Hydrophilized membrane of porous hydrophobic material and process for preparing the same

Claim 1

A process for hydrophilizing a microporous hydrophilic membrane, comprising: (a) dipping said microporous membrane of a hydrophobic polymer material into a solution of a hydrophilizing agent which is solid at about 20° C. and substantially insoluble in water to allow said hydrophilizing agent to adhere to at least a portion of the surface of the membrane; (b) removing said microporous membrane of said hydrophobic material from said solution and evaporating the solvent for said hydrophilizing agent; and (c) heating said microporous membrane to a temperature lower than a temperature that said hydrophobic polymer material starts to shrink thermally and not lower than the temperature which is lower by 10° C. from the melting point of said hydrophilizing agent, and wherein said hydrophobic polymer material is selected from the group consisting of polyethylene, polypropylene, poly-4-methylpentene-1, polyvinylidene fluoride, polytetrafluoropropylene, copolymers of hexafluoropropylene and tetrafluoropropylene, and copolymers of a fluorinated olefin monomer and an olefin monomer; and wherein said membrane has a porosity of 20-90 volume %, and having the surface area of the pores thereof being not less than 10% coated with from 1-100% by weight of a hydrophilizing agent based on the weight of the hydrophobic membrane, said agent being a monoester of propylene glycol and a saturated fatty acid having 12-22 carbon atoms which is solid at about 20° C. and substantially insoluble in water.