It’s a difficult balance to strike. While the introduction of filler in newsprint presents the papermake…
It’s a difficult balance to strike. While the introduction of filler in newsprint presents the papermaker with a valuable alternative for fibre replacement and cost savings, it has a simultaneous and negative impact on strength, linting and dusting properties. These effects have additional and adverse effects on papermachine and printing press runnability. In an attempt to better understand the impact of kaolin-filler introduction in newsprint in North America, Stephan Lafreniere, Jean Paradis and Francois Brouillette of CIPP-UQTR (Centre Intégré en Pates et Papier – Université du Québec a Trois-Rivières) undertook pilot plant runs on the new CIPP pilot papermachine. They presented their findings at the PAPTAC Annual Meeting in Montreal on Feb. 2.
The trio evaluated four different dry strength resin (DSR) additives to determine their benefits — reactive PAM, liquid polymeric starch, cationic starch and polymeric vinylformamide. The authors drew some valuable conclusions. Firstly, the introduction of filler up to 5% does not always have a significant effect on strength properties. Rather, this is dependent upon process sensitivity or operating parameter critical levels at the mill. However, when the filler level escalates to more than 10%, internal and surface strength properties are negatively impacted. As a result, DSR alternatives are required to counteract the lower fibre-to-fibre bonding caused by fibre substitution and high filler coverage.
The introduction of filler typically affects the optical properties as well as the printability of the sheet. When more than 5% filler is introduced to the sheet, an increase in linting and dusting results. However, as the authors noted, the use of a proper DSR technology will offset linting propensity, while maintaining the benefits on brightness, caliper and absorption properties.
Wet end cationic starches are a well-established method of maintaining sheet properties with higher filler levels used in different countries and paper grades. However, cationic starch usage also has a number of drawbacks. The need for alternate DSRs has lead to the development of new technologies, in particular for board grades. As such, the authors note that North American paper manufacturers and chemical suppliers may be advised to introduce DSR alternatives into their newsprint or mechanical based papers in order to permit higher filler loadings.
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