Co-injection is a

polymer A polymer () is a chemical substance, substance or material that consists of very large molecules, or macromolecules, that are constituted by many repeat unit, repeating subunits derived from one or more species of monomers. Due to their br ...

injection technology in which different polymers are injected into the same

mold A mold () or mould () is one of the structures that certain fungus, fungi can form. The dust-like, colored appearance of molds is due to the formation of Spore#Fungi, spores containing Secondary metabolite#Fungal secondary metabolites, fungal ...

. This specialized process can be used to improve part performance and cost while minimizing cycle time and production volume. Co-injection can be used to extend shelf life, improve production efficiencies, and allow for greater design flexibility depending on the materials used and the application. Reasons for using co-injection are: # reducing cost by using a cheaper fill material as the non-visible core of a product # combining desired properties of polymers, such as colour (the differently colored parts in car tail lights), feel (soft-touch toothbrush) or mechanical properties. # alter the density and elasticity of the final project making it either float in water or shock absorbent. Despite these advantages, co-injection requires machinery that is more expensive and difficult to maintain than standard single injection machines. The coinjection process also has difficulty with complex geometric shapes.

References

# # Plastics industry {{polymer-stub