New Generation of AKD Size for the Sizing of PCC Containing Fine Paper, 1994 Papermakers Conference Proceedings

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During the past 6 years, the use of Precipitated Calcium Carbonate (PCC) as a filler in fine paper manufacturing has increased significantly. After the initial success of using relatively low levels of filler in the sheet, mills have started to desire higher filler levels in order to fully utilize the capacity of their on-site PCC plants. Surprising, in many mills the increase in filler levels have resulted in severe problems with sizing and strength properties of the sheet. Both of these problems can be traced back to the Precipitated Calcium Carbonate. The irregular shape of the PCC particle blocks the fibers from being bonded together. At the same time it absorbs synthetic neutral sizes. Leaving the fibers unsized. In order to compensate for the uneven retention of the size, the amount of size required has to be increased. The high amount of synthetic size, especially AKD based size, has been related to the slippery and migration problems during sheeting and converting. Various size reversion cases have also been reported where the paper looses its sizing over time.