Methods of molding multi-layer polymeric articles having control over the breakthrough of the core layer
Disclosed herein are methods and systems for co-extruding multiple polymeric material flow streams into a mold cavity to produce a molded plastic article. At least one interior core stream of a first polymeric material is surrounded by inner and outer streams of at least one other polymeric material. The interior core stream serves as an interior layer of a resultant molded plastic article while the inner and outer streams serve as inner and outer layers, respectively, of the resultant plastic article. The interior core stream is selectively directed to flow into or past a downstream branch channel in a mold cavity. The downstream branch channel branches from a primary channel in the mold cavity at a branch junction. The branch channel defines a protrusion portion of the resultant molded plastic article. The leading edge of the interior core stream is selectively controlled in the branch channel to position the leading edge at or near to the terminal end of the branch channel without having the leading edge of the interior core stream breakthrough a flow-front of the inner and outer streams. The resultant molded plastic article includes an interior layer formed of the first polymeric material that extends into, through and to a distal end of the protrusion while still being encased by inner and outer layers formed from the inner and outer flow streams.
1. A method of co-extruding a plurality of polymeric plastic material streams to produce a resulting molded plastic article having a body portion and a protrusion portion, the method comprising the steps of:
forming a combined polymeric flow stream comprising an inner stream of a first polymeric material and an outer stream of the first polymeric material forming an innermost surface and an outermost surface, respectively, of the resulting molded plastic article and an interior core stream of a second polymeric material defining an interior layer of the resulting molded plastic article;
controlling the inner stream and the outer stream to selectively control the flow of the interior core stream through a branch junction formed at an intersection of an upstream primary channel and a downstream branch channel in a mold cavity downstream from a gate portion of the mold cavity; and
maintaining a first volumetric flow ratio of the inner stream to the outer stream of the first polymeric material in the primary channel throughout flow of the combined polymeric flow stream into the mold cavity.
2. The method of claim 1 , wherein the step of controlling the inner stream and the outer stream to selectively control the flow of the interior core stream through the branch junction comprises controlling the first volumetric flow ratio of the inner stream to the outer stream of the first polymeric material in the primary channel.
3. The method of claim 1 , wherein the interior core stream selectively flows through the branch junction into the downstream branch channel.
4. The method of claim 1 , wherein the interior core stream selectively flows through the branch junction past the downstream branch channel.
5. The method of claim 3 , further comprising the step of controlling a leading edge of the interior core stream to cause the leading edge to flow to, or near, a terminal end of the branch channel.
6. The method of claim 5 , wherein the step of controlling a leading edge of the interior core stream prevents the leading edge of the interior core stream from breaking through a flow front formed by the inner stream and the outer stream.
7. The method of claim 5 , wherein the leading edge of the interior core stream halts near, or at, the terminal end of the branch channel.
8. The method of claim 5 , wherein the leading edge of the interior core stream is wrapped around itself either toward the inner stream, or toward the outer stream at or near the terminal end of the branch channel.
9. The method of claim 5 , wherein the step of controlling a leading edge of the interior core stream to cause the leading edge to flow to, or near, a terminal end of the branch channel comprises controlling an extrusion start time of the interior core stream relative to an extrusion start time of the inner stream and the outer stream.
10. The method of claim 9 , wherein the extrusion start time of the interior stream occurs subsequent to the extrusion start time of the inner stream and the outer stream.
11. The method of claim 1 , wherein the molded plastic article comprises a container with a closed end coupled to a cylindrical side wall defining an open end opposite the closed end and a protrusion portion radially protruding from the side wall, the protrusion portion including an interior layer formed of the second polymeric material that extends into a distal portion of the protrusion portion.
12. The method of claim 11 , wherein the first polymeric material of the inner stream and outer stream encases the interior layer of the second polymeric material at the distal portion of the protrusion portion.
13. The method of claim 11 , wherein the protrusion portion comprises any of a lip, a flange and another cylindrical wall.
14. The method of claim 11 , wherein the protrusion portion extends circumferentially around the cylindrical side wall and has a symmetric shape.
15. The method of claim 11 , wherein the protrusion portion extends circumferentially around the cylindrical side wall and has an asymmetric shape.
16. The method of claim 3 , further comprising controlling a second volumetric flow ratio of the inner stream to the outer stream of the first polymeric material in the branch channel through control of the first volumetric flow ratio, wherein the second volumetric flow ratio is different than the first volumetric flow ratio.
17. The method of claim 1 , wherein controlling the inner stream and the outer stream to selectively control the flow of the interior core stream through the branch junction positions the interior stream on a flow line away from the zero-gradient of velocity flowline downstream of the branch junction.