Coextrusion is a plastic fabrication process in which two or more dissimilar materials are extruded through a single die in order to produce one end product. Through combining two materials with different characteristics, the properties of the end product may be distinct from either of the two materials on their own, thus allowing new solutions to previously challenging manufacturing requirements.
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Coextrusion makes possible the combination of different materials into one product; the different layers of materials add combinations of characteristics that are impossible to achieve through a single material. However, there are some disadvantages to coextrusion, such as accumulation of expensive scrap due to incompatible plastic materials, necessity of a knowledgeable extruder operator and significant forethought in the product design. Coextrusion is utilized in a broad spectrum of industries. In industrial manufacturing, extrusion is used for the creation of films, laminations and various coating applications as well as for plastic containers in material handling applications. In the food and beverage industry, plastic extrusions are used for packaging applications such as storage and transport. In construction, extruded plastic components can be installed in windows, garage doors and fencing. In chemical processing, extruded plastics can be used as containers for sensitive materials handling applications. Plastics materials that are often utilized in coextrusion include polyvinyl chloride (PVC), polyethylene (PE), polypropylene (PP) and acrylonitrile butadiene styrene (ABS).
The standard form of plastic coextrusion is fairly similar to the standard plastic extrusion process. To begin, granules of each raw plastic material, also referred to as pellets, are gravitationally fed into their own extruder through orifices with the help of hoppers. After they are fed into their separate extruders, the materials are heated and squeezed through a single die, forming the combined end product. Overall, co-extrusion is used for the purpose of two types of applications: barrier and non-barrier. For barrier applications, a layer that will provide characteristics such as opacity, coloration and excellent sealing properties must be incorporated. For non-barrier applications, the converter is able to maximize the physical properties of the materials without concentrating on barrier-required properties. Coextrusion is possible using many different plastic fabricating processes including extrusion coating, free film extrusion and blow molding. In extrusion coating, either a cast or blowing process is used to create an additional layer of material over a part. Coextrusion allows multiple layers of coated material instead of a single coating layer. In free film extrusion, plastic materials are extruded onto paper to imbue it with beneficial characteristics. Coextrusion is often used for this process to provide specific characteristics, such as UV-protection, that are required for the intended application.
