Improved retention of filler clay by means of pre-flocculation and selective dosing

Increasing filler content progressively reduces sheet strength because the filler particles interfere with the potential development of fibre-to-fibre bonds and occupy spaces that might otherwise have contained fibres. The research was undertaken to evaluate and compare various polymer pretreatment systems for local filler clay for the production of a highly loaded sheet without sacrificing sheet strength, and at the same time maintaining even filler distribution. A satisfactory filler distribution and retention was achieved by selective dosing of the pre-treated and micro-flocculated filler suspension just before the paper machine headbox. The application of image analysis can be considered as an ideal method of print evaluation. Some of the loaded paper samples were printed in uni-colour on a Prufbau test printing apparatus. The quality of reproduction was evaluated by comparing the irregularity of the half-tone and full colour printed images.