EP1882211A1

EP1882211A1 - Device and method for printing on both faces of a recording medium, comprising a charge shifting and recharging device

Info

Publication number: EP1882211A1
Application number: EP06725285A
Authority: EP
Inventors: Alexander Kreiter; Stefan Scherdel; Karl Zappe; Manfred Viechter
Original assignee: Oce Printing Systems GmbH and Co KG; OC Printing Systems GmbH
Current assignee: Canon Production Printing Germany GmbH and Co KG; OC Printing Systems GmbH
Priority date: 2005-05-20
Filing date: 2006-03-23
Publication date: 2008-01-30
Also published as: US7801472B2; US20080205920A1; WO2006122847A1; DE102005023462A1; JP2008541180A

Abstract

The invention relates to a device and a method for simultaneously printing on both faces of a recording medium (12). The device comprises a revolving first toner image support (78) and a revolving second toner image support (78'), means (80) for producing a first toner image, consisting of a toner that is charged with a first polarity, on the first toner image support (78), and means (80') for producing a second toner image, consisting of a toner that is likewise charged with the first polarity, on the second toner image support (78'). The device also comprises a charge shifting device (108) adapted to charge the first toner image present on the first toner image support (78) with a second polarity opposite the first polarity, and a recharging device (114) adapted to recharge the second toner image present on the second toner image support (78') with the first polarity.

Description

Apparatus and method for double-sided printing of a recording medium with reloading and reloading device

The present invention relates to an apparatus for simultaneous two-sided printing of a recording medium, comprising a circulating first toner image carrier and a circulating second toner image carrier, comprising means for producing a first toner image consisting of toner, which is charged with a first polarity, on the first toner image carrier Means for forming a second toner image consisting of toner, also charged with the first polarity, on the second toner image carrier, with a transfer device adapted to reload the first toner image on the first toner image carrier to a second polarity, that of the first Polarity is opposite, and with a first Umdrucksteile where the recording medium between the first toner image carrier and the second toner image carrier is passed, and on which an electric field can be generated, through which the second to the polarity reversed first To nerbild and the second toner image are detached from the first and second toner image carrier and transferred to the respective toner image carrier side facing the recording medium.

The invention further relates to a printer or copier with such a device and a method for simultaneous double-sided printing of a recording medium.

A device of the aforementioned type is known for example from WO 98/39691 and the parallel US 6,246,856 Bl. In this known device, the recording medium is formed by a paper web and the first toner image carrier and the second toner image carrier are formed by transfer belts which are essentially mirror-like. are arranged symmetrically to the paper web above and below it. The means for generating the first and the second toner image are formed by transfer printing between an associated photoconductor belt and the respective transfer belt.

The known device can be operated in two different modes of operation, a multi-color print collection mode and a continuous print mode. In multicolor printing collection mode, toner images in primary colors or component colors, so-called color separations, are successively produced on the photoconductors in an electrophotographic process and successively transferred to the respective transfer belt. On the transfer belt, the individual color components are "collected", ie superimposed in register, so that a first colored toner image results on the first transfer belt and a second colored toner image on the second transfer belt Paper web swung, and the first and the second toner image are printed on the top or bottom of the paper web.

In continuous printing mode, printing is only monochrome, i. no color separations are collected on the transfer belt. Instead, the first and the second toner image from the associated photoconductor are transferred to the respective transfer ribbon and printed in the course of a continuous processing directly on the first Umdrucksteile reprinted to the top or bottom of the paper web.

However, the first and the second toner image carrier need not be formed by an intermediate carrier, but may for example be formed by photoconductor, in particular photoconductor belts, from which is directly transferred to a recording medium. Into these general In the present document, the term "toner image carrier" is to be understood as meaning.

In EP 1 110 125 Bl (parent application) of EP 1 465 023 A1 (divisional application) and the parallel application US Pat. No. 6,556,804 B1, various embodiments of the first transfer parts and the transfer device are described in detail and their mode of operation is explained. These explanations are not intended to be repeated here, but are incorporated by reference into the present specification.

As explained in the cited documents, the toner of the first toner image and the toner of the second toner image are first charged with the same, first polarity. This charge of the first polarity requires the toner for the electrophotographic process. It is typically generated by triboelectric charging in a developer station. Before the first and the second toner image can be simultaneously transferred to the opposite sides of the recording medium, one of the toner images, in the present case the first toner image, has to be reloaded. Then, both toner images in an appropriate, provided in the Umdruckbereich electric field, an electrical force of attraction in the direction of the recording medium, by which they are reprinted on this.

However, in this known device, the printing result is not always satisfactory. In practice, a different transfer efficiency often results between the first toner image carrier and the one side of the recording medium on the one hand and the second toner image carrier and the other side of the recording medium on the other hand. The resulting print images then differ in their visual appearance from each other. In addition, it can lead to a mutual influence of the two print images. For example, if on one side of the If a solid pattern is printed on a recording medium and isolated characters are printed on the other side, it may happen that the isolated characters in the areal pattern appear dimly.

The present invention has for its object to provide an apparatus and a method in which or the Umdruckwirkungsgrade differ less on the two sides of the recording medium less and a mutual influence of the two printed images is avoided.

This object is achieved by a device according to claim 1 and by a method according to claim 25. Advantageous developments of the invention are specified in the dependent claims.

According to the present invention, there is thus provided a reloading device which is suitable for reloading the second toner image on the second toner image carrier with the first polarity; that is, the second toner image is charged with the same polarity it already has.

The inventors have found that the above

Problems due to divergent electrical and electrostatic properties of the toner of the first and second toner image are due. The electrostatic properties, in particular the absolute charge level, are subject to different fluctuations because the charging is effected by different processes. While the charge of the transferred first toner image is essentially determined by the operating parameters of the transfer device, the charge of the second toner image, which has been generated triboelectrically, depends, inter alia, on the toner throughput and weather influences such as atmospheric moisture, etc. The charge states Therefore, the first and the second toner image are not matched to one another depending on the factors mentioned under certain operating conditions, so that deviations in the transfer printing efficiency and thus in the print image can occur.

Further problems occur when the first and the second toner image have a significantly different level in the toner application, because thereby changing the electrostati- behavioured conditions in Umdruck. A higher toner layer on one of the toner image carriers leads to an increased distance between the toner image carrier and the recording carrier, whereby the capacity of the transfer printing system is changed.

These effects, which all have an influence on the printed image, can not be taken into account solely by the voltage or the current flow m of the transfer printing point and the operating parameters of the transfer printing device. Instead, erfmdungsgemaß proposed to provide a Nachladevorrichtung with which the second toner image can be reloaded. By suitable choice of the operating parameters of the transhipment device and the afterloading device, the first and second toner images can be conditioned to be uniform, i. be re-printed with at least approximately the same Umdruckwirkungsgrad, without affecting each other.

For a better understanding of the present invention, reference will be made below to the preferred embodiments shown in the drawings, which are described with reference to specific terminology. It should be noted, however, that the scope of the invention should not be limited thereby, since such changes and other modifications to those shown

Devices and / or the method and such other applications of the invention, as shown therein are considered to be common current or future expertise of a competent person skilled in the art.

The figures show embodiments of the invention, namely:

1 shows the schematic structure of an electrophotographic printer with two

Printing units;

Figure 2 is a schematic representation of the two transfer tape drives of

Fig. 1.

FIG. 1 shows a high-performance electrophotographic printer 10 for printing on an endless paper web 12 at a printing speed of 0.9 to 2.0 m / s. A printing unit 14 includes a first image forming and transfer unit 16 for printing on the front side of the paper web 12 and a second image forming and transfer unit 18 for printing the back side of the paper web 12. The image forming and transfer units 16, 18 are referred to below as printing units 16 , 18 denotes. The first printing unit 16 is substantially identical to the second printing unit 18. Therefore, identical components in the first printing unit and the second printing unit 18 are denoted by the same reference numerals, wherein the reference numerals of the second printing unit 18 are provided with a bar. Differences between the first printing unit 16 and the second printing unit 18 will be explained below. The printing unit 14 further contains a paper feeder 20, a control unit 22, a toner supply and processing system 24, an image data processing unit 26 and a paper web drive and guidance system 28.

The paper web 12 is by means of Papierbahnantriebsund -führungssystems 28 in the direction of arrow Pl through the Promoted printer 10, wherein the paper web 12 is supplied after printing in the printing unit 14 of a fuser 30 which fixes the toner images generated by the printing unit 14 on the paper web 12. The paper drive and - guiding system 28 includes guide rollers 32 to 40 and a drive roller 42 with an opposing pressure roller 44. Further, two hole sensors 46, 48 are provided which monitor the position of edge holes contained in the paper web 12. In the fuser 30, a further drive roller 50 and a pressure roller 52 are provided for paper withdrawal.

The first printing unit 16 and the second printing unit 18 are arranged on opposite sides of the paper web 12. The first printing unit 16 is also called upper

The printing unit and the second printing unit 18 are also referred to as the lower printing unit. The paper web 12 can be conveyed by means of the drive roller 42 both in the direction of the arrow Pl and in the opposite direction, wherein in the following with forward moving the conveying of

Paper web 12 in the direction of arrow Pl and with backward moving the conveying of the paper web 12 opposite to the direction of the arrow Pl is designated. The function of the printing unit 14 and the fixing station 30 is described in detail in WO 00/34831 and DE 198 27 210 C1, which are incorporated by reference into the disclosure of the application.

The first printing unit 16 includes a tape drive 66 having a photoconductor belt 68, eg, an organic photoconductor belt, which is commonly referred to as an OPC belt. The photoconductor belt 68 is driven by means of the tape drive 66 in the direction of the arrow P2. With the aid of a cleaning and charging unit 70, the photoconductor belt 68 is discharged, toner residues are removed from the photoconductor belt 68 and this is charged to a predetermined potential. With the help of a character generator 72, which is designed as an LED character generator, areas of uniformly charged surface of the photoconductor belt 68 according to the signals supplied to the character generator 72 of the image data processing unit 26 partially, ie pixelwise, depending on the used elektrofotografi- see principle, discharged to a lower potential or charged to a higher potential, creating a charge image on the surface of the photoconductor belt 68 is generated. The charge image on the surface of the photoconductor belt 68 contains a latent print image. With the aid of a developer unit 74, the charge image is developed on the surface of the photoconductor belt 68, ie colored with toner to form a toner image.

The first printing unit 16 further contains a tape drive 76 with a transfer belt 78, which in the direction of

Arrow P3 is driven. The photoconductor belt 68 contacts the transfer belt 78 on a transfer printing part 80 (hereinafter also referred to as "second transfer parts 80"), ie the surface of the photoconductor belt 68 touches the surface of the transfer belt 78. On the second transfer parts 80, a toner image on the photoconductor belt 68 is formed transfer the surface of the transfer belt 78, as will be explained in more detail in connection with FIG. 2 below.

With the help of a roller device 82, whose rollers over

Lever 83 are interconnected, the transfer belt 78 is brought in a first Umdruckbereich 84 to the paper web 12 and led away from this, wherein the transfer belt 78 is brought in the illustration of Figure 1 to the paper web 12. A roller device for advancing and moving the transfer belt 78 to and from the paper web 12 is described in detail in WO 00/54266, the contents of which are hereby incorporated by reference into the present description.

The transfer belt 78 contacts the surface of the paper web 12 on its front side in the introduced state. te, so that a toner image on the transfer belt 78 can be transferred from the transfer belt 78 to the front side of the paper web 12. The feeding of the transfer belt 78 to the paper web 12 is also referred to as pivoting and the removal of the transfer belt 78 from the paper web 12 is also referred to as pivoting.

The transfer belts 78, 78 'of the printing unit 16 and the printing unit 18 are pivoted substantially simultaneously to the paper web 12, whereby a contact pressure is generated between two opposite rollers or roller pairs of the tape drives of the transfer belts.

The fixing station 30 includes a first fixing unit 54 and a second fixing unit 56 arranged on opposite sides of the paper web 12, wherein the first fixing unit 54 fixes the toner images on the front side and the second fixing unit 56 fixes the toner images on the back side of the paper web 12 , The fixing units 54, 56 are designed as radiation fixing units, wherein the fixing units 54, 56 each contain a covering device 58, 60 which cover the heat radiators of the fixing units 54, 56 during operating conditions in which no fixing of the printed images on the paper web 12 is to take place , Viewed in the conveying direction of the paper web 12 after the fixing units 54, 56 cooling elements 62, 64 are provided which cool the paper web 12 before exiting the fuser 30 to prevent damage to the paper web 12, in particular due to low paper moisture.

2 shows an enlarged detail of Figure 1 is shown schematically. Therein, the transfer ribbon tape drive 76 of the first printing unit 16 with the transfer belt 78 (hereinafter referred to as first transfer belt 78) and the transfer belt tape drive 76 'of the second printing unit 18 with the associated transfer belt 78' (hereinafter referred to as the second transfer belt 78 '). Further, a portion of the first photoconductor belt 66 is shown, which abuts the aforementioned second transfer printing 80 on the first transfer belt 78. Likewise, a portion of the second photoconductor belt 66 ^{r is} shown, which rests against a third transfer parts 80 'on the second transfer belt 78'.

As shown in FIG. 2, the first roller device 82 comprises rollers 86, 88, 90, 92, 94, 96, 98 and 100, which are connected by levers 83. The second roller device 82 'comprises rollers 86', 88 ', 90', 92 ', 94', 96 'and 98'.

At the second transfer parts 80, another roller 102 around which the first photoconductor belt 68 is guided is arranged to contact the first photoconductor belt 68 with a portion of the first transfer belt 78 extending between the rollers 98 and 100 , Similarly, on the third transfer parts 80 ', a roller 102', around which the second photoconductor belt 68 'is guided, is arranged to connect the second photoconductor belt 68' to a portion of the transfer belt 78 which extends between the rollers 100 'and 104 'extends, brings into contact. Finally, a first drive roller 106 is provided for driving the first transfer belt 78 and a second drive roller 106 'for driving the second transfer belt 78'.

As mentioned above, the first tape drive 76 and the second tape drive 76 'are constructed substantially mirror-symmetrically with respect to the paper web 12. A deviation from the mirror symmetry consists in the arrangement of the second transfer parts 80 on the one hand and the third transfer printing parts 80 'on the other hand, which, however, only depend on an expedient arrangement of the first photoconductor. Tape drive 66 and the second photoconductive tape drive 66 'in the printer 10 is due (see Figure 1).

Further, deviating from the mirror symmetry in the first transfer belt tape drive 76, there is a transfer device 108 which, in addition to the already mentioned drive roller 106, comprises an AC corotron with a corona wire 110 and a screen 112. The transfer device 108 serves to reload a first toner image located on the first transfer belt 78.

In the second transfer ribbon tape drive 76 ', a recharging device 114 is provided which comprises an AC corotron with a corona wire 116 and a screen 118 and a roller 120 which serves as a counter pole to the screen 118. The reloader 114 serves to reload a second toner image on the second transfer belt 78 'with the same polarity it already has.

In the following, the operation of the printing unit 14 will be described.

On the photoconductor belts 68 and 68 ', charge images are generated by means of the character generators 72 and 72', respectively. These are toned in a known manner by the developer station 74 or 74 'to form a first toner image on the first photoconductor belt 68 and a second toner image on the photoconductor belt 68'. The first and second toner images consist of toner particles charged with a first polarity. The charging of the toner with the first polarity takes place triboelectrically in the developer stations 74 and 74 '. In the embodiment shown, the first polarity is negative.

At the second transfer point 80, the first toner image is transferred from the first photoconductor belt 68 to the first transfer belt 78. The transfer takes place on the one hand by the contact between the first photoconductor belt 68 and the first trans ^¬ ferrule 78, on the other hand by an electric field which exists between the roller 102 on the one hand and the rollers 98 and 100 on the other. The roller 102 is at ground potential, and to the rollers 98 and 100 are applied electrostatic potentials which in sum have a second polarity opposite to the first polarity. The resulting electric field is directed so that the toner is transferred from the first photoconductor belt 68 to the first transfer belt 78. In this case, for example, the roller 98 may have the first polarity and the roller 100 may have the second. The transfer printing on the third transfer printing parts 80 'takes place in the same way.

After the transfer printing is on the first transfer belt 78, a first toner image, which is charged with the first polarity (negative here), and on the second transfer belt 78 ', a second toner image, which is also loaded with the first polarity (negative here).

The first transfer belt 78 is moved in the direction of the arrow P3, so that the first toner image is moved by the transfer device 108 (see Fig. 2). In this case, an AC voltage of 8 to 20 kV _ss (measured from peak to peak) with a frequency of 2 to 20 kHz is applied to the corona wire 110. The transport roller 106 is at ground potential, while on the screen 112, a DC voltage of an amount of 0.1 to 5 kV and a second polarity, which is opposite to the first polarity, is applied. As a result, the first toner image is transferred from the first polarity to the second polarity. In this case, flows over the screen 112, a current of 100 to 1200 uA. Preferably, the shield current is regulated to a target value which is within the stated range.

The second toner image is moved on the second transfer belt 78 'through the afterloading device 114, in which it is subsequently is charged, that is charged with the same, first polarity that it already has. The reloading device 114 is constructed in the same way as the reloading device 108, except for the polarities of the screen 118 and the roller 120

Recharging 114, the roller 120 at the ground potential, while on the screen 118, a DC voltage of the first polarity is applied. The voltage ranges of the DC and AC voltage and the range of the shielding current in the afterloading device 114 correspond in magnitude to those of the transfer device. Preferably, the shield current of the afterloading device 114 is also regulated to a desired value. In the embodiment shown, the nominal values of the screen currents in the transfer device 108 and the afterload device 114 are equal in terms of the amount.

The DC voltage and the AC voltage at the reloading device 108 and the afterloading device 114 are selected such that the reversed first toner image and the reloaded second toner image, apart from their polarity, have the same electrostatic properties.

The transferred first toner image and the reloaded second toner image are then conveyed on their respective transfer belt 78 or 78 'into the first transfer area 84. In the illustration of FIG. 2, the roller device 82 and the roller device 82 'are pivoted to the paper web 12 in such a way that the first transfer belt 78 with the first toner image thereon, the paper web 12 and the second transfer belt 78' with the second toner image on it Umdruckbereich 84 between the rollers 90 and 92 on the one hand and 90 'and 92' pressed together.

At the same time, a DC voltage is applied between the upper pair of rollers 90, 92 on the one hand and the lower pair of rollers 90 ', 92' on the other hand, which forms an electric field for transferring the first and the second toner image on the Paper web 12 is generated. The electric field between the upper pair of rollers 90, 92 and the lower pair of rollers 90 ', 92' is such that in the illustration of Figure 2, the first toner image, which has been reloaded to the second polarization, experiences an electrostatic force downward the top of the paper web 12 is re-printed, while the second toner image, which has been charged triboelectrically with the first polarity and has been recharged with the first polarity, experiences an electrostatic force upward and thus transferred from the second transfer belt 78 'to the underside of the paper web 12 becomes.

The details of the first transfer parts 84 are described in EP 1 110 125 B1, EP 1 465 023 A1 and the corresponding US Pat. No. 6,556,804 B1, in particular in FIGS. 9 to 11 contained therein. The descriptions of the various embodiments of a transfer printing parts contained therein between two transfer ribbons and a carrier material are hereby incorporated by reference into the present specification.

For the function of double-sided simultaneous transfer printing on the first transfer parts 84, it is necessary for the first and second toner images to be charged with different polarities so that they move in different directions with the same electric field (namely the first toner image from the first transfer belt 78) bottom and the second toner image from the second transfer belt 78 'up) can be reversed. For this reason, a transfer device corresponding to the transfer device 108 of FIGS. 1 and 2 was already provided in the devices from the documents EP 1 110 125 B1, EP 1 465 023 A1 and US Pat. No. 6,556,804 B1, but not the afterload device 114.

As already mentioned in the introduction to the description, in this prior art without reloading device 114 the problem arises that the printed images on the upper side and sometimes turn out differently on the underside of the paper web 12. Often the Umdruckwirkungsgrade on the different sides of the paper web 12 from each other. Furthermore, the two printed images can interact with one another, for example if a flat-tinted printed image is printed on one side of the paper and, for example, only isolated characters or lines on the other side. In this case, it could happen that the signs or lines of the second paper web side could be seen in the flat printed image on the first side of the paper web.

These problems could not be solved satisfactorily by adjusting the transfer printing flow at the transfer printing station 84 and adjusting the charge transfer voltage at the transfer device alone. In particular, the recharging voltage of the transfer device 108 can not be chosen too low, since otherwise very small characters or details in the printed image could possibly be lost if the associated toner was not sufficiently transferred. But if the charge voltage is chosen so that no detail can be lost in the first print image, the prior art, the converted first toner image is mostly charged in absolute terms than the second toner image whose toner was charged only triboelectrically. Thus, in the prior art, deviations in the transfer printing efficiency between the two toner images may occur.

Another cause of uneven transfer on the top and bottom of the paper web is in the prior art is that the triboelectric charging of the toner, and thus the charge of the second toner image, on the one hand by the weather conditions (humidity, etc.), on the other hand depends on the toner throughput. Thus, the charge level of the second toner image is

Subject to fluctuations. Furthermore, the electrical and electrostatic properties of the printed image change depending on the height of the toner application, because thereby the distance between the transfer belt and the paper web and thus the capacity of the transfer printing system is changed.

By using two loading devices, namely the reloading device 108 on the one hand and the reloading device 114 on the other hand, the properties of the toner of the first print image and the second print image can be conditioned, i. be adapted to each other in such a way that a uniform transfer without interaction between the two images is achieved. As a result, the print quality on both sides of the paper is identical, largely independent of the electrostatic properties of the toner, the amount of toner applied and the toner throughput. The use of a reloading device 108 in combination with a reloading device 114 makes it possible to achieve identical transfer printing efficiencies in the two printing couples 16 and 18.

In the embodiment shown, both the reloading device 108 and the afterloading device 114 comprise an AC corotron with a corona wire 110 or 116, a screen 112 or 118, to which a DC voltage is applied, and a counter-pole element, which is formed by rollers 106, 120 become. Instead of the rollers 106 and 120, other counter-pole elements may be used, for example a grinding object such as a brush or sheet or an element which does not contact the transfer belt 78 or 78 ', such as a blade element or another corotron.

In the following table, preferred combinations of polarization states of the screen 112, the roller 106, the screen 118 and the roller 120 are summarized, wherein already above the combination No. 1 contained therein has already been described.

The arrangement of the reloading device 108 and the reloading device 114 may differ from that of FIG. 2, as long as they are viewed in the direction of rotation of the respective transfer belt 78 or 78 'between the second transfer parts 80 and the first transfer parts 84 or between the third transfer parts 80' and the first transfer parts 84 are arranged.

Of course, the reloading device 108 can also be arranged in the second or lower printing unit 18 and the reloading device 114 in the first or upper printing unit 16.

In contrast to that shown in FIG. 1, instead of the developer station 74 or 74 ', a plurality of developer stations with differently colored toner can be arranged on the photoconductor belt 66 or 66'. Then, successively different color components of a color image (so-called color separations) can be produced on the photoconductor belt 68 or 68 'and superimposed on the transfer belt 78 or 78' in register. In this case, the transfer belt tape drives 76 and 76 'are in a collection mode in which the transfer belts 78 and 78' are pivoted away from the paper web 12 by the roller devices 82 and 82 '. Only when all color separations ge are superimposed, the transfer belts 78 and 78 'are pivoted to the paper web 12, the collecting image on the first transfer belt 78 is reloaded from the transfer device 108, the collecting image on the second transfer belt 78' reloaded from the afterloading device 114, and the two so Conditioned collecting images are at the transfer printing 84 as described above simultaneously transferred to the respective side of the paper web 12.

Although in the drawings and in the foregoing description preferred embodiments have been shown and described in detail, it should be considered as merely illustrative and not restrictive of the invention herein. It should be understood that only the preferred embodiments are shown and described and all changes and modifications that are presently and in the future within the scope of the invention should be protected.

LIST OF REFERENCE NUMBERS

10 electrophotographic printer

12 endless paper web 14 printing unit

16, 18 printing units

20 paper tray

22 control unit

24 Toner Supply and Processing Unit 26 Print image processing unit

28 Paper web drive and guidance system

30 fuser

32 to 40 pulleys

42, 50 Drive roller 44, 52 Press roller

46, 48 hole sensors

54, 56 fuser unit

58, 60 covering device

62, 64 cooling elements 66, 66 'tape drive photoconductor belt

68, 68 'photoconductor belt

70, 70 'Cleaning and charging unit

72, 72 'character generator

74, 74 'developer station 76, 76' tape drive transfer belt

78, 78 'transfer belt

80, 80 'transfer parts photoconductor belt - transfer belt

82, 82 'roller device

83, 83 'lever 84 first transfer parts

86 to 106, 86 'to 106' rolls

108 transfer device

110 corona wire 112 screen

114 reloading device

116 corona wire 118 screen

120 roller

Claims

claims

1. Device (14) for simultaneous double-sided printing of a recording medium (12),

with a circumferential first toner image carrier (78) and a circumferential second toner image carrier (78 '),

means (80) for generating on the first toner image carrier (78) a first toner image consisting of toner charged with a first polarity;

with means (78 ') for producing a second toner image, consisting of toner, which is also charged with the first polarity, on the second toner image carrier (78'),

a reload device (108) adapted to reload the first toner image on the first toner image carrier (78) to a second polarity opposite to the first polarity,

and with a first transfer parts (84), at which the recording medium (12) between the first toner image carrier (78) and the second toner image carrier (78 ') is passed, and on which an electric field can be generated, by which the second polarity reversed first toner image and the second toner image from the first and second toner image carrier (78, 78 ') are replaced and transferred to the respective toner image carrier (78, 78') facing side of the recording medium (12),

wherein a recharging device (114) is provided which is suitable on the second toner image carrier

(78 ') to reload the second toner image with the first polarity.

2. Device (14) according to claim 1, wherein the first toner image carrier is formed by a first transfer belt (78) and / or the second toner image carrier is formed by a second transfer belt (78 ').

A device (14) according to claim 2, wherein the means for producing the first toner image on the first transfer belt (78) and / or the means for forming the second toner image on the second transfer belt (78 ') is by a second transfer point (80 ) or third Umdrucksteile (80 ') are formed, on which the first or second toner image from a first photoconductor (68) and a second photoconductor (68') on the first and second transfer belt (78, 78 ') reprintable is.

The device (14) of claim 3, wherein the first photoconductor (68) and / or the second photoconductor (68 ') are formed by a photoconductor belt.

5. Device (14) according to claim 4, wherein at the second Umdrucksteile (80) and / or the third Umdrucksteile (80 ') two rollers (98, 100 or 100', 104 ') are arranged side by side over which the Transfer belt (78 or 78 ') is guided, and to each of which an electrostatic potential is applied, which in sum have the second polarity,

and in which a roller (102 or 102 ') around which the photoconductor belt (68 or 68') is guided is arranged such that it engages the photoconductor belt (68 or 68 ') with a section of the transfer belt (78 or 68) 78 ') which extends between the two rollers (98, 100 or 100', 104 ').

6. Device (14) according to claim 5, wherein the roller

(102 or 102 '), around which the first photoconductor belt (68) or the second photoconductor belt (68 ') in the second transfer area (80) and third transfer area (80') is guided, is applied to ground potential.

7. Device (14) according to one of the preceding claims, in which the transfer device (108) and / or the afterloading device (114) comprise a corotron or a scooter.

The apparatus (14) of claim 7, wherein the corotron is a DC corotron.

9. Device (14) according to claim 7, wherein the corotron has at least one corona wire (110, 116) against which an alternating voltage is applied, and a screen (112, 118) against which a DC voltage is applied.

10. Device (14) according to claim 2 and one of claims 7 to 9, wherein the transfer device (108) and / or the afterloading device (114) comprises a counter pole element (106, 120), which is the corotron on the other side the transfer belt (78, 78 ') facing and forms an electrical opposite pole to the charge of the co- rotor.

11. Device (14) according to claim 10, wherein the counter-pole element (106, 120) with the side facing away from the corotron of the transfer belt (78, 78 ') in contact.

12. Device (14) according to claim 11, wherein the Gegenpolelement by a roller (106, 120), a brush o- of a metal sheet is formed.

13. Device (14) according to claim 10, wherein the counter-pole element is formed by a blade-like element which does not touch the transfer belt (78, 78 ').

14. The device (14) according to claim 10, wherein the Gegenpolelement is formed by a further Korotron.

15. Device (14) according to any one of claims 9 to 14, wherein at the at least one corona wire (110, 116) an alternating voltage of 8 to 20 kV _ss is applied.

16. Device (14) according to any one of claims 9 to 15, wherein at the at least one corona wire (110, 116) an alternating voltage with a frequency of 2 to 20 kHz is applied.

17. Device (14) according to one of claims 10 to 16, wherein between the screen (112, 118) and the counter-pole element (106, 120) a voltage of an amount of 0.1 to 5 kV is applied.

18. Device (14) according to one of claims 9 to 17, in which a current of 100 to 1200 μA flows across the screen (112, 118).

19. Device (14) according to one of claims 10 to 18, wherein the screen (112) of the corotron of the transfer device (108) is charged with the second polarity, the Gegenpolelement (106) of the transfer device (108) is at ground potential, the Screen (118) of the corotron of the afterloading device (114) is charged with the first polarity, and the Gegenpolelement (120) of the afterloading device (114) is at ground potential.

20. Device (14) according to one of claims 10 to 18, wherein the screen (112) of the corotron of the transfer device (108) is charged with the second polarity, the Gegenpolelement (106) of the transfer device (108) is at ground potential, the Shield (118) of the corotron of the afterloading device (114) is at ground potential, and the counter-pole element (120) of the reloading device Device (114) is loaded with the second polarity.

21. Device (14) according to one of claims 10 to 18, wherein the screen (112) of the corotron of the transfer device (108) is at ground potential, the Gegenpolelement (106) of the transfer device (108) is loaded with the first polarity, the Screen (118) of the corotron of the afterloading device (114) is charged with the first polarity, and the Gegenpolelement (120) of the afterloading device (114) is at ground potential.

22. Device (14) according to one of claims 10 to 18, wherein the screen (112) of the corotron of the Umladevor- direction (108) is at ground potential, the Gegenpolelement (106) of the Umladevorrichtung (108) is charged with the first polarity the shield (118) of the corotron of the afterloading device (114) is at ground potential, and the opposite polarity element (120) of the recharging device (114) is charged with the second polarity.

The device (14) of any one of the preceding claims, wherein the first polarity is negative and the second polarity is positive.

24. Printer or copier (10) with a device (14) according to one of the preceding claims.

25. A method for simultaneous two-sided printing of a record carrier (12), wherein a first toner image consisting of toner charged with a first polarity is formed on a first toner image carrier (78) and a second toner image consisting of toner, which is also charged with the first polarity, is generated on a second toner image carrier (78 '), wherein the first toner image located on the first toner image carrier (78) is reloaded to a second polarity opposite to the first polarity by means of a transfer device (108),

in which the second toner image on the second toner image carrier (78 ') is recharged by a recharger (114) of the first polarity,

and in which the recording medium (12) is guided at a first transfer point (84) between the first toner image carrier (78) and the second toner image carrier (78 ') and an electric field is generated at the first transfer parts (84), through which the first toner image transferred to the second polarity and the reloaded second toner image are removed from the first and second toner image carriers (78, 78 ') and transferred to the side of the recording carrier (12) facing the respective toner image carrier (78, 78').

The method of claim 25, wherein the first toner image carrier is formed by a first transfer belt (78) and / or the second toner image carrier is formed by a second transfer belt (78 ').

27. The method of claim 26, wherein the first toner image and / or the second toner image on a second Umdrucksteile (80) and a third Umdrucksteile (80 ') of a first photoconductor (68) and a second photoconductor (68') is transferred to the first or second transfer belt (78, 78 ').

28. The method of claim 27, wherein the first Fotolei- ter (68) and / or the second photoconductor (68 ') by a

Photoconductor band are formed.

29. The method of claim 28, wherein at the second transfer parts (80) and / or the third transfer printing parts

(80 ') two rollers (98, 100 or 100', 104 ') are arranged side by side, over which the transfer belt (78 or 78') is guided and to each of which an electrostatic potential is applied, the sum of the have second polarity,

30. The method of claim 29, wherein the roller (102 or 102 '), by which the photoconductor belt (68 or 68') in the second transfer area (80) and third transfer area (80 ') is guided, subjected to ground potential becomes.

A method according to any of claims 25 to 30, wherein the transfer device (108) and / or the afterload device (114) comprises a corotron or a scorotron.

32. The method of claim 31, wherein the corotron is a DC corotron.

33. The method of claim 31, wherein the corotron has at least one corona wire (110, 116) to which an AC voltage is applied and a shield (112, 118) to which a DC voltage is applied.

34. The method according to claim 26 and one of claims 31 to 33, wherein the transfer device (108) and / or the afterloading device (114) has a counter-pole element (106 or 120), which faces the corotron on the other side of the transfer belt (78, 78 ') and forms an electrical opposite pole to the charge of the corotron.

35. The method of claim 34, wherein the Gegenpolelement (106, 120) with the side facing away from the corotron of the transfer belt (78, 78 ') in contact.

36. The method of claim 35, wherein the Gegenpolelement by a roller (106, 120), a brush or a sheet is formed.

37. Method according to claim 34, wherein the counter-pole element is formed by a blade-like element which does not touch the transfer belt (78, 78 ').

38. The method of claim 34, wherein the Gegenpolelement is formed by a further Korotron.

39. The method according to any one of claims 33 to 38, wherein an AC voltage of 8 to 20 kV _{ss is} applied to the at least one corona wire (110, 116).

40. The method according to any one of claims 33 to 39, wherein at the at least one corona wire (110, 116) a

AC voltage is applied with a frequency of 2 to 20 kHz.

41. The method according to any one of claims 34 to 40, wherein between the screen (112, 118) and the Gegenpolelement

(106, 120), a voltage of 0.1 to 5 kV is applied.

42. The method according to any one of claims 33 to 41, wherein over the screen (112, 118) a current of 100 to 1200 uA flows.

A method according to any of claims 34 to 42, wherein the screen (112) of the corotron of the transfer device (108), the counter pole element (106) of the transfer device (108), the screen (118) of the corotron of the afterload device (114) and the counter pole element (120) of the afterloading device (114) are loaded according to one of the combinations of claims 19 to 22.