Combination Sizing. The Use of Synthetic Surface Size with an Alkaline Internal Size, 1991 Papermakers Conference Proceedings

During the last several years, millions of tons of paper have been produced using alkaline internal size. The use and overuse of alkyl ketene dimer (AKD) and alkenyl succinic anhydride (ASA) have created new and difficult problems for both papermakers and customers alike. The use of synthetic surface sizes, such as styrene maleic anhydride (SMA) copolymers and anionic polyurethane dispersions, can help to alleviate many of these problems by making it possible to reduce the amount of internal size needed.

The objective of this study is to show the improvements in various paper properties which can be realized through the use of synthetic surface sizes. Both mill data and laboratory data are incorporated in this report. The significance of the laboratory data was checked using statistical analysis after setting up the appropriate experiments on a pilot paper machine using a fractional factorial design.

Data collected in various paper mills and in the laboratory shows that both SMA copolymers and anionic polyurethane dispersions, added at the size press, significantly improve the aqueous resistance of paper. Furthermore, the SMA copolymers also provide significant improvement in final sheet properties such as coefficient of friction (COF) and porosity.