EP1217459A2 - Method and unit for fixing toner on a support, in particular a printing support - Google Patents

Abstract

Method for fixing toner on a print medium such as paper using a microwave transmitter as a fixing device. The microwaves heat the print medium that causes melting of the toner. A toner is chosen that displays a large reduction in its elastic modulus when heating caused it to change from solid to liquid state. The ratio of liquid to solid elastic modulus is in the range 10<-5> to 10<-7>. An Independent claim is made for a device for fixing toner for a digital printer in which toner fixing is carried out using a microwave transmitter with appropriate shielding. Printing uses a resonator and optimally the ratio of toner elastic modulus before and after melding can be measured.

Description

The invention relates to a method for fixing toner on a carrier or a printing substrate, in particular a sheet-like or a ribbon-shaped printing substrate, preferably for a digital printing machine.

Furthermore, the invention relates to a device for fixing toner on a Carrier or a printing material, in particular a sheet-like or a tape-like Printing material, preferably for a digital printing machine, preferably to carry out the aforementioned method.

In digital, especially electrostatic or electrophotographic printing a latent electrostatic image is generated by means of charged toner particles is developed, which in turn is based on a printing material that receives the image, e.g. Paper, be transmitted. The image transferred to the printing material is there through Heating and softening the toner and / or heating the substrate fixed. Through and during this process, toner particles bind to the substrate and possibly also with each other.

Microwaves are used to fix the toner on the substrate known in principle. Because the absorption of microwave energy in the toner usually is at least one order of magnitude smaller than in the printing material, the is preferred Printing material is heated by the microwaves and the printing material in turn heats up the toner on it, up to a temperature at which the Connects toner with the substrate. As is known, when using Microwaves for fixing the toner characteristic values of the used Substrate, such as weight, moisture and composition, critical and take into account.

For example, an image fixing device is known from US Pat. No. 4,511,778, which is a toner image using high frequency waves, especially microwaves, fixed on a printing material, especially a sheet of paper. An aspect the known device is the possibility of depending on the microwaves of the size of the substrate to give, taking into account this Size as the characteristic value of the substrate, proper melting and to fix the toner.

This is a procedure that is fairly general and only an immediately obvious one Size of the substrate is taken into account and before fixing for operation the device specifies, for example, according to a consideration that a larger to be heated Piece more energy due to its larger heat capacity needed as a smaller piece to be heated.

This general stipulation means that other critical aspects remain in use not considered by microwaves for fixing toner. For example the procedure cited only for black and white printing with paper weights of a small range of variations can be used, while that may be different Behavior of different colored toners and different paper weights with possibly also different water content in this flat rate, on the Size of the substrate is not considered in a coordinated manner. At a Color printing, for example, the toner image can have four different toner layers. The maximum density of each toner layer on the image carrier substrate or printing material 100%, whereby there is a maximum total density of the toner layers results in the toner image of 400%. Usually the density is a single color Toner image in the range of 0% to 100% density, a colored toner image in the Range from 0% to 290%. In addition, the device cited does not include a microwave resonator, in microwave applications with a view to homogeneous heating is desirable, usually even at least two to each other staggered resonators are used, such as from US-A-5 536 921 known for a general microwave heating outside the pressure range.

In addition, the problem can arise when using sheet-shaped printing material, that in the area irradiated with microwaves the edge area of the sheet is processed energetically differently than the central leaf area, so that it becomes a unevenly created printed product can come.

In addition, when fixing conventional toner using only of microwaves under certain circumstances only an incomplete fusion of the toner, depending on the layer thickness, is achieved or there is heating with bubbles in Areas of the toner is coming. Also the adhesion of the toner to the printing material may be insufficient because, for example, the connection to the substrate not sufficiently produced by the too high viscosity of the melted toner becomes. Problems can arise especially when one substrate in two in a row executed printing is printed on both sides.

Because of these potential problems outlined, it becomes conventional and common not familiar with the use of microwave radiation when fixing, instead, the toner is heated in practice without microwave radiation and with a heated pair of rollers connected to the substrate under pressure.

In principle, a contactless fixation is desirable to protect the printed image. Additional advantages of contactless fixation are the avoidance of adhesive wear and the resulting increased service life of the equipment used, as well as better reliability of the facility.

The invention is therefore based on the object of an adequate fixation of toner on a substrate using microwave, preferably also for one multi-color printing on sheet-shaped substrate and using a resonator and preferably in coordination with the prevailing special circumstances, to enable.

In terms of the method, this object is achieved in that the Printing material containing toners with microwaves from at least one microwave transmitter irradiated and heated for melting the toner and that a toner is used that makes a sharp transition from its solid to its liquid Shows the state when heated.

In this way, a dry toner can be used, for example that is still quite hard at an average temperature of around 50 ° C to 70 ° C, so that it uses conventional methods to achieve a desired average toner size from Z. B. 8 - 4 microns can be ground and also at development temperatures does not become sticky or melts yet, but at a higher temperature of e.g. about 90 ° C is already very low viscosity with low viscosity, so that it if necessary. under Utilization of capillarities is possible even without external pressure and without contact and settles and sticks in the printing material and then very quickly when it cools down hard again and is fixed, with a good one, adapted to the substrate Surface gloss, especially due to a lack of grain boundaries. The latter plays a significant role in color saturation, especially with colored toner Role.

In connection with the toner according to the invention, the ratio of Value of the elastic modulus G 'at the reference temperature value, calculated the initial temperature at the start of the glass transition of the toner plus 50 ° C the value of the elastic modulus at the initial temperature itself <1E-5, preferably may even be <1E-7, where E is the exponent based on 10.

The starting temperature of the start of the glass transition of the toner is preferred determined as the temperature value at which the tangents follow the course of the function of the elastic module G 'as a function of the temperature before and after Cut the glass transition.

The transition of the toner from its solid to its liquid state is preferred in a temperature interval or temperature window of approximately 30 ° to 50 ° K Size take place. This range should be above 60 ° C, preferably between approximately 70 ° C to 130 ° C, most preferably between 75 ° C and 125 ° C.

A further development of the method according to the invention, for those who are also more independent Protection is claimed to adapt to special conditions characterized in that at least one physical process parameter is dependent from a printing material with the energy input into the toner correlating parameters is controlled and / or regulated.

According to the invention, therefore, a simple blanket specification is not provided, but rather with advantage on the actual, preferably measured conditions coordinated regulation.

The energy input mentioned can essentially be one of the overall system correspond to the microwave power consumed from printing material and toner, so that according to the actual conditions, the delivered Performance is compared with the recorded power and coordinated. This in turn essentially corresponds to an efficiency control and / or adjustment. In particular, a regulation on the part of the Sender in the broadest sense and / or on the part of the receiving toner-printing material system or handling.

To this end, the invention preferably proposes in detail the power of the microwave transmitter to regulate and / or the speed of the movement of the substrate regulate and / or tune the resonator and / or the frequency of the microwaves to coordinate, the latter two measures preferably also to achieve a higher energy absorption directly in the toner itself, and thereby a more precise To influence its amalgamation as indirect and problematic the substrate.

The invention preferably suggests as measurable parameters for the dependent control the temperature of the substrate or that reflected by the toner-substrate system and therefore not absorbed microwave energy. Other measurable parameters can - without limitation - the weight / thickness or water content of the substrate or density and gloss of the toner layer.

As mentioned earlier in connection with US-A-5,536,921 Usually for a homogeneous heating of the printing material covered with toner at least two resonators are required for the microwaves, which are offset from one another by λ / 4 are arranged to correspond to the maxima of the standing waves in the resonators to move to each other.

A development of the invention instead provides for using only one resonator which oscillates in whole or in part. Independent protection is also claimed for such a measure.
Another development of the invention provides for the use of more than two resonators to offset them by a length of λ divided by two times the number of resonators. This results in a more uniform temperature distribution on the substrate than with an offset of λ / 4. In a preferred embodiment of the invention, four resonators are used, the spacing of which is in each case λ / 8.

In principle, all frequencies in the microwave range from 100 MHz to 100 GHz are used. Usually they become industrial, scientific or medical use approved ISM frequencies, preferably 2.45 GHz. A use of other frequencies in the mentioned wide Frequency range can, however, advantageously lead to the fact that a larger proportion of the Radiant energy is absorbed as usual by the toner and not only by the substrate becomes.

For a facility of the type mentioned above, which is in an independent solution the task is characterized in that for radiation and heating of a sharp transition from its solid to its liquid state at its Heating toner pointing at least one microwave emitting transmitter provided independent protection is claimed.

One or more operating parameters are preferably also provided in a controllable manner.

The advantages resulting according to the invention are already in context have been described with the inventive method, the local one Process parameters correspond to the operating parameters of the device.

It is preferred to use at least one resonator in the direction of movement of the printing material has a width of about 1 to about 10 cm to the Simplify handling of the substrate, but on the other hand it is sufficient Power (for example 1-10 kW per resonator) to allow without it Breakthroughs come. The width of the resonator should also be on the Speed of the substrate to be matched. It is a relative speed (for example up to 100 cm / s) in such a way that also in a kinematic reversal, the fixing device relative to the stationary printing material could move or both components. Even a stationary fixation without any movement would be conceivable.

The device according to the invention is preferred for a digital multicolor printing machine provided so that protection for such a printing press equipped is claimed within the scope of the invention.

Exemplary explanations of the method according to the invention are given below in connection with 6 figures, which constitute further inventive measures result without the invention on the illustrated examples or illustrations is restricted.

Abb. 1

den Funktionalverlauf des elastischen Moduls G' eines Toners als Funktion der Temperatur zur Definition der Anfangstemperatur des Glasübergangs des Toners,

Abb. 2

die gemessenen Funktionalverläufe gemäß Abb. 1 eines erfindungsgemäßen Toners und zweier Toner nach dem Stand der Technik zum Vergleich,

Abb. 3

eine schematische Perspektivansicht eines Ausführungsbeispiels einer erfindungsgemäßen Einrichtung zum Fixieren eines Tonerbildes,

Abb. 4

eine bevorzugte Anordnung von 4 Resonatoren einer erfindungsgemäßen Einrichtung zum Fixieren eines Tonerbildes, die jeweils um λ/8 gleichgerichtet gegeneinander versetzte Maxima stehender Mikrowellen zeigen,

Abb. 5

die Temperaturverteilung eines Papieres, auf dem nach Beispiel 2 mit einer Anordnung nach Abb.4 ein Tonerbild fixiert wurde, gemessen mit einem Zeilenpyrometer Bartec R2610 unmittelbar nach Verlassen der Resonatoren, wobei der Temperaturverlauf über die Papierbreite bei Einschalten des ersten, der ersten beiden, der ersten drei und aller vier Resonatoren bei einer Pixelgrösse, die etwa 3mm entspricht, gezeigt ist und

Abb. 6

eine weitere bevorzugte Anordnung von 4 Resonatoren einer erfindungsgemäßen Einrichtung zum Fixieren eines Tonerbildes in zwei Gruppen von jeweils zwei Resonatoren.

Show it:

Fig. 1

the functional curve of the elastic module G 'of a toner as a function of the temperature to define the initial temperature of the glass transition of the toner,

Fig. 2

the measured functional profiles according to FIG. 1 of a toner according to the invention and two toners according to the prior art for comparison,

Fig. 3

2 shows a schematic perspective view of an exemplary embodiment of a device according to the invention for fixing a toner image,

Fig. 4

1 shows a preferred arrangement of 4 resonators of a device according to the invention for fixing a toner image, each of which shows maxima of standing microwaves which are mutually offset by λ / 8,

Fig. 5

the temperature distribution of a paper on which a toner image was fixed according to Example 2 with an arrangement according to Fig. 4, measured with a Bartec R2610 line pyrometer immediately after leaving the resonators, the temperature curve over the paper width when the first, the first two, the The first three and all four resonators are shown with a pixel size that corresponds to approximately 3 mm and

Fig. 6

a further preferred arrangement of 4 resonators of a device according to the invention for fixing a toner image in two groups of two resonators each.

The G 'ratio is the ratio of the elastic modulus G' at the initial temperature of the glass transition plus 50 ° C to G 'at the initial temperature of the glass transition. The initial temperature of the glass transition is determined from the The intersection of the tangents at G 'before and after the glass transition determines and lies in the example shown at almost 70 ° C.

Fig. 2 shows the measured functional curve of G 'according to Fig. 1 for three examples Toner shown. The functional values of G 'were determined by a rheological Measurement with a Bolin rheometer, equipped with parallel plates of 40 mm Diameter determined. There was a continuous change in temperature at one Frequency of 1 rad / s corresponding to 0.16 Hz carried out between 50 ° C and 200 ° C. The strain of the measurement was chosen so that the sample did not have a shear thinning shows (Newtonian behavior).

Only the toner according to the invention shows a sharp transition from solid to liquid Condition with a final G 'value of around 1.00E-02. This results in a G 'ratio from 5.0E-08.

Example 1:

The toner according to the invention is fixed with microwaves in a structure consisting of 2 resonators, the maxima of which are shifted from one another by λ / 4 and which are each fed by a 2 kW magnetron with a frequency of 2.45 GHz. It was possible to simultaneously fix 10% and 290% toner areas on 4CC art paper, a coated paper for high-quality digital printing, with a basis weight of 130 g / m ² at a process speed of 210 mm / s. A uniform coverage of toner on paper is designated with 100%, which has an optical density of approx. 1.4 when fixed.

Example 2:

The toner according to the invention is fixed with microwaves in a structure consisting of 4 resonators, the maxima of which are shifted from one another by λ / 8 and which are each fed by a 2 kW magnetron.
The resonators are constructed so that the maxima of the following resonators are offset by λ / 8 in the same direction as the previous one (Fig.4). This ensures that the respective subsequent areas are melted one after the other on the pressure, while the toner melted in the previous resonator is still liquid. This results in a particularly even temperature distribution (Fig. 5) and no grain boundaries can be seen after the toner layer has cooled below the melting point of the toner. Another arrangement of the resonators according to Fig. 6 shows the same advantage, while the other possible arrangements show significantly worse results with regard to temperature distribution and grain boundaries.

It has been found that an independent adjustment of the individual resonators to maximum absorption does not lead to satisfactory results. The fixation result is too uneven. The absorption of the printing material in the successive resonators is rather optimized when the preceding resonators are switched on, in order to obtain a uniform fixing result. This procedure made it possible to simultaneously fix 10% and 290% toner areas on 4CC paper with a basis weight of 130 g / m ² , an uncoated paper for high quality digital printing, at a process speed of 500 mm / s. With a paper gloss of 9, measured with a gloss measuring device from Byk-Gardner Type 4520 at an angle of 60 °, a gloss of the areas exposed to toner of up to 12.3 was achieved, the greatest value being achieved with the high area coverage.

Example 3:

Analogously to Example 2, 10% - 290% toner areas were fixed on Magnostar paper, a coated paper for high-quality digital printing, with a basis weight of 300 g / m ² . With a paper gloss of 35 measured at an angle of 60 °, a gloss of the areas exposed to toner of up to 37 was achieved, the greatest value being achieved with the high surface coverage above 100%.

The other two toners from the prior art show much flatter Functional curves of G 'with G' ratios of 1.9E-03 or 2.2E-05. The fixation ratios of the toner according to the invention could with these known toners neither with fixation in a heated pair of rollers according to the prior art still implemented with microwaves analogous to Example 1 and Example 2 become.

Comparative Example 3a:

In a comparison test with toner according to the prior art and fixation in a commercially available hot roll fixation station Magnostar paper can only achieve a maximum 60 ° gloss of 30, which is clear is below the paper gloss of 35 and no satisfactory gloss impression of large ones Offers toner areas.

Fig. 3 shows schematically and only by way of example a perspective view of one possible embodiment a device according to the invention for fixing a toner image, in particular to carry out the procedure outlined above.

In Fig. 3 a section of a conveyor belt 1 is shown, on the sheets of a sheet Printing material can be placed and transported one after the other. This Conveyor belt 1 runs through a fixing device, which among other things consists of two to each other staggered resonators 2 and 3 there. The resonators instruct suitable position on an approximately 3 - 10 mm high slot 4 through which the conveyor belt and the substrate is passed through.

As indicated in Fig. 3, standing microwaves are formed in the resonators 2 and 3 5, of which field strength maxima in the plane of the conveyor belt 1 or of the printing material located thereon and thereby in particular the printing material and heat the toner image thereon so that the toner image melts and when cooled outside the resonators 2, 3 on the printing material fixed. As can be seen in Fig. 3, the resonators 2 and 3 are a quarter of the Wavelength of the microwaves 5 arranged offset to one another by a corresponding one To offset the maxima of the microwave 5 and the substrate and to heat the toner image relatively evenly. It should be noted that the following designated λ wavelength of this standing microwave 5, the course of the energy input into the substrate corresponds to only half the wavelength corresponds to the free microwave originally fed through a waveguide.

To form the microwave field, the resonators 2 and 3 are used as Lines sketched waveguide with a suitable system microwave generation 6 connected. Move the conveyor belt 1 and the printing material on it in the direction of arrow 7 through the resonators 2, 3, for example at a speed of up to one meter per second.

The scattered radiation that emerges from the passage opening of the resonators can be by building a so-called choke structure and / or by using Reduce absorbent materials outside the resonator.

Figure 4 schematically illustrates a preferred sequence of resonators 8 to 11 in a plan view of the conveyor belt 1, on which a substrate or a printing material is conveyed in the conveying direction 7.

In Fig. 4 four resonators 8 to 11 in the conveying direction 7 are exemplarily one behind the other arranged. In general, N resonators could be connected in series in this way to be ordered. In the resonators there are standing microwaves of one wavelength λ generated. The respective wave course leads to areas of different Field strength in the level of the conveyor belt 1 or the printing material in the areas of the resonators 8 to 11 indicated in Fig. 4 with framed fields and are symbolized. Of course, the field strength curve itself is continuous. In particular the areas of the respective field strength maxima are indicated in areas 12. From this it can be seen that these maximum ranges of 12 successive resonators 8 to 11 are offset from one another in the transverse direction to the conveying direction 7, specifically 4 each offset by λ / 8 to each other, which in general Case with N resonators corresponds to an offset of λ / 2N, in which in the present case N = 4.

It is clear from Fig. 5 that the staggered arrangement of the standing microwaves or the field strength profiles in the resonators 8 to 11 according to Fig. 4 with Advantage leads to a particularly uniform heating of the printing material.

In Fig. 5 there are namely temperature profiles of the substrate over the width of the substrate (broken down or measured in pixels) in ° C, at only a switched on resonator 8, with a combination of the resonators 8 + 9, at a combination of the resonators 8 + 9 + 10 and with operation of all resonators 8 + 9 + 10 + 11. The last assigned temperature profile is recognizably uniform given over the substrate width at about 100 ° C.

Fig. 6 shows another preferred arrangement option in accordance with Fig. 4 the following resonators 13 to 16 in the conveying direction. Again, the areas are the field strength maxima in the plane of the printing material designated 12.

As can be seen in Fig. 6, here the resonators 13, 14 and 15, 16 are in two successive groups with two resonators each. In general, resonators could be divided into N / 2 groups. Within each group are Field strength maxima 12 offset by λ / N from each other, i.e. here at N = 4 by λ / 4. moreover are also the field strength maxima of the resonators of the groups to one another offset, in such a way that a total of 7 field strength maxima in the conveying direction 12 each result in turn by λ / 2N, or here by λ / 8, to each other are offset. The result is a temperature curve as in Fig. 5 when all resonators 13 to 16 are switched on.

The arrangement of the resonators is not based on the rectangular arrangement shown in Fig. 3-6 limited. In the case of an arrangement inclined to the transport direction 7 of the printing material this results in a more uniform heating of the substrate, however increased space requirements.

Claims (29)

Method for fixing toner on a carrier or a printing material, in particular a sheet-shaped printing material, preferably for a digital printing machine,
characterized in that the toner-containing printing material is irradiated with microwaves from at least one microwave transmitter and is heated for melting the toner, and in that a toner is used which shows a sharp drop in the elastic module G 'from its solid to its liquid state when heated. Method according to Claim 1, characterized in that the ratio of the value of the elastic module G 'at the reference temperature value, calculated from the starting temperature at the start of the glass transition of the toner plus 50 ° C, to the value of the elastic module at the starting temperature <10 ^-5 , is preferably <10 ^-7 . Method according to one of the preceding claims, characterized in that the transition of the toner from its solid to its liquid state takes place in a temperature interval of approximately 50 ° C or less. A method according to claim 3, characterized in that said temperature interval of the change of state of the toner extends above 60 ° C, preferably in the range from about 75 ° C to about 125 ° C. Method for fixing a toner, in particular according to one of the preceding claims,
characterized in that at least one physical process parameter is controlled and / or regulated as a function of a parameter correlating with the printing substrate having energy input into the toner. Method according to Claim 5, characterized in that the power of the microwave transmitter is regulated as a function of the energy input, in such a way that the power is increased when the energy input is too low and the power is reduced when the energy input is too high, so that on average a substantially constant, to get proper energy input. A method according to claim 5, characterized in that the speed of the movement of the printing material is regulated by an area irradiated with the microwaves as a function of the energy input, in such a way that the printing material is fixed at a lower speed and when the energy input is too high Energy input of the substrate is fixed at a higher speed. Method according to Claim 5, characterized in that the microwave transmitter is tuned as a function of the energy input or is tuned with regard to the frequency of the microwaves emitted by it. Method according to claims 5 to 8, characterized in that the temperature of the printing material is taken as the parameter correlating with the energy input. Method according to one of claims 5 to 8, characterized in that the efficiency of the energy input is taken as the parameter correlating with the energy input. A method according to claim 10, characterized in that the reflected power or energy of the resonator partially or entirely containing a printing material is measured as a parameter correlating with the energy input and is compared or compared with the power emitted by the microwave transmitter. Method according to one of the preceding claims, characterized in that a resonator for the microwaves is used which partly or entirely oscillates with a movement component perpendicular to the transport direction of the printing material which is moved through the area irradiated with microwaves. Method according to one of the preceding claims, characterized in that in a microwave frequency range from 100 MHz to 100 GHz outside the released ISM frequencies, a frequency is selected at which the proportion of the absorption of microwave energy by the toner measured in relation to the total absorption in favor of a higher absorption of the Toner is selected. Method according to one of the preceding claims, characterized in that colored toner is used. Device for fixing toner on a carrier or a printing material, in particular a sheet-shaped printing material, preferably for a digital printing machine, preferably for carrying out the method according to one of the preceding claims,
characterized in that at least one microwave emitting transmitter is provided for the irradiation and heating of the strong drop of the elastic module G 'from its solid to its liquid state when it is heated. Device according to Claim 15, characterized in that at least one physical operating parameter influencing the radiation can be regulated as a function of a parameter which correlates with the energy input into the toner / printing material arrangement. Device for heating, preferably for fixing toner on a carrier or printing material, preferably according to claim 15 or 16, characterized by at least one resonator for microwaves emitted by the transmitter. Device according to claim 17, characterized in that more than one resonator is used and the maxima of the resonators are offset by the microwave length λ divided by twice the number of resonators. Device according to claim 17 or 18, characterized in that more than one resonator is used and the maxima of the following resonators are offset by microwave length λ divided by twice the number of resonators compared to the previous one. Device according to one of claims 17 to 19, characterized in that more than two resonators are used and the maxima of the following resonators are offset by λ divided by twice the number of resonators compared to the previous one. Device according to claim 20, characterized in that an even number of more than two resonators is used and the resonators in N / 2 groups of N / 2 each with λ / N, with N as the number of resonators and λ of the microwave length, against each other staggered microwave field strength maxima are divided and the groups or the resonators are mutually offset by λ / 2N. Device according to one of claims 17 to 21, characterized in that the absorption of the printing material in the following resonators can be optimized when the previous resonators are switched on. Device according to claim 17 and 22, characterized in that the resonator as a whole or a part thereof can be moved in an oscillating manner. Device according to one of claims 17 to 23, characterized in that the width of the resonator along the path of the printing material is chosen as small as possible in order to simplify the handling of the printing material and is chosen large enough to keep the electric field in the resonator below the To maintain air breakdown voltage. Device according to one of claims 17 to 24, characterized in that the width of the resonator is selected as a function of the speed of the printing material and / or the irradiated microwave power of the resonator. Device according to claim 24 or 25, characterized in that the resonator has a width of approximately 1 to approximately 10 cm. Device according to one of claims 15 to 26, characterized in that it is provided for a multi-color printing machine or is part of such a multi-color printing machine which works according to an electrophotographic printing process. Device according to one of claims 15 to 27, characterized in that measures are taken to reduce the scattered radiation. Device according to one of claims 15 to 28, characterized in that the alignment of the resonators deviates from 90 ° with respect to the paper path.

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