GB1578960A

GB1578960A - Electrophotographic imaging member and process

Info

Publication number: GB1578960A
Application number: GB3065477A
Authority: GB
Original assignee: Rank Xerox Ltd
Current assignee: Xerox Ltd
Priority date: 1976-07-27
Filing date: 1977-07-21
Publication date: 1980-11-12
Also published as: FR2360105A1; JPS5315141A; NL7708103A; DE2733052A1; JPS5719779B2

Description

(54) ELECTROPHOTOGRAPHIC IMAGING MEMBER AND PROCESS (71) We, RANK XEROX LIMITED, of Rank Xerox House, 338 Euston Road, London NOW 1 3 BH, a British company, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement : The invention relates to an electrophotographic imaging member.More particularly, it relates to an electrophotographic imaging member having a transparent insulating layer on the exposed surface there- of and which is suitable for use in an electrophotographic process in which an electrostatic latent image is formed by subjecting the element, concurrently with or after the first electrostatic charging, to uniform exposure, secondarily charging using a polarity opposite in sign to that of the first charging followed by imagewise exposure to activating radiation, or by subjecting it successively to an initial charging, charging opposite in polarity to the first charge and imagewise exposure.

An electrophotographic process in which the imaging member of the present invention is useful is that described in detail in United States Patent Specification No.

3,041,167 to R. M. Blakney et al (hereinafter referred to as the Blakney et al process).

The imaging member used in the Blakney et al process is of a structure, as shown in Fig. 1, which comprises a conductive substrate (1) bearing a layer of photoconductive material; (2) with a layer of transparent insulating material; (3) overlaying the photoconductive layer. The Blakney et al process will be briefly illustrated with reference to Figs. 2a to 2d. In this process, the transparent insulating layer of the imaging member is first electrically charged to a given polarity (see Fig. 2a) and is uniformly exposed to activating radiation to allow an electric charge with a polarity opposite to that applied to the surface of the insulating layer to be produced at the interface between the insulating layer (3) and the photoconductive layer (2) (see Fig.

2b). Next, the photosensitive element is subjected to electrical charging opposite in polarity to the first charging whereby the surface electrostatic charge is neutralized and at the same time an electric charge having a polarity opposite to that existing at the interface between the insulating layer and photoconductive layer is caused to be induced in the conductive substrate (1) (see Fig. 2c). The charged element is exposed to light in an imagewise pattern to permit the electric charge existing at the interface to be discharged in correspondence with the amount of exposure, thereby forming an electrostatic latent image at the interface between the insulating layer (3) and the photoconductive layer (2) (see Fig. 2d).

If, upon charging to the opposite polarity, the electric charge corresponding to that of the opposite polarity is fed from the conductive substrate, the uniform exposure may be omitted.

As a result of studies of the Blakney et al process, using an imaging member of the kind described above with reference to Fig. 1, it has been found that when the photoconductor of the layer (2) is selenium (well known as a highly photoconductive material), the selenium being doped with tellurium, rapid deterioration in image quality occurs upon repeated use of the photosensitive element.

When the amount of tellurium is increased so as to improve the sensitivity of the photoconductive material, several prob lems are encountered in obtaining an electrostatic latent image with a suitable level of electrostratic contrast. This is the case because such a system requires a high charging current which in turn requires an expensive charging device. In addition, the high charging current results in generation of an increased amount of ozone which causes an acceleration of the deterioration of the insulating layer resulting in defects in the images reproduced there by and a shortened lifetime of the imaging member.

There is described in Japanese Patent Publication No. 44-12672 the use of an electrophotographic imaging member for use in conventional electrophotographic reproduction which comprises a conductive sup port with a layer of photoconductive material on the support formed of a selenium layer, a selenium/tellurium alloy layer and an arsenic/selenium alloy layer. This publication does not mention imaging this device by the previously described Blakney et al method.

Unexpectedly, it has been found that an electrophotographic imaging member prepared by forming on a conductive substrate a photoconductive layer of a three layer construction and then a transparent insulating layer on the top surface of the photoconductive layer is particularly suitable for imaging by the Blakney et al process. When the three layers of the abovementioned imaging member are caused to serve as an electric charge transfer layer, an electric charge producing layer and a boundary layer, the imaging member is found to be useful in the Blakney et al process with excellent sensitivity upon duplication, good resistance to deterioration and a long useful life.

The present invention provides an imaging member which, in accordance with preferred embodiments, can have a reproduction image sensitivity equivalent to or higher than that employed in the Blakney et al process, can be operated at low charging current, and can have a long life.

According to the present invention, there is provided a electrophotographic imaging member, comprising from the bottom up: (a) a conductive substrate; (b) a layer of an electric charge transferring material overlaying the substrate; (c) a layer of amorphous selenium/tellurium alloy containing from 2 to 50 weight percent tellurium overlaying the layer of charge transferring material said layer having a thickness of 01 to 5 microns; (d) a boundary layer comprising amorphous selenium overlaying the layer of selenium/tellurium alloy, said selenium layer having a thickness of from 50 to 1,000 angstroms; and (e) a transparent insulating layer overlaying the selenium layer.

The present invention also comprehends an electrophotographic process, the process comprising: (a) charging an imaging member in accordance with the invention so as to provide a uniform charge of a first polarity on the upper surface of the imaging member and a uniform charge of a second polarity (opposite to said first polarity) at the surface of said layer of electric charge transferring material which is remote from said layer of amorphous selenium/tellurium alloy; (b) uniformly exposing said imaging member to activating radiation so as to allow charge of said second polarity to move through the imaging member to the surface of said transparent insulating layer which is adjacent said boundary layer; (c) re-charging said imaging member so as to provide a uniform charge of said first polarity at the surface of said layer of electric charge transferring material which is remote from said layer of amorphous selenium/tellurium alloy; and (d) exposing said imaging member to an imagewise pattern of actinic electromagnetic radiation so as to form an electrostatic latent image.

The present invention is more particularly illustrated with reference to Fig. 3.

As illustrated by Fig. 3, the imaging member shown therein, which is in accordance with the present invention includes a conductive substrate (1), on which are successively formed three semiconductive layers, respectively serving as a charge transferring layer (4), a charge producing layer (5), and a boundary layer (6). A transparent insulating layer (3) is formed on the exposed surface of the boundary layer (6).

The conductive substrate (1) is generally made of a metal such as brass, aluminum gold, platinum or copper, for example. The substrate may be in the form of a sheet, web or cylinder and may be covered with a thin plastics layer. For example, the substrate may be metallized paper, a plastics sheet covered with a thin layer of aluminum or copper iodide or a glass sheet covered with chromium or chromium oxide. It is important to note that the substrate should have some conductivity by itself or have a surface with some conductivity by itself or have a surface with some conductivity and should have sufficient mechanical strength to withstand the rigors to which it will be exposed in the copying process.

The charge-transferring layer (4) should have a high degree of mobility of electrons or positive holes so they may pass through this layer and may be made of a photoconductive material which is conventionally employed in electrophotography. In particular, a photoconductive material composed substantially of selenium or poly (vinyl carbazole) can be used to form this layer.

The charge-producing layer (5) is a thin amorphous selenium/tellurium alloy layer having a thickness of from û l to 5 microns which is provided so as to impart good panchromatic characteristics and improved photosensitivity thereto and which functions to produce pairs of electrons and holes absorption of light. The concentra tion of tellurium in the alloy is from 2 to 50 weight percent. The use of tellurium in an amount greater than 50 weight percent is favourable in terms of panebromaticity, but it increases dark conductivity and lowers the charge-retaining ability of the device. In addition, a charge producing Se/Te layer having a thickness below 01 does not show any special characteristics ensuring panchromaticity and thus a sensitizing effect cannot be expected.A thickness for the layer greater than 5 microns is undesirable due to an increase in dark discharge.

The boundary layer (6) which serves to prevent crystallization of the surface of the charge-producing layer (5) and is provided for sensitizing purposes, is a thin layer substantially composed of amorphous selenium and having a thickness of SOA to 1,000A. In order to improve the resistance to crystallization, arsenic is preferably added in an amount of from 05 to 50 weight percent. With the arsenic concentration below 0.5 weight percent, its effect on preventing crystallization of the selenium is lowered. In contrast, an arsenic concentration above 50 weight percent is not desirable since a uniform vitreous composition for the boundary layer of arsenic as its primal component is difficult to obtain.A boundary layer thickness above 1,000A is disadvantageous in that the amount of light reaching the charge producing layer (5) decreases, leading to a considerable reduction in sensitivity. On the other hand, a thickness below 50A is undesirable since such a thin layer does not serve satisfactorily as a boundary layer for preventing crystallization and the imaging member is impaired as a whole with respect to its useful life.

The layer of transparent insulating material is typically an insulating organic resin and will normally have a thickness greater than 10 microns. The insulating resin may be any material which has high resistance against wear, high resistivity and capability of binding electrostatic charge as well as transparency to activating radiation.

Examples of resins which may be used are polystyrene, butadiene polymers and copolymers, acrylic and methacrylic polymers, vinyl resins, alkyd resins, polycarbonate resins, polyethylene resins and polyester resins.

The present invention is further illustrated by the following Examples in which all percentages are by weight unless otherwise specified.

EXAMPLE I An imaging member according to the present invention is prepared by forming an aluminum oxide coating on the surface of a cylindrical aluminum substrate as the first step. The substrate is next coated by vacuum deposition with: i. a 60 micron thick selenium layer; ii. a 02 micron thick layer of 75% /25% amorphous selenium/tellurium alloy; and iii. a 0 05 micron thick layer of an amor phous selenium/arsenic alloy contain ing 0.5 weight percent arsenic.

A 20 micron thick layer of Lexan (Registered Trade Mark) polycarbonate is applied as the transparent insulating layer.

The imaging member prepared as described in this Example was subjected to a cyclic imaging process using the Blakney et al process. No change in image quality was seen even after 100,000 cycles of operation.

EXAMPLE II (CONTROL) An imaging member was prepared as in Example I, except that the boundary layer was omitted, and the imaging member was subjected to a cyclic imaging process using the Blakney et al process. The image quality was substantially deteriorated after 5,000 cycles of operation. Also, it was found that the charging current required to yield the same electrostatic contrast as obtained with the first charging of the imaging member of Example I was about three times that required with the imaging member of Example I, and about double for charging of opposite polarity.

EXAMPLE 111 (CONTROL) An imaging member was prepared as in Example I, except that the thickness of the boundary layer was 015 micron. The sensitivity of the resulting imaging member was compared with that of Example I, using a hot white fluorescent lamp. The photosensivity of the imaging member of the present Example as determined by the test was + or less the similarly determined photosensivity of the imaging member of Example I.

EXAMPLE IV An imaging member was made by forming an aluminum oxide film on a cylindrical aluminum substrate, superimposing on the substrate by vacuum deposition a 60 micron thick layer of selenium, a 01y thick 60%/ 40% amorphous selenium/tellurium alloy layer and a 50A layer of 70%/30% amorphous selenium/arsenic alloy. A 20 micron thick layer of Lexan 4026 polvcarbonate is applied over the outermost vacuum deposited layer. The imaging member so prepared is subjected to the Blakney et al process for image formation and good copy quality is obtained even after 100,000 cycles of operation.

EXAMPLE V An imaging member was prepared by forming an aluminum oxide film on a cylindrical aluminum substrate and superimposing a 60 micron thick selenium layer, a 5 micron thick 90%/ 10% amorphous selenium/tellurium alloy layer, a 01 micron layer of pure amorphous selenium and a 20 micron layer of Lexan 4026 polycarbonate thereon. The imaging member was subjected to the Blakney et al process for image reproduction. As a result it was found that reproduction images of good quality were obtained even after 100,000 cycles of reproduction operations.

WHAT WE CLAIM IS: - I. An electrophotographic imaging member, comprising from the bottom up: (a) a conductive substrate; (b) a layer of an electric charge transferring material overlaying the substrate; (c) a layer of amorphous selenium/tellurium alloy containing from 2 to 50 weight percent tellurium overlaying the layer of charge transferring material said layer having a thickness of 01 to 5 microns; (d) a boundary layer comprising amorphous selenium overlaying the layer of selenium/tellurium alloy, said selenium layer having a thickness of from 50 to 1,000 angstroms; and (e) a transparent insulating layer overlaying the selenium layer.

2. An imaging member according to claim 1, wherein the substrate comprises prass, aluminum, gold, platinum or copper.

3. An imaging member according to claim 1, wherein the substrate is an auminum cylinder having a layer of A1203 on its surface.

4. An imaging member according to any one of claims 1 to 3, wherein the charge transferring material consists substantially of selenium or poly (vinylcarbazole).

5. An imaging member according to any one of claims 1 to 4, wherein the amorphous selenium overlaying the selenium/ tellurium alloy layer is alloyed with arsenic to form a selenium/arsenic alloy.

6. An imaging member according to claim 5, wherein the selenium/arsenic alloy contains from 0 5 to 50 weight percent arsenic.

7. An imaging member according to any one of claims 1 to 6, wherein the insulating layer is at least 10 microns thick.

8. An imaging member according to any one of claims 1 to 7, wherein the insulating layer comprises an insulating organic resin.

9. An imaging member according to claim 8, wherein the organic resin is polystyrene, an acrylic or methacrylic polymer, a vinyl resin, an alkyd resin, a polycarbot nate resin, a poly ethylene resin or a polyester resin.

10. An electrophotographic imaging member, substantially as described with reference to, and as schematically illustrated in, Fig. 3 of the accompanying drawings.

11. An electrophotographic imaging member, substantially as described in any one of the foregoing Examples I, IV and V.

12. An electrophotographic process, comprising: (a) charging an imaging member in accordance with any one of claims 1 to 11 so as to provide a uniform charge of a first polarity on the upper surface of the imaging member and a uniform charge of a second polarity (opposite to said first polarity) at the surface of said layer of electric charge transferring material which is remote from said layer of amorphous selenium/tellurium alloy; (b) uniformly exposing said imaging member to activating radiation so as to allow charge of said second polarity to move through the imaging member to the surface of said transparent insulating layer which is adjacent said boundary layer; ; (c) re-charging said imaging member so as to provide a uniform charge of said first polarity at the surface of said layer of electric charge transferring material which is remote from said layer of amorphous selenium/tellurium alloy; and (d) exposing said imaging member to an imagewise pattern of actinic electromagnetic radiation so as to form an electro static latent image.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **.

Blakney et al process for image formation and good copy quality is obtained even after 100,000 cycles of operation.

EXAMPLE V An imaging member was prepared by forming an aluminum oxide film on a cylindrical aluminum substrate and superimposing a 60 micron thick selenium layer, a 5 micron thick 90%/ 10% amorphous selenium/tellurium alloy layer, a 01 micron layer of pure amorphous selenium and a 20 micron layer of Lexan 4026 polycarbonate thereon. The imaging member was subjected to the Blakney et al process for image reproduction. As a result it was found that reproduction images of good quality were obtained even after 100,000 cycles of reproduction operations.

WHAT WE CLAIM IS: - I. An electrophotographic imaging member, comprising from the bottom up: (a) a conductive substrate; (b) a layer of an electric charge transferring material overlaying the substrate; (c) a layer of amorphous selenium/tellurium alloy containing from 2 to 50 weight percent tellurium overlaying the layer of charge transferring material said layer having a thickness of 01 to 5 microns; (d) a boundary layer comprising amorphous selenium overlaying the layer of selenium/tellurium alloy, said selenium layer having a thickness of from 50 to 1,000 angstroms; and (e) a transparent insulating layer overlaying the selenium layer.
2. An imaging member according to claim 1, wherein the substrate comprises prass, aluminum, gold, platinum or copper.
3. An imaging member according to claim 1, wherein the substrate is an auminum cylinder having a layer of A1203 on its surface.
4. An imaging member according to any one of claims 1 to 3, wherein the charge transferring material consists substantially of selenium or poly (vinylcarbazole).
5. An imaging member according to any one of claims 1 to 4, wherein the amorphous selenium overlaying the selenium/ tellurium alloy layer is alloyed with arsenic to form a selenium/arsenic alloy.
6. An imaging member according to claim 5, wherein the selenium/arsenic alloy contains from 0 5 to 50 weight percent arsenic.
7. An imaging member according to any one of claims 1 to 6, wherein the insulating layer is at least 10 microns thick.
8. An imaging member according to any one of claims 1 to 7, wherein the insulating layer comprises an insulating organic resin.
9. An imaging member according to claim 8, wherein the organic resin is polystyrene, an acrylic or methacrylic polymer, a vinyl resin, an alkyd resin, a polycarbot nate resin, a poly ethylene resin or a polyester resin.
10. An electrophotographic imaging member, substantially as described with reference to, and as schematically illustrated in, Fig. 3 of the accompanying drawings.
11. An electrophotographic imaging member, substantially as described in any one of the foregoing Examples I, IV and V.
12. An electrophotographic process, comprising: (a) charging an imaging member in accordance with any one of claims 1 to 11 so as to provide a uniform charge of a first polarity on the upper surface of the imaging member and a uniform charge of a second polarity (opposite to said first polarity) at the surface of said layer of electric charge transferring material which is remote from said layer of amorphous selenium/tellurium alloy; (b) uniformly exposing said imaging member to activating radiation so as to allow charge of said second polarity to move through the imaging member to the surface of said transparent insulating layer which is adjacent said boundary layer; ; (c) re-charging said imaging member so as to provide a uniform charge of said first polarity at the surface of said layer of electric charge transferring material which is remote from said layer of amorphous selenium/tellurium alloy; and (d) exposing said imaging member to an imagewise pattern of actinic electromagnetic radiation so as to form an electro static latent image.