FLOW RESISTANCE OF WET AND DRY SHEETS USED FOR PREPARATION OF LIQUID PACKAGING BOARD

摘要

The flow resistance of wet and dry sheets is studied in order to increase the resistance against edgewise liquid penetration in liquid packaging board. Since the sizing effect is limited at high levels of sizing, the sheet structure must be taken into account to get further improvement of this important parameter. Preliminary results from liquid packaging board made from typical pulps show that liquid extrusion measurements can be used to determine the wet and dry structure of paper. Recommendations for sample preparation and the appropriate number of sheets needed for analysis are included in the paper. Results show a large difference between dry and wet sheet structure due to expansion. Sheets made from kraft pulp exhibit moderate expansion, while sheets made from CTMP (chemi-mechanical pulp) expand such that the pore radii become 30-35 mm. Porosities and flow resistances, which are easily calculated from pore volumes, display the great impact of sheet density. CTMP based sheets have much lower flow resistance than kraft based sheets. Even a considerable reduction of the porosity in CTMP based sheets gives a small effect in flow resistance.