Influence of Temperature and Type of Coating Latex on the Out-of-Plane Compression Behaviour of Coating Layers, 1999 Coating Fundamentals Symposium Proceedings

Magnus Wikström, Petri Mäkelä, Mikael Rigdahl

Coated papers are often calendered at high roll temperatures. Isolated coating layers without any base paper or other substrate present were here compressed in a platen press at two temperatures, 23 and 150 ºC. Four different types of coating latices were compared with respect to their influence on the compressive properties in the thickness direction of the coating layer; a styrene-acrylate, a poly(vinyl acetate), and a high and a low Tg styrene-butadiene latex. The compression of the coating layers was found to be strongly related to the thermal softening of the coating latex. The surface roughness of the coating layer had a substantial influence on the compression behaviour of the coating layers. This was revealed by a series of model experiments using consecutive loading sequences. A woodfree paper was blade coated with coating colours containing each of the studied latices. When these papers were calendered in a pilot calender at roll temperatures of 37 and 145 ºC, there was a clear relationship between the development of paper gloss and the thermal softening of the latices.