PTFE membranes and gaskets made therefrom
View Patent ↗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 0.25 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 multilayer expanded PTFE, said gasket having:
a thickness in the range of about 1.5 mm to about 9 mm,
a crystallinity index of at least about 60%
a compressibility of at least about 40%,
and a percent bolt load retention versus thickness equal to or greater than the line connecting points A and B in FIG. 18 and defined in the following table:
Point
% BLR at RT
Thickness
A
92%
1.5 mm
B
52%
9 mm.
2. 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).
3. The gasket of claim 1 , wherein said gasket has a durometer of about 85 or less.
4. The gasket of claim 1 , wherein said gasket has a matrix tensile strength of at least about 22,000 psi (151.7 MPa).
5. The gasket of claim 1 , wherein said gasket consists essentially of PTFE.
6. The gasket of claim 1 , wherein said gasket has a percent bolt load retention versus thickness equal to or greater than the line connecting the points C and D in FIG. 18 and defined in the following table:
Point
% BLR at RT
Thickness
C
93%
1.5 mm
D
70%
9 mm.
7. The gasket of claim 6 , wherein said gasket has a tensile strength in at least one direction of at least about 5,500 psi (37.9 MPa).
8. The gasket of claim 6 , wherein said gasket has a durometer of about 85 or less.
9. The gasket of claim 6 , wherein said gasket has a matrix tensile strength of at least about 22,000 psi (151.7 MPa).
10. The gasket of claim 7 , wherein said gasket consists essentially of PTFE.
11. A gasket comprising multilayer expanded PTFE having a nominal thickness of 1.5 mm, a crystallinity index of at least about 60%, a bolt load retention of at least about 91% and a compressibility of at least 40%.
12. The gasket of claim 11 , wherein said gasket has a tensile strength in at least one direction of at least about 5,500 psi (37.9 MPa).
13. A gasket comprising multilayer expanded PTFE having a nominal thickness of 2 mm, a crystallinity index of at least about 60%, a bolt load retention of at least about 90% and a compressibility of at least 40%.
14. The gasket of claim 13 , wherein said gasket has a tensile strength in at least one direction of at least about 5,500 psi (37.9 MPa).
15. A gasket comprising multilayer expanded PTFE having a nominal thickness of 3 mm, a crystallinity index of at least about 60%, a bolt load retention of at least about 85% and a compressibility of at least 40%.
16. The gasket of claim 15 , wherein said gasket has a tensile strength in at least one direction of at least about 5,500 psi (37.9 MPa).
17. A gasket comprising multilayer expanded PTFE having a nominal thickness of 6 mm, a crystallinity index of at least about 60%, a bolt load retention of at least about 65% and a compressibility of at least 40%.
18. The gasket of claim 17 , wherein said gasket has a tensile strength in at least one direction of at least about 5,500 psi (37.9 MPa).