Porous polyethylene hollow fiber membrane of large pore diameter

Details Porous polyethylene hollow fiber membrane of large pore diameter Porous polyethylene hollow fiber membrane of large pore diameter

1992-06-09

1994-03-15

Sever, Frank

Liquid purification or separation

Casing divided by membrane into sections having inlet

Cylindrical membrane

21032189, 21050025, 21050036, 264 41, B01D 6908

Patent

active

052943380

DESCRIPTION:

BRIEF SUMMARY
TECHNICAL FIELD

This invention relates to porous polyethylene hollow fiber membranes having a large pore diameter and a high porosity and hence suitable for use in fields of application requiring a very high filtering flux, such as precision filtration and air cleaning, a process for the production of such hollow fiber membranes, and hydrophilized porous polyethylene hollow fiber membranes.


BACKGROUND ART

Porous hollow fiber membranes consisting of polyethylene and having a membrane structure formed from stacked rectangular pores are conventionally known, and the details thereof are disclosed, for example, in Japanese Patent publication Nos. 35726/'88 and 42006/'88. It is disclosed in the former that, when a high-density polyethylene having a melt index of 1 to 15 and a density of 0.960 g/cm.sup.3 or greater is melt-spun at a spinning draft of 1,000 to 10,000, the spun hollow fibers are cold-stretched at a stretching speed of not less than 50% per second, and the cold-stretched hollow fibers are hot-stretched at a temperature of 80 to 125.degree. C. until a total amount of stretching of 400 to 700% is attained, the resulting porous hollow fiber membranes have characteristic rectangular pores, an average pore diameter of 0.5 to 2 .mu.m as measured with a mercury porosimeter, a porosity of 30 to 90% by volume, and a blue dextran rejection of less than 90%. However, the average pore diameters of the porous hollow fiber membranes described in the Examples of this patent are at most 0.82 .mu.m. In Japanese Patent Publication No. 42006/'88, it is disclosed that, when polyethylene is melt-spun at a spinning draft of greater than 2,000 with a spinning cylinder, 5 to 30 cm long, installed beneath the spinneret, and the spun hollow fibers are stretched until a total amount of stretching of 100 to 400% is attained, the resulting porous hollow fiber membranes have a water permeability of 100 to 2,000 l/m.sup.2 .multidot.hr.multidot.760 mmHg, a human serum albumin permeability of not less than 30%, and a blue dextran rejection of not less than 90%. Thus, the hollow fiber membranes provided by the latter patent have a smaller pore diameter than those provided by the former patent.
Moreover, it is disclosed in Japanese Patent Laid-Open No 86902/'86 that porous hollow fiber membranes having pore diameter of 0.1 to 1.0 .mu.m are produced by forming pores according to the stretching method. These porous hollow fiber membranes are characterized by the fact that the microfibrils oriented in the lengthwise direction of the fibers are broken to a substantial degree. Thus, the pore diameter is increased by breaking the microfibrils to expand the rectangular pores in the lateral direction. As a matter of actual fact, however, the resulting porous hollow fiber membranes have a pore diameter of at most 10 .mu.m.
Furthermore, a hydrophilic composite porous membrane consisting of a porous matrix formed of a polyolefin and a coating layer formed of an ethylenevinyl alcohol copolymer is disclosed in Japanese Patent Laid-Open No. 271003/'86. It is described in the claims of this patent that its average pore diameters is within the range of 0.02 to 4.0 .mu.m. With respect to pore diameter, however, the technique disclosed in this hydrophilic composite porous membrane never exceeds the technical level of the aforementioned Japanese Patent Laid-Open Nos. 35726/'88 and 86902/'86. In fact, the hollow fiber membranes obtained in the Examples of that patent have an average pore diameter of 0.25 to 0.70 .mu.m.
Thus, porous hollow fiber membranes consisting of polyethylene and having rectangular pores whose average diameter exceeds 1.0 .mu.m have not been available in the prior art.
Generally, porous membranes are broadly divided into hydrophilic membranes and hydrophobic membranes according to the properties of the material. Known examples of hydrophilic porous membranes include cellulose, cellulose derivatives, polyvinyl alcohol, ethylenevinyl alcohol copolymers and the like. Hydrophilic porous membranes are characterized by the fact that,

REFERENCES:
patent: 4530809 (1985-07-01), Shindo et al.
patent: 4696748 (1987-09-01), Nitadori et al.

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