JPH0561970B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a method for producing a microporous membrane, and in particular, it is used in the filtration of drugs in the pharmaceutical industry, alcoholic beverages in the food industry, and microporous membranes, including the aforementioned manufacturing industry and semiconductor manufacturing industry. It is used for filtration of purified water, pure water, etc. for the production of ultrapure water used in the electronics industry, nuclear industry, and laboratories of various industries, where processing is carried out.
The present invention relates to a method for producing a microporous membrane for precision filtration that efficiently filters microparticles and microorganisms on the submicron order of 1 μm or less. [Prior art] A microporous membrane for precision filtration, which is conventionally used in the fields of pharmaceutical, food, electronic, and nuclear power industries to remove microparticles of about 0.1 to 5 μm in aqueous and non-aqueous systems, and to remove bacteria, and its manufacturing method. For example, those using cellulose ester, aliphatic polyamide, polyfluorocarbon, polysulfone, polypropylene, etc. as raw materials have been disclosed (for example, Japanese Patent Publication No.
No. 40050, JP-A-58-37842, JP-A-58-91732
(Refer to Japanese Patent Application Laid-Open No. 56-154051). Such a microporous membrane is a so-called symmetric membrane in which the diameter of the micropores existing inside the membrane does not substantially change in the film thickness direction, and the pore diameters on both surfaces of the membrane do not substantially change.
There are so-called asymmetric membranes in which the pore diameter changes continuously or discontinuously in the membrane thickness direction, and the pore diameter on one surface of the membrane is different from the pore diameter on the other surface. It is classified as having a structure called an internal dense layer membrane, which has a layer with the smallest pore size. Among these, symmetrical membranes are described in JP-A No. 58-98015, but during filtration, the entire membrane presents a large resistance to the fluid flow, and only a small flow rate can be obtained (i.e., the unit (Only a small flow rate can be obtained per unit area, per unit time, and per unit differential pressure), and it also has disadvantages such as easy clogging, short filtration life, and lack of blocking resistance. On the other hand, the asymmetric membrane is disclosed in Japanese Patent Publication No. 55-6406 and Japanese Patent Publication No. 56-
As described in No. 154051, the membrane has a layer with small pores called a compact layer on one surface and relatively large pores on the other surface. If the side with large holes faces the flow of the filtrate, the smallest particles that can be filtered out will be captured in this dense layer, making the entire thickness of the membrane an effective filtration material. When used carefully, it is possible to increase the filtration flow rate and extend the life of the membrane, making it an excellent microporous membrane in this sense. However, although the dense layer is extremely important in this case, conventionally, this dense layer has been disadvantageous in that it is easily scratched by abrasion or other causes and easily causes leakage of fine particles because it is located on the surface. In order to compensate for such drawbacks, a structure in which an internal dense layer membrane, that is, a layer with a small pore size exists inside the filtration membrane, is desired, and Japanese Patent Application Laid-open No. 150402/1983 discloses a structure in which two asymmetric membranes are stacked with the dense layers in close contact with each other. Discontinuous structures have been proposed. However, such a filtration system in which two asymmetric membranes are stacked has the disadvantage that when folded and placed in a cartridge, the filtration area in the cartridge becomes small, and the filtration flow rate as a module becomes small. In order to solve the above-mentioned drawbacks, the present inventors studied a microporous membrane that forms a dense layer inside the membrane, and filed an application for such a microporous membrane (Japanese Patent Application No.
No. 60-166984). The method for manufacturing this microporous membrane is to cast a membrane-forming stock solution, which is made by adding a swelling agent and a non-solvent to a polymer and dissolving it in a solvent, onto a support in a completely stable solution state, and then to form the liquid membrane. After evaporating the solvent and absorbing moisture in the air to cause coacelvation, the liquid film is immersed in a coagulation bath, and then the microporous film is peeled off from the casting support. It is characterized by: The membrane-forming polymer that can be produced by this production method is not particularly limited, but among these, polysulfone is particularly preferred, polyvinylpyrrolidone is used as the swelling agent, and water is often used as the nonsolvent. N-methyl-2-pyrrolidone is often used as a good solvent for polysulfone. The polysulfone-based microporous membrane manufactured by the above manufacturing method has an excellent structure and performance as an internal dense layer membrane. [Problems to be solved by the invention] However, although the polysulfone-based microporous membrane with an internal dense layer produced in this way has excellent hydrophilicity, the water permeation rate decreases when used. The disadvantage was that it became smaller. An object of the present invention is to eliminate the above-mentioned drawbacks and provide a method for producing a microporous membrane having a polysulfone-based inner dense layer that has a high water permeation rate and excellent hydrophilicity. [Means and effects for solving the problems] The present inventors have found that when the content of polyvinyl pyrrolidone in the membrane is high, it swells during filtration and closes the pores, resulting in increased water permeation resistance. We discovered this and focused on cleaning polyvinyl pyrrolidone. The above object of the present invention is to provide a method for producing a polysulfone-based microporous membrane, which comprises a step of casting a solution of polysulfone and polyvinylpyrrolidone dissolved in a solvent onto a support, and immersing it in a coagulation bath. A polysulfone-based microporous membrane characterized by washing the membrane with a polyhydric alcohol, such as diethylene glycol, triethylene glycol, polyethyl glycol, glycerin, etc., and then washing with water to adjust the polyvinylpyrrolidone content in the membrane to 1 to 5%. This is achieved by a method for producing a transparent film. Note that the polyhydric alcohol may be used as an aqueous solution. The most effective method for producing a microporous membrane of the present invention
An embodiment will be explained using FIG. 1. In FIG. 1, polysulfone is melted in a jacketed melting pot 1. At this time, water as a non-solvent and polyvinylpyrrolidone as a swelling agent necessary for forming micropores are added and mixed. After defoaming, this solution is sent to a casting injector 3 by a liquid pump 2, and the solution in a stable solution state is poured onto a polyester film as a casting support 4 from the injector 3 into a liquid film. Cast as 5. After air regulated by an air conditioning device 6 is applied to the surface of the cast liquid film 5 from the blow-off port 7, a coagulation liquid tank 8 containing a liquid that is a non-solvent for the polymer and is compatible with the polymer solution is applied. soak it in. After casting, the liquid film 5 is blown by conditioned air to cause coacelvation from the surface of the liquid film toward the inside, thereby causing a fine coacelvation phase from the surface of the liquid film 5 toward the inside. The fine coacelvation phase is fixed as micropores in the coagulation liquid tank (water is used as the coagulation liquid), and at the same time, due to the phase separation of the liquid film 5, pores other than the micropores are A microporous membrane 9 is formed. Thereafter, the microporous membrane 9 is peeled off from the casting support 4. The casting support 4 is transferred to a casting support winding machine 10,
The peeled microporous membrane 9 is washed with water in a water washing tank 11, and then passed through a polyhydric alcohol washing treatment tank 12 where polyvinylpyrrolidone (hereinafter referred to as PVP) is washed out with polyhydric alcohol, and then passed through a water washing tank 13 to reduce the PVP content to 1. ~5% and passed through the dryer 14 and then the winder 15
It is wound up. By the above manufacturing method, an improved polysulfone microporous membrane can be manufactured. Polysulfone used in the present invention and/or
Or polyether sulfone or Polymers represented by repeating units are preferred. The polysulfone microporous membrane of the present invention is produced by dissolving the above polymer in a good solvent, a mixed solvent of a good solvent and a non-solvent, or a mixture of multiple types of solvents having different degrees of solubility for the polymer. Prepare membrane stock solution. In this case, a good solvent for polysulfone is usually one that is a good solvent for membrane-forming polymers and that quickly replaces the coagulating liquid when immersed in the coagulating bath. In many cases, water and/or an organic solvent compatible with water is used as the coagulating liquid, and therefore it is preferable to use a polar solvent that is compatible with the coagulating liquid. For example, dioxane, tetrahydrofuran, dimethylformamide, dimethylacetamide, N-methyl-2-pyrrolidone, or a mixed solvent thereof is suitable. In addition, in the case of mixing nonsolvents in the present invention, examples of nonsolvents include water, cellosolves, methanol,
Examples include ethanol, propanol, acetone, tetrahydrofuran, polyethylene glycol, and glycerin. The ratio of the non-solvent to the good solvent may be in any range as long as the mixed liquid can maintain a uniform state, but it is preferably 5 to 50% by weight. In addition, an inorganic electrolyte, an organic electrolyte, or a polymer or an electrolyte thereof called a swelling agent is added to the polymer solution to control the porous structure. In addition to polyvinylpyrrolidone, swelling agents include common salt, metal salts of inorganic acids such as lithium chloride, sodium nitrate, potassium nitrate, sodium sulfate, and zinc chloride, metal salts of organic acids such as sodium acetate and sodium formate, polyethylene glycol, Polymer electrolytes such as sodium polystyrene sulfonate and polyvinylbenzyltrimethylammonium chloride, ionic surfactants such as sodium dioctyl sulfosuccinate and sodium alkylmethyl taurate, etc. may be used in combination. Although these swelling agents exhibit some effect even when added alone to a solution, they exhibit a particularly remarkable effect when added as an aqueous solution. The amount of the swelling agent aqueous solution added is not particularly limited as long as the addition does not impair the uniformity of the solution, but it is usually 0.5% to 10% by volume based on the solvent.
Further, there is no particular restriction on the concentration of the swelling agent aqueous solution, and the higher the concentration, the greater the effect, but the concentration usually used is 1% by weight to 60% by weight. The concentration of the polymer solution as a membrane forming stock solution is 5 to 35
% by weight, preferably 10-30% by weight. If it exceeds 35% by weight, the water permeability of the resulting microporous membrane becomes so small that it has no practical meaning;
At lower concentrations, microporous membranes with sufficient separation power cannot be obtained. In the method for producing a microporous membrane of the present invention, the membrane forming stock solution obtained as described above is cast onto a casting support, and conditioned air is applied to the surface of the cast liquid film for an appropriate period of time. By applying this method, an internal dense layer film can be produced by appropriately adjusting the amount of solvent vapor and the amount of non-solvent vapor absorbed from the atmosphere (moisture absorption). In this case, in order to cause coacervation only in the vicinity of the surface layer, uniform evaporation of the solvent and absorption of non-solvent vapor takes place in an extremely short period of time.
Needs to solidify immediately. By controlling the evaporation of this solvent and the absorption of non-solvent vapors, the depth of the compact layer and its pore size can be controlled. In addition, in order to effectively create the internal dense layer membrane of the microporous membrane of the present invention, it is necessary to add not only a good solvent for the polymer but also a non-solvent and a swelling agent to the membrane-forming stock solution in advance. be. Examples of these nonsolvents and swelling agents include the aforementioned water, polyethylene glycol, and polyvinylpyrrolidone. The above manufacturing conditions vary depending on the polymer type, solvent type, non-solvent type, swelling agent type, polymer concentration, atmosphere during casting, etc., so the time for microphase separation,
It is necessary to examine the structure of the membrane and find the optimal conditions. The conditions found can be controlled by adjusting the amount of solvent evaporation and absorption of non-solvent vapor from the cast membrane in various ways. A method of adjusting the flow so that a certain amount of solvent evaporates from the cast liquid film and absorbs a certain amount of non-solvent vapor is to cover the path of the polymer solution from the casting part to the coagulation liquid. Methods include adjusting the time until immersion in the coagulation bath after rolling, and adjusting the solvent vapor pressure, non-solvent vapor pressure, temperature, air blowing and air exhaust speed, etc. of this atmosphere. The polymer solution separated from the coagulation solution becomes self-supporting, and is peeled off from the casting support to which it was adhered for reinforcement and immersed in a water washing bath. After washing with water, wash with polyhydric alcohol and then wash with water to adjust the PVP content in the membrane to 1 to 5%.
If 5% or more of the microporous membrane remains in the microporous membrane, it will swell during filtration and close the pores, resulting in increased water permeation resistance. Moreover, if it is less than 1%, there will be no hydrophilic effect and the function as a filter membrane will deteriorate. The desired polysulfone-based microporous membrane can then be manufactured by winding it up. [Example] Examples of the present invention will be shown below, but the present invention is not limited thereto. Examples 1 to 4 Comparative Example 1 15 parts of polysulfone (P-3500 manufactured by UCC), N
- 72 parts of methyl-2-pyrrolidone, 13 parts of polyvinylpyrrolidone, and 1.2 parts of water are uniformly dissolved to obtain a membrane-forming stock solution. This solution was cast in a stable solution state onto a glass plate through a casting coater to a product thickness of 180 μm, and air adjusted to 25°C and relative humidity of 50% was cast at a wind speed of 1.2 m/sec onto the liquid film surface. After exposure to water, the membrane was immediately immersed in a coagulation bath filled with water at 25°C to form a microporous membrane. After solidifying, the microporous membrane peels off from the glass plate in water.
The mixture was treated in diethylene glycol at 75°C for 5 minutes, and then washed with water to obtain a microporous membrane. The average pore diameter of the obtained membrane was 0.2 μm. Table 1 shows the changes in the amount of polyvinylpyrrolidone remaining in the membrane, the hydrophilicity of the membrane, and the water permeation rate of pure water when the diethylene glycol treatment temperature was changed.

【table】

[Table] Examples 5 to 7 Comparative Example 3 A microporous membrane was made under the same conditions as Examples 1 to 4,
A 50% glycerin aqueous solution is used instead of diethylene glycol as a polyhydric alcohol for washing out PVP, and the treatment is performed for 10 minutes at different treatment temperatures. Table 2 shows the properties of the films obtained in the same manner as in Examples 1 to 4 in all other respects.

〔Effect of the invention〕

In the method for producing a polysulfone-based microporous membrane comprising the steps of casting a solution of polysulfone and polyvinylpyrrolidone dissolved in a solvent on a support and immersing it in a coagulation bath, the obtained microporous membrane is A method for producing a polysulfone-based microporous membrane, which is characterized by washing with alcohol and then washing with water to adjust the content of polyvinylpyrrolidone in the membrane to 1 to 5%,
We were able to obtain a microporous membrane that has a high water permeation rate, a large filtration flow rate, and a long filtration life that can efficiently trap fine particles and bacteria. In addition, a small amount of polyvinylpyrrolidone acts as a plasticizer for polysulfone, giving flexibility to the membrane, making it possible to obtain a membrane with excellent cartridge processing suitability (processing into pleats).

[Brief explanation of the drawing]

Figure 1 shows a method for manufacturing a microporous membrane according to the present invention.
It is an explanatory diagram of an example. DESCRIPTION OF SYMBOLS 1...Dissolution pot, 2...Liquid pump, 3...Liquid injection device, 4...Support for casting, 5...Liquid film, 6...Air conditioning device, 7...Blowout port, 8... ...Coagulation liquid tank, 9
...Microporous membrane, 10... Support winder for casting, 1
1... Washing tank, 12... Polyhydric alcohol cleaning treatment tank, 13... Washing tank, 14... Dryer, 15...
Winding machine.

Claims (1)

[Claims] 1. A method for producing a polysulfone-based microporous membrane comprising a step of casting a solution of polysulfone and polyvinylpyrrolidone dissolved in a solvent onto a support and immersing it in a coagulation bath. A method for producing a polysulfone-based microporous membrane, which comprises washing with water after washing to adjust the content of polyvinylpyrrolidone in the membrane to 1 to 5%.