JP2008105016A - Hollow fiber membrane made of polyvinylidene fluoride resin, and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To make a hollow fiber membrane having a high strength/extension and a high pure water permeability by using a polyvinylidene fluoride resin having a high chemical resistance. <P>SOLUTION: The hollow fiber membrane is made by heat-treating a polyvinylidene fluoride resin made by a thermally induced phase separation method or a non-solvent induced phase separation method at a temperature in the vicinity of its melting point to cause shrinkage. The membrane has a pore volume of pores having diameters not smaller than 0.01 μm and smaller than 0.1 μm of 10<SP>-2</SP>cm<SP>3</SP>/g or smaller and a pore volume, of pores having diameters not smaller than 0.1 μm and not larger than 10 μm of 0.2 cm<SP>3</SP>/g or larger when measurement is made by employing a mercury intrusion method. The breaking strength of the hollow fiber membrane is drastically enhanced, and the breaking extension and the pure water permeability are kept at a high level by the heat treatment. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a hollow fiber membrane made of a polyvinylidene fluoride resin 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 or a hollow fiber ultrafiltration membrane made of a polyvinylidene fluoride resin used for water treatment such as waste water 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 the food industry, medicine, water production and wastewater treatment fields. 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. In recent years, separation membranes using polyvinylidene fluoride resin, which is a highly chemical-resistant material, have been developed because the membrane may be washed with an alkali such as sodium hydroxide aqueous solution, chlorine, or a surfactant. ,It's being used. Moreover, in the field of water purification treatment, 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, and the hollow fiber membrane is cut and the raw water is not mixed. Such a high strength and elongation characteristic is required.

  Various manufacturing methods have been disclosed so far, with a hollow fiber membrane having high water permeability, high strength and high chemical resistance as a subject. 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 non-solvent induced phase separation method in which an asymmetric porous structure is formed by contact with a liquid is disclosed. However, in the non-solvent induced phase separation 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.

  Furthermore, in recent years, as described 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, a melt extraction method for forming a porous structure by extracting an organic liquid and inorganic fine particles has been proposed. 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 below the phase separation temperature to be solidified. A thermally induced phase separation method for obtaining a yarn 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, a microfibril oriented in the major axis direction of a hollow fiber membrane and a stack oriented in the thickness direction of the hollow fiber membrane by a so-called stretch opening method in which polyethylene is melt-shaped, subjected to an annealing treatment and stretched. A hollow fiber membrane having slit-like micropores formed from a knot portion with a lamella is disclosed. This film has the advantage that it has excellent breaking strength and is excellent in safety 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.
Japanese Patent Publication No. 1-2003 Japanese Patent No. 2899903 International Publication No. 03/031038 Pamphlet JP-A-57-66114

  In view of the above-described problems of the prior art, the present invention provides a hollow fiber membrane that uses a polyvinylidene fluoride resin having high chemical resistance, has high strength and elongation performance, and has high pure water permeability. For the purpose.

The present invention for solving the above problems is as follows.
(1) The volume of pores having a diameter of 0.01 μm or more and less than 0.1 μm measured by mercury porosimetry is 10 ⁻² cm ³ / g or less, and the pores having a diameter of 0.1 μm or more and 10 μm or less A hollow fiber membrane made of a polyvinylidene fluoride-based resin, wherein the volume is 0.2 cm ³ / g or more.
(2) The hollow fiber membrane according to (1), wherein the hollow fiber membrane has a spherical structure.
(3) The hollow fiber membrane according to (1) or (2), wherein the spherical structure has a diameter of 0.5 μm or more and 3 μm or less.
(4) When a hollow fiber membrane made of a polyvinylidene fluoride resin produced by a thermally induced phase separation method or a non-solvent induced phase separation method is used, the melting point of the hollow fiber membrane is Tm−40 ° C. ≦ T < A method for producing a hollow fiber membrane comprising a polyvinylidene fluoride-based resin, wherein the heat treatment is performed at a temperature T satisfying Tm.
(5) The method for producing a hollow fiber membrane according to (4), wherein a shrinkage ratio in the length direction of the hollow fiber membrane during the heat treatment is 5% or more and 25% or less.
Consists of.

  According to the present invention, a hollow fiber membrane having extremely high chemical and physical durability and high pure water permeation performance can be obtained.

The present invention is a hollow fiber membrane made of a polyvinylidene fluoride-based resin, and has a pore volume of 10 ⁻² cm ³ / g or less having a diameter of 0.01 μm or more and less than 0.1 μm as measured by a mercury intrusion method. And the volume of pores having a diameter of 0.1 μm or more and 10 μm or less is 0.2 cm ³ / g or more.

  The mercury intrusion method is a method of measuring the size of the void from the pressure applied to intrude mercury and the volume of the void from the amount of intruded mercury, utilizing the fact that the surface tension of mercury is large. In this invention, what is necessary is just to perform based on JISR1655 and the method as described in an Example is employ | adopted preferably. The hollow fiber membrane of the sample is thoroughly washed with water, then freeze-dried, and further vacuum-dried and used in an absolutely dry state.

  The pores having a diameter of 0.01 μm or more and less than 0.1 μm are mainly voids in the solid part forming the hollow fiber membrane, and the pores having a diameter of 0.1 μm or more and 10 μm or less between the solid parts forming the hollow fiber membrane It is a void. Small voids in the solid part mean that the polymer molecules constituting the solid part are arranged more densely, and the hollow fiber membrane formed by such a solid part has high breaking strength and breaking elongation. Have

Furthermore, when the space | gap between the solid parts which form a hollow fiber membrane is large, a high pure water permeation performance is shown. That is, the volume of pores having a diameter of 0.01 μm or more and less than 0.1 μm is 10 ⁻² cm ³ / g or less, and the volume of pores having a diameter of 0.1 μm or more and 10 μm or less is 0.2 cm ³ / g or more. A hollow fiber membrane of 9 cm ³ / less can have both high breaking strength, breaking elongation, and pure water permeability.

The volume of pores having a diameter of 0.01 μm or more and less than 0.1 μm is preferably 10 ⁻² cm ³ / g or less, more preferably 10 ⁻³ cm ³ / g or less, still more preferably 10 ⁻⁵ cm ³ / g. g or less. When the volume of pores having a diameter of 0.01 μm or more and less than 0.1 μm exceeds 10 ⁻² cm ³ / g, sufficient breaking strength and breaking elongation cannot be obtained. The volume of pores having a diameter of 0.1 μm or more and 10 μm or less is preferably 0.2 cm ³ / g or more and 5 cm ³ / less, more preferably 0.3 cm ³ / g or more and 2 cm ³ / less, further preferably 0. It is ³ cm ³ / g or more and 1 cm ³ / or less. Blocking diameter and the volume of the following pore 10μm or 0.1 [mu] m, is less than 0.2 cm ³ / g may pure water permeability is low, when it exceeds 5 cm ³ / below the breaking strength, with elongation at break Performance may be significantly reduced.

    The hollow fiber membrane of the present invention is made of a polyvinylidene fluoride resin having high chemical resistance and physical strength. 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 hollow fiber membrane of the present invention preferably has a spherical structure with an average diameter of 0.5 μm to 3 μm. The spherical structure is a structure in which spherical solid portions are connected by sharing a part of each other, as seen in a cross section perpendicular to the length direction of the hollow fiber membrane. Since the relatively large solid part is connected to share many parts, the physical strength is high, and at the same time, the voids are increased, so that the pure water permeation performance is also improved.

  The average diameter of the spherical structure is the average diameter of the spherical solid part (average value of major axis and minor axis). The average diameter of the spherical structure is preferably 0.5 μm or more and 3 μm or less, more preferably 0.9 μm or more and 2 μm or less. If the average diameter is less than 0.5 μm, the gap between the spherical structures becomes small, and the pure water permeation performance deteriorates. On the other hand, when the thickness exceeds 3 μm, the connection between the spherical solid parts decreases, and the physical strength decreases, or the gap between the spherical structures becomes too large, and the blocking performance decreases.

  In the present invention, it is preferably mainly composed of a spherical structure, but may include other structures such as a three-dimensional network structure. In addition, a spherical solid portion is seen in the cross section perpendicular to the length direction of the hollow fiber membrane, but when the same hollow fiber membrane is observed in the cross section perpendicular to the radial direction, a columnar structure is seen, that is, in three dimensions, it is actually a spherical shape. However, even if it is a cylindrical shape, it is determined as a spherical structure in the present invention.

  Next, a preferred method for obtaining the hollow fiber membrane of the present invention will be described.

  Examples of the method for producing a hollow fiber membrane from a polyvinylidene fluoride resin include a heat-induced phase separation method, a non-solvent-induced phase separation method, a melt extraction method, and a stretch-opening method. It is necessary to use a phase separation method or a non-solvent induced phase separation method.

  Thermally induced phase separation is a phase separation in which a resin solution dissolved at high temperature is solidified by cooling, and non-solvent induced phase separation is a phase separation in which a resin solution is solidified by contacting with a nonsolvent.

  When producing a hollow fiber membrane using a heat-induced phase separation method, as a solvent for the polyvinylidene fluoride resin solution, a poor solvent for the resin is preferable, alkyl ketones such as cyclohexanone, isophorone, γ-butyrolactone, dimethyl sulfoxide, A poor solvent having a relatively high resin solubility such as an ester is particularly preferably employed.

    When a hollow fiber membrane is produced using a non-solvent induced phase separation method, the solvent for the polyvinylidene fluoride resin solution is preferably a good solvent for the resin, and the good solvent is N-methyl-2-pyrrolidone. , Dimethylacetamide, dimethylformamide, methyl ethyl ketone, acetone, tetrahydrofuran and other lower alkyl ketones, esters, amides and the like, and mixed solvents thereof. On the other hand, the non-solvent is a non-solvent for the resin, such as water, hexane, pentane, benzene, toluene, methanol, ethanol, carbon tetrachloride, o-dichlorobenzene, trichloroethylene, ethylene glycol, diethylene glycol, triethylene glycol, propylene. Aliphatic hydrocarbons such as glycol, butylene glycol, pentanediol, hexanediol, low molecular weight polyethylene glycol, aromatic hydrocarbons, aliphatic polyhydric alcohols, aromatic polyhydric alcohols, chlorinated hydrocarbons, or other chlorinations Examples thereof include organic liquids and mixed solvents thereof.

    Another embodiment of the present invention relates to a hollow fiber membrane made of a polyvinylidene fluoride resin produced by a thermally induced phase separation method or a non-solvent induced phase separation method, wherein the melting point of the hollow fiber membrane is Tm. Heat treatment is performed at a temperature T satisfying −40 ° C. ≦ T <Tm. Further, it is preferable that the heat treatment causes a shrinkage of 5% or more and 25% or less in the length direction of the hollow fiber membrane.

    Here, as described above, the melting point Tm of the hollow fiber membrane is a peak top temperature when the dry hollow fiber membrane is heated at a rate of 10 ° C./min using a DSC measuring apparatus, and is made of polyvinylidene fluoride. In the case of a hollow fiber membrane, it is around 175 ° C.

    When the hollow fiber membrane is heat-treated at a high temperature close to the melting point of the hollow fiber membrane as described above, after the micro-Brownian motion of the polymer is activated in the amorphous part in the solid part forming the hollow fiber membrane, it is partially crystallized. Or, the crystal part that melts at a temperature lower than the melting point of the hollow fiber membrane in the solid part is once melted and then recrystallized into a crystal part that melts at a higher temperature, so that the solid part contracts and the breaking strength is greatly increased. It is thought that it will improve. However, since the large voids between the solid parts hardly change during the heat treatment, it is considered that the decrease in pure water permeation performance is suppressed. Here, the crystal part melted at a temperature lower than the melting point of the hollow fiber membrane refers to the following crystal part. When the dried hollow fiber membrane is heated at a rate of 10 ° C./min using a differential scanning calorimetry (DSC measurement) device, a broad endothermic peak appears. In this endothermic peak, the crystal part caused by the tailing portion at the lower temperature side than the peak top corresponding to the melting point of the hollow fiber membrane is a crystal part that melts at a temperature lower than the melting point of the hollow fiber membrane. That is, it is considered that the crystal part is unstable in terms of energy in the whole crystal part.

    As described above, in the thermally induced phase separation method and the non-solvent induced phase separation method, the resin and the solvent can be mixed at the molecular level by using a good solvent or a poor solvent having high resin solubility. Solvent molecules are interposed between the resin molecules. Therefore, it is considered that there are more voids between molecules formed, and more crystal parts are melted at a temperature lower than the melting point of the hollow fiber membrane, that is, crystal parts that are energetically unstable. It is considered that the breaking strength is improved by heat-treating the hollow fiber membrane in such a state.

  The thermally induced phase separation method has mainly two types of phase separation mechanisms. One is a liquid-liquid phase separation method in which a resin solution that is uniformly dissolved at a high temperature is separated into a dense phase and a dilute phase due to a decrease in the solution's dissolving ability when the temperature is lowered, and the other is a resin that is uniformly dissolved at a high temperature. This is a solid-liquid phase separation method in which crystallization of a resin occurs when the solution is cooled and phase separation is performed into a polymer solid phase and a polymer dilute solution phase. In the former method, a three-dimensional network structure is mainly formed, and in the latter method, a spherical structure is formed. In the present invention, for the reason described above, it is more preferable to form a spherical structure by the latter phase separation mechanism. In the case of a spherical structure, since the solid part is bulky, it is also preferable that the gap between the solid parts is difficult to shrink and that high pure water permeation performance can be maintained. Therefore, it is preferable to select a resin concentration and a solvent that induce solid-liquid phase separation. Moreover, when cooling, it is preferable to use a cooling bath, and it is preferable to contain the non-solvent of the resin at a low concentration in order to make the resin solution the same as the solvent of the resin solution or to accelerate the solidification.

  In contrast to the heat-induced phase separation method and the non-solvent-induced phase separation method, the melt extraction method is a method in which a resin, inorganic fine particles, and an organic liquid material having low solubility in the resin are kneaded at a high temperature and then solidified after being made into a high temperature liquid material. Thereafter, inorganic fine particles and an organic liquid are extracted, and voids are formed between solid portions where molecules are collected. In this method, since the resin and the organic liquid are not mixed at the molecular level in the high-temperature liquid, no solvent molecules are interposed between the molecules of the resin when solidified. The kneading temperature is not less than the melting point of the resin. For this reason, even if the hollow fiber membrane is heat-treated at a temperature lower than the melting point after solidification, the crystalline state does not change and the breaking strength is not improved.

  The stretch opening method is a method in which a resin is melt-shaped, annealed and stretched. This method is melted without using a solvent as in the case of the melt extraction method. However, after solidifying, the crystal state is changed by stretching at a very high magnification of 3 times or more. However, this change is the promotion of crystallization, and even if heat treatment is performed at a temperature lower than the melting point, the dimensional stability below the heat treatment temperature is improved, but the crystal state is hardly changed, and the effects of the present invention such as improvement in strength are achieved. Does not develop.

  For the above reasons, it is necessary to use a thermally induced phase separation method or a non-solvent induced phase separation method as a method for producing the hollow fiber membrane of the present invention. A solid-liquid phase separation method is more preferably employed, and it is necessary to heat-treat the obtained hollow fiber membrane at a high temperature close to the melting point.

  Here, the hollow fiber membrane manufactured using the non-solvent induced phase separation method or the thermally induced phase separation method is used to expand the voids before heat treatment to improve pure water permeation performance and to enhance the breaking strength. Stretching is also preferably employed. The stretching conditions are preferably 50 to 120 ° C., more preferably 60 to 100 ° C., preferably 1.1 to 4 times, more preferably 1.1 to 2 times. If it is less than 50 ° C., it is difficult to stably and uniformly stretch, and if it exceeds 120 ° C., the hollow fiber membrane may be softened and the hollow portion may be crushed. 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 simple and preferable, but when stretching at about 90 ° C. or higher, it is also preferable to use low molecular weight polyethylene glycol or the like.

  Next, the heat treatment method will be described in detail.

The hollow fiber membrane to be heat-treated is preferably in a dry state or wetted with a resin non-solvent so as not to be dissolved by heating. The heat treatment temperature T needs to satisfy Tm−40 ° C. ≦ T <Tm. From the viewpoint of promoting recrystallization and further improving the breaking strength, Tm−25 ° C. ≦ T <Tm, more preferably Tm−15. C ≦ T <Tm. When T <Tm−40 ° C., the shrinkage of the solid part is small and the breaking strength is not sufficiently improved. Further, the shrinkage in the length direction during heat treatment is preferably 5% or more and 25% or less, more preferably 10% or more and 25% or less from the viewpoint of improving the breaking strength and maintaining the breaking elongation and pure water permeability. More preferably, it is 15% or more and 25% or less. Here, the shrinkage in the length direction is
[(Length of hollow fiber membrane before shrinkage-Length of hollow fiber membrane after shrinkage) / (Length of hollow fiber membrane before shrinkage)] x 100 (%)
Is required. When the shrinkage in the length direction is less than 5%, the breaking strength is not sufficiently improved. Here, when the shrinkage rate in the length direction is controlled to be less than 5% by bringing the hollow fiber membrane into a tension state, the shrinkage is greatly contracted in the radial direction. In this case, the breaking strength is improved, but at the same time, the breaking elongation is lowered or the hollow fiber membrane is crushed by excessive tension.

    As a means for controlling the contraction rate in the length direction, heating is performed between two drive rolls in which the rotational speed of the subsequent drive roll is decelerated from the rotational speed of the previous drive roll in accordance with the contraction rate in the manufacturing process. It is preferably adopted. At this time, one or more drive rolls or free rolls rotating at a rotational speed between the rotational speeds of the two drive rolls may be installed between the two drive rolls. The heating method is not particularly limited, but heat medium circulation, dry heat heating by heating the atmosphere with a heating wire heater or hot air, wet heat heating using steam, or high boiling point such as polyethylene glycol Heating in a high-temperature liquid using the above liquid is preferably employed. In the case of off-line, the heating temperature and the heating time may be adjusted so that the shrinkage rate in the length direction is 5% or more and 25% or less in a tensionless state. The heating method is the same as in the online case.

    The heat treatment of the film is generally known, but in the prior art, it is used for dimensional stability below the heat treatment temperature. Therefore, the heat treatment temperature is lower and the shrinkage rate is smaller than that of the present invention. In the present invention, a spherical film having essentially high physical strength and pure water permeation performance is heat-treated at a high temperature near the melting point where the shrinkage rate increases, thereby significantly increasing the physical strength and improving the pure water permeation performance. It can be maintained.

  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) Melting point Tm of hollow fiber membrane
Using a differential scanning calorimeter (DSC-6200) manufactured by Seiko Denshi Co., Ltd., the dry hollow fiber membrane was sealed in a sealed DSC container and observed in the process of increasing the temperature at a rate of temperature increase of 10 ° C./min. The peak top temperature of the peak is the melting point Tm of the hollow fiber membrane.

(2) Pure water permeation performance of hollow fiber membrane The pure water permeation performance was measured by preparing a small module of about 15 cm in length consisting of about 2 to 5 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 of the above and measuring the permeated water amount (m ³ ) for a certain time is converted per unit time (hr), unit effective membrane area (m ² ), per 50 kPa And 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 has 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) Measurement of pore diameter distribution of hollow fiber membrane by mercury porosimetry The hollow fiber membrane was absolutely dried by the following method. The hollow fiber membrane that was not heat-treated and was wet with water was freeze-dried at -20 ° C for about 50 hours, and then further vacuum-dried at room temperature for about 8 hours. The heat-treated hollow fiber membrane was vacuum dried at room temperature for about 8 hours. This absolutely dry hollow fiber membrane was cut into a length of about 5 mm, and the sample weight was weighed with an electronic balance (AW220 manufactured by Shimadzu Corporation). The pore size distribution was measured with a pore sizer 9320 manufactured by Micromeritex Corporation. The test piece is sealed in a glass cell of about 5 cm ³ attached to the device, and mercury is injected under reduced pressure. Then, it is about 4 kPa to 207 MPa (corresponding to pore diameter of about 7 nm to 350 μm) through oil in a pressure vessel attached to the device. ) Was performed by increasing the pressure within the range. The surface tension of mercury was calculated using 484 dyn / cm, and the contact angle of mercury was 141.3 °.

(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. The vinylidene fluoride homopolymer solution was discharged from the outer tube of the double-tube die, and at the same time, an aqueous solution of 90% by weight of dimethyl sulfoxide was discharged from the inner tube of the double-tube die to obtain an 85% by weight aqueous solution of dimethyl sulfoxide. After solidifying in a bath at a temperature of 10 ° C., it was washed with water and stretched 1.4 times in water at 90 ° C. The resulting hollow fiber membrane had a melting point of 170 ° C. and a spherical structure. After that, between two drive rolls with a rotational speed of 8 m / min and 6.8 m / min, the air is passed through a dry heat atmosphere with hot air at 160 ° C. and contracted at a shrinkage rate of 15% in the length direction. It was. The performance of the obtained hollow fiber membrane is shown in Table 1.

(Example 2)
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. This vinylidene fluoride homopolymer solution was discharged from the outer tube of the double-tube base, and at the same time, an aqueous solution of 85% by weight of γ-butyrolactone was discharged from the inner tube of the double-tube base to obtain 85% by weight of γ-butyrolactone. After solidifying in a bath composed of an aqueous solution of 9 ° C., it was washed with water and stretched 1.5 times in water at 85 ° C. The resulting hollow fiber membrane had a melting point of 173 ° C. and a spherical structure. After that, between two driving rolls with a rotational speed of 10 m / min and 8 m / min, it was passed through a dry heat atmosphere with hot air at 165 ° C. and contracted at a shrinkage rate of 20% in the length direction. The performance of the obtained hollow fiber membrane is shown in Table 1.

(Example 3)
The stretched hollow fiber membrane is passed between two drive rolls with rotational speeds of 10 m / min and 9 m / min through a dry heat atmosphere with hot air at 165 ° C., and the shrinkage rate is 10 in the length direction. The same procedure as in Example 2 was performed except that the shrinkage was%. The performance of the obtained hollow fiber membrane is shown in Table 1.

Example 4
The stretched hollow fiber membrane was allowed to stand in a dry heat atmosphere in which the atmosphere was set to 170 ° C. with hot air in an unstrained state, and was contracted at a contraction rate of 21% in the length direction, as in Example 2. I made it. The performance of the obtained hollow fiber membrane is shown in Table 1.

(Example 5)
Example 2 except that the stretched hollow fiber membrane was allowed to stand in a dry heat atmosphere in which the atmosphere was made 160 ° C. with hot air in a non-tensioned state and contracted at a contraction rate of 18% in the length direction. The same was done. The performance of the obtained hollow fiber membrane is shown in Table 1.

(Example 6)
Example 2 except that the stretched hollow fiber membrane was allowed to stand in a dry heat atmosphere in which the atmosphere was 140 ° C. with hot air in an unstrained state, and contracted at a contraction rate of 17% in the length direction. The same was done. The performance of the obtained hollow fiber membrane is shown in Table 1.

(Example 7)
The stretched hollow fiber membrane was left in a dry heat atmosphere with hot air at 160 ° C. in a tension state with both ends fixed, and the shrinkage in the length direction was 0%, as in Example 2. I made it. The performance of the obtained hollow fiber membrane is shown in Table 1.

(Comparative Example 1)
Table 1 shows the performance of the hollow fiber membrane obtained in the same manner as in Example 2 except that no heat treatment was performed.

(Comparative Example 2)
The stretched hollow fiber membrane was allowed to stand in a dry heat atmosphere in which the atmosphere was 190 ° C. with hot air in an unstrained state, and was contracted in the length direction at a contraction rate of 23%. I made it. The performance of the obtained hollow fiber membrane is shown in Table 1.

(Comparative Example 3)
The stretched hollow fiber membrane was allowed to stand in a dry heat atmosphere in which the atmosphere was 120 ° C. with hot air in an unstrained state, and was contracted at a contraction rate of 8% in the length direction, as in Example 2. did. The performance of the obtained hollow fiber membrane is shown in Table 1.

  The polyvinylidene fluoride-based hollow fiber membrane produced by the method of the present invention has very high chemical durability and physical durability, and has high pure water permeation performance, so that waste water treatment, water purification treatment, industrial water production, etc. It is useful as a hollow fiber membrane used in water treatment.

Claims (5)

The volume of pores having a diameter of 0.01 μm or more and less than 0.1 μm, measured by a mercury intrusion method, is 10 ⁻² cm ³ / g or less, and the volume of pores having a diameter of 0.1 μm or more and 10 μm or less is 0 A hollow fiber membrane made of a polyvinylidene fluoride-based resin, characterized by being 2 cm ³ / g or more. The hollow fiber membrane according to claim 1, wherein the hollow fiber membrane has a spherical structure. The hollow fiber membrane according to claim 1 or 2, wherein the spherical structure has a diameter of 0.5 µm to 3 µm. When a hollow fiber membrane made of a polyvinylidene fluoride resin produced by a thermally induced phase separation method or a non-solvent induced phase separation method is defined as Tm−40 ° C. ≦ T <Tm, where Tm is the melting point of the hollow fiber membrane. A method for producing a hollow fiber membrane comprising a polyvinylidene fluoride resin, characterized by heat treatment at a temperature T to be satisfied. The manufacturing method of the hollow fiber membrane of Claim 4 which makes the shrinkage | contraction rate of the length direction of the hollow fiber membrane at the time of the said heat processing 5% or more and 25% or less.