초록 ▼

Disclosed are a process for forming an open-celled microporous membrane (e.g., in film or fiber form) and a novel microporous membrane formed thereby. The process generally includes sequential cold and hot stretching operations, whereby the cold stretching operation is preferably accomplished in a p

Disclosed are a process for forming an open-celled microporous membrane (e.g., in film or fiber form) and a novel microporous membrane formed thereby. The process generally includes sequential cold and hot stretching operations, whereby the cold stretching operation is preferably accomplished in a plurality of discrete cold stretching steps. In this regard, the total cold stretch extension is of greater than about 30 percent, and advantageously greater than about 40 percent based upon the initial unstretched length of the nonporous precursor, with this total cold stretch ratio being distributed among a plurality of discrete cold stretching steps. The novel membranes of this invention are characterized by decreased pore size and increased pore densities. For example, the membranes of this invention will have an average pore radius as determined by mercury porosimetry of less than about 0.040 micron. The membranes of this invention, moreover, exhibit a distinctive “bluish”color hue (i.e., a Macbeth ColoreyeTMb* value of less than about -10 as determined by placing a single ply sample of the membrane against a black background).

대표청구항 ▼

A process for preparing an open-celled, microporous polymer membrane which comprises the steps of: (a) uniaxially cold stretching a non-porous crystalline polymeric precursor to said membrane at a temperature in the range of between about -20°C. to about 20°C. below the crystalline melting point of

A process for preparing an open-celled, microporous polymer membrane which comprises the steps of: (a) uniaxially cold stretching a non-porous crystalline polymeric precursor to said membrane at a temperature in the range of between about -20°C. to about 20°C. below the crystalline melting point of the polymeric precursor, said uniaxial cold stretching being such that said polymeric precursor is extended greater than about 30% in length as compared to the initial length of said polymeric precursor; and (b) uniaxially hot stretching in the same direction the cold stretched precursor achieved in the practice of step (a) at a temperature in the range of between about 20°C. below the crystalline melting point of the polymeric precursor to about 5°C. below the crystalline melting point of the polymeric precursor whereby to achieve a microporous polymer membrane having an open-celled structure consisting of a dense plurality of interconnected pores and characterized by having a reduced bulk density as compared to the bulk density of a corresponding nonopen-celled structure, and having a pore density of greater than about 75 pores per square micron of membrane surface area, and wherein the pores have an average length of less than about 0.10 micron, an average breadth of less than about 0.035 micron, and an average surface area of less than about 2.5×10-3 square micron.