Photoreceptor comprising the combined use of a quinone and azo compound as charge generating materials

The improved photoreceptor has a light-sensitive layer that contains as carrier generation materials both a polycylic quinone compound selected from among specified anthanthrone pigments, dibenzpyrene pigments and pyranthrone pigments and a specified bisazo pigment, and that also contains a specified stilbene compound as a carrier transport material. This photoreceptor has good spectral sensitivity characteristics over a broad range of wavelengths, has high sensitivity, has a long cycle life on account of reduced residual potential, is adapted for fast copying processes, and is capable of copying red images with improved fidelity of reproduction.

BACKGROUND OF THE INVENTION 
This invention relates to a photoreceptor, particularly to an 
electrophotographic photoreceptor 
Inorganic photoconductive materials including selenium, zinc oxide, 
titanium oxide and cadmium sulfide have conventionally been used as 
light-sensitive materials in electrophotographic photoreceptors. Active 
R&D efforts have recently been made on amorphous silicon. 
Organic photoconductive materials (OPC) are also usable as light-sensitive 
materials and increasing attention is being paid to OPCs since they are 
generally less toxic than inorganic photoconductive materials and since 
they are more advantageous in such aspects as flexibility, 
lightweightness, film-forming property and cost. 
Whichever type of light-sensitive materials are used in electrophotographic 
photoreceptors, "functionally separated" photoreceptors in which different 
materials are used in two layers for fulfilling separate functions of 
charge generation and charge transport have the advantage that the two 
functions can be performed independently of each other, whereby greater 
latitude in photoreceptor design can be attained. Another advantage of 
"functionally separated photoreceptors" is that they have improved 
electrophotographic characteristics such as high sensitivity, long cycle 
life and good mechanical strength. 
Such electrophotographic photoreceptors are extensively used in 
electrophotographic copiers, printers, etc. As recent models of 
electrophotographic copiers and printers are operated at faster speeds, 
the time required for copying processes is significantly shortened and at 
the same time, the number of copying cycles increases so much as to 
require the use of more sensitive and durable photoreceptors. 
Polycyclic quinone compounds and azo pigments may be shown as typical 
examples of high-sensitivity carrier generating materials that are 
suitable for use in electrophotographic photoreceptors. White light 
sources such as an A light source and a fluorescent lamp are commonly 
employed with electrophotographic copiers and the photoreceptor is 
illuminated with light having wavelengths over the entire visible range. 
Polycyclic quinone compounds have excellent photocarrier generating 
ability but their spectral sensitivity is limited to the range of 400-570 
nm. Hence, using polycyclic quinone compounds, it is difficult to 
fabricate electrophotographic photoreceptors having sensitivity to light 
at wavelengths longer than 570 nm. On the other hand, photoreceptors using 
azo pigments, for example, disazo pigments, have their spectral 
sensitivity extended to nearly 700 nm but their photosensitivity is low on 
the shorter wavelength side. Therefore, it is also difficult to fabricate 
photoreceptors with higher sensitivity using azo pigments. 
A more important problem arises from the fact that electrophotographic 
copiers which are indispensable to everyday work in business offices, 
governmental agencies, public organizations, etc. are required to achieve 
faithful reproductions of original documents, particularly seals affixed 
to various documents and underlines marked in red. To meet this need for 
faithful reproduction of red images, the carrier generating materials used 
should not have any sensitivity in the wavelength range beyond 600 nm or 
they must have such a spectral sensitivity characteristic that the 
sensitivity in this longer wavelength range is lower than in the other 
ranges. However, the carrier generation materials available today have 
their own spectral sensitivity characteristics and it is considerably 
difficult to find carrier generating materials that have satisfactory 
electrophotographic characteristics and which yet are capable of 
reproducing red originals to a degree that suits the specific purpose of a 
copying operation. 
With a view to improving the reproducibility of red color, it has been 
proposed that a red cutting cyan filter be inserted into the optical path 
of white light. However, if light at wavelengths longer than 600 nm is cut 
when disazo pigments are used, a substantial decrease in light sensitivity 
occurs. 
As described above, prior art photoreceptors do not have sufficient light 
sensitivity and red color reproducibility to be adapted for use with 
high-speed electrophotographic copiers and small copiers and the advent of 
photoreceptors having higher sensitivity has been desired. 
SUMMARY OF THE INVENTION 
An object, therefore, of the present invention is to provide a 
photoreceptor that has good spectral sensitivity characteristics over a 
broad range of wavelengths, that has high sensitivity, that has a long 
cycle life on account of reduced residual potential, that is adapted for 
fast copying processes, and that is capable of copying red images with 
improved fidelity of reproduction. 
The present inventors conducted intensive studies in order to attain the 
above-stated object and found that it could be attained by a photoreceptor 
having a light-sensitive layer that contains as carrier generation 
materials a polycyclic quinone compound represented by the following 
general formula (A), (B) or (C) and a compound represented by the 
following general formula (I) and that also contains a compound 
represented by the following general formula (ii) as a carrier transport 
material: 
##STR1## 
(where X is a halogen atom, a nitro group, a cyano group, an acyl group of 
a carboxyl group; n is an integer of 0-4; and m is an integer of 0-6); 
##STR2## 
(where X.sup.1 and X.sup.2 independently are a hydrogen atom or a halogen 
atom, provided that X.sup.1 and X.sup.2 are not simultaneously a hydrogen 
atom; A is a group represented by formula [P]; 
##STR3## 
(wherein Ar is an aromatic hydrocarbon ring having a fluorinated 
hydrocarbon group or an aromatic heterocyclic group having a fluorinated 
hydrocarbon group; Z is a group of non-metal atoms necessary to complete a 
substituted or unsubstituted aromatic group or a substituted or 
unsubstituted aromatic heterocyclic group); 
##STR4## 
(where R.sub.1 is a substituted or unsubstituted aryl or styryl group; 
R.sub.2 is a hydrogen atom, a substituted or unsubstituted alkyl grbup, a 
substituted or unsubstituted aryl group or a substituted or unsubstituted 
styryl group, provided that R.sub.1 and R.sub.2 may combine together to 
form a ring; Ar.sub.1 is a substituted or unsubstituted arylene group; 
R.sub.3, R.sub.4 and R.sub.5 are each independently a hydrogen atom, a 
substituted or unsubstituted alkyl group, a substituted or unsubstituted 
aryl group or a substituted or unsubstituted styryl group; l is an integer 
of 0 or 1, provided that when l=0 and R.sub.1 is a substituted or 
unsubstituted aryl group, R.sub.2 is a substituted or unsubstituted alkyl 
group, a substituted or unsubstituted aryl group or a substituted or 
unsubstituted styryl group).