Sizing of Woodfree Papers with a Pre-Metering Size Press, 1991 Coating Conference Proceedings

The performance of a pre-metering size press was studied for a group of woodfree papers. A first set of experiments showed the superior flexibility of the pre-metering size press compared to a conventional size press. The possibility to run higher solids contents with the pre-metering size press led to a tensile strength increase of approx. 50 % vs. a run in a size press with maximum solids content.

In a second set of experiments the influence of film thickness and solids content on paper properties could be demonstrated. Increasing film thickness led to a significant increase of plybond strength and tensile strength. An increase of solids content had a beneficial effect on plybond strength if full penetration of the starch into the sheet could be achieved. It had no or even an adverse effect if the size remained near the surface of the sheet. An increasing solids content positively affected ink flotation time. Machine speed of the pre-metering size press had no impact on paper properties.

In a third set of experiments the performance of different types of starch was studied. Cationic starch showed no superior performance compared to an enzymatically converted starch when only incomplete penetration of the sheet was achieved for both types of starches. In case of full sheet penetration an increase of plybond strength could be reached when using cationic starch vs. oxidized starch, however tensile strength remained unchanged by the different types of starch used in the experiment.

An optimized pre-metering size press operation coupled with the optimal selection of a starch type allows the papermaker to target paper properties with a high degree of accuracy and flexibility. This may lead to considerable economic benefits when sizing papers with a pre-metering size press.