Method of forming dual porosity PTFE tubes by extrusion of concentric preforms

• US 5,641,443 A
• Filed: 06/02/1995
• Issued: 06/24/1997
• Est. Priority Date: 01/29/1993
• Status: Expired due to Term

• Current Assignee: Bard Peripheral Vascular Incorporated (Becton, Dickinson & Co)
• Original Assignee: IMPRA Incorporated (Becton, Dickinson & Co)
• Inventors: Calcote, Robert, Kowligi, Rajagopal R., Wollner, Stacy
• Primary Examiner(s): Kuhns, Allan R.
• Application Number:
  US08/459,545
• Time in Patent Office: 753 Days
• Field of Search: 264/127, 264/209.5, 264/288.8, 264/289.3
• US Class Current: 264/127
• CPC Class Codes: A61F 2/06 Blood vessels
• CPC Class Codes: A61L 27/16 obtained by reactions only involving carbon-to-carbon unsaturated bonds
• CPC Class Codes: A61L 27/56 Porous materials, e.g. foams or sponges
• CPC Class Codes: A61M 2025/0062 having features to improve the sliding of one part within another by using lubricants or surfaces with low friction coatings A61M2025/0046
• CPC Class Codes: A61M 25/0009 Making of catheters or other medical or surgical tubes
• CPC Class Codes: B29C 48/022 characterised by the choice of material
• CPC Class Codes: B29C 48/09 Articles with cross-sections having partially or fully enclosed cavities, e.g. pipes or channels
• CPC Class Codes: B29C 48/21 the layers being joined at their surfaces
• CPC Class Codes: B29C 48/335 Multiple annular extrusion nozzles in coaxial arrangement, e.g. for making multi-layered tubular articles
• CPC Class Codes: B29C 48/475 using pistons, accumulators or press rams
• CPC Class Codes: B29C 55/00 Shaping by stretching, e.g. drawing through a die; Apparatus therefor B29C61/08 takes precedence
• CPC Class Codes: B29C 55/30 Drawing through a die pultrusion B29C70/52
• CPC Class Codes: B29K 2027/18 PTFE, i.e. polytetrafluorethene , e.g. ePTFE, i.e. expanded polytetrafluorethene
• CPC Class Codes: B29L 2031/7534 Cardiovascular protheses
• CPC Class Codes: B29L 2031/7542 Catheters
• CPC Class Codes: C08L 27/18 Homopolymers or copolymers or tetrafluoroethene
• CPC Class Codes: Y10T 428/139 Open-ended, self-supporting conduit, cylinder, or tube-type article
• CPC Class Codes: Y10T 428/1393 Multilayer [continuous layer]
• CPC Class Codes: Y10T 428/249981 Plural void-containing components
• CPC Class Codes: Y10T 428/31544 Addition polymer is perhalogenated

Abstract

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 μ.

Claims

1. A method of producing a dual porosity PTFE tube, comprising the steps of:

a. concentrically joining a first preformed tubular billet and a second preformed tubular billets, each of the first and second preformed tubular billets comprising;

i. PTFE resin particles having an average particle size greater than 355 μ

; and

ii. 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 separately preformed compressed first and second billets to meld the first and second 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; and

d. sintering the extrudate.

2. The method of claim 1, wherein the lube level in either the first billet or the second billet is less than or equal to about 80, and the lube level in the other billet is greater than or equal to about 120.

3. The method of claim 1, wherein the average particle size of the PTFE resin of the first billet and the average particle size of the PTFE resin of the second billet are about the same.

4. The method of claim 1, wherein the intemodal distances at inner and outer surfaces of the dual porosity PTFE tube are within the range of 0.10-200 μ

.

5. The method of claim 1, wherein the average particle size of the PTFE resin of the first billet;

and the average particle size of the PTFE resin of the second billet are different.

6. The method of claim 1, wherein the average particle size of the PTFE resin of the first billet is greater than or equal to about 700 μ

.

7. A method of producing a dual porosity PTFE robe, comprising the steps of:

a. preforming a first tubular billet of PTFE resin particles having an average particle size greater than 355 μ and

a lubricant, the first tubular billet having a lube level in the range of 10-30% by weight of the PTFE resin;

b. proforming a second tubular billet of PTFE resin particles having an average particle size greater than or equal to 450 μ and

a lubricant, the second tubular billet having a lube level in the range of 10 to 30% by weight of the PTFE resin and different from the lube level of the first tubular billet;

c. concentrically joining the first and the second tubular billets thereby forming a tubular extrusion billet;

d. co-extruding the tubular extrasion billet into a composite tubular extrudate;

e. longitudinally expanding the extrudate, thereby providing a PTFE tube having an inner surface with a first porosity and an outer surface with a second porosity different from the first porosity; and

f. sintering the extrudate.

8. The method of claim 7, wherein the lube level in the first billet is less than the lube level in the second billet.

9. The method of claim 7, wherein the lube level in the first billet is greater than the lube level in the second billet.

10. The method of claim 7, wherein the PTFE resin characteristic average particle size of the first and second billets is approximately the same.

11. The method of claim 7, wherein the characteristic average particle size of the first billet PTFE resin differs from that of the second billet.

12. The method of claim 7, wherein the second billet PTFE resin characteristic average particle size is greater than or equal to about 700 μ

.

13. A method of producing a dual porosity PTFE tube, comprising the steps of:

a. preforming a first preformed compressed tubular billet comprised of an admixture of PTFE resin particles and lubricant, the lubricant being present at a ratio in the range of 50 to 150 grams of lubricant to 500 grams PTFE resin;

b. preforming a second preformed compressed tubular billet comprised of PTFE resin paxtides and lubricant, the lubricant being present at a ratio in the range of 50 to 150 grams of lubricant to 500 grams PTFE resin and at a value different from that of the first preformed compressed tubular billet;

c. concentrically joining the first preformed compressed tubular billet within the second preformed compressed tubular billet a first preformed tubular billet and a second preformed tubular billet to form a co-extrusion billet;

d. extruding the co-extrusion billet through an extrusion barrel and die and about an extrusion mandrel to meld the first and second preformed tubular 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;

e. longitudinally expanding the extrudate; and

f. sintering the extrudate.

14. The method of claim 13, wherein the extruding step further comprises the step of heating the extrusion mandrel.

15. The method of claim 13, wherein the extruding step further comprises the step of forwardly positioning the extrusion mandrel within a tapered region of the extrusion die thereby narrowing an extrusion passageway between the extrusion mandrel and the die.

16. The method of claim 15, wherein the extruding step further comprises the step of hearing the extrusion mandrel.

17. The method of claim 16, wherein the extruding step further comprises varying a extrusion rate in the range of about 2.5 to about 5.1 cm/sec.

18. The method of claim 16, wherein the step of heating the extrusion mandrel further comprises the step of heating the extrusion mandrel to within the range of about 25°

to 200°

C.

19. The method of claim 13, wherein the extruding step further comprises the step of varying an extrusion rate in the range of about 7.5 to 15.5 cm/sec.

20. The method of claim 13, wherein the step of longitudinally expanding the extrudate further comprises the steps of:

(a) inserting an expansion plug into each of two opposing open ends of the tubular extrudate;

(b) concentrically engaging a deformable band about each of the two opposing open ends of the tubular extrudate and the inserted expansion plug;

(c) deforming the deformable band about the inserted expansion plug and the tubular extrudate at each of the two opposing open ends of the tubular extrudate, thereby creating an interference fit between the deformable band and the expansion plug to retain each opposing open ends of the tubular extrudate therebetween.

21. The method of claim 20, wherein the step of inserting an expansion plug further comprises the step of providing a plurality of expansion plugs each having an annular recess.