Electro photographic photoconductor and color image forming apparatus

1. A tandem-system color image forming device including a drum type electrophotographic photoconductor, a rotation speed of which is 70 rpm or more,

wherein the color image forming device is provided with a positive charging type electrophotographic photoconductor by which an image density is maintained at a value of 1.3 or more,

wherein the electrophotographic photoconductor comprises a photosensitive layer containing a mixture of at least a charge-generating agent, a hole transfer agent, an electron transfer agent, and a binder resin carried on a conductive substrate,

the conductive substrate comprising an aluminum base tube,

the charge-generating agent comprising an X-type non-metal phthalocyanine,

the binder resin comprising a polycarbonate resin represented by the formula (1)

having a viscosity average molecular weight of from 20,000 to 80,000,

the hole transfer agent comprising a compound represented by formula (2) or (5),

the electron transfer agent is comprising a compound represented by the formula (9),

and

wherein, when Vb (V) denotes a sensitivity in the case where an amount of light exposure per unit area is 0.6 μJ/cm 2 and Va (V) denotes a sensitivity in the case where an amount of light exposure per unit area is 1.5 μJ/cm 2 , a sensitivity ratio represented by (Vb/Va) is adjusted to a value within the range from 1 to 1.73;

wherein the sensitivity (Vb), in the case where the amount of light exposure per unit area is 0.6 μJ/cm 2 , is adjusted to a value of 150 V or less, and

wherein the sensitivity (Va), in the case where the amount of light exposure per unit area is 1.5 μJ/cm 2 , is adjusted to a value within the range from 70 to 120 V.

2. The color image forming device according to claim 1 , wherein an outer diameter of electrophotographic photoconductor is adjusted to a value within the range from 10 to 30 mm.

3. The color image forming device according to claim 1 , wherein the thickness of the photosensitive layer is adjusted to a value within the range from 5 to 50 μm.

4. The color image forming device according to claim 1 , wherein a process speed is adjusted to a value within the range from 80 to 200 mm/sec.

5. The color image forming device according to claim 1 , wherein a cleaner-less system is adopted.

6. The color image forming device according to claim 1 , wherein the photosensitive layer comprises 0.2 to 40 parts by weight of the charge-generating agent, 10 to 100 parts by weight of the hole transfer agent, and 10 to 100 parts by weight of the electron transfer agent, to 100 parts of the binder resin.

7. The color image forming device according to claim 6 , wherein the photosensitive layer comprises 30 to 80 parts by weight of the hole transfer agent.

8. The color image forming device according to claim 6 , wherein the photosensitive layer comprises 20 to 80 parts by weight of the electron transfer agent.

9. The color image forming device according to claim 6 , wherein the photosensitive layer comprises a ratio of the electron transfer agent to the hole transfer agent of 0.25 to 1.3 by weight.

10. The color image forming device according to claim 9 , wherein the photosensitive layer comprises a ratio of the electron transfer agent to the hole transfer agent of 0.5 to 1.25 by weight.