Discrete element modeling of the transient heat transfer and toner fusing process in the Xerographic printing of coated papers
In this study, a computer model based on discrete element method is employed to simulate the unsteady state heat transfer from the fuser roll to the toner and coating layer during the Xerography printing of coated papers. The model coating layers consisted of randomly arranged spherical pigment and latex particles with commercially relevant size distributions. Effects of coating characteristics, toner size, multiple toner layers, toner melting energy, toner thermal conductivity, coating layer thermal conductivity, and fuser roll temperature and pressure were investigated. Iso-thermal contours of fusing time were generated to demonstrate the relative importance of different fusing conditions and toner properties. Simulation results showed that temperature variation highly depended on the toner size, toner melting energy and the fuser roll temperature. Moreover, simultaneous coupling of the compressive stress and heat transfer indicated that the pressure exerted by the fuser roll did not significantly affect the rate of heat transfer.
Modeling the effect of pigment morphology on the dynamic compression of coating layers using DEM
Abstract In the present paper, discrete element method (DEM) was employed to investigate the effect of pigment morphology on packing dynamics and compressive behavior of paper coating layers in calendering process. Spherical, platy, and needle-like particles, representing GCC, delaminated clay, and aragonite PCC pigments, were considered in this study. For each particle shape, the compression of coating structures formed by mono-sized and poly-dispersed pigments were modeled. Stress–strain behavior of the coating layers and in-plane and out-of-plane movements of the pigment particles during the compression were computed under the same maximum compressive stress. Simulation results revealed that the in-plane movements of the pigment particles during compression in the calender nip were small in magnitude (
Modelling coating structure development: Monte-Carlo deposition of particles with irregular shapes
There is an increasing interest in enhancing coated paper performance by combining the unique properties of various pigments, i.e. developing multi-pigment coating formulations. An understanding of the synergy between pigments of different sizes and shapes is therefore becoming critical. The literature on this subject is rather empirical and fragmentary. In this report, we introduce an improved 3D Monte-Carlo deposition model to simulate coating structure development for irregularly shaped particles. The model relies on the minimization of the total energy of the particle system, which is defined as a sum of three terms: a pair interaction that accounts for collisional interactions, a gravitational potential energy, and a drag potential energy that takes into account the drainage rate of the colour. The model predicts that pigments with higher aspect ratios give a more porous structure and a smoother surface when applied at high solids content. Coating at low solids content (<45-55%) is shown to produce “looser” and more disordered structures, especially in the case of platelet pigments like clay. These results agree with practical and experimental observations. When blending clays with calcium carbonates, the model predicts the occurrence of maximum pore volume and surface micro-roughness at specific mixing ratios. The location of these maxima varies significantly with the particle’s aspect ratio, the relative size of the blended pigments, and the solids content of the suspension. With further experimental validation, this model has the potential of being used as a tool for designing and optimizing coating formulations.