EP1217460A2 - Method and unit for heating a printing support and/or toner - 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 heating print media and or toner, especially for fixing toner on a print medium using a microwave transmitter.

Description

The invention relates to a method for fixing toner on a carrier or a printing material, in particular a sheet or a ribbon Printing material, preferably for a digital printing machine.

Furthermore, the invention relates to a device for heating printing material and / or toner, in particular for fixing toner on a carrier or a printing material, in particular a sheet or a ribbon Printing material, preferably for a digital printing machine, preferably for Implementation of the aforementioned procedure.

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. The image transferred to the substrate is there by heating and softening the toner and / or heating the printing material fixed. Through and during this process, toner particles combine with 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 substrate, is preferred the substrate is heated by the microwaves and the substrate in turn heats the toner on it to a temperature where the toner combines with the substrate. As is known, are characteristic when using microwaves for fixing the toner Values of the printing material used, such as weight, moisture and composition, critical and to consider.

For example, an image fixing device is known from US Pat. No. 4,511,778, which is an image made of toner using radio frequency waves, in particular Microwaves, fixed on a printing material, especially a sheet of paper. One aspect of the known device is the possibility of using the microwaves Depend on the size of the substrate to be considered this size as the characteristic value of the printing material To ensure melting and fixing of 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 specifies the operation of the facility, for example according to a consideration that a larger one piece to be heated due to its greater heat capacity overall requires more energy than a smaller piece to be heated.

Due to this blanket specification, other critical aspects remain with the Use of microwaves for fixing toner is not taken into account. So is for Example the procedure cited only for black and white printing with paper weights usable from a small range of variation, while that may different behaviors of different colored toners and different Paper weights with possibly different water content in this generalized, not coordinated with the size of the substrate is. For example, in color printing, the toner image can be four different ones Have toner layers. The maximum density is everyone Toner layer on the image carrier substrate or printing material 100%, with one maximum total density of the toner layers in the toner image of 400%. Usually the density of a single color toner image is in the range of 0% to 100% density, a colored toner image in the range from 0% to 290%.

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

In addition, when fixing conventional toner using only of microwaves may be an incomplete fusion of the toner, depending on its layer thickness, is achieved or it heats up with Blistering occurs in areas of the toner. The toner also adheres on the substrate may be insufficient because, for example, the connection with the substrate due to the high viscosity of the melted toner is not generated sufficiently. Problems can occur especially if a substrate is printed on both sides in two consecutive printing processes is printed.

Because of these potential problems, traditionally and usually not on the use of microwave radiation when fixing familiar, but in practice the toner is heated without microwave radiation and with a heated pair of rollers under pressure with the Printing material connected.

In principle, a contactless fixation is to protect the printed image desirable. Avoidance is another advantage of contactless fixation of adhesive wear and the resulting increased service life of the used Establishment, as well as better reliability of the establishment.

The invention is therefore based on the object of an adequate fixation of toner on a printing material or its preparation by using microwaves, preferably also for multi-color printing on sheet-like substrates and preferably in coordination with the prevailing special circumstances, to enable.

In terms of the method, this object is achieved according to the invention in that the printing material comprising the toner with microwaves from at least one microwave transmitter irradiated and heated for melting the toner and that a toner is used that has a sharp transition from its solid to its shows liquid state when heated.

In this way, a dry toner can be used, for example be quite right at an average temperature of around 50 ° C to 70 ° C is hard, so that it uses conventional methods to achieve a desired medium Toner size of e.g. B. 8 - 4 microns can be ground and also at development temperatures does not become sticky or melts yet, but at higher Temperature of e.g. about 90 ° C is already very low viscosity, so that if necessary. taking advantage of capillarities even without external ones Pressure and contactless on and in the printing material settles and adheres to a cold then hardens very quickly and is fixed, with one good surface gloss adapted to the printing material, especially lack trained grain boundaries. The latter also plays a role with colored toner an important role for the color saturation.

The ratio can be in connection with the toner according to the invention of the value of the elastic module G 'at the reference temperature value from the initial temperature at the start of the glass transition of the toner plus 50 ° C, to the value of the elastic modulus at the initial temperature itself <1E-5, preferably even <1E-7, where E stands for exponent based on 10 should.

The starting temperature of the start of the glass transition of the toner is preferred determined as the temperature value at which the tangents to the Functional curve of the elastic module G 'as a function of the temperature before and cut after the glass transition.

Preferably, the transition of the toner from its solid to its liquid should Condition in a temperature interval or temperature window of approximately 30 ° to 50 ° K size take place. This range should be above 60 ° C, preferably about between 70 ° C and 130 ° C, very preferably between 75 ° C and 125 ° C.

A next development of the method according to the invention, for which too independent protection is required to adapt to special Relationships characterized in that at least one physical process parameter depending on one having the energy input into the toner Printing material correlating parameters are controlled and / or regulated.

According to the invention, therefore, a simple blanket specification is not provided, but 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 invention, according to the actual circumstances, the power output compared with the power input and coordinated becomes. This essentially corresponds to an efficiency check and / or setting. In particular, a Regulation on the part of the transmitter in the broadest sense, which also serves as a microwave source can be addressed, and / or on the part of the recipient Toner-substrate system or its 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 frequency of the microwaves, the latter Measure preferably also to achieve higher energy absorption immediately to achieve in the toner itself, and thereby a more precise influence on its Merge to take as indirect and problematic on the substrate.

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

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 self-sufficient Solution to the problem is characterized in that for radiation and heating a sharp transition from its solid to its liquid state when the toner is heated, it emits at least one microwave 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, wherein the process parameter there corresponds to the operating parameter of the device.

A further development of the device according to the invention, for the more independent Protection is claimed, is characterized by at least one microwave conductor with a meandering or serpentine course.

The structure of the microwave guide according to the invention has the advantage that for application the microwave energy is a relatively long microwave conductor length Interaction length with the substrate for the continuous wave field Is made available. For this purpose, the microwave conductor is preferably made several times back and forth across the transport direction via the transport path for the substrate guided. This ensures a uniform and homogeneous heating of the substrate achieved with high efficiency.

The meandering shape can be provided in a relatively compact manner in that the meandering partial sections be moved close together. In addition, the microwave width can be reduced for a corresponding increase in the field strength. A compact design is particularly useful when printing on the printing material in perfecting and the necessary fixations of the respective toner image is desirable.

Depending on the microwave energy fed in, the field strength should be maximal 3kV / mm, preferably about 0.2 kV / mm to about 1.0 kV / mm.

With each pass through a meander section, the electric field strength E decreases due to the absorption by the printing material or the toner image. Since the absorption is not linearly dependent (~ E ² ) on the electric field strength, the decreasing field strength can be partially compensated for by a suitable successive reduction in the width of the successive meandering sections. Compensation can preferably take place additionally or instead by a suitable convergent or conical profile of the width of the microwave conductor. The goal is in any case a largely constant electric field strength over the length of the microwave conductor and in particular also within a meander section, which can also be achieved by the convergent course mentioned. In addition, these measures reduce the size of the meander in the transport or process direction.

In addition, the drop in absorption within a meandering section can be partially compensated for by the convergent course. For this purpose, the convergent geometry is designed so that a lower electric field strength prevails at the beginning of a meander section than at the end of the meander section. Since the absorption is not linearly dependent (~ E ² ) on the electric field strength E and linearly on the respective width of the microwave conductor, a suitable ratio of the microwave conductor width and electrical field strength can be found with largely constant absorption over the length of the meandering section.

The transport direction of the printing material can be perpendicular to the in both directions Extension of the meander sections take place, however, when entering and Leakage of the printing material takes the microwave power into account in a suitable manner and be regulated.

The number of meandering sections depends on the necessary absorbed Performance or on the temperature of the substrate and the homogeneity of it Heating or drying.

The device according to the invention is not only itself as a fixing device or Fuser suitable, but it could also serve as a preheater for a subsequent one Fixing device can be used with advantage. It would also be a conditioning device for conditioning substrates, especially paper, suitable. A change in the substrate can be caused by heat then take place before the start of the printing process.

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

Exemplary explanations of the invention are given below in connection with 5 illustrations, from which further inventive measures result, without the invention being restricted to the examples or illustrations explained is.

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 Draufsicht auf einen erfindungsgemäßen Mikrowellenleiter,

Abb. 4

eine Seitenansicht des Mikrowellenleiters gemäß Abb. 3 und

Abb. 5

einen zweiten mäanderförmigen Mikrowellenleiter in der Draufsicht mit einer besonders kompakten Bauform.

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 curves according to Fig. 1 of an inventive
Toner and two toners according to the prior art for comparison,

Fig. 3

2 shows a schematic top view of a microwave guide according to the invention,

Fig. 4

a side view of the microwave guide according to Fig. 3 and

Fig. 5

a second meandering microwave guide in plan view with a particularly compact design.

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 shown in Fig. 1 determined from the intersection of the tangents at G 'before and after the glass transition and is just under 70 ° C in the example shown.

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 in diameter. There was a continuous change in temperature at a frequency of 1 rad / s corresponding to 0.16 Hz between 50 ° C and 200 ° C carried out. The voltage (strain) of the measurement was chosen so that the sample shows no shear thinning (Newtonian behavior).

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

Fig. 3 schematically shows a meandering or serpentine shape in plan view extending microwave conductor 1, with one end to a system 2 for Generation of microwaves and at its other end to a system 3 is connected to the end of the microwave conductor and through the direction the arrows 4 progress microwaves. The shape of the wall is parallel to each other Meander sections 11 to 15, which are transverse to a transport direction 5 for one Extend printing stock. In Fig. 3 the meander sections each have the same width. From successive meander sections 11 to 15 can in the transport direction 5, however, opposite the subsequent meander section the previous one have a smaller width and / or it can each meander section converges or narrows in its course, about a constant electric field strength over the entire length of the microwave conductor 1 and / or the meander sections despite microwave absorption to ensure the substrate, not shown.

Fig. 4 shows a side view of the arrangement according to Fig. 3. Same components are, as in the following Fig. 5, with the same reference numbers designated as in Fig. 3.

4 shows a passage slot 6 for the printing material in the microwave guide 1 recognizable.

Fig. 5 shows a microwave guide 1 corresponding to the microwave guide 1 in Fig. 3, but in a particularly compact design with one next to the other moved meander sections 11 to 15.

Claims (22)

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. 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 a colored toner is used. Device for heating printing material and / or toner, in particular 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 13, characterized in that at least one physical operating parameter influencing the irradiation can be regulated as a function of a parameter correlating with the energy input into the toner-printing material arrangement. Device for heating printing material and / or toner, preferably according to claim 13 or 14, characterized by a microwave conductor with a meandering or serpentine course. Device according to claim 15, characterized in that the microwave guide has meandering windings or sections which extend back and forth essentially transversely to a transport direction of the printing material. Device according to claim 16, characterized in that the meandering sections are arranged compactly adjacent to one another. Device according to one of claims 13 to 17, characterized in that the microwave conductor is provided for the provision of an electric field strength of at most about 3 kV / mm, preferably from about 0.2 kV / mm to about 1.0 kV / mm. Device according to one of claims 16 to 18, characterized in that successive meander sections have a different width. Device according to claim 19, characterized in that the respective subsequent meander section has a smaller width than the previous one. Device according to claim 19 or 20, characterized in that at least one meander section narrows in its course. Device according to one of claims 13 to 21, 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.

Images