Methods for injection molding and blow-molding multi-layer plastic articles

A method of injection molding an at least three layer multi-material plastic container by use of a multi-coinjection nozzle, multi-cavity injection molding apparatus, which comprises,

• providing a source of supply for each polymer melt material which is to form a layer of more than one container,
• providing a coinjection nozzle for each cavity, said co-injection nozzle having a central channel,
• providing a separate flow stream from each source of supply of polymer material,
• providing at upstream locations removed from the nozzle means in communication with each flow stream for splitting each separate flow stream into a plurality of flow streams, one or more streams from each separate stream together forming a set of split streams, each set of split streams intended for a predetermined coinjection nozzle,
• moving each of the plurality of flow streams separately to its predetermined coinjection nozzle,
• maintaining the flow streams separate in a portion of each coinjection nozzle, and
• injecting the flow streams through each injection nozzle into a juxtaposed cavity to form the multi-layer, multi-material plastic container.

A method of molding a five-layer, multi-material plastic parison for forming a blow-molded container by use of a multi-coinjection nozzle, multi-cavity injection molding apparatus, which comprises,

• providing a source of supply for each polymer melt material which is to form a layer of more than one parison, the parison having an outside surface layer, an inside surface layer and internal layers therebetween, the internal layers including a buried barrier layer,
• providing a coinjection nozzle for each cavity, said connection nozzle having a central channel,
• providing a separate flow stream from each source of supply of polymer material,
• providing at upstream locations removed from the nozzles means in communication with each flow stream for splitting each separate flow stream into a plurality of flow streams, one or more streams from each separate stream together forming a set of split streams, each set of split streams intended for a predetermined coinjection nozzle,
• moving each of the plurality of flow streams of each set through a separate channel separately to its predetermined coinjection nozzle,
• constructing each nozzle and separate channel and arranging them such that each stream of split material of one set moved from its point of splitting to its intended nozzle and which is to form a layer of a container is provided to have substantially the same experience in its path to its intended nozzle, as is provided to the other split streams of the other sets in their paths to their intended nozzles,
• receiving separately each moved flow stream of a set in its intended nozzle,
• maintaining the flow streams separate in a portion of each coinjection nozzle,
• providing valve means in the central channel of each nozzle, and utilizing the valve means during each injection sequence for initiating and terminating flow into the central channel of at least the materials which are to form the surface layers injecting the flow streams through each injection nozzle so as to cause foldover of internal layer material in a juxtaposed cavity to form the multi-layer, multi-material parison,
• providing a plurality of blow molds which define blow-mold cavities for blow-molding the containers from the parisons,
• providing a plurality of the parisons in a plurality of the blow-mold cavities, and blow-molding the containers from the parisons.

A method of injection molding an at least three-layer, multi-material plastic container having a side wall with a marginal end portion and whose total side wall thickness below the marginal end portion is from about 0.0810 inch to about 0.0990 inch, by use of an injection molding apparatus, which comprises,

• providing a plurality of coinjection nozzles and for each nozzle a single associated injection cavity,
• providing a source of supply and a source of polymer flow movement for each polymer melt material, including providing and utilizing a common source of polymer flow movement for one of the polymer melt materials which is to form two layers of each container,
• channelling a part of each polymer material flow stream from its source of flow movement through separate channels to each of more than one of said coinjection nozzles,
• providing valve means operative in each of the coinjection nozzles and utilizing the valve means in each of said coinjection nozzles for positively controlling flow and non-flow of separately channeled flow streams to form layers of the multi-layer articles substantially simultaneously in each of the coinjection nozzles, and constructing the nozzles and channels and arranging them such that material from the same source of polymer flow movement channeled to each nozzle has substantially the same experience in its path to each nozzle so as to provide the flow streams in one nozzle with substantially the same mass flow characteristics as the flow streams provided in each other nozzle.