Viscosity control for molten plastics prior to molding

Abstract

A method for controlling the viscosity of molten polymers, such as polycarbonate, takes place prior to a molding operation such as injection molding, extrusion, thermoforming or blow molding. When a significant reduction of viscosity is desirable, the plastic melt is submitted, at constant temperature, to the action of a vigorous mechanical extensional shear vibration, with minimum or no external pressure, at a constant amplitude and frequency, causing the melt to become highly elastic, and simultaneously it is fatigued, for a certain time at that temperature, maintaining this high elastic state, until the macromolecules have partially or totally disentangled, in a controllable manner, at which stage the melt is ready for a molding operation such as a simple quenching operation or an extrusion process followed by quenching to produce pellets or compounds with a better mix or a lower viscosity when remelted, or an injection molding operation where the melt viscosity has been greatly reduced allowing a better processability of the injected part, for instance allowing the use of a lower temperature of injection, a lower pressure of injection or both.

Dependencies are inferred from the claim text.