1985 Volume 42 Issue 3 Pages 191-198
This study clarifies the effects of molding conditions on the degree and distribution of frozen molecular orientations for injection-molded polycarbonate disks, through the measurements of the mean birefringence, heat shrinkage and density.
The mean birefringence and heat shrinkage represent the degree of frozen orientation. They increased as the gate came closer. However, they are reduced by increasing the cylinder temperature. They are almost unaffected by the mold temperature, holding pressure, injection rate and holding time. The density increased as the gate came closer and decreased as the cylinder temperature increased. The large birefringence polycarbonate disk shrinks in the diameter direction and expands in the circuit direction in the temperature range above Tg (150°C). The aging during the heat shrinkage was measured at various temperatures, both below and above Tg. The isotherms are closely superposable by horizontal shifts. The frozen orientation is formed by the back-flow of the polymer melt from the mold cavity, due to the short holding time and to the holding pressure.
