Electrophotographic element comprising alloy of selenium and tellurium doped with chlorine and oxygen

The electrophotographic element comprising mounting on an electrically conductive substrate a Se-Te-Cl alloy system photoconductive layer which contains Te in the range of 6 to 12 wt. % of Se, Cl in the range of 10 to 30 ppm of the total amount of Se and Te and O.sub.2 as impurity 10 ppm or less of the whole alloy, is superior especially in temperature and light fatigue characteristics.

BACKGROUND OF THE INVENTION 
(a) Field of the Invention 
The present invention relates to an electrophotographic element having a 
Se-Te-Cl system photoconductive layer. 
(b) Description of the Prior Art 
Since the selenium type electrophotographic element, whose photoconductive 
layer comprises selenium, utilized widely in the Xerox type 
electrophotography is hardly sensitive to the red color region, there is 
also utilized the element having the Te-doped Se layer in order to 
heighten the sensitivity to the red color region. However, the Se-Te 
system photoconductive layer of this type is defective in that the 
residual electric potential is heightened by the hole caused by exposure. 
In view of this, it has also been tried to neutralize the hole by 
additionally doping halogen on the Se-Te system photoconductive layer. 
However, the Se-Te-halogen system like this is defective in that as the 
amount of halogen added has opposite relationships with the temperature at 
the time of repetition use (thermal resistance), light fatigue 
characteristics and residual electric potential, the amount of halogen 
added must inevitably be restricted. For instance, in the case of Cl, 
unless it is added generally in excess of 30 ppm, the effect of 
restricting the residual electric potential is not achieved, and further, 
if it exceeds 30 ppm, the temperature necessary for repetition use 
(thermal resistance) and light fatigue characteristics deteriorate and 
consequently the charged electric potential decreases. It is known that 
said temperature and light fatigue characteristics are improved with 
effect by the addition of Sb, Ge and the like (which see Japanese Laid 
Open Patent Application No. 47654/1979, for instance, concerning the 
addition of Sb), but these components, as seen in the case of Sb, 
inversely bring about other drawbacks such as the increase in residual 
electric potential and the like and furthermore are difficult to be added 
in the thermal vacuum vapordeposition method, namely the generally known 
commercial layer forming method, because the vapor pressure of said 
components is low as compared with that of Se and Te. 
SUMMARY OF THE INVENTION 
The first object of the present invention is to provide an 
electrophotographic element that is capable of restricting the residual 
electric potential and accordingly improving the temperature required for 
repetition use and light fatigue characteristics even when the amont of Cl 
addded to Se-Te system is 30 ppm or less. 
The second object of the present invention is to provide an 
electrophotographic element that is capable of dispensing with the 
addition of a third component to the Se-Te-halogen system and accordingly 
employing the well known commercial methods in the layer formation without 
entailing other new drawbacks. 
The electrophotographic element according to the present invention 
comprises an electrically conductive substrate and a Se-Te-Cl alloy system 
photoconductive layer mounted on said substrate, wherein the amount of Te 
contained in said alloy is in the range of 6 to 12 wt.% of Se, the Cl 
content is in the range of 10 to 30 ppm of the total amount of Se and Te, 
and the content of O.sub.2 as impurity is 10 ppm or less of the whole 
alloy. 
DETAILED DESCRIPTION OF THE INVENTION 
I have now found that even when the contents of Te and Cl in the usual 
Se-Te-Cl system alloy photoconductive layer are constant, the residual 
electric potential varies depending upon the raw material to be used. I 
have further minutely investigated the raw material based on this finding 
to find that the amounts of O.sub.2 contained as impurity in the raw 
material participate in changes of the residual electric potential. The 
present invention has been completed based on these findings. 
The electrophotographic element according to the present invention is 
prepared by vacuum vapor depositing a Se-Te-Cl alloy contaning each of Te, 
Cl and O.sub.2 (impurity) in its predetermined amount onto a heated 
electrically conductive substrate and thus forming a photoconductive layer 
comprising said alloy. The Se-Te-Cl alloy used herein contains O.sub.2 as 
impurity, but its content is regulated to be 10 ppm or less. The 
commercially available Se material and Te material each contains O.sub.2 
as impurity. In contrast, Cl.sub.2 does not contain O.sub.2 therein. 
Accordingly, the control of O.sub.2 amount in the Se-Te-Cl alloy may be 
attained by first calculating the O.sub.2 amount contained in the 
commercially available Se and Te materials and then making the alloy 
taking account of this O.sub.2 amount and the desired Te content. For 
instance, each raw material of commercially available Se and Te actually 
contains O.sub.2 as mentioned below: 
Se material A company: 1 ppm, B company: 10 ppm 
Te material C company: 4 to 10 ppm, D company: 80 to 90 ppm. 
On the supposition that the Te content in the Se-Te-Cl alloy is 8 wt.%, the 
O.sub.2 amounts in the alloys H.sub.1, H.sub.2 and H.sub.3 using these raw 
materials are calculated as follows: 
EQU H.sub.1 (Se material produced by A company+Te material produced by D 
company)=1.times.0.92+90.times.0.08=8.1 ppm 
EQU H.sub.2 (Se material produced by B company+Te material produced by D 
company)=10.times.0.92+90.times.0.08=16.4 ppm 
EQU H.sub.3 (Se material produced by A company+Te material produced by C 
company)=1.times.0.92+4.times.0.08=1.24 ppm 
That is, the alloys H.sub.1 and H.sub.3, the O.sub.2 amount being each less 
than 10 ppm, may be said to be Se-Te-Cl alloys suitable for use in the 
present invention. In this connection, the analytical methods of O.sub.2 
in metals are disclosed, for instance, in the following documents: 
T. Hauskrecht, Dissertationsarbeit, Tech.Hochschule, Gras 1957. 
Ake Olofsson, Analysmetodikundersokning nr 137. 
P W West and G C Gache, Anal. Chem. 28, 1816(1956). 
S Barabas and J Kaminski. Andl. Chem. 35, 1702(1963). 
The Se-Te-Cl alloy available for the present invention can be obtained by 
the steps of previously determining the O.sub.2 amount in the manner as 
described above, then making a Se-Te alloy containing a desired amount of 
Te in a usual manner (vacuum vapor-deposition) useing Se and Te materials 
each in an amount corresponding to this O.sub.2 amount, and further doping 
a desired amount of Cl into the thus obtained Se-Te alloy. 
In the Se-Te-Cl alloy system photoconductive layer according to the present 
invention, Te is a material for sensitizing Se and its optimum content is 
in the range of 6 to 12 wt.% of Se. In case the Te content is less than 
6%, it can not exert a sufficient sensitizing operation upon Se, while in 
case said content is more than 12%, the residual electric potential is 
heightened by holes caused at the time of exposure. Referring to Cl, it is 
a material which acts, as a donor, to neutralize holes, which otherwise 
are trapped in the layer, so as to prevent the residual electric potential 
from increasing, and its optimum content is in the range of 10 to 30 ppm 
of the Se-Te alloy. In case the Cl content is less than 10 ppm, holes are 
neutralized insufficiently, while in case said content is more than 30 ppm 
the temperature and light fatigue characteristics deteriorate. Further, 
although the O.sub.2 content may be controlled to be less than 10 ppm, in 
case it is in excess of 10 ppm, the residual electric potential is 
heightened depending upon the raw materials to be used so that the object 
of the present invention can not be achieved. 
As the electrically conductive substrate for mounting the above mentioned 
Se-Te-Cl alloy system photoconductive layer there is generally used an Al 
plate or an Al drum. In addition thereto, there may be used, for that 
purpose, metals such as stainless, Ni, Ir, Au, Cr, Mo, Pt and the like or 
plates or drums consisting of their alloys; or plastic films, glass 
plates, ceramic plates and the like obtained by conductive treatment of 
aforesaid metals or alloys according to the method using vacuum 
vapordeposition, sputtering, electron beam irradiation or the like.

EXAMPLE 
By subjecting a Se material containing 5 ppm of O.sub.2 and a Te material 
containing 10 ppm of O.sub.2 to the vacuum distillation method, there was 
prepared a Se-Te alloy containing 8 wt.% of Te. Further, by doping said 
alloy with 5, 10, 20, 30, 35 and 50 ppm of Cl respectively, there were 
prepared Se-Te-Cl alloys A containing 5.4 ppm of O.sub.2. By repeating the 
exactly same procedure excepting the use of a Se material and a Te 
material containing 30 ppm and 50 ppm of O.sub.2 respectively, there were 
prepared Se-Te-Cl alloys B containing 31.6 ppm of O.sub.2. 
Next, 12 kinds of respective alloys obtained as described above were each 
placed in a cylindrical stainless boat. Above said boat there was disposed 
an Al drum. Then, under the conditions: drum temperature 70.degree. C. and 
degree of vacuum 1.times.10.sup.-5 Torr, those alloys were subjected to 40 
minutes' vacuum vapordeposition, thereby forming 60 .mu.-thick Se-Te-Cl 
alloy system photoconductive layers thereon. 
Next, the thus obtained electrophotographic elements were subjected to 3 
days' dark adaptation, and thereafter the process comprising 
electrification-exposure-deelectrification was repeated 100 times at the 
rotary speed of 33.3 rpm per one process by means of an 
electrophotographic element tester, thereby measuring the residual 
electric potential respectively. The residual electric potential 
(background electric potential V.sub.L after exposure) referred to herein 
is represented by the difference (the amount increased) between 1st 
V.sub.L and 100th V.sub.L. The thus obtained results are as shown in the 
accompanying drawing. It can be seen from this drawing that until the 
amounts of Cl added amount to 30 ppm, the elements of the present 
invention (Curve A) using the small amount of O.sub.2 -containing alloy A 
are lower in residual electric potential than the control elements (Curve 
B) using the large amount of O.sub.2 -containing alloy B.