In basic terms co – extrusion is a process whereby two or more different plastic materials are fed through a single die to create one product. As there is more than one plastic being used, often the product that is created has greater properties and increased effectiveness.
Co – extrusion can be a cost effective process especially when used in the production of pipe. You will often find that pipe will be created using more than one layer, Whereby the bulk of the pipe might be of a second generation material and the outer layer, or skin, would be a first generation material that is being used for its aesthetic purposes such as providing an attractive finish. Co – extrusion can also be used to create a a dual colour product such as the stripes on a drinking straw.
Co-extrusion is also commonly used to allow a single product to have two uses. Door seals are often created using a soft material, to allow the plastic to move to create the actual seal, attached to a more rigid trim so that the product can be attached or clipped to the door itself. This makes fitting significantly more efficient and increases the life of the product.
Although there are obvious benefits of combining two plastics, there are still some plastics that cannot be co-extruded together because of their individual properties. In order to overcome this issue often a third layer is added. This layer is added in between the plastics that cannot be co – extruded in order to allow the product to still be produced.