Toner for developing electrostatic images, image forming method and image forming apparatus

An image forming apparatus, comprising:

• a latent image-bearing member for holding an electrostatic image thereon, a toner-carrying member for carrying a layer of a magnetic toner thereon, a toner vessel for holding the magnetic toner to be supplied to the toner-carrying member, a toner layer-regulating member for regulating the magnetic toner layer on the toner-carrying member, and a bias application means for applying an alternating bias voltage comprising a DC bias voltage and an unsymmetrical AC bias voltage in superposition between the toner-carrying member and the latent image-bearing member, wherein
• the latent image-bearing member and the toner-carrying member are disposed with a prescribed gap therebetween at a developing station;
• the toner layer-regulating means is disposed to regulate the magnetic toner layer on the toner-carrying member in a thickness thinner than the prescribed gap;
• the magnetic toner comprises a binder resin and magnetic powder and has a volume-average particle size of 4-10 microns, the binder resin comprises a vinyl copolymer having an acid anhydride group, and the binder resin has a total acid value (A) of 2-100 mgKOH/g and a total acid value (B) attributable to acid anhydride group of below 6 mgKOH/g so that [(B)/(A)].times.100 is 60% or less;
• and
• the bias application means is disposed 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 magnetic toner on the toner-carrying member is transferred to the latent image-bearing member to develop the electrostatic image thereon at the developing station.