Roller for electrophotography and production method thereof, and electrophotographic image forming apparatus

1. A method for producing a roller for electrophotography comprising an electro-conductive mandrel and a surface layer having an electro-conductive foam, the method comprising steps (1) to (3), or steps (1) and (4) to (6):

(1) providing an unvulcanized rubber composition comprising an acrylonitrile-butadiene rubber, a hydrin rubber comprising an epichlorohydrin/ethylene oxide/allyl glycidyl ether terpolymer, sulfur, a thiuram type vulcanization accelerator, and a foaming agent;

(2) forming a layer of the unvulcanized rubber composition around a mandrel;

(3) vulcanizing and foaming the layer of the unvulcanized rubber composition, thereby forming the surface layer comprising the electro-conductive foam comprising a vulcanized product of the unvulcanized rubber composition to provide the roller for electrophotography;

(4) obtaining the unvulcanized rubber composition having a tube shape;

(5) vulcanizing and foaming the unvulcanized rubber composition having the tube shape, thereby providing a rubber tube comprising the vulcanized product of the unvulcanized rubber composition; and

(6) pressing the mandrel into the rubber tube to provide a roller for electrophotography having the surface layer around the mandrel, wherein

the unvulcanized rubber composition provides a vulcanized product resulting from step (3) or step (5),

the vulcanized product has a matrix-domain structure comprising a sea phase and an island phase, the sea phase containing the acrylonitrile-butadiene rubber which is vulcanized, and the island phase containing the hydrin rubber which is vulcanized,

the vulcanized product contains 8.0 to 20.0% by mass ethylene oxide based on a total amount of the vulcanized product, and

the vulcanized product has a spin-spin relaxation time T2 of 750 μs<T2<930 μs determined by pulse NMR measurement with a hydrogen nucleus as a measurement nucleus.

2. The method for producing a roller for electrophotography according to claim 1 , wherein the unvulcanized rubber composition comprises 2.5 to 4.0% by mass of the sulfur based on a total amount of a rubber component in the unvulcanized rubber composition,

the unvulcanized rubber composition comprises 1.5 to 2.5% by mass of the thiuram type vulcanization accelerator based on a total amount of a rubber component in the unvulcanized rubber composition, and

the acrylonitrile-butadiene rubber has an average content of acrylonitrile of 15 to 20% by mass.

3. The method for producing a roller for electrophotography according to claim 1 , wherein a content of the foaming agent in the unvulcanized rubber composition is 2.0 to 2.5% by mass relative to a rubber component in the unvulcanized rubber composition.

4. The method for producing a roller for electrophotography according to claim 3 , wherein

the foaming agent comprises p,p′-oxybis(benzenesulfonyl hydrazide), and

the foaming agent comprises 1.5 to 2.0 parts by mass of p,p′-oxybis(benzenesulfonyl hydrazide) having a median diameter (d50) of 2 to 5 μm based on 100 parts by mass of a rubber component in the unvulcanized rubber composition, and 0.5 to 1.0 part by mass of p,p′-oxybis(benzenesulfonyl hydrazide) having a median diameter (d50) of 12 16 μm based on 100 parts by mass of a rubber component in the unvulcanized rubber composition.

5. The method for producing a roller for electrophotography according to claim 1 , wherein the step (3) or step (5) includes vulcanizing and foaming a layer of the unvulcanized rubber composition by use of a microwave vulcanization apparatus.

6. The method for producing a roller for electrophotography according to claim 1 , which comprises steps (1) to (3).

7. The method for producing a roller for electrophotography according to claim 1 , which comprises steps (1) and (4) to (6).