JPH057054B2 - - Google Patents

Description

[Detailed description of the invention]

<<Industrial Application Field>> The present invention relates to a method for producing a microporous membrane, particularly an aqueous system used in the electronic industry, pharmaceutical industry, and food industry.
The present invention relates to a method for manufacturing a filter medium made from polysulfone for precision filtration of non-aqueous liquids. 《Prior art》 Microporous membranes have been known for a long time (for example,
“Synthetic Polymer Membrane” by R. Kesing
Published by McGraw Hill) Widely used in filtration filters, etc. Microporous membranes are disclosed in, for example, U.S. Patent No. 1421341, U.S. Pat.
As described in U.S. Patent No. 39586 and U.S. Pat.
4340479, 4340480, 4450126, German Pat.
No. 4340482, JP-A-55-99934, JP-A-58-
Products manufactured using polyfluorocarbon as raw materials as described in No. 91732, etc., JP-A-56
−154051, JP-A-56-86941, JP-A-56-
There are those made from polysulfone as a raw material, such as those described in German Patent No. 126407, and those made from polypropylene, as described in German Patent No. OLS3003400. These microporous membranes are used for filtering and sterilizing cleaning water for the electronic industry, water for medical purposes, water for pharmaceutical manufacturing processes, water for food use, etc., and their applications and usage have been expanding in recent years. Microporous membranes made from polysulfone are attracting attention because they are capable of filtering liquids containing acids and alkalis, as well as being used for most filtration applications, both aqueous and non-aqueous. family polysulfones are frequently used. However, since aromatic polysulfone is a material with low hydrophilicity, it is difficult to wet with water and has poor water permeability. In addition, when bubbles are mixed in the filtrate, the bubbles tend to stick to the filtrate. This method has the disadvantage that the air lock phenomenon occurs where the filtration efficiency becomes a dead space and the filtration efficiency deteriorates. Therefore, in order to improve water permeability, for example,
Adding inorganic salts such as ZnCl ₂ or organic substances such as alcohol to the membrane forming stock solution as a denaturing agent, or sulfonating polysulfone (journal of polymers).
Science, Vol. 20, p. 1885 (1976)) is conventionally performed. <<Problems to be Solved by the Invention>> However, in the former case, there is a drawback that the modifier dissolves out during use as a filtration membrane, and in the latter case, the sulfonation process is complicated, and Sulfonation causes disadvantages such as deterioration of film-forming ability and deterioration of mechanical performance, and that it cannot be used for liquids containing alkali. As a result of intensive studies to solve these conventional drawbacks, the present inventors found that when polysulfone is blended with a certain amount of sulfonated polysulfone, the film forming ability and the performance of the formed film are lower than that of the original polysulfone. We discovered that microporous membranes with good water permeability can be obtained by adding only a small amount of sulfonated polysulfone by selecting the coagulation liquid during membrane formation. The invention has been achieved. Therefore, the first object of the present invention is to provide a polysulfone microporous membrane with good water permeability. A second object of the present invention is to provide a polysulfone microporous membrane with sufficient biological stability and good water permeability without any eluate in the filtrate. A third object of the present invention is to provide a polysulfone microporous membrane with sufficient acid and alkali resistance and good water permeability. A fourth object of the present invention is to provide a method for imparting hydrophilicity to the surface of polysulfone without degrading its properties as a microporous membrane. <<Means for Solving the Problems>> The above-mentioned objects of the present invention are to combine 5 to 50% by weight of polysulfone having no dissociative groups and sulfonated polysulfone with a sulfonation rate of 0.2 to 2.0 to the polysulfone. A microporous membrane characterized by casting a membrane-forming stock solution dissolved in a polar organic solvent containing an amount of 0.1% by weight or more and less than 5% by weight, and coagulating the cast membrane in a hydrophilic coagulating liquid. This was achieved using the manufacturing method. The polysulfone used in the present invention is generally referred to as polysulfone A, that is, It is indicated by. n is a positive integer. Such polysulfones include, for example, Union Carbide Corporation's Udel P-1700 and Udel P-3500.
It is commercially available as (product name). The sulfonated polysulfone mentioned here is typically represented by the following general formula (). General formula () Here, M represents a cation such as hydrogen, an alkali metal, an amine, or an alkyl-substituted amine. Moreover, the introduction position of the sulfone group is not particularly limited. n is the above n
is the same as , and is a positive integer. These compounds can be prepared using conventional methods such as polysulfone.
Journal of Applied Polymer Science, Volume 20 (J.Appl.Polymer Sci.Vol.20),
It can be synthesized by sulfonation according to the method described on pages 1885-1903 (1976). Also, the sulfonation rate is
Although it can be controlled by the ratio of SO ₃ , in the present invention, it is preferably 0.1 to 4, particularly 0.2 to 2. Furthermore, M in the general formula () is preferably a monovalent cation, particularly preferably a hydrogen type. The film properties of sulfonated polymers deteriorate compared to those without sulfonation, except for the fact that they become hydrophilic, and as the amount of sulfonated polysulfone increases, alkali resistance deteriorates. The amount of sulfonated polysulfone used is preferably 60% by weight or less, particularly 10% by weight or less of the polysulfone in the membrane forming stock solution, and in order to impart hydrophilicity to the surface of the microporous membrane,
It is preferably 0.1% by weight or more. 0.1% by weight
If it is less than 60% by weight, a membrane with sufficient hydrophilicity cannot be obtained, whereas if it is more than 60% by weight, the mechanical strength originally possessed by polysulfone is lost, which is not preferable. The range that satisfies sufficient hydrophilicity and mechanical strength is 1 to 10% by weight. Since the sulfonated polysulfone used in the present invention and polysulfone have the same skeleton, they are easily compatible with each other, and especially when the amount of sulfonated polysulfone is just enough to cover the surface of the microporous membrane, the sulfone group can be transferred to the membrane. By facing outward, only the surface can be stably made hydrophilic while maintaining the original physical properties of polysulfone. Thus, it is extremely important in the present invention to orient the sulfone groups outside the membrane, and this can be achieved by selecting the coagulation liquid. Next, the method for manufacturing the microporous membrane of the present invention will be explained in more detail. First, polysulfone is dissolved in a solvent that dissolves in water, such as dimethylacetamide, dimethylformamide, tetrahydrofuran, 2-pyrrolidone, N-methyl-2-pyrrolidone, etc., and further, if necessary, to control the pore size. Solvents that are poor solvents for water or polysulfone and are soluble in water, such as alcohols such as methanol, ethanol, and isopropyl alcohol, glycols such as ethylene glycol and propylene glycol, polyethylene glycol, polypropylene glycol, polystyrene sulfonic acid, polyvinylpyrrolidone, etc. Add a water-soluble polymer, etc. to prepare a polymer solution. The amount of sulfonated polysulfone used in the present invention is 0.1 to 60% by weight, preferably 1% by weight, based on the polysulfone in this stock solution.
Add and dissolve about 10% by weight to prepare a polysulfone film forming stock solution. This stock solution is cast onto a glass plate using a doctor blade to a thickness of 150 μm, and immersed in water, which is a coagulation solution, to obtain a polysulfone film. Even if the membrane thus obtained is in a dry state, when it is floated on water, water immediately seeps from the back surface to the surface due to the hydrophilic nature of the membrane. <<Effect>> This is due to the fact that when polysulfone precipitates and coagulates in the coagulating liquid, the sulfonic acid groups of the sulfonated polysulfone are preferentially oriented toward the aqueous phase in contact with the surface, and the coagulating liquid This phenomenon occurs only when is water or a hydrophilic solution. That is, in the coagulation liquid, preferential orientation of the sulfone groups occurs due to the surface activity of the sulfonated polysulfone at the polymer phase/water interface, and as a result, only a few percent of the sulfonated polysulfone with respect to the polysulfone Extremely effective hydrophilicity can be exhibited even with the added amount. Therefore, coagulating liquids with weak hydrophilicity, such as butanol and amyl alcohol, are difficult to cause interfacial orientation of sulfonated polysulfone, making it impossible to obtain a film with sufficient hydrophilicity. However, if a coagulating liquid is hydrophilic, Whether they are used alone or in combination, a microporous membrane that achieves the object of the present invention can be obtained. Examples of the hydrophilic coagulating liquid that can be used in the present invention include water, methanol, ethanol, isopropyl alcohol, glycerin, polyethylene glycol, and mixtures thereof. The microporous membrane obtained according to the present invention has a hydrophilic surface while retaining the mechanical properties, acid and alkali resistance, etc. inherent to polysulfone, and thus has significantly improved water permeability. Furthermore, since the amount of sulfonated polysulfone used is small, the complicated step of sulfonation can be kept to a minimum. In addition, since the sulfonated polysulfone has the same skeleton as the polysulfone, the compatibility between the two is good, and the alkali resistance is also sufficient. EXAMPLES The present invention will be explained in more detail below with reference to Examples, but the present invention is not limited thereto. <<Example>> Synthesis Example 1 Synthesis of sulfonated polysulfone A solution of 18.6 g (0.102 mol) of triethyl phosphate dissolved in 125 ml of 1,2-dichloroethane was cooled, and 16.3 g of sulfuric anhydride was added while keeping the temperature below 25°C.
(0.204 mol) was slowly added, SO ₃ /(C ₂ H ₅ O) ₃
PO created a 2/1 complex. Next, this solution was mixed with 45.1 g (0.34 mol, repeating unit) of PSF (polysulfone, Union Carbide Co., Ltd. Udel P3500 [trade name]) in 1,2-dichloroethane.
The solution dissolved in 300 ml was simultaneously dropped into 330 ml of 1,2-dichloroethane while stirring vigorously.
The generated precipitate turned into a slurry when the temperature was raised to 35°C, and this was stirred for 30 minutes. The slurry was collected by filtration, washed twice with 1,2-dichloroethane, and dried under reduced pressure at 60°C. In this way, one _-SO3H was introduced per repeat unit of PSF.
The yield was 60g. Synthesis Example 2 Synthesis of Sulfonated Polysulfone Sodium Salt 165 ml of isopropanol was added to the free acid slurry synthesized in the same manner as in Synthesis Example-1 and dissolved.
Add to this an excess of 22.0g of sodium methoxide.
A 28% methanol solution containing (0.408 mol) was added. After neutralizing with hydrochloric acid, it was washed twice with isopropanol and twice with distilled water. 1.0− with one −SO ₃ Na per repeating unit of PSF after drying under vacuum at 90°C.
51 g of white powder of SO ₃ Na/PSF was obtained. Example 1 Polysulfone (Union Carbide Corporation Udel P3500) 10%, N-methyl-
2-pyrrolidone 75%, polyethylene glycol
For a 100015% solution, add sulfonated polysulfone (acid type) to polysulfone at 0%, 1%, 3%,
It was added to a concentration of 5% and dissolved with stirring. However, all percentages are by weight. The membrane-forming stock solution was cast onto a glass plate to a thickness of 150 μm, and the plate was immersed in water (25°C) to obtain a microporous membrane. In order to examine the hydrophilicity of the obtained membrane, the dried membrane was floated on the water surface, and the time taken for water to penetrate the surface was measured, and the results are shown in the table.

[Table] As is clear from the table, it was demonstrated that the case of the present invention in which sulfonated polysulfone was added had extremely good hydrophilicity. Example 2 The membrane-forming stock solution used in Example 1, in which 5% of sulfonated polysulfone was added to polysulfone, was cast onto a glass plate and immersed in the following coagulation solution to obtain a microporous membrane. The results of examining hydrophilicity in the same manner as in Example 1 were as follows:
It was as shown in the table.

[Table] As is clear from the results in the table, when a hydrophilic coagulation liquid is used, the water permeation time of the resulting microporous membrane is shorter, resulting in a microporous membrane with good hydrophilicity. It has been proven that it is more suitable for

Claims (1)

[Claims] 1 5 to 50% by weight of polysulfone that does not have a dissociative group and a sulfonation rate of the polysulfone.
Casting a film-forming stock solution dissolved in a polar organic solvent containing 0.1% by weight or more and less than 5% by weight of 0.2-2.0 sulfonated polysulfone, and coagulating the cast film in a hydrophilic coagulating liquid. A method for producing a microporous membrane characterized by: