KR20140026118A - Manufacturing method of pvdf asymmetric porous hollow fiber membrane - Google Patents

Abstract

The present invention relates to a method of manufacturing a polyvinyldenfluoride (PVDF) asymmetric porous fiber membrane, and more particularly, to a manufacturing method for forming a spherulite-like structure in which the spherulite-like structure having a gradually increasing diameter is not peeled since the PVDF asymmetric porous fiber membrane is easy manufactured using a dual-injection nozzle and there is no need to separately form a coating layer. Since the spherulite-like structure is formed, the method of the present invention may provide a PVDF asymmetric porous fiber membrane in which, since the mechanical strength thereof is excellent compared to a PVDF porous fiber membrane manufactured with conventional technology, the PVDF asymmetric porous fiber membrane may be effectively used in a membrane cleaning technique such as a backwash and have excellent filtration efficiency that remarkably enhances water flux and concurrently satisfies an excellent rejection rate.

Description

Technical Field [0001] The present invention relates to a method for producing asymmetric porous hollow fiber membranes,

The present invention relates to a method for producing an asymmetric porous hollow fiber membrane of polyvinylidene fluoride (hereinafter abbreviated as " PVDF "), and more particularly to a method for producing an asymmetric porous hollow fiber membrane which is used for water treatment such as wastewater treatment, water treatment, The present invention relates to a hollow fiber membrane using PVDF as a raw material.

The separation membrane technology is a highly separation technology for almost completely separating and removing the materials to be treated present in the treatment water according to the pore size, the pore distribution and the membrane surface charge of the membrane. In the water treatment field, the production of high quality drinking water and industrial water, And clean production processes related to the development of waste water treatment and reuse, and free circulation systems are expanding and are becoming one of the key technologies to be noticed in the 21st century.

The membrane for water treatment may be a hollow fiber membrane. The hollow fiber membrane has a hollow-ring shape, which is advantageous in that it has a larger membrane area per module unit than a flat membrane. If the water treatment separator has a hollow fiber membrane structure, the membrane may be cleaned by backwashing to remove sediments by passing a clean liquid in a direction opposite to the filtration direction, air scrubbing for removing sediments by shaking the membrane by introducing air bubbles into the module Can be effectively used.

Typical properties required for water treatment hollow fiber membranes include adequate porosity (number of pores) for the purpose of separation efficiency, uniform pore distribution for the purpose of improving fractionation accuracy, It is required to have an optimum pore size. In addition, chemical resistance, chemical resistance, heat resistance, and the like for chemical treatment are required as material characteristics. In addition, properties that affect the operating capability are required to have good mechanical strength to extend service life, and water permeability associated with operating costs.

The membrane structure can be divided into a symmetric membrane having a uniform film as a whole and asymmetric membranes having different pore sizes formed in the thickness layer. The asymmetric membrane type has a lower permeation resistance from the viewpoint of mass permeability, It is possible to increase the selectivity of the selective separation layer while securing the physical film strength.

Polymeric materials used in the water treatment process using membrane technology include polysulfone, polyethersulfone, polyacrylonitrile, polyethylene, polypropylene, cellulose (cellulose) actate) and polyvinyldene fluoride (hereinafter referred to as " PVDF "). In particular, in recent years, a fluorine-based polymer material having a stain resistance from an organic pollution source has been attracting attention as a water treatment separator material due to a negative charge atmosphere.

The hollow fiber membrane can be divided into two types according to the manufacturing method. There are NIPS (Nonsolvent induced phase separation) method using a non-solvent and TIPS (Thermally inducedphase separation) method using heat.

The separation membrane prepared by the NIPS method can change various conditions of the spinning conditions to form various structures of the separation membrane, especially asymmetric structure, and it is easy to adjust the pore size by adding various additives, Which is advantageous in that high water permeability can be obtained, but it is disadvantageous in general that the strength is weak.

On the other hand, the separation membrane manufactured by the TIPS method generally has the same structure as the outer surface and the inside of the separation membrane, and has the advantage of obtaining high strength properties. However, it is difficult to easily control the pore size, And it is difficult to solve the additive.

Recently, research on PVDF hollow fiber membranes as a fluorine resin has been actively carried out. However, PVDF hollow fiber membranes prepared by the conventional NIPS method have weak mechanical strength and PVDF hollow fiber membranes prepared by the TIPS method are difficult to form asymmetric structures and control pores There was a problem. And there is a problem that the water permeability is significantly lowered due to the hydrophobicity of PVDF.

In order to manufacture an asymmetric PVDF hollow fiber membrane, an inner support layer solution is conventionally discharged through an intermediate tube 12 through a triple tubular spinning nozzle 10 as shown in FIG. 1, The solution was discharged to prepare a membrane having an asymmetric structure in which the inner supporting layer formed a spherical structure and the outer coating layer formed a sponge structure. However, this manufacturing method has problems in that the manufacturing process is complicated, the manufacturing cost is high due to the production of the polymer solution of the inner supporting layer and the coating layer in a double manner, and the pore size of the surface changes during the backwashing operation due to the weak bonding force between the support layer and the coating layer . Another conventional method for manufacturing an asymmetric PVDF hollow fiber membrane has been proposed in which a PVDF solution is coated on a support. However, the hollow fiber membrane thus produced has a problem in that the PVDF coating layer is easily peeled off.

DISCLOSURE OF THE INVENTION The present invention has been made in order to overcome the above-mentioned problems, and it is an object of the present invention to improve the mechanical strength of the PVDF hollow fiber membrane and satisfy the high water permeability and rejection rate required for the water treatment membrane, The present invention provides a method for producing a PVDF asymmetric porous hollow fiber membrane.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems,

(1) preparing a crude liquid by melt-mixing a mixed plasticizer and polyvinylidene fluoride (PVDF) containing a plasticizer and a low-solubility plasticizer at a temperature of 170 to 300 ° C even if they are employed; (2) extruding the crude solution through a spinning nozzle to form a hollow fiber; And (3) dipping the formed hollow fiber in an external coagulating liquid.

According to a preferred embodiment of the present invention, the solubility parameter difference between the plasticizer and the low-solubility plasticizer may be 5 (cal / ml) ^{2 or} more even if the mixed plasticizer is solubilized.

According to another preferred embodiment of the present invention, the solubility parameter difference between the plasticizer and the low-solubility plasticizer may be 5 to 15 (cal / ml) ² even if the mixed plasticizer is solubilized.

According to another preferred embodiment of the present invention, the low-solubility plasticizer may be any one or more selected from the group consisting of dioctyl phthalate, dioctyl sebacate, dioctyl adipate, ethylene glycol, diethylene glycol, and polyethylene glycol .

According to another preferred embodiment of the present invention, the plasticizer to be employed may be at least one selected from the group consisting of dibutyl phthalate, dimethyl phthalate, glycerol triacetate and gamma-butylolactone.

According to another preferred embodiment of the present invention, the mixed plasticizer comprising the low-solubility plasticizer and the solubilizing plasticizer may include 70 to 300 parts by weight based on 100 parts by weight of PVDF.

According to another preferred embodiment of the present invention, the mixing ratio by weight of the low solubility plasticizer and the solubilizing plasticizer may be 1: 9 to 7: 3.

According to another preferred embodiment of the present invention, the spinning nozzle of the step (2) may be maintained at a temperature of 占 폚 of the melting temperature of the step (1).

According to another preferred embodiment of the present invention, the extrusion of the step (2) may be performed at a speed of 40 to 90 rpm.

According to another preferred embodiment of the present invention, the spinning nozzle of the step (2) is a double tubular spinning nozzle, the spinning solution of the step (1) is discharged to the outer tube of the double tubular spinning nozzle, The inner coagulant can be discharged through the inner tube of the tubular spinning nozzle.

According to another preferred embodiment of the present invention, the internal coagulant is selected from the group consisting of dibutyl phthalate, dimethyl phthalate, diethyl phthalate, dioctyl phthalate, And one or more selected from the group consisting of Dioctyl sebacate, Glycerol triacetate, Polyethylene glycol, Ethylene glycol, Propylene glycol, and Diethylene glycol. .

According to another preferred embodiment of the present invention, the external coagulating solution in the step (3) is selected from the group consisting of water, dibutyl phthalate, dimethyl phthalate, diethyl phthalate, Dioctyl sebacate, Glycerol triacetate, Polyethylene glycol, Ethylene glycol, Propylene glycol, and Diethylene glycol may be used. May be any one or more selected from the group consisting of

According to another preferred embodiment of the present invention, the external coagulation liquid of step (3) may be -10 to 120 ° C.

According to another preferred embodiment of the present invention, the step (4) of stretching the produced hollow fiber membrane may be further included.

According to another preferred embodiment of the present invention, the step (4) may be stretched at a stretching ratio of 1.1 to 2.0 times at a stretching temperature of 15 to 150 ° C.

The method of manufacturing a PVDF asymmetric porous hollow fiber membrane of the present invention can easily produce a PVDF asymmetric membrane even with a double spinning nozzle and can simplify the manufacturing process and does not need to form a coating layer separately, Like structure having an asymmetric sphere structure.

As a result of forming an asymmetric spherical structure, the PVDF hollow fiber membrane is superior in mechanical strength to the PVDF hollow fiber membrane manufactured by the conventional method, and can be effectively used for membrane cleaning such as backwashing. In addition, The present invention can provide a PVDF asymmetric porous hollow fiber membrane excellent in filtration efficiency at the same time.

1 is a cross-sectional view of a triple tubular nozzle for producing a conventional PVDF asymmetric hollow fiber membrane.
2 is a cross-sectional view of a double tubular nozzle for producing a PVDF asymmetric hollow fiber membrane according to the present invention.
3 is a photograph of a section of a PVDF hollow fiber membrane according to a preferred embodiment of the present invention.
4 is a photograph of a section of a PVDF hollow fiber membrane according to another preferred embodiment of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will be described in more detail with reference to the accompanying drawings.

 As described above, in the conventional PVDF asymmetric hollow fiber membrane, an asymmetric membrane having an inner supporting layer formed of a spherical structure and an outer coating layer forming a sponge structure was manufactured through a triple nozzle, but the manufacturing process is complicated, And the pore size of the surface is changed during the backwashing operation of the separation membrane due to the weak bonding force between the support layer and the coating layer. The PVDF solution is coated on the support, The hollow fiber membrane has a problem that peeling of the PVDF coating layer occurs easily.

Accordingly, the present invention provides a method for producing a polyvinylidene fluoride resin composition, comprising the steps of: (1) melt mixing a polyvinylidene fluoride (PVDF) and a mixed plasticizer containing a plasticizer and a low-solubility plasticizer at a temperature of 170 to 300 ° C to prepare a crude liquid; (2) extruding the crude solution through a spinning nozzle to form a hollow fiber; And (3) immersing the formed hollow fiber in an external coagulating solution. The present invention has been made to solve the above-mentioned problems by providing a method for producing a PVDF hollow fiber membrane. As a result, it is possible to manufacture a PVDF asymmetric hollow fiber membrane by using a double spinning nozzle, to facilitate the manufacturing process, to prevent peeling due to no formation of a coating layer and to prevent the surface pore size from being changed during backwashing, Spherulite like structure with a gradient can be formed. By forming a spherical structure like asymmetry, the mechanical strength is excellent, and the excellent rejection rate can be satisfied at the same time while remarkably improving the water permeability.

 In the step (1), a mixed plasticizer containing a plasticizer and a low-solubility plasticizer and polyvinylidene fluoride (PVDF) are melt-mixed at a temperature of 170 to 300 ° C to prepare a crude liquid.

The polyvinylidene fluoride (PVDF) used in the hollow fiber membrane of the present invention preferably has an average molecular weight of 200,000 to 1,000,000. If the PVDF average molecular weight is less than 200,000, it may be difficult to form a hollow fiber membrane due to a low viscosity. If the PVDF average molecular weight is more than 1,000,000, moldability may be deteriorated due to high viscosity during melting.

The present invention relates to a method for producing a PVDF asymmetric membrane by melt-mixing a solution containing at least two mixed plasticizers. The solubility parameter difference between the solubilizing plasticizer and the low solubility plasticizer may be 5 (cal / ml) ^{2 or} more, more preferably 5 to 15 (cal / ml) ² Lt; / RTI >

In the present invention, the solubility parameter refers to the solubility constant of each polymer or solvent, and it can be said that a solvent having a small difference in the intrinsic solubility parameter of the polymer is easier to dissolve with the polymer. The difference in solubility between the polymer and each plasticizer can influence the formation and crystallinity of the primary nucleus when the polymer is solidified after melting, thereby determining the structure of the separator. The solubility parameter can be defined by the Hansen equation as follows:

Where

[delta] = solubility parameter,

δ _d = solubility parameter by disperipon force for the solubility parameter,

δ _p = solubility parameter by dipolar intermolecular force for the solubility parameter,

δ _h = the solubility parameter of the hydrogen bonding force to the solubility parameter.

If the difference in solubility between the plasticizers and the low-solubility plasticizers is less than 5 (cal / ml) ^{2 even} when dissolved, it is difficult to form an asymmetric structure, and a large spherical structure may be formed as a whole to lower the porosity. When the solubility difference of the plasticizer and the low-solubility plasticizer is more than 15 (cal / ml) ² even if the solid solution is solubilized, the connection structure between the internal spheres of the separator may be broken and the tensile strength may be weakened.

The low-solubility plasticizer satisfying the above-described preferable solubility may be a single or a mixed type such as dioctyl phthalate, dioctyl sebacate, dioctyl adipate, ethylene glycol, diethylene glycol, or polyethylene glycol, Butyl phthalate, dimethyl phthalate, glycerol triacetate or gamma-butylolactone, or the like, alone or in combination.

The mixed plasticizer containing the low solubility plasticizer and the solubilizing plasticizer may include 70 to 300 parts by weight based on 100 parts by weight of PVDF. When the amount of the mixed plasticizer is less than 70 parts by weight, the spherical structure is not formed and the structure of the hollow fiber membrane becomes totally dense and water permeability may be lowered. When the amount exceeds 300 parts by weight, the concentration of PVDF may be lowered, .

It is possible to control the thicknesses of the asymmetric membrane supporting layer and the selective layer according to the mixing ratio of the plasticizer to the low solubility plasticizer and the solubilizing plasticizer. Preferably, the mixing ratio by weight of the low solubility plasticizer and the solubilizing plasticizer is 1: 9 to 7: 3. If the ratio exceeds 9, the membrane structure may be deformed to lower the tensile strength and water permeability. More specifically, when the plasticizer ratio is 9 or more, a large spherical structure is formed to lower porosity and water permeability And if the plasticizer ratio is 3 or less even when solubilized, the connecting structure between the spherical structures may be destroyed and the tensile strength may be lowered.

The melting temperature for preparing the crude liquid of the step (1) is preferably 170 to 300 ° C. When the temperature is lower than 170 ° C, the melting temperature is lower than the melting point of the PVDF polymer. Therefore, the melt can not be uniformly melted and the shape of the hollow fiber membrane may become unstable. If the temperature exceeds 300 ° C, the plasticizer may be vaporized and the water permeability may be lowered.

 In the step (2), the crude solution is extruded through a spinning nozzle to form a hollow fiber.

The crude solution may be manufactured outside the spinning nozzle and flowed into the extruder, or may be formed inside the extruder. The spinning nozzle of the step (2) may be maintained at a temperature of ± 20 ° C above the melting temperature of the step (1). If the temperature of the spinning nozzle deviates from the melting temperature of the step (1) by ± 20 ° C, the degree of crystallization of the polymer may change, Porosity and strength.

If the screw speed is less than 40 rpm, the additive or the like may be vaporized in the extruder. If the extruder is operated at 90 rpm or more, mixing of the polymer and the plasticizer is not smoothly performed, It can be difficult.

Conventionally, in order to manufacture a PVDF asymmetric hollow fiber membrane, a manufacturing process is complicated by separately preparing a support layer and an outer coating layer through a triple tubular spinning nozzle, and the coating layer is peeled off in an external harsh condition or washing process, There was a disadvantage that it changed. Accordingly, the present invention can easily produce a PVDF asymmetric hollow fiber membrane with a double tubular spinning nozzle by mixing a mixed plasticizer containing a plasticizer and a low solubility plasticizer at an appropriate mixing weight ratio.

2 is a sectional view of the double tubular spinning nozzle 5 for discharging the spinning liquid. The spinning stock solution in the step (1) may be discharged to the outer tube 2 of the double tubular spinning nozzle 5 and the inner coagulant may be simultaneously discharged to the inner tube 1 of the double tubular spinning nozzle.

The internal coagulant is used for internal hollow formation and is not particularly limited as long as it is uniformly mixed with PVDF and can be mixed at the time of immersion in an external coagulating liquid. More preferred is dibutyl phthalate, dimethyl phthalate Dimethyl phthalate, diethyl phthalate, dioctyl phthalate, dioctyl sebacate, glycerol triacetate, polyethylene glycol, ethylene glycol, Propylene glycol, diethylene glycol, and the like.

In the step (3), the formed hollow fiber is discharged or immersed in an external coagulating solution to produce a hollow fiber membrane. The external coagulating solution in the step (3) is not particularly limited as long as it can be mixed with a plasticizer and an internal coagulant, and more preferably water, dibutyl phthalate, dimethyl phthalate, diethyl phthalate Diethyl phthalate, dioctyl phthalate, dioctyl sebacate, glycerol triacetate, polyethylene glycol, ethylene glycol, propylene glycol, Diethylene glycol, and the like.

The external coagulation liquid in the step (3) may be -10 to 120 캜. If the cooling rate in the external coagulating solution is low, the spherical size inside the hollow fiber membrane may become large, and if the cooling rate is high, the medium size may become small. If the temperature of the external coagulating solution is less than -10 ° C, the cooling rate is too fast and the water permeability may be reduced due to too small spherical structure. If the temperature exceeds 120 ° C, the cooling rate becomes too slow. The density and the connection sites between the spherical structures are reduced, and the porosity and tensile strength may be lowered.

The hollow fiber membrane produced in the step (3) may further include (4) continuously feeding and stretching the hollow fiber membrane into a stretching machine including a stretching solution. In the above stretching step, the stretching solution may be ethylene glycol, glycerol, polyethylene glycol having a molecular weight of 400 or less, water, or the like, and may be stretched at a stretching ratio of 1.1 to 2.0 times at a stretching temperature of 15 to 150 캜.

When the stretching temperature is less than 15 ° C, partial stretching may occur and the hollow fiber membrane may not be uniformly stretched. When the stretching temperature is more than 150 ° C, film shrinkage and trimming are likely to occur. If the stretching ratio is less than 1.1 times the length of the hollow fiber, the effect of pore control and strength increase due to stretching is insufficient. If the stretching ratio is more than 2.0 times, the film thickness may decrease and the mechanical properties may become weak.

 The PVDF hollow fiber membranes prepared by the above-mentioned method are hollow; And a separation layer formed along the periphery of the hollow, the separation layer being capable of forming a spherical-like structure having a diameter gradient gradually increasing from the outer surface to the inner surface. Also, hollow; A supporting layer formed along the outer periphery of the hollow; And a selective layer formed along the outer periphery of the support layer, wherein the support layer and the selection layer form a spherical structure, and a difference in diameter of the spherical structure at the interface between the support layer and the selective layer is 5 lt; RTI ID = 0.0 > m / m. < / RTI >

 The PVDF asymmetric porous hollow fiber membrane as described above has a tensile strength of 9 MPa or more and can secure the mechanical strength, and it is possible to prevent the problem of cutting over time in the actual process. In addition, the hollow fiber membrane produced by the method of coating a PVDF solution on a conventional support is liable to peel off the PVDF coating layer at a peel strength of about 6 MPa, but the PVDF asymmetric hollow fiber membrane of the present invention does not peel off.

In addition, the PVDF asymmetric hollow fiber membrane has a water permeability of 1000 LMH or more and satisfies a BSA removal rate of 96% or more, thereby exhibiting excellent filtration efficiency.

Hereinafter, the present invention will be described in more detail with reference to the following examples. However, the following examples should not be construed as limiting the scope of the present invention, and should be construed to facilitate understanding of the present invention.

≪ Example 1 >

60 parts by weight of glycerol triacetate (solubility: 20 (cal / ml) ² ), 60 parts by weight of diethylene glycol (solubility: 29.9 (cal / ml) ² ) were added to 100 parts by weight of PVDF (Solef 6013, Solvay) 90 parts by weight were simultaneously introduced into the twin-screw extruder (screw diameter: 30 mm). In the extruder at 220 DEG C, the molten mixture was transferred to a nozzle maintained at 200 DEG C using a gear pump. Then, the mixed solution was discharged using glycerol triacetate as an internal coagulant, and the air gap between the nozzle and the coagulation bath was maintained at 1 cm.

The discharged mixture was cooled through a coagulation bath maintained at 35 ° C to induce phase separation, and then wound in a water bath at 80 ° C at a rate of 20 m / min.

≪ Example 2 >

Diethylene glycol ^{(solubility: 29.9 (cal / ml) 2} ) 90 parts by weight in place of parts of diethylene glycol ^{(solubility: 29.9 (cal / ml) 2} ) 40 parts by weight of dimethyl phthalate ^{(solubility: 10.8 (cal / ml) 2} ) Was prepared in the same manner as in Example 1,

≪ Example 3 >

Glycerol triacetate ^{(solubility: 20 (cal / ml) 2} ) 60 parts by weight of diethylene glycol ^{(solubility: 29.9 (cal / ml) 2} ) 90 parts by weight in place of parts of dimethyl phthalate ^{(solubility: 10.8 (cal / ml) 2} ) , And 90 parts by weight of glycerin (solubility: 33.8 (cal / ml) ² ) were mixed in the same manner as in Example 1.

The thus produced hollow fiber membrane was not formed properly due to a large effect of non-solvent, and the tensile strength was lowered.

<Example 4>

Glycerol triacetate ^{(solubility: 20 (cal / ml) 2} ) 60 parts by weight of diethylene glycol ^{(solubility: 29.9 (cal / ml) 2} ) in place of 90 parts by weight of dibutyl phthalate (solubility: 19 (cal / ml) ² ) And 90 parts by weight of a polyethylene glycol (solubility: 23 (cal / ml) ² ) were mixed in the same manner as in Example 1.

The hollow fiber membrane thus formed formed a symmetrical structure having a large spherical shape larger than a predetermined size without forming an asymmetric structure that the spherical size became smaller toward the outer surface, thereby exhibiting a low water permeability.

&Lt; Example 5 >

Except that 60 parts by weight of dimethyl phthalate (solubility: 10.8 (cal / ml) ² ) was used instead of 60 parts by weight of glycerol triacetate (solubility: 20 (cal / ml) ² ) Respectively.

The hollow fiber membrane thus produced does not have a double structure, and the thickness of the external selective layer becomes thick, and the water permeability becomes low.

&Lt; Example 6 >

Except that 90 weight parts of diethylene glycol (solubility: 29.9 (cal / ml) ² ) was replaced by 90 weight parts of dioctyl phthalate (solubility: 18.5 (cal / ml) ² ) .

The hollow fiber membrane thus produced has no double structure and has low tensile strength due to poor interconnection between crystal structures.

&Lt; Comparative Example 1 &

Except that diethylene glycol (solubility: 29.9 (cal / ml) ² ) was not mixed.

The hollow fiber membrane thus formed formed a spherical symmetrical membrane, and the spherical structure had an average diameter of 8 μm.

&Lt; Comparative Example 2 &

240 parts by weight of N-methyl-2-pyrrolidone (N-methyl-2-pyrrolidone) was mixed with 100 parts by weight of PVDF polymer at 120 DEG C to prepare a crude liquid. And then discharged to the external coagulation bath. The mixed solution thus discharged was cooled through a coagulation bath maintained at 35 ° C., and a hollow fiber was produced by a conventional heat-induced phase separation method. Thereafter, the hollow fiber was wound at a rate of 20 m / min in a water bath of 80 ° C.

The hollow fiber membrane thus formed formed a symmetric membrane of sponge like structure.

&Lt; Comparative Example 3 &

240 parts by weight of dimethylacetamide as a solvent was mixed with 100 parts by weight of PVDF polymer at 120 캜 to prepare a crude liquid. The liquid was transferred to a nozzle through a transfer line maintained at a constant temperature, and then discharged into an external coagulation bath. At this time, when the hollow fiber was discharged through a triple nozzle, the same polymer was coated on the surface of the hollow fiber. The composition of the polymer solution to be coated is 630 parts by weight of dimethylacetamide as a solvent and 39 parts by weight of polyvinylpyrrolidone based on 100 parts by weight of PVDF, and is transported through a coating nozzle. The mixed solution thus discharged was cooled through a coagulation bath maintained at 35 ° C., and a hollow fiber was produced by a conventional heat-induced phase separation method. Thereafter, the hollow fiber was wound at a rate of 20 m / min in a water bath of 80 ° C.

The thus prepared hollow fiber membrane was formed into a double hollow structure in which a coating layer was formed on the outside of the hollow fiber having the support layer.

<Experimental Example>

The pure water permeability, tensile strength, rejection rate and backwash strength of the hollow fiber membranes prepared in Examples 1 to 6 and Comparative Examples 1 to 3 were measured by the following methods, and the results are shown in Table 2.

1. Measurement of pure water permeability

The hollow fiber membrane module thus prepared was supplied with pure water at a room temperature at a pressure of 1.0 atm on one side of the module by a DEAD-END method, and the amount of permeated water was measured

After which the permeation amount per unit time, unit membrane area, and unit pressure was calculated.

2. Measurement of rejection rate

BSA (bovine serum albumin, Aldrich, Mw 66,000) was added to pure water at room temperature

To prepare an aqueous solution having a concentration of 1,000 ppm. The hollow fiber membrane module

And the concentration of BSA dissolved in the permeated aqueous solution and the initially supplied raw water was measured using an ultraviolet spectrophotometer (Cary-100, Verian).

Thereafter, the relative ratio of the absorption peaks measured at a wavelength of 278 nm was calculated using the following equation

The BSA exclusion rate was determined as a percentage.

Excretion rate (%) = ((concentration of raw liquid - permeation concentration) / concentration of raw liquid) × 100

3. Measurement of tensile strength

The tensile strength and tensile elongation of the hollow fiber membranes prepared through the tensile tester were measured. The tensile test was carried out at room temperature at a gripping distance of 10 cm and a crosshead speed of 3 cm / min.

(Initial sample length: 100 mm, crosshead speed: 200 mm / min) at a temperature of 23 DEG C and a relative humidity of 50% using a tensile tester ("RTM-100" manufactured by Toyo Baldwin Co., Ltd.).

4. Measurement of pressure test

The filtration water side of the membrane module is closed while the test water is filled in the manufactured hollow fiber membrane module, and the pressure is applied to the feed water side at least 1.5 times the condition of the membrane module for 1 minute and the state is observed.

division Pure permeability
(L / m ² hr) BSA exclusion rate
(%) The tensile strength
(kgf / mm ² ) Example 1 1000 96 9 Example 2 800 99 9 Example 3 900 93 6 Example 4 700 90 8 Example 5 500 93 9 Example 6 800 91 5 Comparative Example 1 600 90 8 Comparative Example 2 600 95 4 Comparative Example 3 600 96 6

 As can be seen from Table 1, when the mixed plasticizer according to the present invention is included, the mechanical strength and the filtration efficiency are superior to those of Comparative Example 1 containing only a single plasticizer. Compared with Comparative Example 2, which is manufactured according to the conventional method and has a sponge structure, the BSA elimination rate is maintained at a high level while the pure water permeability is increased, and the tensile strength is improved to show excellent mechanical strength. In Comparative Example 3, which was manufactured through a triple tubular spinning nozzle, the manufacturing process was complicated, and it was not only costly but also ineffective in terms of water permeability and pore size after backwashing.

Specifically, in Examples 3 to 6 in which the difference in solubility between the plasticizer and the low-solubility plasticizer was more than 15 (cal / ml) ² or less than 5 (cal / ml) ^{2 even} when dissolved, water permeability And the tensile strength was lowered. As a result, Example 2 using the three-kind mixed plasticizer showed the best in terms of filtration efficiency.

Claims (15)

(1) preparing a crude liquid by melt-mixing a mixed plasticizer and polyvinylidene fluoride (PVDF) containing a plasticizer and a low-solubility plasticizer at a temperature of 170 to 300 ° C even if they are employed;
(2) extruding the crude solution through a spinning nozzle to form a hollow fiber; And
(3) dipping the formed hollow fiber in an external coagulating liquid.
The method of claim 1,
Said mixed plasticizer is a solubility difference of a solubility plasticizer and a low solubility plasticizer 5 (cal / ml) ² or more, The manufacturing method of the PVDF hollow fiber membrane.
The method of claim 1,
The mixed plasticizer is a plasticizer and a low solubility difference between the solubility of the plasticizer may be employed 5 (cal / ml) ² to 15 The method of PVDF hollow fiber membranes, characterized in that (cal / ml) ^2.
The method of claim 1,
Wherein the low solubility plasticizer is at least one selected from the group consisting of dioctyl phthalate, dioctyl sebacate, dioctyl adipate, ethylene glycol, diethylene glycol, and polyethylene glycol.
The method of claim 1,
Wherein the plasticizer is at least one selected from the group consisting of dibutyl phthalate, dimethyl phthalate, glycerol triacetate and gamma-butylolactone.
The method of claim 1,
Wherein the mixed plasticizer comprising the low solubility plasticizer and the solubilizing plasticizer comprises 70 to 300 parts by weight based on 100 parts by weight of PVDF.
The method of claim 1,
Wherein the mixing ratio by weight of the low solubility plasticizer and the solubilizing plasticizer is 1: 9 to 7: 3.
The method of claim 1,
Wherein the spinning nozzle of the step (2) is kept at a temperature of 占 0 占 폚 than the melting temperature of the step (1).
The method of claim 1,
Extrusion of the step (2) is PVDF hollow fiber membrane manufacturing method characterized in that at a speed of 40 to 90 rpm.
The method of claim 1,
The spinning nozzle in the step (2) is a double tubular spinning nozzle,
The crude liquid of step (1) is discharged to the outer tube of the double tubular spinning nozzle, and the internal coagulant is discharged to the inner tube of the double tubular spinning nozzle at the same time.
11. The method of claim 10,
The internal coagulant may be selected from the group consisting of dibutyl phthalate, dimethyl phthalate, diethyl phthalate, dioctyl phthalate, dioctyl sebacate, glycerol triacetate, Wherein the PVDF hollow fiber membrane is one or more selected from the group consisting of polyethylene glycol, ethylene glycol, propylene glycol, and diethylene glycol.
The method of claim 1,
The external coagulating solution in step (3) may be selected from the group consisting of water, dibutyl phthalate, dimethyl phthalate, diethyl phthalate, dioctyl phthalate, dioctyl sebacate , Glycerol triacetate, polyethylene glycol, ethylene glycol, propylene glycol, and diethylene glycol. In the present invention, it is preferable that the water-soluble polymer is at least one selected from the group consisting of glycerol monostearate, glycerol triacetate, polyethylene glycol, ethylene glycol, A method for producing a PVDF hollow fiber membrane.
The method of claim 1,
Wherein the external coagulation liquid in step (3) is -10 to 120 ° C.
The method of claim 1,
And (4) stretching the prepared hollow fiber membrane.
15. The method of claim 14,
Wherein the step (4) is conducted at a draw ratio of 1.1 to 2.0 at a draw temperature of 15 to 150 캜.

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