PURPOSE: To make an external layer of a compound hollow yarn membrane having small film thickness and to produce a compound hollow yarn membrane having high water permeability in one stage by adjusting the concn. of an internal layer and an external layer of solns. of high molecular polymers to within specified ranges and adjusting the ratio of the concns. to ≥ a specified value.
CONSTITUTION: A nozzle having two annulus openings around a circular opening is used. For example, a soln. contg. N-methyl-2-pyrrolidone and ethyleneglycol is extruded from the circular opening, a soln. contg. cellulose triacetate, N-methyl-2- pyrrolidone, and ethyleneglycol is extruded from the internal layer of the annulus opening, and a soln. contg. cellulose triacetate and N-methyl-2-pyrrolidone is extruded simultaneously with the above described two solns. from the external layer of the annulus opening. After evaporating the solvent, the product is guided to a coagulating bath, where it is freed of solvent in the water and treated with hot water. Thus, a compound hollow yarn is obtd. In this case, the concn. (Wi%) of the high molecular polymer in the soln. for the internal larer, the concn. (Wo%) of the high molecular polymer in the soln. for the external layer are regulated to satisfy the following relations: Wi/Wo≥5; 75≥Wi≥25; 15≥Wo≥0.5.
NITTA KAZUHIDE
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