DE1572377A1 - Process for the electrostatic charging of a xerographic plate - Google Patents

Description

Patent attorneys Dipl.-Ing. F. Weickmann, Dr. Ing.A. Weickmann

Dipl.-Ing. H. Weickmann, D1PL.-PHYS. Dr. K. Fincke Dipl.-Ing. F. A. Weickmann 1R7 9Q77

8 MUNICH 27, DEN

MÖHLSTRASSE 22, CALL NUMBER 48 3921/22

RANK XEROX LIMITED, Rank Xerox Houae, 358, Euston Road London, N. ¥ .I ₁ England

Procedure for the electrostatic charging of a xerographic plate *

The invention relates to xerography, in particular to a method for the electrostatic charging of a xerographic Plate through which the quality of xerographic images, especially in the case of large-area and continuous Tints is improved.

In a xerographic process such as that described in US Pat. No. 2,297,691; becomes a xerographic plate consisting of a photoconductive insulating material on a conductive base on its surface uniformly electrostatically charged and then exposed to the image to be reproduced, for which generally a usual Production process is used. Because of the exposure the surface parts of the plate are corresponding to the incident Discharged radiation intensity, whereby a latent electro-

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static image is generated on or in the photoconductive layer · The development of the latent image is carried out with a . Electrostatically charged, finely divided substance made, for example, with an electroscopic powder that is in surface contact brought with the photoconductive layer and placed on this in a corresponding to the latent electrostatic image Distribution is held electrostatically · Thereafter, the developed xerographic powder image is applied to a Transferring the image surface on which it is fixed by suitable measures.

Excellent results were obtained in the xerographic process through the cascading development of line images such as letters or lines on a white background as well as halftone images

The cascading development of electrostatic latent images has wide commercial application at von & and and automatically operated xerographic copier machines and generally consists in the fact that a developer, which consists of two components of the type described in U.S. Patent 2,638,416, by gravity over the latent image a xerographic plate is poured · The two components are an electroscopic powder, so-called "toner" and a granular material called a "carrier". By mixing these two components get triboelectric Charges of opposite polarity · In the

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During development, the toner oppositely charged to the latent image is deposited on and does the latent image visible·

A characteristic feature of the xerographic process however, was that after the xerographic plate was exposed to the original image on the photoconductive plate Large charged surface areas remaining in the insulating material layer, which correspond to the black or dark areas of the original image, for example, were not developed by cascading development.

This feature affects with cascading and others Processes developed copies in such a way that large, continuously tinted areas developed only at their edges and do not contain toner in their central part. Continually tinted images show this feature in the same way

This effect is generally attributed to the fact that, in spite of the areal charge, the latent electrostatic image its ability to attract oppositely charged particles, on the nature and strength of the electric field in the air gap close to the image surface depends · The presence of a Surface charge does not yet guarantee the presence of electric fields in this air space. In fact, one poses determines that with a uniformly distributed over a large area -

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th surface charge the electric fields in the middle part this area run within the photoconductor and not in the air space. Therefore, in this middle part of the area only a negligibly small force of attraction on the developer particles exercised

One way to create a field outside of the Fho · » Tolleiters in the air space for better attraction of the toner particles consists in the fact that surface charge differences in a given area or irregularities are generated. Along the edges of a large tinted area and continuously tinted electrostatic latent images, a charge irregularity or change in charge occurs, causing the development of these edges explained

Of course, there are cases in which the development of large areas and continuous tinting would be of great advantage, especially in the case of the commercially used cascading development.For this reason, interesting advancements have been proposed to improve the yiäohenton in these types of development.

The development electrode is an Itösuag »the small one Vorepannuftg leads and near the xerographic view yi * $ t · at the Development parts is arranged. It is hosting a relocation of the electrostatic field from the photoconductive «» layer out "ia ^ deji air space" through the use of a development

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electrode it became possible to produce consistently and continuously tinted images of good quality · However, it is at continuously working in automatic copying machines, in in which the xerographic plate is generally in the form of a drum, the development electrode is not normally possible close enough to the drum surface to allow the formation of large tinted areas and continuous tints improve without severely impairing the flow of the developer and thus the operating speed of the machine to reduce". At the same time, the risk of Inhibition of the developer and the harmful effects the relatively sensitive surface of the xerographic plate due to increased wear and tear on this surface by the developer

A second way of solving the above-mentioned problem consists in the use of grids, by means of which evenly charged areas are converted into point-like hh # or cell-like charged areas. Development is then carried out by means of those generated with the charge differences of the charged areas Fields _c Such a rasterized electrostatic latent image can firstly be generated by initially charging the xerographic plate according to a grid pattern, secondly by appropriate apertures during exposure with the original image, or thirdly by selective discharge of the plate surface either before, during or after exposure .

Further details can be found in "Xerography" by Dessauer

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and Clark, Focal Press, p. 276, 1965 o

The initial charge of a plate in the form of a grid pattern was previously achieved in that a charge was applied through a conductive grid in which a contact charge was made with the grid-shaped surface of a roller of low conductivity. With this possibility of uniform tinting of large areas, however, many problems occurred, for example due to the direct contact with the Charging device with the relatively sensitive surface of the xerographic plate, which increases the risk of wear and tear was ©

A grid-like masking of the original image during the Exposure of the xerographic plate only shows an effect if the discharged smile parts develop! A dimming effect can only be achieved in the exposed areas— parts occur, and only when developing the uncharged surface parts are these surfaces developed · The present Automatic xerographic machines used work almost all on the principle of the development of charged surface parts

A selective discharge of the plate was achieved with a diaphragm, which contains a series of separated opaque lines on a film placed in the exposure slit is arranged with the lines parallel to the direction of movement

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the xerographic plate. This method is described in detail in US Pat. No. 3,120,790 however, has the disadvantage that the quality of line images can be improved by reducing the width of lines contained in the image, which run parallel to the direction of the line mask deteriorates will. A discharge by exposure to produce charge irregularities also charges the exposed one Disk seldom complete under normal operating conditions, i.e. at zero voltage, since under normal conditions a residual potential remains on the plate in the exposed areas. This creates a space in the air above the plate A weaker electric field is generated than if the discharged surfaces were completely discharged. It also turned out that when a plate is exposed to its complete discharge to the value zero, either a long exposure time is required which increases the operating speed of automatic xerographic copying machines, or the radiation intensity of the lamps must be increased, whereby the power supplied increases and costs as well as problems of heat dissipation develop"

Pure many photoconductive substances that have a low upper Örena value for the charging voltage shows the dimming method not satisfactory results. The permissible potential value is practically achievable for a plate upper value to which the potential can be increased before the charge of the. ·

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Plate is diverted and the diverted charge reaches the value of the added charge.

All known grid charging methods also show the common Disadvantage that the charge irregularities were always generated as charge images of the same polarity, the optimal charge irregularity in the difference between the charge potential of the plate and earth or zero potential exists · This is the maximum achievable charge irregularity at best limited to that charge value through which a photoconductive substance is at its permissible potential · Of course, charging to these high potential values creates many problems, for example due to the electrical mechanical stresses in the photoconductive material, whereby its life duration and the quality of the copies produced are reduced · Furthermore, there is an increased power consumption, increased There is a risk of electrical flashovers and increased charge dissipation, even in the absence of an activating one Radiation that normally makes the photo conductor conductive,

The invention now relates to a novel method for elec * · trostatic charging of a xearographic plate in a A number of discrete, charged parts of the plan, their potential alternating has two different values This method is designed in such a way that at least an initial number of Divide the area, the xerograph will see the latte at a first pod «·

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is tially charged and that in a second number of discrete small surface parts, which are not identical to the first-mentioned surface parts, charge-generating particles are deposited, which charge these surface parts evenly to a second potential _e

An exemplary embodiment of the method according to the invention is described below with reference to the figures

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! Fig. 1 is a perspective view of an arrangement for charging a xerographic plate according to the invention. manure,

Figo2 the perspective view of a second arrangement for Charging a xerographic plate according to the invention,

Figo 3 is an _addin} arrangement for charging a xerographi · * See plate according to the invention,

4 shows the schematic cross section of an automatic and continuous working xerographic copier, which is equipped with a device for loading according to the invention is equipped with a xerographic plate, and

5 shows a schematic cross section of the charging device a typical xerographic copier machine whose

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xerographic plate according to the invention is charged o

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In Figure 1 is a xerographic plate 10, an electrical one conductive grid 16 and a source 14 of charge generating particles.

The xe ro graphic plate 10 "consists of a grounded, conductive Pad 11 and a photoconductive insulating material 12. The electrically conductive base 11 is used in a xerographic plate for better electrical connection with the underside of the photoconductive insulating material layer 12 »

The photoconductive insulating material layer 12 consists of each photoconductive insulating material suitable for the present process A material that should preferably be used is amorphous selenium, which can be used to produce extremely good images, da3 is very sensitive to light and has the ability to charge to record and store at different potentials of different polarity · To carry out the invention Any suitable photoconductive insulating material layer can be used in the process. Typical substances of this type are i amorphous selenium, alloys of sulfur, arsenic or tellurium; · with Selenium, selenium doped with substances such as thallium, cadmium sulfide, Cadmium selenide, etc., particulate photoconductive substances v / ie zinc sulfide, zinc cadmium sulfide, zinc oxide (according to the French process manufactured), phthalocyanine, cadmium sulfide, cadmium selenide, Zinc silicate, kaämiumsulfoselenid, linear ohinakridones etc,

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dispersed in a non-conductive, inorganic, film-forming binder such as a glass or a non-conductive, organic, film-forming binder such as an epoxy resin, a silicone resin, an alkyd resin, a styrene-butadiene resin, a wax, etc. Other typical photoconductive insulating materials are: mixtures, copolymers, terpolymers, etc. of photoconductors and non-photoconductive substances, which are either copolymerizable or miscible together and form solid solutions. Organic, photoconductive substances of this type are: anthracene, polyvinylanthracene, anthraquinone, oxidiazole derivatives such as 2,5-bis- (p-aminophenyl-1) 1,3,4-oxidiazole, 2-phenylbenzoxazole, and charge-transferring complex substances that are produced by bringing together Synthetic resins such as polyvinyl carbazole, phenol aldehydes, epoxides, phenoxides, polycarbonates etc. are made with Lewis acids such as phthalic anhydride, 2,4,7-trinitrofluorenone, metal chlorides such as aluminum chlorides, sink chloride or iron chloride, 4,4-bi8 (dimethylamine) benzophenone, chloranil, picric acid , 1.3 _t 5-trinitrobenzene, 1-chloroanthraquinone, bromal, 4-uritrobenzaldehyde, 4-nitrophenol, acetic anhydride, maleic anhydride, boron trichloride, maleic acid, cinnamic acid, benzoic acid, tartaric acid, malonic acid and their mixtures. "

On the surface of the photoconductive insulating material layer 12 a uniformly deposited charge is shown. In the present jail this initial charge is positive polarity, It should be noted, however, that those shown in the figures Polarities also due to the opposite

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Values can be replaced.

The uniform positive charge can be applied to the xerographic plate 10 in a number of known ways. For example, the layer can be covered with a soft fabric such as cotton or silk, a soft brush or a fur rubbed, or the charge is applied by induction, as for example in the US patent 2 934 649 described iot. A roller charge is described by Straugham and Mayer in Proc. Nat. Electronics Oonf., 13, Pp. 959 to 962, 1958. Furthermore, the charge can be applied by a corona discharge device, which can be formed in various ways and deposited with the positive or negative charge generating particles will. For example, devices such as are generally described in U.S. Patents 2,836,725 and 2,777,957 are excellently suited for this purpose · Radioactive sources such as those of Deesauer, Mott ^ Bogdonoff can also be used in Photo Eng. 6, page 250, 1955 describe how other corona discharge devices are also used *

The charge source 14 is similar to that in the U.S. patent pencil 2 836 725 and emits particles that generate a negative charge

Between the uniformly charged plate and the partial height source 14 a grounded conductive grid 17 is arranged

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In operation, the parts of the grid 16 are in the path the negative charge generating particles emanating from the source 14, whereby these particles are diverted to the earth and those located under the grating are uniform positively charged parts of the xerographic plate are shielded. The spaces of the conductive grid 16 allow deposition of the charge generating particles of the source 14 in a pattern corresponding to the grid on the surface of the plate · In the parts of the surface affected in this way, the The plate's positive charge is neutralized, whereupon a pattern of discrete, alternately arranged surface areas of negative charge formed within the positive charge layer of the plate will. The surface parts of negative charge correspond to that formed by the interstices of the conductive grid 16 Template.

The plate should preferably be charged when it is in its state of lowest conductivity or when there is no electromagnetic radiation that makes the photoconductor photoelectrically conductive. To ensure that the charge applied by the device according to the invention remains on the surface of the layer , the charging must be carried out when no light is incident with a wavelength that would make the respective photoconductor conductive ο

The grid 16 can take a number of different shapes and sizes

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from one or more parallel wires, in punched sheets, a wire mesh or the like. The dimensions of the grid parts or the distance between the grid openings can be changed within a wide range, though

it is desirable not to make the maximum linear dimension of the grid parts and the spaces greater than about 0.5 mm in order to achieve a more natural and better continuous tint and large area coverage. I ^{1 For a} few tweaks, coarse grids with 20 or 24 points or lines per cm are favorable, for example for the direct production of halftone images or halftone images, but a better continuous tint of the final image results when grids with .40, 80, 120 , 160 and even more points or lines per era are used / ended.

In the case shown, the grid is earthed, but it can also be biased to its ability to generate charge To influence particles of the source 14, to change. Generally a bias of up to. - suitable for 1000 volts

The distance of the grid from the plate 10 can also can be varied within a wide range, although distances between approximately 0.13 and 0.58 mm from the surface of the Plate enable the creation of images of optimal quality

When using the shown in Figure 1 according to the invention

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Arrangement for charging the xerographic plate result Good quality images with large, continuously tinted areas and continuous tinting as well as line images and raster images. The xerographic plate consists of a photoconductive layer of insulating material amorphous selenium on an aluminum base. On the selenium -will A uniform positive charge is applied by placing over the plate an oorona arrangement of the type described in the US patent 2 836 725 described at a distance of 12.7 mm and crossed twice at a rate of 5 om per second where the Oorona wire carries a positive voltage of about 900 volts. Of course you get the same Results by moving the plate past a fixed corona facility

A grounded grid is placed at a distance of 0.25 mm above the surface of the selenium »The grid has a mesh structure 100 χ 100, square openings 0.13 mm wide and consists of a copper grid, the area of which is too 25 # consists of openings ^. The grille is above of the plate, the same oorona arrangement becomes at one speed of approx. 5 om per second and at a distance of 12.7 mm over the plate surface, but with the corona wire carries a negative voltage of approx. 5500 volts.

Of course, the biases mentioned can be constant or pulsating, as they are, for example, by half-wave '

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rectification of alternating current can be obtained.

After charging according to the invention, the plate 10 is exposed to an original image to be reproduced, whereby a latent electrostatic image is generated. This is made visible, for example, through cascading development. The developed image can then be transferred to an image sheet, e.g. paper, and fixed or bound on this, where & u usual xerographic fixation methods are used «

The improved quality of the xerographic images produced with the described charging system is attributed to the effect of the generation of a cough of small surface charges of one potential immediately next to other surface charges of another potential photo ·· conductive layer in the space immediately above this, where they can attract toner particles _f so that development also takes place in charged areas that correspond to a large, continuously tinted image area and continuous tones of the original image

Of course, the flats have charges, if the electric ones Properties of the respective photoconductive substance as well as the operating conditions make this possible, not only a different potential compared to the surrounding charges,

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There is also an opposite polarity to the directly adjacent surface charges, since this results in the greatest charge difference or the greatest change in charge. In the present description, the surface charges are shown with a polarity opposite to the directly adjacent other surface charges, it being understood, however, that the invention in its various embodiments can also be applied to patterns of charges of one potential, the immediately adjacent surface charges having the same polarity, However, they have a different potential · For example, the cascading development of images with large, continuously tinted areas of good quality is possible with commercially available copying machines if the potential difference between the charge pattern and the immediately adjacent area charges is not less than 300 to 500 yoIt · With a liquid development like them for example described by Gundlach in the US Patent J5 068,115, enough a potential difference of about _o 100 volts to produce good images. Thus, when the method according to the invention is used together with the development of a liquid, the formation of a charge pattern with a positive voltage of 600 volts is immediate

adjacent surface charges with a positive voltage of 700 volts possible, whereby images of good quality are produced _e

It should be noted that in addition to the ICascading and Fluid development also includes other types of development

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are possible with the charging method according to the invention. In addition include, for example, magnetic brush development (US Pat. No. 2,950,351), powder cloud development (US Pat 2,221,776), Friction Development (U.S. Patent 2,895,847) and others.

The sensitized according to the invention plates can also be developed in such a way that initially a toner with a Polarity is charged, to the development of the discrete surface parts negative charge is passed over the plate, after which a negatively charged toner to develop the remaining discrete ones Area parts of positive charge is used or 24 openings per cm of continuously tinted high quality images, as any rastering as indicated by ΤοηβΓ a single Polarity is avoided. The double development with two successive transitions of oppositely charged toner can be used especially in the case of automatically working xerographic copying machines lead to unsatisfactory results. That described in U.S. Patent 3,013,890 Double development process in which the carrier material carries positively and negatively charged toner particles and a double one Development achieved through a single transition of the developer material can bring better results »

In Figure 2, a xerographic plate 10 of the type already described and a prestressed grid 18 is shown »

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On the surface of the photoconductive insulating material layer 12 is a uniform positive charge having one of those mentioned in connection with the arrangement shown in FIG Procedure applied.

located immediately above the loaded xerographic platen the prestressed grid 18, which emits negative charge generating particles

When operating the arrangement it turns out that the grid 18 at f; e it is suitable for pre-tensioning even for a Gorona-3ntla ~ is a source of charge that emits charge-generating particles, ■ which in lattice distribution on the surface of the Plate to be deposited. The deposited negative charges initially neutralize the positive ones already on the plate and then form a pattern of discrete surface charges on the plate that are immediately next to the positive surface charges · This pattern is more negative Charges almost correspond to the shape of the grid 18 »

The prestressed grid 18, which can be formed from similar materials and in a similar shape as the conductive grid In Figure 1, it is in operation as a Ccrona charge source a pattern suitable for carrying out the method according to the invention.

It is of course known to the person skilled in the art that the Durcliines-

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ser the wire-shaped with regard to the commercially available corona wires To change grid parts within a large range, but with the respective applied voltage to generate a corona discharge and must be below the flashover voltage. A practical upper limit for the The diameter of the corona discharge wires was found to be 0.25 mm. For wires with a larger diameter, the risk of Rollover. A suitable wire for the construction of a lattice 18 consists of bare corrosion-resistant steel and has a diameter of 0.09 mm »

The distance of the grid 18 from the plate can also be varied within a fairly wide range. A distance of 0.13 to 3 »2 mm is preferably used to achieve optimal images.

The bias of the grid 18 can change within wide limits as long as it is sufficient to generate a corona discharge and is below the flashover voltage applicable to the respective grid. In general, voltages between 4000 and 10,000 volts give satisfactory results. Is a grating, for example, a steel wire of 0.09 mm diameter so strong with a grid voltage of 6500 volts are corona discharges generated. With this voltage value, I find out, for example, that a corona discharge of approx. 2 seconds is sufficient to develop large, continuously tinted areas of good quality.

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In Figure 3 is a xerographic plate 10, a prestressed one Grid 20 and a source 22 of positive and negative charge generating parts are shown. With this arrangement finds a simultaneous deposition of particles for positive and negative charge on the surface of the xerography Plate instead.

The Oorona source 22 is made up of two discharge devices of FIG formed in the type described in the ÜS patent specification 2 836 725, one of which is positive for emitting positive charge and the other is positive for emitting negative charge generating particles is negatively biased. It can also be just such a device that with an alternating voltage is fed, since particles of both polarities are then generated alternately. Of course can also be designed differently Oorona discharge devices be used.

Between the plate and the charge source 22 is a biased one Arranged grid 20, which consists of a grid or network of isolated and oppositely biased groups of Wires. Such a grid consists of one set of parallel wires that are laid over a second set of parallel ones Wires lies, which run in a plane parallel to the first wires but perpendicular to these. The one set of Wires is connected to one pole of a voltage source other set of wires with the other pole of this voltagea «·

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source connected.

When operating the arrangement it turned out that a grid. of a substance and with a shape similar to the grid 16 in Figure 1 controls the flow of charge carriers of mixed polarity from the source 22 and causes a deposition of these charge carriers in a pattern of alternately charged surface parts of two different polarities and potentials on the surface of the xerographic plate. Because of the low grid voltages mentioned, some negative charge carriers are deflected from the negatively charged grid parts and deposited on the plate and some are attracted by the positively charged grid parts and diverted to earth, which prevents their passage to the plate. Some positive charge carriers are deflected by positively charged parts of the grid and deposited on the plate, and some are attracted to the negatively charged parts of the grid and diverted to earth, preventing their passage to the plate. In this way, alternating surface charges o arise on the plate

The distance des.Gitter 20 from the plate can be within a wide areas can be changed »distances between 0.13 and 3.2 mm result in the best images ·

A wide range of voltages on the wire sets of the grid 20 is suitable for the operation of the arrangement, preferred * however, positive and negative voltages of 10

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used up to 100 volts.

With the voltages specified above for the grid parts, good images with large tinted surface parts result when the two discharge devices are charged with opposite polarity to approx. 6500 volts each and at a speed of approx. 5 cm per second at a distance of approx. 12 , 7 mm above the surface of the plate «,

Both discharge devices are used to simplify operation out together over the plate, but pole operation is also possible here.

In Figure 4, a xerographic copying machine is shown, which at the point 1 is a device for performing the Contains method according to the invention. One to be reproduced Original image is fed from a support table 30 onto a conveyor 31. Here it comes to an endless one Belt 32, which is driven by a motor 33 and is guided past the optical axis of a projection system 34, which is illuminated by the projection lamp IMP-1. That The original image is sent via the mirror 35 to an adjustable lens 36 and then via the mirror 37 to an adjustable lens Slit opening 38 is reflected through which it hits the surface of a xerographic plate in the form of drum 39 falls.

The xerographic drum 59 is located on an axis 40 within

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the machine and is driven clockwise by a motor 41 at a constant speed, which is proportional to the transport speed of the original image, thereby increasing the peripheral speed of the drum surface with the speed of movement of the projected image rays matches »The drum surface 42 consists of a layer of a photoconductive insulating material 43 a conductive pad 44, which prior to exposure by an arrangement operating in accordance with the invention in place is sensitized

The exposure of the drum 39 causes the radiation image, a discharge of the photoconductive layer in the exposed Plächentei ^ / ^1, an electrostatic latent image is formed thereby on the drum corresponding to the projected original image. After exposure, the drum surface is guided past a development point 46 at which a developing agent 47 consisting of two components, as already described, is cascaded over the drum surface by means of a developing device 48 ·

In the development device, the developer is through a conveyor device 49 driven by a motor 50 is conveyed upwards and then released via a chute 51, causing it to fall over the surface of the drum 52 of the developer, which is running during the development

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is consumed, is contained as a supply in a Mach filling device 53 and can be dimensioned accordingly through the opening 54 Quantities to be refilled.

After development, the xerographic powder image is fed past an image transfer point 22 where it is applied a moving image surface 63 is transmitted, for which purpose a corona device 64 is used, which is powered by a high voltage source is fed.

The moving image transfer surface 63 onto which the powder image is transferred, can consist of paper and comes from a supply roll 65 over the guide roller 66 and others suitable tension pulleys in fläohenhaft contact with the Drum right next to the corona facility 64 »After the Image transfer is the image transfer surface 63 of the Drum surface separated and attached to a fixing device 68 passed, which is used for melting or permanent fixation, the "powder image on the transfer surface 63. In the present Trap, this device consists of a heat fixing device operated with resistors. It can, however other fixing methods can also be used, for example with solvent vapors or with radiant heat Procedure. After the fixation, the image transfer surface is wound onto the take-up roller 70 for further use.

Thereafter, the surface of the xerographic drum is attached to a

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Cleaning point 71 passed, at which they with a cleaning brush 75 is brushed off, whereby residual developer is removed.

The loading device shown in FIG. 4 and arranged at point 1 of the xerographic drum 39 operates according to the basic principle shown in FIG. 1 and is modified for use in an automatic xerographic copying machine as shown in FIG. More precisely, the charging system consists of two corona units 82 and 83 which can be designed in accordance with one of the exemplary embodiments described , as well as a moving, endless, conductive grid 81 and grounded conductive shields 84.

The surface of the drum is preserved by the corona discharge device 82 a uniform charge of one polarity.

The grid 81, which is designed similar to the grid 16 in Figure 1, is located near the drum surface and is on guide and tension rollers 79 and 80 guided »It is continuously guided past the drum surface, including a Drive roller 77 driven by motor 78 is used.

The grid can be grounded or biased with voltages within the preferred range of -1000 volts to be used be, for which purpose the drive roller 77 or one of the guide *

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or tension rollers 79 and 80 are used.

The conductive grid 81 is counterclockwise with constant Speed moves, thereby reducing the peripheral speed of the drum surface in the area between the grounded conductive shields 84 match the speed of the grid 81. This is also where the corona discharge source is 83 arranged, which emits negative charge carriers to charge the plate negatively. The shields 84 serve to prevent charge transfer outside the space between the shields, which is clear Formation of differently charged surface parts on the plate contributes

The pattern of alternately charged surface parts - positive and negative polarity - on the drum surface is then on moved past the exposure point, where the photoconductive layer is discharged in an imagewise distribution. The latent Image arrives at development site 46, whereafter the powder image at transfer site 62 onto the moving image transfer surface 63 is transmitted. The result is very good pictures with large, continuously tinted areas and continuous tint

FIG. 5 shows the drum surface in the region of the loading point 1 together with a section of the overall machine another embodiment of the charging device shown '

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• This corresponds to the arrangement shown in FIG however, mechanically differently designed according to their intended use

This charging device consists of a corona discharge source 94, an endless, prestressed grid 90 on a roller 86 of low conductivity and a device for prestressing the grid, which consists of a battery 92 and a contact brush 93 consists, the bias voltage is fed to the electrically conductive, insulated axle 91, from which a connection tion 96 to the grid.

The grid 90 is similar in material and shape to the prestressed one The grid 81 of FIG. 2 is carried out and is arranged near the drum surface. It is rotated on the roller 86, for which purpose the motor 89 drives counterclockwise at a constant speed. The peripheral speed of the The drum surface roughly corresponds to the speed of movement of the grid 90 in the area between the grounded, conductive shields 84. The shields 84 prevent a transition of charge carriers outside the space formed by them, which leads to the clear formation of a Contributes charge pattern on the drum surface.

In operation of the arrangement, the drum surface is moved past the orona discharge device 94 and receives a uniform charge of positive polarity. The drum surface then reaches the area between the shields

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near the grid 90 and receives a corona discharge charge pattern of negative polarity formed by the grid and superimposed on the uniform positive charge. Then . the drum is exposed to an image which is developed and applied to the image transfer surface as a good quality copy is transferred "

The charging system shown in Figure 3 can also be used in an automatic, continuously working xerographic vision Copier machine can be used if changes similar to those made in the loading system in the figures are made 4 and 5 are shown.

Above, a novel charging method based on various Exemplary embodiments for a xerographic imaging method described, with the charges of different polarity in a pattern on the surface of a xerographic Plate can be applied to improve the quality of solid and continuous * tinted images.

There are numerous changes to the elements, substances, process steps and arrangements described after knowledge of the above Description of the method according to the invention possible, which, however, are encompassed as a whole by the basic idea of the invention «,

BAD ORiGiWAL 909887/1366

Claims (1)

- 50 - Ί3Τ73Τ7 Claims Γ 1 .J method for the electrostatic charging of a xerographic plate in a number of discrete charged surface parts, the potential of which has alternating two different values, characterized in that at least a first number of surface parts of the xerographic plate (10) is charged to a first potential and that in a second number of discrete small surface parts, which are not identical to the first-mentioned surface parts, charge-generating particles are deposited, which charge these surface parts uniformly to a second potential. 2 »Method according to claim 1, characterized in that the xerographic plate (10) on its entire surface is charged evenly to the first potential. 3 «Method according to claim 1 or 2, characterized in that the first potential differs from the second potential differs at least 100 volts. 4. Method according to one of claims 1 to 3 »characterized in that the charge-generating particles are passed through a prestressed, conductive grid (16) above the plate (10) before they are deposited, so that they are placed on it in a pattern corresponding to the grid shape are deposited and generate a charge pattern with said second potential. "* ^l 909887 / l36b BA ₀ ORIGINAL 5. The method according to claim 4, characterized in that the Polarity of the charge generating the first potential of the plate (10) opposite to the polarity of the second potential generating charge is. 6. The method according to claim 4, characterized in that the conductive grid (16) with a voltage of up to 1000 Volt is biased. 7. Method according to one of Claims 4 to 6, characterized in that that the conductive grid (16) is biased with earth potential. 8. The method according to any one of claims 4 to 6, characterized in that that the polarity of the bias of the conductive grid (16) corresponds to the polarity of the charge generating particles is opposite. 9. Method according to one of Claims 4 to 8, characterized in that the prestressed conductive grid (16) is arranged above the plate (10) at a distance of 0.13 to 0.38 mm 10. The method according to claim 9j, characterized in that the Grid (16, 18) consists of grid parts and spaces formed by these, and that the maximum size of one The space between the two is now no more than 0.5. · ' 909887/1366 bad OR) GiNAt Method according to one of Claims 1 to 3, characterized in that that the charge-generating particles from a prestressed grid (18) on the plate (10) are deposited in a distribution corresponding to this grid (18), resulting in a grid shape corresponding Charge pattern with the second potential results. Method according to Claim 11, characterized in that the polarity of the one generating the first potential of the plate (10) Charge is opposite to the polarity of the charge generating the second potential. Method according to Claim 11 or 12, characterized in that the prestressed grid (18) is prestressed from 4000 to 10,000 volts. Method according to one of Claims 11 to 13, characterized in that that the prestressed grid (18) is arranged over the plate (10) at a distance of 0.13 to 0.38 mm is· Method according to one of Claims 11 to 14 »characterized in that that the prestressed grid (18) consists of grid parts and spaces formed by them and that the grid parts are formed from a wire with a maximum diameter of 0.25 mm. ORIGINAL 909887/1366 ^mL Method according to claim 1, characterized in that charge-generating particles of both polarities through a above the plate (10) at a distance of 0.13 to 0.38 mm arranged grid (20) are guided, which consists of a first group of parallel and a first Potential between 10 and 100 volts positively biased wires and a second group of in one plane of the first group parallel plane perpendicular to the first wires and negatively biased to a second potential between 10 and 100 volts is. Device for carrying out the method according to one of claims 1 to 16, characterized by a near one to be charged xerographic plate (10) arranged Gorona discharge device (22) and through an between the plate (10) and the Oorona discharge device (22) arranged grid (20), which consists of a first group parallel to each other; wires running and positively biased to a first potential between 10 and 100 volts as well a second group parallel to each other and in a plane parallel to the plane of the first wires to the first Wires running vertically and negatively biased to a second potential between 10 and 100 volts is formed so that the charge generating particles emitted by the Oorona discharge means (22) both Polarities are passed through the grid (20) 909887/1366 and on the plate (10) a plurality of discrete, alternately arranged electrical charges of two different potentials form 909887/1366 zs Blank page