Valmet OptiSizer Hard: Hard-cover rolls increase sheet strength
Valmet points out that, while strength is usually the main targetwhen applying starch on board or paper, the fact is that only thestarch located in fiber bonds has the biggest strengthening effect.The total strength of paper sheet can be improved the most by increasing the bond strength of the paper fiber network. The company's OptiSizer Hard is a completely new size application methodwhich uses higher nip loads to improve sheet strength propertiesby taking advantage of better starch penetration and decreasingfiber-to-fiber distance.
Applying more starch might just end up wetting the sheet without any strength improvement but increasing the need for dryingand using more energy.
With the OptiSizer Hard, starch is first sprayed on the rollswhich transfer the starch into the nip where it is further transferred into the paper web. The roll nip with higher nip pressureincreases the density of fibers.
This way starch enters not only the void volume but also thefiber junction points. When the fiber-to-fiber distance is relativelysmall, the porous volume is small and the pressure for liquid diffusion is large. There will be more starch in fiber junction pointsand better starch penetration. All this leads to better strength properties with OptiSizer Hard.