Dispersion Control of Liquid Toner by Dispersant and Analysis of Adsorption Structure

Abstract

Dispersant which is effective for dispersion of liquid toner and adsorption structure of the dispersant were investigated. In order to disperse polyester toner particles in paraffin oil, a basic dispersant was examined. As the adsorbing unit, polyethyleneimine was selected, which can adsorb to carboxylic acid of polyester toner by acid-base interaction. Homopolymer of 12-hydroxystearic acid was selected as the dispersing unit because it has low polarity and it is easy to control molecular weight. Amide dispersants were synthesized by condensation reaction between adsorbing units and dispersing units of different molecular weight. After the evaluation of liquid toner dispersibility with synthesized or commercially available dispersants, it was found that the dispersant with low molecular weight adsorbing units showed better dispersibility than one with high molecular weight adsorbing units. To compare the adsorption structure of dispersants, interaction force between surfaces adsorbed with each dispersant was analyzed by colloidal probe AFM. It was indicated that the adsorbing unit of high molecular weight forms train-loop-tail structure, while that of low molecular weight forms the brush-like layer. In the case of dispersant of high molecular weight, it was suggested that some of the adsorbing unit may adsorb to more than a single particle, which causes cross-linking between particles and leads to bad dispersibility.