Effects of Mixing Intensity on the Admix Performance of a Xerographic Developer

Abstract

In a working xerographic developer, a portion of the charged toner particles is removed each time a xerographic image is developed. To balance this loss, an equivalent amount of toner is dispensed into the xerographic developer from a reservoir of uncharged toner. Because uncharged or poorly charged toner particles tend to develop in the non-image “background” areas of a latent xerographic image, the uncharged/dispensed toner particles must be rapidly brought to a charged state in order to avoid “background” development. Normally, the “added” toner and the “incumbent” toner (i.e., the charged toner particles already present in the developer) merge to a common level of charge. Clearly, the rate at which this merging process occurs (the so-called “admix rate”) is an important functional property of any xerographic developer design, and a rapid rate is especially desirable. In principle, the charge admix performance of any toner can be optimized via judicious adjustments to the chemical composition of the toner particles and/or that of the xerographic carrier particles. However, even for an apparently optimized xerographic toner/developer design, charge admix deficiencies may still be created as a result of extrinsic factors. For example, for certain developer designs, the admix rate can change from “rapid” to “almost-zero” as the degree of developer mixing is changed from “gentle” to “intense”; paradoxically, this latter admix failure mode actually occurs as a result of an ultra-rapid admixing process. In such a case, the added toner acquires a level of charge higher than that of the incumbent toner, and this increased charge is mirrored by an equivalent decrease in charge for the incumbent toner. In an extreme failure condition, the populations of “added” and “incumbent” toner particles scarcely show any tendency to merge to a common intermediate level of charge and the “added” toner particles remain at a high charge level. In the present report, experimental data taken on a simple black xerographic developer at various levels of developer mixing intensity (e.g., as created via changes in mixing times and modes of developer mixing), demonstrate a progression from an excellent admixing performance to a non-functional level for a single developer design.