EP0551288B1 - Thermo-fixing station with belt conveyor - Google Patents

Abstract

The belt-conveyor thermo-fixing station described includes upper and lower belts (31/1, 31/2) which are disposed above and below a feed channel (32) and are heated by an infra-red heater (36) located between the belts. The fixing belts (33/1, 33/2) pass round the fixing roller and the pressing roller, and round an additional guide roller (34) mounted at the input end of the fixing station. This gives a feed channel (32) which is wedge-shaped in cross-section, making it possible to feed the individual sheets gently into the fixing station. In order to avoid stripping defects, the fixing belts can be passed in addition over guide rollers (45) mounted at the output end of the fixing station.

Description

The invention relates to a thermal fusing station with tape transport and a printing or copying device with a thermal fusing station arranged therein.

Printing or copying devices operating on the principle of electrophotography are generally known. In these devices, a charge image is generated on an intermediate carrier, developed with toner in a developer station and the toner image is transferred to a recording medium 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 Pat. No. 4,147,922, contain a preheating device 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 recording medium by heat and pressure.

If such fusing stations are used to fix toner images on single sheets, there is a risk that when the single sheet is fed to the fixing rollers, the single sheet will first strike the fixing rollers, bulge and only then be gripped and transported by the fixing rollers. The cut sheet suffers a recoil, which can lead to warping of the paper.

In order to avoid this recoil, it is necessary in the known printing devices to only feed the single sheet to the fixing station when it has completely left the transfer printing station. It is therefore necessary to provide a paper transport area between the fixing station and the transfer printing station which is larger than the sheet length of the paper to be processed Single sheet (sheet length + Δ n). A suction table or a paper brake is usually used to check and control the path. A paper brake, as described for example in DE-PS 27 07 170.

The arrangement of such paper control devices enlarges the printing device, reduces the possible printing speed and is also complex.

The achievable printing speed is also limited by the structure of the fusing station itself. In the fusing station, the toner and the paper must be heated to the fusing temperature of 120 to 200 °. Only then is the toner sufficiently doughy that it can be bonded to the paper using pressure. In the known fixing station, the recording medium is therefore preheated and only then fed to the fixing rollers.

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.

From Patent Abstracts of Japan, Vol. 10, No. 300 (P-506) [2356] from October 14, 1986, an electrophotographic copier for double-sided printing of single sheets is known. The copier contains a photoconductor drum with a transfer and fixing station arranged downstream of the photoconductor drum in the paper running direction. The transfer printing and fixing station consists of two transfer belts arranged on both sides of the paper transport channel, which are guided over fixing rollers and can be pivoted onto the photoconductor drum.

As a result, the toner image assigned to the front of the single sheet is first transferred from the photoconductor drum to the one transfer belt and then the toner image assigned to the back of the single sheet to the other transfer belt. The toner images are then simultaneously transferred to the single sheet and fixed there between the fixing rollers in a line-shaped transfer printing and fixing zone.

It is also from Patent Abstracts of Japan, Vol. 13, No. 80 (P-832) [3428], February 23, 1989, a thermal fusing station is known, which is used to fix a toner image on one side of a single sheet. It consists of a fixing belt that is guided around drive rollers, which is heated by an internal heating plate that extends between the drive rollers and that is arranged on one side of an elongated fixing zone, and a heat-resistant feed belt that is guided over deflection rollers and arranged on the other side of the fixing zone for the Single sheet. To feed the single sheet with the toner image arranged thereon into the fusing station, the feed belt is guided obliquely downwards over a deflection roller in relation to the drive roller in the entry region of the fusing station. This results in a short, wedge-shaped entry area for receiving the single sheet fed via a conveyor belt, the single sheet first being brought into contact with the feed belt during feeding and then being transported by the latter to a clamping area between a pressure roller and the fixing belt. An elongated fixing zone for fixing the toner image on the single sheet adjoins the entry area delimited by a deflection roller for the feed belt. To fix the single sheet in the fixing zone, the single sheet is guided over its entire length between the fixing belt and the feed belt, the feed belt pressing the single sheet with its stressed side evenly flat against the fixing belt.

Due to the short, relatively steep entry area in connection with the immediately adjacent clamping zone between the pressure roller and the fixing belt, the single sheet between the fixing belt and the feed belt is hard milled. There is therefore a risk that the single sheet will be exposed to an increased shock load or that warping will occur during the phase-in. The fixation through large-area contact between the fixing belt and the feed belt increases the risk of blurring the not yet adequately fixed toner image, in particular at high printing speeds, and favors an uneven pressure distribution of the fixing pressure over the toner image, which has a negative effect on the fixing quality and thus on the printed image.

The object of the invention is therefore to provide a thermal fuser for a printing or copying machine, which is of simple construction, is suitable for fusing single sheets in simplex and duplex operation and enables a compact construction of the overall machine.

Another object of the invention is to design the thermal fixing station so that the required fixing pressure in the fixing roller area can be reduced. The thermal fuser is said to be particularly suitable for use in printing or copying machines with single sheet operation in duplex operation at high speed.

This object is achieved with a thermal fuser with the features of the first claim. A printer or copier with such a thermal fuser is characterized by the features of claim 11.

Advantageous developments of the invention are characterized in the dependent claims.

The thermal fixing station according to the invention is suitable for fixing toner images on sheet-like recording media in printing or copying machines. It essentially consists of heated fixing belts arranged on both sides of a feed channel, which wrap around the fixing rollers and are guided around an additional deflection point on the input side. The guiding of the fixing belts results in a wedge-shaped cross section of the feed channel, which narrows from a feed area on the input side to a contact area of the fixing rollers at a predeterminable feed angle. In this feed channel, the toner and the recording medium are heated to the fixing temperature and pressed onto the recording medium in the doughy state in the contact zone of the fixing stations.

Since the recording media is already brought to the fixing temperature via the fixing tapes before the individual sheets are fed to the fixing rollers, there is a longer contact time between fixing means and toner layer with the same processing speed compared to conventional fixing points or lines. This enables a higher printing speed compared to these conventional fusing stations.

The slow and constant heating of the toner and recording medium enables a lower fixing pressure, since the toner is doughy before it enters the contact area of the fixing rollers. This results in a gentler paper treatment with less tendency to paper curl.

The tapered fixing area formed by the fixing tapes enables the individual sheets to be smoothly phased into the fixing station and the individual sheets to be transported at the same process speed as in the transfer printing area. The cut sheet does not suffer recoil on the fusing rollers. The greatly reduced impact load also increases the lifespan of the fusing rollers and their mechanics.

Additional control means between the transfer printing station and fusing station are not necessary.

The belt fixing station can connect directly to the transfer station without any space. This significantly reduces the overall structure of the device and reduces the risk of blurring the toner images. The forced guidance of the record carrier between the transfer printing station and the fusing station and in the fusing station itself also reduces paper flow disturbances.

In an advantageous embodiment of the invention, additional deflection elements are provided on the output side to the fixing rollers in the paper transport direction, over which the fixing belts are guided. This avoids stripping errors by deflecting the recording medium from the channel or transport direction when paper emerges from the fixing rollers.

All in all, individual sheets are treated much more gently, which makes additional smoothing devices in the device superfluous and makes subsequent stacking easier.

The thermal fuser can be used for all modes, be it duplex or simplex.

To heat the fixing tapes, infrared elements are arranged between the tapes, which are particularly easy to regulate. However, it is also possible to electrically heat the fixing tapes themselves. The fixing tapes can contain heating fabric or they can be heated by induction heating.

The entire fuser is simple in construction, easy to manufacture and low-maintenance.

• Figur 1 eine schematische Schnittdarstellung eines elektrofotografischen Druckgerätes mit einer Thermofixierstation mit Bandtransport,
• Figur 2 eine schematische Darstellung des Papierlaufes des Gerätes im Einzelblattbetrieb,
• Figur 3 eine schematische Schnittdarstellung einer Thermofixierstation mit Bandtransport,
• Figur 4 eine schematische Schnittdarstellung einer Thermofixierstation mit Bandtransport und zugehöriger integrierter Abstreifeinrichtung für die Einzelblätter und
• Figur 5 eine schematische Schnittdarstellung des Aufbaues der Fixierbänder.

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 sectional illustration of an electrophotographic printing device with a heat-setting station with belt transport,
• FIG. 2 shows a schematic illustration of the paper flow of the device in single sheet operation,
• FIG. 3 shows a schematic sectional illustration of a heat-setting station with belt transport,
• Figure 4 is a schematic sectional view of a heat-setting station with belt transport and associated integrated stripping device for the single sheets and
• Figure 5 is a schematic sectional view of the structure of the fixing straps.

An electrophotographic printing device shown schematically in FIG. 1 contains a band-shaped intermediate carrier 10 in the form of a photoconductor, which is guided in an electrically motorized manner via guide rollers 11. The various units for the electrophotographic process are grouped around the intermediate carrier 10. These are essentially: a charging device LE in the form of a charging corotron for charging the intermediate carrier; a character generator ZG with a light-emitting diode comb for character-dependent exposure of the intermediate carrier; Developer stations EY, EM, EC and EB for coloring the charge-dependent discharged image on the intermediate carrier 10 using colored toner. The developer station EY contains yellow toner, the developer station EM toner with the color magenta, the developer station EC toner with 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 13 integrated therein. The developer stations EY, EM, EC and EB are designed to be interchangeable and can, for. B. pulled out of the device via slide guides and inserted into the device. They are constructed in the usual way and contain developer rollers 14 for coloring the charge image as well as guide rollers 11/1 to 11/4 which can be swiveled in and out for swiveling the intermediate carrier 10 onto and off the developer rollers 14 by means of electromagnetic swivel devices 15. The swivel devices 15 can, for . B. as plunger magnets or z. B. be designed as a swing magnet. They are used to couple the developer stations EY, EM, EC and EB individually to the intermediate carrier 10, controlled by a controller of the device.

At a distance along the intermediate carrier, two transfer printing stations U1 and U2 are arranged, which serve to transfer a toner image generated on the intermediate carrier 10 to a recording medium. The transfer printing stations U1 and U2 each contain a ribbon-shaped transfer element 16, which in the exemplary embodiment shown is designed as a photoconductor ribbon. The transfer elements 16 are driven by an electric motor and are mounted on guide rollers 11. The transfer printing stations have a transfer area T, which serves to transfer toner images on the intermediate carrier 10 to the transfer elements 16. For this purpose, pivotable guide rollers 11/5 and 11/6 are provided, by means of which the intermediate carrier 10 can be pivoted in and out of the transfer elements 16 in the transfer areas T. To transfer a toner image from the intermediate carrier 10 to the transfer elements 16, a transfer printing corotron 17 is located in the transfer area T opposite the guide rollers 11/5 and 11/6. For pivoting the guide rollers 11/5 and 11/6 in and out, they are the same as in the developer stations Electromotive swivel devices 15 are provided. To transfer the toner image from the intermediate carrier 10 to the transfer element 16, the intermediate carrier 10 is brought into contact with the transfer element 16 and transferred to the transfer element 16 via the transfer printing corotron 17 with the aid of charge forces. During this transfer, the transfer element 16 is moved in the area of the transfer areas T in synchronism with the intermediate carrier 10.

It is also conceivable to arrange stationary guide rollers instead of the pivotable guide rollers 11/5 and 11/6 and to design the guide rollers 11 of the transfer area T for the transfer elements 16 so that they can be pivoted on and off.

An additional corotron 19 is arranged downstream of the transfer area T in the direction of movement during the transfer of the transfer element.

It serves to strengthen the toner image on the transfer element 16. The arrangement of such an additional corotron 19 can be favorable if the printing device is used for four-color printing, in which several individual images of different colors are printed one above the other, and consequently a toner image passes through the transfer area T four times.

In order to transfer the toner images located on the transfer elements 16 to a recording medium, the transfer printing stations U1 and U2 have transfer printing areas UB. These exist in each case from a guide roller with a transfer corotron arranged opposite the guide roller. The transfer printing area UB1 of the first transfer printing station is arranged for printing on a front side of the recording medium on one side of a transport channel K and the transfer printing area UB2 of the second transfer printing station for printing on a rear side of a recording medium on the other side of the transport channel K. The transport channel K is used for feeding the Record carrier for the transfer printing areas UB1 and UB2.

Cleaning stations RS are provided for cleaning the transfer elements 16 after transfer printing. These are designed in accordance with the cleaning station RS of the intermediate carrier 10. They also contain a cleaning brush 13 and cleaning corotron 20 for loosening the toner before cleaning or for unloading the transfer element 16 or the intermediate carrier 10 before cleaning.

The transfer elements 16 and the intermediate carrier 10 are driven via electric motors M1 to MN which are arranged on the bottom of the device and are coupled to the guide rollers 11 via belt drives 21. The transfer element 16 of the lower transfer station U1 is only moved in one direction (arrow direction). The direction of movement corresponds to the movement of the transfer element 16 during the transfer of a toner image. However, the transfer element 16 of the upper transfer station U2 can be moved in both directions. When transferring a single toner image from the intermediate carrier 10 to the transfer element 16, the transfer element 16 of the upper transfer printing station U2 is moved with the intermediate carrier 10 in the direction of the arrow. After the transfer of the toner images to the transfer element 16 of the upper transfer station U2, the contact of the transfer element 16 with the intermediate carrier 10 is released and the transfer element 16 of the transfer station U2 is reversed to transfer the toner image onto the record carrier (arrow direction).

The pivotable guide rollers 11/5 and 11/6 are therefore used for the alternative generation of a transfer position in which toner images are transferred from the intermediate carrier 10 to the transfer element 16 and a standby position in which the intermediate carrier 10 and transfer element 16 are spaced apart from one another in such a way that no toner images are transferred.

According to the illustration in FIG. 2, the transfer printing areas UB1 and UB2 are supplied with a sheet-shaped recording medium 22 via the transport channel K. The transport channel K consists of the actual pressure channel KD and a supply channel KZ. Starting from a storage area VB that can be arranged on the side of the printing device, the individual sheets 22 are fed one after the other via the feed channel KZ to the pressure channel KD. The mouth area is arranged in a device area delimited by transfer printing stations U1 and U2 and the intermediate carrier 10.

A direction deflection device for the recording medium is arranged in this mouth region. When the printing device is designed as a single-sheet printer, this consists of fixed stops 23 and movable stops 24 and a paper transport device PT. The fixed stops 23 are fixedly arranged at the rear end of the feed channel KZ in the mouth area between the feed channel and the pressure channel. They limit the rear stop of a single sheet 22 fed via the feed channel KZ. The stops 24, which can be pivoted in and out, are located in the middle of the pressure channel KD in the mouth region. The pivoting in and out is effected by means of electric motors or magnets MO.

The pressure channel KD is designed for the parallel transport of at least two single sheets 22/1 and 22/2 of a first format, in this case A4, arranged next to one another and for the transport of single sheets of a second format, in this case A3. For the parallel transport of two single sheets in A4 format, the single sheets are fed one after the other via the storage area VB. In doing so, a first one comes across Sheet 22/1 with its lateral edges on the fixed stop 23. Then the movable stops 24 are moved centrally into the mouth area between the pressure channel KD and the supply channel KZ, so that the second single sheet 22/2 with its lateral edges lies against the movable stops 24 is coming. The two single sheets 21/1 and 21/2 can now be fed in parallel to the transfer printing areas UB1 and UB2 of the transfer printing stations U1 and U2 with the aid of the paper transport device PT. As shown in FIGS. 1 and 2, the paper transport device consists of motor-driven paper transport rollers 26 which transport single sheets in the printing channel KD and of paper transport belts 25 which are mounted on rollers and which extend into the feed channel KZ. Paper transport belts 25 and paper transport rollers 26 are arranged perpendicular to one another. The paper conveyor belts 25 capture the single sheets 22 in the feed channel KZ and place them on the stops 23 and 24. The individual sheets, which are arranged next to one another in parallel, are then transported further via the paper transport rollers 26.

If single sheets in A3 format are used instead of two single sheets in A4 format, the movable stops 24 are moved out of the transport area of the paper transport channels. A fed A3 sheet thus comes into contact with the fixed stops 23 with its upper edge. It is then transported further in landscape format and printed in landscape format. The orientation of the applied printed image on the single sheets can be done with the help of an electronic page turning device, which is designed in the usual way. This makes it possible to describe sheets specified in landscape format so that a single sheet described in portrait format is created. Such side turning devices are generally known.

If the printing device is to be operated with continuous paper, it is necessary to deflect the continuous paper fed via the supply area VB in the area of the directional deflection device. In this case, in the mouth area of the feed channel KZ and pressure channel KD z. B. a deflecting beam 27 (Figure 2) may be arranged. This deflecting bar 27 can consist of a paper guide roller rotated by 45 ° with respect to the paper feed direction, which deflects the continuous paper by 90 ° and feeds the transfer printing areas. To transport the continuous paper, 27 paper transport rollers can be arranged in front of and behind the deflecting bar in the direction of movement of the paper. When using transfer printing station U1 and U2 with a transfer element 16 which can be driven reversibly in its direction of movement, it is necessary to operate the endless recording medium in the start-stop mode. This can be done by appropriately driving the drive rollers that accomplish the paper transport.

A thermal print fixing station FX is arranged to fix the toner images on the recording medium 22. This can e.g. B. be designed according to the embodiments of Figures 3 or 4. It 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 the recording medium, for example they have a diameter of 60 mm or preferably 80 mm. The feed channel 32 extends in a straight extension to the transport channel K. The feed channel 32 is formed by heat-resistant lower and upper fixing belts 33/1 and 33/2, which each wrap around the fixing roller 28 or the pressure roller 30 and a deflection point 34 on the input side. This input-side deflection point 34 contains rollers which, for. B. are designed in the form of tensioning rollers with a diameter of about 30 mm and the z. B. tighten the fixing straps 33 via springs 39. The deflection point 34 leads in connection with the fixing rollers 28 and the pressure rollers 30, the fixing tapes 33 such that a results in a conical feed channel 32, which decreases from a feed area 35 to the contact zone between the rollers at a predeterminable feed angle α. The feed area 35 has a clear width that is somewhat thicker than the thickness of the record carrier (z. B. 1.5 mm).

Heating elements 36, in the form of electrically heated infrared elements, are located in the space between the forward and returning fixing bands 33. In order to enable a uniform heating of the fixing band 33, the filaments of the heating elements can be arranged offset to one another. The heating elements 36 serve to heat the fixing tapes to a fixing temperature of approximately 120 to 200 °. In the exemplary embodiment shown in FIG. 3, they consist, according to FIG. B. a thickness of about 0.1-0.5 mm and a coating 38 made of toner-repellent material, for. B. PTFE / silicone with a thickness of about 1.5 - 2 mm, for example. Such an elastic fixing tape is suitable for fixing two-component toner. To fix one-component toner, it is necessary to generate an increased pressure between the fixing roller 28 and the pressure roller 30 in the contact zone. It is therefore advantageous in this case to use a steel support layer instead of the support layer of FIG. 5 (fabric) and to coat it. The fixing belt itself is designed as an endless belt. This reduces the risk of breakage, for example at the welding point, and the risk of bulging is reduced. Such an endless belt can be produced in a simple manner by using an endless steel belt or z. B. an endless fabric tape spanned like a roller and coated with a layer of PTFE. It is also conceivable to apply a coating of fabric or laminate to a production roll itself, to coat it, and then to pull off the finished endless belt from the production roll.

Instead of heating with infrared elements 36, it is also possible to dispense with these heating elements and to heat the fixing belt 33 itself electrically. The fixing tape can be with respect to its support layer 37 as a laminate or fabric interspersed with resistance elements, the z. B. is designed according to an elastic electric blanket. Such a support layer can then be supplied with power via sliding contacts 40 which contact the fixing straps 33 from the inside. However, it is also possible to heat the metal mesh using induction heating.

In order to prevent toner from adhering to the fixing rollers 28 or 30, the fixing rollers are usually oiled with separating oil. Oiling stations 41 are provided for this purpose. According to the embodiment in FIG. 4, these can be arranged in the vicinity of the fixing rollers 28 or, in the case of an embodiment in accordance with FIG. 3, in the area of the fixing belts 33. In the oiling stations 41, separating oil is applied to the coated side of the fixing belts with the aid of a wick 42 or a fleece 33 applied.

To reduce the heat loss and to support the uniform heating of the fixing straps 33 to the fixing temperature, the fixing station is covered by an insulating housing 43. It extends on both sides of the fuser station over the entire width of the fixing straps 33. The thermal insulation prevents the surroundings from heating up and enables short heating times when the fusing station is switched on. Furthermore, such a housing reduces heat loss during standby operation.

A problem with thermal printing fusing stations is the so-called "stripping" of the single sheets when fusing. This means the deflection of the single sheet from the direction of the channel by adhesive forces of the roller. Such a deflection can also occur if a toner image is arranged on both sides in duplex mode, as in the present fixing station. The The toner image has a different size depending on the print image generated and the single sheet can thus adhere more strongly to one or the other of the fixing rollers and thus be deflected. The use of mechanical scraper elements in the exit area of the contact zone is not recommended because the toner on the single sheet is still soft after leaving the contact zone. The stripping elements can then blur the still soft toner image.

To avoid such a stripping error, in a preferred embodiment, in the extension of the feed channel 32 in an output channel 44, output-side deflection points 45 are integrated in the belt construction. The fixing belts 33 are additionally guided around these deflection points 45. They have a diameter that is less than the diameter of the fixing rollers 28, for. B. 30 mm with a diameter of the fixing rollers of 60 mm or preferably 80 mm, the diameter of the deflection points 45 is dimensioned such that the single sheets detach themselves directly from the deflection point during implementation. Due to the simultaneous rectilinear guidance in the output channel 44 via the two fixing bands 33, the individual sheets cannot deform and cannot be deflected on one side either.

If 33 elastic bands are used as the fixing bands, it is advisable, as already described, to use tensioning agents in the form of tensioning rollers. In this case, it is favorable to design the deflection points 45 of the so-called "anti-stripping device" as tension rollers. Each shift of the rollers 34 on the input side may change the length of the fixing bands, which leads to fixing bands of different lengths in the upper and lower fixing stations. The result would be different belt speeds with insufficient transport of the single sheets 22 between the fixing belts. Such an elongation of the fixing straps is avoided if the deflection points 45 of the output channel 44 are designed as tension rollers, because such an elongation no longer has an effect on the transport of the individual sheets in the actual fixing area 32.

In order to be able to change the clear width of the feed area 35 depending on the thickness of the recording medium used and thus to enable the feed angle α to be adjusted, the deflection points 34 can be fastened in adjustable bearing elements 46. These adjustable bearing elements 46 can be equipped with servomotors. By actuating the servomotors, the deflection points with the rollers arranged therein can be displaced perpendicular to the direction of transport of the recording medium. It is conceivable that this setting z. B. with the help of the control device of the printing device, wherein the input of the channel angle α can be done via a control panel D with a display on the device.

The thermal fixing station functions as follows: A single sheet provided with a toner image in the transfer printing station UB is fed via the feed area 35 to the fixing area of the thermal fixing station (position 1, FIG. 3). The two fixing straps 33/1 and 33/2 gently grasp the front edge of the single sheet 22, regardless of the thickness of the single sheet (position 2). This is particularly the case if 33 elastic bands are used as the fixing bands. In principle, it is possible to dispense with the bearing elements 46. However, they are favorable for setting the position at which the single sheet comes into contact with the fixing belts 33 for the first time and are therefore favorable for adjusting and coordinating the fixing station with the transport elements of the actual transport channel of the printing device.

The tapered fixing channel 32 thus enables the individual sheets to be smoothly phased into the actual fixing area. The recording medium is then continued at the same process speed VP as in the transfer printing areas UB. Due to the soft phase-in, the record carrier does not suffer any recoil on its leading edge when it enters the fusing station. This means that the paper cannot bulge. The same applies to the feeding of the single sheet to the contact zone between the fixing rollers. There is also one here recoil-free feeding with process speed VP. This reduces the impact load on the edge of the record carrier and the impact load on the fixing rollers because the record carrier is fed in a wedge shape. As a result, the life of the rollers and mechanics is extended.

Due to the forced guidance in the entire fixing station and in particular in the feed channel 32 of the record carrier, the use of suction tables or similar control elements for the record carrier can be dispensed with. The fixing station can be arranged directly adjacent to the transfer printing area or the transfer printing station UB.

After the single sheet 22 has been phased into the fixing area of the fixing station, the fixing tapes 33 lie evenly over the front and back of the single sheet. This results in a slow, constant heating of toner and paper in the fixing area during the transport of the single sheet through the fixing area 32. The toner is brought to the fixing temperature. When entering the actual contact area between the fixing rollers 28, 30, the toner is already pasty. It is thus possible to set the fixing pressure, i.e. H. to keep the pressure of the pressure roller against the fixing roller low. The result is a gentler paper treatment and the risk of paper curl is minimized.

The described thermal fusing station can preferably be used in printing or copying machines with a transfer printing principle, as was described in connection with FIG. 1. However, it is also possible to use a fixing station of this type in conventional printing or copying devices in which a duplex operation involves two passes through the fixing station and in which the fixing station is coupled to a turning device. In this case, the fixing straps 33 only have to be equipped with heating elements 36 on the fixing side. The heating elements, e.g. B. the upper fixing straps 33/2 can be omitted.

It is also conceivable to couple the heating elements 36 of the fixing belts to the control and to control them in dependence on the operating mode. When writing a single sheet in duplex mode, it is then necessary to heat both fixing tapes. If only one side of the single sheet is written in simplex mode, it is necessary to activate the heating elements using only one fixing tape. The heating elements can therefore be designed to be switchable if necessary.

Reference list

10th

Intermediate beam

11

Leadership roles

11/1, 11/2,

guide rollers that can be swiveled in and out

11/3, 11/4 11/5, 11/6

Guide rollers can be swiveled in and out in the transfer area

LE

Loading device

ZG

Character generator

EY

Developer station color yellow

EM

Developer station color magenta (blue)

EC

Developer station color cyan (red)

EB

Developer station color black

RS

Cleaning station

13

Cleaning brush

14

Developer roller

15

electromotive swivel device

U1

Transfer station below

U2

Transfer station above

UB1

Transfer area below

UB2

Transfer area above

16

Transfer element

T

Transfer area

17th

Transfer corotron

19th

Additional corotron

K

Transport channel

20th

Cleaning corotron

M1 ... M4

Electric motor

21

Belt drive

22

Record carrier

22/1, 22/2

Single sheets

KD

Pressure channel

concentration camp

Feed channel

VB

Storage area

23

firm stop

24th

movable stop

PT

Paper transport device

25th

Paper conveyor belts

26

Paper transport rollers

27

Deflection beam

28

Fuser roller

29

feather

30th

Pressure roller

31

Heater

32

Feed channel (fixing area)

33/1, 33/2

lower and upper fixing straps

34

Deflection points

35

Feed area

α

Feed angle

36

Heating elements

37

Fabric, laminate

38

Coating

39

Spring tensioners

40

Sliding contact

41

Oiling station

42

Wick, fleece

43

insulating housing

44

Output channel

45

output deflection points

46

adjustable bearing elements

VP

Process speed

Claims (11)

1. Thermofixing station for a printer or copier for fixing toner images on sheet-like recording carriers (22), with

   - a pair of fixing rollers having a lower (28) and an upper (30) fixing roller, of which at least one roller (28, 30) can be driven electromotively in order to generate a fixing pressure on a recording carrier in a linear contact zone between the fixing rollers (28, 30),

   - a feed channel (32) for feeding the recording carrier (22) to the pair of fixing rollers, and

   - a lower and an upper fixing belt (33/1, 33/2), each with an associated heating device (31, 36) for the simultaneous heating of the fixing belts (33/1, 33/2), each fixing belt (33/1, 33/2) being guided around a fixing roller (28) and at least one further deflection point (34) located on the entry side, in such a way that the fixing belts (33/1, 33/2) extend on both sides along the feed channel (32) and, at the same time, form a fixing region of wedge-shaped cross-section which, starting from a feed region (35), located on the entry side, to the contact zone between the fixing rollers (28, 30) narrows at a predetermined feed angle (α) in the conveying direction of the recording carrier, so that the recording carrier (22) provided with toner images can be phased smoothly into the fixing region and heated slowly and constantly to the fixing temperature.
2. Thermofixing station according to Claim 1, characterized by
   - a delivery channel (44) downstream of the pair of fixing rollers in the extension of the feed channel (32) and having deflection points (45) which are arranged on both sides of the delivery channel (44) and are located on the exit side and around which the fixing belts (33/1, 33/2) are additionally guided, in such a way that the recording carrier (22) peels off from the fixing belts (33) in the region of the deflection points (45).
3. Thermofixing station according to one of Claims 1 or 2, characterized in that the heating device (36) assigned to a fixing belt (33) is arranged on the side of the fixing belts (33) which faces away from the feed channel (32).
4. Thermofixing station according to Claim 1, characterized in that the fixing belts (33) themselves are designed to be electrically heatable.
5. Thermofixing station according to one of Claims 1 to 4, characterized in that a heating device assigned to a fixing roller (28) is designed as a radiant heater (31) and the heating device (36) assigned to the fixing belts (33) is designed as an infrared heater.
6. Thermofixing station according to one of Claims 1 to 6, characterized by a thermally insulating housing (43) extending over the fixing station.
7. Thermofixing station according to one of Claims 2 or 5, characterized by elastically designed fixing belts (33) having a clamping device arranged in the region of the deflection points (35) located on the exit side.
8. Thermofixing station according to one of Claims 1 to 7, characterized by a fixing belt (33) of multi-layer construction, with a carrier layer (37) and with a layer (38) arranged on the latter and consisting of toner-repellent material.
9. Thermofixing station according to one of Claims 1 to 8, characterized in that the fixing belts (33) are designed as endless belts.
10. Thermofixing station according to Claim 1, characterized by
    - means for setting the feed angle (α).
11. Printer or copier, with

    - an intermediate carrier (10) with an associated recording and developing station (ZG, EY, EM, EC, EB) for generating toner images on the intermediate carrier (10),

    - a first and a second transfer-printing station (U1, U2), each with a transfer element (16) for receiving a toner image from the intermediate carrier (10) in a transfer region (T) and for transmitting the toner image from the transfer element (16) onto a recording carrier (22) in a transfer-printing region (UB), the transfer regions (T) of the transfer-printing stations (U1, U2) being arranged at a distance from one another along the intermediate carrier (10),

    - a conveying channel (K) for conveying the recording carrier (22) out of a stock region (VB) to the transfer-printing region (UB) of the transfer-printing stations (U1, U2), the transfer-printing region (UB1) of the first transfer-printing station (U1) being arranged on one side of the conveying channel (K) for the printing of a front side of the recording carrier (22), and the transfer-printing region (UB2) of the second transfer-printing station (U2) being arranged on the other side of the conveying channel (K) for the printing of a rear side of the recording carrier (22), and

    - a thermofixing station (FX) according to Claim 1.

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