Printing ink pigments, dyes, toners and inks make the de-inking process of office waste paper more difficult.
Newspapers, magazines and office waste paper constitute a significant part of the recovered paper to be reprocessed into white graphic paper and sanitary paper. Due to the high requirements regarding these papers – mainly in terms of whiteness and purity, the pulp for their manufacture must undergo de-inking (i.e. ink removal) and bleaching during the preparation process. Flotation and leaching methods or a combination of both are used for ink removal. Flotation is a method of separating dispersed and colloidal impurities from water, based on the ability of the particles to stick to air bubbles and to move with them to the foam layer. In order to improve the efficiency of the process, so-called carriers (xanthogenates) are used to modify the wetting angle (surface tension). Either activators to strengthen the carriers’ operation or depressant to weaken this operation are used in order to improve the selectivity of the carriers’ operation.
