Ink and Speck Dispersion and Removal

Advances in printing technology have posted serious problems for the deinking industry. When ink is fused, as in laser printing and the photocopy process, when water resistant binders are included in coatings or ink formulations, and when varnishes are applied to printed papers, conventional methods fail to disperse inks and specks. The objective of this article is to review different approaches available for removing these inks and specks. Copying processes, coatings, and varnishing processes are discussed prior to discussing deinking and speck removal processes.Deinking ideally involves intense mechanical, chemical, and thermal action needed to detach non-dispersible inks from fibers. The detached ink is then removed by screens, cleaners, washing, and the flotation process. If higher brightness and cleanliness are desired, high-consistency dispersion, together with bleaching or the use of agglomerating chemicals (for photocopy-laser toners), may have to be considered. For coating specks, increasing the pH. increased pulping time, and removal by cleaners are typically used to reduce the number and size of specks. Varnish specks can be more difficult to remove than coating specks, as they are resistant to chemical treatment and are not easily removed by centrifugal cleaners. Flotation removal holds promise for removing varnish specks if particle size is controlled.