Modeling Friction, Wear and Lubrication of Sliding Polyurethane and Polycarbonate Surfaces Representing Printer Components with Molecular Dynamics
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The Xerox Research Centre of Canada has noted that elastomeric cleaning blades in laser printers have a relatively short life expectancy, as they experience high levels of friction and wear while wiping excess toner from commercial photoconducting drums. As such, there has been interest in examining the behaviour related to friction, wear and lubrication of components in laser printers. Molecular dynamics simulations were employed to gain molecular-level insight into the mechanism of wear of the cleaning blade and the effectiveness of lubricants in reducing friction forces. The Dreiding force field was chosen to simulate representations of the photoconducting drum, cleaning blade and the lubricant. They were modeled in bulk and layered forms, and compressed and sheared to examine slip mechanisms and evaluate shear stresses and friction coefficients. It was found that the polycarbonate (PC) component was significantly stronger than either the polyurethane (PU) or octadecane (C18) components, and that the introduction of an interface and/or C18 lubricating material lowered the measured shear strengths to various degrees. The simulations indicated three different slip mechanisms depending on the nature of system. We have observed that shearing may induce structural changes within the PU component (such as ordering) even without a local slip event, which likely contributes to the eventual mechanical failure of the PU cleaning blade. From the models used in this study, it appears that more lubricating material is required than is currently used in practice in order to prevent wear of the PU cleaning blade. As well, the shear strengths and friction coefficients are not significantly reduced with the addition of lubricant for models containing PU. This is, of course, subject to the limitations of the simulations performed.