JPH0533091B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for manufacturing a precision filtration membrane made of polysulfone resin that is excellent in both filtration performance and mechanical properties.

Membrane separation technology has attracted attention for its energy saving and compactness, and has made remarkable progress. Many types of polymers have been researched and developed as membrane materials for permselective separation membranes used in such systems, and cellulose-based, polyamide-based, polyacrylonitrile-based, polysulfone-based polymers, etc. have been used. Among them, polysulfone polymers are originally used as engineering plastics, but their heat resistance and
Due to its good chemical resistance such as acid resistance and alkali resistance, it is also being used as a material for separation membranes.

Particularly suitable for steam sterilization, for food processing,
It is beginning to attract attention for medical and pharmaceutical uses.

However, polysulfone resins have a much stronger intermolecular cohesive force than cellulose acetate and the like, making it difficult to control the pore size. In particular, precision filtration membranes that are not covered with a skin layer as the object of the present invention, that is, membranes that have a porous structure that can be observed with an electron microscope on both the front and back surfaces, have not been known in the past. The current manufacturing method has several problems.

In addition, in the present invention, a membrane having a porous structure that can be observed with an electron microscope generally refers to a microfilter or precision filtration membrane having pores with a pore diameter of 100 Å or more. There are many practical types on the market with pore diameters of 1000 Å (0.1 μ) or more.

(Prior art) For example, in JP-A-57-35906, a method is proposed in which a large amount of polyethylene glycol (hereinafter referred to as PEG) is added to a film forming solution (hereinafter referred to as dope), and the PEG is extracted after film formation to make it porous. is disclosed.

(Problems to be solved by the invention) However, this method requires a lot of effort and time to completely extract PEG, and when a large amount of PEG is added, excessive porosity may occur. , the mechanical properties of the membrane will be significantly impaired.

Furthermore, a method of forming a film using an unstable dope containing a large amount of non-solvent has been proposed, for example, in
154051 and Japanese Patent Application Laid-Open No. 59-58041. However, when considering industrialization, it is extremely difficult to maintain the properties of the dope constant if the dope is unstable, and therefore it is difficult to maintain the quality of the film manufactured using such a dope at all times. That is extremely difficult.

As a result of intensive studies, the present inventors have found a method for manufacturing a polysulfone resin precision filtration membrane that solves the above problems and has excellent filtration performance and mechanical properties, and have arrived at the present invention. .

(Structure of the Invention) That is, the present invention provides ``a method for manufacturing a precision filtration membrane by a wet membrane forming method using a solution of a polysulfone resin, in which a polysulfone resin having an average molecular weight of 100,000 to 1,000,000, Polyethylene oxide is 1% by weight or more and 10% by weight based on the total weight of the solution.
A method for producing a precision filtration membrane, which is characterized by containing the following and using an aqueous solution containing 50% by weight or more and 80% by weight or less of a good solvent for polysulfone resin as a gelling bath for membrane formation. be.

As the polysulfone resin referred to in the present invention, aromatic polysulfone resins having structures of the following formulas (1) to (3) are representative.

As a good solvent used in the present invention, at least one of 2-pyrrolidone, dimethylformamide, dimethylacetamide, dimethyl sulfoxide, N-methyl-2-pyrrolidone, etc. is used, and among them, 2-pyrrolidone is preferably used.

The film-forming dope used in the present invention contains the above-mentioned good solvent as a main component, and contains 5 to 30% by weight of polysulfone resin.
The content is preferably 10 to 20% by weight. This may further contain a non-solvent for the polysulfone resin in an amount equal to or less than the weight of the resin.

Further, normally, a swelling agent is used in addition to the above-mentioned solvent to form a porous layer of a semipermeable membrane, but in the present invention, polyethylene oxide is used as the swelling agent. The effects obtained by adding polyethylene oxide include improving the smoothness of the film surface, improving the mechanical properties of the film, especially improving its elongation and bending properties during pleating, and further reducing the viscosity of the dope during film formation. This is an improvement in film formability by increasing the amount of water. Addition amount is 1-10%, preferably 1-2
%. The molecular weight of the polyethylene oxide used is from 100,000 to 1,000,000, preferably from 500,000 to 1,000,000. Therefore, the dope used in the present invention is in a substantially stable state, and there is an advantage in industrialization that the properties of the dope can be easily controlled.

In the present invention, the above-mentioned good solvent for polysulfone resin is further used in the gelling bath. That is, the present invention is characterized by using polyethylene oxide as a swelling agent and further using an aqueous solution containing 50 to 80% by weight of a good solvent as a gelling bath. If it is less than 50% by weight, it is possible to produce a film with almost the same membrane performance and mechanical properties as those produced in a gelling bath containing only water, that is, a membrane with poor performance. Moreover, if it exceeds 80% by weight, the film will become non-uniform, or in extreme cases, no film will be formed. The precision filtration membrane targeted by the present invention can be produced only within the range of 50 to 80% by weight. The shape of the membrane can be any shape, such as a flat membrane, a cylindrical membrane, a hollow fiber membrane, etc., which can be produced by a normal wet membrane forming method.

As an example showing the biggest difference between film formation using the method of the present invention and film formation using the conventional method, scanning electron microscope photographs of the surface and cross section of a flat film are shown in Figures 1 to 1. Shown in Figure 4.

Figure 1 shows the membrane surface of a precision filtration membrane formed using the combination of the dope composition and gelling bath of the present invention, Figure 2 is a cross-sectional view of the same membrane, and Figure 3 shows the same dope composition. Figure 4 shows a cross section of the membrane surface of a precision filtration membrane formed in a water-only gelling bath.
It is clearly seen that the number of pores per unit area, that is, the open area ratio, is significantly higher in FIG. 1 than in FIG. 3. Moreover, the hole diameter in Fig. 1 is 3.
It is smaller overall than shown in the figure. Also, the fourth
In contrast to the figure, there are large pores, so-called voids, which are defects in the membrane, whereas they are not observed at all in Figure 2, forming a precision filtration membrane with an extremely uniform structure. The observation results of such electron micrographs are consistent with the actual filtration performance of the membrane, and the filtration performance is calculated by the permeability coefficient Lp and bubble point shown below.
When evaluated by BP, the film shown in Figure 1 was Lp
= 19.0 BP = 2.3, whereas the membrane in Figure 3 is
Lp=10.5 and BP=1.9.

Lp = Pure water permeability (ml) / effective membrane area (cm ²
) x Water permeation time (min) x Filtration pressure (Kg/ ^cm2 ) BP: Based on the bubble point method of ASTM-E128,
Measured using pure water. The unit is Kg/ ^cm2 .
In the examples, the estimated maximum pore diameter DM (μm) was determined from the following formula.

D _M = 0.0408 γ cos θ / BP (where γ: surface tension of water at 25°C, 72 dyhe/cm θ: contact angle between polysulfone resin and water, 78° for the resin of formula (1)) Therefore, the result of filtration performance Also, the membrane produced by the production method of the present invention has a smaller maximum pore diameter and a larger Lp than that produced by the conventional method. Therefore, it can be seen that the porosity is high. As an effect brought about by the phenomenon that the maximum pore diameter is reduced while maintaining a high Lp, for example, when a precision filtration membrane is used for sterilization, rapid and complete sterilization can be expected. In addition, when comparing the mechanical properties, for example, the elongation and tensile strength at the breaking point, the membrane shown in Figure 1 has an elongation of 28.
% and tensile strength of 229 g/mm ² , whereas the membrane shown in Figure 3 has an elongation of 24% and a tensile strength of 170 g/mm ^2.The membrane produced by the manufacturing method of the present invention has better not only filtration performance but also mechanical properties. It has also been greatly improved.

(Effects of the Invention) As described above, by using the production method of the present invention, it is possible to produce a polysulfone-based resin precision filtration membrane that is excellent in both filtration performance and mechanical properties. The membrane thus obtained can be used as a precision filtration membrane for sterilization, separation and purification of valuable substances such as proteins, or as a blood treatment membrane for separating specific components from blood, such as plasma separation. In addition, because we use a heat-resistant and chemical-resistant material called polysulfone resin, we can manufacture precision filtration membranes that can withstand harsh usage conditions that conventional cellulose acetate precision filtration membranes cannot withstand. can.

Next, the present invention will be specifically explained with reference to Examples.

Example 1 Polyether sulfone of formula (1) (trade name
Victrex4800P manufactured by ICI) 12 parts by weight, average molecular weight
900,000 polyethylene oxide (manufactured by Aldvich)
2 parts by weight of a mixed solvent mainly composed of 2-pyrrolidone86
A dope having a viscosity of 16,000 centipoise (25° C.) was obtained by dissolving in parts by weight. This was cast onto a glass plate to a thickness of 300 μm, left in a room temperature atmosphere for 100 seconds, immersed in a gelling bath containing 50 parts by weight of 2-pyrrolidone, and washed with water to obtain a smooth precision filter membrane.
The Lp of the obtained membrane was 19.0ml/cm ²・min・Kg/cm ² (25
℃), BP was 2.3 Kg/cm ² and _DM was 0.27 μm. In addition, the elongation at break of this membrane is 28%, and the tensile strength is
It was 229g/ ^mm2 . FIGS. 1 and 2 are photographs of the surface and cross section of the membrane obtained in this example.

Comparative Example 1 A film was formed in the same manner as in Example 1 except that pure water was used as the gelling bath. The Lp of the obtained membrane was 10.5ml/ ^cm2 .
min・Kg/cm ² , BP is 1.9Kg/cm ² Therefore _DM is 0.32μ
m, and although the maximum pore diameter was larger than that of the membrane of Example 1, the water permeation rate was low. Furthermore, the elongation at break of this membrane was 24%, the tensile strength was 170 g/mm ² , and the mechanical properties were also poor. FIGS. 3 and 4 are electron micrographs of the surface and cross section of the precision filtration membrane obtained in this comparative example.

Comparative Example 2 A film was formed in the same manner as in Example 1, except that no polyethylene oxide was added and 88 parts by weight of a mixed solvent mainly containing 2-pyrrolidone was used. The resulting film was wrinkled and uneven. Also, Lp
It was 23.5ml/cm ²・min・Kg/cm ² but BP was 0.9
Kg/cm ² Therefore, _DM was 0.68 μm, and the maximum pore diameter of the membrane was too large.

Example 2 A film was formed in the same manner as in Example 1 except that an aqueous solution of 80 parts by weight of 2-pyrrolidone was used as a gelling bath. The Lp of the obtained membrane is 24.0ml/cm ²・min・Kg/
cm ² , BP was 3.7 Kg/cm ² and _DM was 0.17 μm. In addition, the elongation at break is 46% and the tensile strength is 340g/
It was warm in ^mm2 .

Example 3 A film was formed in the same manner as in Example 1 except that an aqueous solution of 80 parts by weight of dimethylformamide was used as a gelling bath. The Lp of the obtained membrane was 17.1ml/cm ²・min・
Kg/cm ² , BP was 3.0 Kg/cm ² and _DM was 0.20 μm. Also, the elongation at break is 21% and the tensile strength is 270.
g/ ^mm2 .

Example 4 Example except that a dope consisting of 14 parts by weight of the resin of formula (1), 2 parts by weight of the polyethylene oxide of Example 1, and 84 parts by weight of a mixed solvent mainly containing 2-pyrrolidone was used as the film-forming dope. A film was formed in the same manner as in 1. The obtained membrane was added to a 1% glycerin aqueous solution.
After immersing for 15 minutes, the film was dried with hot air at 60°C to prepare a dry film. The Lp of this membrane is 27.4ml/cm ²・min・Kg/cm ² , B.
P. was 2.3 Kg/cm ² and therefore _DM was 0.27 μm. The elongation at break was 30% and the tensile strength was 420 g/mm ² .

Example 5 The dried membrane of Example 4 was placed in a sterilization filter manufactured by Millipore, and after steam sterilization at 121°C for 15 minutes, Ps
-Filtration and sterilization was performed using an aqueous solution of 1.9× ¹⁶⁶ cells/ml of -diminuta. Ps−diminuta is 1.1×10 ⁷ on the membrane surface.
The filtrate contained ^no
Ps-diminuta was not detected, and complete eradication was achieved.

Example 6 12 parts by weight of polyether sulfone of formula (1) and 8 parts by weight of polyethylene oxide having an average molecular weight of 100,000 were dissolved in 80 parts by weight of a solvent mainly containing N-methyl-2-pyrrolidone to prepare a film-forming dope. Obtained. This was cast onto a glass plate to a thickness of 350 μm, left in a room temperature atmosphere for 120 seconds, immersed in a gelling bath containing 80 parts by weight of 2-pyrrolidone, and washed with water to obtain a smooth precision filter membrane. The Lp of the obtained membrane is 79.5ml/cm ²・min・Kg/
cm ² , BP was 1.0 Kg/cm ² and _DM was 0.61 μm. In addition, the elongation at break of this membrane is 36%, and the tensile strength is
It was 370g/ ^mm2 .

[Brief explanation of the drawing]

FIGS. 1 and 2 are scanning electron micrographs of the surface (3000 times magnification) and cross section (200 times magnification) of the membrane obtained in Example 1, respectively. On the other hand, Figures 3 and 4 show the surface (3000x magnification) and cross section (200x magnification) of the membrane obtained in Comparative Example 1, respectively.
This is an electron micrograph taken at a magnified magnification.

Claims (1)

[Claims] 1. A method for producing a precision filtration membrane by a wet film forming method using a polysulfone resin solution, wherein the polysulfone resin solution has an average molecular weight of 100,000 or more.
1 million or less polyethylene oxide is contained in the total weight of the solution from 1% to 10% by weight, and a good solvent of polysulfone resin is mixed at 50% to 80% by weight as a gelling bath for film formation. A method for producing a precision filtration membrane, characterized by using an aqueous solution. 2. The method for producing a precision filtration membrane according to claim 1, wherein the good solvent is 2-pyrrolidone. 3. The method for producing a precision filtration membrane according to claim 1, wherein the good solvent is at least one selected from dimethylformamide, N-methyl-2-pyrrolidone dimethylacetamide, and dimethyl sulfoxide.