JPH0413015B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a membrane forming solution, particularly a low-temperature melting type membrane forming solution using a polysulfone resin.

(Prior Art) Conventionally, many polymeric compounds such as polysulfone, polyacrylonitrile, cellulose such as cellulose acetate, polyamide, polycarbonate, and polyvinyl alcohol have been used as materials for hollow fiber membranes. Among them, polysulfone resin has heat resistance, acid resistance, alkali resistance,
It has excellent chemical resistance such as oxidation resistance, so it can be regenerated by cleaning the membrane with oxidizing agents, acids, alkalis, etc., and it can also be sterilized by heat sterilization, formalin, chlorine, and other chemicals. For this reason, it has recently attracted attention as a hollow fiber membrane material.

The following methods have been proposed as methods for obtaining hollow fiber membranes with high water permeability using polysulfone resins.

(1) Method using microphase separation between different types of polymers (Japanese Patent Publication No. 176-1976, Japanese Patent Application Laid-open No. 144456-1982)
Publication No. ) (2) A method that includes extraction and elution operations after film formation (Japanese Unexamined Patent Publication No. 54-26283.) (Problem to be solved by the invention) However, in method (1), polyethylene glycol, polyvinylpyrrolidone, polyethylene In order to blend large amounts of different polymers such as imines,
The original good performance of polysulfone resin is likely to be lost. Furthermore, in method (2), extraction of the blended polymer was difficult.

All of these conventional membrane forming solutions are characterized by phase separation at low temperatures. For this reason, even if the temperature of the coagulation bath is increased in an attempt to increase the exchange rate between the non-solvent, etc. in the coagulation bath and the good solvent in the membrane during membrane formation, the membrane-forming solution will move toward a homogeneous system in equilibrium, resulting in It has the property of forming a dense layer and is difficult to store at low temperatures.

It is therefore an object of the present invention to overcome the above-mentioned problems of the prior art. It is an object of the present invention to provide a membrane forming solution suitable for producing polysulfone hollow fiber membranes having particularly excellent water permeability.

(Means for Solving the Problems) In order to overcome the limitations of the conventional technology and further improve the performance of hollow fiber membranes, the present inventors investigated various membrane forming solutions and found that polysulfone solutions have high hydrophilic properties. It was observed that as molecules and a non-solvent for the polysulfone resin were added, the concentration changed from a homogeneous solution region to a turbid concentration region where phase separation occurred. In the prior art, it was believed that a solution in this turbid concentration range could not be used at all as a membrane forming solution, but surprisingly, a solution in this turbid concentration range could be used as a membrane forming solution.
It has been found that upon further cooling, the solution turns into a homogeneous and transparent solution, and this solution can be used extremely well as a film forming solution. In order to improve the solubility, the temperature should normally be raised, but in the case of the above film-forming solution, on the contrary, a homogeneous solution is obtained by cooling, and this fact was completely unexpected.

That is, the present invention is a film forming solution in which a polysulfone resin, a hydrophilic polymer, a non-solvent for the polysulfone resin, and a common solvent thereof are uniformly mixed.

Next, the low-temperature dissolution type film-forming solution of the present invention will be specifically explained below.

The polysulfone resin used in the present invention has the usual formula
(1), Or formula (2): Examples include those having repeating units shown in the following.

Among them, polysulfone resins having a repeating unit represented by formula (1) are preferably used because they have excellent basic special properties such as mechanical strength, heat resistance, chemical resistance, and biocompatibility. . The polysulfone resin can be used as long as it can be used to form a membrane and has the characteristics of a hollow fiber membrane, and is usually in the range of 5 to 50%.
Weight % is appropriate.

Hydrophilic polymers are polymers that are compatible with polysulfone-based resins and have hydrophilic properties, and include polyethylene glycol, polyvinylpyrrolidone, polyethyleneimine, etc., which are conventionally used in membrane forming solutions for polysulfone-based hollow fiber membranes. However, it is not limited to these. Usually polyethylene glycol is advantageously used. Polyethylene glycol is commercially available with a molecular weight of 600.
Although it is convenient to use this, it is of course possible to use other molecular weights.

The solvent is a solvent that dissolves both the polysulfone resin and the hydrophilic polymer, and various solvents such as dimethylsulfoxide, dimethylacetamide, dimethylformamide, N-methyl-2-pyrrolidone, and dioxane are used. Particularly preferred are dimethylacetamide, dimethylsulfoxide, dimethylformamide, and N-methyl-2-pyrrolidone.

The non-solvent for the polysulfone-based resin may be anything as long as it serves as a non-solvent or a swelling agent for the polysulfone-based resin, and is usually inorganic salts such as ZnC ₂ , alcohol, etc. described in Japanese Patent Publication No. 176-1983. Examples include organic matter and water. Water is most preferably used in terms of production costs. The type and amount of the non-solvent may be selected in consideration of the coagulability of the polysulfone resin. The present invention is characterized by the addition of this fourth component, and by using such a membrane forming solution, a hollow fiber membrane with excellent water permeability can be obtained.

The solubility of the polysulfone resin used in the present invention in the solvent and the non-solvent of the hydrophilic polymer and polysulfone resin generally increases as the temperature increases, as in the case of polymer solvents. However, in the film-forming solution of the present invention, the fact that, on the contrary, the compatibility of the mixture increases at low temperatures and a homogeneous solution is produced is a completely new finding by the present inventors.

Although the cause of this novel phenomenon is unknown, by utilizing this phenomenon, it is possible to obtain a hollow fiber membrane with greater water permeability than hollow fiber membranes obtained using conventional membrane forming solutions.

Next, a method for manufacturing a polysulfone hollow fiber membrane using the membrane forming solution of the present invention will be described.

The method for producing polysulfone hollow fiber membranes is as follows:
A wet method in which the film-forming solution is directly extruded into a coagulation bath, and a wet-dry method in which it is once exposed to a gas phase before being extruded into a coagulation bath can be used.

Although the coagulating liquid is miscible with the solvent, a non-solvent having coagulating ability is used for polysulfone resin. The non-solvent can be used alone or in combination of two or more types, and it may be preferable to mix an inorganic or organic salt or a solvent with the non-solvent. Among these, water is preferred from the viewpoint of ease of handling.

In the case of hollow fibers, coagulation is performed from the outside and the inside of the hollow fiber simultaneously, or from either the inside or the outside. The internal coagulating liquid may be the same as the external coagulating liquid or may be different. In addition to this, gas may also be injected. In the case of hollow fibers produced by dry-wet spinning, an organic solvent such as ethanol with low coagulation ability alone or a mixture with water is used as the internal coagulation injection liquid, or a mixture of a polysulfone resin solvent such as dimethylformamide and water is used. When used, water permeability may be further improved.

After solidification, washing is performed.

Further, if necessary, moist heat treatment can be carried out in a bath containing water as a main component. Normally, when a wet membrane is dried, its water permeability decreases, but moist heat treatment may be effective in maintaining water permeability even after drying.

Furthermore, since the membrane forming solution used in the present invention is stable at low temperatures, the temperature can be easily adjusted and hollow fiber membranes can be stably manufactured.

Since the hollow fiber membrane obtained by the present invention is made of polysulfone resin, it has excellent heat resistance, chemical resistance, and mechanical properties, and because it was formed using a new membrane forming solution, the membrane has excellent permeability. In particular, it has excellent water permeability and can be used in various precision filtration and ultrafiltration fields. Further, the polysulfone hollow fiber membrane obtained in the present invention can also have a hydrophilic polymer present in the membrane.

(Example) A method for producing a polysulfone-based hollow fiber membrane using the membrane forming solution of the present invention will be described below with reference to Examples.

Example Polysulfone (manufactured by UCC, P-1700) 4 kg,
6.8Kg of polyethylene glycol with a molecular weight of 600, water
0.02 kg and 9.2 kg of N,N-dimethylformamide (DMF) were heated and stirred at 100°C for 3 hours, cooled to 18°C, and defoamed at 18°C for 16 hours to obtain a uniform and transparent film forming solution. This membrane-forming solution became cloudy when heated to 20.5°C and was a low-temperature solution that caused microphase separation. This membrane-forming solution was heated to 18° C., and wet-dry spinning was performed using an annular nozzle with a hole diameter of 1.0 mm and a needle diameter of 0.5 mm. At this time, the injection liquid to be injected into the needle is 20
Using a DMF aqueous solution of DMF/water = 90/10 at °C,
The length of the dry section at a temperature of 15℃ and humidity of 80% is 1cm.
Water at 20°C was used as the coagulation liquid. The flow rate of the stock solution was 2.8 cc/min, and the winding speed was 6.3 m/min. After solidification, it was washed with water and further subjected to a moist heat treatment for 2 hours with hot water at 98°C. The outer diameter of the obtained polysulfone hollow fiber membrane is 800μ, the inner diameter is 550μ, and the water permeability is 1420.
/ ^m2hrKg / ^cm2 . 5000 of these hollow fiber membranes are bundled and sealed with adhesive, and the effective length of the hollow fibers is 100cm.
A hollow fiber bundle with one end open and the other end free-sealed was obtained. This hollow fiber bundle was attached to a casing with a 4-inch straight body, and a 2-inch water faucet was directly connected to it, resulting in an overpressure of 1.4
Kg/cm ² and a temperature of 12 to 14° C., the tap water was subjected to total external pressure over a period of one month. At this time, an average of 5 m ² /hr of purified water was obtained, and the water quality was completely sterilized.

Comparative example: 200 g of polysulfone (manufactured by UCC, P-1700),
300g of polyethylene glycol with a molecular weight of 600 and
A membrane forming solution was obtained by heating, stirring, cooling and defoaming 500 g of DMF. This film-forming solution was a high-temperature solution that became more uniform as the temperature increased. This membrane-forming solution was heated to 30° C. and wet-dry spinning was performed in the same manner as in Example 1. At this time, water at 20°C was used as the injection liquid and coagulation liquid, and the length of the drying part was 25 cm, and the temperature of the drying part was maintained at 20°C and relative humidity at 65%. After solidification, wash with water and further heat to 98℃
A moist heat treatment was performed using hot water for 2 hours. The outer diameter of the obtained polysulfone hollow fiber membrane was 0.6 mm, and the inner diameter was
0.45 mm, and the water permeability was 540/m ² hrKg/cm ² .

(Effect of the invention) Since the polysulfone membrane forming solution of the present invention undergoes microphase separation on the high temperature side, the
The polysulfone-based hollow fiber membrane that can improve water permeability and is resistant to clogging and staining can be used for general industrial purposes, medical purposes, and the like.

Claims (1)

[Claims] 1. A film-forming solution in which a polysulfone resin, a hydrophilic polymer, a non-solvent for the polysulfone resin, and a common solvent thereof are uniformly mixed.