The Effect of Temperature and Relative Humidity on Dimension, Volume Resistivity and Ionic Depletion Rate of Semi-Conductive Polyurethane

Abstract

The effect of temperature and relative humidity on the physical and electrical properties of semi-conductive polyurethane used in EP process bias charge, developer and transfer rollers is investigated. Semi-conductive polyurethane materials are often specified and utilized in these applications due to the relative low cost, high endurance and uniform electrical and dimensional properties of this class of materials. As printing speeds and duty cycles increase, and registration requirements increase, the allowable tolerance to change in dimension and electrical properties of rollers utilized in these functions decreases. This puts added importance to defining and understanding the relative change in these properties across differing end user operating environments, across different environmental conditioning cycles during manufacture, and on the change in the mean expected life of these materials due to ionic depletion under these differing environmental conditions. It is known that polyurethane materials continue to cure and cross-link for as long as 30 to 90 days after initial curing. This continued curing along with absorption of moisture during the manufacturing operation, create a situation where final dimensional and electrical properties are different at each stage of manufacture and continue to change in the field. The magnitude of these changes are often much larger than most EP engineers realize. The time-dependence and relative order of magnitude of these changes is explored, as are predictive process control techniques during manufacture. A basic understanding of this dynamic phenomenon and these predictive techniques is required in order to properly specify both dimensional and electrical properties for these functions.