Integral gradient, skinned, submicroscopically porous, anisotropic, hydrophilic, asymmetric polyamide membranes comprising: (a) a first porous polyamide zone obtained from a polyamide solution formulated to give coagulated film with pores of a given size, (b) a fabric support imbedded in the first porous polyamide layer, and (c) a second porous polyamide zone having a skinned outer surface, obtained from a polyamide solution having the same constituents as the solution used to form the first porous polyamide zone but solution post-treated to give pores substantially smaller than those in the first porous polyamide zone, as well as a process for producing such membranes, are disclosed.
* 5500247 Method for production of a continuous web of fluid purifier membrane filter stock material having a low pressure side permeable layer sandwiched between two membrane carrier layers having cast-in place external membranes
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