Sizing mechanism of rosin emulsion size-alum systems. Part 4. Surface sizing by rosin emulsion size on alum-treated base paper

Sizing and size retention mechanisms of alum-treated base paper by tub sizi ng with anionic rosin emulsion size were studied using some analytical meth ods and model experiments. Alum- or cationic polymer-treated base paper she ets were subjected to tub sizing with anionic rosin emulsion size, anionic and cationic petroleum resin emulsion sizes and anionic fatty acid emulsion size. Size retention ratios in the sheets were measured by pyrolysis-gas c hromatography. Sizing levels as well as size retention ratios of paper by t ub sizing with the anionic emulsion sizes increased with increasing aluminu m content in the base paper sheets. The obtained results indicated that som e cationic sires are formed at the aluminum components in the base paper sh eets in water during the tub sizing process, and thus more anionic rosin si ze particles are adsorbed and retained in the alum-treated base sheets by e lectrostatic interactions. Furthermore, the formation of such electrostatic interactions brings about an anchoring or fixing effect of the size partic les in the sheets with more even size distributions. This anchoring effect by the aluminum components in the base paper sheets enhances sizing perform ance in tub sizing. The cationic polymer-treated base, paper sheets had a s izing and size retention behavior similar to that of the alum-treated base paper, and thus the presence of some cationic sites in the base paper is re quired for tub sizing. Therefore, aluminum components in the base paper she ets participate in both size retention and distributions of size particles in the sheets in tub sizing, and greatly influence the resultant sizing beh avior.