Co-injection apparatus for injection molding

A co-injection molding apparatus comprising:

• a co-injection manifold including a nozzle housing having an inner surface defining a chamber and an outlet;
• and
• a co-injection nozzle pin having downstream and upstream ends, the nozzle pin having therein a central bore including an upstream end adapted to communicate with a first material and a downstream end exiting at the downstream end of the pin, the nozzle pin having an outer surface including a first portion, a second portion and a channel spiraling around the outer surface, the first portion being upstream of the second portion and the channel having a first segment defined in the first portion and a second segment defined in the second portion, the channel being adapted to communicate with a second material,
• the nozzle pin being housed in the nozzle housing such that the first portion and the first segment form a tight fit with the inner surface of the nozzle housing and the second portion and the second segment form a passageway with the inner surface, the passageway communicating with the outlet.

A method of co-injection molding comprising:

• providing a co-injection apparatus attached to a mold defining a mold cavity, the apparatus having a manifold including a nozzle housing having an inner surface defining a chamber, the mold cavity being in communication with the nozzle housing;
• housing a co-injection nozzle pin in the nozzle housing, the nozzle pin having downstream and upstream ends, the nozzle pin having therein a central bore including an upstream end adapted to communicate with a first material and a downstream end exiting at the downstream end of the pin, the nozzle pin having therein a spiraling channel in communication with a second material, the channel having a depth, a width, a first segment traveling axially and circumferentially in a downstream direction and a second segment traveling axially and circumferentially in a downstream direction, the second segment being in communication with and downstream from the first segment and the width being substantially the same distance throughout the channel;
• controlling the flow of the second material through the channel and into the mold cavity, whereby substantially all of the second material entering the channel is forced to flow through the first segment until entering the second segment where at least a portion of the second material leaks out of the channel and along the second portion toward the forward end of the pin and into the mold cavity;
• and
• controlling the flow of the first material through the upstream end of the bore and out the downstream end of the bore and into the mold cavity.