Adjustment of Strength and Air Permeation Resistance of Low Basis Weight Paper by Separated Beating

Abstract

This paper reports a method for improving the air permeation resistance and strength of low basis weight paper by applying separated beating. Sw-BKP was beaten to prepare three pulp stocks with three freeness levels (713, 500, and 300 mL CSF), and the fiber properties and one pass retention of the handsheet were analyzed. In addition, using Scheffe’s three-component simplex design, this study investigated the change in the physical properties of paper according to the mixing of the three types of the pulp. The freeness of the pulp, air permeation resistance, and tensile strength of the paper were evaluated. When the freeness of the Sw-BKP decreased, the average fiber length decreased while external fibrillation and WRV increased. When 400 mL CSF pulp was prepared by mixing 300 mL CSF pulp with unbeaten pulp (713 mL CSF), the tensile strength of the handsheet was slightly lower as compared with the case when the same freeness was obtained by mixing 300 mL CSF pulp with 500 mL CSF pulp. However, the air permeation resistance was improved. The formation of the handsheet was improved when 713 mL CSF pulp and 300 mL CSF pulp were blended, and the air permeation resistance increased significantly as the fines increased. However, the tensile strength decreased because of the incorporation of unbeaten pulp, which weakened the bonds between the fibers of the handsheet. Blending pulp with low freeness and unbeaten pulp is advantageous if separate beating is applied during the manufacturing of the low basis weight paper to improve the air permeation resistance regardless of the decrease in tensile strength under certain freeness conditions.