Charging roller, process cartridge, and electrophotographic image forming apparatus

1. A charging roller comprising:

an electroconductive mandrel; and

an electroconductive layer as a surface layer, the electroconductive layer including a matrix containing a cross-linked product of a first rubber and domains dispersed in the matrix,

each of the domains containing a cross-linked product of a second rubber and an electroconductive particle, and

each of the domains having a volume resistivity lower than a volume resistivity of the matrix, wherein when sampling a cubic sample of the electroconductive layer having a side of 20.0 um from a region from an outer surface of the electroconductive layer to a depth of 20.0 um, 50 number% or more of all the domains in the cubic sample satisfy a condition:

assuming that a domain to be judged in the cubic sample is enveloped by an enveloping cuboid, the enveloping cuboid having two surfaces each of which is perpendicular to a line segment L, the line segment L passing through at least one arbitrary point in the domain to be judged and being perpendicular to a surface of the electroconductive mandrel, “x” is longer than “y” and “z”, where “x” is a length of the enveloping cuboid in an X-axis direction, “y” is a length thereof in a Y-axis direction, and “z” is a length thereof in a Z-axis direction, and a line segment S that is perpendicular to the line segment L and is parallel to an X-axis is able to be drawn.

2. The charging roller according to claim 1 , wherein when a longest line segment out of line segments each connecting a portion of a first YZ surface of the enveloping cuboid in contact with the domain and a portion of a second YZ surface thereof in contact with the domain is defined as a line segment P, and

when a line segment Q having a same starting point as a starting point of the line segment P in the first or second YZ surface and being perpendicular to the surface of the electroconductive mandrel is drawn, and

when an inferior angle formed by the line segment P and the line segment Q is defined as an inferior angle 0 , a mode value of the inferior angle 0 of each of all the domains in the cubic sample is 60° to 90°.

3. The charging roller according to claim 1 , wherein an average value of the length “x” of the enveloping cuboid which envelopes the respective domains satisfying the condition is 0.5 μm to 15.0 μm.

4. The charging roller according to claim 1 , wherein a surface resistance value measured on an outer surface of the charging roller is 1.0x10 -1 Ω to 1.0x 10 3 Ω.

5. The charging roller according to claim 1 , wherein the volume resistivity “d” of each of the domains and the volume resistivity “m” of the matrix satisfy a relationship of m/d≥1.0×10 3 .

6. A process cartridge detachably attachable to a main body of an electrophotographic image forming apparatus, the process cartridge comprising:

an electrophotographic photosensitive member; and

a charging roller arranged so as to be capable of charging the electrophotographic photosensitive member,

the charging roller comprising:

an electroconductive mandrel; and

an electroconductive layer as a surface layer,

the electroconductive layer including a matrix containing a cross-linked product of a first rubber and domains dispersed in the matrix,

each of the domains containing a cross-linked product of a second rubber and an electroconductive particle, and

each of the domains having a volume resistivity lower than a volume resistivity of the matrix,

wherein when sampling a cubic sample of the electroconductive layer having a side of 20.0 um from a region from an outer surface of the electroconductive layer to a depth of 20.0 pm, 50 number% or more of all the domains in the cubic sample satisfy a condition:

assuming that a domain to be judged in the cubic sample is enveloped by an enveloping cuboid, the enveloping cuboid having two surfaces each of which is perpendicular to a line segment L, the line segment L passing through at least one arbitrary point in the domain to be judged and being perpendicular to a surface of the electroconductive mandrel,

“x” is longer than “y” and “z”, where “x” is a length of the enveloping cuboid in an X-axis direction, “y” is a length thereof in a Y-axis direction, and “z” is a length thereof in a Z-axis direction, and

a line segment S that is perpendicular to the line segment L and is parallel to an X-axis is able to be drawn.

7. An electrophotographic image forming apparatus comprising:

an electrophotographic photosensitive member; and

a charging roller arranged so as to be capable of charging the electrophotographic photosensitive member,

the charging roller comprising:

an electroconductive mandrel; and

an electroconductive layer as a surface layer,

the electroconductive layer including a matrix containing a cross-linked product of a first rubber and domains dispersed in the matrix,

each of the domains containing a cross-linked product of a second rubber and an electroconductive particle, and

each of the domains having a volume resistivity lower than a volume resistivity of the matrix,

wherein when sampling a cubic sample of the electroconductive layer having a side of 20.0 μm from a region from an outer surface of the electroconductive layer to a depth of 20.0 pm, 50 number% or more of all the domains in the cubic sample satisfy a condition:

assuming that a domain to be judged in the cubic sample is enveloped by an enveloping cuboid, the enveloping cuboid having two surfaces each of which is perpendicular to a line segment L, the line segment L passing through at least one arbitrary point in the domain to be judged and being perpendicular to a surface of the electroconductive mandrel,

“x” is longer than “y” and “z”, where “x” is a length of the enveloping cuboid in an X-axis direction, “y” is a length thereof in a Y-axis direction, and “z” is a length thereof in a Z-axis direction, and

a line segment S that is perpendicular to the line segment L and is parallel to an X-axis is able to be drawn.