EP0486723B1 - Heating unit for heating an image carrier in a printing or copying machine - Google Patents

Description

The invention relates to a device for heating a record carrier in a printing or copying device according to the features of claim 1.

Printing or copying devices operating on the principle of electrophotography are generally known. In these devices, a charge image is generated on a recording medium in the form of a photoconductor, developed with toner in a developer station and the toner image is transferred to a recording medium in the form of a paper tape or in the form of single sheets in a transfer printing station. The toner images are fixed in a fixing station downstream of the transfer printing station by pressure and heat. The fusing stations used, such as z. B. are described in US-A-4 147 922, contain a preheater in the form of a heating saddle and the actual fixing device consisting of two fixing rollers, at least one of which is heated. The toner particles are melted into the paper by heat and pressure.

Such preheating with the aid of a heating caliper is difficult, however, if a printing device is operated in duplex mode, in which an unfixed printed image is arranged on each side of the single sheet. If such a recording medium is guided over a preheating saddle, there is a risk that the toner image will be blurred.

Furthermore, EP-B-0 212 685 discloses a contact fixing device for an electrophotographic copier, in which a toner image is taken up by a photoconductor drum with the aid of a transfer belt, heated in a heating station and then transferred to paper under the action of pressure.

The transfer ribbon is made of silicone and a flat heating element is used as the heating station, over which the transfer ribbon slides.

However, heating the transfer ribbon alone from the rear requires a high amount of energy and targeted measures to prevent the transfer ribbon from overheating. Contactless heating with the aid of a heater from the toner image side would prevent the toner images from being smeared, but when using heater heaters, a high level of regulation and monitoring is necessary in order to prevent partial overheating of the transfer belts due to the high temperatures of the heater.

From WO 92/06417, which represents a state of the art within the meaning of Article 54 (3) EPC, a heat-setting station with two heated endless belts is known, which has a feed channel with a wedge-shaped cross-section for soft phasing into a fixing area. The actual fixation takes place between two rollers pressing the endless belts together in a fixing gap.

From US-A-4 242 566 a thermal printing fixing device for fixing single sheets printed on one side is known, which has two heated fixing tapes and a fixing zone with a plurality of pressure rollers arranged side by side. The pressure rollers exert a linear pressure on the recording medium in the fixing zone. There is a risk of blurring of the printed image in the area of the fixing belts between the fixing rollers arranged in parallel.

From US-A-3 810 735 a fusing station with two endless belts is known which also serves for fusing single sheets carrying a toner image on both sides. The endless belts are arranged offset from one another and form a fixing zone in their contact area, the fixing zone being heated via heating elements arranged on both sides of the contact zone. The single sheets are fed between the endless belts and heated up very quickly there. There is therefore a risk that the toner image will be blurred and stressed by the rapid heating of the recording media.

Furthermore, EP-A-0 256 770 describes a heating roller for a fixing device with heating elements arranged thereon, which can be adapted to the size of the copy sheets to be fixed with regard to its active heating zone.

The aim of the invention is to provide a device for heating a record carrier in a printing or copying machine, which enables targeted heating of the record carrier without blurring the toner image with the greatest possible efficiency while protecting the record carrier material as much as possible. The device should also be suitable for heating recording media which carry a toner image on both the front and the back.

Another object of the invention is to design the device so that it can be used as a thermal fuser.

This object is achieved in a device of the type mentioned at the outset according to the features of the first claim.

Advantageous developments of the invention can be found in the dependent claims.

Due to the arrangement of electrically driven, heated endless tapes on the front and back of the recording medium, it can be heated evenly and with little loss. The device is for heating any type of recording medium with toner images arranged thereon suitable. These can e.g. B. transfer ribbons, photoconductor ribbons, continuous paper or single sheets. The recording media can carry toner images both on the front and on the back.

The heating station can be used within a heat setting station or can itself be designed as a heat setting station. It is particularly suitable for fixing toner images on sheet-like recording media in duplex mode.

Compared to conventional fixing stations with an exclusive line or point fixing by a pair of fixing rollers, there is a longer contact time between the endless belt serving as a fixing agent and the toner layer at the same processing speed. This enables a higher printing speed compared to these conventional fusing stations.

The slow and constant heating of toner and recording medium enables a lower fixing pressure. This results in a gentler paper treatment with less tendency to paper curl.

The conically tapered inlet area to the fusing station enables the individual sheets to be smoothly phaseed in and the individual sheets to be transported at the same process speed as in the transfer printing area. Additional control means between the transfer printing station and the fixing station are therefore not necessary. The fusing station can connect directly to the transfer station without any clearance. This significantly reduces the overall structure of the device and reduces the risk of blurring the toner images. The positive guidance of the record carrier within the fusing station reduces paper flow disturbances.

In an advantageous embodiment of the invention, at least one endless belt is designed to be pivotable. So that's a easy access to the transport channel possible when servicing.

Single sheets are treated with care, which makes additional smoothing devices in the device unnecessary and makes subsequent stacking easier.

To heat the endless belts, a paper heating saddle is arranged in a special embodiment of the invention, over which the endless belt is guided. The paper heating saddle contains infrared heating elements in the form of so-called heating cartridges. This makes it particularly easy to regulate the supply of heat to the endless belts and thus to the recording medium. The large heat transfer enables the use of several heating elements with lower output and lower operating temperature. This significantly reduces the heat losses in the device and achieves high efficiency. The contact between the recording medium and the heat saddle ensures optical heat transfer. This ensures constant heating of the recording medium immediately after starting the device. Waiting times before putting the device into operation are significantly reduced.

The relatively strong deflection of the endless belts in the exit area of the heating station prevents stripping errors when operating with single sheets by deflecting the single sheets from the channel or transport direction when exiting the heating station.

The entire heating station, whether it is designed as a preheating device or as a fixing station, is simple in construction, easy to manufacture and requires little maintenance.

The heating of the recording medium on both sides prevents the recording medium from being deformed or distorted. This is especially important when processing single sheets. The heating station also enables a short design of the printing or copying machine.

• Figur 1 eine schematische Darstellung einer Thermofixierstation für ein elektrofotografisches Druckgerät im Duplexbetrieb mit Fixierwalzen und einer Wärmestation,
• Figur 2 eine schematische Darstellung einer als Thermofixierstation ausgebildeten Wärmestation,
• Figur 3 eine schematische Darstellung einer Ausführungsform der Wärmestation mit abschwenkbarem oberen Endlosband und
• Figur 4 eine schematische Darstellung einer Thermofixierstation mit Transferband mit darin angeordneter Wärmestation zum Erwärmen des Transferbandes.

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

• FIG. 1 shows a schematic representation of a heat-setting station for an electrophotographic printing device in duplex operation with fixing rollers and a heating station,
• FIG. 2 shows a schematic illustration of a heating station designed as a heat-setting station,
• Figure 3 is a schematic representation of an embodiment of the heating station with swiveling upper endless belt and
• FIG. 4 shows a schematic illustration of a heat-setting station with a transfer belt with a heat station arranged therein for heating the transfer belt.

A thermal printing fixing station shown in FIG. 1 for a printing or copying machine which is operated in duplex mode essentially consists of a heating station W and a fixing area FX. The fixing area FX contains a pair of fixing rollers with a fixed fixing roller 28 and a z. B. under the force of a spring 29 pressing against the fixing roller 28 pressure roller 30. Both pressure roller 30 and fixing roller 28 consist of an aluminum hollow roller with radiator heater 31 arranged therein in the form of a halogen heater. The fixing rollers 28, 30 are arranged with respect to their linear contact zone, the actual printing area of the fixing rollers, at the end of a feed channel 32 for a recording medium 33. The record carriers 33 consist of individual sheets which are fed next to one another to the heat station W and which are printed with toner images on the front and back with an upstream transfer station, not shown here. The fixing rollers 28 and 30 are also assigned an oiling device 34, which is usually constructed, for supplying separating oil.

The heat station W is directly upstream of the fixing rollers FX in the direction of movement of the recording media. It contains a first electromotively driven endless belt 35/1 assigned to a front side of the recording medium 33 and a second electromotive driven endless belt 35/2 assigned to a rear side of the recording medium 33. The endless belts are arranged opposite one another in such a way that a heating channel 36 is formed for the recording medium, which extends in an input area 37 to an exit area 38. It is part of the feed channel 32. The endless belts 35 are elastic, heat-resistant belts made of toner-repellent material, for. B. PTFE silicone tapes. They are guided on the input-side 39 and output-side 40 electromotively driven guide rollers and extend over the entire width of the heating channel 36 and the feed channel 32. To guide the endless belts tightly, the guide rollers, e.g. B. on the output side 40 can be designed as tensioning rollers. Through the input-side guide rollers or rollers 39, the endless belts 35 are guided in such a way that a wedge-shaped entrance area results, which enables the individual sheets 33 to be smoothly phased into the heating station W.

To heat the endless belts, the endless belts 35 are each guided over a heating saddle 41. The heating saddle 41 contains a plurality of heating cartridges serving as heating elements in the form of infrared heating elements which are individually exchangeably mounted in the heating saddle 41. The heating saddle 41 consists of a slightly spherical aluminum block.

A spacer 43 in the form of a metal element extending across the width of the heating channel 32 is located between the input area 37 and the exit area 38. The spacer 43 is resiliently mounted via springs 44 and presses flatly on the inside of the endless belts in the area of the feed channel or the heating channel 36. A spacer 43 of this type is assigned to each of the endless belts.

The spacers 43 ensure an exact guidance of the record carriers 33 in the heating channel 36.

When the recording medium 33 passes through the heating station, it can happen that toner particles adhere to the endless belts 35 and contaminate them. To remove these particles, a cleaning station 45 is therefore assigned to each endless belt. B. clean the endless belts with the help of a brush or a fleece.

Furthermore, in order to reduce the heat loss and to support the uniform heating of the endless belts 35 to the fixing temperature, the heating station W has an insulating housing 46 (FIG. 2). It extends on both sides of the heating station W over the entire width of the endless belts 35. The heat insulation prevents the surroundings from heating up and enables short heating times when the heating station is switched on. Furthermore, such a housing reduces heat loss during standby operation.

The thermal fusing station shown in FIG. 1 functions as follows:
The single sheets 33 provided with toner images in a transfer printing area (not shown here) of the electrophotographic printing or copying device are fed via the feed channel 32 to the input area 37 of the heating station. The two endless belts 35/1 and 35/2 gently grasp the leading edges of the single sheets 33, regardless of the thickness of the single sheets. This is particularly the case if 35 elastic belts are used as endless belts. The endless belts are operated in opposite directions absolutely synchronously, which can be achieved by a drive coupling. Then the single sheets 33 are fed to the heating channel 36 and heated there. The temperature in the heating channel 36 is controlled via the heating saddle 41 so that there is a slow, constant heating of toner and paper in the heating channel 36 is coming. The toner is brought to the fixing temperature. After leaving the heating station via the exit area 38, the toner on the individual sheets 33 already has a pasty consistency. The individual sheets 33 are now gripped by the fixing rollers 28 and 30 and thus passed through the actual fixing area FX. Since the toner is already doughy when entering the actual fixing area between the fixing rollers 28 and 30, it is possible to keep the fixing pressure, ie the pressure of the pressure roller 30 against the fixing roller 28, low. In order to prevent blurring of the toner images on the individual sheets 33, the drive of the fixing rollers is synchronized with the drive of the endless belts in the heating station. The required low pressure in the fusing area between the fusing rollers results in gentle paper handling and the risk of paper curl is minimal.

It has now been found that with a corresponding increase in the pressing force in the heating channel 36 via the springs 44 and the spacers 43 and with a correspondingly increased supply of heat via the heating saddles 41, the fixing rollers 28 and 30 can be dispensed with. It is thus possible, in accordance with the illustration in FIG. 2, to design the heating station W itself as a fixing station. The function of such a heating station corresponds to the heat-setting station of FIG. 1, with the toner being heat-fixed on the individual sheets 33 within the heating channel 36. The function of the fixing rollers is taken over by the spring-loaded spacers 43.

Since no fusing rollers are used, the problem of "stripping" of the individual sheets when fusing, which otherwise occurs in thermal printing fusing stations, cannot occur. "Stripping" means the deflection of the single sheets from the channel direction by the adhesive forces of the roller. The strong deflection of the endless belts in the exit area 38 leads to an immediate lifting of the single sheets 33 from the endless belts.

In an embodiment of the heating station shown in FIG. 3, the upper endless belt 35/1 is designed to be pivotable from the lower endless belt 35/2 with the aid of a pivoting device. So that z. B. possible to easily fix paper flow problems in the heating channel or in the feed channel 32. In order to make this pivoting possible, the guide rollers for the endless belts are supported on one side in upper and lower bearing elements 48/1, 48/2. The bearing elements 48 are coupled to one another via a hinge 49 with an axis of rotation 50. When swiveling in and out, the drives of the endless belts and thus the bearing elements 48/1 and 48/2 are connected via a coupling area 51, for. B. in the form of a gear, engaged and disengaged from each other. The bearing elements 48 are connected to an electric motor 52 for driving the endless belts. A handle 47 is assigned in the upper endless belt 35/1 to facilitate pivoting in and out.

However, it is also possible to design both endless belts 35/1 and 35/2 so that they can be swiveled in and out.

If the described heating station is to be used in a printing or copying machine in simplex operation, it is possible to do without heating an endless belt. It is also conceivable for the heating of the heating saddles to be alternately switchable depending on the operating mode.

The heating station W described with reference to FIGS. 1 and 2 can also be used according to an exemplary embodiment corresponding to FIG. 4 as a heating station for preheating a transfer belt in a contact fixing device, as is described in more detail in EP-B1-0 212 685. In such contact fixing devices, a toner image developed on a photoconductor 54 is transferred to a transfer belt 55. The toner image located on the transfer belt 55 is then brought to the fixing temperature in the heating station W and then transferred to the recording medium 33 between two transfer rollers 56. After the transfer, the transfer belt 55 is cleaned of adhering toner between cleaning rollers 57.

With the heating station it is also advantageously possible to use a recording medium without a toner image, e.g. B. to heat a paper web or a single sheet and then to print the heated recording medium in a subsequent transfer station with a toner image. This transfer printing station can then be designed analogously to the exemplary embodiment in FIG. 4. In the transfer printing station, it would then also be possible with the aid of pressure rollers to fix the toner image on the recording medium. The heating of the transfer ribbon or the transferring photoconductor ribbon could thus be omitted.

If the printing or copying device is designed for processing recording media of different widths or formats, it is expedient to design the heating device to be adaptable to the width of the recording media. Such adaptation is z. B. possible by the arrangement of switchable side by side arranged heating elements (heating cartridges), this connection can be coupled to the device control and is done automatically. However, it is also conceivable, for. B. to achieve this adjustment by sliding panels or by immersing the heating elements in the heating caliper or z. B. to arrange several endless belts next to each other with assigned heating.

Claims (8)

1. Device for heating a recording medium (33) in a printing or copying device having

   - a first continuous ribbon (35/1) which is assigned to a verso of the recording medium (33) and is driven by an electric motor,

   - a second continuous ribbon (35/2) which is assigned to a recto of the recording medium (33) and is driven by an electric motor, the continuous ribbons (35/1, 35/2) being arranged located opposite one another in such a way that a guiding and heating channel is formed for the recording medium (33), which channel extends from an inlet region (37) up to an outlet region, the guiding channel (36, 32) tapering to a predetermined feed angle in the inlet region (37) in the direction of movement of the recording medium (33) and thus allowing a soft phasing-in of the recording medium (33) provided with toner images,

   - spacers (43) for the continuous ribbons (35/1, 35/2), which spacers are arranged on both sides of the guiding and heating channel (36, 32), extend flatly over the continuous ribbons (35/1, 35/2) and exert an even pressing-on force on the latter, and

   - a heating device (41) which evenly heats the continuous ribbons (35/1, 35/2) outside the guiding and heating channel (36, 32).
2. Device according to Claim 1, having spring means (44) for pressing the spacers (43) resiliently against one another in the region of the heating and guiding channel (36).
3. Device according to one of Claims 1 or 2, in which the heating device has a heating saddle (41) with heating elements (42) arranged therein, over which heating saddle the continuous ribbon (35/1, 35/2) is guided.
4. Device according to Claim 3, in which the heating elements (42) consist of infrared heating elements which are arranged so as to be exchangeable in the heating saddle (41).
5. Device according to one of Claims 1 to 4, in which means (49, 53) are provided which allow the continuous ribbons (35/1, 35/2) to be pivoted away from one another.
6. Device according to one of Claims 1 to 5, in which there is provided a thermally insulating housing (46) which extends over the continuous ribbons (35/1, 35/2).
7. Device according to one of Claims 1 to 6, in which the heating device is designed to be adaptable to the width of the recording medium (33).
8. Device according to Claim 7, in which the heating device has heating elements which can be switched on as required in accordance with the width of the recording medium (33).

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