KR101198646B1 - Manufacturing method of asymmetric porous membrane and asymmetric porous membrane thereby - Google Patents

Abstract

The present invention relates to a method for preparing a porous asymmetric membrane that can be controlled in various pore sizes, and to a porous asymmetric membrane prepared therefrom.
In the method of preparing a porous asymmetric membrane of the present invention, the hydrophilicity of the membrane is improved by using a sulfonated polysulfone polymer-containing polymer solution and exposed to air containing water vapor on the surface cast with the polymer solution using a casting process. It is possible to provide a porous asymmetric membrane with an increased average pore size and controllable to various pore sizes. This reduces the time and cost of adjusting the desired asymmetrical structural design, high permeability, and various pore sizes.

Description

MANUFACTURING METHOD OF ASYMMETRIC POROUS MEMBRANE AND ASYMMETRIC POROUS MEMBRANE THEREBY}

The present invention relates to a method for preparing an asymmetric porous membrane and to an asymmetric porous membrane prepared therefrom, and more particularly, to improve hydrophilicity of a membrane using a sulfonated polysulfone polymer-containing polymer solution, and to use the casting process for the polymer. The present invention relates to a method for preparing an asymmetric porous membrane which can be exposed to air-optimized conditions containing water vapor on a surface cast from a solution, thereby increasing the average pore size and controlling to various pore sizes, and an asymmetric porous membrane prepared therefrom.

Polymer membranes have been applied to a variety of applications, including medicine, food, semiconductor, water treatment. In particular, since the polyether sulfone resin has high thermal, oxidative stability, temperature stability, and hydrophilic polymer, it is very widely used because it is advantageous for water treatment. In general, membranes can be divided into symmetrical and asymmetrical membranes in cross-sectional structure. The symmetric membrane has a problem that membrane surface contamination is easily induced by particles in raw water, so that the permeate flow rate is reduced and the service life is reduced.

On the other hand, a membrane with an asymmetric structure is a membrane composed of a very dense selective layer (0.1 to 10 μm) and a porous layer (100 to 200 μm) located outside of the above layer at a certain position in the membrane cross-section to remove particles of a certain size or more. Many research and development has been made because it can be made of a selective layer having a high selectivity and a porous layer for maintaining the mechanical strength can be achieved excellent flow rate.

For example, Patent Document 1 discloses a method for producing a membrane having an asymmetric structure in which the pore size of the front and rear surfaces of the membrane differs at a ratio of 50: 1. According to the above method, a polyethersulfone and a solvent are mixed, and then a non-solvent is added to uniformly prepare a polymer solution, and the solution is cast on a support under conditions exposed to air to precipitate in a coagulation bath to prepare a membrane having an asymmetric structure. It was.

In addition, Patent Document 2 is a fine prepared by exposing a certain range of humidity within a certain time after casting by casting a mixture of sulfone-based polymers such as polyether sulfone, polysulfone, polyaryl sulfone and hydrophilic polymers such as polyvinylpyrrolidone A membrane of asymmetric structure with porosity is disclosed. In other words, when the cast film is exposed to air at a relative humidity of 50 to 80% for 2 to 20 seconds and then solidified in a coagulating solution having a temperature range of 20 to 70 ° C, the average pore size is 0.1 to 10 μm. It states that it can be obtained.

The method for producing the membrane described in Patent Document 3 is based on a dry-wet method, and after mixing with a polysulfone polymer and N-methyl-2-pyrrolidone, polyvinylpyrrolidone which is a hydrophilic polymer and water as a nonsolvent Add and mix uniformly. The cast film is exposed to air for 2-30 seconds step by step under conditions of a temperature of 40 ° C. and a relative humidity of 60%. After coagulation at 20 ° C., it is described that a membrane having a fine asymmetric porous structure can be obtained by drying.

The membrane prepared from the prior art has introduced hydrophilicity into a hydrophobic polysulfone-based membrane, and can provide a polysulfone-based fouling-resistant membrane that maintains the hydrophilicity of the membrane and has a low flow rate reduction rate due to a pollutant. However, the polysulfone porous membrane manufacturing method is difficult to form the membrane pores by exposure to the vapor of the volatile organic solvent during the manufacturing process has the effect of low economic efficiency.

Therefore, the present inventors have tried to solve the problems of the prior art, by improving the steam instead of the vapor of the volatile organic solvent in the membrane manufacturing process, it brings the effect of reducing the difficulty of the process and increase the economic efficiency. In addition, the membrane permeability and the use cycle of the membrane by showing a level equivalent to that of the conventional, by completing the present invention was completed.

Patent Document 1: US Patent No. 5,886,059 Patent Document 2: US Patent No. 5,906,742 Patent Document 3: United States Patent No. 4,933,081

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for preparing an asymmetric porous membrane, by using a polymer solution containing sulfonated polysulfone polymer, which has improved hydrophilicity and can be controlled in various pore sizes.

Another object of the present invention is to provide an asymmetric porous membrane prepared from the above production method.

Method for producing an asymmetric porous membrane of the present invention for achieving the above object comprises the steps of (1) casting a sulfonated polysulfone polymer containing polymer solution on a support; (2) exposing the surface on which the polymer solution is cast to air containing steam to control the size of the pores on the surface and the back of the membrane; And (3) dipping and solidifying the membrane of the pore size controlled membrane in a coagulation bath.

The polymer solution preferably comprises a hydrophobic polymer resin and a sulfonated polysulfone polymer, a pore regulator and a solvent.

The sulfonated polysulfone polymer is preferably contained 1 to 20% by weight based on the total polymer solution.

It is preferable that the support is a metal material that maintains a temperature of -5 to 12 ° C.

It is preferable that the polymer solution is maintained at a temperature of 25 ~ 50 ℃.

The air containing the steam is preferably air of relative humidity 40 ~ 100%, temperature 23 ~ 70 ℃.

Air containing the steam is preferably supplied at a flow rate of 0.01 ~ 1.0m / sec.

Preferably, the cast surface is exposed to air containing water vapor for 5 to 60 seconds.

Porous membrane containing the sulfonated polysulfone polymer polymer prepared by the present invention is a micropore of 0.01 ~ 5㎛ maximum pore on the surface, 0.1 ~ 10㎛ maximum pore on the back.

The present invention improves the hydrophilicity of the membrane by using a sulfonated polysulfone polymer solution, and by using a casting process exposed to the optimum conditions of air temperature and exposure time containing water vapor on the surface cast with the polymer solution It can provide a method for producing asymmetric porous membrane that can be controlled in various pore sizes.

In addition, the present invention can provide an asymmetric porous membrane having improved hydrophilicity of the membrane by using a sulfonated polysulfone polymer-containing polymer solution. Thus, the asymmetric porous membrane of the present invention can increase the fouling resistance to increase the permeability and service life of the membrane, it is possible to reduce the economic cost.

1A and 1B are surface scanning electron microscope (SEM) photographs measured at 5,000 magnifications on the front and back surfaces of the asymmetric membrane prepared in Example 1 of the present invention, respectively.
2A and 2B are surface scanning electron micrographs measured at 5,000 magnifications on the front and back surfaces of the asymmetric membrane prepared in Example 2 of the present invention, respectively.
3A and 3B are surface scanning electron micrographs measured at 5,000 magnifications on the front and back surfaces of the asymmetric membrane prepared in Example 3 of the present invention, respectively.
4A and 4B are surface scanning electron micrographs measured at 5,000 magnifications on the front and back surfaces of the asymmetric membrane prepared in Comparative Example 1 of the present invention, respectively.

The method for producing an asymmetric porous membrane of the present invention comprises the steps of: (1) casting a sulfonated polysulfone polymer-containing polymer solution onto a support; (2) exposing the surface on which the polymer solution is cast to a temperature of 20 to 70 ° C. of air containing steam to control the size of pores on the surface and the back of the membrane; And (3) immersing the membrane in which the pore size is controlled in a coagulation bath to solidify and peeling from the support.

Hereinafter, the present invention will be described in more detail in each step.

The first step in the method for producing an asymmetric porous membrane of the present invention is to cast a sulfonated polysulfone polymer-containing polymer solution on a support.

At this time, the polymer solution is a polymer solution comprises a hydrophobic polymer resin and sulfonated polysulfone polymer, a pore control additive (hereinafter pore control agent) and a solvent.

The hydrophobic polymer resin may be a polymer resin such as polyether sulfone, polysulfone, polyvinylidene fluoride, polyacrylonitrile, and the like. In order to consider mechanical strength, the weight average molecular weight is in the range of 500,000 to 700,000. Is used.

The polymer solution of the present invention contains the sulfonated polysulfone polymer in the hydrophobic polymer resin described above, thereby implementing the hydrophilicity improvement of the membrane. The sulfonated polysulfone polymer refers to a compound represented by the following Chemical Formula 1:

[Formula 1]

In the above formula, m / (n + m) is 0.2 to 0.7 and x is 50 to 1000.

In this case, the sulfonated polysulfone polymer preferably contains 1 to 20% by weight based on the total polymer solution, and when the sulfonated polysulfone polymer is less than 1% by weight, the expected hydrophilicity improvement of the membrane is insufficient, and 20% by weight. If it is exceeded, since the viscosity of a polymer solution becomes low and film formation is difficult, it is not preferable.

The pore control agent used in the polymer solution of the present invention is not particularly limited as long as it is a hydrophilic substance having affinity for water in the humidified air, and more preferably glycols such as ethylene glycol and glycerol; Alcohols such as ethanol and methanol; Ketones such as acetone; Polyvinylpyrrolidone, a polyethylene glycol polymer or the like, or a mixture of two or more thereof can also be used. The preferred content of the pore control agent is 1 to 5% by weight based on the total polymer solution.

The solvent used in the polymer solution of the present invention is any one selected from the group consisting of N-methyl-2-pyrrolidone (NMP), dimethylformamide (DMF), dimethyl sulfoxide (DMSO) and dimethylacetamide (DMAc) One or two or more kinds may be used, and it corresponds to 55 to 95% by weight based on the total polymer solution.

The polymer solution of the present invention is composed of hydrophobic polymer resin, sulfonated polysulfone polymer and pore regulator mixture 5 to 50% by weight and solvent 50 to 95% by weight relative to the total polymer solution, preferably hydrophobic polymer resin, sulfonated Polysulfone polymer and pore modifier mixture of 8 to 45% by weight and solvent of 55 to 92% by weight. If the ratio of the hydrophobic polymer resin, sulfonated polysulfone polymer and pore control agent mixture exceeds 45% by weight, a symmetrical structure is formed, which is not suitable for the purpose of the present invention. A structure is formed that is detrimental to the mechanical performance of the membrane.

In the first step of the present invention, the polymer solution of the composition described above is coated on the paper body, and there is no particular limitation on the constant coating method, gravure coat, bar coat. An appropriate one may be selected and used among coating methods commonly used in the art, such as spray coat, spin coat, knife coat, and roll coat.

At this time, the support may be used stainless steel, aluminum, copper alloy, and the like, in the embodiment of the present invention has been described using a stainless steel support, limited to a material that can induce a temperature difference between the support and the polymer solution. Not.

The temperature of the support is preferably maintained at -5 ~ 12 ° C so that the pores are formed large instantaneously by the temperature difference with the polymer solution cast on the support. At this time, if the temperature of the support is less than -5 ° C, the temperature difference with the polymer solution to be in contact is too large, which makes it difficult to uniformly apply the membrane formation, and if it exceeds 12 ° C, the temperature difference with the polymer solution becomes small and heat It is disadvantageous to control the structure of the pores by the induction phase transition method.

The temperature of the polymer solution in contact with the support is maintained higher than the support temperature, preferably controlling the maximum pore of the membrane by exposure to room temperature (23 ℃) ~ 70 ℃ conditions.

In this step, the cast surface is exposed to air containing water vapor, thereby rapidly forming pores in relatively mild conditions, i.e. at low temperatures. More specifically, the porous membrane of the present invention is exposed to air containing water vapor for a predetermined time simultaneously or immediately after casting the formed polymer solution, so that the components of the cast polymer solution are dissolved and extracted in water in the air. Induces the formation of microporous pores, and can easily control the size of the pores by adjusting the air temperature within a certain range.

At this time, the water vapor content of the air containing the steam is preferably 40 to 100% relative humidity. If the humidity of the air does not reach 40% there is a problem that does not form the pores of the surface properly.

On the other hand, the air containing steam is preferably supplied at a flow rate of 0.01 ~ 1.0m / sec. When supplied at less than 0.0.01 m / sec, there is a problem that pore formation is difficult to be implemented, and when it exceeds 1.0 m / sec, the appearance of the membrane is poor, which is not preferable as a membrane.

By controlling the air temperature containing water vapor in a predetermined range in the above step to 20 ℃ to 70 ℃, it is possible to adjust the pore size of the membrane, if the air temperature is less than 20 ℃ it is difficult to achieve pore formation by the material transfer rate When the air temperature exceeds 70 ° C., the surface shrinkage of the membrane is severe and the appearance of the membrane is poor, which makes it difficult to apply the membrane.

On the other hand, the time for exposing the cast polymer solution to air containing steam is preferably 2 to 60 seconds. If the exposure time is less than 2 seconds, the solvent in the polymer solution is weakly diffused into the air, making it difficult to express an asymmetric structure. If it exceeds 60 seconds, the solvent in the polymer solution is excessively diffused into the air, which causes problems in asymmetric structure expression and productivity.

The third step in the method for producing a highly asymmetric porous membrane of the present invention is a step of immersing and solidifying the membrane in which the pore size is controlled in a coagulation bath to be separated from the support.

In this step, the membrane formed on the support is immersed in the coagulation bath by the above-described method to perform coagulation through sufficient phase separation, and the membrane is peeled from the support to obtain a porous membrane having improved hydrophilicity of the present invention. As the solid solution, water is preferably used.

On the other hand, the washing process to remove the remaining solvent in and outside the prepared membrane membrane may be further performed, water is preferably used as the washing liquid is not particularly limited, washing time is preferably 12 hours or more to 1 day or less. Membrane of the present invention prepared as described above may be further carried out a process of drying in air after immersion in ethanol or methanol, wherein the immersion and drying time is not particularly limited, but is preferably 1 hour or less.

Porous asymmetric membrane prepared by the above method is the maximum pore size of the surface, that is, the surface formed in contact with water vapor is 0.01 ~ 5.0㎛, that is, the maximum pore size of the surface formed in contact with the support is adjusted to 0.1 ~ 10.0㎛ Can be.

Hereinafter, the present invention will be described in detail with reference to examples. The following examples are merely illustrative of the present invention, but the scope of the present invention is not limited to the following examples.

≪ Example 1 >

5% by weight sulfonated polysulfone polymer, 15% by weight polyethersulfone resin, 55% by weight N-methyl-2-pyrrolidone (NMP), 15% by weight polyethylene glycol (molecular weight 1000) and polyvinylpyrrolidone (PVP) A polymer solution composed of 10% by weight was prepared and bubbles were removed while maintaining at 35 ° C. The polymer solution was coated at a rate of 2 m / min so as to have a uniform thickness on the stainless steel support maintained at 0 ° C. At this time, the cast polymer solution was exposed to 25 ° C. and 100% water vapor at a flow rate of 0.1 m / sec for 20 seconds to induce phase separation on the support, and then solidified by passing through a water coagulation bath maintained at room temperature. Thereafter, after a certain period of time, the membrane was peeled off from the support, and the residual solvent component contained in the membrane was extracted in a washing tank, and the membrane was prepared by drying in an air at room temperature.

<Example 2>

A membrane was prepared in the same manner as in Example 1, except that the cast polymer solution was exposed to 30 ° C. and 100% water vapor.

<Example 3>

A membrane was prepared in the same manner as in Example 1, except that the cast polymer solution was exposed to an air temperature of 35 ° C. and 100% water vapor.

&Lt; Comparative Example 1 &

The membrane was prepared in the same manner as in Example 1, except that the polymer solution was exposed to 25 ° C. acetone vapor instead of water vapor.

 <Experimental Example>

For the membranes prepared in Examples 1 to 3 and Comparative Example 1, the physical property was measured by using a porosity evaluator, and the permeation amount was mounted at a sample holder having a diameter of 90 mm to 60 at a constant pressure (1 bar). The amount transmitted per second was measured. The above experimental results are summarized in Table 1 below.

Exposure time
(sec) Atmospheric air temperature
(℃) thickness
(Μm) Maximum pore
(Μm) Permeability
(Ml / min · cm · bar) Remarks surface If Example 1 20 25 140-150 0.45-0.55 1.0-1.15 80.0 5% by weight of sulfonated polysulfone polymer Example 2 20 30 140-150 1.0-1.15 5.0 ~ 5.25 90.0 Example 3 20 35 140-150 4.5 ~ 5.0 9.5-10.0 100.0 Comparative Example 1 20 25 130-135 0.45-0.55 0.55-0.60 40.0 Exposed to water vapor
Stage exclusion (acetone steam)

As shown in Table 1, in the case of the membrane prepared in Examples 1 to 3, when the cast polymer solution was fixed and exposed at the same time condition, as the air temperature of the atmosphere including water vapor increased, the permeability and the maximum of the surface and the back surface were increased. The pore size increased.

On the other hand, it can be seen that the membrane of Comparative Example 1 prepared in the same manner except for exposing the water vapor during the membrane manufacturing process of Example 1 has a small maximum pore difference between the surface and the back.

Thus, the physical properties of the membrane prepared in Examples 1 to 3 compared to the membrane of Comparative Example 1 by controlling the air temperature of the atmosphere including the resulting water vapor, it was confirmed that the maximum pore increase and permeability increase on the front and back surfaces. From these results, it is possible to control the phase separation rate of the membrane according to the difference between the atmospheric air temperature of the steam and the temperature of the support, and to prepare an asymmetric porous membrane having various sizes of the surface and the back surface.

Figure 1a. 2A, 3A and 4A are surface scanning electron microscope (SEM) photographs measured at 5,000 magnifications on the surfaces of the asymmetric membranes prepared in Examples 1, 2, 3 and Comparative Examples, that is, the surfaces formed in contact with water vapor. admit. Figure 1a. 2A, 3A, and 4A, the surfaces of the asymmetric membranes prepared in Examples 1, 2, 3, and Comparative Examples, respectively, can adjust the maximum pore size by controlling the air temperature of the atmosphere in Examples 1 to 3. It could be confirmed.

1B, 2B, 3B, and 4B are surface scanning electron microscopes measured at 5,000 magnifications on the back surface of the asymmetric membranes prepared in Examples 1, 2, 3, and Comparative Examples, that is, the surfaces formed in contact with the support. (SEM) Photos. In Figures 1B, 2B, 3B and 4B, the back surfaces of the asymmetric membranes prepared in Examples 1, 2, 3 and Comparative Examples, respectively, are shown in Examples 1 to 3 by controlling the temperature of the support and thus the atmospheric air temperature of the surface layer. It can be seen that by the asymmetric porous membrane that the maximum pore size is more than doubled.

Although the present invention has been described in detail only with respect to the embodiments described, it will be apparent to those skilled in the art that various modifications and variations are possible within the technical scope of the present invention, and such modifications and modifications belong to the appended claims.

As described above, the present invention improves the hydrophilicity of the membrane by using a sulfonated polysulfone polymer-containing polymer solution, and exposure to the air-optimized condition containing water vapor on the surface cast with the polymer solution using a casting process. By increasing the average pore size and providing a method for producing an asymmetric porous membrane that can be controlled to various pore sizes.

Thus, the production method of the present invention can reduce the time and cost consumed to adjust the desired asymmetrical structure design, high permeability, various pore sizes by devising the optimum conditions for adjusting the average pore size of the membrane.

In addition, the asymmetric porous membrane having improved hydrophilicity of the membrane by using the sulfonated polysulfone polymer-containing polymer solution of the present invention can increase fouling resistance and increase the permeability and service life of the membrane.

Claims (11)

(1) casting a polymer solution containing sulfonated polysulfone polymer but maintaining a temperature of 25 to 50 ° C. on a support of a metal material maintaining a temperature of −5 to 12 ° C .;
(2) exposing the surface on which the polymer solution is cast to air containing steam to control the size of the pores on the surface and the back of the membrane; And
(3) immersing the membrane having a controlled pore size in a coagulation bath to solidify and peeling it from the support. The method of claim 1, wherein the polymer solution comprises a hydrophobic polymer resin and a sulfonated polysulfone polymer, a pore modifier, and a solvent. The method of claim 1, wherein the sulfonated polysulfone polymer of step (1) is contained in an amount of 1 to 20% by weight based on the total polymer solution. delete delete The method of claim 1, wherein the air containing the steam of step (2) is air of a relative humidity of 40 to 100%, a temperature of 23 to 70 ℃. The method of claim 1, wherein the air containing the steam of step 2) is supplied at a flow rate of 0.01 ~ 1.0m / sec. The method of claim 1, wherein the cast surface of step 2) is exposed to air containing water for 5 to 60 seconds. The method of claim 1, wherein the surface average pore size of the cast membrane controlled from the process of the step (2) is 0.01 ~ 5㎛, the back surface average pore size 0.1 ~ 10㎛. A porous membrane containing a sulfonated polysulfone polymer polymer, wherein the asymmetric porous membrane is characterized in that micropores having an average pore size of 0.01 to 5 μm on the surface and an average pore size of 0.1 to 10 μm on the back surface are formed. The asymmetric porous membrane according to claim 10, wherein micropores having an average pore size of 0.4 to 5 mu m on the surface and an average pore size of 1 to 10 mu m on the back surface are formed.

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