JPS62160110A - Manufacture of microporous membrane having large water permeability - Google Patents

Abstract

PURPOSE:To enhance filter flow without lowering separation power of micro porous membrane and offer a much longer life by casting and solidifying poly mer solution melted in polar organic solvent solution. CONSTITUTION:Resin of polysulfone and fluorine bases, polyamide of aliphatic family and the like are solved in good solvent, mixed solvent of good and non-solvents and mixture of several kinds of solvents carrying different dissolving degrees against polymer. Concentration is preferably 5-30 weight % and 1-60 weight % of electrolytic water solution having 0.5-10 volume % may be added. The said raw liquid for preparing membrane is cast over the substrate, which is impregnated immediately after casting or after a specified time. The membrane thus prepared is impregnated in non-solvent or non-solvent solution, and ultrasonic treatment for the same is carried out in the room temperature -60 deg.C for 5-30 minutes, which is then dried in the temperature under 80 deg.C. The porous membrane thus prepared can increase filter flow without lowering separation power.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Field of Application) The present invention relates to a method for producing a microporous membrane used for precision filtration of liquids. More specifically, the present invention relates to a method for producing a microporous membrane with a high filtration rate.

(Prior Art) Microporous membranes have been known for a long time (for example, in Synthetic Pol.
ymer Membrane), McGraw-Hill Company (M
(Published by Graw Hill Co.)) Widely used in filtration filters, etc. Microporous membranes are disclosed in, for example, U.S. Pat. No. 1,421,341, U.S. Pat. No. 39586,
As described in U.S. Pat. No. 48-40050, etc., those manufactured using cellulose ester as a raw material, U.S. Pat. 4,340.480, 4
No. 450.126, German patent DE 3,138,52
5, those manufactured using aliphatic polyamide as raw materials as described in JP-A-58-37842, etc., U.S. Pat. Nos. 4,196,070 and 4,340,482
No., JP-A-55-99934, JP-A-58-9173
Those manufactured using polyfluorocarbon as a raw material as described in No. 2, etc., JP-A-56-154051
No., JP-A-56-86941, JP-A-56-1264
There are those using polysulfone as a raw material as described in No. 0, etc., and those using polypropylene as a raw material as described in German patent oLs 3,003.400 and the like. These microporous membranes are used for filtration and sterilization of electronic industry cleaning water, medical water, water for pharmaceutical manufacturing processes, food water, etc., and their applications and usage have expanded in recent years, especially in terms of particle capture. Highly microporous membranes are attracting attention and are widely used.

(Problems to be Solved by the Invention) However, conventional microporous membranes cannot be said to have a sufficient filtration rate per unit area, and in order to obtain the required filtration flow rate, it is necessary to filter at a higher pressure, or In order to increase the membrane area, it is necessary to use many filtration units in parallel. Therefore, increasing the filtration speed in order to reduce the cost of the filtration process has been a technical challenge in the industry.

From this point of view, it has been known to treat the finished membrane with an organic solvent such as alcohol in order to modify the microporous membrane.
The issue describes a method for increasing the filtration rate by treating polysulfone semipermeable membranes with alcohol. However, in the case of this method, since the increase in filtration rate is due to the increase in the pore size of the membrane, this is not preferable as it involves a decrease in the separation ability that the membrane should originally maintain.

As a result of detailed investigation into the influence of ultrasound on microporous membranes, the present inventors found that when microporous membranes are subjected to ultrasonic treatment in the presence of a non-solvent, microporous membranes with a large amount of water permeate. The present invention was achieved by discovering that the following can be obtained.

Therefore, a first object of the present invention is to provide a method for manufacturing a microporous membrane that can increase the filtration flow rate per unit area.

A second object of the present invention is to provide a method for producing a microporous membrane with a long filtration life that can efficiently trap fine particles, bacteria, and the like.

(Means for Solving the Problems) The above aspects of the present invention include at least a step of casting a film-forming stock solution prepared by dissolving a polymer in a polar organic solvent, and a step of casting a film-forming solution prepared by dissolving a polymer in a polar organic solvent, and solidifying the solution at the same time as or after the casting. A microporous membrane obtained through a step of immersing in a bath to form micropores is immersed in a nonsolvent of the microporous membrane or a liquid mainly containing a nonsolvent,
This was achieved by a method for manufacturing a microporous membrane with a large permeation rate, which is characterized by ultrasonication to such an extent that the micropore size does not substantially change.

Microporous membranes that can be used in the present invention include known polymers such as polyvinylidene fluoride, fluorine-based resins such as polytetrafluoroethylene, polysulfone, polyethersulfone, aliphatic polyamide, cellulose ester, and polypropylene polyimide. These can be used alone or in combination as raw materials.

In the present invention, polysulfones are preferred among these, and polymers represented by the repeating units of or are particularly preferred.

In the production of microporous membranes, the above polymers are usually mixed with ■ a good solvent, and ■
Prepare a membrane-forming stock solution by dissolving it in a mixed solvent of a good solvent and a non-solvent, or a mixture of multiple types of solvents with different degrees of solubility for the polymer, and apply it on a support or directly into a coagulation solution. Cast, wash, and dry. In this case, examples of solvents that dissolve the polymer include dichloromethaneacetone, dimethylformamide, dimethylacetamide,
Dimethyl sulfoxide, 2-pyrrolidone, N-methyl-
Examples include 2-pyrrolidone, sulfolane, hexamethylphosphoramide, and the like.

Examples of nonsolvents added to the above solvent include cellosols, methanol, ethanol, propatool, acetone, tetrahydrofuran, polyethylene glycol, glycerin, and the like. The ratio of the nonsolvent to the good solvent may be in any range as long as the mixed liquid can maintain a uniform state, but is preferably 5% to 50% by weight.

In addition, an inorganic electrolyte, an organic electrolyte, a polymer, or an electrolyte thereof called a swelling agent may be added to control the porous structure.

Electrolytes that can be used in the present invention include salt,
Metal salts of inorganic acids such as sodium nitrate, potassium nitrate, sodium sulfate, zinc chloride, metal salts of organic acids such as sodium acetate, sodium formate, sodium polystyrene sulfonate, polyvinylbenzyltrimethylammonium chloride, polyvinyl alcohol, polyethylene glycol, polyvinylpyrrolidone Polymers such as or electrolytes thereof, ionic surfactants such as sodium dioctyl sulfosuccinate, sodium alkylmethyl taurate, etc. are used. Although these electrolytes exhibit some effects even when added alone to a polymer solution, they exhibit particularly remarkable effects when added as an aqueous solution.

The amount of the electrolyte aqueous solution to be added is not particularly limited as long as the addition does not impair the uniformity of the solution, but usually the solid content of the electrolyte aqueous solution is 0.5% to 10% by volume relative to the solvent. Further, there is no particular restriction on the concentration of the electrolyte 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 to 30% by weight.

If the concentration exceeds 35% by weight, the water permeability of the resulting microporous membrane becomes so low that it has no practical meaning, and if the concentration is lower than 5% by weight, a microporous membrane with sufficient separation ability cannot be obtained. do not have.

The membrane-forming stock solution prepared as described above is cast onto a support, and the polymer solution membrane together with the support is immersed in a coagulation solution immediately after casting or after a certain period of time.

As the coagulating liquid, water is most commonly used, but an organic solvent that does not dissolve the polymer may also be used, or a mixture of two or more of these non-solvents may be used.

The support can be arbitrarily selected from those that can be used as a support in the production of microporous membranes, but it is particularly preferable to use a nonwoven fabric since there is no need to peel off the support.

The nonwoven fabric that can be used in the present invention is generally made of polypropylene, polyester, etc., and is not limited in material.

The cast membrane in which the polymer has precipitated in the coagulation liquid is usually subsequently washed with water, warm water, machine solvent washing, etc.

The ultrasonic treatment performed in the present invention can be performed at any time after the micropores are formed, as long as the pore diameter of the micropores does not substantially change. That is, it may be done immediately after the above-mentioned washing step, before the washing step, or after the drying step; in this case, the above-mentioned normal washing step may be omitted. You can also do it.

In the present invention, in order to prevent the pore size of the micropores from changing due to the ultrasonic treatment, the treatment is performed by immersing the microporous membrane in a nonsolvent of the microporous membrane or a solution mainly containing a nonsolvent. This must be done according to certain conditions. Such processing conditions include a processing temperature ranging from room temperature to 60°C, preferably 40°C.
~55°C, the treatment time is 5 minutes to 30 minutes, preferably 10 minutes to 20 minutes, and after such ultrasonic treatment, the temperature is 80°C.
Thereafter, it is preferably dried at 40°C or lower.

The nonsolvent used during the above treatment is appropriately selected depending on the type of microporous membrane, but water, methanol, ethanol, isopropylpanol, ter-butanol, ethylene glycol, diethylene glycol, and triethylene glycol are particularly preferred. may be used alone or in combination of two or more. Further, in the present invention, a mixed solvent in which a solvent is added to these non-solvents can be used to shorten the processing time. In this case, if the amount of solvent is too large, the micropore diameter will become thick during ultrasonic treatment, which is undesirable.Although it varies depending on the type of solvent, it is preferable that the amount of solvent added is 5% by weight or less. Such solvents are appropriately selected depending on the type of polymer used, but in particular, dimethylacetamide, dimethylformamide, dimethyl sulfoxide, tetrahydrofuran, sulfolane, ethylene carbonate, N-methyl-2-pyrrolidone, 2 -Pyrrolidone and hexamethylphosphoramide are preferred.

The ultrasonic waves used in the present invention are preferably generated at an upper limit output that does not destroy the membrane structure, but generally have a frequency of 20 KHz to 40 KHz, preferably 25 KHz.
At ~28 KHz, the output of the camera is 3~10KW,
'n? It is appropriate to supply a medium with a resistance of about 1.

(Effects of the Invention) According to the present invention, the filtration flow rate of the microporous membrane can be improved very easily without reducing the inherent separation ability of the microporous membrane. Since the filtration efficiency of the membrane obtained according to the present invention is extremely high, the life of the microporous membrane with respect to the filtration flow rate is also greatly improved.

EXAMPLES Hereinafter, the present invention will be explained in more detail according to Examples, but the present invention is not limited thereto.

Note that the pore size measurement was performed according to the method of ASTM-316-70.

Example 1 23 parts of polyvinylidene fluoride, dimethylacetamide (
A mixed solution consisting of 68 parts of DMA) and 9 parts of polyvinyl alcohol was cast onto a glass plate to a thickness of 200 μm using a doctor blade, and after being left in the air for 30 seconds, water/DMA = 1/1 ( weight ratio) in a coagulating solution,
Allowed to solidify for 2 minutes. Next, it was washed with water for 10 minutes and dried at 40°C. The resulting membrane had a pore size of 0.08μ and a filtration flow rate of 20 mJ! /cj-min-atm. 20g of this membrane was placed at a frequency of 2 in 21 water tanks filled with water at 25°C.
Ultrasonic treatment was performed for 20 minutes at 5 KHz and an output of 200 W. The pore size of the membrane after treatment was 0.08μ, which was unchanged from before treatment, but the filtration flow rate was 34ml/-min.
-a t m, and it was demonstrated that the amount of permeated water was significantly improved.

Example 2 A homogeneous solution consisting of 15 parts of polysulfone (UCC P3500), 65 parts of N-methyl-2-pyrrolidone, 15 parts of polyvinylpyrrolidone (molecular weight 40,000) and 3 parts of LiCl was cast onto a glass plate to a thickness of 150 μm. Immediately thereafter, it was immersed in cold water, rinsed with water for 10 minutes, and then dried at 40°C. The pore size of the obtained membrane was 0°2μ, and the filtration flow rate was 3Q m
1/cri-min・atm. When this membrane was subjected to the same treatment as in Example 1, the filtration flow rate was 42 mβ/cIII·min -a t
The pore diameter after treatment was 0.2μ, which was the same as the pore diameter before treatment.

Example 3゜Example 2. The microporous membrane obtained in the same manner as in Example 2 before being subjected to ultrasonic treatment was left at room temperature for 3 days, and then subjected to ultrasonic treatment in the same manner as in Example 2. The same results as in Example 2 were obtained.

Claims (1)

[Claims] 1) At least a step of casting a film-forming stock solution prepared by dissolving a polymer in a polar organic solvent, and immersing it in a coagulation bath at the same time as or after the casting to form micropores. The microporous membrane obtained through the process is subjected to ultrasonic treatment while immersed in the nonsolvent of the microporous membrane or a liquid mainly consisting of a nonsolvent to the extent that the micropore size does not substantially change. A method for producing a microporous membrane with a large amount of permeated water, characterized by: 2) The nonsolvent is water, methanol, ethanol, isopropanol, ter-butanol, ethylene glycol,
The method for producing a microporous membrane with a large permeate amount according to claim 1, wherein the membrane is one or a mixture of two or more selected from diethylene glycol and triethylene glycol. 3) The solvent is one or more selected from dimethylacetamide, dimethylformamide, dimethylsulfoxide, tetrahydrofuran, sulfolane, ethylene carbonate, N-methyl-2-pyrrolidone, 2-pyrrolidone, and hexamethylphosphoramide. A method for producing a microporous membrane with a large permeable water amount according to claim 1 or 2, which is a mixture of.