EP0608264B1 - Printer or copier with an arrangement for printing both sides of a recording medium - Google Patents

Abstract

A printer or copier working according to the transfer printing process has an arrangement for printing the front and/or the back of a recording medium (29). The arrangement has a photoconductive drum (10) and a thermoadhesive transfer band (12) coupled to the photoconductive drum. A transfer printing and fixing station (18) associated to the transfer band (12) has a fixing gap (23) on the one side of which is arranged the transfer band (10) and on the other side of which is arranged a transfer printing and fixing element (22) designed as a heated transfer printing roller. The transfer band (10) and the transfer printing and fixing element (22) are elastically supported on each other. In order to print at the same time the front and the back of a recording medium (29), a first toner image (39/1) associated to the back of the recording medium (29) and a second toner image associated to the front (39/2) of the recording medium (29) are generated on the photoconductive drum and transferred in this order to the transfer band (12). The heated images heated to a pasty state are brought to the fixing gap (23). The heated transfer printing and fixing roller (22) takes up at first the toner image (39/1) of the back side. Then the recording medium (29) is brought to the fixing gap (23) and the transfer band (12) and the printing roller (2) turn on the individual sheet (29), transferring and fixing at the same time the toner images on both sides of the recording medium.

Description

Printing or copying device with an arrangement for printing on both sides of a record carrier

The invention relates to an arrangement for printing on the front or the back of a recording medium in a printing or copying device operating according to the transfer printing principle, and to a method for operating such an arrangement.

Printing or copying machines for simplex or duplex printing are e.g. Known from US-A-4 477 176 and US-A 4 537 493. These are electrophotographic printing devices with a photoconductor, on which at least two charge images can be arranged one behind the other and which have a transfer printing station with associated single sheet positioning device (turning device), which makes it possible to operate the electrophotographic printing device in two operating modes, namely in one first operating mode in which the colored toner images arranged one behind the other on the charge image carrier are arranged one above the other or next to one another on one side of the single sheet and in a second operating mode in which the sequence of the toner images located on the charge image carrier is arranged on the front and back of the single sheet. The toner images are fixed on the single sheets with the help of a roller fixing station using pressure and high temperatures.

In the duplex printing mode, in which a toner image is arranged on each side of the single sheet, the front and back are fixed simultaneously.

For this purpose, the single sheet printed on one side must be turned over and printed again on the other side, and then it becomes contactless with the roller fixing station, e.g. B. transported via an air cushion.

This requires a very high mechanical outlay if a high level of operational reliability is to be guaranteed in the case of a large substrate range.

In general, it should be noted that each braking, acceleration and turning device in the device exerts forces on the recording medium, which complicates exact positioning of the recording medium and thus difficult guidance of the recording medium in the device. This increases the risk of congestion considerably, which can lead to frequent downtimes. The turning of a recording medium provided with toner images before the fixing requires a considerable amount of guidance in order to prevent blurring of the toner images.

Also known from US-A-2 990 278 or GB-A-2 040 226 are electrophotographic printing devices in which character-dependent charge images are generated on an photoconductor with the aid of an exposure device and are fed to a developer station. The developed charge image is then mechanically lifted from the photoconductor by means of a band-shaped transfer element and transferred to a recording medium. In order to be able to fix the toner image on the recording medium, the toner image on the belt-shaped transfer element is heated with the aid of a heating device and the heated toner image is applied to the recording medium by means of pressure and heat via a roller arrangement. After the transfer of the toner image onto the recording medium, the tape-shaped transfer element is cleaned of adhering toner in a cleaning station.

From WO 82/00723 an arrangement and a method for printing on both sides of a record carrier is known. A charge image is generated on a photoconductor and then on one with the help of this charge image dielectric roller or drum generates an electrostatic charge image by ionography. It is also possible to form the charge image directly on the dielectric roller using an ion generator. After development with the aid of a developer station by applying a single-layer toner layer from a one-component developer, the single-layer toner image assigned to the back of the recording medium is transferred solely to a pick-up roller arranged below the dielectric roller by pressure without heat. A toner image assigned to the front of the recording medium is then formed in the same way on the dielectric roller and then the two toner images are transferred to the front and back of the recording medium simultaneously under pressure and without heat.

The aim of the invention is to provide an arrangement for printing on the front and / or back of a recording medium in a printing or copying machine which works according to the transfer printing principle, as well as a method for operating such an arrangement which enables simultaneous printing and fixing of the recording medium the front and the back in one step.

Another object of the invention is to achieve an optimal registration accuracy of the print images on the recording medium with a minimal control effort.

This object is achieved in accordance with the features of the main claims.

Advantageous embodiments of the invention are characterized in the subclaims.

The invention enables simultaneous transfer printing with simultaneous fixation in only one operation. The record carrier can move in a completely straight path through the device at a continuous speed. No acceleration or deceleration processes are required to print and fix the record carrier. A turning device can be omitted.

Due to the rigid, geometrically precisely determined process, high register accuracy is achieved with minimal control effort.

Both before and after the transfer printing and fixing station there is no smearable print image on the recording medium. This makes it possible to guide and transport the record carrier on both sides both before and after the transfer printing and fixing station.

The one-time processing process with simultaneous double-sided transfer printing using a low-temperature fixation leads to a gentle processing of the record carrier. This prevents warping and tension in the record carrier.

The arrangement enables full color printing without additional effort in the transfer printing and fixing station.

With a correspondingly selected material pairing of the surfaces of the transfer belt and the transfer printing and fixing element carrying the toner images, it may be possible to dispense with the arrangement of an additional cleaning device for these device components.

• Figur 1 eine schematische Schnittdarstellung einer Anordnung zum Bedrucken der Vorder- und/oder der Rückseite eines Aufzeichnungsträgers in einem nach dem Umdruckprinzip arbeitenden Druckgerät und
• Figur 2 eine schematische Seitenansicht der in der Anordnung der Figur 1 verwendeten Umdruck- und Fixierstation.

An embodiment of the invention is shown in the drawings and is described in more detail below, for example. Show it

• Figure 1 is a schematic sectional view of an arrangement for printing on the front and / or back of a record carrier in a printing device working on the transfer printing principle and
• Figure 2 is a schematic side view of the transfer printing and fixing station used in the arrangement of Figure 1.

The illustrated electrophotographic single-sheet printing device for single-color or multi-color printing of single sheets in simplex or duplex mode contains an intermediate carrier 10 in the form of a photoconductor drum which is driven by an electric motor. Instead of the photoconductor drum, however, an OPC tape can also be arranged. Grouped around the first intermediate carrier 10 are the various units for the electrophotographic process. These are essentially: a charging device LE in the form of a charging corotron for charging the intermediate carrier 10; a character generator ZG with an LED comb for character-dependent exposure of the intermediate carrier 10; Developer stations EY, EM, EC and EB for coloring the charge-dependent discharge images generated with the help of the character generator ZG on the intermediate carrier 10 with colored toner. The developer station EY contains yellow toner, the developer station EM toner in the color magenta, the developer station EC toner the color cyan and the developer station EB black toner. To remove the residual toner after development and transfer printing, a cleaning station RS is provided with a cleaning brush integrated therein with an associated suction device and a discharge device (not shown here). The developer stations EY, EM, EC and EB are interchangeable designed and z. B. pulled out of the device via slide guides and inserted into the device. They are usually constructed and contain developer rollers for coloring the charge image. They can be controlled individually and can be operated or activated together or individually.

Coupled to the intermediate carrier 10 via a transfer station 11 is a transfer belt 12. The transfer belt 12 can be designed as a thermoadhesive transfer belt with a temperature-resistant carrier fabric, e.g. B. made of glass fiber or temperature-resistant plastic, with an elastic cover layer arranged thereon made of silicone or a silicone-like material, for. B. rubber. The transfer belt 12 is also driven by an electric motor and is guided over deflection rollers 13, 14, 16 and 17. The deflection roller 13 is part of a transfer printing and fixing station 18. It has a relatively large diameter and can be designed to be heatable in the form of a deflection roller. For this purpose, the deflecting roller can contain a heater in the form of a radiator. The deflection rollers 16 and 17 are part of the transfer station 11, which in the case shown contains a transfer corotron 19. However, it is also possible to arrange a mechanical transfer station instead of such an electrostatic transfer station, in which the toner images developed on the intermediate carrier 10 are transferred to the transfer belt 12 by contact between the transfer belt 12 and the intermediate carrier 10. Also assigned to the transfer belt is a heating station 20 with an infrared heating source arranged therein and, if necessary, a cleaning device 15, 21 for the transfer belt, e.g. in the form of cleaning rollers.

In the area of the transfer printing and fixing station 18, a transfer printing and fixing element 22 in is parallel to the deflection roller 13 Form arranged a heated transfer roller. It is guided on both sides and is supported on the deflection roller 13 and thus on the transfer belt 12 via an elastic suspension. It can also be driven by an electric motor. The area between the deflected transfer belt 12 or the deflection roller 13 and the transfer roller 22 is referred to as transfer and fixing gap 23. The transfer roller 22 has a structure as shown, for example, in FIG. 2. It consists of a metal hollow roller 24 made of aluminum with an elastic layer arranged thereon, e.g. B. made of rubber 25 and an outer jacket layer 26 made of fluoroplastic. The fluoroplastic-containing outer jacket can, for. B. have a thickness of 200 to 500 microns, "Teflon" can be used as the fluoroplastic material. Teflon is a trademark of Du Pont. Fluoroplastic materials are e.g. B. materials made of tetrafluoroethylene, photopolymers of tetrafluoroethylene and hexafluoropropylene and similar materials. The hollow roller 24 can have a thickness of 2 to 5 mm, the rubber layer 25 z. B. a thickness of 200 to 500 microns. However, other dimensions are possible, as z. B. are described in EP-B1-0 186 314. A heating device 27 in the form of a radiant heater is arranged in the hollow roller 24. It is also possible to heat the hollow roller 24 from the outside.

To clean the transfer roller 22, a cleaning device 28, for. B. in the form of a movable assembly line or in the form of brushes. The cleaning device 28 can be pivoted in and out on the transfer roller 22 with the aid of a pivoting mechanism in the arrow directions shown in FIG. 1.

For feeding a recording medium 29 in the form of a single sheet or several arranged side by side Single sheets for the transfer printing and fixing gap 23, a paper channel 30 is provided with the recording medium transport devices 31 and 32 assigned to the paper channel, e.g. B. with both sides of the paper channel 30 attacking paper transport rollers 33 or conveyor belts. These record carrier transport devices transport the single sheets 29 from a storage area 34 to the transfer printing and fixing nip 23 and from there to a stacking device 35. This preheating device 36 can be constructed corresponding to the heating station 20 and it can have radiator elements arranged on both sides of the paper transport channel 30. Instead of separate radiators, it is also possible, for. B. to heat the paper transport rollers 33 of the recording medium transport device 31.

The function of the arrangement will now be described in the following using different operating modes. The record carrier 29 to be printed is fed in the form of a single sheet to the transfer printing and fixing station 18 in such a way that its rear side faces upwards and its front side points downwards. The record carrier 29 is thus stacked face down in the stacking device 35. However, the terms "front side" and "back side" are to be understood relatively to describe the two opposite surfaces of the record carrier.

The present printing or copying machine has a format-independent printing performance to reduce the control effort and to achieve a high register accuracy. That means within a certain unit of time it can be A4 or A5 regardless of the size of the formats or US formats a certain number of single sheets can be printed. The print performance is based on the processing speed of the largest possible format. The single sheets 29 of different formats are thus fed to the transfer printing and fixing station 18 with a fixed time grid in fixed time windows and printed within these fixed time windows regardless of their format size.

For this purpose, clocked by the device control, 10 image areas 38 are defined on the photoconductor, within which charge images 37/1, 37/2 can be generated at any point via the character generator ZG by exposing the photoconductor drum 10. The image areas also determine the largest possible charge image that can be generated, the so-called "IMAGE". The image areas 38 of constant size are continuously lined up, their constant length is referred to as the following distance. The following distance must now be dimensioned such that it is larger than the largest possible recording medium format to be processed. The size of the image areas and thus the subsequent distance is determined in such a way that the common DIN and US formats result in a maximum printing performance and thus the predetermined image areas and thus the largest charge image that can be generated is used to the maximum.

As a result of this measure, the individual sheets of different formats can be fed and printed continuously to the printing or copying device in a rigid time sequence predetermined by the geometry. This considerably reduces the control effort. The feed of the single sheets can be rigidly geometrically synchronized with respect to their front edges with the start of the image areas 38, that is to say corresponding to the fixed clock sequence of the edges of the image areas, the front edges of the single sheets are fed to the transfer printing and fixing station 18 and printed. In order to achieve this synchronization and clock sequence, the circumferential length of the transfer printing and fixing element and thus the transfer roller 22 is adapted to the required length of the image areas 38 and thus to the fixed predetermined follow-up distance.

Single color duplex printing mode:

In the single-color duplex printing operating mode, the latent character images of the back 37/1 and the front 37/2 of a sequence of individual sheets 29 to be printed are produced in succession in the image areas 38 of the photoconductor 10 by exposure, specifically the back 37/1 followed by the front 37/2 etc. The latent character images "IMAGES" are then colored by one of the developer stations EB to EY depending on the desired color with toner and thus toner images 39/1 and 39/2 are generated. The toner images 39/1 and 39/2 are then electrostatically transferred to the transfer belt 12 in the transfer station 11. The transfer belt 12 is in a hot state. It is kept at this temperature by the heating device 20. In this way, firstly back side information and then front side information is now transferred to the transfer belt 12. The action of the heating device 27 changes the state of the toner images, they become doughy. The transfer belt 12 transports the toner images of the back side 39/1 and the front side 39/2, which follow one after the other into the transfer printing and fixed nip 23. The outer jacket 26 of the transfer roller 22, which is made of fluoroplastic, lifts the toner image of the back side 39/1 from the transfer ribbon 12 from. It now adheres to the outer surface of the transfer roller 22. Since the circumferential length of the transfer roller 22 corresponds to the following distance and thus the length of the image areas 38, the beginning of the back toner image 39/1 reaches the fixing gap 23 again after one revolution of the transfer roller 22 At this point in time, the start of the front-side toner image 39/2 is also in the same position in the fixing gap 23, as is the front edge of the recording medium 29 to be printed. According to the illustration in FIG. 2, the transfer roller 22 and the transfer belt 12 roll with the toner images arranged thereon 39/1 of the back and the front 39/2 on the single sheet 29 and print it on both sides at the same time. To support the fixation, the recording medium can be preheated via the heating device 36 (preheating device) before being fed to the transfer printing and fixing station 18. The warm single sheet coincides with the pasty toner image of the back 39/1 and the pasty toner image of the front 39/2. The print information can thus be fixed immediately under low temperature influences with the transfer to the recording medium.

In the duplex mode described, a clock sequence is used with which a single sheet is fed after every second toner image. The guidance of the single sheets in the paper transport channel 30 is straight, the transport speed is continuous. Due to the rigid, geometrically precisely determined sequence, a high register accuracy is achieved. Record carriers are printed gently, since the temperatures are low and the transfer and fixing station 18 only has to be passed once in duplex operation.

Single color simplex mode

In the single-color simplex mode, the corresponding charge images are generated one after the other in the image areas 38, colored in the developer station E according to the desired color, transferred to the transfer belt 12 and, in the illustrated case, to the individual sheets fed one behind the other on the front side thereof transfer. Due to the continuous feeding of the single sheets, there is no unwanted transfer of toner images to the transfer roller 22 assigned to the back.

Due to the selected material pairing of the outer surface of the transfer roller 22 and the outer surface of the transfer belt 12, the toner images are normally transferred completely to the single sheets 29 without residues of the toner remaining on the transfer belt 12 or the transfer roller 22. Faults occurring in the electrophotographic process can, however, lead to an accumulation of toner at fault locations, which in some circumstances leads to the fact that toner residues still remain on the transfer roller or transfer belt 12. In order to remove these toner residues, the transfer belt 12 can be assigned a cleaning device 21 in the form of one or more cleaning rollers 15, 21 and the transfer roller 22 a cleaning device 28 e.g. in the form of a fleece cleaning station that can be swung in and out. The fleece cleaning station 28 is pivoted on and off in a controlled manner by the device control as a function of the toner image sequence. The transfer roller 22 can be cleaned with the fleece cleaning station 28 pivoted in, e.g. then take place when there is no toner image to be printed on the transfer roller 22 or e.g. during the transfer to the single sheet. By appropriately controlling the sequence of the toner images in connection with the feeding of the single sheets, cleaning cycles can be inserted as part of the printing cycle sequence.

Color printing mode

With the arrangement described, it is also possible to print the individual sheets in color, specifically with a multicolored image on the back and a monochrome image on the front, or with multicolored images on the back without printing on the front.

For this purpose, a sequence of latent character images associated with partial color images for the rear side and a latent character image for the front side is generated in the image areas 38 via the character generator ZG. These latent character images are then colored via the developer stations EB to EY and the toner images thus generated are transferred to the transfer belt 12. For colored printing on the back, the heated, doughy partial color toner images are then superimposed by the transfer roller 22 and, together with a monochrome toner image for the front side, which is also connected to the transfer belt 12, are transferred simultaneously and in one operation to a single sheet being fed.

By omitting the toner image for the front side, the supplied single sheets 29 can be printed in color on their rear side.

For the color printing of the recording media 29, it is not necessary to change the fixing station 18 and the paper guide. The choice of color and the operating modes are made solely by appropriately controlling the character generator ZG, the developer stations EB to EY.

Due to the long dwell time of the toner images first on the transfer belt 12 and then on the heated transfer roller 22, the fixability of the color toner, which is difficult to fix, is improved.

Appropriate activation of the character generator in connection with a targeted activation of the developer stations EB to EY also enables mixed operation with different operating modes.

Reference list

10th

Intermediate carrier, photoconductor drum

LE

Loading device

ZG

Character generator

EY

Yellow developer station

EM

Magenta developer station

EC

Developer station cyan

EB

Black developer station

RS

Cleaning station

11

Transfer station

12th

Transfer belt

13

Deflection roller (heated)

14

Pulley

15

Cleaning roller

16

Deflection pulley of the transfer station

17th

Deflection pulley of the transfer station

18th

Transfer and fixing station

19th

Transfer corotron

20th

Warming station, heating device

21

Cleaning device, cleaning roller

22

Transfer and fixing element, transfer roller

23

Transfer and fixing gap

24th

Hollow roller

25th

Rubber layer

26

Outer jacket

27

Heater, heater

28

Cleaning device, fleece cleaning

29

Record carrier

30th

Paper transport channel

31/32

Record carrier transport devices

33

Paper transport rollers

34

Storage area

35

Stacking device

36

Preheater

37/1

Charge image (back)

37/2

Charge image (front)

38

Image areas

39/1

Toner image (back)

39/2

Toner image (front)

Claims (10)

1. Arrangement for the single-colour or multi-colour printing of the front and back of a recording medium (29) in a printer or copier operating according to the transfer printing principle, having

   - an electrophotographic device (10, ZG, E) with a photoconductor (10) for producing a sequence of toner images (39/1, 39/2) on the photoconductor (10),

   - a transfer ribbon (12) with associated electrostatic transfer means (19) for receiving the toner images (39/1, 39/2) from the photoconductor (10) and for conveying the toner images to a transfer printing and fusing station (18),

   - one or more heating devices (20, 27) for heating the toner images (39/1, 39/2) in such a way that they are in a pasty, sticky state in the region of the fusing temperature of the toner material,

   - a transfer printing and fusing gap (23) which is assigned to the transfer printing and fusing station (18), on one side of which the transfer ribbon (12) is arranged and on the other side of which a transfer printing and fusing element (22) is arranged in such a way that the transfer ribbon (12) and the transfer printing and fusing element (22) are supported elastically on one another,
      the transfer printing and fusing element (22) and the transfer ribbon (12) having surfaces, which receive the toner images (39/1, 39/2), of such a quality that, on contact with the transfer ribbon (12), the transfer printing and fusing element (22) removes a warm toner image which is arranged on the transfer ribbon (12) and is in a pasty, sticky state and receives it and

   - a recording medium conveying device (31, 32) for feeding the recording medium (29) to the transfer printing and fusing gap (23) such that, as the recording medium (29) passes through the gap (23), the transfer printing and fusing element (22) and the transfer ribbon (12) roll on the recording medium (29) and, in this process, the warm toner images (39/1, 39/2) which are in the pasty, sticky state, are transferred to the recording medium (29).
2. Arrangement according to Claim 1,
   - having a transfer printing and fusing element which is constructed as a heated roller (22).
3. Arrangement according to Claim 1,
   - having a transfer printing and fusing element which is constructed as a heated ribbon.
4. Arrangement according to one of Claims 1 or 2,
   - having a circumferential length of the transfer printing and fusing element (22) which is determined in accordance with a strictly prescribed consecutive spacing of image areas (38), which receive the toner images, on the photoconductor (10).
5. Arrangement according to Claim 1, having a cleaning device (28) which is assigned to the transfer printing and fusing element (22) and can be activated as required.
6. Arrangement according to one of Claims 1 to 5, having a heating device (27, 20) which is assigned to the transfer printing and fusing station (18) and/or to the transfer ribbon (12).
7. Arrangement according to one of Claims 1 to 6, having a pre-heating device (36) which pre-heats the recording medium (29) before it is fed to the fusing gap.
8. Arrangement according to Claim 1, having a surface layer of the transfer ribbon (12) made of silicone or silicone-like material and a fluoroplastics-containing surface layer of the transfer printing and fusing element (22).
9. Method for the simultaneous single-colour or multi-colour printing of the front and back of a recording medium (29) in a printer or copier which operates according to the transfer printing principle and has the following features:

   - production of a sequence of toner images (37/1, 37/2) by means of an electrophotographic process on a photoconductor (10), a first toner image (37/1) of the sequence being assigned to the back of the recording medium (29) and a second toner image (37/2) being assigned to the front of the recording medium (29),

   - electrostatic transfer of the sequence of toner images to a transfer ribbon (12),

   - feeding of the sequence of toner images on the transfer ribbon (12) to a transfer printing and fusing station (18) with a transfer printing and fusing gap (23) for receiving the recording medium (29), on one side of which the transfer ribbon (12) is arranged and on the other side of which a transfer printing and fusing element (22) is arranged,

   - heating of the toner images on the transfer ribbon (12) and/or in the transfer printing and fusing gap (23) as far as the region of the fusing temperature of the toner material,

   - transfer of the first toner image (37/1) to the transfer printing and fusing element (22),

   - feeding a recording medium to the transfer printing and fusing gap (23), the transfer printing and fusing element (22) with the first toner image (37/1) and the transfer ribbon (12) with the second toner image (37/2) rolling on the recording medium (29) in order to print simultaneously the front and back of the recording medium (29) and to fuse the toner images on the recording medium.
10. Method according to Claim 9, the toner images being produced on the intermediate carrier (10) in image areas (38) which are arranged in rows in a strictly prescribed consecutive spacing and the circumferential length of the transfer printing and fusing element (22) being determined in accordance with this consecutive spacing.

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