers and the housing without any gaps, thereby improving the integrity of the seal. As a result, the hollow fiber separation devices of Examples 1 and 2 reduce the incorporation of air bubbles into the sealing material and the deterioration of the porous hollow fibers, resulting in a more uniform diameter of the porous hollow fibers and an expected improvement in yield.

[0143] As described above, the manufacturing methods for the hollow fiber separation devices in Examples 1 and 2 are simple methods for manufacturing hollow fiber separation devices in which the incorporation of air bubbles into the sealing material and the deterioration of porous hollow fibers are reduced.

[0144] It should be noted that the present invention is not limited to the embodiments described above, and can be modified in various ways during implementation without departing from its essence. Furthermore, each embodiment may be combined as appropriate, and in that case, the combined effects can be obtained. Moreover, the above embodiments include various inventions, and various inventions can be extracted by selecting combinations from the multiple constituent elements disclosed. For example, if the problem can be solved and effects obtained even if some constituent elements are deleted from all the constituent elements shown in the embodiment, then the configuration with these deleted constituent elements can be extracted as an invention. [Explanation of Symbols]

[0145] 1…Porous hollow fiber, 2…Sealing material, 2a…First tube, 2b…Second tube, 3…Housing, 4…Heating element, 10…Hollow fiber separation device, 12…Non-porous layer, 13…Node, 14…Fibril, 2L…Length of the area where the sealing material is located, 11L…Distance from the end of the housing to the end of the porous hollow fiber and sealing material.

Claims

1. A hollow fiber separation device comprising a housing containing a bundle of porous hollow fibers, wherein the porous hollow fibers are sealed at their ends between the housing and the porous hollow fibers and between the porous hollow fibers themselves by a thermoplastic sealant, The porous hollow fiber is An axially extended portion whose outer surface is not in contact with the sealing material, It has a shrinkage portion whose outer surface is in contact with the sealing material, The porous hollow fiber contains polytetrafluoroethylene, It has a microstructure that includes nodes and fibrils that are present between the nodes and extend in the axial direction of the porous hollow fiber, Let Dsh be the average distance between the nodes in the contraction section and Dst be the average distance between the nodes in the extension section, then the following equation (1) {(Dst-Dsh) / Dst}×100≧10(%) (1) A hollow fiber separation device that satisfies the requirements.

2. The hollow fiber separation apparatus according to claim 1, wherein the porous hollow fiber further comprises a non-porous layer covering the surface of the porous hollow fiber body.

3. A step of forming a porous hollow fiber by uniaxially stretching a porous hollow fiber precursor containing polytetrafluoroethylene in the axial direction, A heating step is performed in which a thermoplastic sealing material is placed around the porous hollow fibers at the end of the bundle of porous hollow fibers and housed in a housing, the sealing material and the end of the housing in which the bundle of porous hollow fibers is placed are heated to melt the sealing material and cause the heated portion of the porous hollow fibers to shrink by 10% or more, A step of solidifying the molten sealing material and A method for manufacturing a hollow fiber separation device, including the method described above.

4. The manufacturing method according to claim 3, wherein the heating temperature in the heating step is equal to or greater than the melting point of the sealing material.

5. The manufacturing method according to claim 3 or 4, further comprising the step of coating the surface of the porous hollow fiber body with a non-porous layer before the heating step.

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