EP0635146A1

EP0635146A1 - Electrophotographic printing device for the simultaneous printing of both sides of a substrate.

Info

Publication number: EP0635146A1
Application number: EP93905157A
Authority: EP
Inventors: Rudolf Waechtler
Original assignee: Wincor Nixdorf International GmbH
Current assignee: Canon Production Printing Germany GmbH and Co KG
Priority date: 1992-04-10
Filing date: 1993-03-04
Publication date: 1995-01-25
Anticipated expiration: 2013-03-04
Also published as: US5550624A; JPH07505489A; WO1993021566A1; DE59303381D1; EP0635146B1

Abstract

An electrophotographic printing device for the simultneous printing of both sides of a substrate contains two printing modules (10/1 and 10/2) with appropriate electrophotographic processing means (11 to 15) which are secured opposite each other in the printing device in such a way that a conveyor channel (25) for the substrate (21) is opened between the printing modules (10/1 and 10/2). The substrate (21) is guided over conveyors in the form of pairs of rollers to that its front and/or back can be brought into contact with the appropriate intermediate substrate (14) of the appropriate printing module (10/1 and 10/2). The pairs of rollers used are the reversing rollers for the intermediate substrate (14) co-operating with a counter-roller (23) or the opposed reversing rollers (22) for the intermediate substrate (14).

Description

Electrophotographic printing device for simultaneous double-sided printing on a recording medium.

The invention relates to an electrophotographic printing device for simultaneous double-sided printing of a record carrier according to the features of claim 1.

An electrophotographic printing device with which a recording medium can be printed on both sides is known from WO-91/13386. The electrophotographic printing device described there, in particular for printing on single sheets, contains one or more

Print modules in which the process means for carrying out the electrophotographic process are summarized constructively. The printing modules are designed as separate structural units for fastening in a housing of the printing device and have fitting elements for precisely fitting the printing modules in the housing. Each printing module contains an intermediate carrier with associated fixing elements in order to transfer a toner image generated on a photoconductor drum to a recording medium and to fix it there. The printing device can be expanded by a multiple arrangement of the printing modules from a single-color simplex printer to a multi-color duplex printer.

Furthermore, US-A-36 94 073 describes a method for printing on both sides of a record carrier with an electrophotographic printing device, in which a toner image is transferred to a front side of the record carrier with the aid of a first photoconductor drum and with the aid a downstream second photoconductor drum a toner image on the back. Fixed are the toner images in several stages. A radiator connected downstream of the first photoconductor drum initially partially fixes the toner image so that the recording medium does not heat up too much and so that the toner image transfer on the second photoconductor drum is not impeded. A further partial fixation takes place via a further radiator, which is connected downstream of the second photoconductor drum. The actual overall fixing of the toner images is effected by a subsequent fixing station with reinforced emitters arranged on both sides of the recording medium.

This multi-stage fixation is necessary because the toner image consisting of loose toner particles can stand out from the recording medium between the photoconductors. A multiple action of heat on the record carrier in the course of the printing process deforms and stresses the record carrier made of paper, which worsens the print quality and the paper handling. Furthermore, the multiple arrangement of radiators having a high power consumption requires the provision of a powerful, large-scale power supply. This affects the flexible use of the printing device.

The object of the invention is to provide a simply constructed and trouble-prone electrophotographic printing device for simultaneous printing on both sides of a recording medium, which ensures gentle handling of the recording medium with the lowest possible energy consumption.

Another object of the invention is to construct the printing device in such a way that it can be constructed from standard parts depending on customer-specific requirements. These objects of the invention are achieved according to the features of the first claim. Advantageous embodiments of the invention are characterized in the subclaims.

Through the use of standard printing systems, which are arranged against each other in the printing device, so that a transport channel for the recording medium opens between the printing systems and through the arrangement of appropriate guide means with which the recording medium in the trans ¬ port channel is printed and fixed at the same time, there is a simply constructed and trouble-free printing device. It is preferably suitable for simultaneous double-sided printing of endless record carriers. A clearly defined paper path, between a supply area and a receiving area, through the printer without substantial deflections enables gentle and stress-free treatment of the recording medium, which has a positive effect on the print quality. This is particularly favorable if, as recording media, additional papers or the like are used with a very different composition. Since the paper is heated essentially only once as it passes through the printing device, the energy consumption is minimal and the deforming influence of heat-setting stations on the recording medium is considerably reduced. The rolling and polishing effects on the surface of the recording medium, which deteriorate the print quality, do not occur.

Due to the small printing distance when generating the front and back, the memory requirement in the printer control device (page memory, etc.) is significantly reduced. The advantages described are even greater if, in accordance with one embodiment of the invention, a pair of rollers is used as the guide means in the transport channel, which pair has deflecting rollers lying opposite one another and wrapped around by the respective intermediate carrier, between those of the recording medium in a transfer printing and fixing nip is passed through.

Embodiments of the invention are shown in the drawings and are described in more detail below, for example. Show it

Figure 1 is a schematic representation of an electrophotographic printing device for simultaneous printing on both sides of a record carrier with two printing systems and

FIG. 2 shows a schematic illustration of an electrophotographic printing device with two printing systems placed against one another with a common transfer printing and fixing point.

The electrophotographic printing device shown in FIG. 1 is used for simultaneous printing on both sides of a tape-shaped recording medium, but is also suitable for printing single sheets if the paper path is designed accordingly. It contains two printing modules 10/1 and 10/2, on which the process means for printing on a record carrier are summarized. These process means comprise: an electric motor-driven photoconductor drum 11 with associated exposure device 12 for generating a charge image on the surface of the photoconductor drum; a developer station 13 for inking the charge image with toner; an endless belt-shaped intermediate carrier 14 for transferring a toner image formed by coloring the charge image on the photoconductor drum onto the surface of the recording medium; Fixing agents for heat and pressure fixing of the toner image on the recording medium and cleaning agents 15 for cleaning the intermediate carrier 14 and the photoconductor 11, which will be described in more detail later. To finish or recharge the photo conductor drum corona discharge or loading devices are also provided. An LED character generator is used as the exposure device 12, which extends over the entire length of the photoconductor drum 12 and which is controlled by a character generator of the device to generate the charge image on the photoconductor drum 11.

The intermediate carrier 14 arranged for transferring the toner image to the recording carrier 21 consists of a rubber or silicone band, which is mounted on deflection rollers 16 and is referred to as a thermal transfer ribbon and which contacts the surface of the photoconductor drum 11 in the region of a transfer printing location 17. A motor device 18 which can be arranged, if necessary, enables the intermediate carrier 14 to be pivoted on and off against the photoconductor drum 11. By heating the intermediate carrier 14 or the photoconductor drum 11 accordingly, the temperature at the transfer location 17 is set such that the toner of the toner image is in a doughy state and is transferred to the intermediate carrier 14 by adhesive force. However, the transmission can also take place electrostatically via a corresponding corona station. In a downstream heating station 19 with heating elements arranged therein, the toner image located on the intermediate carrier 14 is heated so strongly that the toner is almost liquefied, but is still in the solid state. The almost liquid toner image is transferred to the recording medium 21 at a transfer point 20/1 or 20/2 to the recording medium 21. For this purpose, this transfer printing location 20 contains a pair of rollers comprising a deflection roller 22 with a large diameter and a counter roller 23, between which the recording medium 21 is passed. If appropriate, it may be favorable to preheat the recording medium 21 via a heating station before it enters the transfer printing station 20/1. The fixability can thereby be increased. The intermediate carrier 14 is then cleaned in a cleaning station 24. For this purpose, the cleaning station 24 contains a cleaning roller with an associated pressure roller. The cleaning roller mechanically or chemically removes toner residues from the intermediate carrier 14, which are then wiped off the cleaning roller on a correspondingly designed nonwoven element or in a cleaning bath. Furthermore, it can be favorable to arrange a transport and temperature stabilization unit in the transport direction of the intermediate carrier, arranged downstream of the cleaning station 24, which sets the intermediate carrier 14 to a constant temperature. As an additional heating device for heating the transfer printing point 17, the. Photoelectric drum 11 contain an electrically heated heating element.

All the process means described above are fastened to the chassis elements of the printing modules 10/1 and 10/2 by means of corresponding bearing or fastening means.

In order to be able to print on both sides of the recording medium 14 simultaneously with the electrophotographic printing device, two identically constructed printing modules 10/1 and 10/2 are arranged in the printing device so that a transport channel 25 is arranged between the printing modules opens, through which the recording medium 21 is guided, specifically from a supply roller 26, which is only shown schematically here, to a receiving roller 27. Correspondingly arranged deflection rollers 28 serve for feeding and removing the recording medium 21 in the area of the Print modules 10/1 and 10/2. Controlled by a central control device, which is coupled to both printing modules, the transfer printing takes place at the transfer point 20/1 of the printing module 10/1 with simultaneous fixing of a back toner image on the back of the printing Drawing carrier 21 and in the immediately following transfer printing point 20/2 of the second printing module 10/2 a transfer printing with simultaneous fixing of a front image on the front side of the recording carrier 21. To support the transfer printing and fixing process on the U - printing parts 20/1 and 20/2 one of the rollers 22 and 23 of the roller pair can be additionally heated.

If you want to alternately print the front or back or only the front or only the back, it is possible to use the intermediate carrier 14 of the printing modules 10/1 or 10/2 that is not in use by means of the electromotive device 18 as required swing in and out. For this purpose, however, it is also possible to design the deflecting roller 22 or the counter roller 23 so that it can be swiveled in and out. A possible change in the paper path can be corrected via the control arrangement for the printing modules 10/1, 10/2 or is automatically taken into account when generating images on the photoconductor drums.

A particularly simple and paper-friendly construction of the electrophotographic printing device results from an arrangement of the printing modules 10/1 and 10/2 as shown in FIG. The printing modules 10/1 and 10/2 are arranged against one another in such a way that the deflection rollers 22 for the intermediate carriers 14 lie opposite one another and thus form a single transfer printing and fixing gap 29 through which the recording medium 21 is guided. The deflection rollers can be resiliently mounted to generate a corresponding pressing force on the recording medium 21. Correspondingly arranged stops ensure, if necessary, that the required fixing gap width depends on the thickness of the recording medium. Analogous to the exemplary embodiment in FIG. 1, depending on the operating states (front-back printing, single-page printing, alternate ver front-to-back printing etc.) the inactive intermediate carrier 14 of the printing modules can be pivoted away from the photoconductor drum by means of the motorized device 18. For this purpose, the deflection rollers 22 can also be designed so that they can be swiveled in and out. It is also possible to arrange paper rolls which can be swiveled in and out in front of and behind the transfer printing and fixing gap 29 and which ensure that the recording medium is pressed against the transfer printing rolls or guide the recording medium 14 securely in the gap. It should also be noted that the relative information on the back side toner image, front side toner image or back side and front side of the recording medium are interchangeable relative information regarding the relative position of the toner image on the recording medium.

Claims

1. Electrophotographic printing device for printing on both sides of a recording medium (21)

- A first printing module (10/1) with electrophotographic process means (11 to 15) for generating a rear side toner image assigned to a rear side of the recording medium (21) on a photoconductor (11) and an endless belt-shaped intermediate carrier (14) Transferring and fixing the back toner image on the back of the recording medium (21);

- A second printing module (10/2) with electrophotographic process means (11 to 15) for generating a front side toner image assigned to a front side of the recording medium (21) on a photoconductor (11) and an endless band-shaped intermediate carrier (14) for

Transfer of the front-side toner image to a front side of the recording medium (21), the printing modules (10/1, 10/2) being attached to one another in the printing device in such a way that a transport channel (25) for the recording medium is located between the printing systems (21) opens by the record carrier (21) being guided via guide means (22, 23) in such a way that its rear and / or front side with the corresponding associated intermediate carrier (14) of the printing modules (10 / 1, 10/2) can be brought into contact.

2. Electrophotographic printing device with a pair of rollers (22, 23) as guide means, a deflection roller (22) wrapped around the respective intermediate carrier (14) and a counter roller pressing the recording medium (14) against the deflection roller (22) (23).

3. Electrophotographic printing device according to claim 1, with a pair of rollers as guide means, each other In the transport channel (25) arranged opposite, by the respective intermediate carrier (14) wrapped Umlenkwalze (22), between which the recording medium is guided in a transfer and fixing gap formed by the rollers (22).

4. Electrophotographic printer device according to one of claims 2 or 3, wherein at least one of the rollers (22, 23) of the roller pair is designed to be pivoted on and off.

5. Electrophotographic printing device according to one of claims 2 to 4, wherein at least one of the rollers (22), 23) of the roller pair is designed to be heatable.

6. Electrophotographic printing device according to one of the

Claims 1 to 5 with an electromotive device (18) which can be swiveled in and out of the intermediate carrier on the photoconductor drum as required.

7. Electrophotographic printing device according to one of claims 1 to 6 with a thermal transfer ribbon as inter mediate (14).