In-mold coating (IMC) process for thermoplastic parts

In mold coating (IMC) is an environmentally friendly alternative to painting for injection molded plastic parts. IMC is carried out by injecting a liquid low viscosity thermoset material onto the surface of the thermoplastic substrate while it is still in the mold. The coating then solidifies and adheres to the substrate. IMC process is being integrated with conventional thermoplastic injection miolding to improve the part surface quality and to protect it from outdoor exposure. A power law viscosity model is employed to describe the theological behavior of the coating material. The continuous deformation of the thermoplastic substrate caused by the coating injection is analyzed by means of the PVT relationship of the substrate. The corresponding model is solved using the Control Volume based Finite Element Method (CV/FEM) to predict the fill pattern and pressure distribution during the coating flow. The predicted results are compared to experimentally obtained fill patterns. The need to include the "edge effect" and the probable reasons for deviation of pressures from experimental observations are also discussed.