Novel Solutions to New Problems in Paper Deinking

This paper details both the conventional processes used for effective ink removal during the recycling of printed papers and more novel treatments. Particular attention was paid to methods employed to deal with papers printed with ‘difficult to deink’ inks such as toners from photocopiers, UV-cured ink films and liquid toner suspensions or ElectroInks®.

High intensity ultrasound was applied to pulps derived from papers printed with these newer inks in order to evaluate its effectiveness in detaching the inks from paper and establishing the resultant ink particle size distributions.
In all cases, it was found that the application of ultrasound at a frequency of 20kHz had a significant effect on the resulting ink particle size distributions. In the case of toners, it was found that particle disintegration was more effective at temperatures below the ink softening point. This was attributed to the increased brittleness of the toner at this temperature. ElectroInks® can be effectively de-inked by exposure to ultrasound coupled with washing under neutral conditions. For all the inks, the size distribution of the resultant detached ink particles was such that they could be removed using standard flotation and washing techniques.