PRINTING PRESS HAVING AN INFRARED DRYER UNIT

Abstract

Printing machines are fitted with a printer assembly for application of solvent-containing printing ink onto a printing substrate. A transport device transports the printing substrate from the printer assembly to a dryer unit that has at least one infrared radiator for drying the printing substrate. The dryer unit is improved in terms of homogeneity and rapidity of the drying of solvent-containing printing ink, and in that no active cooling of the infrared radiator is required. The infrared radiator is a planar heating element made of a dielectric, emits infrared radiation when heated, and comprises a heating surface that faces the printing substrate to be dried. The infrared radiator has a contacting surface, onto which a printed conductor of a heating conductor made of an electrically conductive precious metal-containing resistor material is applied, that is connected to an adjustable current source by an electrical contact.

Claims

1. A printing machine comprising: a printing assembly adapted to apply a solvent-containing printing ink onto a printing substrate; a dryer unit having at least one infrared radiator for drying the printing substrate, wherein the infrared radiator is a planar heating element made of a dielectric, emits infrared radiation when heated, and has a heating surface that faces the printing substrate to be dried and a contacting surface onto which a printed conductor of a heating conductor made of an electrically conductive precious metal-containing resistor material is applied that is adapted to be connected to an adjustable current source by an electrical contact; and a transport device for transporting the printing substrate from the printer assembly to the dryer in a transport direction.

2. The printing machine according to claim 1, wherein the heating element is plate-shaped and has a plate thickness of less than 10 mm.

3. The printing machine according to claim 1, wherein the transport device defines a maximum format width for transporting the printing substrate, and the heating element irradiates across the entire format width and includes multiple heating element portions that can be electrically controlled independent of each other.

4. The printing machine according to claim 1, wherein the heating element includes an amorphous matrix component and an additional component in the form of a semiconductor material.

5. The printing machine according to claim 1, wherein the dryer unit has a plurality of heating elements that are arranged one behind the other in the transport direction of the printing substrate and that define an intervening space between the printing substrate and the heating elements.

6. The printing machine according to claim 5, further comprising a device for supplying process air into the intervening space between the printing substrate and the heating elements.

7. The printing machine according to claim 1, further comprising at least one draw roller fitted with a drive motor rearranged downstream from the dryer unit as seen in the transport direction of the printing substrate and wherein the printer assembly includes an inkjet print head.

8. The printing machine according to claim 7, wherein the at least one draw roller is a cooling roller.

9. The printing machine according to claim 1, wherein the heating element attains a power density in excess of 180 kW/m.sup.2.

10. The printing machine according to claim 9, wherein the heating element attains a power density in the range of between 180 kW/m.sup.2 to 265 kW/m.sup.2.

11. A printing machine comprising: a printer assembly adapted to apply a solvent-containing printing ink onto a printing substrate; a dryer unit having at least one infrared radiator for drying the printing substrate, wherein the infrared radiator is a planar dielectric heating element with a plate thickness of less than 10 mm formed of an amorphous matrix component and a semiconductor material, emits infrared radiation when heated, and has a heating surface that faces the printing substrate to be dried and a contacting surface onto which a printed conductor of a heating conductor made of an electrically conductive precious metal-containing resistor material is applied that is adapted to be connected to an adjustable current source by an electrical contact; and a transport device for transporting the printing substrate from the printer assembly to the dryer unit in a transport direction.

12. The printing machine according to claim 11 wherein the transport device defines a maximum format width for transporting the printing substrate, and the heating element irradiates across the entire format width and includes multiple heating element portions that can be electrically controlled independent of each other.

13. The printing machine according to claim 11, wherein the dryer unit has a plurality of heating elements that are arranged one behind the other in the transport direction of the printing substrate and that define an intervening space between the printing substrate and the heating elements.

14. The printing machine according to claim 13, further comprising a device for supplying process air into the intervening space between the printing substrate and the heating elements.

15. The printing machine according to claim 11, further comprising at least one draw roller fitted with a drive motor arranged downstream from the dryer unit as seen in the transport direction of the printing substrate.

16. The printing machine according to claim 15, wherein the at least one draw roller is a cooling roller.

17. The printing machine according to claim 11, wherein the printer assembly includes an inkjet print head.

18. The printing machine according to claim 11, wherein the heating element attains a power density in excess of 180 kW/m.sup.2.

19. The printing machine according to claim 18, wherein the heating element attains a power density in the range of between 180 kW/m.sup.2 to 265 kW/m.sup.2.

20. A printing machine comprising: a printer assembly including an inkjet print head and being adapted to apply a solvent-containing printing ink onto a printing substrate; a dryer unit having at least one infrared radiator for drying the printing substrate, wherein the infrared radiator (a) is a planar dielectric heating element that attains a power density in excess of 180 kW/m.sup.2 with a plate thickness of less than 10 mm formed of an amorphous matrix component and a semiconductor material and with multiple heating element portions that can be electrically controlled independent of each other and that define an intervening space between the printing substrate and the heating element, (b) emits infrared radiation when heated, and (c) has a heating surface that faces the printing substrate to be dried and a contacting surface onto which a printed conductor of a heating conductor made of an electrically conductive precious metal-containing resistor material is applied that is adapted to be connected to an adjustable current source by an electrical contact; a device for supplying process air into the intervening space between the printing substrate and the heating element; a transport device for transporting the printing substrate from the printer assembly to the dryer unit in a transport direction, the transport device defining a maximum format and the heating element irradiating across the entire format width; and at least one draw roller fitted with a drive motor arranged downstream from the dryer unit as seen in the transport direction of the printing substrate.

Description

BRIEF DESCRIPTION OF THE DRAWING

[0048] In the following, the invention is illustrated in more detail based on an exemplary embodiment and a patent drawing. In the drawing are the following figures:

[0049] FIG. 1 shows a schematic depiction of a detail of a printing machine according to the invention with the transport path for the printing substrate through a printer assembly and an infrared dryer unit;

[0050] FIG. 2 shows a schematic depiction and a side view of an embodiment of the heating element according to the invention with a reflector layer;

[0051] FIG. 3 shows a diagram of the start-up behavior of a heating element of the dryer unit;

[0052] FIG. 4 shows a diagram of emission spectra of a tile-shaped heating element compared to a conventional infrared radiator with a quartz glass cladding tube and Kanthal coil;

[0053] FIG. 5 shows a diagram illustrating the irradiation profile of the infrared radiation that is incident on the printing substrate during the use of the printing machine according to the invention; and

[0054] FIG. 6 shows, by way of two diagrams (a) and (b), a comparison of the homogeneity and intensity of the irradiation of a printing substrate by a tile-shaped heating element versus an infrared panel-type radiator according to the prior art.

DETAILED DESCRIPTION OF THE INVENTION

[0055] Referring now to the drawing, in which like reference numbers refer to like elements throughout the various figures that comprise the drawing, FIG. 1 shows a schematic depiction of an embodiment of a printing machine according to the invention in the form of a roller inkjet printing machine, which, in toto, has reference number 1 assigned to it. Starting from an unwinder 2, a material web 3 made of a printing substrate, such as, for example, paper, advances to a printer assembly 40. The printer assembly 40 comprises multiple inkjet print heads 4 arranged one after the other along the material web 3 by which solvent-containing, and, in particular, water-containing printing inks are applied onto the printing substrate.

[0056] Viewed in the transport direction 5, the material web 3 advances from the printer assembly 40 via a deflecting roller 6 to an infrared dryer unit 70. The latter is configured to have multiple infrared heating elements 7 that are designed for drying and/or sweeping away the solvent in the material web 3.

[0057] The further transport path of the material web 3 is via a draw roller 8, which is fitted with its own draw drive motor and is used for setting the web tension, to a winding roller 9.

[0058] Several heating elements 7eight of them in the exemplary embodiment shownare combined into a heating block that extends over the maximum format width of the printing machine 1. The individual heating elements 7 in the heating block are placed against each other without clearance, and can be controlled separately from each other in accordance with the dimensions and ink coverage of the printing substrate. An electrical and thermal insulator is situated between the individual heating elements 7. The free distance between the heating surface of the heating elements 7 and the top side of the material web 3 is 10 mm.

[0059] The transport speed of the material web 3 is set to 5 m/s. This is a comparably high speed that is made possible through an optimization of the individual processing steps and requires, in particular, a high drying rate. The dryer unit 70 required for meeting that requirement is explained in more detail in the following based on FIGS. 2 to 5.

[0060] Insofar as the same reference numbers as in FIG. 1 are used in other figures, these denote components and parts that are identical in design or equivalent as illustrated in more detail above by the description of the printing machine 1 according to the invention.

Heating Element

[0061] The embodiment of the heating element 7 shown schematically in FIG. 2 is an infrared radiator with a tile-shaped base body 20 with a planar emission surface (bottom side 26) and an also planar top side 25. A printed conductor 23, which in turn is embedded in a reflector layer 24, is applied onto the top side 25 of the base body 20.

[0062] The base body 20 has a rectangular shape with a plate thickness of 2.0 mm and lateral dimensions of 10 cm20 cm. It consists of a composite material with a matrix made of quartz glass, in which phase areas of elemental silicon are homogeneously distributed. The weight fraction of the Si phase is 2.5% and the maximum mean dimensions of the Si phase areas (median) are in the range of approximately 1 to 10 m. The composite material is gas-tight, it has a density of 2.19 g/cm.sup.3, and it is stable in air up to a temperature of approximately 1,200 C. It shows high absorption of heat radiation and high emissivity at high temperature.

[0063] The printed conductor 23 is generated from a platinum resistor paste on the top side 25 of the base body 20. Both ends have cables or clamps for the supply of electrical energy welded to them. The printed conductor 23 shows a meandering profile that covers a heating surface of the base body 20 so tightly that an even distance of 2 mm remains between neighboring sections of the printed conductor 23. In the cross-section shown, the printed conductor 23 has a rectangular profile with a width of 1 mm and a thickness of 20 m. Due to the low thickness, the fraction of material accounted for by the expensive printed conductor material (platinum) in the infrared radiator is low compared to the efficiency thereof. The printed conductor 23 is in direct contact with the top side 25 of the base body 20 such that maximally possible heat transmission into the base body 20 is attained. The opposite bottom side 26 serves for the use of the infrared radiator as an emission surface for the heat radiation. The direction of emission is indicated by direction arrow 27.

[0064] The reflector layer 24 consists of opaque quartz glass and has a mean layer thickness between 1.0-1.5 mm. It is characterized by the absence of cracks and a high density of approximately 2.15 g/cm.sup.3 and it is thermally stable up to temperatures above 1,100 C. The reflector layer 24 covers the entire heating area of the base body 20 and it covers the printed conductor 23 completely and thus shields it from ambient chemical or mechanical influences.

Measurement of the Start-Up Behavior

[0065] The dryer unit 70 having a rapid reaction time after the printing machine 1 is switched on is a requirement for low paper wastage during the printing process. The diagram of FIG. 3 shows the temperature profile over time after the heating element 7 described based on FIG. 2 is switched on. A temperature T.sub.ref (in %), standardized to a maximum temperature that is reached in operation with maximum electrical connected load, is plotted on the Y axis against the switch-on time t in seconds plotted on the X axis. In this context, T.sub.ref is measured at a distance of 5 mm from the heating surface using a thermopile measuring sensor.

[0066] Upon the application of the maximum electrical connected load of up to 200 kW/m.sup.2 to the printed conductor 23, the maximum temperature is reached after a short time as compared to conventional medium-wave infrared radiators and stays essentially constant during the further heating process. The reaction time being short as compared to conventional medium-wave infrared radiators reduces the paper wastage. Moreover, the printing machine 1 according to the invention does not require the implementation of an air cooling for the heating elements 7. This increases the process efficiency, because cold cooling air reduces the temperature of the printing substrate and impedes the dissipation of humidity. The combination of heating elements 7 without cooling and warm convective process air for humidity transport optimizes the printing process in modern high-performance printing machines.

Measurement of the Emissivity

[0067] The composite material shows high absorption of heat radiation and high emissivity at high temperature. At room temperature, the emissivity of the composite material is measured using an integrating sphere. This can be used to measure the spectral hemispherical reflectance R.sub.gh and the spectral hemispherical transmittance T.sub.gh from which the normal emissivity can be calculated. The emissivity at elevated temperature is measured in the wavelength range from 2 to 18 m by an FTIR spectrometer (Bruker IFS 66vFTIR) to which a BBC sample chamber is coupled using an additional optical system, applying the above-mentioned BBC measuring principle. In this context, the sample chamber is provided with thermostatic black body environments in the hemispheres in front of and behind the sample holder, and with a beam exit opening with a detector. The measuring samples with a thickness of 2 mm are heated to a predetermined temperature in a separate furnace and, for the measurement, are transferred into the beam path of the sample chamber with the black body environments set to the predetermined temperature. The intensity detected by the detector is composed of emission, reflection, and transmission portions, namely intensity emitted by the sample itself, intensity that is incident on the sample from the front hemisphere and is reflected by the sample, and intensity that is incident on the sample from the back hemisphere and is transmitted by the sample. Three measurements need to be performed to determine the individual parameters, i.e., the degrees of emission, reflection, and transmission.

[0068] The degree of emission measured on the composite material in the wavelength range from 2 to approximately 4 m is a function of the temperature. The higher the temperature, the higher is the emission. At 600 C., the normal degree of emission in the wavelength range from 2 to 4 m is above 0.7. At 1,000 C., the normal degree of emission in the entire wavelength range between 2 and 8 m is above 0.8.

[0069] FIG. 4 shows the emission spectrum of the heating element 7 (curve A) as compared to the emission spectrum of a conventional infrared radiator with a quartz glass cladding tube and heating coil made of Kanthal (curve B) at identical power. The emitted power P.sub.rel (value in % relative to the maximum value) is plotted on the left Y axis and the wavelength (in nm) is plotted on the X axis. In addition, the transmission spectrum of water is included in the diagram (curve C), whereby a relative parameter T.sub.H2O is plotted on the right Y axis.

[0070] The temperature of the printed conductor 23 on the base body 20 is adjusted to 1,000 C. The reference radiator possessing a Kanthal coil is also operated at a temperature of approximately 1,000 C. It is evident that the tile-shaped heating element 7 possesses an emission peak in the wavelength range from 1,500 nm to approximately 2,000 nm that matches the transmission peak of water at 2,750 nm better than the emission profile of the standard radiator. At identical electrical power and identical distance, this results in an approximately 25% higher power density on the printing substrate as compared to the standard infrared radiator.

Measurement of the Spatial Homogeneity of the Emitted Radiation

[0071] The spatial homogeneity of the emitted radiation is tested in accordance with IEC 62798 (2014). For this purpose, the infrared panel radiator is installed in a testing device and mounted on a movable table. The optical power is detected by a thermoelectric detector at a predetermined working distance of 10 mm from the emission surface of the infrared radiator. The irradiation intensity is determined at several measuring sites at steps of 5 mm. The radiation intensity is defined to be sufficiently homogeneous if it varies by no more than +/5% from the measured maximum value at 10 measuring sites near the middle of the sample. This type of measurement is referred to as an axial measurement hereinafter.

[0072] The diagram of FIG. 5 illustrates the result of axial measurements using the tile-shaped heating element 7. A standardized optical power L (in %) is plotted on the Y axis, and the lateral distance A (in mm) from a center line that extends through the origin of the axes and relates to the lateral dimension of the heating element 7 is plotted on the X axis.

[0073] The lateral profile of the optical power is measured at a working distance of 10 mm. The lateral profile is comparably homogeneous at near 100% over an extended area about the center line. This is evident because the optical power does not drop below 95% of the maximum value (100%) in a working area with more than 10 measuring points about the center line.

[0074] Diagrams (a) and (b) of FIG. 6 illustrate, schematically, the relationship between the homogeneity and/or the intensity of irradiation and the distance between the radiator and the printing substrate as well as pertinent differences between an infrared panel radiator composed of several individual radiators (diagram (a)) and the tile-shaped heating element 7 for use in the printing machine 1 according to the invention (diagram (b)). The homogeneity H and the radiation intensity I incident on the heating goods are plotted, respectively, in relative units, on the ordinate of diagrams (a) and (b) over the distance A (also in relative units) between the radiator and the printing substrate. The panel radiator 71 in diagram (a) is represented by multiple medium- or short-wave radiant heaters that are arranged next to each other and whose cladding tubes are indicated by three circles. The tile-shaped heating element 7 of the printing machine 1 according to the invention is indicated in diagram (b). The tile-shaped heating element 7 and the planar arrangement of the carbon radiators forming the panel radiator 71 have the same electrical connected load in this context.

[0075] The profile of the homogeneity H over distance A is indicated by the dashed curve H and the profile of the intensity I is indicated by the continuous curve I. Accordingly, the irradiation intensity I decreases with the distance A approximately to the same degree in the standard panel radiator 71 and in the tile-shaped heating element 7, but the homogeneity of the irradiation is largely independent of the distance A in the case of the heating element 7, whereas it is low, at short distance, in the standard infrared panel radiator 71.

[0076] The grey-hatched area schematically defines a working area, in which an acceptable irradiation homogeneity on the printing substrate is evident. It is evident then that this homogeneity can be attained in the standard infrared panel radiator 71 by maintaining a certain distance, but that this is associated with a significant loss of irradiation intensity. In contrast, the tile-shaped heating element 7 facilitates sufficiently high homogeneity even at very short distances, at which the intensity of the radiation is high as well. Accordingly, the heating element 7 has a significantly improved efficiency as compared to the panel radiator 71 made of individual carbon radiators.

[0077] Although illustrated and described above with reference to certain specific embodiments and examples, the present disclosure is nevertheless not intended to be limited to the details shown. Rather, various modifications may be made in the details within the scope and range of equivalents of the claims and without departing from the spirit of the disclosure. It is expressly intended, for example, that all ranges broadly recited in this document include within their scope all narrower ranges which fall within the broader ranges.