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
wherein said gasket has
a nominal thickness of 3 mm;
a crystallinity index of at least about 60%;
a tensile strength in at least one direction of at least 4,500 psi (31.0 MPa);
a bolt load retention of at least 85%; and
a stress to seal equal to or less than 3500 psi (24.1 MPa).
2. The gasket of claim 1 , wherein said tensile strength in at least one direction is at least 5,500 psi (37.9 MPa).
3. The gasket of claim 1 , wherein said tensile strength is at least 6,000 psi (41.4 MPa).
4. The gasket of claim 1 , wherein said tensile strength is at least 7,000 psi (48.3 MPa).
5. The gasket of claim 1 , wherein said gasket comprises multiple PTFE membranes.
6. The gasket of claim 1 , wherein said gasket comprises at least one rigid layer.
7. The gasket of claim 1 , wherein said rigid layer comprises PTFE.
8. The gasket of claim 1 in the form of a form-in-place tape.