Surface Properties and Print Quality of Coated Paperboard with Coating Colours Containing Different Hydrocolloids, 1995 Coating Conference Proceedings

Nordstrom J-E.P., Royal Institute of Technology

Nordlund J.P., Iggesund PaperboardGrön J.P.L., Åbo Akademi UniversityTriantafillopoulos N., GenCorp

This study investigated the influence of surface properties and surface energetics on sheetfed offset print quality of a one side double-coated solid bleached sulphate (SBS) board. Precoated SBS board was top-coated in a pilot coater, with an applicator roll and bent blade, using three coating colour formulations containing different types of hydrocolloids, or water soluble thickeners, i.e., a carboxymethyl cellulose, a hydroxyethyl cellulose, and a xanthan gum. The addition levels of these thickeners were selected to give similar coating colour viscoelasticity at low strain rates. Calendering was made on-line using a single nip configuration in the pilot coater. Print evaluations were conducted both on a laboratory level and in a commercial four-color sheetfed offset press. Results indicated that surface properties, such as smoothness and paper gloss, primarily influence ink transfer and ink gloss, while surface energetics play a secondary role in offset printing. Under the experimental conditions evaluated, the coating containing CMC gave the roughest surface with the lowest gloss. HEC gave the smoothest surface, the best paper gloss, and consequently had the best ink gloss. Ink density was primarily affected by the amount of printing ink transferred, and secondarily depended on surface morphology. Cobb absorption, ink setting rate, and surface energetics had a minimal effect on final print gloss. With respect to surface energy of the coated SBS, dispersive terms are more dominant than acid-base components: the base contribution being larger than the acid portion. Finally, the progressive drop and levelling out of the fulltone print ink density after each station in ink sequence during four-color printing, and an increase of the fulltone print ink gloss in the last stations, suggests that mechanical stresses and sorption of dampening water cause board surface roughening in the first two printing stations, but this effect stabilizes at the last few printing stations.