Semiconductive roller, and method of producing the same

1. A semiconductive roller comprising a tubular main body formed of a semiconductive rubber composition, wherein the main body has a multiplicity of concavities provided in an outer peripheral surface thereof in at least one of circumferentially overlapping relation and axially overlapping relation, wherein the concavities are each rounded toward a center thereof from an outer periphery thereof.

2. The semiconductive roller according to claim 1 , wherein the concavities each have a depth of not less than 0.5 μm and not greater than 100 μm.

3. The semiconductive roller according to claim 2 , wherein the multiplicity of concavities are arranged circumferentially and axially in rows.

4. The semiconductive roller according to claim 3 , wherein at least some of the multiplicity of concavities have a length such as to extend across a plurality of circumferential or axial rows.

5. The semiconductive roller according to claim 4 , wherein the concavities each have a depth of not less than 0.5 μm and not greater than 50 μm, a width of not greater than 100 μm, and the outer peripheral surface has a developed interfacial area ratio Sdr of not greater than 5.

6. The semiconductive roller according to claim 2 , wherein adjacent ones of the concavities are connected to each other with a continuous curved surface.

7. The semiconductive roller according to claim 1 , wherein the concavities provided in the outer peripheral surface are each defined as a region having a load area ratio of greater than 10% on a volume parameter graph (load curve) specified in International Organization for Standardization ISO 25178-2:2012, and a region (not formed with the concavities) having a load area ratio of not greater than 10% is defined as a projection.

8. The semiconductive roller according to claim 1 , wherein the outer peripheral surface is such that a maximum height Sz specified in International Organization for Standardization ISO 25178-2:2012 is not less than 0.5 μm and not greater than 30 μm, and a developed interfacial area ratio Sdr specified in International Organization for Standardization ISO 25178-2:2012 is not greater than 5.

9. The semiconductive roller according to claim 1 , wherein the main body is a nonporous single-layer body formed of a semiconductive rubber composition.

10. The semiconductive roller according to claim 9 , wherein the main body has an oxide film provided in the outer peripheral surface thereof.

11. The semiconductive roller according to claim 1 ,

wherein the main body includes a porous tubular inner layer formed of a semiconductive rubber composition, and an outer layer of a seamless semiconductive thermoplastic elastomer tube provided on an outer periphery of the inner layer,

wherein the main body has an overall Asker-C hardness of not less than 30 degrees and not greater than 60 degrees,

wherein the multiplicity of concavities are provided in an outer peripheral surface of the outer layer.

12. A semiconductive roller production method, comprising the steps of:

forming a tubular main body of a semiconductive rubber composition; and

forming a multiplicity of concavities in an outer peripheral surface of the formed tubular main body in at least one of circumferentially overlapping relation and axially overlapping relation by a laser processing method, the concavities being each rounded toward a center thereof from an outer periphery thereof.

13. The semiconductive roller production method according to claim 12 , wherein the multiplicity of concavities are arranged circumferentially and axially in rows, and at least some of the multiplicity of concavities have a length such as to extend across a plurality of circumferential or axial rows.

14. The semiconductive roller production method according to claim 12 ,

wherein the tubular main body forming step includes the steps of:

forming a porous tubular inner layer of a semiconductive rubber composition;

covering an outer periphery of the tubular inner layer with an outer layer;

wherein the step of covering the inner layer with the outer layer includes the step of preparing a semiconductive thermoplastic elastomer tube having a wall thickness T of not less than 100 μm and not greater than 400 μm, and press-inserting the tubular inner layer into the tube.

15. The semiconductive roller production method according to claim 14 , wherein the inner layer has an outer diameter D 1 that is greater than an inner diameter D 2 of the tube, and an interference represented by a difference D 1 −D 2 between the outer diameter D 1 and the inner diameter D 2 is not less than 100 μm and not greater than 400 μm in the tubular inner layer forming step.