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EP-4739504-A1 - METHOD AND DEVICE FOR PRINTING ON A FLAT WORKPIECE

EP4739504A1EP 4739504 A1EP4739504 A1EP 4739504A1EP-4739504-A1

Abstract

The invention relates to a method for printing on a flat workpiece by means of a digital printing system which has at least one ink application unit for applying printing ink, wherein the printing ink has an ink temperature when it is applied to the workpiece, wherein the workpiece is brought to a predefined workpiece temperature in a temperature control apparatus before it is supplied to the ink application unit, wherein the predefined workpiece temperature depends on the ink temperature.

Inventors

  • Dicke, Sebastian

Assignees

  • SWISS KRONO Tec AG

Dates

Publication Date
20260513
Application Date
20240704

Claims (17)

  1. 1. Method for printing a plate-shaped workpiece by means of a digital printing system which has at least one ink application unit for applying printing ink, wherein the printing ink has an ink temperature when it is applied to the workpiece, characterized in that the workpiece is brought to a predetermined workpiece temperature in a tempering device before it is fed to the ink application unit, wherein the predetermined workpiece temperature depends on the ink temperature.
  2. 2. Method according to claim 1, characterized in that the ink temperature and the predetermined workpiece temperature have a difference of at most 10 °C, preferably at most 5 °C, particularly preferably at most 2 °C.
  3. 3. Method according to claim 1 or 2, characterized in that the ink temperature is at least 20°C, preferably at least 25°C, particularly preferably at least 30°C and at most 40°C, preferably at most 38°C, particularly preferably at most 35°C.
  4. 4. Method according to one of the preceding claims, characterized in that the digital printing system has a plurality of ink application units for applying printing ink of different colors, wherein the ink temperatures of adjacent ink application units differ by at most 1.5 °C, preferably at most 1.3 °C, particularly preferably at most 1.0 °C.
  5. 5. Method according to claim 4, characterized in that the predetermined workpiece temperature depends on the ink temperature of the first ink application unit or on the average of all ink temperatures.
  6. 6. Method according to one of the preceding claims, characterized in that at least one primer is applied to the workpiece before the workpiece is fed to the tempering device, wherein preferably the workpiece is dried after the application of the at least one primer before it is fed to the tempering device.
  7. 7. Method according to one of the preceding claims, characterized in that the workpiece is cooled in the tempering device to the predetermined workpiece temperature.
  8. 8. Method according to one of the preceding claims, characterized in that the workpiece is sorted out before it is fed to the at least one paint application unit if at least one parameter measured by at least one sensor is not within a predetermined value range, wherein the workpiece is then preferably subjected to a post-treatment in order to influence the at least one parameter such that it is within the predetermined value range after the post-treatment.
  9. 9. Device for carrying out a method according to one of the preceding claims, characterized in that the device has a digital printing system with at least one ink application unit, a tempering device and an electrical control which is set up to carry out a method according to one of the preceding claims.
  10. 10. Device according to claim 9, characterized in that the device has at least one application unit for a primer and/or the digital printing system has several color application units.
  11. 11. Device according to claim 9 or 10, characterized in that the device has at least one dryer which is arranged in the process direction behind at least one ink application unit of the digital printing system.
  12. 12. Device according to claim 11, characterized in that the device has a dryer for each paint application unit and/or for each application unit for a primer, wherein each dryer is arranged behind the respective application unit in the process direction.
  13. 13. Device according to one of claims 9 to 12, characterized in that the tempering device has at least one temperature sensor for determining a current workpiece temperature of the workpiece, which is configured to transmit sensor data to the electrical control.
  14. 14. Device according to one of claims 9 to 13, characterized in that the tempering device has at least one tempering element, preferably at least one heating element and/or at least one cooling element, by means of which the current workpiece temperature of the workpiece can be influenced.
  15. 15. Device according to claim 14, characterized in that at least one tempering element is designed to influence the current workpiece temperature of the workpiece in a spatially resolved manner.
  16. 16. Device according to one of claims 9 to 15, characterized in that the predetermined workpiece temperature prevails within the tempering device and the electrical control is set up to guide the workpiece from the tempering device to the at least one paint application unit only when a difference between the current workpiece temperature and the predetermined workpiece temperature is smaller than a predetermined limit value.
  17. 17. Device according to one of claims 9 to 16, characterized in that the device has a sorting device to sort out a workpiece before it is fed to the at least one paint application unit.

Description

Method and device for printing a plate-shaped workpiece The invention relates to a method for printing a plate-shaped workpiece by means of a digital printing system which has at least one ink application unit for applying printing ink, wherein the printing ink has an ink temperature when it is applied to the workpiece. The invention also relates to a device for carrying out such a method. Printing on a panel-shaped workpiece is now standard technology for many applications and is used, for example, in the manufacture of floor panels, furniture components or worktops. Wood, stone or fantasy decors are printed on panel-shaped cores, which contain a wood-based panel, for example. The digital printing systems used for this often contain primer components to prime the panel cores to be printed in white, possibly in several steps. Each individual primer layer applied is dried in the process, i.e. inline, without stopping the panels on their conveyor belts. This requires a lot of heat energy, which is introduced into the process and thus into the digital printing system. The cores to be printed reach temperatures of more than 70 °C and are often fed to the paint application unit at a temperature of, for example, 55 °C. This has several disadvantages. The warm panels, which are often coated with several layers of primer, introduce a large amount of liquid and moisture into the digital printing system. In addition, it is known from EP 2 927 003 A1, for example, that the temperature of the workpiece to be printed has a significant influence on the printing result. It influences the viscosity of the applied ink droplets and thus the optical impression of the decoration produced, for example the color saturation and the sharpness of the image produced. In order to at least ensure the reproducibility of the printing result, EP 2 927 003 A1 proposes heating or cooling the surface to be printed to a temperature within a predetermined range. Printing on paper presents further difficulties, as the moisture introduced by the warm workpiece influences the surface properties, such as the waviness, of a printing paper to a much greater extent than would be the case with a solid workpiece, such as a wood-based panel. It is therefore known from EP 2 206 605 B2 to create different climate zones with different room humidity in which different parts of the actual printing process take place. This results in a high level of equipment expenditure and a high energy requirement, which makes the process complicated and costly. The invention is therefore based on the object of proposing a method and a device with which the disadvantages of the prior art are at least mitigated and, at best, overcome. The invention solves the problem by a method according to the preamble of claim 1, which is characterized in that the workpiece is brought to a predetermined workpiece temperature in a tempering device before it is fed to the ink application unit, wherein the predetermined workpiece temperature depends on the ink temperature. The invention is based on the finding that there is no absolute workpiece temperature that always delivers the optimal printing result regardless of other parameters. Rather, the predetermined workpiece temperature depends on the temperature of the ink used. In general, it has been shown that a higher ink temperature also results in a higher predetermined workpiece temperature. The digital printing system used preferably has an electrical control system, for example an electronic data processing device, which is set up to process sensor data, for example from temperature sensors. Such a temperature sensor, which can also be part of the digital printing system, is used, for example, to measure the temperature of the used Printing ink. The measured values recorded by the sensor are passed on to the electrical control system, which calculates a predetermined workpiece temperature from them. At least one other temperature sensor, which can also be part of the digital printing system, is used to determine the current workpiece temperature, i.e. the actual value of the workpiece temperature. This measured value is also passed on to the electrical control system, which compares the current workpiece temperature determined in this way with the predetermined workpiece temperature and is set up to control the tempering device so that the current workpiece temperature is adjusted to the predetermined workpiece temperature. The tempering device preferably has at least one heating element to increase the current workpiece temperature and/or at least one cooling element to reduce the current workpiece temperature. The electrical control is designed to control these elements depending on the measured values of the sensors. Preferably, the ink temperature and the predetermined workpiece temperature have a difference of at most 10 °C, preferably at most 5 °C, particularly preferably at most 2 °C. Preferably, the ink temperature is at l