Electrophotography using a magnetic brush

In a method of electrophotography where an electrostatic latent image is formed on the surface of a material layer, a non-magnetic cylinder is provided to confront said surface of said material layer, a permanent magnet roll having a plurality of symmetrically arranged magnetic poles extending axially is provided in said cylinder, a magnetic brush is formed by attracting a semiconducting or insulating magnetic toner having a volumetric resistivity greater than 10.sup.8 .OMEGA.cm under an electric field of DC 4000 V/cm onto said cylinder with the aid of a magnetic attraction force of said permanent magnet roll, said cylinder and permanent magnet roll are moved relatively to permit said magnetic brush to slide along the surface of said material layer thereby to allow said magnetic toner to stick to a predetermined position on the surface of said material layer, and a toner image is transferred onto a transferring member and is then subjected to fixing, the improvement comprising;

• said permanent magnet roll having a magnetic force in the range of 400-1600 gauss rotating said cylinder and said permanent magnet roll in the same direction as the direction of movement of said magnetic toner which is moved in the same direction as that of said material layer and at a speed less than 100 mm/sec irrespective of the speed of movement of the surface of said material layer at a development section, wherein the number of revolutions per minute of said permanent magnet roll is set to a value P defined by:
• ##EQU5## where:
• N.sub.M is the r.p.m. of said permanent magnet roll,
• V is the speed of movement of the surface of said material layer, expressed by the mm/sec.,
• M is the number of magnetic poles forming said permanent magnet roll, and
• P is in the range of 0.2 to 2.5, the r.p.m. of said non-magnetic cylinder is in a range of 1/5 to 1/20 of the r.p.m. of said permanent magnet roll.