Microporous membrane with a stratified pore structure created in situ and process

Abstract

A microporous membrane is described comprising at least two layers, wherein each layer is characterized by nodes interconnected by fibrils, the layers are bonded by means of plastic flow at temperatures below the melting point of either membrane material, and the pore architecture is formed in situ by an expansion process. A stratified microporous membrane is produced wherein the pore architecture of each layer may be discretely controlled. The article is useful for filtration and medical applications where a pore size gradient is required.

Having thus described our invention, we claim:  
     
         1 . A microporous membrane comprising 
 at least two discrete layers, wherein    each layer is characterized by nodes interconnected by fibrils,    the layers of which are bonded by means of plastic flow at temperatures below the melting point of either membrane material, and    the pore architecture of each layer is formed in situ by an expansion process.    
     
     
         2 . The microporous membrane of  claim 1 , wherein 
 at least one layer of the microporous membrane is polytetrafluoroethylene.    
     
     
         3 . The microporous membrane of  claim 1 , wherein 
 at least one layer of the microporous membrane is an interpenetrating polymer network of polytetrafluoroethylene and polysiloxane.    
     
     
         4 . The microporous membrane of  claim 1 , wherein 
 each layer is comprised of different polymer formulations.    
     
     
         5 . The microporous membrane of  claim 1 , wherein 
 each layer has been subjected to different Theological conditions of extrusion.    
     
     
         6 . The microporous membrane of  claim 1 , wherein 
 each layer has been subjected to different expansion conditions.    
     
     
         7 . The microporous membrane of  claim 1 , wherein 
 the mean pore size of each layer is disparate.    
     
     
         8 . The microporous membrane of  claim 1 , wherein 
 at least one layer is polytetrafluoroethylene, and,    each layer has been subject to different rheological conditions of extrusion, and    each layer has been subjected to different expansion conditions, and    the mean pore size of each layer is disparate.    
     
     
         9 . The microporous membrane of  claim 1 , wherein 
 at least one layer is an interp enetrating polymer network of polytetrafluoroethylene and polysiloxane, and,    each layer has been subject to different rheological conditions of extrusion, and    each layer has been subjected to different expansion conditions, and    the mean pore size of each layer is disparate.    
     
     
         10 . The microporous membrane of  claim 1 , wherein 
 at least one layer of the microporous membrane is polytetrafluoroethylene, and    at least one layer of the microporous membrane is an interpenetrating polymer network of polytetrafluoroethylene and polysiloxane, and    each layer has been subjected to disparate expansion conditions.    
     
     
         11 . A process of creating a microporous membrane comprising the steps of 
 extruding a first polymer composition partially saturated with lubricant into a ribbon,    extruding a second polymer of like or dissimilar composition partially saturated with lubricant into a ribbon,    calendering bonding said first ribbon to said second ribbon at temperature below the melting point of either ribbon material,    volatilizing said lubricant from the ribbon,    stretching said laminated ribbon as to create a microporous membrane.    
     
     
         12 . A process of creating a microporous membrane comprising the steps of 
 extruding a first polymer composition partially saturated with lubricant into a ribbon,    extruding a second polymer of like or dissimilar composition partially saturated with lubricant into a ribbon,    calender bonding said first ribbon to said second ribbon at temperature below the melting point of either ribbon material,    volatilizing said lubricant from the ribbon,    stretching said laminated ribbon as to create microporous membrane, and    heating the microporous sheeting above its crystalline melting point.    
     
     
         13 . A process of creating a microporous membrane comprising the steps of 
 extruding a first polymer composition partially saturated with lubricant into a ribbon,    orienting said first ribbon in at least one direction,    extruding a second polymer of like or dissimilar composition partially saturated with lubricant into a ribbon,    calender bonding said first ribbon to said second ribbon at temperature below the melting point of either ribbon material,    volatilizing said lubricant from the ribbon, and    stretching said laminated ribbon as to create microporous membrane.    
     
     
         14 . A process of creating a microporous membrane comprising the steps of 
 extruding a first polymer composition partially saturated with lubricant into a ribbon,    orienting said first ribbon in at least one direction,    extruding a second polymer of like or dissimilar composition partially saturated with lubricant into a ribbon,    calender bonding said first ribbon to said second ribbon at temperature below the melting point of either ribbon material,    volatilizing said lubricant from the ribbon,    stretching said laminated ribbon as to create microporous membrane, and    heating the microporous sheeting above its crystalline melting point.