JP5050499B2 - Method for producing hollow fiber membrane and hollow fiber membrane - Google Patents

Description

  The present invention relates to a method for producing a hollow fiber membrane for selectively separating components of a liquid mixture. More specifically, the present invention relates to a method for producing a hollow fiber microfiltration membrane or a hollow fiber ultrafiltration membrane used for water treatment such as wastewater treatment, water purification treatment, and industrial water production.

  Separation membranes such as microfiltration membranes and ultrafiltration membranes are used in various fields including food industry, medicine, water production and wastewater treatment. Particularly in recent years, separation membranes have come to be used also in the field of drinking water production, that is, water purification treatment. When used in water treatment applications such as water purification, a hollow fiber membrane having a large effective membrane area per unit volume is generally used because of the large amount of water that must be treated.

  Here, the hollow fiber membrane for water treatment has the following performance, that is, excellent in pure water permeation performance, high pressure resistance, high chemical resistance, and high blocking performance against pathogenic microorganisms, etc. And high elongation performance is demanded. First of all, if the hollow fiber membrane has excellent pure water permeation performance, the membrane area can be reduced, and the equipment can be saved because the device is compact, and from the viewpoint of membrane replacement costs and installation area. It will be advantageous. Next, if the pressure resistance is high, the hollow fiber membrane will not be crushed even during long-term operation, and the hollow part will not be clogged, or even if the hollow fiber membrane has the same pure water permeation performance, the amount of treated water can be increased by high-pressure operation. To do. In addition, disinfectants such as sodium hypochlorite are added to the hollow fiber membrane module for the purpose of sterilizing permeated water and preventing biofouling of the membrane, and hydrochloric acid, citric acid, oxalic acid are used for chemical cleaning of the hollow fiber membrane. The membrane may be washed with an acid such as an alkali such as an aqueous solution of sodium hydroxide, chlorine, and a surfactant, so that the material of the hollow fiber membrane must have high chemical resistance. Furthermore, in the field of water purification, the problem that chlorine-resistant pathogenic microorganisms such as Cryptosporidium are mixed in drinking water has become apparent since the end of the 20th century. Therefore, high elongation performance is required so that raw water is not mixed.

  Many of the hollow fiber membranes used in water treatment applications are produced by discharging a single type of membrane-forming solution from the double tube structure die at the same time as the internal coagulation liquid forming the hollow part, and coagulating it. It consists of layers. Such a hollow fiber membrane is easy to manufacture, but it is very difficult to combine the above-mentioned performances with a single layer.

  Thus, a composite hollow fiber membrane consisting of two layers produced using two types of membrane-forming solutions has been developed so far. When the hollow fiber membrane is composed of two layers, the various performances can be shared by the respective layers, and as a result, many performances can be maintained at a high level.

  Conventionally, as a method for producing such a composite hollow fiber membrane, a coating method in which a thin film as a functional layer having a high blocking performance is applied on a support layer having a high strength and elongation performance is known. Problems such as peeling of the interface with the functional layer, uneven thickness of the functional layer and occurrence of pinholes have been pointed out. In addition, since the manufacturing process is complicated, there is a problem that it is difficult to manufacture in large quantities efficiently.

  Further, as a method for solving the drawbacks of the coating method, there has been proposed a method in which two types of film-forming solution and an internal coagulating liquid are simultaneously discharged from a triple tube structure die and immersed in the coagulating liquid. For example, Patent Document 1 discloses that two types of polysulfone resin solutions are discharged simultaneously with a non-solvent or poor solvent internal coagulation liquid of polysulfone resin and immersed in water, which is an external coagulation liquid, to solidify, and the outer layer is a support layer and the inner layer is A method for producing a composite hollow fiber membrane comprising a functional layer is disclosed. In this method, both the support layer and the functional layer are formed by a non-solvent induced phase separation method in which a resin solution dissolved in a good solvent is brought into contact with a non-solvent or a poor solvent to solidify. In general, a layer formed by a non-solvent induced phase separation method has a dense layer and therefore has a high blocking performance, but in order to increase its pure water permeation performance, the resin concentration of the resin solution forming the layer must be lowered. In such a case, sufficient strength / elongation performance cannot be obtained. That is, with this method, it is difficult to achieve both high pure water permeation performance and high strength elongation performance.

  Furthermore, Patent Document 2 discloses that two types of polyvinylidene fluoride resin solutions are discharged simultaneously with the poor internal solvent of the polyvinylidene fluoride resin and immersed in water that is the external solidification solution to solidify the outer layer. A method for producing a composite hollow fiber membrane in which an inner layer is a support layer is disclosed. In this method, the support layer is formed by a thermally induced phase separation method in which a resin solution dissolved at a high temperature is cooled to solidify, and the functional layer is formed by a non-solvent induced phase separation method. The layer formed by the thermally induced phase separation method has low blocking performance, but has high pure water permeation performance even if the concentration of the resin solution forming the layer is relatively high. Therefore, according to such a method, a hollow fiber membrane having high blocking performance, pure water permeation performance and high elongation performance can be obtained.

  However, it is actually difficult to develop only non-solvent induced phase separation in one of the two layers with the same external coagulation liquid, and develop only thermally induced phase separation in the other layer. In the method using water as the external coagulation liquid shown in Patent Document 2, if the functional layer is thin and the support layer is thick, there is a problem that non-solvent induced phase separation occurs in the support layer and the water permeability performance is significantly reduced. In order to increase the performance, it is necessary to make the functional layer thick and the support layer thin, and this causes a problem that the pressure resistance is not sufficient, and it is difficult to produce a two-layer hollow fiber membrane that satisfies the required performance at the same time.

JP-A-4-45830 International Publication No. 03/106545 Pamphlet

  In the present invention, in view of the problems in the prior art described above, a two-layer composite having a high strength elongation performance, a high purity water permeation performance, a high blocking performance, and a high pressure resistance performance using a thermoplastic resin having high chemical resistance. It aims at providing the method of manufacturing a hollow fiber membrane cheaply and easily.

To achieve the above object, the present invention provides:
(1) A solution 1 in which the thermoplastic resin 1 is dissolved in a solvent, a solution 2 in which the thermoplastic resin 2 is dissolved in a solvent, and an internal coagulation liquid are respectively connected to an annular mouth and an inner When the hollow fiber membrane is produced by simultaneously discharging and solidifying into the external coagulation liquid from the annular port and the central tube, the temperature Ts of the die and the crystallization temperature Tc of the solution 2 are Tc + 20 ° C. ≦ Ts ≦ The discharge weight W1 of the solution 1 and the discharge weight W2 of the solution 2 are in the range of 0.1 ≦ W1 / W2 ≦ 1, and the temperature T of the external coagulation liquid is T ≦ Tc. -10 ° C. and 50 wt% or more and 90 wt% or less of the external coagulation liquid is a non-solvent of the thermoplastic resin 1 and 10 wt% or more and 50 wt% or less of the poor solvent or good of the thermoplastic resin 1 Hollow using mixed solvent as solvent Method of manufacturing the film.
(2) The solution 1 discharged from the annular port outside the die is solidified by non-solvent induced phase separation, and the solution 2 discharged from the annular port inside the die is solidified by thermally induced phase separation (1) ) A method for producing a hollow fiber membrane as described above.
(3) The concentration of the thermoplastic resin 1 in the solution 1 is 5 wt% or more and 30 wt% or less, and the concentration of the thermoplastic resin 2 in the solution 2 is 20 wt% or more and 60 wt% or less. The manufacturing method of the hollow fiber membrane as described in said (1) or (2).
(4) The method for producing a hollow fiber membrane according to any one of (1) to (3), wherein the thermoplastic resin 1 and / or the thermoplastic resin 2 is a polyvinylidene fluoride resin.

(5) A hollow fiber membrane having an outer diameter of 1100 μm or more and 2000 μm or less manufactured by the manufacturing method according to any one of (1) to (4) above, wherein the outer layer is a three-dimensional network structure and the inner layer is a spherical structure When the average thickness of the outer layer is Th1 and the average thickness of the inner layer is Th2, 0.2 ≦ Th1 / Th2 ≦ 0.8 and the pure water permeation performance at 50 kPa and 25 ° C. is 0.00. A hollow fiber membrane having 5 m ³ / m ² · hr or more, a breaking strength of 8 MPa or more, a breaking elongation of 80% or more, and a pressure resistance of 200 kPa or more.
(6) A hollow fiber membrane having an outer diameter of 500 μm or more and less than 1100 μm manufactured by the manufacturing method according to any one of (1) to (4) above, wherein the outer layer is a three-dimensional network structure and the inner layer is a spherical structure When the average thickness of the outer layer is Th1 and the average thickness of the inner layer is Th2, 0.2 ≦ Th1 / Th2 ≦ 0.8 and the pure water permeation performance at 50 kPa and 25 ° C. is 0.00. A hollow fiber membrane characterized by being 2 m ³ / m ² · hr or more, a breaking strength of 10 MPa or more, a breaking elongation of 20% or more, and a pressure resistance of 100 kPa or more.
Consists of.

  In the present invention, two types of thermoplastic resin solutions are simultaneously discharged from the triple-tube structure die and simultaneously solidified by immersing them in the external coagulation liquid, thereby solidifying the outer layer as a functional layer and the inner layer as a support layer. When producing a composite hollow fiber membrane composed of two layers, the outer layer is controlled by controlling the non-solvent concentration of the external coagulation liquid, the discharge weight ratio of the two types of resin solutions forming the two layers, etc. to a specific range. Since the inner layer can be formed only by heat-induced phase separation only by non-solvent induced phase separation, the outer layer has high blocking performance and high pure water permeation performance, and the inner layer has high strength elongation performance, high pure water permeation performance and high pressure resistance performance. A composite hollow fiber membrane can be produced.

  Therefore, according to the present invention, it is possible to easily and inexpensively manufacture a hollow fiber membrane having both high strength elongation performance, high pure water permeation performance, high blocking performance, and high pressure resistance performance.

  In the production method of the present invention, the thermoplastic resin 1 solution 1 from the outer annular port of the triple tube structure die, the thermoplastic resin 2 solution 2 from the inner annular port, the internal coagulating liquid from the central tube, When producing a composite hollow fiber membrane consisting of two layers by simultaneously solidifying by discharging into an external coagulation liquid, the non-solvent concentration of the external coagulation liquid, the discharge weight ratio of the two kinds of resin solutions forming the two layers, In addition, by controlling the temperature of the base and the external coagulation liquid within a specific range, the outer layer can be formed only by non-solvent induced phase separation and the inner layer can be formed only by thermally induced phase separation. As a result, it is possible to produce a composite hollow fiber membrane in which the outer layer has high blocking performance and high pure water permeation performance, and the inner layer has high strength elongation performance, high pure water permeation performance and high pressure resistance performance.

  Here, the non-solvent induced phase separation is a phase separation in which a resin solution is brought into contact with a non-solvent to solidify, and the thermally induced phase separation is a phase separation in which a resin solution dissolved at high temperature is solidified by cooling.

  The thermoplastic resin in the present invention refers to a resin that is made of a chain polymer substance and exhibits a property of being deformed / flowed by an external force when heated. Examples of this thermoplastic resin include polyethylene, polypropylene, acrylic resin, polyacrylonitrile, acrylonitrile-butadiene-styrene (ABS) resin, polystyrene, acrylonitrile-styrene (AS) resin, vinyl chloride resin, polyethylene terephthalate, polyamide, polyacetal, Examples thereof include polycarbonate, modified polyphenylene ether, polyphenylene sulfide, polyvinylidene fluoride, polyamideimide, polyetherimide, polysulfone, polyethersulfone, and mixtures and copolymers thereof. Other resins miscible with these and polyhydric alcohols or surfactants may be contained in an amount of 50% by weight or less.

  As the thermoplastic resin used in the present invention, a polyvinylidene fluoride resin having high chemical resistance is preferable. The polyvinylidene fluoride resin means a resin containing a vinylidene fluoride homopolymer and / or a vinylidene fluoride copolymer, and may contain a plurality of types of vinylidene fluoride copolymers. The vinylidene fluoride copolymer is a polymer having a vinylidene fluoride residue structure, and is typically a copolymer of a vinylidene fluoride monomer and other fluorine-based monomers. Examples of the copolymer include a copolymer of vinylidene fluoride and at least one selected from vinyl fluoride, tetrafluoroethylene, hexafluoropropylene, and trifluoroethylene chloride. Further, a monomer such as ethylene other than the fluorine-based monomer may be copolymerized to such an extent that the effects of the present invention are not impaired.

  The thermoplastic resin 1 and the thermoplastic resin 2 may be the same resin or different resins. When the thermoplastic resin 1 and the thermoplastic resin 2 are made of the same resin, the affinity between the two is increased, and the adhesion between the outer layer and the inner layer constituting the manufactured hollow fiber membrane is improved, which is preferable. On the other hand, when it comprises with different resin, performances, such as the strong elongation performance of a hollow fiber membrane manufactured, a pure water permeation performance, a blocking performance, can be adjusted in a wider range. Further, it is also preferable that the thermoplastic resin 1 and the thermoplastic resin 2 are made of a polymer blend containing the same resin as the other. Thereby, the performance of the hollow fiber membrane can be adjusted in a wide range while keeping the affinity between the two high.

  Next, in the manufacturing method of the present invention, the solution 1 discharged from the annular port outside the die is solidified by non-solvent induced phase separation, and the solution 2 discharged from the annular port inside the die is solidified by thermally induced phase separation. This is very important. Therefore, the solvent of the solution 1 is preferably a good solvent for the thermoplastic resin 1 or a mixed solvent of 95% by weight or more of the good solvent for the thermoplastic resin 1 and 5% by weight or less of the non-solvent for the thermoplastic resin 1. . Moreover, as a solvent of the solution 2, the poor solvent or good solvent of the thermoplastic resin 2 is preferable.

  Here, the poor solvent is a solvent that cannot dissolve 5% by weight or more at a low temperature of 60 ° C. or less, but can dissolve 5% by weight or more in a high temperature region of 60 ° C. or more and below the melting point of the resin. Define. On the other hand, a solvent capable of dissolving 5 wt% or more of the resin even at a low temperature of 60 ° C. or less is a good solvent, and a solvent that does not dissolve or swell the resin up to the melting point of the resin or the boiling point of the liquid. It is a solvent.

  Here, as a poor solvent for polyvinylidene fluoride resin, for example, medium chain length such as cyclohexanone, isophorone, γ-butyrolactone, methyl isoamyl ketone, dimethyl phthalate, propylene glycol methyl ether, propylene carbonate, diacetone alcohol, glycerol triacetate, etc. And alkyl ketones, esters, glycol esters, organic carbonates, and the like, and mixed solvents thereof. Examples of good solvents include N-methyl-2-pyrrolidone, dimethyl sulfoxide, dimethylacetamide, dimethylformamide, methyl ethyl ketone, acetone, tetrahydrofuran, tetramethylurea, trimethyl phosphate, and other lower alkyl ketones, esters, amides, and the like, and mixtures thereof. A solvent is mentioned. Furthermore, as the non-solvent, water, hexane, pentane, benzene, toluene, methanol, ethanol, carbon tetrachloride, o-dichlorobenzene, trichloroethylene, ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, butylene glycol, Aliphatic hydrocarbons such as pentanediol, hexanediol, low molecular weight polyethylene glycol, aromatic hydrocarbons, aliphatic polyhydric alcohols, aromatic polyhydric alcohols, chlorinated hydrocarbons, or other chlorinated organic liquids and mixtures thereof A solvent etc. are mentioned.

  The thermoplastic resin concentration of the solution is preferably within the following range in order to exhibit high film performance. The concentration of the thermoplastic resin 1 in the solution 1 is preferably 5% by weight or more and 30% by weight or less, more preferably 10% by weight or more and 20% by weight or less. If it is less than 5% by weight, the physical durability of the layer formed from the solution 1 is low, and if it exceeds 30% by weight, the pure water permeation performance is low. The concentration of the thermoplastic resin 2 in the solution 2 is preferably 20% by weight to 60% by weight, and more preferably 25% by weight to 45% by weight. If it is less than 20% by weight, the strength elongation performance of the layer formed by the solution 2 is low, and if it exceeds 60% by weight, the pure water permeation performance is low.

  Hereinafter, a method for producing a hollow fiber membrane using the solution 1 and the solution 2 prepared as described above will be described.

  The hollow fiber membrane is solidified by discharging the solution 1 from the outer annular port of the triple tube structure die, the solution 2 from the inner annular port, the internal coagulating liquid from the central tube and simultaneously into the external coagulating liquid. To manufacture. Here, the temperature Ts of the die having the triple-tube structure is set in the range of Tc + 20 ° C. ≦ Ts ≦ Tc + 70 ° C. when the crystallization temperature of the solution 2 is Tc. Preferably, Tc + 35 ° C. ≦ Ts ≦ Tc + 60 ° C. When Ts <Tc + 20 ° C., the viscosity of the solution 2 becomes too high and it becomes difficult to discharge from the die. When Ts> Tc + 70 ° C., solidification of the discharged solution 2 is slow, and as a result, a hollow fiber structure cannot be formed.

  Here, the crystallization temperature Tc of the solution 2 is defined as follows. Using a differential scanning calorimetry (DSC measurement) device, a mixture having the same composition as the composition of the solution 2 such as the thermoplastic resin 2 and a solvent is sealed in a sealed DSC vessel, and the temperature is increased to a dissolution temperature at a temperature rising rate of 10 ° C./min. Warm up and hold for 30 minutes to dissolve uniformly, then Tc is the rising temperature of the crystallization peak observed in the process of lowering the temperature at a temperature lowering rate of 10 ° C./min.

  As a solvent that can be used for the internal coagulation liquid, the same solvent as the solvent in the solution 2, a mixed solvent of 70% by weight or more of the same solvent as the solvent in the solution 2 and 30% by weight or less of the non-solvent of the thermoplastic resin 2, Alternatively, a solvent that is immiscible with the solvent in the solution 2 is preferable. In addition, the temperature T of the external coagulation liquid is preferably T ≦ Tc−10 ° C., more preferably, in order to cool the solution 2 discharged from the annular port inside the base at a sufficient temperature-decreasing rate and cause heat-induced phase separation. T ≦ Tc−30 ° C. At T> Tc-10 ° C., the solution 2 does not solidify and a hollow fiber structure cannot be formed. Since the external coagulation liquid is in a liquid state, its temperature is higher than its melting point.

  Next, in the present invention, the external coagulation liquid contains 50 wt% or more and 90 wt% or less of the non-solvent of the thermoplastic resin 1 and 10 wt% or more and 50 wt% or less of the poor solvent or good solvent of the thermoplastic resin 1. A mixed solvent consisting of Furthermore, the composition of the mixed solvent may be 60% by weight or more and 80% by weight or less of the non-solvent of the thermoplastic resin 1 and 20% by weight or more and 40% by weight or less of the poor or good solvent of the thermoplastic resin 1. preferable. When the ratio of the non-solvent in the external coagulation liquid is higher than 90% by weight, a large amount of non-solvent diffuses from the external coagulation liquid in the layer of the solution 1, and the non-solvent comes into contact with the layer of the solution 2. The solution 2 to be thermally induced phase-separated is subjected to non-solvent-induced phase separation, a dense layer is formed on the outer portion of the inner layer of the manufactured hollow fiber membrane, and the pure water permeation performance is significantly lowered. If the non-solvent of the external coagulation liquid is less than 50% by weight, solidification of the layer of the solution 1 is too slow, so that the solution 1 diffuses into the external coagulation liquid or the thickness of the outer layer of the hollow fiber membrane to be manufactured is uneven. Or the dense layer is not formed on the outer surface and the blocking performance is lowered.

  In the present invention, when the discharge weight of the solution 1 is W1 and the discharge weight of the solution 2 is W2, 0.1 ≦ W1 / W2 ≦ 1. Furthermore, it is preferable that 0.2 ≦ W1 / W2 ≦ 0.8. When W1 / W2 <0.1, the volume ratio of the solution 1 layer to the solution 2 layer is small, and the non-solvent diffuses in the solution 1 layer from the external coagulation liquid before the solution 2 undergoes heat-induced phase separation. A non-solvent comes into contact with the layer, and a dense layer is formed on the outer portion of the inner layer of the produced hollow fiber membrane, so that the pure water permeation performance is significantly lowered. When W1 / W2> 1, the inner layer of the manufactured hollow fiber membrane becomes too thin, and the strength elongation performance or pressure resistance performance is significantly lowered.

  In addition to the above production method, it is useful and preferable to perform stretching in order to expand the voids of the hollow fiber membrane to improve the pure water permeation performance and to enhance the breaking strength. The stretching method is preferably higher than the glass transition point of the thermoplastic resin constituting the hollow fiber membrane and lower than the melting point, preferably 1.1 to 4 times, more preferably 1.1 to 2 times. The following draw ratio is used. Further, stretching is preferably performed in a liquid because temperature control is easy, but it may be performed in a gas such as steam. As the liquid, water is simple and preferable, but when stretching at about 90 ° C. or higher, a high boiling point liquid that does not dissolve the thermoplastic resin constituting the hollow fiber membrane can be used. On the other hand, in the case where such stretching is not performed, in many cases, the pure water permeation performance and the breaking strength are lowered as compared with the case where stretching is performed, but the breaking elongation and blocking performance are improved. Therefore, the presence / absence of stretching and the stretching ratio can be appropriately set according to the use of the hollow fiber membrane.

  By taking the conditions of the production method of the present invention, the solution 1 discharged from the outer annular port of the die is subjected to non-solvent induced phase separation, and the solution 2 discharged from the inner annular port of the die is thermally induced phase separated. It can be solidified. In the hollow fiber membrane produced by this method, the outer layer has a three-dimensional network structure and the inner layer has a spherical structure. At this time, the outer layer is a functional layer responsible for high blocking performance and high pure water permeation performance, and the inner layer is a support layer responsible for high strength elongation performance and high pure water permeation performance.

  The three-dimensional network structure that constitutes the outer layer refers to a structure in which solid content spreads in a three-dimensional network. The three-dimensional network structure has pores and voids partitioned by solid contents forming a network. In addition, it is preferable that a dense layer having pores smaller than the internal pores is formed on the outer surface, thereby improving the blocking performance. Although the average pore diameter of the outer surface varies depending on the application, it is preferably 0.005 μm or more and 0.5 μm or less, more preferably 0.007 μm or more and 0.2 μm or less. When the average pore diameter is within this range, both high pure water permeation performance and high blocking performance can be achieved. Further, it is preferable that the pore size distribution is narrow. Furthermore, dirt substances in water are less likely to clog the pores, and even when clogged, the dirt substances can be easily removed by so-called backwashing or air washing, and the hollow fiber membrane can be used continuously for a longer time.

  Next, the spherical structure constituting the inner layer refers to a structure in which a large number of spherical or substantially spherical solids are connected directly or via streak-like solids. The average diameter of the spherical structure is 0.1 μm or more and 5 μm or less, more preferably 0.5 μm or more and 2 μm or less. If it is less than 0.1 μm, the space between the spherical structures becomes small, and the high elongation performance increases, but the pure water permeation performance decreases. On the other hand, if it is larger than 5 μm, the gap between the spherical structures is increased and the pure water permeation performance is improved, but the strength elongation performance is lowered.

  The hollow fiber membrane obtained by the production method of the present invention preferably has 0.2 ≦ Th1 / Th2 ≦ 0.8 when the average thickness of the outer layer is Th1 and the average thickness of the inner layer is Th2. Preferably, 0.25 ≦ Th1 / Th2 ≦ 0.7. Furthermore, 40 μm ≦ Th1 ≦ 150 μm and 70 μm ≦ Th2 ≦ 300 μm are preferable from the viewpoint of strong elongation performance, pressure resistance performance, and pure water permeation performance, and more preferably 50 μm ≦ Th1 ≦ 120 μm and 100 μm ≦ Th2 ≦ 250 μm. Here, the average thickness of each layer is obtained by taking a photograph of the cross-section of the hollow fiber membrane using a scanning electron microscope, measuring the thickness of the layer at 10 or more, preferably 20 or more, and the number average. Can be obtained.

  The outer diameter of the hollow fiber membrane needs to be selected according to the operation method of the water treatment. First, when used in a high-pressure operation of 100 kPa or more, the outer diameter is preferably 1100 μm or more and 2000 μm or less in order to increase pressure resistance. If the pressure is less than 1100 μm, the pressure resistance is insufficient, and the hollow portion is closed during operation. Next, when used for low pressure operation of less than 100 kPa, the outer diameter is preferably 500 μm or more and less than 1100 μm in order to increase the effective membrane area per unit volume. If it is less than 500 μm, the pressure resistance is insufficient, and the flow resistance becomes high because the hollow portion is small, and the pure water permeation performance is lowered. If it is 1100 μm or more, the effective membrane area per unit volume is reduced, and the pure water permeation performance is degraded.

  Here, the outer diameter of the hollow fiber membrane is obtained by measuring the short diameter and long diameter of the ten hollow fiber membranes and averaging the numbers.

The hollow fiber membrane obtained by the production method of the present invention has the following characteristics according to the outer diameter from the viewpoint of having high pure water permeability performance, high strength elongation performance, and high pressure resistance performance suitable for water treatment applications. It is desirable to do. That is, when the outer diameter is 1100 μm or more and 2000 μm or less, the pure water permeability at 50 kPa and 25 ° C. is 0.5 m ³ / m ² · hr or more, the breaking strength is 8 MPa or more, and the breaking elongation is 80% or more. It is desirable that the withstand voltage is 200 kPa or more. Furthermore, the pure water permeation performance at 50 kPa and 25 ° C. is 0.5 m ³ / m ² · hr or more and 10 m ³ / m ² · hr or less, the breaking strength is 8 MPa or more and 30 MPa or less, and the breaking elongation is 80% or more. It is preferably 1000% or less and the pressure resistance is 200 kPa or more and 1000 kPa or less.

Further, when the outer diameter is 500 μm or more and less than 1100 μm, the pure water permeation performance at 50 kPa and 25 ° C. is 0.2 m ³ / m ² · hr or more, the breaking strength is 10 MPa or more, and the breaking elongation is 20% or more. And the pressure resistance is preferably 100 kPa or more, and more preferably 50 kPa, pure water permeability at 25 ° C. is 0.2 m ³ / m ² · hr to 5 m ³ / m ² · hr, The breaking strength is from 10 MPa to 30 MPa, the breaking elongation is from 20% to 400%, and the pressure resistance is from 100 kPa to 500 kPa.

  Hereinafter, the present invention will be described with reference to specific examples, but the present invention is not limited to these examples. Here, physical properties related to the present invention were measured by the following methods.

(1) Crystallization temperature Tc of thermoplastic resin solution
Using a DSC-6200 made by Seiko Electronics, a mixture of the same composition as the film-forming resin solution composition such as a thermoplastic resin and a solvent was sealed in a sealed DSC container, and the temperature was raised to the dissolution temperature at a heating rate of 10 ° C./min. The temperature at which the crystallization peak was observed in the process of lowering the temperature at a rate of temperature decrease of 10 ° C./min after maintaining for a minute and uniformly dissolving was defined as the crystallization temperature Tc.

(2) Outer Diameter of Hollow Fiber Membrane The short diameter and long diameter of the outer diameters of 10 hollow fiber membranes were measured and obtained by number averaging.

(3) Average layer thickness Th1 and Th2
The average thickness of the layer was determined by taking a photograph of the cross section of the hollow fiber membrane using a scanning electron microscope, measuring the thickness of any 20 layers, and averaging the number.

(4) Pure water permeation performance of hollow fiber membrane The pure water permeation performance was measured by preparing a small module having a length of about 20 cm consisting of about 1 to 10 hollow fiber membranes at a temperature of 25 ° C and a filtration differential pressure of 16 kPa. The value obtained by feeding the reverse osmosis membrane treated water under the conditions and measuring the permeated water amount (m ³ ) for a certain time was converted to unit time (hr), unit effective membrane area (m ² ), per 50 kPa. Calculated.

(5) Breaking strength and breaking elongation of hollow fiber membrane Using a tensile tester (TENSILON / RTM-100 manufactured by Toyo Baldwin Co., Ltd.), a hollow fiber membrane wetted with reverse osmosis membrane treated water was tested with a test length of 50 mm. Measurement was made at a crosshead speed of 50 mm / min with a full scale load of 5 kg.

(6) Pressure resistance of hollow fiber membrane (pressure resistance at filtration differential pressure of 150 kPa)
A metal tube miniature module having an inner diameter of 10 mm made of a single hollow fiber membrane having a length of 200 mm is prepared, and external pressure total filtration of reverse osmosis membrane treated water is performed for 5 minutes at a predetermined level of filtration differential pressure. The outer diameter of the outer diameter was measured at intervals of 50 mm, the respective (minor axis) / (major axis) were calculated, number averaged, and the roundness was determined. The roundness obtained by repeating this 10 times was number averaged to obtain the average roundness.

  Here, when a hollow fiber membrane having an outer diameter of 1100 μm or more and 2000 μm or less was used, the filtration differential pressure was set to 200 kPa. And when the obtained average roundness is 0.5 or more, it is determined that the pressure resistance performance is 200 kPa or more (◯), and when the average roundness is less than 0.5, The pressure resistance was determined to be less than 200 kPa (x).

  Moreover, when the hollow fiber membrane whose outer diameter is 500 micrometers or more and less than 1100 micrometers is used, the filtration differential pressure was 100 kPa. And when the obtained average roundness is 0.5 or more, it is determined that the pressure resistance performance is 100 kPa or more (◯), and when the average roundness is less than 0.5, The pressure resistance was determined to be less than 100 kPa (x).

Example 1
Solution 1 was prepared by mixing and dissolving 13% by weight of vinylidene fluoride homopolymer having a weight average molecular weight of 284,000, 5% by weight of polyethylene glycol having a weight average molecular weight of 20,000, 79% by weight of dimethylformamide, and 3% by weight of water. . Also, 38% by weight of vinylidene fluoride homopolymer having a weight average molecular weight of 41,000 and 62% by weight of γ-butyrolactone was dissolved at 150 ° C. to obtain a solution 2. Solution 2 had a Tc of 51 ° C.

  At 104 ° C. (= Ts), 3.5 g (= W1) of the solution 1 from the outer annular port of the triple tube structure die, 15.5 g of the solution 2 (= W2) from the inner annular port, and γ from the central tube -A 85% by weight aqueous solution of butyrolactone was simultaneously discharged and solidified in a 30% by weight aqueous solution of γ-butyrolactone at 13 ° C (= T). Then, it extended | stretched 1.5 time in 85 degreeC water. The obtained hollow fiber membrane has a three-dimensional network structure in the outer layer and a spherical structure in the inner layer. Table 1 shows the performance.

(Example 2)
Solution 1 was prepared by mixing and dissolving 13% by weight of vinylidene fluoride homopolymer having a weight average molecular weight of 284,000, 5% by weight of polyethylene glycol having a weight average molecular weight of 20,000, 79% by weight of dimethylformamide, and 3% by weight of water. . Also, 38% by weight of vinylidene fluoride homopolymer having a weight average molecular weight of 41,000 and 62% by weight of γ-butyrolactone was dissolved at 150 ° C. to obtain a solution 2. Solution 2 had a Tc of 51 ° C.

  5 g (= W1) of the solution 1 from the outer annular port of the triple tube structure die at 104 ° C. (= Ts), 14 g (= W2) of the solution 2 from the inner annular port, and 85 weight of γ-butyrolactone from the central tube % Aqueous solution was simultaneously discharged into a 32 wt% aqueous solution of γ-butyrolactone at 12 ° C. (= T) and solidified. Thereafter, the film was stretched 1.5 times in water at 80 ° C. The obtained hollow fiber membrane has a three-dimensional network structure in the outer layer and a spherical structure in the inner layer. Table 1 shows the performance.

(Example 3)
14% by weight vinylidene fluoride homopolymer having a weight average molecular weight of 284,000, 1% by weight cellulose acetate (manufactured by Eastman Chemical Co., CA435-75S: cellulose triacetate), 77% by weight N-methyl-2-pyrrolidone, poly A solution 1 was prepared by mixing and dissolving 5% by weight of oxyethylene coconut oil fatty acid sorbitan (Sanyo Kasei Co., Ltd., trade name: IONET T-20C) and 3% by weight of water. Also, 36% by weight of vinylidene fluoride homopolymer having a weight average molecular weight of 41,000 and 64% by weight of γ-butyrolactone was dissolved at 150 ° C. to obtain a solution 2. Solution 2 had a Tc of 48 ° C.

  4 g (= W1) of solution 1 from the outer annular port of the triple tube structure die at 104 ° C. (= Ts), 15 g (= W2) of solution 2 from the inner annular port, and 85 weight of γ-butyrolactone from the central tube % Aqueous solution was simultaneously discharged into a 30% by weight aqueous solution of γ-butyrolactone at 7 ° C. (= T) and solidified. Thereafter, the film was stretched 1.5 times in water at 80 ° C. The obtained hollow fiber membrane has a three-dimensional network structure in the outer layer and a spherical structure in the inner layer. Table 1 shows the performance.

Example 4
Solution 1 was prepared by mixing and dissolving 13% by weight of vinylidene fluoride homopolymer having a weight average molecular weight of 284,000, 5% by weight of polyethylene glycol having a weight average molecular weight of 20,000, and 82% by weight of dimethylformamide. Also, 38% by weight of vinylidene fluoride homopolymer having a weight average molecular weight of 41,000 and 62% by weight of γ-butyrolactone was dissolved at 150 ° C. to obtain a solution 2. Solution 2 had a Tc of 51 ° C.

  3.5 g (= W1) of the solution 1 from the outer annular port of the triple tube structure die at 104 ° C. (= Ts), 15.5 g (= W2) of the solution 2 from the inner annular port, and γ from the central tube -A 85% by weight aqueous solution of butyrolactone was simultaneously discharged and solidified in a 30% by weight aqueous solution of γ-butyrolactone at 6 ° C (= T). Thereafter, the film was stretched 1.6 times in water at 80 ° C. The obtained hollow fiber membrane has a three-dimensional network structure in the outer layer and a spherical structure in the inner layer. Table 1 shows the performance.

(Example 5)
14% by weight of vinylidene fluoride homopolymer having a weight average molecular weight of 284,000, 1% by weight of cellulose acetate (manufactured by Eastman Chemical Co., CA435-75S: cellulose triacetate), 77% by weight of N-methyl-2-pyrrolidone, poly A solution 1 was prepared by mixing and dissolving 5% by weight of oxyethylene coconut oil fatty acid sorbitan (Sanyo Kasei Co., Ltd., trade name: IONET T-20C) and 3% by weight of water. Also, 36% by weight of vinylidene fluoride homopolymer having a weight average molecular weight of 41,000 and 64% by weight of γ-butyrolactone was dissolved at 150 ° C. to obtain a solution 2. Solution 2 had a Tc of 48 ° C.

  4.0 g (= W1) of solution 1 from the outer annular port of the triple tube structure die at 104 ° C. (= Ts), 5.5 g (= W2) of solution 2 from the inner annular port, and γ from the central tube -A 85% by weight aqueous solution of butyrolactone was simultaneously discharged and solidified in a 26% by weight aqueous solution of γ-butyrolactone at 10 ° C (= T). Thereafter, the film was stretched 1.5 times in water at 80 ° C. The obtained hollow fiber membrane has a three-dimensional network structure in the outer layer and a spherical structure in the inner layer. Table 1 shows the performance.

(Example 6)
12% by weight of vinylidene fluoride homopolymer having a weight average molecular weight of 284,000, 5% by weight of cellulose acetate (Eastman Chemical Co., CA435-75S: cellulose triacetate), and 83% by weight of N-methyl-2-pyrrolidone were mixed. Solution 1 was dissolved. A solution 2 was prepared by dissolving 36% by weight of vinylidene fluoride homopolymer having a weight average molecular weight of 41,000 and 64% by weight of γ-butyrolactone at 150 ° C. Solution 2 had a Tc of 48 ° C.

  3.5 g (= W1) of the solution 1 from the outer annular port of the triple tube structure die at 104 ° C. (= Ts), 5.0 g (= W2) of the solution 2 from the inner annular port, and γ from the central tube -A 85% by weight aqueous solution of butyrolactone was simultaneously discharged into a 28% by weight aqueous solution of γ-butyrolactone at 10 ° C (= T) and solidified. Thereafter, the film was stretched 1.4 times in water at 80 ° C. The obtained hollow fiber membrane has a three-dimensional network structure in the outer layer and a spherical structure in the inner layer. Table 1 shows the performance.

(Example 7)
13.5% by weight of vinylidene fluoride homopolymer having a weight average molecular weight of 284,000, 9% by weight of cellulose acetate (Eastman Chemical Co., CA435-75S: cellulose triacetate), 76.5% by weight of N-methyl-2-pyrrolidone % Were mixed and dissolved to make Solution 1. Also, 38% by weight of vinylidene fluoride homopolymer having a weight average molecular weight of 41,000 and 62% by weight of γ-butyrolactone was dissolved at 150 ° C. to obtain a solution 2. Solution 2 had a Tc of 51 ° C.

  104 g (= Ts) of the triple tube structure mouthpiece, the outer ring mouth of the solution 1 is 2.5 g (= W1), the inner ring mouth is 4.0 g (= W2), the center pipe is γ -A 85% by weight aqueous solution of butyrolactone was simultaneously discharged into a 25% by weight aqueous solution of γ-butyrolactone at 8 ° C (= T) and solidified. The hollow fiber membrane obtained by solidification has a three-dimensional network structure in the outer layer and a spherical structure in the inner layer. Table 1 shows the performance.

(Comparative Example 1)
A hollow fiber membrane was produced under the same conditions as in Example 1 except that Ts was set to 65 ° C. However, it was difficult to discharge from the die, and a hollow fiber membrane could not be obtained.

(Comparative Example 2)
A hollow fiber membrane was produced under the same conditions as in Example 1 except that Ts was 125 ° C., but the solidification of the discharged solution was slow and a hollow fiber membrane could not be obtained.

(Comparative Example 3)
A hollow fiber membrane production was attempted under the same conditions as in Example 1 except that T = 50 ° C., but the solidification of the discharged solution was slow and a hollow fiber membrane could not be obtained.

(Comparative Example 4)
A hollow fiber membrane was produced under the same conditions as in Example 1 except that the external coagulation liquid was changed to a 60% by weight aqueous solution of γ-butyrolactone. The solution 1 diffused into the external coagulation liquid, and the resulting hollow fiber membrane was There was little outer layer.

(Comparative Example 5)
A hollow fiber membrane was produced under the same conditions as in Example 1 except that the external coagulation liquid was changed to water. The obtained hollow fiber membrane has a three-dimensional network structure in the outer layer and a spherical structure in the inner layer. Table 1 shows the performance.

(Comparative Example 6)
A hollow fiber membrane was produced under the same conditions as in Example 1 except that W1 = 1.0 and W2 = 15.5 g. The obtained hollow fiber membrane has a three-dimensional network structure in the outer layer and a spherical structure in the inner layer. Table 1 shows the performance.

(Comparative Example 7)
A hollow fiber membrane was produced under the same conditions as in Example 1 except that W1 = 12, W2 = 5 g. The obtained hollow fiber membrane has a three-dimensional network structure in the outer layer and a spherical structure in the inner layer. Table 1 shows the performance.

(Comparative Example 8)
A hollow fiber membrane was produced under the same conditions as in Example 4 except that W1 = 12, and W2 = 6 g. The obtained hollow fiber membrane has a three-dimensional network structure in the outer layer and a spherical structure in the inner layer. Table 1 shows the performance.

  The hollow fiber membrane according to the present invention has high chemical resistance and has high strength elongation performance, high pure water permeation performance, high blocking performance, and high pressure resistance performance, so that it can be effectively used in fields such as water treatment.

Claims (6)

A solution 1 in which the thermoplastic resin 1 is dissolved in a solvent, a solution 2 in which the thermoplastic resin 2 is dissolved in a solvent, and an internal coagulating liquid are respectively divided into an outer annular port, an inner annular port, and a triple tube structure die. When producing a hollow fiber membrane by simultaneously discharging into the external coagulation liquid from the central tube and solidifying, the temperature Ts of the die and the crystallization temperature Tc of the solution 2 are Tc + 20 ° C. ≦ Ts ≦ Tc + 70 ° C. The discharge weight W1 of the solution 1 and the discharge weight W2 of the solution 2 are in the range of 0.1 ≦ W1 / W2 ≦ 1, and the temperature T of the external coagulation liquid is T ≦ Tc−10 ° C. In addition, as the external coagulation liquid, 50 wt% or more and 90 wt% or less is a non-solvent of the thermoplastic resin 1 and 10 wt% or more and 50 wt% or less is a poor solvent or a good solvent of the thermoplastic resin 1. Specially using mixed solvents Method for producing a hollow fiber membrane to. The solution 1 discharged from the annular port outside the die is solidified by non-solvent induced phase separation, and the solution 2 discharged from the annular port inside the die is solidified by thermally induced phase separation. Item 2. A method for producing a hollow fiber membrane according to Item 1. The concentration of the thermoplastic resin 1 in the solution 1 is 5 wt% or more and 30 wt% or less, and the concentration of the thermoplastic resin 2 in the solution 2 is 20 wt% or more and 60 wt% or less. The method for producing a hollow fiber membrane according to claim 1 or 2. The method for producing a hollow fiber membrane according to any one of claims 1 to 3, wherein the thermoplastic resin 1 and / or the thermoplastic resin 2 is a polyvinylidene fluoride resin. A hollow fiber membrane having an outer diameter of 1100 μm or more and 2000 μm or less manufactured by the manufacturing method according to claim 1, wherein the outer layer has a three-dimensional network structure and the inner layer has a spherical structure, When the average thickness is Th1 and the average thickness of the inner layer is Th2, 0.2 ≦ Th1 / Th2 ≦ 0.8 and the pure water permeation performance at 50 kPa and 25 ° C. is 0.5 m ³ / m ^2. A hollow fiber membrane characterized by being at least hr, having a breaking strength of 8 MPa or more, a breaking elongation of 80% or more, and a pressure resistance of 200 kPa or more. A hollow fiber membrane having an outer diameter of 500 μm or more and less than 1100 μm, manufactured by the manufacturing method according to claim 1, wherein the outer layer has a three-dimensional network structure and the inner layer has a spherical structure, When the average thickness is Th1 and the average thickness of the inner layer is Th2, 0.2 ≦ Th1 / Th2 ≦ 0.8, and the pure water permeation performance at 50 kPa and 25 ° C. is 0.2 m ³ / m ^2. A hollow fiber membrane characterized by being at least hr, having a breaking strength of 10 MPa or more, a breaking elongation of 20% or more, and a pressure resistance of 100 kPa or more.