A co-injection nozzle having a central injection channel with an open end and providing an injection path for injecting streams of melt materials to form a multi-layer article from the melt material streams. The nozzle comprises interfitting axially concentric members, including at least an interfitting shell and an outer nozzle cap, each having inner and outer surfaces. The nozzle cap has an inner surface with a frustoconical portion enclosing at least a portion of the outer surface of the interfitting shell. An enclosed portion of the outer surface of the shell has a frustoconical shape. The outer and inner frustoconical surface portions are adapted and cooperate to form an annular melt material flow passageway having a fixed tapered frustoconical portion of substantially invariable dimension which terminates at a fixed, annular orifice whose dimension is substantially invariable for flow of a melt material therethrough, for injection of the material from the nozzle.
This application is a continuation of Ser. No. 08/341,700, filed Nov. 18, 1994, now U.S. Pat. No. 5,523,045, which is a continuation of Ser. No. 07/740,749 filed Aug. 5, 1991, now abandoned, which is a continuation of Ser. No. 07/563,169, filed Aug. 3,1990, now U.S. Pat. No. 5,037,285, which is a continuation of Ser. No. 07/397,348, filed Aug. 22, 1989, now U.S. Pat. No. 4,946,365, which is a continuation of Ser. No. 07/283,000, filed Dec. 2, 1988, now abandoned, which is a continuation of Ser. No. 06/909,941, filed Sep. 19, 1986, now abandoned, which is division of Ser. No. 06/484,707, filed Apr. 13, 1983, now U.S. Pat. No. 4,712,990.
A co-injection nozzle pin (20) having downstream and upstream ends. The nozzle pin has therein a central bore (30) including an upstream end (32) adapted to communicate with a first material and a downstream end (34) exiting at the downstream end of the pin. The nozzle pin also has an outer surface (36) including a first portion (38) having a diameter D.sub.1, a second portion (40) having a diameter D.sub.2, wherein D.sub.2 is less than D.sub.1 and the first portion is rearward of the second portion. The pin further includes a channel (46) spiralling around the outer surface and being adapted to communicate with a second material. The channel (46) includes a first segment (52) defined in the first portion (38) of the outer surface and increasing in depth as it travels in a downstream direction and a second segment (54) defined in the second portion (40) of the outer surface and decreasing in depth as it travels in a downstream direction.
The invention provides a method of co-injection molding. The method includes mixing a plastic inner material and an endothermic-blowing agent to form a core mixture. A plastic outer material is injected from a first injection unit into a co-injection manifold to create a flow of outer material therethrough. The core mixture is injected from a second injection unit into the co-injection manifold to create a flow of core mixture therethrough. The flow of the outer material and the flow of the core mixture are then controlled through the co-injection manifold and into a mold cavity. The core mixture expands as heat is provided for the endothermic-blowing agent to absorb.
