Deinkability of thermochromic offset inks

Abstract

This paper evaluates the deinkability of thermochromic offset inks. For this purpose, three thermochromic inks were printed on white uncoated paper, in laboratory conditions. These prints were mixed in equal shares and recycled by means of chemical deinking flotation under defined conditions in the laboratory according to INGEDE method 11p. Deinkability is evaluated by calculating the flotation yield, pulp’s brightness and whiteness increase and the colour properties, determination of residual ink area, as well as ash content elimination. The obtained results indicate that thermochromic prints are poorly deinkable. The image analysis shows that flotation deinking managed to eliminate only 12.8% of the total dirt area of thermochromic ink. Only a small increase in deinked handsheets brightness and whiteness (approx. 5% and 2%) is noticed. The results of surface properties determination showed that the adhesion of inks on the paper is high. Thermochromic inks can affect wastewater too, by affecting its colouration due to their interactions with deinking solution and/or as a result of their mechanical damage during defibration.