METHOD AND APPARATUS FOR FINISHING PAPERBOARD TO ACHIEVE IMPROVED SMOOTHNESS AND BULK

摘要

A paperboard product having at least one layer of bleached or semi-bleached pulp and having improved smoothness and reduced bulk loss. For paperboard having sizing without pigment, the smoothness on the printed side as measured by the Parker test is better (lower) than 6.5 when measured using a pressure of 10 kgf/cm2 while the smoothness measured by the Hagerty/Sheffield test is not below 280 Sheffield units. For paperboard having sizing with pigment, the Parker smoothness is less than 5.0 and the Hagerty/Sheffield smoothness is not less than 180 Sheffield units. The web is finished by applying temperature and moisture gradients to the web and then smoothing the web surface using extended nip calendering. The surface of the calendering roll is maintained at a temperature of 250-400° F. Prior to entering the extended nip, the web surface is moisturized using steam showers. The nipload applied in the heated extended nip is preferably in the range of 300 to 2,500 pli.