Process for producing an asymmetric porous film
It is intended to provide asymmetric porous films which are usable in blood dialysis, plasma separation, etc. and particularly excellent in the performance of selectively separating (fractionating) plasma protein, show little endogenous coagulation, complement or quinine activily and have an extremely high biocompatibility. Porous films made mainly of a synthetic polymer and having an asymmetric structure wherein, in the sectional structure, a dense layer substantially not charged at least on the outermost surface is provided in the side on which a liquid to be treated is loaded and at least part of the film other than the outermost surface is negatively charged. In the above films, the dense layer non-charged at least on the outermost surface serves as a size barrier while the part of the film other than the outermost surface serves as a charge barrier.
1. A method for manufacturing an asymmetric porous membrane, comprising providing a porous substrate membrane with an asymmetric structure mainly made from a synthetic polymer substantially free from electric charges and having a dense layer on the side on which a liquid is loaded and filtering or diffusing a solution of a negatively charged polymer that can be blocked by the dense layer from the side opposite to the dense layer to block the negatively charged polymer from permeating through the dense layer, thereby introducing negative charges to the part excluding the dense layer and immobilizing the negatively charged material to the part excluding the dense layer.
2. The method according to claim 1 , wherein the negative charges are introduced at a high density immediately below the dense layer by blocking the negatively charged polymer immediately below the dense layer.