Patent ID: 6126826
Filing Date: 2000-10-03
Classification: B01D

Abstract:
A method of making a microporous membrane, comprising:a) providing a first solution comprising polyvinylidene fluoride polymer and a solvent: co-solvent mixture, said solvent:co-solvent mixture comprising at least one solvent selected from the group of solvents consisting of N-methyl-2-pyrrolidone, dimethyl formamide, tetrahydrofuran, methyl ethyl ketone, dimethyl acetamide, tetramethyl urea, dimethyl sulfoxide and trimethyl phosphate, and at least one co-solvent selected from the group of co-solvents consisting of formamide, methyl isobutyl ketone, cyclohexone, diacetone alcohol, diisobutyl ketone, ethyl acetoacetate, triethyl phosphate, propylene carbonate, glycol ethers, glycol ether esters, and n-butylacetate, and heating said first solution to a temperature corresponding to a desired pore size;b) spreading said first solution on a solid surface to form a film of said first solution;c) displacing said solvent: co-solvent mixture from said film with a co-solvent: non-solvent mixture, said co-solvent: non-solvent mixture comprising said at least one co-solvent of said solvent: co-solvent mixture and a non-solvent, said non-solvent miscible with said at least one co-solvent and selected from the group of non-solvents consisting of methanol, ethanol, propanol and butanol, said polyvinylidene polymer forming a fixed pore structure as said solvent: co-solvent mixture is displaced by said co-solvent: non-solvent mixture;d) removing said co-solvent: non-solvent mixture from said porous membrane by displacement with a non-solvent; ande) separating said fixed pore structure from said solid surface to form a porous membrane, wherein the heating in step a) corresponds to a temperature range associated with the group of temperatures and pore sizes consisting of 30-32.degree. C. and a pore size of 0.03 to 0.081 micron. 32-36.degree. C. and a pore size of 0.03 to 0.06 micron, 36-40.degree. C. and a pore size of 0.08 to 0.112 micron, 40-45.degree. C. and a pore size of 0.14 to 0.22 micron, 45-48.degree. C. and a pore size of 0.45 micron, 48-50.degree. C. and a pore size of 0.60 to 0.85 micron, 50-52.degree. C. and a pore size of 0.85 micron, 52-55.degree. C. and a pore size of 1.0 to 2.0 micron, 55-60.degree. C. and a pore size of 2.0 to 4.0 micron, and 60-65.degree. C. and a pore size of 4.0 to 6.0 micron.