Patent ID: 7035575

Claim:
A developing device comprising: a developer carrying unit including a non-magnetic sleeve rotatable and a magnetic field generating unit; a developer receptacle configured to receive a two-component developer including toner and a magnetic carrier; and an opening through which a portion of the developer carrying unit opposite to a latent image carrying unit configured to carry a latent image is exposed, wherein the magnetic field generating unit is configured to draw the two-component developer onto a surface of the developer carrying unit so as to carry the two-component developer to the opening, form a magnetic brush by erecting the two-component developer on the developer carrying unit at the opening, apply a developing bias on the developer carrying unit so as to develop the latent image with the toner supplied to the latent image on the latent image carrying unit from the magnetic brush, and an amount of weakly charged toner in the two-component developer passing through the opening per unit time is not greater than 200 g·mm/min, wherein the amount of weakly charged toner is expressed by an equation, which is the ⁢ ⁢ amount ⁢ ⁢ of ⁢ ⁢ weakly ⁢ ⁢ charged ⁢ ⁢ toner ⁢ [ g · mm ⁢ / ⁢ min ] = total ⁢ ⁢ amount of ⁢ ⁢ the ⁢ ⁢ two ⁢ - ⁢ component ⁢ ⁢ developer ⁢ ⁢ to ⁢ ⁢ be ⁢ ⁢ drawn ⁢ [ g ⁢ / ⁢ min ] × length of ⁢ ⁢ the ⁢ ⁢ opening ⁢ [ mm ] × a ⁢ ⁢ concentration ⁢ ⁢ of ⁢ ⁢ toner ⁢ [ wt ⁢ ⁢ % ] × percentage ⁢ ⁢ of ⁢ ⁢ weakly ⁢ ⁢ charged ⁢ ⁢ toner ⁢ [ % ] wherein the total amount of the two-component developer to be drawn is expressed by an equation, which is the ⁢ ⁢ total ⁢ ⁢ amount ⁢ ⁢ of ⁢ ⁢ the ⁢ ⁢ two ⁢ - ⁢ component ⁢ ⁢ developer ⁢ ⁢ to ⁢ ⁢ be ⁢ ⁢ drawn [ g ⁢ / ⁢ min ] = an ⁢ ⁢ amount ⁢ ⁢ of ⁢ ⁢ the ⁢ ⁢ two ⁢ - ⁢ component ⁢ ⁢ developer ⁢ ⁢ to ⁢ ⁢ be drawn ⁢ [ g ⁢ / ⁢ mm 2 ] × drawing ⁢ ⁢ width ⁢ [ mm ] × linear ⁢ ⁢ velocity ⁢ ⁢ of ⁢ ⁢ a developing ⁢ ⁢ roller ⁢ [ mm ⁢ / ⁢ min ] and the percentage of weakly charged toner [%] is a percentage of toner having a charge of not less than −0.1 fC/μm if the toner is negatively charged, and is a percentage of toner having a charge not greater than 0.1 fC/μm if the toner is positively charged, according to a distribution of charge per particle size.