Ink Particles and Recycle Paper Explanation, 1995 Recycling Symposium Proceedings

M.R.W.Walmsley

John Chapman

Monash University

Luigi Silveri

Beloit Corporation

Wastepaper deinking is now extensively practiced world wide. However, the effect of ink specks on recycle paper optical properties, like brightness, is still not well understood. This lack of understanding limits the optimal use of waste paper and process equipment. Thus, the effect of ink specks and fibres on recycle paper brightness has been experimentally studied over a range of ink and fibre conditions. Theoretical considerations extend these results to form a recycle paper brightness model which is used to explain and predict the brightness of recycle sheets.

Dominant variables controlling brightness include ink color, ink surface area, fibre scattering and absorption coefficients, and ink position in the sheet. Black ink readily absorbs light and this in turn reduces paper brightness. The amount of light absorbed by visible platelet specks is not equal on all surfaces. The top side absorbs more light than the underside. The behaviour is influenced strongly by speck diameter and fibre properties. Ink at the paper surface absorbs more light than ink within the sheet. The effect of ink position is predicted by the integral of the Kubelka-Munk transmittance equation.