The role of print layer thickness and cohesiveness on deinking of toner-printed papers

Reproductions of an image, made up of 400- mu m dots on an acid- and an alkaline-sized paper by four copiers and two laser printers, were used to establish the role of toner layer cohesiveness on the speckiness problem associated with flotation deinking of toner-printed papers. Toner prints from various machines were found to fragment to different degrees upon repulping at low and high consistencies. The response of the prints to the same mechanical treatment was related to toner layer thickness and density, which in a printer or copier, are largely set in the development step prior to image fixing on paper by toner fusing. Thus, the cohesive strength of the print rather than the degree of bonding of the toner layer to the paper appears to govern the number of large, visible specks in the pulp after repulping. Low-consistency repulping at 5% was ineffective at breaking up thin or thick toner layers, but as repulping consistency was raised to 16%, thin prints were well dispersed whereas thick layers were hardly broken up. The larger the number of visible specks after repulping, the larger their number after flotation.