Characterization of titanium dioxide pigment for use in a masterbatch mixer

摘要

The paper investigates the mixing of Titanium Dioxide pigment with low density polyethylene polymer in a Masterbatch mixer at 70% weight pigment loading. The properties of 5 grades of pigment were measured and compared with their mixing characteristics, in order to predict the peak torque of the mixing process. Observations of mixing in a lab mixer indicated that the peak torque was a function of pigment properties and charge-weight. Furthermore, particle size analysis showed that the polymer did not melt until quite late in the mixing process, and the mechanisms contributing to the peak torque were therefore dominated by solids properties, rather than pastes. Visual observations showed significant voids in the system, indicating that the mixer was not flooded and the charge ram could not exert stresses on the contained materials. A simple 'nip' model was developed for the mixer blade moving over material at the wall of the mixer. The blade force required to move a blade over a bed of powder was calculated. This correlated well with peak torque for all 5 grades of pigment.