The effects of TMP and filler stratifying on wet web runnability and end product quality of fine paper

Increase of filler content in paper improves quality of the final product and reduces raw material costs. However, this is often accompanied by deterioration of paper machine runnability. In this paper the effects of stratifying PCC (precipitated calcium carbonate) and TMP on fine paper quality and the mechanical properties of dry and wet paper were studied. In addition, a new method was introduced for evaluating the layer purity of pulp and filler stratifying by measuring the fibre length distribution in the thickness direction of the paper. The filler addition reduced the mechanical properties of paper more with chemical than mechanical pulps, with similar dry tensile indices. Stratifying filler onto paper surfaces gave higher dry tensile strength properties than samples with mixed structures, whereas only a small positive effect was detected for wet tensile and relaxation properties as a result of stratifying. Stratifying fillers only had a small negative effect on the internal bond strength. Stratifying or mixing TMP with a chemical pulp blend was shown to enable an increase in the filler content of 10% without significant changes in the residual tension (tension after 0.475 s of relaxation) or tensile index of wet samples. Based on layer purity analysis, stratifying TMP and filler was found to be successful in these trials.