Lubricant applying unit and image forming apparatus

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 lubricant applying unit applies the lubricant in an amount of 1.2×10−7 g/cm2 to 1.3×10−6 g/cm2 per unit area 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/sec) 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.