Charging member, process cartridge, electrophotographic image forming apparatus, and method for manufacturing charging member
A charging member includes an electro-conductive substrate, an elastic layer, and a surface layer provided in this order. The elastic layer has, on an outer surface thereof, concave portions that are independent of each other, and hold insulating particles. The insulating particle is exposed to the surface of the elastic layer. A site in which an outer edge of the projection image derived from each of the insulating particles and an outer edge of a projection image derived from each of the concave portions are separated, exists. The charging member has convex portions derived from the insulating particles exposed to the surface of the elastic layer, and concave portions derived from the concave portions of the elastic layer. The surface layer has a volume resistivity of 1.0×10 15 Ωcm or more.
1. A charging member comprising in this order:
an electro-conductive substrate;
an elastic layer comprising an outer surface having concave portions holding insulating particles, the insulating particles being exposed to the surface of the elastic layer; and
a surface layer, wherein
when an orthogonal projection image is obtained by orthogonally projecting each of the concave portions and the insulating particles held in the respective concave portions on a surface of the electro-conductive substrate, a site exists in which an outer edge of the orthogonal projection image derived from each of the insulating particles and an outer edge of the orthogonal projection image derived from each of the concave portions are separated,
a surface of the charging member has convex portions derived from the insulating particles exposed to the surface of the elastic layer, and concave portions derived from the concave portions of the elastic layer, and
the surface layer has a volume resistivity of 1.0×10 15 Ω·cm or more.
2. The charging member according to claim 1 , wherein a maximum value T max of a film thickness of the surface layer is 5 μm or less, and
a minimum value T min of the film thickness is 1 μm or more.
3. The charging member according to claim 1 , wherein in the orthogonal projection image, an average value of acute angles is 0° to less than 45° each of the acute angles being formed by a longitudinal direction of the charging member and a line segment connecting (i) a center of gravity of a gap formed by separation of each of the insulating particles and each of the concave portions, and (ii) a center of gravity of each of the insulating particles.
4. The charging member according to claim 1 , wherein the insulating particles have spherical shape having an average particle size Dm of 6 to 20 μm, and
a length L of a longest line segment including an intersection point of a straight line drawn in a normal direction from the outer edge A of each of the spherical particle in the orthographic view with the outer edge B of each of the concave portions is at least 2·Dm.
5. The charging member according to claim 4 , wherein the concave portion has a depth of 0.10×L or more with respect to the average height of the surface layer.
6. The charging member according to claim 1 , wherein the surface layer contains a binder resin having a polyolefin skeleton.
7. The charging member according to claim 6 , wherein the polyolefin skeleton is a polyisobutylene skeleton.
8. The charging member according to claim 1 , wherein the height of the convex portion is higher than the average height of the surface layer.
9. The charging member according to claim 8 , wherein the convex portion is higher than the average height of the surface layer by 3 μm or more.
10. The charging member according to claim 1 , wherein each of the concave portions has a depth Dr of ⅓ or more of the average particle size Dm of the insulating particles.
11. A process cartridge configured to be detachably attachable to a body of an electrophotographic image forming apparatus, the process cartridge comprising an image bearing member and a charging member disposed in contact with the image bearing member,
the charging member comprising in this order:
an electro-conductive substrate;
an elastic layer comprising an outer surface having concave portions holding insulating particles, the insulating particles being exposed to the surface of the elastic layer; and
a surface layer, wherein
when an orthogonal projection image is obtained by orthogonally projecting each of the concave portions and the insulating particles held in the respective concave portions on a surface of the electro-conductive substrate, a site exists in which an outer edge of the orthogonal projection image derived from each of the insulating particles and an outer edge of the orthogonal projection image derived from each of the concave portions are separated,
a surface of the charging member has convex portions derived from the insulating particles exposed to the surface of the elastic layer, and concave portions derived from the concave portions of the elastic layer, and
the surface layer has a volume resistivity of 1.0×10 15 Ω·cm or more.