Monocomponent-type developer for developing electrostatic image and image forming method

An image forming method, comprising:

• disposing a latent image-bearing member for holding an electrostatic image thereon and a developer-carrying member for carrying a monocomponent-type developer with a prescribed gap at a developing station;
• the monocomponent-type developer comprising a magnetic toner containing at least a binder resin and magnetic powder, and 0.5-10 wt. % (based on the magnetic toner) of inorganic fine powder having a length-average particle size 0.1-5 .mu.m;
• wherein the developer has a number-basis particle size distribution such that particles of 2.00-2.52 .mu.m are contained in a larger proportion than particles of 2.52-3.17 .mu.m, particles of 4 .mu.m or smaller are contained at 5-18% by number and particles of 4-10 .mu.m are contained at at least 60% by number;
• the developer has a volume basis particle size distribution such that particles of 12.7 .mu.m or larger are contained at at most 10% by volume, and the developer has a weight-average particle size of 7-11 .mu.m;
• conveying the monocomponent-type developer in a layer carried on the developer-carrying member and regulated in a thickness thinner than the prescribed gap to the developing station;
• and
• applying an alternating bias voltage comprising a DC bias voltage and an asymmetrical AC bias voltage in superposition between the developer-carrying member and the latent image-bearing member at the developing station to provide an alternating bias electric field comprising a development-side voltage component and a reverse-development side voltage component, the development-side voltage component having a magnitude equal to or larger than that of the reverse development-side voltage component and a duration smaller than that of the reverse-development side voltage component, so that the developer on the developer-carrying member is transferred to the latent image-bearing member to develop the electrostatic image thereon at the developing station.