JP2014144390A - Method for producing hollow fiber membrane - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a hollow fiber membrane where a streak is difficult to be made on a membrane surface.SOLUTION: A method for producing a hollow fiber membrane comprises: a step to immerse a mold having an inner tube to discharge solidification water from a discharge port and an outer tube to discharge a resin solution from a discharge port into a non-solvent in a solidification chamber; a step to form an air space between the discharge port and the non-solvent in the solidification chamber; and a step to produce the hollow fiber membrane by discharging the resin solution from the discharge port of the outer tube, passing through the air space and being in contact with the non-solvent.

Description

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

  Conventionally, in water purification such as clarification of river water and groundwater, clarification of industrial water, drainage and sewage treatment, pretreatment for seawater desalination, etc., a water treatment device provided with a polymer water treatment membrane has been used. The polymer water treatment membrane used in this water treatment apparatus often uses a hollow fiber-like porous membrane (hereinafter also referred to as “hollow fiber membrane”) formed of a polymer material. This is because the hollow fiber membrane has high performance for separating various components contained in the water to be treated.

  This hollow fiber membrane has a straw-like form and is usually produced using a double mold. The double die is literally a double cylindrical die having a hollow inside, and has a double round cross section. Hereinafter, the inner tube of the double mold is referred to as an “inner tube”, and the tube surrounding the outer side at a certain distance from the inner tube is referred to as an “outer tube”. As shown in Patent Document 1 (Japanese Patent Laid-Open No. 4-343707), a hollow fiber membrane using a double mold is produced by flowing a solid component resin solution into an outer tube in a water tank in which a coagulating liquid is stored. This is done by flowing a coagulation liquid through the inner tube.

  By the way, in recent years, it has been required to supply water more efficiently and more economically. In order to meet this need, hollow fiber membranes having a larger diameter than those in the past are being developed. The large-diameter hollow fiber membrane has an advantage of high performance for separating various components contained in the water to be treated and also has a high treatment speed for the water to be treated.

JP-A-4-343707

  In the production method described in Patent Document 1, a hollow fiber membrane having a relatively small inner diameter can be produced. However, even if an attempt is made to produce a hollow fiber membrane having a large diameter required in recent years, the hollow fiber membrane is stably produced. Could not be produced. Specifically, in order to produce a hollow fiber membrane having a large diameter, when the diameter of each pipe of the double mold is increased, streaks are often formed on the membrane surface of the hollow fiber membrane.

  This invention is made | formed in view of the said present condition, The objective is to provide the manufacturing method of the hollow fiber membrane which cannot make a streak on a membrane surface.

  The inventors have investigated the cause of streaks on the membrane surface of the hollow fiber membrane, and when discharging the resin solution from the outer tube of the double mold to the non-solvent, the resin solution and the non-solvent are formed inside the outer tube. And a resin lump was formed, and the resin lump was adhered to the inner surface of the outer tube, and it was found that this formed a streak on the membrane surface of the hollow fiber membrane. This streak is not a problem because the inner diameter of the outer tube is small in the production of hollow fiber membranes with an inner diameter of about 0.1 μm as in the prior art, and is a specific problem that occurs only when producing a hollow fiber membrane with a large diameter. It is. In order to solve the problem, the present inventors have intensively studied a structure for preventing contact between the resin solution inside the outer tube and the non-solvent, thereby completing the present invention described below.

The method for producing a hollow fiber membrane of the present invention includes a step of immersing a mold having an inner tube for discharging coagulated water from a discharge port and an outer tube for discharging a resin solution from the discharge port in a non-solvent in the coagulation tank;
Forming an air layer between the discharge port and the non-solvent in the coagulation tank;
And a step of producing a hollow fiber membrane by discharging the resin solution and the coagulating liquid from the discharge port, passing the air layer, and then contacting the non-solvent.
After the step of producing the hollow fiber membrane, further comprising the step of removing the air layer,
It is preferable that the resin solution and the coagulation liquid are continuously discharged from the discharge port even after the step of removing the air layer is finished.
Preferably, the mold includes an air reservoir member that holds the air layer in the non-solvent, and one end of the air reservoir member is in contact with the same plane of the discharge port.
In the step of producing the hollow fiber membrane, it is preferable that the resin solution is passed through an air layer having a length of 1 mm or more and 200 mm or less and then contacted with the non-solvent.
It is preferable that the air reservoir member has a shape in which a cross-sectional area widens from the discharge port toward the discharge direction.
It is preferable to further include a step of inserting a core material extending in the discharge direction from the discharge port into the inner tube before the step of manufacturing the hollow fiber membrane.

  According to the method for producing a hollow fiber membrane of the present invention, it is possible to easily produce a hollow fiber membrane in which streaks are hardly formed on the membrane surface.

3 is a schematic cross-sectional view showing an example of a method for producing the hollow fiber membrane of Embodiment 1. FIG. 6 is a schematic cross-sectional view showing an example of a method for producing a hollow fiber membrane of Embodiment 3. FIG. 6 is a schematic cross-sectional view showing an example of a method for producing a hollow fiber membrane according to Embodiment 4. FIG.

  The method for producing a hollow fiber membrane of the present invention is a method using a phase separation method, particularly a non-solvent induced phase separation method. As shown in FIG. 1, the resin solution may be discharged vertically downward ( Embodiment 1) As shown in FIG. 2, the resin solution may be discharged in the horizontal direction (Embodiment 3). In the method for producing a hollow fiber membrane of the present invention, the discharge direction of the resin solution is not particularly limited as described above. A hollow fiber membrane is produced in a state where is provided. The hollow fiber membrane thus produced has the advantage that streaks are unlikely to occur on the membrane surface.

<Embodiment 1>
In this embodiment, a hollow fiber membrane is produced using the coagulation tank 10 and the double-pipe structure mold shown in FIG. In the manufacturing method of the hollow fiber membrane of this embodiment, the mold 17 having the inner tube 12 that discharges the coagulated water 14 from the discharge port and the outer tube 11 that discharges the resin solution 15 from the discharge port, The step of immersing in the solvent 16, the step of forming the air layer 18 between the discharge port and the non-solvent 16 in the coagulation tank 10, the resin solution 15 and the coagulation liquid 14 are discharged from the discharge port, and the air layer 18 is And a step of producing a hollow fiber membrane by contacting with the non-solvent 16 after passing through. Below, each process which comprises this embodiment is demonstrated.

(1) Step of immersing mold in non-solvent in coagulation tank First, as shown in FIG. 1, the mold 17 is immersed in the non-solvent 16 in the coagulation tank 10. In this embodiment, it arrange | positions so that the discharge outlet of a metal mold | die may become the vertical direction downward, ie, the discharge outlet of the metal mold | die 17 may be immersed in the non-solvent 16. FIG. By arranging in this way, a hollow fiber membrane can be produced using the dead weight of the resin solution 15, so that there is an advantage that the production apparatus becomes simple.

(Mold)
In the present embodiment, the mold 17 has a double tube structure having an inner tube 12 that discharges the coagulated water 14 from the discharge port and an outer tube 11 that discharges the resin solution 15 from the discharge port.

  The mold 17 preferably includes the air reservoir member 13 that holds the air layer 18 in the non-solvent 16, but the air reservoir member 13 may not necessarily be provided. When the air reservoir member 13 is provided, it is more preferable that one end of the air reservoir member 13 is in contact with the same plane of the discharge port of the outer tube 11. By providing the air reservoir member 13 at such a position, there is an advantage that an air layer 18 described later can be easily formed at a desired position. The details of the air reservoir member 13 will be described later.

(Coagulation tank)
Any material can be used for the coagulation tank 10 as long as it can hold the non-solvent 16 without being limited in material and shape.

(Non-solvent)
Since the non-solvent 16 in the coagulation tank 10 is in direct contact with the resin solution 15, it is preferably a solvent that is hardly compatible with the resin solution 15, more preferably water or a solvent mainly composed of water. It is. The temperature of the non-solvent is preferably kept constant. Thereby, the phase separation behavior of the resin solution can be stably maintained, and performance such as water permeability and strength can be easily stabilized.

(Coagulation liquid)
The coagulating liquid 14 to be supplied to the inner tube varies depending on the composition of the resin contained in the resin solution 15, but is preferably water or a solvent mainly composed of water. The coagulation liquid 14 may be the same as the non-solvent 16 filled in the coagulation tank 10. The coagulation liquid is preferably discharged simultaneously with the discharge of the resin solution, but the discharge of the coagulation liquid may be started after the discharge of the resin solution.

(2) Step of forming an air layer An air layer 18 is formed between the discharge port of the mold and the non-solvent 16 in the coagulation tank 10. By forming the air layer 18 at this position, it is possible to prevent the resin solution 15 and the non-solvent 16 from coming into direct contact with each other, and it is difficult for the resin mass generated by the contact to be generated. For this reason, streaks on the membrane surface of the hollow fiber membrane based on the resin mass are less likely to occur, and a hollow fiber membrane having no stripe on the membrane surface can be easily produced.

(Air layer)
The air layer 18 may be formed by immersing the mold so that air remains between the discharge port and the non-solvent 16 in the step of immersing the mold in the non-solvent. After the immersion, air may be sent to the discharge port of the mold using an air cylinder or the like. The air layer 18 is not limited to air as long as it is a gas that is difficult to dissolve in the non-solvent 16, and may be composed of, for example, nitrogen gas, oxygen gas, argon gas, helium gas, etc. And air is preferred.

(Air reservoir member)
The air reservoir member 13 installed in the mold may have any shape as long as it has a shape capable of holding gas therein, and examples thereof include an umbrella shape, a cylindrical shape, and a truncated cone shape. As shown in FIG. 1, when the air reservoir member 13 has an umbrella shape, it is preferable that the air reservoir member 13 is installed so as to have a shape in which a cross-sectional area widens from the discharge port toward the discharge direction. From the viewpoint of forming the air layer at a desired position, the upper surface of the air reservoir member 13 (that is, the surface of the smaller circle) is sized to cover the entire discharge port of the mold and to a position that covers the entire discharge port. It is preferable to be installed. The thickness of the air reservoir member 13 is not particularly limited as long as it does not deform when the air layer is held.

(3) Step of producing hollow fiber membrane The resin solution 15 is discharged from the discharge port of the outer tube 11, passed through the air layer 18, and then brought into contact with the non-solvent 16 to produce a hollow fiber membrane. Thus, by producing a hollow fiber membrane in a state where the air layer 18 is interposed between the resin solution 15 and the non-solvent 16, it is difficult to generate a resin lump that occurs due to contact between the resin solution 15 and the non-solvent 16. It is possible to make streaks difficult to form on the membrane surface of the hollow fiber membrane caused by the resin mass. Since the air layer 18 is provided at the start of the discharge of the resin solution and in order to avoid an initial unstable state, the air layer 18 may be removed after the production of the hollow fiber membrane is once stabilized. . In addition, the process of removing an air layer is demonstrated in Embodiment 2 mentioned later.

  Here, in this step, the resin solution is preferably passed through an air layer having a length of 1 mm or more and 200 mm or less and then brought into contact with a non-solvent. By providing an air layer having such a length, the resin solution and the non-solvent are less likely to come into contact with each other, so that a resin lump caused by these contacts can also be less likely to occur. The length of the air layer is more preferably 3 mm or more and 100 mm or less, and further preferably 5 mm or more and 50 mm or less. The longer the air layer that passes through, the lower the water permeability of the hollow fiber membrane, while the strength of the hollow fiber membrane tends to improve.

(Resin solution)
As the resin solution used as the material constituting the hollow fiber membrane, any material may be used as long as it contains a substantially single material resin. “Substantially single” means substantially single, that is, one main constituent material, specifically, one resin is 50% by weight or more, preferably 60% by weight or more, More preferably, it means 70% by weight or more. In addition, it is intended that the single material and the single main constituent material do not include additives usually used in the production of the resin or in the production of the hollow fiber membrane described later.

  As the substantially single material, materials / materials generally used in the field can be used. For example, polysulfone (PS), polyethersulfone (PES), polyvinylidene fluoride (PVDF) , Polyethylene (PE), cellulose acetate (CA), polyacrylonitrile (PAN), polyvinyl alcohol (PVA), polyimide (PI), polyvinyl chloride, cellulose (cellulose acetate), cellulose acetate Etc.) and the like. Among these, a vinyl chloride resin is preferable. You may use these individually or in combination of 2 or more types.

  As vinyl chloride resin, vinyl chloride homopolymer (vinyl chloride homopolymer), copolymer of copolymerizable unsaturated bond monomer and vinyl chloride monomer, and graft copolymerized with vinyl chloride monomer. Examples thereof include a graft copolymer and a (co) polymer composed of those chlorinated vinyl chloride monomer units. These may be used alone or in combination of two or more. In particular, in order to improve stain resistance, it is suitable that a hydrophilic monomer is copolymerized.

  In order to improve moldability, heat stability, etc., the resin solution may be used alone or in combination of two or more lubricants, heat stabilizers, film forming aids and the like. Examples of the lubricant include stearic acid and paraffin wax. Examples of the thermal stabilizer include tin-based, lead-based, and Ca / Zn-based stabilizers that are generally used for molding a vinyl chloride resin. Examples of the film forming aid include hydrophilic polymers such as polyethylene glycol and polyvinyl pyrrolidone having various polymerization degrees.

  The solvent used for the resin solution is not particularly limited as long as it is soluble in the resin, and usually the solvent used when synthesizing the resin can be used. When a vinyl chloride resin is used as the resin, for example, dimethyl sulfoxide, N, N-dimethylformamide, tetrahydrofuran, N, N-dimethylacetamide, N-methyl-2-pyrrolidone and the like can be mentioned. A mixture of seeds or more can be used.

  In the resin solution, the ratio of the resin component to the total weight of the resin solution is preferably 15% by weight or more, more preferably 20 to 40% by weight, and further preferably 20 to 30% by weight. By setting this range, the phase separation can be accelerated moderately, the strength of the hollow fiber membrane can be sufficiently secured, and the short-term strength and fatigue strength are remarkably improved when a large-diameter hollow fiber membrane is formed. be able to.

  The viscosity of the resin solution is, for example, preferably 500 to 4000 mPa · s, and more preferably 1000 to 3000 mPa · s. By having such a viscosity, the roundness of the outer shape of the hollow fiber membrane can be secured, and thus a membrane having a uniform thickness and film thickness can be produced. As the viscosity, a value measured using a vibrating viscometer (manufactured by Seconic Corporation, VM-100A-M) after directly introducing the resin solution into the sample tube is adopted.

(Hollow fiber membrane)
The hollow fiber membrane manufactured by this embodiment has an outer diameter of 3.6 mm or more and 10 mm or less. The thickness of the hollow fiber membrane can be 0.15 to 2.4 mm. The measured value using an electron micrograph shall be employ | adopted for the internal diameter and thickness of a hollow fiber membrane.

  The strength of the hollow fiber membrane is usually determined by various factors such as material, inner diameter, wall thickness, roundness, internal structure, etc. Among them, the SDR value (outer diameter / thickness ratio) should be used. The SDR value of the hollow fiber membrane is preferably 3.6 to 34. When the SDR value is 34 or less, the pressure resistance of the hollow fiber membrane is 0.3 MPa or more, and when the SDR value is 3.6 or more, it is easy to secure a membrane filtration area in the water treatment module. The SDR value is more preferably 4.0 or more and 20 or less, and further preferably 5.0 or more and 16 or less. In particular, when the outer diameter is about 5 to 7 mm, the SDR value is preferably 4 to 16, and more preferably 6.5 to 11.

  The hollow fiber membrane produced by the production method of the present embodiment can usually be a porous membrane having a large number of micropores on its surface. The average pore diameter of the fine pores is, for example, about 0.001 to 10 μm, preferably about 0.01 to 1 μm. The size and density of the pores on the membrane surface can be adjusted as appropriate according to the above-mentioned inner diameter, thickness, characteristics to be obtained, and the like, but it is preferable that the permeated water amount described later can be realized.

  The porosity of the hollow fiber membrane is, for example, about 10 to 90%, preferably about 20 to 80%. The porosity here means the ratio of the total area of the pores to the total area of the hollow fiber membrane in an arbitrary cross section (the cross section in the radial direction of the hollow fiber membrane, the same applies hereinafter), and a micrograph of the membrane cross section The value calculated from the value of each area is adopted.

  In the cross section in the radial direction of the hollow fiber membrane, the porosity with respect to the cross-sectional area of the hollow fiber membrane is preferably about 30 to 85%, and is preferably 50 to 85%, 40 to 75%, or 50 to 75%. More preferred. In addition, it is preferable that the innermost layer, the inner layer, the outer layer, and the pores constituting the outermost layer are distributed in layers from the center to the radial direction. This makes it possible to maintain the strength of the entire membrane by dispersing the stress concentration when an internal pressure / external pressure is applied to the hollow fiber membrane while maintaining water permeability.

The hollow fiber membrane obtained by the production method of this embodiment has a permeated water amount of about 100 L / (m ² · h) or more and about 200 L / (m ² · h) or more at a transmembrane differential pressure of 100 kPa. It is suitable, and about 600 L / (m ² · h) or more can be realized. Also, the internal pressure strength of the film can be about 0.3 MPa or more, about 0.5 MPa or more, and further about 1.0 MPa or more.

Further, the external pressure strength of the film can be about 0.1 MPa or more, about 0.3 MPa or more, and further about 0.7 MPa or more. In particular, the amount of permeated pure water at a transmembrane differential pressure of 100 kPa is about 100 L / (m ² · h) or more, the internal pressure resistance of the film is about 0.3 MPa or more, and the external pressure resistance is about 0.1 MPa or more. Can do.

(Use of hollow fiber membrane)
Since the hollow fiber membrane produced by the production method of the present embodiment has a uniform thickness, it has an excellent balance between the amount of permeated water and physical strength. For this reason, it is suitable for separation membranes, ultrafiltration (UF) membranes and microfiltration (MF) membranes of existing water treatment equipment, and water treatment for the purpose of water purification, especially water treatment of high-concentration wastewater. It becomes possible.

<Embodiment 2>
This embodiment is the same as Embodiment 1 except that it further includes a step of removing the air layer with respect to Embodiment 1. Below, the description which overlaps with Embodiment 1 is omitted, and the process of removing an air layer is described.

(4) Step of removing air layer The present embodiment further includes a step of removing the air layer 18 after the step of producing the hollow fiber membrane. Even after the completion of this step, by continuously discharging the resin solution 15 from the discharge port of the outer tube, a hollow fiber membrane having no streaks on the membrane surface can be continuously produced. The air layer 18 is provided at the start of discharge of the resin solution 15 and in order to avoid an initial unstable liquid supply state. Therefore, once the production of the hollow fiber membrane is once stabilized, the embodiment is thereafter performed. It may be removed as follows. By including the step of removing the air layer 18 as in this embodiment, the hollow fiber membrane can be stably produced.

  As a method for removing the air layer, a coagulating liquid or a non-solvent may be injected into the air layer 18, or the air reservoir member 13 may be removed to release the air. The timing of removing the air layer may be any time after the hollow fiber membrane has started to be stably produced. For example, the air layer may be removed if it is 1 second or longer after the resin solution starts to be discharged from the discharge port. Well, more preferably 3 seconds or more. Since the air layer is not necessarily removed, there is no particular upper limit.

<Embodiment 3>
The manufacturing method of the hollow fiber membrane of this embodiment is the same as that of Embodiment 1 except that the direction of producing the hollow fiber membrane is different from that of Embodiment 1. That is, in this embodiment, as shown in FIG. 2, the hollow fiber membrane is produced by discharging the resin solution in the horizontal direction (that is, the direction perpendicular to the vertical direction of Embodiment 1). By discharging the resin solution in the horizontal direction as in this embodiment, there is an advantage that the gas constituting the air layer can be easily introduced from the outside in the step of forming the air layer. Moreover, after the production of the hollow fiber membrane is stabilized, the step of removing the air layer can be performed more simply.

<Embodiment 4>
The manufacturing method of the hollow fiber membrane of the present embodiment is the same as that of the first embodiment except that the method includes a step of inserting the core material 19 into the inner tube of the mold, and the hollow fiber membrane is the same as in the first embodiment. Is made. FIG. 3 is a schematic cross-sectional view showing a method for producing the hollow fiber membrane of the present embodiment. Below, the process of inserting the core material 19 will be described.

(5) Step of Inserting Core Material In this embodiment, the core material 19 is attached to the inner tube 12 of the mold before the step of immersing the mold 17 in the non-solvent 16 in the coagulation tank 10. The core material 19 is inserted in consideration of the simplicity of the core material mounting operation, but after the step of immersing the mold 17 in the coagulation tank 10, the core material 19 is inserted into the inner pipe of the mold. It may be inserted. Thus, by inserting the core material 19 into at least a part of the inner tube, the cross-sectional area of the discharge port of the inner tube 12 from which the coagulating liquid 14 is discharged can be reduced by the cross-sectional area of the core material. As a result, the discharge of the coagulation liquid is easily stabilized. When the discharge of the coagulating liquid is stabilized, the thickness of the obtained hollow fiber membrane tends to be uniform, and the hollow fiber membrane can be stably produced. The uniform thickness of the hollow fiber membrane increases the mechanical strength and water permeability of the hollow fiber membrane. In addition, by disposing the core material at the discharge port of the inner tube, it is possible to reduce the supply amount of the coagulating liquid by the amount corresponding to the cross-sectional area of the core material.

(Core material)
In the present embodiment, a case where a cylindrical core material extending in the direction in which the resin solution is discharged is used (that is, either the top surface or the bottom surface of the core material is inserted into the discharge port of the inner tube) will be described. The shape of the material is not limited to a cylindrical shape, but may be an elliptical column shape, a triangular column shape, a quadrangular column shape, a pentagonal column shape, or a conical shape such as a cone, a triangular pyramid, a quadrangular pyramid, or a pentagonal pyramid. It may be a frustum type such as a truncated cone type, a triangular frustum type, or a quadrangular frustum type. From the viewpoint that the inside of the hollow fiber membrane can be easily approximated to a perfect circle, the core material is more preferably a cylindrical shape, a conical shape, or a truncated cone shape. When the truncated cone type core material is used, it is more preferable that the core material is arranged so that the cross-sectional area gradually increases in the direction in which the resin solution is discharged.

  Regarding the arrangement of the core material in the inner pipe, it is preferable that the center of the cross section of the core material is arranged so as to coincide with the center of the cross section of the discharge port of the inner pipe 12. That is, it is preferable that the columnar, conical or frustum-shaped core material is disposed concentrically or coaxially with the inner tube. By arranging the core material in this way, it is possible to make the hollow fiber membrane have an inner diameter that is close to a perfect circle shape, and a product with a more uniform thickness. Here, “the center of the cross section” is used in the same meaning as the center of gravity of the cross section.

  Further, the core material may be inserted into the discharge port of the double-pipe structure mold, but is not limited thereto, and one end of the core material is on the same plane as the plane formed by the discharge port. There is no problem even if there is. The arrangement position of the core material is not particularly limited as long as the core material is arranged so as to reduce the discharge section of the discharge port. If the distance between the discharge port of the inner pipe and one end of the core material is defined, one end of the core material is preferably inserted from 0 mm to 30 mm from the plane formed by the discharge port, more preferably from 5 mm to 10 mm. It is inserted. Within this range, the discharge cross-sectional area of the inner tube can be effectively reduced, and the hollow fiber membrane can be produced more stably.

  The length of the core material is preferably 0.1 mm or more and 500 mm or less, more preferably 1 mm or more and 300 mm or less, and further preferably 5 mm or more and 100 mm or less. Further, the cross-sectional diameter of the core material is preferably 0.5 mm or more and 10 mm or less, more preferably 1 mm or more and 8 mm or less, and further preferably 2 mm or more and 6 mm or less.

  Hereinafter, the manufacturing method of the hollow fiber membrane of this invention is demonstrated in detail based on an Example. In addition, this invention is not limited only to these Examples. Moreover, the compounding quantity in an Example is shown on a weight basis unless there is particular notice.

Example 1
A resin solution was prepared by blending the following components in the following blending amounts.
Chlorinated vinyl chloride resin (Product name: HA58K (manufactured by Sekisui Chemical Co., Ltd.)) 20%
Polyethylene glycol 1000 12%
Polyethylene glycol 200 11%
N'N-dimethylacetamide 57%

  Next, a frustoconical air reservoir member having an upper surface circle diameter of 8 mm, a lower surface circle diameter of 12 mm, and a distance from the upper surface to the lower surface of 2 mm is prepared. The tube structure was mounted on the same plane as the surface formed by the discharge port of the mold. Such a double-pipe structure mold is submerged in a coagulation tank so that air is accumulated in the air reservoir member, and the spinning direction of the membrane is perpendicular to the water surface of the coagulation tank (that is, vertically downward). The direction of the outlet of the mold was adjusted. The air reservoir member was formed with an air layer having a length of 10 mm from the upper surface thereof. This air layer was filled with air.

  Thereafter, in the coagulation tank, the resin solution adjusted to 60 ° C. was supplied to a double-pipe structure mold at 200 g / min, and at the same time, pure water was supplied at 200 g / min as an internal coagulation liquid. Then, the resin solution was discharged from the discharge port of the outer tube, passed through the air layer having a length of 10 mm, and then contacted with a non-solvent to produce a hollow fiber membrane. The hollow fiber membrane was continuously taken up by a take-up machine installed at the bottom of the coagulation tank. The obtained hollow fiber membrane had an outer diameter of 6.0 mm, an SRD of 8.1, and no streaks were found on the membrane surface.

(Example 2)
A hollow fiber membrane was produced in the same manner as in Example 1, except that the air layer was removed after the production of the hollow fiber membrane was stabilized. The hollow fiber membrane of this example had the same outer diameter and SRD as that of Example 1, and no streaks were found on the membrane surface.

(Example 3)
Compared to Example 1, 5 mm of the center of one side surface of a cylindrical core material having a diameter of 3.0 mm and a length of 6 mm was inserted into the center of the cross section of the discharge port of the inner pipe of the mold and screwed to the inner pipe. A hollow fiber membrane was produced in the same manner as in Example 1 except that the hollow fiber membrane was produced in the state (FIG. 3). The obtained hollow fiber membrane had an outer diameter of 6.0 mm, an SRD of 8.1, and no streaks were found on the membrane surface. In addition, by supplying the core material, the supply amount of the internal coagulating liquid became 180 g / min.

(Comparative Examples 1-3)
Comparative Example 1 is similar to Examples 1 to 3 except that the air reservoir member is not attached to the discharge port of the double-pipe mold and the air layer is not formed. ~ 3 hollow fiber membranes were prepared. In addition, each comparative example number respond | corresponds to each example number, for example, the comparative example 1 differs in having eliminated the air layer in manufacture of Example 1, and is a hollow fiber on the manufacturing conditions similar to Example 1. A membrane was prepared. The hollow fiber membranes produced in each comparative example were all the same as the outer diameter and SRD values of the hollow fiber membranes of the corresponding examples, but a plurality of streaks were confirmed on the membrane surface.

(Discussion)
In the hollow fiber membranes of Examples 1 to 3, no streaks were formed on the membrane surface, whereas in Comparative Examples 1 to 3, streaks were confirmed on the membrane surface. From this result, it is difficult to form streaks on the membrane surface of the hollow fiber membrane by providing an air layer between the discharge port and the non-solvent and passing the resin solution through the air layer to produce the hollow fiber membrane. It became clear that the effect of the present invention was shown.

  The present invention is used for water purification such as pretreatment for river water and groundwater clarification, industrial water clarification, drainage and sewage treatment, seawater desalination regardless of the aspect of the water treatment apparatus, etc. It can be widely used like a water treatment membrane, a microfiltration membrane, etc., and can be used particularly advantageously for MBR.

10, 20 Coagulation tanks 11, 21 Outer pipes 12, 22 Inner pipes 13, 23 Air reservoir members 14, 24 Coagulating liquids 15, 25 Resin solutions 16, 26 Non-solvents 17, 27 Molds 18, 28 Air layer 19 Core material

Claims (6)

A step of immersing a mold having an inner tube for discharging the coagulation liquid from the discharge port and an outer tube for discharging the resin solution from the discharge port in a non-solvent in the coagulation tank;
Forming an air layer between the discharge port and the non-solvent in the coagulation tank;
And a step of producing a hollow fiber membrane by discharging the resin solution and the coagulating liquid from the discharge port, passing through the air layer, and contacting the non-solvent. Yarn membrane manufacturing method. After the step of producing the hollow fiber membrane, further comprising the step of removing the air layer,
The method for producing a hollow fiber membrane according to claim 1, wherein the resin solution and the coagulation liquid are continuously discharged from the discharge port even after the step of removing the air layer is finished. The mold has an air reservoir member that holds the air layer in the non-solvent,
The hollow fiber membrane manufacturing method according to claim 1, wherein one end of the air reservoir member is in contact with the same plane of the discharge port.   The process of producing the said hollow fiber membrane makes the said resin solution and the said coagulation liquid pass through the air layer of the length of 1 mm or more and 200 mm or less, and is made to contact with the said non-solvent. The method for producing a hollow fiber membrane according to one item.   The method for producing a hollow fiber membrane according to claim 3 or 4, wherein the air reservoir member has a shape in which a cross-sectional area is widened from the discharge port toward the discharge direction.   The hollow according to any one of claims 1 to 5, further comprising a step of inserting a core material extending in the discharge direction from the discharge port into the inner tube before the step of manufacturing the hollow fiber membrane. Yarn membrane manufacturing method.