Apparatus for developing electrostatic latent images using developing roller having specific ionization potential

摘要

A developing roller (1) having a thin layer of a developer (4) carried thereon and a drum (3) bearing an electrostatic latent image on its surface are rotated in close relationship, thereby feeding the developer (4) to the surface of the drum (3) for visualizing the electrostatic latent image thereon. The ionization potential of the developing roller (1) surface is adjusted to be below the ionization potential of the developer (4) surface when the developer is charged negative and above the ionization potential of the developer (4) surface when the developer is charged positive. The developer has an ionization potential of 4.5-5.5 eV. When using negatively charged developer, the development roller should preferably contain a lubricant or non-ionic surfactant and should preferably be made of a polyurethane containing a polyisocyanate so as to obtain the desired ionization potential.