PTFE Membranes and Gaskets Made Therefrom

Abstract

Improved expanded PTFE materials and improved gasket materials made therefrom, the gaskets being capable of forming a seal with greater bolt load retention than is possible with existing PTFE gaskets. The expanded PTFE membranes of the invention can be tailored to exhibit a matrix tensile strength in at least one direction of at least 25,000 psi, a matrix tensile strength ratio in two orthogonal directions of between 0.025 and 4, an orientation index of 50° or less, and a density of 2.0 g/cc or less. The improved gaskets exhibit improved mechanical properties such as high bolt load retention, low creep, high tensile strength, low stress to seal and high crystallinity index.

1 . A gasket comprising PTFE having a nominal thickness of 1.5 mm, a bolt load retention of at least about 91% and a durometer of 85 or less. 
   
   
       2 . A gasket comprising PTFE having a nominal thickness of 2 mm, a bolt load retention of at least about 90% and a durometer of 85 or less. 
   
   
       3 . A gasket comprising PTFE having a nominal thickness of 3 mm, a bolt load retention of at least about 85% and a durometer of 85 or less. 
   
   
       4 . A gasket comprising PTFE having a nominal thickness of 6 mm, a bolt load retention of at least about 65% and a durometer of 85 or less. 
   
   
       5 . The gasket of  claim 1 , wherein said gasket has a crystallinity index of at least about 60%. 
   
   
       6 . The gasket of  claim 1 , wherein said gasket has a tensile strength in at least one direction of at least about 5,500 psi (37.9 MPa). 
   
   
       7 . The gasket of  claim 2 , wherein said gasket has a crystallinity index of at least about 60%. 
   
   
       8 . The gasket of  claim 2 , wherein said gasket has a tensile strength in at least one direction of at least about 5,500 psi (37.9 MPa). 
   
   
       9 . The gasket of  claim 3 , wherein said gasket has a crystallinity index of at least about 60%. 
   
   
       10 . The gasket of  claim 3 , wherein said gasket has a tensile strength in at least one direction of at least about 5,500 psi (37.9 MPa). 
   
   
       11 . The gasket of  claim 4 , wherein said gasket has a crystallinity index of at least about 60%. 
   
   
       12 . The gasket of  claim 4 , wherein said gasket has a tensile strength in at least one direction of at least about 5,500 psi (37.9 MPa).