초록 ▼

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: extru

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 including a simultaneous controlled machine direction relax.

대표청구항 ▼

1. A method of making a microporous membrane comprising the steps of: extruding a semi-crystalline polymer into a nonporous precursor, andbiaxially stretching the nonporous precursor, the biaxial stretching including a machine direction stretching and a transverse direction stretching, the transvers

1. A method of making a microporous membrane comprising the steps of: extruding a semi-crystalline polymer into a nonporous precursor, andbiaxially 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 having an aspect ratio in the range of 0.75 to 1.25,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. 2. The method of claim 1 wherein the polymer being selected from the group consisting of polyolefins, fluorocarbons, polyamides, polyesters, polyacetals (or polyoxymethylenes), polysulfides, polyvinyl alcohols, co-polymers thereof, and combinations thereof. 3. The method of claim 1 further comprising the step of: annealing the non-porous precursor after extruding and before biaxially stretching. 4. The method of claim 3 wherein annealing being conducted at a temperature in the range of Tm−80° C. to Tm−10° C. 5. The method of claim 1 wherein biaxially stretching comprising the steps of: machine direction stretching, andthereafter transverse direction stretching including a simultaneous restrained machine direction relax. 6. The method of claim 5 wherein machine direction stretching being conducted either hot or cold or both. 7. The method of claim 6 wherein cold machine direction stretching being conducted at a temperature