Developing roller, process cartridge, and electrophotographic image forming apparatus

A developing roller, comprising:

• a substrate having a conductive outer surface;
• and
• a conductive layer on the outer surface of the substrate, wherein
• an outer surface of the developing roller is formed of at least a first region and a second region having higher conductivity than the first region,
• the first region and the second region are placed adjacent to each other,
• the first region is placed on an outer surface of the conductive layer,
• when a metal film is directly provided on the outer surface of the developing roller, and while changing a frequency between 1.0×10−1 to 1.0×105 Hz, an AC voltage with an amplitude of 50 V is applied between the outer surface of the substrate and the metal film while a DC voltage of 50 V is applied in an environment at a temperature of 23° C. and a relative humidity of 50%, an impedance at a frequency of 1.0×100 to 1.0×101 Hz is 1.0×106Ω or more,
• in a case where when a corona discharger having a grid portion with a width of 3.0 mm is placed in an environment at a temperature of 23° C. and a relative humidity of 50% such that a distance between the grid portion and the outer surface of the developing roller is 1.0 mm and a direction of the width of the grid portion is aligned with an axial direction of the developing roller, then a voltage of 8 kV is applied to the grid portion and the corona discharger is relatively moved along the axial direction of the developing roller at a speed of 400 mm/sec to charge the outer surface of the developing roller, and a potential of the outer surface at t seconds after passage of the grid portion is measured,
• the potential at t=0.06 [sec] is denoted by VINI [V],
• a change in the potential at 30.00≤t≤100.00 is fitted to a formula (X′) below by a least squares method to obtain V0,1 [V] and τ1 [sec], when a value of a potential V1(t) at the time of substituting t=0.06 [sec] into the formula (X′) is denoted by V1 [V], VINI−V1 is less than 20.0 V:
• V
• 1
• (
• t
• )
• =
• V
• 0
• ,
• 1
• ⁢
• exp
• ⁡
• (
• -
• t
• /
• τ
• 1
• )
• .
• (
• X
• ′
• )