Itoh, Tetsuya; Yamamoto, Takafumi; Sugiura, Hiroki; Kawano, Atsuhiro; Imamura, Wataru; Hayashi, Saburou;

Charging roll

A charging roll which is held in contact with an outer circumferential surface of an image bearing medium for charging the surface of the image bearing medium by application of a DC voltage and an AC voltage which is superimposed on the DC voltage, the charging roll comprising: a center shaft; an electrically conductive base layer formed on an outer circumferential surface of the shaft; an outer structure formed on an outer circumferential surface of the conductive base layer; and the charging roll having Asker C hardness of less than 48 degrees as measured upon application of 1 kg load thereto and micro rubber hardness in a range of 65-85 degrees as measured upon application of 33.85 g load thereto.

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What is claimed is:

1. A charging roll which is held in contact with an outer circumferential surface of an image bearing medium for charging said surface of said image bearing medium by application of a DC voltage and an AC voltage which is superimposed on said DC voltage, said charging roll comprising:

a center shaft;

an electrically conductive base layer formed on an outer circumferential surface of said shaft;

an outer structure formed on an outer circumferential surface of said conductive base layer; and

said charging roll having Asker C hardness of less than 48 degrees as measured upon application of 1 kg load thereto and micro rubber hardness in a range of 65-85 degrees as measured upon application of 33.85 g load thereto.

2. A charging roll according to claim 1, wherein said conductive base layer has a thickness in a range of 2 .mu.m-5 mm.

3. A charging roll according to claim 1, wherein said conductive base layer has a volume resistivity of not more than 10.sup.6 .OMEGA.cm.

4. A charging roll according to claim 1, wherein said conductive base layer is a conductive rubber foamed body.

5. A charging roll according to claim 1, wherein said conductive rubber foamed body is formed of a foamable conductive rubber composition comprising a rubber foamable material and an electron conductive material.

6. A charging roll according to claim 1, wherein said outer structure consists of a resistance adjusting layer which is made of a non-foamable semi-conductive rubber material.

7. A charging roll according to claim 6, wherein a hardness increasing agent is contained in said resistance adjusting layer for increasing its hardness.

8. A charging roll according to claim 6, wherein said resistance adjusting layer has a thickness in a range of 100 .mu.m-800 .mu.m.

9. A charging roll according to claim 6, wherein said resistance adjusting layer has a volume resistivity in a range of 10.sup.7 .OMEGA.cm-10.sup.10 .OMEGA.cm.

10. A charging roll according to claim 1, wherein said outer structure consists of: a resistance adjusting layer formed on said outer circumferential surface of said conductive base layer and made of a non-foamable semi-conductive rubber material, and a protective layer formed on an outer circumferential surface of said resistance adjusting layer and made of a soft resin material.

11. A charging roll according to claim 10, wherein a hardness increasing agent is contained in said resistance adjusting layer for increasing its hardness.

12. A charging roll according to claim 10, wherein said resistance adjusting layer has a thickness in a range of 100 .mu.m-800 .mu.m.

13. A charging roll according to claim 10, wherein said resistance adjusting layer has a volume resistivity in a range of 10.sup.7 .OMEGA.cm-10.sup.10 .OMEGA.cm.

14. A charging roll according to claim 10, wherein said protective layer has a thickness in a range of 1 .mu.m-20 .mu.m.

15. A charging roll according to claim 10, wherein said protective layer has a volume resistivity in a range of 10.sup.7 .OMEGA.cm-10.sup.10 .OMEGA.cm.

16. A charging roll according to claim 1, wherein said outer structure consists of: a non-foamable conductive elastic layer formed on said outer circumferential surface of said conductive base layer and made of a thermoplastic elastomer material, a resistance adjusting layer formed on an outer circumferential surface of said conductive elastic layer and made of a non-foamable semi-conductive rubber material, and a protective layer formed on an outer circumferential surface of said resistance adjusting layer and made of a soft resin material.

17. A charging roll according to claim 16, wherein said conductive elastic layer has a thickness in a range of 5 .mu.m-10 .mu.m.

18. A charging roll according to claim 16, wherein said conductive elastic layer has a volume resistivity in a range of 10.sup.2 .OMEGA.cm-10.sup.6 .OMEGA.cm.

19. A charging roll according to claim 16, wherein a hardness increasing agent is contained in said resistance adjusting layer for increasing its hardness.

20. A charging roll according to claim 16, wherein said resistance adjusting layer has a thickness in a range of 100 .mu.m-250 .mu.m.

21. A charging roll according to claim 16, wherein resistance adjusting layer has a volume resistivity in a range of 10.sup.7 .OMEGA.cm-10.sup.10 .OMEGA.cm.

22. A charging roll according to claim 16, wherein said protective layer has a thickness in a range of 1 .mu.m-20 .mu.m.

23. A charging roll according to claim 16, wherein said protective layer has a volume resistivity in a range of 10.sup.7 .OMEGA.cm-10.sup.10 .OMEGA.cm.