Method and device for manufacturing decorative panels

Abstract

The invention relates to a method for manufacturing decorative panels, comprising the following steps: a. preparing a surface of an engineered wood board in a preparation unit such that a prepared surface is produced; b. applying a primer to the prepared surface by means of a primer application unit such that a primed surface is produced; c. printing a decoration onto the primed surface by means of a digital printing unit such that a printed surface is produced; d. detecting actual colour measured values of the decoration and carrying out a comparison of the actual colour measured values with stored target colour measured values by means of an electrical controller; e. determining a degree of similarity from the result of the comparison; wherein the electrical controller is configured to control the preparation unit, the primer application unit and the digital printing unit and, on the basis of the comparison, to change at least one operating parameter of the preparation unit, the primer application unit and / or the digital printing unit if the degree of similarity satisfies a predetermined criterion.

Description

[0001] SWISS KRONO Tec AG Legal File: Museggstrasse 14 2459-0773 PCT-1 6004 Lucerne Date:

[0002] Switzerland, October 28, 2025

[0003] Method and apparatus for manufacturing decorative panels

[0004] The invention relates to a method for manufacturing decorative panels and a device for carrying out such a method.

[0005] Decorative panels have long been used, for example, as flooring, wall or ceiling coverings. They are also used as components in furniture production.

[0006] Decorative panels consist of a core made of a wood-based panel, such as MDF or HDF, onto whose surface a decorative finish is applied. The finish can be printed directly onto the surface of the wood-based panel, or it can be applied as printed paper, known as decorative paper, which is glued to the surface or laminated with resin. Regardless of how the finish is applied to the surface, the wood-based panel is typically coated with a resin and pressed under high pressure and temperature in a press, such as a short-cycle press. Different layers can also be applied to the underside of the wood-based panel, which faces the surface with the finish, and these are then pressed together. These processes have been known for a long time as part of the state of the art.

[0007] Especially in the production of floor panels, but also with other decorative panels, it is desirable and highly advantageous if the decorative panels do not exhibit any color differences. This is particularly relevant when panels with the same decor are produced at different times, meaning that wood-based panels are printed at different times to create the same decor. To achieve reproducibility and color fidelity, allowing decorative panels produced at different times and in different batches to be used together, various methods are known from the prior art.

[0008] For example, WO 2019 / 234147 A1 discloses a method in which a digital target image is generated from hyperspectral digital images. Hyperspectral images are images that contain information not only about visible colors, i.e., frequencies in the visible light range, but also about a higher frequency range. These target images are then compared with actual images produced from a printed sample. In the aforementioned print, the decor is not applied directly to the wood-based panel and its surface, but is printed onto decorative paper. EP 3 961 166 A1 also discloses a method in which hyperspectral measurement data of a print result are compared with reference measurement data to determine the quality of a print result.

[0009] However, a disadvantage is that this "re-sampling," i.e., checking, adjusting, and setting the various production parameters of a digital printing system, is complex and time-consuming. Furthermore, a multitude of parameters influence print quality, some of which are not parameters of the digital printing system itself. For example, temperature and humidity, the ink used, and / or the surface quality of the wood-based panel can affect the print result.

[0010] The invention is therefore based on the objective of eliminating or at least mitigating these disadvantages in the prior art.

[0011] The invention solves the stated problem by a method for producing decorative panels, comprising the following steps: a. Preparing the surface of a wood-based panel in a preparation unit, resulting in a prepared surface; b. Applying a primer to the prepared surface using a primer application unit, resulting in a primed surface; c. Printing a decorative design onto the primed surface using a digital printing unit, resulting in a printed surface; d. Acquiring actual color measurements of the decorative design and comparing these measurements with stored target color measurements using an electronic control system; e.Determining a degree of similarity from the result of the comparison, wherein the electrical control is set up to control the preparation unit, the primer application unit and the digital printing unit, and to change at least one operating parameter of the preparation unit, the primer application unit and / or the digital printing unit on the basis of the comparison, if the degree of similarity meets a predetermined criterion.

[0012] The invention is based on the understanding that many parameters and properties that are not part of the actual printing process, i.e., the application of the printing ink by the digital printing unit, influence the printing result and thus, for example, color fidelity and reproducibility. According to the invention, the electrical control is therefore not only capable of controlling the digital printing unit, as is the case in the prior art. Instead, other elements, devices, and / or workstations and machines can be controlled by the electrical control, so that the electrical control is also configured to change the operating parameters of these elements, in particular the preparation unit and the primer application unit, if the comparison between the actual color measurements and the target color measurements shows that the deviation is too large.The predetermined criterion is preferably chosen such that it is met when the degree of similarity between the actual color measurements and the target color measurements is too low, i.e., the deviation is too large. The preparation unit is used to prepare the surface of the wood-based panel for the application of the primer and the decorative layer. This can be done in several steps, preferably in several units that are part of the preparation unit.

[0013] Since the electrical control system preferably allows at least one operating parameter of the preparation unit to be changed when the degree of similarity meets the predetermined criterion, it is possible to correct and / or influence the effect of preparatory steps performed on the surface to be printed on the finished design and its color effect. This can be done, if necessary, without altering the actual printing process, which involves printing the design onto the primed surface. Of course, it is also possible, in addition to or as an alternative to the operating parameters of the preparation unit, to change operating parameters of the digital printing system if the degree of similarity meets the predetermined criterion.

[0014] According to the invention, the prepared surface is provided with a primer. Preferably, the primer application unit comprises an application roller and / or a doctor blade for applying the primer to the surface. This allows the amount of primer applied to the surface to be adjusted. The distance between the doctor blade and the surface of a wood-based panel fed through the primer application unit, and / or the speed of an application roller, and / or the amount of primer applied are operating parameters of the primer application unit that can be changed by the electrical control system when the degree of similarity meets the predetermined criterion.

[0015] Preferably, the wood-based panel with the printed surface is pressed with a synthetic resin before the actual color measurements are taken. The wood-based panel is preferably pressed with the synthetic resin in a short-cycle press. Particularly preferably, a structure is pressed into the top surface, which is especially preferably designed to correspond to the decor.

[0016] Preferably, temperature, pressure and / or pressing duration are operating parameters of the short-cycle press that can be changed by the electrical control if the degree of similarity meets the predetermined criterion.

[0017] Preferably, the synthetic resin comprises at least one additive, for example, corundum or glass beads. The at least one additive is preferably mixed into the synthetic resin or sprinkled or applied to the surface of the printed wood-based panel before, after, or during the application of the synthetic resin. Preferably, the quantity and / or distribution of the additive are operating parameters that can be varied by the electrical control system if the degree of similarity meets the predetermined criterion.

[0018] It is particularly advantageous to determine the actual color measurements only after the decorative panel is finished. While this means that the decorative panel produced in this step can no longer be altered, subsequent decorative panels can be modified during production by adjusting at least one of the aforementioned operating parameters. The decorative panel is considered finished when all work steps that could influence the decorative quality, especially the print quality and / or color quality, have been completed. This is generally the case after the wood-based panel leaves the short-cycle press in which it is pressed with the synthetic resin.

[0019] Preferably, in this case, the electrical control system is set up to control the press and, based on the comparison, to change at least one operating parameter of the press when the degree of similarity meets a predetermined standard.

[0020] Preferably, the preparation unit includes at least one grinding unit for sanding the surface, wherein the operating parameters of the preparation unit also include at least one operating parameter of the grinding unit. In the grinding unit, the surface of the wood-based panel, preferably an HDF panel, is sanded. This improves the surface's adhesion properties for a primer, such as the primer to be applied. Preferably, the grinding unit has several grinding elements, such as sanding belts or sanding brushes, which are used sequentially. For this purpose, they are preferably arranged one behind the other in such a way that the wood-based panel, which is moved along a feed direction through the preparation unit and thus also through the grinding unit, is guided successively along these grinding elements. This ensures a uniform sanding of the wood-based panel.Preferably, the surface of the wood-based panel is sanded in at least one sanding unit.

[0021] Preferably, the grinding unit has at least one sensor with which the surface roughness of the wood-based panel and / or its structure can be detected. Such a sensor can be, for example, an optical sensor, such as a camera. The operating parameters, which can be adjusted and changed by the electrical control, include, for example, the grinding speed and / or the grinding pressure of individual or all grinding elements of the grinding unit. The electrical control is preferably also configured to output a signal when, for example, a grinding element needs to be replaced because it is worn or a different grit size is required. This is also considered a change in an operating parameter.

[0022] Preferably, the preparation unit comprises at least one priming unit for priming the surface, wherein the operating parameters of the preparation unit also include at least one operating parameter of the priming unit. Preferably, the surface of the wood-based panel is primed in the priming unit with a melamine resin or another synthetic resin. Particularly preferably, the surface of the wood-based panel has been sanded beforehand using the sanding unit. The resin to be applied is preferably mixed from several components, so that, for example, the viscosity of the resin to be applied can be adjusted. The quantity and / or the viscosity of the resin to be applied are preferably operating parameters of the priming unit. Preferably, the surface of the wood-based panel is primed in the priming unit.

[0023] Preferably, the priming unit includes a resin application unit, for example, an application roller and / or a doctor blade, for applying a synthetic resin to the surface. This allows the amount of synthetic resin applied to the surface in the priming unit to be adjusted. The operating parameters of the preparation unit then also include at least one operating parameter of the resin application unit. The distance between the doctor blade and the surface of a wood-based panel passed through the resin application unit and / or the speed of an application roller are operating parameters of the resin application unit. Preferably, when priming the surface of the wood-based panel, a resin is applied to the surface of the wood-based panel in the resin application unit.

[0024] Advantageously, the priming unit includes a dryer through which the wood-based panel is passed after being primed with the synthetic resin. In the dryer, the applied primer is dried to a predetermined moisture content. The degree of drying can be adjusted, for example, by the temperature in the dryer and / or by the feed rate at which the primed wood-based panel is conveyed through the dryer. The temperature and / or the feed rate in the dryer are preferably operating parameters of the dryer and thus of the preparation unit. Preferably, the wood-based panel is dried in the dryer.

[0025] Preferably, the priming unit includes a scale. This is used to weigh the primed and preferably already dried wood-based panel, so that the amount of primer applied can be determined from the value obtained and the known area of ​​the primed surface, usually in g / m². 2The priming unit preferably comprises at least one priming applicator, and more preferably three priming applicators. This primes the surface with white paint. Preferably, each priming applicator is followed by a separate dryer, so that a wood-based panel is passed through a dryer after passing through a priming applicator. The white paint applied by the at least one priming applicator is preferably mixed from several components. This allows, for example, the viscosity to be adjusted. The operating parameters of the priming unit preferably also include at least one operating parameter of a priming applicator. A priming applicator preferably has an application roller and / or a doctor blade, with which the amount of white paint applied can be adjusted.The distance between the squeegee and the surface of a wood-based panel fed through the primer application unit, and / or the speed of an application roller, are operating parameters of the primer application unit. Preferably, white paint is applied to the surface of the wood-based panel in the primer application unit during priming.

[0026] In a particularly preferred embodiment, at least one primer application unit is provided for tinting the white paint by adding pigments. Preferably, the electrical control system is configured to control the amount of pigment added and / or the selection of pigments added. These parameters are preferably operating parameters of the primer application unit.

[0027] In a preferred embodiment of the invention, the preparation unit comprises at least one plate heater, wherein the operating parameters of the preparation unit also include at least one operating parameter of the plate heater. The plate heater preferably comprises at least one infrared emitter, which is arranged and configured to emit infrared radiation onto a surface of a wood-based panel guided through the plate heater. The plate heater is preferably arranged upstream of the priming unit in the feed direction, so that a wood-based panel passing through a device for carrying out the processes described herein is first heated by the plate heater and then primed by the priming unit. The temperature to which the wood-based panel, and in particular its surface, is heated in the plate heater is preferably an operating parameter of the plate heater.This temperature depends, for example, on the radiant power of the infrared emitters and the feed rate in the panel heater. Preferably, this radiant power and / or this feed rate are operating parameters of the panel heater and also operating parameters of the preparation unit. Preferably, the wood-based panel is heated in the panel heater.

[0028] Preferably, the preparation unit and / or the primer application unit and / or the digital printing unit includes a dryer. Preferably, the wood-based panel is dried in this dryer, wherein the operating parameters of the preparation unit and / or the operating parameters of the primer application unit and / or the operating parameters of the digital printing unit also include at least one operating parameter of the dryer.

[0029] In a preferred embodiment of the invention, at least one sensor is used that determines a plate parameter, for example, the surface roughness, the surface temperature, the surface moisture content, and / or the viscosity of an applied synthetic resin, an applied white paint, and / or a primer. The control system is configured to decide, among other things, which operating parameter is to be adjusted and in what way, based on the measured values ​​determined by the at least one sensor. Preferably, at least one sensor is located in or on each production station described herein.

[0030] Preferably, the electrical control system is configured for machine learning, using the operating parameters and actual color measurements from previous process runs to train the control system. Preferably, the sensor measurements from previous process runs are also used to train the control system. It is particularly advantageous to perform process runs with operating parameter settings that did not yield a satisfactory degree of similarity. This allows the control system to be trained on which operating parameter settings led to which deviations in the printed image and / or print and / or color quality.

[0031] The invention further solves the stated problem by means of a device for carrying out one of the methods described herein, which has an electrical control unit configured to compare actual color measurements with stored target color measurements, to determine a degree of similarity from the comparison, and to change at least one operating parameter of the preparation unit, the primer application unit, and / or the digital printing unit based on the comparison, if the degree of similarity meets a predetermined criterion. The preparation unit preferably has at least one grinding unit, at least one priming unit, and / or at least one plate heater, which are particularly preferably present in the embodiments described above.To capture the actual color measurements, the device preferably includes an optical system, for example a camera, capable of capturing and digitally storing a spectral and / or hyperspectral image of the surface decorated with the design. Systems that process this digital data, determine actual color measurements, and compare them with target color measurements are known in principle from the prior art and are abbreviated, for example, as ICMS or ACMS.

[0032] The electrical control system of the device is preferably configured to control each workstation of the device and to change its operating parameters. This preferably occurs fully automatically, without the need for a human, such as an operator, to perform error analysis or determine corrective measures. This is particularly possible if the software is a so-called AI ("artificial intelligence"), such as a neural network or similar software that has been trained with training data to not only detect deviations between the actual color measurements and the target color measurements, but also to recognize and initiate appropriate countermeasures.Countermeasures include, in particular, the modification of at least one operating parameter, whereby the electrical control system is preferably configured to decide fully automatically whether and, if so, which countermeasures are to be taken. The electrical control system also decides whether one or more countermeasures are necessary.

[0033] The training data used to teach the electronic control system preferably includes all operating parameters of the device and, more preferably, all sensor data from all sensors in the device that were recorded or configured for various runs of the manufacturing process. The training data also includes the actual color measurements recorded during each run of the manufacturing process, as well as the degrees of similarity to and deviations from the target color measurements. From this data, the electronic control system can learn which operating parameters and sensor data led to which results.

[0034] The electrical control system is provided with the set operating parameters of the device as well as the measured values ​​acquired by the device's sensors, which the electrical control system uses to determine corrective measures to be taken when the specified degree of similarity meets the predetermined criterion.

[0035] Preferably, the device has sensors that can detect the temperature of the surface of the wood-based panel after preparation, before and / or after the application of a primer, before and / or after the application of the primer and / or before or after the printing of the decor.

[0036] Preferably, the device has sensors for detecting the humidity and temperature of the room, for example, the production hall, in which the process is carried out. The various workstations of the device preferably have sensors for detecting the respective results of each workstation. In the grinding unit, this preferably includes at least one sensor for detecting the surface roughness and / or surface structure of the ground surface. In the priming unit, this preferably includes at least one sensor for detecting the whiteness of an applied primer and / or the temperature and / or humidity of the primer. Preferably, the priming unit also has a sensor configured to detect the application quantity of a resin primer and / or a color primer.A suitable sensor is preferably present in the primer application unit, so that the quantity of primer applied can be recorded.

[0037] Preferably, the preparation unit comprises at least one grinding unit, at least one plate heater and / or at least one priming unit, wherein the priming unit preferably comprises at least one resin application unit, wherein the at least one operating parameter that can be changed by the electrical control includes at least one operating parameter of the grinding unit, the plate heater, the priming unit and / or the resin application unit.

[0038] In a first specific embodiment, the device features a 4-color CRYK digital printing system, which can print four different colors (cyan, red, yellow, black). The printing width is 210 cm. Wood, stone, and fantasy decors are printed onto flat HDF cores measuring 280 cm x 207 cm. The device includes a plate loading unit, a preparation unit with a sanding unit, a priming unit with three primer application units for applying a white primer and a dryer, a primer application unit with a dryer in the feed direction upstream of the digital printing unit, a dryer in the feed direction downstream of the digital printing unit, a protective resin unit for applying a synthetic resin with an additional dryer, a plate cooling device, and a plate stacking unit.The digital printing system is designed as an indirect single-pass digital printing system, with a separate rubber transfer roller and printheads for each of the four colors CRYK (cyan, red, yellow, black), arranged in two rows. In the production of a white oak decor for a laminate floor, the coating of the raw HDF wood-based panel was carried out fully automatically without any intervention from production personnel. All production steps of the system were monitored by control devices and automatically adjusted within tolerances by the electronic control system. The color of the finished laminate flooring matches a reference color sample by 98.6% according to a similarity index, which is significantly above the tolerance of 96.0%.The data analysis revealed that the electrical control system made corrections to the application quantity of white primer during production compared to previous runs, regardless of tolerances within the white primer application device. This was because the color measurements of the final product showed that the decor was produced slightly too dark twice overall (similarity index 96.5%). This correction allowed the final product to be automatically color-matched to the reference sample and delivered to the customer without manual intervention.

[0039] In a specific second embodiment, a dark walnut decor is produced using the device defined in the first embodiment. In the first eight production runs, i.e., cycles of the process for manufacturing the decor panels, 30 g / m² was used. 2 White primer, 5 g / m² 2 Primer and 8 g / m² 2Ink applied. The similarity value to the reference sample was between 96.4% and 98.9% in all runs. For the ninth run, the electronic control system determines corrections for the production steps of white primer, primer application, and printing of the decoration. The aim is to achieve a largely unchanged color final product by optimizing the amount of white primer, primer, and printing ink applied. These corrections result in a weight of 26 g / m² instead of 30 g / m². 2 White primer, 6.5 g / m² instead of 5 g / m² 2 Primer and 6.5 instead of 8 g / m² 2 Ink is required. Color measurement of the final product yielded a similarity value of 97.9% to the reference sample. With consistent color fidelity of the final product, 4 g / m² could be automatically applied. 2 White primer and 1.5 g / m² 2 Ink can be saved, with the amount of primer reduced by 1.5 g / m². 2The price has increased. Since the ink is about three times as expensive as the primer, these corrections reduced production costs by approximately 4 cents per square meter. 2 Consumables were reduced. Since less liquid was applied to the surface of the wood-based panel, the dryer's output could also be reduced. With an annual volume of 1,000,000 m³ 2 The savings for this decor amount to €40,000.

[0040] In a specific third embodiment, a "White Oak" decor is produced using the device defined in the first two embodiments. In the initial runs of the process, the degree of similarity in the final product is always at the color tolerance limit. The main cause of this can be determined from the sensor readings. It was found that the decor was produced slightly too light compared to the reference sample. Nevertheless, the criterion for the degree of similarity was considered met, so the electronic control system determined and initiated corrective measures. The application rate of the white primer was reduced to 32 g / m². 2 to 31 g / m² 2 The degree of similarity has thus increased to 98.6% to the reference sample. The change therefore results in improved print quality and simultaneously reduced printing costs.

[0041] In a specific fourth embodiment, the device defined in the preceding embodiments was used to determine whether it influences the color quality of a laminate decor when it is processed in production facilities or when it is removed from the device after digital printing in the coating facility and processed with an overlay on a laboratory press, using the same structure as in production. The overlay is identical in both cases, and the press's operating parameters have already been optimized. The degree of similarity between the production and laboratory samples is 89.4%, with the production sample exhibiting a degree of similarity of 96.4% to the reference sample, thus meeting the requirements for sufficient quality.The reason for the discrepancy is that the gloss level of the press plate used in the laboratory no longer matches that of the press plate used in the device. Furthermore, the overlay had been exposed for six weeks and has different flow properties than the sample from production, which was processed directly. This demonstrates that many different parameters can influence print quality, and thus color quality and the reproducibility of the design, parameters that do not originate directly from the digital printing unit.

Claims

SWISS KRONO Tec AG Legal File: Museggstrasse 14 2459-0773 PCT-1 6004 Lucerne Switzerland Date: October 28, 2025 Patent claims 1. A method for manufacturing decorative panels, comprising the following steps: a. Preparing the surface of a wood-based panel in a preparation unit to create a prepared surface; b. Applying a primer to the prepared surface using a primer application unit to create a primed surface; c. Printing a decorative design onto the primed surface using a digital printing unit to create a printed surface; d. Acquiring actual color measurements of the decorative design and comparing these measurements with stored target color measurements using an electrical control system; e.Determining a degree of similarity from the result of the comparison, wherein the electrical control is set up to control the preparation unit, the primer application unit and the digital printing unit, and to change at least one operating parameter of the preparation unit, the primer application unit and / or the digital printing unit on the basis of the comparison, if the degree of similarity meets a predetermined criterion.

2. Method according to claim 1, characterized in that the wood-based panel provided with the printed surface is pressed with a synthetic resin in a short-cycle press before the actual color measurements are recorded, wherein preferably a structure is pressed into the top surface during pressing in the short-cycle press, which preferably corresponds to the decor, wherein a temperature, a pressure and / or a pressing duration an operating parameter that can be changed by the electrical control if the degree of similarity meets the predetermined criterion.

3. Method according to claim 2, characterized in that the synthetic resin comprises at least one additive, for example corundum or glass beads, and the quantity and / or distribution of the additive is an operating parameter that can be changed by the electrical control if the degree of similarity meets the predetermined criterion.

4. Method according to one of the preceding claims, characterized in that the preparation unit has at least one grinding unit for grinding the surface, wherein the operating parameters of the preparation unit also include at least one operating parameter of the grinding unit.

5. Method according to one of the preceding claims, characterized in that the preparation unit comprises at least one primer unit for priming the surface, wherein the operating parameters of the preparation unit also include at least one operating parameter of the primer unit.

6. Method according to claim 5, characterized in that the primer unit has a resin application unit for applying a synthetic resin to the surface, wherein the operating parameters of the preparation unit also include at least one operating parameter of the resin application unit.

7. Method according to one of the preceding claims, characterized in that the preparation unit has at least one plate heater for heating the wood-based panel, wherein the operating parameters of the preparation unit also include at least one operating parameter of the plate heater.

8. Method according to one of the preceding claims, characterized in that the wood-based panel is dried in a dryer, wherein the operating parameters include at least one operating parameter of the drying process.

9. Method according to one of the preceding claims, characterized in that at least one sensor is used which determines a plate parameter, for example the surface roughness, the surface temperature, the surface moisture and / or the viscosity of an applied synthetic resin, wherein the control is configured to decide, among other things, on the basis of the measured values ​​determined by the at least one sensor, which operating parameter is to be adjusted in what form.

10. Method according to claim 9, characterized in that at least one sensor is arranged in each production station.

11. Method according to one of the preceding claims, characterized in that the electrical control is set up for machine learning, wherein the operating parameters and the actual color measurement values ​​of previous method runs are used to train the electrical control.

12. Device for carrying out a method according to one of the preceding claims, characterized in that the device has an electrical control which is configured to compare actual color measurements with stored target color measurements, to determine a degree of similarity from the comparison and to change at least one operating parameter of the preparation unit, the primer application unit and / or the digital printing unit on the basis of the comparison, if the degree of similarity meets a predetermined criterion.

13. Device according to claim 12, characterized in that the preparation unit comprises at least one grinding unit, at least one plate heater and / or at least one priming unit, which preferably comprises at least one resin application unit, wherein the at least one operating parameter that can be changed by the electrical control includes at least one operating parameter of the grinding unit, the plate heater, the priming unit and / or the resin application unit.