Microporous membranes of ultrahigh molecular weight polyethylene
AssigneeMillipore Corporation
InventorsGeorge Lopatin, Larry Y. Yen
Life of this patent
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Abstract
Microporous membranes and methods for producing such membranes from ultrahigh molecular weight polyethylene are described. The method employs extrusion of a solution of UHMW-PE and porogen through a forming die followed by thermal phase separation of polymer and porogen. Microporous structures are created by removing porogen. Microporous membranes produced include membranes with good permeability to air and water making them particularly useful as filtration media and water-resistant breathable membranes.
Claims18
A microporous UHMW-PE membrane having microporosity and permeability sufficient to provide a water flow rate above the curve of FIG. 5 at a methanol bubble point plotted thereon.
A water-resistant breathable microporous membrane formed from UHMW-PE and having microporosity and permeability sufficient to provide an air flow rate of at least 0.1 lit/min/cm.sup.2 at differential pressure equal to 10 psi, a minimum water intrusion pressure of about 2 psi and a water flow rate above the curve of FIG. 5 at a methanol bubble point plotted thereon.
A microporous ultra-high molecular weight polyolefin membrane produced by a method comprising:
- a. forming a mixture comprising an ultra-high molecular weight polyolefin and a porogen;
- b. heating the mixture to an elevated temperature to produce a solution of ultra-high molecular weight polyolefin and porogen;
- c. extruding the solution of ultra-high molecular weight polyolefin and porogen through a forming die under moderate shear sufficient to enable the employment of conventional extrusion equipment and/or techniques to thereby form a membrane;
- d. cooling the membrane sufficiently to cause phase separation resulting in a polymer-rich, porogen-poor phase and a polymer poor, porogen-rich phase in said membrane;
- e. creating a microporous structure in the membrane by removing porogen from said membrane;
- and
- f. drying the microporous membrane under restraint to minimize collapse of the microporous structure.
A microporous membrane produced by a method including the steps of:
- a. forming a mixture comprising UHMW-PE and a porogen;
- b. heating the mixture to an elevated temperature to produce a solution of UHMW-PE and porogen;
- c. extruding the solution of UHMW-PE and porogen through a forming die under moderate shear sufficient to enable the employment of conventional extrusion equipment and/or techniques to thereby form a membrane;
- d. cooling the membrane sufficiently to cause phase separation resulting in a polymer-rich, porogen-poor phase and a polymer-poor, porogen-rich phase in said membrane;
- e. creating a microporous structure in the membrane by removing porogen from said membrane;
- f. drying the microporous membrane under restraint to minimize collapse of the microporous structure.
Dependencies are inferred from the claim text.