Effective thermal conductivity of liquid saturated coatings and their liquid vaporisation behaviour, 2010 TAPPI Advanced Coating Fundamentals Symposium

Please Note: This document will be available in PDF format in the "My Electronic Documents" link on the home page once your order has been completed. Please make sure you have the latest version of Acrobat Reader. Click on the Acrobat Reader icon to check for the latest version, it’s FREE. To print a hardcopy of a PDF file correctly you must have a postscript printer. If you are not sure if your printer is a postscript printer please refer to your owner’s manual.

The effective thermal conductivity is an important element in understanding the thermal response to heating of a paper coating, e.g. during drying in heatset web-offset, and thus it not only affects the drying efficiency but also print quality detriments like web fluting. This work examines both the effective thermal conductivity of liquid saturated ground calcium carbonate coating structures as well as the vaporisation behaviour from these structures. The liquids used for saturation were mineral oil and water in order to resemble ink and fountain solution, respectively, both of which are present in the traditional heatset web-offset process. The effective thermal conductivities of liquid saturated coating structures are discussed in regard to the corresponding unsaturated systems by using a Lumped Parameter Model (LPM). It is shown that the liquid saturation has a dominant effect in determining the effective thermal conductivity. Since this effect is not fully captured by the model, other mechanisms like an apparent pigment-pigment connectivity increase by liquid bridging and the role of liquid in changing the contact resistance during the measurement of thermal conductivity are discussed. Additionally, the transformation of three-dimensional structures to an equivalent two-dimensional modelling is evaluated. The vaporisation behaviour of mineral oil and water is studied by a thermogravimetric analysis. In spite of different maximum evaporation temperatures and evaporation rates, the addition of binder leads to a reduction in the vaporisation rate of both liquids. Since little to no interaction between the liquids and the binder is observed, the confinement caused by the geometry change in the coating structure induced by the binder addition is identified as the mechanism resulting in elevated vapour pressure within the structure.