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.
Study of temperature and melting conditions during flash fusing
Temperature and melting conditions during flash fusing are studied. As a first step to clarify the microscopic behavior of toner, the temperature changes, considering thermal nonlinearity and the local melt viscosity dependence on the temperature changes, are examined. Consideration of the nonlinearity is performed by modification of the thermophysical properties employed in the temperature calculations, on the bases of the qualitative results of experiments. Suitable modification methods are a thermal conduction constant model and increment of the heat capacity model. The modification is necessary for the region from the start to the time the peak temperature appears on the toner surface. The local melt viscosity is analyzed by superposition of the calculated temperature changes and measured melt viscosity of the bulk toners. The melt viscosity varies a little with the kind of toner for the mid region in the toner layer. The melt viscosity calculated for the mid-region is one requirement determining the fixing strength. This means that to get good fixing strength, not only is it necessary to lower the melt viscosity, but also the thermophysical properties of the toner must be raised.
Coating layer formation in dry surface treatment of paper substrates
Dry surface paper coating can potentially eliminate drying after coating and produce a final surface quality equal to that achieved with conventional coating processes. This work reports on recent experiments involving pigmented coating of paper substrates with a dry surface treatment process. In the process, powdered coating, exposed to a corona charge and an electric field, is directed and guided onto paper. In a subsequent step, the dry coating powder is anchored to the paper surface by thermomechanical treatment in a nip formed between heated rolls, forming the final coating layer. In dry surface treatment, coating is applied without wetting the paper substrate, thus eliminating the possibility for fiber swelling and surface roughening. Coating penetration into the paper is minimal, as a distinct boundary forms between the coating layer and paper. Sufficient cohesion and adhesion to the paper surface are needed to obtain an appropriate coating layer. The greatest challenge is to reduce surface openness and create a structure similar to that obtained with conventional coating methods. In this study, we investigated factors affecting coating structure. The focus was on the influence of the applied pressure and temperature on fixation of coating powder onto paper. We achieved adequate surface strength and were able to improve paper surface properties. Application: This report provides insights into the experimental technique of dry coating and its possible applications.