EP1369751B1 - Method and apparatus for fixing toner on a substrate - Google Patents

Abstract

The device (7,8) is fixing toner on a substrate and comprises a heatable fixture roller (7) contacting the toner, heating to a temperature greater than or equal to its glass transition temperature. Before the heating of the toner by the fixture device, a pre-heating (1,2) is carried out without contact, with which the toner is heated to a temperature less than or equal to its glass transition temperature. A transport device for moving the substrate from the location of the pre-heating to that of fixing the toner is tempered at a constant temperature of preferably 40 degrees Celsius. The pre-heating device is connected to at least one microwave source.

Description

The invention relates to a method for fixing toner on a recording material, wherein a fuser comprising a heatable fuser roller contacting the toner is used to heat the toner to a temperature greater than or equal to its glass transition temperature, and wherein before heating the toner by the fixing device, a preheating is performed, with which the toner is first heated to a temperature less than or equal to its glass transition temperature.

The invention further relates to a device for fixing toner on a recording material, comprising a fuser, with a heatable fuser roller contacting the toner to heat the toner to a temperature greater than or equal to its glass transition temperature, comprising a preheater Non-contact preheating of the toner to a temperature less than or equal to its glass transition temperature, preferably for carrying out the aforementioned method.

In electrostatic or electrophotographic printing, an electrostatic latent image with charged toner particles is developed on a imaging drum and transferred to a substrate such as, in particular, paper in the form of sheets or in the form of a continuous belt. In the case of four-color printing, for example, four latent images in the four color separations cyan, magenta, yellow and black are transferred successively and one above the other onto the substrate. In particular, the finished single-color or multi-color latent image is then fixed on the substrate by means of a fixing device. This is usually done by means of a heatable fuser roll, which is rolled on the toner image and the toner heated to above its glass transition temperature, ie melts, and at the same time incorporates pressurized in the substrate to which it is fixed after cooling.

In this case, adjacent toner particles combine and ultimately form a polymer layer on and on the substrate.

A problem can occur in the described procedure, if a larger number of printing operations in a certain time unit to be performed, the process is thus to be accelerated. In that case, the fixing process can prove to be the speed-limiting factor of the printing process because it can not be linearly accelerated.

If the fixing operation is to be accelerated, it may be considered to increase the temperature of the fixing roller and / or to increase the fixing area between the fixing roller and a counter-pressure roller in the substrate transporting direction.

However, an increase in the temperature leads to a reduced service life of the fixing roller, in particular its coating or sheathing. In addition, when fixing with a fixing roller, a silicone oil is used as a release agent to prevent toner from adhering to the fixing roller and adversely affecting subsequent printing operations. Also, this oil must be refilled more frequently and is increased in its consumption, with the additional risk that it adheres to transport facilities, this is dirty and carried on, so that this oil can affect subsequent printing operations.

If the fixing area is to be increased, this can in principle be done in two ways, by increasing the pressure between the fixing roller and the counter-pressure roller, thereby producing a larger flattened area, or by using a fixing roller with a larger diameter. By a larger pressure, in turn, the life of the fixing roller, in particular its coating, can be reduced, and it can lead to damage, especially to crumpling, of the substrate. If the diameter of the fuser roller is increased, it can easily lead to substrate jams. In addition, the construction costs and the size are problematic.

From the GB-A-1 376 957 are known a method and a device of the aforementioned types. There, a preheating is done with a non-specified preheating and fixation is performed with a fixing roller.

The PATENT ABSTRACTS OF JAPAN vol. 004, no. 160 & JP-A-55/108677 disclose a fixing device with a xenon flash lamp, which is preceded by an unspecified microwave heating device for preheating.

The U.S. Patent 4,897,691 relates to a drying and fixing device for express liquid toner.

The invention is based on the object, in particular for an increase in speed, to improve the fixing device in a method or a device of the aforementioned type with respect to a uniform preheating.

This object is achieved according to the invention in process view, that the preheating of the toner is carried out without contact by means of a resonant microwave application, wherein a plurality of microwave resonators with horizontally extending microwaves in the transport direction of the recording material behind each other and each offset by a fraction of a microwave length are arranged transversely to each other.

"Preheating" means that the toner is heated to within the range of its glass transition temperature, but this temperature is not exceeded in order to avoid melting of the toner. In contrast, "fixing" involves heating the toner above its glass transition temperature. Preferably, however, a toner is used with a sharp as possible defined glass transition temperature, so that therefore a preheating and fixing with their temperature ranges can be close together.

As a result of the non-contact preheating according to the invention, the fixing process is particularly time-relieved and also with regard to the risk of recording material jams, without the problems of the fixing area being pre-displaced into the preheating area. Here, the non-contact preheating is of particular advantage.

Contacting preheating by means of a heatable saddle, which can be pressed onto the toner-carrying recording material for its heating, is in principle, for example, also from US Pat US-A-4147922 , known. However, saddles of this type are relatively large in size and can pose particular problems in so-called duplex printing, double-sided printing of a recording material in perfecting, since saddles of this type must be heated to such an extent that, in particular, an already on a first side ( Bottom) of the recording material fixed printed image can be softened and smeared again, especially as a counter-pressure element just rests against this underside. By contrast, in the case of the preheating without contact according to the invention, a temperature clearly below the glass transition temperature can be set precisely and constantly, and the recording material can possibly even be transported "floating", for example on an air cushion. The preheating is carried out according to the invention by a microwave application, with the advantage of the substrate and indirectly via the recording material, but partly also directly the toner is heated.

In particular, the method according to the invention can be applied to sheets of recording material or (continuously) to recording material tapes. The actual fixing step is the fixation with a fixing roller. In this case, other print quality parameters, such as toner gloss, can be considered.

In addition, the method according to the invention provides that resonant or standing microwaves are used. This can be done by the selection and / or tuning of the resonators very targeted and needs-based and, in particular, various print quality features will be taken into account, as will be explained below.

In order to achieve a better energy input, the recording material can be moistened before the microwave application. This can be done, for example, with 100 ° C hot steam. In this case, the recording material may preferably be moistened on both sides to avoid tensions and bends of the recording material. In addition, by condensation heat, the toner-carrying substrate is also already heated.

Another embodiment of the method according to the invention provides that a means of transport, for. B. a suction belt or an electrostatic conveyor belt, is heated to transport the recording material from the place of preheating to the place of fixing the toner to a constant temperature of preferably about 40 ° C.

To save energy or for a high degree of efficiency, waste heat or energy waste in the broadest sense can be used or co-used for preheating. For example, waste heat or energy waste from a magnetron, a circulator, or a water load can be used. Thus, for example, scavenging air can be heated.

Distances bridging or avoiding waveguides towards the applicator may be used on a magnetron. Against leakage radiation in the region of the applicator can be provided on material columns, a so-called choke structure with lip-like projections. Also, absorbent material may be used on the outside of the applicator.

For a device according to the invention for fixing toner on a recording material according to claim 5 independent protection is claimed. The resulting advantages are analogously already described in connection with the method according to the invention.

The device according to the invention comprises a microwave source to which the preheating device is connected for preheating by microwave application. In this case, the preheating device comprises a plurality of microwave resonators for generating standing microwaves. There are a plurality of resonators with horizontally extending microwaves in the substrate transport direction behind each other and each offset by a fraction of a microwave length to each other in order to achieve the most uniform possible heating across the width of the recording material.

A basic design of a device according to the invention can be designed, for example, on a combination of a preheater and a fixing device in which at least one transport means transports the recording material into the preheater and transports it from the preheater to the fixing device, followed by a cooling path for the recording material carrying toner to achieve a cooling of the toner back below its glass transition temperature.

The device may be easily opened, for example clamp-like, to access the recording material path in the event of a jam of material for eliminating this jam.

For resonant microwave generation, a contacting or non-contacting plunger is usually used to tune the microwave applicator. With a precise determination of the applicator geometry, such a plunger or a tuner is not necessary. The plunger may be replaced with a defined end wall and the tuner may be replaced by fixed metal stubs and / or blocks of polytetrafluoroethylene in a waveguide to adjust the length of the waveguide between the microwave source and the aperture. The aperture which defines the resonant chamber can have any desired shape, in particular a rectangular or spherical or curved shape.

In particular, when using a TE10N resonator, the wavelength in the resonator, that is the distance of the maxima, can be optimized by the width of the resonator perpendicular to the plane of the substrate. With a width of 94 mm, for example, the distance between the maxima is 84 mm. Therefore, with an overlap of two applicators, an absolute tolerance of the substrate temperature of 6 ° C (± 3 ° C, corresponding to ± 5%) can be achieved. With a width of, for example, 109 mm, the distance of the maxima is only 73 mm, which leads to a tolerance of 4 ° C (± 2 ° C, corresponding to ± 3%).

The height of a resonator in the recording material transport direction is optimized to achieve a high electric field strength, without discharges in the applicator. Therefore, good results are achieved with heights of, for example, 54 mm, 34 mm, 24 mm and 20 mm. The smaller values are preferred for higher electric field strength. Higher electric field strength increases the efficiency of the microwave system for lower loss recording materials, such as paper.

The frequency adaptation of a resonant applicator is dependent on the size in the longitudinal direction. After a longer period of operation, heating the applicator by wall loss due to surface currents on the inner surface of the applicator induced by microwave radiation in the applicator can result in detuning of the resonant applicator. To avoid this, it is proposed that the frequency-determining parts of the resonant applicator (aperture and plunger) independent of temperature, possibly temperature-stabilized, to position each other, wherein the applicator itself is movably mounted so that the inner dimensions of the resonant applicator do not change during a continuous operation.

Fig. 1

einen experimentellen Aufbau einer erfindungsgemäßen Kombination aus einer Vorheizeinrichtung und einer Fixiereinrichtung,

Fig. 2

eine erste Temperaturverteilung bei einer ersten Anwendung eines Aufbaues gemäß Fig. 1 und

Fig. 3

eine zweite Temperaturverteilung bei einer zweiten Anwendung eines Aufbaues gemäß Fig. 1.

Embodiments and applications from which further inventive features may result, to which the invention is not limited in scope, are shown in the drawing and are explained in more detail in connection with the figures. Show it:

Fig. 1

an experimental structure of a combination of a preheater and a fixing device according to the invention,

Fig. 2

a first temperature distribution in a first application of a structure of FIG. 1 and

Fig. 3

a second temperature distribution in a second application of a structure according to FIG. 1.

Fig. 1 shows a basic, experimental structure of a device according to the invention. It comprises a preheating device which comprises two resonators 1 and 2 and to which a recording material to be preheated is fed on a conveyor belt 3 in the transporting direction 4. The conveyor belt 3 could fix the recording material with vacuum or electrostatically.

The resonators 1, 2 are TE10N resonators, which are aligned transversely to the transport direction 4 and are arranged one behind the other in the transport direction, transversely offset in a manner and to a degree that the maxima of the microwave of the first resonator 1 exactly to the gap Maxima of the microwave of the subsequent resonator 2 are positioned. The temperature given with the resonators 1, 2 as uniformly as possible across the width of the recording material to the toner-carrying recording material can be measured in the experimental arrangement of Fig. 1 at the exit from the resonators with a line pyrometer. If the device has been satisfactorily measured and adjusted, in principle the same device as in Fig. 1, omitting the pyrometer 5, can also be used as an installation in an electrophotographic printing machine.

From the resonators 1, 2 towards the fixing device, the preheated recording material is transported by means of a second conveyor belt 6. With this conveyor belt 6, the recording material can continue to be tempered.

The fixing means comprises substantially a fixing roller 7 shown in cross-section, which is heated by means of an internal heat source 12, for example a radiation source, to a temperature above the glass transition temperature of the toner on the recording material. In the region of this fixing device, a toner-carrying, sheet-shaped recording material 9 is once schematically indicated, which is supplied after fixing in the direction of the arrow 10 to a cooling.

The fixing roller 7 is supplied from a schematically indicated oil reservoir 11 with a silicone oil as a release agent for preventing adhesion of toner to the fixing roller 7. As an abutment for the recording material 9 also pressurizing fixing roller 7 is a counter-pressure roller. 8

Fig. 2 shows the course of the temperature generated by the resonators 1, 2 in the recording material, once in a dashed line, when only the resonator 2 is turned on, once in a solid line, when only the resonator 1 is turned on, the maxima of which standing microwave to the maxima of the microwave of the resonator 2 exactly to the gap or by half a wavelength of the wave shown in Fig. 2 (and Fig. 3) of the standing wave, which corresponds to the energy input and only half as large as the wavelength of originally enveloped free microwave, out of phase, and once in a solid line envelope for both resonators 1 + 2 turned on. The envelope in the recording material gives a nearly uniform temperature of about 75 ° C ± 3 ° over the abscissa-plotted width of the recording material C. The temperatures were measured with the line pyrometer 5 of FIG. As a recording material, a paper having a specific basis weight of 220 g / m ² , a recording material driving speed of 50 cm / sec, a microwave power of 2 kW per resonator and a pixel size of 3.1 mm was used.

In Fig. 3, a second temperature profile corresponding to FIG. 2 is applied, but this time with microwave maxima, which have a slightly smaller distance from each other than in the illustration of Figure 2, which, as mentioned above, adjusted by means of the selected width of the resonator or can be specified. Due to the smaller maximum spacings in FIG. 3, the temperature profile over the recording material width can be seen to be even more uniform than in the case of FIG. 2.

The relief of the fixing device by means of a preheating according to the invention will be clarified in the following again by means of tables. In particular, the tables can be seen that a higher preheating of the paper as a recording material results in a shortening of the duration of the fixing process and therefore allows an increase in the paper transport speed, whereby a total of no problems in fixing a higher printing speed can be achieved with a printing press.

In this case, in Example 1 of Table 1, a paper having a specific basis weight of 80 g / m ² and in the second example in Table 2 a paper having a specific basis weight of 300 g / m ^{2 is} used. Example 1 (Table 1): paper speed Fixture Papiertemp. fixing roll Toner / paper surface temperature comment 30cm / s 60ms 27 ° C 160 ° C 110 ° C No preheating 45cm / s 40ms 44 ° C 160 ° C 110 ° C 2x 1500kW 60cm / s 30ms 54 ° C 160 ° C 110 ° C 2x 2000kW paper speed Fixture Papiertemp. fixing roll Toner / paper surface temperature comment 30cm / s 60ms 27 ° C 160 ° C 112 ° C No preheating 45cm / s 40ms 40 ° C 160 ° C 112 ° C 2x 1500kW 60cm / s 30ms 48 ° C 160 ° C 112 ° C 2x 2000kW

Claims (5)

1. Method for fusing toner to a sheet-shaped or web-shaped substrate (9), wherein a fusing device (7, 8, 11, 12) comprising a toner-contacting, heatable fuser roller (7) is used in order to heat the toner to a temperature that is higher than or equal to its glass transition temperature, and wherein, before heating the toner with the fusing device (7, 8, 11, 12), a pre-heating is performed in order to heat the toner initially to a temperature that is lower than or equal to its glass transition temperature,
   characterized in that
   the pre-heating of the toner is performed in a contactless manner by means of a resonant microwave application, whereby several microwave resonators (1, 2) applying horizontally propagating microwaves are arranged in series in transport direction (4, 10) of the substrate (9) and are transversely offset relative to each other by a fraction of a microwave length.
2. Method as in Claim 1, characterized in that the substrate (9) is moistened prior to the application of the microwaves.
3. Method as in one of the previous Claims, characterized in that a transport means (6) for the transport of the substrate (9) from the site of pre-heating to the site of fusing the toner is heated to a constant temperature of preferably approximately 40°C.
4. Method as in one of the previous Claims, characterized in that, in the broadest sense, waste heat and/or energy drops are utilized for pre-heating.
5. Device for fusing toner to a sheet-shaped or web-shaped substrate (9), comprising a fusing device (7, 8, 11, 12) with a heatable fuser roller (7) that contacts the toner in order to heat the toner to a temperature that is higher than or equal to its glass transition temperature, comprising a pre-heating device for contactless pre-heating of the toner to a temperature that is lower than or equal to its glass transition temperature, preferably for performing the method in accordance with one or more of the previous Claims,
   characterized in that
   the pre-heating device is connected to at least one microwave source comprising microwave resonators (1, 2) by means of which the toner can be heated in a contactless manner, with several microwave resonators (1, 2) which apply horizontally propagating microwaves being arranged in series in the substrate transport direction (4, 10) and being transversely offset relative to each other by a fraction of a microwave length.

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