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AssigneeAsahi Kasei Chemicals Corporation
InventorsHirokazu Fujimura, Noboru Kubota, Masatoshi Hashino, Tetsuo Shimizu
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A porous hollow fiber membrane which has high blocking performance and high water permeability suitable for filtration and the like and exhibits excellent strength, and a process for stably producing the porous hollow fiber membrane are disclosed. The process utilizes a hollow fiber molding nozzle having two or more circular discharge ports which are disposed concentrically. Multilayer melt-extrusion is performed by discharging molten mixtures which include a thermoplastic resin and an organic liquid and differ in composition from the adjacent discharge ports. The resulting product is cooled to solidify to obtain a hollow fiber. The organic liquid is then removed from the hollow fiber by extraction to produce a porous hollow fiber membrane. The molten mixture discharged from at least one circular discharge port includes an inorganic fine powder in addition to the thermoplastic resin and the organic liquid. The inorganic fine powder is removed by extraction after cooling in addition to the organic liquid.
A process for producing a porous multilayer hollow fiber membrane by a hollow fiber molding nozzle with a circular discharge port, the process comprising discharging a molten mixture including a thermoplastic resin and an organic liquid from a circular discharge port of a hollow fiber molding nozzle to obtain a multilayer hollow fiber, and removing the organic liquid from the multilayer hollow fiber by extraction to obtain a porous multilayer hollow fiber membrane, the hollow fiber molding nozzle having two or more circular discharge ports which are disposed concentrically, molten mixtures which differ in composition being discharged from the adjacent discharge ports, the molten mixture discharged from at least one of the circular discharge ports further including an inorganic fine powder, and the inorganic fine powder being also removed from the resulting multilayer hollow fiber by extraction.
A porous multilayer hollow fiber membrane comprising at least two layers, the porous multilayer hollow fiber membrane being formed of a thermoplastic resin, at least one layer (A) among the two layers being a support layer having an isotropic three-dimensional mesh structure and a surface pore diameter 0.6 to 1.4 times a cross-sectional center pore diameter, and the other layer (B) among the two layers having a surface pore diameter less than half of the cross-sectional center pore diameter and having an isotropic three-dimensional mesh structure.
Dependencies are inferred from the claim text.