CA1075068A

CA1075068A - Imaging system

Info

Publication number: CA1075068A
Application number: CA250,755A
Authority: CA
Inventors: Robert S. Waugh
Original assignee: Xerox Corp
Current assignee: Xerox Corp
Priority date: 1975-04-28
Filing date: 1976-04-22
Publication date: 1980-04-08
Also published as: DE2615624C2; AU1331576A; NL7604387A; GB1530355A; IT1064004B; SE7604586L; FR2309906B1; SE415299B; AU497863B2; DE2615624A1; JPS5913021B2; FR2309906A1; JPS524240A

Abstract

ABSTRACT OF THE DISCLOSURE
A photosensitive element having a three layered photo-conductive portion comprising a first layer of vitreous selenium or a vitreous arsenic-selenium alloy, a second layer comprising a vitreous arsenic-tellurium-selenium alloy and a third layer comprising a vitreous arsenic-selenium alloy. A method of imaging the photosensitive element is also described.

Description

- ~075068 BACKGROUND OF THE INVENTION
This invention relates to xerography, and in particular to a system utilizing a photoreceptor having a stable middle layer. The art of xerography involves the use of a photosensi-tive element containing a photoconductive insulating layer which is first uniformly electrostatically charged in order to sensi-tize its surface. The plate is then exposed to an image of activating electromagnetic radiation such as light, x-ray, or the like, which selectively dissipates the charge in the irradiated areas of the photoconductive insulator while leaving behind an electrostatic latent image in the non-irradiated areas. The latent electrostatic image may then be developed and made visible by depositing finely divided electroscopic marking particles on the surface of the photoconductive insu-lating layer. This concept was originally disclosed by Carlson, ~ -in U.S. Patent 2,297,691, and is further amplified and described by many related patents in the field.
The use of vitreous selenium as described by Bixby in U.S. Patent 2,970,906, remains the most widely used photocon-ductor in commercial xerography in that it is capable of holdingand retaining an electrostatic charge for relatively long periods of time when not exposed to light, and because it is relatively - sensitive to light as compared to other photoconductive materials.
Ullrich, U.S. Patent 2,803,542 and Mayer et al, U.S.
Patent 2,822,300, both teach the concept of improving the pro-perties of vitreous selenium by the addition of elemental arsenic in amounts of up to about 50 percent by weight. Arsenic concentrations greater than about 10 percent by weight exhibits increased spectral response in the yellow-red band of electro-magnetic spectral.

~k -~0750~8 Paris, U.S. Patent 2,803,541, discloses two-layered photoreceptor structures having layers of selenium and selenium-arsenic alloys. Improved photosensitivity is attributed by using a top layer of vitreous selenium-tellurium over a layer of selenium. This structure, however, does not provide adequate abrasion resistance for automatic xerographic machine operation and also exhibits high dark discharge. Protective organic and inorganic overcoatings have been developed to provide improved abrasion resistance but a major problem with these overcoatings is their inability to function properly through a wide range of environmental conditions.
Sechak, U.S. Patent 3,655,377, discloses a three-layered structure, i.e., a tri-layer photoreceptor, comprising a top layer of arsenic-selenium alloy for abrasion resistance, temperature stability and improved dark decay; a second layer of selenium-tellurium alloy to yield panchromatic light response;
and a bottom bulk layer of xerographic grade selenium or halogen doped arsenic-selenium. Sechak does not disclose the member of the instant invention, i.e., a ternary alloy, as the middle layer. Sechak instead discloses a binary alloy as the middle layer. Neither does Sechak appreciate the problem associated with the loss of electrical properties of a tri-layer photo-receptor upon aging at elevated temperatures, i.e., 115F and above.
Chiou, U.S. Patent 3,861,913, discloses a xerographic plate comprising a conductive substrate, a charge transport layer and a charge generation layer consisting essentially of from 5 to 35 percent by weight tellurium and from 0.5 to 20 per-cent by weight arsenic, with the substantial balance being vitreous selenium. This patent does not disclose the tri-layer 10750~8 member of the instant invention nor does this patent appreciate the problem associated with the loss of electrical properties of a tri-layer photoreceptor upon aging at elevated temperatures, i.e., 115F. and above.
It has been discovered that when using a tri-layer photo-receptor comprising a top layer of arsenic-selenium alloy; a second or middle layer of selenium-tellurium alloy and a third layer of vitreous selenium or arsenic-selenium, that upon accel-erated heat aging or over an extended period of time at elevated - ---temperatures, the electrical properties of the photoreceptor greatly deteriorates. It is believed that a portion of the tellurium in the middle layer migrates from this middle layer -- -into the adjacent top or bottom layers resulting in the above-mentioned degradation of electrical properties. Therefore, it has been discovered that the addition of arsenic to the middle layer forming an arsenic-tellurium-selenium alloy for the middle layer in the tri-layer photoreceptor prevents degradation of these electrical properties, upon accelerated heat aging or over an extended period of time at above ambient temperatures. It is believed that the addition of arsenic prevents migration of the tellurium from this middle layer greatly extending the maximum ` capability of the tri-layer photoreceptor.
OBJECTS OF THE INVENTION
It is, therefore, an object of this invention to provide a system for utilizing a composite three-layered photoreceptor which overcomes the above noted disadvantages.
It is another object of this invention to provide a three-layered photoreceptor having greatly improved stability of electrical properties over an extended period of time at elevated temperatures.

`` iO75~t;8 It is yet another object of this invention to provide a method of imaglng a novel photoreceptor.
It is another object of this invention to provide a novel photoreceptor.
SUMMARY ~F THE INVENTION
The foregoing objects and others are accomplished in accordance with this invention by providing a composite three-layered photoreceptor. The three-layered photoreceptor comprises a top layer of an arsenic-selenium alloy; a second or middle layer of an arsenic-tellurium-selenium alloy which prevents degradation of the electrical properties of the photoreceptor upon accelerated heat aging or over an extended period of time when exposed to above ambient temperatures; and a bottom layer of vitreous selenium or an arsenic-selenium alloy or a halogen doped arsenic-seLenium alloy. This multi-layered photoreceptor may be coated or evaporated onto a standard xerographic base by conventional techni~ues known to the art.
T~hus, in accordance with the present teachings, a composite photoreceptor member is provided which comprises a first layer of vitreous selenium, a second layer which comprises a vitreous arsenic-tellurium-selenium alloy which overlies the fLrst seleniam layer and a third layer which comprises a vitreous arsenic-selenium alloy which overlies the second layer of arsenic-tellurium-selenium alloy.
In accordance with a further embodiment of the present teachings, a photoconductive member is provided which comprises a support, a first layer of vitreous selenium which overlies the support, a second layer of vitreous arsenic-tellurium-selenium alloy which overlies the first selenium layer and a third layer of vitreous arsenic-selenium alloy overlying the second arsenic-tellurium-selenium layer.

More specifically in accordance with the present B ~ s ` 10750f~
teachings, a photoconductive member is provided which comprises a conductive support, a 40 to 100 microns thick first layer of vitreous arsenic-selenium containing from about 0.1 to 2.0 percent by weight arsenic, a 0.1 to 1.0 micron thick second layer of - -vitreous arsenic-tellurium-selenium alloy which contains from about 15.0 to 25.0 percent by weight of tellurium and from about 3.0 to 5.0 percent by weight of arsenic which overlies the first layer of arsenic selenium, and a 0.1 to 5.0 micron thick third layer of vitreous arsenic-selenium alloy which contains from about 0.1 to 3.0 percent by weight arsenic which overlies the second layer of arsenic-tellurium-selenium alloy.
By yet a further embodiment of the present teachings, - an imaging method is provided which comprises providing a photoconductive member comprising a conductive substrate coated with a first layer of vitreous selenium, about 40 to 100 microns thick, a second layer of vitreous arsenic-tellurium-selenium - -alloy about 0.1 to 1.0-microns thick which overlies the first layer of selçnium and a third layer of vitreous arsenic-selenium alloy about 0.1 to 5.0 microns thick overlying the arsenic-tellurium-selenium layer. A latent electrostatic image is formed on the member and the image is subsequently developed.
BRIEF DESCRIPTION OF THE DRAWINGS
The advantages of this improved photoreceptor will become apparent upon consideration of the following disclosure of the invention, especially when taken in conjunction with the accompanying drawings wherein:
Fig. 1 is a schematic illustration of a cross-` sectional view of one of the embodiments of a multi-layered ~ xerographic photoreceptor as contemplated by this invention;
- 30 Figs. 2, 3 and 4 represent a plot of sensitivity, initially and after accelerated heat aging, of a multi-layered photoreceptor which contains a top layer of arsenic-selenium, a ,B ~ -5a-`~` 1075068 middle layer of a binary alloy of tellurium-selenium and a bottom layer of an arsenic-selenium alloy doped with a halogen.
The middle layer does not contain arsenic, :

B -5b-10750~;~

Figs. 5, 6, 7 and 8 represent a plot of the sensitivity of the multi-layered device of the instant invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring now to Fig. 1 which shows a schematic drawing of one of the embodiments of the instant invention which com-prises a multi-layered xerographic photoreceptor. The multi- -layered, i.e., three-layered structure, is referred to as a "tri-layer" photoreceptor. Photoreceptor 4 may be self-supporting or it may have a conventional support member 5 which may be either electrically insulating or electrically conductive. Preferably, support member 5 is a conventional electrical support such as -brass, aluminum, nickel, steel or any other suitable material.
The support member 5 may be of any conventional thickness, rigid or flexible and may be in any desired form such as a sheet, web, plate, cylinder, drum or any other suitable shape. It may also comprise any other materials such as metallized paper, plastic -sheets coated with a thin layer of metal such as aluminum or copper oxide or glass coated with a thin layer of chromium or tin oxide. If desired, the photoreceptor may also be formed on an electrically insulating support and electrically charged by xerographic processes well known to the art of xerography for photoreceptors having insulating backings. As mentioned above, member 5 may, in some cases, be dispensed with entirely.
Layer 1 may comprise a first layer of vitreous selenium or a vitreous arsenic-selenium alloy. Preferably, layer 1 com-prises a vitreous arsenic-selenium alloy containing up to about 3.0 percent by weight arsenic. Layer 1 may contain from about 0.1 to about 2.0 percent by weight arsenic. More preferably, layer 1 contains up to about 1.0 percent by weight arsenic and most preferred, layer 1 contains up to about 0.5 percent by weight arsenic with the balance selenium. When layer 1 is either ' 10750~

vitreous selenium or an arsenic-selenium alloy, layer 1 may also contain a halogen dopant. The preferred halogen dopant consists essentially of chlorine, bromine and iodine. The halogen dopant is preferably present in concentrations of from about 5 parts per million to about 10,000 parts per million. Layer 1 may be from about 10 to about 300 microns thick, preferably from about 40 to 100 microns thick, more preferably from about 52.0 to 68.0 microns thick and most preferred 60 microns thick.
Layer 2, which is a second or middle layer, may comprise a second layer of vitreous arsenic-tellurium-selenium alloy which overlies the first layer 1. Middle layer 2 comprising a second layer of vitreous arsenic-tellurium-selenium alloy may contain from about 0.1 to about 40.0 percent by weight arsenic and from about 1.0 to about 50.0 percent by weight tellurium and from about 50.0 to 90.0 percent by weight selenium. More pre-ferably, the arsenic-tellurium-selenium alloy layer 2 may contain from about 3.0 to about 5.0 percent by weight arsenic and from about 15.0 to about 25.0 percent by weight tellurium with the balance selenium. Arsenic in the range of about 3.0 to 5.0 per-cent by weight has been found to be particularly desirable inthe alloy of layer 2. The particularly desired composition of layer 2 is about 4.0 percent by weight arsenic, about 20.5 per-cent by weight tellurium and about 75.5 percent by weight selenium. It is critical that layer 2 contain arsenic since the presence of arsenic results in the photoreceptor retaining its electrical properties upon accelerated heat aging or over an extended period of time at elevated temperatures. i.e., above Middle layer 2 may preferably also comprise a vitreous arsenic-tellurium-selenium alloy containing a halogen dopant.
The halogen dopant may be of the same material and concentration as disclosed for layer 1.

':

-' 10750~;~

Layer 2 may be from about 0.1 to about 2.0 microns thick, preferably from about 0.1 to 1.0 microns thick, more preferably from 0.1 to 0.5 microns thick, and is most preferred at a thick-ness of 0.3 microns.
Layer 3, the top or third layer, comprises a layer of vitreous arsenic-selenium alloy which overlies layer 2. Layer 3 preferably comprises an arsenic-selenium alloy containing from about 0.1 to about 40.0 percent by weight arsenic and preferably from about 0.1 to about 5.0 percent by weight arsenic, and more 10 preferably from about 0.1 to about 3.0 percent by weight arsenic with the balance selenium. Layer 3 may be doped with a halogen.
The halogen dopant may be the same material and in the same concentration as disclosed for layers 1 and 2.
Layer 3 may be from about 0.1 to about 5.0 microns thick, preferably from about 1.0 to 4.0 microns thick and is most pre-ferred at a thickness of about 3.0 microns.
Member 4 may comprise a photoconductive member. The member may comprise a support 5 and a first layer 1 of vitreous selenium overlying support 5. Overlying layer 1 may be a second 20 layer 2 of a vitreous arsenic-tellurium-selenium alloy. Over-lying layer 2 may be a third layer of a vitreous arsenic-selenium alloy. The first layer 1 may be from about 40 to 100 microns thick and contain up to about 1.0 percent by weight arsenic, pre-ferably up to about 0.5 percent by weight arsenic with the balance selenium. The second layer 2 of arsenic-tellurium- -selenium may be from about 0.1 to about 1.0 microns thick and may A contain up to about 40.0 percent by weight arsenic and up to about 50.0 percent by weight tellurium, preferably up to about 5.0 percent by weight arsenic and up to about 25.0 percent by - 30 weight tellurium with the balance selenium. The third layer 3 of arsenic-selenium alloy may be from about 0.1 to about 5.0 microns thick and may contain up to about 40.0 percent by weight arsenic preferably up to about 5.0 percent by weight arsenic with the balance selenium. All three layers, i.e., layers 1, 2 and 3, may be doped with a halogen. Preferably, a halogen selected from the group consisting of chlorine, bromine and iodine in a preferred concentration of from about 5 parts per million to about 10,000 parts per million.
In conventional xerography when substrate 5 is electri-cally conductive, it is generally grounded during a charging step to facilitate the deposit of a uniform layer of charge upon layer 3. Charging of the photoreceptor 4 is readily accomplished in a variety of ways, for example, by rubbing layer 4 with a soft brush or fur or more preferably, by utilizing corona charging techniques and devices, for example, as described in Vyverberg, U.S. Patent 2,836,725 and Walkup, U.S. Patent

2,777,957. Charging is usually accomplished in the absence of actinic radiation, i.e., that radiation which makes the photo-receptor 4 relatively more electrically conductive in radiation struck portions. After charging, the next conventional xero-graphic process step may be to expose the photoreceptor to apattern of electromagnetic actinic radiation thereby discharging light struck areas of photoreceptor 4 relative to non-light struck areas thereby forming a latent electrostatic image upon or in the surface of the photoreceptor.
Other methods of forming a latent image on photoreceptor 4 are known in the art and include first forming such a charge pattern on a separate photoconductive insulating layer according ~ to conventional xerographic reproduction techniques and then - transferring this charge pattern to layer 3 of photoreceptor 4 by bringing the two layers into very close proximity and utilizing breakdown techniques as described, for example, in U.S. Patents ~: .

~0750~i~

2,982,647 to Carlson and 2,825,814 and 2,937,943 to Walkup. In addition, charge patterns conforming to selected, shaped elec-trodes or combinations of electrodes may be formed on layer 3 by the "TESI" discharge technique as more fully described in U.S.
Patents 3,023,731 and 2,919,967 to Schwertz or by techniques described in U.S. Patents 3,001,848 and 3,001,849 to Walkup as well as by the preferred electron beam recording techniques known in the art and as illustratively described in Glenn, U.S.
Patent 3,113,179.
Thereafter, the latent image is then generally rendered visible, i.e., developed by contacting the latent image with finely divided marking material generally electrostatically charged to a polarity opposite to the polarity of the latent electrostatic image, by bringing such material into surface con-tact with layer 3 causing the material to be held thereon in a pattern corresponding to the latent image.
Any suitable developing system may be used to develop latent images on the photoreceptor of this invention and many such systems exist in the art.
For example, the system of cascade development has found extensive commerical acceptance and generally consists of gravi-tationally flowing developer material consisting of a two com-ponent material of the type disclosed in Walkup et al, U.S.
Patent 2,638,416, over the photoreceptor bearing the latent image.
The two components consist of an electroscopic powder called "toner" and a granular material called "carrier" and which by mixing acquire triboelectric charges of opposite polarity. In development, the toner component, usually oppositely charged to the latent image is deposited on the latent electrostatic image to render that image visible.

- : , . .

1075~68 Other typical developing systems include magnetic brush development, for example, see Giamo, U.S. Patent 2,930,351;
Simmons et al, U.S. Patent 2,791,949 and Hall et al, U.S. Patent

3,015,305; fluid development, for example, see Carlson, U.S.
Patents 2,221,776; 2,551,582; 2,690,394; 2,761,416 and 2,928,575;
Thompson, U.S. Patent 3,064,622; Gundlach, U.S. Patents 3,068,115 and 3,084,043 and Metcalfe, U.S. Patents 2,907,674; 3,001,888;
3,032,432 and 3,078,231; skid development, for example, Mayo, U.S. Patent 2,895,847, and others.
Once developed, the loosely adhering powder image may be transferred to another support surface to which it may be affixed by solvent vapors, heat or other suitable means to render the image indefinitely usable or the loose powder image may be affixed directly on the photoreceptor either as a result of developing or a separate step thereafter.
Referring now to Fig. 2 which represents a sensitivity plot of a tri-layer photoreceptor member with a top layer about 3.0 microns thick, of an alloy of about 0.5 percent by weight arsenic and 99.5 percent by weight selenium, a middle layer, about 0.3 microns thick, of an alloy of about 25 percent by weight tellurium and 75 percent by weight selenium and a bottom layer about 60.0 microns of an alloy of about 0.33 percent by weight arsenic and 99.66 percent by weight selenium doped with 20 parts per million of chlorine. As mentioned above, this photoreceptor does not have arsenic in the middle or second layer. This member is exposed to a helium neon beam laser which emits activating radiation at 6328 angstroms. Up the left side of the graph is shown surface potential in volts. Across the bottom of the graph is relative exposure in microwatts of laser power. The above described member was initially charged to a surface potential of 800 volts and stepwise discharged by pro-` ' 1075068 gressively exposing the photoreceptor to larger amounts of acti-vating radiation measured in microwatts using a helium neon laser emitting activating radiation at 6328 angstroms. After a number of exposures, the member was discharged significantly, i.e., to approximately 110 volts. The initial sample was then subjected to accelerated heat aging for 7 days at 125F. The member was again recharged to a surface potential of 800 volts and stepwise exposed to activating radiation under the same con-ditions as initially. After the same number of exposures and ; 10 under the same conditions as used initially, the member dis-charged to about 700 volts. This is represented by the top line in Fig. 2.
Referring now to Fig. 3 which also represents sensitivity curves using a tri-layer member similar to the one described in conjunction with Fig. 2, which also has no arsenic in the middle - layer. The member was exposed initially, after accelerated heat aging for 3 days at 125F. and then after accelerated heat aging for 7 days at 125F.
Referring now to Fig. 4 which illustrates using a similar 20 member as in Fig. 3 under the same conditions except that the member was exposed initially, and after accelerated heat aging ? for 7 days at 125F. --- Referring now to Fig. 5 which represents standard sensi-tivity curves of a member of the instant invention taken initially and after 7 days accelerated heat aging at 125F. The member of Fig. 5 represents a member containing a top layer, about 3.0 microns thick, of an alloy of about 0.5 percent by weight arsenic and 99.5 percent by weight selenium and a middle layer, a ternary alloy, about 0.65 microns thick, of about 3.5 percent by weight 30 arsenic and 20.5 percent by weight tellurium with the balance being selenium and a bottom layer, about 60 microns thick, of an .. . . .
.
.' : . ' - --:

107506~

alloy of about 0.33 percent by weight arsenic and 99.66 percent by weight selenium which is doped with 20 parts per million of chlorine. The member was initially charged sufficiently to a surface potential of 800 volts then discharged by exposing to activating radiation, i.e., microwatts, from a helium neon laser emitting activating radiation at 6328 angstroms. The member initially discharged to a surface potential of about 75 volts.
After accelerated heat aging for 7 days at 125F. the same mem-ber also discharged to a surface potential of about 75 volts.
Referring now to Figs. 6, 7 and 8 where the member was, -in both Fig. 6 and Fig. 8, accelerated heat aged and tested initially, after 3 days at 125F. and after 7 days at 125F. As the Figs. 6, 7 and 8 indicate, none of the members substantially lose their sensitivity or electrical properties after accelerated heat aging. The same results were observed as shown in Fig. 7 except that the member in Fig. 7 was tested initially and aft~r accelerated heat aging for 7 days at 125F.
It has been discovered that when using a tri-layer photo-receptor comprising a top layer of arsenic-selenium alloy, a second or middle layer of selenium-tellurium alloy and a third or bottom layer of vitreous selenium or arsenic-selenium that upon accelerated heat aging or over an extended period of time at elevated temperatures, i.e., above 115F., the electrical properties of this tri-layer photoreceptor greatly deteriorates.
It is believed that a portion of the tellurium in the middle layer of this tri-layer photoreceptor migrates from the middle layer into the adjacent top or bottom layers of the photoreceptor resulting in the degradation of the electrical properties of the photoreceptor. Therefore, it has been discovered that the addi-tion of arsenic to the middle layer of the tri-layer photoreceptor forming a ternary alloy of arsenic-tellurium-selenium in the ` 10750~8 middle layer, prevents degradation of these electrical properties upon accelerated heat aging or over an extended period of time at above ambient temperatures, i.e., above 115F. It is believed that the addition of the arsenic prevents migration of the tel-lurium from the middle layer thereby greatly extending the maxi-mum capability of the tri-layer photoreceptor.
The tri-layer photoreceptor of this invention may be prepared by any suitable technique. A typical technique includes vacuum evaporation wherein each photoconductive layer is sequen-tially evaporated onto its corresponding base material. In thistechnique, the bottom or first layer of selenium or arsenic-selenium alloy, the middle or second layer of arsenic-tellurium selenium alloy and the top or third layer of arsenic-selenium alloy layers are each evaporated by separate steps, under vacuum conditions varying from about 10 5 to 10 7 torr. In another embodiment of this technique, the three photoreceptor layers are continuously vacuum evaporated, one right after another, in the --same vacuum chamber without breaking the vacuum, by sequentially activating three separate sources of selenium or selenium-arsenic 20 for the bottom or first layer, and arsenic-tellurium-selenium - --for the middle or second layer and arsenic-selenium for the top or third layer.
Another typical technique includes co-evaporation, where-in the appropriate amount of material for each of the alloy layers is placed in separate heated crucibles maintained under vacuum conditions, with a source temperature of each alloy constituent being controlled so as to yield the appropriate percentage of the alloy desired. This technique is illustrated in U.S. Patent 3,940,903.
Another typical method of evaporation includes flash evaporation under vacuum conditions similar to those defined in 750~i~

co-evaporation, wherein a powder mixture such as arsenic, tellur-ium and selenium, are selectively dropped into a heated crucible maintained at a temperature of about 400C. to 600C. The vapors formed by the heated mixture are evaporated upward onto a substrate supported above the crucible.
In all the above methods, it is desired that the substrate onto which the photoconductive material is evaporated, is main-tained at a temperature of from about 50C. to about 80C. If desired, a water cooled platen or other suitable cooling means may be used in order to maintain a constant substrate tempera-ture. In general, a selenium base or bulk layer thickness of about 60 microns is obtained when evaporation is continued for about 1 hour at a vacuum of about 5 x 10 5 torr at a crucible temperature of about 280C.
Ullrich, U.S. Patent 2,803,542; Mayer et al, U.S. Patent 2,822,300; Dessauer et al, U.S. Patent 2,901,348, Schaffert, U.S.
Patent 2,963,376; Bixby, U.S. Patent 2,970,906 and Blakney et al, U.S. Patent 3,077,386 all illustrate vacuum evaporation techniques which are suitable for the formation of alloy layers of the instant invention. The crucibles which are used for evaporation for the photoreceptor layers may be of any inert material such as quartz, molybdenum, stainless steel vacuum coated with silicon monoxide, or any other equivalent materials. The selenium or selenium alloy being evaporated is maintained at a temperature between above its melting and boiling points.
The photoreceptor of the instant invention exhibits the ability to maintain its electrical properties upon accelerated heat aging or over an extended period of time at above ambient temperatures, i.e., temperatures above 115F. The photoreceptor of the instant invention also has improved dark decay properties.
Furthermore, sensitivity curves and the increase in the Mottling 10750~;8 index, i.e., step-by-step charging of the photoreceptor, indicates that the photoreceptor of the instant invention does not sub-stantially lose its electrical properties upon accelerated heat aging or over an extended period of time at above ambient temper-atures, i.e., above 115F. Mottling indexes clearly show that the photoreceptor of the instant invention after accelerated heat aging retains substantially the same sensitivity, i.e., electrical properties, as when initially tested.
When a photoreceptor does not have the ability to be uniformly charged and uniformly maintain a surface potential, it is not a desirable photoreceptor for cyclic use. The instant photoreceptor has excellent charge uniformity properties and exhibits the ability to uniformly maintain a surface potential.
; Tri-layer photoreceptors without arsenic in the middle or second layer, i.e., a middle layer of arsenic-tellurium-selenium, lose their ability to be uniformly charged and to maintain a uniform surface potential upon accelerated heat aging or over an extended period of time at elevated temperatures, i.e., temperatures above 115F.
The following examples further specifically define the present invention with respect to the method of making a tri-layer photoreceptor member of the instant invention. The per-; centages in the disclosure, examples and claims are by weight unless otherwise indicated. The examples below are intended to illustrate various preferred embodiments of making a tri-layer photoreceptor. The photoreceptor alloy elements described in the specification and examples; arsenic, tellurium and selenium, are all high purity xerographic grade materials (arsenic and - selenium 99.999 percent by weight pure and tellurium 99.99 percent by weight pure) available from Canadian Copper Refiners.

~ 1075C~

EXAMPLE I
An oxidized aluminum substrate, i.e., an aluminum drum with a thin aluminum oxide coating thereon, approximately 3 3/8 inches in diameter and 10 3/8 inches long, is placed in a vacuum chamber. A starting alloy for the first or bottom layer of the tri-layer photoreceptor is prepared by placing elemental selenium shots about 1/16 to 3/16 inches in diameter in an SiO coated stainless steel evaporation boat. The evaporation boat is posi-tioned above 6 inches below the surface of the drum.
A starting alloy for the second or middle layer of the tri-layer photoreceptor is prepared by weighing pellets about 1/16 to 3/16 inches in diameter of elemental arsenic, tellurium and selenium in a ratio of 20.5 percent by weight of tellurium;

4.0 percent by weight arsenic and 75.5 percent by weight selenium in a second SiO coated stainless steel boat which is placed adjacent to the first SiO coated stainless steel boat.
A starting alloy for the third or top layer of the tri-layer photoreceptor i5 prepared by weighing pellets about 3/8 to 1/2 inches in diameter of elemental arsenic and selenium in a ; 20 ratio of 0.5 percent by weight arsenic and 99.5 percent by weight selenium in a CrO, chromic oxide, boat which is placed adjacent to the first SiO coated stainless steel boat. Each boat is con-nected directly to a source of electrical power adaptable to control the temperature of the respective boats. The chamber is then evacuated to a vacuum of about 10 5 torr while the drum is rotated about 10 RPM. The first boat containing the selenium is heated to a temperature of about 310C. over a period of about 35 minutes to form a layer of vitreous selenium about 60 microns thick on the aluminum drum. The electrical power to the first boat containing the selenium is still maintained in order to pre-vent any buildup on the boat of the other materials being evapo-750~;~

rated. Without brea~ing the vacuum, the drum speed is increased to about 30 RPM. The temperature of the second boat containing the arsenic-tellurium-selenium alloy is gradually increased to 450C. over a period of about 8.5 minutes and maintained at that temperature for about 1 minute to form an arsenic-tellurium-selenium alloy coating about 0.3 microns thick on the first or bottom selenium layer. The power to the second boat is main-tained. The drum speed is maintained at 30 RPM.
The temperature of the third boat containing the arsenic-selenium alloy is gradually increased to 350C. over a period of about 10 minutes and maintained at that temperature for about 7 minutes to form a 3.0 micron thick top layer of arsenic-selenium alloy on the middle layer of the arsenic-tellurium-selenium alloy. At the end of this time the vacuum chamber is cooled to room temperature, the vacuum broken, and the drum containing the tri-layer photoconductor is removed from the chamber.
EXAMPLE II
The drum containing the tri-layer photoreceptor of Example I is then charged to a positive potential by the method described by Carlson in U.S. Patent 2,588,699. The corona charging unit is maintained at about 7,500 volts thereby charging the drum to an acceptance potential of about 850 - 900 volts.
An analog signal obtained from a written document is put into a helium-neon laser which emits activating radiation at about 6328 angstroms, modulating the laser's intensity in accordance with - -the video information onto the drum. As a result, the drum is imagewise exposed forming a latent electrostatic image thereon.
This method is described by Mason in U.S. Patent 3,870,816. The drum bearing the latent electrostatic image is then developed by cascading an electroscopic marking material over the photocon-ductive surface of the drum. The developed image is transferred ' 10750f~

to a sheet of paper and heat fused to make it permanent. The final image exhibits good resolution, high density and is an excellent copy of the original.

EXAMPLE I I I
A drum as prepared in Example I is placed in a Xerox X200 telecopier and a line copy of an original image of black on white on conventional printing paper is made. This image also exhibits good resolution and high density.
EXAMPLE IV
A drum as prepared in Example I and as charged in Example I is exposed to a black on white line copy original image contained on conventional printing paper. A 15 watt General Electric cool white fluorescent lamp No. F15T8CW is used as the exposure source to form a latent electrostatic image. The drum bearing the latent electrostatic image is then developed by cascading an electroscopic marking material over the photoconductive surface of the drum. The developed image is transferred to a sheet of paper and heat fused to make it permanent. The final image exhibits good resolution and high density and is an excellent copy of the original.
.

~ 30

Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A composite photoreceptor member comprising:
(a) a first layer of vitreous selenium;
(b) a second layer comprising a vitreous arsenic-tellurium-selenium alloy overlying said first selenium layer; and (c) a third layer comprising a vitreous arsenic-selenium alloy overlying said second layer of arsenic-tellurium-selenium alloy.

2. The member of Claim 1 wherein said first layer is from about 40.0 to 100.0 microns thick.

3. The member of Claim 2 wherein said first layer is from about 52.0 to 68.0 microns thick.

4. The member of Claim 3 wherein said first layer is about 60 microns thick.

5. The member of Claim 1 wherein said second layer is from about 0.1 to 1.0 microns thick.

6. The member of Claim 5 wherein said second layer is from about 0.1 to 0.5 microns thick.

7. The member of Claim 6 wherein said second layer is 0.3 microns thick.

8. The member of Claim 1 wherein said third layer is from about 0.1 to 5.0 microns thick.

9. The member of Claim 8 wherein said third layer is from about 1.0 to 4.0 microns thick.

10. The member of Claim 9 wherein said third layer is about 3.0 microns thick.

11. The member of Claim 1 wherein said first layer of vitreous selenium contains up to about 3.0 percent by weight arsenic.

12. The member of Claim 1 wherein said first layer of vitreous selenium contains up to about 1.0 percent by weight arsenic.

13. The member of Claim 1 wherein said first layer of vitreous selenium contains up to about 0.50 percent by weight arsenic.

14. The member of Claim 1 wherein said first layer of vitreous selenium contains a halogen dopant.

15. The member of Claim 14 wherein said halogen dopant is selected from the group consisting of chlorine, iodine and bromine.

16. The member of Claim 14 wherein said halogen dopant is present in a concentration amount from about 5 parts per million to about 10,000 parts per million.

17. The member of Claim 1 wherein said second layer of arsenic-tellurium-selenium alloy contains from about 0.1 to about 40.0 percent by weight arsenic and from about 1.0 to about 50.0 percent by weight tellurium.

18. The member of Claim 1 wherein said second layer of arsenic-tellurium-selenium alloy contains from about 3.0 to about 5.0 percent by weight arsenic, and from about 15.0 to about 25.0 percent by weight tellurium.

19. The member of Claim 1 wherein said second layer of arsenic-tellurium-selenium alloy contains about 4.0 percent by weight arsenic, and about 20.5 percent by weight tellurium.

20. The member of Claim 1 wherein said second layer of arsenic-tellurium-selenium alloy contains a halogen dopant.

21. The member of Claim 1 wherein said third layer of arsenic-selenium alloy contains from about 0.1 to about 40.0 percent by weight arsenic.

22. The member of Claim 1 wherein said third layer of arsenic-selenium alloy contains from about 0.1 to about 5.0 percent by weight arsenic.

23. The member of Claim 1 wherein said third layer of arsenic-selenium alloy contains from about 0.1 to about 3.0 percent by weight arsenic.

24. The member of Claim 1 wherein said third layer of arsenic-selenium alloy contains a halogen dopant.

25. A photoconductive member comprising:
(a) a support;
(b) a first layer of vitreous selenium overlying said support;
(c) a second layer of vitreous arsenic-tellurium-selenium alloy overlying said first selenium layer; and (d) a third layer of a vitreous arsenic-selenium alloy overlying said second arsenic-tellurium-selenium layer.

26. The member of Claim 25 wherein said first layer of vitreous selenium is from about 40.0 to about 100.0 microns thick.

27. The member of Claim 25 wherein said second layer of arsenic-tellurium-selenium is from about 0.1 to about 1.0 microns thick.

28. The member of Claim 25 wherein said third layer of arsenic-selenium is from about 0.1 to about 5.0 microns thick.

29. The member of Claim 25 wherein said first layer of vitreous selenium contains up to about 1.0 percent by weight arsenic.

30. The member of Claim 25 wherein said first layer of vitreous selenium contains up to about 0.5 percent by weight arsenic.

31. The member of Claim 25 in which said support com-prises an electrically conductive material.

32. The member of Claim 25 wherein said second layer of arsenic-tellurium-selenium alloy contains up to about 40.0 percent by weight arsenic and up to about 50.0 percent by weight tellurium.

33. The member of Claim 25 wherein said second layer of arsenic-tellurium-selenium alloy contains up to about 5.0 percent by weight arsenic and up to about 25.0 percent by weight tellurium.

34. The member of Claim 25 wherein said third layer of arsenic-selenium alloy contains up to about 40.0 percent by weight arsenic.

35. The member of Claim 25 wherein said third layer of arsenic-selenium alloy contains up to about 5.0 percent by weight arsenic.

36. The member of Claim 25 wherein said first layer of vitreous selenium contains a halogen dopant.

37. The member of Claim 25 wherein said second layer of arsenic-tellurium-selenium alloy contains a halogen dopant.

38. The member of Claim 25 wherein said third layer of arsenic-selenium alloy contains a halogen dopant.

39. A photoconductive member comprising:
(a) a conductive support;
(b) a 40 to 100 micron thick first layer of vitreous arsenic-selenium containing from about 0.1 to 2.0 percent by weight arsenic;
(c) a 0.1 to 1.0 micron thick second layer of vitreous arsenic-tellurium-selenium alloy containing from about 15.0 to 25.0 percent by weight tellurium and from about 3.0 to 5.0 per-cent by weight arsenic overlying said first layer of arsenic-selenium; and (d) a 0.1 to 5.0 micron thick third layer of vitreous arsenic-selenium alloy containing from about 0.1 to 3.0 percent by weight arsenic overlying said second layer of arsenic-tellurium-selenium alloy.

40. The member of Claim 39 wherein the first layer of vitreous arsenic-selenium alloy is doped with a halogen.

41. The member of Claim 40 wherein said third layer of vitreous arsenic-selenium alloy is doped with a halogen.

42. The member of Claim 41 wherein said second layer of vitreous arsenic-tellurium-selenium alloy is doped with a halogen.

43. An imaging method comprising:
(a) providing a photoconductive member comprising a conductive substrate coated with a first layer of vitreous selenium about 40 to 100 microns thick, a second layer of vitreous arsenic-tellurium-selenium alloy about 0.1 to 1.0 microns thick overlying said first layer of selenium and a third layer of vitreous arsenic-selenium alloy about 0.1 to 5.0 microns thick overlying said arsenic-tellurium-selenium layer;
(b) forming a latent electrostatic image on said member;
and (c) developing said image.

44. The method of Claim 43 wherein said first layer of vitreous selenium contains arsenic.

45. The method of Claim 44 wherein said first layer of vitreous arsenic-selenium alloy is doped with a halogen.

46. A method of forming a latent electrostatic image which comprises:
(a) providing a photoconductive member having a conduc-tive support, a first layer of vitreous selenium about 40 to 100 microns thick overlying said support, a second layer of vitreous arsenic-tellurium-selenium alloy about 0.1 to 1.0 microns thick overlying said first selenium layer and a third layer of vitreous arsenic-selenium alloy about 0.1 to 5.0 microns thick overlying said second arsenic-tellurium-selenium alloy layer;
(b) substantially uniformly electrostatically charging said member; and (c) exposing said member to a pattern of activating electromagnetic radiation to form a latent electrostatic image.

47. The method of Claim 46 wherein said first layer of vitreous selenium contains arsenic.

48. The method of Claim 47 wherein said first layer of vitreous arsenic-selenium alloy is doped with a halogen.