THE ROLE OF THE MIDDLE PLY IN MULTI LAYERED COPY PAPER

The possibilities of reducing the grammage of copy paper while maintai ning its functional and printing properties were investigated by means of a multi-ply study on a pilot scale. The main purpose was to clarif y the influence of the middle ply in a three layered structure on bend ing stiffness, formation and surface properties. The pilot scale study was done at the Swedish Pulp and Paper Research Institute using pilot paper machine with a three layer, stratified forming mode, Convention al copy paper (80g/m(2)) was compared to three layered copy paper with the same grammage but with various pulps in the middle ply. In this s tudy the middle plies of the three layered sheet were prepared from eu calypt sulfate, office waste and aspen CTMP, The single layered refere nce sheet was made entirely of the same mixture of softwood and hardwo od as the outer plies in the three layered test sheets. The results re veal that by optimizing the most appropriate fibres in the different l ayers, the desired properties, bulk and thus stiffness and formation c an be improved simultaneously. In this study, however, the stratified technology used in the pilot scale trials did not allow proper coverag e over the middle ply.