JPS6130803B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a reinforced permeable membrane, and particularly to a reinforced permeable membrane that has excellent mechanical strength, heat resistance, PH resistance, etc. Membrane separation processes using permeable membranes are widely used for reverse osmosis, ultrafiltration, precision filtration, etc. Among these, permeable membranes used for reverse osmosis and ultrafiltration generally have a skin layer on the surface. It is a polymer membrane in which a dense and thin layer called a sponge layer is integrally supported by a coarse porous structure called a sponge layer, so the mechanical strength of the permeable membrane as a single unit is extremely low.
As it is, it is difficult to put it into practical use industrially. For example, in actual membrane separation using a tubular permeable membrane, the inside of the tube is not only pressurized, but also negative pressure may be applied when the operation is interrupted, and sponge balls larger than the inner diameter of the tube are placed inside the tube. Although it is common practice to allow the membrane to pass through and scrub the membrane surface, a single tubular permeable membrane is easily damaged in such a case. In order to solve these problems, reinforced permeable membranes have already been proposed in which the permeable membrane is directly formed on a sheet-like or tubular base material made of woven fabric, non-woven fabric, or the like. For example, JP-A-54-14376 discloses a tubular permeable membrane in which a polysulfone ultrafiltration membrane is formed on the inner surface of a polyester nonwoven fabric tube. but,
Regarding this polysulfone membrane example, originally,
While polysulfone has a high glass transition temperature and excellent alkali resistance, polyester is easily hydrolyzed in alkaline aqueous solutions, so it can only permeate under limited conditions that do not impair the properties of polyester. It is only possible to improve the mechanical strength of the membrane. Additionally, reinforced permeable membranes based on polyethylene nonwoven fabric are already known, but polyethylene generally does not have sufficient heat resistance and cannot be used for membrane separation at high temperatures. On the other hand, as membrane separation processes become more widespread, reinforced permeable membranes with superior mechanical strength at higher temperatures and in a wider PH range are required. is still unknown. As a result of intensive research to meet this demand, the present inventors have found that when a nonwoven fabric made of polypropylene single fibers with specific physical properties is used as a base material, it has excellent mechanical strength, heat resistance, and PH resistance. The inventors have discovered that it is possible to obtain a reinforced permeable membrane, and have arrived at the present invention. The reinforced permeable membrane of the present invention is made of polypropylene single fibers with a diameter of 10 to 33μ, and has a thickness of 0.05 to 2 mm.
Basis weight 20~600g/ ^m2 , air permeability 0.2~55c.c./ ^cm2 /
It is characterized in that a permeable membrane is formed on a base material having a sec nonwoven fabric layer on its surface. Air permeability here is a value measured at a differential pressure of 12.7 mm in the water column using a Frazier type air permeability tester in accordance with the method specified in JIS L1079.
It is a measure of the ease with which air passes through a woven fabric. In the present invention, the anisotropic permeable membrane having a skin layer on the surface and integrally supporting the skin layer with a sponge layer preferably includes single fibers of a nonwoven fabric layer in at least a part of the sponge layer. Tsutsu,
It is formed integrally with this. For this purpose, when an organic solvent solution of the polymer that is the membrane material, that is, a dope, is applied onto the nonwoven fabric layer, a portion of it must penetrate into the network structure of the nonwoven fabric. By bringing the doped film applied onto the layer into contact with a coagulating solvent, a permeable film is formed that is free from defects such as pinholes, has excellent uniformity, and has a peeling force between it and the nonwoven fabric layer that is large enough for practical use. In order to achieve this, it is necessary that the dope be uniformly applied onto the nonwoven fabric. In order to satisfy these conditions, the polypropylene nonwoven fabric must have strictly specified physical properties. Therefore, in the present invention, the polypropylene nonwoven fabric is formed from single fibers with a diameter of 10 to 33μ, preferably 12 to 25μ. and has a thickness of 0.05 to 2 mm, preferably 0.10 to 0.50 mm, particularly preferably 0.12 to 0.40 mm, and a basis weight of 20 to 600 g/m ² , preferably 70 to
250 g/m ² and an air permeability of 0.2 to 55 c.c./cm ² /sec, preferably 0.5 to 50 c.c./cm ² /sec. It is desirable that the nonwoven fabric is made entirely of polypropylene single fibers, but if the amount is 30% by weight or less, polyethylene, polyester,
Synthetic fibers such as polyamide, acrylic, vinylon, etc.
Even if it contains natural fibers such as cotton and silk, and inorganic fibers such as glass fibers, there is no particular problem since the properties of the polypropylene nonwoven fabric are substantially maintained. Further, in the present invention, the base material may be formed from either a single layer or a multilayer nonwoven fabric layer, but the surface on which the permeable membrane is formed is required to be a polypropylene nonwoven fabric layer as described above. On the other hand, as mentioned above, the wettability between the dope and the nonwoven fabric and the viscosity of the dope are also important factors in order for the dope to impregnate the nonwoven fabric and be applied uniformly thereon. The dope is prepared using the common organic solvents used in its preparation, such as dimethylformamide (DMF), dimethylacetamide (DMA), dimethyl sulfoxide (DMSO), N-
Methylpyrrolidone (NMP), sulfolane, hexamethylphosphoramide, ethylene carbonate,
It was confirmed that as long as dioxane, tetrahydrofuran, cyclohexanone, acetone, etc. were included, there were no particular problems over a wide viscosity range of 1.5 to 3000 poise. The dope may also contain any additives conventionally used for this purpose in order to adjust the pore size of the resulting permeable membrane. Specific examples of such additives include inorganic salts such as sodium chloride, lithium chloride, lithium nitrate, sodium sulfate, potassium thiocyanate, ammonium nitrate, acetone, methanol, propanol, ethylene glycol, glycerin, methoxyethanol, cellosolve, Low molecular weight organic compounds such as urea, ethylenediamine, formic acid, acetic acid, potassium formate, sodium acetate, sodium citrate, sodium polysulfonesulfonate, polyvinyltrimethylammonium chloride, polyacrylic acid, polyvinyl alcohol, polyvinylpyrrolidone, polyvinyl methyl ether, polyethylene Mention may be made of high molecular weight organic compounds such as glycols. However, as is well known, these additives need to be dissolved uniformly in the dope and also in the coagulation solvent of the dope. In the present invention, the shape of the base material is not particularly limited, but a tubular base material is preferably used. As explained above, the tubular permeable membrane is particularly required to have mechanical strength because negative pressure is applied inside the tube and the membrane surface is cleaned using a sponge ball. In the present invention, the polymer as a membrane material is not particularly limited, and various polymers such as polysulfone, polyimide, polybenzimidazole, polyamide, polyacrylonitrile, polyvinyl alcohol, and crosslinked polyethyleneimine can be used, but in particular,
Polysulfone is preferred because it can enhance mechanical strength while fully exhibiting the excellent properties of the polymer. As is already known, polysulfone is A polymer having structural units such as As mentioned above, such polysulfone has excellent heat resistance and PH resistance, and on the other hand, the properties of polypropylene nonwoven fabric do not substantially change at temperatures up to 125°C and in the PH range of 0 to 14. This is because mechanical strength can be maintained under any conditions in which a semipermeable membrane made of polysulfone is used. In the present invention, as described above, it is preferable that the dope is coated on the base material to impregnate the nonwoven fabric layer on the surface of the base material, and that the film is formed integrally with the base material. A single permeable membrane obtained by applying a dope to a base material may be adhered onto a polypropylene nonwoven fabric layer. For example, a film is formed by coating the inner surface of a glass tube with dope and immersing it in a coagulating solvent.
A polypropylene nonwoven fabric is wrapped around the single tubular permeable membrane thus obtained and fused using an ultrasonic welder or the like. In addition, whether the permeable membrane is integrally formed on the nonwoven fabric or a single permeable membrane is bonded onto the nonwoven fabric, the surface of the nonwoven fabric must be corona treatment, flame treatment,
It may be subjected to sputter etching treatment, mechanical roughening treatment, or undercoated with resin such as melamine resin or chlorinated polypropylene. The reinforced permeable membrane according to the present invention has a permeable membrane formed on a polypropylene nonwoven fabric layer having specific physical properties, so it has excellent mechanical strength, heat resistance, PH resistance, etc. Peeling force
A reinforced membrane having a mechanical strength of 15 g/10 mm width or more can be obtained. If it has such a peeling force, it is practically sufficient in terms of pressure resistance and negative pressure resistance, especially in the case of commonly used tubular permeable membranes with a tube diameter of about 3 to 30 mm, and it is also effective when cleaning sponge balls. No abnormality occurs even when the sponge ball passes over 10,000 times back and forth. The invention is particularly advantageous when the permeable membrane is integrally formed with the nonwoven layer. That is, when the dope is applied onto the nonwoven fabric layer during film formation, the dope penetrates into the nonwoven fabric layer and forms a uniform coating on the nonwoven fabric layer, so there are no film defects such as pinholes,
In addition, a permeable film with a high peeling force can be obtained. Below are reference examples of dope preparation and examples of the present invention applied to tubular permeable membranes. Parts indicate parts by weight. Note that although the examples show a reinforced permeable membrane for relatively low pressures, which has performance equivalent to that of a so-called ultrafiltration membrane, the present invention is naturally applicable to reinforced membranes for high pressures, that is, reverse osmosis membranes. can. Further, although the following examples relate to tubular membranes, the present invention is naturally applicable to flat membranes used in spiral-type modules, plate-and-frame types, and the like. Reference Example (Preparation of Dope) Dope (1) was obtained by uniformly dissolving 15 parts of polysulfone (Union Carbide P-1700) consisting of the structural unit of the above formula () and 3 parts of lithium chloride in 82 parts of dimethylformamide. Ta. Similarly, the first
Dopes (2) to (4) shown in the table were obtained. In addition, ethylene-vinyl alcohol copolymer (vinyl alcohol content 31 mol%, saponification degree 99.6
Add 22 parts of a DMSO solution (mol%, 3 wt% viscosity 12 centipoise at 30°C) to 70 parts of DMSO and 8 parts of water, stir at a temperature of 80°C for 6 hours to dissolve,
Got dope (5). Add 18 parts of polyvinylidene fluoride (Kureha Chemical Industry Co., Ltd. KF Polymer #1100) to 82 parts of DMSO and stir at a temperature of 90°C for 6 hours to dissolve.
Got dope (6).

[Table] Example 1 A polypropylene nonwoven fabric tape with a width of 28 mm having the physical properties shown in Table 2 was spirally wound on a mandrel with the side edges partially overlapping each other, and the overlapping portion was heated using an ultrasonic welder. The inner diameter
A 12.0 mm polypropylene nonwoven tube was manufactured. The dope (1) shown in Table 1 was applied to the inner surface of the tube using a bob, and then immediately immersed in water at 5° C. to gel the dope, thereby forming a polysulfone ultrafiltration membrane on the inner surface of the nonwoven tube. This reinforced membrane has a pure water permeation rate and a molecular weight of 20,000 as measured by the method explained later.
The rejection rate of polyethylene glycol is 12 respectively.
m ³ /m ² ·day and 85%. When this ultrafiltration membrane was subjected to a heat resistance test using the method described later, the pure water permeation rate after heating was 11 m ³ /m ² ·day, and the rejection rate was 87%. In addition, regarding PH resistance, the pure water permeation rate is 11 after immersion in alkaline aqueous solution.
m ³ /m ² ·day, the above exclusion rate was 85%. Examples 2 to 9 Reinforced tube permeable membranes were obtained in the same manner as in Example 1.
Table 2 shows the physical properties of these permeable membranes. Comparative examples 1 to 4

[Table] A reinforcing membrane was manufactured according to the method of Example 1, and the physical properties of the membrane were evaluated. In Comparative Example 1, a nonwoven fabric made only of polyester was used, in Comparative Examples 2 and 3, a two-layer nonwoven fabric with an inner layer made of polyethylene and an outer layer made of polyester was used, and in Comparative Example 4, the fiber diameter was within the range specified in the present invention. A polypropylene nonwoven fabric consisting of large single fibers was used. Example 10 A uniform dope was prepared by dissolving 19 parts of the same polysulfone and 5 parts of lithium chloride as in Example 1 in 76 parts of dimethylformamide, and this dope was applied to the inner surface of a glass tube in the same manner as in Example 1 to form a film. did. next,
The polypropylene nonwoven fabric shown in the table was immersed in a 3% toluene solution of chlorinated polypropylene, then treated with chlorinated polypropylene by volatilizing the toluene at 120°C, and then spirally wound on the surface of a tubular permeable membrane extracted from a glass tube. Then, the overlapped parts were fused using an ultrasonic welder to obtain a reinforced permeable membrane, which was further inserted into a porous glass fiber reinforced plastic tube, and heated with 80℃ hot water for 1 hour under a pressure of 5Kg/ ^cm2 . After passing the liquid through it, the items shown in the table were tested.
The results are shown in the table. The abbreviations and test methods among the items in the table are as follows. (1) Nonwoven fabric material: PP is polypropylene, PET is polyester (polyethylene terephthalate), PE is polyethylene, and the number in parentheses indicates the material of the outer layer of a two-layered nonwoven fabric tube. (2) Film thickness: The value obtained by subtracting the thickness of the nonwoven fabric from the thickness of the reinforcing film after film formation. (3) Peeling force: The reinforcing tubular membrane was cut open along the cohesive zone and peeled at a temperature of 20°C for 4 days, then at a temperature of 50°C for 3 days.
After drying for a period of time to remove water from the reinforcing membrane, a 1 mil thick polyester-based adhesive tape (Nitto Electric Industry Co., Ltd. No. 31B) was pasted on the surface of the dried membrane at a temperature of 23°C. Peel resistance was measured at a relative humidity of 60%, a peel angle of 90°, and a peel rate of 300 mm/min. (4) Pressure resistance: Close one end of a reinforced tubular membrane with a length of 1 m, and gradually pressurize it by introducing air from the other end while immersed in water, and measure the pressure when air bubbles form from the outer surface of the base material. It was displayed in (5) Negative pressure resistance: A reinforced tubular membrane with a length of 1 m is inserted into a 1 m long transparent tube with an inner diameter 0.1 to 0.5 mm larger than its outer diameter and 50 small holes of 1 mm in diameter, and submerged in water. The membrane was immersed in water and maintained for 5 minutes at a reduced pressure of 600 mmHg, and the presence or absence of dents or peeling of the permeable membrane was observed. (6) Sponge ball test: A polyvinyl formal sponge ball with a diameter 2 mm larger than the inner diameter of the reinforced permeable membrane was moved back and forth within the permeable membrane at a rate of 2 times/minute using water pressure, and no abnormality was observed after 10,000 reciprocations. It was judged as good when it did not occur, and bad when abnormalities such as breakage of the permeable membrane were observed after 2000 reciprocations or less. (7) Heat resistance: After immersing the tubular permeable membrane in heated water at 120°C for 30 minutes, measure the water permeation rate and rejection rate under the conditions described below. When the value decreased, it was considered a failure and expressed as the number of failed products/number of tested products (10 products). (8) PH resistance: After immersing the tubular permeable membrane in an aqueous sodium hydroxide solution of PH 13.5 at 40°C for 10 days, it was thoroughly washed with water and evaluated in the same manner as in the case of heat resistance. (9) Water permeation rate: A tubular reinforced membrane was inserted into a porous glass fiber reinforced plastic tube, and water was supplied at a temperature of 25℃ and a pressure of 2Kg/cm ² to measure the pure water permeation rate, and the average molecular weight was 16000. A 0.5% by weight aqueous solution of polyethylene glycol was supplied at a temperature of 25°C, a pressure of 2 Kg/cm ² , and an average linear velocity of 3.0 m/s, and rejection rate = (1 - concentration in permeate / concentration in feed stock solution) × 100
(%) The exclusion rate of polyethylene glycol was also determined from the following.

Claims (1)

[Claims] 1. A nonwoven fabric layer made of polypropylene single fibers with a diameter of 10 to 33μ, a thickness of 0.05 to 2 mm, a basis weight of 20 to 600 g/m ² and an air permeability of 0.2 to 55 c.c./cm ² /sec. A reinforced permeable membrane characterized in that a permeable membrane is formed on a base material having a surface thereof. 2. The reinforced permeable membrane according to claim 1, wherein the sponge layer of the permeable membrane is integrally formed within a polypropylene nonwoven fabric layer. 3. The reinforced permeable membrane according to claim 1 or 2, characterized in that the permeable membrane is formed on the inner surface of a tubular base material having a polypropylene nonwoven fabric layer on the inner surface. 4. The reinforced permeable membrane according to any one of claims 1 to 3, characterized in that the permeable membrane is made of polysulfone.