Method and apparatus for moulding cannulae
The present invention provides apparatus and methods for injection molding polymeric cannulae from liquid polymeric materials. The method includes injecting pressurized liquid polymer into a mold cavity and into an overflow and forming a conduit by forcing pressurized working fluid through the solidifying liquid polymer into the overflow. The invention provides a mold for fluid-assisted injection molding articles from polymeric materials, the mold comprising at least two parts defining a cavity having a conduit portion incorporating a needle portion; a channel for liquid polymer ingress; a channel for pressurized fluid ingress; and an overflow in communication with the conduit portion. The mold may incorporate a plurality of cavities. Preferably the volume of the overflow is equal to or greater than the volume of the conduit portion. Preferably the mold incorporates a separating means for separating the overflow from a cannula portion of an article formed in the mold.
1. A mould for fluid-assisted injection moulding of polymeric materials, the mould comprising at least two parts defining a cavity having:
a conduit portion incorporating a needle portion;
a channel for liquid polymer ingress;
a channel for pressurised fluid ingress; and
a defined overflow in communication with the conduit portion, wherein the overflow is spaced upstream from a tip of the needle portion.
2. The mould as claimed in claim 1 further incorporating a plurality of cavities.
3. The mould according to claim 1 , wherein the volume of the defined overflow portion is equal to or greater than the volume of the conduit portion.
4. The mould according to claim 1 , further incorporating a separating means for separating the defined overflow portion from a cannula portion of an article formed in the mould.
5. The mould according to claim 4 wherein the separating means is a mechanical means.
6. The mould according to claim 5 wherein the mechanical means is a cutting means.
7. The mould according to claim 6 where the cutting means is a rotary knife.
8. The mould according to claim 2 , wherein the volume of the defined overflow portion is equal to or greater than the volume of the conduit portion.
9. The mould according to claim 2 , further incorporating a separating means for separating an overflow portion from a cannula portion of an article formed in the mould.
10. The mould according to claim 3 , further incorporating a separating means for separating the defined overflow portion from a cannula portion of an article formed in the mould.
11. A method for forming an article from liquid polymeric material, the method comprising the steps of:
injecting pressurised liquid polymer into the cavity of a mould having a defined overflow, wherein the overflow is spaced upstream from a tip of a needle portion;
filling the cavity and a portion of the defined overflow with liquid polymer;
injecting pressurised fluid into the solidifying polymer to form a conduit in the polymer, the pressurised fluid forcing liquid polymer into the defined overflow;
allowing the polymer to solidify; and
removing the article from the mould.
12. The method of claim 11 further comprising the step of forming a port in the conduit by removing the solidified polymer in the defined overflow before removing the article from the mould.
13. The method according to claim 11 , wherein the entry of the polymer into the defined overflow is constrained.