JP2006297383A - Hollow fiber membrane and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a hollow fiber membrane which uses a high chemical resistant polyfluorovinylidene resin, and has high strength-elongation capacity and high pure water permeability. <P>SOLUTION: The polyfluorovinylidene resin is dissolved in a solvent to obtain a polyfluorovinylidene resin solution. When the hollow fiber membrane having a fibrous structure oriented in the lengthwise direction of the hollow fiber membrane is manufactured by discharging the polyfluorovinylidene resin solution from a pipe sleeve into cooling liquid to cool and solidify it, the polyfluorovinylidene resin solution is held under a pressure of 0.5 MPa or higher, and at a temperature of (Tc+35°C) to (Tc+60°C) for 10 seconds or longer in a liquid supply line before the discharge from the pipe sleeve. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

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

  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 been used in the field of drinking water production, that is, in the process of water purification. 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. Furthermore, if the hollow fiber membrane has excellent pure water permeation performance, the membrane area can be reduced, and the equipment can be made compact, so that the equipment cost can be saved, and the membrane replacement cost and installation area are advantageous. Come.

  In addition, a disinfectant such as sodium hypochlorite is added to the membrane module for the purpose of sterilizing the permeated water and preventing biofouling of the membrane, and acid such as hydrochloric acid, citric acid, and oxalic acid is used for cleaning the membrane. In recent years, separation membranes using polyvinylidene fluoride resin as a highly chemical-resistant material have been developed, as the membrane may be washed with alkali such as sodium hydroxide aqueous solution, chlorine, surfactant, etc. It's being used. Moreover, in the field of water purification treatment, a problem that pathogenic microorganisms having resistance to chlorine such as Cryptosporidium have been mixed in drinking water has become apparent since the end of the 20th century, and the hollow fiber membrane is cut and the raw water is not mixed. Such a high strength and elongation characteristic is required.

  Up to now, various methods have been disclosed with the object of a hollow fiber membrane having high water permeability and high strength and high chemical resistance. For example, Patent Document 1 includes a polymer solution in which a polyvinylidene fluoride resin is dissolved in a good solvent and is extruded from a die at a temperature considerably lower than the melting point of the polyvinylidene fluoride resin, and includes a non-solvent of the polyvinylidene fluoride resin. A wet solution method is disclosed in which an asymmetric porous structure is formed by contact with a liquid by non-solvent induced phase separation. However, in the wet solution method, it is difficult to cause phase separation uniformly in the film thickness direction. There is a problem that the mechanical breaking strength is not sufficient because the film has an asymmetric three-dimensional network structure including. Further, since there are many film forming condition factors to give to the film structure and film performance, there are drawbacks that the film forming process is difficult to control and the reproducibility is poor.

  In recent years, as disclosed in Patent Document 2, inorganic fine particles and an organic liquid are melt-kneaded into a polyvinylidene fluoride resin and extruded from the die at a temperature equal to or higher than the melting point of the polyvinylidene fluoride resin to be cooled and solidified. Then, there is a melt extraction method in which a porous structure is formed by extracting an organic liquid and inorganic fine particles. In the case of the melt extraction method, it is easy to control the porosity, a macro-void is not formed and a relatively homogeneous three-dimensional network structure film is obtained and the elongation at break is high, but the break strength is not sufficient, and inorganic If the dispersibility of the fine particles is poor, defects such as pinholes may occur. Furthermore, the melt extraction method has the disadvantage that the production cost is extremely high.

  In Patent Document 3, a polyvinylidene fluoride resin and a poor solvent for the resin are contained, and a polyvinylidene fluoride resin solution having a temperature equal to or higher than the phase separation temperature is discharged into a cooling bath having a temperature equal to or lower than the phase separation temperature to be solidified. A method for obtaining a membrane is disclosed. The hollow fiber membrane obtained by this method has a spherical structure of 0.3 to 30 μm and has a relatively high strength elongation performance, but it is not always sufficient.

Further, as a hollow fiber membrane having a high breaking strength, a membrane composed of an organic polymer fibrous structure (fibril) oriented in the long axis direction of the hollow fiber membrane has been reported. For example, in Patent Document 4, microfibrils oriented in the long axis direction of a hollow fiber membrane and stacked layers oriented in the thickness direction of the hollow fiber membrane by a so-called stretch opening method in which polyethylene is melt-shaped, stretched by annealing, and stretched. A hollow fiber membrane having slit-like micropores formed from a knot portion with a lamella is disclosed. This film is excellent in breaking strength and has excellent safety characteristics because no solvent is used in the production process. However, in melt spinning, drawing is performed at a very high magnification in order to form micropores. Therefore, the elongation at break is low, and the pore diameter becomes large to obtain sufficient pure water permeation performance.

  Further, in Patent Document 5, in a spinning process in which an organic polymer solution is extruded from a nozzle, passed through the air and allowed to solidify in a coagulation bath, the water content in the air is increased, and a spinning draft (take-off speed / discharge linear speed) is set. A hollow fiber membrane is disclosed in which the outer surface and the vicinity thereof are composed of a fibrous structure highly oriented in the length direction of the hollow fiber by increasing the height. However, this method has a drawback that the fibrous structure layer that bears the breaking strength is very thin, and if the layer is not formed uniformly, stress concentrates on the thinnest part and causes thread breakage.

Japanese Patent Publication No. 1-2003 Japanese Patent No. 2899903 International Publication No. 03/031038 Pamphlet JP-A-57-66114 Japanese Patent No. 2954327

  In the present invention, in view of the problems as described above, an object is to provide a hollow fiber membrane having a high strength and elongation performance and a high pure water permeability performance using a polyvinylidene fluoride resin having high chemical resistance. And

The present invention for solving the above problems is as follows.
(1) A hollow fiber membrane made of a polyvinylidene fluoride-based resin, and a fibrous structure having a diameter of 0.9 μm or more and 3 μm or less oriented in the length direction of the hollow fiber membrane accounts for 30% or more of the entire hollow fiber membrane A hollow fiber membrane characterized by comprising:
(2) A hollow fiber membrane made of a polyvinylidene fluoride-based resin, wherein a fibrous structure having a diameter oriented in the length direction of the hollow fiber membrane of 0.9 μm or more and less than 1.4 μm is 30% or more of the entire hollow fiber membrane A hollow fiber membrane having a pure water permeation performance at 50 kPa and 25 ° C. of 0.7 m ³ / m ² · hr or more, a breaking strength of 13 MPa or more, and a breaking elongation of 150% or more.

(3) A hollow fiber membrane made of a polyvinylidene fluoride-based resin, and a fibrous structure having a diameter of 1.4 μm to 3 μm oriented in the length direction of the hollow fiber membrane accounts for 30% or more of the entire hollow fiber membrane A hollow fiber membrane having a pure water permeation performance at 50 kPa and 25 ° C. of 2.0 m ³ / m ² · hr or more, a breaking strength of 11 MPa or more, and a breaking elongation of 80% or more.
(4) The hollow fiber membrane according to any one of (1) to (3), wherein a spherical structure occupies 0.5% or more and less than 30% of the entire hollow fiber membrane.

  (5) A polyvinylidene fluoride resin is dissolved in a solvent to obtain a polyvinylidene fluoride resin solution, and the polyvinylidene fluoride resin solution is cooled and solidified by discharging the polyvinylidene fluoride resin solution from a die into a cooling liquid. When producing a hollow fiber membrane having a fibrous structure oriented in the vertical direction, the polyvinylidene fluoride resin solution is added to the polyvinylidene fluoride resin solution at any location on the liquid feed line before discharging the polyvinylidene fluoride resin solution from the die. While applying a pressure of 0.5 MPa or more, the temperature T of the polyvinylidene fluoride resin solution satisfies Tc + 35 ° C. ≦ T ≦ Tc + 60 ° C. when the crystallization temperature of the polyvinylidene fluoride resin solution is Tc. A method for producing a hollow fiber membrane, comprising a step of retaining the polyvinylidene fluoride resin solution for 10 seconds or more.

(6) When a pressure of 0.5 MPa or more is applied to the polyvinylidene fluoride resin solution at any part of the liquid feed line before the polyvinylidene fluoride resin solution is discharged from the die, the polyvinyl fluoride resin solution is pumped by two or more pumps. The method for producing a hollow fiber membrane according to (5), wherein the vinylidene fluoride resin solution is pressurized.
Consists of.

  According to the present invention, a hollow fiber membrane having very high chemical and physical durability and high pure water permeability is provided.

  The polyvinylidene fluoride resin in the present invention 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 electron micrograph (1000 times) of the cross section of the length direction of the hollow fiber membrane of this invention is shown in FIG.

  The hollow fiber membrane of the present invention is characterized by having a fibrous structure of polyvinylidene fluoride resin oriented in the length direction of the hollow fiber membrane. Here, the structure is a solid substance. In addition, the orientation in the length direction of the hollow fiber membrane is defined as the case where the angle of the acute portion of the angle formed by the length direction of the tissue and the length direction of the hollow fiber membrane is within 20 degrees, A fibrous structure is defined as a structure having an aspect ratio (length / diameter) of 3 or more. Here, the length means the longest diameter of the tissue, and the diameter means the longest diameter in the width direction of the hollow fiber membrane of the tissue.

  The diameter of the fibrous tissue needs to be 0.9 μm or more and 3 μm or less. When the diameter of the fibrous structure is less than 0.9 μm, the gap between the fibrous structures becomes small, and the pure water permeation performance is significantly lowered. When the diameter of the fibrous structure exceeds 3 μm, the gap between the fibrous structures becomes excessively large, and the blocking performance may be lowered. Moreover, if the diameter of the fibrous structure is 0.9 μm or more and 3 μm or less, high strength elongation performance and high pure water permeation performance can be obtained. However, the larger the diameter of the fibrous structure, the lower the strength elongation performance. The transmission performance tends to be high. Therefore, by setting the diameter of the fibrous structure to 0.9 μm or more and less than 1.4 μm, the high elongation performance can be preferentially increased, and by making the diameter of 1.4 μm or more and 3 μm or less, the pure water permeation performance is Can be preferentially high.

Further, the fibrous tissue may be partially bonded to a fibrous tissue other than the fibrous tissue or other tissues. In that case, what is necessary is just to determine whether it corresponds to the said fibrous structure according to the schematic diagram (1)-(3) of FIG. In FIG. 2, the dotted line is the boundary line of the tissue. When the boundary line of the tissue can be confirmed as in (1), it is determined separately. When the structure 4 determined as a fibrous structure can be confirmed as in (2), the structure corresponding to the portion extending in the length direction is also determined as the same fibrous structure (in this case, the length of the fibrous structure is 2). As shown in (3), when the structure 5 that has an aspect ratio of less than 3 but is regarded as a part of the fibrous structure is extended in the length direction, the structure 5 is regarded as a part of the fibrous structure other than the structure. In this case, all of the tissues and the tissue corresponding to the extended portion are determined as the same tissue (in this case, the length of the fibrous tissue is represented by 2).

  Further, the hollow fiber membrane of the present invention preferably has a spherical structure having a major axis of 0.9 μm or more and 3 μm or less in addition to the fibrous structure. By containing the spherical structure, voids formed between the fibrous structures are increased, and the pure water permeation performance is improved. Here, the spherical structure is a structure having a perfect circle ratio (major axis / minor axis) of 2 or less.

  In addition, the spherical structure may be partially bonded to a spherical structure other than the adjacent spherical structure, a fibrous structure, or other tissues. In this case, the major axis 7 and the minor axis 8 of the tissue considered to be a part of the spherical structure are measured by drawing a straight line (dotted line) as shown in the schematic diagrams (4) to (6) of FIG. Is 2 or less, the structure is a spherical structure. When the structure is a spherical structure, the dotted line is the boundary line of the structure.

  The tissue that does not correspond to either the fibrous tissue or the spherical tissue is a tissue that is neither the fibrous tissue nor the spherical tissue of the present invention. When two tissues appear to overlap each other in the depth direction of the electron micrograph, the tissue on the back side is determined by the visible part, and the outline of the tissue on the near side is used as the boundary line between the two tissues.

  Note that when the tissue is interrupted at the end of the electron micrograph used for the determination, there is no substantial difference in the occupation ratio even if the end is used as the boundary line of the tissue.

  In the hollow fiber membrane of the present invention, it is necessary that the fibrous structure having a diameter oriented in the length direction of the hollow fiber membrane of 0.9 μm or more and 3 μm or less occupies 30% or more of the entire hollow fiber membrane, Is 50% or more. When the fibrous structure accounts for less than 30% of the entire hollow fiber membrane, sufficient strength and elongation performance cannot be obtained. Further, the spherical structure preferably accounts for 0.5% or more and less than 30% of the entire hollow fiber membrane, and more preferably 0.5% or more and less than 10%. When the spherical structure occupies 30% or more of the entire hollow fiber membrane, sufficient strength and elongation performance may not be obtained, and when the spherical structure occupies less than 0.5% of the entire hollow fiber membrane This is because sufficient pure water permeation performance may not be obtained.

Here, the occupation ratio (%) of each structure is a magnification at which the fibrous structure and the spherical structure can be clearly confirmed using a scanning electron microscope or the like in the longitudinal direction of the hollow fiber membrane, preferably 1000 to 5000 times. Photographs are taken at arbitrary 10 or more, preferably 20 or more, and {(average of the area occupied by the tissue) / (average of the area of the entire photograph)} × 100. Here, a method of obtaining the area of the entire photograph and the area occupied by the tissue by replacing it with the corresponding weight of each photographed tissue can be preferably employed. That is, the photographed photograph is printed on paper, and the weight of the paper corresponding to the entire photograph and the weight of the paper corresponding to the tissue portion cut from the photograph are measured.

The outer diameter and the film thickness of the hollow fiber membrane are within the range that does not impair the breaking strength of the membrane. You can decide as follows. That is, when the outer diameter of the hollow fiber membrane is large, it is advantageous in terms of pressure loss, but the number of filled hollow fiber membranes is reduced, which is disadvantageous in terms of membrane area. On the other hand, when the outer diameter of the hollow fiber membrane is small, the number of filled hollow fiber membranes can be increased, which is advantageous in terms of membrane area but disadvantageous in terms of pressure loss. Further, the film thickness is preferably small as long as the breaking strength of the film is not impaired. Therefore, the outer diameter of the hollow fiber membrane is 0.3 to 3 mm, more preferably 0.5 to 2 mm, and the thickness of the hollow fiber membrane is 0% of the outer diameter.
. It is 08 to 0.4 times, more preferably 0.1 to 0.3 times.

The hollow fiber membrane of the present invention requires a pure water permeation performance at 50 kPa and 25 ° C. of 0.7 m ³ / m ² · hr or more, a breaking strength of 11 MPa or more, and a breaking elongation of 80% or more. More preferably, the pure water permeation performance at 50 kPa and 25 ° C. is 0.7 m ³ / m ² · hr or more, the breaking strength is 13 MPa or more and the elongation at break is 150% or more, or the pure water permeation performance at 50 kPa and 25 ° C. 2.0 m ³ / m ² · hr or more, breaking strength is 11 MPa or more, and breaking elongation is 80% or more.

The pure water permeation performance at 50 kPa and 25 ° C. is 0.7 m ³ / from the viewpoint of a high-performance hollow fiber membrane that has both high pure water permeation performance suitable for water treatment and high strength and elongation performance. m ² · hr to 5.0 m ³ / m ² · hr or less, breaking strength of 11 MPa to 25 MPa, and elongation at break of 80% to 500%, more preferably 50 kPa, pure water permeability at 25 ° C Is 0.7 m ³ / m ² · hr or more and 5.0 m ³ / m ² · hr or less, the breaking strength is 13 MPa or more and 25 MPa or less, and the elongation at break is 150% or more and 500% or less, or 50 kPa at 25 ° C. pure water permeability is 2.0m ³ / ^m 2 · hr or more 5.0m ³ / ^m 2 · hr or less, breaking strength 11MPa or 25MPa or less, and a breaking elongation of 80% or more 500% or more Is that it in the range.

The pure water permeation performance is measured by preparing a small module of about 20 cm in length consisting of about 1 to 10 hollow fiber membranes, and sending reverse osmosis membrane treated water under conditions of a temperature of 25 ° C. and a filtration differential pressure of 16 kPa. The value obtained by measuring the permeated water amount (m ³ ) for a certain time was calculated by converting per unit time (hr), unit effective membrane area (m ² ), and 50 kPa. The measurement method of the breaking strength and breaking elongation was measured by using a tensile tester and measuring a membrane with a test length of 50 mm wetted with reverse osmosis membrane-treated water under a full scale load of 5 kg at a crosshead speed of 50 mm / min. Asked.

In the present invention, for example, by producing a hollow fiber membrane by the production method described below, a hollow fiber membrane having high pure water permeation performance and high strength elongation performance can be obtained.
First, a polyvinylidene fluoride resin is dissolved at a relatively high concentration of about 20 to 60% by weight in a poor solvent or a good solvent of the resin at a temperature higher than the crystallization temperature. If the resin concentration is high, a hollow fiber membrane having high strength and elongation characteristics can be obtained. However, if the resin concentration is too high, the porosity of the produced hollow fiber membrane is reduced and the pure water permeation performance is lowered. If the viscosity of the adjusted resin solution is not within an appropriate range, it cannot be formed into a hollow fiber membrane.

  Here, the poor solvent means that the polyvinylidene fluoride resin cannot be dissolved by 5% by weight or more at a low temperature of less than 60 ° C., but it is 60 ° C. or more and below the melting point of the polyvinylidene fluoride resin (for example, polyvinylidene fluoride resin). Is a solvent that can be dissolved by 5 wt% or more in a high temperature region of about 178 ° C. when the polyvinylidene fluoride homopolymer is used alone. Solvent capable of dissolving 5% by weight or more of a polyvinylidene fluoride resin at a low temperature of less than 60 ° C. with respect to a poor solvent, dissolves the polyvinylidene fluoride resin to a good solvent, the melting point of the polyvinylidene fluoride resin or the boiling point of the solvent A solvent that does not swell nor swell is defined as a non-solvent.

  Here, the poor solvent of the polyvinylidene fluoride resin used in the present invention is cyclohexanone, isophorone, γ-butyrolactone, methyl isoamyl ketone, propylene carbonate, etc., medium chain length alkyl ketone, ester, organic carbonate, etc. A solvent is mentioned. Examples of good solvents include N-methyl-2-pyrrolidone, dimethyl sulfoxide, dimethylacetamide, dimethylformamide, methyl ethyl ketone, acetone, tetrahydrofuran, tetramethyl urea, trimethyl phosphate, and other lower alkyl ketones, esters, amides, and mixed solvents thereof. Can be mentioned.

  Further non-solvents include water, hexane, pentane, benzene, toluene, methanol, ethanol, carbon tetrachloride, o-dichlorobenzene, trichloroethylene, ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, butylene glycol, pentanediol. , Hexanediol, aliphatic hydrocarbons such as low molecular weight polyethylene glycol, aromatic hydrocarbons, aliphatic polyhydric alcohols, aromatic polyhydric alcohols, chlorinated hydrocarbons, or other chlorinated organic liquids and mixed solvents thereof Is mentioned.

  Here, the hollow fiber membrane of the present invention is produced by a thermally induced phase separation method in which phase separation is induced by a temperature change. In the case of producing by a thermally induced phase separation method, two types of phase separation mechanisms are mainly used. One is a liquid-liquid phase separation method in which a polymer solution that has been uniformly dissolved at high temperature is separated into a polymer rich phase and a dilute phase due to a decrease in solution dissolving ability at the time of cooling, and then the structure is fixed by crystallization. One is a solid-liquid phase separation method in which a polymer solution that is uniformly dissolved at a high temperature causes crystallization of the polymer when the temperature falls and phase-separates into a polymer solid phase and a solvent phase. The former method mainly forms a three-dimensional network structure, and the latter method forms a spherical structure mainly composed of a spherical structure.

  In the present invention, the latter phase separation mechanism is used, and it is necessary to select a resin concentration and a solvent that induce solid-liquid phase separation. In the former phase separation mechanism, it is difficult to develop a fibrous structure having a diameter of 0.9 μm or more and 3 μm or less oriented in the length direction of the hollow fiber membrane as in the present invention. This is because the polymer-rich phase forms a very fine phase by phase separation before the structure is fixed, and thus the diameter of the fibrous structure cannot be made 0.9 μm or more. For this reason, the former phase separation mechanism cannot achieve both high elongation performance and pure water permeation performance.

  Next, in the present invention, the polyvinylidene fluoride resin is dissolved in a solvent to obtain a polyvinylidene fluoride resin solution, and the polyvinylidene fluoride resin solution is discharged from the outer tube of the double tube die for hollow fiber membrane spinning. Then, the hollow portion forming liquid is obtained by cooling and solidifying in a cooling bath while discharging the hollow portion forming liquid from the tube inside the double tube type die. At this time, as shown in FIG. 3, the pressure of the resin solution is 0.5 MPa or more, more preferably 1.0 MPa or more in any part 13 of the liquid feed line 12 before the resin solution is discharged from the die 11. While maintaining this state, the temperature T of the polyvinylidene fluoride resin solution is preferably Tc + 35 ° C. ≦ T ≦ Tc + 60 ° C. when the crystallization temperature of the polyvinylidene fluoride resin solution is Tc. Has a step of retaining the polyvinylidene fluoride resin solution for 10 seconds or more, more preferably 20 seconds or more in a state where Tc + 40 ° C. ≦ T ≦ Tc + 55 ° C. is satisfied.

Although it does not specifically limit as a pressurizing means, As shown in FIG. 3, the method of installing two or more pumps 9 and 10 in the liquid feeding line 12, and pressurizing in the somewhere 13 between them is employ | adopted preferably. Here, examples of the pump include a piston pump, a plunger pump, a diaphragm pump, a wing pump, a gear pump, a rotary pump, and a screw pump, and two or more types may be used. Further, the residence time of the polyvinylidene fluoride resin solution at the location 13 can be adjusted by the discharge speed and the volume in the location 13. Since pressure is applied under conditions where crystallization is likely to occur in this step, it is presumed that a fibrous structure in which the crystal growth is anisotropic and oriented in the length direction of the hollow fiber membrane is expressed.

  Here, the temperature of the polyvinylidene fluoride resin solution at the location 13 is T> Tc + 60 ° C., or the pressure applied to the polyvinylidene fluoride resin solution at the location 13 is less than 0.5 MPa, or the polyvinyl fluoride at the location 13 If the residence time of the vinylidene chloride resin solution is less than 10 seconds, the structure of the obtained hollow fiber membrane is likely to be composed of a spherical structure, and sufficient strength and elongation performance cannot be obtained. In addition, the lower the temperature of the polyvinylidene fluoride resin solution at the location 13, the easier it is to form a fibrous structure, and the diameter of the fibrous structure tends to be small. At T <Tc + 35 ° C., the diameter of the fibrous structure Is less than 0.9 μm, or the occupation ratio of the spherical structure is less than 0.5%, sufficient pure water permeation performance cannot be obtained, the viscosity becomes high, and the discharge of the polyvinylidene fluoride resin solution from the die is possible. As a result, the hollow fiber membrane cannot be manufactured.

  Here, the crystallization temperature Tc of the polyvinylidene fluoride resin solution is defined as follows. Using a differential scanning calorimetry (DSC measurement) apparatus, a mixture of the same composition as the film forming polymer stock solution composition such as a polyvinylidene fluoride resin and a solvent is sealed in a hermetically sealed DSC container, and the melting temperature is 10 ° C./min. The temperature of the crystallization peak is observed, and the rising temperature of the crystallization peak observed in the process of lowering the temperature at a rate of temperature decrease of 10 ° C./min after maintaining for 30 minutes and uniformly dissolving is Tc.

  Next, in the cooling bath used in the present invention, since it is necessary to induce solid-liquid phase separation by thermally induced phase separation, a poor solvent having a concentration of 50 to 95% by weight lower than the crystallization temperature by 20 ° C. or more. Or the liquid mixture which consists of a good solvent and a non-solvent with a density | concentration of 5 to 50 weight% is preferable. Further, it is preferable to use the same poor solvent as the resin solution as the poor solvent. However, when a high concentration good solvent is used, solidification may not occur unless the temperature is sufficiently lowered, or the hollow fiber membrane surface may not be smooth due to slow solidification. In addition, a poor solvent and a good solvent may be mixed as long as the concentration range is not deviated. However, if a high concentration non-solvent is used, a dense layer may be formed on the outer surface of the hollow fiber membrane, and the water permeability may be significantly reduced. The hollow portion forming liquid is preferably a mixed liquid composed of a poor solvent or a good solvent having a concentration of 50 to 95% by weight and a non-solvent having a concentration of 5 to 50% by weight, like the cooling bath. Further, it is preferable to use the same poor solvent as the resin solution as the poor solvent.

  In addition to the above manufacturing steps, it is also useful and preferable to perform stretching in order to enlarge the voids between the fibrous structures to improve the pure water permeation performance and to strengthen the breaking strength. The stretching method is preferably 50 to 140 ° C, more preferably 55 to 120 ° C, still more preferably 60 to 100 ° C, preferably 1.1 to 4 times, more preferably 1.1 to 2 times. It is a draw ratio. When stretching in a low temperature atmosphere of less than 50 ° C., it is difficult to stably and uniformly stretch. When it is stretched at a temperature exceeding 140 ° C., it becomes close to the melting point of the polyvinylidene fluoride resin, so that the structural structure is melted and the voids are not enlarged and the water permeability is not improved. Further, stretching is preferably performed in a liquid because temperature control is easy, but may be performed in a gas such as steam. As the liquid, water is convenient and preferable, but when stretching at about 90 ° C. or higher, it is also possible to preferably employ a low molecular weight polyethylene glycol or the like. On the other hand, when such stretching is not performed, pure water permeation performance and breaking strength are reduced, but breaking elongation and blocking performance are improved as compared with the case of stretching. Therefore, the presence / absence of the stretching step and the stretching ratio of the stretching step can be appropriately set according to the use of the hollow fiber membrane.

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

  (1) Crystallization temperature Tc of polyvinylidene fluoride resin solution Using DSC-6200 manufactured by Seiko Denshi, a mixture of the same composition as the film forming polymer stock solution composition such as polyvinylidene fluoride resin and solvent is sealed in a sealed DSC container. The rising temperature of the crystallization peak observed in the process of lowering the temperature at a cooling rate of 10 ° C./min after raising the temperature to the dissolution temperature at a heating rate of 10 ° C./min and holding it for 30 minutes to dissolve uniformly is the crystallization temperature. Tc.

(2) Pure water permeation performance of hollow fiber membrane The pure water permeation performance was measured by preparing a small module of about 20 cm in length 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.

(3) 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.

(4) Average diameter of fibrous structure A cross section in the length direction of the hollow fiber membrane was photographed at a magnification of 3000 using a scanning electron microscope or the like, and the diameters of 10 fibrous structures were averaged.

(5) Occupancy rate of tissue Take 20 photographs of the hollow fiber membrane in the longitudinal direction at 3000 times using a scanning electron microscope or the like, and {(average of the area occupied by the tissue) / (photo The average of the entire area)} × 100. Here, the area of the entire photograph and the area occupied by the tissue were obtained by printing the photographed photograph on paper and replacing it with the weight of the paper corresponding to the entire photograph and the weight of the paper corresponding to the tissue portion cut out therefrom. .

Example 1
28% by weight of vinylidene fluoride homopolymer having a weight average molecular weight of 41,000 and 72% by weight of dimethyl sulfoxide were dissolved at 120 ° C. Tc of this vinylidene fluoride homopolymer solution was 20 ° C. The solution was pressurized to 2.0 MPa on the line between the two by installing two gear pumps, allowed to stay at 64 to 66 ° C. for 22 seconds, and then discharged from the outer pipe of the double-tube type base. A 90% by weight aqueous solution of sulfoxide was discharged from the inner tube of the double-tube type die, and solidified in a bath composed of 85% by weight aqueous solution of dimethyl sulfoxide at a temperature of 10 ° C. Thereafter, the film was stretched 1.4 times in 90 ° C. water. The performance and structure of the obtained hollow fiber membrane are shown in Table 1.

(Example 2)
28% by weight of vinylidene fluoride homopolymer having a weight average molecular weight of 41,000 and 72% by weight of dimethyl sulfoxide were dissolved at 120 ° C. Tc of this vinylidene fluoride homopolymer solution was 20 ° C. The solution was pressurized to 1.8 MPa on the line between them by installing two gear pumps, allowed to stay at 66-68 ° C. for 235 seconds, then discharged from the outer tube of the double-tube base, and simultaneously dimethyl A 90% by weight aqueous solution of sulfoxide was discharged from the inner tube of the double-tube base, and solidified in a bath composed of 85% by weight aqueous solution of dimethyl sulfoxide at a temperature of 8 ° C. Thereafter, the film was stretched 1.5 times in water at 85 ° C. The performance and structure of the obtained hollow fiber membrane are shown in Table 1.

(Example 3)
36% by weight of vinylidene fluoride homopolymer having a weight average molecular weight of 41,000 and 64% by weight of γ-butyrolactone were dissolved at 150 ° C. The vinylidene fluoride homopolymer solution had a Tc of 48 ° C. The solution was pressurized to 1.1 MPa on the line between them by installing two gear pumps, allowed to stay at 98-100 ° C. for 19 seconds, and then discharged from the outer tube of the double-tube type die. -A 85% by weight aqueous solution of butyrolactone was discharged from the inner tube of the double-tube base, and solidified in a bath at a temperature of 13 ° C consisting of an 85% by weight aqueous solution of γ-butyrolactone. Thereafter, the film was stretched 1.5 times in water at 85 ° C. The performance and structure of the obtained hollow fiber membrane are shown in Table 1.

Example 4
36% by weight of vinylidene fluoride homopolymer having a weight average molecular weight of 41,000 and 64% by weight of γ-butyrolactone were dissolved at 150 ° C. The Tc of this vinylidene fluoride homopolymer solution was 48 ° C. The solution was pressurized to 1.2 MPa on a line between the two by installing two gear pumps, allowed to stay at 101-103 ° C. for 250 seconds, and then discharged from the outer pipe of the double-tube type base. -A 85% by weight aqueous solution of butyrolactone was discharged from the inner tube of the double-tube base, and solidified in a bath at a temperature of 13 ° C consisting of an 85% by weight aqueous solution of γ-butyrolactone. Thereafter, the film was stretched 1.5 times in water at 85 ° C. The performance and structure of the obtained hollow fiber membrane are shown in Table 1.

(Example 5)
38% by weight of vinylidene fluoride homopolymer having a weight average molecular weight of 41,000 and 62% by weight of γ-butyrolactone were dissolved at 150 ° C. The vinylidene fluoride homopolymer solution had a Tc of 51 ° C. The solution was pressurized to 1.4 MPa on the line between them by installing two gear pumps, allowed to stay at 101-103 ° C. for 23 seconds, and then discharged from the outer pipe of the double-tube type base, -A 85% by weight aqueous solution of butyrolactone was discharged from the inner tube of the double-tube base, and solidified in a bath at a temperature of 13 ° C consisting of an 85% by weight aqueous solution of γ-butyrolactone. Thereafter, the film was stretched 1.5 times in water at 85 ° C. The performance and structure of the obtained hollow fiber membrane are shown in Table 1.

(Example 6)
38% by weight of vinylidene fluoride homopolymer having a weight average molecular weight of 41,000 and 62% by weight of γ-butyrolactone were dissolved at 160 ° C. The vinylidene fluoride homopolymer solution had a Tc of 51 ° C. The solution was pressurized to 1.1 MPa on the line between them by installing two gear pumps, allowed to stay at 103-105 ° C. for 19 seconds, and then discharged from the outer pipe of the double-tube type base, -A 85% by weight aqueous solution of butyrolactone was discharged from the inner tube of the double-tube base, and solidified in a bath at a temperature of 13 ° C consisting of an 85% by weight aqueous solution of γ-butyrolactone. Thereafter, the film was stretched 1.5 times in water at 85 ° C. The performance and structure of the obtained hollow fiber membrane are shown in Table 1.

(Example 7)
38% by weight of vinylidene fluoride homopolymer having a weight average molecular weight of 41,000 and 62% by weight of γ-butyrolactone were dissolved at 160 ° C. The vinylidene fluoride homopolymer solution had a Tc of 51 ° C. The solution was pressurized to 1.3 MPa on the line between them by installing two gear pumps and allowed to stay at 102-104 ° C. for 21 seconds, then discharged from the outer pipe of the double-tube base, and at the same time γ -A 85% by weight aqueous solution of butyrolactone was discharged from the inner tube of the double-tube base, and solidified in a bath at a temperature of 13 ° C consisting of an 85% by weight aqueous solution of γ-butyrolactone. Thereafter, the film was stretched 1.5 times in water at 85 ° C. The performance and structure of the obtained hollow fiber membrane are shown in Table 1.

(Example 8)
52% by weight of vinylidene fluoride homopolymer having a weight average molecular weight of 358,000 and 48% by weight of propylene carbonate were dissolved at 170 ° C. The vinylidene fluoride homopolymer solution had a Tc of 72 ° C. The solution was pressurized to 1.6 MPa on the line between them by installing two gear pumps and allowed to stay at 125-127 ° C. for 25 seconds, then discharged from the outer pipe of the double-tube base, and at the same time propylene A carbonate 100% by weight aqueous solution was discharged from the inner tube of the double-tube base, and solidified in a bath composed of 85% by weight propylene carbonate aqueous solution at a temperature of 5 ° C. Thereafter, the film was stretched 1.8 times in water at 80 ° C. The performance and structure of the obtained hollow fiber membrane are shown in Table 1.

Example 9
52% by weight of vinylidene fluoride homopolymer having a weight average molecular weight of 358,000 and 48% by weight of propylene carbonate were dissolved at 170 ° C. The vinylidene fluoride homopolymer solution had a Tc of 72 ° C. The solution was pressurized to 1.9 MPa on the line between them by installing two gear pumps, allowed to stay at 123-125 ° C. for 240 seconds, then discharged from the outer pipe of the double-tube type die, and at the same time propylene A carbonate 100% by weight aqueous solution was discharged from the inner tube of the double-tube base, and solidified in a bath composed of 85% by weight propylene carbonate aqueous solution at a temperature of 5 ° C. Thereafter, the film was stretched 1.6 times in water at 80 ° C. The performance and structure of the obtained hollow fiber membrane are shown in Table 1.

(Comparative Example 1)
A hollow fiber membrane was obtained in the same manner as in Example 3 except that the solution pressure between the two gear pumps was 0.2 MPa. The performance and structure of the obtained hollow fiber membrane are shown in Table 1.

(Comparative Example 2)
A hollow fiber membrane was obtained in the same manner as in Example 3 except that the solution temperature between the two gear pumps was 118 to 120 ° C. The performance and structure of the obtained hollow fiber membrane are shown in Table 1.

(Comparative Example 3)
A hollow fiber membrane was obtained in the same manner as in Example 3 except that the solution temperature between the two gear pumps was 79 to 81 ° C. The performance and structure of the obtained hollow fiber membrane are shown in Table 1.
(Comparative Example 4)
Except that the solution temperature between the two gear pumps was set to 73 to 75 ° C., the same procedure as in Example 3 was performed, but it was difficult to discharge from the die, and a hollow fiber membrane could not be obtained.

(Comparative Example 5)
A hollow fiber membrane was obtained in the same manner as in Example 3 except that the solution residence time between the two gear pumps was 5 seconds. The performance and structure of the obtained hollow fiber membrane are shown in Table 1.

It is a cross-sectional photograph of the length direction of the hollow fiber membrane which concerns on one embodiment of this invention. It is a schematic diagram of the fibrous structure and spherical structure oriented in the length direction of the hollow fiber membrane prescribed | regulated by this invention. It is a manufacturing process of the hollow fiber membrane which concerns on one embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Fibrous structure orientated in the length direction of hollow fiber membrane 2 Length 3 Diameter 4 Structure determined to be fibrous structure 5 Structure having an aspect ratio of less than 3 but considered to be a part of fibrous structure 6 Spherical structure 7 Long diameter 8 Short diameter 9 Pump 10 Pump 11 Cap 12 Liquid feed line 13 Of the liquid feed line, the resin solution is pressurized at a predetermined pressure or higher and kept at a predetermined temperature for a predetermined time.

Claims (6)

A hollow fiber membrane made of a polyvinylidene fluoride-based resin, and a fibrous structure having a diameter of 0.9 μm or more and 3 μm or less oriented in the length direction of the hollow fiber membrane accounts for 30% or more of the entire hollow fiber membrane A hollow fiber membrane characterized by A hollow fiber membrane made of a polyvinylidene fluoride-based resin, wherein a fibrous structure having a diameter oriented in the length direction of the hollow fiber membrane of 0.9 μm or more and less than 1.4 μm accounts for 30% or more of the entire hollow fiber membrane. A hollow fiber membrane having a pure water permeation performance at 50 kPa and 25 ° C. of 0.7 m ³ / m ² · hr or more, a breaking strength of 13 MPa or more, and a breaking elongation of 150% or more. A hollow fiber membrane made of a polyvinylidene fluoride-based resin, the fibrous structure having a diameter oriented in the length direction of the hollow fiber membrane of 1.4 μm or more and 3 μm or less occupies 30% or more of the entire hollow fiber membrane, A hollow fiber membrane having a pure water permeation performance at 50 kPa and 25 ° C. of 2.0 m ³ / m ² · hr or more, a breaking strength of 11 MPa or more, and a breaking elongation of 80% or more. The hollow fiber membrane according to any one of claims 1 to 3, wherein a spherical structure occupies 0.5% or more and less than 30% of the entire hollow fiber membrane. A polyvinylidene fluoride resin is dissolved in a solvent to obtain a polyvinylidene fluoride resin solution, and the polyvinylidene fluoride resin solution is cooled and solidified by discharging the polyvinylidene fluoride resin solution from a die into a cooling liquid, so that the length of the hollow fiber membrane is increased. In producing a hollow fiber membrane having an oriented fibrous structure, 0.5 MPa is applied to the polyvinylidene fluoride resin solution at any location on the liquid feed line before discharging the polyvinylidene fluoride resin solution from the die. While the above pressure is applied, the polyfluorination is performed in a state where the temperature T of the polyvinylidene fluoride resin solution satisfies Tc + 35 ° C. ≦ T ≦ Tc + 60 ° C. when the crystallization temperature of the polyvinylidene fluoride resin solution is Tc. A method for producing a hollow fiber membrane, comprising a step of retaining a vinylidene resin solution for 10 seconds or more. When applying a pressure of 0.5 MPa or more to the polyvinylidene fluoride resin solution at any location on the liquid feed line before discharging the polyvinylidene fluoride resin solution from the die, the polyvinylidene fluoride system is applied with two or more pumps. 6. The method for producing a hollow fiber membrane according to claim 5, wherein the resin solution is pressurized.