Shoe Nip Calender Possibilities for Board and Paper, 2003 Spring Technical Conference Proceedings

In shoe nip calendering, board and paper structural changes can be dramatically reduced, while at the same time improving surface properties. The main mechanisms behind this technology are extended nip dwell time, reduced specific nip pressure and gradient calendering. Measurements and visual evaluation have shown that shoe nip calendering produced a clearly more uniform surface than traditional methods, no matter whether the board or paper was printed or unprinted. Shoe nip calendering is based on the shoe roll technology used in press sections, which makes it possible to independently control nip dwell time and specific nip pressure. An elastic calender belt enables a uniform contact with the board or paper surface in the shoe nip, which is beneficial for optimum gloss evenness and low micro scale roughness. Shoe nip calendering produced clearly higher bulk and stiffness at a given surface property when compared to traditional calendering methods. This allows bulk to develop favorably without compromising printing results. Consequently, consumption of fiber can be reduced. Comparisons with different wetstack calendered packaging boards are shown as well as lower basis weight paper grades.