Deinking of Thermal Inkjet Newsprint

Abstract

The advantages of digital printing are emerging into commercial printing. Deinking of inkjet prints is important because they will become a sizable portion of the waste stream. Thermal inkjet ink dispersions are water-based and under certain chemical environments can remain suspended in the process water during flotation, potentially causing discoloration in a closed-loop water system during deinking [1]. Newsprint has not been a major inkjet printing category for digital commercial inkjet prints but the recycling industry has expressed concern about the deinkability of this combination. Also, while newsprint is rarely used in the office, the advent of the commercial inkjet web press will see increasing interest in the recyclability of inkjet on newsprint media, since it provides the option for deployment of newsprint media for short-life (non-archival) printing. When inkjet inks are printed on newsprint, made from wood-containing pulp with lignin, which is then included in the papermaking furnish, the problem of process water darkening can be exacerbated under some chemical conditions. Ideally, the individual sub-micron pigments and molecular dyes in inkjet ink dispersions should be collected to form larger particles of the appropriate size and also made hydrophobic for efficient flotation.In this paper, we show that inkjet-printed newsprint can be satisfactorily deinked via chemistry based on our near-neutral HPES deinking chemistry, described previously [2]. Two kinds of chemicals are used; the “E” in HPES is ethoxylated fatty alcohol, which interacts with the ink and fibers, separates them and prevents the ink from reattaching, while aggregating small ink particles into larger ones. The “S” in HPES is a small amount of an ionic surfactant added into the flotation cell, which facilitates the creation of bubbles which carry particles to the top where they can be skimmed off with the froth, leaving the clean pulp fibers to be recovered. We studied the effect of pH, collecting and clarifying agents, water hardness, chemical loading, and bleaching chemistry on filtrate darkening. In particular, we have found that the color shade and brightness of the deinked pulp and the process water can be significantly enhanced with the addition of a suitable collector or flocculating agent, in this case aluminum sulfate.