Mandrel for thermoplastic tubing manufacture and method relating thereto
A mandrel for the extrusion of thermoplastic tubing includes a metal wire, an optional plated barrier material over the wire, and a polymer coating over the wire or barrier material. The polymer coating is preferably a thermoset polyimide resin with embedded PTFE particles. The PTFE particles are preferably concentrated in the upper surface of the polyimide resin and purer polyimide resin is concentrated at the lower surface in contact with the metal. In use, a thermoplastic is extruded over the mandrel. The polymer coating seals the metal surface and due to the location of the PTFE particles, the polymer bonds strongly to the wire but does not bond with the plastic being extruded thereover. Under appropriate tension, the polymer-coated metal mandrel is elongated and drawn down in diameter to release the thermoplastic tubing from the mandrel.
1 . A mandrel for the manufacture of plastic tubing, comprising:
a) a metal wire having an outer diameter;
b) an elastic thermoset polymer coating on the wire, the polymer coating having a lower surface in contact with the metal wire and an upper surface; and
c) particles of a thermoplastic fluoropolymer provided in the polymer coating, where the particles are provided in a higher concentration nearer the upper surface than nearer the lower surface.
2 . A mandrel according to claim 1 , wherein:
the thermoplastic fluoropolymer is PTFE.
3 . A mandrel according to claim 1 , wherein:
at or near the upper surface the ratio of thermoset polymer to particles is approximately 1 to 20.
4 . A mandrel according to claim 1 , wherein:
at or near the lower surface, the ratio of thermoset polymer to particles is approximately 3 to 2.
5 . A mandrel according to claim 1 , wherein:
at or near the lower surface, the ratio of thermoset polymer to particles is greater than approximately 3 to 2.
6 . A mandrel according to claim 1 , wherein:
the polymer coating is a polyimide.
7 . A mandrel according to claim 1 , wherein:
the polymer coating is bonded to the wire and when the wire is placed under sufficient tension to reduce the outer diameter, the polyimide coating is also reduced in diameter.
8 . A mandrel according to claim 1 , wherein:
the metal wire is made of one of copper, stainless steel and nickel-titanium alloy.
9 . A mandrel according to claim 8 , wherein:
the copper is plated with a biocompatible surface.
10 . A mandrel for the manufacture of plastic tubing, comprising:
a) a copper wire;
b) a metal or metal alloy plating on the wire to form a plated wire; and
c) an elastic polyimide coating bonded to the plated wire, wherein when the plated wire is placed under sufficient tension to draw down its diameter, the polyimide coating is also reduced in diameter.
11 . A mandrel according to claim 10 , further comprising:
particles of a thermoplastic fluoropolymer provided in the polyimide coating.
12 . A mandrel according to claim 11 , wherein:
the thermoplastic fluoropolymers is PTFE.
13 . A mandrel according to claim 11 , wherein:
the particles are not uniformly distributed in the polyimide coating.
14 . A mandrel according to claim 11 , wherein:
the polyimide coating has a lower surface in contact with the plated wire and an upper surface and the particles are provided in a higher concentration nearer the upper surface than nearer the lower surface.
15 . A mandrel for the manufacture of tubing, comprising:
a metal wire having an elastic material coated thereon, the elastic material having a surface and including PTFE particles along its surface.
16 . A mandrel according to claim 15 , wherein:
the elastic material has a first concentration of PTFE particles at its surface and a second lower concentration of PTFE particles below its surface.
17 . A method of manufacturing a mandrel, comprising:
a) providing a metal wire;
b) coating the metal wire with a flowable polymer coating, the polymer coating including particles of a thermoplastic fluoropolymer;
c) passing the polymer coated metal wire through at least one die to define a predetermined outer diameter to the polymer coated metal wire; and
d) heating the polymer coated metal wire to solidify the polymer on the wire and cause the particles of thermoplastic fluoropolymer to have a higher concentration at a surface of the mandrel than at an interface between the wire and the polymer coating.
18 . A method according to claim 17 , wherein:
said coating includes coating with a polymer coating including PTFE.
19 . A method according to claim 18 , wherein:
said coating includes coating with a polyimide.
20 . A method according to claim 17 , wherein:
said providing a metal wire includes providing a copper wire.
21 . A method according to claim 17 , wherein:
said providing a metal wire includes providing a silver covered copper wire.
22 . A method according to claim 17 , wherein:
said providing a metal wire includes providing a metal-coated metal wire.
23 . A method according to claim 17 , wherein:
said coating includes coating the polymer at a thickness of 0.0003-0005 inch.
24 . A method of manufacturing plastic tubing, comprising:
a) providing a mandrel having a metal core and an outer surface including PTFE;
b) coating the outer surface of the mandrel in a flowable plastic material;
c) solidifying the plastic material on the mandrel;
d) placing ends of the mandrel under sufficient tension to reduce its diameter so as to cause separation of the mandrel from the plastic material dried thereover; and
e) removing the mandrel from within the plastic material to define the tubing.
25 . A method according to claim 24 , further comprising:
cutting the mandrel and the plastic material prior to placing the ends of the mandrel under tension.