Application of foamed additives to the surface of wet handsheets

Abstract

We explored the application of foamed wet-end additives onto wet handsheets to qualify our method of application and to demonstrate the method’s usefulness for prescreening additives and foaming agents for packaging applications. We modified a laboratory drawdown coating machine to allow coating of wet handsheets with foamed additives. Initial sheet solids were adjusted to a target of 8%–25% by vacuum. Foam layer thickness was set mechanically. After application, the foamed additives were drawn into the sheet with vacuum. The additive dosage was adjusted by altering its concentration within the foaming formulation. We evaluated more than 100 foaming agents and 10 strength additives, comparing wet-end and foam-assisted addition with no addition on recycled linerboard and virgin linerboard furnish. Foam-assisted addition typically displayed a much steeper dose-response curve and much higher maximum strength levels than wet-end addition. Our results suggest potential target applications for this technology, such as lightweighting, and improved strength performance in mills with relatively closed water systems, where strength aids added into the wet end are adversely influenced by accumulation of inorganic ions and organic species.