Options for Soft Sizing of Mechanical Papers, 2000 Papermakers Conference Proceedings

Paul Rankin, Kari Luukkonen, Mari Lindstrom - Raisio Chemicals Canada, Inc.--A degree of soft sizing has historically been desired in certain mechanical papers to optimize performance. By controlling the rate and extent of water uptake during printing and converting processes, hydrophobic sizing technology minimises problems of sheet cockle, waviness, hygroexpansitity and low rewetted paper strength that can give rise to poor efficiency and quality in several coating and printing operations. Current industry trends to multicolour offset printing of all mechanical papers, including newsprint and directory grades, have resulted in more water contacting the paper during printing. This increases the potential for paper dimensional stability and strength loss problems. Increasing use of water based inks and hydrophilic fillers add to the concern. For these reasons, there is increasing interest from manufacturers of mechanical grades on effective hydrophobic sizing technologies for all mechanical grades, from Newsprint to LWC. This paper reviews traditional hydrophobic sizing technologies available for mechanical grades and experience to date in applying these technologies. It also introduces Raisafob 30S technology, a newly developed unique hydrophobic low molecular weight cationic starch (HLWCS) soft sizing technology specifically developed by Raisio Chemicals for water uptake control and printability enhancement in mechanical papers.