Tribology and Abrasive Wear of Mo Lecularly Doped Polycarbonate Coatings
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TRIBOLOGY AND ABRASIVE WEAR OF MOLECULARLY DOPED POLYCARBONATE COATINGS
D. K. MURTI *
,
P. G. ODELL* AND H. A. MIZES **
Xerox Research Centre of Canada, 2660, Speakman Drive, Mississauga, Ontario, LSK 2L1, CANADA ** Xerox Webster Research Center, Webster, NY, 14580, U.S.A *
ABSTRACT Molecularly doped polymers are widely used in copiers and printers. During the imaging process, toner particles and the cleaning blade wear the photoconductor drum as it rotates. This paper quantizes the abrasive wear of molecularly doped polycarbonate coatings. No clear correlation is found between the wear rate and measured mechanical properties. The surface topography is dominated by a series of parallel grooves with a spacing of approximately 0.1 pm. INTRODUCTION Some toner is left behind as a xerographic image is transferred from the photoreceptor to the paper. This toner is removed by passing the photoreceptor under a polymer blade, which removes the toner. However, with each pass a small amount of the photoreceptor surface may also be removed. This wear is usually considered to occur by fatigue or abrasion[1]. Fatigue wear is defined as the wear which occurs by repeated action of cyclic stresses. The rate of fatigue wear should depend sensitively on the friction coefficient. This dependence occurs because as the friction increases, multiple deformations of the polymer occur at separate points of contact leading to fracture and subsequent tearing of the material. Abrasive wear is defined as the wear resulting from damage to sliding surfaces by the action of solid particles present in the sliding zone. For photoreceptors, the wear may be in part due to particles forced into the surface by the cleaning blade. In this study, the wear of molecularly doped polycarbonate coatings was measured using a test fixture to simulate the interactions of toner particles and cleaning blade in a copier. The morphology of the unabraded and abraded surfaces was studied with atomic force microscopy (AFM). The abraded surface is dominated by abrasion grooves with a spatial period of approximately 0.1 pm parallel to the cleaning direction. EXPERIMENTAL The samples consisted of a Mylar® substrate with a thin evaporated film of titanium (20 nm in thickness) anda thicker layer of a polycarbonate doped with the hole transporting molecule TPD [2]. The charge transporting layers were coated from a solution of 50 wt% TPD and 50% polycarbonate in dichloromethane using a film applicator [3]. The thickness of the layer is about
Mat. Res. Soc. Symp. Proc. Vol. 239. §1992 Materials Research Society
612
15 pm after drying at 135oC for 20 minutes. The wear test was carried out in a simulated test fixture set up to measure the relative wear and wear rate of charge transport layers subjected to interactions with toner particles (typical size of 10 to 15 pm) and blade cleaning. Devices fabricated as described above were used by wrapping around an aluminum drum in a test fixture. The drum speed is controlled by a stepper motor and can be varied in the range of 2
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