Method of and apparatus for molding multi-layer polymer plastic articles having inner, outer and interior or core layers, with control of relative volumetric flow rates of the inner and outer layers enabling relative shifting of the position of the core layer and control of the relative thickness of the inner and outer layers in the molded articles

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.

What is claimed is:  
     
         1 . 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.  
     
     
         2 . The method of  claim 1  wherein the relative thickness of the inner or outer layers is correspondingly varied substantially in said ratio.  
     
     
         3 . The method of  claim 1  wherein, prior to the termination of the extrusion, the flow ratio of the inner and outer layers is varied to shift the terminal end of the interior core stream back along substantially said zero gradient.  
     
     
         4 . The method of  claim 1  wherein the inner and outer stream ratio is varied after a few percent of the core layer stream flow has initially flowed.  
     
     
         5 . The method of  claim 1  wherein the adjusting of the flow stream initially causes the inner and outer streams to start to flow with substantially equal volumetric flow rates.  
     
     
         6 . The method of  claim 1  wherein said forcing is effected by disposing a longitudinal pin within and along the extruder to force the combined streams into said concentric annular flow paths.  
     
     
         7 . The method of  claim 1  wherein the relative volumetric flow ratio of the inner and outer streams is controlled by relatively restricting the respective flow channels of the streams within the extruder.  
     
     
         8 . The method of  claim 7  wherein the timing of said relative flow restricting is controlled to coincide with one or both of (1) a short time after the start of the flow of the core stream, and (2) near the termination thereof.  
     
     
         9 . The method of  claim 7  wherein the timing of said relative flow restricting is controlled intermediate the flow of the streams to the mold cavity.  
     
     
         10 . The method of  claim 7  wherein the relative flow restricting is effected by inserting a flow restrictor into the inner or outer flow stream within the extruder.  
     
     
         11 . The method of  claim 7  wherein the inner, outer and core layer flow streams are fed into respective entry channels in the extruder nozzle from respective material sources, and the flow restrictor is inserted into one of either a source flow channel, or near a nozzle entry channel.  
     
     
         12 . The method of  claim 11  wherein a plurality of similar nozzles are similarly simultaneously fed from respective material sources, with flow restrictors inserted near corresponding inner or outer layer entry flow channels in each nozzle or in common feed channels from said sources.  
     
     
         13 . The method of  claim 1  wherein the inner and outer layer streams are fed from the same plastic material source and the plastic core material stream from a different source, and the annular co-extensive streams of the core material stream encased by the inner and outer layer streams are combined near said gate region and laterally injected in opposite transverse directions into the mold cavity.  
     
     
         14 . The method of  claim 13  wherein the molded article thereby formed is a hollow plastic container in which the interior core layer encased by inner and outer container walls is of material that serves as a barrier layer for such purposes as resisting the flow of gases through the container walls and/or scavenging oxygen.  
     
     
         15 . The method of  claim 1  wherein a three-material plastic article is to be molded comprising inner and outer layers and two interior or core layer materials and wherein the inner and outer layer material streams are divided within the nozzle to form the inner and outer annular covering wall layers, one of the interior layer streams being directed within the nozzle to form an interior annular layer adjacent said inner layer, and the other interior stream being directed within the nozzle to form an interior annular layer adjacent the outer layer.  
     
     
         16 . 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.  
     
     
         17 . The method claimed in  claim 16  wherein said flow ratio is varied back to substantially 50:50 near the terminal end of the flow into the cavity.  
     
     
         18 . The method claimed in  claim 16  wherein the ratio is varied after a few percent of the core layer stream flow has initially flowed.  
     
     
         19 . The method in  claim 16  wherein the ratio is further varied during the continued flow to the gate region, and into the mold.  
     
     
         20 . The method of  claim 19  wherein said ratio is varied back to substantially 50:50 near the terminal end of the flow to re-establish the interior core stream flow back along substantially said zero gradient.  
     
     
         21 . The method of  claim 16  wherein the core layer stream material is selected for barrier function characteristics such as at least one of gas permeation control, gas-scavenging, and electromagnetic shielding.  
     
     
         22 . Apparatus 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, the apparatus having, in combination, a longitudinally extending extruder nozzle for receiving plastic material from sources thereof and co-extrusively flowing the material as inner and outer layer streams of plastic material encasing an interior core layer to inject the same through the gate region into the mold cavity; flow control means for initially starting the flow with a substantially 50:50 ratio of inner and outer layer stream volumetric flow rates 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; means for thereupon, for the major portion of the flow, adjusting the flow control means to change 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 in the cavity wherein the major portion of the core layer within the article is closer to one of the inner or outer article wall.  
     
     
         23 . The apparatus claimed in  claim 22  wherein the flow control means is adjusted to vary the flow ratio back to substantially 50:50 near the terminal end of the flow into the cavity.  
     
     
         24 . The apparatus claimed in  claim 22  wherein the flow control means is operated to change the ratio after a few percent of the core layer stream flow has initially flowed.  
     
     
         25 . The apparatus claimed in  claim 22  wherein the flow control is adjusted to further vary the ratio during the continued flow to the gate region.  
     
     
         26 . The apparatus of  claim 25  wherein the flow control means is adjusted to vary said ratio back to substantially 50:50 near the terminal end of the flow to re-establish the interior core stream flow back along substantially said zero gradient.  
     
     
         27 . The apparatus of  claim 22  wherein the core layer stream material is selected for barrier function characteristics such as at least one of humidity control, gas permeation, gas scavenging and electromagnetic shielding.  
     
     
         28 . Apparatus for co-extruding multiple plastic materials as for injecting through a gate region into a mold cavity to produce a molded article, having, in combination, a longitudinally extending tubular extrusion nozzle provided with entry channels for receiving plastic materials from sources thereof and co-extensively flowing the materials as inner and outer layer streams with 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; a longitudinal throttle means for forcing the streams to flow along concentric annular flow paths within and along a longitudinally extending tubular-extruder nozzle to the cavity gate region; means for 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; means operable thereupon for 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 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.  
     
     
         29 . The apparatus of  claim 28  wherein the relative thickness of the inner or outer layers is correspondingly varied substantially in said ratio.  
     
     
         30 . The apparatus of  claim 28  wherein, prior to the termination of said extrusion, the adjusting means is controlled to vary the flow ratio of the inner and outer layers to shift the terminal end of the interior core stream back along substantially said zero gradient.  
     
     
         31 . The apparatus of  claim 28  wherein the adjusting means varies the inner and outer stream ratio after a few percent of the core layer stream flow has initially started.  
     
     
         32 . The apparatus of  claim 28  wherein the adjusting means initially causes the inner and outer streams to start with substantially equal volumetric flow rates.  
     
     
         33 . The apparatus of  claim 28  wherein said adjusting means comprises an axial pin for forcing the combined streams into said concentric annular flow paths.  
     
     
         34 . The apparatus of  claim 28  wherein the relative volumetric flow ratio of the inner and outer streams is controlled by restrictors disposed in the respective flow channels of the streams within the extruder.  
     
     
         35 . The apparatus of  claim 34  wherein means is provided for controlling the timing of the relative restricting by the restrictors to coincide with one or both of shortly after the start of the flow of the core stream, and near the termination of the core stream flow.  
     
     
         36 . The apparatus of  claim 35  wherein means is provided for controlling the timing of the relative flow restricting intermediate the flow of the streams to the mold cavity.  
     
     
         37 . The apparatus of  claim 35  wherein the relative flow restricting is effected by means for inserting a flow restrictor into one of the inner or outer flow streams.  
     
     
         38 . The apparatus of  claim 28  wherein the inner, outer and core layer flow streams are fed into respective entry channels in the nozzle from respective material sources, and the flow restrictor is inserted into one of (1) a source flow channel or (2) near a nozzle entry channel.  
     
     
         39 . The apparatus of  claim 28  wherein a plurality of similar nozzles is provided, the nozzles of which are similarly simultaneously fed from respective material sources, with flow restrictor means inserted in corresponding inner or outer layer entry flow channels in each nozzle or in common feed channels from said sources.  
     
     
         40 . The apparatus of  claim 28  wherein the inner and outer layer streams are fed from the same plastic material source and the plastic core material stream from a different source, and the annular co-extensive streams of the core material stream encased by the inner and outer layer streams are combined near said gate region and laterally injected in opposite transverse directions into the mold cavity.  
     
     
         41 . The apparatus of  claim 40  wherein the molded article thereby formed is a hollow plastic container in which the interior core layer is of material that serves as a barrier layer for such purposes as resisting the flow of humidity and or gases through the container walls and/or scavenging oxygen through chemical combination therewith.  
     
     
         42 . The apparatus of  claim 28  wherein a 3-material plastic article is to be molded comprising inner and outer layers and two interior or core layer materials, and wherein the inner and outer layer material streams are divided within the nozzle to form the inner and outer annular covering wall layers, one of the interior layer streams is directed within the nozzle to form an interior annular layer adjacent said inner layer, and the other interior stream is directed within the nozzle to form an interior annular layer adjacent the outer layer.  
     
     
         43 . The method of  claim 1  wherein a plurality of similar extruder nozzles is provided similarly simultaneously fed from respective material sources, and with flow restriction inserted in corresponding inner and outer layer entry flow channels into each nozzle or in common feed channels from said sources.  
     
     
         44 . The method of  claim 1  wherein two interior streams are flowed within said inner and outer streams, with the flow of one of the interior stream started before the flow of the other interior stream and with its leading edge starting on said zero-gradient, and the subsequent initiation of the flow of said other interior stream offsetting the later-flowing portions of said one interior stream flow from said zero gradient, and with the completing of the injecting of the other interior stream before the completion of the injecting of said one interior stream through said gate region and into said mold cavity, and finishing the injecting of said interior stream on said zero gradient.  
     
     
         45 . The method of  claim 44  wherein the materials of the inner, outer and interior streams constitute three molding materials forming a four-layer molded article.  
     
     
         46 . The method of  claim 45  wherein the relative thickness and position of each of the interior streams is chosen to enhance the properties of the molded article.  
     
     
         47 . The method of  claim 46  wherein the innermost of the interior streams is of gas scavenging material in order to reduce the permeation rate of gas through said outer wall of the molded article, and to increase the rate of gas scavenging from the contents of the article if the scavenger material is intended to absorb gas permeating from the exterior of the article.  
     
     
         48 . The method of  claim 46  wherein the outermost of the interior streams is of humidity sensitive gas barrier material in order to position such barrier at a position within the molded article that is closer to the exterior atmosphere surrounding the article.  
     
     
         49 . The method of  claim 44  wherein the article is one of a cylindrical-shaped hollow container, such as a bottle, and a flat-shaped article.  
     
     
         50 . The apparatus of  claim 22  wherein said inner core layer comprises a pair of interior core streams, with said adjusting means enabling one of the interior streams to start flow before the other of the pair of interior streams and with its leading edge starting on said zero gradient, and enabling the subsequent initiation of the flow of said other interior stream offsetting the later-flowing portions of said one interior stream through said gate region and into said mold cavity, with the finishing of the injecting of said one interior stream lying on said zero gradient.  
     
     
         51 . The apparatus of  claim 50  wherein the materials of the inner, outer and interior streams constitute three molding materials forming a four-layer molded article.  
     
     
         52 . The apparatus of  claim 51  wherein the relative thickness and position of each of the interior streams is chosen to enhance the properties of the molded article.  
     
     
         53 . The apparatus of  claim 52  wherein the innermost of the interior streams is of gas scavenging material in order to reduce the permeation rate of gas through said outer wall of the molded article, and to increase the rate of gas scavenging from the contents of the article if the scavenger material is intended to absorb gas permeating from the exterior of the article.  
     
     
         54 . The apparatus of  claim 52  wherein the outermost of the interior streams is of humidity sensitive gas barrier material in order to position such barrier at a position within the molded article that is closer to the exterior atmosphere surrounding the article.  
     
     
         55 . The apparatus of  claim 50  wherein the article is one of a cylindrical-shaped hollow container, such as a bottle, and a flat-shaped article.  
     
     
         56 . A molded plastic material article having an interior plastic core layer encased within inner and outer plastic wall layers wherein the major portion of the core layer within the article is closer to one of the inner or outer article walls.  
     
     
         57 . The molded article of  claim 56  wherein the article is hollow and bounded by the core-encased inner and outer walls.  
     
     
         58 . The molded article of  claim 57  wherein the initial portion the core layer lies substantially on the centerline of the core-encased inner and outer article walls.  
     
     
         59 . The molded article of  claim 58  wherein said initial portion constitutes a few percent of the length of the core layer.  
     
     
         60 . The molded article of  claim 59  wherein the core layer near its terminal end again lies substantially on said centerline.  
     
     
         61 . The molded article of  claim 59  wherein the core layer material is selected for barrier function characteristics such as at least one of humidity control, gas permeation, gas scavenging and electromagnetic shielding.  
     
     
         62 . The molded article of  claim 59  wherein the inner and outer walls and the core are of three molding materials forming a four-layer molded article.  
     
     
         63 . A pre-form for a hollow molded plastic material article having an interior plastic core layer encased within inner and outer plastic wall layers wherein the major portion of the core layer within the pre-form is closer to one of the inner and outer article walls.  
     
     
         64 . The pre-form of  claim 63  wherein the initial portion of the core layer lies substantially on the centerline of the core-encased inner and outer article walls.  
     
     
         65 . The pre-form of  claim 64  wherein said initial portion constitutes a few percent of the length of the core layer.  
     
     
         66 . The pre-form of  claim 65  wherein the core layer near its terminal end again lies substantially on said centerline.  
     
     
         67 . The pre-form of  claim 65  wherein the core layer material is selected for barrier function characteristics such as at least one of humidity control, gas permeation, gas scavenging and electromagnetic shielding.