Towards improved surface sizing

At PTS 2017 CH-Polymers and Chemec proudly presented with BTG Instruments our joint dive into deeper testliner surface sizing process understanding, based on a Master’s thesis work in collaboration with Åbo Akademi (Misla Lagus 2016-2017).

More and more paper is used in packaging. Corrugated board is increasingly recycled based and recycled-based testliners need to have adequate water resistance. Surface sizing is an easy and cost efficient way of doing this, compared to internal sizing. Lack of understanding the surface sizing process variables still causes headache to the manufacturers. In our study different surface sizing agents were used to size base papers from several different sources. Basic paper analyses, surface sizing agent analysis, dynamic water retention (DWR) and Hg-porosimetry were done. We could find some interesting correlations with starch pickup, surface sizing agent performance and strength improvement in the size press. We could also replicate real on-machine problems in lab-scale, confirming the applicability of our methods.

Our findings:

Lab scale surface sizing performance correlates well with production scale performance.
Confirmed applicability of our lab scale surface sizing method.
DWR measurement can be used to predict starch pick-up in surface sizing.
Hg-Porosimetry gave the most accurate porosity determination for the basepapers with distinct surface and internal porosity. Surface porosity seemed to be the main driver for starch pick-up.
Parameters affecting most SCT (Short Span Compression Test) strength were:
SCT strength and porosity of base paper
Applied starch amount
The hydrophobic character and smaller particle sizes of the surface sizing agent both improved sizing efficiency.