Patent ID: 6072974
Filing Date: 2000-06-06
Classification: G03G

Abstract:
A color image forming method for operating a moving image-bearing member bearing an electrostatic latent image and a plurality of developing units disposed near the image-bearing member and being selectively operable, said color image forming method developing said electrostatic latent image by using a magnetic developer brush formed on the surface of a developer support and conveyance means, and comprising the steps of:providing a rotating cylinder for supporting and conveying said magnetic developer, said cylinder including a permanent magnet with a plurality of magnetic poles on the cylinder surface;supplying a magnetic developer containing non-magnetic color toner for color image formation;attracting and conveying a layer of magnetic developer having a thickness smaller than the gap between the image-bearing member and said developer support and conveyance cylinder on the cylinder surface; andapplying in the developing region an alternate electric field with an AC bias superimposed on a DC bias between the image-bearing member and the magnetic developer for the developing of an electrostatic latent image on the image-bearing member, whereinletting Vp (mm/s) be the moving speed of the image-bearer, and D (mm), M, and Vm (mm/s) be the outer diameter, the number of magnetic poles, and peripheral speed of the permanent magnet, respectively,a value of h, being defined as .pi.D.multidot.Vp/(M.multidot.Vm), has a value of 2 or less, andthe surface magnetic flux density ranges from 50 to 1200 G.