Electrophotographic photoreceptor, electrophotographic photoreceptor cartridge and image forming apparatus

1. An electrophotographic photoreceptor, comprising:

a conductive support; and

a photosensitive layer on the conductive support,

wherein the photosensitive layer comprises:

a charge transport substance represented by formula (2);

a charge transport substance represented by formula (5); and

a polyester resin having a structural unit represented by formula (6) as a binder resin,

wherein

the charge transport substances represented by formulae (2) and (5) and the polyester resin represented by formula (6) are present in the same layer;

wherein the photosensitive layer comprises 70 to 110 parts by weight in total of the charge transport substances represented by formulae (2) and (5) to 100 parts by weight of the polyester resin having a structural unit represented by formula (6); and

the mixing ratio between the charge transport substance represented by formula (5) and the charge transport substance represented by formula (2) is 40:60 to 90:10:

wherein

each of Ar 4 to Ar 7 independently represents an aryl group having a carbon number of 30 or less, which may have a substituent, and

X represents a divalent substituent represented by the following formula (3) or (4);

wherein

each of R 1 to R 5 independently represents a hydrogen atom or an alkyl group having a carbon number of 6 or less, provided that when X is the divalent substituent represented by formula (3) and in formula (2), all of Ar 4 to Ar 7 are each independently a phenyl group which may have a substituent, and

each of Ar 4 and Ar 6 independently has at least one substituent on the ortho-position or para-position with respect to the nitrogen atom, and the substituents in Ar 4 to Ar 7 may combine with each other to form a ring;

wherein

each of Ar 8 and Ar 9 independently represents an aryl group having a carbon number of 30 or less, which may have a substituent, and

each of R 6 and R 7 independently represents a hydrogen atom or an alkyl group having a carbon number of 6 or less;

wherein

each of Ar 10 to Ar 13 independently represents an arylene group which may have a substituent,

X represents a single bond, an oxygen atom, a sulfur atom or an alkylene group,

m represents an integer of 0 to 2, and

Y represents a single bond, an oxygen atom, a sulfur atom or an alkylene group.

2. The electrophotographic photoreceptor as claimed in claim 1 , wherein the polyester resin is a polyester resin having a structural unit represented by the following formula (X) or (Y):

3. The electrophotographic photoreceptor as claimed in claim 1 , wherein the photosensitive layer contains gallium phthalocyanine as a charge generating substance.

4. An electrophotographic photoreceptor cartridge comprising: the electrophotographic photoreceptor claimed in claim 1 ; and at least one member selected from the group consisting of a charging device for charging the electrophotographic photoreceptor, an exposure device for exposing the charged electrophotographic photoreceptor to form an electrostatic latent image and a developing device for developing the electrostatic latent image formed on the electrophotographic photoreceptor.

5. An image forming apparatus comprising: the electrophotographic photoreceptor claimed in claim 1 ; a charging device for charging the electrophotographic photoreceptor; an exposure device for exposing the charged electrophotographic photoreceptor to form an electrostatic latent image; and a developing device for developing the electrostatic latent image formed on the electrophotographic photoreceptor.

6. The image forming apparatus as claimed in claim 5 , which employs a contact developing system.

7. The image forming apparatus as claimed in claim 5 , which employs a contact charging system.