An experimental study on the injection molding of thermosetting polyester resin

An experimental study was conducted on the injection molding of a thermosetting polyester resin. For the study, a general‐purpose unsaturated polyester resin was used, with benzoyl peroxide as initiator. A differential scanning calorimeter (DSC) was used for studying the curing kinetics, under isothermal curing conditions. A plunger‐type injection‐molding apparatus was constructed, and a rectangular mold cavity with glass windows on both sides was constructed, which permitted us to record on a film the changes in stress birefringence patterns in the mold cavity during the molding operation (i.e., during the isothermal cure, post cure, and subsequent cooling), using a crossed circular polariscope. The injection‐molded specimens were used to determine the distribution of the degree of cure at various positions in the flow direction, and to relate the degree of cure to the dynamic mechanical properties.