Electroconductive roller

1. An electroconductive roller comprising an electroconductive cellular material layer, comprised of a polyurethane composition, which has an average foamed cell diameter not less than 20 μm nor more than 100 μm and a variation ΔD of said cell diameter not more than 50 μm, and

said electroconductive roller having a hardness variation ΔHs not more than 8 degrees and an index R MAX /R MIN of a circumferential non-uniformity in an electrical resistance (Ω) thereof not more than 1.3.

2. The electroconductive roller according to claim 1 , wherein said electroconductive cellular material layer is comprised of a thermosetting one-part polyurethane composition foamed by a mechanical foaming method.

3. The electroconductive roller according to claim 1 , wherein a relationship of log 10 R LL −log 10 R HH ≦1.4 is satisfied between an electric resistance R LL (Ω) of said electroconductive roller at a low temperature and a low humidity (10° C., relative humidity: 15%) and an electrical resistance R HH (Ω) thereof at a high temperature and a high humidity (32.5° C., relative humidity: 90%).

4. The electroconductive roller according to claim 1 , wherein an electrostatic capacity measured at 100 Hz is not more than 50 pF; and an electrical resistance (Ω) at an applied voltage of 1000V is not more than 10 12 Ω.

5. The electroconductive roller according to claim 1 , wherein when a component is extracted from said electroconductive cellular material layer for 6 hours by using a Soxhlet apparatus and acetone as a solvent, a ratio of a weight of said component to a weight of a resin measured before said extraction is not more than 20%.

6. The electroconductive roller according to claim 1 , wherein when a component is extracted from said electroconductive cellular material layer for 6 hours by using a Soxhlet apparatus and acetone as a solvent, a ratio of a weight of said component to a weight of a resin measured before said extraction is not less than 5%.

7. The electroconductive roller according to claim 1 , wherein a polyurethane prepolymer and a latent curing agent are added to said thermosetting one-part polyurethane composition.

8. The electroconductive roller according to claim 1 , wherein a polyurethane prepolymer prepared by a reaction between an excessive amount of an aliphatic polyisocyanate compound and a trifunctional polyether polyol is added to said thermosetting one-part polyurethane composition.

9. The electroconductive roller according to claim 1 , wherein an anionic salt which is indicated by any one of chemical formulas 1, 2, and 3 (X 1 , X 2 , and X 3 are identical to or different from each other and show functional groups, having 1 to 8 carbon atoms, which contain carbon atoms, fluorine atoms, and sulfonyl group (—SO 2 —)) shown below is added to said thermosetting one-part polyurethane composition of said electroconductive cellular material layer as an ionic-electroconductive agent:

10. The electroconductive roller according to claim 1 , wherein a filler consisting of organic polymer particles is added to said thermosetting one-part polyurethane composition.

11. The electroconductive roller according to claim 1 , wherein 0.5 to 30 wt % of organic polymer fine particles, having a diameter of 0.1 μm to 50 μm, which comprise of methyl methacrylate, styrene, acrylonitrile or a homopolymer of a monomer having vinyl double bond groups or a copolymer of said monomer are added to said thermosetting one-part polyurethane composition as a filler.

12. The electroconductive roller according to claim 1 , wherein a salt compound of strong basic tertiary amine is added to said thermosetting one-part polyurethane composition as a catalyst.