DE2328492A1 - METHOD FOR PRODUCING AN ELECTROPHOTOGRAPHIC FILM OR ELECTROPHOTOGRAPHIC FILM - Google Patents

Description

PATENT AGENCIES L V £ QH v3 £

DR. PHIL. G. NICKEL · DR.-ING. J. DORNER

8 MUNICH 15

LANDWEHRSTR. 35 POST BOX IO4

TEL. (0811) 55 5719

Munich, June 1, 1973 Attorney's files: 181 - Pat. 2

Coulter Information Systems, Inc., 7 De Angelo Drive, Bedford, Massachusetts, United States of America

Method of making an electrophotographic film or electrophotographic film

The invention relates aiii to the manufacture of an electrophotographic Films as well as one in particular after one of these Electrophotographic film produced by the method, which, having been pointed out here, has the novel property has that a photoconductor material, for example cadmium sulfide, Zinc indium sulfide or the like, as a thin film coating a carrier is sprayed or splintered, one ohmically conductive layer between the support and the thin photoconductive layer Layer is arranged.

In electrophotographic image recording processes, as is known, a latent electrostatic image is formed on the surface of a photoconductor. "The photoconductive component is first charged over its entire surface in a dark environment Maintenance of the charge depends on the physical properties of the material in question. Immediately after

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The surface is charged in a certain form Exposed to radiant energy, which according to the image to be recorded in a certain arrangement of tones, lines, Characters and the like. The radiant energy the shape of the projected light can be arranged in a certain way, in the form of an X-ray, etc. Those areas of the surface of the photoconductive component which are the lighter Areas exposed to the radiation distribution are more conductive than those areas which are less are exposed to parts of the radiation distribution that are heavily exposed. This leads to the result that the electric charge of the different areas of the surface of the photoconductive member according to the respective degree of exposure the surface is discharged selectively and proportionally.

The spatial arrangement of charges obtained in this way forms the above-mentioned latent image. The charge can now to attract fine particles electrostatically and in xerographic processes such fine particles are in the form of fine powder or in a liquid suspension brought into contact with the surface. The particle marriages adhere selectively on the surface to varying degrees according to the charge distribution representing the latent image, whereupon the excess Particles are brushed off or otherwise removed from the surface while the remaining toner as the particles are also called, that creates visible images. This image is generally on a support, for example a sheet of paper, transferred and permanently fused onto the surface of the carrier by methods known per se or burned in.

In general, the widely used, commercially available devices as a photoconductive member large, selenium-coated drum use «, The recording process goes in a complicated and expensive machine in front of you, with the achievable speeds ,,

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solvency and the versatility of these devices and the corresponding procedures leave much to be desired.

The known methods and devices cannot easily be used for the type of photography as they are carried out by high-speed photographic apparatus and cameras are realized in which a photographic film with fine grain Silver halide emulsion is used. Those for the known methods, devices and photoconductor materials and -Films peculiar disadvantages have hitherto prevented their use in many fields of application, for example in the High speed photography, microphotography with the finest Resolution and in many other technical fields. Archiving using projectable microfilms is an area where there has long been a need for a method of quickly and economically producing projectable photographs Resolving power existed, with simple devices to use should come and there should be the possibility of storing the records for a long time. For example it would also be * very beneficial from time to time with microfilming To be able to add information without the already on adversely affects information captured in the microfilm will .

Common photographic microfilms can be added Do not expose information or records several times. The inherent structure and treatment of the films cause the emulsion to be destroyed as the microfilm develops will. The electrophotographic process described above would produce a suitable microfilm record, if it were possible to make an electrophotographic film of high resolution and great storability. It will be seen that if the photoconductive thin film layer could be made indefinitely, in the case of an addition to the supports already on the surface

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drawing each time only a charge of the surface of the thin film covering, an exposure of the same and a fixation of the new image would have to take place on the surface. It is assumed here that the toner is applied directly to the surface and is permanently fixed or fused onto it.

Transparent photographic recording media known so far are destroyed if they are exposed to light, elevated temperatures and moisture for a long time. They have to be handled carefully and stored under certain conditions and can only be repeated a limited number of times be exposed. Their use for record keeping Kind is very limited. For this reason, the use of such recording media for recordings of this type has developed proved impractical.

The above considerations take into account the disadvantages of known ones Systems only from a limited perspective. Considering some of the problems posed by the present invention are solved, it follows that the progress made is not limited to a small area.

The known silver halide gelatin layers of the photographic Films give higher speed and better resolution than known electrophotographic films of the so-called xerographic type. Nonetheless, the gelatin emulsion layers have drawbacks which are addressed by the invention can be avoided. In addition, it is noteworthy that the electrophotographic film proposed here can be repeatedly exposed to information and records without removing the existing record is adversely affected or destroyed.

Common silver halide films have an emulsion layer with a thickness of 140M- . The thin film covering of a film

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according to the invention has a strength of a fraction of an Ai . For this reason, conventional silver halide films cannot be easily bent without damage occurring. The resolving power of these films is also limited by the degree of undercutting of the flanks if the silver precipitates during development. Air bubbles in the emulsion create clouds or imperfections in the developed transparent photographic film. During production, the film cannot be examined in normal light and handling or transport is only possible in special dark packs. The emulsion is soluble in most liquids and is hygroscopic.

There has long been a need for an electrophotographic Film of great durability. The thin film layer or the active layer should be as hard as glass. Besides, she should be insoluble in most liquids and allow extremely high dissolution. The shift should continue be tight, not free from bubbles, which will be discussed later is, according to the invention by a sputtering process or spraying process is achieved in pressure vessels. The layer should also not be able to be changed by light, so that a free Handling and easy examination in bright light possible is. Furthermore, the layer should not be hygroscopic and not at all Sustained destruction by those influences which lead to the destruction of conventional silver emulsion film layers. Fungi or other microorganisms are said to be on an electrophotographic Film have no influence.

It should also be mentioned that the usual photographic emulsions and the layers of known electrophotographic films only respond in a limited spectral range, thereby limiting its use. The photoelectric gain of known electrophotographic coatings is important less than that of the electrophotographic of the present invention Films. This fact is largely for that

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Inability of previously known electrophotographic films responsible to achieve the extremely high resolution of the film proposed here. The greater thickness of known films or its active layer is a major factor in reducing the resolution.

Examples of previously known methods and devices are as follows US patents can be found in:

2 861 903 3 003 869

2,995,474 3,545,969

3 379 527 3 398 021 3 519 480 3 393 070 3 535 112 3 095 324 3 573 905 3 104 229 3 574 615 3 677 816 3 592 643 2 732 313 3 615 404 2 844 493

The invention is therefore essentially intended to achieve the object of combining the advantages of electrophotographic films with those of the films with the silver halide emulsion layer without having to accept the respective defects.

This object is achieved in a method for producing an electrophotographic film according to the present invention by the following method steps solved:

a) Deposition of a thin film layer of an ohmically conductive material on a thin, flexible, organic, transparent support with intimate connection with this and in a thickness in which the film layer is essentially transparent and flexible, and

b) sputtering on a thin film covering a completely

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inorganic photoconductor material on the film layer made of an ohmically conductive material with an intimate connection with this film layer and in a thickness, which leads to a photoconductor gain factor greater than one and is transparent and flexible Film layer results, the film in its overall thickness and not more than 30% light absorption below about 15%.

In addition, the invention proposes a film that features is by a carrier, which is able to carry film layers, also by a sputtered onto this carrier, thin film covering made of a completely inorganic, photoconductive material and a thin one between the support and a layer of film located on said thin film covering which enables easy selective removal of charges from the film covering with a corresponding selective exposure of the film covering with a certain radiation.

Expedient embodiments of the method indicated above or of an electrophotographic film according to the invention otherwise form the subject of the attached claims. Exemplary embodiments are described below with reference to the drawing explained in more detail. They represent:

FIG. 1 shows a highly schematic section of a transparent electrophotographic film according to the invention with a schematic indication of a circuit for charging the surface of the photoconductive top layer,

Figure 2 is a further sectional view of a similar, slightly modified electrophotographic film;

Figure 3 is a similar representation to Figure 2, but showing a slight modification,

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Figure k is a similar illustration to Figure 2, however

showing schematically the manner in which toner is applied to the surface of the photoconductive Layer is applied after exposure of the same and

Figure 5 is a graph from which the

Charge and discharge voltages for one electrophotographic film according to the invention in comparison with the example of a xerographic Plate are applied.

It should be briefly summarized again that an object is given here which can be used as an electrophotographic film and has a support made of a flexible, transparent, sheet or film-like polymer plastic body contains on which there is a thin film layer. The thin film covering contains a photoconductive material, for example η-conductive cadmium sulfide or zinc indium sulfide, with between the support body and the photoconductive layer is provided with a thin intermediate layer which is an ohmically conductive layer of indium oxide or the like contains or consists of these.

The term "thin film" shall be defined herein to include a layer of a material, for example the semiconductor or the above-mentioned photoconductor material, which is applied to a surface. Such a thin film layer has a thickness which measures several thousand angstroms and is, for example, about 5000 Å or 0.5, ^ * thick. on the other hand shall the term "electrophotographic film" or Efcer "Photographic film" in the remarks below Designate a complete object, which is composed of different layers or plies and in a photographic Method is usable. If a carrier or a carrier body or a carrier element is mentioned, this is not intended to mean a film be designated in the above sense, although the carrier that is used according to the invention, in the conventional

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a film can be in the first sense of the word.

It can be seen that the carrier is preferably a thin, flexible, transparent body made of a plastic sheet or a plastic film is what is commonly referred to as a plastic film has been.

The electrophotographic film of the invention contains one thin sputtered film layer made of an inorganic photoconductor material, which is also sputtered on Thin film layer of a conductor material is located, which in turn is connected to a thin flexible insulation carrier layer is, for example with a sheet-like plastic body high stability. The intended properties of the electrophotographic Films are transparency, flexibility, great sensitivity, high photoelectric gain, Economy, ease of manufacture, use and handling, the possibility of a complete exposure that can be repeated as often as required, stability under changing conditions with regard to light, temperature and humidity as well as other properties, which result from the following description. The properties of the film proposed here open up the Possibility for a variety of important applications, of which microfilming is by no means the least important.

The three important components of the electrophotographic film 10 are the sputtered thin film layer 12 made of photoconductive material, the split ohmically conductive thin film layer lh and the carrier body 16 "

If you first look at Fig. 5 of the drawings, you can see that here a diagram is drawn in which the properties of this typical xerogic carrier of the type known up to now (A) are unequal . a- ©! © tetroptootographic film when used in the here aiagegetoeinien way and are juxtaposed »

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The horizontal axis in FIG. 5 is the time axis with values increasing to the right, which are not necessarily plotted on a constant scale and the ordinate is increasingly calibrated upwards in potential values, again not necessarily on a constant scale. In the xerographic recording process, the photoconductive surface, for example a mixture of amorphous selenium or zinc oxide and resin, is charged by exposing the surface to a corona discharge in the dark. For the characteristic thicknesses of the corresponding surface layers, namely in the order of magnitude of 20 ^ u to 160 ^ u. the potential generated by the charge follows the solid line 30 and increases to, for example, about 500 volts. This takes place in a period of the order of about 60 seconds. While it is still dark, the charge begins to flow slowly, the characteristic curve initially following the curve section 32 shown in a solid line and then following the line 34 indicated by dashed lines. The point at which the corona current is approximately the same as the discharge current is referred to as the saturation level 35.

At the point in time indicated by the vertical dashed line 36, for example at the 90 second point, the xerographic plate is exposed to a certain distribution of light and dark areas which of course contain the information projected onto the plate. Here, the charge is selectively diverted to an extent that is proportional to the amount of light hitting the surface. Each photon of light brings an electron from the surface to combine with an elementary charge hole. The complete absence of electrons is shown by the state of the areas of the surface at the residual potential at 38 at the very bottom of the diagram, this residual potential being, for example, in the order of magnitude of JO volts to 50 volts. This last viewed © state corresponds to a pure white of the recording «, completely black area _:

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namely, those who have lost absolutely no electrons because they have not been exposed to light remain at the saturation level or the state of practically complete charging according to the curve part 3 ^. All the rest Areas are somewhere between these two extreme states.

The charge decay continues as shown, but at some point during the process, toner particles expediently become on the surface of the xerographic Plate applied and these are then as it were in an offset process on a sheet of paper and transferred through Burned-in permanently fixed in the paper. Then the toner, as far as it is still on the xerographic plate, is removed from this is brushed off and the plate can then be used again. In the meantime, the Plate made by a complete, very strong exposure.

The invention suggests the use of what is referred to as a plate to make a transparent photographic Make movie record so that no transfer of the toner takes place. Rather, it can be seen that the toner fused directly into the electrophotographic film itself is after this has been exposed and the toner has been applied, which is due to the extraordinary economy the method proposed here and the materials is possible. As far as is known, none exist commercially available Xerographic devices which provide the xerographic plate or support itself as a transparent end product. In any case, a transfer takes place. Copying processes with zinc oxide paper are an exception, but here it is no transparent recording medium received. Indeed The known recording media cannot be used as an end product can be used usefully if they are not transparent and can be used as a negative or as a transparent film record are.

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Looking at the support body itself, which is a fraction of a millimeter thick, the thickness of the electrophotographic element according to the invention is in most cases a fraction of Λ * - . The voltages to be used are therefore much lower than those required for the treatment of thick xerographic plates for known processes. In order to be able to carry out a comparison, an extrapolation of the characteristic curves is carried out in the diagram according to FIG. 5, assuming a structure in which the photoconductive layer is assumed to have essentially the same thickness as the photoconductive layer of the xerographic plate.

For the extrapolated structure of the electrophotographic film, therefore, the dark decay of the charge is so rapid that it is complete different conditions prevail. First, it should be noted that the corona discharge, which is the photoconductive surface whose potential increases to a value in the order of 2000 volts or above, which is many times greater than the value of the saturation potential. The potential achieved should of course not be higher than that which leads to a breakdown of the photoconductive layer. When the corona discharge is allowed to act, the potential increases of the photoconductive surface layer along the line 40 on the desired peak value, which happens within a fraction of a second, here within half a second. As soon the charging by corona discharge is finished, whereby the film is still in darkness, it begins to unload along the steeply sloping line 42 leading to the same Like the small section 32, the characteristic curve belongs to the dark decay characteristic curve for case A. At some point in time, for example 1/100 of a second later, the surface of the photoconductive layer a projected image or a Radiation in some other form, for example X-rays, exposed. The speed of exposure can be very large because of the steepness of the drop in the characteristic

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after this volume represents the ease of removal of electrons from the surface of the photoconductive layer. The dark decay curve continues in the dashed line kk , which finally hits the saturation level well below the charging potential, while the exposure-discharge line falls along the line 46 to the residual potential. It can be seen how quickly all operations can be carried out in order to be able to use the electrophotographic film proposed here in very fast cameras and the like.

A great advantage of such very fast electrophotographic It is films that brought the corona discharge into effect

can
become ⁷ when the photoconductive surface covering is already exposed, ie the corona can act in light and the toner can be added when a desired potential is reached. Compared to the relationships shown above, this can take place at a point on curve 52 and even near apex 48 ..

If one now looks at the potentials actually used, it follows that because of the extremely small thickness of the photoconductive layer, the actual potential am Points of maximum charge corresponding to vertex 48 no more than 50 volts to 60 volts or any voltage within this Range is. The other voltages are correspondingly proportionally smaller, which means that the facilities for exercising the The method proposed here is very simple in its structure will. The residual potential is, for example, a few volts in the method proposed here, while in the Case of the common xerographic plates is 30 volts to 50 volts. It can be noted that the operational Voltage range for the electrophotographic film of the present invention fully below the lowest voltage which are used in conventional xerographic processes.

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A closer look will now be given to FIGS. 1 to 3, in which an electrophotographic film according to the invention is shown in section, the dimensions being exaggerated and not coordinated in their mutual relationship in order to better explain the individual parts of the film. In each case, a carrier body 16, a photoconductive layer 12 and a conductive or ohmic layer Ik located between them are present. In the illustration according to FIG. 1, a contact with the ohmically conductive layer is made at 18 in that the photoconductive layer does not completely cover the ohmically conductive layer, so that part of the conductive layer Ik is exposed. A high-voltage source is denoted by 20, while 21 symbolizes a corona generator, which schematically indicates a circuit as a charging device which is able to apply a surface charge to the photoconductive, thin film covering 12.

In the exemplary embodiment according to FIG. 2, a part of the ohmically conductive layer Ik or a separate strip of a conductor material, for example aluminum, is provided along the edge in the manner indicated at 22 in order to facilitate the contacting of the ohmically conductive layer Ik. In the embodiment according to FIG. 3, this strip has the shape of a part 24 which engages around the edge and part of the underside of the carrier body 16. The contact strip 22 or 2k makes good contact with the ohmically conductive layer Ik and can easily be formed with a considerable thickness in order to be resistant to wear.

The three components of the basic structure are combined by an injection molding process or by sputtering, which is shown in a suitable pressure chamber is carried out. The carrier body is preferably cut out to the correct width before the coating takes place and is then passed through a first pressure chamber in which the ohmically conductive thin film

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layer 14 is applied to one of the surfaces of the carrier body. In another method, the entire supply for delivery and removal of the strip-shaped carrier body is arranged completely within the pressure chamber. In a corresponding W _e ise the second layer or the photoconductive film covering 12 is then sputtered over the resistive conductive film layer Ik. The contact areas 18 or the edge parts 22 or the lateral parts 2k can be applied by vacuum techniques or sputtering processes and / or by masking, which usually takes place before the two film layers Ik and 12 are applied.

The photoconductive layer 12

The photoconductive layer 12 is the most important component of the electrophotographic film because it is the most effective and physical Has properties which establish the particular advantages of the film proposed here over known films.

The material from which the layer 12 is made consists of a photoconductive compound or alloy which has the properties described. In the two examples which are considered below, n-1-sided! Cadmium sulfide (CdS) and zinc-indium sulfide (ZnIn ₂ S ^) are used. Other materials that can be used as the photoconductive film covering 12 are Si_N., ZnS, Sb-S ,, ASgS-, GaAs, CdSe, ZnSe and possibly other materials. These can be doped in various ways. The properties of the material are considered in more detail below.

1. The material is in any case completely inorganic, microcrystalline material with a thickness of several thousand Sngstrom. Previously known photoconductive layers or plates are considerably stronger and are therefore not in highly flexible and transparent. Known layers are very strong with resinous binders and other substances

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offset, which increase the opacity and are in generally applied by vacuum evaporation to a Avoid crystal structure, as large crystals make the layers brittle. The thickness of the thin film layer 12 is preferably below 3500 angstroms, but can also reach 5000 angstroms. The conduction of electrons and holes through the layer is in no way obstructed by such thin layers. The crystalline structure for at least one of the materials mentioned is oriented vertically, i.e. perpendicular to the surface on which the Layer is applied, which is based on the sputtering method of application, which is used according to the invention.

As an example of the flexibility of the photoconductive layer when deposited on a sheet-like, flexible polyester support, in a thickness of 0.125 mm, it is indicated that the electrophotographic film can be wrapped around a mandrel or cylinder with a diameter of 6 ^ 25 mm without that cracks or cracks occur. The possibility of the electrophotographic Loop film around cylindrical bodies or mandrels that are fractions of a centimeter in diameter to be able to make it clear that the electrophotographic film of the invention can be easily processed by processing machines and playback devices can be transported.

Another property related to the fact that layer 12 is inorganic, thin and crystalline is, consists in their hardness. The requirement that the surface should be as hard as glass was already mentioned above. Abrasion resistance is in use and handling of the film is important as it helps avoid scratches, scrapes and the like, which can lead to damage or a Loss of details and data can result, especially if the information recorded is very fine is. When making the electrophotographic film

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no difficulties arise when necessary is to apply the film by friction between the adjacent film surface and the friction wheels or rollers or the like move.

Due to its low strength and semiconductor properties, the material is electrically anisotropic. That means, that the material has a non-uniform distribution of electrons for at least a substantial period of time and holes embossed on the layer or made in the layer can be maintained, such as is required in the method of using "the electrophotographic film described herein.

The material has the property of a high photoelectric amplification factor. The two special materials mentioned here, for example, are η-conductive cadmium sulfide and zinc indium sulfide. The former has a dark resistance of 10 SL · cm, a specific light resistance or exposure resistance of 10 Sa / cm, and a forbidden band of about 2.45 eV. The last-mentioned material has a specific dark resistance of 10 S2t cm and a specific light resistance of 10 Su cm to 10 _ß- cm. The optical transmittance should be 70% and not more than 85%. A relationship of the specific dark repulsion

4 Standes for the specific light resistance of 10 or more is particularly advantageous for creating extremely fast electrophotographic films.

Zinc indium sulfide is because of its high specific dark resistance and the low specific light resistance in many areas of application of electrophotography advantageous according to the invention, while cadmium sulfide due of the rapid decline in darkness, preferably used in finds the method in which images have to be generated very quickly.

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The property of high photoelectric amplification factor is important as it increases the sensitivity of the electrophotographic Films according to the invention are increased to the extent that the film speed is comparable with the sensitivity of the fastest photographic Films will, but not necessarily, have the same peculiar loss of subtleties due to large grains occurs. The films according to the invention have practically no grain after the crystalline structure of the surface layer is microscopic. In the case of a photoconductive material, a high gain means that upon impact A photon on the material releases a plurality of electrons instead of a single electron will. The more electrons are released, the higher the gain factor.

The increase in the gain of the photoconductor of the electrophotographic film of the present invention is believed to be due on the release of free electrons from energy levels in the forbidden band of the photoconductor and stands in exponential relationship with the low strength of the photoconductor. In other words, the thinner the photoconductive Layer, the greater the release of electrons and the more sensitive the electrophotographic film.

The photoconductive film layer must be applied by sputtering in order to obtain the properties given above. No other coating or deposition process of the type known today leads to the specified properties.

Some considerations will be given to the gain factor of the photoconductive layer. If from the photoconductive. Layer an electron is removed when a photon is absorbed, one can say that the gain factor has the value one. Are several electrons ejected ₉

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so the gain factor is greater than one. It can be seen that the thickness of the photoconductive layer 12 should be so that there is sufficient material to produce the desired light absorption and the desired abrasion resistance while at the same time the layer is thin enough to achieve the desired gain factor. Practically can proceed in such a way that a layer thickness is deposited which gives the maximum gain factor with the minimum thickness. This can easily be done experimentally for a given material by measuring the light absorption and determining the amount of light Determine the abrasion resistance and the strength by suitable means, taking into account the deposition of photoconductor material continues until a practical compromise between the mentioned properties of the layer and the desired one photoelectric gain is achieved.

The requirements regarding light absorption must be met in any case. In the method according to the invention this is possible, whereby one obtains a photoconductive layer which has an amplification factor of substantially above. Has one and is excellent in abrasion resistance.

It goes without saying that the proportions of the individual elements which are involved in the photoconductive layer are stoichiometric are correct, which can be achieved by appropriate control of the deposition conditions. The proportions of the dopant must also be controlled, which, however, after the "entire layer is inorganic." is feasible with conventional control methods and is relatively simple.

3. The material has a sensitivity in a wide range Spectral range. A sensitivity spike in the area of 5000 sng currents is particularly beneficial for a variety of use cases of electrophotography. The above

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materials mentioned as the material for the thin film layer 12 show a broad spectral sensitivity. It understands that it is desirable; that most types of radiation, with which recording is to be made, on the electrophotographic film of the one proposed here Art can produce pictures «The responsiveness of the film of the present invention covers the entire range of visible light as well as X-rays and Radiations that can be found in physical laboratories and are currently recorded by other means »

Cadmium sulfide doped with an appropriate donor material exhibits panchromatic responsiveness. Zinc indium sulfide has a more universal response sensitivity, but has to be doped selectively in order to be able to use certain. Areas to improve the Ansprechemp · ⁴ -findlichkeit "Normally the Ansprechempf indlichkeit her -Maximum% at about 800 angstroms," As dopant for cadmium sulphide the examples mentioned herein copper is used in..

The material can be easily deposited xfsrden _o This property is of Bedeutungj, since it allows a gleicliförmige _s controllable high speed production, "The application of the layer is done by sputtering or spraying in a correspondingly it Brwstk.B, mmer using a high frequency field © s _o it do not need pastes ,, masses or resins gehandhafot be "SäEatliehe materials are introduced into the pressure chamber ^ either in Fora of consumable AnocäsEa", right? oe gas © n ₉ or sublimated connections ₉ of the bet reff in the Ätiaogpiiärs end sin pressure vessel eisagebraciit "- / earth, after the procedure has been set in LaMf _o The s'iöcliiometres correct files let them»! sees sinregialiersn, so that nan

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a substantially flawless and uniform product can achieve.

The advantageous properties mentioned above are by no means complete. The use of a photoconductive layer of the type proposed here results in a number of others Benefits. In addition, the order given above is not to be understood as an order of importance.

The ohmically conductive layer 14

The ohmic layer 14 is a conductive layer on which the carrier body 16 is deposited before the photoconductor layer 12 is applied. The main purpose of the senior Layer 14 is to drain electrons from the surface to promote the photoconductive layer when the latter absorbs photons. In addition, the conductive layer serves to ensure the adhesion to improve the photoconductive layer on the support body.

The ohmically conductive layer is significantly thinner than the photoconductive one Layer 12 and is preferably on the order of 500 Angstroms thick. This strength does not lead to any disadvantage Influence the transparency and flexibility of the finished photoelectric film. The conductive layer forms a separation layer between the photoconductive layer 12 and the Support body 16. The conductive layer is as part of a capacitive arrangement during the charging of the surface of the photoconductive layer effective in addition to the function of removing the released electrons from the photoconductive layer.

A certain purity grade of indium oxide semiconductor material is suitable as material for the ohmically conductive layer 14. It can be easily connected with the aluminum edges or with conductor strips. Also, it can be easily put in by sputtering the same devices are applied that are also used to apply the photoconductor layer. Other application

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drive or deposition processes of the previously known type do not result in the density, the connection and durability as well as the Flexibility as required in photographic film.

A metallic layer with a thickness of the order of magnitude of 100 Angstroms can be applied directly to the support body 16 between the ohmically conductive layer 14 and the support body 16 in order to ensure the adhesion and connection between the support body 16 at the edge of the overlying, inorganic, non-invasive conductive or to improve photoconductive layers Ik and 12, but this is not absolutely necessary. Such a metal layer may be made of titanium and is denoted in FIG h with 15 °. This layer can easily be applied in the same way as the other layers, ie preferably by sputtering, but possibly also by other deposition or coating processes.

The carrier body 16

The carrier body 16 is the carrier or the mechanical holder for the photoconductive layer 12 and the ohmic conductive layer lh. The properties of the carrier body have been dealt with above, but not discussed in detail. The mechanical properties are flexibility, strength, Transparent _r ence, the ability of a good adhesion to the deposited layers and what is very significant stability. Stability includes dimensional stability, stability in maintaining a certain strength, stability in terms of resistance to any changes which might occur due to exposure to certain temperatures and electrical processes which are present within the pressure vessel during the coating process. When choosing a suitable carrier material, abrasion resistance is also an important aspect.

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Sheet-like polyester material with a _{thickness of Ø 9} 125 mm is, for example, a carrier material which delivers uniformly dividing results. This material is an organic polymer. Excellent properties for example, has Oer under the trademark "Mylar" commercially erfaä ¹ tliche material. This material comes into a state of internal tensions ote sale, which are in the material due to the way in which it is manufactured. Before use, such stresses are preferably removed j, which is done by a process called normalization. For this purpose, the film can be exposed to an environment -w & n 80% relative humidity and a temperature of 10 ° S for a period of 30 minutes in a manner that is per se feel-good.

The material of the carrier body should not contain any gases, and if necessary, such gases can be degassed in appropriate chambers. In addition, the film material should be completely clean and free from static charges With so-called radioactive brushing carried out, the method of making the electro-photographic film 10 should be described in more detail

If we go from the already fully prepared interrogator l6 from ρ so! first step in the manufacture of I Issiag in the application of the ohiiisch conductive layer lh, wele-Ens aiiea order from several layers of conductor material kamia ims] fösig the conductive layer 15 contains *

In the case of the BescßiGtotuagsverfaiiirs used here necessary a DrsiGlikasäiaer for. Use and the coating gssc by sputtering or spraying with a PlassaaiSanipf Issi presence of an electrical high frequency field, öer interfering body becomes on. an anode arranged or via an Aaiseie BalEiwegge - j xvsiiK a manufacturing process carried out χ-ϊΐτά ₅ t-jobei the anode is made of stainless steel and by means of water or © ines

ο
other coolant is cooled to about 80 C _o SenäE a b®-

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3 ·. , ι ο ο Ί / 1 0 7 9

Preferably in the form of a coating device, the carrier body is moved in the form of a long strip over the anode, which is then formed by a pulp or drum. Small support bodies with a side length of, for example, 5 cm can be placed on the anode of known sputtering devices for laboratory-standard production or for production in lower quality.

The cathode of the device consists of the material from which the layer to be deposited is to be made or contains several of the elements contained in the layer. Next © Elements can be added by introducing them into the chamber. In an example carried out for experimental purposes, the cathode consisted of an indium oxide semiconductor type, it was used to deposit the ohmic conductor layer 14. The cathode is removed from the anode according to the physical properties of the chamber in question, the geometry of the arrangement, the voltages used and the like must be taken into account. In the example mentioned, the chamber was evacuated to a pressure close to the range of 10 Torr. This essentially represents a vacuum. Then high-purity argon, GLiI _{0, became} an argon that contained less than 0.01 parts per thousand of water and nitrogen , admitted into the sputter coating canal via an auxiliary vent valve until a pressure of about 50 millitorr was reached.

At a suitable point the high frequency eld is switched on and the ionization of the argon leads to the generation of electrons or ions, which hit the cathode or the anode and knock particles of the indiumoside out of the impingement electrode, creating a plasma ampoule between the cathode and the anode and the particles * are transported in the Sicntiang to the anode, where they are stored on this carrier body »

This sputterwrfahress. oü & r Amispritsvsrfahrsn gsfet sit © iner speed before siefcu the el ure Ia ca ie 3ecä ing wear within the coating system Ibeeisiismt is unü characteristic

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.3 09861/107

is slightly less than approximately 75 Angstroms per second. the Formation of the layer thickness is monitored by optical devices, which are known per se, up to a layer thickness of about 500 angstroms is reached.

The carrier body is then removed from the coating chamber and as the manufacturing progresses into another Chamber introduced or guided through the chamber. Will If the procedure is carried out in the laboratory or if it is a very small production, the same chamber can be used replace the cathode or the target.

In any case, the carrier body 16 with its first coating in the form of the ohmically conductive layer 14, in the case of the present example with its indius oxide layer, is again attached to an anode holder or passed over a rotating anode or the like. In this case, the anode is cooled hardened, so that it is cooled down to about 40 ° C, since when the pliotoconductive layer 12 is deposited, greater energy ?! effective and "Cold water or liquid nitrogen can be used as a coolant"

For the production of a photoconductive layer made of cadmium sulfide, which is n-type3 becomes the cathode or the landing electrode formed from kaemia sulfide or even from cadmium alone.

-8th
The pressure is first lowered to 10 torr before it is raised again to 60 millitorr and argon gas and hydrogen sulfide are added later. The hydrogen sulfide supplies the correct amount of sulfur in the plasma vapor so that the stoichiometrically correct proportions of cadmium and sulfur are deposited on the ohmically conductive layer. It should be noted that in both coating processes the rear surface of the carrier body i6 is covered in order to avoid deposition on the rear side during the normal process. In the case of a cadmium sulfide cathode, the amount of hydrogen sulfide added is about 0.05 per thousand based on the argon. In other cases

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30985 1/1079

len in which a cadmium cathode is used _s this proportion can be increased,

A small amount of copper in the form of sublimed copper chloride is let into the handling chamber for sputtering, what happens in such a way that the copper salt is kept in an evacuated container with the Behänd treatment chamber over a Has control valve connection. In the present case, copper is the dopant, which the. Cadmium sulfide semiconductor n-type power.

Other methods of doping are ion implantation, that Diffusing and the like.

The application of a high-frequency high voltage produces the necessary plasma to the deposition of the Kadmiums.iilfids on the ohmic layer to srreichsn _s so that the photoconductor layer may be formed 12th The rate of deposition in an experiment carried out was approximately 50 Angstroms per second. The copper is added in small, controlled amounts which are sufficient to cause the cadinium sulfide to be doped on the

-k

Ohmic conductive layer with a thickness of 5 · 10 percent by weight to reach. The sputtering continues until the thickness of layer 12 reaches 3000 Angstroms. In the case of the executed In the experiment, the layer had a microcrystalline structure with an average diameter of the crystals of about 0 or about one third the thickness of the layer itself.

The electrophotographic film thus prepared has the properties given above with respect to film 10. Of the The film produced in the experiment had a yellowish appearance, which is characteristic of the thin layers that were applied had been. Electrophotographic Films Including Sink Indium Sulphide Is used, do not require any copper doping In this case the color of the film is bluish,

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309851/1079

For use, the - electrophotographic filai by means of a Corona arrangement charged to high potential, as in Ina context with Figure 5, this potential being compared to the normal saturation level of electrophotographic Film is very high «, the exposure is on a very high point located on the dark decay curve. So the movie will charged to the apex 48 of the characteristic curve 40 and then exposed a fraction of a second later, just naelndem the section% 2 of the characteristic curve due to the Dux & fcel charge drop has gone through "

The correct time is set under the control of an exposure meter, so that the charge builds up to an optimum value for the respective lighting conditions, depending on which the electrophotographic film is "exposed" _or this is done automatically.

It is noteworthy j that the preferred © kind is exercises using the electro-photographic film 10 disjeiaigs, wherein the _t film is substantially a charge shock receives "In feerlcömmlichen xerögraphisehen method" ö © r Aiiissiciiiniiigstrager or plate is charged to saturation ;, ü _o h _a to & nf eim © n points in which the charge conducted by the carrier is approximately equal to the charge build-up. This is the case with respect to curve 3® at approximately the height 35. When the ele & trepiiotographic film 10 is used, this becomes If the saturation level is charged very quickly and then exposed, the voltage must be lowered quickly.

After the elektrophotograpliiscfcis Fila beliciitet xj © 2 °! Ä © a, the surface of the photoleitemdea Sohich-t sesar rassii umd uniform toner supplied _o Bsr toner is vorauagsx? Sise applied in the presence of a bias voltage. Which rer in MMuiitmlh & vicinity of .Filmoberf lach © effective is unu ßi® ToimerpairMEsslGfiiea accelerated towards the surface, which si®Sa © results in a more uniform distribution of the particles “Bis

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31 ■ 9851/1079

Fine carbon! ^ Toner particles can be used to produce black and white film images can be used. They can also be colored or use colored resins.

Eventually, excess toner is immediately wiped off the surface and the remaining toner adheres to the film surface by uniform infrared irradiation or the like melted solidly so that the entire process is completed before the surface tension of the electrophotographic film the lowest value or the background value has fallen. This time is on the order of a small fraction one second and is preferably about 10 milliseconds. The toner is then permanently adhered to the surface 28, as in FIG Figure 4 is indicated at 26.

In using the electrophotographic film 10, it is after the toner has been applied and before the fixing by melting down, the toner distribution is already determined. The subsequent drop in charge therefore does not have any significant effect the image now made visible, which is represented by the position of the toner particles. For fusing the toner immediately after spreading and removing the excess is not a high speed facility necessary. Rather, the fixing can be done within a reasonable amount of time take place over a long period of time. However, another advantage is achieved, particularly in the case of use of the electrophotographic film is valuable in experimental work. Before the toner is melted down, the operator can namely examine the film or the toner distribution carefully to determine whether the desired image quality has been achieved. If the image is not satisfactory, he can adjust the exposure conditions, the exposure time, the setting of the optics, etc. change to finally get a better picture. The toner image generated during the previous exposure process only needs to be wiped off the film, which is in

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0 9851/1079

can be done easily by means of a rag or cloth, so that a clean surface remains. So there is no Loss of electrophotographic film and there is no loss of time to achieve the desired results to take.

The resulting object is a transparent film image, which projected or used to make prints. The picture is characterized by a high degree of resolution from what the film and the proposed method of use are particularly advantageous for the production of microfilm images. The image produced is extremely rich in contrast and has a very pure background. When projecting at a greatly enlarged Scale for viewing or for copying purposes, the resulting enlarged image is still very much in the details good and is relatively free of defects in the white or light areas.

The above-mentioned compounds, which also include cadmium sulfide and zinc-indium sulfide, have properties similar to those of compound to connection are different. The requirements regarding the spectral response sensitivity, the specific Dark and light resistance, the dark and light decay characteristic, the gain factor, the ease of application a carrier by sputtering etc .. must be considered and may require an experimental determination for the circumstances under which the connection in question is to be used. In general, it should be noted that all connections known as photoconductors, if also to varying degrees, are useful.

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3 0 9 8 5 1/10 7 9

Claims (19)

Claims 1. Method of making an electrophotographic film, characterized by the following process steps: a) Deposition of a thin film layer of an ohmically conductive material on a thin, flexible, organic, trans parent carrier in intimate association with this and in a thickness in which the film layer is substantially is transparent and flexible and b) sputtering on a thin film coating of a completely inorganic one Photoconductor material on the film layer Ohmically conductive material in close connection with this film layer and in a thickness which leads to a photoconductor gain factor greater than one and Trans parence and flexibility of the film covering results, the overall thickness of the film does not absorb light above 30% and not below about 15%. 2. The method according to claim 1, characterized in that the Sputtering takes place in the presence of a high-frequency field. 3. The method according to claim 2, characterized in that a doping of the photoconductor material by during the sputtering Introducing a dopant into the high frequency field takes place. 4. The method according to any one of claims i to 3, characterized in that that sputtering to build up the required thickness of the photoconductor material, takes place gradually and that the sputtering is continued until a thickness of the photoconductor material has set which is an optimal combination of - 30 - 309851/1079 Photoconductor — gain, transparency, flexibility, and abrasion resistance results, 5. Electrophotographic recording medium, which in particular is manufactured according to a method according to one of claims 1 to 4, characterized by a carrier body (l6) on which thin film layers can be applied, furthermore by a sputtered thin film covering (12) made of photoconductor material, which is completely inorganic and is located on the carrier body and through a thin film layer (l * t) which is between the carrier body and the thin film covering made of photoconductor material and a selective derivation of charges from the photoconductor material in the case of selective Exposure of the same facilitated by radiation. 6. Recording medium according to claim 5, characterized in that that the carrier body (16) is a flexible, transparent, organic film material or sheet material consisting of a polymer is that the thin film covering (12) made of photoconductor material is a semiconductor with a light transmittance of over 70%. is and that the thin film covering (14) is made of an ohmically conductive material. 7. Recording medium according to claim 5 or 6, characterized in that that the thin film covering (12) made of photoconductor material 12 O a specific dark resistance of at least 10 -A ^ cm has and that its relationship between specific dark resistance and specific light resistance is at least about 10. 8. Recording medium according to one of claims 5 to 7, characterized in that the thin film covering (12) made of photoconductor material and the thin film layer (lk) made of ohmically conductive material are less than about 5000 angstroms thick, are flexible and together with the carrier body ( l6) essentially have such transparency that less than 30%, but not less than 15% - 31 - 0 9 8 5 1/10 7 of the incident light are absorbed. 9. Recording medium according to one of claims 6 to 9, characterized characterized in that the semiconductor is η-conductive. 10. Record carrier according to one of claims 5 to 9, characterized characterized in that the thin film covering (12) of photoconductor material consists mainly of cadmium sulfide. 11. Record carrier according to one of claims 5 to 9, characterized characterized in that the thin film coating (12) made of photoconductor material consists mainly of zinc indium sulfide. 12. Record carrier according to one of claims 5 to 11, characterized characterized in that the thin film coating (12) made of photoconductor material is doped with copper. 13 »Recording medium according to one of Claims 5 to 12, characterized characterized in that the thin film covering (12) made of photoconductor material about 3000 angstroms thick and that the thin film layer (14) of ohmically conductive material is less than 1000 Angstrom is thick. Ik. Recording medium according to one of Claims 5 to 13, characterized in that the thin film layer (14) made of an ohmically conductive material consists essentially of indium oxide. 15. Recording medium according to one of claims 5 to ik, characterized in that between the thin film layer (14) made of ohmically conductive material and the thin film covering (12) made of photoconductor material on the one hand and the carrier body (16) on the other hand, a thin metallic film intermediate layer ( 15) is arranged. 16. Record carrier according to one of claims 5 to 15, characterized characterized in that comprising the thin film layer (14) - 32 - 309851/1079 Ohmic conductive material conductor elements (22, 24) connection have, which establish the connection to external circuits or devices. 17. Record carrier according to one of claims 5 to 16, characterized characterized in that the thin film coating (12) of photoconductor material has a photoconductor gain factor which is much greater than one. 18. A method for forming a film image using an electrophotographic film comprising a flexible, film-like, transparent carrier body, a flexible, transparent, thin, ohmically conductive film layer, which is connected to the carrier body and a flexible, transparent, inorganic, has thin film coating made of photoconductor material, which is connected to the ohmically conductive layer, wherein the The total thickness of the ohmically conductive film layer and the film covering made of photoconductor material is less than about 5000 Angstroms, in particular using a recording medium according to one of claims 5 to ± 7, characterized by the following process steps: a) Charging of the surface of the film layer made of photoconductor material through corona to a potential that is significantly above the saturation level of the photoconductor coating, b) Exposing the surface of the film covering made of photoconductor material with a certain radiation distribution after the surface has been charged, but before a substantial one Cargo has been dropped and c) supplying toner to the surface of the film coating made of photoconductor material as soon as possible after exposure, to obtain a toner distribution corresponding to the radiation distribution. - 33 - 30985 1/107 9 19. The method according to claim 18, characterized in that the toner is fused or burned solid after supply. 30 985 1/1079 Blank page