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US 11,420,416 B2Granted
Biaxially oriented microporous membrane
AssigneeCelgard, LLC
InventorsXiangyun Wei, Charles Haire
Life of this patent
Estimating the term…
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 membrane comprising:
- a microporous multi-layer polymer film having outer layers made of a semi-crystalline polymer and at least one inner layer made of a polyethylene, wherein the layers are formed by co-extrusion followed by a dry-stretch process, the film having 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;
- wherein said dry-stretched process excludes the use of oils for subsequent removal to form pores or pore-forming materials to facilitate pore formation and pore formation results from stretching, and wherein said semi-crystalline polymer is polypropylene polymer, a polypropylene polymer or polypropylene co-polymer blend, or a co-polymer of polypropylene, wherein the polymer film has a thickness of from about 7.5 to about 20 microns and an TD tensile strength of at least 500 kg/cm2.
Dependencies are inferred from the claim text.