Influence of Engineered Kaolin on Web Offset Blister Resistance, 1996 Finishing and Converting Conference Proceedings

DO Cummings & AV Lyons

ECCI

With the advent of on-line hot soft nip calendering, a renewed interest in controlling the occurrence of blisters in web offset print has emerged. The economic advantages offered the coated paper producer with on-line calendering are attractive. However, the higher temperatures and line pressures required to make saleable paper have a tendency to seal the coating structure resulting in increased blister tendency. A comparison was made of the blister tendency for coating formulations containing a standard fine coating clay with commercially available latexes of distinct glass transition temperatures, calcined clay, or engineered kaolin. The engineered kaolin, high glass transition latex, and calcined clay were found to increase the resistance to blister as compared to the fine coating clay formulation. Examination of the respective coating structures with air flow permeability, mercury porosimetry, and water interference mottle suggest both the engineered kaolin and calcined clay create a pore network which is characterized as having larger pore diameters than the standard clay. The associated larger pore diameters provide a structural porosity which is thought to allow water vapor to escape during the drying phase of web offset printing. Furthermore,