Electrophotographic light-sensitive media having a dis-azo compound

An electrophotographic light-sensitive medium is described comprising at least an electrically conductive layer, a charge generation layer and a charge transport layer, the charge generation layer containing a dis-azo compound represented by Formula (1) wherein A represents a single bond, ##STR1## B represents a coupler having aromatic properties; and R represents a group selected from hydrogen, a halogen and a lower alkyl having 1 to 4 carbon atoms.

BACKGROUND OF THE INVENTION 
This invention relates to an electrophotographic light-sensitive medium 
prepared using a dis-azo compound containing therein two oxadiazole rings. 
Various types of light-sensitive media having an electrically conductive 
layer, and an organic pigment-containing layer provided on the 
electrically conductive layer, have heretofore been known, including: 
(a) a light-sensitive medium as disclosed in Japanese Patent Publication 
No. 1667/1977 in which a layer prepared by dispersing a pigment in an 
insulative binder is provided on an electrically conductive layer; 
(b) a light-sensitive medium as disclosed in Japanese Patent Application 
(OPI) Nos. 30328/1972 (corresponding to U.S. Pat. No. 3,894,868) and 
18545/1972 (corresponding to U.S. Pat. No. 3,870,516) in which a layer 
prepared by dispersing a pigment in a charge transport substance or a 
charge transport medium comprising the charge transport substance and an 
insulative binder (which may also be a charge transport substance) is 
provided on an electrically conductive layer; 
(c) a light-sensitive medium as disclosed in Japanese Patent Application 
(OPI) No. 105537/1974 (corresponding to U.S. Pat. No. 3,837,851) which 
comprises an electrically conductive layer, a charge generation layer 
containing a pigment, and a charge transport layer; and 
(d) a light-sensitive medium as disclosed in Japanese Patent Application 
(OPI) No. 91648/1974 and in which an organic pigment is added to a charge 
transfer complex. 
As pigments for use in light-sensitive media, a number of organic pigments, 
such as phthalocyanine based pigment, polycyclic quinone based pigment, 
azo based pigment and quinacridone based pigment, have been proposed, but 
few of them have been put in practice. 
The reason for this is that these organic photoconductive pigments are 
inferior in sensitivity, durability, etc., to inorganic pigments such as 
Se, CdS, ZnO, etc. 
However, light-sensitive media prepared using inorganic photoconductive 
pigments also suffer from disadvantages. 
For example, with a light-sensitive medium prepared using Se, 
crystallization of Se is accelerated by heat, moisture, dust, finger 
print, etc., and, in particular, when the atmospheric temperature of the 
light-sensitive medium exceeds about 40.degree. C., the crystallization 
becomes significant, resulting in a reduction in charging properties and 
the formation of white spots on the image formed. Although Se-based 
light-sensitive medium can theoretically produce 30,000 to 50,000 copies, 
it often fails to produce so many copies because it is adversely 
influenced by the above-stated environmental conditions of the location 
where the copying machine in which it is used is placed. At the present 
time, it is generally believed that only about 10,000 copies can be 
produced by the Se-based light-sensitive medium. 
In the case of a CdS-based light-sensitive medium covered with an 
insulative layer, its durability is nearly the same as that of the 
Se-based light-sensitive medium. Additionally, use of CdS results in 
deterioration of the moisture resistance of the CdS-based light-sensitive 
medium, and it is very difficult to improve this poor moisture resistance. 
At the present time, therefore, it is necessary to provide an auxiliary 
means, e.g., a heater. 
With a ZnO-based light-sensitive medium, sensitization thereof is caused by 
the use of dyes exemplified by Rose Bengale and, therefore, problems such 
as deterioration due to corona charging and discoloration of the dye by 
light arise. 
Furthermore, both the Se-based and CdS-based light-sensitive media are 
expensive, and cause pollution problems. 
The sensitivity of conventional light-sensitive media, when expressed as an 
exposure amount for half decay (E 1/2), is as follows: a Se-based 
light-sensitive medium which is not sensitized, about 15 lux.multidot.sec; 
a Se-based light-sensitive medium which is sensitized, about 4 to 8 
lux.multidot.sec; a CdS-based light-sensitive medium, about the same as 
that of the sensitized Se-based light-sensitive medium; and a ZnO-based 
light-sensitive medium, about 7 to 12 lux.multidot.sec. 
When the light-sensitive medium is used in a PPC (plane paper copier) 
copying machine (manufactured by Copyer Co., Ltd.), its sensitivity should 
be 20 lux.multidot.sec or less as E 1/2, whereas when used in a PPC 
copying machine whose rate of duplication is higher, its sensitivity is 
more desirably 15 lux.multidot.sec or less as E 1/2. Of course, 
light-sensitive media having lower sensitivities than above described can 
also be used, depending on the purpose for which they are used, i.e., 
cases where the light-sensitive medium is not necessary to be repeatedly 
used, such as, for example, cases where the light-sensitive medium is used 
as a coating paper and a toner image is directly formed on the coating 
paper in copying of a drawing, etc. 
SUMMARY OF THE INVENTION 
As a result of extensive investigation to overcome the above-described 
defects of the conventional inorganic light-sensitive media, and to 
overcome the above described defects of the organic electrophotographic 
light-sensitive media heretofore proposed, it has now been found that a 
light-sensitive medium prepared using a dis-azo compound containing 
therein two oxadiazole rings has high sensitivity and durability to such 
an extent that it can satisfactorily be put into practical use, and that 
it overcomes disadvantages of the inorganic light-sensitive media, e.g., 
poor heat resistance (crystallization of Se), poor moisture resistance, 
discoloration by light, pollution, etc. 
This invention, therefore, provides an electrophotographic light-sensitive 
medium comprising a light-sensitive layer containing a dis-azo compound 
represented by Formula (1) 
##STR2## 
wherein A represents a single bond, 
##STR3## 
B represents a coupler having aromatic properties; and R represents a 
group selected from hydrogen, a halogen and a lower alkyl having 1 to 4 
carbon atoms. 
DETAILED DESCRIPTION OF THE INVENTION 
The oxadiazole ring-containing dis-azo compound which is used in this 
invention is represented by Formula (1) 
##STR4## 
wherein A represents a single bond, 
##STR5## 
B represents a coupler having aromatic properties; and R represents a 
group selected from hydrogen, a halogen and a lower alkyl having 1 to 4 
carbon atoms. 
The term "a coupler having aromatic properties" referred to herein means an 
aromatic coupler containing therein a phenolic hydroxy group, such as, for 
example, a hydroxynaphthoic acid amide type coupler, a hydroxynaphthalic 
acid imide type coupler and an aminonaphthol type coupler. 
Preferably, B is selected from those couplers represented by Formulae (2) 
to (5) 
##STR6## 
wherein X represents a group capable of being condensed with the benzene 
ring of Formula (2) to form a naphthalene ring, an anthracene ring, a 
carbazole ring or a dibenzofuran ring, and Y is --CONR.sub.1 R.sub.2 
wherein R.sub.1 is a group selected from hydrogen, an alkyl group, and a 
phenyl group, and R.sub.2 is a group selected from an alkyl group, a 
phenyl group, a naphthyl group, a pyridyl group, and a hydrazino group, 
each of which groups for R.sub.1 and R.sub.2 may be unsubstituted or 
substituted. 
Examples of the substituents for R.sub.1 and R.sub.2 include an alkyl 
group, e.g., methyl, ethyl, etc., a halogen atom, e.g., fluorine, 
chlorine, etc., an alkoxy group, e.g., methoxy, ethoxy, etc., an acyl 
group, e.g., acetyl, benzoyl, etc., an alkylthio group, e.g., methylthio, 
ethylthio, etc., an arylthio group, e.g., phenylthio, etc., an aryl group, 
e.g., phenyl, etc., an aralkyl group, e.g., benzyl, etc., a nitro group, a 
cyano group, a dialkylamino group, e.g., dimethylamino, diethylamino, 
etc., and so forth. 
##STR7## 
wherein R.sub.3 is a substituted or unsubstituted alkyl group or a 
substituted or unsubstituted phenyl group. 
In more detail, R.sub.3 represents an alkyl group, e.g., methyl, ethyl, 
etc., a hydroxyalkyl group, e.g., hydroxymethyl, hydroxyethyl, etc., an 
alkoxyalkyl group, e.g., methoxymethyl, ethoxymethyl, ethoxyethyl, etc., a 
cyanoalkyl group, an aminoalkyl group, an N-alkylaminoalkyl group, an 
N,N-dialkylaminoalkyl group, a halogenated alkyl group, an aralkyl group, 
e.g., benzyl, phenethyl, etc., a phenyl group, a substituted phenyl group 
(examples of such substituents include those described in R.sub.1 and 
R.sub.2 of Formula (2)) or the like. 
##STR8## 
In Formula (1), R can represent hydrogen, a halogen, e.g., fluorine, 
chlorine, bromine, or iodine, a lower alkyl group, e.g., methyl, ethyl, 
propyl, etc. with hydrogen, chlorine and methyl being preferred. 
The dis-azo compound represented by Formula (1) can easily be prepared: (a) 
by tetrazotizing a starting material, e.g., a diamine represented by 
Formula (6) 
##STR9## 
wherein A and R are the same as described in Formula (1), by the usual 
procedure (e.g., the method as described in K. H. Saunders, The Aromatic 
Diazo Compounds And Their Technical Applications (1949)) to form the 
corresponding tetrazonium salt and coupling the tetrazonium salt with the 
coupler represented either Formula (2), (3), (4), or (5) in the presence 
of an alkali; or (b), by isolating the tetrazonium salt of the diamine 
represented by Formula (6) in a boron fluoride or zinc chloride salt form, 
and then coupling the tetrazonium salt with the coupler represented by 
Formula (2), (3), (4), or (5) in a suitable solvent, e.g., 
N,N-dimethylformamide, dimethyl sulfoxide, etc., in the presence of an 
alkali. 
The electrophotographic light-sensitive medium of this invention is a 
light-sensitive layer containing therein the dis-azo compound represented 
by Formula (1), and it may be used in any of the types of light-sensitive 
media of the prior art (a) to (d) as hereinbefore described, as well as in 
other known types. In order to increase the transport efficiency of charge 
carriers produced by light-absorption of the dis-azo compound represented 
by Formula (1), it is desirable to use the dis-azo compound in the 
light-sensitive medium of the prior art type (b), (c), or (d). The most 
desirable structure of the light-sensitive medium in which the dis-azo 
compound of this invention is used is that of the type (c) in which the 
function of generating charge carriers and the function of transporting 
the charge carriers are separated, so that the characteristics of the 
dis-azo compound are most efficiently exhibited. 
The following explanation, therefore, is provided with respect to the 
electrophotographic light-sensitive medium of the optimum structure, i.e., 
type (c). 
An electrically conductive layer, a charge generation layer, and a charge 
transport layer are essential in the light-sensitive medium. The charge 
generation layer may be provided either on the charge transport layer or 
under the charge transport layer. In an electrophotographic 
light-sensitive medium of the type that is repeatedly used, it is 
preferred that they are laminated in the order of the electrically 
conductive layer, the charge generation layer, and the charge transport 
layer, mainly from a viewpoint of physical strength, and in some cases 
from a viewpoint of charging properties. For the purpose of increasing the 
adhesion between the electrically conductive layer and the charge 
generation layer, if desired, an adhesion layer can be provided 
therebetween. 
As the electrically conductive layer, those having a surface resistance of 
about 10.sup.10 .OMEGA. or less, preferably, about 10.sup.7 .OMEGA. or 
less, such as a metal (e.g., aluminum) plate or foil, a metal (e.g., 
aluminum) vapor deposited plastic film, a sheet prepared by bonding 
together an aluminum foil and paper, a paper rendered electrically 
conductive, etc., can be used. 
Materials which can be effectively used in forming the adhesion layer 
include casein, polyvinyl alcohol, water-soluble polyethylene, 
nitrocellulose and the like. The thickness of the adhesion layer is from 
about 0.1.mu. to 5.mu., and preferably from about 0.5.mu. to 3.mu.. 
Fine particles of the dis-azo compound of Formula (1) are coated, if 
necessary after being dispersed in a suitable binder, on a charge 
generation layer or an adhesion layer provided on the electrically 
conductive layer. The coating techniques, however, are known in the art 
and are not an integral part of the invention claimed herein. The 
dispersion of the dis-azo compound can be carried out by known methods, 
using a ball mill, an attritor or the like. The particle size of the 
dis-azo compound is usually about 5.mu. or less and preferably about 2.mu. 
or less, with the optimum particle size being 0.5.mu. or less. 
The dis-azo compound can be dissolved in an amine-based solvent, e.g., 
ethylenediamine and coated. The coating can be performed by known methods, 
such as blade coating, Meyer bar coating, spray coating, soak coating, 
etc. 
The thickness of the charge generation layer is usually about 5.mu. or less 
and preferably from about 0.01.mu. to 1.mu.. Where a binder is used in the 
charge generation layer, the proportion of the binder in the charge 
generation layer is usually about 80% or less, and preferably about 40% or 
less, because if the amount of the binder is large, the sensitivity of the 
light-sensitive medium will be adversely affected. 
Binders which can be used include polyvinyl butyral, polyvinyl acetate, 
polyester, polycarbonate, a phenoxy resin, an acryl resin, polyacrylamide, 
polyamide, polyvinyl pyridine, a cellulose resin, an urethane resin, an 
epoxy resin, casein, polyvinyl alcohol, etc. 
In order to achieve uniform injection of charge carriers from the charge 
generation layer into the charge transport layer lying on the charge 
generation layer, if necessary, the surface of the charge generation layer 
can be ground and planished. 
On the charge generation layer so formed is provided the charge transport 
layer. Where the charge transport substance has no film-forming 
capability, a binder is dissolved therewith in a suitable solvent and 
coated by the conventional method to form the charge transport layer. The 
charge transport substance is divided into an electron transport substance 
and a positive hole transport substance. 
Examples of such electron transport substances include electron attractive 
substances such as chloranil, bromanil, tetracyanoethylene, 
tetracyanoquinodimethane, 2,4,7-trinitro-9-fluorenone, 
2,4,5,7-tetranitrofluorenone, 2,4,7-trinitro-9-dicyanomethylenefluorenone, 
2,4,5,7-tetranitroxanthone, 2,4,8-trinitrothioxanthone, etc., and their 
polymerization products. 
Examples of positive hole transport substances include pyrene, N-ethyl 
carbazole, N-isopropyl carbazole, 
2,5-bis(p-diethylaminophenyl)-1,3,4-oxadiazole, 
1-phenyl-3-(p-diethylaminostyryl)-5-(p-diethylaminophenyl)pyrazoline, 
1-(pyridyl-(2))-3-(p-diethylaminostyryl)-5-(p-diethylaminophenyl)pyrazolin 
e, 
1-(quinolyl-(2))-3-(p-diethylaminostyryl)-5-(p-diethylaminophenyl)pyrazoli 
ne, 
1-(lepidyl-(2))-3-(p-diethylaminostyryl)-5-(p-diethylaminophenyl)pyrazolin 
e, p-diethylaminobenzaldehyde-N,N-diphenylhydrazone, 
p-diethylaminobenzaldehyde-N-naphthyl-N-phenylhydrazone, 
N-methyl-N-phenylhydrazino-3-methylidene-9-ethyl carbazole, 
N,N-diphenylhydrazino-3-methylidene-9-ethyl carbazole, triphenylamine, 
poly-N-vinyl carbazole, halogenated poly-N-vinyl carbazoles, polyvinyl 
pyrene, polyvinyl anthracene, polyvinyl acridine, poly-9-vinylphenyl 
anthracene, pyrene-formaldehyde resins, ethyl carbazole-formaldehyde 
resins, etc. 
Charge transport substances which can be used are not limited to the 
above-described ones, and they can be used alone or in combination with 
each other. The thickness of the charge transport layer is usually from 
about 5.mu. to 30.mu., and preferably from about 8.mu. to 20.mu.. 
Binders which can be used include an acryl resin, polystyrene, polyester, 
polycarbonate, etc. As the binders for low molecular weight positive hole 
transport substances, positive hole transport polymers such as 
poly-N-vinyl carbazole can be used. On the other hand, as binders for low 
molecular weight electron transport substances, polymers of electron 
transport monomers as described in U.S. Pat. No. 4,122,113 can be used. 
In the light-sensitive medium comprising the electrically conductive layer, 
the charge generation layer on the electrically conductive layer, and the 
charge transport layer on the charge generation layer wherein the charge 
transport substance is the electron transport substance, the surface of 
the charge transport layer is required to be charged positively, and when 
the light-sensitive medium is exposed to light after charging, electrons 
generated in the charge generation layer are injected into the charge 
transport layer at exposed areas and then reach the surface of the charge 
transport layer, neutralizing positive charges thereon, as a result of 
which a decay of surface potential occurs, and electrostatic contrast is 
formed between exposed areas and unexposed areas. On developing the 
thus-formed electrostatic latent image with negatively charged toners, a 
visible image is obtained. This visible image can be fixed either directly 
or after being transferred to paper or a plastic film. 
Alternatively, the electrostatic latent image may be transferred onto an 
insulative layer of a transfer paper, and then developed and fixed. The 
type of the developer, the developing method and the fixing method are not 
critical, and any known developer, developing method and fixing method can 
be employed. 
On the other hand, when the charge transport layer is composed of a 
positive hole transport substance, the surface of the charge transport 
layer is required to be charged negatively, and when the light-sensitive 
medium is exposed to light after the charging, positive holes generated in 
the charge generation layer are injected into the charge transport layer 
at exposed areas and then reach the surface of the charge transport layer, 
neutralizing the negative charges, as a result of which the decay of 
surface potential occurs and the electrostatic contrast is formed between 
exposed areas and unexposed areas. In this case, therefore, it is 
necessary to use positively charged toners for development of 
electrostatic latent images. 
A light-sensitive medium of type (a) according to the present invention can 
be obtained by dispersing the dis-azo compound of Formula (1) in an 
insulative binder solution as used in the charge transport layer of the 
light-sensitive medium of type (c) and coating the resulting dispersion on 
an electrically conductive support. 
A light-sensitive medium of type (b) according to the present invention can 
be obtained by dissolving an insulative binder as used in the charge 
transport substance and charge transport layer of the light-sensitive 
medium of type (c) in a suitable solvent, dispersing the dis-azo compound 
of Formula (1) in a solution as above, and by coating the resulting 
dispersion on the electrically conductive support. 
A light-sensitive medium of type (d) according to the present invention can 
be obtained by dispersing the dis-azo compound of Formula (1) in a 
solution of a charge transfer complex, which is formed on mixing the 
electron transport substance described in the light-sensitive medium of 
type (c) and the positive hole transport substance, and coating the 
resulting dispersion on the electrically conductive support. 
In any type of light-sensitive medium according to the present invention, 
at least one member selected from the dis-azo compounds represented by 
Formula (1) is used. If desired, the dis-azo compound of Formula (1) may 
be used in combination with other compounds as pigments having different 
light absorption ranges, in order to increase the sensitivity of the 
light-sensitive medium. Furthermore, for the purpose of obtaining 
panchromatic light-sensitive media, two or more of the dis-azo compounds 
may be combined together, or the dis-azo compound may be used in 
combination with charge generating substances selected from known dyes and 
pigments. 
The electrophotographic light-sensitive medium of this invention can be 
used not only in an electrophotographic copying machine, but also in other 
applications wherein electrophotography is utilized, such as in laser 
printing, CRT (cathode-ray tube) printing, etc. Hereinafter, preparation 
of the dis-azo compound used in this invention will be explained by 
reference to the preparation thereof. 
SYNTHESIS EXAMPLE 
Preparation of Compound No. 1 
##STR10## 
A dispersion consisting of 5.2 g (0.0162 mol) of 
5,5'-di(4-aminophenyl)-bis[1,3,4-oxadiazolyl]-2,2' which had been prepared 
in accordance with the method described in J. Heterocyclic Chemistry, 2 
(4), 441-6 (1965), 100 ml of water and 9.7 ml (0.11 mol) of concentrated 
hydrochloric acid was cooled to 5.5.degree. C. A solution prepared by 
dissolving 2.4 g (0.034 mol) of sodium nitrite in 10 ml of water was 
dropwise added to the above dispersion over a period of 20 minutes while 
controlling the temperature at 5.5.degree. C. or lower. After completion 
of the dropwise addition, the resulting mixture was stirred at that 
temperature for an additional 15 minutes to obtain a tetrazonium salt 
solution. 
Next, 14.4 g (0.36 mol) of caustic soda and 9.4 g (0.036 mol) of Naphthol S 
(3-hydroxy-2-naphthoic acid anilide) were dissolved in 400 ml of water, 
and the above obtained tetrazonium salt solution was dropwise added 
thereto with stirring over a period of 15 minutes while controlling the 
temperature within the range of from 5.degree. C. to 10.degree. C. The 
resulting mixture was stirred for an additional 2 hours and then allowed 
to stand overnight at room temperature. The reaction solution was filtered 
to obtain a solid portion which was then washed successively with water 
and acetone, and dried to obtain 12.1 g of a crude pigment (yield from 
diamine: 86%). The crude pigment was heat-filtered five times with 400 ml 
portions of dimethylformamide and one time with acetone, and then dried to 
obtain 8.6 g of Compound No. 1 (yield from diamine: 61%). The 
decomposition point was more than 300.degree. C. 
Elemental analysis for C.sub.50 H.sub.32 N.sub.10 O.sub.6 : Calculated (%): 
C 69.11, H 3.72, N 16.12. Found (%): C 68.97, H 4.02, N 16.01. 
IR Absorption Spectrum: Amide 1665 cm.sup.-1. 
Other dis-azo compounds represented by Formula (1) can be synthesized in an 
analogous manner to the Synthesis Example described above.

The following Examples of electrophotographic media are provided to 
illustrate this invention in greater detail. 
EXAMPLE 1 
An aqueous ammonia solution of casein (casein 11.2 g, 28% aqueous ammonia 1 
g and water 222 ml) was coated on an aluminum plate with a Meyer bar and 
dried to form an adhesion layer of a coating amount of 1.0 g/m.sup.2. 
Next, 5 g of Compound No. 1 and a solution prepared by dissolving 2 g of a 
butyral resin (degree of butyralation, 63 mol %) in 95 ml of ethanol were 
ball-milled, and the dispersion so obtained was coated on the adhesion 
layer with a Meyer bar and dried to form a charge generation layer of a 
coating amount of 0.2 g/m.sup.2. 
A solution of 5 g of 
1-phenyl-3-(p-diethylaminostyryl)-5-(p-diethylaminophenyl)pyrazoline and 5 
g of poly-4,4'-dioxydiphenyl-2,2'-propanecarbonate (molecular weight, 
30,000) in 70 ml of tetrahydrofuran was coated on the charge generation 
layer prepared above and dried to form a charge transport layer of a 
coating amount of 10 g/m.sup.2. 
The thus-obtained electrophotographic light-sensitive medium was 
conditioned at 20.degree. C. and 65% (relative humidity) for 24 hours, 
corona-charged at -5 KV with an electrostatic copying paper testing 
apparatus, Model SP-428 produced by Kawaguchi Denki Co., Ltd., according 
to the static method, and held in a dark place for 10 seconds. Then, the 
resulting medium was exposed to light at an intensity of illumination of 5 
lux, and its charging characteristics were examined. 
The results are as follows, wherein V.sub.o (-v), V.sub.k (%) and E 1/2 
(lux.sec.) indicate, respectively, the initial potential, the potential 
retention in a dark place for the period of 10 seconds, and the exposure 
amount for half decay. 
______________________________________ 
V.sub.o -540 v 
V.sub.k 91% 
E 1/2 6.9 lux .multidot. sec 
______________________________________ 
EXAMPLE 2 
On a charge generation layer prepared as in Example 1 was coated a solution 
of 5 g of 2,5-bis(p-diethylaminophenyl)-1,3,4-oxadiazole and 5 g of the 
same polycarbonate as used in Example 1 in 70 ml of tetrahydrofuran with a 
Meyer bar so that the coating amount after drying was 10 g/m.sup.2. 
The thus-obtained light-sensitive medium was measured in charging 
characteristics in the same manner as in Example 1. The results are as 
follows: 
______________________________________ 
V.sub.o -555 v 
V.sub.k 90% 
E 1/2 6.8 lux .multidot. sec 
______________________________________ 
EXAMPLE 3 
On a charge generation layer prepared as in Example 1 was coated a solution 
of 5 g of 2,4,7-trinitrofluorenone and 5 g of the same polycarbonate as 
used in Example 1 in 70 ml of tetrahydrofuran with a Meyer bar so that the 
coating amount after drying was 12 g/m.sup.2. 
The thus-obtained light-sensitive medium was measured in charging 
characteristics in the same manner as in Example 1. The results are as 
follows: 
______________________________________ 
V.sub.o +570 v 
V.sub.k 95% 
E 1/2 14.5 lux .multidot. sec 
______________________________________ 
In this case, the charging polarity was positive. 
EXAMPLES 4 TO 25 
5 g of a dis-azo compound (A, B and R of Formula (1) are shown in Table 1), 
10 g of a polyester resin solution (Polyester Adhesive 49000, produced by 
E. I. du Pont; solid content, 20%) and 80 ml of tetrahydrofuran were 
ball-milled, and the resulting dispersion was coated on an 
aluminum-deposited Mylar (trademark of E. I. du Pont for polyethylene 
terephthalate) film at the side of the aluminum surface with a Meyer bar 
so that the coating amount after drying was 0.3 g/m.sup.2. 
Next, a solution of 5 g of 
1-(lepidyl-(2))-3-(p-diethylaminostyryl)-5-(p-diethylaminophenyl)pyrazolin 
e, and 5 g of the same polycarbonate as used in Example 1 in 70 ml of 
tetrahydrofuran was coated on the charge generation layer prepared above 
with a Baker applicator and dried to form 10 g/m.sup.2 of a charge 
transport layer. 
The thus-obtained light-sensitive media were measured in charging 
characteristics in the same manner as in Example 1. The results are shown 
in Table 2. 
TABLE 1 
__________________________________________________________________________ 
Exam- 
Com- 
ple pound 
Dis-azo Compound 
No. No. A B R* 
__________________________________________________________________________ 
4 1 -- (single bond) 
##STR11## H 
5 2 -- 
##STR12## H 
6 3 -- 
##STR13## H 
7 4 -- 
##STR14## H 
8 5 -- 
##STR15## CH.sub.3 (o-position) 
9 6 -- 
##STR16## Cl (m-position) 
10 7 
##STR17## 
##STR18## H 
11 8 
##STR19## 
##STR20## H 
12 9 
##STR21## 
##STR22## H 
13 10 
##STR23## 
##STR24## Cl (m-position) 
14 11 
##STR25## 
##STR26## CH.sub.3 (o-position) 
15 12 
##STR27## 
##STR28## CH.sub.3 (o-position) 
16 13 
##STR29## 
##STR30## CH.sub.3 (o-position) 
17 14 CHCH 
##STR31## H 
18 15 CHCH 
##STR32## H 
19 16 CHCH 
##STR33## H 
20 17 CHCH 
##STR34## CH.sub.3 (o-position) 
21 18 
##STR35## 
##STR36## H 
22 19 CHCH 
##STR37## H 
23 20 CHCH 
##STR38## H 
24 21 -- 
##STR39## H 
25 22 -- 
##STR40## H 
__________________________________________________________________________ 
*The designation in the parenthesis means a position to the azo group. 
TABLE 2 
______________________________________ 
Charging Characteristics 
Example Compound V.sub.o V.sub.k 
E 1/2 
No. No. (-v) (%) (lux .multidot. sec) 
______________________________________ 
4 1 610 98 8.2 
5 2 590 94 8.6 
6 3 540 96 8.8 
7 4 580 96 11.0 
8 5 590 91 7.0 
9 6 560 94 8.8 
10 7 590 97 7.0 
11 8 570 92 8.4 
12 9 570 92 9.0 
13 10 560 89 11.0 
14 11 590 95 6.8 
15 12 560 89 10.0 
16 13 550 88 9.0 
17 14 570 95 8.4 
18 15 560 89 9.5 
19 16 580 92 12.0 
20 17 580 93 10.0 
21 18 580 8.0 
22 19 560 88 8.8 
23 20 510 83 15.0 
24 21 530 91 14.0 
25 22 500 89 13.0 
______________________________________ 
EXAMPLE 26 
5 g of a compound represented by the formula 
##STR41## 
and 5 g of poly-N-vinyl carbazole (molecular weight, 300,000) were 
dissolved in 70 ml of tetrahydrofuran. To the solution was added 1.0 g of 
Compound No. 7 shown in Table 1, and the mixture was ball-milled and 
dispersed. The dispersion so obtained was coated on an aluminum plate 
provided thereon a casein layer prepared as in Example 1 at the side of 
the casein layer with a Meyer bar so that the coating amount after drying 
was 9.5 g/m.sup.2. 
The thus-obtained light-sensitive medium was measured in charging 
characteristics in the same manner as in Example 1. The results are as 
follows: 
______________________________________ 
V.sub.o +510 v 
V.sub.k 84% 
E 1/2 15 lux .multidot. sec 
______________________________________ 
In this case, the charging polarity was positive. 
EXAMPLE 27 
On an aluminum drum surface there was coated by the dipping method a 
dispersion prepared by dissolving 200 g of a polyamide resin (Ultramid IC, 
produced by Bayer AG) in 9.5 l of methanol, adding 500 g of Compound No. 
14 shown in Table 1 to the solution and then ball-milling and dispersing 
the mixture so that the coating amount after drying was 0.25 g/m.sup.2. 
Thereafter, a solution of 500 g of 
2,5-bis(p-diethylaminophenyl)-1,3,4-oxazole and 500 g of a polymethyl 
methacrylate resin dissolved in 7 l of tetrahydrofuran was coated on the 
charge generation layer and dried to form a charge transport layer of a 
coating amount of 10 g/m.sup.2. 
A test piece prepared by subjecting to coating on an aluminum-deposited 
Mylar film in the same manner as in Example 1 was measured in charging 
characteristics in the same manner as in Example 1. The results are as 
follows: 
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V.sub.o -580 v 
V.sub.k 90% 
E 1/2 8.2 lux .multidot. sec 
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The thus-obtained drum was mounted on a PPC copying machine (testing 
apparatus) (produced by Copyer Co., Ltd.) in which a two component 
developer was used. The surface potential was set to -600 v, and a copying 
operation was carried out. As the result, excellent quality copies were 
obtained. 
While the invention has been described in detail and with reference to 
specific embodiments thereof, it will be apparent to one skilled in the 
art that various changes and modifications can be made therein without 
departing from the spirit and scope thereof.