Investigation on solubility of polymeric binder of xerographic toner and de-inking by emulsion process

An investigation of xerography wastepaper recycling by estimating the solubility parameter of toner to select a suitable de-inking agent has been accomplished in aqueous media. The major de-inking agents used in this study were composed of combinations of a suitable organic solvent and a surfactant. This research focused on the addition of water insoluble solvents, with their solubility parameters closely proximate to the polymeric binders in toner, to assist its initial dissolution. Subsequently, the addition of surfactant to the mixture promotes the formation of an emulsion. The ink could then be easily washed away from the pulp aqueous slurry. The most suitable de-inking agent has been identified to be the mixture of naphthalene (20%), isoamyl acetate (80%) and surfactant. At 20 °C, styrene–acrylate copolymer binder in the toner was emulsified in the pulp aqueous slurry to form a stable emulsion with a particle size of 527 nm. After repeated water washings of the pulp, the ink specks on the paper were washed away as a water emulsion and the speck of the recycled paper was lowered from 5760 ppm to less than 10 ppm. In the meantime, the brightness of the final de-inked pulp was improved from 80% GE to 85% GE, which is almost identical to the brightness of virgin unprinted paper (86% GE).