Blow-molding coextrusion coinjection

Multilayered articles can be made by coinjection blow-molding or coextrusion methods. A three-layer system generally contains a barrier layer sandwiched between two exterior layers. These are actually laminar products. In the coextrusion sequence, several extruders can be used to place the material into the mold. The multilayer container is then produced from blowing air into the preform. 

Technology to successfully produce multilayer injection blow molded bottles is much newer than that to produce multilayer extrusion blow molded bottles. Heinz Inc. s ketchup bottle was the first U.S. example (Fig. 12.22). The use of PET bottles made by coinjection blow molding has grown rapidly. As is the case for coextrusion blow molding, the key is production of the parison. Once the multilayer parison is produced, the remainder of the process is essentially the same as for single layer materials. Even stretch blow molding can be used. 

Plastic users have made a market for recycled plastic by modifying machinery for two and three layer coextrusion heads. Coextrusion is a method applied primarily to HDPE and sandwiches a recycled plastic layer in between virgin resins. It is used because it produces a uniform appearance of bottle exteriors and a market safe container. Coinjection stretch blow molding of PET is another fabrication method being looked at. It is capable of producing multi-layer bottles with recycle PET sandwiched in between. Examples of... 

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