Dye based inks have been the standard for production inkjet printing applications for over 40 years. These are water-based inks and common for imprinting and digital print applications.
Unlike the colorants in pigment inks, dyes are not insoluble particles that can be attached to air bubbles and flotated to the surface froth of a flotation deinking process stage. Dye inks therefore, are thought to be only flotation deinkable if the dye molecules can be fixed to components which are flotated, such as special paper coating components. In processes using a bleaching step, however, most dyes can de-colorized with reductive bleaching chemicals used in many current deinking mills. In all cases in which dyes cannot be flotated, however, dye inks lead to an undesirable coloration of the process waters and in the case of bleaching, to a higher bleaching chemical dosage requirement. In general, large amounts of water soluble colorants from any printing technology in a deinking plant can, therefore, contribute to significant difficulties.
In 2010, the DPDA conducted extensive research with CTP in Grenoble France, a leading research organization for paper and recycling technologies. The results were very positive and we conclude that some dye based inks printed on uncoated wood-free papers can be successfully de-colorized with widely used recovered paper bleaching processes in the deinking plants which utilize these processes. In fact the typical chemicals used to re-pulp the paper before deinking is sufficient to de-colorize some dye colorants. A link to this report can be found here.