JPH0585576B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a method for producing a microporous membrane, and is particularly 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. Used for filtration of purified water, pure water, etc. used in the electronics industry, nuclear power industry, and laboratories of various industries that perform various processing, and other precision filtration. The following describes a method for manufacturing a microporous membrane for precision filtration that efficiently filters submicron-order fine particles and microorganisms. [Prior Art] Regarding microporous membranes for precision filtration, which are conventionally used for removing fine particles of about 0.1 to 5 μm in aqueous and non-aqueous systems and bacteria in the fields of pharmaceutical, food, electronic, and nuclear industries, and their manufacturing method. Disclosed are those made from cellulose ester, aliphatic polyamide, polyfluorocarbon, polysulfone, polypropylene, etc.
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.
It is classified as having a structure called an asymmetric membrane, 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. Among these, symmetrical membranes are described in JP-A-58-98015, but during filtration, the entire membrane presents a large resistance to the flow of fluid, 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 of the membrane, and relatively large pores on the lower surface of the other membrane. This dense layer captures virtually all the smallest particles that can be filtered out, allowing the entire membrane thickness to be effectively utilized as a filter medium, increasing the filtration flow rate if used carefully. In this sense, it is an excellent microporous membrane. [Problem to be solved by the invention] However, although the dense layer is extremely important in this case, conventionally, this dense layer is on the surface and is easily damaged by scratches or other causes, preventing the leakage of fine particles. The drawback is that it is easy to break. In order to compensate for this drawback, a structure in which a dense layer, that is, a layer with a small pore size, exists inside the filtration membrane is desired. A structure has 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. For these reasons, there has been a strong desire in the art to realize a structure having a dense layer within a single film. In order to solve the above-mentioned drawbacks, the inventors of the present invention have attempted to cause microphase separation by leaving a polymer stock solution in the air for a certain period of time after casting, which has been one of the conventional methods for producing microporous membranes. As a result of a detailed study of the dry wet method, which controls the diameter of micropores, we found a method in which the solvent is sufficiently evaporated (e.g., JP-A No. 102416/1983), and a method in which the solvent is immersed in a coagulation bath without evaporating much of the solvent. (For example, JP-A No. 55-8887 and JP-A No. 56-154051). Surprisingly, when the evaporation of the solvent and the amount of absorption of non-solvent vapor are appropriately controlled, microporous membranes It has been found that a layer with the minimum pore size can be formed inside the membrane in the direction perpendicular to the membrane surface. The present inventors also analyzed the mechanism of filtration and clogging, and the relationship between specific surface area and filtration life, and found that if the membrane structure is made extremely asymmetric, the specific surface area of the membrane becomes smaller, and the inlet side upstream of the minimum pore size layer decreases. The reason is that the part of the membrane does not function effectively as a prefilter, and that the particles that are captured are not necessarily captured in the pores that are smaller than the particle diameter, and that most of the particles are attached to the inner wall of the membrane and are captured. These two points are important factors related to filtration life, and therefore, it is rational to extend filtration life by increasing the specific surface area of the membrane without creating an extremely asymmetric membrane. As a result of this discovery and further intensive research, we found that by controlling the evaporation of the solvent and the amount of non-solvent absorbed from the atmosphere during the period from casting the film-forming stock solution to immersing it in the coagulation solution, 8.
We discovered that it is possible to achieve a specific surface area of m ² /g or more, thereby extending the life of a microporous membrane, and filed an application for such a microporous membrane (patent application). (Sho 61-148192). An object of the present invention is to provide an improved manufacturing method for the microporous membrane previously applied for. Accordingly, a first object of the present invention is to provide a method for producing a microporous membrane with low filtration resistance and high filtration flow rate. A second object of the present invention is to provide a method for producing a microporous membrane whose filtration performance is less likely to deteriorate due to surface defects. A third object of the present invention is to provide a method for producing a microporous membrane that can efficiently trap fine particles, bacteria, etc. and has a long filtration life. [Means and effects for solving the problems] The above-mentioned object of the present invention is to apply a membrane-forming stock solution prepared by adding a swelling agent and a non-solvent to a polymer and dissolving it in a solvent onto a casting support in a solution state. The solvent was evaporated and the moisture in the air was absorbed into the cast liquid film by blowing controlled moist air or by infrared radiation and blowing controlled wet air to cause coacelvation. After that, the liquid film is immersed in a coagulation bath to perform phase separation and coagulation to form a microporous film, and then the microporous film is peeled off from the casting support. This was achieved by a method for producing a transparent membrane. In the present invention, a preferable result can be obtained by evaporating the solvent and absorbing the moisture in the air by irradiating the liquid film with infrared radiation and/or blowing temperature-controlled moist air. The first embodiment of the method for producing a microporous membrane of the present invention is described below.
This will be explained using figures. In FIG. 1, a polymer is melted in a melting pot 1 with a jacket. At that time, non-solvents, swelling agents, etc. necessary for forming micropores are added and mixed. After defoaming, this solution is sent to a casting injector 3 by a liquid feed pump 2, and the solution in a stable solution state is poured from the injector 3 onto a polyester film serving as a casting support 4. It is cast as a membrane 5. By applying air regulated by an air conditioner 6 to the surface of the cast liquid film 5 from the outlet 7, or by applying regulated air from the outlet 7 and irradiating infrared rays from the infrared irradiation panel 14, After coacervation occurs in the liquid film by controlling the evaporation of the solvent and the absorption of moisture in the air, a coagulation liquid tank is provided that absorbs a liquid that is a non-solvent for the polymer and is compatible with the polymer's solvent. 8. After the liquid film 5 is cast, it is exposed to air whose temperature, humidity, and air volume are adjusted, or when it is exposed to this adjusted air, core cells are formed from the surface of the liquid film inward by infrared radiation. A fine coacelvation phase is formed inside the liquid film 5 from the surface thereof, and the coagulation phase is fixed as micropores in the coagulation liquid tank 8, and at the same time, the liquid film 5 undergoes phase separation. is caused to form pores other than micropores, and the 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 passed through a washing tank 11, a dryer 12, and then wound up by a winder 13. The membrane-forming polymer used in the present invention is not particularly limited, and can be selected depending on the use of the porous membrane and other purposes. Examples of such polymers include cellulose acetate, nitrocellulose, polysulfone, sulfonated polysulfone, polyethersulfone, polyacrylonitrile, styrene-acrylonitrile copolymer, styrene-butadiene copolymer, saponified ethylene-vinyl acetate copolymer, polyvinyl alcohol, and polycarbonate. , organosiloxane-polycarbonate copolymer, polyester carbonate, organopolysiloxane, polyphenylene oxide, polyamide, polyimide, polyamideimide, polybenzimidazole, and the like. In the present invention, it is particularly preferable to use polysulfone and/or polyether sulfone as the membrane-forming polymer.

[ka] or

〔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 13 parts of polysulfone (P-3500 manufactured by UCC),
N-methyl-2-pyrrolidone, 72 parts, polyvinylpyrrolidone, 12 parts, lithium chloride, 2 parts, water 1,
Two parts were uniformly dissolved to obtain a membrane forming stock solution. This was cast onto a glass plate in a stable solution state to a product thickness of 180 μm, and passed under an infrared panel heater surface temperature of 300°C for varying passing times.
Immediately immersed in a coagulation bath filled with water at 25°C to obtain a microporous membrane. Table 1 shows the results of measuring the depth of the dense layer of each film using an electron microscope. In addition,
The average pore diameter was measured using the ASTM-316-80 method.

[Table] As is clear from the above, the average pore diameter can be changed by changing the transit time of infrared radiation. It can also be seen that the depth of the compact layer changes. Examples 5 to 10, Comparative Example 2 15 parts of polysulfone (manufactured by UCC P-3500),
70 parts of N-methyl-2-pyrrolidone, 15 parts of polyvinylpyrrolidone, and 3.0 parts of water were dissolved to form a uniform solution. This solution is cast onto a glass plate using a casting coater using a doctor blade in a stable solution state to a product film thickness of 180 μm, and air at 70°C and relative humidity of 9% is applied to the surface of the cast liquid film. 0 seconds, 4 seconds, 8 seconds, 10 at wind speed 1.2m/sec
Immediately after hitting for 2 seconds, 15 seconds, 30 seconds, and 60 seconds.
A microporous membrane was obtained by immersion in a coagulation bath filled with water at 25°C. Table 2 shows the results of measuring the depth of the dense layer of each film using an electron microscope.

[Table] As is clear from the above, when the temperature-controlled moist air exposure time is 0 seconds, the dense layer is on the top surface, which is not desirable because it cannot protect the surface from friction. It has been shown that the pore size and the depth of the compact layer vary. Comparison of Comparative Examples 3 and 4 and Example 6 A polyvinylidene fluoride membrane with an average pore diameter of 0.2 μm commercially available as a symmetric membrane (Comparative Example-3), and a commercially available asymmetric membrane with an average pore diameter of 0.2 μm having a dense layer on the outermost surface. Comparison of water permeation rate and fine particle removability for three types of membranes: a polysulfone membrane (Comparative Example 4), and the membrane of Example 6 of the present invention (average pore size 0.2 μm), which is an asymmetric membrane with a dense tank inside the membrane. Polystyrene latex with an average particle diameter of 0.236 μm manufactured by Dow Corning was filtered through 10 ⁶ particles per unit area, and the number of leaked particles was measured. The filtration area is ^15cm2 .

[Table] From the above results, it can be seen that the membrane of the present invention is excellent in both water permeation rate and particle trapping performance. Examples 11 to 13 The same film forming solution as in Examples 5 to 10 was cast onto a glass plate using a casting coater using a doctor blade so that the product film thickness was 180 μm. 30
The casted glass plate was placed in an atmosphere controlled by an infrared panel heater so that the surface temperature was 100°C, with a relative humidity of 65%, a wind velocity of 1.2 m/s, and a passing time of 0 seconds. 4 seconds, 8 seconds,
25 immediately after passing at such a speed as to be 10 seconds.
A microporous membrane was obtained by immersion into a coagulation bath filled with water at .degree. Table 3 shows the results of measuring the depth of the dense layer of each film using an electron microscope.

〔Effect of the invention〕

The membrane manufactured by the method for manufacturing a microporous membrane of the present invention has a minimum pore size layer inside the membrane and also has a thick dense layer, so it has high particle trapping performance. Furthermore, since the membrane has a pore size distribution in the thickness direction, the entire membrane can be effectively used as a filter medium. Therefore, the filtration resistance is small, the water permeation rate is fast, and the filtration flow rate can be increased.
It also has a long life as a filter medium. Furthermore, since the minimum pore size layer exists inside the membrane rather than on the surface of the membrane, the risk of damage due to external trauma is alleviated, and it is not only extremely advantageous in handling, but also a single sheet of ordinary microporous membrane. It is extremely advantageous because it can also be used in cartridge type filters in exactly the same way as in the case of . It has become possible to efficiently and stably manufacture such membranes, and the improvement in filtration membrane performance will greatly contribute to the industry.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of one embodiment of the manufacturing process according to the method for manufacturing a microporous membrane of the present invention. 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... Dryer, 13... Winder, 14... Infrared irradiation panel.

Claims (1)

[Claims] 1. A film-forming stock solution made by adding a lubricant and a non-solvent to a polymer and dissolving it in a solvent is cast in a solution state onto a casting support, and the cast liquid film contains evaporation of the solvent and moisture in the air. The liquid film is absorbed by blowing temperature-controlled moist air or by infrared radiation and temperature-controlled moist air blowing to cause coacelvation, and then the liquid film is immersed in a coagulation bath to undergo phase separation and coagulation. A method for producing a microporous membrane, which comprises forming a porous membrane and then peeling the microporous membrane from the casting support.