Porous polyethylene hollow fiber membrane of large pore diameter, production process thereof, and hydrophilized porous polyethylene hollow fiber membranes

A process for the production of a porous polyethylene hollow fiber membrane of large pore diameter, the hollow fiber membrane having:

• (a) rectangular pores formed by microfibrils that are oriented in the lengthwise direction of the fiber and joint portions that are composed of stacked lamellae, the pores being contiguous with each other from the inner wall surface to the outer wall surface of the hollow fiber membrane to form a stacked, multicellular structure;
• (b) an average pore diameter ranging from greater than 2 .mu.m up to 10 .mu.m as measured with a mercury porosimeter;
• (c) a porosity of 75-95%;
• and
• (d) an air permeability of not less than 8.times.10.sup.5 l/m.sup.2 .multidot.hr.multidot.0.5 atm, which comprises the steps of:
• melt-spinning polyethylene through a nozzle which forms hollow fibers;
• annealing the resulting unstretched hollow fiber at a temperature of 100.degree.-130.degree. C. for 30 minutes or more;
• cold-stretching the annealed hollow fiber;
• and then hot-stretching the stretched hollow fiber under conditions such that the deformation rate during hot stretching is not greater than 10% per second, with the total stretching during cold- and hot-stretching ranging from 750-2500%, the said stretching rendering the hollow fiber porous.

A hydrophilized porous polyethylene hollow fiber membrane comprising a porous polyethylene hollow fiber membrane of large pore diameter having a saponification product of an ethylene-vinyl acetate copolymer held on at least a part of the pore surfaces thereof, the porous polyethylene hollow fiber membrane of large pore size having:

• (a) rectangular pores formed by microfibrils that are oriented in the lengthwise direction of the fiber and joint portions that are composed of stacked lamellae, the pores being contiguous with each other from the inner wall surface to the outer wall surface of the hollow fiber membrane to form a stacked, multicellular structure;
• (b) an average pore diameter ranging from greater than 2 .mu.m up to 10 .mu.m as measured with a mercury porosineter;
• (c) a porosity of 75 to 95%;
• and
• (d) an air permeability of not less than 8.times.10.sup.5 l/m.sup.2 .multidot.hr.multidot.0.5 atm.

A hdyrophilized porous polyethylene hollow fiber membrane comprising a porous polyethylene hollow fiber membrane of large pore diameter having a hydrophilic crosslinked polymer held on at least a part of the pore surfaces thereof, the hydrophilic crosslinked polymer being formed by polymerizing monomers including diacetone acrylamide and a crosslinkable monomer, the porous polyethylene hollow fiber membrane of large pore size having:

• (a) rectangular pores formed by microfibrils that are oriented in the lengthwise direction of the fiber and joint portions that are compsoed of stacked lamellae, the pores being contiguous with each other from the inner wall surface to the outer wall surface of the hollow fiber membrane to form a stacked, multicellular structure;
• (b) an average pore diameter ranging from greater than 2 .mu.m as measured with a mercury porosimeter;
• (c) a porosity of 75 to 95%;
• and
• (d) an air permeability of not less than 8.times.10.sup.5 l/m.sup.2 .multidot.hr.multidot.0.5 atm.