Supported microporous filtration membrane and method of using same

DETAILED DESCRIPTION The present invention provides a supported microporous filtration membrane comprising a porous nonwoven fibrous support material having first and second sides, and a continuous microporous membrane with first and second layered zones.
The first side of the support material is integral with the first zone while not protruding into the second zone, and the first zone has a pore size at least about 50% greater than the pore size of the second zone.
The present invention further provides a method of preparing such a supported microporous filtration membrane.
The method comprises providing a porous nonwoven fibrous support material having first and second sides, applying a first casting solution onto the first side of the support material to form a first casting solution layer having a substantially smooth surface, applying a second casting solution onto the substantially smooth surface of the first casting solution layer to form a second casting solution layer prior to the complete formation of a membrane from the first casting solution, and forming a continuous microporous membrane having first and second zones from the first and second casting solutions such that the first side of the support material is integral with the first zone while not protruding into the second zone, and the first zone has a pore size at least about 50% greater than the pore size of the second zone.