KR20070105759A - Pvdf membrane with high porosity and permeation and method for manufacturing the same - Google Patents

Abstract

A preparation method of a filtration membrane, and a preparation method of a high porosity filtration membrane with a high flux are provided to control easily pores of the filtration membrane. A high porosity polyvinylidene fluoride filtration membrane with high flux comprises a membrane having distribution of various pores in an absolute pore size range of 0.1 to 0.8 mum, wherein the membrane has a thickness of 100 to 140 mum, and a formation ratio of micropores except polymer on the membrane crossing section has a space volume of at least 70%, preferably 70 to 75%. The membrane is constructed in such a structure that a surface of the membrane has a nodular structure by seed growth.

Description

High porosity polyvinylidene fluoride membrane showing high flow rate and manufacturing method thereof {PVDF membrane with high porosity and permeation and method for manufacturing the same}

1 is a SEM photograph showing the surface and cross section of a conventional filtration membrane.

Figure 2 is a SEM photograph showing the surface and cross section of the filtration membrane according to the present invention.

The present invention relates to a method for producing a porous polyvinylidene floride (PVDF) filtration membrane having high flow performance.

PVDF resins are very widely used in the environment or the metal industry because of their excellent acid and alkali resistance.

In particular, due to their excellent acid resistance, PVDF resin has been selected as a suitable material for use as a filtration membrane. In general, in order to manufacture a filtration membrane it has to be made into a myriad of pores, that is, porous structure. Currently, polyvinylidene fluoride (PVDF), which is in the limelight in the manufacture of filtration membranes, has excellent chemical resistance, and much research has been made in the development of filtration membranes using the same.

As one method of making porous filtration membranes, it is known to use inorganic fillers that can be dissolved in water. This method has the advantage that the manufacturing process is simple, not demanding, and high in reproducibility. As inorganic fillers which can be used for this, silica, titania, alumina powders are known. However, such an oxide has a problem that it is difficult to elute the chemical because it is very stable chemically.

As commercially available, Millipore products are manufactured using phase separation that occurs by mixing with different insoluble solvents, and are characterized by fine pores of 20 μm or less. Usually the pore size of commercialized membranes is determined in the range of 0.005-20 μm.

The method described in U.S. Patent No. 3,518,332 is obtained by mixing PVDF particles with water-soluble metal salt particles in paraffin, mixing the resin in a molten state and molding the resin, and then removing paraffin with an organic solvent and removing metal salt from water. To make a film. At this time, the metal salt used is Na ₂ CO ₃ or calcium formate.

 U.S. Patent No. 3,518,384 discloses a process for producing PVDF by mixing it with water, LiCl, dimethyl formamide (DMF) and then applying it onto a net, then passing it through a water bath to cause aggregation. In other words, a water-soluble metal salt is mixed with PVDF resin to be molded at high temperature and eluted in water or acid solution to make porous membrane.

Subsequently, various methods of causing phase separation using an organic solvent have been tried. Among the methods using the phase separation developed up to now, a method of mixing and injecting other insoluble solvents and PVDF resins to form a phase separation occurs to make porosity and melt blending using PVDF resin and solvent After forming a single-phase melt, forming it into a suitable membrane, removing the heat applied, cooling it, and extracting the diluent with a suitable extractant, this part becomes the void volume in the polymer matrix. Gelation (Gelation) method is generally predominantly imparted porosity in the polymer matrix.

The method of Japanese Patent No. 51-8268 includes a step of forming a film by using a cyclonucleic acid as a solvent, using a solution after heating and cooling.

 European patent EP 223,709 uses acetone and dimethylformamide (DMF). According to this, a method of forming a porosity by rapidly cooling a solution and then putting it in another kind of solvent is disclosed.

In the method described in US Pat. No. 4,203,847, the PVDF resin is dissolved in a hot acetone solution and poured onto a moving belt, which is immersed in a solvent and non-solvent mixed solution to form a membrane.

US 4,666,607 discloses a thermal gelation process. Here, by using a quenching apparatus, PVDF resin is mixed with a solvent and a non-solvent, and kept at a temperature above which phase separation occurs, followed by quenching.

In EP 378,441 A2, high boiling point diethyl phthalate, dibutyl phthalate and phosphoric acid are added as an organic solvent, and hydrophobic silica powder is added as a filler and then immersed in a 1,1,1-trichloroethane solution after molding. Solvents are eluted and then silica is eluted in a caustic soda solution.

As mentioned above, methods for making microporous membranes that have been used to date can be broadly classified into two types. It is a method of making porosity by removing an insoluble solvent from a polymer resin solution and a method of adding a functional polymer contained in a resin and easily leaking. The former method has a disadvantage in that it is difficult to control the phase separation, so that a small space is hardly produced. The latter method is advantageous in space generation, but it is difficult to control the pore size, making it difficult to manufacture a high porosity and high flow rate membrane.

These conventional membranes have a low porosity structure and do not meet the service life requirements of the semiconductor and electrical and electronic fields.

Therefore, the present invention is to overcome the problems of the prior art, to provide a method for producing a filtration membrane easy pore control.

It is another object of the present invention to provide a method for producing a high porous filter membrane exhibiting a high flow rate.

According to an aspect of the present invention, the membrane includes a membrane having various pore distributions in the range of 0.1 to 0.8 μm of absolute pore size, and has a thickness of 100 to 140 μm. A high porosity polyvinylidene fluoride filtration membrane having a high volume of at least 70%, preferably at least 70% to 75%, is provided.

According to another aspect of the present invention, a polymer resin is dissolved in a mixed solvent (of NMP and butyl acetate) together with an additive to form a polymer solution as a substrate of the porous support; Coating the polymer solution onto the film support; Precoagulating the coated solution using a temperature and humidity gradient device; The pregelled solution is immersed in the mixed solution in a coagulation bath and finally coagulated to form a membrane; Peeling the formed membrane from the film support; Completely removing the solvent component contained in the membrane in the washing tank to form pores; And drying the porous membrane with air at 80 ° C., to provide a method for producing a highly porous filter membrane having high flow performance.

The manufacturing process of the present invention is distinguished from the conventionally known methods in terms of the resin composition ratio and the solution dissolving solution. In order to obtain the desired high porosity high flow membrane cross-sectional structure, the nucleating agent was first applied in the PVDF resin solution, the pores of uniform size range were formed by controlling the nuclear growth, and the porosity in the region was maximized. . In addition, based on the resin, solvent, and non-solvent composition, the composition ratio of the solvent / non-solvent and the polymer concentration are controlled to improve the cross-sectional porosity, and the membrane pore size is classified and controlled by temperature, thereby improving the porosity.

In the present invention, it is also possible to obtain the desired high porosity cross-sectional structure through operating conditions in the manufacturing process, namely temperature and humidity gradients.

Since PVDF is a very hydrophobic material, it is difficult to form pores because the non-solvent and solvent are not easily exchanged during the phase transition process. Therefore, the present inventors used the following method to solve the above-mentioned problem.

In order to produce improved high porosity PVDF membranes from PVDF membranes manufactured by the conventional single phase transition process, partial phase transition is performed by using gas of low temperature and high temperature and high temperature and low humidity in the previous process of complete pore formation. In this case, the phase change refers to a phenomenon in which a non-solvent is separated into two phases, that is, a solid and a liquid, in a single phase in which a solid and a liquid are mixed in a matrix.

When the process of low temperature and high humidity and high temperature and low humidity is described in detail, the belt speed at which the PVDF resin formed to a certain thickness during the solidification process moves is set to 0.1 m / min, the temperature gradient range is 20 to 50 ° C, and the humidity gradient range is 30 to This is the case where the solidification process is performed using 80% of non-solvent in the gas state. At this time, the change in the momentum of water at the high temperature and the low temperature, and the change in phase inversion and pore size due to the second humidity are correlated. That is, at low temperatures, unlike the high temperature, the activity of the water is inferior, so it is impossible to penetrate deeply. In the three-dimensional description, the pore distribution is formed by a mechanism phenomenon that allows pores to be formed uniformly in the entire depth. In low temperature and high humidity, the momentum of water in the unit volume falls shorter than in the high temperature phase, but the penetration into the short depth occurs. Since the volume is large, phase transition occurs in a large area, thereby providing a passage for penetrating during a high temperature and low humidity process. In addition, at high temperatures, the momentum of the water in the gaseous state is increased to penetrate deeply into the hydrophobic PVDF resin solution within a short time, thereby preparing a membrane having a high porosity but a high porosity as a whole.

Specifically, the high-porosity polyvinylidene fluoride (PVDF) resin membrane manufacturing method having high flow performance of the present invention first melts the polyvinylidene fluoride resin and additives in a solvent to form a mixed solution. Next, some solidification process is performed on the crude polyvinylidene fluoride resin solution using a temperature and humidity gradient device, and the resultant some solids are immersed in a water or alcohol mixture solution to remove additives and solvents from the sample. It is characterized by forming fine pores.

Additives effective in the present invention may be acetate based, ether based, alcohol based, ketone based, ester based or mixtures thereof. These additives are suitably mixed in the ratio of 2-20 weight part with respect to 100 weight part in the composition of the polyvinylidene fluoride resin crude liquid sample.

Examples of preferred solvents capable of dissolving both polyvinylidene fluoride resin and additives include N-methyl-2-pyrrolidone (NMP), dimethylformamide (DMF), dimethyl sulfoxide, dimethylacetamide (DMAc) or Mixtures of these may be used.

In the present invention, the polyvinylidene fluoride resin mixed solution is subjected to a first solidification process through a temperature / humidity gradient equipment. In this process, additives that are plastic and hydrophilic and well soluble in PVDF resin solutions are used to create many effective pores that can interpenetrate into the primary solidified membrane.

That is, as described above, the primary solid membrane is immersed in water or an alcohol mixed solution to remove the additives and the solvent so as to form fine pores in the space occupied by them.

What is important when making porous membranes is that the PVDF resin and the additives and solvents must be mixed very uniformly, and the additives and solvents must be effectively released when extracted with water or alcohol-based mixtures after processing. The former is made possible by selecting the appropriate additives and solvents, while the latter is made possible by applying the appropriate coagulation solution.

According to the present invention, as the additive, an acetate compound which can be chemically uniformly mixed but is not easily separated is preferable. For example, when butyl acetate, PVDF resin and solvent are mixed and molded, and then the above-mentioned acetate compound and solvent are removed with an alcohol-based mixture or water, very fine pores are formed therein to form a porous PVDF membrane.

Hereinafter, a method of manufacturing the polyvinylidene fluoride resin membrane of the present invention will be described in detail.

Acetate-based compounds are well soluble in water and dispersible. Soluble in methyl or ethyl alcohols, but PVDF resins are insoluble in water and these lower alcohols. Therefore, solvents capable of dissolving both additives and PVDF resins include NMP (N-methyl-2-pyrrolidone), DMF (dimethyl formamide), DMS (dimethyl sulfoxide) and DMAc (dimethyl acetamide). have. These solvents may be used alone or as a mixed solvent.

When preparing the polyvinylidene fluoride resin membrane of the present invention, first, the additive is dissolved in the solvent capable of dissolving the polyvinylidene fluoride resin and the additive together, and then the polyvinylidene fluoride resin is added to give a light brown color. Get a solution. At this time, the additive serves to disperse the pores in the membrane. Preferably, the additive is used in a proportion of 10 to 40 parts by weight based on 100 parts by weight of the polyvinylidene fluoride resin solids.

A solution containing polyvinylidene fluoride resin and additives is applied onto the surface treated film and then formed into a desired thickness with a casting knife. After film formation, some solidification process is performed using a temperature / humidity gradient device and then immersed in water or alcohol mixture to remove additives and solvents from the membrane. It may be heated to speed up the leaching of the additives and solvent. When the additives and the solvent are removed, pores are formed therein, through which the solution can move.

When the acetate compound is used as an additive, the color of the membrane changes from dark brown to light brown or yellow, and if there is no further change, the remaining additive and the solvent are volatilized with a hot gas.

Finally, a hydrophilic function was imparted to the membrane by an ultraviolet treatment process.

In conclusion, the pore-forming process of the polyvinylidene fluoride resin membrane prepared according to the present invention is a nucleating agent, growth rate control, the appropriate ratio of additives and processing temperature of the polyvinylidene fluoride resin solution, process temperature / humidity It features an adjustment. When visually observed at all stages of manufacture, the clarity of the solution or shaped body should be maintained.

 Hereinafter, the present invention will be described in more detail with reference to the following examples. However, these examples are only some examples of the present invention, and the scope of the present invention is not limited thereto.

The polyvinylidene fluoride resin used in the following examples used a resin having a molecular weight ranging from 100,000 to 350,000. Pellets or powdered polyvinylidene fluoride is dissolved in a solvent to form a transparent and highly viscous liquid, which can be used as N-methyl-2-pyrrolidone, dimethyl formamide, dimethyl sulfoxide and dimethyl acetamide. , Isopron, and the like. In the following examples, N-methyl-2-pyrrolidone was used to dissolve and some acetate-based additives were added thereto to adjust the working temperature of the polyvinylidene fluoride solution.

(Example)

Example 1 (pore size: 0.1 μm)

PVDF (Solef 1015, Solvay co.) Resin was made of a solution consisting of 15 to 25%, NMP 60 to 75%, butyl acetate 5 to 15% and maintained at 30 ℃. This solution was uniformly coated on the continuous film support so as to have a thickness of 110 ~ 120㎛. After using the temperature range 20 ~ 50 ℃, humidity range 30 ~ 80% gradient device and the coating was maintained in the circulating air. A solidification process was carried out to remove solvents and additives from the coating, which had undergone a temperature / humidity gradient. To this end, IPA / N- butyl acetate / water / nucleating agent mixed solution of a constant composition ratio was continuously added to the coagulation bath. Thereafter, the membrane is peeled off from the film support, and then transferred to a water bath to completely extract the residual solvent contained in the microporous membrane, and dried with air at 80 ° C. to prepare a membrane. Since the physical properties of the membrane prepared through the above-mentioned hydrophilization treatment was measured based on a predetermined evaluation method, the results are summarized in Table 1. As a comparative example, based on the same evaluation method, the result compared with the product manufactured by the prior art is shown in Table 2.

(Comparative Examples 1 to 5)

The membrane was prepared in the same manner as in Example 1 except that no temperature / humidity gradient device was used. The changes in the prepared membrane properties were evaluated in the same manner and are shown in Table 3.

 (Examples 2-5)

The membrane was prepared in the same manner as in Example 1 except that the pore size was increased by changing the concentration of PVDF. Preparation conditions and physical property evaluation results are summarized in Table 1.

<Table 1>

<Table 2>

<Table 3>

As described above, the present invention provides a method for producing a highly porous microfiltration membrane having high flow performance by using liquid phase separation and nucleating agent.

As shown in the data obtained in the examples, the membrane prepared according to the present invention had a 25% porosity improvement over the conventional separation membrane (see Tables 2 and 3), and the flow rate also improved by 50-100% depending on the pore size. Indicated. This not only promoted the gelation process faster than the conventional liquid phase process using the temperature / humidity gradient principle, but also artificially added a nucleating agent, and thus, showed excellent performance in terms of porosity. It also increases the efficiency and costs of treatment in some chemical refining, drinking water, pre-treatment and pre-treatment processes for food production, requiring higher flow rates at the same pressure, than those produced by conventional methods in food manufacturing processes. It has the effect of reducing it.

Claims (9)

Absolute pore size includes a membrane having a variety of pore distribution in the range of 0.1 ~ 0.8 ㎛, the film thickness is 100 ~ 140 ㎛, the micropore rate other than the polymer on the membrane cross-section is at least 70% or more, preferably Is a polyvinylidene fluoride filtration membrane having a high porosity, having a volume volume of 70% to 75% or more. The polyvinylidene fluoride filtration membrane of claim 1, wherein the membrane has a high flow rate, the surface of which has a nodular structure by nuclear growth. As a base material of the porous support, a polymer resin is dissolved together with an additive in a mixed solvent of NMP and butyl acetate to form a polymer solution; Coating the polymer solution onto the film support; Precoagulating the coated solution using a temperature and humidity gradient device; The pregelled solution is immersed in the mixed solution in a coagulation bath and finally coagulated to form a membrane; The formed membrane is peeled from the film support, Completely removing the solvent component contained in the membrane in the washing tank to form pores; And And drying the porous membrane with air at 80 ° C., wherein the porous membrane has a high flow performance. The method for producing a highly porous filter membrane according to claim 3, wherein the temperature gradient device adjusts a temperature gradient in a temperature range of 20 to 50 ° C. 4. The method of claim 3, wherein the humidity gradient device adjusts the humidity gradient in a humidity range of 30 to 80%. The method of claim 3, wherein the polymer resin is polyvinylidene fluoride, and the additive is an acetate compound. 4. The method of claim 3, wherein the mixed solution of the coagulation bath comprises IPA, an acetate compound, water, and a nucleating agent. 5. 8. The method of claim 7, wherein the acetate compound is selected from the group consisting of methoxypropyl acetate, butyl acetate, mespropoxy propanol and mixtures thereof. 8. The method of claim 7, wherein the nucleating agent is selected from the group consisting of benzoic acid, lithium chloride and mixtures thereof.

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