Tailoring Printing Paper Properties-Potential and Weakness of Mechanical Pulps in Multilayered Sheets, 2007 International Mechanical Pulping Conference

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A factorial design was applied to investigate and quantify the effects of layering, surface pulp quality, centre pulp quality and the weight distribution between surface and centre layers in oriented laboratory sheets. Three-layered and non-layered reference sheets were made of different mechanical pulp furnishes on a dynamic sheetformer. Surface smoothness, paper gloss, light scattering, bendability and surface compressibility were significantly improved upon layered forming, while the bonding-sensitive properties, such as tensile index, rupture elongation, TEA and especially z-directional strength declined.

The positive impact of layered forming on for example surface properties may even be enhanced by exploiting synergistic effects from optimal combinations of centre and surface layer pulp qualities. TMP accept with a low degree of splitting and low fibre coarseness performed superior in the surface of layered sheets, compared to a highly split but coarser groundwood pulp of equal fines content and freeness. However, pure laboratory sheets, made of either the groundwood pulp or TMP accept, had equal surface roughness. The importance of the centre pulp quality was verified not only for mechanical properties, such as in-plane tensile and z-strength, bendability and compressibility, but also for light scattering and surface properties.