Structural Printability of Coated Board, 1991 Coating Conference Proceedings

Substrate component in print quality may be independently analyzed in three major categories, namely: structural, interactive, and optical, in accordance with the substrate response to printing force, ink/water emulsion and light.

Internal structure and surface topography of the substrate subjected to the printing force collectively determine, to a great extent, the amount of ink transferred as well as the uniformity of the ink layer distribution on the print. The term "Structural Printability" covers these interactions.

A method and device to characterize structural printability is described in detail. The total system consists of two parts: Graphite Printability Tester and Graphite Print Analyzer. The former is a means to apply a thin layer of graphite to the surface of the paper or board under controlled conditions of pressure and speed. The resulting image visualizes the pressure distribution in the contact zone on a millimeter scale (fiber flocs) if the substrate is supported by a rigid

backing, and micron scale (individual fibers) if the backing is made of a resilient material, an offset blanket, for example. The first image is referred to as printing formation, and second, as printing smoothness. Corresponding indices may be generated as a result of image analysis process employing certain algorithms.

Nine samples of coated board from North America and Europe were measured for printing formation and printing smoothness. The results were compared to the overall full color sheetfed offset print quality as judged by 18 experts from Europe. The print quality rank order was predicted by our measurements and calculations with 90% accuracy.