The Application of High Intensity Ultrasound to the De-inking of Recycled Papers.

This paper presents the original work carried out into the novel application of high intensity ultrasound to the de-inking of waste papers printed with digitally printed inks. These inks include fused toners, Indigo inks (ElectroInks) and UV cured coatings. They were previously considered to be ‘difficult to de-ink’ when present in conventional recycling de-inking plants because they are difficult both to detach from paper fibres and to break down into particle sizes that can be removed by conventional flotation techniques.

The significance of this work is that for all the systems investigated it was possible to both detach and reduce the size of ink particles down to a desired flotatable size range of between 20 to 120 microns. Thus digitally printed papers that had been seen as presenting a treat to effective paper recycling can be recycled using the techniques described.

Temperature was found to play a role in heat fusible toner printed materials. De-inking of the tough films produced by UV curing inks showed no temperature dependence. Indigo ink that had been feared to present problems to the recycling industry was found to be relatively easy to de-ink using these techniques. The general conclusions are that the application of ultrasound can be used to aid the de-inking of waste paper and reduce the number of chemicals used.

The paper was an invited presentation for the Non-impact Printing Conference (NIP 23) held in Anchorage, Alaska during September 2007. The NIP conference is organised the Society for Imaging Science and Technology (IS&T) with assistance from the Imaging Society of Japan and is considered to be the premiere event in evaluating the latest research developments in digital printing, attracting world class researchers from Japan and the USA.

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