Deinking Difficulties Related to Waterbased Ink Printed Papers Analysis of Redeposition Phenomena, 2000 Recycling Symposium Proceedings

Gérard GALLAND, Bruno CARRÉ, Xavier ROUSSET, & Yves VERNAC --The paper will describe trials performed in order to get a better understanding of redeposition phenomena when recycling waterbased ink printed papers. Even if waterbased ink fragmentation is much greater in alkaline than neutral conditions. The redeposition ink particles on fibres is much more pronounced in neutral than in alkaline conditions. The pH increase induces a higher ionisation of the fibre carboxylic groups which causes stronger electrostatic repulsive forces. The higher redeposition in neutral conditions can be reduced by the addition of a surfactant, however still at a higher level than that obtained in alkaline conditions. In neutral conditions, this redeposition seems mostly to be on the fibre surface (extra-fibre) and not inside the lumen. In alkaline conditions, with a high load of ink, as in the case when there is heavy recycling of the thickening waters containing flexo inks, this redeposition can be very high. The redeposition could then be a compromise between an intra-fibre redeposition (fibres suck in the small flexo inks during alkaline swelling) and an extra-fibre redeposition. The intra-fibre redeposition would be more detrimental than that observed in neutral conditions because it seems to be irreversible. All these observations are translated into recommendations for the deinkers which face to significant amounts of waterbased inks in their furnish.