JP6577781B2 - Hollow fiber membrane and method for producing hollow fiber membrane - Google Patents

Description

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

  Separation techniques using hollow fiber membranes are used in various fields because of their high safety, high quality, energy saving and low carbon process. Specifically, separation techniques such as membrane filtration using a hollow fiber membrane are widely used in water purification treatment, drinking water production, food industry, pharmaceutical production, and the like. Furthermore, the membrane filtration method using a hollow fiber membrane is desired to further expand its application range. For example, application to membrane separation for high-load raw water is being studied. Specifically, the so-called membrane separation activated sludge method (MBR), which directly drains biological wastewater such as anaerobic treatment and aerobic treatment, membrane filtration of lubricants in the grinding and polishing steps, and suspension Application of a separation technique such as a membrane filtration method using a hollow fiber membrane is being studied for membrane separation with respect to high-load raw water containing a large amount of suspended substance (SS) components.

  When a hollow fiber membrane is used for membrane separation with respect to such high-load raw water, the hollow fiber membrane is easily contaminated. For this reason, it is necessary to periodically clean the hollow fiber membrane by using chemicals, that is, chemical washing to remove contaminants attached to the hollow fiber membrane. On the other hand, when chemical washing is performed on the hollow fiber membrane, not only contaminants are removed, but also the hollow fiber membrane itself is affected by the contact of chemicals. For this reason, chemical strength such as chemical resistance is increasingly required for hollow fiber membranes. Under such circumstances, a separation membrane using a vinylidene fluoride resin such as polyvinylidene fluoride has attracted attention because it not only has high physical strength but also high chemical strength.

  Examples of the separation membrane using such a vinylidene fluoride-based resin include porous membranes described in Patent Document 1 and Patent Document 2.

In Patent Document 1, in a polyvinylidene fluoride porous film, a value R ₁ obtained by dividing an absorbance (A ₇₆₃ ) of ₇₆₃ cm ⁻¹ obtained by IR measurement by an absorbance (A ₈₄₀ ) of ₈₄₀ cm ⁻¹ is 1.5 or more. A polyvinylidene fluoride porous membrane is described.

  According to Patent Document 1, it is disclosed that safety at the time of fresh water generation is improved, and it is possible to extend the life of the porous membrane.

Patent Document 2 discloses a porous film containing a polymer component mainly composed of polyvinylidene fluoride (PVDF) resin, and the degree of crystallinity of the PVDF resin is 50% or more and 90% or less. A porous film is described in which the value obtained by multiplying the crystallinity of the PVDF resin by the specific surface area of the film is 300 (% · m ² / g) or more and 2000 (% · m ² / g) or less. . Patent Document 2 also describes that the total amount of β-type structure crystals and γ-type structure crystals in the crystal part of the PVDF resin is 30% or less with respect to the total crystal part of the PVDF resin. Yes.

  According to Patent Document 2, since it has high water permeability and high chemical resistance, it can be used with contact with chemicals such as cleaning chemicals, and can be easily recovered from deterioration of water permeability due to membrane surface blockage. It is disclosed that it can be done. In addition, it is disclosed that since a decrease in film strength can be suppressed against degradation caused by chemicals such as cleaning chemicals, it can be used over a long period of time. Moreover, since it can be manufactured simply and stably, it is disclosed that it is excellent in productivity and economy.

JP 2008-62229 A International Publication No. 2007/119850

  The hollow fiber membrane used for the separation technique is not only required to improve the chemical resistance as described above, but also to improve the permeation performance and the fractionation characteristics. That is, the hollow fiber membrane is required to further improve permeation performance, fractionation characteristics, and chemical resistance. In order to satisfy such a demand, further investigation is required for the hollow fiber membrane.

  In view of such circumstances, an object of the present invention is to provide a high-quality hollow fiber membrane having excellent permeation performance and fractionation characteristics and excellent chemical resistance. Moreover, an object of this invention is to provide the manufacturing method of the hollow fiber membrane which can manufacture the said hollow fiber membrane easily.

  Porous hollow fiber membranes are known as hollow fiber membranes excellent in permeation performance and fractionation characteristics. Such a hollow fiber membrane is considered to have different permeation performance and fractionation characteristics depending on pores formed in the membrane, specifically, the number, shape, size, and the like of the pores. In order to improve the fractionation characteristic, it is conceivable to make the film dense. On the other hand, it is considered that when the entire membrane is made dense, the permeation performance is lowered. In order to obtain a hollow fiber membrane with both excellent permeation performance and fractionation characteristics, it is important to first thin the dense part that expresses the fractionation characteristics, that is, the separation layer that is directly involved in the separation. It is thought that. For this reason, it is conceivable that the size of the pores in the hollow fiber membrane changes with respect to the film thickness direction and the separation layer becomes thinner. And it is thought that a part other than the separation layer necessary for maintaining the strength of the hollow fiber membrane becomes a coarse porous body, and this porous body becomes a support layer. That is, both the permeation performance and the fractionation characteristics can be improved by adopting an inclined structure in which the pore diameter in the hollow fiber membrane gradually decreases toward at least one side of the inner and outer peripheral surfaces. it is conceivable that. As described above, in order to obtain a hollow fiber membrane having both excellent permeation performance and fractionation characteristics, the hollow fiber membrane has a structure in which pores formed in the membrane gradually decrease toward one side. It is conceivable that the pore size is preferably different in the film thickness direction.

  In order to improve the chemical resistance of such a hollow fiber membrane, it is conceivable to increase the chemical strength of the chemical resistance of the membrane material constituting the hollow fiber membrane. Therefore, as described above, it is considered to use a hollow fiber membrane containing a vinylidene fluoride resin such as polyvinylidene fluoride, which is known not only to have high physical strength but also high chemical strength. It is done.

  Therefore, the present inventors first focused on the crystal structure of a vinylidene fluoride resin such as polyvinylidene fluoride contained in the hollow fiber membrane, and examined the crystal structure. Specifically, the inventors have focused on the fact that a vinylidene fluoride resin such as polyvinylidene fluoride has an α crystal structure as a crystal structure, resulting in higher chemical resistance. From this, the present inventors considered that increasing the ratio of the α crystal structure can further improve the chemical resistance.

  Furthermore, the inventors of the present invention, in the hollow fiber membrane containing a polyvinylidene fluoride resin such as polyvinylidene fluoride, not only the pore size formed in the membrane differs in the film thickness direction, but also has an α crystal structure. The ratio was also examined. As a result, not only the pore size formed in the film is different in the film thickness direction, but also the ratio of the α crystal structure is different, so that not only the permeation performance and fractionation characteristics but also chemical resistance is improved. I found out. Furthermore, it has also been found that the production conditions of the hollow fiber membrane are different by changing the ratio of the α crystal structure in such a film thickness direction. From these facts, the inventors have arrived at the present invention described later.

  The hollow fiber membrane according to one aspect of the present invention is a porous hollow fiber membrane containing a vinylidene fluoride resin, and the pore diameter in the hollow fiber membrane is on at least one side of the inner and outer peripheral surfaces. The first ratio which is the abundance ratio of the α crystal structure to the β crystal structure in the surface on the side where the pore diameter is small, which gradually decreases toward the surface, is the surface on the side where the pore diameter is large In which the difference between the first ratio and the second ratio is 50 to 350%, and the β crystal in the entire hollow fiber membrane The third ratio, which is the abundance ratio of the α crystal structure to the structure, is more than 0% and not more than 120%.

  According to such a configuration, it is possible to provide a high-quality hollow fiber membrane excellent in permeation performance and fractionation characteristics and excellent in chemical resistance.

  This is considered to be due to the following.

  First, this hollow fiber membrane has a slanted structure in which the pore diameter of the pores in the membrane gradually decreases from one side of the inner and outer peripheral sides toward the other side, so it is considered that the hollow fiber membrane is involved in fractionation characteristics. It is considered that a layered portion and other portions where relatively large pores (pores) are formed are formed. It is considered that the dense layered portion considered to be involved in the fractionation characteristics serves as a separation layer, and the other portion serves as a support layer. And since this hollow fiber membrane has parts other than the part which functions as a separation layer, the part which functions as a separation layer becomes thin. From this, even if this hollow fiber membrane has a portion that works as a separation layer, since the portion is thin, it has a portion that works as a separation layer while suppressing a decrease in permeation performance. It is thought that the characteristics can be enhanced. Moreover, since it also has a portion that functions as a support layer, it is considered that the strength is maintained even if the portion that functions as a separation layer is thin.

  In this hollow fiber membrane, the first ratio, which is the abundance ratio of the α crystal structure with respect to the β crystal structure, on the surface on the side where the pore diameter is small is the α ratio relative to the β crystal structure on the surface where the pore diameter is large. Lower than the second ratio, which is the abundance ratio of the crystal structure. That is, the abundance ratio of the α crystal structure in the portion serving as the separation layer is lower than the abundance ratio of the α crystal structure in the portion serving as the support. And the difference is 50 to 350%. The third ratio, which is the abundance ratio of the α crystal structure to the β crystal structure, in the entire hollow fiber membrane is more than 0% and 120% or less. Thus, even if the abundance ratio of the α crystal structure is not increased throughout the hollow fiber membrane, the permeation performance and fractionation characteristics, etc. It is considered that the chemical resistance can be sufficiently enhanced while suppressing the decrease.

  From the above, it is considered that a high-quality hollow fiber membrane excellent in permeation performance and fractionation characteristics and excellent in chemical resistance can be obtained by adopting the configuration as described above.

  In the hollow fiber membrane, the second ratio is preferably greater than 50% and not greater than 400%.

  According to such a configuration, it is possible to obtain a hollow fiber membrane that maintains excellent permeation performance and fractionation characteristics and is superior in chemical resistance.

  The hollow fiber membrane preferably has a crystallinity of 30 to 80%.

  According to such a configuration, it is possible to obtain a hollow fiber membrane that maintains excellent permeation performance and fractionation characteristics and is superior in chemical resistance.

  In the hollow fiber membrane, the vinylidene fluoride resin preferably has a heterogeneous bond ratio of 5 to 30 mol%.

  According to such a configuration, it is possible to obtain a hollow fiber membrane that maintains excellent permeation performance and fractionation characteristics and is superior in chemical resistance.

  The hollow fiber membrane preferably comprises a single layer.

  According to such a configuration, it is possible to obtain a hollow fiber membrane that is excellent in permeation performance, fractionation characteristics, and chemical resistance and is less likely to cause damage such as peeling in the membrane.

  Further, a method for producing a hollow fiber membrane according to another aspect of the present invention is a method for producing the hollow fiber membrane, the step of preparing a membrane-forming stock solution containing a vinylidene fluoride resin and a solvent, It comprises an extrusion step of extruding the membrane-forming stock solution into a hollow fiber shape, and a forming step of coagulating the membrane-forming stock solution extruded into a hollow fiber shape to form a hollow fiber membrane.

  According to such a configuration, a high-quality hollow fiber membrane having excellent permeation performance and fractionation characteristics and excellent chemical resistance can be produced. Moreover, when manufacturing such a hollow fiber membrane, in order to satisfy the crystal structure in this hollow fiber membrane, when heat treatment is separately provided or when the membrane forming stock solution is extruded, for example, at a high temperature such as 180 ° C. or higher. It is not necessary to do so, and the hollow fiber membrane can be easily manufactured.

In the method for producing the hollow fiber membrane, the membrane forming stock solution has a solubility parameter distance between a component other than the vinylidene fluoride resin and the vinylidene fluoride resin of 0.1 to 15 (MPa). ^1/2, the temperature of the casting dope in the extrusion step is preferably lower than 180 ° C..

  According to such a configuration, a high-quality hollow fiber membrane having excellent permeation performance and fractionation characteristics and excellent chemical resistance can be more easily produced.

Further, in the method for producing the hollow fiber membrane, the extrusion step includes a circular outer discharge port, and a hollow fiber forming nozzle including a circular or annular inner discharge port disposed inside the outer discharge port. In the step of bringing the extruded hollow fiber-shaped film-forming stock solution into contact with the internal coagulating liquid by extruding the film-forming stock solution from the outer discharge port while extruding the internal coagulating liquid from the inner discharge port. Yes, the distance of the dissolution parameter between the internal coagulation liquid and the film-forming stock solution is preferably 5 to 1000 (MPa) ^1/2 , and the viscosity of the internal coagulation liquid at 20 ° C. is preferably 50 to 3000 cP. .

  According to such a configuration, it is possible to easily manufacture a hollow fiber membrane having excellent permeation performance, fractionation characteristics, and chemical resistance and having pores existing on the outer peripheral surface smaller than those existing on the inner peripheral surface. . That is, a hollow fiber membrane can be obtained in which a portion serving as a support layer is present on the inner peripheral surface side and a portion serving as a separation layer is present on the outer peripheral surface side. This is considered to be due to the fact that the second ratio increases when the above-mentioned coagulating liquid is used as the internal coagulating liquid.

Further, in the method for producing a hollow fiber membrane, the forming step is a step of forming a hollow fiber membrane by bringing the hollow fiber-shaped stock solution extruded in the extrusion step into contact with an external coagulation liquid, It is preferable that the distance of the dissolution parameter between the external coagulation liquid and the film-forming stock solution is 5 to 1000 (MPa) ^1/2 and the viscosity of the external coagulation liquid at 20 ° C. is 50 to 3000 cP.

  According to such a configuration, it is possible to easily manufacture a hollow fiber membrane having excellent permeation performance, fractionation characteristics, and chemical resistance and having pores existing on the inner peripheral surface smaller than those existing on the outer peripheral surface. . That is, a hollow fiber membrane is obtained in which a portion that functions as a support layer exists on the outer peripheral surface side and a portion that functions as a separation layer exists on the inner peripheral surface side. This is considered to be due to the increase in the first ratio when the above-mentioned coagulating liquid is used as the external coagulating liquid.

  According to the present invention, it is possible to provide a high-quality hollow fiber membrane that is excellent in permeation performance and fractionation characteristics and excellent in chemical resistance. Moreover, according to this invention, the manufacturing method of the hollow fiber membrane which can manufacture the said hollow fiber membrane easily can be provided.

FIG. 1 is a partial perspective view of a hollow fiber membrane according to an embodiment of the present invention. FIG. 2 is a schematic view showing an example of a hollow fiber molding nozzle used in the manufacturing method according to the embodiment of the present invention. FIG. 3 is a schematic diagram illustrating an example of a membrane filtration device including a hollow fiber membrane according to an embodiment of the present invention. 4 is a view showing a scanning electron micrograph of the outer peripheral surface of the hollow fiber membrane according to Example 2. FIG. 5 is a view showing a scanning electron micrograph of the inner peripheral surface of the hollow fiber membrane according to Example 2. FIG. 6 is a view showing a scanning electron micrograph of a cross section of the hollow fiber membrane according to Example 4. FIG. 7 is a view showing a scanning electron micrograph of the outer peripheral surface of the hollow fiber membrane according to Example 4. FIG. FIG. 8 is a view showing a scanning electron micrograph of the inner peripheral surface of the hollow fiber membrane according to Example 4.

  Hereinafter, although the embodiment concerning the present invention is described, the present invention is not limited to these.

  A hollow fiber membrane according to an embodiment of the present invention is a porous hollow fiber membrane containing a vinylidene fluoride resin. The hollow fiber membrane has an inclined structure in which the pore diameter in the hollow fiber membrane gradually decreases toward at least one side of the inner and outer peripheral surfaces. That is, the hollow fiber membrane according to the present embodiment is a hollow fiber membrane having an asymmetric structure in the film thickness direction. As described above, this hollow fiber membrane is considered to have a portion serving as a separation layer, which is a dense layered portion considered to be involved in the fractionation characteristics, and a portion serving as a support layer. From this, compared with the case where the whole hollow fiber membrane is concerned with a fractionation characteristic, as for this hollow fiber membrane, the part which acts as a separation layer becomes thin. Therefore, since this hollow fiber membrane has such a part that functions as a separation layer, it is considered that separation characteristics can be improved while suppressing a decrease in permeation performance. Moreover, since it also has a portion that functions as a support layer, it is considered that the strength is maintained even if the portion that functions as a separation layer is thin.

  And this hollow fiber membrane has the following crystal structure of vinylidene fluoride resin contained in the hollow fiber membrane.

  First, the crystal structure of the vinylidene fluoride resin indicates the crystal structure of the crystal part of the vinylidene fluoride resin constituting the hollow fiber membrane. As a crystal structure of a vinylidene fluoride resin such as polyvinylidene fluoride, there are various crystal structures such as an α-type crystal structure, a β-type crystal structure, and a γ-type crystal structure. Among these, the α crystal structure is considered to be the most thermodynamically stable crystal structure than other crystal structures. For this reason, from the viewpoint of enhancing chemical resistance, it is conceivable to increase the abundance ratio of the α crystal structure with respect to other crystal structures, for example, the abundance ratio of the α crystal structure with respect to the β crystal structure. This is presumably because the α crystal structure has less hydrogen and fluorine atoms delocalized than the β crystal structure, resulting in less charge bias. That is, when the hydrogen crystal and the fluorine atom are localized and the α crystal structure having a relatively low polarity is present in a higher ratio than the β crystal structure having a relatively high polarity, it is considered that excellent chemical resistance can be exhibited.

  The hollow fiber membrane has an abundance ratio (first ratio) of the α crystal structure to a β crystal structure on the surface on the side where the pore diameter is small, which is the second ratio on the surface on the side where the pore diameter is large. ) Lower. That is, the abundance ratio of the α crystal structure to the β crystal structure in the portion serving as the separation layer is relatively low. In addition, the abundance ratio of the α crystal structure to the β crystal structure in the portion serving as the support layer is relatively high. Specifically, the difference between the first ratio and the second ratio is 50 to 350%. By setting such a ratio, a hollow fiber membrane excellent in chemical resistance can be obtained while maintaining the excellent permeation performance and fractionation characteristics realized by the inclined structure as described above. This means that even if the abundance ratio of the α crystal structure is not increased throughout the hollow fiber membrane, the abundance ratio of the α crystal structure of the portion that functions as the support is preferentially increased, so that the permeation performance, the fractionation characteristics, etc. It is considered that the chemical resistance can be sufficiently enhanced while suppressing the decrease. Specifically, the abundance ratio (third ratio) of the α crystal structure to the β crystal structure in the entire hollow fiber membrane is more than 0% and 120% or less. If the α crystal structure excess ratio in the entire hollow fiber membrane is within the above range, the chemical resistance cannot be sufficiently enhanced if it is normal. However, if it is the hollow fiber membrane which concerns on this embodiment, ie, if the difference of a 1st ratio and a 2nd ratio is in the said range, chemical resistance can fully be improved. From this, it is possible to sufficiently increase the chemical resistance without increasing the α crystal structure excess ratio of the entire hollow fiber membrane and deteriorating the permeation performance and the fractionation characteristics.

  From the above, it is considered that the hollow fiber membrane according to the present embodiment is a high-quality hollow fiber membrane that is excellent in permeation performance and fractionation characteristics and excellent in chemical resistance.

  The difference between the first ratio and the second ratio (second ratio−first ratio) is 50 to 350%, preferably 50 to 300%, and more preferably 100 to 300%. . If this difference is too small, there is a tendency that the effects such as the above-described improvement in chemical resistance cannot be sufficiently exhibited. This is because the second ratio is too low with respect to the first ratio, the difference between the first ratio and the second ratio is too small, or the second ratio is lower than the first ratio. It is. On the other hand, if the difference is too small, it is necessary to increase the abundance ratio of the α crystal structure of the entire hollow fiber membrane in order to improve chemical resistance. When such a hollow fiber membrane needs to be heated to a high temperature such as 180 ° C. or higher, for example, when heat treatment is separately provided or the film-forming stock solution is extruded in order to increase the abundance ratio of the α crystal structure. There is. For example, when the porous film described in Patent Document 1 is manufactured, in order to maintain high crystallinity, crystal state, and the like, heat treatment is separately performed in addition to the steps necessary for manufacturing the porous film. Further, when the porous film described in Patent Document 2 is manufactured, according to the study by the present inventors, it is necessary to perform a crystallinity improving process such as a heat treatment above the melting point of polyvinylidene fluoride or a stretching shrinkage process. . Thus, in order to heat above the melting point of polyvinylidene fluoride, for example, it is difficult to heat with steam, which is usually used as a heat source in a factory, and high-temperature melting such as an electric heater or kneading equipment Facility is necessary. Moreover, when the said difference is too large, there exists a tendency for manufacture of a hollow fiber membrane to become difficult. From these facts, when the difference is within the above range, a hollow fiber membrane excellent in permeation performance, fractionation characteristics, and chemical resistance can be obtained. Further, such a hollow fiber membrane can be easily produced without requiring a high temperature of, for example, 180 ° C. or higher when a heat treatment is separately provided or a membrane-forming stock solution is extruded.

The abundance ratio of the α crystal structure with respect to the β crystal structure is an index indicating how much the α crystal structure is, and is also referred to as an α crystal structure excess ratio. If the α crystal structure excess is 100%, it indicates that the same amount of α crystal structure and β crystal structure exist, and if it is less than 100%, more β crystal structure exists than α crystal structure. If it is larger than 100%, more α crystal structures are present than β crystal structures. Further, this α crystal structure excess ratio is, for example, the ratio of the absorbance (A ₇₆₃ ) of ₇₆₃ cm ^{−1 to} the absorbance (A ₈₄₀ ) of ₈₄₀ cm ⁻¹ in the infrared absorption spectrum obtained by infrared spectroscopy (IR). (A ₇₆₃ / A ₈₄₀ × 100) and the like. That is, the ratio between the peak intensity at 763 cm ⁻¹ and the peak intensity at 840 cm ⁻¹ in the infrared absorption spectrum (763 cm ⁻¹ peak intensity / 840 cm ⁻¹ peak intensity × 100) and the like can be mentioned. The absorbance at ₇₆₃ cm ⁻¹ (A ₇₆₃ ), that is, the peak intensity at ₇₆₃ cm ⁻¹ is the absorbance attributed to the α crystal structure. The absorbance at ₈₄₀ cm ⁻¹ (A ₈₄₀ ), that is, the peak intensity at ₈₄₀ cm ⁻¹ is the absorbance attributed to the β crystal structure.

Further, when IR analysis is performed on the α crystal structure of the polyvinylidene fluoride resin, characteristic peaks (characteristic absorption) are observed in the vicinity of 1212 cm ⁻¹ , 1183 cm ⁻¹ , and 763 cm ⁻¹ . Further, when powder X-ray diffraction analysis is performed on the α crystal structure of the polyvinylidene fluoride resin, there are characteristic peaks in the vicinity of 2θ = 17.7 °, 18.3 °, and 19.9 °. Further, when IR analysis is performed on the β crystal structure of the polyvinylidene fluoride resin, characteristic peaks (characteristic absorption) are present in the vicinity of 1274 cm ⁻¹ , 1163 cm ⁻¹ , and 840 cm ⁻¹ . Further, when powder X-ray diffraction analysis is performed on the β crystal structure of the polyvinylidene fluoride resin, it has a characteristic peak in the vicinity of 2θ = 21 °. From this, the method of calculating the α crystal structure excess ratio can be calculated using these characteristic peaks in addition to the above method using A ₇₆₃ and A ₈₄₀ .

  Further, since the first ratio is the α crystal structure excess ratio on the surface on the side where the pore diameter is small, the surface on the side where the pore diameter of the hollow fiber membrane is small is measured by infrared spectroscopy. It is a value calculated from the obtained infrared absorption spectrum. Since the second ratio is the α crystal structure excess ratio on the surface having the larger pore diameter, the surface having the larger pore diameter of the hollow fiber membrane was measured by infrared spectroscopy. It is a value calculated from an infrared absorption spectrum. The first ratio is the α crystal structure excess ratio on the peripheral surface acting as the separation layer, and the second ratio is the α crystal structure excess ratio on the peripheral surface acting as the support layer.

  Further, the α ratio of the α crystal structure on the second ratio, that is, the peripheral surface on the side serving as the support layer is not particularly limited, but it is preferably as high as possible from the viewpoint of improving chemical resistance. Specifically, the second ratio is preferably greater than 50%, and more preferably 100% or more. If the second ratio is too low, there is a tendency that the effect of enhancing chemical resistance cannot be sufficiently exhibited. However, in practice, if the second ratio is too high, it tends to be difficult to maintain excellent transmission performance and fractionation characteristics. This is considered to be because it becomes difficult to form pores having a suitable size as the pores formed in the portion serving as the support layer. From this viewpoint, the second ratio is, for example, preferably 400% or less, more preferably 350% or less, and further preferably 300% or less. Therefore, the second ratio is preferably greater than 50% and 400% or less, more preferably greater than 50% and 350% or less, and even more preferably 100 to 300%. If the second ratio is within this range, a hollow fiber membrane that is superior in chemical resistance can be obtained while maintaining excellent permeation performance and fractionation characteristics.

  Moreover, the α crystal structure excess ratio on the first ratio, that is, the peripheral surface on the side serving as the separation layer is not particularly limited, but it is preferably as high as possible from the viewpoint of improving chemical resistance. On the other hand, if the difference between the first ratio and the second ratio is within the above range, the second ratio is high to some extent, and the chemical resistance of the portion acting as the separation layer is high, so the first ratio is low, for example, The α crystal structure may not exist. For this reason, the first ratio may be larger than 0%. Further, if the first ratio is too high, it tends to be difficult to maintain excellent transmission performance and fractionation characteristics. This is considered to be because it becomes difficult to form pores having a suitable size as the pores formed in the portion serving as the separation layer. In this respect, the first ratio is, for example, preferably 250% or less, more preferably 2% or less, and further preferably 150% or less. Therefore, the first ratio is preferably greater than 0% and 250% or less, more preferably greater than 0% and 200% or less, and even more preferably greater than 0% and 150% or less. If the first ratio is within this range, a hollow fiber membrane with excellent chemical resistance can be obtained while maintaining excellent permeation performance and fractionation characteristics.

  Further, the third ratio which is the abundance ratio of the α crystal structure to the β crystal structure in the whole hollow fiber membrane is more than 0% and not more than 120%, preferably 20 to 100%, and preferably 20 to 90%. It is more preferable that If the α crystal structure excess is too high, the film-forming property tends to decrease. Furthermore, even if the difference between the first ratio and the second ratio is not within the above range, the chemical resistance can be improved, but it tends to be difficult to improve both the permeation performance and the fractionation characteristics. . In addition, if the α crystal structure excess in the entire hollow fiber membrane is within the above range, the chemical resistance cannot be sufficiently enhanced if it is normal. However, if it is the hollow fiber membrane which concerns on this embodiment, ie, if the difference of a 1st ratio and a 2nd ratio is in the said range, chemical resistance can fully be improved. From this, it is possible to sufficiently increase the chemical resistance without increasing the α crystal structure excess ratio of the entire hollow fiber membrane and deteriorating the permeation performance and the fractionation characteristics. Therefore, it is possible to obtain a hollow fiber membrane that maintains excellent permeation performance and fractionation characteristics and is superior in chemical resistance.

  The third ratio, that is, the excess α crystal structure ratio of the entire hollow fiber membrane can be measured using, for example, a differential scanning calorimeter (DSC).

  Further, the crystallinity of the hollow fiber membrane according to the present embodiment is not particularly limited, for example, it may be a normal crystallinity of a hollow fiber membrane containing a vinylidene fluoride resin such as polyvinylidene fluoride, From the viewpoint of enhancing chemical resistance, the higher the better. This is considered to be because when the degree of crystallinity is high, there are few amorphous parts in the polymer chain and there are many crystal parts, so that the energy becomes stable and chemical resistance becomes high. Specifically, the crystallinity is preferably 30% or more, and more preferably 40% or more. Further, if the crystallinity is too low, there is a tendency that the effect of improving chemical resistance cannot be sufficiently exhibited. This is considered to be due to the fact that even if the relationship between the first ratio and the second ratio satisfies the above relationship, the vinylidene fluoride resin crystals contained in the hollow fiber membrane are few and α crystals are few. It is done. On the other hand, if the crystallinity is too low, the rigidity of the hollow fiber membrane tends to be low, or it tends to be unsuitable for filtration, such as deformation during filtration. However, in practice, if the crystallinity is too high, it tends to be difficult to maintain excellent transmission performance and fractionation characteristics. This is thought to be because it becomes difficult to form pores of a suitable size as pores formed in the hollow fiber membrane. On the other hand, if the crystallinity is too high, the hollow fiber membrane tends to be brittle and easily broken. This is presumably because the amorphous part contributes to the flexibility of the hollow fiber membrane, and if the degree of crystallinity is too high, the amorphous part contributing to this flexibility becomes too small. From these viewpoints, the crystallinity is, for example, preferably 80% or less, more preferably 70% or less, and further preferably 58% or less. Therefore, the crystallinity is preferably 30 to 80%, more preferably 40 to 70%, and still more preferably 40 to 58%.

  The crystallinity is the mass ratio of the crystal part to the entire hollow fiber membrane. This crystallinity can be measured using, for example, a differential scanning calorimeter (DSC).

Moreover, the ratio of the heterogeneous bond of the vinylidene fluoride resin contained in the hollow fiber membrane according to the present embodiment is not particularly limited, but it is preferably as high as possible from the viewpoint of enhancing chemical resistance. For example, in the case of polyvinylidene fluoride (PVDF), the heterogeneous bond is usually “CF ₂ ” and “CH ₂ ” which are alternately bonded, and among them, “CF ₂ ” and “CH ₂ ” Is the part which is adjacently joined. That is, in the polymer to be head-to-tail bonded, head-to-head binding, tail-to-tail binding, etc. are heterogeneous bonds. The more this heterogeneous bond, the higher the chemical resistance. This is considered to be because as the number of heterogeneous bonds increases, the number of head-to-tail bonds decreases, and the chain defluorination reaction by chemicals can be suppressed. On the other hand, as the number of different bonds increases, it tends to be difficult to produce the vinylidene fluoride resin. From these facts, the proportion of heterogeneous bonds in the vinylidene fluoride-based resin is preferably, for example, 5 to 30 mol%, more preferably 5 to 20 mol%, based on the total number of bonds. More preferably, it is 5-10 mol%. When the ratio of the heterogeneous bonds is within the above range, a hollow fiber membrane having higher chemical resistance can be obtained while maintaining excellent permeation performance and fractionation characteristics. The ratio of abnormal linkage, for ^example, can be determined from the 1 H-NMR measurement and ¹⁹ F-NMR measurement.

  Further, as described above, the hollow fiber membrane has an inclined structure in which the pore diameter of the pores (pores) in the membrane gradually decreases toward at least one side of the inner and outer peripheral surfaces. Specifically, for example, there is a case in which the diameter of the pores formed on the outer peripheral surface of the hollow fiber membrane has an inclined structure inclined so as to be smaller than the diameter of the pores formed on the inner peripheral surface. It is done. Also, different from this, there may be mentioned a case where the hollow fiber membrane has an inclined structure inclined so that the diameter of the pores formed on the inner peripheral surface is smaller than the diameter of the pores formed on the outer peripheral surface. It is done. In addition, the diameter of the pore formed on the peripheral surface on the side where the diameter of the pore is small, that is, the peripheral surface on the side serving as the separation layer is also referred to as the separation-side pore diameter. Further, the diameter of the pores formed on the peripheral surface on the side where the diameter of the pores is large, that is, the peripheral surface on the side serving as the support layer is also referred to as the support-side pore diameter. Specifically, the separation-side pore diameter is preferably 0.01 to 1 μm, more preferably 0.1 to 0.5 μm, and further preferably 0.1 to 0.3 μm. . Further, the support-side pore diameter is not particularly limited, but specifically, it is preferably 0.2 to 20 μm, more preferably 0.5 to 10 μm, and 1 to 8 μm. preferable. The ratio of the support-side pore diameter to the separation-side pore diameter (support-side pore diameter / separation-side pore diameter) is greater than 1, preferably 10 to 100, and preferably 20 to 50, It is preferable that it is 30-50. The hollow fiber membrane according to the present embodiment preferably has an inclined structure that is inclined so that the separation-side pore diameter and the support-side pore diameter are within the above range. Here, the diameter is an average value of the diameters, and examples thereof include an arithmetic average value of the diameters.

  The vinylidene fluoride resin contained in the hollow fiber membrane is a main component of the hollow fiber membrane, specifically, preferably 85% by mass or more, and 90 to 99.9% by mass. Is preferred.

  The vinylidene fluoride resin is not particularly limited as long as it is a vinylidene fluoride resin that can form a hollow fiber membrane. Specific examples of the vinylidene fluoride resin include a homopolymer of vinylidene fluoride, a vinylidene fluoride copolymer, and the like. The vinylidene fluoride copolymer is not particularly limited as long as it is a copolymer having a repeating unit based on vinylidene fluoride. Specific examples of the vinylidene fluoride copolymer include a copolymer of vinylidene fluoride and at least one selected from the group consisting of vinyl fluoride, tetrafluoroethylene, hexafluoropropylene, and trifluorochloroethylene. Examples include coalescence. As the vinylidene fluoride-based resin, among the above examples, polyvinylidene fluoride which is a homopolymer of vinylidene fluoride is preferable. Further, as the vinylidene fluoride resin, the above-exemplified resins may be used alone or in combination of two or more.

  Moreover, although the molecular weight of vinylidene fluoride resin changes with uses of a hollow fiber membrane etc., it is preferable that it is 50,000-1,000,000 in a weight average molecular weight, for example. When the molecular weight is too small, the strength of the hollow fiber membrane tends to decrease. Moreover, when molecular weight is too large, there exists a tendency for the film forming property of a hollow fiber membrane to fall. In addition, when a hollow fiber membrane is used for water treatment that is exposed to chemical cleaning, the hollow fiber membrane is required to have higher performance, so that it has excellent strength, and in order to obtain a suitable hollow fiber membrane, It is required to have excellent film forming properties. For this reason, the weight average molecular weight of the vinylidene fluoride resin contained in the hollow fiber membrane is preferably 100,000 to 900,000, and more preferably 150,000 to 800,000.

  The hollow fiber membrane may be hydrophilized by including not only the vinylidene fluoride resin but also a crosslinked body of a hydrophilic resin. The hydrophilic resin is not particularly limited as long as it is a resin containing a hydrophilic group in the molecule. Specific examples of the hydrophilic resin include cellulose ester, ethylene-vinyl alcohol, polyvinyl alcohol, polyvinyl pyrrolidone, a copolymer of vinyl pyrrolidone and vinyl acetate, a copolymer of vinyl pyrrolidone and vinyl caprolactam, and an acrylate ester. And the like. Among the above examples, the hydrophilic resin is preferably a polyvinyl alcohol-based resin in terms of easy handling. Moreover, as hydrophilic resin, the resin of the said illustration may be used independently, and may be used in combination of 2 or more type.

Further, the hollow fiber membrane according to the present embodiment, the water permeability in the transmembrane pressure 0.1MPa is, it is preferably time 100~20000L / ^{m 2} /, is when 100~15000L / ^{m 2} / More preferably, it is more preferably 100 to 10,000 L / m ² / hour. If the water permeation amount is too small, the permeation performance tends to be inferior, and if the water permeation amount is too large, the fractionation characteristics tend to deteriorate. From this, if the amount of water permeation is within the above range, a hollow fiber membrane having better permeation performance and fractionation characteristics can be obtained. In addition, the water permeation amount at the transmembrane pressure difference of 0.1 MPa is obtained as follows, for example. First, a hollow fiber membrane as a measurement object is immersed in a 50% by mass aqueous solution of ethanol for 15 minutes, and then subjected to a wet treatment such as washing with pure water for 15 minutes. Using a porous hollow fiber membrane module having an effective length of 20 cm in which one end of this wet-treated hollow fiber membrane is sealed, pure water is used as raw water, the filtration pressure is 0.1 MPa, and the temperature is 25 ° C. Filter and measure the amount of water per hour. From this measured water permeation amount, the water permeation amount (L / m ² / hour: LMH) at a transmembrane differential pressure of 0.1 MPa is obtained in terms of the permeation amount per unit membrane area, unit time and unit pressure.

  Moreover, it is preferable that the hollow fiber membrane which concerns on this embodiment has a fraction particle diameter of 1 micrometer or less. This fractionated particle size refers to the particle size of the smallest particle that can prevent passage of the hollow fiber membrane, and specifically includes, for example, a particle size that provides a blocking rate of 90% by the hollow fiber membrane. Such a fractional particle size is preferably as small as possible, but in order to maintain excellent transmission performance, the limit is about 0.001 μm. For this reason, the minimum value of the fractional particle diameter is about 0.001 μm, and is preferably about 0.01 μm from the viewpoint of transmission performance. From these, the fractional particle diameter is preferably 1 μm or less, more preferably 0.001 to 0.5 μm, further preferably 0.01 to 0.5 μm, 0.02 It is especially preferable that it is -0.1 micrometer. The hollow fiber membrane preferably has a molecular weight cut-off of 1000 to 300,000. The molecular weight cut off refers to the molecular weight of the smallest polymer that can prevent passage through the hollow fiber membrane, and specifically includes, for example, the weight average molecular weight of the polymer with a blocking rate of 90% by the hollow fiber membrane. It is done. If the fractionated particle diameter and the fractional molecular weight of the hollow fiber membrane are too large, even if the permeation performance is increased, the fractionation characteristics are lowered and the application range to be removed tends to be narrowed. From this, if the fractional particle diameter and the fractional molecular weight of the hollow fiber membrane are within the above ranges, excellent fractionation characteristics can be exhibited while suppressing a decrease in permeation performance.

  Moreover, the applicable range of the hollow fiber membrane varies depending on the fractional particle diameter. Specifically, if the fractional particle size is 0.05 to 0.1 μm, it can be applied to the removal of microorganisms as a microfiltration membrane. Moreover, if a fraction particle diameter is 0.001-0.01 micrometer, it can apply to removal of a micropathogenic microbe and protein as an ultrafiltration membrane. Moreover, if a fraction particle diameter is 0.002 micrometer or less, it can apply to desalination etc. as a reverse osmosis membrane.

  From the above, the hollow fiber membrane according to the present embodiment has excellent fractionation characteristics that can be applied to the removal of microorganisms as a microfiltration membrane when the fractional particle diameter is within the above range. Excellent transmission performance can be demonstrated.

  Moreover, it is preferable that the hollow fiber membrane which concerns on this embodiment consists of a single layer. That is, as described above, even if the hollow fiber membrane has an asymmetric structure in which the size of the pores and the like are different in the film thickness direction, the material is preferably composed of the same layer. More specifically, the hollow fiber membrane is preferably formed of a single layer, rather than a separate layer and a support layer as described above, which are laminated. By doing so, it is possible to obtain a hollow fiber membrane which is excellent in permeation performance and fractionation characteristics and hardly causes damage such as peeling in the membrane.

  This is considered to be due to the following.

  A dense layered portion considered to be involved in the fractionation characteristics as described above is considered thin when the permeation performance is high as in the hollow fiber membrane according to the present embodiment. In such a case, if such a dense layer is separately prepared, it may not be formed suitably. On the other hand, it is considered that when the dense layered portion and other portions are formed of the same layer, that is, a single layer, the dense layered portion can be uniformly formed in the surface direction. Further, if the dense layered portion and the other portion are a single layer, it is considered that the occurrence of peeling or the like at the interface can be sufficiently suppressed.

  From these facts, it is considered that a hollow fiber membrane is obtained which is excellent in permeation performance and fractionation characteristics and hardly causes damage such as peeling in the membrane.

Moreover, the intensity | strength of the said hollow fiber membrane will not be specifically limited if it can be used as a hollow fiber membrane. Strength of the hollow fiber membrane, specifically, a tensile strength is preferably 3~15N / mm ^2, more preferably 3~13N / mm ^2, is 3~11N / mm ² More preferably. In addition, the strength of the hollow fiber membrane is specifically 30 to 250% in terms of tensile elongation, more preferably 50 to 200%, and further preferably 50 to 180%. preferable. As the strength of the hollow fiber membrane, if the tensile strength or tensile elongation is within the above range, it can be suitably used as a hollow fiber membrane. The tensile strength is obtained from the load when the hollow fiber membrane cut to a predetermined size is pulled at a predetermined speed and the hollow fiber membrane breaks, and the tensile elongation is the value when the fracture occurs. It represents the elongation of the hollow fiber membrane.

  Moreover, the shape of the hollow fiber membrane which concerns on this embodiment is not specifically limited. The hollow fiber membrane has a hollow fiber shape, and one side in the longitudinal direction may be open, and the other side may be open or closed. Examples of the shape of the hollow fiber membrane include a hollow fiber shape in which one side in the longitudinal direction is left open and the other side is closed. Moreover, as a shape of the open | release side of a hollow fiber membrane, the case where it is a shape as shown in FIG. 1, etc. are mentioned, for example. FIG. 1 is a partial perspective view of a hollow fiber membrane according to an embodiment of the present invention.

  The outer diameter R1 of the hollow fiber membrane is preferably 0.5 to 7 mm, more preferably 1 to 2.5 mm, and further preferably 1 to 2 mm. Such an outer diameter is a suitable size as a hollow fiber membrane provided in an apparatus for realizing a separation technique using a hollow fiber membrane.

  Further, the inner diameter R2 of the hollow fiber membrane is preferably 0.4 to 3 mm, more preferably 0.6 to 2 mm, and further preferably 0.6 to 1.2 mm. When the inner diameter of the hollow fiber membrane is too small, the permeate resistance (pressure loss in the tube) increases and the flow tends to be poor. Further, if the inner diameter of the hollow fiber membrane is too large, the shape of the hollow fiber membrane cannot be maintained, and the membrane tends to be crushed or distorted.

  Moreover, the film thickness T of the hollow fiber membrane is 0.2 to 1 mm, more preferably 0.25 to 0.5 mm, and further preferably 0.25 to 0.4 mm. When the hollow fiber membrane is too thin, deformation such as distortion tends to occur due to insufficient strength. On the other hand, if the film thickness is too thick, it is difficult to obtain a suitable film structure, for example, it is difficult to suppress the generation of macrovoids. In some cases, the strength may decrease. On the other hand, since the hollow fiber membrane according to the present embodiment can maintain high water permeability even if the film thickness is changed, from the viewpoint of strength, the hollow fiber having a relatively thick film thickness depending on the use environment such as a module. It is also possible to form a film.

  If the outer diameter R1, inner diameter R2, and film thickness T of the hollow fiber membrane are within the above ranges, respectively, the hollow fiber membrane has a suitable size as a hollow fiber membrane provided in a device that realizes a separation technique using a hollow fiber membrane. In addition, the apparatus can be miniaturized.

  Moreover, the manufacturing method of the hollow fiber membrane which concerns on this embodiment will not be specifically limited if the above-mentioned hollow fiber membrane can be manufactured. Examples of the method for producing the hollow fiber membrane include a method for producing a porous hollow fiber membrane. As a method for producing such a porous hollow fiber membrane, a method utilizing phase separation is known. Examples of a method for producing a hollow fiber membrane utilizing this phase separation include a non-solvent induced phase separation method (NIPS method) and a thermally induced phase separation method (TIPS method). Can be mentioned.

  The NIPS method refers to a polymer stock solution solvent in which a uniform polymer stock solution in which a polymer is dissolved in a solvent is brought into contact with a non-solvent that does not dissolve the polymer, and the concentration difference between the polymer stock solution and the non-solvent is a driving force. This is a method of causing a phase separation phenomenon by substitution with a non-solvent. In the NIPS method, the pore diameter of the formed pores generally changes depending on the solvent exchange rate. Specifically, the slower the solvent exchange rate, the larger the pore size. In addition, in the production of the hollow fiber membrane, the solvent exchange rate is the fastest at the contact surface with the non-solvent, and becomes slower as it goes into the membrane. For this reason, the hollow fiber membrane produced by the NIPS method is dense in the vicinity of the contact surface with the non-solvent and has an asymmetric structure in which pores are gradually coarsened toward the inside of the membrane.

  In addition, the TIPS method means that a polymer can be dissolved at a high temperature but dissolved at a high temperature in a poor solvent that cannot be dissolved when the temperature is lowered, and the solution is cooled to cause a phase separation phenomenon. It is a method to make it. Since the heat exchange rate is generally faster than the solvent exchange rate in the NIPS method and it is difficult to control the rate, the TIPS method tends to form uniform pores in the film thickness direction.

  The method for producing the hollow fiber membrane is not particularly limited as long as the hollow fiber membrane can be produced. Specifically, this manufacturing method includes the following manufacturing methods. As this manufacturing method, the process (preparation process) of preparing the film forming stock solution containing resin and solvent which comprise a hollow fiber membrane, the process of extruding the said film forming stock solution in a hollow fiber shape (extrusion process), and the extruded And a method including a step (formation step) of forming a hollow fiber membrane by coagulating a hollow fiber membrane-forming stock solution. And in such a manufacturing method, what adjusted various conditions as follows so that the said hollow fiber membrane may be obtained is mentioned.

  First, the preparation step in the production method according to the present embodiment is not particularly limited as long as a film-forming stock solution containing a vinylidene fluoride resin as a resin constituting the hollow fiber membrane and a solvent can be prepared. Moreover, this film-forming stock solution may contain other than the resin and the solvent, and may contain, for example, a phase separation accelerator. Moreover, as resin which comprises a hollow fiber membrane, what is necessary is just to contain vinylidene fluoride resin, and resin other than vinylidene fluoride resin may be included. Moreover, specifically as a preparation process, the method etc. which heat-stir the raw material of a film forming undiluted solution etc. are mentioned, for example. Moreover, it is preferable to knead | mix at the time of heating and stirring. That is, a method of mixing a vinylidene fluoride resin, a solvent, and, if necessary, a phase separation accelerator and the like, which are raw materials for the film-forming stock solution, at a predetermined ratio and kneading in a heated state is preferable. By doing so, it is considered that a membrane-forming stock solution in which each component that is a raw material of the membrane-forming stock solution is uniformly dispersed is obtained, and a hollow fiber membrane can be suitably produced. Moreover, in kneading | mixing, a biaxial kneading equipment, a kneader, a mixer, etc. can be used, for example.

  Moreover, the extrusion process in the manufacturing method which concerns on this embodiment will not be specifically limited if it is a process of extruding the said film forming undiluted | stock solution to hollow fiber shape. Examples of the extrusion step include a step of extruding the film-forming stock solution from a hollow fiber molding nozzle shown in FIG. FIG. 2 is a schematic view showing an example of a hollow fiber molding nozzle used in the manufacturing method according to the embodiment of the present invention. FIG. 2A is a cross-sectional view, and FIG. 2B is a plan view showing a discharge port side of a hollow fiber molding nozzle for discharging a film-forming stock solution. Specifically, the hollow fiber molding nozzle 21 here includes an annular outer discharge port 26 and a circular or annular inner discharge port 27 arranged inside the outer discharge port 26. The hollow fiber molding nozzle 21 is provided at the end of the flow pipe 24 through which the film-forming stock solution is circulated, and the film-forming stock solution flowing in the flow pipe 24 is discharged outside through the flow path 22 in the nozzle. Discharge from the outlet 26. In addition, the hollow fiber molding nozzle 21 causes the internal coagulating liquid to flow through the flow pipe 25 at the same time as the film-forming stock solution is discharged from the outer discharge port 26, and passes through the flow path 23 in the nozzle. Discharge from the outlet 27. By doing so, the hollow fiber-shaped film-forming stock solution extruded from the hollow fiber molding nozzle 21 is brought into contact with the internal coagulation liquid.

  Moreover, the formation process in the manufacturing method which concerns on this embodiment will not be specifically limited if it is the process of coagulating the extruded hollow fiber-shaped film forming stock solution and forming a hollow fiber membrane. Specific examples of the forming step include a step of immersing the hollow fiber-shaped film-forming stock solution extruded in the extrusion step in an external coagulation solution stored in an external coagulation bath.

  The resin is a resin contained in the hollow fiber membrane. Specifically, it is a resin containing a vinylidene fluoride resin as described above.

  Moreover, the said solvent will not be specifically limited if it is a solvent which can dissolve the said resin at the time of preparation of a film-forming stock solution, or an extrusion process. The solvent is preferably water-soluble. If it is water-soluble, it is possible to use water when extracting the solvent from the hollow fiber membrane after membrane formation, and the extracted solvent can be disposed of by biological treatment or the like.

  Examples of the solvent include caprolactone such as γ-butyrolactone and ε-caprolactone, dimethylformamide, dimethyl sulfoxide, dimethylacetamide, dimethyl sulfoxide, and acetone. Among the solvents exemplified above, γ-butyrolactone and dimethylformamide are preferable as the solvent from the viewpoints of environmental burden, safety, cost, and the like. Moreover, as said solvent, the solvent resin of the said illustration may be used independently, and may be used in combination of 2 or more type.

  Further, the phase separation accelerator is not particularly limited. The phase separation accelerator plays a role of promoting the start of phase separation in the porous formation process of the hollow fiber membrane. The phase separation accelerator is preferably water-soluble. If it is water-soluble, it is possible to use water when extracting the phase separation accelerator from the hollow fiber membrane after membrane formation, and the extracted phase separation accelerator can be disposed of by biological treatment or the like. Is possible.

  Examples of the phase separation accelerator include water, polyol compounds, saccharides, polyol compounds and hydrophilic resins other than saccharides (other hydrophilic resins), nonionic surfactants, cationic surfactants, and An anionic surfactant etc. are mentioned. Examples of the polyol compound include ethylene glycol, propylene glycol, triethylene glycol, polyethylene glycol, glycerin, hexylene glycol, butanediol, polyvinyl alcohol, and derivatives thereof. Examples of the saccharide include cellulose, cellulose acetate, cellulose diacetate, ethyl cellulose, and derivatives thereof. Examples of other hydrophilic resins include polyvinyl acetate, polyvinyl pyrrolidone, and polyacrylic acid. Examples of the nonionic surfactant include polyglycerin fatty acid esters such as decaglyceryl monolaurate, polyoxyethylene glycerin fatty acid esters such as polyoxyethylene glyceryl monostearate, polyoxyethylene lauryl ether and polyoxyethylene. Polyoxyethylene alkyl ethers such as ethylene cetyl ether, polyoxyethylene polyoxypropylene alkyl ethers such as polyoxyethylene polyoxypropylene cetyl ether, polyoxyethylene alkylphenyl ethers such as polyoxyethylene nonylphenyl ether, monopalmitin And polyoxyethylene sorbitan fatty acid esters such as acid polyoxyethylene sorbitan, and copolymers thereof. Moreover, as said phase-separation promoter, the said exemplary compound may be used independently and may be used in combination of 2 or more type.

  Moreover, as content of each component in the said film forming undiluted | stock solution, the following are mentioned. First, the content of the resin is preferably 20 to 40% by mass, and more preferably 20 to 35% by mass with respect to the film-forming stock solution. It is preferable that content of the said solvent is 15-70 mass% with respect to the said film forming undiluted | stock solution, and it is more preferable that it is 20-65 mass%. The content of the phase separation accelerator is preferably 5 to 20% by mass and more preferably 8 to 20% by mass with respect to the membrane-forming stock solution.

  Moreover, the said film-forming stock solution should just contain the said resin and the said solvent, and may consist of these two components. Moreover, since it is preferable that the said film forming undiluted solution contains the said phase-separation promoter, it is preferable that the said resin, the said solvent, and the said phase-separation promoter are included, and even if it consists of these three components Good. The film-forming stock solution may contain other components (additives) in addition to these three components.

  The additive is not particularly limited. For example, the role of a filler for adjusting the viscosity of the film-forming stock solution at the time of the extrusion process, and the core of the porous body can be mentioned. Examples of the additive include silica, calcium silicate, aluminum silicate, magnesium silicate, calcium carbonate, magnesium carbonate, calcium phosphate, metal oxide, metal hydroxide, and salts. Moreover, as a metal oxide, oxides, such as iron and zinc, etc. are mentioned, for example. Examples of the metal hydroxide include hydroxides such as iron and zinc. Examples of the salts include salts such as sodium, potassium, and calcium. In particular, an additive having a cohesive property is usually added to a composition in which the vinylidene fluoride resin and the solvent are phase-separated, so that the solution stability of the vinylidene fluoride resin and the solvent is improved. It can also have an improved function. Moreover, the additive which has cohesiveness can also give the function as a thickening filler at the time of mixing. From such a point, as the additive, silica is preferable among the above-exemplified additives. The silica may be any of hydrophilic, hydrophobic, spherical, or amorphous silica. Moreover, as said additive, the additive of the said illustration may be used independently, and may be used in combination of 2 or more type.

Further, as described above, the membrane forming stock solution includes a vinylidene fluoride resin as a resin constituting the hollow fiber membrane, and further includes a vinylidene fluoride resin such as a solvent and, if necessary, a phase separation accelerator. Including other ingredients. In this film forming stock solution, the distance (HSP distance) of the solubility parameter (SP value) between the component other than the vinylidene fluoride resin and the vinylidene fluoride resin is 0.1 to 15 (MPa) ^1/2. It is preferable that it is 1-13 (MPa) ^1/2 , and it is more preferable that it is 2-12 (MPa) ^1/2 .

  Here, the HSP distance is a parameter for evaluating the affinity between one substance and another substance, and is defined by the following formula using Hansen's three-dimensional solubility parameters (dD, dP, dH) (details) Non-patent literature: Hansen, Charles (2007). See Hansen Solubility Parameters: A user's handbook, Second Edition. Boca Raton, Fla: CRC Press.). Further, the HSP distance between the substance A and the substance B can be expressed as HSP (dA-B) and obtained by the following equation.

HSP (dA−B) = [4 × (dD _A −dD _B ) ² + (dP _A −dP _B ) ² + (dH _A −dH _B ) ² ] ^0.5
This HSP (dA-B) is a comparison of the solubility of the substance A and the substance B by a multidimensional vector, and the smaller this value, the higher the solubility. Here, the HSP (dA-B) and the three-dimensional solubility parameters (dD, dP, dH) in the formula are values related to the SP value [(MPa) ^1/2 ]. Specifically, dD represents a van der Waals force, that is, an SP value dispersion force term. Further, dP represents a dipole moment force, that is, an SP-dipole force. Moreover, dH shows hydrogen bond strength, ie, hydrogen bond strength of SP value. In the case of two or more kinds of mixed substances, calculation is performed by multiplying the respective weight fractions. In addition, when an additive such as silica or inorganic salt is used for the film forming stock solution, since the SP value cannot be calculated for these, the HSP distance is not considered.

  From this, the distance (HSP distance) of the solubility parameter (SP value) between the component other than the vinylidene fluoride resin and the vinylidene fluoride resin is calculated from the above formula. And if this HSP distance is in the said range, it will be easy to prepare the said membrane forming undiluted solution, and it will be easy to manufacture the said hollow fiber membrane. This is presumably because the vinylidene fluoride resin is easily dissolved in the preparation step and the extrusion step. And from this, it is considered that the preparation process and the extrusion process do not require more energy than necessary. Moreover, since the solubility of vinylidene fluoride resin is high, the membrane forming stock solution is stable, and the performance of the obtained hollow fiber membrane tends to be stable.

  And the temperature of the said film forming undiluted | stock solution in the said extrusion process can be made low by using such a film forming undiluted | stock solution. Specifically, the temperature is preferably less than 180 ° C, more preferably less than 150 ° C, and even more preferably less than 120 ° C. When a hollow fiber membrane is produced using a membrane-forming stock solution that can be extruded in such a temperature range, the hollow fiber membrane according to this embodiment can be suitably produced. If this temperature is too high, it exceeds the temperature range of steam used as a general industrial heat source, so special and melting equipment such as high-temperature steam and electric heaters are required, and the manufacturing cost tends to increase. On the other hand, when a film-forming stock solution having high solubility of the vinylidene fluoride resin is used, a crystal structure other than the α crystal structure tends to be formed. However, the hollow fiber membrane according to this embodiment does not need to have a large α crystal structure as a whole, and the ratio of the α crystal structure on one surface side may be increased under the conditions described later.

Moreover, as a manufacturing method of the hollow fiber membrane which concerns on this embodiment, in addition to the said conditions, it is preferable to satisfy | fill the following conditions, for example. Of the coagulating liquid that is contacted when the film-forming stock solution is coagulated in the extrusion process or the forming process, the coagulating liquid that comes into contact with the surface on which the surface having the larger pore diameter is formed is the film-forming stock solution. It is preferable that the distance (HSP distance) of the solubility parameter (SP value) is 5 to 1000 (MPa) ^1/2 . And it is preferable that the viscosity in 20 degreeC of this coagulation liquid is 50-3000 cP.

More specifically, when producing a hollow fiber membrane in which the holes existing on the outer peripheral surface are smaller than the holes existing on the inner peripheral surface, the solubility parameter (SP value) of the internal coagulating liquid and the membrane forming stock solution The distance (HSP distance) is preferably 5 to 1000 (MPa) ^1/2 , and the viscosity of the internal coagulation liquid at 20 ° C. is preferably 50 to 3000 cP.

Moreover, when manufacturing a hollow fiber membrane in which the holes existing on the inner peripheral surface are smaller than the holes existing on the outer peripheral surface, the distance (HSP distance) of the solubility parameter (SP value) between the external coagulating liquid and the membrane forming stock solution ) Is 5 to 1000 (MPa) ^1/2 , and the viscosity of the external coagulation liquid at 20 ° C. is preferably 50 to 3000 cP.

  Hereinafter, the case where the hole present on the outer peripheral surface is smaller than the hole present on the inner peripheral surface will be described, but as described above, by replacing the internal coagulating liquid and the external coagulating liquid, A hollow fiber membrane in which the holes present on the inner peripheral surface are smaller than the holes present on the outer peripheral surface can be produced.

As the internal coagulating liquid here, the distance (HSP distance) to the dissolution parameter (SP value) of the film-forming stock solution, which is the above condition, is 5 to 1000 (MPa) ^{1/2 and} at 20 ° C. A coagulation liquid having a viscosity of 50 to 3000 cP is preferable.

Specifically, the distance (HSP distance) of the dissolution parameter (SP value) between the internal coagulation liquid and the film-forming stock solution is preferably 5 to 1000 (MPa) ^1/2 , and 5 to 900 (MPa). More preferably, it is ^1/2 , and more preferably 5-800 (MPa) ^1/2 . If this HSP distance is too small, solidification from the inner peripheral surface side tends not to proceed sufficiently. On the other hand, if the HSP distance is too large, the α crystal structure ratio tends not to be sufficiently increased. This is considered to be because solidification from the inner peripheral surface side proceeds too much and the pores formed on the inner peripheral surface side become too small. From these facts, by using the internal coagulation liquid with the HSP distance within the above range, it is easy to form a hollow fiber membrane having an appropriate second ratio on the inner peripheral surface, that is, the surface on the side where the pore diameter is large. Can be manufactured.

  Moreover, it is preferable that the viscosity at 20 degreeC of the said internal coagulation liquid is 50-3000 cP, It is more preferable that it is 50-1500 cP, It is further more preferable that it is 100-1500 cP. If the viscosity is too low, the ratio of the α crystal structure tends not to be sufficiently increased. This is considered to be because solidification from the inner peripheral surface side proceeds too much and the pores formed on the inner peripheral surface side become too small. Moreover, when the said viscosity is too high, there exists a tendency for solidification from an inner peripheral surface side not to fully advance. From these facts, by using the internal coagulation liquid having the viscosity within the above range, a hollow fiber membrane having an appropriate second ratio can be easily produced on the inner peripheral surface, that is, the surface on the side where the pore diameter is large. can do.

  Examples of the internal coagulation liquid include a high viscosity liquid such as glycerin, ethylene glycol, and a polymer aqueous solution having a relatively high concentration of 10% by mass or more, and a structure similar to the solvent included in the film forming stock solution. Is mentioned.

  Examples of the internal coagulation liquid include glycerin, ethylene glycol, a mixed solvent of dimethylformamide and glycerin, a mixed solvent of dimethylacetamide and glycerin, a mixed solvent of γ-butyrolactone and glycerin, and γ-butyrolactone and polyvinyl alcohol. Examples thereof include a mixed solvent, a mixed solvent of γ-butyrolactone and polyvinylpyrrolidone, and a mixed solvent of water and polyvinyl alcohol. As the internal coagulation liquid, the above exemplified solvents may be used alone or in combination of two or more.

  Moreover, it is preferable that the temperature of an internal coagulation liquid is 40-170 degreeC from a viewpoint of ensuring the uniformity of an internal coagulation liquid. That is, the temperature of the internal coagulation liquid is preferably adjusted between 40 and 170 ° C.

  The external coagulation liquid is not particularly limited as long as it can coagulate the extruded hollow fiber-shaped film-forming stock solution by contacting with the extruded hollow-fiber film-forming stock solution. In this case, the external coagulation liquid comes into contact with the side acting as a separation layer to form an outer peripheral surface. And, as described above, the α crystal structure excess ratio on the outer peripheral surface does not need to be increased as long as the above-mentioned relationship is satisfied as the first ratio and the second ratio. A general thing can be used as an external coagulation liquid to be used. Specific examples of the external coagulation liquid include water and aqueous solutions containing salts or solvents. Examples of the salts here include various salts such as sulfates, chlorides, nitrates, and acetates. Examples of the solvent contained in the external coagulation liquid include dimethylformamide.

  Further, the forming step may run in a gas, usually in the air, before the extruded hollow fiber-shaped film-forming stock solution is brought into contact with the external coagulation liquid. That is, in the forming step, the hollow fiber-shaped film-forming stock solution extruded in the extruding step may be brought into contact with an external coagulation liquid after traveling in gas. The distance traveled in the gas is not particularly limited, and is preferably 5 to 300 mm, for example. Traveling in this gas can suitably perform solvent exchange between the extruded hollow fiber-shaped film-forming stock solution and the internal coagulation liquid, and the hollow fiber shape is stabilized and the spinnability is improved. In the manufacturing method according to this embodiment, traveling in the gas may not be performed.

  Moreover, the manufacturing method which concerns on this embodiment may extend | stretch the hollow fiber membrane formed by the said formation process to a longitudinal direction. Although this extending | stretching method is not specifically limited, For example, the extending | stretching process etc. in a water bath, for example, a warmed water bath, etc. are mentioned. In addition, after extending | stretching, if the force concerning extending | stretching is open | released, it will shrink | contract in a longitudinal direction. When such stretching and contraction are performed, the hollow fiber membrane is improved in permeation performance and gas permeability. This is considered that the independent hole existing in the membrane is cleaved to become a communication hole, the communication in the membrane is improved, and the permeation performance and gas permeability are improved. Furthermore, when such stretching and shrinking are performed, there is an advantage that the direction of the fibers of the hollow fiber membrane is homogenized and the strength is improved. In the manufacturing method according to the present embodiment, this stretching and shrinking need not be performed.

  Moreover, the manufacturing method which concerns on this embodiment may wash | clean the hollow fiber membrane formed by the said formation process. Examples of the washing method include a method of washing the hollow fiber membrane in a water bath. By this washing, the solvent, phase separation accelerator and the like remaining inside can be suitably removed from the formed hollow fiber membrane.

  Moreover, the manufacturing method according to the present embodiment may include a step of imparting hydrophilicity to the hollow fiber membrane. The step of imparting hydrophilicity is not particularly limited as long as the hydrophilicity of the hollow fiber membrane can be enhanced. Examples of this step include a step of immersing the hollow fiber membrane in a hydrophilic resin solution and then crosslinking the hydrophilic resin impregnated in the hollow fiber membrane. More specifically, in this step, the hollow fiber membrane is immersed in a 3% by weight aqueous polyvinyl alcohol solution, and the hollow fiber membrane immersed in the aqueous polyvinyl alcohol solution is 1% by weight glutaraldehyde and 4% by weight sulfuric acid. Soak in an aqueous solution containing By doing so, the polyvinyl alcohol impregnated in the hollow fiber membrane is crosslinked. This makes the hollow fiber membrane hydrophilic.

  Moreover, as a method for imparting hydrophilicity to the hollow fiber membrane, in addition to the above steps, a method for containing a hydrophilic resin in a film-forming stock solution, or a method in which a hydrophilic resin is contained in an internal coagulation liquid, and the hydrophilic resin is used. And a method of imparting diffusion to the hollow fiber membrane.

  Moreover, the hollow fiber membrane which concerns on this embodiment can be used for a membrane filtration method. Specifically, for example, a hollow fiber membrane is used to be modularized as follows, and this modularized product can be used for membrane filtration. More specifically, a predetermined number of hollow fiber membranes according to this embodiment are bundled, cut into a predetermined length, and filled into a casing having a predetermined shape, and the end of the hollow fiber bundle is a polyurethane resin or an epoxy resin. It is fixed to the casing by a thermosetting resin such as a module to form a module. In addition, as the structure of this module, there are various types such as a type in which both ends of the hollow fiber membrane are fixed open, one end of the hollow fiber membrane is fixed open and the other end is sealed, but the type is not fixed. A structure having a known structure is known, and the hollow fiber membrane according to this embodiment can be used in any module structure.

  Moreover, the hollow fiber membrane which concerns on this embodiment is modularized as mentioned above, for example, can be integrated in a membrane filtration apparatus as shown in FIG. FIG. 3 is a schematic view showing an example of a membrane filtration device provided with a hollow fiber membrane according to an embodiment of the present invention. The membrane filtration device 31 includes the membrane module 32 obtained by modularizing the hollow fiber membrane as described above. And as for this membrane module 32, what has opened the hollow part in the upper end part 33 of a hollow fiber membrane, and the lower end part 34 has sealed the hollow part with the epoxy resin, for example. Examples of the membrane module 32 include those made of 70 hollow fiber membranes having an effective membrane length of 100 cm. In the membrane filtration device 31, the liquid to be treated (filtered water) filtered from the membrane module 32 is discharged from the introduction port 36 through the introduction port 35. By doing so, filtration using a hollow fiber membrane is implemented. The air introduced into the membrane filtration device 31 is discharged from the air vent 37. In the membrane filtration method here, the liquid to be treated is filtered by allowing the liquid to be treated to permeate from the outer surface to the inner surface of the hollow fiber membrane. Therefore, the outer surface side of the hollow fiber membrane is called a primary side, and the inner surface side is also called a secondary side. When a hollow fiber membrane having holes smaller on the inner peripheral surface than pores existing on the outer peripheral surface is used, the liquid to be treated permeates from the inner surface to the outer surface of the hollow fiber membrane, thereby The treatment liquid is filtered.

  The hollow fiber membrane which concerns on this embodiment is modularized in this way, and is used for various uses, such as purified water processing, drinking water manufacture, industrial water manufacture, and waste water treatment. That is, in the membrane filtration method, the liquid to be treated which is a treatment target is a liquid for achieving such an application, and includes an aqueous medium containing water as a main component.

  Moreover, the hollow fiber membrane which concerns on this embodiment can perform a liquid process, specifically, a filtration process, by using for the above membrane filtration methods. Specifically, the liquid treatment method using the hollow fiber membrane includes a filtration step of filtering the liquid to be treated using the hollow fiber membrane, and a chemical washing step of washing the hollow fiber membrane with a chemical solution. The method etc. which perform the said filtration process and the said chemical washing process alternately are mentioned. If it is such a liquid processing method, the liquid processing by the filtration process using a hollow fiber membrane can be performed suitably over a long period of time. Specifically, first, the chemical washing step performed between the filtration step and the filtration step is periodically performed, so that the reduction in the filtration efficiency in the filtration step using the hollow fiber membrane can be sufficiently suppressed. Therefore, the liquid process by the filtration process using a hollow fiber membrane can be suitably performed over a long period of time.

  The present invention will be described more specifically with reference to the following examples. However, the scope of the present invention is not limited to these examples.

[Example 1]
First, as a resin constituting the hollow fiber membrane, polyvinylidene fluoride (PVDF 1: Kynar 741 manufactured by Arkema Co., Ltd.) which is a vinylidene fluoride resin, and dimethylformamide (DMF: DMF manufactured by Mitsubishi Gas Chemical Co., Ltd.) as a solvent. ) And polyvinyl alcohol (PVA: PVA-505 manufactured by Kuraray Co., Ltd.) as a phase separation accelerator was prepared in a mass ratio of 30:52:18. The mixture was dissolved in a dissolution tank at a constant temperature of 95 ° C. to obtain a film-forming stock solution. Table 1 shows the dissolution parameter (SP value) of the film-forming stock solution and the SP value distance (HSP distance 1) between components other than the vinylidene fluoride resin and the vinylidene fluoride resin.

  The obtained membrane forming stock solution was extruded from a double-ring nozzle (hollow fiber membrane forming nozzle) having an outer diameter of 1.6 mm and an inner diameter of 0.8 mm as shown in FIG. At this time, a mixture obtained by mixing dimethylformamide (DMF) and glycerin (purified glycerin manufactured by Kao Corporation) so as to have a mass ratio of 60:40 as an internal coagulation liquid was simultaneously discharged with the film forming stock solution. At this time, when the temperature of the raw film forming solution was gradually increased and reached a temperature at which stable discharge was possible, extrusion was started. This temperature (discharge temperature) was 100 ° C. The dissolution parameters (SP value) of the internal coagulating liquid, the SP value distance (HSP distance 2) between the internal coagulating liquid and the film forming stock solution, and the viscosity at 20 ° C. of the internal coagulating liquid are shown in Table 1.

  The film-forming stock solution extruded together with the internal coagulating liquid was immersed in an external coagulating liquid composed of a 20% by mass dimethylformamide (DMF) aqueous solution through an idle running distance of 30 mm. By doing so, the membrane-forming stock solution was solidified, and a hollow fiber membrane was obtained. Table 1 shows the dissolution parameter (SP value) of the external coagulation liquid, the SP value distance (HSP distance 3) between the external coagulation liquid and the film-forming stock solution, and the viscosity at 20 ° C. of the external coagulation liquid. The viscosity of the internal coagulation liquid at 20 ° C. and the viscosity of the external coagulation liquid at 20 ° C. were measured using a viscometer (Brookfield viscometer manufactured by Toki Sangyo Co., Ltd.).

  Next, the obtained hollow fiber membrane was washed in water. By doing so, the solvent and the phase separation accelerator were extracted and removed from the hollow fiber membrane. The hollow fiber membrane thus obtained is the hollow fiber membrane according to Example 1. The hollow fiber membrane thus obtained had an outer diameter of 1.3 mm, an inner diameter of 0.8 mm, and a film thickness of 0.25 mm.

  Moreover, the inner peripheral surface and outer peripheral surface of the hollow fiber membrane which concerns on Example 1 were observed using the scanning electron microscope (S-3000N by Hitachi, Ltd.). From the obtained image, it was found that the hollow fiber membrane according to Example 1 was a hollow fiber membrane having an inclined structure in which the holes existing on the outer peripheral surface are smaller than the holes existing on the inner peripheral surface. In addition, a photograph obtained by observing the inner peripheral surface of the hollow fiber membrane with a scanning electron micrograph is binarized using image measurement software (Image-Pro Plus, manufactured by Planetron Co., Ltd.), and a threshold value is obtained using the Otsu method. And the diameter of the pores existing on the inner surface of the hollow fiber membrane was measured. This diameter was the support side pore diameter and was 2 μm.

  First, the α crystal structure excess rate, crystallinity, and heterogeneous bond rate of the obtained hollow fiber membrane were measured.

[Α crystal structure excess (peripheral surface)]
First, each infrared absorption (IR) spectrum of the inner peripheral surface and outer peripheral surface of the obtained hollow fiber membrane was measured using an infrared spectrophotometer (JIR-5500, JEOL Ltd.). Specifically, the measurement was performed from both the separation layer side and the support layer side of the hollow fiber membrane by a single reflection ATR (Attenuated Total Reflectance) method with a diamond cell (with a depth of about 5 μm or less). . Then, in the resulting IR spectrum was calculated the ratio (peak intensity × 100 peak intensity / 840 cm ^-1 of 763cm ^-1) of the peak intensity of the peak intensity and 840 cm ^-1 of 763cm ^-1. This ratio was defined as the α crystal structure excess ratio in each of the inner peripheral surface and the outer peripheral surface.

[Α crystal structure excess (overall)]
First, using a differential scanning calorimeter (DSC: DSC Q2000 manufactured by TA Instruments Japan Co., Ltd.), the resulting hollow fiber membrane was heated from 25 ° C. to 200 ° C. at a rate of temperature increase of 10 ° C. / The endothermic peak detected when the temperature was raised in minutes was measured. Ratio of the endothermic peak at 168 to 175 ° C. and the endothermic peak at 162 to 168 ° C. in the obtained endothermic peak curve (DSC curve) [peak (J / g) / 162 endothermic at 168 to 175 ° C.] Peak (J / g) × 100] that absorbs heat at ˜168 ° C. was calculated. This ratio was defined as the α crystal structure excess ratio of the entire hollow fiber membrane.

  As the peak that absorbs heat at 168 to 175 ° C., the peak detected on the highest temperature side was adopted because the melting point changes with the additive depending on the composition. This peak is a peak attributed to the α crystal structure. The peaks that absorb heat at 162 to 168 ° C. are all peaks detected at a low temperature other than the peak attributed to the α crystal structure because the melting point varies depending on the composition depending on the additive. This peak is a peak attributed to the β crystal structure.

[Crystallinity]
The total endothermic peak (J / g) detected at 25 to 200 ° C., which is the entire measurement region, was measured from the DSC curve obtained by the same method as the above α crystal structure excess (overall). Here, since the endothermic amount of the completely crystalline PVDF was 93.1 J / g, the ratio of the endothermic amount of the completely crystalline PVDF to the total endothermic peak was calculated. This ratio was defined as the crystallinity.

[Heterogeneous binding rate]
The obtained hollow fiber membrane was measured for ¹ H-NMR (manufactured by JEOL RESONANCE Co., Ltd.) using heavy DMSO as a heavy solvent. When the peak of the methyl group of residual DMSO is 2.50 ppm, the ratio of the integrated value of the proton peak detected at around 2.25 ppm to the integrated value of the proton peak detected at around 2.90 ppm (2.25 ppm The integral value of the proton peak detected in the vicinity / the integral value of the proton peak detected in the vicinity of 2.90 ppm × 100) was calculated. This ratio was defined as the heterogeneous binding rate. The proton peak detected in the vicinity of 2.25 ppm is a peak derived from a different bond, and the proton peak detected in the vicinity of 2.90 ppm is a peak derived from a normal bond.

[Permeation performance: water permeability]
In addition, the water permeability of the obtained hollow fiber membrane was determined by measuring the amount of filtrate per unit time in the following operation using the hollow fiber membrane, and from the obtained amount and the membrane area. Calculated.

  Using this hollow fiber membrane, a membrane filtration device 31 as shown in FIG. 3 was produced. The membrane module 32 loaded in the membrane filtration device 31 has an effective membrane length of 20 cm and 20 hollow fibers, and the upper end portion 33 is sealed with an epoxy resin. The upper end portion 33 has an open hollow portion of the hollow fiber membrane, and the lower end portion 34 has the hollow portion of the hollow fiber membrane sealed with an epoxy resin. This membrane filtration device 31 filtered pure water from the outer peripheral surface side of the hollow fiber membrane through the inlet port 35 and obtained filtered water from the outlet port 36 on the inner peripheral surface side of the upper end portion. At this time, the pressure difference between the membranes was adjusted to 0.1 MPa.

The water permeation amount obtained by this measurement method, that is, the water permeation amount at a transmembrane pressure difference of 0.1 MPa was 800 L / m ² / hour (800 LMH).

[Fractionation characteristics: fractional particle size, fractional molecular weight]
Next, the fraction particle diameter of the obtained hollow fiber membrane was measured by the following method.

  At least two kinds of particles having different particle diameters (cataloid SI-550, cataloid SI-45P, cataloid SI-80P, manufactured by JGC Catalysts & Chemicals, Inc., particle diameters 0.1 μm, 0.2 μm, manufactured by Dow Chemical Co., Ltd. , 0.5 μm polystyrene latex, etc.) was measured, and based on the measured value, the value of S at which R was 90 was determined in the following approximate formula, and this was taken as the fractional particle size.

R = 100 / (1−m × exp (−a × log (S)))
“A” and “m” in the above formula are constants determined by the hollow fiber membrane, and are calculated based on measured values of two or more types of rejection.

  The fractional particle size obtained by this measurement method was 0.02 μm.

  In some cases, the molecular weight cut-off may be measured instead of the fraction particle size. Using at least two or more kinds of polymers having different molecular weights instead of the above particles, the value of S at which R is 90 in the above formula was determined, and this was defined as the fractional molecular weight.

[Chemical resistance: chemical durability]
First, using a 5000 ppm hypochlorous acid aqueous solution as a chemical solution, the obtained hollow fiber membrane was immersed in a chemical solution heated to 60 ° C. for 30 days. The chemical solution was changed every day in consideration of the deactivation of hypochlorous acid. And the tensile strength of the hollow fiber membrane which was not immersed in a chemical | medical solution and the tensile strength of the hollow fiber membrane after being immersed for 30 days were each measured. From this obtained value, the tensile strength retention ratio (tensile strength of hollow fiber membrane after 30 days immersion / tensile strength of hollow fiber membrane not immersed in chemical solution × 100) was measured. The retention obtained by this measuring method was 90%. This retention rate was used as an index of chemical resistance. It can be seen that the higher the retention rate, the higher the chemical resistance.

  The tensile strength was measured as follows. First, the hollow fiber membrane which is a measuring object was cut | disconnected so that it might become 5 cm. The cut hollow fiber membrane was subjected to a tensile test at 100 mm / min in water at 25 ° C. using an autograph (AG-Xplus manufactured by Shimadzu Corporation), and the load when the hollow fiber membrane broke Was measured. The tensile strength was determined from the measured load.

[Film formation stability]
The permeation performance, fractionation characteristics, and strength were measured at a plurality of locations on the obtained hollow fiber membrane. If all the coefficient of variation (CV value) of the measured values are 5% or less, it is evaluated as “◯”, and if the coefficient of variation (CV value) of any of the measured values exceeds 5%, “×” It was evaluated.

  These results are shown in Table 2.

[Examples 2 to 5 and Comparative Examples 1 to 5]
A hollow fiber membrane was obtained in the same manner as in Example 1 except that the composition of the membrane-forming stock solution, the internal coagulating liquid, and the external coagulating liquid was changed to the compositions shown in Table 1. The discharge temperature and the support-side pore diameter are shown in Table 2.

  In the table, “PVDF 2” indicates polyvinylidene fluoride (Solef 6010 manufactured by Solvay Co., Ltd.). “GBL” indicates γ-butyrolactone (GBL manufactured by Mitsubishi Chemical Corporation). “PEG” indicates polyethylene glycol (PEG-600 manufactured by Sanyo Chemical Industries, Ltd.). “Silica 1” indicates silica (Aerosil 50 manufactured by Nippon Aerosil Co., Ltd.). “DMAc” indicates dimethylacetamide (DMAc manufactured by Mitsubishi Gas Chemical Company, Inc.). “PVP” indicates polyvinylpyrrolidone (Sokalan K-90P manufactured by BASF Japan Ltd.). “Silica 2” indicates silica (Fine Seal F-80 manufactured by Tokuyama Corporation). “Dioctyl phthalate” refers to dioctyl phthalate (dioctyl phthalate manufactured by Tokyo Chemical Industry Co., Ltd.).

  Moreover, when each hollow fiber membrane which concerns on Example 2, Example 4, Example 5, and Comparative Examples 1-3 was observed using the scanning electron microscope (S-3000N by Hitachi, Ltd.), it implemented. Similar to the hollow fiber membrane according to Example 1, it was found that the hollow fiber membrane has an inclined structure in which the holes existing on the outer peripheral surface are smaller than the holes existing on the inner peripheral surface.

  Specifically, the hollow fiber membrane which concerns on Example 2 and the hollow fiber membrane which concerns on Example 4 are shown as the example. 4 is a view showing a scanning electron micrograph of the outer peripheral surface of the hollow fiber membrane according to Example 2. FIG. FIG. 5 is a view showing a scanning electron micrograph of the inner peripheral surface of the hollow fiber membrane according to Example 2.

  FIG. 6 is a scanning electron micrograph of the cross section of the hollow fiber membrane according to Example 4. FIG. 7 is a scanning electron micrograph of the outer peripheral surface of the hollow fiber membrane according to Example 4. Moreover, FIG. 8 is a figure which shows the scanning electron micrograph of the internal peripheral surface of the hollow fiber membrane which concerns on Example 4. FIG.

  As can be seen from these photographs, the hollow fiber membranes according to Example 2, Example 4, Example 5, and Comparative Examples 1 to 3 are present on the outer peripheral surface in the same manner as the hollow fiber membrane according to Example 1. It is a hollow fiber membrane having an inclined structure in which the holes are smaller than the holes existing on the inner peripheral surface.

  Moreover, when the hollow fiber membrane which concerns on Example 3 was observed using the scanning electron microscope (S-3000N by Hitachi, Ltd.), the hole which exists in an inner peripheral surface is more than the hole which exists in an outer peripheral surface. It was a hollow fiber membrane having a small inclined structure.

  From these things, the hollow fiber membrane which concerns on each hollow fiber membrane which concerns on Examples 1-5 and Comparative Examples 1-3 is a porous hollow fiber membrane, Comprising: The hole diameter of the pore in the said hollow fiber membrane is The inclined structure gradually decreases toward at least one of the inner and outer peripheral surfaces. That is, it can be seen that the pore sizes in the hollow fiber membrane are sequentially different in the thickness direction. Further, it can be seen that a dense layered portion is formed on the outer peripheral surface or the vicinity of the inner peripheral surface, and a sparser portion is formed on the other portions.

  Note that, as described above, the hollow fiber membrane according to Example 3 is a hollow fiber membrane having an inclined structure in which the holes existing on the inner peripheral surface are smaller than the holes existing on the outer peripheral surface. The diameter of the pores existing on the outer surface is the support-side pore diameter. Moreover, the diameter of the hole which exists in the internal peripheral surface of a hollow fiber membrane is a separation side pore diameter.

  Moreover, the hollow fiber membrane which concerns on the comparative example 4 was a hollow fiber membrane which cannot measure a fraction characteristic appropriately. For this reason, the fractionation characteristics and the support-side pore diameter are indicated as “−”.

  Moreover, the hollow fiber membrane which concerns on the comparative example 5 was not able to manufacture a hollow fiber membrane. For this reason, the results are not shown in Table 2.

  From Tables 1 and 2, when the difference between the first ratio and the second ratio (second ratio-first ratio) is 50 to 350% (Examples 1 to 5), α of the entire hollow fiber membrane It was found that even when the crystal structure excess ratio (α crystal structure / β crystal structure × 100) was 120% or less, the hollow fiber membrane was excellent in water permeability, fractionation characteristics, and chemical resistance.

  In contrast, when the difference between the first ratio and the second ratio (second ratio-first ratio) is less than 50% and the α crystal structure excess of the entire hollow fiber membrane is low (Comparative Example 1). Compared with Examples 1-5, it was inferior to water-permeable performance and chemical resistance. Further, when the difference between the first ratio and the second ratio (second ratio-first ratio) was less than 50% (Comparative Examples 2 and 3), the film-forming stability was poor. In addition, if the discharge temperature was higher than 100 ° C., the film could be formed. However, when the film was formed at the same temperature as in Examples 1 to 5, a suitable hollow fiber membrane could not be obtained. Furthermore, in the hollow fiber membranes according to Comparative Examples 2 and 3, the α crystal structure excess ratio of the entire hollow fiber membrane is higher than Examples 1 to 5 and exceeds 120%. For this reason, the hollow fiber membranes according to Comparative Examples 2 and 3 can be improved in chemical resistance as compared with Examples 1 to 5, but are excellent in water permeability and fractionation characteristics. I could not say.

  From the above, when the difference between the first ratio and the second ratio (second ratio-first ratio) is 50 to 350%, the α crystal structure excess ratio (α crystal structure / It has been found that a hollow fiber membrane excellent in water permeability, fractionation characteristics, and chemical resistance can be obtained even if the β crystal structure × 100) is not particularly high, for example, 120% or less.

21 Nozzle for hollow fiber molding 22, 23 Flow path 24, 25 Flow pipe 26 Outer outlet 27 Inner outlet 31 Membrane filtration device 32 Membrane module 33 Upper end 34 Lower end 35 Inlet 36 Outlet 37 Air vent

Claims (9)

A porous hollow fiber membrane containing a vinylidene fluoride resin,
The pore diameter of the pores in the hollow fiber membrane has an inclined structure that gradually decreases toward at least one side of the inner and outer peripheral surfaces,
The first ratio, which is the abundance ratio of the α crystal structure with respect to the β crystal structure, on the surface having the smaller pore diameter is the abundance ratio of the α crystal structure with respect to the β crystal structure on the surface having the larger pore diameter. Below a certain second ratio,
The difference between the first ratio and the second ratio is 50 to 350%,
A hollow fiber membrane, wherein a third ratio, which is an abundance ratio of an α crystal structure to a β crystal structure, in the entire hollow fiber membrane is more than 0% and 120% or less.   The hollow fiber membrane according to claim 1, wherein the second ratio is greater than 50% and equal to or less than 400%.   The hollow fiber membrane according to claim 1 or 2, wherein the crystallinity is 30 to 80%.   The hollow fiber membrane according to any one of claims 1 to 3, wherein the vinylidene fluoride resin has a heterogeneous bond ratio of 5 to 30 mol%.   The hollow fiber membrane according to any one of claims 1 to 4, comprising a single layer. It is a manufacturing method of the hollow fiber membrane according to any one of claims 1 to 5,
A step of preparing a film-forming stock solution containing a vinylidene fluoride-based resin and a solvent;
An extrusion process for extruding the film-forming stock solution into a hollow fiber shape;
Forming a hollow fiber membrane by coagulating a membrane-forming stock solution extruded into a hollow fiber shape ,
Temperature of the casting dope in the extrusion step, the production method of the hollow fiber membrane, characterized in der Rukoto 120 ° C. or less. The film-forming stock solution, the component other than the vinylidene fluoride resin, distance solubility parameter of the vinylidene fluoride resin is as claimed in claim 6 is 0.1 to 15 (MPa) ^1/2 A method for producing a hollow fiber membrane. From the inner discharge port of the hollow fiber forming nozzle, the extrusion step includes an annular outer discharge port and a circular or annular inner discharge port disposed inside the outer discharge port. While extruding the membrane-forming stock solution from the outer discharge port to bring the extruded hollow fiber-shaped membrane-forming stock solution into contact with the internal coagulation solution,
The distance of the dissolution parameter between the internal coagulation liquid and the film-forming stock solution is 5 to 1000 (MPa) ^1/2 ,
The method for producing a hollow fiber membrane according to claim 6, wherein the internal coagulation liquid has a viscosity at 20 ° C of 50 to 3000 cP. The forming step is a step of forming a hollow fiber membrane by contacting the hollow fiber-shaped film-forming stock solution extruded in the extrusion step with an external coagulation liquid,
The distance of the dissolution parameter between the external coagulation liquid and the film-forming stock solution is 5 to 1000 (MPa) ^1/2 ,
The method for producing a hollow fiber membrane according to claim 6, wherein the external coagulation liquid has a viscosity at 20 ° C. of 50 to 3000 cP.

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