KR100581206B1 - Polyvinylidene fluoride Porous Hollow Fiber Membrane and the Manufacturing Process thereof - Google Patents

Abstract

The present invention is a polyvinylidene fluoride (PVDF) porous hollow fiber membrane having excellent solvent permeability, mechanical strength, and excellent ozone resistance and chemical resistance, and is located at the innermost side of the hollow fiber membrane and has a dense structure to separate the solvent from the solution. Inner skin layer (Inner skin layer) having a thickness of 1 to 5㎛ for; A macroporous support layer having a thickness of 50 to 300 μm formed on an outer portion of the inner surface active layer to support the inner surface active layer and having a plurality of macropores formed therein; An outer macrovoid layer having a thickness of 50 to 100 μm formed on an outer surface of the macroporous support layer and supporting a large outer surface active layer by forming a plurality of macrovoids having a smaller size than the macroporous; A polyvinylidene fluoride-based porous hollow fiber membrane having a four-layer structure formed at an outermost surface of the hollow fiber membrane and having a dense structure for separating a solvent from a solution; The manufacturing method is related.

Polyvinylidene fluoride system, porous hollow fiber membrane

Description

Polyvinylidene fluoride porous hollow fiber membrane and its manufacturing process {Polyvinylidene fluoride Porous Hollow Fiber Membrane and the Manufacturing Process}

1 is an electron scanning microscope (SEM) photograph of a single skin structure of a polyvinylidene fluoride-based porous hollow fiber of the present invention.

Figure 2 is an electron scanning microscope (SEM) photograph of an enlarged cross section of a single skin structure of the polyvinylidene fluoride-based porous hollow fiber of the present invention.

Figure 3 is an electron scanning microscope (SEM) photograph of the four-layer structure of the polyvinylidene fluoride-based porous hollow fiber of the present invention.

Figure 4 is an electron scanning microscope (SEM) photograph of an enlarged four-layer structure of the polyvinylidene fluoride-based porous hollow fiber of the present invention.

5 is an electron scanning microscope (SEM) photograph of the outer surface active layer in the single skin structure of the polyvinylidene fluoride-based hollow fiber membrane of the present invention.

6 is an electron scanning microscope (SEM) photograph of the outer surface active layer of the polyvinylidene fluoride-based porous hollow fiber of the present invention.

7 is a schematic view of a cross section of a polyvinylidene fluoride-based porous hollow fiber of the present invention.

8 is a schematic diagram of a humidity control chamber in which the hollow fiber membrane of the present invention is radiated to block or control moisture on an air gap.

Description of the main parts of the drawings

10 Tube in orifice nozzle 20 Humidity control chamber

21 Dry air inlet 22 Dry air outlet

30 coagulation tank 40 hollow fiber membrane

The present invention relates to a polyvinylidene fluoride-based porous hollow fiber membrane and a method for manufacturing the same, and more particularly, it is used as an ultrafiltration membrane or a microfiltration membrane, and has excellent heat resistance, mechanical strength and solvent permeability, and excellent chemical resistance such as ozone resistance. The present invention relates to a polyvinylidene fluoride-based porous hollow fiber membrane capable of exhibiting excellent performance in various water treatment fields such as water treatment, and a manufacturing method thereof.

Since the manufacturing technology of hollow fiber membranes using polymer materials became widespread in the 1970s, various membrane materials and membrane separation processes using them have been developed for various applications to date, and these membrane separation processes are used for separating valuable materials and increasing wastewater. It has been actively used in the treatment field, and recently, it has become an important use in the advanced water treatment process.

Conventionally, a polysulfone-based material or a polyolefin-based material has been mainly used. Recently, attention has been focused on polyvinylidene fluoride (PVDF) -based materials having excellent heat resistance and mechanical strength and excellent chemical resistance, particularly ozone resistance.

Korean patent application (Application No. 10-1998-0705623) dissolves 15 to 20% by weight of PVDF in solvent DMAC or NMP to form a dope, then casts to make a thin film, then exposes the thin film to a gas phase and then precipitates in a coagulation bath. The membrane was made of a porous support formed from a microporous surface consisting of minimum pores, an opposite surface consisting of maximum pores, and a filamentous web of polymeric material. In this case, it is useful for the purpose of producing a flat membrane, but it is very difficult to produce a hollow fiber membrane. In addition, there is a disadvantage that it is not easy to maintain the pressure resistance enough to be used even when manufactured by the hollow fiber membrane.

Korean Patent Application No. 10-2001-0046172 discloses a hollow fiber membrane by dissolving 9% to 17% by weight of PVDF in DMAC, using a wet spinning method, followed by hot water treatment, immersion in ethyl alcohol, and drying for separation membrane contactors. However, even in this case, there is a disadvantage in that the pressure resistance is low for use in water treatment processes, such as water treatment process.

Korean Patent (Application No. 10-2003-7009175) is a hollow fiber membrane by dissolving 30 to 50% by weight of PVDF with a poor solvent such as cyclohexanone at a high temperature of 140 ° C. or above and lowering it below the crystallization temperature above the crystallization temperature. Was prepared. This method is attractive because of its high strength, but it dissolves at high temperatures of 140 degrees Celsius and also has a high phase separation temperature of 80 degrees Celsius and higher, which makes it difficult to control the manufacturing process at high temperatures, and also has disadvantages in terms of energy efficiency. .

In order to solve the above problems, the present invention is manufactured through a simple manufacturing process, and in addition to the inherent properties of the material having excellent ozone resistance, it provides a polyvinylidene fluoride-based porous hollow fiber membrane having excellent solvent permeability and mechanical strength and a method of manufacturing the same. It aims to do it.

It is another object of the present invention to provide a polyvinylidene fluoride-based porous hollow fiber membrane having a long-term operation at high pressure as a double skin hollow fiber membrane having excellent solvent permeability.

The present invention for achieving the above object,

1) a first additive selected from the group consisting of polyvinylidene fluoride resin and polyvinylpyrrolidone, polyvinyl alcohol, polyethylene glycol, polyethyleneimine and mixtures thereof and selected from lithium chloride, zinc chloride, magnesium chloride, magnesium sulfate and mixtures thereof Preparing a polymer solution by mixing a second additive and a solvent capable of dissolving the polyvinylidene fluoride and the first and second additives substantially uniformly;

2) a first phase separation step of spinning the polymer solution using a double nozzle to form a hollow fiber membrane while passing through a dehumidification chamber having a dew point temperature of 10 ° C. or lower; And

3) a secondary phase separation step in which the hollow fiber membrane is immersed in a coagulation tank and completely precipitated;

It relates to a polyvinylidene fluoride porous hollow fiber membrane having a and a method of manufacturing the same.

In addition, the present invention,

Iii) an inner skin layer having a dense structure located at the innermost side of the porous hollow fiber membrane and having a thickness of 1 to 5 μm for separating the solvent from the solution;

Ii) a macroporous support layer having a thickness of 50 to 300 μm formed on an outer portion of the inner surface active layer to support the inner surface active layer and having a plurality of macropores formed therein;

Iii) an outer macrovoid layer having a thickness of 50 to 100 μm formed on the outside of the macroporous support layer and having a plurality of macrovoids of a relatively small size compared to the macroporous to support the outer surface active layer;

Iii) an outer skin layer having an outer thickness of 1 to 5 μm having a dense structure formed at the outermost side of the hollow fiber membrane to separate the solvent from the solution;

It provides a polyvinylidene fluoride-based porous hollow fiber having a.

Hereinafter, the present invention will be described in detail.

The most commonly used method of manufacturing a polymer film is a phase transition method. In order to prepare a polymer membrane using the phase transition method, first, a uniform polymer solution composed of a polymer and a solvent dissolving it is prepared, and a non-solvent forming a heterogeneous mixture with the polymer solution is added as an additive to induce phase transition to form a polymer membrane. do. The process of forming the polymer film generally consists of three processes as follows.

1. Proper formulation of the polymer solution (dope)

2. Casting of polymer solution or spinning through double nozzles (dry, wet spinning)

3. Formation of phase asymmetry in non-solvent coagulation bath to form asymmetric membrane consisting of active layer and porous support

Phase separation in the coagulation bath, which is the third of the three processes, is a well-known process, and thus, the most important factors for determining the structure and performance of the polymer membrane may be a composition blending and spinning process.

The hollow fiber polymer membrane prepared by the above process has an asymmetric structure consisting of layers having opposite structural characteristics, that is, an active layer having a microporous structure and a plurality of pores formed therein and a porous support layer supporting the active layer. In order to use the hollow fiber polymer membrane as an ultrafiltration membrane or a microfiltration membrane for high water purification treatment, the structures of the active layer and the porous layer should be appropriately controlled. That is, it is preferable to increase the porosity of the porous layer supporting the active layer to the maximum to reduce the solvent permeation resistance to increase the solvent permeability as much as possible.

In large-capacity water purification processes, the external surface active layer plays a very important role because a separation method is generally used to remove foreign substances by applying pressure from the outer side of the hollow fiber membrane and backwash by periodically applying pressure from the inside. Therefore, a double skin layer of the inner surface active layer and the outer surface active layer is essential, and the structure of the porous support layer mainly supporting the outer surface active layer under pressure is advantageous in that it can secure the pressure resistance. Therefore, in order to manufacture a hollow fiber membrane having a support structure capable of supporting a high solvent permeability and an outer surface active layer effectively, it is necessary to suppress phase separation of the outer surface layer as much as possible in the first phase separation process on an air gap that is primarily phase separated.

In general, in the phase separation of most polymer solutions such as polysulfone or polyacrylonitrile, liquid-liquid phase separation occurs while separating into a polymer rich phase and a polymer poor phase, but polyvinylidene fluoride type Phase separation of the polymers has been reported to not yet exist a solvent causing liquid-liquid-phase separation at room temperature. The polyvinylidene fluoride polymer solution of the present invention causes a solid-liquid phase separation that is separated into a solid phase and a polymer poor phase.

The inventors of the present invention can efficiently phase-separate the polyvinylidene fluoride polymer solution from the outer surface exposed to the air during the phase separation process of the polyvinylidene fluoride polymer solution, that is, the phase separation from the inner wall surface of the hollow fiber by a bore liquid on the air gap. The outer surface active layer can be densely manufactured through the method of suppressing and controlling the same. Also, by controlling the thickness and size of the outer macrovoid layer appropriately, the outer surface active layer can be manufactured in a structure that is excellent in solvent permeability and more resistant to pressure. I could see that. In general, polyvinylidene fluoride-based polymer solution has a very slow phase separation on the air gap, and the diameter of the pores of the outer surface active layer is formed to be very large (5 µm or more), and thus the selective separation in the separation of the liquid mixture applied to the outer surface. Is not possible and also has a weak fatal weakness in pressure.

Therefore, in the present invention, the humidity control chamber as shown in FIG. 8 was used to reliably form the outer surface active layer and to control the outer macrovoid layer. Humidity is controlled by using a dehumidifying gas separation membrane module developed by Chemicoa Co., Ltd., flowing dry air at a dew point temperature of 10 ° C at a rate of 5 L / min until reaching a set humidity value and setting the humidity in the chamber. When the humidity value was reached, the humidity was controlled by automatically closing the valve of the dry air supply line.

In order to manufacture a four-layer hollow fiber membrane including a double active layer of the present invention, the relative humidity should be adjusted in the range of 20 to 40%. In a range of 50% or more relative humidity, a single active layer is prepared in which only an inner surface active layer is present without an outer surface active layer as shown in FIGS. 1, 2 and 5.

The polyvinylidene fluoride-based hollow fiber membrane of the present invention is a polymer material which is an asymmetric membrane component capable of selectively separating and concentrating a material to be separated in a liquid mixture, a solvent for the polymer material, the thickness of the separation layer, and the porosity of the porous layer. The polymer solution composed of the first additive and the second additive for controlling the membrane structure of the back filtration membrane is spun through a controlled air gap, and then precipitated into a non-solvent to cause a phase transition, as shown in FIG. 7. An asymmetric film is prepared, the cross section of which consists of four layers: an inner surface active layer, a macroporous support layer, an outer macrovoid layer, and an outer surface active layer.

Hollow fiber membrane having a four-layer structure of the present invention is well developed for the external surface active layer and the external macrovoid layer to be suitable for the external pressure purification process, it is possible to selectively separate the foreign matter flowing from the outside and to withstand the pressure applied from the outside It is a structure that can reduce the permeation resistance as much as possible, and the solvent permeability is very high.

As described above, the present invention,

1) a first additive selected from polyvinylidene fluoride resin and polyvinylpyrrolidone, polyvinyl alcohol, polyethylene glycol, polyethyleneimine and mixtures thereof and a second selected from lithium chloride, zinc chloride, magnesium chloride, magnesium sulfate and mixtures thereof Preparing a polymer solution by mixing an additive and a solvent capable of dissolving the polyvinylidene fluoride and the first and second additives substantially uniformly;

2) a first phase separation step of spinning the polymer solution using a double nozzle to form a hollow fiber membrane while passing through a dehumidification chamber having a dew point temperature of 10 ° C. or lower; And

3) a secondary phase separation step in which the hollow fiber membrane is immersed in a coagulation tank and completely precipitated;

It relates to a polyvinylidene fluoride porous hollow fiber membrane having a and a method for producing the same.

In the polymer solution of the present invention, the polymer material is a constituent of an asymmetric membrane having the property of separating the solute by permeating only the solvent in the solution. Generally, polyacrylonitrile, polysulfone, polyvinylidene fluoride, and polycarbonate Synthetic polymer materials such as polyimide, polyamide, and polyaramid may be used, but polyvinylidene fluoride should be used in order to achieve the four-layer polymer membrane structure of the present invention.

At this time, the content of the polymer material is preferably used 15 to 25% by weight, preferably 17 to 24% by weight. When the content of the polymer is less than 15% by weight, the solute blocking rate of the hollow fiber membrane is low, the mechanical strength is weak, and when the content exceeds 25% by weight, solvent permeation is low.

The solvent serves to uniformly dissolve the polyvinylidene fluoride, which is an additive and a membrane component, and is typically selected from N-methylpyrrolidone, N, N-dimethylformamide, and N, N-dimethylacetamide. It is preferred to use any one or two or more mixtures thereof, more preferably N, N-dimethylacetamide having a relatively high solubility of polyvinylidene fluoride. The solvent N, N-dimethylacetamide may be used 50 to 80% by weight, preferably 60 to 75% by weight.

The first additive is mainly a water-soluble polymer, and serves to control the pore size and pore volume of the inner surface active layer, the outer surface active layer, and the macroporous support layer and the outer macrovoid layer in the asymmetric membrane structure. Pyrrolidone, polyvinyl alcohol, polyethylene glycol, polyethyleneimine and mixtures thereof can be preferably used as the first additive, and more preferably polyvinylpyrrolidone or polyvinyl alcohol can be used.

In this case, the polyvinylpyrrolidone preferably has a molecular weight of 10,000 (Mw) or more, and the polyvinyl alcohol preferably has a molecular weight (Mw) of 30,000 or more, but is not necessarily limited to the above range.

In addition, the polyvinylpyrrolidone is preferably added about 1 to 25% by weight, more preferably 5 to 20% by weight. When the amount of the polyvinylpyrrolidone added is less than 1% by weight, the porosity of the macroporous support layer and the outer macrovoid layer is lowered, thereby lowering the solvent permeability. And when added in more than 25% by weight, the viscosity of the polymer solution rises rapidly, it is difficult to form the hollow fiber membrane, the pore size is too large, there is a problem that the mechanical strength is lowered.

The second additive may be selected from the group consisting of any one or a mixture of two or more selected from lithium chloride, zinc chloride, magnesium chloride, magnesium sulfate. The second additive may also have an effect of increasing the viscosity of the dope according to the degree of interaction with the solvent, affecting the solvent exchange rate during phase separation to a solid phase and a polymer poor phase When separated, the particle size of the crystals of the solid phase may be reduced to induce an effect of reducing the porosity of the polymer matrix, thereby increasing the mechanical strength. The second additive of the inorganic salt system may add 0.1 to 10% by weight, more preferably about 1 to 5% by weight within the range that does not lower the physical properties.

 After removing bubbles from the polymer solution prepared in this way, using a gear pump, and then, the air is controlled and controlled to control the humidity while spinning through a tube-orifice-type spinning nozzle 10 at a flow rate of 10 to 30 ml / min The polymer membrane is prepared by passing through a gap and precipitation into non-solvent water. At this time, the polymer solution exits through the outer hole of the double nozzle and discharges the internal coagulant at a flow rate of 5.0 to 20 ml / min inside the double nozzle.

Herein, the internal coagulant refers to a non-solvent in contact with the polymer solution to induce phase transition. The internal coagulant includes a non-solvent selected from water or alcohols having 1 to 4 carbon atoms, triethylene glycol, 1-butoxyethanol, glycerol and Preference is given to using alcohols selected from the group consisting of mixtures thereof.

 The internal coagulant induces a slow phase transition rate while controlling the solvent exchange rate during the phase transition process, thereby controlling the size of the inner surface active layer, the outer surface active layer and the macroporous support layer, and the outer macrovoid layer, thereby improving the mechanical strength and backwashing process of the hollow fiber membrane. Contributes to improving the pressure resistance of the membrane. The inner diameter of the outer nozzle of the double nozzle is 1.5 to 2.5 mm, the inner and outer diameter of the inner nozzle is 0.2 to 0.5 mm and 0.5 to 1.0 mm, respectively.

Thus, when the hollow fiber membrane is formed through the phase transition process of the non-solvent and the polymer solution, the polymer concentration increases toward the inner surface active layer and the outer surface active layer, and the macroporous support layer and the outer macrovoid layer portion have a relatively low polymer concentration. The porosity increases, and the permeation resistance of the hollow fiber membrane can be greatly reduced due to the formation of the macroporous support layer formed therein, thereby increasing the solvent permeability. Water containing 1 to 4 carbon atoms or 30 to 50% by weight of an alcohol selected from the group consisting of triethylene glycol, 1-butoxyethanol, glycerol and mixtures thereof as an internal coagulant to control the formation of such a macroporous support layer. Preference is given to using alcohol solutions.

Using such an internal coagulant, the solvent exchange rate at the interface can be controlled slowly, and the thickness of the macroporous support layer can be adjusted to 50 to 300 μm. If the internal coagulant contains more than 50% by weight of the alcohol, the thickness of the inner surface active layer is increased to 10 μm or more, so that the permeation resistance of the membrane is increased, which is not a factor of reducing flux (solvent permeation). If the alcohol content of less than 30% by weight is included, the development of the macroporous support layer is insignificant, so that the porosity of the macroporous support layer is also lowered, and thus the solvent permeability is also lowered.

The hollow yarn thus formed is wound up in a rotating bobbin while being washed with water. At this time, the winding speed may be adjusted to change the inner diameter and the outer diameter of the hollow fiber polymer membrane. The hollow yarn wound on the bobbin is immersed in a washing tank containing water for about 24 to 48 hours to wash out a small amount of residual solvent or residual additive. The washed hollow yarns are deposited into aqueous solution of glycerin to maintain the surface and structure of the membrane. At this time, the glycerin content of the aqueous glycerin solution is preferably 10 to 50% by weight, more preferably 20 to 40% by weight.

The deposition time is within 12 hours and more advantageously within 6 hours. The hollow fiber deposited with aqueous solution of glycerin is transferred to a drying apparatus and dried at room temperature or below 50 ° C, preferably at 20 ° C to 40 ° C. The membrane is dried to prepare an experimental module having a membrane area of 0.05㎡ to measure the water permeability and solute rejection.

The cross-sectional structure of the hollow yarn of the present invention thus produced is shown in FIG. 7. As shown in FIG. 7, the hollow fiber membrane has a dense structure inside and outside and has an inner surface active layer, an outer surface active layer, a macroporous support layer on which a plurality of macropores are formed, and a plurality of macrovoids for separating a solvent from a solution. It is an asymmetric membrane having a four-layer structure, such as an outer macrovoid layer supporting the outer surface active layer.

The inner surface active layer and the outer surface active layer each have a thickness of 1 to 5 µm, and extremely fine pores having a diameter of 0.005 to 0.1 µm are formed, and the macroporous support layer and the outer macrovoid layer are 50 to 300 µm, respectively. And has a thickness of 50 to 100㎛, therein is formed micropores having a diameter of 1 to 10㎛. It is preferable that the total film thickness of the said hollow fiber membrane is 300-400 micrometers.

3 and 4 show electron scanning microscope (SEM) photographs of the polyvinylidene fluoride porous hollow fiber membranes of the present invention. Thus, the formation of the macroporous support layer and the external macrovoid layer can reduce the permeation resistance of the hollow fiber membrane to improve solvent permeability, and also to withstand the pressure acting as the outer surface active layer in the water treatment process used by the external pressure method. The external macrovoid layer is developed so that it is possible.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited by the following Examples.

The ratio of this invention shows the weight% unless there is particular notice.

EXAMPLES 1-4

Polyvinylidene fluoride (PVDF, Solvay product, Mw: 219,000) was gradually added to N, N-dimethylacetamide (DMAC), and polyvinylpyrrolidone (PVP, Sigma product, Mw: 10,000) and the first additive were added. Magnesium chloride as an additive 2 was mixed as described in Table 1 below to prepare a uniform solution.

Bubbles were removed from the prepared uniform polymer solution using a vacuum pump. After the polymer solution was transferred using a gear pump, a hollow fiber membrane having an inner diameter of 0.8 mm and an outer diameter of 1.4 mm was prepared by spinning through a double nozzle having an inner diameter of 0.65 mm and an outer diameter of 1.65 mm. At this time, the solution discharge amount is 25cc / min, 1-butoxy ethanol 30% aqueous solution was used as the internal coagulant, the discharge amount was 15cc / min, the hollow fiber membrane production temperature was 25 ℃. In addition, the air gap was set to 35 cm, and dry air at a dew point temperature of 10 ° C. was injected into the humidity control chamber at a rate of 5 L / min. The hollow fiber was washed for 24 hours in a water washing tank in order to wind up continuously spun and solidified hollow fiber and remove the remaining organic mixture, and then it was immersed in a glycerin solution for 6 hours. The completely washed hollow fiber was transferred to a drying apparatus and dried in air below 50 ° C. A membrane module having a membrane area of 0.05 m 2 was prepared using 100 strands of the hollow fiber polymer membrane.

TABLE 1

Experimental Examples 1 to 3

Using the membrane modules prepared in Examples 1 to 4, the permeability of pure water, dextran (Sigma, Mw: 428,000), blocking rate, and tensile strength at break were measured by the following method and described in Table 2.

1) Pure Transmission Conditions

The hollow fiber membrane was cut to 30 cm in length to make a module about 100 strands, and the effective membrane area was 0.05 m 2. Pure water at a temperature of 25 ° C. was injected into the module at an average pressure of 2 kg / cm 2, and the pure water permeability was measured, and the unit time, the membrane area, and the permeate per unit pressure were calculated.

2) Dextran blocking rate

A dextran 2000 ppm solution was prepared by dissolving dextran having a molecular weight of about 428,000 (manufactured by Sigma) in 25 ° C pure water. The aqueous solution was supplied at an average pressure of 2 kg / cm 2 toward the inside of the module having an effective membrane area of 0.05 m 2 as described above. After 20 minutes of circulation permeation, the stock solution and permeate were collected and analyzed by GPC. The blocking rate R can be calculated as follows, and the larger the value of R, the smaller the fraction molecular weight. Where Cp is the dextran concentration of the purified solution and Co is the dextran concentration of the crude solution.

R = (1-Cp / Co) × 100 (%)

3) tensile strength at break

The tensile load applied to the specimen at any given point divided by the original cross-sectional area (average value for elastic modulus and minimum cross-sectional area for elastic modulus) between the marks of the specimen is called tensile stress. The tensile stress of is called tensile fracture strength. In accordance with ASTM D 638, the tensile strength at break can be determined by the following equation. In the present invention, Instron Corporation's Series Ⅸ Automated Materials Testing System 1.16 instrument was used to measure tensile strength at break.

σ = F / A

σ: tensile strength at break (N / cm 2, kg / cm 2)

F: Load at break (N, kg)

A: Original minimum short distance (cm 2) of the test piece

TABLE 2

[Comparative Examples 1 to 3]

The hollow fiber membranes were prepared in the same manner as in Examples 1 to 4, except that dry air having a dew point temperature of 10 ° C. was not injected, and the results were shown in Table 3 by experiments in the same manner as in Experiments 1 to 3. .

TABLE 3

As in Examples 1 to 4, dope was prepared using polyvinylpyrrolidone as a first additive and magnesium chloride as a second additive in preparing an ultrafiltration membrane made of polyvinylidene fluoride, and a dew point on an air gap was used. Injecting dry air at a temperature of 10 degrees Celsius at a rate of 5 L / min to inhibit and control the phase separation of the outer surface layer to induce phase transition slowly, compared to the two-layer hollow fiber membrane without the outer surface active layer, has a better dextran blocking rate. It is possible to manufacture a hollow fiber membrane having a four-layer structure with an tensile strength at least 50%. In addition, the presence of the outer surface active layer and the outer macrovoid increases the strength of the hollow fiber membrane during the backwashing process.

As described above, the polyvinylidene fluoride hollow fiber membrane of the four-layer structure of the present invention can be manufactured by a simple process, and has excellent solvent permeability and tensile breaking strength, and excellent heat resistance, chemical resistance, and ozone resistance, thereby treating water. Not only can be used in the process, but also pressure and external pressure can be used in various water treatment fields can be easily applied.

Claims (11)

1) at least one first additive selected from polyvinylidene fluoride, polyvinylpyrrolidone, polyvinyl alcohol, polyethylene glycol and polyethyleneimine, and at least one agent selected from lithium chloride, zinc chloride, magnesium sulfate, and magnesium chloride Preparing a polymer solution comprising a second additive and a solvent capable of dissolving the polyvinylidene fluoride and the first and second additives substantially uniformly; 2) a first phase separation step of spinning the polymer solution using a double nozzle to form a hollow fiber membrane while passing through a dehumidification chamber having a dew point temperature of 10 ° C. or lower; And 3) a secondary phase separation step in which the hollow fiber membrane is immersed in a coagulation tank and completely precipitated; Method for producing a polyvinylidene fluoride porous hollow fiber having a. The method of claim 1, The solvent is a method for producing a polyvinylidene fluoride porous hollow fiber membrane, characterized in that any one or more selected from N-methylpyrrolidone, N, N-dimethylformamide, N, N-dimethylacetamide. The method of claim 1, The polymer solution is a polyvinylidene fluoride porous hollow fiber membrane, characterized in that consisting of 15 to 25% by weight of polyvinylidene fluoride, 75 to 85% by weight of the solvent / first additive / second additive. The method of claim 3, Method for producing a polyvinylidene fluoride porous hollow fiber membrane, characterized in that 5 to 20% by weight of the first additive in the polymer solution. The method of claim 3, Method for producing a polyvinylidene fluoride porous hollow fiber membrane, characterized in that containing 1 to 5% by weight of the second additive in the polymer solution. The method according to any one of claims 1 to 5, In the first phase separation step, a non-solvent selected from water or an alcohol having 1 to 4 carbon atoms, triethylene glycol, 1-butoxyethanol, and glycerol as an internal coagulant to induce phase transition by contacting the polymer solution inside the hollow fiber membrane. And polyvinylidene fluoride porous hollow membranes, characterized in that alcohols selected from the group consisting of a mixture thereof are used. It is formed on the outermost side of the hollow fiber membrane, and formed on the outermost surface of the hollow fiber membrane, the outer macrovoid layer having a macropore formed on the outer surface of the inner surface active layer, the outer surface active layer, and the outer surface of the large air support layer. A polyvinylidene fluoride porous hollow fiber formed, having a compact structure and having an outer surface active layer for separating a solvent from a solution. The method of claim 7, wherein Polyvinylidene fluoride porous hollow fiber membrane, characterized in that the thickness of the macroporous support layer is 50 to 300μm. The method of claim 7, wherein Polyvinylidene fluoride porous hollow fiber membrane, characterized in that the porous pore support layer and the outer macrovoid layer is formed with pores having a diameter of 1 to 10μm. The method of claim 7, wherein The polyvinylidene fluoride porous hollow fiber membrane, characterized in that the inner surface active layer and the outer surface active layer is 1 to 5 ㎛. Iii) a surface active layer having a dense structure and having a pore size of 0.005 to 0.1 μm and a thickness of 1 to 5 μm for separating the solvent from the solution; Ii) a macroporous support layer formed on the outside of the inner surface active layer and having a thickness of 50 to 300 μm in which a plurality of 1 to 10 μm macropores are formed; Iii) an outer macrovoid layer formed on the outside of the macroporous support layer and having a thickness of 50 to 100 μm in which a plurality of macrovoids of 1 to 10 μm are formed; Iii) an outer surface active layer formed on the outside of the outer macrovoid layer and formed on the outermost side of the hollow fiber membrane and having a dense structure for separating the solvent from the solution and having a pore of 0.005 to 0.1 μm and a thickness of 1 to 5 μm; Polyvinylidene fluoride porous hollow fiber membrane, characterized in that consisting of.

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