Patent ID: 8406645

Claim:
An image forming apparatus of non-contact developing type comprising an image carrier, a developing roller for giving non-magnetic mono-component toner to the image carrier, wherein toner particles of the toner are within a range of toner charge quantity and a voltage application section for applying a developing bias between the image carrier and the developing roller, wherein the voltage application section applies, as the developing bias, a developing voltage Vmin, which is predetermined by the image forming apparatus, for forming an electric field in a direction that causes at least a portion of the toner particles to fly from the developing roller to the image carrier, and a collecting voltage Vmax for forming an electric field in a direction that causes at least a portion of the toner particles to fly from the image carrier to the developing roller so that the developing voltage and the collecting voltage are alternately repeatedly applied, and the voltage application section sets the developing voltage Vmin so that a value defined by |Vmin−Vb| for the background area of an electrostatic latent image on the image carrier falls within a range of ±20% of Fa·d/q, where “Vb” is a potential of the background area, “Fa” is an adhesion force acting on the toner adhering to the developing roller, “d” is the interval between the image carrier and the developing roller, and “q” is an average charge quantity of the toner, so that an electric field intensity in an image area of an electrostatic latent image on the image carrier is sufficient to cause toner particles of the toner within a flying range of the range of the toner charge quantity to fly from the developing roller to the image area of the electrostatic latent image on the image carrier and an electric field intensity in a background area of the electrostatic latent image on the image carrier is insufficient to cause, thereby preventing, toner particles that are on the developing roller and within the range of the toner charge quantity to fly from the developing roller to the background area of the electrostatic latent image on the image carrier.