DE2217860A1 - Method and apparatus for developing latent electrostatic images with a plurality of electrodes - Google Patents

Description

DR. ING. E. HOFFMANN · DIPL. ING. W. EITJLB DR. RER. NAT. K. HOFFMANN

FATXNTASWlLTS D-8000 MUNICH Il · ARABELIASTRASSE * · TELEPHONE (0811) »11087

Xerox Corporation, Rochester, Ν.Υ, / üSA

Method and apparatus for developing latent electrostatic images with a plurality of electrodes

The invention relates to an electrophotographic apparatus comprising a photoreceptor, a device for building up an electrostatic latent image on the photo receptor and means for Developing the image on the photoreceptor by supplying toner powder to the photoreceptor, a device for developing an electrostatic latent image and a method for developing an electrostatic latent image Image

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In conventional electrophotographic processes, such as shown in U.S. Pat. No. 2,297,691 or as elsewhere, Referring to electrophotographic techniques known to those skilled in the art, a photoreceptor is charged and selectively exposed so that the object to be copied is exposed representing latent electrostatic image as a result of the selective discharge of the surface of the photoreceptor according to a chiaroscuro pattern, which represents the object to be copied, is built. The built-up electrostatic latent image then becomes general developed or visualized by the application of charged finely divided particles known as toner to the image area of the photoreceptor in such a way that these charged particles appear in a selective pattern on the photoreceptor Image area of the photoreceptor are deposited in accordance with the charge pattern of the built-up latent electrostatic image. The developed image thus constructed can then be fixed on the surface of the photoreceptor or, as is usually the case, transferred to a transfer member such as a sheet of paper and fixed thereon so that the photoreceptor can be used again Use is available.

When developing an electrostatic latent image by applying charged toner particles on the surface of a photoreceptor, the outline of the electric field Ib area of the electrostatic latent image plays a critical role in the manner in which the toner particles are removed from the surface of the Are attracted to the photoreceptor and deposited on it. In detail, the toner particles in areas where the electrostatic latent image has sharp electrostatic contrasts, such as in parts of the image which

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correspond to a boundary between light and dark parts of the object to be copied and so by a Edge field are marked, adhere tightly. However, in areas which are extensive dark areas of the correspond to the object to be copied, an edge field build-up will only occur at the edges, and if so such an area is developed by the application of oppositely charged toner particles, become the edges such an area is solidly developed black due to the deposition of high density charged toner particles while parts of the photoreceptor are in the No high density toner deposit was obtained in the middle of such an area and therefore did not develop densely black will. This phenomenon in development occurs due to the different charge levels and therefore the greater field intensity or the sharp tension contrasts at the borders between light and dark Sharing an electrostatic image and due to the fact that there are more toner particles in areas of sharp potential differences be deposited. In the middle parts of a large solid or continuous area of the image the voltage contrast between adjacent dots is small and the deposition of toner during development is reduced accordingly.

While the above phenomenon is advantageous due to the resultant high-contrast development is related to the development of latent electrostatic images from line drawings or the like, the same phenomenon actually excludes electrophotographic copying of objects, which have continuous tone qualities, and in particular

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special τοη those which are characterized by large continuous or solid areas in connection with a dark image pattern, because the resulting developed image derived therefrom would have halo effects and would generally result in a washed-out appearance. However, it is well known to those skilled in the art that the adverse effects which characterize the above development phenomenon can be completely prevented or alleviated by a device known as a development electrode. Development electrodes, in their simplest construction, can be in the form of a conductive sheet placed near and parallel to the surface of a photoreceptor on which the electrostatic charge meter is built. The developing electrode normally has a bias voltage with respect to the charge pattern or the electrostatic latent image formed on the photoreceptor, and the bias voltage can be selected to be equal to the potential level of the background of the electrostatic latent image so that the background is developed evenly white Development electrode consists in changing the field configuration of the latent electrostatic image and effectively modifying the image in the space over large continuous areas of charge. So we ken development electrode for varying the field configuration of the latent electrostatic image so that the different parts of such a latent electrostatic image can be developed in a manner that is more proportional to their electric Ladun ^ sdichte instead proportional to the voltage gradient occurring in a relationship. Further, a developing electrode acts closely to intensify the electric field

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the surface of the photoreceptor, eo that the field strength at each point between the surface of the photoreceptor and the development electrode proportional to the potential the surface of the photoreceptor will be on which the electrostatic latent image is built up, and inversely proportional to the distance between the photoreceptor and the developing electrode. In order to be used effectively, a developing electrode must be relatively be located close to the photoreceptor on which the latent electromagnetic image is built up. So is how well known to those skilled in the art, the use of a developing electrode or a device with the properties thereof indeed imperative for the development of continuous high quality tones from electrostatic latent Images and for the reproduction of solid or solid black areas of a to be developed Image.

Of the many development techniques known to those skilled in the art, modified cascade development techniques have been used have found wide application areas and are commonly used in electrophotographic processing equipment, because with their help, large amounts of toner powder can basically easily get onto the surface of a photoreceptor can be applied, causing an image development high density can be achieved. Cascade development techniques are based on triboelectric principles, according to which two dissimilar materials are brought into contact with each other and each material a resulting one Has charge polarity opposite to that of the other. Accordingly, as for example in the US-PS 2,297,691 in cascade development techniques relatively fine toner particles with a coarse

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like material, called carrier, mixed to form a developing cartridge, whereupon the toner particles are triboelectrically charged and attached to the surfaces of the Carrier particles adhere. The development of an electrostatic latent image can be carried out by that such a composed developer powder cascade-like scattered over the surface of the photoreceptor becomes or flows. If the carrier particles now move over the parts of the surface of the photoreceptor which are occupied by the latent electrostatic image, the electrostatic forces created by the electrostatic latent image become the electrostatic ones Overcoming bonding between the toner particles and carrier particles, so that such toner particles are on the image area of the photoreceptor. The cascading scattering of the developer powder can be achieved by simply passing developer powder over a photoreceptor is poured in the form of a plate and the photoreceptor is reciprocated to effect the developer movement and the removal of the carrier particles. Alternatively can in a continuous electrophotographic copier in which the photoreceptor is normally in the form of a drum or continuous belt, the developer powder is poured over the surface of the photoreceptor using gravity and the large quantities of toner and carrier powder are captured and returned to the cycle for reuse will.

The cascade development technique briefly described above represents a fairly ideal type of development for latent ones electrostatic images of line drawings and the like, because the field configuration occurring there such as

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mentioned along with the large amount of available toner particles guided to a visible image build-up which has solid black characteristics and sharp contrasts. However, if cascade development techniques related to electrostatic latent If images are used which have continuous toner characteristics and / or large or solid black areas, the resulting developed image will die have washed-out appearance with halos as described above. Correspondingly must for a successful Application of Cascade Development Techniques to the Development of Electrostatic Latent Images with Continuous Tone Development in the presence of a development electrode from those detailed above Reasons take place.

In typical two-component developer materials or powders commonly used, show the carrier particles used for the triboelectric charge of the toner powder typical size variations in the range of 25o to 600 / u diameter, although Carrier particles as small as 1oo / u in diameter are known. Therefore, when developer having such carrier particles is used in a continuous process electrophotographic apparatus, it can be understood that when a developing electrode is sufficiently close is arranged on the surface of the photoreceptor that its field-changing properties have a significant effect the developer powder will tend to get between the surface of the photoreceptor and the developing electrode to clump. This clumping of the developer powder not only prevents good development in the Application of cascade development required free flow

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In addition to this, it often results in soiling of the developed image and in scratching and damage due to abrasion of the surface of the photoreceptor along with significantly reduced development times. Since cascade development techniques are generally preferable, considerable efforts have been made to solve the problem which arises from the conflicting requirements of _{placing the development electrode close to the surface of the photoreceptor on the one hand and} using sufficient amounts of developer powder which cascade freely over on the other hand the surface of the photoreceptor can flow so that a densely populated, rapidly developed toner image can be built up. However, since the spatial requirements of a properly arranged development electrode as mentioned above are generally opposite to the requirements of the cascade development technique, the solutions presented so far have tended to compromise on the parameters used for both the development electrode used and the one used To proceed cascade development technique. For example, in certain electrophotographic copier systems, smaller amounts of developer powder are cascaded over the surface of the photoreceptor in order to reduce the clumping effect caused by the development electrode, and the development electrode is placed at a greater distance from the surface of the photoreceptor than would otherwise have been selected. However, this compromise has proven to be not very useful and desirable, because it leads to largely reduced development speeds and thus i. ^r : machine speeds, while the development electrode

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called effects are weakened _c According to other solutions, special development electrodes are used, as shown for example in US Pat. No. 3,147,147 and 3,011,474, where the development electrode has openings in its shape or is layered and thus shaped that the flow of developer powder is optimized while developing electrode spacings are used, which are calculated so that a clumping of developer powder is avoided. However, these solutions have proven to be far from ideal, since grooved, layered, or apertured development electrodes are expensive to manufacture and, due to the discontinuous surfaces used, must have fairly large surface areas, and further such specialized development electrodes are not close to the surface of the Photoreceptor can be arranged on which the electrostatic latent image is built up.

Next, although in fact, all of the commonly used electrophotographic devices have continuous Process a separate cleaning station for removing residual toner particles from the surface of a reusable one Use the photoreceptor before each use of the photoreceptor, recent advances in cascade development technology, as described in TJS application serial number 789 o31, filed December 31, 1968 for the applicant, have indicated that the step of cleaning or removing remaining Toner particles from the surface of the photoreceptor following the formation of a new electrostatic latent image and during the development of such a new latent electrostatic Image can be done. The-

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This development cleaning technique is likely to have possible properties which are very desirable in a continuous process electrophotographic apparatus and is useful because successful development cleaning techniques of eliminating a special cleaning device in electrophotographic machines with continuous Methods using cascade development techniques made possible. So not only would the resulting one Construction of electrophotographic devices can be greatly simplified when using development cleaning, but rather in addition, manufacturing and maintenance costs associated with a separate cleaning stage would be avoided.

The aim of the invention is therefore to provide a method and an apparatus for developing latent electrostatic To create images with development electrodes in which the development electrode structure used caused field changes are brought to a maximum, while large amounts of toner powder during development such an electrostatic latent image can be supplied. Further through the invention Process for developing with simultaneous cleaning and an apparatus therefor are provided in which residual toner particles from a previous development can be removed during development high quality with continuous tone of an electrostatic latent image.

The invention is intended to create a development device with a split electrode, at wely'her the properties of one part of the split electrode for use with large amounts of developer

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powder is optimized for high flow rates » while another part of the divided electrode has properties which are optimum for development of low density parts and extended areas of an electrostatic latent image, but developer powder can only accommodate at relatively reduced flow rates.

This aim is achieved according to the invention with an electrophotographic device of the type described in the opening paragraph achieved by having a first development electrode adjacent the surface of the photoreceptor and in the llhe the place where the photoreceptor toner powder is placed at such a distance from the surface of the photoreceptor that a considerable Amount of toner powder between the surface of the photoreceptor and the first development electrode feasible is a second development electrode adjacent the surface of the photoreceptor near the first Development electrode closer to the surface of the photoreceptor than the first development electrode to allow only a reduced amount of toner powder to pass between the surface of the photo » receptor and the second development electrode. net, wherein the second development electrode is a sufficient distance from the first development electrode to the Passing an amount of toner powder at least equal to the difference between the substantial amount and that having reduced amount, and potential sources for applying a reference potential to the first and second Development electrode for modifying the fields of the latent electrostatic built up on the photoreceptor Image are provided by the first and second developing electrodes.

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An apparatus according to the invention for developing an electrostatic latent image on a surface is characterized in that a feed device for the cascade-like scattering of developer powder over the surface with a high flow rate is, a first developing electrode adjacent the surface at a location where the developing powder is applied to the surface, at such a distance from the surface that a considerable Amount of developer powder between the surface and the first development electrode feasible and a second development electrode adjacent the surface of the photoreceptor in the vicinity of the first development electrode at a closer distance from the surface of the photoreceptor than the first developing electrode for passing only a reduced amount of toner powder between the surface of the photoreceptor and the second development electrode is disposed with the second development electrode a sufficient distance apart from the first developing electrode for passing an amount of toner powder at least equal to the difference between the substantial amount and the reduced amount.

The method of the present invention for developing an electrostatic latent image is that High-flow developer powder cascades over an electrostatic latent image Surface is guided, a first development electrode adjacent the surface at a location near the Application of developer powder to the surface and arranged at such a distance from the surface wir4 that developer powder between the surface and

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of the first development electrode with the high flow rate can flow through a second development electrode adjacent to the surface near the first development electrode at a smaller distance from the Surface is arranged as the first development electrode, thereby only reducing the flow through a Allow amount of developer powder between the surface and the second development electrode, and the second development electrode further disposed at such a distance from the first development electrode that developing powder which flows through between the first developing electrode and the surface and exceeds the reduced amount, can flow between the first and second developing electrodes, and a reference potential is applied to the first and second development electrodes for modifying the fields of the latent electrostatic image on the surface by the first and second developing electrodes

According to the invention there is provided a method and apparatus for developing latent electrostatic Images with development electrodes created in which at least two development electrodes in one Development station of the electrophotographic device are used, the first development electrode, which the electrostatic image to be developed is exposed to properties which are optimum for large flow rates of developers and therefore only a reduced development of parts of low charge density and extended image areas, however, give optimal cleaning, the second developing electrode, which the electrostatic latent image to be developed has properties which are optimum for

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represent the completion of the development of parts of low contrast and extensive areas, however, since most of the developing powder has already been removed, no lump or obstruction to flow of the developer occurs under the second development electrode.

Further developments or expedient embodiments of the invention result from the claims

In the drawings, exemplary embodiments of the invention are shown and are also used in connection below with the aims and advantages of the invention for a better understanding of the invention described in more detail. In of the drawing

FIG. 1 shows an embodiment of the invention in which the development method and apparatus according to FIG Invention shown in combination with typical electrophotographic apparatus, and

Pig. Fig. 2 shows another embodiment of the invention in which development cleaning method and device according to the invention in combination with a modified version of the electrophotographic Device in Pig. 1 are shown.

In Pig. 1 of the drawing shows an embodiment of the invention in which the proposed development method embodied in a development electrode structure for this purpose by way of example and in connection with a typical electrophotographic processing machine is shown. This in Pig. 1 shown and described below

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was written electrophotographic processing device is chosen because the development method and development electrode structure therefor are best according to the invention and can be displayed most fully in an environment in which they can be represented according to their functions will ordinarily be found. However, it will be apparent to those skilled in the art that the details of electrophotographic Processing device and the corresponding method per se do not form part of the invention and therefore are shown for purposes of illustration but not limitation.

As shown in Fig. 1, the illustrated electrophotographic equipment is in the form of a continuous working electrophotographic device based on the idea as originally stated in the US PS 2 297 691 are deposited. It accordingly comprises a photoreceptor 2, a charging station 4, an exposure station 6, a development station 8, and an image transfer station 1o and a cleaning station 12. The photoreceptor 2, as shown in FIG Drum or an endless belt which rotate in the direction of arrow A in FIG. Alternatively can the photoreceptor 2 have the shape of a belt, a sheet or a plate, which with conventional winding, Winding or conveying processes are conveyed past horizontally arranged processing stations. In any In this case, the photoreceptor 2 can have any known structural design and is for the purpose of simplicity of illustration here as a simple drum with an insulating part 14 and a conductive part 16 is shown. Since the photoreceptor 2 per se does not form part of the present invention, it is here for a sufficient understanding of the invention

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sufficient to recognize that when the embodiment of the invention shown in Fig. 1 is used in conjunction with conventional electrophotographic processes, the conductive member 16 may be constructed from any suitable conductive material or from a nonconductor coated with a conductive foil. Similarly, the insulating member 14 will usually be constructed of a material having photoconductive properties such that the insulating member 14 is normally insulated and exhibits very good retention of charge, but is rendered selectively conductive by exposure to electromagnetic radiation via a chiaroscuro pattern, which represents an object to be copied. Alternatively, methods with reflection exposure can be used. The materials used to form the insulating member 14 can be selected from any of any of the known groups of materials conventionally used for electrophotographic processes. Examples include amorphous selenium, alloys of sulfur, arsenic or tellurium with selenium doped with materials such as thallium, cadium sulfide and the like, particulate photoconductive materials such as zinc sulfide, zinc cadium sulfide, zinc oxide, produced according to the French process, phthalocyanine, cadium sulfide, potassium selenide, Zinc silicate, cadium sulfoselenide, linear quinacridones, etc. dispersed in an insulating inorganic film-forming binder such as glass or an insulating organic film-forming binder such as an epoxy resin, a silicone resin, an alkyd resin, a styrene-butadiene resin, a wax or the like. Other typical photoconductive insulating materials are, for example, mixtures, copolymers, terpolymers

and
etc. of photoconductive / non-photoconductive materials that

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are either copolymerizable or miscible with one another, to form solid solutions. Organic photoconductive Materials of this type are, for example, anthracene, polyvinyl anthracene, anthraquinone, oxidiazole derivatives such as 2,5-bis- (p-aminophenyl) -i, 3,4-oxadiazole; 2-phenylbenzoxazole as well as charge transfer complexes that are formed by complex formation of resins such as polyvinyl carbazole, phenol aldehydes, epoxy resins, phenoxy resins, polycarbonates etc. with Lewis acids, such as phthalic anhydride, 2,4,7-trinitrofluorenone, metal chlorides such as aluminum, Zinc or iron (III) chloride, 4,4-bis (thylamino) -benzophenone, chloranil, picric acid, 1,3,5-trinitrobenzene, 1-chloranthraquinone, bromal, 4-nitrobenzaldehyde, 4-nitrophenol, Acetic anhydride, maleic anhydride, boron trichloride, maleic acid, stannic acid, benzoic acid, tartaric acid, Malonic acid and mixtures thereof. The insulating part 14 can by the choice of the photoconductive insulating material from can be made up of either translucent or radiation absorbing. The person skilled in the art is without further ado it can be seen that instead of the insulating part 14 in a single layer as shown in FIG. 1, a multi-layered one Insulating material can be used. The photoreceptor 2 is in such a working position with respect to the one on his. Scope of the processing stations provided arranged that when the illustrated electrophotographic device is switched on, the rotation of the photoreceptor 2 in the direction indicated by the arrow A as mentioned will lead to the fact that each point on the circumference of the insulating part 14 is carried out at the individual processing stations Processing steps is suspended.

The charging station 4 can have the usual form of one or more charging devices 18 to 2o, which are based on known Way sensitize the photoreceptor 2 by

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that the surface of the insulating part H is charged to a uniform potential. Although any conventional form of charging devices 18-2o can be used herein to apply a charge to the surface of the photoreceptor 2, Pig. 1. Caronas or corotrons have been shown with a semicircular screen structure because the use of corotrons is usually preferred in typical electrophotographic equipment. The structure and mode of operation of corotrons as shown in Fig. 1 are known and are described in detail in U.S. Patents 2,836,725 and 2,879,395. For the present explanation it is therefore sufficient to recognize that each of the carona electrodes 21 to 23 of the illustrated corotrones is connected in common to a suitable potential source V _{1 of} high potential, and that the corotrones in the usual manner a charge of uniform potential on the surface of the one below Apply photoreceptor 2. In Fig. 1 a plurality of charging devices 18 to 20 are shown, since a multiple corotron arrangement normally gives a more uniform charge across the width of the photoreceptor 2 than would otherwise be achieved. This effect arises because the ion charge current from the various parts of a single corona electrode longitudinally arranged across the width of a photoreceptor will usually not be uniform uniform height will result. However, if a special charger is used, or if slight irregularities in the charge applied are allowed, only a single corotron or other charger can be used. Furthermore, for the purpose of the present presentation,

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It can be assumed that in the charging station 4 the surface parts of the photoreceptor passing under the charging station 2 can be charged to an even level of 1ooo Y, although other arbitrary voltage levels can also be used can be selected as known to those skilled in the art.

The exposure station 6 is also arranged on the circumference of the photoreceptor 2 and can have the usual shape a projection system or the like in which using optical transmission or reflection methods a chiaroscuro pattern is imaged, which is the object to be copied onto the surface of the insulating part 14 located at the exposure station represents. In Fig. 1, an exposure device with a slot is indicated, but it can easily any optical System with linden trees or the like can be used. Further, it is clear, although the exposure station 6 in Fig. 1 is shown in such a position that the rotating photoreceptor is only sensitized in the charging station 4 and exposure is then carried out, the processing steps of charging and exposure are also carried out at the same time can be when the position of the exposure station 6 and / or the charging station 4 is changed. It is further Obviously, although in Fig. 1 only the simplified processing steps of a single loading process and a single exposure, additional electrophotographic processing steps like another Charging can be used in the formation of the electrostatic latent image, or the built-up electrostatic image through the use of such additional processing steps are well known to those skilled in the art V / can be reversed or changed differently. Next, the photoreceptor 2 is generally designated as 8-

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Neten development station exposed, where the built-up electrostatic image according to the teaching of the present Invention is developed.

The one in Pig. The development station 8 shown in FIG. 1 includes a feed device 24 which is suitable for subjecting corresponding parts of the photoreceptor 2 to a cascade development step or the like, divided or first and second development electrodes 26 and 28 which are arranged in a predetermined position on the periphery of the insulating part 14 that they work according to the development process shown here, and a container 3o for the supply of developer material or developer powder. The funnel-like feed device 24 can have the usual shape as are generally used in electrophotographic devices for applying developer powder to selected parts of the surface of the photoreceptor 2 arranged therebelow. The feed device 24 is filled to a suitable height with conventional developer powder 32 which contains the carrier and toner particles described above. The feed device 24 also has a lateral wall 34 with such an inclination that developer powder is fed from the feed device 24 with preferably high flow rates over the surface of the photoreceptor 2 arranged below it, so that rapid cascade development is achieved in order to achieve images with high contrasts can be. The Durchflußmen _£, e of the developing powder from the supply means 24 may typically be approximately at a size of 2o g per cm length of the photoreceptor and a second (2og / cm s) are, when used in the developer material or developer powder usual carrier particles with glass core. In contrast, there are much larger flow rates

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Use if the usual carrier particles with a steel core are used will. The flow rates with which the developer powder from the supply device 24 cascades up the surface of the photoreceptor 2 is scattered or worn are preferably large and, depending on the developer powder selected, can range between about 0.4 and 4og / cm / s vary. Further, although preferably relatively high flow rates for the developer powder are preferred the flow of developer powder from the supply device 24 can be substantially reduced when lower rotational speeds of the photoreceptor 2 are possible and acceptable.

The container 3o can have a conventional shape and is arranged below the part of the photoreceptor 2, which developer powder receives from the supply device 24 »The container 3o is usually up to a predetermined one Height kept filled with developer powder 32 and acts to absorb excess developer powder from the surface of the photoreceptor 2 and carrier particles, of which toner powder during the development process has been removed. In addition, the container 3o has devices (not shown) through which periodically Toner powder can be introduced so that the toner powder consumed during development can be replaced can. Next is between the feed device 24 and the container 3o a conventional conveying device is provided, so that when the electrophotographic Device as shown, developer powder 32 can be fed from the container 3o to the feed device 24, to thereby reduce the amount of developer powder 32 in the supply device 24 to be kept at a predetermined height. There is also a partition wall 36 in the one shown in FIG 'Way provided which by a lower part of the

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Wall 34 of the feed device 24 to the container 3o runs so that a chamber is formed which contains the photoreceptor 2 and the first and second development electrodes 26 and 28 isolated from the conveying device, not shown, and the developer powder contained therein. Even though in Pig. 1 a feed device 24 for application of developing powder is used on the surface of the photoreceptor 2, those skilled in the art will recognize that Conveying devices separately or in combination with an inclined wall for cascading application of Developer powder 32 on the surface of the photoreceptor 2 as well as any other conventional devices known to the person skilled in the art can be used.

The first and second development electrodes 26 and 28 are within those formed by the partition wall 36 Chamber and arranged opposite the circumferential surface parts of the photoreceptor 2 in the manner shown in FIG. Each of the first and second development electrodes 26 and 28 may be in the form of a conductive plate with a preferably have a curved cross-section such that the surfaces of the plate are parallel to the adjacent peripheral parts the photoreceptor surface · Alternatively, however, development electrodes can also be more planar in the shape Plates are used. The first and second development electrodes 26 and 28 are each continuous and therefore preferably give a continuous surface from the peripheral parts of the photoreceptor 2, though also layered developing electrodes or the like with openings in the surface could be used. In addition, the surfaces of the first and second Development electrodes 26 and 28 and in particular the surface of the first development electrode 26 in the direction

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the flow of the developer powder be grooved in order to thereby increase the flow rate of the developer powder. Each of the first and second development electrodes 26 and 28 has a width measured along the axial width of the photoreceptor 2 or the paper, which corresponds substantially to the width of the photoreceptor, and one typical length measured along the perimeter of the fatoreceptor of about 2.54 cm when using drums as a photoreceptor relatively small diameter can be used. The length of each of the development electrodes 26 and 28 can be broad vary, and it can be assumed that the combined or combined length is approximately equal to $ 25 of the circumference the drum as the photoreceptor, provided that such a length can accommodate in the housing used leaves. For example, if a standard 63.5 cm drum is used as the photoreceptor, the common Length of the first and second developing electrodes 26 and 28 would be about 6 inches and larger drums would of course allow longer electrode lengths. For high-speed electrophotographic devices, a larger development electrode area is needed to achieve a longer development time, and therefore here given preference to relatively large development electrodes « Other factors to consider when choosing the length for the first and second developing electrodes 26 and 28, as is well known to those skilled in the art, are the associated bias levels, the amount of latent built up electrostatic image, the distance of the first and second development electrodes 26 and 28 from the photoreceptor 2 as well as the potential level generally associated with the built-up latent electrostatic image. However, it is note that the lengths of the first and second developing electrodes 26 and 28 should be chosen so that their common land does not have a sufficient

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restricted space or the free flow of developer powder under the influence of gravity is prevented. If further the lengths of the first and second development electrodes are chosen to be different, r.oll is the length of the second Development electrode 28 preferably be larger than that of the first development electrode 26 because of how described in more detail below, with the second development electrode 28, a low density development and over a extensive area and therefore a fine image development is carried out, which of larger field-modifying Properties should be accompanied.

The first development electrode 26 is typically about 5.08 mm from the surface of the photoreceptor 2, although any distance between 2.03 mm and 12.7 mm would be suitable. The optimum spacing of the first development electrode 26 will change essentially in accordance with the bias voltage used here, the size of the developer powder particles and in particular the diameter of the carrier particles used, the flow rate of the developer powder from the supply device 24 and the potential levels associated with the latent electrostatic image built up. However, as will be explained below, the actual distance chosen for the first developing electrode 26 from the photoreceptor 2 should be chosen after taking into account each of the above factors with a view to maintaining a high flow of developer powder although the development of parts is extended area and lower The electrostatic latent image density is substantially reduced. The first development electrode 26 is connected to a suitable potential _{source V 2} , which here can have the form of a conventional direct current source. The Po

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t ent ialqu eile Vp leads according to the in fig. 1 shown pure development operation of the first development electrode 26 to a bias voltage which is at a level equal to or approximately greater than the potential level associated with the background of the built-up latent electrostatic image can be chosen so that the background portions of the electrostatic latent image are neutral or appear under the same charge polarity as the triboelectrically charged toner powder, whereby the Background pure white is developed. If so, in a typical case, the background of the one on the PR 2 build up a latent electrostatic image in general has a voltage between 5o and 1oo V, the potential source Vp will be selected so that at the first Development electrode 26 has a voltage of 100 to 300 volts.

The second development electrode 28 operates here, as will be seen below, at a reduced rate Flow rate of developer powder for fine development of large parts and / or parts of low density of the electrostatic image built up on the photoreceptor 2. The distance becomes accordingly of the second developing electrode 28 from the surface of the photoreceptor 2 in view of such fine development optimized. Typically, the second development electrode 28 is about half as far from the photoreceptor 2 as removed as the first development electrode 26. Thus, the second development electrode 28 is typically about 1.9 mm be removed from the surface of the photoreceptor 2, generally a distance range of 1.02 mm to 6.35 dm is available to such factors as flow rate of developer powder, which is part of the second

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lun selelectrode associated bias level, the size of the Developer powder particles and in particular the diameter of the carrier particles used and the potential levels associated with the built-up latent electrostatic image to compensate. The ^ second development electrode 28 is connected to a suitable potential source V, which can have the same shape as the i-potential source Vp. The potential source V i applies to the second development electrode 28 a potential, the level of which is also equal to or greater than that of the background of the built-up latent Electrostatic image associated potential level can be selected, so that when developing such electrostatic latent image which takes place under the second developing electrode 28, these background parts pure white can be developed. So here the potential source V, to the second development electrode The voltage applied to 28 is exactly the same as that by the potential source Vp to the first developing electrode 26 applied voltage, although it can sometimes produce very beneficial results let the potential applied to the second developing electrode 28 be opposite that to the first developing electrode 26 applied potential is slightly increased or decreased, so that a more precisely controlled Development can be achieved. It is clear that instead of the individual potential sources shown, a common Potential source can be used when the first and second development electrodes 26 and 28 are connected to the same Bias are placed.

After completing the rotation of the circumference of the photoreceptor 2 moves through development station 8

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that part of the photoreceptor 2 on which the developed image is located next into the image transfer station 1o where the image transfer takes place. The image transmission station 1o comprises a transmission part and charging means 39 to 41 for applying a predetermined one Charge on the transfer member 38 to thereby to effect the transfer of the toner image from the surface of the 3Otoreceptor 2 to the transfer member 38. The transfer member 38 may be in the form of a sheet, belt, or drum of suitable transfer material such as paper, plastic, or any other known material as is customary is used as the transfer material. The charging devices 39 to 41 may have the shape as shown of several semicircular gorotrons, which are shown in the same way as those shown in the charging station 2 and the charging devices described above are constructed «Alternatively, any other conventional form of charging devices, as they have also been explained in connection with the charging station 2, instead of that shown in FIG Charging devices 39 to 41 are used. Bs it will be understood that in the image transmission station 1o each Charging device can be used, with the help of which a predetermined charge level on the surface of the transfer part 38 can be applied. The charging devices shown in Fig. 1 39 to 41 are with a suitable potential source V. connected, which again the Can have the form of a standard DC power supply. Even though in the embodiment of the invention shown in Fig. 1 only a single polarity charging process in the Image transmission station 1o is indicated, the Facninann recognizes that the image transmission by a following Removal process using a pair of opposing

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sets polarized and connected to an ungrounded or floating supply corotrons can be achieved, such as it is described in U.S. Patent 3,244,083.

After completion of the electrophotographic process in the image transfer station 1o, the image part of the Photoreceptor 2 next passed to cleaning station 12 where excess toner particles were removed from the surface of the potentiometer 2 in preparation for the following build-up of a new electrostatic latent image on the potentiometer 2 are removed. The cleaning station 12 can take the usual form of a cleaning device with rotating fur brushes, wiper devices or cascade cleaning devices that have on Remove the residual toner from the surface of the potentiometer 2 in a well-known manner. Any of these procedures is known to the person skilled in the art, so that it is sufficient here to state that in the cleaning station 12 the remaining Toner particles are removed from the surface of the Potoreceptors 2, thereby in the state for the To bring reuse.

When operating the Pig. 1 embodiment of the invention illustrated is by the combined effect the charging station 4 and the exposure station 6 first a latent electrostatic image of the to be copied Object built on the Potoreceptor 2. When switching on the in Pig. 1 drawn electrophotographic The device becomes the electrostatic latent image via conventional electrophotographic methods well known to those skilled in the art Processes built up. So if that shown in FIG electrophotographic device is switched on, the charging devices 18 to 2o in the charging station 4 a charging

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Application to the parts of the photoreceptor running through the charging station by causing them to charge an ionic current is fed. The surface of the photoreceptor 2 is thus determined by the action of the charging devices 18 to 2o, which are shown in Fig. 1 as conventional corotrons, charged to a uniform potential. Corresponding it can be seen that the charging station 4 is used in the usual way to sensitize the surface of the photoreceptor 2 acts by charging to a uniform potential, which is assumed to be 1ooo V in the present case Although any suitable size and / or polarity of charge configuration can be selectively applied to the surface of the photoreceptor 2 can be applied. After completion of the charging or sensitization process, which takes place at the charging station 4 takes place, the rotation of the photoreceptor 2 in the direction of arrow A brings the previously charged parts of the photoreceptor 2 in an effective position to the exposure station 6. The exposure station 6 is working known way and sets the photoconductive part of the photoreceptor 2, which here the shape of the insulating part 14 has, selectively an electromagnetic radiation from the object to be copied. In the exposure station 6, a chiaroscuro pattern is thus depicted, which shows the on the charged surface of the insulating part 14 of the Photoreceptor 2 represents the image to be built up. After exposure, the photoconductive insulating member 14 is known Way selectively made conductive so that the charge in its light-struck parts is substantially reduced while the charge in the parts corresponding to the dark parts of the image area is on the relative high charge level applied in the charging station. So by the combined effect of the Loading station 4 and the exposure station 6 on the circumference of the

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Photoreceptor 2 built up a latent electrostatic image on the photoreceptor in a known manner. For the For the purposes of the development process described below, it can be assumed that the variation in the charge level of the raised electrostatic latent image to voltage levels of about 8oo V in the dark Parts of the chiaroscuro exposure pattern result in corresponding parts of the image area, while those struck by the light Portions of the image area on the surface of the photoreceptor 2 which are the background areas of the image remain at about 1oo V. The image area or the parts of the photoreceptor 2 with the one built on it electrostatic latent images are next due to the rotation of the photoreceptor 2 in the direction of the Arrow A brought into an effective position at the development station 8.

For the description of the processes in the development station 8, it will be assumed that a development process is positive to positive and that the photoreceptor is positively charged. Therefore, the developer powder is chosen so that it contains negatively charged toner particles. However, it is clear to those skilled in the art that by choosing the developer powder with positively charged toner particles, a development process could be chosen negatively to positive, or that in the case of a negatively charged photoreceptor the developer powder could be selected so that development processes would result in negative to negative or positive to negative. According to the container 3o will be filled in the developing station 8 to a predetermined height with developing powder, whose properties are such that the carrier particles have a positive charge while the toner particles owing

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the effect of static electricity has a negative charge assume · Y / pus becomes when the container 3o is filled with developing powder up to a predetermined level is, the feed device 24 due to the action of the conveyor device, not shown, also to a desired one Height to be filled with developer powder. As mentioned above, the inclined wall 34 has in the feeder 24 is an angle of inclination calculated in such a way that a cascade-like flow of developer powder 32 over the surface of the photoreceptor 2 disposed below the feeder with a relatively high flow rate is ensured when considering the core material of the selected carrier powder. So, as in Fig. 1 indicated, developer powder in the form of carrier particles with on their surface due to electrostatic Attractive forces of oppositely charged negative toner powder cascade across the surface of the photoreceptor 2 is scattered in a flow rate which is preferably large with respect to that for the carrier particles chosen core material. For the embodiment shown, the flow rate with which developer powder is fed from the feed device 24 to the photo receptor 2, as an example a value of approximately 2o g / cffl / s can be assumed, although this value is derived from the reasons given above can be varied widely.

That from feeder 24 to the photoreceptor 2 supplied developer powder is over the surface of the photoreceptor 2 in the form of carrier particles flow, on the surface of which a plurality of toner particles due to the electrostatic attraction force hang. When the developer powder 32 touches the surface of the

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Photoreceptor 2 is supplied, the latent electrostatic built up on the surface of the photoreceptor 2 becomes Image are first exposed to the field-modifying effects of the first development electrode 26, which by the potential source Vp to such a calculated Voltage is biased to develop the background portions of the electrostatic latent image is ensured on the photoreceptor 2 pure white. It can therefore, as for the background parts of the latent electrostatic Image voltage levels of 5o V to 1oo V have been assumed, here it is assumed that the first development electrode is biased to a value of 2oo V, although each value between 15V and 500V is dependent of the desired success would be possible. The first developing electrode 26 is spaced a suitable distance from the Surface of the photoreceptor 2, which can be assumed here to be about 5.08 mm, to a high flow rate of the developing powder, although the distance suitable for such a high flow rate the field modifying effects of the first developing electrode 26 is reduced, so that the development of low density parts and extensive areas of the electrostatic latent image

there-

will. This high flow rate can be further ensured by the first development electrode 26 to increase the flow rate is grooved or otherwise machined »Therefore, when these conditions in the space between the periphery of the photoreceptor 2 and the first developing electrode 26 is maintained are, the developing powder cascaded over the surface of the photoreceptor 2 in the vicinity such a first development electrode in a

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Move in a quantity and speed that is not significantly impeded. Me on the surface of the photoreceptor however, development under the first development electrode 26 will be such that only the Portions of the electrostatic latent image with substantial voltage contrasts are sufficiently electrostatic Forces are produced in order to overcome the connection between carrier particles and toner of the developer powder so that the toner powder is deposited on these parts. The first developing electrode 26 thus leads to one Optimization of the flow rate of developing powder in the space affected by it, while * the for field modifying the development of a latent electrostatic image with continuous tone Effects are reduced so that there is no toner powder on parts of low density or extended areas of the developed latent electrostatic image is deposited.

The second development electrode 28 is arranged close to the surface of the potoreceptor 2 and can in the embodiment of the invention shown in Fig. 1 for pure development on the same voltage as the first development electrode 26 are biased · So it can be assumed here that the second development electrode 28 from the surface of the photoreceptor 2 is a distance of about 1.9 mm and is biased to a voltage level of about 200 V, so that the flow rate of developer powder is significantly reduced, while the field-influencing properties of the second Developer electrode 28 are essential. If these conditions are met as indicated in Fig. 1, is the flow rate of developer powder between the two

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th developing electrode 28 and the surface of the photoreceptor 2 to about 5.21 g / cm of photoreceptor per second reduced under the conditions assumed above, while the photoreceptor 2 from the feeder 24 supplied excess developer powder will thereby flow directly into the container 3o that it is through a gap between the first and second developing electrodes 26 and 28 as indicated in FIG. 1 flows. Further As those skilled in the art will readily appreciate, the first development electrode 26 can be in precise circumferential location positioned over the surface of the photoreceptor and constructed and / or shaped to ensure is that the major part of the flow rate of developing powder between the first development electrode 26 and the photoreceptor 2 through the gap between the first and second electrodes 26 and 28 into the container 3o will. Thus, under these conditions, the second developing electrode 28 becomes very effective have the field formed by the latent electrostatic image on the photoreceptor 2, so that all parts of the latent electrostatic image is essentially proportional to the charge levels of the for the reasons mentioned above Image to be developed. Correspondingly, the increased field created by all parts of the latent electrostatic Image which exceeds the bias level of the second developing electrode 28 Have tension level, the binding of the toner particles to the carrier particles of the cascade-like flowing Developer powder according to its size overcome when the electrostatic latent image is below the influence of the second developing electrode 28 is located. This makes all parts of the latent electrostatic Image with the inclusion of its background

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areas have a dense toner deposition corresponding to the charge levels associated with these image parts. Next, there is the flow rate of developing powder is substantially reduced in the area between the second developing electrode 28 and the photoreceptor 2, none Lumps of the developer powder occur, so that the aforementioned adverse effects are avoided.

It can be seen that there is the use of first and second development electrodes 26 and 28, respectively The present invention allows large amounts of developer powder to be cascaded over the image area To guide the photoreceptor 2 to ensure there large amounts of toner powder and correspondingly high development speeds, while parts of the built electrostatic latent image with low density and extensive areas under the influence of the second development electrode 28, which has substantial field-modifying effects ensure that development is terminated under conditions which are optimum for development a continuous tone image covering solid areas. Next is due to the nature of the first and second development electrodes 26 and 28 the optimized development under conditions described here carried out under which a large flow rate of developing powder is maintained in order to achieve ensure high development speeds without interfering with the flow of the developer powder in any way it is prevented that a lump of the developing agent can occur and the development of the image is unfavorable influenced. Accordingly, it enables the development process and the device for this according to the teaching of

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Invention, as shown in combination with the electrophotographic apparatus shown as an example in Fig. 1, to employ advantageous cascade development techniques in the development of latent electrostatic images with continuous tone without compromising the requirements of the developing electrodes used with regard to the built-up image or the speed of development.

After the development step has been carried out in the manner described in the development station 8, due to the electrostatic attraction between negatively charged toner particles and the positively charged latent electrostatic image, toner powder is deposited on the image area of the photoreceptor 2 in accordance with the charge configuration of the built-up latent electrostatic image. When the image area of the photoreceptor 2 arrives at the image transfer station 1o, the transfer member 38 is placed on the surface of the photoreceptor 2 so that it is only at a few points due to the absence of strong attraction between the adjacent surfaces of the transfer member 38 and the photoreceptor 2 surface is in physical contact with the assembled toner image, while the other adjacent surface parts and separated by an air gap of a few / _s the transfer member 38 as mentioned in the present embodiment, as shown in Fig. 1, have the form of a strip which can move in the direction of arrow B in FIG. 1 so that the speed of the transfer member 38 adjacent the surface of the photoreceptor 2 is equal to the angular speed or peripheral speed of the photoreceptor 2. When the

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other parts of the photoreceptor with the transfer member 38 arranged thereon are displaced so that they are in the loading position with respect to the loading devices 39 to 41, parts of the transmission part 38 become in the charging position take up a positive ion charging current along its width, so that such surface parts be positively charged to a uniform potential. Those supplied to the surface of the transfer part 38 Charges will and will migrate to the opposite surface adjacent the toner image in a known manner therefore generate negative charges in the corresponding parts of the conductive part 16 of the photoreceptor 2. the Charge on the parts of the transfer member 38 which carry the positive ion charging current from the charging devices 39 to 41, there will be a very substantial force of attraction between corresponding parts of adjacent surfaces of the transmission part 38 and the potentiometer 2 generate and thereby these parts of the transfer member 38 in intimate contact with the parts of the toner image on the Bring adjacent parts of the photoreceptor 2. When these conditions are met, the field strength is between the charged part of the transfer part 38 and the adjacent part of the photoreceptor 2 will be sufficient, a transfer of most of the negatively charged toner particles from the photoreceptor 2 to the transfer member 38 to effect. This process is continued continuously for successive parts of the transfer part 38 until all of the toner image has been transferred to the transfer member 38. So is known on This is done on the photoreceptor 2 by the development step carried out in the development station 8 The built-up toner image is transferred to the transfer member 38 so that only excess toner powder from the developing step remains on the surface of the photoreceptor 2.

209850/1035 -38-

The image portion of the photoreceptor 2 is next in an operative position with respect to the cleaning station 12 brought so that excess before re-use Toner powder can be removed from the image part of the photoreceptor 2. The cleaning station 12 can, as mentioned be completely conventional, so that the use of non-tacky toner material or toner powder the image portion of the photoreceptor 2 wiped with a conventional rotating fur brush or a Cotton wiping device can be used. Alternatively, a cascade cleaning technique can be used in the cleaning station 12 are used in which granular material, which is similar to the carrier particles in one Two component developer powder acts in a known manner in a cascade manner across the image portion of the photoreceptor is guided and excess toner particles by triboelectric attraction from the surface of the photoreceptor 2 are tightened without the risk of damage or scratching of the surface PR occurs. After the cleaning step has been completed, the electrophotographic shown in FIG Equipment used again to build a toner image of an original to be copied, followed by the steps of electrostatic latent image formation, development, transfer and cleaning are repeated will.

In the typical electrophotographic apparatus shown in Fig. 1 and described above, there was a dedicated one Cleaning stage intended for removing excess or residual toner, and that in context embodiment of the invention described here was accordingly only based on the aspects of development

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- 39 - 221781

ment according to the invention directed, wherein a split electrode arrangement or an arrangement with first and second developing electrode came to be used, the application of cascade developing techniques or the like for developing a continuous tone image without compromising the developing technique used to enable and just to be able to use the development electrodes. The characteristics of the present Invention, however, are not limited to advantageous development techniques, but also enable that cleaning and development take place in a single processing stage. An embodiment of the Invention in which cleaning and development are combined in a single processing step is as follows described in connection with FIG.

Pig. Fig. 2 shows a further embodiment of the invention in which a method for developing and Cleaning and a device for this in combination with a modified version de3 in Pig. 1 shown electrophotographic Device are shown. Like looking at the pig. 2 shows, the structure shown there corresponds to FIG essentially the structure shown in Pig * 1 with the only exception that the cleaning station 12 is omitted is, as will be explained hereinafter, the purification in this embodiment of the invention in FIG . Development station is carried out. Therefore, in order to avoid unnecessary repetition, are in Pig. 2 shown Parts and superstructures, which are already in connection with Pig. 1 described structures are similar, with the same Reference numerals, and relating to the description of Pig. 1 and Pig. 2 common parts will be on the above description in connection with Pig. 1 reference

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took. Accordingly, it should be noted that each of the Changes, modifications or varying parameter ranges as described in connection with FIG. 1, too is fully applicable to the structure shown in Fig. 2, unless otherwise stated.

The electrophotographic processing apparatus shown in Fig. 2 comprises a photoreceptor 2, a charging station 4, an exposure station 6, a development station 8 and an image transfer station 1o. The PR 2, the charging station 4, the exposure station 6 and the image transfer station 1o can each have the have the same structural form, fulfill the same functions and are subject to the same variations as the correspondingly designated structures shown in FIG. 1. Similarly, the development station 8 is on one Part of the circumference of the photoreceptor 2 in the same way arranged as has been described in connection with FIG. It comprises a feed device 24, one Container 3o and a conveyor device, not shown, which all have the same structural form and functions as. can meet described above. In this embodiment of the invention, however, the inclined wall 34 of the feed device 24 is preferred arranged at an angle of inclination, which ensures that the flow rate with which developing powder is performed in a cascade over the surface of the photoreceptor 2, is particularly high because not only from Such high flow rates from the standpoint of rapid development and dense toner image build-up are desirable, but also the removal of residual toner images by cascading of developer powder in an electrode system

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relatively high flow rates of the developer powder used is supported, as is well known to the person skilled in the art is. It is so, although flow rates for the developer powder 34 are in the range mentioned in connection with FIG are fully applicable to the present embodiment of the invention, expedient that a relatively high Amount is chosen, again taking into account the core material of the chosen carrier, so that a results in more effective development cleaning.

The development station 8 also includes first and second development electrodes 46 and 28. The first and second development electrodes 46 and 28 are on the periphery of the photoreceptor 2 and in the development station 8 in exactly the same manner as in context with the first and second developing electrodes 26 and 28 shown in Fig. 1 as described. Further the first and second developing electrodes 46 and 28 may be as shown in FIG. . 2 also shown the same structural Have structure, have the same displacement from the surface of the photoreceptor 2 and which The same variations as those associated with the first and second developing electrodes shown in FIG 26 and 28 have been described. However, there can be a slightly larger shift here than above described for the first development electrode 46 may be useful in order to adapt to a larger flow rate of developer powder 32 from the supply device 24 to reach. The second development electrode 28 is used here with a significantly reduced flow of developer powder, equal in height and in the same way as described in connection with Fig. 1, in addition, Parts of the extensive area and / or low density of the

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developed latent electrostatic image. The second development electrode 28 therefore has, as indicated by the associated reference number, the same Shape, fulfills the same punctures and is subject to the same variations as the second development electrode 28 as related to Pig. 1 has been described. The one in Pig. Second developing electrode shown in FIG is connected to a potential source V, which it as described with a suitable bias for applied to the background.

The first developing electrode 46 fulfills here
however, the dual function of cleaning the surface
of the photoreceptor 2 and the development of parts of the
electrostatic image, which big differences in
of the cargo. The cleaning function of the first developer electrode 46 is achieved by the cleaning ability of the developing powder, which flows down in a cascade-like manner, and in particular of the carrier particles contained therein, which are not sufficiently large in number
of toner particles opposed to the resulting
To make developer particles electrically neutral, so that
Excess toner particles are rinsed from the surface of the photoreceptor 2 if such residual toner particles are not firmly adhered to the surface of the photoreceptor 2 by a latent electrostatic image that is subsequently built up. In order to ensure that there is a sufficient number of carrier particles with correspondingly fewer toner particles adhering to them, such cleaning of the surface of the photoreceptor from residual toner particles should not only be carried out with a high flow rate, but also with a sufficiently high bias voltage on the photoreceptor

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Surface of the first development electrode 46 to facilitate the removal of toner particles from the carrier particles effective in the falling developing powder to support. For this purpose, the first developing electrode 46 is provided with a. Potential source "VV connected, which can have a completely conventional structure and the first development electrode 46 preferably to a substantial one Brings bias. While so in the embodiment of the invention according to 3Pig. 1 to the first developing electrode 26 applied bias to the voltage level of the background of the built up electrostatic Here, the bias voltage applied to the first developing electrode 46 can be combined in one Range from 0 to 1ooo V and should preferably move at or above the voltage level of parts of the latent electrostatic image, which correspond to the dark parts of the light-dark exposure pattern · The Development function of the first development electrode 46, in which due to the substantial distance between the surface of the potentiometer and the first development electrode only those parts of the latent electrostatic image with high voltage contrasts are developed, is done in the same way as in the context of Pig. 1 described. However, here the development which takes place under the first developing electrode 46 is somewhat less effective than in the case of the embodiment after Pig. 1 because the conditions are preferable in view of cleaning with a high flow rate and high bias rather than being optimized for development. This is how the -in Pig works. 2 shown Embodiment of the development electrode assembly according to the invention both for cleaning and also to the reduced development under the first development

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Winding electrode 46, while the fine development of low density parts and extensive areas of the latent electrostatic image under the second developing electrode 28 in the same manner as in the embodiment according to Fig. 1 is achieved.

For explaining the operation of the photographic processing apparatus shown in Fig. 2, and in particular for the description of the type of development and cleaning process shown here, it is assumed again, that a type of development is intended positive for positive. It goes without saying that on the other hand too the alternatives mentioned with regard to FIG. 1 can easily be carried out. So it is believed that the present in the container 3o and in the feed device 24 Developer powder is such that negative toner particles for the build-up of a toner image be available. It is also assumed that there is an operation before the operation to be described here has been performed in which a toner image has been developed and transferred so that residual toner particles, are present on the surface of the photoreceptor 2, which then corresponds to that described below Operation is subjected.

When operating the embodiment of the invention shown in FIG. 2 it can be seen that a latent electrostatic image of the object to be copied is built up on the surface of the photoreceptor 2 by that the photoreceptor 2 is charged to a uniform potential and for this purpose according to a light-dark exposure pattern, which corresponds to the object to be copied is selectively discharged. This can be done in the usual way

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by the charging station 4 and the exposure station 6 due to the same procedures as related to Pig. 1 described. Before building the latent electrostatic image, however, it can be advantageous to use the surface of the Potoreceptors 2 in a known manner Electromagnetic radiation to sweep over, so that the photoconductive layer before the build-up of a new latent electrostatic image is completely discharged. In any case, a latent electrostatic image will appear the same way as related to Pig. 1 described built up, and the image part of the potentiometer 2 is then shifted by turning in the direction of arrow A so *, that the development and cleaning in the development station 8 can be carried out. Ea is to be noted that under the conditions shown here, the image part of the potentiometer 2 is not just one built on it has a latent electrostatic image, but that as a result of previous use, additional residual toner particles may be present on the surface of the potentiometer 2.

When the image part of the Potoreceptora 2 in the development station 8 arrives, the container 3o and the feeder 24 are both up to their respective ones predetermined levels with developer powder related to Pig. 1 type described be filled. Accordingly, developing powder from the supply device 24 is in an amount over the surface of the potoreceptor be scattered or guided, which again can be assumed to be about 20 g / cm and per second, although as mentioned above, slightly too, depending on the density of the carrier particles used in the developing powder other flow rates for the developer powder use

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can find. When the developer powder is cascaded across the surface of the photoreceptor and a path between the first development electrode 46 and follows the photoreceptor 2, the carrier particles, which do not have a complete counterpart of toner particles, rinse the remaining toner particles from the portions of the surface of the photoreceptor other than the portions of the newly built latent electrostatic south with large charge contrasts, while the toner particles adhering to the surface of the other carrier particles will be deposited on the surface parts of the photoreceptor 2, which will be the parts of the newly built electrostatic image with large charge contrasts. The rinsing carried out in this way causes removal of residual toner particles, while the toner deposition does not only lead to a development of parts of the latent electrostatic image with large voltage contrasts, but also more carrier particles for cleaning purposes. As mentioned above, is in the present embodiment of the invention, that of the first developing electrode 46 from the potential source Vc applied bias is preferably high in order to remove debris on the surface of the photoreceptor in the development and subsequent transfer of a pre-established electrostatic latent Image remaining toner. This high bias voltage acts on the first development electrode 46 not only for modifying the field associated with the latent electrostatic image for the purpose of development in a manner similar to that described for the first development electrode 26 in connection with FIG additionally supports the

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- 47 '- 22178

treatment electrode 4-6 during the cleaning process that more carrier particles can be used for cleaning purposes by helping to remove toner therefrom Will be provided'. The manner in which the first developing electrode 46 assists in cleaning can be understood by "considering that some toner particles separate from the falling carrier particles and drawn toward the development electrode so long as a positive bias is applied to the first development electrode 46 is created. As a result, additional carrier particles, which are not a complete Opposite to associated toner particles have been released for the purpose of development, and when the bias of the first developing electrode 46 is enlarged, the number of carrier particles thus provided becomes substantial gain weight. When the bias voltage applied to the first developing electrode 46 is only 100 volts or a few above the voltage level of the background of the latent electrostatic If high flow rates are used as indicated above, a soft, gentle one will be used Purification takes place while in a manner similar to that in connection with the embodiment of the invention according to fig. 1, a suitable coarse development

of parts of the latent electrostatic image with correspondingly high voltage contrasts will take place. However, if the bias level of the first developing electrode 46 is substantially higher than the voltage level of the background of the built-up electrostatic latent image is enlarged, the degree of purification becomes due the manner in which the first developing electrode 46 overcomes the bond between toner and carrier particles and attracts toner particles, greatly enlarged will. Under these conditions, however, less development occurs in the area of the first development electrode 46.

209850/1035 - 48 -

winding take place because more parts of the latent electrostatic Image will be negative with respect to the first developing electrode 46. You can continue in this Regarding the cleaning and development taking place under the influence of the first developing electrode so that suitable conditions are weighed in favor of cleaning, e.g. by applying a bias voltage the first developing electrode 46, which determines the voltage level of all parts of the electrostatic latent image exceeds that the degree of purification is significantly increased, but with a corresponding reduction in the Degree of development. However, if the degree of purification is to be increased to a point where the second Development electrode 28 can no longer compensate for the development loss, for example, a third Development electrode spaced for high flow rates of developer powder between the first and second Development electrodes 46 and 28 can be arranged, and the first development electrode 46 can be coated with one layer made of conductive Teflon or the like to prevent the build-up of toner. So it can be seen that both cleaning the potentiometer of residual toner powder and developing parts of the latent electrostatic image with substantial voltage contrasts at high flow rates of developer powder can be achieved under the influence of the first development electrode 46.

As the second development electrode 28 as mentioned above compared with the first development electrode 46 is only about half as far from the surface of the photoreceptor 2, the flow rate is on Developer powder, which cascades between the two

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th development electrode 28 and the surface of the photoreceptor 2 flows through, be greatly reduced «It can be assumed that the reduced flow rate the is the same as in connection with the embodiment according to Fig. 1 described. However, the person skilled in the art will recognize that the flow rate and therefore the decisive factor for this The spacing of the second development electrode 28 can be increased to extremely reduce coarse development under the first development electrode 46 to compensate. The developer powder, which is the difference corresponds to the flow rates under the first and second development electrodes 46 and 28, is determined via the in FIG The indicated path between the first and second development electrodes 46 and 28 cascade into the container 3o fall while developing powder not used for the fine development under the second developing electrode 28 falls via the indicated flow path into the container 3o. So here are both purification and development in development station 8 by first and second development electrodes 46 and 28 and through these matched flow rates of developer powder carried out. After completion of the development and cleaning process carried out in development station 8 the built-up toner image can be described in the same manner as in connection with FIG Image transmission station 1o transmitted and then fixed will. A new latent electrostatic can be added to this Image can be built up because, according to this embodiment of the invention, there is no independent cleaning process is required.

Although the process of development and development cleaning as well as the devices for this according to the

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Invention in connection with two described in detail Embodiments have been illustrated, it is understood that numerous modifications and changes the techniques shown are possible and are therefore proposed according to the invention. E.g. the structure was of the developing electrodes here as having a continuous surface parallel to the surface of the photoreceptor described. However, it can be grooved, layered, apertured, or other discontinuous ones Surface shapes can be used for such electrode assemblies, especially when due to use such surface shapes the flow rate of developer powder or whose promotion to the container or sump are to be supported. Further must the development electrode structure do not have a surface area which is parallel to the surface of the photoreceptor runs, and it need not have a surface area which is from the surface of the photoreceptor represents constant distance. Further, it should be understood that although there are first and second development electrodes have been shown, a shared unitary structure can be used, especially when a common one Bias voltage is applied, or that, alternatively, more than two development electrodes are used can, if the gradations in relation to the flow rates of developer powder, the coarse and used Fine development and / or the amounts related to cleaning and development are to be increased further. It is further understood that although a special electrophotographic process is used here in a complementary manner the invention has been described, the ideas of the invention set forth in connection with each other electrophotographic process, which is used to develop

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development of a toner image can be used.

The invention is related to some Embodiments have been described. Briefly, the invention includes development methods and apparatus for their implementation, in particular development electrode assemblies, in which at least two development electrodes in a development station of electrophotographic device can be used · The first developing electrode, which is a latent electrostatic Image exposed to development has properties polygamy an optimum for high flow rates to represent developer powder. Therefore, there will be only a reduced development of parts of the electrostatic latent Image obtained with low charge densities and extensive areas, however, can be of an optimal Be accompanied by cleaning. The second development electrode, which holds the electrostatic latent image for development is exposed has properties which are lower with a view to completing the development Contrasts and extensive areas are optimized} since most of the developer powder is removed there is no obstruction to the flow of developing powder under the second developing electrode.

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Claims (13)

Claims Electrophotographic apparatus comprising a photoreceptor, means for building an electrostatic latent image on the photoreceptor, and means for developing the image on the photoreceptor by supplying toner powder to the photoreceptor, characterized in that a first developing electrode (26, 46) is adjacent the surface of the photoreceptor (2) and in the vicinity of the point at which the photoreceptor (2) is supplied with toner powder, at such a distance from the surface of the photoreceptor (2) that a considerable amount of toner powder is between the surface of the Photoreceptor (2) and the first development electrode (26, 46) is feasible, a second development electrode (28) adjacent the surface of the photoreceptor (2) in the vicinity of the first development electrode (26, 46) at a smaller distance from the surface of the photoreceptor (2) as the first developing electrode (26, 46) for passing only one v A reduced amount of toner powder is disposed between the surface of the photoreceptor (2) and the second development electrode (28), the second development electrode (28) being a sufficient distance from the first development electrode (26, 46) to allow a quantity of toner powder to pass through at least equal to the difference between the substantial amount and the reduced amount, and potential sources (V ₂ , V ₅ , V,) for applying a reference potential to the first and second development electrodes - 53 209850/1035 (26, 46, 28) for modifying the fields of the latent electrostatic built up on the photoreceptor (2) Image are provided by the first and second developing electrodes (26, 46, 28). 2. Electrophotographic device according to claim 1, characterized in that the at least a reference potential applied to the second development electrode (28) is a magnitude for preventing deposition of toner powder on parts of the photoreceptor (2), which are the background areas of the on the photoreceptor (2) correspond to the built-up electrostatic latent image. 3. Electrophotographic device according to claim 1 or 2, characterized in that the means for developing the latent image on the photoreceptor (2) a feeder (24) for cascading Scatter developer powder (32) consisting of carrier powder and toner powder over part of the Surface of the photoreceptor (2) comprises, whereby the toner powder on the parts with the built-up latent electrostatic image of the photoreceptor (2) can be deposited. 4. Electrophotographic device according to claim 3 »characterized in that with the feed device (24) for cascading developing powder (32) over a portion of the surface of the photoreceptor (2) The photoreceptor (2) developer powder (32) can be supplied with high flow rates. 5. Electrophotographic device according to one of the - 54 «SteiS. ^ .. ,, ^^ 0 9 8 5 0/1035 Proverbs 1 to 4, thereby denying nnze, that the reference potential applied to at least the first development electrode (26, 46) is a magnitude for preventing the deposition of toner powder on parts of the photoreceptor (2) has "which are the background areas of the electrostatic latent image built up on the photoreceptor (2). 6. Electrophotographic device according to one of the preceding claims, characterized in that that the first development electrode (26, 46) is such a distance from the surface of the photoreceptor (2) and biased to a potential level such that high density development of parts of the photoreceptor (2) with sharp voltage contrasts due to the presence of the electrostatic latent image on the photoreceptor is ensured while the second development electrode (28) is such a distance of the surface of the photoreceptor (2) and is biased to such a potential level that at low Flow rates of developer powder (32) ensure the development of parts of the photoreceptor (2) which Corresponding to parts of low density and extended areas of the electrostatic latent image thereon. 7. Device according to one of the preceding claims, characterized in that the at least a reference potential applied to the first development electrode (46), a magnitude for promoting purging of residual toner powder from the surface of the photoreceptor (2) through the cascading Has developer powder (32), whereby development cleaning can be carried out. - 55 - 209850/1035 8. The device according to claim 7 »characterized in that the first development electrode (46) has such a distance from the surface of the photoreceptor and is biased to such a potential level that at high flow rates of developing powder (32) a cleaning of the surface of the photoreceptor ( 2) of residual toner powder is ensured, while the second winding electrode (28) has such a distance from the surface of the photoreceptor (2) and is biased to such a potential level that at relatively low flow rates of developer powder a development of parts of the J ¹ Otoreceptors (2) is ensured that correspond to soft parts of low density and extensive areas of the electrostatic image built up on it. 9. Apparatus for developing an electrostatic latent image on a surface, characterized in that a supply means (24) for cascading scattering of developer powder (32) over the surface is provided at high flow rate, a first development electrode (26, 46) adjacent the surface at a location where the developing powder (32) is applied to the surface, at such a distance from the surface that de3 -3χη ^{Λ a} considerable amount of developing powder (32) between the surface and the first developing electrode (26, 46 ) is feasible, and a second development electrode (28) adjacent the surface of the photoreceptor (2) in the vicinity of the first development electrode (26, 46) at a smaller distance from the surface of the photoreceptor (2) than the first development electrode (26, 46) ) to let through only a reduced number of ■ - 56 209850/1035. ge of toner powder between the surface of the potoreceptor (2) and the second development electrode (28) is arranged, the second development electrode (28) a sufficient distance from the first development electrode (26, 46) to allow an amount of Toner powder at least equal to the difference between the substantial amount and the reduced kenge. 10. The device according to claim 9 »characterized in that potential sources (Vp, V ₁ -, V ~) for applying a reference potential to the first and second development electrodes (26, 46, 28) for coding the fields of the latent electrostatic image on the Surface provided by the first and second development electrodes (26, 46, 28). 11. The device according to claim 1o, characterized in that the /, at least to the second development electrode (28) applied reference potential is an amount for preventing deposition of in the developing powder (32) has toner powder present on parts of the surface which - the background areas of the latent electrostatic image on the surface. is avoidable 12. Device according to one of claims 9 to 11, characterized in that the to the second development electrode (28) applied reference potential a quantity for preventing the deposition of toner powder on parts of the surface, which corresponds to the background areas of the latent electrostatic image on the Surface. 13. Device according to one of claims 9 to 12, there- - 57 209850/1035 characterized in that the reference potential applied to the first development electrode (46) a size to aid in flushing residual Has toner powder from the surface by the cascade-like falling developer powder (32), whereby development cleaning is feasible. 14 · Method of developing a latent electrostatic Image, characterized in that developer powder with a high flow rate is cascaded over a surface having the latent electrostatic image, a ferste developing electrode adjacent the surface at a location near the. Apply developer powder on the surface and at a such distance from the surface that developer powder is placed between the surface and the first development electrode can flow through with the high flow rate, a second development electrode adjacent the surface in the vicinity of the first development electrode at a closer distance from the surface than the first development electrode is arranged to thereby allow only a reduced amount of developer powder to flow through between the surface and the second development electrode, and the second development electrode is further arranged at such a distance from the first development electrode that developer powder, which flows through between the first development electrode and the surface and exceeds the reduced amount, can flow through between the first and second development electrodes, and a reference potential to the first and second development electrodes are placed to modify the fields of the latent electrostatic Image on the surface by the first and second developing electrodes. 209 850/103 5