Patent ID: 7505728

Claim:
A lubricant applying unit comprising: a lubricant applying member; and a lubricant that is disposed at a position to be applied to a surface of an image carrier by the lubricant applying member, the image carrier being charged by a charging unit, and the charging unit being applied with a voltage including an AC voltage, wherein the lubricant applying member applies an amount of the lubricant no less than an amount calculated by 3.75×10< SUP>− 4</ SUP>×A×f ×( Vpp/ 2− Vth )/ L [mg/s] to the surface of the image carrier, where f is a frequency [kHz] of an AC component of the AC voltage, Vpp [kV] is a peak-to-peak voltage of the AC voltage, L [mm] is a circumference of the image carrier in a direction of movement, A [cm<SUP>2</SUP>] is a total area of a portion of image formation on the image carrier, and Vth [kV] is a starting voltage calculated by 312+6.2×(d/εopc+Gp/εair)+√(7737.6×d/εopc), where d is a film-thickness [μm] of a portion subjected to charging of the image carrier, εopc is a specific inductive capacity of the portion subjected to charging of the image carrier, εair is a specific inductive capacity in space between the image carrier and the charging unit, and Gp is a shortest distance [μm} between the charging unit and the surface of the image carrier.