Magnetic toner, apparatus unit and image forming method

An apparatus unit that is capable of being detached from a main body of an image forming apparatus, comprising a development unit having a container in which frictional electrification magnetic toner is held, a development sleeve for feeding said magnetic toner, and a toner layer thickness regulating member for coating said toner on said development sleeve while pressing said development sleeve,

• wherein said magnetic toner is composed of magnetic toner particles containing a magnetic substance of 20 to 150 parts by weight for a binder resin of 100 parts by weight;
• said magnetic toner has a frictional electrification property whereof an absolute value for a frictional electrification amount relative to iron powder of 250 mesh-pass to 350 mesh-on is 25 to 40 mc/kg;
• assuming that a weight-average particle diameter (D.sub.4) of said magnetic toner in a particle distribution of said magnetic toner is X (.mu.m) and that a % by number in a number distribution of said magnetic toner particles that have a diameter of 3.17 .mu.m or smaller is Y (%), expressions (1) and (2) are satisfied
• -5X+35.ltoreq.Y.ltoreq.-25X+180 (1)
• 3.5.ltoreq.X.ltoreq.6.5 (2);
• sphericity (.psi.) of said magnetic substance is 0.80 or greater and a product (.sigma..sub.r .times.H.sub.c) of remanence ›.sigma..sub.r (Am.sup.2 /kg)! and coercive force ›H.sub.c (kA/m)! of said magnetic substance in a magnetic field of 795.8 kA/m (10 k oersted) is 10 to 56 (kA.sup.2 m/kg);
• in said development sleeve is provided a fixed magnet, which has at least a first magnetic pole of 520 to 870 gauss that is positioned opposite a magnetic toner mixing member located in said container, a second magnetic pole of 600 to 950 gauss that is positioned opposite said toner layer thickness regulating member, and a third magnetic pole of 700 to 1000 gauss that is a development magnetic pole;
• and
• a center line average roughness (R.sub.a ) of a surface of said development sleeve is 0.3 to 2.5 .mu.m.

An image forming method, comprising the steps of:

• charging an electrostatic latent image bearing member by using electrification means,
• forming an electrostatic latent image by exposing said electrified electrostatic latent image bearing member,
• developing said electrostatic latent image to form a magnetic toner image by using a development unit, which is positioned opposite said electrostatic latent image bearing member,
• transferring said magnetic toner image to a transfer material by using or without using an intermediate transfer member, and
• fixing said magnetic toner image to said transfer material;
• wherein said development unit has a container in which frictional electrification magnetic toner is retained, a development sleeve for feeding said magnetic toner, and a toner layer thickness regulating member for coating said magnetic toner on said development sleeve while pressing against said development sleeve;
• said magnetic toner is composed of magnetic toner particles containing a magnetic substance of 20 to 150 parts by weight for a binder resin of 100 parts by weight;
• said magnetic toner has a frictional electrification property such that the absolute value of a frictional electrification amount relative to iron powder of 250 mesh-pass to 350 mesh-on is 25 to 40 mc/kg;
• assuming that a weight-average particle diameter (D.sub.4) of said magnetic toner in a particle distribution of said magnetic toner is X (.mu.m) and that % by number in a number distribution of said magnetic toner particles having a diameter of 3.17 .mu.m or smaller is Y (%), expressions (1) and (2) below are satisfied
• -5X+35.ltoreq.Y.ltoreq.-25X+180 (1)
• 3.5.ltoreq.X.ltoreq.6.5 (2);
• sphericity (.psi.) of said magnetic substance is 0.80 or greater and a product (.sigma..sub.r .times.H.sub.c) of remanence ›.sigma..sub.r (Am.sup.2 /kg)! and coercive force ›H.sub.c (kA/m)! of said magnetic substance in a magnetic field of 795.8 kA/m (10 k oersted) is 10 to 56 (kA.sup.2 m/kg);
• in said development sleeve is provided a fixed magnetic, which has at least a first magnetic pole of 520 to 870 gauss that is positioned opposite a magnetic toner mixing member located in said container, a second magnetic pole of 600 to 950 gauss that is positioned opposite said toner layer thickness regulating member, and a third magnetic pole of 700 to 1000 gauss that is a development magnetic pole;
• and
• a center line average roughness (R.sub.a ) of a surface of said development sleeve is 0.3 to 2.5 .mu.m.