Electrophotographic photoreceptor, process cartridge and image forming apparatus

1. An electrophotographic photoreceptor comprising, in this order:

a substrate;

a photosensitive layer; and

a protective layer including oxygen and gallium, the protective layer including a first region and a second region that is present closer to the substrate than the first region and has a ratio of the number of atoms of oxygen to the number of atoms of gallium (oxygen/gallium) larger than that in the first region, the first region and the second region each comprising oxygen, the second region having a ratio of the number of atoms of oxygen to the number of atoms of gallium (oxygen/gallium) of from about 1.30 to 1.65, and the first region having a ratio of the number of atoms of oxygen to the number of atoms of gallium (oxygen/gallium) of from 1.00 to 1.30.

2. The electrophotographic photoreceptor of claim 1 , wherein the second region has a ratio of the number of atoms of oxygen to the number of atoms of gallium (oxygen/gallium) of from about 1.30 to about 1.50.

3. The electrophotographic photoreceptor of claim 1 , further comprising zinc in the second region.

4. The electrophotographic photoreceptor of claim 3 , wherein the content of zinc in the second region is from about 0.4% by atom to about 25% by atom.

5. The electrophotographic photoreceptor of claim 3 , wherein the content of zinc in the second region is from about 0.5% by atom to about 20% by atom.

6. The electrophotographic photoreceptor of claim 3 , wherein the second region has a ratio of the number of atoms of oxygen to the sum of the number of atoms of gallium and zinc (oxygen/(gallium+zinc)) of from about 1 to about 1.40.

7. The electrophotographic photoreceptor of claim 1 , wherein the protective layer has a thickness of about 1.0 μm or more.

8. The electrophotographic photoreceptor of claim 1 , wherein the protective layer further includes a third region that is present closer to the substrate than the second region, contacts with the photosensitive layer, and has a ratio of the number of atoms of oxygen to the number of atoms of gallium (oxygen/gallium) smaller than that in the second region.

9. The electrophotographic photoreceptor of claim 1 , wherein the protective layer includes a first layer that is the first region and a second layer that is the second region, and further includes, between the first layer and the second layer, an intermediate layer that has a ratio of the number of atoms of oxygen to the number of atoms of gallium (oxygen/gallium) equal to or larger than the ratio of the number of atoms of oxygen to the number of atoms of gallium (oxygen/gallium) of the first layer and equal to or smaller than the ratio of the number of atoms of oxygen to the number of atoms of gallium (oxygen/gallium) of the second layer.

10. The electrophotographic photoreceptor of claim 1 , wherein:

the second region has a ratio of the number of atoms of oxygen to the number of atoms of gallium (oxygen/gallium) of from about 1.30 to about 1.50; and

the first region has a ratio of the number of atoms of oxygen to the number of atoms of gallium (oxygen/gallium) of from 1.00 to 1.20.

11. The electrophotographic photoreceptor of claim 1 wherein the second region is directly adjacent to the photosensitive layer.

12. A process cartridge comprising;

the electrophotographic photoreceptor of claim 1 ; and

at least one selected from the group consisting of a charging unit, a developing unit and a cleaning unit.

13. An electrophotographic photoreceptor comprising, in this order:

a substrate;

a photosensitive layer; and

a protective layer including oxygen and gallium, the protective layer including a first region and a second region that is present closer to the substrate than the first region and has a ratio of the number of atoms of oxygen to the number of atoms of gallium (oxygen/gallium) larger than that in the first region,

wherein the protective layer comprises zinc in the second region, the content of zinc in the second region being from about 10 % by atom to about 20 % by atom.

14. An image forming apparatus comprising:

an electrophotographic photoreceptor comprising, in this order

a substrate,

a photosensitive layer, and

a protective layer including oxygen and gallium, the protective layer including a first region and a second region that is present closer to the substrate than the first region and has a ratio of the number of atoms of oxygen to the number of atoms of gallium (oxygen/gallium) larger than that in the first region, the first region and the second region each comprising oxygen, the second region having a ratio of the number of atoms of oxygen to the number of atoms of gallium (oxygen/gallium) of from about 1.30 to 1.65, and the first region having a ratio of the number of atoms of oxygen to the number of atoms of gallium (oxygen/gallium) of from 1.00 to 1.30;

a charging unit that charges the electrophotographic photoreceptor;

a latent image forming unit that forms a latent image on the surface of the charged electrophotographic photoreceptor;

a developing unit that develops the latent image formed on the surface of the electrophotographic photoreceptor with a toner to form a toner image; and

a transfer unit that transfers the toner image formed on the surface of the electrophotographic photoreceptor onto a recording medium.

15. The image forming apparatus of claim 14 , wherein the second region has a ratio of the number of atoms of oxygen to the number of atoms of gallium (oxygen/gallium) of from about 1.30 to about 1.50.

16. The image forming apparatus of claim 14 , further comprising zinc in the second region.

17. The image forming apparatus of claim 16 , wherein the second region has a ratio of the number of atoms of oxygen to the sum of the number of atoms of gallium and zinc (oxygen/(gallium+zinc)) of from about 1 to about 1.40.

18. The image forming apparatus of claim 14 , wherein the protective layer has a thickness of about 1.0 μm or more.

19. The image forming apparatus of claim 14 , wherein the protective layer further includes a third region that is present closer to the substrate than the second region, contacts with the photosensitive layer, and has a ratio of the number of atoms of oxygen to the number of atoms of gallium (oxygen/gallium) smaller than that in the second region.

20. The image forming apparatus of claim 14 , wherein the protective layer includes a first layer that is the first region and a second layer that is the second region, and further includes, between the first layer and the second layer, an intermediate layer that has a ratio of the number of atoms of oxygen to the number of atoms of gallium (oxygen/gallium) equal to or larger than the ratio of the number of atoms of oxygen to the number of atoms of gallium (oxygen/gallium) of the first layer and equal to or smaller than the ratio of the number of atoms of oxygen to the number of atoms of gallium (oxygen/gallium) of the second layer.