JPH0337181B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an electrophotographic recording material and a method for producing the same. One very important use of photoconductive materials is in electrophotographic techniques to create and develop electrostatic images. Electrophotographic members and their manufacture and uses are also encompassed by this invention. The coating of the present invention has a wide range of applications.
The most well-known application is in electrostatic technology, where an electrophotographic member is uniformly charged in the dark and then exposed to light by directing light from an object onto the charged member to selectively remove the charge. The image is then dissipated or discharged, developed by applying charged particles to the formed electrostatic latent image of the object, and further processed. Other processes are for retaining the developed image of the object by transferring it to a carrier or by fixing the developed image on an electrophotographic member. Both processes are better known as xerox and facsimile, respectively. Basic techniques, ie, charging, exposure, development, and other processing, can be performed using the electrophotographic members of this invention having as part of the photoconductive coatings of this invention. The electrophotographic member of the present invention differs in composition from known electrophotographic members, and its performance is significantly superior to that of known electrophotographic members. The electrophotographic members of the present invention are characterized by high speed, high field strength, high photoelectric gain, ability to achieve infinite gray scale, absence of residual charge upon discharge, absence of fatigue, low cost, durability, high Conventional or different in resolution and panchromaticity. When deposited on a polyester or other stable plastic sheet substrate, it is highly flexible and transparent to the extent that the image formed can be projected exposed. When processed in the same manner as photographic film, ie using the same conditions of light and exposure, the electrophotographic film of this invention is superior to photographic film. The reason for this is that it has a natural memory, has high resolution, images can be added to it, and the film can be reused without post-development processing. The films are made in ambient light from readily available materials and handled and stored without the care required for halogenated films. The film is manufactured without using rare metals such as silver. The present invention is useful in almost any field where photoconductive materials can be used, including their high quantum gain, their anisotropy, their flexibility (when deposited on a flexible substrate), their transparency, etc. It is more advantageous depending on the gender. The primary material making up the photoconductive coating of the present invention is cadmium sulfide, which is deposited by a sputtering process using radio frequency energy. Cadmium sulfide has been known as a photoconductive material for many years, and there is an extensive literature on work done on this and similar materials. As far as I know,
Prior art techniques have not been successful in achieving the coatings of the present invention and obtaining the advantages and benefits detailed herein. Further, to the best of our knowledge, coatings having the characteristics of the present invention have not been used on electrophotographic members. Some of the conventional photoconductive coatings used specifically in electrophotography are zinc oxide and polyvinyl carbazole. Selenium is used in amorphous form, is soft and easily wears out. High voltages are required for charging, and once charged they have a surface voltage on the order of 600 volts, i.e., this voltage is about 20 times the voltage achieved on the surface of the coating of the electrophotographic members of the present invention. . Despite this, the electric field strength, expressed in voltage V/cm per thickness, is significantly lower than that achieved in the present invention.
Selenium has a higher noise voltage than the surface potential of the charged coating of the present invention. It has a residual charge, is fatigued, and its gain is very low, resulting in low photosensitivity. Zinc oxide is used in the binder matrix. It is conductive and also adheres to paper at low speeds. It is soft, does not form high resolution images, and is practically opaque when used. Polyvinylcarbazole is an organic material that is subordinate to all special organic compounds; it is unstable, has low photosensitivity, is soft, is not transparent, has limited spectral response, etc. The coatings of the present invention include cadmium sulfide or other materials as described herein, but cadmium sulfide is preferred, and are deposited as a generally sputtered inorganic deposited layer on several types of substrates to provide the following physical, electrical and chemical properties. Characteristics: 1 Single crystal, the crystal has a hexagonal morphology and uniformity commensurate with the single crystal deposit, with a diameter of 700-800 Å
The degree and length should be approximately 1000 ~ to get the best results.
It can be in the range of 10,000 Å, is formulated nearly perpendicular to the substrate, and has nearly perfect stoichiometry. 2. Transparent enough to allow 70-85% of visible light to pass through in a suitable manner. 3 The electrical structure consists of a deep trapping surface layer (see 6) that traps electrons when charged, a depletion layer that extends over the entire residual volume of the coating, and a depletion layer that is substantially smaller than the lifetime of the electron and thus The electric field maintains the transit time for the electron motion during the carrier's movement, and the region of positive energy states near the deep trap promotes secondary bombardment and additional electrons during the discharge. 4 Panchromatic over the visible range to a greater extent than unsensitized photographic film or any known electrophotographic material due to the occurrence of traps in the internal microcrystalline structure as far as cadmium sulphide is concerned when charged. Other materials have superior spectral responses at some wavelengths that are accentuated by specific compounds. 5 has a quantum efficiency greater than unity for most of the visible spectrum that is easily amplified by doping. 6 Having a barrier layer on the surface that gives a lateral surface resistivity of the order of 10 ²⁰ Ω/□ due to the orientation of the molecules during deposition using external sulfur atoms that are used to combine with the background gas to form an oxygen-containing compound. . This barrier layer has deep traps in the sense that there are negative surface states that bind strongly and are not easily released when charged. The barrier layer is therefore negative in character and the coating layer below it is positive because it is depleted of negative carriers, the degree of depletion being minimal just above the ohmic resistance layer and therefore slightly positive here. Become. The thicker the coating, the less positive the layer directly above the ohmic resistive layer. 7. Inert to moisture, normal temperature changes and most radiation, almost completely dense, with high abrasion resistance and glass-like hardness and an extremely smooth surface. 8 Although it is an N-type semiconductor material, it has an NPN structure (see 3 above), and has electrical anisotropy to accept and maintain high-speed charges at gradation levels, and has a gradation level of 1000 line pairs (cycles)/mm. High definition can be achieved. 9 When charged, it has a dark resistivity of the order of 10 ¹⁴ Ωcm and a dark-to-light resistivity ratio of at least about 10 ⁶ , but the surface resistance when charged or uncharged, both in light and in the dark. There is almost no change in resistivity, and the electron anisotropy related to 8 above is obtained. 10 The discharge is complete and practically free of all residual charge, persistent photoconductivity, fatigue, edge effects and lack of interaction. The electrophotographic members of the present invention include a coating of a suitable cadmium sulfide as described above on an approximately 100-500 Å thick layer of an ohmic resistive material such as tin-indium oxide, which is transparent and coated with a polyester resin on the order of 1 mm thick. or other stable plastic sheet substrate, preferably with an ohmic resistive layer and a 30 Å
or a thinner substrate with an intervening bonding layer of the same material as the coating. In the preferred form this is cadmium sulphide. In addition to the above-mentioned properties for coatings, this electrophotographic member has the following properties: 1. 12.7 mm without cracking or flaking.
(2/1") or less in diameter. 2. Transparent to the same extent as the coating. 3. Can be used in transfer methods or fused to a surface. 4 The width is limited by the size of the sputtering machine, but can be manufactured in practically unlimited lengths. Typically about 51 mm. ~76 cm (20-30 inch) rolls can be coated in a continuous process. Coatings as thin as 1000 Å can be copied using extremely bright light and long toning times to achieve certain objectives at the expense of some advantages. The method of depositing cadmium sulfide or other materials in the present invention consists of the following steps or processes carried out under the conditions described: 1. Roll feeder and winding of the substrate in a low pressure vessel. A device is installed to continuously move and heat the substrate,
The layer is softened and deposited in a continuous manner simultaneously with the coating, but without destruction, by slightly shrinking and preventing wrinkles. 2 The gas mixture during sprinkling in the vacuum chamber is argon to supply bombarded ions, hydrogen sulfide to maintain the correct deposition stoichiometry, and to control and promote the presence of a barrier layer on the surface of the deposition. There is a small amount of oxygen for 3 Sputtering is carried out using radio frequency (RF) energy, the anode having an insulating drum with a shield, the substrate passed over this drum, the target consisting of pure cadmium sulfide or other materials as exemplified, and the cathode having an insulating drum with a shield. and in all cases the shield is at ground and the cathode is maintained at a voltage substantially below ground. 4 The anode is held at a slightly lower voltage than ground, so there is actually a negative voltage bias between the anode and ground. This bias need not be more than about 10 volts negative and no more than about 50 volts positive. The voltage at the cathode with respect to ground in a typical device is about 1800 to 2000 volts of negative DC, which is caused by the action of a diode. 5. Under the above conditions, a second dark region exists between the sputtered plasma and the anode, engages the anode, and performs sputtering during this period through the substrate. This is in addition to the first dark region at the cathode, the latter known as the Kurtchus' dark region, and the second dark region recognized as the Langmiur probe at the crosslink. The prior art of electrophotographic materials primarily surrounds two major technologies: electrofaxing and xerography. In both cases, quality, resolution and reproduction accuracy are compromised to some extent due to the physical properties of the coating, the substrate on which it is deposited, and the carrier for transferring the image, for example. These defects are other than those inherent in the nature of the coating. Apart from the electrical point of view, in terms of quality and resolution, the surfaces of known photoconductive coatings are relatively rough, consisting of grains, pits, etc. This can be easily seen by comparing the surface of the coating of the present invention with the surface of a zinc oxide and selenium member under a microscope, for example. The coating of the invention has a surface that only appears as consisting of microcrystals when viewed under an electron microscope. Irregularities in conventional coatings are manifested by microscopic protrusions, depressions, granules, etc. that are hundreds, and even typically thousands of times larger, than the smallest protrusions of the coating of the present invention. Toner particles are generally nearly perfect spheres, with diameters on the order of a few microns. When fused onto a perfectly flat surface, the toner particles melt into a perfect disk and form a perfect spot. This is what happens on the surface of the coating of the present invention. When toner particles are melted on a conventional surface,
That is, when toner particles move to a rough surface and melt,
The toner particles flow and melt into irregular or amorphous spots. A perfectly formed spot gives a better image than an irregularly shaped spot. Plastic sheet substrates are not inherently dimensionally stable as they sag, stretch, and deform under stress or changing temperature and humidity conditions. Therefore, it is not expected to image accurately or maintain exactly what is to be reproduced. It is believed that the belt or tensioning member of the electrophotographic material is deformed. Since in the present invention sputtering occurs while the substrate is shrinking, the resulting deposit of microcrystals is under compressive stress, has high strength and has an intact shape. It is therefore dimensionally stable even when exposed to moisture, heat and strain. The invention will now be explained with reference to the drawings. As previously mentioned, the present invention relates to coatings, electrophotographic members made using the coatings, and methods of applying the coatings.
The coating is photoconductive and is useful in all applications of photoconductive materials other than electrophotographic members. FIG. 1 shows an enlarged dimensional representation of an electrophotographic member having a coating of the present invention. The entire electrophotographic member is indicated at 10. The member 10 consists of three basic parts: a substrate 12, an ohmic resistive layer 14, and a photoconductive coating 16. The substrate is preferably a transparent polyester film having a thickness of approximately 0.13 mm (0.005"). The material is an organic polymer of good industrial grade quality, having a uniform thickness, and a smooth surface. An example is Mylar (manufactured by DuPont, USA, trade name).Ohmic resistance layer 14 is a conductive deposited layer, preferably formed by the same sputtering method as coating 16; The preferred layer 14 is formed of pure grade semiconducting indium oxide alone or a mixture of indium oxide and pure tin oxide in small amounts, the ratio of the two being generally about 9 Its thickness is approximately 100-300 Å. The coating 16 is made of pure or doped cadmium sulfide (CdS).
Then, this cadmium sulfide is sputtered onto the ohmic resistance layer 14 to a certain thickness. This thickness is about 2000 ~
Preferably it is 6500 Å. Depending on the sedimentary layer
It can be made as thick as 2000 Å or less, or about 2 μ. As can be seen from the graph in FIG. 7, the properties vary to some extent with different thicknesses. This will be discussed later. Two other layers are shown in FIG. These layers are a bonding layer 18 and a surface barrier layer 20. Bonding layer 18 is for the purpose of ensuring adhesion of ohmic resistive layer 14 to the surface of substrate 12, and is preferably a very thin layer of cadmium sulfide sputtered onto the substrate. The thickness of this layer is not easily measured even by interferometric techniques. The layer is estimated to be in the range of 10-50 Å. Layer 18 is deposited by operating the sputtering machine in the same manner as used to deposit photoconductive coating 16, except that the bonding layer 18 is deposited by operating the sputtering machine at high speed. Make sure that there is a "please" in the layer. This deposited layer is so thin and transparent that it cannot be easily seen. Although the electrophotographic member 10 can be made without this layer 18, variations in the many parameters involved during the sputtering process often result in slight imbalances, etc., which cause the deposition of the ohmic resistive layer 14 to the substrate 12 in areas. make it unreliable. Bonding layer 18
provides reliable adhesion for industrial manufacturing. Barrier layer 20 is also so thin that its thickness cannot be easily ascertained. Its composition is also not well known or understood, but its existence was demonstrated by removal by ion bombardment experiments. The thickness is estimated to be 20-50 Å. Its composition is an oxide of sulfur, and in the case of cadmium sulfide, it is thought to be in the form of a combination with cadmium. In the deposition of coating 16 the topmost atoms are
It is sulfur that readily combines with oxygen, at least when oxygen is helpful toward completion of the deposition. FIG. 2 shows the structure of the coating 16 and the coating 16 with a few layers and the ohmic resistance layer 1.
FIG. 4 is an enlarged partial cross-sectional view of FIG. The illustrated structure is based on direct and indirect measurements and tests performed on the electrophotographic member 10. This depends on the logic of the operation described below. Substrate 12, bonding layer 18 and ohmic resistance layer 14
is shown diagrammatically. The coating 16 is shown to be comprised of microcrystalline or microscopic crystals 22, the vertical dimension T (longitudinal) of the crystals being the same as the thickness of the coating, and therefore a typical preferred coating.
It is about 3500Å. The crystals are hexagonal, as determined from crystallographic studies, and have a diameter L (lateral) of the order of 700-800 Å. The crystals are densely packed in crystallographic terms and vertically oriented as confirmed by X-ray diffraction measurements. The exposed tips of the crystallites are surrounded, as shown at 24, and these tips provide a smooth, hard, glass-like surface that is significantly more abrasion resistant compared to known electrophotographic members. Attempts to abrade the surface using bladed instruments will cause the surface to withstand such attempts and behave similarly to glass, while zinc oxide and selenium components are easily scratched. The tip is microscopic, related to the size of the toner particles, and the surface is considered to be extremely smooth. The area of the crystal tip is 1/30 of the toner particle with a diameter of 2 microns. It is believed that each tip 24 has an electric field independent of the others when the coating is charged and acts to prevent charge transfer between the tips of the surface. This will be discussed below regarding the logic of operation. The crystallites consist of platelets or tiny fragments 26 of approximately 65 angstroms, approximately 50 in each crystallite.
There is some degree of stacking of platelets, with slight irregularities in such stacking. This is believed to establish a number of depletion conditions throughout the microcrystal that increase the panchromaticity. Barrier layer 20 provides an extremely high surface resistance to prevent charge migration and, in combination with the action of the microcrystalline tips as a more independent field, provides extremely high resolution. When the coating is charged, the layer 20
It has high energy surface states. This effect is so strong that the boundaries or interfaces between crystallites are not important to the electrical properties of the film. FIG. 3 sequentially shows, from left to right, various steps performed when using the electrophotographic member for image formation.
In the diagram on the left labeled Step No. 1, the corona supply source 28 is connected to the corona wire 30, and negative ions are supplied from the corona wire 30 to the surface of the electrophotographic member 10 to charge it, and the surface potential is approximately Increase to 30-40 volts. The ohmic resistive layer 14 and the corona source are connected in any suitable manner, either directly by wire 32 or by some type of contact. This process is done in the dark. Corona source 28 applies a DC voltage of 5000 to 7000 volts across the air between corona wire 30 and xerographic member 10. As a result of the charging process, the surface 20 of the electrophotographic member 10
is uniformly charged with a negative charge, and this negative charge is about 30~
Reaches a DC voltage of 50 volts. Such charge may be present on the outermost plane of barrier layer 20 of coating 16, but may be below the outermost plane, but all such charge is present within barrier layer 20 anyway. There is no charge in the body. These charges are tightly bound to energy states that do not easily collapse. Therefore, surface 2
It has been found that a neutral material such as paper or a mechanical roller can be brought into contact with the surface 20 and the surface 20 will lose its charge. For convenience, the surface charge is 30 volts and the thickness is 3000 Å.
Then, the electric field strength across the material created by the charge is approximately 1,000,000 volts/cm ² . For example,
This can be compared to the charge on selenium; for a thickness of 60 microns, the charge on selenium results in a surface voltage of about 600 volts, which represents an electric field strength of about 10,000 volts/cm ² . The second step, indicated as step No. 2 in FIG. 3, is called "exposure." In this part of the process, the electrophotographic member, which has been uniformly charged in the dark, is exposed immediately after charging to an object to be projected with light. This object is indicated at 34 in FIG. 3 and is illuminated by a suitable light source, not shown. The object 34 is moved to a suitable optical device 3
6 onto the charged surface. The applied uniform surface charge disappears selectively depending on the degree of irradiation of the projected image. This results in selective discharge, creating a double latent image on the electrophotographic member 10, where the increments present in the darkest areas of the projected image have the smallest discharge and the increments present in the lightest areas of the projected image have a double latent image. ment shows maximum discharge. A charged latent image is thus formed. The next step in the process is called "development" and is shown as step number 3 in FIG. In currently known electrostatic devices, development is accomplished by depositing charged particles onto a latent image. Such particles are charged by triboelectric action or electrophoresis. For example, if the latent image on electrophotographic member 10 is negative where it contains dark areas and relatively less negative where there are relatively bright areas, then if the deposited particles are positive; shows that such particles tend to adhere to negatively charged increments and not to uncharged increments. In this way a visible image can be obtained. FIG. 3 shows a block 38 labeled "toner supply device." Toner particles fall onto the surface of electrophotographic member 10, as shown at 40, and selectively accumulate, as shown at 42. Toner is made from fine carbon, resin, etc. It is applied as a dry powder or in some cases in an insulating hydrocarbon solvent. Although there are many different types of applicators, block 38 does not represent any special construction. After the toner has been deposited and the latent image has become a visible image, ie, developed, it is further processed in one of two ways. Figure 3 shows process No. 4A and process.
Shows No.4B. Any of these steps may be used. The developed image in step No. 4A is subjected to a flash of light from a heat source, such as a heat lamp 44, to permanently fuse the toner particles to the electrophotographic member 10. After step No. 3, excess toner particles are removed with a brush or washed away with a solvent. In electrophotographic members that have been processed by fixing toner to the surface thereof, the member is typically not reused.
With the present invention, additional images can be superimposed on the toned image by repeating the charging, exposing and toning steps. In the case of electrofaxing, where the electrophotographic element is a sheet of conductive paper with a coating of zinc oxide in a resin matrix, the electrophotographic element is removed from the imaging machine as a finished article. The finished article is highly opaque due to the opacity of the paper and coating. In the case of the electrophotographic member of the present invention, the substrate 12 is preferably a sheet of transparent plastic, such as polyester, and the developed image is fused to produce a projectable transparency. Before the fixing step 4A in FIG. 3, if necessary,
The visible image represented by toner accumulation areas 42 can be mechanically wiped off the surface of the electrophotographic member 10 of the present invention. This member 10 can then be reused. Even if the image is fixed as shown in step 4A, additional images can be added via steps 1, 2 and 3 to the image already fixed in place as described above. In FIG. 3, step 4B shows another step of the above-mentioned process. In step 4B, the unfixed visible image is transferred to a carrier, such as a sheet of paper, by pressing the surface of the sheet of paper, or to an intermediate medium. FIG. 3 shows the latter arrangement. roller 48
A backup roller can be used, which is often a type of offset printing blanket roller. Image area 42 is carried on roller 48 as shown and pressure roll 5
2 onto a piece of paper 50 held on its surface. The exposure and development steps can be performed quite quickly by electronic devices using toner. FIG. 4 shows an apparatus 53 for carrying out the method used to apply the coating 16 and preferably the ohmic resistive layer 14. As described above, bonding layer 18 is also provided by the same apparatus and method. Box 54 of apparatus 53 represents a suitable low pressure vessel of the type used for processes such as sputtering. Mechanical and electrical connections are not shown, but this nature will be apparent from the description below. The following items are placed inside the low pressure container 54: a supply roll 56, a guide roller 5
8. Attach the insulating drum 60, guide roller 62, take-up roll 64, arcuate targets 66 and 68, and shield members 70, 72 and 74.
Although only two guide rollers are shown, 58 and 62, for purposes of illustration, the actual apparatus would include other rollers and guides to achieve the required web movement. Drive motors, clutches, speed controls, etc. are all suitably connected to the shafts of the various rollers, drums, rolls, etc., as required. Although these parts are not shown, they are conveniently located outside the low pressure vessel 54, for example behind the rear wall 76 of the low pressure vessel 54. All shield members are grounded as shown. Shield member 70 is more complex than shown as being mechanically necessary to protect drum 60 and prevent build-up on the drum and to control capacitive coupling between the drum and the ground. Shield members 72 and 74 protect targets 66 and 68 from sputtering plasma returning to their sides and back. Device 53 is supplied with radio frequency energy at a suitable frequency from radio frequency power source 80. A suitable frequency is 13.5 MHz in the United States. Power supply 80 is connected to suitable transmission line and matching network 82
connects to targets 66 and 68 by. The power supply line to the target is shown at 84. drum 6
0 is connected by line 86 to node 88, which is in a voltage-divider relationship to the capacitance between high voltage point 90 and ground. A capacitor 92 and a variable capacitor 94 are provided. Since the voltage from high voltage point 90 to ground is divided by the capacitive reactance of capacitors 92 and 94, node 88 has a portion of the total voltage applied to the drum. This voltage may be indicated by a suitable voltmeter 96, which is connected to line 86 via a high frequency choke 98. The circuit described above is basic and simplified. The reason for this is that it becomes complicated depending on the frequency used.
Therefore, the capacitive reactance caused by the many leakage paths from the target and drum to ground must be taken into account when assembling the device and adjusting for proper operation of the device. The operation of device 53 is in the form of a diode, the gap between the electrodes being that between the cathode (targets 66 and 68) and the anode (drum 60). The cathode is considered to be negative with respect to the anode because current in the form of electrons flows from the cathode to the anode. The voltage of the cathode is a negative DC voltage of approximately 1400 to 2000 volts with respect to earth.
This voltage is formed by rectifying the radio frequency using plasma 108. The voltage at the anode is slightly below ground, ie negative with respect to ground. This latter DC voltage applied to the drum 60 is referred to as a bias voltage.
The concept of bias voltage is important in the method of the invention. The reason for this is that the presence of a bias is essential when sputtering the coating 16. When sputtering coating 16, substrate 12 is bonded to bonding layer 18 and ohmic resistive layer 1.
4, the manufactured long substrate S, which can have a manufactured length of several hundred meters, is wound into a roll and the low pressure container 54 is opened. A roll of manufactured substrate S is placed at position 56 and passed around roller 58, around the bottom of drum 60, around roller 62, and connected to take-up roll 64. The low-pressure container 54 is closed, and the inside thereof is pumped with a suitable pump 1 through the port 100.
Exhaust by 02. Background gas is then introduced from gas source 106 via port 104;
Supply electricity. When conditions are stable, the substrate S is moved around targets 66 and 68. A sputtering plasma is present at this location, which causes target material to be deposited on the exposed surface of the manufactured substrate S. FIG. 5 shows this arrangement. As shown, a sputtering plasma occupies the gap between the electrodes. The actual gap is relatively narrow, only a few centimeters at most. As is well known, when there is a dark area surrounding the target during sputtering, there is a normal dark area called the Kurkus dark area.
Indicated by 0. Due to the presence of the bias described above, a second dark area is formed on the anode or drum 60 and the substrate S
passes through the second dark region in direct contact with this. The second dark region is known in the literature to be referred to as a Langmiur prog, and the second dark region is known to be used in sputtering photoconductive material in a controlled manner in accordance with the present invention. Achieving the above-mentioned properties has hitherto been completely unknown. As mentioned above, the preferred coating material of the present invention is cadmium sulfide. When deposited as described above by radio frequency sputtering using the bias and conditions described above, this material has the properties described below. 1 All coatings are inorganic. The coating 16 is made of cadmium sulfide (CdS) deposited in thin layers as a pure chemical compound. There are no organic substances used to bind, affect sensitivity or total color, or for any other purpose. Therefore, there are no substances to degrade, so the shelf life of the coating is unlimited, limited only by the arcuate nature of the substrate on which it is deposited. Cadmium sulfide in deposited form is not completely soluble in water and is therefore impermeable to water. Cadmium sulfide is inert to temperature changes, from sub-breezing temperature to 200°C.
The polyester substrate on which the cadmium sulfide is deposited first melts at such high temperatures. Cadmium sulfide deposits are impermeable to fungi. Due to the special method used to obtain the deposit, the deposit is produced in almost perfect stoichiometry, so that there is no excess of cadmium or sulfur. This provides chemical and physical stability. Electrical characteristics are also improved. 2 The coating is crystalline, consisting of microscopic crystallites. The crystallinity of the coating is explained with reference to FIG. The crystallites are similar in length to the thickness of the cadmium sulfide coating;
2000 to about 6000 Å. The microcrystals are hexagonal in morphology and consist of stacks of small slopes approximately 700–800 Å wide and 65 Å thick. The microcrystals are oriented perpendicular to the substrate on which they are deposited and are extremely uniform in size. The common nomenclature in crystallography classifies such microcrystals as closely packed.
Additionally, microcrystals exhibit a single crystalline morphology when formed as a coating. 3. The coating is dense and wear resistant. Tests conducted to determine the density of cadmium sulfide coatings have shown that the actual density is very close to the calculated maximum theoretical density possible for cadmium sulfide. This test is performed by removing the coating from the sputtered test, measuring its volume and weight, calculating the density, and then comparing it to the maximum theoretical value calculated from the atomic weight. Representative tests showed that it was 94.8-99% of the maximum theoretical value. Tests performed on the coating include a scratch hardness test using a blade device and the results are compared to known xerographic members such as selenium and zinc oxide members. The scratch resistance of cadmium sulfide deposits is much greater than known electrophotographic members. 4. The coating is almost transparent. The preferred thickness of the coating is 2000-7000Å
It is. As can be seen from the graph in Figure 7, the transmission of visible light through the coating varies between 85% and 70% due to such thickness. The idea is that photons are captured during the exposure,
and the ability to project light through the coating, as is the case when it is intended to be used in making transparencies or in other applications where light must pass through regardless of the exposure conditions. For some applications, primarily copying operations, coatings as thin as 1000 Å can be used. The coating is non-static and requires bright light for exposure.
Longer gradation is required than the preferred coating thickness of 2500-6500 Å. In some applications where clarity and speed are not important, thicknesses up to 2 microns can be used. The reason for the loss of transparency is obvious. The reason for the velocity loss is that, at thicknesses greater than about 1.5 microns, free carriers (negative charges) occur in the body of the coating 16 below the barrier layer 20 and close to the ohmic resistive layer 14.
is not completely absent, which adversely affects attenuation in the dark and reduces the ability of the coating to discharge rapidly and completely in the light. 5 The coating is a high-speed photoconductor. The coating has a high quantum yield, which is greater than 1 in most visible light.
It can be seen from the following table that the coating speed is comparable to that of selenium coating, which is considered to be one of the best currently known. The criterion is based on the number of electrons that can be lost or discharged from the coating as a result of one photon being absorbed.

[Table] The coating shown as SeTe+As is a commercially available coating of selenium tellurate doped with arsenic. CdS coatings are coatings deposited according to the present invention. The above values are pure cadmium sulfide without the addition of dopants. To move the red end of the visible spectrum upwards,
Small amounts of dopants can be added to create additional traps that can provide additional electrons when the coating is charged. For example, when adding a small amount of phosphine (PH ₃ ), which provides phosphorus, the values obtained for the coating of the invention increased to 1.4, 1.15 and 0.6 for blue, yellow-green and red, respectively. Other dopants that have increased gain at the red end of the vector are carbon, cobalt, iodine and copper. The use of doping agent is 100ppm of the main material
A small amount of water should be used. The speed of a photoconductive coating is related to its charge acceptance and discharge properties. Charging is discussed below, and at this point rapid charging and discharging can be achieved in 10 ^-9 seconds (nanoseconds), which is unknown in prior art xerographic coatings. is important. The usefulness of the coating can be extended to many areas other than normal imaging in reproduction, copying and photography. The above-mentioned discharge is not a discharge to a conductive member,
Electrons and positive energy states (resting holes) recombine and lose their original charge. Such development is believed to occur in the coating at various levels that occur on the body during the sputtering process of depositing the material. The explanation of the action of the coating is complex; its band gap,
Including Fermi level, electron lifetime, transition time and other considerations. Very simply, the electric field produced by the discharge persists during the carrier transition. As in the case of a selenium drum, the discharge is not to a conductive member; for example, the ohmic resistive layer 14 of the electrophotographic member 10 is needed only for charging. A member without an ohmic layer can be used and placed adjacent to the coating when the plate or the like is to be charged. Practical considerations dictate the structure of the electrophotographic member as described above. 6 The coating is panchromatic. The coating has charge dissipation properties over a wide range of radiant energies. FIG. 8 shows a graph of the response of an example of a cadmium sulfide coating sputtered according to the present invention. Reference may also be made to the above table showing the response to specific frequencies. The frequency response is considered for a charged coating that is discharged by white light.
As with virtually all electrophotographic materials, the response decreases at the red end of the visible spectrum. Red visible light is only slightly absorbed, but by adding appropriate dopants this red end can be raised quite dramatically. The coatings of the present invention also respond well to radiation outside the visible spectrum and are sensitive to X-rays, gamma radiation, and the like. The graph of FIG. 8 shows the relationship between spectral response and transmittance for a prior art cadmium sulfide coating that does not have the properties of the present invention and for the coating 16 of the present invention. Both axes of this graph are wavelength (angstroms) and transmittance, as shown in FIG. The visible part of the spectrum is shown by lines 13 and 15. Curve 17 shows the thickness of a photoconductive cadmium sulfide coating deposited according to the present invention as measured by interferometric methods.
The response is shown at 4120 Å. Curve 19 is a prior art curve for a cadmium sulfide coating resulting from deposition by conventional sputtering methods and having a thickness of about 5000 Å. The transparency of the cadmium sulfide coating of the present invention is 8000 Å outside the visible range and in the infrared region.
It is better than prior art coatings in all areas except for small areas nearby. The coating is therefore not heat sensitive. The coating of the present invention exhibits a relatively flat response over the entire visible range, whereas a similar material, shown by curve 19, exhibits a distorted response that is high in the infrared and low in the blue-green region. For this reason, prior art coating 19 is heat sensitive. Coating 16
The red end of the visible spectrum can be enhanced by adding small amounts of carbon, cobalt, iodine, copper or phosphine, which helps to increase the gain in other parts of the spectrum. 7 The coating is electrically anisotropic. By "anisotropic" we mean that the specific resistance of the coating is different in different directions. The table below shows the resistivity of the coating under various conditions and in various directions. From this table it can be concluded that the coating has a high resistivity on its surface of the order of 10 ²⁰ Ω/□. The specific resistance is in the vertical direction.
It is about 10 ⁸ Ωcm. As can be seen from this table, the effect of surface resistivity is superior to all other uses. Specific resistance of cadmium sulfide coating used in electrophotography

[Table] The measurements described above may be carried out in several ways, if practicable. The first method is the classical method, in which the electrode is placed laterally, a small current is passed through the material, and measurements are taken of the lateral body. The second measurement method is
The method assumes that the discharge of the coating acts like a capacitor, analyzes the discharge in this way, and fits the known capacitive discharge curve to the discharge curve of the material. A third method is to bombard the coating with a low power electron beam in a vacuum and measure the current through the coating. Because the anisotropy prevents the movement of charge,
Each increment of surface maintains its relative surface potential, precisely defining the gradient of the latent image. Edge effects and gradual blending of light and dark areas of the untoned latent image over time do not occur. The resolution of the developed image is limited only by the size of the toner particles. The smallest theoretical increment is the size of one crystallite, ie 700-800 Å in diameter. The particles of toners currently available on the market are not this small. 8 This coating has advantageous charging and discharging properties. As previously stated, the coating of the present invention is primarily intended for use in environments typified by electrophotographic members. The structure of the coating of the invention is shown in detail in FIGS. 1 and 2. Coating 16 should be uniformly charged.
If the purpose is to obtain a latent image, the coating 16 should selectively discharge when exposed to light on the object. It should be kept in mind that a high degree of flexibility is required to achieve quality results comparable to those expected for silver halide films. The electrophotographic film performance of the present invention provides infinite gray scale and natural rendering of contrast and image quality in a wide variety of lighting conditions. All of this is relevant to the charging and discharging properties of the coating of the present invention. The gamma curve (density vs. exposure) can be adjusted electrically. In addition to its use as an imaging agent, the coating can be charged and discharged within 10 ⁻² seconds and thus can be used for information storage and retrieval in a variety of different fields. In other words, it has the ability to quickly connect/break electrical discharges, which is not known in other coatings. Attention is drawn to FIG. 6, which shows the charging and discharging characteristics of the electrophotographic film of the present invention when used in imaging. On the horizontal axis, time is scaled in seconds for practical considerations in the case of image formation.
Included in such considerations are cameras, copiers, and similar devices that have mechanisms that physically move or are moved and thus have constraints on the time in which the movement can be accomplished. As can be seen from FIG. 6, time constraints on charging and discharging are not present with the coating of the present invention, which is capable of rapid charging and discharging. The charging curve 110 of certain electrophotographic members having the coating of the present invention is shown to be linear in nature because the coating of the present invention accepts charge as quickly as it supplies charge. The charge achieved is a function of the application time and the corona current, ie Q=TA or the charge is the product of time and current. However, Q is electric charge (clone), T is time (second), and A is current (ampere). This concept allows control of the surface potential. In the case of conventional electrostatic techniques, the photoconductor is normally charged and saturated with an uncontrolled corona (as much charge as is supplied leaks away), and then exposed to the maximum amount of light to ensure a residual voltage. (maximum discharge) so that there is little or no intermediate voltage to help obtain multiple degrees of gray scale. 6th
As can be seen, the coating of the present invention can be charged to any desired intermediate level.
This can be achieved by changing either or both the charging time and the corona current. For charging curve 110, the coating is charged to maximum potential. This maximum potential is approximately
It is shown that there is -50V (DC) on the surface in 0.3 seconds. This point is indicated by 112 in FIG. Assuming coating 16 is approximately 3500 Å thick, this surface potential exhibits a charge acceptance of approximately 14.3 V per 1000 Å. It has been found that to enable good contrast and gray scale imaging and gradation, the charge of the coating must be at least a few volts per 1000 Å or more. Obviously, acceptance of 14.3V per 1000Å is excellent. Regarding electronic photographic film,
There is a great deal of leeway in the intermediate charging voltage to provide excellent imaging at voltages below the maximum. The degree of charge acceptance of the coating of the present invention is
Significantly larger than any known commercially available electrophotographic member and most coatings reported in the literature. Cadmium sulfide coating deposits reported in the literature are known to be unable to accommodate any real charge. Those that are chargeable will accept a fraction of the charge that the coating of the present invention can accommodate. The charge acceptance of a coating is believed to be related to the physical structure of the coating. Deep traps or surface energy states within barrier layer 20 allow the capture of electrons at energies that are inside the forbidden band. Charges are strongly attracted due to the highly regular crystal structure and independent domain effects of individual crystallites. Therefore, the mutual domain effect between charges is small, and charges stay in place regardless of what happens nearby. There is no edge effect if the discharge occurs selectively. Pre-exposure charges do not move easily. On the other hand, main body 7
The free carriers are sufficiently reduced to a thickness of less than 1μ or perhaps slightly greater than 1μ. The curve 114 shown in FIG.
2 is the surface potential derived from the coating remaining in the dark after charging. This curve 114 is a dark decay curve that begins with a relatively steep portion 116 characteristic of a capacitor discharge and then flattens out. From this curve 114, it can be seen that a large amount of charge exists after a long period of time. The coating of the present invention retains a large amount of charge for long periods of time in the dark. An example of a dark place attenuation test was conducted on an electrophotographic member, and its discharge was measured. This film had the structure shown in FIG. Substrate 14
is a polyester film with a thickness of a fraction of a millimeter, and the ohmic resistance layer 14 is mainly a polyester film with a thickness of a fraction of a millimeter.
266 Å of indium oxide and coating 16 was 3687 Å of pure cadmium sulfide. This film was charged using a corona in the dark. This corona provided a current of −400 μA for 0.9 seconds and reached a surface potential of −33 V. The decay in the dark is logarithmic, with −
It drops to 20V, drops to −16.4V within 50 seconds,
Drops to -10V within 5 minutes, -7.3V within 10 minutes
It declined to . At about 12 minutes, -6.7V was still present on the film, and this voltage was sufficient to provide excellent grayscale images and gradations if necessary. At this point, the film was suddenly discharged through a 4.5 neutral density filter using a Model 252 Vivitar flash unit. The surface voltage was reduced to -2.5V, which was still capable of providing imaging and gradation. After about 20 seconds, the filter was removed and the film was discharged again with a flash of light to bring the surface voltage to zero. Curve 118 shows the light decay curve from the coating's maximum charge, assuming that the film is exposed to bright light as soon as it achieves maximum charge. The discharge occurs immediately and progresses sufficiently to reach zero, and no residual voltage remains as shown at point 122. The elapsed time of discharge is shown as approximately 200 milliseconds. Discharge of the coating upon exposure to light is achieved when photons enter the coating and recombine holes and electrons. The coating of the present invention is 2μ
Since the depletion layer extends over the entire body of the thin film, the surface potential can be completely discharged to zero. Furthermore, this discharge can be achieved within 10 ^-9 seconds as described with respect to FIG. The only constraint on the total cycle time, including discharge, is the practical problem of exposing charged surfaces to light at high speeds. In some image forming apparatuses, this high-speed exposure must be performed by projection exposure, such as when the shutter of a camera is opened and then closed. The coating 16 below the barrier layer 20 must be depleted of free carriers upon charging. In the case of other materials such as selenium, the electric field can never drive out all free carriers. In the case of the present invention, the free carriers are electrons, which are completely expelled for thicknesses up to about 2μ. If the thickness is greater than this, some carrier will remain near the ohmic resistance layer. In fact, in the case of preferred thin layer thicknesses of about 2000 to about 7000 Å, a global depletion exists and a discharge can variably rise to zero when exposed to light. When projecting an object onto a charged coating for imaging purposes, partial discharges of the coating increments reduce the voltage across the coating surface, and at this point a shifted dark decay curve begins, having a very sharp cutoff point. Thus, in FIG. 6 the partial discharge of the coating is illustrated by three increments that are not fully discharged. These increments include one that increases the surface potential level to 122, one that increases the surface potential level to 124, and one that increases the surface potential level to 126. The dark decay curves following these discharges are 128 and 128, respectively.
130 and 132. From these curves,
It can be seen that because the dark decay discharge curves are nearly parallel, an almost infinite gray scale can be obtained in the latent image achieved when the coating is exposed to light. Also, the overall discharge of the coating is well below zero at point 120. No known electrophotographic member has the ability to discharge to zero immediately. In fact, the amorphous selenium coatings of xerographic equipment used today have noise voltages comparable to the total surface voltage of the coating of the present invention when fully charged to maximum potential. To clarify the ability of the coating of the present invention to achieve almost infinite grayscale, the third
Process No. 1 in the figure occurs in the time range labeled "Charging" in Figure 6, the second stage in Figure 3 occurs in the time range labeled "Exposure" in Figure 6, and It is assumed that the three stages occur in the time range marked as "gradation" in FIG. Since the toner is deposited in proportion to the surface voltage of each increment, there is no charge transfer between increments (see section 7 above, ``This coating is electrically anisotropic''); Each increment follows a dark decay curve similar to dark decay curves 128, 130 and 132, always maintaining a certain slope between them, thus creating a photographic grayscale with better resolution than conventional silver halide film. Provide quality. The smoothness of the plane and the complete dots produced when the toner is fused onto the surface are other factors of good image quality. The slope of the dark decay curve for every increment of the coating of the present invention changes slightly depending on the voltage charged to the increment. For example, it can be easily seen that the dark attenuation curve 114 in FIG. 6 is steeper than the dark attenuation curve 132. This can be logically explained by considering the discharge characteristics of capacitors. Because the difference in slope of these dark decay curves becomes smaller and smaller over time, these curves tend to approach an iso-slope or parallel state. This characteristic is
It is possible to control the gamma curve of the coating for development for different purposes. Charging an electrophotographic member to a high voltage and exposing it quickly produces a grayer image than charging the electrophotographic member to a lower voltage or exposing it later, or charging it to a lower voltage and exposing it later. It is possible to obtain a greater degree of change in darker and darker parts of the gradation. This gives a wide range of flexibility. It has been found that at charges above about 10 volts, the sensitivity of the electrophotographic film of the present invention is largely independent of the charge being applied to the coating. The incremental discharge voltage is proportional to the exposure dose and establishes a specific dark decay curve as soon as the exposure ends. The amount of discharge is equal for all increments for any given intensity of light. These intermediate charge levels remain in a proportional relationship to each other for very long periods of time, even minutes, and thus function to reproduce tonal images with sufficient fidelity without gray scale distortion. shall be. The selection of charging voltage, exposure time, and toning length can be varied, providing great flexibility when using the invention for imaging. In FIG. 6, if desired, the user can charge the coating to a low voltage, e.g., to a point 122 along the line, at which point 122 the light available in the object to be imaged is ,point
It is larger than when charging up to 112. Charging along line 134 does not always result in a loss of gray scale, even when the light conditions are weak and it is desirable to have a less steep gamma curve than in the case of high charging conditions. However, it requires some extension of the toning time. Other charging curves for lower maximum values are shown as 136,138. If desired, the charging time can be increased, charging along line 140 and stopping at 142. The dark decay curve 144 from this point 142 is
Since it is at approximately the same voltage as point 122, it is the same as curve 128, but it soon deviates from curve 128. The exposure actually takes place immediately after time 146, and line 1
With selective discharge along 48, several increments abruptly change to different dark decay curves depending on the respective exposure. Toning then begins and lasts for different times depending on the type of image desired and the voltage obtained after exposure. The intermediate discharge curve for the charging state shown at point 142 is not shown in the graph. In FIG. 6, which shows the charging and discharging characteristics of a coating, it is assumed that the coating has been charged to the maximum value at point 112 and has been kept in the dark without exposure for a predetermined period of 5 seconds. At this point, the surface charge of the coating is
It has decayed to point 152, which still has a DC voltage of about 35V. If exposed at this point, a maximum photodischarge will occur along line 150 and go to zero. When exposing objects to different lights, there are still a large number of gray scales that can be achieved with intermediate degrees of illumination, which results in the existence of an almost infinite number of different voltages on the coating, This still gives a good gray scale. Although toning must be done for a slightly longer time than if exposure were done earlier, the quality of the resulting developed image is good. In FIG. 7, the charging and discharging of the same coating is shown on different time scales. The unit of the horizontal axis is nanoseconds. The coating of the present invention quickly accepts charge along line 154 to the voltage at point 156. This has been shown to occur in approximately 3×10 ^-9 seconds. If, due to the anisotropy of the coating, the coating is considered to consist of a number of mutually independent storage increments or parts, it is clear that this charge represents a change in state of one storage increment. Furthermore, the intensity of the electron beam can establish various states of charge, allowing a fully variegated view to be read on a piece of electrophotographic film. The change in state of this scene, or each increment, is accumulated at a charged voltage for a different time depending on the dark decay curve of the member, and the increments can be as small as the tips of individual crystallites. In FIG. 7, a dark decay curve 158 of member charge is shown, which curve shows a gradual decay due to the time scale. If a single charged increment is discharged immediately, the discharge will occur along line 160 within a few nanoseconds, or after a short delay along line 162. The coating's ability to be charged and discharged at high speed and its storage capacity allows this electrophotographic member to be used for a wide variety of purposes. 9 This coating is itself flexible. A preferred form of the electrophotographic member 10 of the present invention is as follows:
As shown in FIGS. 1 and 2. The thickness as described above, ie coating 16 is less than 2μ thick, ohmic resistance layer 14 is about 400 Å thick,
The substrate 12 is a fraction of a millimeter thick in this structure, and all components are highly flexible. This member can be wrapped around a 6.35 mm (1/4 inch) diameter mandrel without cracking or cracking. This property is one that would not easily occur in a component having a coating that is crystalline, since brittleness has always been considered to be a property of crystals. The density of the crystals and their surface hardness also appear to be inconsistent with flexibility. The compressive stress applied during sputtering is believed to be due to the greater strength, elasticity and integrity of the coating, which allows the coating to be easily bent without causing damage. It will be done. Flexibility is not necessarily a result of any type of component based on glass or metal substrates, but even in such cases the flexibility of the coating applied to such relatively rigid substrates is important. allows vibrations and folded parts to withstand without causing damage to the coating. The flexible nature of the preferred electrophotographic member 10 allows it to pass over the rolls and around the guide members of processing machinery without risk of damage or cracking. 10 This coating is non-fatiguing or long-lasting. Selenium drums for xerogelafies lose their photoconductivity, so they cannot be used for long periods of time.
Thus, they must be replaced from time to time. In the case of the coating according to the invention, fatigue is essentially absent. Testing quickly put the coating through millions of charging and discharging cycles.
The gain and other properties of the coating are not affected in any way. In some electrophotographic members, discharge of the member continues even after the light exposing the member has ceased. This disturbs the developed image and causes fog. With the coating of the present invention, the moment the light applied to any component is stopped, the discharge stops and the component immediately assumes its dark discharge curve. This sudden cut-off was discussed above. The foregoing ten properties are not intended to be limiting, but primarily encompass the principal properties of the coating when used as part of an electrophotographic member, such as those detailed with respect to FIGS. 1 and 2. These properties result in numerous benefits and advantages not specifically mentioned. The theory of operation of the coating has been described to some extent in connection with the catalog of properties, and is additionally explained below. Before considering the theory of operation, we believe it is useful to describe the effect of varying coating thickness as a way of explaining how properties change. FIG. 9 is a graph showing how some properties of the coating vary with coating thickness. A study of this graph will assist in using the present invention in various types of applications. The horizontal axis of FIG. 9 is the thickness of the coating considered to be deposited on the substrate 12 and ohmic resistive layer 14, in Å. The vertical axis shows the transmittance T, the acceptance voltage Vac, and the lateral specific resistance logρ of the charged body (unit: Ωcm).
and surface resistivity logR/□ (unit: Ω/□)
4 different parameters are shown. Considering first the curve 180 showing the change in transmittance with coating thickness, it is logical that the thicker the coating, the less light will be transmitted. When the coating thickness decreases to zero, the transmittance becomes 100%. From this curve 180, after the thickness exceeds 1 μ or 10000 Å, the transmittance is approximately
It can be noted that below 65% it starts to drop. Because the exposure or discharge requires the absorption of photons, if the light cannot penetrate into the body of the coating, it will not be able to dissipate the charge sufficiently. The gain of the coating is controlled by the physical replenishment of the deposited material and is therefore constant regardless of thickness, but photons must be able to enter the body and cause hole-electron combinations. It's useless. Best results are when the transmittance is around 70~
About 85% is obtained, and such transmission occurs for thicknesses of about 2000 to about 6500 Å. Thinner coating thicknesses are inadequate to absorb enough photons to obtain sufficient combination of electrons and holes for good imaging, but may require longer exposure times and longer toning. For example, coatings as thin as 1000 Å can be used for copying operations. Such coatings cannot achieve high speed imaging, high resolution, good grayscale, etc. Thick coatings, such as up to or as thick as 2μ, have applications, but their applications are not as numerous as those that are practically transparent. The acceptance voltage of the coating is directly proportional to the thickness of the coating, as shown by line 182.
The slope of the acceptance voltage line is a function of the type of material used, the surface resistivity of the material used under charging and discharging conditions, and the lateral and transverse resistivity of the body. The straight line 182 shown is for cadmium sulfide deposited according to the present invention, but different deposits will have slight differences and slightly altered slopes. At a thickness of approximately 2500 Å, the total voltage acceptance value, to be understood as a maximum value, is approximately 30V. The accepted voltage per 1000V is about 12V, which is excellent for good image formation. Barring other properties, a coating of any thickness will produce a good image. However, a thin coating does not have a sufficient absolute voltage tolerance to be able to be supplied with a charge of even a few volts. Surface resistivity 184 is shown as a straight line having a value of approximately 10 ²⁰ Ω/□, independent of coating thickness. When the coating thickness is at its thinnest, the surface resistivity value cannot be considered reliable. The reason for this is that the measured value of the resistivity is difficult to separate from the measured value of the main body even if the resistivity can be measured. The difficulty in separating is due to the fact that in such thin dimensions it is extremely difficult to distinguish the main body of the coating 16, the ohmic resistive layer 14 and the barrier layer 20 separately.
The contribution of each of these layers to all measurements cannot be ascertained in practice. At thicknesses greater than a few hundred Å, the surface barrier begins to act as an independent element. It should be appreciated that the practical effect of a resistivity value of 20Ω/□ is that of an infinite resistivity.
Variations in the range below this value, for example up to 10 ¹⁷ Ω/□, do not significantly reduce the effectiveness of the surface barrier layer in maintaining the charge independence of regions of adjacent increments. In other words, the specific resistance is from about 10 ¹⁷ Ω/□
It can be considered that it extends to 10 ²⁰ Ω/□ or more, and along with this, the resolution increases and charge movement disappears. This element also prevents edge effects inherent in photoconductors such as amorphous selenium by ensuring that potential differences between adjacent charges cannot create unnatural preferences for toner particles.
Incidentally, it should be noted that the fact that the absolute value of the surface voltage of the coating of the present invention is small also has the effect of preventing the edge effect of selenium. The surface resistivity does not change depending on whether the coating 16 is charged or not, nor does it change depending on whether it is in the dark or in the light. Thus, the value of the surface resistivity remains the same regardless of the thickness of the coating, which is greater than about 1000 Å. This establishes and maintains electrical anisotropy. The property of lateral resistivity is shown by curve 186 and increases with decreasing thickness. This curve 18
The value of the lateral resistivity of 6 is the value (in Ωcm) that exists when the coating is charged.
Values on the order of 10 ¹⁴ Ωcm are achieved at thicknesses of about 2000 Å. Even at a thickness of about 10,000 Å, the specific resistance is still much greater than 10 ¹² Ωcm, although the decrease in value is rather steep. The body of the coating almost reaches its maximum value after the coating thickness increases to more than 10000 Å and remains constant thereafter. The value of the lateral resistivity of the body is the same as the lateral resistivity of the body if the coating is charged, but decreases to about 10 ⁸ Ωcm when discharged due to the high gain of the coating. This reduction in lateral resistivity enables high speed imaging of electrophotographic film using this coating and also provides ideal properties for other applications. In this discussion, "thin films" are mentioned. Although the general definition of a thin film is that it refers to a layer that has no bulk properties throughout its scope, it may be appropriate to define a thin film as it is meant herein. In the thin film according to the present invention, the depletion layer extends throughout the layer thickness.
This imparts the desired properties. Thus, for a cadmium sulfide coating such as that shown at 16, when charged, the depletion layer extends from about 1.5 to about 2 microns across the coating, in practice about 3 microns.
It is complete. If the coating is for example selenium and 25μ thick, the depletion layer is only a small part of the body. The coating is definitely not a thin film. The preferred coating 16 thickness for most applications is from about 2000 to about 7000 Å, which is clearly a thin film as defined above. Referring again to the method of forming a coating on a substrate 12, such as a flexible polyester member, this formation technique has been described as radio frequency sputtering. For the purpose of illustrating the manner in which the coating process is carried out, the pre-deposited indium/
Deposition of cadmium sulfide on a layer of tin oxide is described. When starting the sputtering device 53, 1
Assume that a roll of bulk substrate S is installed as a roll 56, engaged by various rollers, wound around a drum 60, and wound onto a take-up roll 64. The vacuum pump 102 is then started and the container 54 is
Evacuate the entire interior to create a suitable vacuum. After the vacuum is created, power can be applied and the circulation of coolant begins to cool the cadmium sulfide targets 66 and 68, drawing the heat exchange fluid (including the hot oil) into the drum near the drum surface. cycle begins. Background gas is introduced from one or more sources 106 as a mixture of argon, hydrogen sulfide, and oxygen in predetermined ratios, all to reach steady state and regulated parameters. On the other hand, since the motor controlling the movement of the substrate is started, the heated drum surface does not melt the substrate. After reaching steady state, the apparatus 53 is operated continuously until all rolls of the base are coated. device 53
The internal conditions are kept as steady as possible throughout. After all rolls have been coated, the apparatus 53 is shut down, the power is turned off, the gas is turned off, and the chamber is opened. The fully wound roll 64 is then removed, a new coated roll is installed in place 56, and the process is repeated. Various conditions for a typical operation established and maintained in apparatus 53 are shown: 1. Provide sintered members 66 and 68 of ultra-purity cadmium sulfide that are secured to target-water cooled stainless steel bodywork fittings. Purity is 99.9999998%
That's about it. When doped, the dopant is supplied by gas, by applying a small amount of solution to the cadmium sulfide, or by using other targets containing the dopant mixed during preparation. The amount of doping agent used is in parts per million.
Make it a very small amount, such as less than 100. 2. Pressure etc. in the chamber - First, the chamber is evacuated to a relatively good vacuum by mechanical diffusion and/or cryogen vacuum pump. This exhaust air above all degasses the chamber and substantially removes moisture. Typical exhaust pressures should be in the range of 10 ^-6 to ^{10 -7} Torr (mmHg).
Angone gas with hydrogen sulfide is introduced to maintain a pressure of about 6 mTorr, with a change during sputtering of 5-9 mTorr. The proportion of gas is 93.3% ultra-pure argon and 6.1% ultra-pure hydrogen sulfide. Oxygen is simultaneously introduced in extremely small quantities at a rate of several hundred or several thousand parts.
The doping gas can be introduced in small amounts, such as 1 million minutes, and phosphine can be introduced for phosphorus doping and methane for carbon doping. The target can have a metal dopant incorporated therein. 3 Substrate - As mentioned above, the substrate 12 is polyester less than 1 millimeter thick. The substrate is preferably degassed and dehumidified before use through a heating device that heats it to about 100°C. Aluminum, stainless steel, etc. can be used as other substrates under other conditions. 4 Energy - A radio frequency (RF) oscillator 80 in a typical system provides approximately 4 KW of energy during sputtering operations. For a typical supply, the rms volts applied to the target is 1000 volts RF self-rectified by the plasma to achieve a half-wave rectified peak direct current (dc) voltage of approximately -1400 volts at the target;
It is influenced to some extent by the target material. Of course, the target temperature for cadmium sulfide is influenced by its voltage and current flow. As will be discussed below, this temperature is influenced by the properties of the target material and must be controlled to prevent macroscopic explosion hot spots and to prevent the formation of dents and cracks in the target if not kept from spreading. . The voltage on the target is about -1000 to -2000 volts under good sputtering conditions.
The bias voltage on the anode is typically maintained at -20 volts. It can be as high as about -150 volts before removing too much deposits. 5. Mechanical Considerations - The transport mechanism in the chamber is arranged to maintain a sufficiently low tension by means of a structure that senses the tension and is responsive to maintain the tension constant. It was originally thought that the substrate would expand as it softened, but it was confirmed that the width and length actually contracted. This creates compressive stress on the crystal, giving it strength and dimensional stability. The actual substrate tension can vary during the sputtering operation due to slight changes in temperature, substrate thickness, and other parameters. Typical tension should be about 50 pounds or less. 6 Deposition Rate - For the two target configuration described below, the deposition rate is typically 3 microns per hour. The entire deposition of coating 16 is accomplished by passing the substrate once through a plasma generated between the target and the drum. To this end, the deposition rate can be controlled by the speed of substrate movement, which is controlled by varying the speed of the transport mechanism. At the above-mentioned speed of 3 microns/hour, a typical deposited layer of about 3000 Å can be deposited by moving the substrate past the target at a speed of about 14-15 millimeters/second. can. When increasing the size and number of targets, change the substrate.
The same deposit layer can be deposited by passing at a speed of 15 mm/sec or higher. Thin coatings can be deposited in one pass by increasing the speed. For example, bonding layer 18 is deposited at faster substrate speeds and lower powers than conventional deposition. 7 Temperature - Increase the target temperature to around 350℃. The temperature of the polyester during deposition is approximately 165°C. The drum 60 is heated with hot oil circulating within the drum 60 and maintained at approximately 150°C.
The ohmic resistance layer generates heat due to eddy currents due to some radio frequency oscillators present in the plasma in the device. As a result, the substrate becomes considerably softer and sputtering progresses. This eliminates any shrinkage that may occur. High temperatures create energy at the surface where the colliding molecules impact, promoting stable, dense deposition. The ohmic resistance layer raises the base temperature by about 15 degrees Celsius above the drum temperature. 8. Geometry - Typical equipment geometry will assist in understanding the following properties of equipment 53 and sputtering conditions: Drum diameter - 40 cm (approx. 18 inches) Substrate width S - 50.8 cm (approx. 20 inches) ) Approximate dimensions of the target
-56 x 25 cm (22 x 10 inches) Gap between target and drum -50 mm Plasma 108 approx. radians - Approximately π/2 Dark area on target
- Approximately 1.3 mm (approximately 1/2 inch) Dark area at the anode - Approximately 6.4 mm (approximately 1/4 inch) 9 Electric field, etc. - The electric field between the cathode and anode is measured with a negative bias, and the total voltage on the cathode or such total voltage exists from the cathode to the shield, which is at ground potential. A plasma 108 in the gap rectifies the RF voltage to a DC voltage.
The impact energy from the ionized gas produces energy that is delivered to the particles reaching the substrate. This thing is evaluated as 100 electron volts. More than 10 times greater compared to the energy of particles deposited by the use of steam technology. To achieve the extraordinary properties of the coating 16, the bias voltage applied to the anode during sputtering was increased; the anode was maintained at a negative voltage, a fraction of the voltage of the cathode, negative 2000 volts dc. The shield around the target and the unexposed portion of the anode are maintained at ground potential. This establishes a dark area at the anode in addition to the normal dark area at the cathode, and the substrate engages the second dark area on its outer surface. This is called a Langmuir probe and is known as so-called back-sputtering, which is used only for cleaning purposes. As far as is known,
It is not used for the purpose of achieving the desired properties described for the coating 16 of the present invention. It is not known for making electrophotographic parts. It has been determined that the amount of bias controls over a range of charge acceptance of the resulting electrophotographic film with the sputtered coating. FIG. 10 shows a curve showing the results of a test measuring the charge acceptance of a cadmium sulfide coating versus bias. Experience has determined that a charge acceptance of about 7 volts per 1000 angstroms or more is required for satisfactory imaging. This fact tells us that the curve is 200
The results are unsatisfactory until reaching the level part of . The rapidly changing portion of the curve at 202 means that charge acceptance cannot be confident at lower values of bias. Starting at about -10 volts, charge acceptance per 1000 angstroms achieves about 9 volts and remains nearly constant with bias up to high values. When biases on the order of -150 volts or more are used, back sprinkling of cadmium sulfide from the substrate occurs, reducing the deposition rate.
A typical bias is -20 volts. This bias provides an electric field that tends to orient the dipole-like CdS molecules as they impact the substrate, directing the more reactive S atoms outward. For example, the theory of operation and operation of incorporating a coating into an electrophotographic member considers its crystal structure, its electrical structure, etc. Deposition occurs under conditions of high electrical energy density, bias applied, ultrapure target and a suitable mixture of background gases to ensure perfect stoichiometry, RF power applied,
This is believed to be the result of substrate heating and bias field effects. The resulting crystalline deposit has sulfur atoms at the top because they are deposited like dipoles. This combines with the introduced oxygen to form a complex oxide barrier layer. The heated substrate has a temperature that is increased by the action of eddy currents in the ohmic resistance layer, so that when molecules are bombarded, they do not necessarily remain in a static state, but still have some mobility and energy. are doing. It is believed that eddy currents are caused by the intense electric field generated by the second dark region. The arriving molecules seek and achieve the most perfect and stable bonds to form a crystalline deposit. This thing achieves high regularity and creates platelets. The morphology of the crystallites is almost perfect, vertically oriented, giving rise to surface layer effects, i.e. individual field regions which give high resolution in addition to anisotropy. Because the deposit behaves as a single crystal structure in response to diffraction measurements, the uniformity of the deposited crystals appears to span the crystal lattice structure. When charged, the charge is uniformly supplied and shared with each microcrystal. The forbidden band width is 2.4 electron volts. Surface charging creates excessive negative charges. Bandgap energy photons of light generate electrons and holes in the bandgap, and the drift of these carriers under an electric field reduces the initial surface charge.
Direct excitation of electrons in surface states can be ignored. Electron traps in the barrier layer provide strongly held electrons. The carrier transition time is shorter than the lifetime, so that the electric field in the coating during exposure is maintained during the carrier progression. From the above description and testing, coating 1
6 and its operation when charging and discharging appear. This image points the way to other compounds that can be sputtered as well and may achieve similar, if not identical, effects. Compounds other than cadmium sulfide alone that have been tested and found acceptable are zinc sulfide, zinc telluride, and mixtures of zinc sulfide and cadmium sulfide. When deposited as a coating, these compounds have many, but not all, of the superior properties of cadmium sulfide alone, and they are dielectric materials. These are N-type compounds having exactly the same bandgap width, dielectric constant, Fermi unit, and other points as cadmium sulfide. However, they differ from cadmium sulfide primarily in their kinetics and spectral response. The following description provides information on cadmium sulfide as deposited according to the invention, from which the properties of the compounds used may be evaluated. The charge acceptance and electric fields achieved with cadmium sulfide coatings are superior to known photoconductive compounds, including commonly used commercial compounds such as zinc oxide and selenium. Significantly better than any known cadmium sulfide deposits. The coating is deposited as a thin film with a suitable structure and has a special physical structure; furthermore, the coating has a uniform crystalline structure, i.e., hexagonal system, and furthermore the coating has a uniform It has a crystalline diameter and length, and also has a specific orientation consisting of a perpendicular relationship to the substrate on which it is deposited, its stoichiometry is almost perfect, and the upper layer is dominated by sulfur due to the molecular orientation during deposition. exists on the upper side,
This provides a bond to trap oxygen, resulting in a particularly thin barrier layer of infinite resistivity (in zinc telluride, the tellurium atoms are on top); the coating is diffraction tested as if it were a single crystal. Uniform to respond to. As mentioned above, the forbidden band width of cadmium sulfide is
It is 2.41 electron volts. The Fermi level of cadmium sulfide is 0.35 electron volts from the conduction band when charged, and 0.7 electron volts from the conduction band when uncharged. The dielectric constant of cadmium sulfide is approximately 8.6
×10 ^-14 . In operation, the depletion layer extends through the entire thickness of the coating up to the thickness defined here. There is no positive charge mobility within the body of the coating. The electron fly time is 10 ^-3 seconds and the transfer time is 10 ^-10 seconds, ie the transfer time is significantly shorter than the electron fly time. For this reason, the electric field is maintained during carrier operation and the gain of the coating is extremely high. As noted, a single photon generally produces more than one electron during a discharge. Crystal deposits consist of small platelets that are evenly stacked but not perfectly aligned. This creates significant irregularities in the photons when exposing the coating. This aids the total orthochromaticity of the coating. It is believed that there is a layered structure in the coating and that there is so-called electric field conversion similar to NPN semiconductor devices. The coating acts as if there were an excess of electrons and then no electrons in the body.
The depletion decreases towards the ohmic resistance layer. Deep traps are established in the barrier layer during charging. When photons of light are directed toward the film, they produce amplification. The response of the coating of the present invention is obtained when compared to other coatings such as mercury halide emulsions. The exposure energy applied, ie the photon energy amplified by the exposure time in the coating of the present invention, is constant. Therefore, if the time is shortened, less energy is required to produce the same response, and vice versa. For mercury emulsions less than 1 micron thick, this rule does not apply. Emulsions cannot respond quickly enough. The concept of inactivity to response is referred to as a reciprocity defect, and this does not occur in the coating of the present invention. When increasing the exposure energy, the time required for a given response is decreased to maintain a constant relationship. A mixture of zinc sulfide and cadmium sulfide is 7-
When 1/2% to 100% zinc sulfide and cadmium sulfide are present, a target with the balance cadmium sulfide is used for deposition. Zinc sulfide has a large energy gap in the ultraviolet light, and for this reason the higher the content of zinc oxide, the more transparent the coating obtained, the greater its response to ultraviolet light and the lower its response to the visible part of the spectrum. becomes smaller. Small proportions of zinc sulfide coatings behave like cadmium sulfide coatings, but with slightly improved UV response. Oxygen is mixed in in small amounts during the deposition of the photoconductive coating to aid in the formation of the barrier layer. This presumes that there is an effort to remove oxygen from the chamber and the roll of substrate. The reason for this is to achieve uniformity in the product deposition. Tongzo,
It has been determined that some oxygen is absorbed in the roll of substrates mounted in a chamber even though they are essentially evacuated prior to coating. Preheating the unwound roll before loading it into the chamber essentially reduces this amount of oxygen so that the added oxygen becomes more uniform in volume. Addition of oxygen provides better control. Although the theory of operation of the present invention will be described in some detail, it is noted that the coating of the present invention is described without regard to theory. The purpose of stating theory is to aid in understanding the invention, not to limit it. Those skilled in the art are able to practice the present invention from the above description. The coating and the electrophotographic member with the coating, along with the method of depositing the coating, are essential components of the invention. The scope of the invention is not intended to limit the use of the coating in other applications within the scope of the claims.

[Brief explanation of drawings]

FIG. 1 is a partial sectional view of an electrophotographic member made according to the present invention using the coating of the present invention, FIG. 2 is a partially enlarged view showing the theoretical microscopic structure of the electrophotographic member of FIG. 1, and FIG. 1 is an explanatory diagram showing an example of the use of the electrophotographic member shown in FIG. 1, FIG. 4 is a partial cross-sectional system diagram of a sputtering apparatus used to carry out the method of the present invention, and FIG. 5 is a diagram showing an example of the sputtering device shown in FIG. A partially enlarged view of the device; FIG. 6 is an electrical characteristic diagram of the coating of the present invention; FIG. 7 is an electrical characteristic diagram similar to FIG. 6; FIG. FIG. 9 is a curve diagram showing the relationship of characteristics to coating thickness of the present invention, and FIG. 10 is a curve diagram showing the relationship of charge acceptance voltage to changes in anode bias voltage. . 10... Electrophotographic member, 12, S... Substrate, 1
4... Ohmic resistance layer, 16... Photoconductive coating, 18... Bonding layer, 20... Barrier layer, 22
... Microcrystal, 28 ... Corona source, 36 ... Optical device, 38 ... Toner supply device, 44 ... Heat lamp, 48 ... Roller, 52 ... Pressure roll, 5
3... Sputtering device, 54... Chamber or box (low pressure container), 56... Supply roll, 58... Guide roller, 60... Insulated drum, 62... Guide roller, 64... Winding roll, 66, 68... Target, 70, 72, 74... Shield member, 76
... Rear wall of low pressure vessel, 80 ... Radio frequency power supply, 8
2... Matching network, 84... Power supply line, 92,
94...Capacitor, 96...Voltmeter, 98...
High frequency radio, 108...Plasma, 110,
112...Dark part.

Claims (1)

[Scope of Claims] 1. An electrophotographic recording material having a substrate, or a substrate and a bonding layer and/or a conductive layer, and a generally inorganic photoconductor layer of sputtered microcrystals, wherein said photoconductor layer is Consisting of cadmium sulfide,
An electrophotographic recording material comprising an oxidized cadmium sulfide diffusion upper layer as part of the cadmium sulfide layer on the cadmium sulfide layer. 2 Sputtering the photoconductor in a high-frequency electric field under the simultaneous action of a bias voltage onto a substrate that may be provided with an electrically conductive layer, introducing a background gas during sputtering to determine the theoretical role of the photoconductive layer to be sputtered. in producing an electrophotographic recording material having a substrate, or a substrate and a bonding layer and/or a conductive layer, and a generally inorganic photoconductor layer of sputtered microcrystals, comprising a conductive layer. Cadmium sulfide as a photoconductor is sputtered on a substrate in some cases under the simultaneous action of a bias voltage in a high-frequency electric field, and a background gas is introduced during sputtering to maintain the theoretical proportion in the cadmium sulfide layer to be sputtered. , also photoreceptors, CdS
characterized in that a small amount of oxygen gas is introduced in the sputter, thereby causing a reaction with the formed surface to form a partially oxidized diffusion upper layer at and near the final photoreceptor surface. A method for producing an electrophotographic recording material.