To make the driving torque of a developing roller smaller and to attain excellent development, in a contact developing system developing device using nonmagnetic one-component toner and a developing roller.
The coefficient of surface dynamic friction μ between the developing roller 25 and the surface of a photoreceptor drum 11 is set 0.2≤μ≤2.5. Further, the apparent density(AD) of the toner used is set 0.25(g/cc)≤AD≤0.55(g/ cc). Thus, on both end parts of the developing roller 25, parts to which the toner is not stuck exist and when the parts come into contact with the drum 11, as well, the friction of the contact parts is not too large, so that the driving torque of the developing roller 25 can be small. Further, a thin layer of the toner formed on the developing roller 25 is made uniform and the excellent development can be attained.
WATANABE MASARU
TERADA YUKIFUMI
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