A disazo compound, having the general formula, ##STR1## wherein Y represents a substituted or non-substituted cyclic hydrocarbon or substituted or non-substituted heterocycle; R represents hydrogen, substituted or non-substituted alkyl group, or substituted or non-substituted phenyl group; and PA1 Z represents a substituted or non-substituted cyclic hydrocarbon or heterocycle fused with phenyl nucleus.

BACKGROUND OF THE INVENTION 
This invention relates to a disazo compound, method for preparing the same, 
and electrophotographic element containing the same for use in 
electrophotography. More particularly, this invention relates to an 
electrophotographic element having a photosensitive layer containing a 
disazo compound as a charge generating substance which generates a charge 
carrier by light irradiation. 
Heretofore, there were used inorganic photosensitive materials such as 
selenium, selenium alloy, cadmium sulfide, zinc oxide and the like. Among 
them, selenium type photosensitive material was widely used because it has 
generally superior properties in respect to receiving potential, dark 
decay, sensitivity and the like. However, the selenium type 
electrophotographic element has such disadvantages as that the control of 
properties is difficult since it is prepared by vapor deposition; that the 
manufacturing cost is high; that it is difficult to work the element into 
a belt-like product due to lack of flexibility; and that the handling of 
the element is not easy because it is too sensitive to mechanical impact 
and heat. 
There was also used an element having a photosensitive layer containing an 
organic photosensitive material superior in flexibility and easy in 
production, for example, a charge transfer comples of 
2,4,7-trinitro-9-fluorenone and poly-N-vinylcarbazole. However, the 
sensitivity of this element was too low and therefore unsuitable as an 
electrophotographic element for a high speed copying machine. 
Recently, various studies have been carried out to remove disadvantages for 
these electrophotographic elements. Among them, there is noted a separate 
function type electrophotographic element wherein the generation of a 
charge carrier and the transfer of the generated charge carrier are 
respectively conducted by separate substances. As the separate function 
type electrophotographic element, there are enumerated a laminated type 
electrophotographic element having a photosensitive layer prepared by 
laminating a charge generating layer containing a charge generating 
substance to generate a charge carrier by light irradiation and a charge 
transfer layer containing a charge transfer substance to transfer the 
generated charge, a dispersed type electrophotographic element prepared by 
dispersing a charge generating substance in a charge transfer medium 
containing a charge transfer substance, and the like. Since these 
photosensitive materials are widely selected and it is possible to enhance 
the sensitivity, they are noted as an electrophotographic element for a 
plain paper copier. 
Examples of these electrophotographic elements include: 
(1) a laminated type electrophotographic element using a thin layer formed 
by vapor depositing perillene derivatives as a charge generating layer and 
oxadiazole derivatives as a charge transfer layer (U.S. Pat. No. 
3,871,882); 
(2) a laminated type electrophotographic element using a thin layer formed 
by coating an organic amine solution of Chloro Dian Blue as a charge 
generating layer and hydrazone compound as a charge transfer layer 
(Japanese Patent Publication No. 55-42380); and the like. 
However, these conventional laminated type electrographic elements have not 
only advantages but also various disadvantages. For example, the above 
electrophotographic element (1) using perillene derivatives and oxadiazole 
derivatives has a disadvantage that the manufacturing cost is very high 
because of forming a charge generating layer by vapor deposition. The 
above electrophotographic element (2) using Chloro Dian Blue and hydrazone 
compound must use an organic amine (for example, ethylene diamine) as a 
coating solvent for forming a charge generating layer, which is difficult 
in handling. 
As a photosensitive material having a good sensitivity which can be easily 
manufactured, there are enumerated a photosensitive material using a 
disazo pigment having styrylstilbene structure as a charge generating 
substance (Japanese Laid Open No. 53-133445); a photosensitive material 
using a disazo pigment having dibenzothiophene structure as a charge 
generating substance (Japanese Laid Open No. 54-21728); a photosensitive 
material using a disazo pigment having carbazole structure (Japanese Laid 
Open Nos. 53-95033 and 53-95966); a photosensitive material using a 
trisazo pigment having triphenyl amine structure (Japanese Laid Open No. 
53-132347); a photosensitive material using a disazo pigment having 
oxazole structure (Japanese Laid Open No. 54-12742); a photosensitive 
material using a disazo pigment having disstyrylcarbazole structure 
(Japanese Laid Open No. 54-14967); a photosensitive material using a 
disazo pigment having bisstilbene structure (Japanese Laid Open No. 
54-17733); a photosensitive material using a disazo pigment having 
fluorenone structure (Japanese Laid Open No. 54-22834); and the like. 
However, these conventional photosensitizers also have merits and 
demerits, and a development of new photosensitive materials having better 
properties is desired. 
SUMMARY OF THE INVENTION 
An object of the present invention is to provide a disazo compound 
expressed by the general formula (I), 
##STR2## 
wherein Y represents a substituted or non-substituted cyclic hydrocarbon 
or substituted or non-substituted heterocycle; R represents hydrogen, 
substituted or non-substituted alkyl group, or substituted or 
non-substituted phenyl group; and Z represents a substituted or 
non-substituted cyclic hydrocarbon or substituted or non-substituted 
heterocycle fused with phenyl nucleus. 
Another object of the present invention is to provide a method for 
preparing a disazo compound expressed by the general formula (I), 
##STR3## 
wherein Y, R and Z are the same as mentioned above, characterized by 
diazotizing 4,4'-diaminotriphenyl amine expressed by the general formula 
(II), 
##STR4## 
to produce a tetrazonium salt expressed by the general formula (III), 
##STR5## 
wherein X represents an anion functional group, and reacting the thus 
produced tetrazonium salt with a coupler expressed by the general formula 
(IV), 
##STR6## 
wherein Y, R and Z are the same as mentioned above. 
The other object of the present invention is to provide a photosensitive 
material for use in electrophotography, characterized by that said 
photosensitive material has on an electroconductive substrate a 
photosensitive layer containing a disazo compound expressed by the general 
formula (V), 
##STR7## 
wherein A represents a residue of a coupler. 
DETAILED DESCRIPTION OF THE INVENTION 
Examples of the cyclic hydrocarbon of Y in the general formula (I) of the 
disazocompound of the present invention include benzene ring, naphthalene 
ring or the like, and examples of the heterocycle of Y include 
dibenzofuran ring, carbazole ring or the like. Examples of a substituent 
of the cyclic hydrocarbon or heterocycle of Y include a lower alkyl group 
such as methyl, ethyl, propyl, butyl and the like; a lower alkoxy group 
such as methoxy, ethoxy, butoxy and the like; a lower dialkyl amino group 
such as N,N-dimethylamino, N,N-diethylamino, N,N-dibutylamino groups and 
the like; a halogen atom such as fluorine, chlorine, bromine and the like; 
a halomethyl group such as trifluoromethyl and the like; a lower 
alkylcarboxyl group such as ethylcarboxyl group; carboxyl group; cyano 
group; nitro group; --SO.sub.3 Na and the like. 
Examples of the alkyl group of R include a lower alkyl group such as 
methyl, ethyl, and the like. Examples of the substituent of the alkyl 
group or phenyl group of R include a halogen atom such as chlorine. 
Examples of the cyclic hydrocarbon of Z include benzene ring, naphthalene 
ring, and the like, and examples of the heterocycle include indole ring, 
benzofuran ring, carbazole ring and the like. Examples of the substituent 
of the cyclic hydrocarbon or the heterocycle include a halogen atom such 
as chlorine. 
Examples of the coupler of the disazocompounds expressed by the general 
formula (V) include a compound having a phenolic hydroxyl group such as 
phenol type, naphthol type compounds and the like; an aromatic amino 
compound having an amino group; an aminonaphthol type compound having an 
amino group and a phenolic hydroxyl group; a compound having an aliphatic 
or aromatic enol type ketone group (active methylene group); and the like. 
Preferably, the residue A of the coupler is expressed by the following 
general formula (VI), (VII), (VIII), (IX), (X), (XI), (XII), (XIII), 
(XIV), (XV), (XVI), (XVII) and (XVIII). 
##STR8## 
wherein X.sub.1, Y.sub.1, Z, m and n in the above formula (VI), (VII), 
(VIII) and (IX) represent the following groups: 
X.sub.1 : 
##STR9## 
(wherein R.sub.1 and R.sub.2 represent hydrogen or a substitured or 
non-substituted alkyl group, and R.sub.3 represents a substituted or 
non-substituted alkyl or a substituted or non-substituted aryl group); 
Y.sub.1 : hydrogen, halogen, substituted or non-substituted alkyl group, 
substituted or non-substituted alkoxy group, carboxyl group, sulfo group, 
substituted or non-substituted sulfamoyl group or 
##STR10## 
(wherein R.sub.4 represents hydrogen, alkyl group or its substituted 
compound, phenyl group or its substituted compound, and Y.sub.2 represents 
cyclic hydrocarbon or its substituted compound, heterocycle or its 
substituted compound, or 
##STR11## 
wherein R.sub.5 represents a cyclic hydrocarbon or its substituted 
compound, heterocycle or its substituted compound, or styryl group or its 
substituted compound, and R.sub.6 represents hydrogen, alkyl group, phenyl 
group or their substituted compound, or R.sub.5 and R.sub.6 may form a 
ring with carbons bonded thereto); 
Z: cyclic hydrocarbon or its substituted compound, or heterocycle or its 
substituted compound; 
n: an integer of 1 or 2; 
m: an integer of 1 or 2. 
##STR12## 
wherein R.sub.7 in the above formula (X) and (XI) represents a 
substituted or non-substituted hydrocarbonyl group, and X.sub.1 is the 
same as mentioned above; 
##STR13## 
wherein R.sub.8 represents an alkyl group, carbamoyl group, carboxyl 
group or its ester, and Ar.sub.1 represents a cyclic hydrocarbon or its 
substituted compound, and X.sub.1 is the same as mentioned above; 
##STR14## 
wherein R.sub.9 in the above formula (XIII) and (XIV) represents hydrogen 
or substituted or non-substituted hydrocarbonyl group, and Ar.sub.2 
represents cyclic hydrocarbon or its substituted compound. 
Examples of the cyclic hydrocarbon expressed by Z in the above general 
formula (VI), (VII), (VIII) or (IX) include benzene ring, naphthalene ring 
and the like, and examples of the heterocycle expressed by the same 
include indole ring, carbazole ring, benzofuran ring, dibenzofuran ring 
and the like. Examples of the substituent of the ring expressed by Z 
include a halogen atom such as chlorine, bromine, and the like. 
Examples of the cyclic hydrocarbon expressed by Y.sub.2 or R.sub.5 include 
phenyl, naphthyl, anthryl, pyrenyl and the like, and examples of the 
heterocyclic group expressed by the same include pyridyl, thienyl, furyl, 
indolyl, benzofuranyl, carbazolyl, dibenzofuranyl and the like. Examples 
of the ring formed by bonding R.sub.5 and R.sub.6 include fluorene ring. 
Examples of the substituents for the cyclic hydrocarbon or heterocycle 
expressed by Y.sub.2 or R.sub.5 or for the ring formed by bonding R.sub.5 
and R.sub.6 include an alkyl group such as methyl, ethyl, propyl, butyl or 
the like; an alkoxy group such as methoxy, ethoxy, propoxy, butoxy or the 
like; a halogen atom such as chlorine, bromine or the like; a dialkyl 
amino group such as dimethyl amino, diethyl amino or the like; a diaralkyl 
amino group such as dibenzyl amino or the like; a halomethyl group such as 
trifluoromethyl or the like; nitro group; cyano group; carboxyl group or 
its ester; hydroxyl group; sulphonate group such as --SO.sub.3 Na; and the 
like. 
Examples of the substituent for the phenyl group expressed by R.sub.4 
include a halogen atom such as chlorine or bromine. 
Examples of the hydrocarbonyl group expressed by R.sub.7 and R.sub.9 
include an alkyl group such as methyl, ethyl, propyl, butyl and the like; 
an aralkyl group such as benzyl and the like; an aryl group such as 
phenyl; or their substituted compounds. 
Examples of the substituent for the hydrocarbonyl group expressed by 
R.sub.7 or R.sub.9 include an alkyl group such as methyl, ethyl, propyl, 
butyl and the like; an alkoxy group such as methoxy, ethoxy, propoxy, 
butoxy and the like; a halogen atom such as chlorine, bromine and the 
like; hydroxyl group; nitro group; and the like. 
Examples of the cyclic hydrocarbon expressed by Ar.sub.1 or Ar.sub.2 
include phenyl, naphthyl and the like, and examples of the substituents 
for these groups include an alkyl group such as methyl, ethyl, propyl, 
butyl or the like; an alkoxy group such as methoxy, ethoxy, propoxy, 
butoxy or the like; nitro group; and halogen group such as chlorine, 
bromine or the like; cyano group; and a dialkyl amino group such as 
dimethyl amino, diethyl amino or the like. 
Among the groups expressed by X.sub.1, hydroxyl group is particularly 
suitable. 
Among the above coupler residues, preferable ones are expressed by the 
general formula (VII), (X), (XI), (XII), (XIII) and (XIV), and X.sub.1 in 
the general formula is preferably hydroxyl group. Among them, the coupler 
residue expressed by the general formula (XV) 
##STR15## 
(wherein Y.sub.1 and Z are the same as mentioned above) is preferable, and 
the coupler residue expressed by the general formula (XVI) 
##STR16## 
(wherein Z, Y.sub.2 and R.sub.2 are the same as mentioned above) is more 
preferable. 
Still more preferable coupler residue among the above mentioned groups is 
expressed by the general formula (XVII) or (XVIII) 
##STR17## 
(wherein Z, R.sub.2, R.sub.5 and R.sub.6 are the same as mentioned above, 
and R.sub.10 is the same as those illustrated with regard to the 
substituents for Y.sub.2). 
Examples of the disazo compound of the present invention are illustrated by 
the following structural formula showing the coupler residue A. 
______________________________________ 
##STR18## 
Disazo 
Pigment 
No. A 
______________________________________ 
1 
##STR19## 
2 
##STR20## 
3 
##STR21## 
4 
##STR22## 
5 
##STR23## 
6 
##STR24## 
7 
##STR25## 
8 
##STR26## 
9 
##STR27## 
10 
##STR28## 
11 
##STR29## 
12 
##STR30## 
13 
##STR31## 
14 
##STR32## 
15 
##STR33## 
16 
##STR34## 
17 
##STR35## 
18 
##STR36## 
19 
##STR37## 
20 
##STR38## 
21 
##STR39## 
22 
##STR40## 
23 
##STR41## 
24 
##STR42## 
25 
##STR43## 
26 
##STR44## 
27 
##STR45## 
28 
##STR46## 
29 
##STR47## 
30 
##STR48## 
31 
##STR49## 
32 
##STR50## 
33 
##STR51## 
34 
##STR52## 
35 
##STR53## 
36 
##STR54## 
37 
##STR55## 
38 
##STR56## 
39 
##STR57## 
40 
##STR58## 
41 
##STR59## 
42 
##STR60## 
43 
##STR61## 
44 
##STR62## 
45 
##STR63## 
46 
##STR64## 
47 
##STR65## 
48 
##STR66## 
49 
##STR67## 
50 
##STR68## 
51 
##STR69## 
52 
##STR70## 
53 
##STR71## 
54 
##STR72## 
55 
##STR73## 
56 
##STR74## 
57 
##STR75## 
58 
##STR76## 
59 
##STR77## 
60 
##STR78## 
61 
##STR79## 
62 
##STR80## 
63 
##STR81## 
64 
##STR82## 
65 
##STR83## 
66 
##STR84## 
67 
##STR85## 
68 
##STR86## 
69 
##STR87## 
70 
##STR88## 
71 
##STR89## 
72 
##STR90## 
73 
##STR91## 
74 
##STR92## 
75 
##STR93## 
76 
##STR94## 
77 
##STR95## 
78 
##STR96## 
79 
##STR97## 
80 
##STR98## 
81 
##STR99## 
82 
##STR100## 
83 
##STR101## 
84 
##STR102## 
85 
##STR103## 
86 
##STR104## 
87 
##STR105## 
88 
##STR106## 
89 
##STR107## 
90 
##STR108## 
91 
##STR109## 
92 
##STR110## 
93 
##STR111## 
94 
##STR112## 
95 
##STR113## 
96 
##STR114## 
97 
##STR115## 
98 
##STR116## 
99 
##STR117## 
100 
##STR118## 
101 
##STR119## 
102 
##STR120## 
103 
##STR121## 
104 
##STR122## 
105 
##STR123## 
106 
##STR124## 
107 
##STR125## 
108 
##STR126## 
109 
##STR127## 
110 
##STR128## 
111 
##STR129## 
112 
##STR130## 
113 
##STR131## 
114 
##STR132## 
115 
##STR133## 
116 
##STR134## 
117 
##STR135## 
118 
##STR136## 
119 
##STR137## 
120 
##STR138## 
121 
##STR139## 
122 
##STR140## 
123 
##STR141## 
124 
##STR142## 
125 
##STR143## 
126 
##STR144## 
127 
##STR145## 
128 
##STR146## 
129 
##STR147## 
130 
##STR148## 
131 
##STR149## 
132 
##STR150## 
133 
##STR151## 
134 
##STR152## 
135 
##STR153## 
136 
##STR154## 
137 
##STR155## 
138 
##STR156## 
139 
##STR157## 
140 
##STR158## 
141 
##STR159## 
142 
##STR160## 
143 
##STR161## 
144 
##STR162## 
145 
##STR163## 
146 
##STR164## 
147 
##STR165## 
148 
##STR166## 
149 
##STR167## 
150 
##STR168## 
151 
##STR169## 
152 
##STR170## 
153 
##STR171## 
154 
##STR172## 
155 
##STR173## 
156 
##STR174## 
157 
##STR175## 
158 
##STR176## 
159 
##STR177## 
160 
##STR178## 
161 
##STR179## 
162 
##STR180## 
______________________________________

The preparation of disazocompound of the present invention is further 
illustrated by the following Examples. 
Preparation Example 1 (preparation of disazo compound No. 1) 
4,4'-diaminotriphenylamine 5.51 g was added to hydrochloric acid comprising 
water 10 ml and conc. hydrochloric acid 17 ml, and the mixture was stirred 
for 1 hour at room temperature. The resultant mixture was then cooled to 
-2.degree. C., and a solution obtained by adding sodium nitrite 3.31 g to 
water 12 ml was added drop-wise to the cooled mixture at a temperature of 
-2.degree. C. to 1.degree. C. for 30 minutes. 
Thereafter, the resultant mixture was stirred at the same temperature for 1 
hour and half, and undissolved portion (minute amount) was removed from 
the system. To this reaction liquor, was added 42% borofluoric acid 20 ml, 
and the mixture was cooled to stand. The produced red-orange colored 
needle-like crystal was filtered out, and was washed with ethanol. The 
washed crystal was dried, thus producing tetrazonium difluoroborate 8.55 
g(yield=90.3%). According to an infrared absorption spectrum (KBr Tablet 
Method), an absorption band on the basis of N.sub.2.sup.+ was recognized 
at 2230 cm.sup.-1. 
0.95 g of the tetrazonium salt thus obtained and 1.26 g of 
2-hydroxy-3-naphthoic acid anilide as a coupler were dissolved in cooled 
230 ml of N,N-dimethylformamide. To this solution, was added drop-wise a 
solution comprising sodium acetate 0.66 g and water 10 ml at a temperature 
of 17.degree.-21.degree. C. for 5 minutes. Thereafter, the resultant 
mixture was stirred for 3 hours at room temperature. The produced 
precipitate was filtered out, and was washed with N,N-dimethylformamide 
300 ml for 5 times and further with water 300 ml for 2 times. The washed 
precipitate was dried at 80.degree. C. under a reduced pressure of 2 mm 
Hg, thus obtaining 1.11 g (yield=67.4%) of the above disazo compound No. 
1. 
Various properties of the disazo compound No. 1 thus obtained were as 
follows: 
______________________________________ 
Melting Point: 300.degree. C. or higher 
Elementary Analysis: 
C H N 
______________________________________ 
Measured Value 75.57 4.70 11.76 
Calculated Value 
75.80 4.53 11.90 
______________________________________ 
The infrared absorption spectrum (KBr Tablet Method) of this compound is 
shown in FIG. 1. 
Preparation Examples 2 to 16 
The same procedure as in the above Example 1 was repeated, except that 
compounds as mentioned in Table 1 were used as a coupler, and the disazo 
compounds thus obtained are shown in Table 1. Absorption of .nu..sub.c=o 
(amide I) of infrared absorption spectrum (KBr Tablet Method), melting 
point and elementary analysis values with regard to the disazo compounds 
obtained are also shown in Table 1. 
3 TABLE 1 
Elementary Analysis (%) Disazo C Measured H Measured N Measured 
Preparation Compound .nu..sub.c=o (cm.sup.-1) Melting Value Value Value 
Ex. No. No. Coupler (Amide I) Point (Calculated Value) (Calculated 
Value) (Calculated Value) 
2 10 
##STR181## 
1670 morethan300.degree. C. 73.24(73.37) 4.58(4.68) 11.06(11.09) 3 4 
##STR182## 
1670 morethan300.degree. C. 76.11(76.12) 4.72(4.85) 11.34(11.51) 4 16 
##STR183## 
1670 morethan300.degree. C. 69.67(69.95) 3.88(3.95) 10.72(10.98) 5 33 
##STR184## 
1680 290.degree. 
C.(Decom-position) 68.66(68.34) 3.82(3.86) 13.89(13.79) 
6 62 
##STR185## 
1680 294.degree. 
C.(Decom-position) 77.45(77.18) 4.65(4.86) 11.66(11.91) 
7 66 
##STR186## 
1670 morethan300.degree. C. 74.36(74.63) 4.49(4.46) 11.72(11.87) 8 65 
##STR187## 
1675 morethan300.degree. C. 74.34(74.63) 4.29(4.46) 11.57(11.87) 9 64 
##STR188## 
1670 morethan300.degree. C. 74.99(74.63) 4.09(4.46) 11.55(11.87) 10 70 
##STR189## 
1680 morethan300.degree. C. 71.60(71.77) 3.67(3.86) 11.75(11.77) 11 71 
##STR190## 
1680 morethan300.degree. C. 71.90(71.77) 3.99(3.86) 11.79(11.77) 12 59 
##STR191## 
1680 morethan300.degree. C. 76.63(76.95) 4.43(4.60) 11.96(12.24) 13 60 
##STR192## 
1680 morethan300.degree. C. 76.75(76.95) 4.48(4.60) 12.00(12.24) 14 61 
##STR193## 
1670 morethan300.degree. C. 76.91(76.95) 4.35(4.60) 12.04(12.24) 15 74 
##STR194## 
1680 morethan300.degree. C. 70.07(70.39) 3.59(3.78) 13.85(14.11) 16 75 
##STR195## 
1680 morethan300.degree. 
C. 69.95(70.39) 3.52(3.78) 13.74(14.11) 
The disazo pigment of the present invention is used as a charge generating 
material in a photosensitive layer of an electrophotographic element. 
FIGS. 2 and 3 illustrate a typical structure of the electrophotographic 
element. 
The electrophotographic element of FIG. 2 comprises a laminated type 
photosensitive layer 19 on an electroconductive substrate 11, said 
photosensitive layer 19 comprising a charge generating layer 15 containing 
disazo pigment 13 as the main component and a charge transfer layer 17 
containing charge transfer material as the main component. 
In the electrophotographic element of FIG. 2, exposed light passes through 
a charge transfer layer to a charge generating layer 15 wherein charge is 
generated in disazo pigment 13. The charge thus generated is transferrred 
by the charge transfer layer 17. Thus, the generation of charge necessary 
for light decay is effected in disazo pigment 13, and the transfer of the 
generated charge is effected by the charge transfer layer 17. 
The electrophotographic element shown in FIG. 3 is composed of a 
photosensitive layer 19' on an electroconductive substrate 11, the 
photosensitive layer 19' comprising essentially of disazo pigment 13, 
charge transfer material and insulative binder. The disazo pigment 13 is a 
charge generating material. 
It is possible to modify the basic structure of the electrophotographic 
element of FIG. 2, for example, by applying the charge generating layer 
and the charge transfer layer is reverse order. 
The thickness of the charge generating layer 15 of the photosensitive layer 
of FIG. 2 is preferably 0.01-5.mu., more preferably 0.05-2.mu.. If this 
thickness is less than 0.01.mu., the generation of charge is not 
satisfactory. On the other hand, if this thickness is more than 5.mu., the 
residual potential becomes too high for practical use. 
The thickness of the charge transfer layer 17 is preferably 3-50.mu., more 
preferably 5-30.mu.. If this thickness is less than 3.mu., a charged 
amount is insufficient. On the other hand, if this thickness is more than 
50.mu., the residual potential becomes too high for practical use. 
The charge generating layer 15 contains disazo pigment expressed by the 
above general formula as the main component, and further binder, 
plasticizer and the like. The amount of disazo pigment in the charge 
generating layer is more than 30% by weight, more preferably 50% by 
weight. 
The charge transfer layer 17 contains charge transfer material and binder 
as the main components and further plastilcizer and the like. The amount 
of the charge transfer material in the charge transfer layer is 10-95% by 
weight, preferably 30-90% by weight. If the amount of the charge transfer 
material is less than 10% by weight, the transfer of the charge is not 
substantially carried out. On the other hand, if this amount is more than 
95% by weight, the mechanical strength of the photosensitive film is too 
poor for practical use. 
The photosensitive layer 19' of the photosensitive element of FIG. 3 is 
preferably 3-50.mu., more preferably 5-30.mu.. The amount of the disazo 
pigment in the photosensitive layer 19' is preferably less than 50% by 
weight, more preferably less than 20% by weight, and the amount of the 
charge transfer material is preferably 10-95% by weight, more preferably 
30-90% by weight. 
The essential feature of the present invention resides in the use of 
specific disazo pigments as expressed by the above general formula I, and 
other components such as electroconductive substrate, charge transfer 
material and the like are the same as the conventionally known materials. 
Examples of these materials are illustrated hereinafter. 
Examples of the electroconductive substrate used in the electrophotographic 
element of the present invention include: metallic plates such as 
aluminum, copper, zinc and the like; plastic sheets such as polyester and 
the like; plastic film composite obtained by vapor depositing 
electroconductive materials such as aluminum, SnO.sub.2 and the like; or 
electroconductively treated paper and the like. 
Examples of binders include: condensation type resins such as polyamide, 
polyurethane, polyester, epoxy resin, phenoxy resin, polyketone, 
polycarbonate and the like; vinyl polymers such as polyvinyl ketone, 
polystyrene, poly-N-vinyl carbazole, polyacrylamide, and the like. Any 
resin can be used if it is insulative and adhesive. 
Examples of plasticizers include halogenated paraffin, 
polybiphenylchloride, dimethylnaphthalene, dibutyl phthalate and the like. 
Silicone oil may also be added to improve surface properties of the 
photosensitive material. 
The charge transfer material includes a positive hole transfer material and 
an electron transfer material. Examples of the hole transfer material 
include compounds as expressed by the following general formula (1) to 
(11). 
##STR196## 
(wherein R.sub.1 represents methyl, ethyl, 2-hydroxyethyl or 
2-chloroethyl; R.sub.2 represents methyl, ethyl, benzyl or phenyl; and 
R.sub.3 represents hydrogen, chlorine, bromine, alkyl having 1 to 4 carbon 
atoms, alkoxy having 1 to 4 carbon atoms, dialkylamino or nitro.) 
##STR197## 
(wherein Ar represents naphthalene ring, anthracene ring, styryl and their 
substituents or pyridine ring furan ring, or thiophene ring; and R 
represents alkyl or benzyl.) 
##STR198## 
(wherein R.sub.1 represents alkyl, benzyl or phenyl; R.sub.2 represents 
hydrogen, alkyl having 1 to 3 carbon atoms, alkoxy having 1 to 3 carbon 
atoms, dialkylamino, diaralkylamino or diarylamino; n represents an 
integer of 1 to 4; when n is 2 or more, R.sub.2 may be the same or 
different; and R.sub.3 represents hydrogen or methoxy.) 
##STR199## 
(wherein R.sub.1 represents alkyl having 1 to 11 carbon atoms, substituted 
or non-substituted phenyl or heterocyclic group; R.sub.2 and R.sub.3 may 
be the same or different and represent hydrogen, alkyl having 1 to 4 
carbon atoms, hydroxyalkyl, chloroalkyl, substituted or non-substituted 
aralkyl; R.sub.2 and R.sub.3 may be bonded with each other to form a 
heterocyclic ring containing nitrogen; R.sub.4 may be the same or 
different and represent hydrogen, alkyl having 1 to 4 carbon atoms, alkoxy 
or halogen.) 
##STR200## 
(wherein R represents hydrogen or a halogen atom; and Ar represents 
substituted or non-substituted phenyl, naphthyl, anthryl or carbazolyl.) 
##STR201## 
(wherein R.sub.1 represents hydrogen, halogen, cyano, alkoxy having 1 to 4 
carbon atoms or alkyl having 1 to 4 carbon atoms; Ar represents 
##STR202## 
wherein R.sub.2 represents alkyl having 1 to 4 carbon atoms, R.sub.3 
represents hydrogen, halogen, alkyl having 1 to 4 carbon atoms, alkoxy 
having 1 to 4 carbon atoms or dialkyl amino, n is an integer of 1 or 2; 
when n is 2, R.sub.3 may be the same or different; R.sub.4 and R.sub.5 
represent hydrogen, substituted or non-substituted alkyl having 1 to 4 
carbon atoms or substituted or non-substituted benzyl group.) 
##STR203## 
(wherein R represents carbazolyl, pyridyl, thienyl, indolyl, furyl, or 
substituted or non-substituted phenyl, styryl, naphthyl or anthryl group; 
these substituents are selected from the group of dialkylamino, alkyl, 
alkoxy, carboxyl or its ester, halogen atom, cyano, aralkylamino, 
N-alkyl-N-aralkylamino, amino, nitro and acetyl amino groups.) 
##STR204## 
(wherein R.sub.1 represents a lower alkyl or benzyl group; R.sub.2 
represents hydrogen, lower alkyl, lower alkoxy, halogen, nitro, amino, or 
amino group substituted with lower alkyl or benzyl; and n is an integer of 
1 or 2.) 
##STR205## 
(wherein R.sub.1 represents hydrogen, alkyl, alkoxy or halogen; R.sub.2 
and R.sub.3 represent alkyl, substituted or non-substituted aralkyl, or 
substituted or non-substituted aryl group; R.sub.4 represents hydrogen or 
substituted or non-substituted phenyl; and Ar represents phenyl or 
naphthyl group.) 
##STR206## 
(wherein n is an integer of 0 or 1; R.sub.1 represents hydrogen, alkyl or 
substituted or non-substituted phenyl; A represents 
##STR207## 
9-anthryl, or substituted or non-substituted N-alkylcarbazolyl group, 
wherein R.sub.2 represents hydrogen, alkyl, alkoxy, halogen or 
##STR208## 
wherein R.sub.3 and R.sub.4 represent alkyl, substituted or 
non-substituted aralkyl, or substituted or non-substituted aryl group, and 
R.sub.3 and R.sub.4 may form a ring; and m is an integer of 0, 1, 2 or 3, 
when m is 2, R.sub.2 may be the same or different.) 
##STR209## 
(wherein R.sub.1, R.sub.2 and R.sub.3 are hydrogen, lower alkyl, lower 
alkoxy, dialkylamino, or halogen; and n is 0 or 1.) 
Examples of the compound expressed by the general formula (1) include: 
9-ethylcarbazole-3-aldehyde-1-methyl-1-phenylhydrazone, 
9-ethylcarbazole-3-aldehyde-1-benzyl-1-phenylhydrazone, 
9-ethylcarbazole-3-aldehyde 1,1-diphenylhydrazone, and the like. 
Examples of the compound expressed by the general formula (2) include: 
4-diethylaminostyrene-.beta.-aldehyde-1-methyl-1-phenylhydrazone, 
4-methoxynaphthalene-1-aldehyde-1-benzyl-1-phenylhydrazone, and the like. 
Examples of the compound expressed by the general formula (3) include: 
4-methoxybenzaldehyde 1-methyl-1-phenylhydrazone, 
2,4-dimethoxybenzaldehyde 1-benzyl-1-phenylhydrazone, 
4-diethylaminobenzaldehyde 
1,1-diphenylhydrazone, 
4-methoxybenzaldehyde 1-benzyl-1-(4-methoxy)phenyl hydrazone, 
4-diphenylaminobenzaldehyde-1-benzyl-1-phenylhydrazone, 
4-dibenzylaminobenzaldehyde 
1,1-diphenylhydrazone and the like. 
Examples of the compound expressed by the general formula (4) include: 
1,1-bis(4-dibenzylaminophenyl)propane, 
tris(4-diethylaminophenyl)methane, 
1,1-bis(4-dibenzylaminophenyl)propane, 
2,2'-dimethyl-4,4'-bis(diethylamino)-triphenylmethane and the like. 
Examples of the compound expressed by the general formula (5) include: 
9-(4-diethylaminostyryl)anthracene, 
9-bromo-10-(4-diethylaminostyryl)anthracene, and the like. 
Examples of the compound expressed by the general formula (6) include: 
9-(4-dimethylaminobenzylidene)fluorene, 
3-(9-fluorenylidene)-9-ethylcarbazole, and the like. 
Examples of the compound expressed by the general formula (7) include: 
1,2-bis(4-diethylaminostyryl)benzene, 
1,2-bis(2,4-dimethoxystyryl)benzene and the like. 
Examples of the compound expressed by the general formula (8) include: 
3-styryl-9-ethylcarbazole, 
3-(4-methoxystyryl)-9-ethylcarbazole, and the like. 
Examples of the compound expressed by the general formula (9) include: 
4-diphenylaminostilbene, 
4-dibenzylaminostilbene, 
4-ditolylaminostilbene, 
1-(4-diphenylaminostyryl)naphthalene, 
1-(4-diethylaminostyryl)naphthalene, and the like. 
Examples of the compound expressed by the general formula (10) include: 
4'-diphenylamino-alpha-phenylstilbene, 
4'-methylphenylamino-alpha-phenylstilbene, and the like. 
Examples of the compound expressed by the general formula (11) include: 
1-phenyl-3-(4-diethylaminostyryl)-5-(4-diethylaminophenyl)pyrazoline, 
1-phenyl-3-(4-dimethylaminostyryl)-5-(4-dimethylaminophenyl)pyrazoline, and 
the like. 
Other examples of positive hole transfer material include: oxadiazole 
compounds such as 
2,5-bis(4-diethylaminophenyl)-1,3,4-oxadiazole, 
2,5-bis(4-(4-diethylaminostyryl)phenyl)-1,3,4-oxadiazole, 
2-(9-ethylcarbazolyl-3-)-5-(4-diethylaminophenyl)-1,3,4-oxadiazole, and the 
like; low molecular oxazole compounds such as 
2-vinyl-4-(2-chlorophenyl)-5-(4-diethylaminophenyl)-oxazole, 
2-(4-diethylaminophenyl)-4-phenyloxazole, and the like; and high molecular 
compounds such as poly-N-vinyl carbazol, halogenated poly-N-vinyl 
carbazole, polyvinyl pyrene, polyvinyl anthracene, pyrene formaldehyde 
resin, ethylcarbazole formaldehyde resin, and the like. 
Examples of electron transfer material include: chloroanil, bromoanil, 
tetracyanoethylene, tetracyanoquinonedimethane, 
2,4,7-trinitro-9-fluorenone, 
2,4,5,7-tetranitro-9-fluorenone, 
2,4,5,7-tetranitro-xanthone, 
2,4,8-trinitrothioxanthone, 
2,6,8-trinitro-4H-indeno(1,2-b)thiophene-4-on, 
1,3,7-trinitrodibenzothiophene-5,5-dioxide, and the like. 
These charge transfer materials are used alone or in the form of a mixture 
of two or more. 
With regard to the electrophotograpnic elements as prepared above, an 
adhesive layer or barrier layer may optionally be applied between an 
electroconductive substrate and a photosensitive layer. Examples of these 
layers include polyamide, nitrocellulose, aluminum oxide and the like. The 
thickness of the layer is preferably not more than 1.mu.. 
The electrophotographic element as shown in FIG. 2 is prepared by 
vapor-depositing disazo pigment on an electroconductive substrate in 
accordance with vacuum vapor depositing method as disclosed in U.S. Pat. 
Nos. 3,973,959 and 3,996,049 or coating and drying on an electroconductive 
substrate a dispersion of disazo pigment particles in an appropriate 
solvent optionally having a binder dissolved; and then coating and drying 
a solution containing charge transfer material and binder on the charge 
generating layer, the surface of which may optionally be subjected to a 
buff polishing as disclosed in Japanese Patent Laid Opent No. 51-90827, or 
the thickness of which may be regulated. 
The electrophotographic element as shown in FIG. 3 is prepared by 
dispersing disazo pigment particles in a solution having charge transfer 
material and binder dissolved, coating the dispersion on an 
electroconductive substrate and drying. In any case, disazo pigment used 
in the present invention is powdered by a ball mill or the like to a 
particle size of not more than 5.mu., preferably not nore than 2.mu.. 
Coating can be effected by ordinary method by means of doctor blade, 
dipping, wire bar and the like. 
Copying by the electrophotographic element of the present invention can be 
effected by developing after charging and explosing the photosensitive 
layer surface and, if necessary, transferring the developed image to paper 
and the like. 
As clearly seen from the above description and the following Examples, the 
electrophotographic element of the present invention using disazo pigment 
having the triphenylamine structure as a charge generating material can be 
easily produced and has a high sensitivity in comparison with the 
conventional electrophotographic elements. In addition to these 
advantages, performances of the electrophotographic element of the present 
invention are stable even if it is repeatedly used a great number of 
times. 
The present invention is further illustrated by the following Examples, but 
the present invention should not be limited thereto. 
EXAMPLE 1 
76 parts by weight of disazo pigment No. 75, 1260 parts by weight of 
tetrahydrofuran solution (solid content=2%) of polyester resin ("Byron 
200" manufactured by Toyo Boseki Ltd.), and 3700 parts by weight of 
tetrahydrofuran are powdered and mixed in a ball mill. The dispersion thus 
obtained was coated on an aluminum surface of an aluminum-deposited 
polyester base (electroconductive substrate) by a doctor blade, and the 
coated film was allowed to stand for drying, thereby forming a charge 
generating layer having a thickness of about 1 .mu.m. 
On this charge generating layer, was coated a solution prepared by 
dissolving and mixing 2 parts by weight of 9-ethylcarbazole-3-aldehyde 
1-methyl-1-phenyldrazone, 2 parts by weight of polycarbonate resin 
("Panlight K-1300" manufactured by Teijin Co. Ltd.) and 16 parts by weight 
of tetrahydrofuran by a doctor blade, and the coated film was dried at 
80.degree. C. for 2 minutes and 105.degree. C. for 5 minutes, thereby 
forming a charge transfer layer having a thickness of about 18 .mu.m. The 
laminated type electrophotographic element No. 1 thus prepared is shown in 
FIG. 2. 
EXAMPLES 2 to 5 
Electrophotographic elements Nos. 2 to 5 were prepared in the same manner 
as in Example 1, except that disazo pigments as shown in the following 
Table 2 were used in place in disazo pigment No. 75 used in Example 1. 
EXAMPLES 6 to 10 
Electrophotographic elements Nos. 6 to 10 were prepared in the same manner 
as in Example 1, except that 
1-phenyl-3-(4-diethylaminostyryl)-5-(4-diethylaminophenyl)pyrazoline was 
used as a charge transfer material and disazo pigments as shown in the 
following Table 2 were used. 
EXAMPLES 11 to 15 
Electrophotographic elements Nos. 11 to 15 were prepared in the same manner 
as in Example 1, except that 9-(4-diethylamionstyryl)anthracene was used 
as a charge transfer material and disazo pigments as shown in the 
following Table 2 were used. 
EXAMPLES 16 to 20 
Electrophotographic elements Nos. 16 to 20 were prepared in the same manner 
as in Example 1, except that 4'-diphenylamino-alpha-phenylstibene was used 
as a charge transfer material and disazo pigments as shown in the 
following Table 2 were used. 
The thus prepared electrophotographic elements Nos. 1 to 20 were subjected 
to -6 KV corona discharge for 20 seconds by an electrostatic copying paper 
tester (SP428 Type produced by Kawaguchi Denki Works), and were charged 
negatively. Thereafer, these elements were left to stand in the dark for 
20 seconds to measure the surface potential Vpo (V) at that time, and were 
exposed to radiation of a tungsten lamp so that the intensity of surface 
illumination may become 4.5 Lux. Then, the time (sec.) required until the 
surface potential was reduced to 1/2 of Vpo was measured, and the exposure 
amount E.sub.1/2 (Lux-sec) was calculated. The results this obtained are 
shown in Table 2. 
TABLE 2 
______________________________________ 
Photo- Disazo E1/2 
Example sensitizer 
Pigment Vpo (V) 
(Lux. sec) 
______________________________________ 
1 1 75 -784 1.7 
2 2 60 -1367 2.9 
3 3 16 -1201 4.5 
4 4 83 -838 5.7 
5 5 100 -1095 8.3 
6 6 1 -1062 4.3 
7 7 62 -760 2.2 
8 8 94 -882 1.9 
9 9 59 -784 0.7 
10 10 114 -186 9.2 
11 11 33 -1394 6.5 
12 12 97 -1186 9.3 
13 13 116 -1114 14.3 
14 14 60 -1530 3.1 
15 15 75 -1066 2.7 
16 16 71 -1266 1.0 
17 17 64 -1174 1.5 
18 18 19 -838 2.6 
19 19 50 -946 4.2 
20 20 106 -1204 3.2 
______________________________________ 
The electrophotographic elements Nos. 4 and 7 were set in an 
electrophotographic copying machine (Ricopy-P-500 Type produced by RICOH 
K. K.), and the image-formation was repeated 10,000 times. As the results, 
each electrophotographic element was found to form a clear-cut image. It 
should be understood from this results that the electrophotographic 
element of the present invention is excellent in durability.