Coating liquid for forming undercoat layer, photoreceptor having undercoat layer formed of the coating liquid, image-forming apparatus including the photoreceptor, and electrophotographic cartridge including the photoreceptor

1. A coating liquid, comprising:

metal oxide particles combined with a binder resin, wherein the metal oxide particles have a number average particle diameter (Mp) of 0<Mp≦0.10 μm and a 10% cumulative particle diameter (D10) of 0<D10≦0.060 μm, in the coating liquid for forming an undercoat layer of an electrophotographic photoreceptor.

2. A process for preparing a coating liquid comprising liquid metal oxide particles and a binder resin, comprising:

dispersing the metal oxide particles with a medium having an average particle diameter of 5 to 200 μm in a wet agitating ball mill, wherein the metal oxide particles have a number average particle diameter (Mp) of 0<Mp≦0.10 μm and a 10% cumulative particle diameter (D10) of 0<D10≦0.060 μm which are measured by a dynamic light-scattering method, to form the coating liquid for forming an undercoat layer for an electrophotographic photoreceptor.

3. The process for preparing a coating liquid according to claim 2 , wherein the wet agitating ball mill includes a stator, a slurry-supplying port disposed at one end of the stator, a slurry-discharging port disposed at the other end of the stator, a rotor for agitating and mixing the medium packed in the stator and slurry supplied from the supplying port, and a separator that is rotatably connected to the discharging port and separates the medium and the slurry by centrifugal force to discharge the slurry from the discharging port.

4. The process for preparing a coating liquid according to claim 3 , wherein the separator of the wet agitating ball mill is connected to the discharging port to rotate in synchronization with the rotor and separates the medium and the slurry by the centrifugal force to discharge the slurry from the discharging port, and the separator is of an impeller-type including two disks having blade-fitting grooves on the inner faces facing each other, a blade fitted to the fitting grooves and lying between the disks, and supporting means which supports the disks having the blade therebetween from both sides.

5. A coating liquid for forming an undercoat layer prepared by the process according to claim 2 .

6. An electrophotographic photoreceptor comprising an undercoat layer formed by applying and drying the coating liquid according to claim 1 .

7. The electrophotographic photoreceptor according to claim 6 , wherein the undercoat layer has a thickness of from 0.1 μm to 10 μm, and wherein the electrophotographic photoreceptor is a multilayered photoreceptor of which one layer is a charge transporting layer that is formed of material having a thickness of from 5 μm to 15 μm.

8. An image-forming apparatus comprising an electrophotographic photoreceptor, charging means for charging the electrophotographic photoreceptor, image exposure means for forming an electrostatic latent image by subjecting the charged electrophotographic photoreceptor to image exposure, development means for developing the electrostatic latent image with toner, and transfer means for transferring the toner to a transfer object, wherein the photoreceptor is the electrophotographic photoreceptor according to claim 6 .

9. The image-forming apparatus according to claim 8 , wherein the charging means is in contact with the electrophotographic photoreceptor.

10. The image-forming apparatus according claim 8 , wherein the exposure light used in the image exposure means has a wavelength of from 350 nm to 600 nm.

11. An electrophotographic cartridge comprising an electrophotographic photoreceptor and at least one of a charging means for charging the electrophotographic photoreceptor and a development means for developing an electrostatic latent image formed in the photoreceptor with toner, wherein the photoreceptor is the electrophotographic photoreceptor according to claim 6 .

12. The electrophotographic cartridge according to claim 11 , wherein the charging means is arranged so as to be in contact with the electrophotographic photoreceptor.

13. An electrophotographic photoreceptor comprising an undercoat layer formed by applying and drying the coating liquid for forming an undercoating layer according to claim 5 .

14. An image-forming apparatus comprising an electrophotographic photo-receptor, charging means for charging the electrophotographic photoreceptor, image exposure means for forming an electrostatic latent image by subjecting the charged electrophotographic photoreceptor to image exposure development means for developing the electrostatic latent image with toner, and transfer means for transferring the toner to a transfer object, wherein the photoreceptor is the electrophotographic photoreceptor according to claim 13 .

15. An electrophotographic cartridge comprising an electrophotographic photoreceptor and at least one of charging means for charging the electrophotographic photoreceptor and development means for developing an electrostatic latent image formed on the photoreceptor with toner, wherein the photoreceptor is the electrophotographic photoreceptor according to claim 13 .

16. The coating liquid of claim 1 , wherein the metal oxide particles have a number average particle diameter of from 0.02 to 0.10 μm, and a 10% cumulative particle diameter of from 0.01 to 0.060 μm.

17. The coating liquid of claim 1 , wherein the particle diameters are measured by a dynamic light-scattering method.