Surface Sizing with Cationic Starch: Its Effect on Paper Quality and Papermaking Process, 2001 Papermakers Conference Proceedings

Characteristic of starches used in surface sizing greatly affects not only paper properties but also the efficiency of broke recycling processes. Oxidized starches commonly used for surface sizing have disadvantages in improving paper properties since they tend to penetrate deeply into the paper structure rather than remaining on the surface. Furthermore, oxidized starches act as anionic trash in the broke recycling process. To solve the problems associated with oxidized starches, cationic starches were prepared and the effects of cationic starch on paper properties and papermaking processes were investigated. Both laboratory research and mill evaluation were carried out and analyzed. Results showed that cationic starches have pronounced effects in improving opacity, brightness, print gloss and ink density due to its better holdout property. Effectiveness in surface holdout of cationic starches was verified using a confocal laser scanning microscope (CLSM). Adsorption ratio of the cationic starch was twice larger than that of oxidized starch, and this decreased COD load in white water and increased fines retention and strength. Improvement in stiffness, opacity, brightness, printing quality, and picking resistance of paper was observed when cationic starch was used in the film transfer size press. And this allowed the use of more filler. Diverse beneficial effects of improving white water quality including the reduction of COD and cationic demand were obtained when cationic size press starch was used. It was shown that better picking resistance and ink receptivity of coated paper were obtained when base paper surface sized with cationic starch was used than when APS surface sized base paper was used.