Patent ID: 7832089

Claim:
A method for making an insulated microwire comprising a electrically conductive metallic core and an insulative polymer sheath, comprising the steps of: selecting a metal of suitably high electrical conductivity and of relatively low melting point; selecting a polymer of relatively high melting point and of melt flow index so as to retain substantial polymer matrix strength when heated to a temperature above the melting point of said metal; wherein said quantity of said metal is heated while disposed within a first elongated inner crucible, and said polymer is heated while disposed in a second elongated outer crucible concentric with said first inner crucible; wherein said first and second crucibles are oriented vertically, with exit orifices at their lower extremities, wherein the exit orifice of the inner crucible is between about 50 mils and 75 mils, and the exit orifice of the outer crucible is at least about 300 mils; heating said metal and said polymer such that said metal is substantially liquified while said polymer is softened, whereby an inner cone of said metal exits said exit orifice of the inner crucible and is contained within an outer cone of said polymer exiting said exit orifice of the outer crucible; and codrawing said cones of said polymer and said metal simultaneously and to a large extent, such that a microwire of no more than about 8 mils outside diameter is produced comprising an elongated tube of said polymer sheathing a continuous filament of said metal.