Transfer roll and image forming apparatus

1. A transfer roll comprising:

a cylindrical conductive substrate;

an inner elastic layer having an Asker-C hardness of from 5° to 20°; and

an outer elastic layer having an Asker-C hardness of from 30° to 45° in this order,

wherein the transfer roll satisfies the following Expression (1):

ρ 0 (in)>ρ 0 (out)  Expression (1):

wherein ρ 0 (in) is a volume resistivity of the inner elastic layer that is measured by applying an applied voltage of 1000 V in an environment of a temperature of 22° C. and a humidity of 55 RH % in an unloaded state, and ρ 0 (out) is a volume resistivity of the outer elastic layer that is measured by applying an applied voltage of 1000 V in an environment of a temperature of 22° C. and a humidity of 55 RH % in an unloaded state.

2. The transfer roll according to claim 1 ,

wherein the transfer roll satisfies following Expression (2):

ρ α (in)<ρ α (out)  Expression (2):

wherein ρ α (in) is a volume resistivity of the inner elastic layer that is measured by applying an applied voltage of 1000 V in an environment of a temperature of 22° C. and a humidity of 55 RH % in a state where load is applied from above the outer elastic layer so that the thickness of the inner elastic layer may become at least any thickness of from 20% to 30% of the thickness in an unloaded state, and ρ α (out) is a volume resistivity of the outer elastic layer that is measured by applying an applied voltage of 1000 V in an environment of a temperature of 22° C. and a humidity of 55 RH % in a state where load is applied from above the outer elastic layer so that the thickness of the inner elastic layer may become the thickness of 30% of the thickness in an unloaded state.

3. The transfer roll according to claim 1 ,

wherein the inner elastic layer contains a conductive material with electron conductivity and the outer elastic layer contains a conductive material with ion conductivity.

4. The transfer roll according to claim 2 ,

wherein the inner elastic layer contains a conductive material with electron conductivity and the outer elastic layer contains a conductive material with ion conductivity.

5. The transfer roll according to claim 1 ,

wherein the thickness of the inner elastic layer is within a range of from 1 mm to 10 mm and the thickness of the outer elastic layer is within a range of from 1 mm to 10 mm.

6. The transfer roll according to claim 1 ,

wherein the inner elastic layer is an elastic layer having bubbles.

7. The transfer roll according to claim 1 ,

wherein the outer elastic layer is an elastic layer having bubbles.

8. The transfer roll according to claim 6 ,

wherein the average bubble diameter of the inner elastic layer is smaller than the average bubble diameter of the outer elastic layer.

9. The transfer roll according to claim 6 ,

wherein the average bubble diameter of the inner elastic layer is from 100 μm to 300 μm.

10. The transfer roll according to claim 7 ,

wherein the average bubble diameter of the outer elastic layer is from 150 μm to 400 μm.

11. An image forming apparatus comprising:

an image holding member;

a latent image forming device that forms an electrostatic latent image on the surface of the image holding member;

a developing device that develops the electrostatic latent image with a toner to form a toner image;

an intermediate transfer belt;

a primary transfer device that is arranged so as to face the image holding member via the intermediate transfer belt and form a nip by a load applied from the image holding member, and applies a voltage for transferring the toner image on the image holding member to the surface of the intermediate transfer belt; and

a secondary transfer device that transfers the toner image transferred to the intermediate transfer belt to a recording medium,

wherein the primary transfer device includes the transfer roll according to claim 1 .

12. The image forming apparatus according to claim 11 , comprising a primary transfer device in which the transfer roll satisfies the following Expression (3-1):

ρ β-1 (in)<ρ β-1 (out)  Expression (3-1):

wherein ρ β-1 (in) is a volume resistivity of the inner elastic layer at the voltage in a state where the nip is formed, and ρ β-1 (out) is a volume resistivity of the outer elastic layer in a state where the nip is formed.

13. An image forming apparatus comprising:

an image holding member;

a latent image forming device that forms an electrostatic latent image on the surface of the image holding member;

a developing device that develops the electrostatic latent image with a toner to form a toner image;

an intermediate transfer belt;

a primary transfer device that transfers the toner image on the image holding member to the surface of the intermediate transfer belt; and

a secondary transfer device including a secondary transfer roll contacting the outer peripheral surface side of the intermediate transfer belt and having a recording medium inserted between the secondary transfer roll and the intermediate transfer belt, and a facing roll arranged so as to face the secondary transfer roll via the intermediate transfer belt and form a nip by a load applied from the secondary transfer roll, and applying a voltage for transferring the toner image on the intermediate transfer belt to a recording medium,

wherein the facing roll is the transfer roll according to claim 1 .

14. The image forming apparatus according to claim 13 , comprising a secondary transfer device in which the facing roll satisfies the following Expression (3-2):

ρ β-2 (in)<ρ β-2 (out)  Expression (3-2):

wherein ρ β-2 (in) is a volume resistivity of the inner elastic layer at the voltage in a state where the nip is formed, and ρ β-2 (out) is a volume resistivity of the outer elastic layer in a state where the nip is formed.

15. An image forming apparatus comprising:

an image holding member;

a latent image forming device that forms an electrostatic latent image on the surface of the image holding member;

a developing device that develops the electrostatic latent image with a toner to form a toner image;

an intermediate transfer belt;

a primary transfer device that transfers the toner image on the image holding member to the surface of the intermediate transfer belt; and

a secondary transfer device including a secondary transfer roll contacting the outer peripheral surface side of the intermediate transfer belt and having a recording medium inserted between the secondary transfer roll and the intermediate transfer belt, and a facing roll arranged so as to face the secondary transfer roll via the intermediate transfer belt and form a nip by applying a load to the secondary transfer roll, and applying a voltage for transferring the toner image on the intermediate transfer belt to a recording medium,

wherein the secondary transfer roll is the transfer roll according to claim 1 .

16. The image forming apparatus according to claim 15 , comprising a secondary transfer device in which the secondary transfer roll satisfies the following Expression (3-3):

ρ β-3 (in)<ρ β-3 (out)  Expression (3-3):

wherein ρ β-3 (in) is a volume resistivity of the inner elastic layer at the voltage in a state where the nip is formed, and ρ β-3 (out) is a volume resistivity of the outer elastic layer in a state where the nip is formed.