The effect of ink types and printing processes on flotation deinking efficiency of wastepaper recycling

摘要

Wastepaper is the largest fraction of solid waste. Flotation deinking plays an essential role in the product quality and process cost of wastepaper recycling. This paper investigated the effect of ink types and print- ing processes on flotation deinking. Examination of ink types in this study revealed that newsprint oil-based off set-cold and offset--heat inks contain substantia1 oil (45 tc 60) and resin (5 to 35); water--based ink contains wa- ter (40) and resin (polystyrene, 30); and these inks are liquids with densities around l g/cm3 at 25 deg. C. On the other hand, photocopy and laser-print toners were found to be solid powders with particle diameters of about 20 mu m, densities of l to l.5 g/cm3, and a composition that consists primarily of styrene-acrylate copolymers (60 to 90). Except for water-based ink, which is water sol- uble, all inks in their initial state are hydrophobic. It was found that for newsprint oil based offset--cold inks there is little change in their surface chemical properties, and their hydrophobic character is retained. These inks in the newsprint wastepaper pulp can be effectively removed by flotation. On the other hand, it was found that during the printing processes, the toner particles undergo polymeri- zation (fusion) and oxidation with the subsequent forma- tion of peroxide bonds due to exposure to heat, light, and oxygen (air). The fusion due to polymerization causes bonding to the paper fibers and the creation of larger toner particle sizes. The oxidation creates a greater polarity at the toner particle surface. These effects ac- c