De-inking of thick film UV-cured coatings using high intensity ultrasound

The research area is the recycling of post consumer waste paper using novel techniques.

The aim of this work was to investigate the use of high intensity ultrasound in the de-inking of papers printed with UV-cured inks. Thick ink films printed by screen process printing were subjected to 20kHz ultrasound. The effects of different exposure times were studied under conditions of neutral pH.

The treatment resulted in the controlled breakdown and detachment of solid and halftone printings into particle sizes that could be removed by commercial flotation and washing methods.

The temperature rise during sonication does not appear to influence either ink particle breakdown or their degree of removal. This suggests that ultrasound treatments could be used successfully to assist the de-inking of UV-cured inks at the temperatures employed in conventional de-inking plants without significant loss of ultrasound efficiency.

This paper is the first reported use of ultrasound to breakdown UV-cured ink films. Previously it had been assumed that UV-cured inks would present a recycling problem as they form an impenetrable layer that resists alkaline recycling solutions. Some reports suggested that UV-cured inks were either ‘difficult or impossible to de-ink,’ the findings reported here present a solution to that problem.