This application is directed to new and/or improved MD and/or TD stretched and optionally calendered membranes, separators, base films, microporous membranes, battery separators including said separator, base film or membrane, batteries including said separator, and/or methods for making and/or using such membranes, separators, base films, microporous membranes, battery separators and/or batteries. For example, new and/or improved methods for making microporous membranes, and battery separators including the same, that have a better balance of desirable properties than prior microporous membranes and battery separators. The methods disclosed herein comprise the following steps: 1.) obtaining a non-porous membrane precursor; 2.) forming a porous biaxially-stretched membrane precursor from the non-porous membrane precursor; 3.) performing at least one of (a) calendering, (b) an additional machine direction (MD) stretching, (c) an additional transverse direction (TD) stretching, and (d) a pore-filling on the porous biaxially stretched precursor to form the final microporous membrane. The microporous membranes or battery separators described herein may have the following desirable balance of properties, prior to application of any coating: a TD tensile strength greater than 200 or 250 kg/cm.sup.2, a puncture strength greater than 200, 250, 300, or 400 gf, and a JIS Gurley greater than 20 or 50 s.

A microfilter comprising a polymer layer formed from epoxy-based photo-definable dry film, and a plurality of apertures each extending through the polymer layer. A method of forming a microfilter is also disclosed. The method includes providing a first layer of epoxy-based photo-definable dry film disposed on a substrate, exposing the first layer to energy through a mask to form a pattern, defined by the mask, in the first layer of dry film, forming, from the exposed first layer of dry film, a polymer layer having a plurality of apertures extending therethrough, the plurality of apertures having a distribution defined by the pattern, and removing the polymer layer from the substrate.

Thin, self-supporting biaxially expanded polytetrafluoroethylene (ePTFE) membranes that have a high crystallinity index, high intrinsic strength, low areal density (i.e., lightweight), and high optical transparency are provided. In particular, the ePTFE membrane may have a crystallinity index of at least about 94% and a matrix tensile strength at least about 600 MPa in both longitudinal nd transverse directions. In addition, the ePTFE membrane is transparent or invisible to the naked eye through a complete conversion of the PTFE primary particles into fibrils. The ePTFE membrane may have a thickness per layer of less than 100 nm and a porosity reater than 50%. Further, the ePTFE membrane is stackable, which, in turn, may be used to control permeability, pore size, and/or bulk mechanical properties. The ePTFE membrane may be used to form composites, laminates, fibers, tapes, sheets, tubes, or three-dimensional objects. Additionally, the ePTFE membrane may be used in filtration applications.

A composite porous membrane contains at least one porous base layer and at least one uniaxially stretched coating layer located on at least one side surface of the porous base layer. For example, the composite porous membrane comprises at least one porous base layer and at least one nanofiber-like non-polyolefin polymer porous layer oriented along the transverse stretching direction of the composite porous membrane and located on one or two side surfaces of the porous base layer, or the composite porous membrane comprises a biaxially stretched polypropylene porous base layer and a uniaxially stretched coating layer located on at least one side surface of the porous base layer. The composite porous membrane is coated with a coating solution prior to transversely stretching. The nanofiber-like non-polyolefin polymer porous layer may reduce cracking of the composite porous membrane in the machine direction.

The disclosure provides a method for preparing a hollow fiber membrane by melt spinning-stretching and selective swelling, including: preparing a nascent hollow fiber by melt spinning in an inert gas protective atmosphere by using an amphiphilic block copolymer as a film forming material, and stretching the nascent hollow fiber in the cooling process, a stretch rate being controlled at 200-540 mm/min, and a stretch ratio being controlled at 150-600%; immersing the obtained hollow fiber in a swelling solvent, and treating the hollow fiber in a water bath at 65° C. for 1 h; and then transferring the hollow fiber into a long-chain alkane solvent, treating the hollow fiber at the same temperature for 1-12 h, and after the completion of the treatment, immediately taking out the hollow fiber and drying the hollow fiber to obtain the hollow fiber membrane with a bicontinuous porous structure. By combining the melt spinning-stretching and the selective swelling, the method of the disclosure can synchronously and continuously improve the permeability and selectivity of the hollow fiber membrane. The treatment in the long-chain alkane solvent can make the polar chain excessively enriched on the surface of the membrane migrate inward, thereby improving the performance of the hollow fiber membrane.

An object of the present invention is to provide a porous hollow-fiber membrane having high strength while maintaining high pure-water permeation performance. A porous hollow-fiber membrane of the present invention is a porous hollow-fiber membrane including a fluororesin-based polymer, in which the porous hollow-fiber membrane has a columnar texture oriented in a longitudinal direction of the porous hollow-fiber membrane, and a molecular chain of the fluororesin-based polymer is oriented in the longitudinal direction of the porous hollow-fiber membrane.

A porous membrane laminate of the present disclosure includes a porous support layer and a porous membrane laminated on one surface of the support layer and containing polytetrafluoroethylene as a main component. The porous membrane is formed of a uniaxially stretched material, the porous membrane has a mean pore size of 25 nm to 35 nm and a maximum pore size of 49 nm or less, and the porous membrane has an average thickness of 0.6 μm to 3.5 μm.

A hollow-fiber membrane according to an aspect of the present disclosure includes a porous, tubular filtration layer containing polytetrafluoroethylene as a main component and having a fibrous skeleton. A mean pore diameter in an outer peripheral surface of the filtration layer is smaller than a mean pore diameter in an inner peripheral surface of the filtration layer. A ratio of the mean pore diameter in the inner peripheral surface to the mean pore diameter in the outer peripheral surface is 2.0 or more and 5.0 or less.

A polyolefin multilayer microporous membrane includes at least first microporous layers which form both surface layers of the membrane and at least a second microporous layer disposed between the both surface layers, wherein static friction coefficient of one of the surface layers of the polyolefin multilayer microporous membrane against another surface layer in a longitudinal direction (MD) is 1.1 or less, and wherein pore density calculated from an average pore radius measured by mercury porosimetry method and porosity, according to Formula (1) is 4 or more:
Pore density=(P/A.sup.3)×10.sup.4  (1)
wherein A represents the average pore radius (nm) measured by mercury porosimetry method and P represents the porosity (%).

A catalytic composite is formed of a catalytic layered assembly including a porous catalytic fluoropolymer film and one or more felt batts connected with the porous catalytic fluoropolymer film. At least one felt batt is positioned adjacent the upstream side of the porous catalytic fluoropolymer film to form the catalytic composite. The fluoropolymer film is perforated to allow for enhanced airflow therethrough while retaining the capability of catalyzing the reduction or removal of chemical species in fluid flowing through the catalytic composite.