Electrophotographic photoreceptor, process cartridge, and image forming apparatus

1. An electrophotographic photoreceptor comprising, over an electroconductive substrate, a photosensitive layer and a surface protection layer in this order, the surface protection layer satisfying each of the following requirements (1) to (3):

(1) comprising a crosslinked substance of at least one selected from a compound having a guanamine structure or a compound having a melamine structure, and at least one charge transporting material having at least one substituent selected from —OH —OCH 3 , —NH 2 , —SH or —COOH;

(2) comprising the at least one selected from a compound having a guanamine structure or a compound having a melamine structure in an amount of from about 0.1% by weight to about 5% by weight; and

(3) having a universal hardness of from about 180 N/mm 2 to about 220 N/mm 2 and a creep ratio of from 5.1% to about 8%, the universal hardness and the creep ratio being obtained by performing a hardness test by pushing a Vickers quadrangular pyramid diamond indenter against the surface protection layer at a maximum load of 20 mN, in an environment of 25° C. and a relative humidity of 50%.

2. The electroconductive photoreceptor according to claim 1 , wherein the charge transporting material comprises a compound represented by the following formula (I):

F—((—R 11 —X) n1 (R 12 ) n2 —Y) n3   (I)

wherein, in formula (I), F represents an organic group derived from a compound having a hole transporting capability, each of R 11 and R 12 independently represent a linear or branched alkylene group having 1 to 5 carbon atoms, n 1 represents 0 or 1, n 2 represents 0 or 1, n 3 represents an integer of 1 to 4, X represents an oxygen atom, NH, or a sulfur atom, and Y represents —OH, OCH 3 , —NH 2 , —SH or —COOH.

3. The electroconductive photoreceptor according to claim 1 , wherein the charge transporting material comprises a compound represented by the following formula (II):

wherein, in formula (II), Ar 1 to Ar 4 each independently represent a substituted or unsubstituted aryl group; Ar 5 represents a substituted or unsubstituted aryl group or a substituted or unsubstituted arylene group; each D independently represents —(—R 11 —X) n1 (R 12 ) n2 —Y, wherein R 11 and R 12 each independently represent a linear or branched alkylene group having 1 to 5 carbon atoms, n 1 represents 0 or 1, n 2 represents 0 or 1, X represents an oxygen atom, NH or a sulfur atom, and Y represents —OH, —OCH 3 , —NH 2 , —SH or —COOH; each c independently represents 0 or 1; k represents 0 or 1; and the total number of Ds is from 1 to 4.

4. The electroconductive photoreceptor according to claim 1 , wherein the surface protection layer has a universal hardness of from about 1.80 N/mm 2 to about 200 N/mm 2 .

5. The electroconductive photoreceptor according to claim 1 , wherein the surface protection layer has a creep ratio of from 5.1% to about 7%.

6. The electroconductive photoreceptor according to claim 1 , wherein the surface protection layer has a creep ratio of from about 5.5% to about 7%.

7. The electrophotographic photoreceptor according to claim 1 , wherein a solid content concentration of the at least one charge transporting material in the surface protection layer is 80% or more by weight.

8. A process cartridge comprising an electrophotographic photoreceptor and at least one selected from the group consisting of a charging unit that charges the electrophotographic photoreceptor, a toner image forming unit that forms a toner image by developing, with a toner, an electrostatic latent image formed on the electrostatic photoreceptor, and a toner removal unit that removes toner remaining on the surface of the electrophotographic photoreceptor,

the electrophotographic photoreceptor comprising, over an electroconductive substrate, a photosensitive layer and a surface protection layer in this order, the surface protection layer satisfying each of the following requirements (1) to (3):

(1) comprising a crosslinked substance of at least one selected from a compound having a guanamine structure or a compound having a melamine structure, and at least one charge transporting material having at least one substituent selected from —OH, OCH 3 , —NH 2 , —SH or —COOH;

(2) comprising the at least one selected from a compound having a guanamine structure or a compound having a melamine structure in an amount of from about 0.1% by weight to about 5% by weight; and

(3) having a universal hardness of from about 180 N/mm 2 to about 220 N/mm 2 and a creep ratio of from 5.1% to about 8%, the universal hardness and the creep ratio being obtained by performing a hardness test by pushing a Vickers quadrangular pyramid diamond indenter against the surface protection layer at a maximum load of 20 mN, in an environment of 25° C. and a relative humidity of 50%.

9. The process cartridge according to claim 8 , wherein the surface protection layer has a universal hardness of from about 180 N/mm 2 to about 200 N/mm 2 .

10. The process cartridge according to claim 8 , wherein the surface protection layer has a creep ratio of from 5.1% to about 7%.

11. The process cartridge according to claim 8 , wherein the surface protection layer has a creep ratio of from about 5.5% to about 7%.

12. An image forming apparatus comprising:

an electrophotographic photoreceptor;

a charging unit that charges the electrophotographic photoreceptor;

an electrostatic latent image forming unit that forms an electrostatic latent image on the electrophotographic photoreceptor by exposing the charged electrophotographic photoreceptor to light;

a toner image forming unit that forms a toner image by developing, with a toner, the electrostatic latent image formed on the electrostatic photoreceptor;

a first transfer unit that transfers the toner image from the electrophotographic photoreceptor to an intermediate transfer medium;

a second transfer unit that transfers the toner image from the intermediate transfer medium to an image receiving medium;

and a toner removal unit that removes toner remaining on the surface of the electrophotographic photoreceptor,

the electrophotographic photoreceptor comprising, over an electroconductive substrate, a photosensitive layer and a surface protection layer in this order, the surface protection layer satisfying each of the following requirements (1) to (3):

(1) comprising a crosslinked substance of at least one selected from a compound having a guanamine structure or a compound having a melamine structure, and at least one charge transporting material having at least one substituent selected from —OH, OCH 3 , —NH 2 , —SH or —COOH;

(2) comprising the at least one selected from a compound having a guanamine structure or a compound having a melamine structure in an amount of from about 0.1% by weight to about 5% by weight; and

(3) having a universal hardness of from about 180 N/mm 2 to about 220 N/mm 2 and a creep ratio of from 5.1% to about 8%, the universal hardness and the creep ratio being obtained by performing a hardness test by pushing a Vickers quadrangular pyramid diamond indenter against the surface protection layer at a maximum load of 20 mN, in an environment of 25° C. and a relative humidity of 50%.

13. The image forming apparatus according to claim 12 , wherein a velocity difference Δv represented by the following expression (a) is from about 1.5% to about 5%:

Δ v=|v 2 −v 1 |v 1×100  (a)

wherein, in expression (a), v 1 (mm/s) represents the velocity of rotation of the electrophotographic photoreceptor, and v 2 (mm/s) represents the velocity of rotation of the intermediate transfer medium.

14. The image forming apparatus according to claim 13 , wherein the velocity difference Δv is from about 2% to 4%.

15. The image forming apparatus according to claim 12 , wherein a solid content concentration of the at least one charge transporting material in the surface protection layer is 80% or more by weight.