A method of fabricating a gas separation membrane includes providing a coextruded multilayer film that includes a first polymer layer formed of a first polymer material and a second polymer layer formed of a second polymer material, the first polymer material having a first gas permeability. The coextruded multilayer film is axially oriented such that the second polymer layer has a second gas permeability that is greater than the first gas permeability.

An ion exchange membrane having a structure that an ion exchange resin is filled in spaces of a porous base film, the porous base film has a structure that at least two porous olefin resin layers are laminated with a bonding strength of 100 gf/cm or more to less than 700 gf/cm and a Gurley air permeance of 500 sec/100 ml or less in terms of a 100 μm thick film. In this ion exchange membrane, base film has high air permeability though it has a multi-layer structure that a plurality of porous resin films are bonded together, and therefore a rise in electric resistance caused by the lamination of the base sheets is effectively suppressed.

The present invention relates to a composite porous hollow-fiber membrane including a first layer and a second layer which each include a fluororesin-based polymer, in which at least a part of molecular chains of the fluororesin-based polymer is oriented in a longitudinal direction of the composite porous hollow-fiber membrane, the molecular chains of the fluororesin-based polymer have a degree of orientation it in the longitudinal direction of the composite porous hollow-fiber membrane of 0.4 or higher but less than 1.0, the degree of orientation it being calculated with the specific formula.

A method suppresses membrane thickness variation and air resistance variation after a compression at 60° C. or 80° C. Stretching is performed at least twice in at least different axial directions before the extraction of the solvent, and at the same time, at least one of (i) and (ii) is satisfied. (i) The step (c) is a first stretching step of stretching the sheet-shaped product at least once in a sheet transport direction (MD direction) and at least once in a sheet width direction (TD direction) individually, and the MD stretching magnification and the TD stretching magnification in the step (c) satisfy (TD stretching magnification≥MD stretching magnification−2). (ii) The stretching temperature (T1) of a first axial stretching performed firstly in the step (c) and the maximal stretching temperature (T2) of a second stretching performed after the first axial stretching satisfy (T1−T2≥0).

At least a selected 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 6.0. The method of making the foregoing microporous membrane may include 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. At least selected embodiments of the invention may be directed to biaxially oriented porous membranes, composites including biaxially oriented porous membranes, biaxially oriented microporous membranes, biaxially oriented macroporous membranes, battery separators, filtration media, humidity control media, flat sheet membranes, liquid retention media, and the like, related methods, methods of manufacture, methods of use, and the like.

Self-supporting uniaxially expanded polytetrafluoroethylene (ePTFE) membranes that have high intrinsic strength, a high matrix modulus, and a high crystallinity index are provided. In some embodiments, the ePTFE membrane is stretched in the machine direction. Uniaxially oriented ePTFE membranes have a matrix tensile strength at least about 1000 MPa in the machine direction, a matrix modulus at least about 100 GPa ambient temperature (i.e., about 20° C.), and a crystallinity index of at least about 94%. In some embodiments, the ePTFE membrane has a tenacity greater than or equal to about 5 gf/d and a denier less than or equal to about 750 g/9000 m. In addition, the uniaxially oriented ePTFE membranes have a <P2> orientation of at least about 0.98. Also, the fibrils in the ePTFE membranes have a nearly perfect parallel alignment. The ePTFE membrane may be used to form composites, laminates, fibers, tapes, sheets, tubes, or other three-dimensional objects.

An embodiment of the present invention provides a polyolefin microporous membrane, including: a first porous layer containing a polyolefin and having a structure including a first rod-shaped crystal extending in one direction and plural first plate-shaped crystals arranged in a separated state and intersecting the first rod-shaped crystal, and a second porous layer containing a polyolefin and having a structure including a second rod-shaped crystal extending in another direction intersecting the one direction and plural second plate-shaped crystals arranged in a separated state and intersecting the second rod-shaped crystal.

A tetrafluoroethylene polymer is provided in an air filter medium having a pressure loss that can be reduced and made uniform at a plurality of positions. The tetrafluoroethylene polymer may also be provided in an air filter medium, a filter pack, or an air filter unit. The tetrafluoroethylene polymer has drawability and non-melt processability. The tetrafluoroethylene polymer has a ratio S.sub.2/S.sub.1 of 0.60 or more, where S.sub.2 represents an endotherm mJ/mg in a range of T.sub.0° C. or higher and 350° C. or lower, T.sub.0° C. is a temperature 2.5° C. lower than a temperature T.sub.p° C. (340≤T.sub.p≤345) at which a minimum point is given on a heat-of-fusion curve obtained by measuring an unbaked polymer for measurement having no history of heating to a temperature of 300° C. or higher using a differential scanning calorimeter at a temperature-increasing rate of 2° C./min, and S.sub.1 represents an endotherm mJ/mg in a range of 320° C. or higher and T.sub.0° C. or lower.

A hollow-fiber membrane according to an aspect of the present disclosure contains a polytetrafluoroethylene or a modified polytetrafluoroethylene as a main component and has an average outer diameter of 1 mm or less and an average inner diameter of 0.5 mm or less. In a measurement of a heat of fusion of the polytetrafluoroethylene or the modified polytetrafluoroethylene with a differential scanning calorimeter, when the polytetrafluoroethylene or modified polytetrafluoroethylene is subjected to a first step of heating from room temperature to 365° C., a second step of cooling from 365° C. to 350° C., maintaining the temperature, subsequently cooling from 350° C. to 330° C., and further cooling from 330° C. to 305° C., and a third step of cooling from 305° C. to 245° C. at a rate of −50° C./min and subsequently heating from 245° C. to 365° C. at a rate of 10° C./min, a heat of fusion from 296° C. to 343° C. in the third step is 30.0 J/g or more and 45.0 J/g or less.

A porous fluorine resin film in which a fibril structure is stabilized through impregnation coating of a water-repellent and oil-repellent polymer having a high oil repellency grade, and free shrinkage also proceeds before impregnation and application of the water-repellent and oil-repellent polymer, thereby improving dimensional stability, and a method for preparing the porous fluorine resin film.