Conductive roller, process cartridge and electrophotographic image forming apparatus

A process cartridge detachably attached to a main body of an electrophotographic image forming apparatus,

• the process cartridge, comprising:
• an electrophotographic photosensitive member;
• and a charging member disposed such that the electrophotographic photosensitive member is chargeable, wherein
• the charging member is a conductive roller, comprising:
• a support member having a conductive outer surface;
• and
• a conductive layer disposed on the outer surface of the support member, wherein
• the conductive layer comprises a matrix which comprises first rubber, and a plurality of domains dispersed in the matrix, wherein
• volume resistivity of the matrix is 1.00×108 to 1.00×1012 Ω·cm,
• the plurality of domains comprises a plurality of domains A, and
• each of the domains A satisfies <Condition 1> to <Condition 3> below:
• <Condition 1> each domain A has a core-shell structure constituted of a core and a shell surrounding the core, the core comprises second rubber, which is different from the first rubber, and an electronic conductive agent, and the shell comprises third rubber, which is different from the first rubber and the second rubber;
• <Condition 2> a centroid of volume of each domain A exists inside the core of the domain A;
• <Condition 3> on a cross section of each domain A passing through the centroid of volume, volume resistivity of the core of the domain A is not more than 1.00×104 Ω·cm, and volume resistivity of the shell is more than 1.00×1012 Ω·cm;
• wherein
• in a case where a platinum electrode is directly disposed on an outer surface of the conductive roller, impedance is measured by applying AC voltage having a 1V amplitude between the outer surface of the support member and the platinum electrode in an environment of a 23° C. temperature and 50% relative humidity, while changing a frequency in a range of 1.0×10−2 to 1.0×107 Hz, and the frequency is plotted on an abscissa and the impedance is plotted on an ordinate of a log-log graph, a slope at the frequency range of 1.0×105 to 1.0×106 Hz is −0.80 to −0.30, and the impedance in the frequency range of 1.0×10−2 to 1.0×101 Hz is 1.00×103 to 1.00×107Ω, wherein
• the outer surface of the conductive layer is constituted of a portion M originated from the matrix, and a portion D originated from the domain, and in a case where a 100 μm square observation region is disposed on the outer surface of the conductive layer, such that one side of the square is parallel with a circumferential direction of the conductive roller, at a total of 12 locations of the center of L (L is the length of the conductive layer in a longitudinal direction) and L/4 from each end toward the center at 90° intervals in the circumferential direction, and in this state, a ratio (R2/R1), which is a ratio of an area R2 where the portion D occupies with respect to an area R1 where the portion M occupies in the observation region, is at least 0.50, wherein
• in a case where 99 lines are drawn in the observation region, along a rotation shaft of the conductive roller, at 1 μm intervals in the circumferential direction of the conductive roller, a plurality of lines, out of the lines, cross the portion M, and in a case where in each line crossing the portion M, a line portion overlapping with the portion M is assumed to be a line segment LS, a ratio of the number of line segments LS, of which length is at least 20 μm, with respect to the total number of line segments LS, is not more than 5%, and wherein
• in a case where a portion containing the second rubber and the electronic conductive agent, out of the portion D, is assumed to be a portion C, a portion E which contains the third rubber exists directly under the portion C on the outer surface of the conductive layer in a cross-sectional view of the conductive layer in a thickness direction thereof.

An electrophotographic image forming apparatus, comprising:

• an electrophotographic photosensitive member;
• and a charging roller disposed such that the electrophotographic photosensitive member is chargeable, wherein
• the charging roller is a conductive roller, comprising:
• a support member having a conductive outer surface;
• and
• a conductive layer disposed on the outer surface of the support member, wherein
• the conductive layer comprises a matrix which comprises first rubber, and a plurality of domains dispersed in the matrix, wherein
• volume resistivity of the matrix is 1.00×108 to 1.00×1012 Ω·cm,
• the plurality of domains comprises a plurality of domains A, and
• each of the domains A satisfies <Condition 1> to <Condition 3> below:
• <Condition 1> each domain A has a core-shell structure constituted of a core and a shell surrounding the core, the core comprises second rubber, which is different from the first rubber, and an electronic conductive agent, and the shell comprises third rubber, which is different from the first rubber and the second rubber;
• <Condition 2> a centroid of volume of each domain A exists inside the core of the domain A;
• <Condition 3> on a cross section of each domain A passing through the centroid of volume, volume resistivity of the core of the domain A is not more than 1.00×104 Ω·cm, and volume resistivity of the shell is more than 1.00×1012 Ω·cm;
• wherein
• in a case where a platinum electrode is directly disposed on an outer surface of the conductive roller, impedance is measured by applying AC voltage having a 1V amplitude between the outer surface of the support member and the platinum electrode in an environment of a 23° C. temperature and 50% relative humidity, while changing a frequency in a range of 1.0×10−2 to 1.0×107 Hz, and the frequency is plotted on an abscissa and the impedance is plotted on an ordinate of a log-log graph, a slope at the frequency range of 1.0×105 to 1.0×106 Hz is −0.80 to −0.30, and the impedance in the frequency range of 1.0×10−2 to 1.0×101 Hz is 1.00×103 to 1.00×107Ω, wherein
• the outer surface of the conductive layer is constituted of a portion M originated from the matrix, and a portion D originated from the domain, and in a case where a 100 μm square observation region is disposed on the outer surface of the conductive layer, such that one side of the square is parallel with a circumferential direction of the conductive roller, at a total of 12 locations of the center of L (L is the length of the conductive layer in a longitudinal direction) and L/4 from each end toward the center at 90° intervals in the circumferential direction, and in this state, a ratio (R2/R1), which is a ratio of an area R2 where the portion D occupies with respect to an area R1 where the portion M occupies in the observation region, is at least 0.50, wherein
• in a case where 99 lines are drawn in the observation region, along a rotation shaft of the conductive roller, at 1 μm intervals in the circumferential direction of the conductive roller, a plurality of lines, out of the lines, cross the portion M, and in a case where in each line crossing the portion M, a line portion overlapping with the portion M is assumed to be a line segment LS, a ratio of the number of line segments LS, of which length is at least 20 μm, with respect to the total number of line segments LS, is not more than 5%, and wherein
• in a case where a portion containing the second rubber and the electronic conductive agent, out of the portion D, is assumed to be a portion C, a portion E which contains the third rubber exists directly under the portion C on the outer surface of the conductive layer in a cross-sectional view of the conductive layer in a thickness direction thereof.