Internal Sizing of Paper and PaperBoard With Ethylene Copolymers, 1996 Papermakers Conference Proceedings

Internal sizing of paper under neutral to mildly alkaline conditions can now be achieved with ethylene copolymers. In principle, aqueous emulsions of polymers based on an ethylene backbone should be good candidates for paper sizing. This is due to the hydrophobicity associated with polyolefins and the potential for film formation on the surface of the paper fibers. Such emulsions are generally prepared using surfactants as stabilizers. Upon drying, the water is removed but the surfactant is not and the dried film is no longer hydrophobic. There is, however, a class of ethylene copolymers which can be prepared as hydrolytically stable aqueous dispersions without the use of surfactants. Experimental work both with handsheets and on a pilot papermaking machine has now established the capability of these dispersions to provide a high level of sizing to paper and paperboard. The dispersions have smaller particle sizes than commercial paper sizing emulsions. The smaller particle size of these polymeric dispersions offers significant advantages in terms of sizing distribution and uniformity, as compared to either alkenyl succinic anhydride (ASA) or alkyl ketene dimer (AKD) sizing emulsions. The potential advantages of using ethylene copolymer sizing agents include: a sizing chemistry with the speed of ASA, a high degree of hydrophobicity, an absence of machine deposit problems, and an absence of shelf-life problems.