Abstract: A developing roll for use in an image-forming apparatus using electrophotography includes a cylindrical core made of metal; an annular elastic layer made of rubber and arranged around the core; and an annular surface layer arranged around the elastic layer. The surface layer includes a central portion and end portions. The central portion is located at the center of the developing roll in the longitudinal direction, the end portions are located at opposite end portions of the developing roll in the longitudinal direction. A coefficient of kinetic friction of the outer peripheral surface of each end portion of the surface layer is less than or equal to 0.1, and a ten-point average roughness Rz of the outer peripheral surface of each end portion of the surface layer is less than or equal to 1.8 ?m.

Abstract: A developing roll has a metal core, an elastic layer, and a surface layer. A value X is 65.6 N/mm3 or more and a value Y is 229 ?m or more. The value X is P1/(D1×A)?P2/(D2×A). P1 is the load to displace the roll 100 ?m when a metal probe is pressed against the roll. D1 is the displacement of the roll caused by the probe under the load P1. A is the area of the probe. P2 is the load to displace a material roll by 100 ?m when the probe presses against the material roll with the core and the elastic layer and without the surface layer. D2 is the displacement of the material roll caused by the probe under the load P2. The value Y is the displacement of the roll when the probe pierces the surface layer.

Abstract: A developing roll used in an electrophotographic image forming apparatus has a metal core member, an elastic layer made of a rubber disposed around the core member, and a surface layer disposed around the elastic layer. The texture aspect ratio of the surface Str of the surface layer is equal to or greater than 0.55.

Abstract: A developing roll used in an electrophotographic image forming apparatus has a metal core member, an elastic layer made of a rubber disposed around the core member, and a surface layer disposed around the elastic layer. The texture aspect ratio of the surface Str of the surface layer is equal to or greater than 0.55.

Abstract: An electroconductive roll includes a core member, a rubber base material disposed around the core member, and a surface layer disposed around the rubber base material. The arithmetic mean peak curvature Spc of a surface of the surface layer is equal to or greater than 1,880 (1/mm), and is equal to or less than 14,024 (1/mm) The density of peaks Spd of the surface of the surface layer is equal to or greater than 93,406 (1/mm2), and is equal to or less than 151,476 (1/mm2). The surface area of the surface layer per unit projected area is equal to or greater than 1.255, and is equal to or less than 5.132.

Abstract: A developing roll has a metal core, an elastic layer, and a surface layer, A value X is 65.6 N/mm3 or more and a value Y is 229 ?m or more. The value X is P1/(D2×A) P2/(D2× A). P1 is the load to displace the roll by 100 ?m when a metal probe is pressed against the roll. D1 is the displacement of the roll caused by the probe under the load P1. A is the area of the probe. P2 is the load to displace a material roll by 100 ?m when the probe is pressed against the material roll with the core and the elastic layer and without the surface layer. D2 is the displacement of the material roll caused by the probe under the load P2. The value Y is the displacement of the developing roll when the probe pierces the surface layer.

Abstract: A charging roll includes a core member, a rubber base material disposed around the core member, and a surface layer disposed around the rubber base material. The average of heights of contours of convex portions on a surface of the surface layer relative to an average cylindrical surface obtained by averaging surface irregularities of the surface layer is equal to or greater than 0.8 micrometers and is equal to or less than 2.1 micrometers. The average of intervals between apexes of the convex portions on the surface of the surface layer is equal to or greater than 6.6 micrometers and is equal to or less than 11.5 micrometers.

Abstract: A charging roll includes a core member, a rubber base material disposed around the core member, and a surface layer disposed around the rubber base material. The average of heights of contours of convex portions on a surface of the surface layer relative to an average cylindrical surface obtained by averaging surface irregularities of the surface layer is equal to or greater than 2.0 micrometers and is equal to or less than 8.4 micrometers. The average of intervals between apexes of the convex portions on the surface of the surface layer is equal to or greater than 6.7 micrometers and is equal to or less than 39.8 micrometers.

Abstract: A charging roll includes a core member, a rubber base material disposed around the core member, and a surface layer disposed around the rubber base material. The ten point height of irregularities RZ of a surface of the surface layer is equal to or greater than 3.9 micrometers, and is equal to or less than 6.1 micrometers. The mean spacing between peaks Sm of the surface of the surface layer is equal to or greater than 12.5 micrometers and is equal to or less than 13.5 micrometers.

Abstract: A charging roll includes a core member, a rubber base material disposed around the core member, and a surface layer disposed around the rubber base material. The average of heights of contours of convex portions on a surface of the surface layer relative to an average cylindrical surface obtained by averaging surface irregularities of the surface layer is equal to or greater than 0.8 micrometers and is equal to or less than 2.1 micrometers. The average of intervals between apexes of the convex portions on the surface of the surface layer is equal to or greater than 6.6 micrometers and is equal to or less than 11.5 micrometers.

Abstract: An electroconductive roll includes a core member, a rubber base material disposed around the core member, and a surface layer disposed around the rubber base material. The arithmetic mean peak curvature Spc of a surface of the surface layer is equal to or greater than 1,880 (1/mm), and is equal to or less than 14,024 (1/mm) The density of peaks Spd of the surface of the surface layer is equal to or greater than 93,406 (1/mm2), and is equal to or less than 151,476 (1/mm2). The surface area of the surface layer per unit projected area is equal to or greater than 1.255, and is equal to or less than 5.132.

Abstract: A charging roll includes a core member, a rubber base material disposed around the core member, and a surface layer disposed around the rubber base material. The average of heights of contours of convex portions on a surface of the surface layer relative to an average cylindrical surface obtained by averaging surface irregularities of the surface layer is equal to or greater than 2.0 micrometers and is equal to or less than 8.4 micrometers. The average of intervals between apexes of the convex portions on the surface of the surface layer is equal to or greater than 6.7 micrometers and is equal to or less than 39.8 micrometers.

Abstract: A charging roll includes a core member, a rubber base material disposed around the core member, and a surface layer disposed around the rubber base material. The ten point height of irregularities RZ of a surface of the surface layer is equal to or greater than 3.9 micrometers, and is equal to or less than 6.1 micrometers. The mean spacing between peaks Sm of the surface of the surface layer is equal to or greater than 12.5 micrometers and is equal to or less than 13.5 micrometers.

Abstract: A charging roll includes a core member, a rubber base material disposed around the core member, and a surface layer disposed around the rubber base material. The ten point height of irregularities RZ of a surface of the surface layer is equal to or greater than 6.5 micrometers, and is equal to or less than 11.7 micrometers. The mean spacing between peaks Sm of the surface of the surface layer is equal to or greater than 16.5 micrometers and is equal to or less than 18.8 micrometers.