Optimizing Sizing and Retention Efficiency in Bleached Board Applications ,2006 Papermaker’s Conference
Rosin sizing at pH between 4.2 – 5.5 remains the dominant means of imparting basesheet water repellency for the bleached board market in North America. While rosin sizing agents based on either liquid or dispersion sizes are fairly inexpensive, readily available, and their response on-machine is quick while having a gradual dosage-response curve, they generally require alum or another multi-valent cationic species as a mordant. Controlling the alum dosage is critical to the success of these products, and alum hydrolysis is a key aspect of their functionality.
The same alum chemistry which assists in sizing of bleached board has made the use of drainage and retention aids for enhancing machine production a challenge. Typical microparticle programs based on colloidal silica can encounter problems in efficiency at lower pH due to interactions with excess dissolved alumina. A niche for improving drainage and retention in bleached board manufacture exists, and should be compatible with alum chemistry. One means of satisfying this need is to combine the benefits of traditional rosin sizing with an inorganic microparticle into a single product that is also compatible with cationic flocculants. StaFlex is a DSA technology (drainage and sizing aid) which not only enhances vacuum and free drainage but also provides for more efficient rosin sizing. The product also meets the requirement of being easy to meter and handle on-machine.