Patent ID: 7226558

Claim:
A method for producing a high density microwall (HDM) expanded polytetrafluoroethylene (ePTFE) structure, comprising the steps of: providing an ePTFE tube having a first inner diameter; radially expanding said ePTFE tube to form a radially expanded tube having a second inner diameter greater than said first inner diameter; calendering said radially expanded tube while maintaining said second inner diameter substantially constant to form a calendered tube; and heating said calendered tube above the crystalline melt-point for polytetrafluoroethylene while maintaining said second inner diameter substantially constant to form said HDM ePTFE structure, wherein said calendering step further comprises the steps of: positioning said radially expanded tube over a cylindrical mandrel having an outer diameter approximately equal to said second inner diameter to form a loaded mandrel; placing said loaded mandrel between a first metallic plate and a second metallic plate, wherein said first metallic plate is maintained in a substantially parallel position with respect to said second metallic plate; applying a force to said first metallic plate, wherein said loaded mandrel is compressed between said first and second metallic plates, and wherein said radially expanded tube is contacted by both of said first and second metallic plates during the applying step; and moving said second metallic plate in reciprocal fashion along a direction perpendicular to the central axis of said loaded mandrel while said first plate is held stationary under a constant load.