Patent ID: 7496324

Claim:
A lubricant applying unit for use in an image forming apparatus having a photosensitive member and a charge device, comprising: a lubricant applying member configured to apply lubricant on a surface of the photosensitive member; and a leveling member configured to level off the lubricant applied on the surface of the photosensitive member, wherein the charge device is configured to apply a bias voltage, having direct current voltage and alternating current voltage superimposed to the direct current voltage, to the photosensitive member, and a metal element percentage EP(%) of the lubricant on the photosensitive member, measured by X-ray photoelectron spectroscopy after applying the lubricant, satisfies a relationship of EP≧ 1.52×10 −4 ×( Vpp− 2 ×Vth )×( f/v ), wherein Vpp is a voltage amplitude of an alternating current component applied to the charge device, f is frequency (Hz) of the alternating current component applied to the charge device, v is a moving speed (mm/see) of the surface of the photosensitive member, and Vth is a discharge initiation voltage defined by a formula of Vth= 312+6.2×( d/εopc+Gpp /εair)+√(7737.6 ×d /ε) wherein d(μm) is a layer thickness of a to-be-charged portion of the photosensitive member, Gpp is a minimum distance (μm) between a surface of the charge device and a surface of the photosensitive member, εopc is a relative dielectric constant of the photosensitive member, and εair is a relative dielectric constant of space between the charge device and the photosensitive member.