A method for manufacturing a microporous film comprising the steps of:
(a) providing a first polymer which is a hydrophobic thermoplastic polymer
and a second polymer which is a hydrophilic polymer or copolymer of
N-vinylpyrrolidone;
(b) dissolving said first and second polymers in a solvent system which is
compatible with both polymers, said solvent system comprising a blend of
an aprotic organic solvent and an alcohol;
(c) coating the resulting solution on a support;
(d) effecting at least a partial drying of the resulting coating; and
(e) washing the coating in an aqueous medium so as to extract at least 50%
by weight of the said second polymer.
