JP2013000619A - Method for producing porous hollow fiber membrane - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a porous hollow fiber membrane, by which a film production stock solution ejected from a spinning nozzle is prevented from attaching onto the outside of a reinforcement support in a lump shape and a porous hollow fiber membrane of high quality can be produced with excellent process stability when the porous hollow fiber membrane in which a porous membrane layer is formed outside the hollow reinforcement support.SOLUTION: The method for producing the porous hollow fiber membrane has a spinning coagulation process for imparting the film production stock solution outside the reinforcement support and then coagulating the film production stock solution by coagulation liquid. When spinning starts, a set value Wa of supply amount of the film production stock solution supplied to stock solution channels 15, 16 from the spinning nozzle 1 is made larger than a set value Wb in a stationary state and then supply amount of the film production stock solution is used as the set value Wb.

Description

  The present invention relates to a method for producing a porous hollow fiber membrane.

  Due to increasing interest in environmental pollution and stricter regulations, water treatment using filtration membranes with excellent separability and compactness has attracted attention. As a filtration membrane in water treatment, a hollow fiber membrane having a hollow porous membrane layer is suitably used (for example, Patent Document 1). For the production of such a hollow fiber membrane, for example, a spinning nozzle 101 illustrated in FIGS. 12 to 14 is used.

The spinning nozzle 101 has a first nozzle 111 and a second nozzle 112. In addition, the spinning nozzle 101 has a support passage 113 through which a hollow reinforcing support (hereinafter sometimes simply referred to as “reinforcing support”) passes, and film formation for forming a porous membrane layer. And a stock channel 114 for circulating the stock solution. The stock solution flow path 114 includes an introduction unit 115 into which a film-forming stock solution is introduced, a liquid storage unit 116 that stores the film-forming stock solution in an annular cross-section, and a shaping unit 117 that shapes the film-forming stock solution in a cylindrical shape. have. In the spinning nozzle 101, a hollow reinforcing support body is supplied from the support body supply port 113a and led out from the support body outlet port 113b, and a film-forming stock solution is supplied from the stock solution supply port 114a and the reinforcing support body from the discharge port 114b. It is designed to be discharged in a cylindrical shape.
In the spinning of the porous hollow fiber membrane by the spinning nozzle 101, the raw film forming solution discharged from the discharge port 114b of the spinning nozzle 101 is applied to the outside of the hollow reinforcing support body that is simultaneously led out from the support body outlet port 113b. . Thereafter, the membrane-forming stock solution is coagulated in a coagulation bath to form a porous membrane layer, and a porous hollow fiber membrane is produced through steps such as washing and drying.

JP 2009-50766 A

  However, in the production of the porous hollow fiber membrane using the spinning nozzle 101, the membrane forming stock solution discharged from the spinning nozzle is applied in the form of a hump on the outside of the reinforcing support, thereby reducing the process stability and quality. May cause a drop.

  When producing a porous hollow fiber membrane in which a porous membrane layer is formed on the outer side of a hollow reinforcing support, the present invention provides a membrane-forming stock solution discharged from a spinning nozzle on the outer side of the reinforcing support. It is an object of the present invention to provide a method for producing a porous hollow fiber membrane that can suppress the impartation of the porous hollow fiber membrane and can produce a high-quality porous hollow fiber membrane with excellent process stability.

The method for producing a porous hollow fiber membrane of the present invention is a method for producing a porous hollow fiber membrane in which a porous membrane layer is formed on the outside of a hollow reinforcing support,
A spinning coagulation step in which a film-forming stock solution for forming the porous membrane layer is applied to the outside of the reinforcing support by spinning with a spinning nozzle, and the film-forming stock solution is coagulated with a coagulating liquid;
After starting the spinning with the set value Wa of the supply amount of the film-forming stock solution supplied to the spinning nozzle at the start of spinning being larger than the set value Wb in the steady state, the supply amount of the film-forming stock solution is set to the set value. This is a method of making Wb.
In the method for producing a porous hollow fiber membrane of the present invention, the ratio Wa / Wb between the set value Wa and the set value Wb is preferably 1.2 to 3.0.

  According to the method for producing a porous hollow fiber membrane of the present invention, when producing a porous hollow fiber membrane in which a porous membrane layer is formed on the outside of a hollow reinforcing support, a product discharged from a spinning nozzle is produced. It is possible to suppress the membrane stock solution from being applied to the outside of the reinforcing support in the form of a bump, and it is possible to produce a high-quality porous hollow fiber membrane with excellent process stability.

It is the top view which showed an example of the spinning nozzle. It is sectional drawing when the spinning nozzle of FIG. 1 is cut | disconnected by the straight line I-I '. It is sectional drawing when the spinning nozzle of FIG. 2 is cut | disconnected by the straight line II-II '. It is sectional drawing explaining the malfunction at the initial stage of spinning. It is sectional drawing which showed the other example of the spinning nozzle. It is sectional drawing which showed the other example of the spinning nozzle. It is sectional drawing which showed the other example of the spinning nozzle. It is the schematic block diagram which showed an example of the support body manufacturing apparatus. It is the figure which showed the structure of the hollow knitted string. It is the enlarged view which showed the mesh of the hollow knitted string. It is the schematic block diagram which showed an example of the porous hollow fiber membrane manufacturing apparatus. It is the top view which showed an example of the spinning nozzle. It is sectional drawing when the spinning nozzle of FIG. 12 is cut | disconnected by the straight line III-III '. It is sectional drawing when the spinning nozzle of FIG. 13 is cut | disconnected by straight line IV-IV '.

The method for producing a porous hollow fiber membrane of the present invention is a method for producing a porous hollow fiber membrane in which a porous membrane layer is formed on the outside of a hollow reinforcing support using a spinning nozzle described later. .
The porous hollow fiber membrane produced by the method for producing a porous hollow fiber membrane of the present invention may be a porous hollow fiber membrane in which a single porous membrane layer is formed on the outside of a reinforcing support. It may be a porous hollow fiber membrane in which a plurality of porous membrane layers are laminated outside the support.

  Examples of the reinforcing support include hollow knitted cords and braids made of various fibers. Moreover, what used various raw materials independently may be used, and what combined may be sufficient. Examples of the fiber used for the hollow knitted string and braided string include synthetic fiber, semi-synthetic fiber, regenerated fiber, and natural fiber. The form of the fiber may be any of monofilament, multifilament, and spun yarn.

A membrane-forming stock solution is used to form the porous membrane layer. The film-forming stock solution is a solution in which a film-forming resin and a pore-opening agent for the purpose of controlling phase separation are dissolved in an organic solvent serving as a good solvent for both.
As the film-forming resin, ordinary resins used for forming porous hollow fiber membranes can be used. For example, polysulfone resin, polyethersulfone resin, sulfonated polysulfone resin, polyvinylidene fluoride resin, polyacrylonitrile resin, polyimide Resin, polyamide imide resin, polyester imide resin, etc. are mentioned. These can be appropriately selected and used as necessary, and among them, polyvinylidene fluoride resin is preferable because of excellent chemical resistance.
As the pore-opening agent, for example, a hydrophilic polymer resin such as monool-based, diol-based, triol-based, or polyvinylpyrrolidone represented by polyethylene glycol can be used. These can be appropriately selected and used as necessary. Among them, polyvinylpyrrolidone is preferable because of its excellent thickening effect.
The organic solvent is not particularly limited as long as it can dissolve both the film-forming resin and the pore-opening agent, and for example, dimethyl sulfoxide, dimethylacetamide, dimethylformamide and the like can be used.
It should be noted that other additives other than the pore-opening agent can be used as an optional component in the film-forming stock solution used here as long as the control of phase separation is not hindered.

Hereinafter, an example of a spinning nozzle used in the method for producing a porous hollow fiber membrane of the present invention will be described.
1 to 3 are schematic views showing a spinning nozzle 1 which is an example of a spinning nozzle used in the method for producing a porous hollow fiber membrane of the present invention. The spinning nozzle 1 is a spinning nozzle for producing a porous hollow fiber membrane in which two porous membrane layers are laminated on the outside of a hollow reinforcing support.
Hereinafter, the inner porous membrane layer in the porous hollow fiber membrane manufactured using the spinning nozzle 1 is referred to as a first porous membrane layer, and the outer porous membrane layer is referred to as a second porous membrane layer. Further, the film-forming stock solution for forming the first porous membrane layer is referred to as a first film-forming stock solution, and the film-forming stock solution for forming the second porous membrane layer is referred to as a second film-forming stock solution.

The spinning nozzle 1 has a first nozzle 11, a second nozzle 12, and a third nozzle 13 as shown in FIGS. In the spinning nozzle 1, as shown in FIG. 2, a support passage 14 through which a hollow reinforcing support is passed, a stock flow path 15 through which the first film-forming stock solution is circulated, and a second film-formation A stock solution flow path 16 through which the stock solution is circulated is formed.
As shown in FIG. 2 and FIG. 3, the stock solution flow path 15 includes an introduction portion 17 into which the first film-forming stock solution is introduced into the first nozzle 11 and the second nozzle 12, and a support passage 14. A first liquid storage unit 18 for storing the first film-forming stock solution in an annular cross-section at the outer periphery of the first and a first film-forming solution cylindrically shaped at the outer periphery of the support passage 14 And a shaping portion 19. The stock solution flow path 16 includes an introduction portion 20 into which the second film-forming stock solution is introduced, and a second storage solution that stores the second film-forming stock solution in a circular cross-section on the outer periphery of the support passage 14. Part 21 and a second shaping part 22 for shaping the second film-forming stock solution in a cylindrical shape on the outer periphery of the support passage 14. Further, in this example, a composite portion 23 is formed by the second shaping portion 22 and the first shaping portion 19. That is, the second film-forming stock solution is shaped into a cylindrical shape by the second shaping unit 22 and at the same time, the second film-forming stock solution has been circulated through the first shaping unit 19. It is designed to be laminated and compounded outside the stock solution. The center axis | shaft of the support body channel | path 14, the 1st liquid storage part 18, the 1st shaping part 19, the 2nd liquid storage part 21, the 2nd shaping part 22, and the composite part 23 each corresponds. .
Further, in the spinning nozzle 1, the first film-forming stock solution and the second film-forming stock solution respectively pass from the side into the inside of the first liquid storage unit 18 and the inside of the second liquid storage unit 21. Porous elements 31, 32 are provided.

  As the material of the first nozzle 11, the second nozzle 12 and the third nozzle 13, those normally used as spinning nozzles for porous hollow fiber membranes can be used. From the viewpoint of heat resistance, corrosion resistance, strength, etc. Stainless steel (SUS) is preferred.

The cross-sectional shape of the support passage 14 is circular.
What is necessary is just to set the internal diameter of the support body channel | path 14 suitably according to the outer diameter of the hollow-shaped reinforcement support body to be used.
The cross-sectional shape of the introduction part 17 of the stock solution channel 15 and the introduction part 20 of the stock solution channel 16 is preferably circular as in this example. However, the cross-sectional shape of the introduction part 17 and the introduction part 20 is not limited to a circular shape.
The diameters of the introduction part 17 and the introduction part 20 are not particularly limited.

The first liquid storage unit 18 is a part that stores the first film-forming stock solution that has circulated through the introduction unit 17 in an annular cross-section.
The cross-sectional shape of the first liquid storage unit 18 is annular as shown in FIG. 3, and the center of the first liquid storage unit 18 and the center of the support passage 14 are coincident. In the first liquid storage unit 18, the first film-forming stock solution is bifurcated from the introduction unit 17 side and circulates in an arc shape, and merges at the junction 18 a on the side opposite to the introduction unit 17. Yes.
Further, as shown in FIG. 2, a slit portion 18 b may be provided in the vicinity of the first shaping portion 19 in the first liquid storage portion 18. In particular, when the first film-forming solution only passes from the outer peripheral surface of the porous element 31 described later toward the inner peripheral surface, the discharge uniformity in the circumferential direction does not reach a desired level, the flow resistance is reduced by the slit portion 18b. The imparting is preferable from the viewpoint of improving the uniformity of ejection in the circumferential direction.

The first shaping part 19 is a part for shaping the first film-forming stock solution in the first liquid storage part 18 into a cylindrical shape concentric with the reinforcing support that allows the support passage 14 to pass therethrough.
The width (distance between the inner wall and the outer wall) of the first shaping portion 19 can be appropriately set according to the thickness of the first porous membrane layer to be formed.

The second liquid storage unit 21 is a part that stores the second film-forming stock solution that has circulated through the introduction unit 20 in an annular cross-section.
The cross-sectional shape of the second liquid storage unit 21 is an annular shape like the first liquid storage unit 18, and the center of the second liquid storage unit 21 and the center of the support passage 14 are aligned. In the second liquid storage part 21, the second film-forming stock solution is bifurcated from the introduction part 20 side and circulates in an arc shape, and joins at the joining part 21 a opposite to the introduction part 20. ing.
Further, as shown in FIG. 2, a slit portion 21 b may be provided in the vicinity of the second shaping portion 22 in the second liquid storage portion 21. In particular, when the second film-forming solution only passes from the outer surface to the inner surface of the porous element 32, which will be described later, when the circumferential discharge uniformity does not reach a desired level, the slit portion 21b provides flow resistance. It is preferable to improve the uniformity of discharge in the circumferential direction.

The second shaping portion 22 is a portion that shapes the second film-forming stock solution in the second liquid storage portion 21 into a cylindrical shape concentric with the reinforcing support that allows the support passage 14 to pass therethrough. In this example, a composite portion 23 is formed by the first shaping portion 19 and the second shaping portion 22. That is, the second film-forming stock solution that is shaped cylindrically in the second shaping part 22 is simultaneously concentrically laminated on the outside of the first film-forming stock solution that has circulated through the first shaping part 19. It has come to be combined. In the composite part 23, each film-forming stock solution is laminated and combined inside the nozzle, so that the bonding strength of each formed porous membrane layer is improved as compared with the case where they are laminated and combined outside the nozzle. Moreover, it is advantageous also in terms of simplification of the nozzle structure and simplification of processing. Further, even if the respective film-forming stock solutions are laminated and combined in the composite part 23, there is almost no adverse effect on the structure of each porous film layer due to solvent mutual diffusion in these solutions.
The width (distance between the inner wall and the outer wall) of the composite portion 23 can be set as appropriate according to the thickness of the second porous film layer to be formed.

  In the spinning nozzle 1, porous elements 31 and 32 through which the raw film forming solution passes from the side surfaces are provided inside the first liquid storage unit 18 and the second liquid storage unit 21, respectively. The porous elements 31 and 32 in this example are cylindrical, and in the first liquid storage part 18 and the second liquid storage part 21, the film-forming stock solution moves from the outer peripheral surface of the porous elements 31 and 32 toward the inner peripheral surface. Pass through.

  As the porous elements 31, 32, one having micropores through which the film-forming stock solution passes from the outer peripheral surface toward the inner peripheral surface can be used. For example, a filter for filtering the film-forming stock solution is used. Among these, a sintered body of metal fine particles is preferable from the viewpoint of strength, thermal conductivity, chemical resistance, and structural uniformity. However, the porous elements 31 and 32 are not limited to metal fine particle sintered bodies, but are sintered metal fibers, metal mesh laminates and sintered laminates, ceramic porous bodies, porous plate laminates and sintered bodies. It may be a laminate or a filler of metal fine particles.

In the spinning nozzle 1, the provision of the porous elements 31 and 32 suppresses the formation of crack initiation points along the axial direction in the porous film layer formed by the film-forming stock solution. The reason why the effect is obtained by the porous elements 31 and 32 is not clear, but is considered as follows.
In the case where the porous element is not provided as in the spinning nozzle 101 illustrated in FIGS. 12 to 14, when the spinning speed is increased, a crack starting point along the axial direction is formed in the porous membrane layer, and the porous hollow fiber membrane is formed. Cracks may occur when deformed into a flat shape. The starting point of the crack is formed at a position corresponding to the merged portion 116a (FIG. 14) where the two separate film-forming stock solutions are merged inside the liquid storage unit 116. In this merging portion 116a, the entanglement between the film-forming resins tends to be smaller than in portions other than the merging portion 116a, and this becomes a stress concentration point when a load such as a flattening occurs, and the origin of cracks along the axial direction It is thought that this is a factor that forms.
On the other hand, the spinning nozzle 1 is provided with the porous element 31 in the first liquid storage section 18, so that the first porous film layer formed by the first film-forming stock solution extends along the axial direction. The formation of a crack starting point is suppressed. This is because when the first film-forming stock solution passes through the porous element 31 from the outer peripheral surface toward the inner peripheral surface, the first film-forming stock solution is totally microscopically stirred, and the first film-forming stock solution This is considered to be because the entanglement between the film-forming resins is uniformized and the stress is dispersed. For the same reason, the porous element 32 is provided in the second liquid storage part 21, so that the second porous film layer formed by the second film-forming stock solution is aligned along the axial direction. It is suppressed that the starting point of a crack is formed.

The porous elements 31 and 32 are preferably porous bodies having a three-dimensional network structure from the viewpoint of easily obtaining a porous hollow fiber membrane in which cracking is unlikely to occur. A porous body having a three-dimensional network structure means that the film-forming stock solution does not flow linearly when passing through the inside of the porous element from the outer peripheral surface toward the inner peripheral surface, but also moves in the vertical and circumferential directions. However, it is a porous body having a structure in which a three-dimensional channel that passes inward is formed. By using a porous body having a three-dimensional network structure as the porous elements 31 and 32, the film-forming stock solution is easily made uniform by repeating fine branching and joining as a whole, and even when the spinning speed is increased, it is porous. It is considered that the starting point of the crack along the axial direction is hardly formed in the membrane layer. Moreover, a porous element having the same pore diameter and the same thickness is advantageous in that the pressure loss is reduced. Furthermore, it is preferable also in terms of removing foreign matters in the film-forming stock solution and gel fragmentation.
Examples of the porous element having a three-dimensional network structure include a porous element having a fiber winding structure and a porous element having a structure in which resin or metal fine particles are sintered and integrated.

  The shape of the porous elements 31 and 32 is not particularly limited as long as the raw film forming solution flows from the outer peripheral surface toward the inner peripheral surface, and an annular shape is preferable. In particular, the shape of the porous elements 31 and 32 is preferably cylindrical as in this example from the viewpoint of easily increasing the area through which the film-forming stock solution passes and easy to increase the spinning speed.

  Further, the porous elements 31 and 32 are preferably seamless elements such as a flat candle-shaped element wound in a cylindrical shape and welded at the joint as in a general candle filter. By using a porous element that does not have such a seam, it becomes easy to make the passage characteristics of the film-forming stock solution uniform. As a structure of such a seamless porous element, for example, a cylindrical fiber winding structure, a metal tube etching processing structure, a metal tube laser hole processing structure, a three-dimensional honeycomb structure, and a plurality of outer peripheral and inner peripheral communication Examples include a structure in which a plurality of donut-shaped discs having minute holes are stacked and integrated concentrically, and a structure in which resin or metal fine particles are sintered and integrated in a cylindrical shape.

The pressure loss when the first film-forming stock solution passes through the porous element 31 is the pressure loss until the first film-forming stock solution reaches the porous element 31, and the first film-forming stock solution passes through the porous element 31. It is preferable that the pressure pressure loss after reaching the discharge port 23a is larger. Thereby, the flow of the 1st film forming undiluted solution at the time of passing through porous element 31 becomes easy to make uniform in the peripheral direction, and the thickness of the 1st porous film layer formed becomes easy. Similarly, the pressure loss when the second film-forming stock solution passes through the porous element 32 is the pressure loss until the second film-forming stock solution reaches the porous element 32, and the second film-forming stock solution is the porous element. It is preferable that the pressure loss is larger than the pressure loss until the discharge port 23a is reached after passing through the nozzle 32.
The pressure loss when the film-forming stock solution passes through the porous elements 31 and 32 can be adjusted by adjusting the structure and pore diameter of the porous elements 31 and 32.

  In spinning by the spinning nozzle 1, a hollow reinforcing support is supplied to the support passage 14 from the support supply port 14a, and the first film-forming stock solution and the second film-forming solution are supplied by each stock-solution supply device that quantitatively supplies the film-forming stock solution. The film-forming stock solution is supplied from the stock solution supply ports 15a and 16a to the stock solution channels 15 and 16, respectively. The first film-forming stock solution flows into the first liquid storage part 18 from the introduction part 17, and in the first liquid storage part 18, the outside of the porous element 31 is bifurcated and circulated in an arc shape. It merges at the opposite merging portion 18a, passes through the porous element 31 from the outer peripheral surface toward the inner peripheral surface, flows into the first shaping portion 19 and is shaped into a cylindrical shape. The second film-forming stock solution flows from the introduction part 20 into the second liquid storage part 21, and in the second liquid storage part 21, the outside of the porous element 32 is bifurcated and flows in an arc shape. It merges at the opposite merging portion 21a, passes through the porous element 32 from the outer peripheral surface toward the inner peripheral surface, flows into the second shaping portion 22, and is shaped into a cylindrical shape. Moreover, in this example, since the composite part 23 is formed by the 1st shaping part 19 and the 2nd shaping part 22, the 1st shaping | molding liquid solution is shape | molded by the 1st while forming the 2nd film forming undiluted | stock solution. The first film-forming stock solution that has circulated through the shaping portion 19 is concentrically laminated and composited. Then, the first film-forming stock solution and the second film-forming stock solution are discharged from the discharge port 23a in a state where they are laminated and combined concentrically, and are simultaneously applied to the outside of the reinforcing support that has been led out from the support-outlet outlet 14b. Is done.

Next, as an example of the method for producing a porous hollow fiber membrane of the present invention, a method for producing a porous hollow fiber membrane using the spinning nozzle 1 will be described. Examples of the production method include a method having the following spinning and coagulating step, washing step, removing step, drying step and winding step.
Spinning coagulation step: a step of forming a porous hollow fiber membrane precursor by applying a membrane-forming stock solution to the outside of the hollow reinforcing support by the spinning nozzle 1 and coagulating the membrane-forming stock solution in the coagulating solution.
Washing step: a step of washing the porous hollow fiber membrane precursor after the spinning and coagulating step to remove the solvent remaining in the porous hollow fiber membrane precursor.
Removal step: a step of removing the pore-opening agent remaining in the porous hollow fiber membrane precursor after the washing step to form a porous hollow fiber membrane.
Drying step: a step of drying the porous hollow fiber membrane after the removing step.
Winding step: A step of winding the porous hollow fiber membrane after drying.

Spinning and coagulation process:
Each stock solution supply device supplies the first film forming stock solution and the second film forming stock solution to the stock solution flow paths 15 and 16 of the spinning nozzle 1, and supplies the reinforcing support to the support passage 14 of the spinning nozzle 1. The first film-forming stock solution and the second film-forming stock solution are laminated and combined to be discharged in a cylindrical shape, and are applied to the outside of the reinforcing support that has passed through the support passage 14, so that these film-forming stock solutions are coagulated. To form a porous hollow fiber membrane precursor. At this time, the coagulating liquid diffuses into the film-forming stock solution applied to the outside of the reinforcing support, and the film-forming resin and the pore-opening agent coagulate while causing phase separation, respectively. Forms a solidified film layer having a three-dimensional network structure. By removing the pore-opening agent of the solidified membrane layer in a removing step described later, pores are formed in the portion where the pore-opening agent remains, and a porous membrane layer is formed.

In the production method of the present embodiment, in the spinning coagulation step, the supply amount of the film-forming stock solution supplied to the spinning nozzle 1 at the start of spinning (the supply amount of the first film-forming stock solution and the second film-forming stock solution) is set. Spinning with the value Wa larger than the set value Wb of the supply amount of the film-forming stock solution supplied to the spinning nozzle 1 in the steady state (the total supply amount of the first film-forming stock solution and the second film-forming stock solution) After starting, the supply amount of the film-forming stock solution is set to the set value Wb.
In the present invention, the “steady state” means a porous hollow fiber membrane in which the membrane-forming stock solution is continuously applied with a uniform thickness to the outside of the reinforcing support that passes through the support passage of the spinning nozzle, and the outer diameter is uniform. The state where the precursor is obtained continuously is said. That is, the set value Wb is a value obtained by setting the supply amount of the film-forming stock solution to the spinning nozzle so that the running speed of the reinforcing support in the steady state and the discharge linear speed of the film-forming stock solution are the same. . The set value Wb can be determined by testing in advance.

As a result of examining the spinning by the spinning nozzle, the supply amount of the film-forming stock solution supplied to the spinning nozzle is set to a set value Wb that corresponds to the discharge linear speed of the film-forming stock solution and the running speed of the reinforcing support in a steady state. It has been found that when spinning is started, the application of the film-forming stock solution to the outside of the reinforcing support may become uneven in the initial stage of spinning. Specifically, at the initial stage of spinning, the discharge linear speed of the raw film forming solution becomes slower than the running speed of the reinforcing support, so that the film is discharged from the discharge port 23a of the spinning nozzle 1 as shown in FIG. It was found that the stock solution Y was pulled and divided by the reinforcing support X, and the film-forming stock solution Y was intermittently applied to the reinforcing support X to form a plurality of bump-shaped portions Z. In addition, when a porous element is provided in the liquid storage part like the spinning nozzle 1, the discharge linear velocity of the raw film forming solution at the start of spinning tends to be slower due to the resistance of the porous element, and a hump-like portion Z is further formed. I found it easy to do. Such a hump-shaped portion Z can cause a film to become unguided or a yarn in a later step.
In the present invention, the spinning is started by setting the set value Wa of the film-forming stock solution supplied to the spinning nozzle at the start of spinning to be larger than the set value Wb of the film-forming stock solution in the steady state. Compared to the case where spinning is started with the supply amount of the membrane stock solution set value Wb, the discharge linear velocity of the membrane forming stock solution in the initial stage of spinning becomes closer to the traveling speed of the reinforcing support. Therefore, it can suppress that the film forming stock solution discharged from a nozzle is pulled and divided | segmented by the reinforcement support body, and can reduce the frequency with which the film formation stock solution is provided in the shape of a hump on the outer side of a reinforcement support body as a result. Therefore, a high-quality porous hollow fiber membrane can be manufactured with higher process stability.

  Specifically, in the stock solution supply device that supplies the first film-forming stock solution to the stock solution flow path 15 and the stock solution supply device that supplies the second film-forming stock solution to the stock solution flow path 16, The set value Wa of the supply amount of the first film-forming stock solution and the second film-forming stock solution to the spinning nozzle 1 is set to be larger than the set value Wb in the steady state, and spinning is started. Continue spinning with Wb.

  The set value Wa of the supply amount of the film-forming stock solution to the spinning nozzle 1 at the start of spinning (the total amount of the first film-forming stock solution and the second film-forming stock solution), and the film-forming stock solution to the spinning nozzle 1 in the steady state The ratio Wa / Wb of the set value Wb of the supply amount (total amount of the first film-forming stock solution and the second film-forming stock solution) is preferably 1.2 to 3.0, and more preferably 1.5 to 2.5. More preferred. If the ratio Wa / Wb is equal to or higher than the lower limit value, the frequency at which the film-forming stock solution is applied in the form of a bump on the outside of the reinforcing support can be further reduced. If the ratio Wa / Wb is less than or equal to the upper limit value, the amount of the stock solution to be used is hardly excessive, and the film thickness becomes excessively thick and it is easy to suppress waste of raw materials. This is industrially advantageous.

After the start of spinning, after the thickness of the film-forming stock solution applied to the outside of the reinforcing support becomes constant, the set value of the amount of film-forming stock solution supplied to the spinning nozzle 1 is set to the set value Wb. That is, after the discharge linear velocity of the film forming raw solution becomes constant, the set value of the supply amount of the film forming raw solution supplied to the spinning nozzle 1 is set to the set value Wb.
The criteria for determining that the thickness of the membrane-forming stock solution applied to the outside of the reinforcing support has become constant varies depending on the spinning speed and the like. For example, the formation of a porous hollow fiber membrane precursor with a uniform outer diameter is 20 m. For example, there may be a standard in which the time point when the film is continuously formed becomes the time point when the thickness of the film forming stock solution becomes constant. The determination may be made by measuring the outer diameter of the porous hollow fiber membrane precursor or by measuring the discharge linear velocity of the membrane forming stock solution.
Here, in order to clarify the positional relationship between the porous membrane layer (coagulated membrane layer) and the reinforcing support, it is expressed as the outside of the reinforcing support, but the porous membrane layer (coagulated membrane layer) is reinforced. The case where it is immersed in the inside of the support through the gap of the support is also included. In this case as well, the determination criterion that the thickness of the film forming stock solution is constant is determined by the uniformity of the outer diameter.

The supply amount of the film-forming stock solution supplied to the spinning nozzle 1 is a set value Wb when it is determined that the thickness of the film-forming stock solution applied to the outside of the reinforcing support has become constant from the viewpoint of improving process stability. It is preferable to make it.
The timing at which the set value of the amount of the membrane-forming stock solution supplied to the spinning nozzle 1 is set to the set value Wb may be determined by testing in advance, and the outer diameter or the manufacturing of the porous hollow fiber membrane may be determined during the process. It may be determined by performing spinning while measuring the discharge linear velocity of the membrane stock solution.

Further, in the spinning coagulation step, the spinning speed Va of the reinforcing support that passes through the support passage 14 of the spinning nozzle 1 at the start of spinning is set slower than the running speed Vb in the steady state, and then spinning is started. It is preferable to set the traveling speed of the body to the traveling speed Vb in the steady state. Thereby, it can further reduce that the membrane forming undiluted solution is applied to the outside of the reinforcing support in the form of a bump.
The ratio Va / Vb between the running speed Va of the reinforcing support at the start of spinning and the running speed Vb of the reinforcing support in the steady state is preferably 0.3 to 0.8, more preferably 0.4 to 0.6. preferable. If the ratio Va / Vb is equal to or greater than the lower limit value, the frequency at which the film-forming stock solution is applied to the outer side of the reinforcing support can be further reduced. If the ratio Va / Vb is equal to or less than the upper limit value, it is easy to reduce the occurrence of so-called smears in which the film-forming solution is not uniformly applied to the outside of the reinforcing support.

Cleaning process:
In the porous hollow fiber membrane precursor formed in the spinning and coagulation step, a solution-like pore opening agent or solvent remains. As a method for washing the porous hollow fiber membrane precursor, a method usually used as a method for removing the solvent remaining in the porous hollow fiber membrane precursor can be adopted. For example, there is a method of removing the solvent remaining in the porous hollow fiber membrane precursor by running the porous hollow fiber membrane precursor in a cleaning liquid such as water and washing it.

Removal process:
As a method for removing the pore opening agent, a method usually used as a method for removing the pore opening agent remaining in the porous hollow fiber membrane precursor can be adopted. For example, a porous hollow fiber membrane is run in a chemical solution containing an oxidizing agent such as hypochlorite, and the porous hollow fiber membrane is held in the chemical solution, and then heated in a gas phase to form a pore-opening agent. Examples include a method of removing the pore-opening agent reduced in molecular weight by performing oxidative decomposition and then washing the porous hollow fiber membrane.
By removing the pore-opening agent remaining in the coagulation membrane layer of the porous hollow fiber membrane precursor, pores are formed in the portion where the pore-opening agent has remained to form a porous membrane layer. A yarn membrane is obtained.

Drying and winding processes:
As a method for drying the porous hollow fiber membrane, a method usually used for drying the porous hollow fiber membrane can be adopted. For example, the method of drying a porous hollow fiber membrane using dryers, such as a hot air dryer, is mentioned.
The porous hollow fiber membrane after drying is wound up by a winding means such as a bobbin.

  According to the method for producing a porous hollow fiber membrane of the present invention described above, the set value Wa of the amount of the raw film forming solution supplied to the spinning nozzle at the start of spinning is set to be larger than the set value Wb in the steady state to perform spinning. By starting the process, it is possible to reduce the film-forming stock solution being applied to the outer side of the reinforcing support at the initial stage of spinning. Therefore, a high-quality porous hollow fiber membrane can be produced with excellent process stability. In addition, if a spinning nozzle having a porous element in the liquid storage part is used, the film-forming stock solution is reduced from being applied to the outer side of the reinforcing support in the form of a hump, and the porous film layer to be formed is further axially The formation of the starting point of the crack along the line can also be suppressed, and a higher quality porous hollow fiber membrane can be produced with excellent process stability.

In addition, the manufacturing method of the porous hollow fiber membrane of this invention is not limited to the manufacturing method mentioned above. For example, the method for producing a porous hollow fiber membrane of the present invention may be a method of forming a single porous membrane layer outside the reinforcing support.
The method for producing a porous hollow fiber membrane of the present invention uses a spinning nozzle such as the spinning nozzle 1 to set the supply value Wa of the membrane-forming stock solution supplied to the spinning nozzle at the start of spinning. After the spinning is started with a value larger than the set value Wb in the above, any process may be used as long as it has a spinning coagulation step in which the supply amount of the film-forming stock solution is set to the set value Wb, and the other steps are not particularly limited.

The method for producing the porous hollow fiber membrane of the present invention is not limited to the method using the spinning nozzle 1. Each film-forming stock solution that does not have a composite part inside the nozzle and forms a plurality of porous film layers is separately ejected into a cylindrical shape, laminated and combined outside the nozzle, and applied to the outside of the reinforcing support Alternatively, a method using a spinning nozzle may be used. Specifically, a method using the spinning nozzle 2 illustrated in FIG. 5 may be used. In the spinning nozzle 2, the same parts as those of the spinning nozzle 1 are denoted by the same reference numerals and description thereof is omitted.
The spinning nozzle 2 includes a first nozzle 11, a second nozzle 12 </ b> A, and a third nozzle 13 </ b> A. The first film-forming stock solution flowing from the first liquid storage unit 18 is used as the support passage 14. A first shaping part 19A shaped into a concentric cylindrical shape and a second film-forming stock solution flowing in from the second liquid storage part 21 are shaped into a concentric cylindrical shape with the support passage 14. It has two shaping portions 22A. The first film-forming stock solution is supplied from the stock solution supply port 15a to the stock solution flow path 15, and after being shaped by the first shaping unit 19A, is discharged from the discharge port 15b. The second film-forming stock solution is supplied to the stock solution channel 16 from the stock solution supply port 16a, and after being shaped by the second shaping unit 22A, is discharged from the discharge port 16b. The first film-forming stock solution and the second film-forming stock solution discharged from the discharge ports 15b and 16b, respectively, are laminated and combined outside the nozzle, and are applied to the outside of the reinforcing support derived from the support outlet 14b. .

The spinning nozzle 1 has porous elements 31 and 32 through which the film-forming stock solution passes from the outer peripheral surface toward the inner peripheral surface. However, the porous element in the spinning nozzle used in the manufacturing method of the present invention is a film-forming device. It is sufficient if the stock solution passes from the side. For example, a method using the spinning nozzle 3 illustrated in FIG. 6 may be used. The spinning nozzle 3 is a nozzle for spinning a porous hollow fiber membrane having a single porous membrane layer.
The spinning nozzle 3 has a first nozzle 41 and a second nozzle 42, and circulates a support passage 43 through which a hollow reinforcing support passes and a film-forming stock solution for forming a porous membrane layer. A stock solution channel 44 is provided. The stock solution flow path 44 supports an introduction part 45 for introducing the film-forming stock solution, a liquid storage part 46 for storing the film-forming stock solution in a circular cross section, and a film-forming stock solution flowing from the liquid storage part 46. It has a reinforcing support that passes through the body passage 43 and a shaping portion 47 that is shaped into a concentric cylindrical shape. In addition, a porous element 51 through which the film-forming stock solution passes from the inner peripheral surface toward the outer peripheral surface is provided inside the liquid storage unit 46. As the porous element 51, the same elements as those mentioned for the porous elements 31 and 32 can be used.
The film-forming stock solution in spinning by the spinning nozzle 3 is supplied from the stock solution supply port 44a to the stock solution flow path 44, is supplied to the inside of the porous element 51 in the liquid storage section 46, is bifurcated, and circulates in an arc shape. Merge on the other side. Then, the raw film forming solution passes through the porous element 51 from the inner peripheral surface toward the outer peripheral surface, is shaped into a cylindrical shape by the shaping portion 47 and is discharged from the discharge port 44b, and simultaneously from the support outlet port 43a. It is applied to the outside of the reinforcing support that has been derived. As described above, even when the porous element 51 through which the membrane-forming stock solution passes from the inner peripheral surface toward the outer peripheral surface is provided, a crack starting point is generated in the porous membrane layer of the obtained porous hollow fiber membrane. Can be suppressed.

Further, the method for producing the porous hollow fiber membrane of the present invention may be a method using the spinning nozzle 4 illustrated in FIG. The spinning nozzle 4 is a nozzle for spinning a porous hollow fiber membrane having a single porous membrane layer.
As shown in FIG. 7, the spinning nozzle 4 has a first nozzle 81 and a second nozzle 82, a support passage 83 through which a hollow support passes, and a porous membrane layer. And a stock solution channel 84 through which the film-forming stock solution for forming the liquid is circulated. The stock solution flow path 84 includes an introduction part 85 into which the film-forming stock solution is introduced, a liquid storage part 86 that stores the film-forming stock solution in an annular cross section, and a shaping part 87 that shapes the film-forming stock solution into a cylindrical shape. And have. Inside the liquid reservoir 86, a packed bed 89 filled with particles 88 is provided. By using the spinning nozzle 4, it is easy to suppress the formation of crack starting points along the axial direction in the porous membrane layer of the porous hollow fiber membrane to be obtained. This is because the film-forming stock solution passing through the gaps of the particles 88 in the packed bed 89 repeats three-dimensional fine branching and merging, so that the entanglement of the film-forming resin in the film-forming stock solution is reduced overall. This is considered to be because the stress is evenly distributed.

  Further, the method for producing a porous hollow fiber membrane of the present invention may be a method using a spinning nozzle not provided with a porous element. That is, a method using the spinning nozzle 101 may be used.

EXAMPLES Hereinafter, although an Example demonstrates this invention in detail, this invention is not limited by the following description.
[Example 1]
Manufacturing process of reinforced support:
A reinforcing support made of a hollow knitted string was manufactured using the support manufacturing apparatus 60 shown in FIG. The support manufacturing apparatus 60 supplies a string that pulls a bobbin 61, a circular knitting machine 63 that circularly knits the yarn 62 drawn from the bobbin 61, and a hollow knitted string 64 knitted by the circular knitting machine 63 with a constant tension. A device 65, a heating die 66 for heat-treating the hollow knitted string 64, a take-up device 67 for picking up the reinforcing support X obtained by heat-treating the hollow knitted string 64, and a winding for winding the reinforcing support X around the bobbin And a take-off machine 68.
As the raw yarn, polyester fiber (fineness: 84 dtex, number of filaments: 36) was used. As the bobbin 61, five pieces of the polyester fiber wound with 5 kg were prepared. As the circular knitting machine 63, a table type knitting machine (manufactured by Sakurai Textile Machinery Co., Ltd., number of knitted needles: 12, needle size 116 gauge, spindle circumferential diameter: 8 mm) was used. A Nelson roll was used as the string supply device 65 and the take-up device 67. As the heating die 66, a stainless steel die having a heating means (inner diameter D (inlet side): 5 mm, inner diameter d (outlet side): 2.2 mm, length: 300 mm) was used.
The polyester fibers drawn from the bobbin 61 are combined into one yarn 62 (total fineness is 420 dtex), and then circular knitted by a circular knitting machine 63 to form a hollow knitted string 64. The hollow knitted string 64 Was passed through a heating die 66 at 195 ° C., and the heat-treated hollow knitted string 64 was wound around the winding device 68 at a winding speed of 100 m / hr as the reinforcing support X. The production of the reinforcing support X was continued until the polyester fiber of the bobbin 61 was exhausted.
The obtained reinforcing support X had an outer diameter of about 2.1 mm and an inner diameter of 1.3 mm. As shown in FIGS. 9 and 10, the hollow knitted string 64 constituting the reinforcing support X is formed by continuously forming a loop 62a (black portion in FIG. 10) in which a thread 62 is curved in a spiral shape, These loops 62a are connected vertically, and as shown in FIG. 10, a mesh 64a is provided in the loop 62a and at the connecting portion between the loops 62a. The number of loops 62a was 12 per round, and the maximum opening width L of the mesh 64a was about 0.05 mm. The length of the reinforcing support X was 12000 m.

Preparation process of film forming stock solution:
Polyvinylidene fluoride (PVDF) (made by Arkema, trade name Kyner 301F) as a film-forming resin (hydrophobic polymer), and polyvinylpyrrolidone (PVP) (made by Nippon Shokubai, trade name PVP- as a pore opening agent (hydrophilic polymer)) K79) is introduced into N, N-dimethylacetamide (DMAc) and kneaded and dissolved, whereby the first PVDF is 20% by mass, PVP is 10% by mass, and DMAc is 70% by mass. A film-forming stock solution was prepared.
Moreover, PVDF which mixed 1st PVDF (made by Arkema, brand name Kyner 301F) and 2nd PVDF (made by Arkema, brand name Kyner 9000HD) by mass ratio 1.1: 1, and PVP (made by Nippon Shokubai Co., Ltd., The product name PVP-K79) is introduced into DMAc and kneaded and dissolved, whereby a second film-forming stock solution having a mass ratio of 39% by mass of PVDF, 19% by mass of PVP and 42% by mass of DMAc. Was prepared.

Spinning and coagulation process:
Subsequently, the hollow porous membrane M was manufactured using the porous hollow fiber membrane manufacturing apparatus 70 shown in FIG. The porous hollow fiber membrane production apparatus 70 includes a spinning nozzle 1 that continuously applies a film-forming stock solution to a reinforcing support X that is continuously supplied from an unwinding device (not shown), and a film-forming stock solution that is applied to the spinning nozzle 1. A coagulating bath 72 containing a coagulating liquid for coagulating the film-forming stock solution applied to the reinforcing support X, and a reinforcing support X applied with the film-forming stock solution to the coagulating bath 72. And a guide roll 73 that is continuously introduced.
The reinforcing support X is supplied to the support passage 14 of the spinning nozzle 1 maintained at 30 ° C., the first film-forming stock solution is supplied to the stock solution channel 15, and the second film-forming stock solution is supplied to the stock solution channel 16. The first film-forming stock solution was applied to the outer peripheral surface of X, and the second film-forming stock solution was applied to the outside thereof. In this spinning, the running speed Va at the start of spinning of the reinforcing support X was determined to be 1/2 of the running speed Vb of the reinforcing support X in a steady state (that is, Va / Vb = 0.5). Further, the set value Wa of the supply amount of the film-forming stock solution to the spinning nozzle 1 at the start of spinning (the sum of the supply amounts of the first film-forming stock solution and the second film-forming stock solution) is set to the spinning nozzle 1 in a steady state. Spinning so as to be twice the set value Wb (Wa / Wb = 2.0) of the supply amount of the film-forming stock solution to be supplied (the sum of the supply amounts of the first film-forming stock solution and the second film-forming stock solution) In the initial stage (about 1 minute), adjustment of the set value of the supply amount of the film-forming stock solution was sequentially performed until a steady state was reached.
Next, the reinforcing support X coated with the first film-forming stock solution and the second film-forming stock solution is passed through a coagulation bath 72 containing an 8% by mass DMAc aqueous solution kept at 80 ° C. Was solidified to form a porous hollow fiber membrane precursor M, and the direction was changed by the guide roll 73 and pulled up from the coagulation bath 72.
With respect to the obtained porous hollow fiber membrane precursor, the number of humps formed was measured and found to be 2 per spindle.

[Comparative Example 1]
The set value Wa of the film-forming stock solution supply amount at the start of spinning is set to be the same as the set value Wb of the film-forming stock solution supply amount in a steady state (Wa / Wb = 1.0), and the film-forming stock solution to the spinning nozzle 1 is set. A porous hollow fiber membrane precursor was obtained in the same manner as in Example 1 except that the supply amount was not changed as it was from the beginning of spinning.
With respect to the obtained porous hollow fiber membrane precursor, the number of bump-shaped portions formed was measured and found to be 100 per spindle.

DESCRIPTION OF SYMBOLS 1 Spinning nozzle 11 1st nozzle 12 2nd nozzle 13 3rd nozzle 14 Support body channel | path 15 Stock solution flow path 16 Stock solution flow path 18 1st liquid storage part 19 1st shaping part 21 2nd liquid storage Part 22 Second shaping part 31, 32 Porous element X Reinforcement support Y Film-forming stock solution

Claims (2)

A method for producing a porous hollow fiber membrane in which a porous membrane layer is formed on the outside of a hollow reinforcing support,
A spinning coagulation step in which a film-forming stock solution for forming the porous membrane layer is applied to the outside of the reinforcing support by spinning with a spinning nozzle, and the film-forming stock solution is coagulated with a coagulating liquid;
After starting the spinning with the set value Wa of the supply amount of the film-forming stock solution supplied to the spinning nozzle at the start of spinning being larger than the set value Wb in the steady state, the supply amount of the film-forming stock solution is set to the set value. A method for producing a porous hollow fiber membrane, wherein Wb is used.   The method for producing a porous hollow fiber membrane according to claim 1, wherein a ratio Wa / Wb between the set value Wa and the set value Wb is set to 1.2 to 3.0.

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