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.
Effects of coating formulation on coating thermal properties and coated paper print quality in xerography
Abstract The effects of coating formulation on thermal characteristics of coating layers (namely thermal diffusivity, specific heat capacity and heat conductivity) were systematically studied and their impact on xerography print quality was evaluated. Model coatings were prepared using ground calcium carbonate or kaolin pigment mixed with styrene butadiene latex binder in various proportions (from 6 to 25 pph). As expected, porosity was shown to be a key parameter for thermal conductivity of the coating layers, and is mainly determined by the latex concentration. Particle size distribution (PSD) and pigment morphology also affected the thermal characteristics of the coating layers. It was found that the bulk thermal conductivity of the coating layers can be accurately predicted by a geometric mean model based on the pigment, latex and air contents. Print quality on model coated papers was evaluated in terms of print gloss, toner adhesion and pairwise visual ranking. It was demonstrated that print gloss is improved by decreasing the bulk thermal conductivity of the coatings. The coating formulated with the pigments with the steepest PSD and 10 pph of latex had a relatively low thermal conductivity and the best print quality.
Observed non-linearity of Darcy-permeability in compacted fine pigment structures
Abstract Liquid permeability was measured on a range of porous samples, using a specially-constructed high pressure permeation cell. The samples consisted of compacted fine isotropic mineral pigment—calcium carbonate—compressed over a range of compaction pressures. These samples have pore diameters typically (number basis) finer than 0.1 μm. The porosities and the pore size distributions of the samples have been determined by means of mercury porosimetry. The permeability of these fine-pore network systems is seen under certain conditions not to obey the well-known linearity of the Darcy relation as a function of applied liquid pressure differential. A considerable pressure–flux hysteresis is observed following saturation by imbibition. Furthermore, it is seen that there is no direct linear correlation between permeability and porosity despite the use of a constant pigment particle size distribution and, hence, skeletal size distribution. The measured permeability displays a local maximum at a fractional porosity of approximately 0.26 with a further distinct drop at around 0.27. Interestingly, this phenomenon is also confirmed using a computer-based porous network simulator which provides a relative permeability based on matching the mercury percolation data. Taking into account the effects of earlier-proposed mechanisms of preferred pathway flow and film flow during imbibition, it is postulated that some pores remain unfilled during imbibition and saturation prior to the permeability study, such that there remains entrapped air or vapour phase in microscopic ganglia. This air does not dissolve in the aliphatic mineral oil used in the experiments. Structures with a delineated pore-throat structure will probably lead generally to observed non-linear phenomena within the range of dimensions studied here, which can have implications, amongst others, for microscopic filtration, catalysis and absorption phenomena.