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A dual porosity PTFE tube including an inner surface of expanded PTFE material having a first porosity and an outer surface of expanded PTFE material having a porosity different from that of the inner surface. The preferred method includes the step of forming inner and outer preformed tubular billet

A dual porosity PTFE tube including an inner surface of expanded PTFE material having a first porosity and an outer surface of expanded PTFE material having a porosity different from that of the inner surface. The preferred method includes the step of forming inner and outer preformed tubular billets of PTFE resin particles mixed with a lubricant; the outer billet is adapted to closely fit around and concentric to the inner billet. Porosity of the inner and outer surfaces is varied by changing, in the respective billets, the lubrication level and/or the PTFE resin characteristic average particle size. The inner billet is placed inside the outer billet, and the two are extruded together, thereby melding the two billets. The extrudate is then longitudinally expanded and sintered. The inner surface of the resulting PTFE tube exhibits a different porosity than the outer surface of the tube; the porosities of the inner and outer surfaces are both within a range of about 0.10-200 .mu..

대표청구항 ▼

[ We claim:] [1.] A dual porosity tube made by a method comprising the steps of:a. concentrically joining a first preformed tubular billet and a second preformed tubular billet each of the first and second preformed tubular billets comprising;i. PTFE resin particles having an average particle size g

[ We claim:] [1.] A dual porosity tube made by a method comprising the steps of:a. concentrically joining a first preformed tubular billet and a second preformed tubular billet each of the first and second preformed tubular billets comprising;i. PTFE resin particles having an average particle size greater than or equal to 355 .mu.; andii. a lubricant, the first and second tubular billets having predetermined lube levels in the range of 50 to 150 grams of lubricant to 500 grams PTFE resin and different from one and other;b. co-extruding the first and second preformed tubular billets to meld the inner and outer billets into a composite tubular extrudate having an inner surface with a first porosity and an outer surface with a second porosity different from the first porosity;c. longitudinally expanding the extrudate; andd. sintering the extrudate.