Browsing by Author "Zhang, Hai"

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The effect of coating pore structure on drying efficiency in heatset web offset printing
(2010) Zhang, Hai
School of Chemical Engineering | Master's thesis
In this thesis, drying of offset ink in heatset printing was investigated from a pore level perspective. Specially formed "coating colour tablets" and a mineral oil have been used to represent the role of paper coating and the solvent/diluent of offset ink, respectively. Two representative pigments were employed, one being a monomodal broad size distribution ground calcium carbonate (GCC), the other being an internally porous modified calcium carbonate (MCC), which, when packed as in a coating, displays a discrete bimodal pore size distribution. The weight loss behaviour of offset ink oil saturated coating structures was traced with the help of thermogravimetric analysis (TGA). The experimental method is seen to be applicable to the general problem of drying of porous media. Based on the weight loss curve, the mechanism involved in drying of porous media has been outlined: in the rising rate period, temperature dominates if the internal mass supply can meet the demand of transport of liquid to the evaporating interface. The effect of film flow as being a major internal mass transport mechanism has been confirmed by the experimental results; in the failing rate period, diffusion resistance dominates due to the development of fully dried regions. The link between vapour diffusivity within the porous structure and the liquid permeability has been discussed. Lastly, specific heat of coating colour tablets was measured by differential scanning calorimetry (DSC).