Location of Softwood Sulfate Pulp in Three-Ply Office Paper, 1998 Multi-Ply Forming Forum Proceedings

The initial aim of this study was to clarify the role of softwood sulfate pulp in three-ply copy paper. The location of softwood in a multi-layered structure was studied by producing three-ply copy papers with a pilot paper machine at STFI, Sweden.

The furnish of the three-ply samples consisted of 70% hardwood, birch and eucalyptus, and 30% soflwood sulfate pulp. The location of softwood chemical pulp varied in three-ply samples. The basis weight of the samples was 80 g/m*. Some samples were also produced for basis weights 70 and 60 g/m*. The target basis weight of the top and back plies were kept constant at 20 g/m*. The filler content was 20% and was used identically in all layers.

The results revealed that bending stiffness was improved compared to the reference, if softwood was located in the middle ply instead of the outer layers. This result was the same for all basis weights used in this study. Simuhaneously formation and smoothness were improved.

The calendered samples showed that when eucalyptus was used in the middle ply, the paper structure was more bulky thus giving higher bending stiffness at a certain smoothness level compared to the sample with entirely birch as hardwood. It can be concluded that good stiffness and surface properties can best be achieved by using softwood in the middle layer together with eucalyptus sulfate and using birch sulfate in the outer layers. The amount of softwood in the middle ply could be decreased as the required fiber network for good runnability can be achieved easier when all long fibers are concentrated in the middle ply.