Magnetic, two-component developer containing fluidity improver and image forming method

An image forming method, comprising:

• providing a developer comprising at least colored resin particles, a fluidity improver and magnetic particles wherein the colored resin particles have a volume-average particle size of 4-10 microns and a volume-basis particle size distribution such that they contain 1% by volume or below of particles having a particle size of 20.2 microns or larger, and the fluidity improver has a triboelectric charging characteristic such that it provides an absolute value of triboelectric charge amount of 100 .mu.c/g or smaller with respect to the magnetic particles;
• supplying the developer to a surface of a developer-carrying member disposed opposite to a latent image-bearing member having thereon an electrostatic latent image;
• carrying the developer on the surface of the developer-carrying member;
• and
• developing the electrostatic latent image on the latent image-bearing member with the developer in a developing zone where the latent image-bearing member is disposed opposite to the developer-carrying member to form a toner image;
• wherein an alternating electric field comprising an AC component and a DC component is imparted to the developing zone;
• the maximum electric field strength F (V/micron) formed in the minimum clearance G (micron) between the surface of the developer-carrying member and the surface of the electrostatic latent image-bearing member satisfies the following relationships:
• 1.5.ltoreq.F.ltoreq.3.5, and
• F=(.vertline.VppMax/2.vertline.+.vertline.V.sub.DC -V.sub.L .vertline./G,
• wherein V.sub.L (V) denotes the potential of the electrostatic image portion (i.e., portion supplied with image exposure), V.sub.DC (V) denotes the voltage of the DC component of the alternating electric field having the same polarity as that of V.sub.L, and VppMax (V) denotes the voltage at the maximum electric field application point which is at the opposite side of the image portion potential V.sub.L, with respect to the V.sub.DC ;
• the frequency .nu. (KHz) of the alternating electric field satisfies 0.8.ltoreq..nu..ltoreq.3.0;
• the relative volumetric ratio Q (%) of the magnetic particles satisfies 15.0.ltoreq.Q.ltoreq.45.0;
• and the ratio .sigma. between the peripheral speed of the developer-carrying member and that of the electrostatic image-bearing member in the developing zone satisfies 1.2 .ltoreq..sigma..ltoreq.2.5.