WO2007123004A1 - Porous hollow-fiber membrane of vinylidene fluoride resin and process for producing the same - Google Patents

Abstract

A porous hollow-fiber membrane which comprises a vinylidene fluoride resin having a weight-average molecular weight of 200,000-600,000 and has the following properties (A) and (B): (A) when one end of the membrane is coated with an epoxy resin having a hardness of 98, the flex life as measured under a load of 48 g is 100 or more; and (B) the ratio of the value (F) obtained by converting the water permeability as measured at a test length (L) of 200 mm under the conditions of a differential pressure of 100 kPa and a water temperature of 25°C to a value corresponding to a porosity (v) of 70% (L=200 mm; v=70%) (m/day) to the square (Pm2) of an average pore diameter (Pm) (µm ) as measured by the half-dry method, i.e., F (L=200 mm, v=70%)/Pm2, is 2,000 (m/day•µm2) or higher. The porous hollow-fiber membrane not only has excellent flex resistance (A) but has a high water permeability (B) despite the satisfactory microparticle (bacterium) rejection efficiency due to micropores. This porous vinylidene fluoride resin hollow-fiber membrane is especially suitable for use in water filtration by the membrane-separation activated sludge process (MBR method). The porous hollow-fiber membrane is produced by a process for porous hollow-fiber membrane production in which various production conditions are regulated so as to result in an increased outer diameter and an increased wall thickness.

Description

 Specification

 Vinylidene fluoride resin hollow fiber porous membrane and method for producing the same

 Technical field

 The present invention relates to a hollow fiber porous membrane (hollow fiber porous membrane) made of vinylidene fluoride resin having both (filter) water treatment performance and durability, and a method for producing the same.

 Background art

 [0002] Since vinylidene fluoride resin is excellent in weather resistance, chemical resistance, and heat resistance, its application to a porous membrane for separation is being studied. (Filtration) When used for water treatment, especially for producing water or treating sewage, a hollow fiber porous membrane that can easily increase the membrane area per volume of the filtration device is often used. Many proposals have been made including V (for example, Patent Documents 1 to 3 below).

 [0003] Further, the present inventors also melt-extruded vinylidene fluoride resin having specific molecular weight characteristics into a hollow fiber shape together with a plasticizer and a good solvent of the polyvinylidene fluoride resin. The method of extracting and removing the post plasticizer to make it porous is effective for the formation of a porous vinylidene fluoride resin porous membrane having fine pores of appropriate size and distribution and excellent mechanical strength. A series of proposals have been made (Patent Document 4, etc. below). However, there is a strong demand for further improvements in the overall performance including the filtration performance and mechanical performance required when using a hollow fiber porous membrane as a filtration membrane. In particular, in addition to a large amount of water permeability (filtration performance), it is desirable to have a pore size of an appropriate size for removing particles to be removed and to have durability to withstand long-term filtration.

[0004] As an application that requires particularly durability, a membrane separation activated sludge method (MBR method) that combines activated sludge method and membrane treatment is adopted in the fields of sewage and wastewater treatment. This involves immersing the membrane directly in an activated sludge tank and performing solid-liquid separation by suction filtration. At this time, an aeration treatment is performed using a blower, which combines oxygen supply for biological treatment and membrane surface cleaning by vibrating the membrane surface, and is always in operation. Therefore, it is effective for suppressing film fouling, but if the film itself is weak, there is a greater risk of thread breakage. Therefore, in the MBR method, a film having high strength (high resistance against load under load) is particularly required. In order to increase the strength of the film, in addition to increasing the tensile stress of the film itself, it is effective to increase the size (increase the film thickness). For this reason, in Patent Documents 5 and 6 below, high film strength is achieved by expanding dimensions. However, as the film thickness increases, the membrane permeation resistance increases and the water permeability decreases significantly. Therefore, in these hollow fiber membranes, the average pore diameter is increased to 0.5 to 1. O / zm, and the increase in membrane permeation resistance is mitigated to maintain the water permeability. The membrane used in the MBR method is expected to be a microfiltration membrane with turbidity and sterilization ability, and the above average pore size is too large.

 [0006] In addition, proposals have been made to increase the strength by including reinforcing fibers in the hollow fiber film thickness (Patent Document 7 below). However, in this case, the membrane permeation resistance and flow resistance increase and the water permeation rate tends to decrease because the film thickness is inevitably large and it is difficult to increase the inner diameter. There is a point.

 [0007] Thus, under the present circumstances, a microfiltration membrane having sufficiently high strength and high water permeability has not been realized.

 [0008] On the other hand, the present inventors described in Patent Document 8 below, "A plasticizer and a vinylidene fluoride-based resin with respect to 100 parts by weight of a vinylidene fluoride resin having a weight average molecular weight of 300,000 or more. The total amount of the good solvent for the resin is 100 to 300 parts by weight, and the proportion of the good solvent is 8 to 22% by weight, and the resulting composition is melt extruded into a hollow fiber, and the hollow part is not melted. A method for producing a vinylidene fluoride-based rosin porous hollow fiber, characterized by injecting an active gas into an inert liquid, cooling and solidifying, and then extracting a plasticizer to recover a porous hollow fiber ”Is proposed. The hollow fiber porous membrane (porous hollow fiber) formed in this way has the characteristics that the flow resistance in the hollow fiber is small due to expansion and the length dependency of the water permeability is small. Yes. However, it still does not have high durability (high strength) enough to withstand the MBR method (see Comparative Examples 1 and 2 below).

 Patent Document 1: Japanese Patent Laid-Open No. 63-296939

 Patent Document 2: WO02 / 070115A Publication

 Patent Document 3: Japanese Patent Laid-Open No. 2003-210954

 Patent Document 4: WO 2004/081109 A Publication

Patent Document 5: Japanese Patent No. 2899903 Patent Document 6: WO02 / 070115A Publication

 Patent Document 7: Japanese Unexamined Patent Application Publication No. 2002-166141

 Patent Document 8: WO2005Z032700A.

[0009] Disclosure of the Invention

 Accordingly, the main object of the present invention is to provide a highly durable polyvinyl biliary fluorinated hollow fiber porous membrane having a high durability capable of withstanding the MBR method and having a high particulate removal performance and a high water permeability. It aims at providing the manufacturing method.

[0010] The polyvinylidene fluoride based hollow fiber porous membrane of the present invention has been developed to achieve the above-mentioned object, and more specifically has a weight average molecular weight of 200,000 to 600,000. It is made of a vinylidene fluoride resin and has the following characteristics (A) and (B): (A) One end of the resin is covered with an epoxy resin with a hardness of 98 g. Porosity of water permeability at the test length L = 200mm measured under the conditions of 100 or more bending breaks measured under the load of (B) and differential pressure 100kPa, water temperature 25 ° C v = 70% and the converted value F (L = 200mm, v = 70%) (m / day), the ratio F (L = 200mm, the square value P m ² having an average pore size Pm as measured by the half dry method (mu m) = 70%) /? 111 ² is more than 2000 (111 / (1 &'111 ² ).

 [0011] In the course of research for the development of a highly durable hollow fiber porous membrane that can withstand the MBR method, the inventors of the present invention mainly ruptured the hollow fiber membrane when used in the MBR method. It was noted that this was caused by local bending fatigue of the hollow fiber membrane in the vicinity of the interface with the adhesive used to fix the yarn membrane at at least one end. That is, the above-described characteristic (A) of the hollow fiber porous membrane of the present invention means that it has high bending resistance, which is representative of durability in the MBR method or the like. On the other hand, the characteristic) shows that the standardized water permeability F (L = 200 mm, v = 70%) is large despite the small average pore diameter Pm.

[0012] Further, according to the study by the present inventors, the hollow fiber porous membrane having such characteristics (A) and (B) is further added with a stretching step in the method of Patent Document 4 or 8, By adjusting the melt extrusion rate, the residence time after extrusion and the draw ratio, and forming a hollow fiber porous membrane having an outer diameter of 1.50 to 3,000 mm and a wall thickness of 0.30 to 0.75 mm In other words, it was found that the resulting high cross-sectional area 匕 hollow fiber membrane can be effectively manufactured by increasing the thickness and further preferably expanding the diameter. That is, the vinylidene fluoride cage of the present invention The method for producing a hollow hollow fiber membrane comprises a plasticizer and a good solvent for vinylidene fluoride resin for 100 parts by weight of vinylidene fluoride resin having a weight average molecular weight of 200,000 to 600,000. The total amount is 100 to 300 parts by weight, and the proportion of the good solvent is 12.5 to 35% by weight. The resulting composition is melt extruded into a hollow fiber and introduced into an inert liquid from the outside. When the hollow fiber porous membrane is produced by drawing after cooling and solidification and further extracting the plasticizer, the melt extrusion speed, the inert liquid bath temperature, the residence time to the bath after the extrusion, and the elongation By adjusting the magnification, a hollow fiber porous membrane having an outer diameter of 1.50 to 3.OO mm and a wall thickness of 0.30 to 0.75 mm is formed.

 [0013] The hollow fiber membrane produced by such a method causes the crystallization of the vinylidene fluoride resin to be finer on the outer side and larger on the inner side by cooling the outer force of the melt-extruded hollow fiber membrane. As a result, it has a feature that it has an inclined hole diameter distribution (asymmetric hole diameter distribution) with a small hole diameter on the outer surface (near) and a large hole diameter on the inner surface (near). As a result of such an inclined pore size distribution, the effective filtration layer thickness having an average pore size Pm that governs fine particle removal performance and membrane permeation resistance is relatively small, and the hollow fiber membranes that have been made thick overall This part contributes to an increase in mechanical strength such as bending resistance, but does not contribute so much to an increase in the effective filtration layer thickness (and hence an increase in membrane permeation resistance). In addition, it is considered that the hollow fiber membrane having an inclined pore size distribution provides greater bending flexibility than a hollow fiber membrane having a uniform pore size distribution. It is understood that these factors contribute synergistically to realize the characteristics (A) and (B) of the hollow fiber porous membrane of the present invention. In relation to the above characteristic (A), the hollow fiber membrane of the present invention has a constant stress (0.136 MPa) as a result of the large cross-sectional area represented by diameter expansion and thickening as described above. It is noted that even under the conditions, the bending resistance is improved (the number of bending breaks is increased) (see Table 1 showing the results of Examples and Comparative Examples described later).

 Brief Description of Drawings

 FIG. 1 is a schematic explanatory view of a hollow fiber porous membrane sample used for a bending resistance test.

 [Fig.2] Principle of the bending resistance test equipment.

FIG. 3 is a schematic explanatory diagram of a water permeability measuring device used for evaluating the water treatment performance of the hollow fiber porous membranes obtained in Examples and Comparative Examples. BEST MODE FOR CARRYING OUT THE INVENTION

 Hereinafter, the vinylidene fluoride based hollow fiber porous membrane of the present invention will be sequentially described according to the production method of the present invention which is a preferred production method thereof.

 [0016] (Vinylidene fluoride resin)

 In the present invention, it is preferable to use a vinylidene fluoride resin having a weight average molecular weight (Mw) of 200,000 to 600,000 as the main film material. When the Mw is 200,000 or less, the mechanical strength of the obtained porous film becomes small. When the Mw is 600,000 or more, the phase separation structure between the vinylidene fluoride resin and the plasticizer becomes excessively fine, and the water permeability when the obtained hollow fiber porous membrane is used as a microfiltration membrane is small. descend.

 In the present invention, as the vinylidene fluoride-based resin, homopolymers of vinylidene fluoride, ie, poly (vinylidene fluoride) and other copolymerizable with vinylidene fluoride are used. Copolymers with monomers or mixtures thereof are used. As the monomer copolymerizable with vinylidene fluoride, one or two or more of tetrafluoroethylene, hexafluoropropylene, trifluoride styrene, trifluoride salt, ethylene, butyl fluoride, etc. may be used. it can. The vinylidene fluoride resin preferably contains 70 mol% or more of vinylidene fluoride as a structural unit. Among them, it is preferable to use a homopolymer composed of 100% by mole of vinylidene fluoride because of its high mechanical strength.

 [0018] The above-mentioned relatively high molecular weight vinylidene fluoride-based resin can be preferably obtained by emulsion polymerization or suspension polymerization, particularly preferably suspension polymerization.

 [0019] As described above, the vinylidene fluoride resin forming the hollow fiber porous membrane of the present invention has a relatively large molecular weight of 200,000 to 600,000 as described above. The difference between the original melting point Tm2 (° C) and the crystallization temperature Tc (° C) due to Tm2—Tc is less than 32 ° C, preferably less than 30 ° C. At this time, it is preferable to have crystal characteristics that suppress the growth of spherical crystals and promote the formation of a network structure.

[0020] Here, the original melting point Tm2 (° C) of the resin is the melting point Tml (° C) measured by subjecting the obtained sample resin or the resin forming the porous film to the temperature rising process by DSC as it is. C) is distinct. In other words, generally available vinylidene fluoride resin is produced by heat and mechanical history received during its production process or thermoforming process. It shows a melting point Tml (° C) different from the original melting point Tm2 (° C) of the resin, and the melting point Tm2 (° C) of the above-mentioned fluoride-redene resin is the sample obtained. It is defined as the melting point (endothermic peak temperature associated with crystal melting) found again in the DSC heating process after heat and mechanical history are removed by subjecting the resin to a predetermined heating and cooling cycle. The details of the measurement method will be described prior to the description of Examples described later.

 [0021] The condition of Tm 2-1 ^ ≤32 that represents the crystallization temperature of vinylidene fluoride resin preferably used in the present invention can be achieved even if the reduction of 1¾12 is caused by copolymerization, for example. However, in this case, there is a case where the chemical resistance of the resulting porous film tends to be lowered. Accordingly, in a preferred embodiment of the present invention, 70 to 98% by weight of a vinylidene fluoride resin having a weight average molecular weight (Mw) of 150,000 to 600,000 is used as a matrix (mainly) resin. The Mw was 1.8 times or more, preferably 2 times or more and 1.2 million or less, obtained by adding 2 to 30% by weight of a high molecular weight vinylidene fluoride resin for crystal property modification. A vinylidene fluoride-based resin mixture is used. According to such a method, the crystallization temperature Tc can be significantly increased without changing the crystal melting point of the matrix resin alone (preferably represented by Tm2 within the range of 170 to 180 ° C.). More specifically, by preferentially cooling the outer surface force of a hollow fiber membrane formed by melt extrusion by increasing Tc, the vinylidene fluoride system from the inside of the membrane to the inside surface is slower to cool than the membrane surface. It is possible to speed up the solidification of the coconut and to suppress the growth of spherical particles. Tc is preferably 143 ° C or higher.

 [0022] If the Mw of the high molecular weight vinyl fluoride-redene resin is less than 1.8 times the Mw of the matrix resin, it is difficult to sufficiently suppress the formation of the spherical particle structure. In some cases, it is difficult to disperse uniformly in the matrix resin.

 [0023] If the amount of the high molecular weight vinylidene fluoride resin is less than 2% by weight, the effect of suppressing the formation of the spherical particle structure is not sufficient. On the other hand, if it exceeds 30% by weight, the vinylidene fluoride type resin is added. There is a tendency that the phase separation structure of the resin and the plasticizer becomes excessively fine and the water permeability of the membrane decreases.

According to a preferred embodiment of the present invention, a raw material for forming a film by adding a plasticizer and a good solvent for the vinylidene fluoride resin to the above-mentioned vinylidene fluoride resin. Form a composition. [0025] (Plasticizer)

 The hollow fiber porous membrane of the present invention is mainly formed of the above-mentioned vinylidene fluoride resin, but for its production, in addition to the above-mentioned vinylidene fluoride resin, at least its plastics are used. It is preferable to use an agent as a pore-forming agent. As the plasticizer, generally, an aliphatic polyester including a dibasic acid and a glycolic acid, for example, an adipic acid-based polyester such as adipic acid monopropylene glycol-based, adipic acid 1,3-butylene glycol-based, or the like; And azelaic acid polyesters such as azelaic acid-propylene glycol type and azelaic acid 1,3 butylene glycol type.

 [0026] (good solvent)

 In order to form the hollow fiber membrane of the present invention through melt extrusion with a relatively low viscosity, it is preferable to use a good solvent of vinylidene fluoride resin in addition to the plasticizer. As this good solvent, a solvent capable of dissolving vinylidene fluoride resin in a temperature range of 20 to 250 ° C. is used. For example, N-methylpyrrolidone, dimethylformamide, dimethylacetamide, dimethylsulfoxide, methylethyl Examples include ketones, acetone, tetrahydrofuran, dioxane, ethyl acetate, propylene carbonate, cyclohexane, methyl isobutyl ketone, dimethyl phthalate, and mixed solvents thereof. Of these, N-methylpyrrolidone (NMP) is preferred for its stability at high temperatures.

[0027] (Composition)

 The raw material composition for forming a hollow fiber membrane is preferably 100 to 300 parts by weight of a plasticizer and a good solvent for vinylidene fluoride resin in a total amount of 100 parts by weight of vinylidene fluoride resin. Parts by weight, more preferably 140 to 220 parts by weight, and the ratio of the good solvent is 12.5 to 35% by weight, more preferably 15.0 to 32.5% by weight and mixed. Can be obtained.

[0028] When the total amount of the plasticizer and the good solvent is too small, the viscosity of the composition at the time of melt extrusion becomes excessive, and when it is too large, the viscosity is excessively decreased. In either case, it is difficult to obtain a porous hollow fiber having a homogeneous and moderately high porosity, and thus filtration performance (water permeability). In addition, when the proportion of the good solvent in the total amount of both is less than 12.5% by weight, the pore diameter characterized by the present invention It is difficult to obtain a uniform effect. On the other hand, when the proportion of the good solvent exceeds 35% by weight, crystallization of the resin in the cooling bath becomes insufficient, and the yarn is liable to be crushed and the formation of the hollow fiber itself becomes difficult.

 [0029] The raw material composition for producing the hollow fiber membrane used in the present invention contains various stabilizers and a small amount of additives such as a granular filler in addition to the plasticizer and good solvent described above. However, it is preferable not to include a fibrous reinforcing material. Including fibrous reinforcing material, in addition to unstable mixing and melt extrusion, the control of inner and outer diameters and wall thickness controls the strength and balances water permeability and microfiltration performance. This is because it is difficult to achieve the object of the present invention to obtain a hollow fiber porous membrane. Therefore, for the hollow fiber porous membrane product obtained by the present invention, “substantially only the strength of the vinylidene fluoride resin” also means that the porous membrane is not only the vinylidene fluoride resin. In addition to residual plasticizers and good solvents near or below detection limits, optional stabilizers or small granular fillers may be included, but no fibrous reinforcement is included. .

 [0030] (Mixing and melt extrusion)

The melt-extruded composition is generally formed into a film by extrusion through a hollow nozzle cover at a temperature of 140 to 270 ° C, preferably 150 to 200 ° C. Therefore, as long as a homogeneous composition in the above temperature range is finally obtained, mixing of the vinylidene fluoride resin, the plasticizer and the good solvent, and the molten form are arbitrary. According to one preferred embodiment for obtaining such a composition, a biaxial kneading extruder is used (preferably also having a mixture power of the main resin and the crystal characteristic modifying resin). -The redene-based resin is supplied from the upstream side of the extruder, and a mixture of a plasticizer and a good solvent is supplied downstream and is made into a homogeneous mixture before being discharged through the extruder. This twin-screw extruder can be controlled independently by dividing it into a plurality of blocks along its longitudinal direction, and appropriate temperature adjustment is made according to the contents of the passing material at each part. In obtaining a hollow fiber porous membrane having a large wall thickness and cross-sectional area, it is effective to increase the melt extrusion speed, which is the amount of raw material discharged per length (m) of the melt-extruded material. The melt extrusion speed is preferably 2.0 to 0. OgZm, more preferably 2.5 to 9. OgZm, and particularly preferably 2.5 to 6. OgZm. 2. If it is less than OgZm, the durability of the resulting film will be reduced, and if it exceeds 10. OgZm, the melt-extruded product will be crushed and hollow parts will be formed. May be impossible.

 [0031] Next, the melt-extruded hollow fiber membrane is introduced into a cooling bath, and the outer surface force is preferentially cooled to solidify and form a film. At that time, a hollow fiber membrane having an expanded diameter is obtained by cooling while injecting an inert gas such as air or nitrogen into the hollow portion of the hollow fiber membrane material. This is advantageous for obtaining a hollow fiber porous membrane with a small reduction in water permeability (Patent Document 8: WO2005 / 03700A). In addition, obtaining a hollow fiber membrane whose diameter has been expanded by blowing inert gas into the hollow portion is larger than the case of simply increasing the thickness of the hollow fiber membrane produced by the present invention. It is preferable for easily achieving the cross-sectional area 匕 and increasing the bending resistance. The inert gas injection rate as the feed rate per length (m) of the melt-extruded material is 0.7 to 6.8 mlZm, more preferably 1.2 to 3. Oml / m, especially 1.4 to 2. The range of OmlZm is preferred. If it is less than 7 mlZm, the inner diameter of the hollow portion becomes small, and the water permeability decreases due to flow resistance. If it exceeds 6.8 mlZm, the melt-extruded membrane may be punctured.

 [0032] The larger the elapsed time (air gap passage time = air gap Z melt extrusion take-off speed) until entering the inert liquid bath after extrusion, the more uneven the yarn diameter (inner / outer diameter) due to yarn fluctuation in the longitudinal direction. However, it has the effect of suppressing the formation failure of the hollow fiber porous membrane due to thread crushing, and stabilizing the yarn diameter in order to gently reduce the yarn diameter and thickness while blowing inert gas. More than 0 seconds, especially 2.0 to 7.0 seconds is preferred.

[0033] As the cooling liquid, generally a liquid which is inert (that is, non-solvent and non-reactive) to vinylidene fluoride-based resin, preferably water is used. In some cases, a good solvent for vinylidene fluoride resin (similar to that contained in the melt-extruded composition described above) that is compatible with an inert liquid (preferably NMP compatible with water) is cooled. When mixed in a proportion of 30 to 90% by weight, preferably 40 to 80% by weight in the liquid, the pore diameter on the outer surface side of the finally obtained hollow fiber porous membrane is increased, and air scrubbing It is also possible to obtain a hollow fiber porous membrane having a minimum pore size layer inside the membrane advantageous for regeneration (WO2006Z087963A1). The temperature of the cooling bath is 0 to 120 ° C., a force that can select a force in a wide temperature range, preferably 5 to 100 ° C., particularly preferably 10 to 80 ° C. [0034] (Extraction)

 The cooled and solidified film is then introduced into the extract bath and subjected to extraction removal of the plasticizer and good solvent. The extract is not particularly limited as long as it does not dissolve the polyvinylidene fluoride-based resin but can dissolve the plasticizer or good solvent. For example, polar solvents having a boiling point of about 30 to 100 ° C. such as methanol and isopropyl alcohol for alcohols and dichloromethane and 1,1,1-trichloroethane for chlorinated hydrocarbons are suitable.

[0035] (stretching)

 It is preferable to stretch the hollow fiber membrane before and / or after the extraction of the plasticizer to increase the porosity and pore diameter and improve the strength. In general, the hollow fiber membrane is preferably stretched uniaxially in the longitudinal direction of the hollow fiber membrane by a pair of rollers having different peripheral speeds. This is because, in order to harmonize the porosity and the strong elongation of the vinylidene fluoride resin hollow fiber porous membrane of the present invention, the stretched fibril (fiber) portion and the unstretched node ( This is because it has been found that a fine structure in which sections) appear alternately is preferable. Stretching is a powerful means for adjusting the thickness when obtaining a hollow fiber membrane having a large cross-sectional area according to the present invention, and is also effective for obtaining a high-strength hollow fiber membrane. The draw ratio is suitably about 1.2 to 4.0 times, particularly about 1.4 to 3.0 times. If the draw ratio is too low, the relaxation ratio cannot be increased, and it is difficult to obtain the effect of improving the water permeability due to the relaxation. On the other hand, when the draw ratio is excessive, the tendency of the hollow fiber membrane to break increases. The stretching temperature is preferably 25 to 90 ° C, particularly 45 to 80 ° C. If the stretching temperature is too low, the stretching becomes non-uniform and the hollow fiber membrane is easily broken. On the other hand, if the stretching temperature is too high, the pores will not advance even if the stretching ratio is increased, and even if the stretching is relaxed, it is difficult to obtain the effect of improving the water permeability. In order to improve the stretching operability, heat treatment is performed in advance at a temperature in the range of 80 to 160 ° C., preferably 100 to 140 ° C. for 1 second to 18000 seconds, preferably 3 seconds to 3600 seconds, to improve the crystallinity. Also preferred to increase.

[0036] (relaxation treatment)

The hollow fiber membrane after the stretching treatment is preferably subjected to relaxation treatment. The relaxation is preferably performed in at least two stages in a non-wetting atmosphere with respect to the vinylidene fluoride resin (PCTZJP2006Z318028 specification). The non-wetting atmosphere has a surface tension (JIS K6768) that is greater than the wetting tension of vinylidene fluoride resin near room temperature. It is composed of a non-wetting liquid, typically water or almost any gas including air, especially a non-condensable gas near room temperature, or the vapor of the non-wetting liquid. In order to achieve a large relaxation effect at a relatively low temperature for a short time, treatment with a non-wetting liquid with a large heat capacity and heat transfer coefficient (wet heat treatment) is preferably used, but if the relaxation treatment temperature is raised, A treatment in a heated gas (or steam) (dry heat treatment) is also preferably used. 25 ~ 100 ° C, especially 50 ~ 100 ° C underwater heat treatment and Z or 80 ~ 160 ° C in terms of giving good permeability and good working environment through a large relaxation rate Dry heat treatment with air (or water vapor) is preferably used. In particular, a two-stage relaxation treatment in which the first-stage relaxation is a wet heat treatment in water and the second-stage relaxation is a wet heat treatment in water or a dry heat treatment in air (or water vapor) is preferably used.

 [0037] The relaxation treatment in each stage is performed by stretching the previously obtained non-wetting, preferably heated atmosphere, disposed between the upstream roller and the downstream roller where the peripheral speed is gradually reduced. It is obtained by passing through a hollow fiber porous membrane. (1 (downstream roller circumferential speed Z upstream roller circumferential speed)) The relaxation rate determined by X 100 (%) is preferably 2 to 20% at each stage, and the total relaxation rate is preferably about 4 to 30%. If the relaxation rate at each stage is less than 2%, it is difficult to obtain the desired effect of improving water permeability, which means that the meaning of multistage relaxation is insufficient. The same applies when the total relaxation rate is less than 4%. On the other hand, if the step relaxation rate exceeds 20%, or the total relaxation rate exceeds 30%, it is difficult to achieve the force depending on the draw ratio in the previous process, or is the water permeability improvement effect saturated even if realized? It is preferable because it is lowered.

 [0038] The relaxation processing time in each stage may be short or long as long as a desired relaxation rate is obtained. In general, the force is about 5 seconds to 1 minute.

 [0039] The effect of the multistage relaxation treatment described above is a remarkable effect that the water permeability of the obtained hollow fiber porous membrane is increased, but the pore size distribution does not change so much and the porosity tends to be slightly lowered. . The thickness of the hollow fiber membrane slightly increases, and the inner diameter and outer diameter tend to increase.

 [0040] After the multistage relaxation treatment according to the present invention, a heat treatment with a relaxation rate of 0%, that is, a heat setting treatment may be performed.

 [0041] (Vinylidene fluoride resin hollow fiber porous membrane)

One characteristic of the hollow fiber porous membrane of the present invention obtained by force is that it has a large number of bending breaks. It is characterized by having excellent bending resistance (characteristic (A)) as represented.

[0042] The property (A) (number of bending breaks) described in the present specification is basically based on a value measured in accordance with ASTM-D2176. More specifically, a hollow fiber porous membrane sample was cut to a length of 100 mm, and its lower end was sealed with about 10 mm by heat sealing, and then the lower end was epoxy resin (manufactured by SUNREC Co., Ltd. RN5 ”) and cured completely, then the epoxy resin was cut off, and the bottom edge was measured with a type A durometer (length 10mm x width 20mm x height 8mm according to J IS K6253) A bending line fracture sample as shown in Fig. 1 fixed with an epoxy resin having an A hardness of 98 was obtained. This is then applied to the rotating lower fixture of the bending tester (“MIT-D” manufactured by Toyo Seiki Co., Ltd.) that conforms to ASTM-D2176 in the configuration shown in FIG. The upper extension is fixed with the upper fixing jig, and the weight is set so that a load of 48g'f (= weight weight upper fixing jig weight) is applied to the hollow fiber sample set to a test length of 50mm. Was placed (placed inside the device). In this state, rotate the lower rotating jig to ± 45 ° to the left and right (total 90 °) at a speed of 200 times Z, bending the sample hollow fiber located at the center of rotation to the contact area with the epoxy resin. Gave. As a result, the number of bends until rupture was measured as one for each one-side bend, and the number was determined as the number of bend ruptures.

[0043] Further, in order to eliminate the influence of the difference in the cross-sectional area of the sample, the weight was changed so that the stress calculated as stress = load Z cross-sectional area was constant at 0.136 MPa, and the bending fracture was performed under the constant stress. The number of times was also measured.

 [0044] The hollow fiber porous membrane of the present invention has a number of bending breaks of 100 times or more, preferably 1000 times or more, more preferably 5000 times or more, more preferably 48 times or less under a load of 48 g measured as described above. Is characterized in that the number of bending breaks under a constant stress of 0.136 MPa is 10 times or more, more preferably 50 times or more, and still more preferably 100 times or more.

 [0045] (B) The hollow fiber porous membrane of the present invention shows a large amount of water permeability despite the small average pore diameter.

Another feature is that the hole has good communication. This feature is that the permeability V (70 kPa, L = 200 mm) measured at a differential pressure of 100 kPa and a water temperature of 25 ° C, converted to a porosity of v = 70% F ( L = 200mm, v = 70%) (mZday) and the ratio of the mean pore diameter Pm (μm) measured by the half-dry method to the square value Pm ² F (L = 200mm, v = 70%) / Pm ² is represented by 2000 (m / day / zm ² ) or more. More specifically, if the relationship between the water permeability and the (average) pore diameter follows the Hagen-Poiseuille rule, the water permeability force S (average) is proportional to the fourth power of the pore diameter, while the number of holes is 2 of the average pore diameter. Therefore, the water permeability is proportional to the square of the (average) pore diameter. According to the present inventors, this square law does not hold when the porosity (V) is different, but since an experimental result in which the water permeability is proportional to the porosity is obtained, a constant porosity is obtained. (V = 70% in the present invention), the square law between the water permeability and the average pore diameter is satisfactorily established, and the above-mentioned F (L = 200 mm, v = 70%) ZPm ² was found to be a good indicator of water permeation performance, taking into account the ability to remove fine particles based on good pore connectivity in the porous membrane. The characteristic (B) of the hollow fiber porous membrane of the present invention is based on this finding.

[0046] The hollow fiber porous membrane of the present invention preferably has an average pore diameter Pm of 0.05-0.20 μm, particularly 0.08 to 0.18 / zm by a half dry method. If the average pore size Pm is less than 0.05 m, the water permeability of the membrane will decrease. On the other hand, if it exceeds 0.20 m, the ability of the membrane to remove fine particles (contaminants or bacteria) may decrease. Similarly, the maximum diameter Pmax force by the bubble point method SO. 15 to 0.50 111, especially 0.20 to 0.40 m, is preferable. If the maximum pore size Pmax is less than 0.15 m, the water permeability of the membrane will decrease. On the other hand, if it exceeds 0.50 / zm, the membrane's ability to remove fine particles (contaminants or bacteria) may decrease.

[0047] Other general characteristics of the hollow fiber porous membrane obtained by the present invention include an outer diameter of 1.50 to 3.00 mm, preferably 1.75 to 2.5 mm, and a wall thickness. ~0. 75 mm, preferably 0. 35-0. 60 mm, empty mosquito larva and rate (v) power 55-90 _^0/0, preferably ί or 60 to 85 _^0/0, particularly preferably ί or 65-80%, tensile Properties with a strength of 6 MPa or more and a breaking elongation of 5% or more can be obtained.

 [0048] In addition, the hollow fiber porous membrane of the present invention obtained through the stretching process has a fine structure in which a crystal orientation part and a crystal non-orientation part (random orientation part) are recognized by an X-ray diffraction method. It is understood that this corresponds to the stretched fibril part and the unstretched node part, respectively.

[0049] Further, the hollow fiber porous membrane of the present invention obtained by cooling from the outside of a hollow fiber-like melt-extruded product of vinylidene fluoride resin having an appropriate crystallinity is made of vinylidene fluoride resin. Finer crystallization occurs on the outside and larger on the inside. As a result, it has an asymmetrical hole size distribution in which the inner outer surface has a larger hole diameter than the outer outer surface hole diameter, and the outer outer surface (near) has a smaller hole diameter and the inner outer surface (near) has a larger hole diameter. It has a feature. In the present invention, the preferred graded pore size distribution is such that the ratio of the inner outer surface average pore size to the outer outer surface average pore size measured by the method described later is 1.5 or more, particularly about 1.5 to 5.0. It is expressed by that.

[0050] [Example]

 Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples. The characteristics other than the above (A) described in this specification, including the following description, are based on the measured values by the following method.

 [0051] (Weight average molecular weight (Mw))

 A GPC device “GPC-900” manufactured by JASCO Corporation was used, “Shode x KD—806M” manufactured by Showa Denko Co., Ltd. as a column, “Shodex KD—G” used as a precolumn, NMP as a solvent, and a temperature of 40. The molecular weight was measured as a polystyrene-equivalent molecular weight by gel permeation chromatography (GPC) method at C, flow rate of lOmLZ.

 [0052] (Crystal melting point Tml, Tm2 and crystallization temperature Tc)

 Using DSC7, a differential scanning calorimeter manufactured by PerkinElmer Co., Ltd., set sample oil lOmg in the measuring cell, and in a nitrogen gas atmosphere at a temperature increase rate of 30 ° C to 10 ° CZ at 250 ° C. Then, the temperature was maintained at 250 ° C for 1 minute, and then the temperature was decreased from 250 ° C to 30 ° C at a rate of 10 ° CZ to obtain a DSC curve. In the DSC curve, the endothermic peak velocity in the temperature rising process was defined as the melting point Tml (° C), and the exothermic peak temperature in the temperature decreasing process was defined as the crystallization temperature Tc (° C). Subsequently, after maintaining at a temperature of 30 ° C for 1 minute, the temperature was raised again from 30 ° C to 250 ° C at a rate of 10 ° CZ, and the DSC curve was measured. The endothermic peak temperature in the reheated DSC curve was defined as the original resin melting point Tm2 (° C) that defines the crystal characteristics of the vinylidene fluoride resin of the present invention.

 [0053] (Porosity)

Calculate the apparent volume V (cm 2) of the hollow fiber membrane by measuring the length, outer diameter and inner diameter of the hollow fiber membrane, then measure the weight W (g) of the hollow fiber membrane and The rate was determined: [Number 1]

 Porosity (%) = (1— WZ (VX p)) X 100

p: Specific gravity of PVDF (= 1. 78g / cm ² ) ₀

 [0054] (Water permeability)

で表 わす。 Sample length L (see Fig. 3) = 200mm or 800mm hollow sample porous fiber membrane is immersed in ethanol for 15 minutes, then immersed in pure water for 15 minutes, wetted, water temperature 25 ° C, differential pressure 100k Pa The amount of water per day (m ³ / day) measured in (1) was divided by the membrane area (m ² ) of the hollow fiber porous membrane (= calculated as outer diameter X π X test length L). For example, a sample with a test length L = 200 mm is written as F (100 kPa, L = 200 mm), etc., and the unit is 1117 (1 & (

It expresses with.

 [0055] For the water permeability F (100 kPa, L = 200 mm) at the test length L = 200 mm, the converted value F (L = 200 mm, v = 70%) to the porosity v = 70%

 [Equation 2]

 F (L = 200mm, v = 70%)

 = F (100kPa, L = 200mm) X (70 (%) / v (%))

The ratio of the average pore diameter to the square of Pm F (L = 200 mm, v = 70%) / Pm ² (unit: mZday μ m ² ) is calculated as follows. Obtained as a bundle and evaluated the water permeation performance in consideration of the ability to remove fine particles.

[0056] (Maximum pore size (Pmax), average pore size (Pm) and minimum pore size (Pmin))

It was determined by the bubble point Z half-dry method (measurement method of maximum pore size Pmax and pore size distribution suitable for porous membranes, especially hollow fiber porous membranes as defined in ASTM-F316-86 and ASTM · E 1294-86). More specifically, in the bubble point method, pressurized air with gradually increasing pressure is fed into a hollow fiber porous membrane sample immersed in the test solution, and the first bubble generation point (bubble point) from the test solution is measured. Air pressure force Obtain the maximum pore size Pmax (m) of the sample membrane. In the half-dry method, the wetting flow rate curve (WET FLOW CURVE) when the hollow fiber porous membrane sample is wet with the test solution and the dry flow rate curve (DRY FL OW CURVE) with a 1Z2 slope curve (HALF DRY) Calculate the average pore size Pm m) of the sample membrane from the air pressure at the point where it intersects with (CURVE). Wet flow curve and dry flow curve The hole diameter determined from the air pressure at the line coincidence point was determined as the minimum hole diameter (Pin gm). The values stated in this document are “Palm Porometer CFP-2000AEXJ” manufactured by Porous Materials, Inc. as the measuring instrument, and perfluoropolyester (trade name “Galwick”) as the test solution. Based on the measurement results of the hollow fiber membrane samples.

[0057] (Measurement of outer surface average pore diameter by SEM observation)

 Using a scanning electron microscope (SEM), the outer and inner outer surfaces of the hollow fiber porous membrane were photographed at an observation magnification of 5000 times. The obtained SEM photograph (observation range is about 19 m square) was binarized using the “nexusNewQube Version4.01” manufactured by Nexus Co., Ltd. After classifying, the equivalent circle diameter D (the diameter of the circle when the area is assumed to be given by a circle) of all the voids equal to or larger than the minimum pore diameter Pmin obtained by the half dry method within the observation range and its The number n was measured, and the number average value (= ∑nDZ∑n) was defined as the average pore diameter of each outer surface. The reason why the voids having D less than the minimum pore size Pmin by the half dry method are excluded is that these are not effective voids for filtration forming the communication holes (for example, unevenness of the rosin phase). It is.

 [0058] (Tensile test)

 Using a tensile tester (“RTM-100” manufactured by Toyo Baldwin) in an atmosphere with a temperature of 23 ° C and a relative humidity of 50% under the conditions of an initial sample length of 100 mm and a crosshead speed of 200 mmZ The tensile strength (maximum tensile strength (unit: N)) and maximum tensile stress (unit: MPa) were determined.

 [Example 1]

Polyvinylidene fluoride (PVDF) (powder) with a weight average molecular weight (Mw) of 4.12 X 10 ⁵ and polyvinylidene fluoride (PVDF) for crystal property modification with Mw of 9.36 X 10 ⁵ (Powder) was mixed using a Henschel mixer in proportions of 95% by weight and 5% by weight, respectively, to obtain a PVDF mixture having Mw of 4.38 × 10 ⁵ .

[0060] Adipic acid polyester plasticizer (“PN-150” manufactured by Asahi Denka Kogyo Co., Ltd.) as the aliphatic polyester and N-methylpyrrolidone (NMP) as the solvent, 82.5 wt. ⁰ / oZl 7 The mixture was stirred and mixed at room temperature at a ratio of 5% by weight to obtain a liquid agent (plasticizer / solvent) mixture. [0061] Co-rotating and rotating in the same direction, using a twin-screw extruder (“BT-30” manufactured by Plastics Engineering Laboratory Co., Ltd., screw diameter 30 mm, LZD = 48) at a position 80 mm from the most upstream part of the cylinder The supplied powder supply force also supplies the PVDF mixture, and the cylinder uppermost flow force is the liquid supply (plasticizer + solvent) mixture heated to 160 ° C from the liquid supply provided at the position of 480mm. Z liquid mixture = 6Z10.8 (weight ratio) is supplied and kneaded at a barrel temperature of 220 ° C. The mixture is discharged from a nozzle with a circular slit with an outer diameter of 7mm and an inner diameter of 5mm. 16.6gZ Extruded into a hollow fiber in minutes. At this time, air was injected into the hollow portion of the yarn at a flow rate of 8. OmLZ through a vent hole provided in the center of the nozzle. The extruded mixture is maintained in a molten state at a temperature of 40 ° C. and is led to a water cooling bath having a water surface at a position 280 mm away from the nozzle (ie, the air gap is 280 mm). Elapsed time to enter the cooling bath: 3.5 seconds, dwell time in the cooling bath: about 6 seconds), 4. After taking up at a take-up speed of 8mZ, this is applied to a force sensor with a circumference of about lm. The first intermediate formed body was obtained by scraping. The melt extrusion speed was 3.5 gZm, and the amount of air per discharge length (inert gas injection speed) was 1.7 mlZm.

 [0062] Next, the first intermediate molded body was immersed in dichloromethane at room temperature for 30 minutes while being vibrated, and then the dichloromethane was replaced with a new one and immersed again under the same conditions to remove the plasticizer and the solvent. Extraction was then performed in an oven at a temperature of 120 ° C. for 1 hour to remove dichloromethane and heat treatment was performed to obtain a second intermediate molded body.

 [0063] Next, the second intermediate formed body was passed through a 60 ° C water bath with a first roll speed of 20. OmZ, and the second roll speed was 37. OmZ. Stretched 1.85 times in the longitudinal direction. Next, the sample was passed through a warm water bath controlled at a temperature of 90 ° C., and the third roll speed was reduced to 3 4. OmZ, thereby performing 8% relaxation treatment in warm water. Furthermore, 4% relaxation treatment was performed in the dry heat tank by passing it through a dry heat tank (2. Om length) controlled to a space temperature of 140 ° C and dropping the fourth roll speed to 32.7 mZ. . This was wound up to obtain a polyvinylidene fluoride hollow fiber porous membrane (third molded body) according to the method of the present invention.

[0064] The obtained polyvinylidene fluoride hollow fiber porous membrane has an outer diameter of 2.023 mm, an inner diameter of 1.218 mm, a film thickness of 0.402 mm, a porosity of 73.1%, and a differential pressure. l Pure water permeation rate at OOkPa F (L, 100kPa) i, test length L = 200mm [Koo! Satoshi F (L = 200mm, 100kPa) = 38. Om / day, the porosity 70% equivalent value F (L = 200mm, v = 70%) = 36.4m / day, test length L = 800mm F (L = 800mm, lOOkPa) = 36.5mZday, test length Maximum pore size at 10 mm Pmax (lOmm) = 0.213 μm, average pore size Pm = 0.103 μm, minimum pore size Pmin = 0.080 ^ m, outer surface average pore size by SEM observation = 0.193 / ζ πι, inner outer surface average pore diameter = 0.381 m, and an inclined pore size distribution was confirmed in which the pore diameter from the inside to the inner outer surface and its vicinity was larger than that of the outer outer surface and its vicinity. Pure water permeation flux F (L = 200mm, v = 70%) / Pm ² = 3464, tensile stress 9.3MPa, tensile strength 19.0N, flexural breakage (under load 48g) = 32000, flexural breakage Number (under stress 0.136 MPa) = 275 times.

 [0065] Production conditions and physical properties of the obtained polyvinylidene fluoride hollow fiber porous membrane are shown together in Table 1 below together with the results of the following Examples and Comparative Examples.

 [0066] (Example 2)

 Except for changing the discharge amount of nozzle force to 27.lgZ, water bath temperature to 25 ° C, air flow rate from the air vent in the center of the nozzle to 12.4mlZ, and take-up speed to 8.OmZ A hollow fiber porous membrane was obtained in the same manner as in 1.

[0067] (Example 3)

 The air volume is the same as in Example 1 except that the discharge amount of the nozzle force is 21.6 gZ, the air flow rate of the vent hole force provided at the center of the nozzle is 11. lmlZ, and the take-up speed is 8. OmZ. A thread porous membrane was obtained.

[Example 4]

 Except for changing the discharge amount of nozzle force to 22.8 gZ, water bath temperature to 25 ° C, air flow rate from the air vent provided in the center of the nozzle to 11.5 mlZ, and take-up speed to 5. OmZ. A hollow fiber porous membrane was obtained in the same manner as in 1.

[0069] (Example 5)

 Hollow fiber as in Example 1, except that the discharge amount of the nozzle force is 18. OgZ, the air flow rate of the vent hole provided in the center of the nozzle is 4. lmlZ, and the take-up speed is 5. OmZ. A porous membrane was obtained.

[Example 6] Mixture AZ mixture B = 6Z10 (weight), discharge rate from nozzle is 23.8gZ, air flow rate at the center of nozzle is changed to 11.3mlZ, take-up speed is changed to 7.OmZ Obtained a hollow fiber porous membrane in the same manner as in Example 1.

[Example 7]

 Mixture AZ mixture B = 6Z10 (weight), discharge rate from nozzle is changed to 27. OgZ, air flow rate of vent hole provided at the center of nozzle is changed to 8.3 mlZ, take-up speed is changed to 5. OmZ A hollow fiber porous membrane was obtained in the same manner as Example 1 except for the above.

[Example 8]

 Discharge amount of nozzle force is 10.3gZ, water bath temperature is 70 ° C, air flow rate from the air vent provided in the center of the nozzle is 4.6mlZ, take-up speed is 3.OmZ, draw ratio 2.4 times A hollow fiber porous membrane was obtained in the same manner as in Example 1 except that the one-step relaxation ratio was changed to 12%.

[0073] (Example 9)

 Mixture AZ mixture B = 6Z8 (weight), discharge rate from nozzle is changed to 27. OgZ, air flow rate of vent hole provided in the center of nozzle is changed to 8.3 mlZ, and take-up speed is changed to 5. OmZ A hollow fiber porous membrane was obtained in the same manner as Example 1 except for the above.

[0074] (Comparative Example 1)

 The mixing ratio of adipic acid-based polyester plasticizer (“PN-150” manufactured by Asahi Denki Kogyo Co., Ltd.) and N-methylpyrrolidone (NMP) is 72.5 / 27.5 (weight ratio). Discharge rate is 8.5gZ, water bath temperature is 50 ° C, air flow rate from the vent in the center of the nozzle is 5. Oml Z min, take-up speed is 5. OmZ min, draw ratio is 2.0 times, one step A hollow fiber porous membrane was obtained in the same manner as in Example 1 except that the relaxation ratio was 10% and the two-stage relaxation temperature was changed to 110 ° C.

[0075] (Comparative Example 2)

 Hollow fiber as in Example 1, except that the discharge amount of the nozzle force is 16.6 gZ, the air flow rate of the air hole force provided in the center of the nozzle is 12.4 mlZ, and the take-up speed is 11. OmZ A porous membrane was obtained.

 [0076] The production conditions of the above Examples and Comparative Examples and the physical properties of the obtained polyvinylidene fluoride hollow fiber porous membrane are summarized in Table 1 below.

[table 1]

Industrial applicability

 According to the results of Table 1 above, according to the present invention, the polyvinylidene fluoride hollow fiber obtained by increasing the outer diameter and the wall thickness by variously changing the production conditions and obtaining a large cross-sectional area Porous membranes have (A) significantly improved flex resistance and (B) excellent fine particle removal performance, but have a large amount of water permeability and are particularly suitable for MBR (filter) water treatment membranes. I can understand that.

Claims

The scope of the claims  [1] A hollow fiber porous membrane comprising a vinylidene fluoride resin having a weight average molecular weight of 200,000 to 600,000 and further having the following characteristics (A) and (B):  (A) One end is covered with an epoxy resin with a hardness of 98, and the number of bending breaks measured under a load of 48 g is 100 times or more, and (B) Permeability of water permeability at test length L = 200mm measured under conditions of differential pressure 100kPa and water temperature 25 ° C v = converted to 70% F (L = 200mm, v = 70%) (mZday ) And the square value Pm ^{2 of} the average pore diameter Pm m measured by the half-dry method F (L = 200 mm, v = 70%) ZPm ² force 000 (m / day μ m ² ) or more.  [2] The hollow fiber porous membrane according to claim 1, wherein one end of the hollow fiber is covered with an epoxy resin having a hardness of 98, and the number of bending breaks measured under a constant stress of 0.136 MPa is 10 or more. [3] The hollow fiber porous membrane according to claim 1 or 2, wherein the hollow fiber porous membrane has an asymmetric pore size distribution in which the inner surface pore size is larger than the outer surface pore size. [4] The hollow fiber porous membrane according to any one of [1] to [3], wherein the hollow fiber porous membrane has an inclined pore size distribution in which a pore size from the inside to the inner surface is large relative to the outer surface and the vicinity of the outer surface. 5. The hollow fiber porous membrane according to claim 3 or 4, wherein the ratio of the inner surface average pore diameter to the outer surface average pore diameter is 1.50 to 5.0.  [6] The method according to any one of claims 1 to 5, wherein the outer diameter is substantially 1.50 to 3,000 mm and the wall thickness is 0.30 to 0.775 mm. The hollow fiber porous membrane described.  [7] For 100 parts by weight of vinylidene fluoride resin having a weight average molecular weight of 200,000 to 600,000, the total amount of plasticizer and good solvent for vinylidene fluoride resin is 100 to 300 parts by weight. In addition, a good solvent is added so that the proportion of the good solvent is 12.5 to 35% by weight, the obtained composition is melt extruded into a hollow fiber shape, and an inert gas is injected into the hollow portion into the inert liquid. When producing a hollow fiber porous membrane by drawing, cooling and solidifying from the outside, and then extracting the plasticizer, the melt extrusion rate is set to 2.0 to 10 OgZm, and the inert gas injection rate is set to 0.7. A vinylidene fluoride resin hollow fiber porous membrane characterized by forming a hollow fiber porous membrane having an outer diameter of 1.50 to 3.00 mm and a wall thickness of 0.30 to 0.75 mm as 6.8 mlZm. Production method. [8] Hollow fiber-like melt extrudate is introduced into an inert liquid after 2.0 to 7.0 seconds after melt extrusion The manufacturing method according to claim 7, wherein the cooling is performed. [9] The production method according to claim 7 or 8, wherein the film is stretched by 1.2 to 4.0 times in the length direction. [10] The production method according to any one of [7] to [9], wherein the stretched hollow fiber membrane is subjected to at least two-stage relaxation treatment in a non-wetting atmosphere with respect to the vinylidene fluoride-based resin. [11] The production method according to claim 10, wherein the relaxation treatment is performed as a wet heat treatment in water at 25 to 100 ° C and a dry heat treatment with air or water at Z or 80 to 160 ° C. [12] Relaxation rate power in relaxation treatment 2 to 20% in each stage, 4 to 30% in total. Manufacturing method according to any one of claims 7 to L1.