Effect of developer properties on print quality

We investigated the dependence of the toner charge-to-mass ratio (q/m) in a two-component electrophotographic developer on the shaking time, toner con centration (T/C), carrier sizes, and the carrier core and the coating mater ials, as well as the resulting print qualities in terms of print density, b ackground density, tone reproduction, resolution, and dot gain. Four differ ent sizes of spherical ferrite carriers, four different carrier coating mat erials, and an irregular iron carrier were used with two types of toner: 14 mu m red toner (NP-4080) and 8 mu m cyan toner (CLC-500). The q/m measurem ent by the blow-off method showed that the red toner charge was positive wh ile the cyan toner charge was negative with these carriers. The toner q/m v alues, which depended on the shaking time and decreased with the increasing T/C were much more affected by the larger carrier and the smaller toner. T he carriers which yielded charges in the proper range produced better print qualities than did the other carriers that yielded a toner q/m that was to o low or too high. The TIC latitude which produced a high print density wit hout a background fog, corresponding to the red toner q/m range of 15 to 20 mu C/g and the cyan toner q/m range of -15 to -25 mu C/g was wider by the smaller carrier or the larger toner. Therefore, to control a small toner si ze, the carrier size should be reduced to maintain a wider latitude of T/C. Additionally, the maximum toner coverage on a carrier surface, related to the maximum T/C of a good quality print, was about 120%.