EP1110125A2

EP1110125A2 - Printer or copier for simultaneously printing a supporting material on both sides

Info

Publication number: EP1110125A2
Application number: EP99947276A
Authority: EP
Inventors: Markus LÖBEL; Vilmar Eggerstorfer; Manfred Viechter; Albrecht Gerstner; Karl Zappe
Original assignee: Oce Printing Systems GmbH and Co KG
Current assignee: Canon Production Printing Germany GmbH and Co KG
Priority date: 1998-09-03
Filing date: 1999-09-03
Publication date: 2001-06-27
Anticipated expiration: 2019-09-03
Also published as: DE59915218D1; WO2000014607A2; US6556804B1; WO2000014607A3; DE59911378D1; EP1465023B1; EP1110125B1; EP1465023A1

Abstract

The invention relates to a printer or copier for simultaneously printing a supporting material on both sides. Two transfer bands (41, 42) transfer toner images (44, 45) onto a supporting material (43). A transfer corotron (47a) recharges the toner particles in the polarity thereof. The toner particles are transferred onto the supporting material (43) at the transfer point by an electric field (F). The invention also relates to a corotron device comprising counter-electrodes having small surfaces.

Description

description

Printer or copier for simultaneous printing on both sides of a carrier material

The invention relates to a printer or copier with a transfer station for simultaneous printing on both sides of a carrier material. The invention further relates to a corotron device which can be used in the transfer station mentioned.

High performance printers and high performance copiers often have the ability to print on the front and back of a substrate such as paper. This mode of operation is also called duplex printing. It is known to first print a toner image on one side, for example the front side, and then to turn the carrier material. The same printing station is then requested again in order to then print the second side, usually the back side, with a second toner image. This type of duplex printing is known both for tape-shaped carrier material and for Emzelblatt carrier material. In such a printing operation, the total throughput is not high due to the additional transport and the turning of the carrier material. In another known solution, a printer or copier system contains two printing units, each printing unit printing on one side of the carrier material. In this case, considerable space is required for the two printing units within the system and the technical outlay is great.

In a printing device known from US-A-5, 526, 107, continuous paper is fed to a transfer printing point of a photoconductor cylinder, which has electrophotographic units on two surfaces for producing differently colored toner images. The continuous paper is opened at the transfer location printed on the front with a first color, then the continuous paper is deflected and fed to a printing point opposite the transfer point on the same photoconductor cylinder and printed there with the reverse side.

From EP-A-0 320 985 it is known to use a transfer belt which carries toner images which have been transferred from a photoconductor drum to the transfer belt. The toner images on the transfer belt are then transferred to the carrier material at the transfer location.

From DE-A-197 13 964, which has the same content as US-A-5, 797, 077, a transfer station for simultaneous printing on both sides of a carrier material is known (duplex printing). The transfer station contains a pivotable transfer printing station which, in a first position, holds a transfer belt away from the carrier material, so that no toner images are transferred to this carrier material. In this position, toner images are superimposed on the transfer belt to enable multi-color printing. In a second position, the transfer printing station is pivoted to the carrier material and transmits the multicolored toner image.

WO 87/02792 describes a corotron device with a corotron electrode, the counter electrode of which is designed as a metal plate. This metal plate is at ground potential. The electric field generated between the corotron electrode and the counter electrode leads to an influence on the charge of the toner particles.

It is an object of the invention to provide a printer or copier which enables simultaneous printing of the front and back of a carrier material with little effort and with high printing quality. This object is achieved by the features of claim 1. Advantageous further developments are given in the dependent claims.

According to the invention, two transfer bands face each other at the transfer printing location, the toner particles of which have different polarity. An electrostatic field is now generated, which is directed in such a way that the toner particles are repelled both by the first transfer belt and by the second transfer belt and are deposited on the respective surfaces of the carrier material. A simultaneous transfer printing is achieved in this way. The transport path of the carrier material remains short, since the carrier material does not have to be passed two printing stations or two printing stations. In addition, there is no intermediate fixation of the toner images transferred to the carrier material, as a result of which the technical outlay is reduced and the print quality remains high.

In a preferred exemplary embodiment, both transfer belts, seen in the feed direction of the carrier material, have toner images with toner particles of the same polarity in a section in front of the transfer printing station, a charge transfer corotron being arranged in front of the transfer printing station along one of the transfer belts, which generates an electric field that polarizes the toner reverses this transfer band by reloading. Through these measures, a uniform toner system, for example a positive or negative toner system with positive or negative charge of the toner image, can be used for both transfer bands. Accordingly, the print quality on both sides of the carrier material is almost identical. Another embodiment is characterized in that two transfer rollers face each other at the U printing point, and that a direct voltage is applied to the transfer rollers, which generates the electric field for transfer printing of the toner particles. On the one hand, the transfer rollers ensure precise guidance of the carrier material and the transfer belt in the area of the transfer printing point. On the other hand, they make it easy to build up an electric field in the area of the transfer printing point.

In practice, an exemplary embodiment has proven itself in which, seen in the feed direction of the carrier material, two guide elements are arranged in front of the transfer rollers, between which the transfer belt and the carrier material are guided. In this way, the transfer tapes and the carrier material are guided along a relatively large distance with mutual contact. The fogging effect is reduced because the toner particles have only a small or no spacing from the surface of the carrier material and have such a location-accurate transfer printing occurs at the transfer printing ^'.

According to a further aspect of the invention, a corotron device is specified with the features of claim 25. This corotron device can advantageously be used in conjunction with the transfer modules mentioned.

To print an end image carrier, for example paper, a toner image present on an intermediate carrier is transferred mechanically, thermodynamically or electrostatically to the end image carrier. For an electrostatic transfer of the toner image from a photoconductor belt to an intermediate carrier or to an end image carrier, the toner particles must have a certain voltage potential. The electrostatic transfer of the toner particles takes place through forces in the electrical field and is based on a potential difference between the toner particles and the final image carrier to which the toner image is to be transferred. The force by the electric field must be greater than the binding forces by which the toner particles are held on the intermediate carrier for toner images from which they are to be transferred.

In electrographic printing and / or copying devices, dry toner particles are used for the electrographic transfer with a suitable voltage potential, so that the transfer of the toner particles to ^" a material can be carried out in the printer or copier without additional influence on the charge of the toner particles. If the final image carrier is to be printed on both sides (Duplex printing), the end image carrier must be turned over, or a simultaneous or time-delayed transfer of the toner particles from both sides to the end image carrier takes place. In order to carry out the transfer without intermediate fixing of the toner image transferred to the end image carrier, the toner particles must be on the first side of the intermediate carrier The toner particles are preferably transferred from a positive voltage potential to a negative voltage potential with respect to the ground potential ie the toner particles are transferred from the intermediate carrier to the final image carrier from both sides at the same time or with a time delay without intermediate fixation. The toner particles on both sides of the final image carrier are attracted by their different potentials through the final image carrier and / or are attracted by the potential difference to the final image carrier, so that they adhere to the final image carrier.

After the transfer process, toner particles stick to the intermediate carrier from which they are to be transferred, ie they have not been successfully transferred. It deals are toner particles of a few percent of the toner image, usually considerably less than 20 percent. These untransferred toner particles usually have a low or incorrect voltage potential. In order to carry out a further transfer of these untransferred toner particles, for example for cleaning the intermediate carrier, with high efficiency, it is necessary to charge the toner particles to a defined potential. This loading process takes place with a corotron device. The intermediate carrier forms the counter electrode to the corotron device. If the intermediate carrier is a conductive material with a specific resistance of less than 10 ^ ohm cm, the intermediate carrier is connected to ground potential or to another suitable voltage potential and thus serves as a counter electrode. If, for example in the case of a photoconductor, the intermediate carrier is provided with a light-sensitive cover layer whose dark resistance is very high-resistance (for example greater than 10 ⁶ ohm cm), a counter electrode must be arranged on the back of the intermediate carrier. Counter electrodes are preferably designed as metal plates or as conductive deflection rollers. Since deflection rollers are associated with a high mechanical outlay, increased space requirements and high costs, metal plates are primarily used as counter electrodes.

The counter electrode should have a low contact resistance to the intermediate carrier. The intermediate carrier is guided past the fixed counter electrode without contact. In order to achieve the low contact resistance, the intermediate carrier must be guided past the fixed counterelectrode at a short distance. This distance is preferably 0.2 mm to 1.0 mm. The forces between two bodies, the potential difference of which creates an electric field, are comparable to the forces between two plates of a plate capacitor, one plate of the plate capacitor through the counter electrode and the other Plate is formed by the underside of the intermediate carrier. A force then acts on the intermediate carrier in the direction of the fixed counter electrode. This force causes the band-shaped intermediate support on the counterelectrode to deflect in its direction, touch it and adhere to it. The contact between the moving band-shaped intermediate carrier and the stationary counter electrode creates static and sliding friction. The mechanical energy required in addition to driving the intermediate carrier due to this friction between the intermediate carrier and counter electrode must be applied by the drive unit of the intermediate carrier. In addition, the intermediate carrier and / or the counter electrode is worn as a result of the sliding friction.

It is therefore the task of specifying a corotron device in which low attractive forces occur between the intermediate carrier for toner images and the counterelectrode and the charge carrier exchange is ensured.

According to the novel corotron device, the counter electrode has conductive elevations, the end points of which protrude in the direction of the corotron wire and which lie in a plane parallel to the longitudinal axis of the corotron wire. This configuration of the counter electrode ensures that the attractive force between the intermediate carrier and the counter electrode is considerably reduced. This attraction depends crucially on the effective area. The decisive effective area is the area of the counterelectrode facing the intermediate carrier. The arrangement of electrically conductive elevations, the end points of which represent the decisive effective area, ensures that the effective area and thus also the attractive forces between the intermediate carrier and the counterelectrode are low. This arrangement also ensures that the curvatures on the elevations result in a strong exchange of charge carriers due to peak discharge.

A preferred embodiment provides that the elevations of the counter electrode are arranged along the longitudinal axis of the corotron wire. It is thereby achieved that the electric field for influencing the charge of the toner particles is formed uniformly and the arrangement of the counter electrode is possible in a space-saving manner.

Another embodiment is characterized in that the counter electrode contains individual pins as elevations. This ensures that the counterelectrode can be manufactured inexpensively from standardized components.

Another preferred embodiment variant is that the counter electrode contains tapered elevations. It is thereby achieved that the effective area of the counter electrode and thus the attractive force between the intermediate carrier for toner images and counter electrode is further reduced.

According to a further aspect, in a corotron device for an electrographic printing and / or copying device, it is provided that the counterelectrode is designed in the manner of a blade with a cutting edge, the cutting edge being arranged parallel to the longitudinal axis of the corotron wire. With this configuration it is achieved that, for example, a sheet metal plate, which is arranged perpendicular to the intermediate carrier for toner images and runs across the width of the intermediate carrier for toner images, is used as the counter electrode. Such an arrangement is space-saving and inexpensive. This arrangement also ensures that the curvatures on the cutting edge lead to an independent exchange of charge carriers (to a peak discharge). Another favorable embodiment of the corotron device provides that the cutting edge of the counterelectrode is serrated and that the serrations taper in the direction of the corotron wire, so that the end points and / or end faces of the pegs protrude in the direction of the corotron wire and parallel to the longitudinal axis of the corotron wire lie. It is thereby achieved that the effective area, on which the amount of attractive force between the intermediate carrier for toner images and counter electrode is dependent, is reduced compared to the continuous blade, whereby the attractive force is further reduced. The peak discharge is further favored.

According to a further aspect, in a corotron device for an electrographic printing and / or copying device it is provided that the counter electrode is formed by a wire, the longitudinal axis of which is arranged parallel to the longitudinal axis of the corotron wire. With this configuration it is achieved that e.g. a corotron wire is also arranged as a counter electrode. This wire runs across the width of the intermediate beam. Such an arrangement saves space and reduces the number of components used.

Embodiments of the invention are explained below with reference to the drawings. In it shows

FIG. 1 shows a schematic sectional illustration of an electrophotographic printing device for monochrome and / or colored printing on one or both sides of a band-shaped carrier material, in which the transfer station according to the invention can be used,

Figure 2 is a schematic sectional view of a

Printing device according to FIG. 1, which prints the carrier material on both sides, FIG. 3 schematically shows an arrangement of essential parts of the transfer station with the transfer of the toner particles,

FIG. 4 shows a detailed illustration of the arrangement according to FIG. 3 to explain the mode of operation,

FIG. 5 shows an electrical equivalent circuit diagram which shows the resistance and current conditions at the transfer printing point,

FIG. 6 shows an arrangement similar to that of FIG. 3 with a negative toner system,

FIG. 7 shows schematically the possible potential relationships on the transfer printing rollers,

FIG. 8 shows an exemplary embodiment in which the transfer belts partially wrap around the transfer rollers,

FIG. 9 shows an exemplary embodiment with guide rollers,

FIG. 10 shows a detailed illustration of the arrangement according to FIG. 9,

FIG. 11 shows an arrangement similar to that according to FIG. 9, in which the electrical field required for transfer printing between the guide roller and the

Transfer roller is built up

FIG. 12 shows an electrical equivalent circuit diagram for the exemplary embodiment according to FIG. 11, FIG. 13 shows an arrangement according to FIG. 11, feed rollers additionally being provided,

FIG. 14 shows an exemplary embodiment with deflection brackets,

FIG. 15 the current conditions in the exemplary embodiment according to FIG. 14,

FIG. 16 shows the exemplary embodiment according to FIG. 14 with insulated Umiehkbügeln,

FIG. 17 shows an exemplary embodiment with electrically conductive deflection brackets, which are guided through a resistance to ground potential,

FIG. 18 shows an exemplary embodiment similar to that according to FIG. 13,

FIG. 19 shows several exemplary embodiments for a transfer roller,

Figure 20 shows a transfer roller from a high-resistance

Material with side electrode connections,

FIG. 21 a transfer roller with an electrically conductive core and a high-resistance coating, FIG. 22 shows a recharging corotron device with two corotron wires and with two counter electrodes designed as blades,

FIG. 23 a recharging corotron with a corotron wire and one used as counter electrode

Blade, the field lines of the effective electric field being indicated,

FIG. 24 shows the representation of a counterelectrode, which as

Blade is executed

Figure 25 shows a blade, the

Edge is jagged,

FIG. 26 shows a counter electrode consisting of an arrangement of individual pins,

FIG. 27 shows a counter electrode consisting of a wire, and

FIG. 28 shows a transfer printing corotron device with a corotron wire and with a counter electrode designed as a blade.

FIG. 1 shows a printing device for monochrome and / or colored printing on one or both sides of a strip-shaped carrier material, for example a paper web. The printing device has a modular structure and has a feed module M1, a printing module M2, a fixing module M3 and a post-processing module M4. The feed module Ml contains elements for feeding a continuous paper drawn off from a stacker to the printing module M2. This printing module M2 contains the transfer station, which prints the carrier material, which is then in the fixing module M3 is fixed and cut and / or stacked in the post-processing module M4.

The printing module M2 contains the units required for printing a tape-shaped carrier material 10 with toner images, which are arranged on both sides of a transport channel 11 for the carrier material 10. These units essentially comprise two differently configurable electrophotography modules E1 and E2 with associated transfer modules T1 and T2, which together form the transfer station T. The modules E1 and T1 are assigned to the front ^" of the carrier material 10, the modules E2 and T2 to the rear of the carrier material 10.

The essentially identically constructed electrophotography modules E1 and E2 contain a preferably seamless photoconductor belt 13 which is guided over deflection rollers 12 and driven by an electric motor in the direction of the arrow, which e.g. is an organic photoconductor, also called an OPC. The units for the electrophotographic process are arranged along the light-sensitive outside of the photoconductor belt 13. These units are used to generate 13 individual color separations on the photoconductor belt associated toner images. For this purpose, the photoconductor 13 moved in the direction of the arrow is first charged to a voltage of approximately -600 V using a charging device 14 and discharged to approximately -50 V using a character generator 15 consisting of an LED comb, depending on the characters to be printed.

The latent charge image thus produced, located on the photoconductor 13, is then colored with toner using developer stations 16/1 to 16/5. The toner image is then loosened with the aid of the intermediate exposure device 17 and in an intermediate transfer area 18 onto a transfer belt 19 of the transfer belt module T1 using a transfer corona device 20. Thereafter, the entire photoconductor belt 13 is discharged over the entire width with the aid of the discharging device 21 and cleaned of adhering toner dust by means of a cleaning device 22 with cleaning brushes. A subsequent intermediate exposure device 23 ensures appropriate charge-related conditioning of the photoconductor belt 13, which, as already described, is then charged uniformly with the aid of the charging device 14.

Using the electrophotography module E1 or E2, individual color separations are assigned to toner images, the entirety of which forms the color image to be printed. For this purpose, the developer stations 16/1 to 16/5 are designed to be switchable. They each contain the toner assigned to a single color separation. For example, the developer station 16/1 contains black toner, the developer station 16/2 toner of yellow color, the developer station 16/3 toner of magenta color, the developer station 16/4 toner of cyan color and, for example, the developer station 16/5 contains blue toner or toner a special color. Both one-component and two-component toner developer stations can be used as developer stations. One-component toner developer stations which work with fluidizing toner, as are known, for example, from US Pat. No. 477106 (applicant Fotland), are preferably used. The subject matter of this U.S. patent is part of the present disclosure.

In order to achieve the switchability of the developer stations, ie in order to be able to operate each individual developer station individually, these stations can be designed when using fluidizing toner in accordance with German patent application DE 196 52 866. Switching the developer The station accordingly takes place by changing the electrical pretension of the transfer roller or by changing the electrical pretension of the applicator roller. It is also possible to switch the developer stations by mechanically moving them and thereby bringing them into contact with the photoconductor belt 13. Such a principle is known for example from DE-A-196 18 324.

During operation of the printing device, a toner image "^'is generated by the developer stations 16/1 to 16/5 by a single developer station, which is assigned to a single color separation. This toner image is then electrostatic via the transfer printing device 18 in connection with the transfer corona device 20 transferred to the transfer belt 19. The transfer module T1 contains this transfer belt 19, which consists of a rubber-like substance, is guided around several deflection devices and is driven by a motor, similar to the photoconductor belt 13, the transfer belt 19 is preferably endless and has no seam specifically from the transfer area with the roller 18 and the transfer corona device 20 to a transfer printing station 24 with transfer rollers, from there further around a deflection roller 25 to a cleaning station 26 and from there again to the transfer area 18, 20 with the deflection roller arranged there 27.

The transfer belt 19 in the transfer module T1 serves as a collector for the individual toner images assigned to the color separations, which are transferred to the transfer belt 19 via the transfer device 18, 20. The individual toner images are arranged one above the other so that an overall toner image corresponding to the color image is produced. In order to be able to generate the overall toner image and then to transfer it to the front of the carrier material 10, the transfer module contains Tl a switchable transfer printing station 24. According to the illustration in FIG. 1, this can contain a plurality of mechanically displaceable transfer printing rollers 28 with the associated transfer printing corona device 29. In the “collecting” operating state, the transfer printing rollers 28 and the transfer printing corona device 29 are shifted upwards in the direction of the arrow, so that the transfer belt 19 is spaced apart from the carrier material 10. In this state, the individual toner images are taken over by the electrophotography module E1 and superimposed on the transfer belt 19. The cleaning station 26 is deactivated by pivoting it away. In this operating state, the carrier material 10 is at rest in the area of the transfer printing station 24.

The electrophotography module E2 and the transfer module T2 for the rear of the recording medium 10 are constructed in accordance with the modules E1 and T1. Here, too, an overall toner image is generated on the transfer belt by collecting individual toner images for the back, the corresponding transfer printing station 24 also being pivoted away in the operating state * collecting ".

For simultaneous printing on the front and back of the carrier material 10, the transfer ribbons 19 of the transfer modules T1 and T2 are brought into contact with the carrier material 10 in the region of their transfer printing stations 24 and the carrier material 10 is moved in the process. At the same time, the cleaning stations 26 of the transfer modules T1 and T2 are pivoted and activated. After the two toner images have been transferred to the front or the back of the carrier material 10, toner image residues adhering to the transfer belts 19 are removed by the cleaning stations 26. This is followed by another collection cycle for generating new toner images, in which the transfer belts 19 have been pivoted away and the carrier material 10 is at a standstill. The above- Transfer of the toner images from the transfer modules T1 and T2 to the carrier material 10 thus takes place during a start-stop operation of the carrier material 10.

The carrier material 11 is moved in the paper transport belt with the aid of motor-driven transport rollers 38. In the area between the transport rollers 38 and the transfer printing stations 24, charging or corona devices 39 for paper conditioning can be arranged so that the paper 10 is transferred to the load, e.g. is set uniformly.

So that during the start-stop operation the paper support material 10 does not tear and can also be fed continuously, the feed module Ml contains a loop puller 30. This loop puller 30, which acts as a tape store, buffers the support material 10 continuously drawn off by a stacking device 31 .

After the transfer of both colored toner images in the area of the transfer stations 24 onto the carrier material 10, these still have to be fixed. The fixing module M3 serves this purpose. It contains an upper and a lower row of infrared radiators 32, between which the paper transport channel for the carrier material 10 runs. The toner image, which is located both on the front side and on the rear side of the carrier material 10 and is fixed by the infrared emitters 32, is still hot and soft and is guided without contact after the area of the infrared steel 32 via a deflection roller 33 arranged on the output side. The fixation is carried out by the heat generated by the infrared radiators 32. In a cooling section with cooling elements 34 and deflecting rollers 35 which adjoins the infrared radiators 32, the carrier material 10 is cooled and smoothed, for example by means of appropriate decurler devices. As Kuhlele- elements 34 can serve fan-driven air chambers. After both toner images have been fixed and cooled, the carrier material 10 is correspondingly post-processed within the post-processing module M4, which can contain, for example, a cutting device 36 with a stacking device 37.

In order to be able to implement the various operating states, a microprocessor-controlled control device ST, which is connected to the device control GS of the printer, is used, which is connected to the components to be controlled and regulated by the feed module Ml, print module M2 and fixing module ^"~ M3 or post-processing module M4 Modules, it is coupled to the individual units, for example with the electrophotography modules El and E2 and the transfer modules T1 and T2.Connected to the device controller GS or controller ST, which can be part of the device controller, is a control panel B, via that the various operating states can be entered. The control panel B can contain a touch screen screen or a personal computer PC with a coupled keyboard. The control itself can be constructed conventionally.

In the embodiment according to FIG. 2, the electrophotography modules E1 and E2 contain two independently working, image-generating devices B1 and B2. The first image-forming device B1 contains a character generator 15, a charging device 14, an intermediate exposure device 23, a cleaning device 22, an unloading corotron device 21 and a developer station 16/1. The second image-forming device B2 is constructed analogously to this with a charging device 14, character generator 15, a development station 16/2 and an intermediate exposure device 17. The developer station 16/1 can be assigned a first color, for example black, and the developer station tion 16/2 of a second color, e.g. blue or another color. It is thus possible to first generate a first toner image of the color black with the aid of the electrophotography modules E1 or E2 and to superimpose a toner image with the additional color onto this black toner image with the second image-forming device B2. The toner image (spot color toner image) superimposed in this way is then transferred to the transfer modules T1 and T2 and from there directly to the carrier material 10. This makes it possible to apply two-color toner images to the continuously moving carrier material 10 on both sides. If only one of the ^"" imaging devices B1 or B2 is activated, monochrome printing is carried out continuously. In both operating modes, the transfer modules T1 and T2 are used solely for transferring the toner images, without the operating mode "collecting" being necessary. However, it is also conceivable to operate both image-generating devices B1 and B2 alternately and the transfer modules T1 and T2 as at the beginning to operate in the "Collect" operating mode.

The transfer devices T1 and T2 shown in FIGS. 1 and 2 belong to the transfer station T, the essential parts of which are explained below with reference to FIGS. 3 to 21. FIG. 3 shows an exemplary embodiment of the transfer station T, in which two transfer rollers are used. The toner image 44 for the front side of the carrier material 43 is located on the transfer belt 41. The toner image 45 for the rear side of the carrier material 43, which is preferably a paper web, is located on the second transfer belt 42. Both toner images 44 and 45 have been transferred, for example, to the transfer belts 41, 42 using the electrophotographic devices E1 and E2 according to FIG. In the present case according to FIG. 3, a positive toner system is used, ie after the toner images 44, 45 have been applied, the toner particles have positive electrical charge. fertilize as indicated in Figure 3. The carrier material 43, which is conveyed in the direction of the arrow P1, is arranged between the two transfer belts 41, 42.

Two electrically conductive transfer rollers 49a, 49b guide the transfer belts 41, 42 in such a way that they touch the carrier material 43. An electrical direct voltage U is applied to the transfer rollers 49a, 49b and is fed from a direct voltage source 40. In the area of the transfer rollers 49a, 49b facing each other, the transfer printing process takes place, in which toner particles are transferred from the transfer belts 41, 42 to the respective surface of the carrier material 43. This area is also known as the transfer point. A transfer corotron 47a is arranged on the transfer belt 42 in front of the transfer printing point and is fed with negative direct voltage with respect to ground from a direct voltage source 48. The charge transfer corotron 47a is opposed by a ground electrode 47b.

In principle, the transmission bands 41, 42 can consist of an insulating material or a conductive material. It is desirable that the transfer belts 41, 42 and the carrier material 43 have the same surface speeds. Too large a relative movement of the surfaces to one another would cause the toner images 44, 45 to be mechanically blurred and could thus have a negative influence on the print quality.

FIG. 4 shows the mode of operation of the simultaneous transfer printing when using a positive toner system. Due to the electric field generated by the recharge corotron 47a, the polarity of the toner particles arranged on the lower transfer belt 42 is reversed, ie the toner particles 46 no longer have a positive charge but a negative charge. fertilizer, as indicated in Figures 3 and 4. The toner particles of the toner image 44 are still positively charged. Due to the voltage U applied to the transfer rollers 49a, 49b, an electrostatic field F is formed, the field lines of which depend on the shape of the transfer rollers 49a, 49b, that is to say in particular on the radius of curvature. FIG. 4 indicates that the electric field F m of the plane of the central axes of the transfer rollers 49a, 49b is largely homogeneous and becomes more inhomogeneous towards the edge along the plane of the carrier material 43. Depending on the electric field strength adjustable by the voltage U, the toner particles of the upper toner image 44 separate from the transfer belt 41 and are deposited on the front of the carrier material 43. Since the potential of the upper transfer roller 49a is positive, there is a repulsive force for the toner particles of the toner image 44, which repels the toner particles on the surface of the carrier material 43. The lower transfer roller 49b has a negative voltage potential with respect to the potential of the toner particles 46 with a negative charge. Accordingly, these toner particles 46 are repelled from the surface of the lower transfer belt 42, migrate against the direction of the electric field F to the back of the carrier material 43 and accumulate there.

In the inhomogeneous area, for example in the area of the field line F1, of the electric field F, individual toner particles can get loose early. Due to the inhomogeneity of the field and due to the increased distance between the surfaces of the carrier material 43 and the transfer belts 41, 42, the impact of the toner particles on the carrier material 43 is not exactly determined; it can lead to a nebulizing effect, which is known under the technical name "Foggmg". This effect is discussed in more detail below. FIG. 5 shows an electrical equivalent circuit diagram, which is shown as a circuit with series resistors R. The flowing current i results from Ohm's law, ie the current i is the quotient of the voltage U divided by the sum of the individual resistors R. The aim should be that the resistances R of the two transfer rollers 49a, 49b are as small as possible. This can be achieved using conductive materials, ie metal transfer rollers are used. It should also be provided that the resistances R of the transmission bands 41, 42 are as large as possible so that the total current i remains small. With a large total current i, the wear of the transmission bands 41, 42 is increased. The resistance R of the transmission bands 41, 42 must, however, assume a finite value so that the electric field F is formed with high intensity on the surface of the respective transmission bands 41, 42. If the resistance R of the transmission bands 41, 42 is too large, the effective distance for the electric field F is increased; it extends from the surface of the transfer roller 49a to the surface of the transfer roller 49b. With the same voltage U, the field strength within field F is then weakened. With a certain conductivity of the transmission bands 41, 42, the effective distance for the electric field F between the transmission bands 41, 42 is reduced and thus the field strength is increased while the voltage U is otherwise the same.

FIG. 6 shows essential parts of the transfer station T when using a negative toner system, ie in which the charges of the toner particles are negatively charged after being applied to the transfer belts 41, 42. The polarity reversal is in turn effected by the recharge corotron 47a, which in this case, however, has a positive potential. Likewise, the transfer rollers 49a, 49b are driven with a voltage U, so that an electric field is created, the field strength of which is reversed compared to the exemplary embodiment according to FIG. The function of transfer printing corresponds to that previously described, only with the opposite sign of the charge and the field strength.

FIG. 7 shows the possible potential relationships on the transfer rollers 49a, 49b. In FIGS. 7a and 7b, one of the transfer rollers 49a, 49b is grounded. Likewise, an electrode of the DC voltage source 40 is grounded. FIG. 7c shows a symmetrical voltage control, the center of voltage being connected to ground. FIG. 7d shows an asymmetrical voltage control for the transfer rollers 49a and 49b.

FIG. 8 shows a development of the arrangement according to FIG. 3. The carrier material 43 to be printed is guided by the transfer rollers 49a and 49b in such a way that it wraps around the transfer rollers 49a, 49b in each case by a predetermined wrap angle. In this way, the area in which the respective toner image 44 or 45 rests on the surfaces of the carrier material 43 is enlarged. Inhomogeneities of the electric field F at its edge have a less pronounced effect; the fogging effect is reduced.

FIG. 9 shows an exemplary embodiment in which two guide rollers 49c, 49d are arranged in front of the transfer rollers 49a and 49b, as seen in the feed direction of the carrier material 43, between which the transfer belts 41 and 42 and the carrier material 43 are guided. The two guide rollers 49c and 49d are connected to ground potential, while the voltage U for generating the electric field is applied to the transfer rollers 49a and 49b. The two guide rollers 49c, 49d bring the transfer belts 41 and 42 into contact with the carrier material 43 or reduce the distance to a minimum. When the toner images 44, 46 reach the inhomogeneous area (cf. FIG. 4) of the electric field during forward transport and first toner particles are transferred to the surface of the carrier material 43, the flight distance for these toner particles is minimal or zero and an exact location takes place Toner transfer. In this way, the fogging effect mentioned is avoided and high print quality is achieved.

FIG. 10 shows a detailed representation of the transfer printing area according to FIG. 9. The electric field F is effective between the two transfer rollers 49a and 49b. Due to the contact of the toner particles on the transfer belts 41, 42 with the surface of the carrier material, a precise transfer printing takes place in the electric field 41.

FIG. 11 shows a variant of the embodiment according to FIG. 9. The lower transfer roller 49b and the upper guide roller 49c are subjected to a voltage potential, so that the electric field F between the rollers 49b and 49c is effective. The transfer roller 49a and the guide roller 49d are mounted insulated and have floating potential. As a result of the measures mentioned, the electrical field F required for transfer printing is effective over a longer distance, so that the transfer printing process proceeds more gently because the effective area on which the transfer of the toner particles from the transfer belts 41, 42 to the surface of the carrier material 43 takes place, is enlarged.

FIG. 12 schematically shows the physical relationships using an electrical equivalent circuit diagram. Is the specific material resistance p of the transmission 41, 42 low, then relatively high currents l result due to Ohm's law. With a fixed voltage U this can result in an undesirably high electrical power P according to the relationship:

P = U • l.

Due to the inhomogeneities of the materials for the transmission bands 41, 42, local current peaks are possible which briefly break down the electrical field and thus interfere with the process of transfer printing. By increasing the distance between the rollers that form the electrodes for the electrical field, the electrical resistance R of the transmission bands 41, 42 and also that of the carrier material 43 increases. Accordingly, the flowing current I is reduced due to the relationship

R = p ^• 1 / A,

where R is the total electrical resistance, p is the electrical specific material resistance of the transmission bands, 1 is the effective material length and A is the effective material cross section

FIG. 13 shows a combination of the exemplary embodiments according to FIGS. 9 and 11. In front of the guide rollers 49c and 49d, two feed rollers 49e and 49f are arranged, between which the transfer belts 41, 42 and the carrier material 43 are guided. The feed rollers 49e and 49f lead to ground potential, while the arrangement of the rollers 49a, 49b, 49c, 49d and the potential lead correspond to those according to FIG. 11. This creates an electrically neutral zone in the area of the feed rollers 49e, 49f, the attraction forces of the toner particles with different potential being neglected. sigen is. This prevents premature skipping of toner particles in the area of increased distance between the transfer belts 41, 42.

FIG. 14 shows a variant of the arrangement according to FIG. 9. Instead of the earthed guide rollers 49c, 49d, earthed deflection brackets 49g, 49h are used. These deflection brackets 49g, 49h can be arranged near the transfer roller 49a, 49b, which shortens the length of the contact of the transfer belts 41, 42 with the carrier material 43. If one compares the arrangement according to FIG. 9 with that according to FIG. 14, it can be seen that in FIG. 9 the minimum path in which there is contact between the transfer belts 41, 42 with the carrier material 43 is the sum of the radii of the transfer rollers 49a or 49b and the guide rollers 49c or 49d. If speed differences dv now occur between the speed of the transfer belts 41, 42 and the carrier material 43, this leads to mechanical slippage and thus to undesired blurring of the toner images to be transferred. The longer the contact path or the greater the difference in speed, the greater the wiping effect. In practice, it is hardly possible to reduce the speed difference between the transfer belts 41, 42 and the carrier material 43, since length tolerances have to be compensated for in the case of pre-printed forms. In order to keep the wiping effect small, the length of contact between the transfer belt 41, 42 and the carrier material 43 is reduced in accordance with the exemplary embodiment according to FIG. 14 by using narrow deflection brackets 49g, 49h, the sliding surfaces of which are arranged near the surface of the transfer rollers 49a, 49b can be. In order to reduce frictional forces, it makes sense to provide the deflection brackets 49g, 49h with a friction-reducing layer, for example with a layer made of a plastic material containing fluorine, for example PFA, ETFE, FEP, PVDC, Teflon or polyimide (PI). The surface wear of the deflection brackets 49g, 49h can be reduced by using hard, wear-resistant materials, for example chrome-nickel steel, VA steel, or by providing the deflection brackets 49g, 49h with a layer of a wear-reducing material, for example by Nickel plating, using silicate or using surface hardening.

FIG. 15 shows the current conditions in the example according to FIG. 14, the deflection brackets 49g / - "49h being at ground potential. The total current Iges results from the sum of the currents Iu at the transfer pressure point and the cross currents Iql and Iq2. It is desirable that

Ium »Iql + Iq2

is or that

Iql = Iq2 = 0

is. If the cross-current components Iql, Iq2, which flow through the transmission bands 41, 42 directly into the grounded deflection brackets 49g, 49h, are undesirably high, the deflection brackets 49h, 49g can also be arranged in an electrically insulated manner so that they assume floating potential ( see Figure 16).

FIG. 17 shows an exemplary embodiment in which the deflection brackets 49g, 49h are electrically conductive, but are guided via a resistor R to ground potential. The cross currents are also reduced in this exemplary embodiment according to FIG. 17. FIG. 18 shows a variant of the exemplary embodiment according to FIG. 13. The feed rollers 49e, 49f are replaced by deflection brackets 49i, 49j. These deflection brackets 49i, 49j can be designed electrically, as is indicated in the examples according to FIGS. 16 and 17.

Figure 19 shows various embodiments for the transfer rollers. In the upper part of the picture, the transfer roller is cylindrical and made of an electrically conductive metal as a solid component. In the middle section of FIG. 19, the transfer roller is made from metal in the form of a tube, ie hollow inside. The lower part of the picture in FIG. 19 shows a metallic core, which can consist of solid material or of a tube. This core is provided with a jacket made of high-resistance material. The use of a metallic core for the transfer roller is expedient since it has to be manufactured very precisely with little out-of-roundness. In order to minimize runout errors, the circumference of the transfer roller and the length of the transfer belt should be in an integer relationship to one another. However, the transfer belts have a certain fluctuation in thickness, which interferes with the transfer printing process, for example local detachment of the transfer belts from the roller can occur. Therefore, an elastic coating is advantageously applied to the transfer roller, which can compensate for small mechanical tolerances of the components by elastic deformation. This coating should have an electrical conductivity in order to be able to build up a strong electrical field in the transfer printing zone on its outer skin. The electrical conductivity of the coating should be in the range from 0.5 x 10 ^-6 to 5 x 10 ^ 2 icm, but preferably in the range from 0.5 x 10 ^ to 5 x 10 ⁹ Ωc. The elastic coating should have a Shore hardness in the range from 10 to 90 S (A), preferably in the range from 20 to 70 Sh (A). The thickness of the elastic coating is 0.2 to 15 mm, preferably 0.5 to 2 mm. The elastic coating can additionally have a layer of fluorine-containing plastic material, preferably PFA, ETFE, FEP, PVDC or Teflon, or a polyimide layer. The additional layer can also be electrically insulating and have a maximum thickness of 40 m, preferably from 0.1 to 20 µm. Conductive fillers, preferably carbon black, silicates, oxides, can be added to the elastic layer, which enables an increased layer thickness.

FIG. 20 shows a transfer roller which does not have a continuous metallic core, but has lateral metallic contacting cylinders 50. The central part 52 of the cylindrical roller consists of a high-resistance material. In the figure, the resistance R is plotted over the length 1 of the roller. It can be seen that the resistance R increases with increasing length 1, as a result of which the local current I decreases over length 1 when voltage U is applied. This results in different potentials along length 1, which is undesirable.

FIG. 21 shows an exemplary embodiment of a transfer roller with a low-resistance, metallic core 56, on which a coating 54 is applied, which consists of a relatively high-resistance material. The resistance R remains constant along the length 1, which also results in a constant potential along the length 1 on the surface of the high-resistance sheath coating. The core can also be made of an electrically conductive plastic, e.g. from the material PA, which contains soot particles.

FIG. 22 shows a recharging corotron device 110 with two corotron wires 112 and with two counter electrodes 114 designed as blades. As an intermediate carrier is a Photoconductor tape 116 is provided. However, a transfer belt can also be used.

The photoconductor belt 116 with an as yet unfixed toner image 118, which contains positively charged toner particles 120 or, after the charge has been negatively charged, toner particles 122, is carried out between the two corotron wires 112 and the two counter electrodes 114, it being guided and driven by deflection rollers 124. The blades 114 are fastened to a holder 126, which also establishes the electrical connection to the ground potential of the printing and / or copying device 128. The corotron wires 112 are surrounded on the side facing away from the photoconductor band 116 by two screens 130. The photoconductor tape 116 is guided past the counter electrodes 114 at a distance in the range from 0.2 mm to 4 mm, preferably in the range from 0.2 mm to 1 mm. The negatively charged toner particles 122 of the latent toner image 118 are recharged by the electric field between the corotron wires 112 and the counter electrodes 114.

FIG. 23 shows a recharging corotron device 110 with a corotron wire 112 and a single blade used as counter electrode 114, the field lines 132, 134 of the effective electrical field being indicated. The effective area, on which the magnitude of the attractive force between the photoconductor band 116 and the counter electrode 114 depends, is designated by 136. The counter electrode 114 has ground potential. Alternatively, the counter electrode can have a negative potential with respect to the ground potential. An electrical field is formed between the corotron wire 112 and the counter electrode 114. This field 134 acts on the toner particles 122 which have a negative potential. The toner particles 122 are discharged as they pass the corotron wire 112 and charged to a positive potential. The magnitude of the potential of the now positively charged toner 120 depends on the Dwell time of the toner in the electric field and on the density of the electric field. The photoconductor tape 116 is attracted by the counter electrode 114. The attractive force F is determined from the relationship: SQ ^• ε _r • A • U ²

F =

2 ^• d ² where ε _{r is} the dielectric constant of the air between photoconductor band 116 and counter electrode 114, A is the surface 136 of counter electrode 114 effective in the electric field, U is the potential difference and d is the distance between the underside of photoconductor band 116 and counter electrode 114.

FIG. 24 shows a further counter electrode 114 which is designed as a blade. This blade 114 has a rectangular cross section and is fastened by a holder 126 in the printer and / or copier 128.

A blade 114 is shown in FIG. 25, the edge of which is serrated. The blade 114 is arranged in the printer / copier 128 such that the teeth 140 taper towards the photoconductor belt 116. The tines 140 are arranged at equal intervals. This arrangement ensures uniform transfer of the latent toner image 118. The holder 126 of the blade 114 is not shown in this figure 25.

FIG. 26 shows a counter electrode 114 which consists of an arrangement of individual pins 142. The pins 142 are arranged on a holder 126 at symmetrical intervals. The holder 126 is arranged in the printer and / or copier 128 such that the ends of the individual pins 142 lie in a plane parallel to the photoconductor band 116 or to the corotron wire 112, and parallel to the corotron wire. FIG. 27 shows a counter electrode 114 which consists of a wire 144. The wire 144 is arranged in the printer and / or copier 128 by a suitable holding device 126 such that it lies in a plane parallel to the photoconductor band 116 and parallel to the corotron wire 112. A screen 130 is arranged on the side of the wire 144 facing away from the photoconductor band 116. A wire 144 similar to the corotron wire 112 is used as the wire 144.

FIG. 28 shows a transfer printing corotron device 146 with a corotron wire 112 and with a counter electrode designed as a blade 114. Two photoconductor tapes 116a and 116b are provided as intermediate carriers. Alternatively, two transfer belts can also be used. A not yet fixed toner image 118a on the photoconductor belt 116a contains positively charged toner particles 120. A not yet fixed toner image 118b on the photoconductor belt 116b contains negatively charged toner particles 122. The photoconductor belts 116a and 116b and a paper web 148 are between the corotron wire 112 and the blade 114 performed without touching them, the photoconductor belts 116a, 116b being guided and driven by deflection rollers 124. The drive and the guidance of the paper web 148 is not shown in this figure. Corotone wire 112 has a positive potential and blade 114 has a negative potential with respect to ground potential. The corotron wire 112 is surrounded by a screen 130 on the side facing away from the photoconductor band 116a. The positively charged toner particles 120 of the latent toner image 118a are repelled by the positively charged corotron wire 112 and attracted by the negatively charged toner particles 122 of the latent toner image 118b and by the negatively charged blade 114. Analogously, the negatively charged toner particles 122 of the latent toner image 118b are repelled by the negatively charged blade 114 and by the positively charged toner particles 120 of the latent toner image 118a and attracted by the positively charged corotron wire 112. A force which is greater than the binding forces between the toner particles 120, 122 and the photoconductor belts 116a, 116b acts on the positively and negatively charged toner particles 120, 122 through the transfer printing corotron 146. The positively and negatively charged toner particles 120, 122 are printed onto the paper web 146 by the field forces of the electrical field. The toner particles 120, 122 remain adhered to the paper web 146 by the binding forces between the toner particles 120, 122 and the paper web 146 and by the attraction between the positively charged toner particles 120 on the one side of the paper and the negatively charged toner particles 122 on the other side of the paper.

Reference list

Ml feed module

M2 printing module M3 fixing module

M4 post-processing module

10 record carriers, paper, single sheet or continuous paper

11 Transport channel El electrophotography module, front

E2 electrophotography module, rear

Tl transfer module, front

T2 transfer module, rear

12 deflection rollers 13 photoconductors

14 charging device

15 character generator 16/1 to

16/5 developer stations 17 intermediate exposure device

18 transfer printing device, transfer area

19 transfer belt

20 transfer corona device

21 discharge corona device 22 cleaning station

23 intermediate exposure device

24 transfer station

25 deflection roller

26 cleaning station 27 deflection roller

28 transfer roller

29 transfer corotron

30 loop pullers

31 stacking device 32 infrared heaters

33 deflection roller

34 cooling element

35 deflection roller 36 cutting device

37 stacking device

GS device control

ST control device

B Control unit 38 transport rollers

39 charging corona device

Bl imaging facility

B2 imaging facility

40 DC voltage source 41 upper transmission band

42 lower transmission band

43 carrier material

44 Toner image

45 toner image 46 transferred toner particles

47a reloading corotron

47b ground electrode

48 DC voltage source

49a, 49b transfer rollers 49c, 49d guide rollers

49e, 49f feed rollers

49g, 49h deflection bracket

49i, 49 deflection bracket against ground

Pl transport arrow T transfer station

50 contacting

52 middle section

54 coating

56 core F electric field

Fl field line

R resistance

U voltage i current

1 length

A effective area

P specific resistance

110 reloading corotron facility

112 corotron wire

114 counter electrode

116 photoconductor tape

118 latent toner image

120 positively charged toner particles

122 negatively charged toner particles

124 deflection roller

126 holder

128 printing and / or copying device

130 umbrella

132 field lines

134 field lines

136 effective area of the counter electrode in the electric field

140 pips

142 single pens

144 wire

146 transfer corotron

148 paper web

Claims

Expectations

1. Printer or copier, with a transfer station (T) for simultaneous printing on both sides of a carrier material (10, 43),

in which a first endless transfer belt (19, 41) of a first transfer module (T1) carries toner particles of a first polarity in the area of a transfer printing point,

a second endless transfer belt (19, 42) of a second transfer module (T2) carries toner particles of a second polarity in the area of the transfer printing point,

at the transfer location the carrier material (10, 43) is guided between the first transfer belt (19, 41) and the second transfer belt (19, 42),

An electrostatic field (F) is generated at the transfer location, which causes the toner particles of each transfer belt (41, 42) to detach from the respective transfer belt (41, 42) due to electrostatic forces and on the opposite surface of the carrier material ( 43) cling to

in which each transfer module (T1, T2) contains a switchable transfer printing station (24),

which in a first mode of operation (“collecting and printing *) initially holds the respective transfer belt (19) at a distance from the carrier material (10), while on the respective transfer belt (19) a plurality of toner images are arranged one above the other and the carrier material (10) itself the transfer point does not move forward, and then the respective transfer belt (19) leads close to the carrier material (10) in order to jointly transfer the toner images arranged one above the other,

and which, in a second operating mode (“continuously printing *), guides the respective transfer belt (19) near the carrier material (10) in order to continuously print monochrome toner images on the carrier material (10).

2. Printer or copier according to claim 1, characterized in that both transfer bands (41, 42) seen in the feed direction of the carrier material in a section in front of the transfer location have toner images (44, 45) with toner particles of the same polarity, and that in front of the transfer parts A recharge corotron (47a) is arranged along one of the transfer belts (42) and generates an electric field which reverses the polarity on this transfer belt (41) of the toner particles by recharging.

3. Printer or copier according to claim 2, characterized in that the same polarity of the toner particles in the section in front of the transfer corotron (47a) is positive.

4. Printer or copier according to claim 2, characterized in that the same polarity of the toner particles in the

The area in front of the transfer corotron is negative.

5. Printer or copier according to one of the preceding claims, characterized in that two transfer rollers (49a, 49b) face each other at the transfer location, and that a direct voltage (U) is applied to the transfer rollers (49a, 49b), which electric field (F) generated for transfer printing of the toner particles.

6. Printer or copier according to one of the preceding claims, characterized in that one of the transfer rollers (49a, 49b) leads to ground potential.

7. Printer or copier according to one of the preceding claims, characterized in that the transfer rollers (49a, 49b) have symmetrical or asymmetrical potential with respect to ground.

8. Printer or copier according to one of the preceding claims, characterized in that the transfer rollers (49a, 49b) are arranged so that the carrier material (43) wraps around the transfer rollers in each case by a predetermined wrap angle.

9. Printer or copier according to one of the preceding claims, characterized in that, seen in the feed direction of the carrier material (43), two guide elements (49c, 49d) are arranged in front of the transfer rollers (49a, 49b), between which the transfer belts (41, 42) and the carrier material (43) is guided.

10. Printer or copier according to one of the preceding claims, characterized in that the electric field (F) for transfer printing of the toner particles between a transfer roller (49b) and one of the diagonally opposite guide elements (49c) is formed.

11. Printer or copier according to claim 10, characterized in that the other transfer roller (49a) and the other guide element (49d) have floating potential.

12. Printer or copier according to one of the preceding claims, characterized in that the guide elements (49c, 49d) are designed as rollers.

13. Printer or copier according to one of the preceding claims, characterized in that the guide elements are designed as rigid deflection brackets (49e, 49f), the sliding surfaces of which are arranged near the transfer rollers (49a, 49b).

14. Printer or copier according to one of the preceding claims, characterized in that, seen in the feed direction of the carrier material (43), two feed elements (49g, 49h) are arranged in front of the guide elements (49e, 49f), between which the transfer belts (41, 42) and the carrier material (43) is guided.

15. Printer or copier according to one of the preceding claims, characterized in that the feed elements (49g, 49h) have ground potential.

16. Printer or copier according to one of the preceding claims, characterized in that the transfer rollers have a metallic core, and that an elastic coating with a predetermined electrical conductivity is provided on the metallic core.

17. Printer or copier according to one of the preceding claims, characterized in that the conductivity of the coating in the range from 0.5 x 10 ^{~ 6} to 5 x 10 ¹² Ωcm but preferably in the range from 0.5 x 10 ^ to 5 x 10 ⁹ Ωcm.

18. Printer or copier according to one of the preceding claims, characterized in that the elastic coating has a Shore hardness in the range from 10 to 90 Sh (A), preferably a range from 20 to 70 Sh (A).

19. Printer or copier according to one of the preceding claims, characterized in that the elastic coating has a thickness of 0.2 to 15 mm, preferably a thickness of 0.5 to 2 mm.

20. Printer or copier according to one of the preceding claims, characterized in that the elastic layer additionally has a layer of fluorine-containing plastic material, preferably of PFA, ETFE, FEP, PVDC or Teflon or of polyimide.

21. Printer or copier according to one of the preceding claims, characterized in that the additional layer is electrically insulating and has a maximum thickness of 40 microns, preferably from 0.1 to 20 microns.

22. Printer or copier according to one of the preceding claims, characterized in that conductive fillers, preferably carbon black, silicates, oxides, are added to the elastic layer.

23. Printer or copier according to one of the preceding claims, characterized in that conductive fillers, preferably carbon black, silicates, oxides, are added to the additional layer.

24. Printer or copier according to one of the preceding claims, characterized in that as carrier material Tape material, preferably a paper web, or single sheets is provided.

25. Corotron device (110) for an electrographic printing and / or copying device (128),

with at least one corotron wire (112) with a first potential,

with at least one counter electrode (114) with a second potential different from the first potential,

and with at least one intermediate carrier (116) for toner images, which is guided between the corotron wire (112) and the counter electrode (114),

characterized in that

the counter electrode (114) has electrically conductive elevations (140, 142), the end points of which protrude in the direction of the corotron wire (112) and which lie in a plane parallel to the longitudinal axis of the corotron wire (112) and parallel to the intermediate carrier (116).

26. Corotron device (110) according to claim 25, characterized in that these elevations (140, 142) run parallel to the longitudinal axis of the corotron wire (112).

27. Corotron device (110) according to any one of the preceding claims, characterized in that the counter electrode (114) contains individual pins (142) as elevations.

28. Corotron device (110) according to one of the preceding claims, characterized in that the counter electrode (114) contains tapered elevations (140, 142).

29. Corotron device (110) for an electrographic printing and / or copying device (128), with at least one corotron wire (112) with a first potential,

characterized in that

the counter electrode (114) is designed in the manner of a blade with a cutting edge, the cutting edge being arranged parallel to the longitudinal axis of the corotron wire (112).

30. Corotron device (110) according to claim 29, characterized in that the cutting edge is serrated and that the end points and / or end faces of the serrations (140) protrude in the direction of the corotron wire (112) and lie parallel to the longitudinal axis of the corotron wire (112) .

31. Corotron device (110) according to claim 30, characterized in that the prongs (140) taper to a point in the direction of the corotron wire (112).

32. Corotron device (110) according to one of the preceding claims, characterized in that the cross section the blade (114) tapers in the direction of the corotron wire (112).

33. Corotron device (110) according to one of the preceding claims, characterized in that the cutting edge

Width that is in the range of 0.02 mm to 0.5 mm, preferably in the range of 0.02 mm to 0.1 mm.

34. Corotron device (110) for an electrographic printing and / or copying device (128),

with at least one corotron wire (112) with a first potential,

characterized in that

the counter electrode (114) is designed as a wire (144), the longitudinal axis of the wire (144) being arranged parallel to the longitudinal axis of the corotron wire (112).

35. Corotron device (110) according to one of the preceding claims 25 to 34, characterized in that the corotron wire (112) and the counter electrode (114) lie in a plane which is perpendicular to the intermediate carrier (116).

36. Corotron device (110) according to one of the preceding claims, characterized in that the intermediate carrier (116) is a photoconductor belt or a transfer belt.

37. Corotron device (110) according to one of the preceding claims, characterized in that the corotron device (110) is a transfer corotron, a charging corotron, a transfer printing corotron or an extinguishing corotron.

38. Corotron device (110) according to one of the preceding

Claims, characterized in that the intermediate carrier

(116) at a distance in a range from 0.2 mm to 4 mm, preferably in a range from 0.2 mm to 1 mm, past the counter electrode (114).

39. Corotron device (110) according to one of the preceding claims, characterized in that the counter electrode (114) has ground potential.

40. Corotron device (110) according to one of the preceding claims, characterized in that the intermediate carrier (116) consists of a high-resistance material which has a specific resistance of> 10 ⁶ ohm cm.

41. Printer or copier according to one of claims 1 to 24, characterized in that each transfer module (Tl, T2) contains a corotron device (110) according to one of the preceding claims 25 to 40.