KR101002597B1 - Method of producing porous membrane - Google Patents

Abstract

The present invention provides a method for producing an asymmetric porous membrane comprising a portion consisting of micropores and a portion consisting of large pores, the method comprising: (1) forming a liquid film on a support; (2) preparing a polymer solution comprising a polymer and a pore regulator; (3) casting the polymer solution onto the liquid film; And (4) exposing the polymer solution cast on the liquid film of the support to an atmosphere comprising a solvent; It is made, including.

According to the method of manufacturing the porous membrane of the present invention, it is not necessary to control each factor such as humidity, temperature, and exposure time individually, thereby increasing manufacturing efficiency and greatly reducing manufacturing cost.

Porous membrane

Description

Method for Manufacturing Porous Membrane

The present invention relates to a method for producing a porous membrane, specifically a method for producing a high flow porous membrane using a casting process.

Polymer membranes are used in various fields such as medicine, food, semiconductor, or water treatment.

In particular, the polymer membrane made of a polyether sulfone resin has not only high thermal, oxidative stability and temperature stability, but also hydrophilic property, which is advantageous for water treatment, and is widely used.

In general, membranes can be classified as either symmetrical or asymmetrical membranes depending on the cross-sectional structure.

However, in such a symmetric membrane, membrane surface contamination may easily occur due to particles in raw water used, so that the permeate flow rate decreases as the service period elapses, resulting in a short service life.

 Asymmetric membranes, on the other hand, consist of asymmetry such that the membrane cross section consists of a selective layer (0.1-10 µm) with a very large pore size and a porous layer (100-200 µm) with a large pore size. That is, the asymmetric membrane can remove particles of a predetermined size or more, and can be made of a selective layer having a high selectivity and a porous layer for maintaining the mechanical strength required for the membrane, thereby achieving an excellent selective transmission flow rate. As a result, a lot of research and development has been made on such asymmetric membranes.

For example, U. S. Patent No. 5,886, 059 discloses a method of making a membrane of asymmetric structure with a pore size difference of 50: 1 on the surface and back of the membrane. Here, a polyethersulfone resin and a solvent are mixed, and then a non-solvent is added to uniformly prepare a polymer solution, and then a polymer having an asymmetric structure is formed by casting it on a support under conditions that expose the prepared polymer solution to air. To manufacture.

In addition, U.S. Patent No. 5,906,742 discloses a mixture of sulfone-based polymers such as polyethersulfone, polysulfone, and polyarylsulfone and a hydrophilic polymer such as polyvinylpyrrolidone to be exposed to a certain range of humidity within a predetermined time period. It is disclosed that a membrane having an asymmetric structure having fine porosity is prepared.

In addition, the method of preparing the membrane described in US Pat. No. 4,933,081 is based on a dry-wet method, and after mixing polysulfone polymer with N-methyl-2-pyrrolidone and polyvinylpyrrolidone as a hydrophilic polymer, Water is added as a medium and mixed uniformly. The cast film is exposed to air for 2-30 seconds step by step under a temperature of 40 ° C. and a relative humidity of 60%. After coagulation at a temperature of 20 ° C., a method of obtaining a membrane of microporous asymmetric structure through drying is disclosed.

In addition, US Patent No. 6,565,782 is almost similar to the method described in the above-mentioned US Patent No. 5,906,742, the pore size is 5 ~ 1000 times the difference between the surface and the back surface, the average pore of 0.1 ~ 10㎛ Eggplant discloses a method for producing a membrane.

However, such a conventional technology has a problem in that a lot of time and cost are required to control the asymmetric structure because the control factors are complicated such as requiring a constant humidity, a constant temperature and a constant exposure time.

In order to solve the above problems of the prior art, the present invention is to provide a new method for producing a porous membrane having an asymmetric structure and high flow characteristics without having to individually control factors such as humidity, temperature, and exposure time. do.

 The present invention for solving the above problems is a method for producing an asymmetric porous membrane comprising a portion made of micropores and a portion of the cross-sectional structure, to prepare an asymmetric porous membrane according to one feature of the present invention The method includes the steps of (1) forming a liquid film on a support; (2) preparing a polymer solution comprising a polymer and a pore regulator; (3) casting the polymer solution onto the liquid film; And (4) exposing the polymer solution cast on the liquid film of the support to an atmosphere containing a solvent.

The step (4) of the porous membrane production method of the present invention is preferably performed immediately after the step (3) or at the same time as the step (3).

In addition, the step (1) may be performed by adjusting the temperature around the support to less than 10 ℃ to form a moisture film on the support.

In the step (4), the polymer in the polymer solution is dissolved and extracted in a solvent in the air, and the pore regulator is dissolved in water in the air and extracted.

In the porous membrane manufacturing method, the polymer is to form the large pores, the pore control agent is to form the fine pores.

In the porous membrane production method, the polymer is preferably used in combination of one or two selected from the group consisting of polyethersulfone, polysulfone, polyvinylidene fluoride, or polyacrylonitrile.

In addition, the pore control agent is preferably used in combination of one or two selected from the group consisting of ethylene glycol, glycerol, ethanol, methanol, acetone, polyvinylpyrrolidone, or polyethylene glycol.

In addition, the polymer solution may include 5 to 30% by weight of the polymer / pore regulator mixture with respect to the polymer solution.

And, the ratio of the polymer / pore regulator is preferably 0.5 to 3 or less.

And, in the porous membrane manufacturing method, it is preferable to cast by maintaining the temperature of the polymer solution at 25 ℃ to 70 ℃.

At this time, it is preferable to maintain the temperature of the polymer solution 20 ℃ to 35 ℃ higher than the temperature of the support.

In this case, the solvent is included in a saturated concentration in the atmosphere, the solvent is preferably selected from the group consisting of acetone, methanol, isopropyl alcohol, or tetrahydrofuran.

And, in the porous membrane production method, the exposure time of the step (4) is preferably 10 seconds to 60 seconds.

In the present invention, a membrane having excellent asymmetric structure and high flow characteristics can be produced by simply casting a polymer solution on a support on which a liquid film is formed in advance and exposing it to an atmosphere containing a solvent component for a predetermined time at the same time or immediately thereafter.

Accordingly, according to the method of manufacturing the porous membrane of the present invention, it is not necessary to control each factor such as humidity, temperature, and exposure time individually, thereby increasing manufacturing efficiency and greatly reducing manufacturing cost.

In addition, the porous membrane manufacturing method of the present invention can easily control the porosity and pore size of the membrane to be produced, it is possible to manufacture a membrane excellent in terms of service life and strength.

The porous membrane of the present invention forms a liquid film on a support, and simultaneously or immediately after casting the polymer solution on the formed liquid film, by exposure to an atmosphere containing a constant concentration of solvent for a certain time, the components of the cast polymer solution Soluble extraction in heavy solvents and moisture to induce the formation of a large number of pores, including micropores and large pores, thereby allowing the membrane to be produced in an asymmetric structure. At this time, the liquid film is formed on the support to a thickness of several microns. In the present invention, the fine pores mean pores formed with a diameter of 0.01 to 1.0 μm, and the large pores mean pores formed with a diameter of several micrometers.

Specifically, micropores are formed in the surface layer of the cast polymer solution exposed to the atmosphere containing a certain concentration of solvent, and air pores are formed at the interface between the polymer solution and the support to form an asymmetric structure. Then, the membrane formed on the support is immersed in the coagulation bath to peel the membrane from the support to obtain the porous membrane of the present invention.

Thereafter, after the exfoliated membrane is immersed in a washing tank, further extraction of the residual solvent component contained in the membrane matrix may be further performed to fix the pore formation.

In such a porous membrane of the asymmetric structure of the present invention, the polymer solution to be cast comprises a polymer, a solvent and an additive for pore control (hereinafter pore control agent).

As a suitable polymer in the present invention, polyether sulfone, polysulfone, polyvinylidene fluoride, polyacrylonitrile, and the like are used, and in consideration of mechanical strength, the weight average molecular weight of the polymer is preferably in the range of 500,000 to 700,000. Used.

The pore control agent is not particularly limited as long as it is a hydrophilic substance that has affinity with moisture in humidified air and can be extracted by being dissolved in moisture in humidified air, preferably glycols such as ethylene glycol or glycerol; Alcohols such as ethanol or methanol; Ketones such as acetone; And polyvinylpyrrolidone, a polymer of polyethylene glycol, or the like is used alone or in combination of two or more thereof.

As the solvent, N-methyl-2-pyrrolidone (NMP), dimethylformamide (DMF), dimethyl sulfoxide (DMSO), or dimethylacetamide (DMAc) may be used alone or in combination of two or more thereof. .

 The polymer solution of the present invention is composed of 5 to 30% by weight of the polymer / pore regulator mixture, and 70 to 95% by weight of the solvent, preferably 8 to 25% by weight of the polymer / pore regulator mixture, And 75 to 92% by weight of solvent.

Here, the content ratio of the weight% of the polymer to the weight% of the pore regulator in the polymer / pore regulator mixture is preferably 0.5 to 3 or less. Specifically, when the polymer / pore modifier content ratio is less than 0.5, the pores formed are not controlled so that the membrane structure is formed symmetrically, and thus, the object of the present invention cannot be achieved for a membrane having an asymmetric structure.

On the other hand, if the polymer / pore regulator content ratio exceeds 3, the pores become excessively large, resulting in low heat performance of the membrane membrane.

 On the other hand, the liquid film of the support is formed by lowering the ambient temperature of the support to condense moisture in the air, wherein the support temperature is maintained below 10 ℃.

And, when casting the polymer solution on the support, the temperature of the polymer solution is preferably maintained about 20 ℃ to about 35 ℃ higher than the temperature of the support.

Therefore, the temperature of the polymer solution is preferably maintained at 25 ℃ to 70 ℃. Specifically, when the temperature of the polymer solution is less than 25 ℃ the permeate flow rate is reduced excessively due to the increase in viscosity, if the temperature of the polymer solution exceeds 70 ℃ viscosity becomes too low and casting is difficult.

 The polymer solution thus prepared is cast on a support having a liquid film pre-formed with a few microns of moisture, and then exposed to an atmosphere containing a solvent component in a saturated concentration in the cast polymer solution for a predetermined time. As such, when the cast polymer solution is exposed to an atmosphere containing a solvent component at a saturation concentration for a predetermined time, the polymer and the pore regulator component of the polymer solution are dissolved in the solvent component and water contained at a saturation concentration in the atmosphere and cast. Large pores and fine pores are generated in the polymer solution, respectively.

In the present invention, a metal material is preferably used as the support, and stainless steel, aluminum, copper alloy, and the like are more preferably used.

On the other hand, the solvent contained in the atmosphere used for the casting of the polymer solution may be used without limitation as long as it is volatile at room temperature and compatible with the coagulating solution, but acetone, methanol, isopropyl alcohol, tetrahydrofuran, etc. are preferably used. .

The exposure time to the atmosphere including the solvent component of the cast polymer solution is preferably 10 seconds to 60 seconds.

If the exposure time of the cast polymer solution is less than 10 seconds, the diffusion of the polymer in the polymer solution into the solvent in the air is weak and difficult to express an asymmetric structure. If the exposure time exceeds 60 seconds, the diffusion of the polymer in the polymer solution into the solvent in the air is difficult. This is a problem for asymmetric expression and productivity.

 As such, the polymer solution exposed to the atmosphere including the solvent component is precipitated in a coagulation solution at a predetermined temperature to perform coagulation through sufficient phase separation. In the present invention, water is preferably used as the coagulating solution.

On the other hand, a washing process for removing the remaining solvent in and outside the prepared membrane may be carried out.

Water is preferably used as such a washing liquid, and the washing time is not particularly limited, but is preferably 12 hours or more to 1 day or less.

Thus prepared porous membrane of the present invention may be further carried out a process of drying in air after immersion in ethanol or methanol, wherein the immersion and drying period is not particularly limited, but is preferably less than 1 hour.

Hereinafter, the present invention will be described in detail with reference to a preferred embodiment so that those skilled in the art can easily practice the present invention. As those skilled in the art would realize, the described embodiments may be modified in various different ways, all without departing from the spirit or scope of the present invention.

Example 1

A polymer solution comprising 15% by weight of polyethersulfone resin, 55% by weight of N-methyl-2-pyrrolidone (NMP), 15% by weight of polyethylene glycol (molecular weight 1000) and 15% by weight of polyvinylpyrrolidone (PVP) Bubbles were removed while preparing and maintaining at 35 ° C. While maintaining the stainless steel support on which the liquid film was formed at 0 ° C., casting was performed at a rate of 2 m / min so as to have a uniform thickness with the polymer solution.

The polymer solution thus cast is exposed to an atmosphere saturated with acetone vapor for 30 seconds to induce the polymer component of the casting polymer solution to dissolve in acetone vapor on the support and to dissolve the pore regulator component in water in the air. Passed through the coagulation bath to solidify the cast polymer solution to obtain a membrane.

Thereafter, the membrane obtained after a predetermined time was peeled off from the support, the residual solvent component contained in the membrane was extracted in a washing tank, and the membrane was dried under an ambient temperature atmosphere.

Example 2

A membrane was obtained in the same manner as in Example 1, except that casting was performed on the support while maintaining the support at 10 ° C.

Example 3

A membrane was obtained in the same manner as in Example 1 except that the cast polymer solution was exposed for 50 seconds.

Comparative Example 1

Casting was carried out by maintaining the support at 25 ° C., and the membrane was obtained in the same manner as in Example 1 except that the support was exposed to an atmosphere containing no solvent for 30 seconds.

Comparative Example 2

Casting was carried out while maintaining the support at 25 ° C., and the membrane was obtained in the same manner as in Example 1 except that the support was exposed to an atmosphere containing no solvent for 60 seconds.

In order to evaluate the properties of the membranes prepared in Examples 1 to 3 and Comparative Examples 1 to 3, the membranes prepared in Examples 1 to 3 and Comparative Examples 1 to 3 were mounted on a sample holder having a diameter of 90 mm. The amount of permeation was measured for 60 seconds at constant pressure (1 bar) using deionized water.

Support temperature
(℃) Exposure time
(sec) Membrane thickness
(Μm) flux
(Ml / min · cm · bar) Example 1 0 30 130-140 55-60 Example 2 10 30 125-130 15-20 Example 3 0 50 120-125 75-80 Comparative Example 1 25 30 140-150 1-5 Comparative Example 2 25 60 130-140 1-5

As shown in Table 1, in Examples 1 to 3, the flow increased as the exposure time was increased or the support temperature was lowered. The results of Examples 1 to 3 show that exposure to the atmosphere comprising a preformed liquid membrane and a solvent can sufficiently induce phase separation before solidification of the polymer solution, resulting in an increase in porosity of the membrane, further improving flow rate. And it can be seen that the membrane obtained according to Examples 1 to 3 from Figures 1 to 3 has an asymmetric structure.

However, in Comparative Examples 1 and 2, the temperature of the support is high, the liquid film is not sufficiently formed on the support, the solvent was not exposed to the asymmetric structure, it can be seen that the flow rate did not improve. In particular, from Figure 4, in the case of Comparative Example 1 shows that a large pore of too large diameter did not express an asymmetric structure.

As described above, the membranes according to Examples 1 to 3 of the present invention can be seen that the asymmetric structure is expressed through the exposure to the liquid film and the solvent formed on the support, thereby improving the flow rate.

Although the preferred embodiments of the present invention have been described above, the present invention is not limited thereto, and various modifications can be made within the scope of the technical idea of the present invention, and it is obvious that the present invention belongs to the appended claims. Do.

1 shows a cross-sectional structure of a porous membrane prepared according to Example 1 of the present invention.

Figure 2 shows a cross-sectional structure of a porous membrane prepared according to Example 2 of the present invention.

3 shows a cross-sectional structure of a porous membrane prepared according to Example 3 of the present invention.

4 shows a cross-sectional structure of a porous membrane prepared according to Comparative Example 1 of the present invention.

Claims (14)

In the method for producing an asymmetric porous membrane comprising a section consisting of micropores and a section consisting of large pores, (1) forming a liquid film on a support; (2) preparing a polymer solution comprising a polymer and a pore regulator; (3) casting the polymer solution onto the liquid film; And (4) exposing the polymer solution cast on the liquid film of the support to an atmosphere containing a solvent; Porous membrane manufacturing method comprising a. The method of claim 1, Said step (4) is carried out immediately after said step (3) or simultaneously with said step (3). The method of claim 1, Step (1) is The method of producing a porous membrane, characterized in that it comprises forming a moisture film on the support by controlling the temperature around the support to less than 10 ℃. The method of claim 1, In the step (4) The polymer membrane in the polymer solution is dissolved in the solvent in the air is extracted, the pore regulator is dissolved in water in the air is extracted method of producing a porous membrane. The method of claim 4, wherein Wherein said polymer forms said large pores and said pore control agent forms said micropores. 6. The method according to any one of claims 1 to 5, The polymer is a method of producing a porous membrane, characterized in that the combination of one or two selected from the group consisting of polyethersulfone, polysulfone, polyvinylidene fluoride, or polyacrylonitrile. 6. The method according to any one of claims 1 to 5, The pore control agent is a porous membrane manufacturing method, characterized in that the combination of one or two selected from the group consisting of ethylene glycol, glycerol, ethanol, methanol, acetone, polyvinylpyrrolidone, or polyethylene glycol. 6. The method according to any one of claims 1 to 5, The polymer solution is a porous membrane manufacturing method characterized in that it comprises a polymer / pore regulator mixture of 5 to 30% by weight relative to the polymer solution. The method of claim 8, The ratio of the polymer / pore regulator is a porous membrane manufacturing method, characterized in that 0.5 to 3 or less. 6. The method according to any one of claims 1 to 5, The porous membrane manufacturing method, characterized in that the casting by maintaining the temperature of the polymer solution at 25 ℃ to 70 ℃. The method of claim 10, The porous membrane manufacturing method, characterized in that for maintaining the temperature of the polymer solution 20 ℃ to 35 ℃ higher than the temperature of the support. 6. The method according to any one of claims 1 to 5, The solvent is a porous membrane manufacturing method, characterized in that contained in a saturated concentration in the atmosphere. The method of claim 12, Wherein said solvent is selected from the group consisting of acetone, methanol, isopropyl alcohol, or tetrahydrofuran. 6. The method according to any one of claims 1 to 5, In the step (4) The exposure time is 10 seconds to 60 seconds characterized in that the porous membrane manufacturing method.

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