Effect of wavelength selection on determination of ink content and ink elimination at 700 or 950 nm

Abstract

Effective residual ink concentration (ERIC) and ink elimination (IE) are often used to evaluate the removal of printing ink in deinking. For these measurements, the light reflectance is recorded at 950 nm or 700 nm even though only the use of the former for effective residual ink concentration is instructed in the ISO and TAPPI standards. In this study, these two wavelengths were compared using a set of recycled pulp samples having variable fiber fines, fillers, and ink contents. It was seen that both wavelengths are well suited for the determination of effective residual ink concentration, especially when the recovered papers are not green or blue. Effective residual ink concentration values measured at 700 nm are higher than those obtained with 950 nm because, in addition to black printing ink, the presence of cyan-colored inks contributes to the former. Ink elimination values are similar for both wavelengths because ink elimination is a percentage ratio of ink removal in flotation. The fine materials and printing ink also affect light scattering at 950 nm, although the range appears narrower for 950 nm than for 700 nm.