Fabrication and Electrical Characteristics of Fluorinated Carbon/Fluoroelastomer Coatings for Electrophotographic Applications

摘要

The electrical properties of fluoroelastomer (trade name Viton~(TM)) coatings containing carbon and fluorinated carbon fillers have been studied. The resistivity vs. loading plot for the carbon/Viton layers was found to follow the percolation type behavior of a conductive filler-binder system. Namely, the filled Viton layers are electrically insulating at low filler concentrations. Once the threshold concentration is reached, the resistivity of the Viton layer decreases by several orders of magnitude and becomes electrically conducting over a very small increase in filler concentration. Examination of the bulk resistivity of these materials by the AC technique showed that the resistivity of the Viton layer is sensitive to an electric field, and that it decreases as the strength of the electrical field increases. The resistivity also shows hysteresis behavior. Owing to the percolation behavior, attempts to prepare semiconducting layers predictably have been found to be difficult. Different results were obtained from fluorinated carbons. Coating dispersions made from fluorinated carbons and Viton were relatively stable and the filler particles are found to disperse well throughout the coated layers. Three fluorinated carbons, trade names Accufluor~(TM) 2010, 2028, and 2065, with fluorine content of 11%, 28% and 65% by weight, respectively, have been studied in this work. While the plot of surface resistivity vs. loading for Accufluor 2010 is comparable to the carbon system, different results were obtained for Accufluor 2028 and 2065. The surface resistivity of the Accufluor 2028/Viton layers was found to decrease gradually after the threshold concentration. Layers from Accufluor 2065 remain electrically insulating even at high loading, > 35%. The result is discussed in terms of the semiconducting nature of these two fluorinated carbons. The shallow percolation transition for the Accufluor 2028/Viton layers enables fabrication of semiconducting layers predictably, reproducibly and consistently. Examination of the bulk resistivity of the fluorinated carbon filled layers indicates that the resistivity is well behaved. The resistivity is relatively insensitive to electric field and environmental variation. Moreover, it exhibits very little hysteresis effect. The improvement in electrical behavior for the fluorinated carbon layers appears to be associated with the high compatibility between the filler particles and the fluoroelastomer binder.