EP0665964B1 - Thermofixing arrangement for printing or copying machines with a low temperature preheating saddle - Google Patents

Abstract

A thermofixing arrangement for fixing toner images on a strip-shaped recording medium (17) of an electrophotographic printing or copying machine has a thermoprinting fixing station (11, 12) and a heated preheating saddle (15) arranged upstream of the thermoprinting fixing station in the direction of transport of the recording medium. The preheating saddle (15) is designed as a low temperature saddle which is as long as possible, so that the temperature difference between the recording medium (17) and the saddle surface (24) is as reduced as possible. It has several heating zones (21, 23) arranged in the direction of transport of the recording medium. A regulating arrangement regulates the heating zones (21, 23) in such a way that an approximately constant thermal energy flow is set along the preheating saddle (15) at the surface (24) of the saddle on the recording medium (17). In order to adapt the preheating saddle (15) to recording media having different widths, the preheating saddle is subdivided into individually controllable transverse heating zones (30/1 to 30/3) which extend across the direction of transport of the recording medium.

Description

For thermal printing fixing of toner images on a recording medium mostly made of paper, heat-fixing devices are used in printing or copying devices, which have a preheating saddle with a downstream fixing zone consisting of a heated fixing roller and a pressure roller.

Such heat fixing devices are known for example from US-A-4147922 or Japan Abstract Vol. 13, No. 120, March 24, 1989 (JP-A-63-292177).

It is also known from US-A-4,835,573 to automatically adjust the temperature of the fixing station to the thickness or the specific weight of the paper.

In the known fixing devices it has previously been assumed that it is necessary to preheat the paper very quickly over a relatively short distance via the preheating saddle and then to fix the toner image on the paper via the rollers. For this purpose, the heating elements are arranged in the preheating saddle in such a way that the greatest amount of heat is emitted to the recording medium at the area of the paper inlet of the preheating saddle and that the amount of heat emitted is then reduced in the direction of the paper outlet via the heating elements. This makes the paper inlet the relatively hottest area of the saddle.

However, it has been found that rapid heating of the paper over a short distance leads to high stress on the paper. This stress manifests itself in deformation, embrittlement or aging of the paper and in an uneven water loss of the paper as it passes through the fuser. This is a post-processing of the paper by cutting or Sorting becomes more difficult or the toner images are fixed unevenly and thus the quality of the print deteriorates.

Rapid heating also requires a high specific heating output with powerful heating elements and complex control. Because of the high heating power, it is therefore necessary to lift the record carrier off the saddle immediately when the printer stops to prevent the paper from burning. This makes extensive control devices necessary, which worsens paper handling as a whole.

In modern electrophotographic printing devices, recording media of various widths are also processed in the same device. If the saddle is supplied with the same amount of energy over the entire width, it heats up strongly in the area where no paper is running, since in this area no energy is dissipated apart from losses due to convection.

Such a temperature distribution has considerable disadvantages. The paper heats up unevenly, which leads to fluctuations in the fusing quality and can also cause paper running problems. The maximum heating saddle temperature must be reduced as there is a risk of the heating elements overheating and the life of the heating elements is shortened. The energy losses are relatively large and the interior of the device is unnecessarily heated.

In heat fixing devices with a preheating saddle, the recording medium is guided over a heated sliding surface of the saddle. Direct contact between the paper and the saddle is essential for good heat transfer between the paper and the saddle surface. At high printing speeds and when using pre-folded or unevenly thick papers, the paper may flutter in the area of the saddle. As a result, the paper partially lifts off the saddle, which worsens the heat transfer. Paper also contains a relatively high proportion of water that is released when heated. The released water vapor can precipitate in the device and lead to malfunctions or corrosion.

The aim of the invention is therefore to provide a heat fixing device and a method for fixing, in which the record carrier is exposed to the lowest possible heat load when it passes through the fixing device.

A further object of the invention is to provide a heat-fixing device which makes it possible to fix recording media of various widths without fluctuations in the fixing quality and to avoid warping and deformation of the fixed recording medium.

These goals are achieved in a heat fixing device of the type mentioned according to the features of independent claims 1 and 17.

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

If you design the saddle as a low-temperature saddle with the largest possible length, so that the temperature difference between the recording medium and saddle is as small as possible, and if you divide the saddle into individually adjustable, evenly heated heating zones in the direction of the recording medium, then the heating zones can be set regulate in such a way that an approximately constant flow of thermal energy from the saddle to the recording medium is established along the saddle.

This measure makes the heat load on the recording medium very low. Nevertheless, the heat fixing device can also be used in printing devices with high and very high printing speeds.

It is also advantageous to divide the saddle into heating zones transverse to the direction of the recording medium, which can be controlled as a function of the width of the recording medium.

The heating behavior of the saddle can thus be adapted directly to the width of the continuous recording medium, which guarantees a constant fixing quality regardless of the width of the recording medium used.

In order to enable good contact between the recording medium and the sliding surface of the saddle, regardless of the printing speed and the paper used, in an advantageous embodiment of the invention, openings can be arranged on the sliding surface, which are connected to a device that generates negative pressure. Due to the negative pressure, the recording medium is sucked flat onto the sliding surface and at the same time the released water vapor in the paper is sucked out through the openings.

If one continues to use heating cartridges as heating elements, which are arranged in through openings of the heating saddle, these can be easily exchanged and the saddle itself can be produced inexpensively from extruded profile.

A curved shape of the sliding surface of the saddle provides a force component over the entire length of the saddle that presses the record carrier against the saddle surface. This measure supports the installation of the record carrier on the saddle surface, stabilizes the record carrier guidance and thus leads to improved heat transfer.

In a further advantageous embodiment of the heat fixing device, peripheral input means, e.g. provided in the form of a keyboard, via which the heating power of the fixing device is automatically adapted to these parameters by input of operating parameters such as paper weight, fixing temperature, etc.

• Figur 1 eine schematische Schnittdarstelltung einer Wärmefixiereinrichtung für eine elektrofotografische Druckeinrichtung,
• Figur 2 eine schematische Darstellung eines in der Wärmefixiereinrichtung verwendeten beheizten Sattels mit darin angeordneten Heizpatronen,
• Figur 3 ein Blockschaltbild einer Regelungsanordnung zur Regelung einer Heizzone des Sattels,
• Figur 4 eine schematische Darstellung der Beschaltung der Heizelemente im Sattel bei einem Betrieb der Druckeinrichtung an einem Drehstromnetz nach US-Norm,
• Figur 5 eine schematische Darstellung der Beschaltung der Heizelemente bei einem Betrieb der Druckeinrichtung an einem Drehstromnetz nach Europ. Norm,
• Figur 6 eine Darstellung des Temperaturverlaufes entlang des Sattels in Papierlaufrichtung,
• Figur 7 eine schematische Darstellung eines Heizsattels mit einer Glättungskante.

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 a heat fixing device for an electrophotographic printing device,
• FIG. 2 shows a schematic illustration of a heated saddle used in the heat fixing device with heating cartridges arranged therein,
• FIG. 3 shows a block diagram of a control arrangement for controlling a heating zone of the saddle,
• FIG. 4 shows a schematic representation of the wiring of the heating elements in the saddle when the printing device is operated on a three-phase network according to the US standard,
• Figure 5 is a schematic representation of the wiring of the heating elements when operating the printing device on a three-phase network according to Europ. Standard,
• FIG. 6 shows a representation of the temperature profile along the saddle in the paper running direction,
• Figure 7 is a schematic representation of a heating saddle with a smoothing edge.

When heat-fixing a recording medium with a toner image arranged thereon, the polymeric material, e.g. Polyester, existing toner image is heated up to the melting area via a heated fuser roller and thus connected to the recording medium.

The recording medium is pressed against the fixing roller via one or more pressure rollers. The interface between the toner particles and the surface of the recording medium is decisive for the fixation. In this area, the melting temperature of the toner must be reached gently and without excessive heating, so that it connects to the recording medium or adheres to it. If the recording medium has a substantially lower temperature than the toner when fixing in the fixing zone (fixing gap), heat is removed from the interface via the recording medium, which can lead to incorrect fixing. For this reason, the recording medium with the toner image arranged thereon is preheated before being fed into the fixing gap. It is advantageous if the recording medium is preheated to a temperature that is already in the melting range of the toner material. In this area, which is between 90 ° and 125 ° for polymeric toner, the toner already becomes slightly sticky at the interface with the recording medium, which facilitates the actual fixing in the fixing gap. In printing and copying machines that work with continuous paper, the recording medium is usually preheated via a preheating saddle, over which the non-stressed side of the recording medium slides and thus absorbs heat. The problem here is that the heat is absorbed on the side facing away from the toner, so that the interface to the toner is only heated after the actual recording medium has been heated. Depending on the thickness of the recording medium and its structure and the printing speed, this requires a rapid supply of heating power via the preheating saddle. The processes of heat fixation are described in detail in US-A-3938992, the disclosure of which forms part of this application.

In order to preheat the recording medium to a temperature in the melting range of the toner material, the recording medium in the preheating zone must be supplied with a heating power which is essentially dependent on the temperature difference between the inlet and outlet temperatures and the thermal capacity of the recording medium.

It has now been found that if the heating power is supplied too quickly and unevenly due to a temperature shock occurring in the recording medium, permanent deformations occur in the form of waves or curvatures which adversely affect the overall fixing process and in particular the post-processing of the printed recording medium. It is therefore advantageous to heat the recording medium as slowly and evenly as possible in the preheating zone. The temperature rise coefficient was determined as an essential criterion for the speed at which the recording medium can be heated without permanent deformation. The temperature rise coefficient measured in degrees Kelvin per second denotes a limit value for a permissible temperature rise per second when the recording medium is heated. It is a material-dependent value that can be determined by experiment. Material samples are dynamically loaded with heat as a function of time and examined for any permanent deformation and warping. With paper as the recording medium, it was found that the temperature rise coefficient depends on the basis weight. The heavier the paper, the lower the coefficient. This means that to avoid warping, heavy papers have to be heated more slowly than thin, light ones. However, if different types of paper are processed in a printing or copying machine, the geometry and the type of preheating of the heat-fixing device must be designed according to this heaviest type of paper. The temperature rise coefficient of the paper is 120 K / sec at 160 g / m basis weight; at 70 gr / m basis weight 155 K / sec.

The temperature coefficient is therefore an essential parameter when dimensioning the length of the preheating zone or the preheating saddle used for heating. If, depending on the melting temperature to be set and the heaviest recording medium used and other parameters, such as printing speed, the required heating output has to be determined, the required heating zone length or sliding surface length on the preheating saddle can be observed while observing the other boundary conditions, such as constant specific power distribution (watts each cm) or even heat energy flow (watts per surface) along the saddle with a minimal temperature difference between the saddle surface and the record carrier. For this purpose, the surface temperature is determined, for example, based on a calculated saddle length in a concrete test setup using non-contact infrared measuring devices of the record carrier when entering the saddle surface and when leaving the saddle surface with the heaviest record carrier measured with the highest permissible printing speed and the temperature rise per second determined therefrom. Optimization is possible by comparison with the previously determined temperature rise coefficient of the recording medium, the overall length having to be dimensioned at least so that the temperature rise lies below the temperature rise coefficient. However, it should be pointed out that the temperature rise coefficient is a statistical limit value, when exceeded a permanent quantitative change in the material structure occurs, which has a disturbing effect.

Once the minimum saddle length and saddle structure have been optimized for the worst-case scenario, the saddle length can be maintained for other lighter papers. However, it may be necessary to adjust the heating power required to record the thinner recording medium accordingly. In order for this process to take place automatically, an input keyboard can be provided on the device for entering operating parameters, such as the basis weight of the paper, printing speed, etc. One in the device e.g. The computer-controlled device arranged as part of the device control then automatically determines the required heating output and sets it on the heating elements of the heating zone.

In the case of a preheating saddle, as shown in FIG. 1, which is composed of a preheating saddle and a heating saddle, the following relationship resulted for the calculation of the total heating saddle power.

An electrophotographic printing device for printing on continuous paper contains a heat fixing device shown schematically in FIG. 1. The heat fixing device is designed as a thermal pressure fixing device. It contains a heating roller 11 which is heated by radiators 10 and a pressure roller 12 which can be pivoted to and from the heating roller 11 by an electric motor. The heating roller consists of an aluminum cylinder with a heat-resistant coating arranged thereon, the pressure roller likewise consists of an aluminum cylinder with a silicone coating. The heating roller 11 is driven by an electric motor. The heating roller 11 is assigned an oiling device 13 for applying separating oil to the heating roller. A heated preheating caliper 15 with associated vacuum brake 16 is arranged upstream of the rollers in the recording medium transport direction, which serves to preheat a recording medium 17 designed as continuous paper and to supply it to the actual fixing gap between the rollers 11 and 12 in the preheated state. Braked by the vacuum brake 16 and driven by the rollers, the recording medium 17 is guided tightly over the preheating caliper 15. A loose toner image on the recording medium is preheated on the preheating saddle 15 and fixed between the rollers 11 and 12 by heat and pressure.

A cooling device 18 arranged downstream of the rollers 11 and 12 in the paper running direction ensures cooling of the heated paper. For this purpose, the cooling device 18 contains a cooling surface 19 provided with openings, which is swept by the recording medium 17, with cold air supplied via an air supply channel 20 flowing out of the openings and a cooling air cushion being created under the recording medium 17. At the same time, air is blown onto the concrete side of the recording medium via an opposite profile.

In the heat-fixing device described, the continuous paper 17 is preheated via a preheating saddle 15, which consists of two heated saddles connected in series, namely a fixed preheating saddle 21 and a heating saddle 23 that can be pivoted about a pivot point 22 Heating zones. The entire preheating section has a length of approximately 500 mm to 700 mm. During preheating, the paper 17 slides with its toner-free side on sliding surfaces 24 of the preheating saddle 21 or heating saddle 23.

In order to make good contact between the saddles and the paper and thus to keep the temperature difference small, the sliding surfaces or the saddles are curved with a curvature radius which in the example shown is 700 mm. Due to the curvature of the sliding surfaces in connection with the train through the rollers 11 and 12 and the braking by the vacuum brake 16, a force component acts over the entire length of the saddle, which presses the paper 17 against the sliding surfaces 24. It also jeopardizes the stability of the paper run on the saddle. As can also be seen from FIG. 2, the saddles 21 and 23 have elongated depressions 25 which extend transversely to the paper running direction and extend over the entire width of the saddles. They are connected to a vacuum channel 27 by lateral bores 26. The vacuum channel runs below the saddles and is equipped with a vacuum generating device, e.g. a pump. Due to the negative pressure, the recording medium (paper) is sucked onto the sliding surfaces 24 of the saddles and the water vapor released by the preheating is sucked out.

The saddles 21 and 23 are heated by electrical resistance elements in the form of interchangeably arranged ones Heating cartridges 28. To accommodate the heating cartridges 28, the saddles 21 and 23 have through bores 29. These holes allow the replacement of each individual heating cartridge 28 in the event of a defect. In addition, the saddles 21 and 23 can be manufactured inexpensively from an extruded aluminum profile.

By arranging the cartridges in the saddles, each saddle 21 or 23 is divided into three heating zones 30/1, 30/2 and 30/3 transversely to the direction of paper travel (FIG. 2). These transverse heating zones 30/1 to 30/3 are used to adapt the saddles to different recording medium widths. The first heating zone 30/1 is delimited on one side by the fixed paper running edge 31. This heating zone 30/1 is as wide as the minimum width of the recording medium. The remaining area of the saddles up to the maximum recording medium width is divided into the equally wide heating zones 30/2 and 30/3. Each of the transverse heating zones 30/1 to 30/3 has a temperature sensor 32/1 to 32/3 for regulating the heating zones. It is located approximately in the middle of the respective heating zones across the paper running direction. Seen in the direction of paper travel, the sensor position is selected so that the same temperature can be controlled both in the standby state of the printing device (standby) and in the printing mode itself. This simplifies the temperature control. The control temperature and the position of the sensors 32/1 to 32/3 are selected so that the paper temperature at the end of the saddle is just as high during the starting phase as during a longer printing phase. The area from the middle to the last third of the saddles has proven to be a favorable sensor position.

The heating zones 30/1 to 30/3 are generated by the arrangement of the heating cartridges 28 in the bores 29.

This is as follows:

A cartridge for the two outer heating zones 30/1 and 30/3 is inserted into the first hole of a saddle in the direction of paper travel. A heating cartridge 29 for the middle zone 30/2 is inserted into the second hole. The third hole is equipped like the first, etc. There are therefore six heating cartridges 28 in each heating zone 30/1 to 30/3.

As shown in FIGS. 4 and 5, the heating cartridges 28 of the heating zones 30/1 to 30/3 are operated on phases R, S, T and N of a three-phase network. Depending on the type of three-phase network (USA, Europe), the heating cartridges are connected in pairs in series (Fig. 5) (European three-phase network) or in parallel (Fig. 4) (three-phase network USA).

This means that there are three pairs of heating cartridges in each heating zone 30/1 to 30/3. In order to achieve uniform loading of all three phases, a first pair of heating cartridges is connected to phases R, S; a second pair of heating cartridges to phases S, T; and the connection of a third pair of heating cartridges to phase R, T. However, the possible wiring of the individual heating cartridges 28 shown in FIGS. 4 and 5 can be varied as desired depending on the operating network used.

The surface temperature of the saddles and thus the temperature of the recording medium are controlled with the aid of a control arrangement as shown in FIG. 3.

The control arrangement contains an actuator 33, for example in the form of individual relays for coupling the heating cartridges 28 to a power supply unit 34. The control path is connected downstream of the actuator 35 with the heating cartridges 28. The actual temperature is recorded by the temperature sensors 32/1 to 32/3 and converted by the sensors into an electrical control signal and amplified in a subsequent amplifier 37. A control arrangement 39 compares the actual temperature with a predeterminable target temperature <TS and regulates to the target temperature TS as a function of the control deviation.

The microprocessor-controlled control arrangement 39 contains an analog-digital converter 40 with an associated program-controlled two-point controller 41. It also has a central processing unit CPU, which is connected to corresponding memory areas SP1 and SP2. The microprocessor-controlled control arrangement 39 is also coupled to the controller 42 of the printing device, which is usually constructed with a control panel 43 on the device. The entire control arrangement can be part of the device control of the device. An additional low-voltage power supply unit 44, which is coupled to the actual power supply unit 34, provides the power supply for the device control and thus for the microprocessor-controlled control arrangement 39.

As already explained at the beginning, when using recording media with different material structure, in particular different basis weight, the heating power that is supplied to the preheating saddle must be adjusted accordingly. The same applies to the adaptation of the saddle outlet temperature to the record carrier to be printed. In order to be able to set this heating power or other parameters on the preheating saddle, such as the outlet temperature, the device contains a control panel 43 for entering various operating parameters, such as the basis weight of the recording medium, the desired outlet temperature on the preheating saddle, etc. The control panel is connected to a computer-controlled arrangement which can be part of the control arrangement 39 and which contains a central processing unit CPU which is connected to corresponding memories SP1 and SP2.

Assignment tables or characteristic curves are stored in the memories SP1 to SP2, via which the corresponding electrical values of the preheating saddle to be controlled and regulated are assigned after the corresponding parameters have been entered via the control panel 43. These values are then fed to the control arrangement 39 as a setpoint. In the illustrated embodiment, the target temperature TS is entered via the control panel 43, the target temperature being the temperature at which the paper leaves the saddle arrangement (preheating saddle 15) or the entry temperature of the paper into the fixing zone between the rollers 11 and 12. The The specification of the operating parameters was only an example. If the printing speed changes or the paper width changes, the heating output must also be adjusted. This is done automatically by appropriately connecting the individually controllable transverse heating zones 30/1, 30/2 and 30/3 arranged transversely to the direction of recording medium on the saddle 15 or by detecting the set printing speed, the change of which affects many units of the device as a whole . Normally, electrophotographic printing devices that work with continuous paper work with a constant record carrier feed speed (printing speed).

The function of the control device is explained on the basis of the diagram in FIG. 6. The abscissa X of the diagram denotes the position in millimeters from the paper entry on the saddle surface, the ordinate Y the temperature in degrees Celsius. There is in curve P1 the temperature curve is shown on the paper or record carrier. The curves VD and VS denote the temperature profile on the saddle surface of the preheating saddle 21 in the pressure mode VD and in the standby mode VS. The curves HD and HS show the temperature profile in print mode HD and standby mode HS on the heating caliper surface. The positions of the sensors of the preheating saddle and the heating saddle are marked with SV and SH in the curves. It should be noted that the diagram shows the temperature profile within the heating zone 30/1 of both the preheating saddle and the heating saddle, if only this heating zone 30/1 is active, ie a recording medium with a minimal width sweeps over the saddle. If recording media of a different width are used, a similar temperature curve applies if the heating zones 30/2 or 30/3 are activated.

The saddle temperature of the preheating saddle 15 is regulated by the control arrangement, specifically by regulating the heating zones, namely the heating saddle 23 and the preheating saddle 21. The aim of the regulation is a constant target saddle temperature, the outlet temperature of the paper after leaving the control panel 43 as the saddle temperature the saddle can be entered. The microprocessor-controlled control arrangement 39 then converts this target saddle temperature into corresponding target temperatures on the preheating saddle 21 and on the heating saddle 23 and controls them together. The level of the target temperature to be set depends on the type and material structure of the recording medium used and the printing speed, ie the paper feed of the device. With normal paper and a printing speed corresponding to a paper feed speed of approximately 0.89 m / sec, the paper at the saddle inlet has a temperature of 20 ° and should be heated to a paper outlet temperature of approximately 100 °. The heating cartridges 28 are now arranged along the heating zones 21 and 23 of the saddle 15 and are regulated so that the heat energy flow per area from the saddle to the paper along the saddle is constant. Furthermore, the length of the saddle is basically determined so that the temperature difference Δ T between the saddle surface (sliding surface) and the paper becomes constant and as small as possible. However, the length of the saddles is limited by the available maximum length and can vary from device to device. However, the greatest possible length is aimed at, so that the paper is heated as gently as possible.

One problem is the dynamic behavior of the temperature profile during the transition from the standby or start phase to printing. In the starting phase, i.e. without paper or with paper on standby, heat is removed from the saddle solely by convection. Nevertheless, it must be ensured that the paper is not overheated in the start or standby phase. This is ensured by the described saddle structure and by the regulation.

The temperature of the saddle is kept constant both in standby mode and in pressure mode, the preheating saddle having a temperature of approximately 80 ° and the heating saddle having a temperature of approximately 130 °. This results in the temperature profile shown in FIG. 6. In standby mode, the preheating saddle has a temperature of 80 ° over its entire surface in accordance with curve VS and the heating saddle over its entire surface has a temperature of 130 ° in accordance with curve HS. After the start of printing, the temperature curve tilts around the sensor positions SV and SH, so that the steady temperature curve represented by the curves VD and HD is established in printer mode. In this steady state, the temperature difference is Δ T between the saddle surface and paper along the saddle surface about constant.

An even more precise setting of the constant temperature difference is possible if the number of controlled heating zones is increased. However, this leads to additional effort. As shown, the condition can also be approximately achieved with a saddle that has two heating zones, namely preheating saddle and heating saddle. The detailed procedure is as follows:
After inserting the paper into the printer device and threading through the fusing station, the desired temperature TS is entered via the control panel 43 in accordance with the paper used. The microprocessor-controlled control arrangement 39 switches the heating cartridges 28 to the phases of the three-phase network of the power supply unit 34 via the actuator 33. After the target temperature has been reached, the controller 42 of the device is informed of the operational readiness of the fixing station. After the start of printing, depending on the paper temperature, the paper weight, the printing speed, the paper thickness, the surface quality of the paper and the width of the paper, heat is removed from the saddle via the paper. This influence of disturbance is symbolically represented in the control circuit of FIG. 3 as disturbance SG. The actual temperature resulting after subtracting the disturbance variable is recorded via the temperature sensors 32/1 to 32/3 and supplied to the microprocessor-controlled control arrangement 39 in the form of electrical signals. This activates the actuator 33 in a corresponding manner until the predetermined target temperature is reached and the temperature profile shown in FIG. 6 is established.

As described at the beginning in connection with FIG. 1, the heating saddle 23 of the preheating saddle 15 can be pivoted arranged in the device. For this purpose - as can be seen from FIG. 7 - the heating caliper is detachably pivotably mounted at its input end via a bearing 22 in the device frame. It has a cam roller 45 which is rotatably mounted on the heating saddle approximately in the center and which interacts with an eccentric screw 46 which is movably mounted in the device frame. The eccentric screw 46 is driven by a camshaft 47, which is connected to a stepper motor, not shown here. By rotating the eccentric screw 46, the heating saddle 23 pivots about the pivot point 22. It can thus be positioned in different positions depending on the operating states of the device, namely in an operating position assigned to the fixing operation (position A; shown in solid lines in FIG. 2). with the pressure roller 12 swung in and into a standby position assigned to standby mode (position B; shown in broken lines in FIG. 2) with the pressure roller 12 swung out. In the standby position, the recording medium 17 is pivoted away from the hot fixing roller 11. However, it still lies on the heated preheating saddle 15.

When the recording medium 17 is preheated, be it made of paper or paper-like material or e.g. made of plastic, there is the problem that the recording medium shrinks due to the outgassing of the recording medium material or due to other effects such as water loss, etc., which leads to a certain reduction in width. This means that small waves or distortions occur during the transition to the unheated paper run area.

This effect can be observed in particular in standby mode, in which the immobile recording medium is exposed to the heat of the heating saddle for a very long time when the heating saddle is continuously heated. Will then with another Starting the printing operation of the saddle by swiveling it into the operating position and feeding the preheated recording medium into the fusing gap between the fusing roller and the pressure roller, the resulting warpage is ironed into the recording medium by pressure and heat as it passes through the fusing gap, which sensitively disturbs the printed image.

To prevent this, the heating saddle 23 has a smoothing edge 48 at its end assigned to the fixing gap, which is designed as a relatively sharp-edged rounding of the sliding surface 24. If the recording carrier web wraps around this heating saddle edge (smoothing edge 48) arranged at the preheating saddle outlet area when leaving the heating saddle 23 at the largest possible angle 49, then these warpage of the recording medium is smoothed over the looped saddle edge 48 before it enters the fixing gap.

The heating saddle edge or smoothing edge 48 should be positioned as close as possible to the fixing gap. A deflection angle of at least seven degrees of angle or greater has proven to be advantageous, the smoothing effect also occurring to a limited extent at a deflection angle of 5 ° or 6 °. Deflection angle 49 is the angle by which the running direction of the recording medium 17 changes when leaving the sliding surface 24 of the heating saddle 23. In the exemplary embodiment in FIG. 7 with a curved sliding surface 24 of the heating saddle 23, this is the angle between the sliding surface direction (tangential) in the region of the smoothing edge 48 and the direction in which the recording medium approaches the fixing gap between the smoothing edge 48 and the fixing gap.

So that the smoothing edge 48 does not impress in the recording medium 17 in the standby position (standby mode), the heating saddle 23 is pivoted so far in standby mode that the recording medium 17 does not rest on the smoothing edge 48 or is wrapped by it.

In the exemplary embodiment of the heat-fixing device shown in FIG. 1, the preheating saddle 15 consists of a fixed preheating saddle 21 and a pivoting heating saddle 23. Such a division is also useful because only a small saddle mass has to be pivoted over the heating saddle 23. The subdivision also opens up the possibility of assembling the preheating saddle 15 from heating zone modules, e.g. from a stationary heating zone module "preheating saddle" and a pivotable module "heating saddle" or, for example, from a module forming the heating saddle and several modules forming the preheating saddle, which then together form the preheating saddle 15. In this way, preheating saddles for different device variants with e.g. different printing speed can be built up in a simple manner. Is e.g. the printing speed and thus the record carrier running speed of a device variant also reduces the preheating saddle length required. If necessary, the "preheating saddle" module can thus be completely dispensed with and only a swiveling heating saddle module is required as a preheating saddle. On the other hand, if the printing speed is increased, the length of the preheating saddle can be extended by adding further heating zone modules.

A cross-linked toner has emerged as the toner material that is particularly well suited for fixing on paper using the heat-fixing device described. Due to the gentle warming up during the fixation, the advantageous fixation properties that are already present become cross-linked toner improved. A crosslinked toner that can be used is, for example, a toner that has at least 25 percent by weight of toner particles made of a polymer consisting of a polyester or a styrene group or a polymer consisting of styrene groups, which is covalently or ionically crosslinked to such a degree that the melting area the toner particles are increased by at least 10% compared to corresponding toner particles with uncrosslinked polymer.

Reference list

10th

Spotlights

11

Heating roller, fixing roller

12th

Pressure roller

13

Oiling device

15

Preheating saddle

16

Vacuum brake

17th

Record carrier

18th

Cooling device

19th

Cooling surface

20th

Air supply duct

21

Preheating saddle

22

Pivot point, bearing point

23

Heating caliper

24th

Sliding surface

25th

elongated recess, slot, opening

26

drilling

27

Vacuum channel

28

Heating cartridge, heating element

29

Bores for heating cartridges

30/1

first transverse heating zone

30/2

second transverse heating zone

30/3

third transverse heating zone

31

fixed paper edge

32/1

Temperature sensor

32/2

Temperature sensor

32/3

Temperature sensor

R, S, T, N

Phases of a three-phase network

33

Actuator

34

power adapter

35

Controlled system

36

Summation element

37

amplifier

39

microprocessor-controlled control device

40

Analog-to-digital converter

41

Two-point controller

42

Controller

43

Control panel

TS

Target temperature

44

Low voltage power supply

X

Position in millimeters

Y

Temperature in degrees Celsius

P1

Temperature curve on the record carrier

VD

Temperature curve in printer operation on the surface of the preheating saddle

VS

Temperature profile in stand-by mode on the surface of the preheating saddle

HD

Temperature curve on the surface of the heating saddle during printing

HS

Temperature curve on the surface of the heating saddle in stand-by mode

T

Temperature difference between record carrier and saddle surface

SG

Disturbance variable

GS

Device control

CPU

Central unit

SP1, SP2

Storage

45

Cam roller

46

Eccentric screw

47

camshaft

48

Smoothing edge

49

Deflection angle

Claims (19)

1. Thermofixing device for fixing toner images on a strip-shaped recording substrate (17) in a printing or copying machine, having

   - a thermoprinting fixing device (11, 12) for thermoprinting fixing of the toner images on the recording substrate (17),

   - a heated preheating saddle (15), which is located upstream of the thermoprinting fixing device (11, 12) in the recording substrate running direction, for preheating and guiding the recording substrate (17), with the following features:

   - the preheating saddle (15) is subdivided in the recording substrate running direction into a plurality of heating zones (21, 23), the heating zones having heating elements (28), which, at least within the heating zones (21, 23), uniformly heat a gliding surface (24) receiving the recording substrate (17), and having temperature sensors (32/1, 32/2, 32/3) for determining the surface temperature;

   - a control arrangement is provided which is assigned to the heating zones (21, 23), is coupled to the temperature sensors (32/1, 32/2, 32/3) and, taking into account

   a) the desired temperature (TS) entered via peripheral entry means (43),

   b) further operating parameters, such as type of material of the recording substrate, basis weight, printing speed, and

   c) relationships, which are determined empirically and stored in memory elements (SP1, SP2) in the form of allocation tables, between the parameters mentioned under a) and b), on the one hand, and the thermal energy flow or coefficient of temperature rise, on the other hand, controls the surface temperature of the heating zones (21, 23) so that, along the preheating saddle (15), an approximately constant thermal energy flow occurs from the gliding surfaces (24) to the recording substrate (17) and

   - the preheating saddle (15) is designed as a low temperature saddle with a minimum total length of the heated gliding surfaces (24) at which a coefficient of temperature rise in the recording substrate (17) and dependent on the recording substrate material is not exceeded.
2. Thermofixing device according to Claim 1, having a recording substrate (17) of paper or paper-like material and a coefficient of temperature rise in the recording substrate (17) of a maximum of 180° Kelvin per second.
3. Thermofixing device according to Claim 1, having a sensor (32/1, 32/2, 32/3) arranged in the heating zones (21, 23) in a region approximately centrally up to the last third of the preheating saddle (15) in the recording substrate running direction.
4. Thermofixing device according to one of Claims 1 to 3, having a preheating saddle (15) having a first heating zone of low temperature designed as a preheating saddle (21) and a second heating zone of higher temperature designed as a heating saddle (23) and arranged downstream in the paper running direction.
5. Thermofixing device according to one of Claims 1 to 4, having holes (26) arranged in the saddle for the exchangeable accommodation of heating elements.
6. Thermofixing device according to one of Claims 1 to 5, having a plurality of transverse heating zones (30/1, 30/2, 30/3), designed to be drivable individually as a function of the width of the recording substrate (17) and arranged on the saddle (15) transversely to the recording substrate running direction.
7. Thermofixing device according to Claim 6, having a sensor (32/1 to 32/3) assigned to each transverse heating zone (30/1 to 30/3) and arranged transversely to the recording substrate running direction, approximately centrally to each transverse heating zone (30/1 to 30/3).
8. Thermofixing device according to Claim 6 or 7, having a first transverse heating zone (30/1) assigned to a minimum recording substrate width and further second and third transverse heating zones (30/2, 30/3) of approximately equal width adjoining the first transverse heating zone (30/1).
9. Thermofixing device according to one of Claims 1 to 8, having openings (25) arranged on the gliding surfaces (24) of the heating zones (21, 23) and connected to a suction device (27) producing a vacuum.
10. Thermofixing device according to Claim 9, the openings (25) being designed as slot-shaped depressions having lateral suction openings (26) and extending over the width of the heating zones (21, 23).
11. Thermofixing device according to one of Claims 1 to 10, having

    - a preheating saddle (15) with a domed gliding surface (24), the gliding surface having a doming radius which is dimensioned in such a way that, in fixing operation, the recording substrate (17) rests on the gliding surface (24) over the entire saddle length.
12. Thermofixing device according to one of Claims 1 to 11, having

    - a preheating saddle (15) which has, at one end facing the thermoprinting fixing device (11, 12), a smoothing edge (48), over which the recording substrate (17) is deflected out of a running direction determined in the region of the smoothing edge (48) by the gliding surface (24) into an approach direction towards the thermoprinting fixing device (11, 12), the deflection angle (49) being dimensioned in such a way that a smoothing effect is exerted on the recording substrate (17).
13. Thermofixing device according to Claim 12, having a deflection angle of at least seven degrees of angle.
14. Thermofixing device according to either of Claims 11 and 12, having

    - a heated fixing roller (11) assigned to the thermoprinting fixing device (11, 12) and

    - a preheating saddle (15) which is pivotably arranged in front of the fixing roller (11) in the recording substrate running direction in such a way that, in an operating condition assigned to fixing operation, the recording substrate is fed to the fixing roller (11) over the smoothing edge (48) and, in a condition assigned to a standby operation, is lifted off from the fixing roller (11), no deflection over the smoothing edge (48) taking place.
15. Thermofixing device according to one of Claims 1 to 14, having

    - a preheating saddle (15) which is composed of heating zone modules which can be built in independently and are designed as preheating modules which can be built in in a fixed position or as heating modules which can be pivotably built in, at least one heating zone (21, 23) being assigned to each heating zone module.
16. Printing or copying machine having a thermofixing device according to one of Claims 1 to 15.
17. Process for fixing toner images on a recording substrate (17), having the following process steps:

    - preheating of the recording substrate (17) along a heated preheating zone (15) to a melting temperature assigned to a melting range of the toner image material, the heating power required for heating the recording substrate (17) being supplied to the recording substrate (17) along the preheating zone (15) in such a way that, along the preheating zone (15), an approximately constant thermal energy flow to the recording substrate (17) occurs and that a coefficient of temperature rise, which is dependent on the recording substrate material, is not exceeded

    - fixing of the toner images on the preheated recording substrate (17) by means of pressure and by heating the toner images to a melting temperature assigned to the melting range of the toner image material.
18. Process according to Claim 17, having a melting range of the toner material of 100 to 140°C.
19. Process according to Claim 17 or 18; having toner images which contain thermally fixable toner particles of a polymeric compound, at least 25 % by weight of the toner particles comprising a covalent or ionically crosslinked polymer having polyester or styrene groups.

Images