Charging system, process cartridge and image forming apparatus

A process cartridge detachably mountable on a main body of an image forming apparatus, the process cartridge comprising:

• an image bearing member;
• a charging member for forming a nip with said image bearing member thereby charging said image bearing member, wherein conductive particles are provided in said nip;
• wherein a time factor a represented by a following equation satisfies a condition α>15:
• α=2π·k·Nc·(W/Vc)/(ρ·Cd·Z) Z=−0.5·1n(π·k·Nc)−1n({square root}{square root over (β)}·D/2) (β=1.1932)
• in which ρ (Ω) represents a surface resistivity of said image bearing member;
• Cd (F/mm2) represents an electrostatic capacitance of the image bearing member;
• D (mm) represents a diameter of said conductive particle;
• Nc (particle/mm2) represents a density of said conductive particles present on said charging member;
• Vc (mm/sec) represents a surface moving speed of said charging member;
• Vd (mm/sec) represents a surface moving speed of said image bearing member;
• k=Vc/Vd;
• and W (mm) represents a width of said nip in the moving direction of said image bearing member.

A charging system comprising:

• a member to be charged;
• a charging member for forming a nip with said member to be charged thereby charging said member to be charged, wherein conductive particles are provided in said nip;
• wherein a time factor a represented by a following equation satisfies a condition α>15:
• α=2π·k·Nc·(W/Vc)/(ρ·Cd·Z) Z=−0.5·1n(π·k·Nc)−1n({square root}{square root over (β)}D/2) (β=1.1932)
• in which ρ (Ω) represents a surface resistivity of said member to be charged;
• Cd (F/mm2) represents an electrostatic capacitance of the member to be charged;
• D (mm) represents a diameter of said conductive particle;
• Nc (particle/mm2) represents a density of said conductive particles present on said charging member;
• Vc (mm/sec) represents a surface moving speed of said charging member;
• Vd (mm/sec) represents a surface moving speed of said member to be charged;
• k=Vc/Vd;
• and W (mm) represents a width of said nip in the moving direction of said member to be charged.