Hollow porous membrane and process for producing the same
View Patent ↗A hollow porous membrane with a reduced cost and excellent separation characteristic, water permeability, and mechanical strength and a process of producing the hollow porous membrane with an excellent adhesive property between a support and a porous membrane layer at a low cost are provided. The hollow porous membrane includes a porous membrane layer in which dense layers are disposed in the vicinities of an outer surface and an inner surface. In the process of producing the hollow porous membrane, membrane-forming dopes of a first membrane-forming dope and a second membrane-forming dope, which contain the material of the porous membrane layer and a solvent, are successively applied and stacked onto the outer circumferential surface of a hollow support and the applied membrane-forming dopes are simultaneously coagulated. In the process of producing the hollow porous membrane, a porous membrane layer is formed by applying a membrane-forming dope containing a material of the porous membrane layer and a solvent to the outer circumferential surface of the hollow support and coagulating the applied dope, and a hollow braid obtained by circularly knitting a yarn formed of multi-filaments is used as the support.
1. A hollow porous membrane, comprising:
a porous membrane layer comprising an outer dense layer disposed near an outer surface and an inner dense layer disposed near an inner surface; and
a hollow support, which is a heat treated hollow braid obtained by circularly knitting a single yarn comprising multi-filaments, to obtain a hollow braid, and heat treating the hollow braid,
wherein the porous membrane layer is disposed on the hollow support.
2. The hollow porous membrane according to claim 1 , wherein an intermediate porous layer having a maximum pore-diameter portion is disposed between the outer dense layer and the inner dense layer.
3. The hollow porous membrane according to claim 2 , wherein an average pore diameter of the inner and outer dense layers is in a range of 0.01 to 2 μm, and an average pore diameter of the intermediate porous layer is in a range of 2 to 8 μm.
4. The hollow porous membrane according to claim 1 , wherein a thickness of the porous membrane layer is 200 μm or less.
5. The hollow porous membrane according to claim 1 , wherein the inner dense layer is located at a position less than 50 μm from the inner surface.
6. The hollow porous membrane according to claim 1 , wherein the porous membrane layer permeates the hollow support through meshes of the hollow support by 50% or more of a thickness of the hollow support.
7. The hollow porous membrane according to claim 6 , wherein the porous membrane layer permeates the hollow support through meshes of the hollow support by 50% or more and less than 100% of the thickness of the hollow support and a part of the hollow support is covered with the porous membrane layer.
8. The hollow porous membrane according to claim 6 , wherein a portion not permeated by the porous membrane layer exists among monofilaments of the hollow support.
9. The hollow porous membrane according to claim 1 , wherein the inner dense layer is located at a position less than 50 μm from the outer surface of the support.
10. The hollow porous membrane according to claim 1 , wherein the multi-filaments are a mixture of two or more different fibers.
11. A hollow porous membrane, comprising:
a hollow support, and
a porous membrane layer disposed on an outer circumferential surface of the hollow support,
wherein the hollow support is a heat treated hollow braid obtained by circularly knitting a single yarn comprising multi-filaments, to obtain a hollow braid, and heat treating the hollow braid.
12. The hollow porous membrane according to claim 11 , wherein the porous membrane layer permeates the hollow support through meshes of the hollow support by 50% or more of a thickness of the hollow support.
13. The hollow porous membrane according to claim 12 , wherein the porous membrane layer covering a part of the hollow support extends in a fiber axis direction on an inner surface side of the hollow support.
14. The hollow porous membrane according to claim 13 , wherein the porous membrane layer covering a part of the hollow support extends in a spiral shape in the fiber axis direction on the inner surface side of the hollow support.
15. A process of producing a hollow porous membrane, the process comprising:
forming a porous membrane layer by applying a membrane-forming dope, comprising a material of the porous membrane layer and a solvent, to an outer circumferential surface of a hollow support; and
coagulating the dope applied, to obtain a porous membrane layer disposed on the hollow support,
wherein the hollow support is a heat treated hollow braid obtained by circularly knitting a single yarn comprising multi-filaments, to obtain a hollow braid, and heat treating the hollow braid.
16. A process of producing the hollow porous membrane according to claim 1 , the process comprising:
successively applying and stacking membrane-forming dopes of a first membrane-forming dope and a second membrane-forming dope onto an outer circumferential surface of a hollow support with an annular nozzle; and
simultaneously coagulating the membrane-forming dopes which have been applied to the outer circumferential surface.
17. The process according to claim 16 , wherein the membrane-forming dopes comprise a polymer resin, an additive, and an organic solvent.
18. The process according to claim 16 , wherein the first membrane-forming dope has a high viscosity is applied first onto the outer circumferential surface of the hollow support, to give an applied layer, and the second membrane-forming dope, which has a low viscosity, is applied onto the applied layer of the first membrane-forming dope.
19. The process according to claim 18 , wherein the membrane-forming dopes comprise a polymer resin, an additive, and an organic solvent, and a concentration of the polymer resin comprised in the first membrane-forming dope is higher than the concentration of polymer in the second membrane forming dope.