Hydrophobic ozone-stable membrane made of polyvinylidene fluoride

A hydrophobic, integrally asymmetrical hollow-fiber membrane made of a vinylidene fluoride homopolymer or copolymer, which has a wall with an outer surface on its outer side and an inner surface on its inner side and a wall thickness, and a lumen enclosed by the inner side, wherein the wall of said hollow-fiber membrane has a microporous supporting layer with a sponge-like, open-pored, pore structure that is essentially isotropic across the wall thickness and without finger pores, and wherein said supporting layer extends across at least 90% of the wall thickness and has pores with an average diameter of less than 0.5 μm,

• characterized in that
• the hollow-fiber membrane has in the wall a separating layer adjacent to the supporting layer on the outer surface thereof with a thickness in the range from 0.01 to 5 μm and a structure that is denser in contrast to the supporting layer, and the outer surface under scanning electron microscopic examination at 5000 times magnification has a homogeneous, uniform structure without pores,
• said hollow-fiber membrane has a porosity in the range from 40 to 80 vol. %, a wall thickness in the range from 25 to 100 μm, and a lumen diameter in the range from 100 to 500 μm, and
• the permeability for nitrogen is at least 25 ml/(cm2·min·bar), and the elongation at break is at least 250%.