Biaxially oriented microporous membrane
AssigneeCelgard, LLC
InventorsXiangyun Wei, Charles Haire
Life of this patent
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Abstract
A microporous membrane is made by a dry-stretch process and has substantially round shaped pores and a ratio of machine direction tensile strength to transverse direction tensile strength in the range of 0.5 to 5.0. The method of making the foregoing microporous membrane includes the steps of: extruding a polymer into a nonporous precursor, and biaxially stretching the nonporous precursor, the biaxial stretching including a machine direction stretching and a transverse direction stretching, the transverse direction stretching including a simultaneous controlled machine direction relax.
Claims11
A method of making a microporous membrane comprising the steps of:
- extruding a semi-crystalline polymer into a nonporous precursor, and
- biaxially stretching the nonporous precursor, the biaxial stretching including a machine direction stretching and a transverse direction stretching, the transverse direction stretching including a simultaneous restrained machine direction relax in the range of 5 to 80% to form substantially round shaped pores;
- wherein the total transverse direction stretch being in the range of 100 to 1200%;
- and
- wherein the method is a dry stretch process and the polymer excludes any oils for subsequent removal to form pores or any pore-forming particulate to facilitate pore formation.
Dependencies are inferred from the claim text.