Preparation of Polymer Microspheres by Phase-Separation/ Aggregation (PSA) Technique for Color Toner Applications

摘要

A particle formation method related to controlled phase separation of organic and aqueous phases, and limited aggregation/coalescence is reported. The method can be applied effectively to form microspherical polymer particles for use as electrophotographic toners. An organic solution containing a polymer resin dissolved in a solvent and an aqueous phase containing an anti-aggregation agent are prepared. The aqueous solution is added to the organic solution during vigorous stirring to facilitate aggregation of gel colloids and diffusion of solvent into the aqueous phase due to the partial aqueous solubility of the solvent. As opposed to the case when the organic phase is added to the aqueous phase under an extremely high speed of agitation (> 10,000 rpm), this phase-separation/aggregation process only requires an agitation speed of 1,000～1,500 rpm. Furthermore, removal of solvents due to diffusion into the aqueous phase is in process at the same time as the formation of gel particles. The depletion of solvents in the organic phase results in solid particle formation. Fine control of particle size distribution can be achieved by careful adjustments of the viscosity values of both the organic and the aqueous solutions. This phase-separation/ aggregation method offers numerous advantages for preparation of toners including fast production run and extremely sharp particle size distribution, with mean volume-averaged diameter to mean number-averaged diameter ratios d_l/d_n smaller than 1.1. The particle shape can also be tuned by the selection of different aqueous solubility of the solvents. Both styrene/acrylate based and polyester based materials can be applied for formation of microspherical particles by using the phase-separation/ aggregation technique.