(297b) In-Mold Coating for Thermoplastic Substrates: Flow Modeling and Rheology

In-mold coating (IMC) for thermoplastic parts is an environmentally friendly alternative to priming and painting processes commonly employed to protect products from outdoor exposure and/or improve their surface appearance as in case of automotive parts. The coating operation is performed by injecting a coating material onto the surface of the substrate with the mold closed. The coating flows by compressing the substrate under pressure. There are key issues that need to be addressed for a successful IMC operation. The location of IMC nozzle should be located such that total coverage is achieved and the potential for air trapping is minimized. The selected location should be cosmetically and be accessible for ease of maintenance. This necessitates the use of fill patterns. To avoid leakage of the coating material, the generated hydraulic force must never exceed the clamping force. Therefore it is imperative that we predict the pressures generated during coating injection. A Control Volume Finite Element Method (CV/FEM) based simulation tool has been developed to accurately predict the fill pattern and pressure distribution during the coating flow using the Carreau viscosity model and considering slip at the wall, which is needed due to the micro flow characteristics of the coating operation. The rheological and slip parameters are measured by using a micro slit rheometer built in our laboratory. In this paper, the predictions of the model are compared to experimental results.