Magnetic brush development method

A magnetic brush development method comprising supplying a two-component type developer comprising a mixture of magnetic carrier particles with toner particles chargeable by friction with the magnetic carrier particles onto a developing sleeve consisting of a non-magnetic sleeve having a magnet installed therein to form a magnetic brush of the developer, and bringing the magnetic brush in sliding contact with the surface of a photosensitive material having an electrostatic latent image formed thereon in the state where a bias voltage is applied between the photosensitive material and the sleeve, whereby a toner image corresponding to the electrostatic latent image is formed, wherein the two-component type developer comprises a ferrite carrier having a particle size of from about 20 to about 100 microns and electroscopic toner particles at a weight ratio of from 4/1 to 20/1 and wherein the development is carried out under conditions satisfying requirements represented by the following formulae:

• 5.times.10.sup.9 .gtoreq.R.gtoreq.1.times.10.sup.8,
• d.ltoreq.(1.485.times.10.sup.5)/(log R).sup.5.3
• and
• d.ltoreq.(1.485.times.10.sup.5)/(log R).sup.5.5
• wherein d stands for the clearance (mm) between the sleeve and the photosensitive material and R stands for the electric resistance (.OMEGA.) of the two-component type developer located between the sleeve and the photosensitive material,
• wherein the non-magnetic sleeve is moved at the position for the sliding contact with the developer in the direction opposite to the moving direction of a drum and the magnet in the sleeve is kept stationary during the development, and the development is carried out under conditions satisfying requirements represented by the following formulae:
• 2.4.gtoreq..vertline.v/V.vertline..gtoreq.1.5,
• .vertline.v/V.vertline..gtoreq.-0.12.theta.+1.8
• and
• .theta..ltoreq.5
• wherein .theta. stands for the preset angle (degrees), in the downstream direction of rotation of the drum, of the magnetic pole closest to the standard line connecting the center of the drum to the center of the sleeve, V stands for the peripheral speed of the drum and v stands for the peripheral speed of the sleeve.