Surface sizing with emulsion rosin size

Surface sizing has been applied to practical papermaking in combination with internal sizing systems. Emulsion rosin sizes have been used under not only acidic but also recently neutral or alkaline papermaking conditions containing calcium carbonate as a filter. Thus, the application of surface sizing with emulsion rosin sizes may be expected also to solve some troubles due to white water quality in the closed systems. In this study, a nonionic fatty acid emulsion size was prepared from ¹³C-labeled fatty acid and Tween 85, as used as a model of the rosin emulsion size. The base handsheets were prepared from a fines-free bleached hardwood kraft pulp with 0-4% aluminum sulfate or 0-0.2% cationic polymer PAE. The handsheets soaked in diluted size emulsions were pressed between blotting papers, and were dried at 20°C. Some dried handsheets were cured at 105°C for 30 min. These surface-sized handsheets were analyzed by pyrolysis-GC, X-ray fluorescence, solid-state ¹³C-NMR, SEM and others. The following results were obtained: (1) sizing degrees increased with an increase in aluminum content of base handsheets, (2) most size components (i.e. fatty acid) in the handsheets had free acid structures without forming aluminum salts, and (3) size emulsion particles in the handsheets having good sizing properties were sufficiently distributed on the pulp fiber surfaces without flocculation. These results indicate that, in the surface sizing, some ionic interactions must be present between anionic sites of each emulsion particle surface and cationic ones on pulp fiber surfaces formed by aluminum compounds or PAE in the base handsheets. These so-called anchor effects may consequently contribute to sizing developments.