Strength Properties of Wet-combination Paper Containing Dry Strength Resin

摘要

カチオン性ポリアクリロアミド系紙力増強剤（C-PAM）を加えて強度を増加させた紙をモデル的にすき合わせ、それらの強度的性質に及ぼすすき合わせ、すなわちすき合わせ層数およびC-PAM を加えた高強度の紙屑内位置の影響を検討した。その結果すき合わせは、微小破壊が徐々に増大する塑性引張変形域の増加をもたらし、微小破壊が急激に増大して破壊に至るまでの引張破断伸びを増加させ、結果として引張強度を増大させる。ただしC-PAM 含有紙屑が偏在するとその増分は比較的小さい。他方紙面方向の圧縮強度は、すき合わせの影響をあまり受けずに、単に紙力増強剤量の増加と共に増大する。ただし、C-PAM 含有紙屑が全紙層の中央あるいは片側に偏在するとその増分は比較的小さい。厚さ方向の引張強度でもある内部結合強度は、強度の低いC-PAM 非含有紙屑のそれで決まり、さらにすき合わせ面に生じる欠陥によりさらに強度を減少させる。%The effect of wet-combination on some basic strength properties was examined by using a series of wet-combined papers made from paper plies containing cationic polyacrylamide (C-PAM) dry strength resin. As the basic in-plane and out-of plane strength properties, tensile, compressive, and internal bond strength were examined. Microfailures, which are detectable as acoustic emissions (AEs) and occurred during the tensile deforming process, were further analyzed to investigate the effect of the paper ply combination on in-plane tensile strength. The results showed that wet-combination with paper plies containing C-PAM brought about an increase in the plastic deformation region with a gradual increase in microfailures and delayed the acute occurrence of microfailures just before the maximum load. The higher strain at breakage rather than the increase in fiber bonding led to an increase in tensile strength. Heterogeneous location of strong paper ply containing C-PAM, especially on one side, decreased the increment of the tensile strength. The compressive strength in the X-Y direction increased with increasing total C-PAM content, regardless of wet-combination, although the increment was small for papers in which the strong paper ply containing C-PAM was located at the center or on one side. Tensile strength in the Z-direction measured as internal bond strength was governed by that of the weakest paper ply, and wet-combination brought about a further decrease in the Z-directional tensile strength.