Method of molding multi-layer polymer plastic articles with control of relative shifting of the core layer
AssigneeKortec, Inc.
InventorPaul Swenson
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Abstract
A novel technique for molding multi-layer polymer plastic articles having inner, outer and interior or core layers by controlling relative volumetric flow rates of the inner and outer layers to enable relative shifting of the position of the core, and also the relative thickness of the inner and outer layers in the molded articles; and with leading, and, where desired, trailing ends of the interior layer flow into the mold cavity substantially positioned on the zero gradient of the velocity profile of the flowing polymer streams.
Claims28
A method for co-extruding multiple polymer plastic materials as for injecting through a gate region into a mold cavity to produce a molded article, that comprises, co-extrusively flowing streams of polymer plastic materials with at least one interior stream that is to serve as an interior core of a resulting molded plastic article within inner and outer streams of plastic material that serve as covering wall plastic material layers for the core;
- forcing the flowing streams to flow along concentric annular flow paths within and along a longitudinally extending tubular extruder nozzle to the cavity gate region;
- adjusting the flow streams initially to cause the core stream to start to flow at a region of substantially zero gradient in the transverse flow velocity profile of the extrusion;
- thereupon varying the relative volumetric flow ratio of the inner and outer layer streams after the zero-gradient flow of the core layer has started, in order to offset the core layer flow from the zero gradient and to shift the core layer closer to one of the inner or outer annular flow boundaries, thereby to produce a molded article wherein the major portion of the core layer is closer to one of the inner or outer article walls than the other.
A method for co-extruding multiple plastic materials as for injecting through a gate region into a mold cavity to produce a molded article having an interior core layer encased within inner and outer wall layers, that comprises, co-extrusively flowing inner and outer layer streams of plastic material encasing an interior core layer to inject the same though the gate region into the mold cavity;
- initially starting the flow with a substantially 50:50 ratio of inner and outer layer stream volumetric flows to cause the interior core stream to flow at a mid-plane region of substantially zero gradient in the transverse flow velocity profile of the extrusion;
- thereupon, for the major portion of the flow, varying the relative volumetric flow ratio of the inner and outer layer streams to offset the core layer stream from the mid-plane and shift the core layer closer to one of the inner or outer flow boundaries, thereby to produce a molded article wherein the major portion of the core layer within the article is closer to the inner or outer article wall.
Dependencies are inferred from the claim text.