OPTICAL PROPERTIES OF DEINKED PULP CONTAINING THERMOCHROMIC OFFSET INKS

Abstract

This paper evaluates the efficiency of thermochromic offset prints recycling using deinking flotation method. Since offset thermochromic inks differ in their composition from conventional offset inks, the aim of this research was to determine how effectively they can be recycled. In the experimental part of the work, the laboratory printing of two thermochromic inks was conducted. For both types of inks, white uncoated paper was used as a substrate. After accelerated aging, the prints were mixed in equal proportions and then recycled in laboratory conditions, by means of deinking flotation. During the recycling process, handsheets and filter pads were prepared from the pulp obtained before and after deinking flotation. Handsheets and filter pads were also prepared from unprinted paper that was used as printing substrate, in order to obtain reference samples. The deinking flotation efficiency was evaluated by calculating the flotation loss, ash elimination, pulp’s brightness and whiteness increase and determination of residual ink area. The obtained results indicate that thermochromic prints are poorly deinkable. A small increase in deinked pulp’s brightness and whiteness (approx. 7% and 11%) is noticed. The image analysis shows that flotation deinking managed to eliminate around 40% of the total dirt area of thermochromic ink.