Image forming apparatus and image forming method

1. An image forming apparatus comprising:

a rotatable photoconductor that is provided with a charge generation layer and an overcoat layer;

a charging unit that charges the rotating photoconductor before an image is formed;

an exposure unit that irradiates the rotating photoconductor with light having a wavelength to which a relative sensitivity of the charge generation layer is larger than a relative sensitivity of the overcoat layer, the relative sensitivity of the charge generation layer being a sensitivity to light having a wavelength range normalized by a maximum sensitivity of the charge generation layer in the wavelength range and the relative sensitivity of the overcoat layer being a sensitivity to light having a wavelength range normalized by a maximum sensitivity of the overcoat layer in the wavelength range;

a development unit that applies toner to an electrostatic latent image formed on the rotating photoconductor by the charging unit and the exposure unit;

a transfer unit that transfers an image developed on the rotating photoconductor to a medium;

a first light irradiation unit that irradiates the rotating photoconductor with light having a wavelength to which the relative sensitivity of the overcoat layer is larger than the relative sensitivity of the charge generation layer, the first light irradiation unit irradiating the rotating photoconductor with light before formation of the electrostatic latent image; and

a reverse charging unit that charges the rotating photoconductor having been irradiated with light by the first light irradiation unit to a polarity opposite to a polarity of the rotating photoconductor initially charged by the charging unit, the reverse charging unit charging the rotating photoconductor before formation of the electrostatic latent image.

2. The image forming apparatus according to claim 1 , wherein an absolute value of voltage applied to the reverse charging unit is larger than an absolute value of voltage applied to the charging unit.

3. The image forming apparatus according to claim 1 , wherein

the photoconductor is mounted on an image forming unit that is attached to and detached from a body of the image forming apparatus; and

the image forming apparatus further comprises a controller that causes the first light irradiation unit to execute a light irradiation operation on the photoconductor of the image forming unit and that causes the reverse charging unit to execute a reverse charging operation on the photoconductor of the image forming unit, after the image forming unit is mounted on the body and before the electrostatic latent image is formed.

4. The image forming apparatus according to claim 3 , wherein the controller further causes execution of a density correction operation of an image formed on the photoconductor after causing the first light irradiation unit to execute the light irradiation operation and causing the reverse charging unit to execute the reverse charging operation.

5. An image forming apparatus comprising:

a rotatable photoconductor that is provided with a charge generation layer and an overcoat layer;

a charging unit that charges the rotating photoconductor before an image is formed;

an exposure unit that irradiates the rotating photoconductor with light having a wavelength to which a relative sensitivity of the charge generation layer is larger than a relative sensitivity of the overcoat layer, the relative sensitivity of the charge generation layer being a sensitivity to light having a wavelength range normalized by a maximum sensitivity of the charge generation layer in the wavelength range and the relative sensitivity of the overcoat layer being a sensitivity to light having a wavelength range normalized by a maximum sensitivity of the overcoat layer in the wavelength range;

a development unit that applies toner to an electrostatic latent image formed on the rotating photoconductor by the charging unit and the exposure unit;

a transfer unit that transfers an image developed on the rotating photoconductor to a medium;

a first light irradiation unit that irradiates the rotating photoconductor with light having a wavelength to which the relative sensitivity of the overcoat layer is larger than the relative sensitivity of the charge generation layer, the first light irradiation unit irradiating the rotating photoconductor with light before formation of the electrostatic latent image; and

a heating unit that heats the rotating photoconductor having been irradiated with light by the first light irradiation unit, the heating unit heating the rotating photoconductor before formation of the electrostatic latent image.

6. The image forming apparatus according to claim 5 , wherein the development unit is provided with a developer carrier that is arranged opposed to the photoconductor and that rotates while holding the toner; and

the heating unit heats the photoconductor at a temperature not exceeding a glass transition point of the toner when the toner held in the developer carrier is in contact with the photoconductor.

7. The image forming apparatus according to claim 5 , wherein

the photoconductor is mounted on an image forming unit that is attached to and detached from a body of the image forming apparatus; and

the image forming apparatus further comprises a controller that causes the first light irradiation unit to execute a light irradiation operation on the photoconductor of the image forming unit and that causes the heating unit to execute a heating operation on the photoconductor of the image forming unit, after the image forming unit is mounted on the body and before the electrostatic latent image is formed.

8. The image forming apparatus according to claim 7 , wherein the controller retracts the development unit from the photoconductor when causing the first light irradiation unit to execute the light irradiation operation and causing the heating unit to execute the heating operation.

9. The image forming apparatus according to claim 1 , wherein the first light irradiation unit irradiates the overcoat layer with light having a wavelength of 400 nm and longer and 500 nm and shorter.

10. The image forming apparatus according to claim 1 , further comprising a second light irradiation unit that irradiates the photoconductor with light having a wavelength range to which the relative sensitivity of the charge generation layer is larger than the relative sensitivity of the overcoat layer, after the transfer by the transfer unit.

11. The image forming apparatus according to claim 10 , wherein

the first light irradiation unit and the second light irradiation unit are arranged substantially in parallel in a peripheral direction of the photoconductor along a rotation axis direction of the photoconductor; and

the image forming apparatus further comprises a power supply that supplies electric power to the first light irradiation unit and the second light irradiation unit while switching voltage.

12. An image forming apparatus comprising:

a rotatable photoconductor that is provided with a charge generation layer and an overcoat layer;

a charging unit that charges the rotating photoconductor before an image is formed;

an exposure unit that irradiates the rotating photoconductor with light having a wavelength at which a charge pair is generated more readily in the charge generation layer than in the overcoat layer;

a development unit that applies toner to an electrostatic latent image formed on the rotating photoconductor by the first charging unit and the exposure unit;

a transfer unit that transfers an image developed on the photoconductor to a medium;

a first light irradiation unit that irradiates the rotating photoconductor with light having a wavelength at which a charge pair is generated more readily in the overcoat layer than in the charge generation layer, the first light irradiation unit irradiating the rotating photoconductor with light before formation of the electrostatic latent image; and

a reverse charging unit that charges the rotating photoconductor having been irradiated with light by the first light irradiation unit to a polarity opposite to a polarity of the rotating photoconductor initially charged by the first charging unit, the reverse charging unit charging the rotating photoconductor before formation the electrostatic latent image.

13. The image forming apparatus according to claim 12 , wherein an absolute value of voltage applied to the reverse charging unit is larger than an absolute value of voltage applied to the charging unit.

14. The image forming apparatus according to claim 12 , further comprising a second light irradiation unit that irradiates the photoconductor with light having a wavelength range to which a relative sensitivity of the charge generation layer is larger than a relative sensitivity of the overcoat layer, after the transfer by the transfer unit, the relative sensitivity of the charge generation layer being a sensitivity to light having a wavelength range normalized by a maximum sensitivity of the charge generation layer in the wavelength range and the relative sensitivity of the overcoat layer being a sensitivity to light having a wavelength range normalized by a maximum sensitivity of the overcoat layer in the wavelength range.

15. The image forming apparatus according to claim 14 , wherein

the first light irradiation unit and the second light irradiation unit are arranged substantially in parallel in a peripheral direction of the photoconductor along a rotation axis direction of the photoconductor; and

the image forming apparatus further comprises a power supply that supplies electric power to the first light irradiation unit and the second light irradiation unit while switching voltage.

16. An image forming method for an image forming apparatus including a rotatable photoconductor having a charge generation layer and an overcoat layer, the image forming method comprising:

charging the rotating photoconductor before an image is formed;

irradiating the rotating photoconductor with light having a wavelength to which a relative sensitivity of the charge generation layer is larger than a relative sensitivity of the overcoat layer and exposing the photoconductor, the relative sensitivity of the charge generation layer being a sensitivity to light having a wavelength range normalized by a maximum sensitivity of the charge generation layer in the wavelength range and the relative sensitivity of the overcoat layer being a sensitivity to light having a wavelength range normalized by a maximum sensitivity of the overcoat layer in the wavelength range;

developing an electrostatic latent image formed on the rotating photoconductor by charging and irradiating, through application of toner;

transferring an image developed on the rotating photoconductor;

irradiating the rotating photoconductor with light having a wavelength to which the relative sensitivity of the overcoat layer is larger than the relative sensitivity of the charge generation layer, before forming the electrostatic latent image; and

erasing a charge from the rotating photoconductor irradiated with light.

17. The image forming method according to claim 16 , wherein, when the charge is erased from the photoconductor, the photoconductor is charged to a polarity opposite to a polarity at the time of charging the photoconductor.

18. The image forming method according to claim 16 , wherein the photoconductor is heated and the charge is erased from the photoconductor.

19. The image forming apparatus according to claim 5 , wherein the first light irradiation unit irradiates the overcoat layer with light having a wavelength of 400 nm and longer and 500 nm and shorter.

20. The image forming apparatus according to claim 5 , further comprising a second light irradiation unit that irradiates the photoconductor with light having a wavelength range to which the relative sensitivity of the charge generation layer is larger than the relative sensitivity of the overcoat layer, after the transfer by the transfer unit.

21. The image forming apparatus according to claim 20 , wherein

the first light irradiation unit and the second light irradiation unit are arranged substantially in parallel in a peripheral direction of the photoconductor along a rotation axis direction of the photoconductor; and

the image forming apparatus further comprises a power supply that supplies electric power to the first light irradiation unit and the second light irradiation unit while switching voltage.