JP2015182060A - Hollow fiber membrane and manufacturing method of hollow fiber membrane - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a hollow fiber membrane which is excellent in both of permeability and fractionation characteristic, and to provide a manufacturing method of the hollow fiber membrane.SOLUTION: A hollow fiber membrane which contains vinylidene fluoride resin, has pure water permeation coefficient of 1×10mor more and 22×10mor less and has a cut-off particle diameter of 0.5 μm or less is used. Further, a manufacturing method of the hollow fiber membrane including: a preparation process for preparing membrane manufacturing original liquid containing a poor solvent which gets to compatible with the vinylidene fluoride resin at a specified temperature or more to produce one phase state and can cause phase separation due to temperature lowering and a polyvinyl pyrrolidone type resin; an extrusion process for extruding the membrane manufacturing original liquid into hollow fiber shape; and a process for bringing the extruded hollow fiber shaped membrane manufacturing original liquid into contact with external coagulation liquid to form the hollow fiber membrane, therein, a temperature of the external coagulation liquid being higher than a temperature at which the phase separation due to the temperature change starts is used.

Description

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

  Separation technology using hollow fiber membranes has advantages such as downsizing of the apparatus, so various fields, for example, water treatment fields such as water purification treatment, drinking water production, industrial water production and wastewater treatment, food industry field, Widely used in the pharmaceutical manufacturing field.

  The hollow fiber membrane used in such a separation technique is required to further improve permeation performance, fractionation characteristics, and the like. Specifically, if the permeation performance of the hollow fiber membrane is increased, the required membrane area is reduced, and the apparatus for realizing the separation technique using the hollow fiber membrane can be further downsized. For this reason, equipment costs and membrane replacement costs can be reduced, which is advantageous in terms of cost. Further, the hollow fiber membrane has an advantage that the removal object is widened if the fractionation characteristics can be enhanced.

  However, a separation membrane such as a hollow fiber membrane generally has a permeation performance and a separation performance such that if the permeation performance increases, the fractionation characteristics deteriorate, and if the fractionation characteristics increase, the permeation performance decreases. The image characteristics tend to be in a so-called trade-off relationship. For this reason, it is difficult for the hollow fiber membrane to improve both the permeation performance and the fractionation characteristics.

  On the other hand, a separation membrane using a fluorine-based material such as a vinylidene fluoride-based resin has attracted attention because of its high chemical durability, physical durability, and the like. Examples of the separation membrane using such a fluorine-based material include the hollow fiber membranes described in Patent Documents 1 to 3.

  Patent Document 1 discloses a sponge structure filtration region including pores having an average diameter of 0.01 μm to 0.5 μm, a support region having a sponge structure including pores having an average diameter of 0.5 μm to 5 μm, and an average diameter of 2 μm to 10 μm. A fluorine-containing hollow fiber membrane comprising a backwash region having a sponge structure including pores, wherein the filtration region, the support region, and the backwash region are sequentially formed from an outer surface to an inner surface. Yes.

  Patent Document 2 discloses a porous film for producing a porous film by a non-solvent induced phase separation method by discharging a film-forming stock solution containing at least a polyvinylidene fluoride resin and a solvent and bringing it into contact with a coagulating liquid containing at least a non-solvent. A method for manufacturing the membrane is described. Patent Document 2 discloses that, in this production method, the discharge temperature of the film-forming stock solution is equal to or higher than the melting point of the polyvinylidene fluoride resin and lower than the decomposition temperature of the polyvinylidene fluoride resin, and the temperature of the coagulation liquid. Is higher than the porous structure formation start temperature of the film-forming stock solution.

  Patent Document 3 discloses a fluororesin polymer separation membrane having both a three-dimensional network structure and a spherical structure, wherein the three-dimensional network structure is selected from cellulose ester, fatty acid vinyl ester, vinyl pyrrolidone, ethylene oxide, and propylene oxide. A polymer separation membrane containing a hydrophilic polymer having at least one kind is described.

Special table 2012-525966 gazette JP2013-202461A JP 2006-239680 A

  According to Patent Document 1, it is disclosed that excellent backwash performance and filtration performance can be exhibited while having excellent mechanical strength.

  Further, according to Patent Document 2, it is disclosed that a porous membrane capable of sufficiently removing micropathogens stably for a long period of time can be manufactured, as well as excellent water permeability and blocking performance against micropathogens, and extremely high chemical resistance. Has been.

  However, according to the study by the present inventors, the hollow fiber membrane described in Patent Document 1 and the porous membrane described in Patent Document 2 are not sufficiently high in permeation performance with respect to the fractionation characteristics, and the permeation performance is further improved. It is considered necessary.

  Further, according to Patent Document 3, it is disclosed that various performances such as separation characteristics, water permeability, chemical strength (chemical resistance), physical strength, and stain resistance can be increased.

  However, according to the study by the present inventors, the separation membrane described in Patent Document 3 sufficiently causes the separation between the three-dimensional network structure layer and the spherical structure layer and the unevenness of the thickness of the three-dimensional network structure layer. In some cases, it was not possible to suppress it. In addition, in the separation membrane described in Patent Document 3, the thickness unevenness of the three-dimensional network structure layer is large, and a minute hole may be formed in the three-dimensional network structure layer. For example, the following can be considered. As a method for producing this polymer separation membrane, Patent Document 3 discloses that the fluororesin polymer solution containing the hydrophilic polymer is applied to the surface of the spherical structure layer, and the spherical structure layer is formed into a three-dimensional network structure. A method of coating with a layer is described. In such a manufacturing method, when the polymer solution for forming a three-dimensional network structure layer is apply | coated on the surface of a spherical structure layer, it is possible that it cannot apply | coat uniformly. This is considered to occur remarkably if an attempt is made to reduce the thickness of the three-dimensional network structure layer. From these facts, it is considered that minute holes may be formed in the three-dimensional network structure layer. In addition, such a manufacturing method requires separate formation of a three-dimensional network structure layer and a spherical structure layer, which is disadvantageous in terms of manufacturing cost.

  This invention is made | formed in view of this situation, Comprising: It aims at providing the hollow fiber membrane excellent in both the permeation performance and the fractionation characteristic, and its manufacturing method.

  Porous hollow fiber membranes are known as hollow fiber membranes excellent in permeation performance and fractionation characteristics. 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. However, at a portion far from the contact surface, the solvent exchange rate becomes too slow, and coarse pores called macrovoids are formed, which tends to lower strength and chemical resistance.

  The TIPS method, on the other hand, causes a phase separation phenomenon by dissolving a polymer in a poor solvent that can be dissolved at a high temperature but cannot be dissolved when the temperature is lowered, and cooling the solution. 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 hollow fiber membrane is considered to have different permeation performance and fractionation characteristics depending on the number, shape, size, and the like of pores formed in the membrane. 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. Therefore, in order to obtain a hollow fiber membrane having both excellent permeation performance and fractionation characteristics, first, a dense layered portion that expresses fractionation characteristics in the film thickness direction, that is, directly involved in separation. It is thought that it is important to make the separation layer to be thin. And by making a hollow fiber membrane having an asymmetric structure with a coarse porous body other than the separation layer, which is necessary for maintaining the strength of the hollow fiber membrane, etc., both the permeation performance and the fractionation characteristics are obtained. It is thought that it can be improved. The inventors of the present invention have focused on the fact that the transmission performance and the fractionation characteristics can be controlled by controlling the structure in the membrane.

  Therefore, the present inventors do not pay attention only to the amount of liquid actually permeated, but the transmittance according to the thickness (film thickness) of the hollow fiber membrane even when the fractionation characteristics are excellent. The inventors have found that a hollow fiber membrane having both excellent permeation performance and fractionation characteristics can be obtained by controlling the permeation coefficient, which is an indicator of the above, and have come to the present invention described later.

The hollow fiber membrane according to one embodiment of the present invention includes a vinylidene fluoride resin, has a pure water permeability coefficient of 1 × 10 ⁻¹⁵ m ² or more and 22 × 10 ⁻¹⁵ m ² or less, and has a fractional particle size. , 0.5 μm or less.

According to such a configuration, a hollow fiber membrane excellent in both permeation performance and fractionation characteristics can be obtained. Specifically, since the pure water permeability coefficient is 1 × 10 ⁻¹⁵ m ² or more and 22 × 10 ⁻¹⁵ m ² or less, it is considered that the permeation performance with respect to a liquid containing water is excellent. Further, the obtained hollow fiber membrane has a fractional particle diameter of 0.5 μm or less, and has an excellent fractionation characteristic that can be applied to the removal of microorganisms and viruses as a microfiltration membrane, and the required strength. Excellent transmission performance can be achieved even at a film thickness that can achieve the above.

In the hollow fiber membrane, the pure water permeability coefficient is 0.4 × 10 ⁻¹¹ × L (m ² ) or more and 6 × 10 ⁻¹¹ × L when the thickness of the hollow fiber membrane is L (m). It is preferably (m ² ) or less.

  According to such a configuration, it is possible to obtain a hollow fiber membrane that is superior in permeation performance while maintaining excellent fractionation characteristics. Specifically, the pure water permeability coefficient increases as the thickness of the hollow fiber membrane increases. From this, even if the thickness of the hollow fiber membrane increases, it is considered that this increased portion is unlikely to contribute to the decrease in permeability, and the pores formed in the portion are relatively large. The dense layered portion considered to be involved in the fractionation characteristics does not become thick even when the thickness of the hollow fiber membrane is increased, while maintaining the excellent fractionation characteristics, and the hollow fiber membrane that is superior in permeation performance. It can be realized.

  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 superior in permeation performance and fractionation characteristics and is less likely to cause damage such as peeling in the membrane.

  This is considered to be due to the following.

  The 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 one embodiment of the present invention. 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.

  Further, the method for producing a hollow fiber membrane according to another aspect of the present invention is a method for producing the hollow fiber membrane, wherein the vinylidene fluoride resin and the vinylidene fluoride resin are phased at a specific temperature or higher. A preparation process for preparing a film-forming stock solution containing a poor solvent that can be dissolved into a one-phase state and causing phase separation due to a temperature drop and a polyvinylpyrrolidone-based resin, and an extrusion process for extruding the film-forming stock solution into a hollow fiber shape And forming a hollow fiber membrane by bringing the extruded hollow fiber-shaped membrane forming stock solution into contact with an external coagulation liquid, and the temperature of the external coagulation liquid is a temperature at which phase separation due to the temperature change starts It is characterized by being higher than.

  According to such a structure, the said hollow fiber membrane can be manufactured suitably.

  This is considered to be due to the following. First, when producing a stock solution, a good solvent for vinylidene fluoride resin is not used, but a poor solvent for vinylidene fluoride resin as described above is used, and phase separation due to the temperature change does not occur. Then, the hollow fiber-shaped film-forming stock solution is brought into contact with the external coagulation liquid. By doing so, solvent exchange between the solvent in the film-forming stock solution and the external coagulation liquid occurs, and the resin in the film-forming stock solution is solidified. For this reason, when the good solvent is used, the speed of the solvent exchange is considered to be more preferable than the so-called conventional NIPS method.

  From these facts, it is considered that a hollow fiber membrane excellent in both permeation performance and fractionation characteristics can be preferably produced.

  Further, in the method for producing the hollow fiber membrane, the preparation step is a step of preparing the membrane forming stock solution by kneading the vinylidene fluoride resin, the poor solvent, and the polyvinyl pyrrolidone resin. It is preferable.

  According to such a configuration, a hollow fiber membrane excellent in permeation performance and fractionation characteristics can be produced.

  This is considered to be because a film-forming stock solution containing the vinylidene fluoride resin, the poor solvent, and the polyvinylpyrrolidone-based resin can be obtained as a suitable film-forming stock solution in which each component is uniformly dispersed. . For this reason, since a suitable membrane forming stock solution is obtained, it is considered that a hollow fiber membrane excellent in permeation performance and fractionation characteristics can be produced.

  Moreover, in the manufacturing method of the said hollow fiber membrane, it is preferable to perform the said preparation process at the temperature higher than the temperature which is less than melting | fusing point of the said vinylidene fluoride-type resin, and the phase separation by the said temperature fall starts.

  According to such a configuration, a hollow fiber membrane excellent in permeation performance and fractionation characteristics and excellent in strength can be produced.

  This is suitable for a film-forming stock solution containing the vinylidene fluoride resin, the poor solvent, and the polyvinylpyrrolidone resin, while suppressing the occurrence of heat damage and the like of the polyvinylpyrrolidone resin. It is thought that it can be obtained. For this reason, since a suitable membrane forming undiluted solution is obtained, it is considered that a hollow fiber membrane excellent in permeation performance and fractionation characteristics and excellent in strength can be produced.

Moreover, in the method for producing the hollow fiber membrane, the extrusion step includes a circular outer discharge port, and a hollow fiber molding nozzle provided with 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. The internal coagulation liquid preferably has a solubility parameter distance of 5 to 200 (MPa) ^1/2 with the film-forming stock solution.

  According to such a configuration, it is possible to more suitably manufacture the hollow fiber membrane that is excellent in both permeation performance and fractionation characteristics.

  This is presumably because the solvent exchange between the inner peripheral surface side of the hollow fiber-shaped film forming stock solution extruded from the hollow fiber molding nozzle and the internal coagulation liquid is performed at a suitable speed. For this reason, it is considered that a hollow fiber membrane having a structure near the inner peripheral surface side can be obtained, and the hollow fiber membrane excellent in both permeation performance and fractionation characteristics can be produced more suitably.

  ADVANTAGE OF THE INVENTION According to this invention, the hollow fiber membrane excellent in both permeation | transmission performance and a fractionation characteristic and its manufacturing method 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. FIG. 4 is a graph showing a change in the pure water permeability coefficient K with respect to a change in film thickness in Example 1. FIG. 5 is a graph showing the results of a long-term test using a hollow fiber membrane. 6 is a view showing a scanning electron micrograph of a cross section of the hollow fiber membrane according to Example 1. FIG. 7 is a view showing a scanning electron micrograph of the vicinity of the outer peripheral surface in the cross section of the hollow fiber membrane according to Example 1. FIG. FIG. 8 is a view showing a scanning electron micrograph of the vicinity of the central portion in the cross section of the hollow fiber membrane according to Example 1. FIG. 9 is a view showing a scanning electron micrograph of the vicinity of the inner peripheral surface in the cross section of the hollow fiber membrane according to Example 1. FIG. 10 is a view showing a scanning electron micrograph of the outer peripheral surface of the hollow fiber membrane according to Example 1. FIG. FIG. 11 is a view showing a scanning electron micrograph of the inner peripheral surface of the hollow fiber membrane according to Example 1. 12 is a view showing a scanning electron micrograph of a cross section of the hollow fiber membrane according to Reference Example 2. FIG. FIG. 13 is a view showing a scanning electron micrograph of the outer peripheral surface of the hollow fiber membrane according to Reference Example 2. 14 is a view showing a scanning electron micrograph of the inner peripheral surface of the hollow fiber membrane according to Reference Example 2. FIG.

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

The hollow fiber membrane according to an embodiment of the present invention includes a vinylidene fluoride resin. The hollow fiber membrane has a pure water permeability coefficient K of 1 × 10 ⁻¹⁵ m ² or more and 22 × 10 ⁻¹⁵ m ² or less, and a fractional particle diameter of 0.5 μm or less.

  The hollow fiber membrane is considered to be excellent in strength by including a vinylidene fluoride resin. The vinylidene fluoride resin will be described later.

Further, as described above, the hollow fiber membrane has a pure water permeability coefficient K of 1 × 10 ⁻¹⁵ m ² or more and 22 × 10 ⁻¹⁵ m ² or less. Here, the pure water permeability coefficient K is a permeability coefficient when allowing pure water to pass through the hollow fiber membrane, and is calculated using the following equation (1) according to Darcy's law. (Dalcy's transmission coefficient).

K = (μ · T · Q) / (ΔP · A) (1)
In the formula (1), K represents a transmission coefficient (m ² ). Further, μ represents a viscosity (Pa · sec), and here represents a viscosity of pure water (Pa · sec). Moreover, T shows a film thickness (m) and shows the thickness (m) of a hollow fiber membrane here. Q represents a flow rate (m ³ / second), and here represents a water flow rate (m ³ / second). ΔP represents the transmembrane pressure difference (Pa). A represents the film area (m ² ).

  Next, a method for measuring the pure water permeability coefficient K will be described.

  The method for measuring the pure water permeability coefficient K is not particularly limited as long as it can be calculated by the above formula (1). Specifically, examples of the method for measuring the pure water permeability coefficient K include the following measuring methods.

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 in which one end of this wet treated hollow fiber membrane is sealed, pure water is used as raw water, external pressure filtration is performed at a filtration pressure of 100 kPa and a temperature of 25 ° C. Measure the water permeability. From the measured water permeability, converted into water permeability per unit membrane area, unit time, and unit pressure, each of the effective lengths of 10 cm, 15 cm, 20 cm, 25 cm, and 30 cm at a transmembrane differential pressure of 0.1 MPa. (L / m ² / hour) is obtained. From the obtained measurement data of water permeability, it is substituted into the Darcy equation, and Darcy's permeability coefficient K at each effective length is calculated.

  Thereafter, the effective length is plotted on the horizontal axis and the Darcy transmission coefficient K is plotted on the vertical axis, and the Darcy transmission coefficient K at an effective length of 0 cm is calculated from the extrapolated value of the obtained plot. The coefficient is K.

  Next, the pure water permeability coefficient K will be described.

  The pure water permeability coefficient K is a coefficient of passage resistance when pure water passes through the hollow fiber membrane. That is, it is suggested that the larger the calculated pure water permeability coefficient K, the smaller the pure water passage resistance of the hollow fiber membrane and the easier the water flows. On the other hand, it is suggested that the smaller the calculated pure water permeability coefficient K is, the higher the pure water passage resistance of the hollow fiber membrane is, and the structure in which water does not flow easily. More specifically, when the hollow fiber membrane is a structure in which each of the pores existing in the membrane is large and the porosity is large and the pressure loss is small, the pure water permeability coefficient K is large. . On the other hand, when the hollow fiber membrane is a dense structure with small pores and small porosity, the pure water permeability coefficient K is small.

  In addition, the pure water permeability coefficient K is determined depending on the pressure fluctuation at the time of measurement or the length (film thickness) of the passage of the hollow fiber membrane if the structure of the hollow fiber membrane, particularly the structure in the film thickness direction is uniform. Regardless, it becomes a constant value. On the other hand, the fact that the pure water permeability coefficient K varies depending on the film thickness suggests that the structure of the hollow fiber membrane, for example, the porosity, the pore diameter, the pore shape, etc. are changing in the film thickness direction. doing.

  Specifically, the pure water permeability coefficient K of the hollow fiber membrane having an asymmetric structure that changes in the film thickness direction from a region where the pure water permeability coefficient K is small to a region where the pure water permeability coefficient K is large is as follows: Become. First, K in a region where the pure water permeability coefficient K is small is Ks, and K in a region where the pure water permeability coefficient K is large is Kl. The thickness of the region where the pure water permeability coefficient K is small is Ts, the thickness of the region where the pure water permeability coefficient K is large is T1, and the thickness (film thickness) of the entire hollow fiber membrane is T. In such a case, the pure water permeability coefficient K of the hollow fiber membrane is defined as the following formula (2).

T / K = Ts / Ks + Tl / Kl (2)
From this, the ratio of the area where the pure water permeability coefficient K is small and the area where the pure water permeability coefficient K is large and the difference between the absolute values of Ks and Kl with respect to the entire thickness of the hollow fiber membrane The pure water permeability coefficient K of the hollow fiber membrane having an asymmetric structure is determined depending on the size. That is, the pure water permeability coefficient K of the hollow fiber membrane varies depending on the degree of asymmetry of the hollow fiber membrane. Specifically, when the degree of asymmetry is small, the pure water permeability coefficient K of the hollow fiber membrane tends to be small. Further, when the degree of asymmetry is large, the pure water permeability coefficient K of the hollow fiber membrane tends to increase. Thus, by obtaining the pure water permeation coefficient K of the hollow fiber membrane, the pure water permeation performance and the degree of asymmetry of the hollow fiber membrane can be evaluated. Specifically, it can be said that when the pure water permeability coefficient K of the hollow fiber membrane is large, the pure water permeability is high, and when the pure water permeability coefficient K of the hollow fiber membrane varies, the degree of asymmetry changes.

Here, the pure water permeability coefficient K of the hollow fiber membrane according to the present embodiment is a value contributing to the membrane structure as described above. The pure water permeability coefficient K contributing to this membrane structure is 1 × 10 ⁻¹⁵ m ² or more and 22 × 10 ⁻¹⁵ m ² or less, and 2 × 10 ⁻¹⁵ m ² or more and 17 × 10 ⁻¹⁵ m ² or less. It is preferably 2.3 × 10 ⁻¹⁵ m ² or more and most preferably 10 × 10 ⁻¹⁵ m ² or less. When this pure water permeability coefficient K is too small, as above-mentioned, the passage resistance of pure water becomes large, and there exists a tendency for it to become difficult to exhibit sufficient permeation performance. On the other hand, when the pure water permeability coefficient K is too large, excellent permeation performance can be exhibited, but the fractionation characteristics tend to be deteriorated too much. From these facts, it is considered that when the pure water permeability coefficient K is within the above range, it is possible to improve the permeation performance with respect to the liquid containing water while suppressing the deterioration of the fractionation characteristics.

  Further, the hollow fiber membrane according to the present embodiment has a fractional particle diameter of 0.5 μm 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 size is 0.5 μm or less, preferably 0.001 to 0.5 μm, more preferably 0.01 to 0.5 μm, and 0.02 to 0 More preferably, it is 1 μm. When the fractional particle diameter of the hollow fiber membrane is 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, when the particle diameter of the hollow fiber membrane is within the above range, 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 and viruses 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 an excellent fractionation characteristic that can be applied to the removal of microorganisms and viruses as a microfiltration membrane, and at a film thickness that can achieve the required strength. Excellent transmission performance can be demonstrated.

The hollow fiber membrane according to the present embodiment preferably has a water permeability of 1000 to 40000 L / m ² / hour at a transmembrane pressure difference of 0.1 MPa, and preferably 3000 to 30000 L / m ² / hour. More preferably, it is 3500-20000L / 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.

Further, the hollow fiber membrane according to the present embodiment has a pure water permeability coefficient of 0.4 × 10 ⁻¹¹ × L (m ² ) or more and 6 × 10 when the thickness of the hollow fiber membrane is L (m). It is preferably ⁻¹¹ × L (m ² ) or less, more preferably 0.8 × 10 ⁻¹¹ × L (m ² ) or more and 4 × 10 ⁻¹¹ × L (m ² ) or less, and 1 × More preferably, it is 10 ⁻¹¹ × L (m ² ) or more and 3 × 10 ⁻¹¹ × L (m ² ) or less. That is, in the hollow fiber membrane, the inclination when the horizontal axis is the film thickness L (m) and the vertical axis is the pure water permeability coefficient K (m ² ) is 0.4 × 10 ^{−11 to} 6 × 10 ^−11. The following is preferable, 0.8 × 10 ⁻¹¹ to 4 × 10 ⁻¹¹ is more preferable, and 1 × 10 ^{−11 to} 3 × 10 ⁻¹¹ is further preferable.

  As described above, the pure water permeability coefficient K is a value that depends on the in-membrane structure of the hollow fiber membrane. If the in-membrane structure of the hollow fiber membrane is homogeneous in the film thickness direction, the film thickness varies. Even if it is a value that does not change. It is considered that the structure of the hollow fiber membrane is preferably asymmetric when the inclination is within the above range. That is, there is a dense layered part that is thought to be involved in the fractionation characteristics near one surface, etc., and the other part hardly contributes to the decrease in permeability, and the pores formed in that part are compared. It is thought that it is a big thing. It is considered that this dense layered portion functions as a separation layer, and the other portion functions as a support layer. This support layer is considered to have a so-called three-dimensional network structure in which coarse pores called macrovoids do not exist in the cross section of the membrane, and communication holes exist in any of the three-dimensional directions. Further, if the inclination is within the above range, even if the thickness of the entire hollow fiber membrane is changed, the thickness of the dense layer portion that functions as the separation layer is hardly changed, and the thickness of the portion that functions as the support is It will change. For this reason, even if the thickness of the hollow fiber membrane increases, the dense layered portion considered to be involved in the fractionation characteristics does not become thick, while maintaining excellent fractionation characteristics and excellent hollow fiber membranes by permeation performance Can be realized. That is, it is considered that the inclination is within the above range because the ratio of the separation layer to the entire thickness of the hollow fiber membrane tends to decrease even when the thickness of the hollow fiber membrane is increased. From these facts, if the inclination is too small, the degree of asymmetry of pores in the film thickness direction is not sufficiently high, and if the entire thickness of the hollow fiber membrane is increased, sufficient permeation performance tends not to be exhibited. Further, if the inclination is too large, the degree of asymmetry becomes too large, and a portion that should function as a support layer tends not to function sufficiently as a support layer due to occurrence of macrovoids or the like in a portion that functions as a support layer. . That is, the strength of the hollow fiber membrane tends to decrease, and in some cases, the hollow fiber membrane tends to be difficult to manufacture suitably. Therefore, if the inclination is within the above range, it is considered that a hollow fiber membrane having superior permeation performance can be obtained while maintaining excellent fractionation characteristics.

  Further, as described above, the hollow fiber membrane is considered to be a hollow fiber membrane having an asymmetric structure that changes in the film thickness direction. Specifically, the hollow fiber membrane is considered to have an inclined structure in which the pore diameter in the membrane gradually decreases toward at least one of the inner and outer peripheral surfaces. As the pores formed in the hollow fiber membrane, for example, the diameter of the pores formed on the outer peripheral surface of the hollow fiber membrane (outer peripheral pore diameter) is the diameter of the pores formed on the inner peripheral surface (inner peripheral surface). If it is smaller than (side pore diameter), there is no particular limitation. Specifically, the outer peripheral 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. . The inner peripheral pore diameter is not particularly limited, but specifically, it is preferably 1 to 20 μm, more preferably 1 to 10 μm, and preferably 2 to 8 μm. The ratio of the inner peripheral pore diameter to the outer peripheral pore diameter (inner peripheral pore diameter / outer peripheral pore diameter) is greater than 1, preferably 10 to 100, and preferably 20 to 50. Preferably, it is 30-50. From these, the hollow fiber membrane has a pore size (pore diameter) in the membrane from the inner peripheral surface side toward the outer peripheral surface side so as to satisfy the outer peripheral pore diameter and the inner peripheral pore diameter. Is considered to have an inclined structure that gradually decreases in the thickness direction. Here, the diameter is an average value of the diameters, and examples thereof include an arithmetic average value of the diameters.

  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.

  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 preferably contains a crosslinked product of not only the vinylidene fluoride resin but also a polyvinylpyrrolidone resin. Since the hollow fiber membrane contains a vinylidene fluoride resin, it is considered that the hydrophobicity tends to increase. Even in such a hollow fiber membrane, it is considered that hydrophilicity can be enhanced by including a crosslinked product of polyvinylpyrrolidone resin. In addition, it is considered that not including polyvinyl pyrrolidone-based resin, but including a cross-linked product of polyvinyl pyrrolidone-based resin, the dropping of polyvinyl pyrrolidone-based resin is suppressed and the effect of enhancing hydrophilicity can be maintained. . By increasing the hydrophilicity in this manner, it is considered that the hollow fiber membrane has improved permeability to liquids containing water. Moreover, it is thought that contamination resistance can also be improved by improving hydrophilicity. From these facts, the hollow fiber membrane contains a cross-linked polyvinyl pyrrolidone resin, so that a hollow fiber membrane having excellent permeation performance and excellent contamination resistance can be obtained while maintaining excellent fractionation characteristics. It is thought that.

  Here, the polyvinyl pyrrolidone resin is not particularly limited as long as it is a resin containing vinyl pyrrolidone in the molecule. Specific examples of the polyvinyl pyrrolidone resin include polyvinyl pyrrolidone, a copolymer of vinyl pyrrolidone and vinyl acetate, a copolymer of vinyl pyrrolidone and vinyl caprolactam, and the like. Among the above examples, polyvinyl pyrrolidone is preferable as the polyvinyl pyrrolidone resin. Moreover, as a polyvinylpyrrolidone-type resin, the resin of the said illustration may be used independently, and may be used in combination of 2 or more type.

  The degree of crosslinking of the crosslinked product of polyvinylpyrrolidone resin is not particularly limited. Examples of the degree of crosslinking include a degree of crosslinking such that polyvinyl pyrrolidone-based resin is not detected from the filtrate when water is passed through the obtained hollow fiber membrane. Specifically, the degree that the polyvinylpyrrolidone-based resin is not detected is as follows.

First, pure water is allowed to flow through the hollow fiber membrane to perform flushing washing, and then a 40 vol% ethanol aqueous solution is circulated through the washed hollow fiber membrane at 40 ° C. for 1 hour. The concentration of the polyvinylpyrrolidone resin in the circulated ethanol aqueous solution is measured. From the polyvinyl pyrrolidone resin concentration and the membrane area of the used hollow fiber membrane, the extraction amount of the polyvinyl pyrrolidone resin per 1 m ^{2 of} the membrane area is calculated. The calculated extraction amount per 1 m ^{2 of} membrane area is preferably 300 mg or less, more preferably 100 mg or less, and even more preferably 10 mg or less.

  Further, the content of the crosslinked product of the polyvinyl pyrrolidone resin is such that the effect of containing the crosslinked product of the polyvinyl pyrrolidone resin can be sufficiently exerted, that is, the hollow fiber membrane containing the vinylidene fluoride resin is preferably hydrophilic. The amount is not particularly limited as long as the amount can be changed. Specifically, the content of the crosslinked product of the polyvinylpyrrolidone-based resin is preferably 0.1% by mass or more and less than 15% by mass with respect to the mass of the hollow fiber membrane, and is 0.1 to 10% by mass. More preferably, it is more preferably 0.5 to 5% by mass. When the content is too small, the hydrophilicity of the hollow fiber membrane tends not to be sufficiently increased. For this reason, the stain resistance is not sufficiently increased, and suitable pores (pores) cannot be formed in the hollow fiber membrane, and the permeability to a liquid containing water cannot be sufficiently increased. is there. Moreover, when there is too much said content, there exists a tendency for permeation | transmission performance to fall. This is presumably because the moldability of the hollow fiber membrane is lowered and it is difficult to form a suitable hollow fiber membrane. In addition, it is considered that the hollow fiber membrane is likely to cause a decrease in water permeability due to swelling of the pores of the membrane due to swelling of the polyvinylpyrrolidone resin in the membrane. From these, if the content of the crosslinked product of the polyvinylpyrrolidone resin is within the above range, the hollow fiber membrane containing the vinylidene fluoride resin can be appropriately hydrophilized, and the pores of the membrane It is considered that the hydrophilicity can be enhanced while suppressing the occurrence of a decrease in water permeability due to blockage or the like. For this reason, it is considered that a hollow fiber membrane excellent in permeation performance and excellent in stain resistance can be obtained while maintaining excellent fractionation characteristics.

  Moreover, the measuring method of content of the crosslinked body of polyvinylpyrrolidone-type resin is not specifically limited, For example, it can measure as follows. Specifically, the obtained hollow fiber membrane can be analyzed from a trace amount of nitrogen and measured from the abundance of nitrogen (N). More specifically, first, the obtained hollow fiber membrane and the polyvinyl pyrrolidone-based resin alone are each analyzed for a small amount of nitrogen, and the abundance of nitrogen (N) is measured. From this abundance, the content of the crosslinked product of the polyvinylpyrrolidone resin is calculated.

  In addition, the polyvinyl pyrrolidone-based resin preferably has a K value of 30 to 120, more preferably 50 to 120, and still more preferably 60 to 120. The K value of this polyvinyl pyrrolidone resin is the K value of the polyvinyl pyrrolidone resin before crosslinking. The K value is a viscosity characteristic value that correlates with the molecular weight. The K value can be calculated from, for example, the description of a catalog or the like, but can be calculated by using, for example, the Fikentscher equation. The K value can be calculated, for example, by applying a relative viscosity value at 25 ° C. measured by a capillary viscometer to the following Fikenscher equation.

K value = (1.5 log η _rel −1) / (0.15 + 0.003c) + (300 clog η _rel + (c + 1.5 clog η _rel ) ² ) ^1/2 /(0.15c+0.003c ² )
In the formula, η _rel indicates the relative viscosity of the aqueous solution of the polyvinyl pyrrolidone resin that is the measurement object to water, and c is the concentration (mass) of the aqueous solution of the polyvinyl pyrrolidone resin that is the measurement object. %).

  If the K value of the polyvinyl pyrrolidone resin is too small, even if the polyvinyl pyrrolidone resin is cross-linked, it hardly remains in the hollow fiber membrane containing the vinylidene fluoride resin, and the hydrophilicity of the hollow fiber membrane is suitably maintained. It tends to be difficult. Moreover, when K value of polyvinylpyrrolidone-type resin is too large, there exists a tendency for film forming property to fall and it becomes difficult to manufacture a suitable hollow fiber membrane. For these reasons, polyvinyl pyrrolidone resins having such a K value are likely to remain moderately in hollow fiber membranes containing vinylidene fluoride-based resins, and make the hollow fiber membranes moderately hydrophilic. It is thought that you can. For this reason, it is considered that the permeability of a liquid containing water can be improved because the hydrophilicity can be enhanced while suppressing the occurrence of a decrease in water permeability due to the blocking of the pores of the membrane. Therefore, it is considered that a hollow fiber membrane having excellent permeation performance and excellent stain resistance can be obtained while maintaining excellent fractionation characteristics.

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 3~10N / mm ^2, is 3~7N / 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 even more preferably 70 to 200%. 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 hollow fiber membrane which has the above-mentioned structure can be manufactured. As this manufacturing method, the following manufacturing methods are mentioned, for example. This manufacturing method includes a preparation step of preparing a film-forming stock solution containing a vinylidene fluoride-based resin, a poor solvent for the vinylidene fluoride-based resin, and a polyvinylpyrrolidone-based resin, and the film-forming stock solution is extruded into a hollow fiber shape. Examples include a method including an extrusion step and a step of forming a hollow fiber membrane by bringing the extruded hollow fiber-shaped membrane-forming stock solution into contact with an external coagulation liquid. Here, the poor solvent of the vinylidene fluoride resin is, for example, compatible with the vinylidene fluoride resin at a specific temperature or more to become a one-phase state, and phase separation is caused by a compatibility decrease due to a temperature decrease. Solvents that can be raised are mentioned. And in this manufacturing method, the temperature of the said external coagulation liquid is made higher than the temperature which the phase separation by the said temperature change starts. That is, the method for producing a hollow fiber membrane according to another embodiment of the present invention is a method for producing the hollow fiber membrane, wherein the vinylidene fluoride resin and the vinylidene fluoride resin are phased at a specific temperature or higher. A preparation process for preparing a film-forming stock solution containing a poor solvent that can be dissolved into a one-phase state and causing phase separation due to a temperature drop and a polyvinylpyrrolidone-based resin, and an extrusion process for extruding the film-forming stock solution into a hollow fiber shape And a step (formation step) of forming the hollow fiber membrane by bringing the extruded hollow fiber-shaped membrane forming stock solution into contact with an external coagulation liquid, and the temperature of the external coagulation liquid is phase-separated by the temperature change This is a production method higher than the temperature at which the process starts.

  The hollow fiber membrane can be preferably manufactured by such a manufacturing method.

  This is considered to be due to the following. First, when producing a stock solution, a good solvent for vinylidene fluoride resin is not used, but a poor solvent for vinylidene fluoride resin as described above is used, and phase separation due to the temperature change does not occur. Then, the hollow fiber-shaped film-forming stock solution is brought into contact with the external coagulation liquid. By doing so, solvent exchange between the solvent in the film-forming stock solution and the external coagulation liquid occurs, and the resin in the film-forming stock solution is solidified. For this reason, when the good solvent is used, the speed of the solvent exchange is considered to be more preferable than the so-called conventional NIPS method. Therefore, it is considered that a hollow fiber membrane excellent in both permeation performance and fractionation characteristics can be preferably produced.

  First, the preparation process in the manufacturing method according to the present embodiment is not particularly limited as long as a film-forming stock solution containing the vinylidene fluoride resin, the poor solvent, and the polyvinylpyrrolidone resin can be prepared. Specifically as a preparation process, the method etc. which heat-stir the raw material of film forming undiluted | stock solution are mentioned, for example. Moreover, it is preferable to knead | mix at the time of heating and stirring. That is, it is preferable to mix the vinylidene fluoride resin, the poor solvent, and the polyvinyl pyrrolidone resin, which are raw materials for the film forming stock solution, at a predetermined ratio and knead them in a heated state. 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.

  The preparation step is preferably performed at a temperature lower than the melting point of the vinylidene fluoride resin and higher than the temperature at which phase separation due to the temperature decrease starts. That is. It is preferable that the temperature at the time of preparation of the membrane forming stock solution is lower than the melting point of the vinylidene fluoride resin and higher than the temperature at which phase separation starts due to the temperature decrease. Furthermore, the temperature at the time of preparing this film-forming stock solution is more preferably 60 ° C. or higher and lower than the melting point of the vinylidene fluoride resin, and more preferably 90 to 140 ° C. If this temperature is too low, the viscosity of the membrane-forming stock solution increases, and there is a tendency that a hollow fiber membrane having a suitable membrane structure cannot be obtained. Specifically, a suitable three-dimensional network structure cannot be formed in the layer serving as the support layer of the hollow fiber membrane, and spherulites and macrovoids are easily formed in the layer, and the strength of the obtained hollow fiber membrane Tends to decrease. Moreover, even if this temperature is too high, there is a tendency that a hollow fiber membrane having a suitable membrane structure cannot be obtained. Specifically, due to thermal degradation of the polyvinylpyrrolidone-based resin, a suitable three-dimensional network structure cannot be formed in the layer serving as the support layer of the hollow fiber membrane, and macrovoids are easily formed in the layer, or the opposite In addition, there is a tendency to become a dense layer. As a result, it tends to be difficult to obtain a hollow fiber membrane excellent in both fractionation characteristics and permeation performance. From these, if the temperature during the preparation step is within the above range, a film-forming stock solution containing the vinylidene fluoride resin, the poor solvent, and the polyvinylpyrrolidone resin is used as the polyvinylpyrrolidone resin. It is thought that it can be suitably obtained while suppressing the occurrence of damage due to heat. For this reason, since a suitable membrane forming undiluted solution is obtained, it is considered that a hollow fiber membrane excellent in permeation performance and fractionation characteristics and excellent in strength can be produced.

  Moreover, the membrane-forming stock solution obtained here is used for the production of a hollow fiber membrane. At that time, it is preferable that the obtained film-forming stock solution is sufficiently deaerated. And after measuring with metering pumps, such as a gear pump, it is used for manufacture of the hollow fiber membrane mentioned later.

  Moreover, the resin mentioned above can be used for the vinylidene fluoride resin and the polyvinyl pyrrolidone resin.

  The poor solvent is not particularly limited as long as it is compatible with the vinylidene fluoride resin at a specific temperature or higher to be in a one-phase state and can cause phase separation due to a temperature drop. The poor solvent is preferably a water-soluble solvent. If it is a water-soluble solvent, it is possible to use water when extracting the solvent from the hollow fiber membrane after film formation, and the extracted solvent can be disposed of by biological treatment or the like. Examples of the poor solvent include γ-butyrolactone, ε-caprolactone, methanol, acetone, caprolactone, and the like. As the poor solvent, γ-butyrolactone is preferable from the viewpoints of environmental load, safety, cost, and the like among the exemplified solvents. Moreover, as said poor solvent, the solvent resin of the said illustration 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 vinylidene fluoride resin is 20 to 35 parts by mass with respect to the total mass of the vinylidene fluoride resin, the poor solvent, and the polyvinylpyrrolidone resin, and 20 to 30 parts by mass. It is more preferable that Content of the said poor solvent is 45-70 mass parts with respect to the said total mass, It is more preferable that it is 50-70 mass parts, It is further more preferable that it is 55-65 mass parts. The content of the polyvinyl pyrrolidone-based resin is 5 to 20 parts by mass, more preferably 8 to 20 parts by mass, and still more preferably 10 to 15 parts by mass with respect to the total mass. Moreover, it is preferable that content of the said vinylidene fluoride resin is 1.54 to 4.38 by mass ratio with respect to content of the said polyvinylpyrrolidone resin, and is 1.6 to 3.91. More preferably, it is more preferably 1.67 to 3.13.

  Moreover, the said film forming undiluted | stock solution should just contain the said vinylidene fluoride type resin, the said poor solvent, and the said polyvinyl pyrrolidone type resin, and may consist of these. In addition to these three components, the film-forming stock solution may contain other components. Examples of other components include surfactants, antioxidants, ultraviolet absorbers, lubricants, antiblocking agents, dyes, and various additives such as additives that promote phase separation of the film-forming stock solution. . Examples of the additive that promotes phase separation of the membrane forming stock solution include solvents other than the above poor solvents such as glycerin, ethylene glycol, tetraethylene glycol, water, ethanol, methanol, and polyethylene glycol, polyethylene oxide, polyvinyl Examples thereof include resins such as alcohol, polymethyl methacrylate, and polymethyl acrylate. This resin may be a copolymer of each of the above resins. Moreover, as an additive which accelerates | stimulates the phase separation of a film forming undiluted | stock solution, the compound of the said illustration may be used independently, and may be used in combination of 2 or more type.

  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.

And as this internal coagulation liquid, if it is a coagulation liquid which can be used when manufacturing the hollow fiber membrane containing a vinylidene fluoride resin, it will not specifically limit. The internal coagulating liquid, for example, a distance of solubility parameters between the film-forming stock solution (HSP distance) is preferably 5 to 200 ^{(MPa) 1/2,} is 50 to 200 ^{(MPa) 1/2} More preferably, it is more preferably 100 to 180 (MPa) ^1/2 . By using the internal coagulation liquid having such an HSP distance, the hollow fiber-shaped film-forming stock solution extruded from the hollow fiber molding nozzle can be suitably coagulated from the inner peripheral surface. That is, it is considered that the solvent exchange between the inner peripheral surface side of the hollow fiber-shaped film forming stock solution extruded from the hollow fiber molding nozzle and the internal coagulating liquid is performed at a suitable speed. For this reason, it is considered that a hollow fiber membrane having a structure near the inner peripheral surface side can be obtained, and the hollow fiber membrane excellent in both permeation performance and fractionation characteristics can be produced more suitably. Therefore, the said hollow fiber membrane excellent in both the permeation | transmission performance and the fractionation characteristic can be manufactured more suitably.

  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.).

HSP distance = [4 × (dD undiluted solution−dD solvent) ² + (dP undiluted solution−dP solvent) ² + (dH undiluted solution−dH solvent) ² ] ^0.5
Here, dD is van der Waals force, dP is dipole moment force, and dH is hydrogen bond force. As the HSP distance on the three-dimensional coordinate calculated by the above definition formula approaches zero, The component is judged to be highly compatible, the solvent exchange rate in the NIPS method is slowed, and the pore diameter of the contact surface becomes coarse.

  In addition, although the solubility parameter used in this specification is a Hansen parameter, the Hoy parameter can be used for those not described in the Hansen parameter. What is not described in both can be estimated by Hansen's parameter formula (see Allan FM Barton, “CRC Handbook of solubility parameters and other cohesion parameters” CRCRC Corp. 1991). In the case of a mixed solvent, parameters obtained by calculating each solubility parameter based on its mass according to the additive law are used.

  An example of the solubility parameter is shown in Table 1 below.

In the present embodiment, it is preferable to select a poor solvent, a polyvinyl pyrrolidone-based resin, and an internal coagulating liquid contained in the film forming raw solution so as to satisfy the above HSP distance. The internal coagulation liquid may be composed of a single solvent, or may be used in combination of two or more solvents. When two or more solvents are used in combination, for example, as the internal coagulation liquid, a film-forming stock solution and a solvent with a long HSP distance are mixed at an arbitrary ratio with a film-forming stock solution and a solvent with a short HSP distance, Examples thereof include a mixed solvent in which the HSP distance from the membrane stock solution is adjusted. There are no particular restrictions on the type and number of solvents to be mixed. Examples of the solvent having a long HSP distance from the film-forming stock solution include water and glycerin. Examples of the solvent having a HSP distance close to that of the film forming stock solution include γ-butyrolactone and dimethylacetamide.

  Examples of the mixed solvent used as the internal coagulation liquid include a mixed solvent of dimethylacetamide and glycerin, a mixed solvent of γ-butyrolactone and glycerin, a mixed solvent of γ-butyrolactone and ethylene glycol, and a mixed solvent of γ-butyrolactone and water. Examples thereof include a mixed solvent, a mixed solvent of dimethylacetamide and water, a mixed solvent of dimethylacetamide and ethylene glycol, and a mixed solvent of dimethylformamide and water. Among these, a mixed solvent of γ-butyrolactone and glycerin or a mixed solvent of dimethylacetamide and water is preferable from the viewpoint of good moldability of the hollow fiber membrane.

  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.

  Moreover, the formation process in the manufacturing method which concerns on this embodiment will not be specifically limited if it is the process of making the extruded hollow fiber-shaped membrane forming undiluted solution contact an external coagulation liquid, 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 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. 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. Among these, sodium sulfate is preferable. Further, the aqueous solution containing salts preferably has a salt concentration of 30 to 300 g / L, more preferably 50 to 300 g / L, and still more preferably 100 to 280 g / L. If this concentration is too low or too high, a hollow fiber membrane having a suitable membrane structure tends to be difficult to obtain. Specifically, if the concentration is too low, the solvent exchange rate in the forming step is increased, the densification of the obtained hollow fiber membrane proceeds too much, and the permeation performance tends to be reduced. Moreover, when this density | concentration is too high, the solvent exchange rate in a formation process will become slow, and there exists a tendency for the fractionation characteristic of the obtained hollow fiber membrane to fall.

  The temperature of the external coagulation liquid is higher than the temperature at which the phase separation due to the temperature change starts, specifically 45 ° C. or higher, more preferably 50 ° C. or higher. Further, the temperature of the external coagulation liquid is preferably not more than the boiling point of the external coagulation liquid, more preferably 90 ° C. or less, and further preferably 85 ° C. or less. When the temperature of the external coagulation liquid is too low, the obtained hollow fiber membrane tends to be dense and it is difficult to form an asymmetric structure. Further, when the temperature of the external coagulation liquid is equal to or lower than the temperature at which phase separation due to the temperature change starts, the TIPS method is used, and it is difficult to form a suitable hollow fiber membrane. On the other hand, if the temperature of the external coagulation liquid is too high, the viscosity of the film-forming stock solution is lowered, so that the fractionation characteristics are lowered and the water permeability is liable to be increased. Furthermore, when the temperature of the external coagulation liquid is equal to or higher than the boiling point thereof, the external coagulation liquid boils and vibrates, so that the production of the hollow fiber membrane tends to be unstable.

  The temperature at which the phase separation starts is reduced by reducing the temperature of the solution containing the vinylidene fluoride resin, the poor solvent, and the polyvinyl pyrrolidone resin, for example, the film-forming stock solution. It is temperature to do. Specifically, the temperature at which phase separation starts is measured as follows (for details, see Non-Patent Documents; Polymer Alloy Structure / Property Control and Latest Technology, Toshiaki Ogizawa, Noriyuki Sewa, Akio Imai, reference). First, a slide glass and a cover glass are placed on a stage of an optical microscope with a temperature controller, and the slide glass and the cover glass are heated to 120 ° C. A uniform film-forming stock solution is sandwiched between the heated slide glass and the cover glass. Then, the temperature of the slide glass and the cover glass is gradually decreased or increased, for example, by 3 ° C., and the white turbidity (due to the difference in refractive index between the two phases) generated by phase separation is visually observed. Confirm the temperature and measure the temperature. This temperature is a temperature at which phase separation starts. That is, in this measurement method, if the film-forming stock solution is transparent, it is in a homogeneous phase state, and if it is cloudy, it is in a phase-separated state, and phase separation starts at the temperature at which partial cloudiness is confirmed. This is a method of measuring the temperature (phase separation start temperature).

  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 permeation performance of the hollow fiber membrane is improved. This is considered that an independent hole existing in the membrane is cleaved to become a communication hole, the communication in the membrane is improved, and the permeation performance is 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. As a washing | cleaning method, the method etc. which wash | clean a hollow fiber membrane in a water bath etc. are mentioned, for example. This washing suitably improves the hydrophilicity of the hollow fiber membrane. This is considered to be due to the diffusion of the polyvinylpyrrolidone resin in the hollow fiber membrane within the membrane by this washing.

  Moreover, the manufacturing method which concerns on this embodiment may be equipped with the bridge | crosslinking process which bridge | crosslinks the polyvinylpyrrolidone-type resin contained in the said hollow fiber membrane. Examples of the crosslinking step include a step of immersing the hollow fiber membrane (hollow fiber membrane before crosslinking) in an aqueous solution containing a radical initiator, a step of immersing the hollow fiber membrane in a strong acid or strong alkali, and heat treating the hollow fiber membrane. And a step of performing radiation treatment on the hollow fiber membrane. Among the above steps, the crosslinking step is preferably a step of immersing the hollow fiber membrane in an aqueous solution containing a radical initiator from the viewpoint that the deterioration of the vinylidene fluoride resin can be suppressed and the handling is easy.

  The step of immersing in an aqueous solution containing a radical initiator is preferably performed by heat treatment during or after the immersion. Further, the aqueous solution containing the radical initiator may be an aqueous solution containing a radical initiator capable of initiating the crosslinking reaction of the polyvinylpyrrolidone resin, and examples thereof include a 1% by mass aqueous solution of the radical initiator. Examples of the radical initiator include sodium persulfate, ammonium persulfate, and hydrogen peroxide. Among these, hydrogen peroxide is preferable because a hollow fiber membrane having high permeation performance is easily obtained.

  In addition, the heating temperature in the heat treatment step may be any temperature that can initiate a crosslinking reaction of the polyvinylpyrrolidone resin, and is preferably about 170 to 200 ° C., for example.

  Moreover, the hollow fiber membrane which concerns on this embodiment can be used for membrane filtration. 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 that is the object to be treated is filtered from the introduction port 35, and the liquid (filtrated water) that has been filtered by the membrane module 32 is discharged from the outlet port 36. 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.

  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.

  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 vinylidene fluoride-based resin, polyvinylidene fluoride (hereinafter sometimes abbreviated as PVDF) (Kynar 741 manufactured by Arkema Co., Ltd.), and γ-butyrolactone (GBL manufactured by Mitsubishi Chemical Corporation) as a solvent, As a polyvinyl pyrrolidone-based resin, a mixture was prepared such that polyvinyl pyrrolidone (BASF Japan K.K. 90P, K value: 90) was in a mass ratio of 25:62:13. Note that γ-butyrolactone is a poor solvent for polyvinylidene fluoride.

After kneading the film-forming stock solution obtained by dissolving the above mixture in a dissolution tank at a constant temperature of 95 ° C., a double ring having an outer diameter of 1.6 mm and an inner diameter of 0.8 mm as shown in FIG. The product was extruded from a nozzle having a structure (nozzle for forming a hollow fiber membrane). At this time, γ-butyrolactone (GBL made by Mitsubishi Chemical Corporation) and glycerin (purified glycerin made by Kao Corporation) were mixed as an internal coagulation liquid at a constant temperature of 65 ° C. to a mass ratio of 15:85. The film was simultaneously discharged with the stock solution. This internal coagulation liquid has an HSP distance of 163 (MPa) ^{1/2 from the} film-forming stock solution.

  The film-forming stock solution extruded together with the internal coagulation liquid was immersed in an external coagulation liquid at 60 ° C. composed of a 180 g / L aqueous sodium sulfate solution through an idle running distance of 40 mm. By doing so, the membrane-forming stock solution is solidified and a hollow fiber membrane is obtained. This external coagulation liquid is a non-solvent for polyvinylidene fluoride.

  Next, the obtained hollow fiber membrane was washed after being stretched and contracted. By doing so, the solvent (γ-butyrolactone) and the polyvinylpyrrolidone resin (polyvinylpyrrolidone) are extracted and removed from the hollow fiber membrane. Thereafter, the obtained hollow fiber membrane was subjected to a crosslinking treatment (crosslinking insolubilization treatment) by heating polyvinylpyrrolidone in a 1% hydrogen peroxide solution. The content of the crosslinked product of polyvinylpyrrolidone at this time was 1.9% by mass.

  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.

It was 4 * 10 <^-15> m < ^{2 >} when the pure water permeability coefficient K of the obtained hollow fiber membrane was computed by said method.

In addition, a plurality of hollow fiber membranes having different film thicknesses were produced in the same manner except that the amount of the membrane-forming stock solution was changed, and the pure water permeability coefficient K was calculated for each. Then, as shown in FIG. 4, the change of the pure water permeability coefficient K with respect to the film thickness change was plotted, and the slope at that time was calculated. The inclination was 2.29 × 10 ⁻¹¹ . In addition, FIG. 4 is a graph which shows the change of the pure water permeability coefficient K with respect to the film thickness change in Example 1. The vertical axis represents the pure water permeability coefficient K (m ² ), and the horizontal axis represents the film thickness (m).

  Moreover, the fraction particle diameter of the obtained hollow fiber membrane was measured by the following method.

  Measure the blocking rate of at least two kinds of particles having different particle sizes (cataloid SI-550, cataloid SI-45P, cataloid SI-80P, etc., manufactured by JGC Catalysts & Chemicals Co., Ltd.), and based on the measured values, In the following approximate expression, the value of S at which R is 90 was determined, and this was defined 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. In addition, about the ultrafiltration membrane area | region, the molecular weight (weight average molecular weight) of the standard polyethylene oxide (The Tosoh Corporation make, TSKgel) which could be removed 90% or more was described.

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

Moreover, the membrane filtration apparatus 31 as shown in FIG. 3 was produced using this hollow fiber membrane. The membrane module 32 loaded in the membrane filtration device 31 has an effective membrane length of 100 cm and 70 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 filters the river water having a turbidity of 1.0 NTU (manufactured by HACH: measured by 2100Q) from the outer peripheral surface side of the hollow fiber membrane through the inlet 35, and the inner peripheral surface of the upper end portion. Filtrated water was obtained from the outlet 36 on the side. After filtering for 30 minutes at a set flow rate of 2.5 m / day (the set flow rate is (m / day) divided by the filtration flow rate (m ³ / day) by the hollow fiber membrane outer area m ² ), the outlet port 36, air was pressed for 10 seconds with 0.2 MPa air, and at the same time, air scrubbing was performed for 60 seconds with air of 0.1 MPa from the inlet 35 at the bottom of the module to clean the film (to remove the introduced air). The mouth was secured by opening the air vent 37). The cleaned dirt was extracted from the inlet 35 and filtration was started again. The results are shown in FIG. FIG. 5 is a graph showing the results of a long-term test using a hollow fiber membrane. In FIG. 5, when the hollow fiber membrane according to the first embodiment is used, it is indicated by a line 41. As can be seen from the result of this line 41, even if the above cycle was continued, it was possible to operate at a stable transmembrane pressure difference for 30 days or more. Moreover, when the hollow fiber membrane (reference example 2) which does not satisfy | fill the structure of this invention is used, it shows in FIG.

  From these facts, the hollow fiber membrane according to Example 1 was able to realize excellent permeation performance and fractionation characteristics with a high pure water permeability coefficient K and a small fraction particle size.

  Moreover, the membrane structure of the hollow fiber membrane which concerns on Example 1 was confirmed using the scanning electron microscope (S-3000N by Hitachi, Ltd.). The results are shown in FIGS.

  First, FIG. 6 is a view showing a scanning electron micrograph of a cross section of the hollow fiber membrane according to Example 1. FIG. Next, FIG. 7 is a view showing a scanning electron micrograph of the vicinity of the outer peripheral surface in the cross section of the hollow fiber membrane according to Example 1. FIG. FIG. 8 is a view showing a scanning electron micrograph of the vicinity of the central portion in the cross section of the hollow fiber membrane according to Example 1. Moreover, FIG. 9 is a figure which shows the scanning electron micrograph of the inner peripheral surface vicinity in the cross section of the hollow fiber membrane which concerns on Example 1. FIG. Specifically, FIG. 7 is an enlarged view of the surrounding line 61 shown in FIG. FIG. 8 is an enlarged view of the surrounding line 62 shown in FIG. FIG. 9 is an enlarged view of the surrounding line 63 shown in FIG.

  From these figures, it can be seen that a dense layered portion is formed in the vicinity of the outer peripheral surface, and a sparser portion is formed in the other portions. Specifically, the porosity near the outer peripheral surface shown in FIG. 7 is binarized using image measurement software (Image-Pro Plus manufactured by Planetron Co., Ltd.), and the porosity calculated by determining the threshold value using the Otsu method is At 34%, the porosity calculated with the threshold 210 was 67%. 9 is similarly binarized using image measurement software (Image-Pro Plus manufactured by Planetron Co., Ltd.), and the porosity calculated by determining the threshold value using the Otsu method is At 50%, the porosity calculated with the threshold 210 was 78%.

  FIG. 10 is a view showing a scanning electron micrograph of the outer peripheral surface of the hollow fiber membrane according to Example 1. FIG. 11 is a view showing a scanning electron micrograph of the inner peripheral surface of the hollow fiber membrane according to Example 1. From these figures, it can be seen that a dense layered portion is formed in the vicinity of the outer peripheral surface, and a sparser portion is formed in the other portions.

[Example 2]
A hollow fiber membrane was obtained in the same manner as in Example 1 except that the temperature of the external coagulation liquid (external coagulation bath temperature) was 70 ° C. and a 230 g / L sodium sulfate aqueous solution was used as the external coagulation liquid. The content of the crosslinked product of polyvinyl pyrrolidone in the obtained hollow fiber membrane was 0.5% by mass. The obtained hollow fiber membrane was able to realize excellent permeation performance and fractionation characteristics as in Example 1.

[Example 3]
A hollow fiber membrane was obtained in the same manner as in Example 1 except that the temperature of the external coagulation liquid (external coagulation bath temperature) was 50 ° C. and a 140 g / L sodium sulfate aqueous solution was used as the external coagulation liquid. The content of the crosslinked product of polyvinylpyrrolidone in the obtained hollow fiber membrane was 8.2% by mass. The obtained hollow fiber membrane was able to realize excellent permeation performance and fractionation characteristics as in Example 1.

[Example 4]
A hollow fiber membrane was obtained in the same manner as in Example 1 except that the temperature of the external coagulation liquid (external coagulation bath temperature) was 80 ° C. and a 280 g / L sodium sulfate aqueous solution was used as the external coagulation liquid. The content of the crosslinked product of polyvinyl pyrrolidone in the obtained hollow fiber membrane was 0.2% by mass. The obtained hollow fiber membrane was able to realize excellent permeation performance and fractionation characteristics as in Example 1.

[Comparative Example 1]
A hollow fiber membrane was obtained in the same manner as in Example 1 except that dimethylacetamide (DMAc manufactured by Mitsubishi Gas Chemical Co., Ltd.) was used as the solvent for the membrane forming stock solution. DMAc is a good solvent for polyvinylidene fluoride. The phase separation start temperature of the prepared membrane-forming solution was 10 ° C. or lower, which is the lowest measurable temperature. As a result of the test, when a good solvent for polyvinylidene fluoride was used as the solvent for the film forming stock solution, the solvent exchange rate was slow, the permeation performance was low, and a sufficient asymmetric structure was not obtained. The content of the crosslinked product of polyvinylpyrrolidone in the obtained hollow fiber membrane was 1.8% by mass.

[Comparative Example 2]
A hollow fiber membrane was obtained in the same manner as in Example 1 except that the hollow coagulation liquid was formed at a temperature of 20 ° C., which is equal to or lower than the phase separation start temperature of the membrane-forming stock solution. This manufacturing method is a manufacturing method by a so-called TIPS method. As shown in the test results, when the temperature became lower than the phase separation start temperature, phase separation by TIPS was developed, the permeation performance was low, and a sufficient asymmetric structure was not obtained. The content of the crosslinked product of polyvinylpyrrolidone in the obtained hollow fiber membrane was 1.5% by mass.

[Comparative Example 3]
As in Example 1, except that a mixed solvent of DMAc: water = 30: 70 in mass ratio (the HSP distance to the film forming stock solution at this time is 347 (MPa) ^1/2 ) was used as the internal coagulating liquid. Thus, a hollow fiber membrane was obtained. The inner peripheral surface of the hollow fiber membrane had a dense structure, the permeation performance was low, and a sufficient asymmetric structure could not be obtained. The content of the crosslinked product of polyvinylpyrrolidone in the obtained hollow fiber membrane was 2.0% by mass.

[Reference Example 1]
The same procedure as in Example 1 was performed except that a mixed solvent having a mass ratio of GBL: Gly = 97: 3 (the HSP distance to the film forming stock solution at this time was 0) was used as the internal coagulation liquid. However, in this case, the inner surface side of the hollow fiber was not sufficiently solidified and could not be formed into a hollow fiber shape.

[Reference Example 2]
Reference Example 2 is a hollow fiber membrane manufactured using the TIPS method, which has the same fractionation characteristics as those of the above Examples, but in principle the gradient of the inclined structure is small. In such a hollow fiber membrane, since the gradient of the inclined structure is small, not only the permeability coefficient K but also the slope of the permeability coefficient K when changing the film thickness is not in a suitable range, that is, in a sufficiently asymmetric structure. I understand that there is no. The reference example 2 is a hollow fiber membrane manufactured by the following manufacturing method.

  Polyvinylidene fluoride (hereinafter sometimes abbreviated as PVDF) as a vinylidene fluoride-based resin (SOLEF6010 manufactured by Solvay Solexis Co., Ltd.), γ-butyrolactone (GBL manufactured by Mitsubishi Chemical Corporation) as a solvent, and inorganic particles Silica (Aerosil 50 manufactured by Nippon Aerosil Co., Ltd.) and polyethylene glycol (PEG 200 manufactured by Sanyo Chemical Industries Co., Ltd.) as a flocculant are prepared in a mass ratio of 34: 21: 25: 20. did.

  The above mixture was supplied to a twin screw extruder and heated and kneaded (temperature: 155 ° C.) to extrude the solution from a double ring structure nozzle having an outer diameter of 1.6 mm and an inner diameter of 0.8 mm. At this time, polyvinyl alcohol (PVA-205, average polymerization degree: 500, saponification degree 87-89 mol%, manufactured by Kuraray Co., Ltd.), dimethylacetamide (DMAC, manufactured by Mitsubishi Gas Chemical Co., Ltd.) and glycerin (internal coagulating liquid) Purified glycerin manufactured by Kao Co., Ltd.) and a mixed solution at a ratio of 2: 58.8: 39.2 at a ratio of 2: 58.8: 39.2 and discharged at the same time through a 3 cm air travel distance, It was placed in an external coagulation bath made of an aqueous solution (temperature 80 ° C.) and cooled and solidified. Next, after drawing, the resulting hollow fiber-like material is washed with hot water, and the solvent (γ-butyrolactone), the flocculant (PEG200), the injection solution (DMAC, glycerin), and excess polyvinyl alcohol are extracted and removed. It was. At this time, the cleaning rate of polyvinyl alcohol was 70%. Thereafter, polyvinyl alcohol was acetalized to make it insoluble. Subsequently, it was immersed in an aqueous sodium hydroxide solution to extract and remove inorganic particles (silica) and dried. The hollow fiber membrane thus obtained had an outer diameter of 1.2 mm and an inner diameter of 0.6 mm.

  The membrane structure of the hollow fiber membrane according to Reference Example 2 was confirmed using a scanning electron microscope. The results are shown in FIGS.

  First, FIG. 12 is a view showing a scanning electron micrograph of a cross section of the hollow fiber membrane according to Reference Example 2. FIG. 13 is a view showing a scanning electron micrograph of the outer peripheral surface of the hollow fiber membrane according to Reference Example 2. 14 is a view showing a scanning electron micrograph of the inner peripheral surface of the hollow fiber membrane according to Reference Example 2. FIG. These figures also show that the hollow fiber membrane does not have a sufficient asymmetric structure.

Table 2 below shows the conditions, pure water permeability coefficient, and the like in the above Examples, Comparative Examples, and Reference Example 2. When the phase separation start temperature is low, “<10” is indicated. Moreover, when a hollow fiber membrane cannot be formed suitably, content of the crosslinked body of polyvinylpyrrolidone, a pure water permeability coefficient, a fraction particle diameter, etc. are shown as "-". In Reference Example 2, items relating to phase separation and the like are indicated as “−”. In addition, the inclination when the horizontal axis is the film thickness L (m) and the vertical axis is the pure water permeability coefficient K (m ² ) is simply expressed as “inclination”, and when the value is too small, “< 0.3 ". Further, as described above, the fractional particle diameter is “0.001” in the ultrafiltration region, and not only the particle diameter but also the weight average molecular weight that can be removed by 90% or more. In addition, when the value is smaller than the ultrafiltration region but is smaller, “<0.01” is indicated.

As can be seen from Table 2 and the above description, Examples 1 to 4 are superior in transmission performance and fractionation characteristics as compared with Comparative Examples 1 to 3. Reference Example 1 could not produce a suitable hollow fiber membrane.

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

Claims (7)

Including vinylidene fluoride resin,
The pure water permeability coefficient is 1 × 10 ⁻¹⁵ m ² or more and 22 × 10 ⁻¹⁵ m ² or less,
A hollow fiber membrane having a fractional particle size of 0.5 μm or less. The pure water permeability coefficient is 0.4 × 10 ⁻¹¹ × L (m ² ) or more and 6 × 10 ⁻¹¹ × L (m ² ) or less when the thickness of the hollow fiber membrane is L (m). Item 2. The hollow fiber membrane according to Item 1.   The hollow fiber membrane according to claim 1 or 2, comprising a single layer. It is a manufacturing method of the hollow fiber membrane according to any one of claims 1 to 3,
A product comprising a vinylidene fluoride resin, a poor solvent that is compatible with the vinylidene fluoride resin at a specific temperature or higher to form a one-phase state and can cause phase separation due to a temperature drop, and a polyvinylpyrrolidone resin. A preparation step of preparing a membrane stock solution;
An extrusion process for extruding the film-forming stock solution into a hollow fiber shape;
A step of forming a hollow fiber membrane by contacting the extruded hollow fiber-shaped membrane forming stock solution with an external coagulation liquid,
A method for producing a hollow fiber membrane, wherein the temperature of the external coagulation liquid is higher than a temperature at which phase separation due to the temperature decrease starts.   The manufacturing of the hollow fiber membrane according to claim 4, wherein the preparation step is a step of kneading the vinylidene fluoride resin, the poor solvent, and the polyvinylpyrrolidone resin to prepare the membrane forming stock solution. Method.   The method for producing a hollow fiber membrane according to claim 4 or 5, wherein the preparation step is performed at a temperature lower than the melting point of the vinylidene fluoride-based resin and higher than a temperature at which phase separation due to the temperature decrease starts. . From the inner discharge port of the hollow fiber molding nozzle, the extruding step includes an annular outer discharge port and a circular or annular inner discharge port disposed inside the outer discharge port. A 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,
The method for producing a hollow fiber membrane according to any one of claims 4 to 6, wherein the internal coagulation liquid has a solubility parameter distance of 5 to 200 (MPa) ^1/2 with respect to the membrane forming stock solution.