The image-density-decrease phenomenon, which occurs at the initial printing with a brand new developing cartridge and at a printing done after several days of rest, during which printing is not done, was studied in the mono-component developing process. The toner charge,
q/
m, and toner supply,
m/
a, were measured by a suction type Faraday cage. The mechanism of the image-density-decrease phenomenon is discussed based on
q/
m,
m/
a and fluidity of toner. The image-density-decrease phenomenon was found to occur with decrease in
m/
a, and not with increase in
q/
m. The cause of the decrease in
m/
a is the shortage of the toner supply to the supply roller. Finally, modifications of the developing unit and the toner additives to eliminate the image-density-decrease phenomenon are proposed.
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