Modeling the injection molding processing of a polypropylene closure having an integral hinge

The process of filling a closed mold with polymer resin has been simulated using an injection molding software package. The resin is polypropylene and the mold is a dispensing closure having a nominal diameter of 38 mm. This one-piece closure consists of a main body, which would be screwed onto a bottle, as well as its integral cap or lid. The body and cap are connected with an integral or living hinge. At the hinge, the directional orientation of the polymer molecular chains determines its flexibility and life as the hinge must sustain many cycles of flexing. The injection molding parameters input to the simulation program included an injection pressure of 9.5 MPa, a resin melt temperature of 230 °C, and a mold temperature of 50 °C. The analysis results include illustrations of the resin melt filling the cavity at 10% increments. Special attention is given to the hinge region where the filling process affects molecular orientation. The complete cavity filling time is predicted to take 0.71 s.