DE2027323A1 - Electrophotographic plate and imaging method using it - Google Patents

Description

Patent attorneys Dipl.-Ing. R Weickmann, 2Ö27323

DlPLi-lNG. H. Weickmann, D1PL.-PMYS. Dr. K. iPiisrcKE

DiPL.-lNG. R A.WfiiCKMANNj Dipl.-CHEM. B. HuBER

S MUNICH 86, DEN

PO Box 860 820

MOHLSTRASSE 22, NUMBER 48 3 $ 2ί / 22

XEROX COEIORAiION

Rochester * New York 14603, V. St. A.

Electrophotographic plate and utilizing same - Fig il manure traverse en

The invention is generally in the field of electrophotography more particularly, it relates to an improved electrophotographic plate and method for using such a plate as an imaging device.

It is common practice in the field of electrophotography * to generate an electrostatic image by first uniformly electrical on the surface of a photoconductor part Charge is distributed and that then the surface of an activating radiation corresponding to a desired image is exposed. One containing a photoconductive insulating layer electrophotographic plate is in particular initially evenly charged electrostatically in order to be on its Surface to become sensitive * Then the plate in question becomes an image-wise distributed activating electromagnetic Exposed to radiation, such as light radiation, X-ray

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. radiation or the like radiation, which selectively dissipates the charge in the "exposed". ¹ regions of the photoieitenden insulator is derived, while in the "non-exposed" areas of an electrostatic latent image remains, The latent electrostatic image can then be developed and visualized 'are by depositing finely divided electroscopic markings on the surface of the insulating layer * This concept is

f ..

originally described in US Pat. No. 2,297,691; it is further elaborated in many other patents.

The discovery of the photoconductive insulating properties of high purity vitreous selenium has led to this Material the standard material for reusable commercial electrophotographic plates has become * Others Types of electrophotographic plates are known; they contain e.g. paper with a photoconductive layer is coated with zinc oxide particles contained in an insulating resin forming a film. Vitreous selenium However, electrophotographic plates containing electrophotographic plates are still most commonly used because of their electrostatic charge Be able to hold on for long periods of time when not exposed to light. Another reason for that Use of such an electrophotographic plateii exists in that they are relatively photosensitive compared to other electrophotographic plates. Another iiöcfa Reason for using such electrophotographic Plates consists in the fact that they are suitable for reuse are persistent many hundreds of times, or even deodorizing times. However, the plate containing vitreous selenium shows a Somewhat limited spectral value receives eil * The spectral behavior is in fact very strong in the blue or near ultraviolet range of the spectrum limited * An improvement

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the photosensitivity to longer wavelength light of vitreous selenium is described in US Pat. No. 2,803,542. In this patent specification is
stated that the addition of arsenic to selenium causes a general increase in the photosensitivity of the electronhotographic plate and also that of the plate to light
sensitive to longer wavelengths. Another one
The experiment is known from US Pat. No. 3,312,54-8. In
this patent describes the addition of halogens to arsenic-selenium alloys. This leads to an improved spectral sensitivity of the light receiving layer.

Although the electrophotographic processes and apparatus employing plates containing selenium doped with halogen have produced highly satisfactory results
it should be recognized that the doped vitreous selenium layers, when used as individual layers, are far from ideal in terms of the electrical properties of the dark decay and the
Residual potential. The dark decay is the electrophotographic plate's own phenomenon, which, accordingly, in the absence of light, a loss of supposed surface tension occurs. If this property is measured per side unit, it is called the dark decay rate. This value represents an effective measure of the retention of the latent electrostatic image by the respective plate. A high discharge rate thus indicates that a plate is exhausted, ie the latent charge image is quickly discharged. The residual stress is the stress remaining on the plate after exposure by means of an exposure
an erase lamp in a conventional electrophotographic cycle using a reusable electrophotographic plate. Will be a sensitive one

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BATH ORIGINAL

In particular, if the electrophotographic plate is exposed, the electrical potential experiences a rapid initial drop, followed by a relatively slow drop. The plate voltage at the point beyond which no further light discharge occurs is referred to as the residual voltage or residual potential. This potential can vary between zero and a value that is $ 20 or $ 30 of the original potential. A low residual potential is a desirable property of electrophotographic plates because of the greater voltage contrast that can be achieved between the background and the dark areas of the copy Copy to put on.

A plate with ideal electrical properties would be a have a low dark discharge and a low residual potential. A plate with low residual potential is always for the achievement of a satisfactory tension contrast is desirable. In practice, however, it has proven difficult to produce a photoconductive material exhibiting the aforementioned electrical properties.

Obtaining the aforementioned desirable electrical properties is even more difficult in view of Plates for commercial use in high speed machines. Because of the fast rotating machines The speed used means that there is insufficient time for the photo-effect holes in the photoreceptor available to be neutralized. As a result, the phenomenon of build-up of the residual potential occurs with each cycle or the build-up of a positive residue on «As a result, the exposed areas of the plate are not able to effectively, discharge, and the apparent surface tension in the exposed

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Area increases with each cycle.

It has been found that when a vitreous selenium photoreceptor is doped with a halogen at a concentration of about 2 × 10 # in bulk, it has been found to be extraordinarily effective in controlling the residual stress that builds up under moderate velocity or circulation conditions. If a halogen above 2 10 % is used, the entire residual potential can also be reduced to zero. It has also been found that in the Pail that the halogen concentration is greater than is necessary for reducing the build-up of the residual potential, ie over 2 × 10 ", the light occurring on the surface of the photoreceptor in the vitreous selenium conductivity areas with the following higher dark discharge values. These values result in a persistent electrical conduction condition known as "exhaustion" after a number of cycles Contains a halogen-doped selenium layer, an effect called "ghost" can be observed, which is formed by a positive residual image, which means that the previous image remains on the plate and that, when recharged, the image in question comes second in subsequent duplication runs or another picture appears again. An explanation for this phenomenon can be found in de r The fact that the background areas of the plate are depleted at a point where, upon recharge, the background areas dissipate the charge. This leaves a potential for contrast with the darkened copy areas of the plate.

Although it is possible to use halogen doping to reduce the residual potential in an amount of up to about 2 χ AQ ~%

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to regulate and still a minimal dark discharge speed to maintain them in machines of medium rotational speeds brings the build-up of the residual potential of such a doped photoreceptor, however, an increase in rotational speed is associated with it. Therefore, the sensitivity decreases a doped plate with increasing rotational speed. This means that the plate's ability to to contrast objects having a weak density decreases with increasing rotational speed. It exists thus the requirement for modern, fast-working copying machines in which a selenium plate doped with halogen is used to use a heavily doped plate, which is a low even under high speed conditions has building up residual potential.

The invention is accordingly based on the object of providing a new, halogen-doped electrophotographic plate that has a relatively low sest potential and that exhibits minimal ghost effect. The new one to be created electrophotographic plate is said to be distinguished by improved physical and electrical properties. Further It is intended to provide a system using an electrophotographic plate which is a glass-like plate doped with halogen Contains selenium layer, which is characterized by improved light-depletion properties. After all, supposed to the electrophotographic plate to be newly created has a minimum of residual potential.

The above object is achieved by producing an electrophotographic plate having a double coated photoconductive segment, the one lower transport slide is made of vitreous selenium, which with is doped with a halogen, and contains a relatively thin cover layer, which consists of undoped vitreous selenium.

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The halogen concentration in the lower transport layer is between 6 χ 10 " % and 1 $... ·

The invention is explained below with reference to drawings explained in more detail using an exemplary embodiment. Fig. 1 shows schematically in a sectional view an embodiment an electrophotographic hat used to illustrate the present invention. Fig. 2 and 3 show characteristic discharge curves for doped vitreous selenium at different circulation speeds.

Fig. 4- shows discharge curves for one doped with halogen vitreous selenium and a plate containing this covering vitreous selenium according to the invention.

In Fig. 1 is an embodiment of an improved electrophotographic Plate 10 according to the invention shown. With a carrier layer or a mechanical carrier is referred to. The carrier layer can contain a metal, such as brass, aluminum, gold, platinum, steel or the like. It can be of any suitable thickness, strength or flexibility and in the form of a sheet, sheet, cylinder Or the like. Be present and coated with a thin layer of plastic. The carrier layer can also contain other materials included, like metallized paper, with a thin Aluminum or copper iodide coated plastic sheets or glass coated with a thin layer of chromium or tin oxide. It is generally preferred that the support part is somewhat electrically conductive or has a somewhat conductive surface and that it is stable enough to a to allow certain handling. In certain cases, however, the carrier 11 does not need to be conductive or it can be entirely can be omitted.

209808/1545 _B AD ORIGINAL

With a storage layer 12 is referred to, which contains highly pure vitreous selenium, which is heavily doped with a halogen, such as chlorine, fluorine, bromine or iodine. The halogen is present in relatively large quantities, which are in the order of 10 '%. Concentrations are between about 60 χ 10 ~ ° /> to 1 $ preferred for the purposes of the invention, an effective doped layer of vitreous selenium to As already stated above, a doping amount below 2 10 "% leads to the build-up of a residual potential at high circulation speeds, while concentrations above 1 $ are unnecessary in order to achieve the electrical properties desired in the case of the invention.

The storage layer 12 can be of any suitable thickness can be used for conventional photoconductor layers. Typical Thickness ranges are between about 20 and 200 microns. A range between about 40 and 80 microns is preferred since thicknesses within this range are generally in conventional electrophotographic machines can be used.

The layer 12 is overlaid by a control layer 13, which is undoped vitreous selenium in a thickness contains between about 5 and 20 microns. Thicknesses below about 5 microns do not allow the strong dark discharge properties the highly halogenated vitreous selenium transport layer, while thicknesses over 20 microns die Cover the lower transport layer so that the selenium doped with chlorine no longer acts as a low residual photoreceptor.

It should thus be seen that the photoconductive part of the plate according to FIG. 1 is divided into two functional layers is in

1) a heavily doped transport or transfer layer, which during the rapid circular discharge the build-up of a

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prevents positive residual charge and thus ensures a charge contrast, and in

2) a control layer overlying this layer of more than 5 microns thick, which is the highly halogenated Layer shields from harmful radiation and thus prevents an excessively strong dark discharge in the layer doped with a halogen.

Fig. 2 clearly shows the effect of increasing speed depending on the residual potential on an individual Layer of vitreous selenium with moderate amounts of halogen shown. Here, the developing residual potential became one single layer photoreceptor containing vitreous selenium with 2 χ 10 "^ chlorine dopant measured in that an exposure - with the help of a cold white light emitting fluorescent lamp was made, namely with an oxidized aluminum support layer in the form of a cylindrical Drum with a diameter of about 12 cm and a length of about 26 cm, this drum rotating with 5 »20 or 50 revolutions rotated per minute. The residual potential was measured after the plate reaches its maximum residual potential value had what generally after 30 to 40 cycles or revolutions was the case. The exposure values ranged from 0.32 to 320 lux sec (corresponding to 0.03 up to 30 foot candle seconds). From Fig. 2 should be apparent be that a concentration of 2 χ 10 "^ chlorine at a drum speed of 5 revolutions per minute is sufficient to prevent the selenium layer from reaching a maximum residual potential allow. This means that after an exposure of about 20.1 lux sec (corresponding to 1.87 foot candle seconds) there is no apparent tension. Slows down However, as the drum advances, this leads to the development of a maximum residual potential which increases as the speed increases from 20 revolutions per minute to 50 revolutions per minute

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Minute is increased. The consequence of this is that at higher speeds a reduced contrast potential, for one, A given amount of light is present or, in other words, a decrease in sensitivity becomes apparent in the effectiveness of copying areas of low density can. . . ,.

In contrast, Fig. 3 graphically shows the advantages of Use of a heavily doped, vitreous selenium-containing photoreceptor plate at high speed working machines. Here, the residual potential of a vitreous selenium containing single-layer photoreceptor,

-2

which contains i -10 chlorine by discharging at speeds of 5 »20 or 50 revolutions per minute in the same Measured manner, as it has been explained in connection with FIG. It should be obvious that that the discharge leads to a complete dissipation of the surface charge at any speed and is thus effective Prevents build-up of residual potential. The curves of Fig. 3 clearly show the usefulness of the heavily doped photoreceptor in fast rotating machines.

In Fig. 4 are the effects of the coating of the invention on the discharge properties of a heavily doped, vitreous Selenium containing layer illustrated. Here are the discharge properties a vitreous selenium containing monolayer, which is doped with 6 χ .1CL ^ LChlor, with the discharge properties the same single or monolayer compared to a 5 micron thick layer of a selenium according to FIG Invention is overdone. From Fig. 4- it follows that the Selenium coating does not affect the discharge properties to a large extent:. has changed. This shows that the selenium coating is the Sensitivity of heavily doped vitreous selenium photo; receptors not adversely affected. % *

For the production of electrophotographic plates according to Invention can be used selenium, which the Canadian company

2 0 9 8 0 8/1 5 k 5.

Copper Itefiners is a supplier for the supply of pre-doped selenium. If desired, the selenium can through. Using any conventional laboratory procedure as by physically mixing the dopant with the selenium and by vapor deposition of the mixture on the conductive support. Bromine can be found in selenium In the form of liquid droplets, the is preselected. This allows chlorine and fluorine to be added be that chlorine or fluorine gas is introduced into an evacuated tube in which pre-cooled selenium is located. The gas flow is maintained as long as until the selenium contains the desired amount of doping. Suitable doping methods, such as the doping methods listed above, which can be used herein are set forth in U.S. Patent 3,312,5-8. It should also be pointed out, that the halogen to selenium in the form of a compound with selenium or with other compounds such as silver halogens can be added. .

To illustrate the dark discharge properties of heavily doped plates, two halogen-doped cover plates were made from vitreous selenium. Any plate contains a 50 micron thick photoresceptor layer vitreous selenium doped with halogen. The panels are

- • 5 <doped with chlorine in a concentration of 6.6 χ 10 ^y %.

In an embodiment illustrative of the invention is the plate H with a 5 micron thick layer of not coated with doped selenium.

The doped plates are then tested for their dark discharge rate to measure, under conditions of rest and under conditions of exhaustion. Both Plates were left overnight and in the form of a

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cylindrical drum on one made of aluminum fixed test arrangement. The cylindrical drum had a diameter of about 12 cm and one Length of approximately 26 cm (corresponding to 4.75 inches by 10.2 inches). For the determination of the dark discharge values in the recovered State, the plate was charged to an initial potential of 800 volts. A double corona charging device is used for this purpose. The dark discharge rate was measured at 4, 10 and $ 0 second intervals. To determine The correspondingly arranged plates were emitting the exhaustion values by means of a cold white light Fluorescent lamp exposed for five cycles or revolutions with 16,700 lux sec (corresponding to 1550 foot Candle seconds). The exhausted plates were then charged to 800 volts on the sixth cycle, and then the dark decay values were measured in the same way, as described above with respect to the recovered disks. The results are summarized in the table below.

Tabel Dark discharge values

recovered disk exhausted disk

4 sec. 10 sec. 30 sec. 4 sec. 10 sec. 30 sec.

Plate I $ 4 10 # 2Λ% 8 # $ 18 $ 38

(vitreous selenium

^with 6.6 χ 10 " ³ # chlorine)

Plate II 4 # 8.5 # 19 $ 5% 11 $ 22 $

(vitreous selenium

with 6.6 χ 10 ~ ⁵ # chlorine
and one overlying 5 microns thick
Layer of selenium that
is not halogenated)

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A review of the dark discharge values in the above Table reveals the following: In accordance with the above statements with regard to heavily doped photoreceptors, omitted glass-like selenium, it can first be established that plate I shows a noticeable increase in the dark discharge speed is present when one passes from the state of recovery to the state of exhaustion. Second, it can be seen that the difference between the recovered and the exhausted Plates reduced by the application of the sieve coating as indicated by the values of plate II. The difference in discharge values between the recovered and the exhausted plates is responsible for training the positive Responsible for the residual image, i.e. for the formation of ice on the uncoated, heavily doped plate. This is likely be understandable when one takes into account that when measuring the recovered plate, the dark discharge of the copy or the dark areas of a copy are actually measured while dark discharging an exhausted plate effectively measuring the value of the background of a copy. It is therefore a sufficiently high percentage difference exists between these values, then with recharging there will be such a contrast potential that a copy reproduction or a ghost occurs when the plate is being developed.

To illustrate the effectiveness of the selenium coating two examples below considered in more detail * _

Beis_p_iel__I

An oxidized aluminum drum about 12 cm in diameter and about 26 cm in length (4.75 "and 10.2" respectively) and with an arsenic-selenium light receiving layer that is about 6.6 χ 10 ^ ψ » chlorine contains, was

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and put into a Xerox 813 office copier used. An ON-OFF switch is switched on and off in conjunction with a white light emitting lamp. and the pre-cleaning corona charger and erase lamp were turned off. After the drum is over After recovering overnight, three exposures were made and the exposure lamp was then turned off. When circulating without using the exposure lamp, a ghost or a ghost image of the original copy. This indicated that the background areas had become permanently conductive and thus contrasted with the dark areas of the copy. .

Example II

The same drum was then coated with a 5 micron thick layer of pure, non-doped selenium, and 'the above test was repeated. The copy obtained then showed no ghost after the exposure lamp was turned off. This indicated that the pure selenium coating prevented the contrast between the background and the dark areas of the copy.

The panels of the invention can be made by any method the known conventional processes, as described in US Pat. No. 2,803,542, 2,822,300 and 3,312,548 are described. Such procedures briefly involve preparing a suitable mixture of selenium, arsenic and a halogen in a container and allowing these elements to react at elevated temperatures. The finally obtained alloy is then cooled and vacuum evaporation onto a suitable conductive material Carrier base plate applied.

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" ^Λ3 " 2027523

In a corresponding way, the transport or Transfer layer onto the conductive carrier layer Vapor deposition using any conventional technique such as disclosed in U.S. Patents 2,753,278 and 2,970,906, among others is described. If desired, the transport b-zw can be used. Transfer layer as well as the control layer one after the other be evaporated without breaking the vacuum. In this way the possible risk of contamination of the surface of the plate is avoided.

Although in the course of the above statements of the preferred embodiments special components of the coated electrophotographic plate containing high chlorinated selenium and ratios have been given, it should be noted that suitable materials other than those listed above are also suitable can be used with corresponding results. In addition, other materials, such as sensitizers, can additionally be used to increase the properties of the new plate according to the invention, synergistically to change or otherwise modify.

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BATH

Claims (8)

Claims Electrophotographic plate containing a photoconductive segment consisting of two superimposed layers, characterized in that one layer (12) of the photoconductive segment (10) consists of glass-like selenium doped with a halogen and that the other layer (13) is undoped, almost pure contains vitreous selenium at a thickness of at least about 5 microns. 2. Plate according to claim 1, characterized in that the halogen is present in a concentration between about 6 χ 10 " % and 1 $. 3. Plate according to claim 1 or 2, characterized in that that said other layer (13) has a thickness between about 5 microns and 20 microns. 4. Plate according to one of claims 1 to 3, characterized in that that the halogen contains chlorine. 5. Plate according to claim 4-, characterized in that the chlorine-doped, vitreous selenium-containing layer (12) has a thickness between about 20 and 200 microns. 6. Plate according to one of claims 1 to 3, characterized in that that said one layer (12) has a thickness between about 40 and 80 microns. 7. Plate according to one of claims 1 to 6, characterized in that that a conductive carrier layer (11) is provided which carries the first layer (12) and above this the second layer (13). 209808/1545 8. Imaging process using an electrophotographic Plate according to one of Claims 1 to 7 *, characterized in that an electrostatic Image is generated and that this image is developed for visualization. 9 »Method according to claim 8, characterized in that the latent image is formed by the surface of the plate is initially evenly charged and then exposed to an image-wise distributed activating radiation « 0 9 8 0 8/1545 • Blank page