Effect of web tension on load- and moisture-induced waviness

Research has been carried out to explore the moisture-induced waviness in paper dried under tension between rolls. The role of the web tension in out-of-plane buckling was investigated. A paper web was preconditioned at 40% RH and tensions of 480-1400N/m applied to the web while the humidity was increased to 80%RH. The topography of the paper was measured at intervals of 180s. A 70gsm paper made on a hybrid former and coated and calendered and the tensile stiffness measured after conditioning at humidities of 50%RH, 70%RH and 85%RH. When the web tension was increased from 480N/m to 1,400N/m, the wavelength decreased from 34mm to 16mm. No significant web tension effect was observed after drying. Under all tensions, the average roughness was approximately 50 micron. When moisture was involved, even when the tension was maintained in the elastic range, the waviness was permanent