Method and apparatus for printing decorative surfaces on workpieces.

Abstract

This invention relates to a method for printing a decorative workpiece surface using a digital printing system, wherein the printing system has at least one coating tool for applying liquid to the workpiece and at least one drying unit for drying the workpiece, wherein the method includes the following steps: a. providing information about the expected humidity of the workpiece to be dried in an electronic controller of the printing system; b. determining drying parameters based on the provided information, through which the at least one drying unit can be operated; and c. drying the workpiece by means of the at least one drying unit based on the determined drying parameters.

Description

Technical Field

[0001] This invention relates to a method for printing a decorative surface of a workpiece using a digital printing system, wherein the printing system has at least one coating tool for applying liquid to the workpiece and at least one drying unit for drying the workpiece. The invention also relates to a digital printing system for performing this method. Background Technology

[0002] Digital printing systems with coating tools and drying units have long been known in the prior art. They are used for printing entirely different workpieces. For example, a corresponding system for printing on the surface of a non-absorbent substrate is known from WO 2020 / 078606 A1. The surface tension of this substrate surface must first be altered so that it can be fully wetted, for example, by a water-based ink. After the ink is applied, the applied liquid layer, i.e., the decoration, is intensely heated within one second using a drying unit, ensuring rapid evaporation of the solvent contained in the liquid. This fixes the applied ink and improves the printed image.

[0003] On the other hand, EP 2 927 003 B1 describes a method for changing the surface temperature of a workpiece using a drying unit. The method described here is based on the knowledge that the solvent contained in the applied ink evaporates more quickly on the hot surface of the workpiece, thus rapidly increasing the ink viscosity. Consequently, when color dots are applied in digital printing, the color dots are difficult to diffuse and may diffuse too little. Conversely, if the workpiece surface is cold, the solvent evaporates only slowly, and the ink viscosity remains low for a long time, allowing the color dots to diffuse easily and potentially excessively. By using a drying unit, the surface temperature of the workpiece to be printed can be adjusted to the desired value.

[0004] When printing, for example, paper pulp using a digital printing system, drying by means of at least one drying unit is also very important. If the workpiece is wetted (e.g., printed) with liquid in a coating tool, the moisture content of the printed surface has a significant impact on whether the applied liquid penetrates the surface or how far it spreads across the surface. The evaporation and degassing of the solvent also strongly depend on the moisture content of the printed or wetted surface.

[0005] Humidity itself depends on various parameters. For example, the humidity of the workpiece to be printed, such as the humidity of the base paper. This is affected by hygroscopicity during storage, such as the temperature and humidity of the room where the base paper is stored. Furthermore, the amount of primer, optional multi-color embellishments, or sealant applied can affect the humidity of the workpiece and its upper and surface surfaces. However, this affects not only the printed image but also the movement of the paper core. The paper core to be printed is typically guided in a digital printing system by multiple guide rollers, which, on the one hand, transport the paper core through the printing system, and on the other hand, ensure the paper core has the smoothest possible structure. Paper core tension must be maintained and adjusted so that, on the one hand, the paper core is transported without tearing, and on the other hand, the paper core rests against the corresponding roller as smoothly and completely as possible, i.e., without forming wrinkles, and in particular, can be guided along at least one coating tool.

[0006] A primer is a layer on which colored printing dots are applied to form the corresponding decoration. This layer can also be called a base coat (Grundierung). This layer does not have a base color, such as white, to compensate for color irregularities on the surface of the workpiece to be printed and to provide reproducible and predictable basic conditions for the printing of the decoration. Alternatively or additionally, this layer is designed as a color-receiving layer and does not change, or only changes, the optical appearance of the surface, such as its color, but rather its ability to absorb color.

[0007] Currently, the drying unit, and any existing air ducts and guide rollers, are manually adjusted by the printing system operator based on their experience to optimize the process as much as possible and minimize waste. This is achieved by adjusting the drying capacity, the conveying speed of the workpiece within the system, and the roller tension via a control panel. This, in turn, controls the paper moisture content and paper fiber guidance.

[0008] The downside is that it requires experienced operators whose experience can be leveraged, and the above cannot be performed in a repeatable and predictable manner. Summary of the Invention

[0009] Therefore, the purpose of this invention is to overcome or at least alleviate the disadvantages of the prior art.

[0010] The present invention achieves the above objective by means of a method for printing on the surface of a decorated workpiece using a digital printing system, wherein the printing system has at least one coating tool for applying liquid to the workpiece and at least one drying unit for drying the workpiece, and wherein the method includes the following steps:

[0011] a. Provide information on the expected humidity of at least one workpiece to be dried in the electronic controller of the printing system.

[0012] b. Based on the provided information, determine the drying parameters, which enable the operation of the at least one drying device.

[0013] c. Based on the determined drying parameters, the workpiece is dried using the at least one drying unit.

[0014] The method according to the invention allows for automated and reproducible printing on workpiece surfaces. Even large quantities of workpieces can be produced in the same or at least nearly identical manner, with minimal waste. First, information regarding the expected humidity of the workpiece to be dried is provided to an electronic controller (e.g., an electronic data processing device). Then, the electronic controller determines drying parameters, specifically, control parameters for the drying unit. These drying parameters include, for example, dryer power, dryer temperature, transport speed of the workpiece moving through the drying unit, and / or dryer type. The dryer type parameter is particularly advantageous if the drying unit has different dryers available for use as needed. Using the drying parameters determined in this way, the drying unit is operated to dry the corresponding workpiece.

[0015] Preferably, providing information includes the following steps:

[0016] a1. The humidity of the workpiece surface is measured using at least one humidity sensor.

[0017] a2. The measured humidity is provided in the electronic controller.

[0018] The apparatus for performing this method has at least one humidity sensor configured to measure the humidity of the surface of the workpiece. The at least one sensor is also configured to transmit its determined measurement to an electronic data processing device or another type of electronic controller. The measurement allows conclusions to be drawn about the actual humidity of the workpiece surface to be dried and is provided in the electronic controller as information about the expected humidity. Preferably, the humidity is determined as close as possible to the drying unit before it is dried, such that the measurement accurately describes the humidity of the workpiece upon entering the drying unit. On the other hand, the transport speed at which the workpiece is conveyed to the drying unit and the distance between the measurement location and the start of drying must be coordinated so that the electronic controller, particularly the electronic data processing device, has sufficient time to determine the drying parameters before the workpiece is fed into the dryer. This distance depends on both the transport speed and the speed of the measurement data and the data processing device.

[0019] Preferably, humidity is determined by infrared (IR), near-infrared (NIR), or microwave measurement methods and / or L-value determination. Of course, combinations of different methods are also possible and potentially advantageous. The choice of practical method depends particularly on the information needed to determine the drying parameters as optimally as possible. Therefore, it may be advantageous to measure humidity only in the narrowest possible area on the surface (e.g., to a depth of 1 mm). In other methods, it is advantageous to measure humidity even in deeper layers (e.g., to a depth of 3 mm or 5 mm), rather than just on the surface of the workpiece. If the workpiece to be printed is, for example, paper pulp or pre-cut decorative paper, it is preferable to measure to a depth of a few hundredths to a few tenths of a millimeter, for example, from 0.01 mm to 0.5 mm.

[0020] In a preferred embodiment, the expected humidity is calculated. This is preferably based on information about the amount of at least one liquid applied to the workpiece before drying, particularly the temperature of at least one of the workpiece, the surrounding environment, and / or the applied liquid, preferably a time-temperature profile, and / or the humidity of the workpiece. If at least one liquid has been applied to the workpiece before drying, this naturally has a significant impact on the humidity, particularly on the upper side and surface of the workpiece. The applied liquid can be, for example, a primer, adhesive, ink, or protective layer. The temperature of the workpiece, the surrounding environment, and / or the applied liquid affects how much humidity the workpiece can absorb and / or how much humidity penetrates into the workpiece.

[0021] Preferably, the information provided regarding the expected humidity and the determined drying parameters are functions of the location on the surface of the workpiece. In other words, both the expected humidity and the drying parameters depend on the location. This is particularly advantageous if, for example, the expected humidity is unevenly distributed on the surface of the workpiece. This may happen, for example, if printing ink is applied with different intensities, because, for example, some areas of the workpiece surface are printed more intensely, and therefore more ink is printed than in other areas. Using different inks, such as inks for different colors, will also result in different amounts of humidity being applied to the surface of the workpiece and / or penetrating into the upper part of the workpiece.

[0022] Applying primer with varying intensities to different locations on the upper surface of a workpiece can also lead to uneven humidity. This can occur, for example, when primer is needed to compensate for color fluctuations (such as the turbidity of the workpiece to be printed, like paper pulp), which are typically detected and evaluated beforehand using a camera. In this case, it makes sense to apply more primer to the darker areas on the upper surface of the workpiece compared to the lighter areas. This results not only in applying different amounts of primer but also different levels of humidity.

[0023] Advantageously, at least one drying unit is provided to dry different areas of the workpiece surface with varying intensities. This allows for a response to varying amounts of humidity in different areas of the workpiece surface and produces uniform humidity. The drying unit may, for example, have multiple dryer modules, such as three, five, or seven dryer modules, arranged to dry different areas of the workpiece. They may, for example, be arranged side-by-side in a direction perpendicular to the direction of transport of the workpiece through the printing system. However, this arrangement not only allows for the transformation of a generally non-uniform humidity distribution on the workpiece surface before the drying unit into uniform humidity, but also allows for the targeted generation of non-uniform humidity on the workpiece surface, which may be advantageous. As previously mentioned, the humidity of the workpiece surface affects, for example, the behavior of inks or other coating liquids on the surface. This can also present different requirements at different locations, thus non-uniform humidity is beneficial.

[0024] This "target humidity distribution" (also referred to as target humidity) is preferably stored in an electronic data storage device, which can be accessed by the electronic controller of the printing system, particularly the electronic data processing equipment. These target humidity values ​​are preferably taken into account when determining the dryer parameters.

[0025] In a preferred embodiment of the method, the workpiece is dried multiple times, advantageously in different drying units. Before each drying, steps a and b of the method are preferably performed to provide information about the expected humidity and determine drying parameters for the drying unit. This data is transmitted to the drying unit so that the drying unit can be operated via the data. Particularly preferably, the workpiece is dried before and / or after at least one liquid is applied to it. Preferably, the liquid is applied multiple times to the surface of the workpiece. This is preferably done in multiple coating tools, which can be, for example, rollers, printheads, or other coating devices. Depending on the position on the surface of the workpiece, the liquid applied each time is stored in an electronic data memory and provided to an electronic controller. For example, a primer may be applied to the surface first, and then different colors of ink may be applied, for example, through multiple printheads (i.e., coating tools) in multiple printing processes. Preferably, after each application of liquid, the workpiece, particularly its surface, is dried. For this purpose, the workpiece is advantageously run through the drying unit after each application. Particularly preferably, it is also run through the drying unit before the first application of liquid and after the last application of liquid.

[0026] Therefore, the printing system preferably includes a plurality of coating tools through which at least one liquid is applied to the workpiece, wherein the workpiece is dried before and / or after the application of at least one liquid.

[0027] Advantageously, after drying by at least one drying unit, the humidity of the workpiece surface is measured by at least one humidity sensor and compared with a predetermined target value, wherein the degree of deviation between the measured humidity and the predetermined target value is incorporated into the future determination of drying parameters. Therefore, it is advantageous not only to determine the humidity of the workpiece surface to determine drying parameters before actual drying, but also to measure the humidity again or for the first time after actual drying. On the one hand, this allows it to be checked whether the target humidity has been reached, i.e., whether the determined drying parameters have met the desired target. If this is the case, there is no need to change the routines and settings in the electronic controller that determines the drying parameters. However, if the deviation exceeds a predetermined limit value, the calculations used to determine the drying parameters are adjusted and modified in the electronic controller.

[0028] By measuring the actual humidity, the expected humidity of drying units deployed later in the production process can be better determined, thus providing better information for the electronic controller. The determination of future drying parameters may relate to the drying parameters of drying units used later when printing the same surface of the workpiece. However, future determinations may also relate to the drying parameters used when printing the surfaces of other workpieces.

[0029] The workpiece is preferably paper pulp, and the degree of wrinkling of the paper pulp is detected in the printing system. This is preferably accomplished by 2-D and / or 3-D profile measurement, which is particularly preferably performed by a laser scanner. Preferably, the detected degree of wrinkling is compared with a predetermined target value. If the deviation between the detected degree and the target value is greater than a predetermined limit, the tension applied to the workpiece in the printing system is changed. The tension is increased or decreased according to the deviation.

[0030] The present invention also achieves the above objectives by means of a digital printing system for performing one of the methods described herein, the printing system having: at least one coating tool for applying liquid to a workpiece and at least one drying unit for drying the workpiece, and an electronic controller, particularly an electronic data processing device, the digital printing system being configured to perform one of the methods described herein.

[0031] The working width of the digital printing system is preferably at least 1300 mm, more preferably at least 1600 mm, particularly preferably at least 2000 mm, and at most 2300 mm, preferably at most 2200 mm, and particularly preferably at most 2100 mm. When printing paper, the speed of the system, i.e., the speed at which the surface to be printed moves through the system, is preferably at least 80 m / min, more preferably at least 100 m / min, particularly preferably at least 130 m / min, and at most 270 m / min, preferably at most 200 m / min, and particularly preferably at most 140 m / min. When printing heavier objects, such as wood panels, the speed is preferably at least 60 m / min, more preferably at least 70 m / min, particularly preferably at least 80 m / min, and at most 110 m / min, preferably at most 100 m / min, and particularly preferably at most 90 m / min.

[0032] If the primer is applied to the surface to be printed, the application amount is preferably at least 1 g / m². 2 More preferably at least 2g / m 2 Particularly preferred is at least 3 g / m 2 And at most 10 g / m 2 Preferably, at most 6 g / m 2 Especially preferably up to 4g / m 2 .

[0033] The humidity of the surface to be printed is an important factor in achieving the best and most realistic printed image while minimizing waste. Other factors include printing parameters and the resulting digital template.

[0034] In the method described herein, the decoration is preferably printed on multiple printing surfaces using a digital printing system, wherein the method includes the following steps:

[0035] A. Provides digital templates and reference measurement data for the printed decoration in both hyperspectral and spatial resolution.

[0036] B. Using digital templates, the decoration to be printed is printed onto the printing surface.

[0037] C. Measure the decorative elements printed on the printed surface to obtain hyperspectral and spatially resolved printing measurement data.

[0038] D. Compare the printing measurement data with the reference measurement data and determine the degree of deviation of the printing measurement data relative to the reference measurement data.

[0039] E. If the deviation meets the predetermined standard, then change the number template.

[0040] F. Repeat steps B through F.

[0041] In the method of this invention, a comparison is made between the printed decoration and the decoration to be printed based on various measurement data. The printed measurement data is compared with reference measurement data. Therefore, the reference measurement data corresponds to data measured or to be measured on the decoration that can be used as a reference, i.e., it accurately corresponds to the desired decoration. Thus, the discovery upon which this invention is based is that when measurement data can be defined, it is unnecessary to compare entire images to each other to determine the quality of the printed decoration; comparing the measurement data of the printed decoration and the decoration to be printed makes comparison of the image or the entire decoration redundant. The measurement data is spatially resolved, thus allowing the detection of fluctuations in print quality, particularly those arising from the parameters listed above, even if they occur at a small spatial scale, such as within a single printed decoration. Furthermore, the measurement data is hyperspectral, therefore containing information beyond visible light, which can be adjusted.

[0042] The digital template preferably corresponds to control parameters for controlling the printing system. This is particularly applicable to control instructions regarding the amount and location of ink to be applied to the printing surface. Preferably, the control parameters contain all the information required to operate the printing unit of the printing system.

[0043] If, in this method, a deviation from a predetermined standard is detected when comparing printed measurement data with reference measurement data, such as exceeding a predetermined deviation, the deviation is responded to appropriately. This is specifically achieved by changing the digital template. This results in a smaller degree of deviation when printing decoration using a changed digital template, thus potentially no longer meeting the predetermined standard. If the standard is not met, the printed decoration corresponds in quality to the desired decoration. However, if the standard is met, adjustments to the digital template are required, so it can be assumed that the printed decoration does not meet the printing quality requirements and must be classified as waste.

[0044] In a preferred embodiment, the time interval between the two consecutive implementations of step B is independent of whether the digital template has been changed. Therefore, the production cycle, particularly the printing of decorations on the printed surface, remains unchanged, allowing for online correction or modification of the digital template without interrupting or delaying the production process.

[0045] Preferably, providing reference measurement data in step A includes the following steps:

[0046] A1. Provide digital templates of the decorations to be printed.

[0047] A2. Using the digital template, print the decoration to be printed on the reference surface.

[0048] A3. Measure the decorative elements printed on the reference surface to obtain reference measurement data.

[0049] A digital template of the decoration to be printed is provided to a printing system in a manner known in the prior art. The printing system is controlled by the digital template to print the decoration onto a reference surface. The reference surface preferably corresponds in material, size, tactile feel, and / or color to the printing surface to be printed during the process. The decoration printed on the reference surface is then measured by measuring values. Reference measurement data is thus obtained. The better the correspondence between the reference surface and the printing surface, the easier and more accurate the comparison between the reference measurement data and the printing measurement data. If the deviation between the reference surface and the printing surface is known, a conversion tool can be used to convert the different measurements so that they correspond better to each other. However, in principle, this is prone to error, therefore optimal matching of the corresponding surfaces is advantageous.

[0050] The main advantage of this method is that the reference measurement data used for comparison in step D is actual measurement data, which cannot be obtained from existing digital models stored in electronic data memory. This solves the common problem of colorfastness because, in this method, the actual measurement data of the actually printed decoration (i.e., the reference measurement data) can be compared with the actual measurement data of another actually printed decoration (i.e., the printing measurement data). It is only necessary to ensure that the decoration printed on the reference surface corresponds exactly to the desired decoration. Otherwise, the digital template must be adjusted until the decoration printed on the reference surface corresponds to the desired decoration.

[0051] In a preferred embodiment of the method, a predetermined criterion is met when the deviation of one or more printed measurement data from the corresponding reference measurement data exceeds a predetermined limit value for the corresponding measurement value. Particularly preferably, the predetermined limit value depends on color and / or position. Weighting can be applied in this manner. For example, if a particular color has a very significant effect on a particular decoration, such as because it is brightly prominent or is used extensively in printed decoration, it is advantageous to ensure that the deviation of this color is particularly small. In this case, a color-related limit value for that color is chosen to be particularly small, so that even a relatively small deviation will necessitate changes to the digital template. On the other hand, if a color is not very important to the decoration because it is almost non-existent or barely perceptible to the human eye, a color-related limit value can be chosen. The same applies to positional dependence. A deviation at the edge of the decoration may be less significant than a deviation directly in the field of vision (e.g., at the center of the decoration).

[0052] Preferably, changing the digital template in step E includes the following steps:

[0053] E1. Check whether the degree of deviation meets the correction standard, and

[0054] E2a. Change the number template, or

[0055] E2b. Issue an optical and / or acoustic and / or electronic warning signal and terminate the method.

[0056] Some deviations between the reference measurement data and the printed measurement data are caused by reasons that cannot be eliminated by changing the digital template, for example. This may involve applying the wrong primer, or color changes due to changing the supplier of printing ink or base paper. These cannot or are difficult to eliminate by changing the digital template, and therefore do not meet the calibration criteria in this case. The calibration criteria indicate whether the deviation detected by the degree of deviation can be corrected by changing the digital template. If so, the decoration is changed according to step E2a. Otherwise, the method is aborted and a corresponding warning signal is output according to step E2b.

[0057] In a preferred embodiment, during steps C to E of the method, at least one additional printing surface is printed with the decoration to be printed. In this case, corrections or changes to the digital template have no effect on the decoration printed directly thereafter. Changes to the digital template only take effect in the next, or even later, decoration. However, it is advantageous to print as few additional decorations as possible. Since they are printed using the unchanged digital template, they contain the same errors as those that have not yet been corrected. Therefore, they are also defective and may result in scrap. The question of how many additional printing surfaces are printed during steps C to E depends on the performance of the electronic data processing equipment responsible for and performing these steps. The faster the data processing equipment performs these steps, the faster the necessary changes to the digital template become available, and the less additional decoration is printed. Of course, the cycle frequency of the printing system also has a significant impact on this.

[0058] Preferably, the changes to the digital template and / or the degree of deviation determined for different executions of the method are stored, and preferably stored in an electronic data storage device.

[0059] The printed measurement data preferably pertains to the same location and / or the same area as the reference measurement data on the decoration. This makes the individual measurement data particularly easy to compare with each other. In a particularly preferred embodiment, the printed measurement data and the reference measurement data pertain to the entire decoration. This specifically means that there are multiple measurement points at which corresponding measurement data is determined, and these multiple measurement points extend across the entire decoration. Preferably, the measurement points are equidistantly distributed across the decoration.

[0060] The apparatus for performing the method of the type described herein preferably includes an electronic data processing device, particularly a computer or microchip, configured to perform the method. The apparatus has at least one sensor configured to receive measurement data. The at least one sensor transmits the measurement data as a signal to the electronic data processing device, which receives the measurement data via a receiving module. A comparison module compares the measurement data transmitted by the at least one sensor with reference measurement data, preferably stored in an electronic data memory accessible to the receiving module. The degree of deviation is determined in this manner and then transmitted to an evaluation module. The evaluation module checks whether the degree of deviation meets a predetermined criterion. If the predetermined criterion is met, a modification module determines the necessary changes to the digital template. The cover plate is then conveyed to a printing system for printing the next decoration to be printed according to the modified digital template. The receiving module, comparison module, evaluation module, and modification module are implemented in the electronic data processing device and can be designed as software, particularly a computer program product.

[0061] In a preferred embodiment, the digital template does not correspond to the entire decoration, but only to a portion thereof. This is meaningful, for example, when data processing capabilities are insufficient to base the entire decoration on the method. Furthermore, it must be ensured that deviations detected only in a portion of the decoration corresponding to the digital template are meaningful for the entire decoration. For example, monitoring systems such as ACMS or AVT can be used to detect measurement data. Measurement data are recorded, for example, in a laboratory system. These measurement data can be easily compared to each other, where, for example, laboratory values ​​or hyperspectral lines are compared, for example, with a preferred resolution of 80 to 100 dpi, particularly preferably 90 dpi, for each measurement. The degree of deviation can be determined in this way, expressed as a percentage, using software known from the prior art, such as software from ICP. This makes it particularly easy to determine if the criteria for changing the digital template are met.

[0062] In a preferred embodiment, the method is terminated when the degree of deviation no longer meets the predetermined standard after 3, preferably 5, or particularly preferably 10 consecutive changes of the digital template, i.e., the printed decoration corresponds to the desired quality.

[0063] Preferably, if the degree of deviation does not meet a predetermined standard, i.e., the desired quality exists, an electronic certificate is created for the decoration printed on the printed surface, and particularly preferably, the electronic certificate is stored. Detailed Implementation

[0064] Example 1

[0065] Wooden decorations are printed on paper using a paper digital printing system. In a specific embodiment, the working width is 2070 mm. The speed in the specific embodiment is 135 m / min. The surface weight used is 65 g / m². 2 White decorative paper and water-based CRYK ink with approximately 3 g / m 2 The inner primer is applied. The repeating pattern specifications (Rapportabmessungen) of the wood trim are 1400 mm long and 2070 mm wide. In the production system, an ipac online monitoring system is installed along the entire width (2070 mm). A digital template of the trim is saved. During production, printing measurement data for each repeating pattern (i.e., each printed trim) is detected and stored. Based on these printing measurement data, a similarity index, i.e., the degree of deviation, is calculated with reference measurement data. Before production begins, the predetermined standard is set at 92%. Therefore, if the degree of deviation is lower than 92% in this case, the digital template must be changed. For repeating pattern 1.264 produced, a similarity index of 89% is calculated. The measurement data indicates that the deviation in this case is essentially on the b-axis, i.e., on the yellow-blue line (e.g., 5% to blue). Since the deviation is higher than the specified tolerance, the measurement data is automatically transferred to Colorgate software, and a corrected digital template for the wood trim is calculated and saved. After being automatically transferred to the output device (i.e., the printing system), the printing file (digital template) previously used for the printing job is automatically replaced with a corrected digital template of the wood trim, which is then used as the printing file for subsequent repeating patterns. After the corrected digital template of the wood trim is output, the similarity index between the next printing measurement data and the reference measurement data is calculated to be 94%.

[0066] The cycle from measuring the print data for the entire decoration to outputting a digital template of the altered wood trim is the repeat pattern length (approximately 0.62 seconds). In this case, the entire repeat pattern is measured, saved, and deviations are identified. Subsequent repeat patterns are still printed using the uncorrected digital template because this time is required for calculations and replacements.

[0067] Example 2 - Digital Printed Decorative Panel

[0068] On a digital printing system (working width 2070mm, board size 2070 x 2800 mm, speed 80m / min, 8mm HDF board, white primer, CRYK water-based ink, approximately 3 g / m²), the printing was performed. 2 The wood trim was fabricated using an inline primer coating. The wood trim's grain dimensions were 2800 mm long and 2070 mm wide. The gap between the boards was 140 cm. In the production system, Ipac's online monitoring system was installed across the entire width (2070 mm). A digital template of the trim was stored.

[0069] During production, printing measurement data for each repeating pattern (i.e., each printed decoration) is detected and stored. Based on this printing measurement data, a similarity index with reference measurement data is calculated. A predetermined standard of 94% is set before production begins. Therefore, if the deviation in this case is less than 94%, it is preferable to modify the digital template. For the produced repeating pattern 863, a similarity index of 92% is calculated. The measurement data indicates that the deviation is essentially > light to dark (e.g., 4% to dark) on the L-axis. Since the deviation is higher than the specified tolerance, the measurement data is automatically transferred to the Colorgate software, and a correction digital template for the wood decoration is calculated and saved. After automatic transfer to the output device, the printing file (digital template) previously used for the printing job is automatically replaced by the correction digital template for the wood decoration and used as the printing file for subsequent repeating patterns. After outputting the correction digital template for the wood decoration, a similarity index of 96% is calculated based on the first printing measurement data.

[0070] The time frame from detecting printed measurement data to correcting, replacing, and outputting the digital template for the wood trim corresponds to the gap between two boards (140 cm = approximately 0.95 seconds). In this case, measurements were taken, the entire repeating pattern was saved, and deviations were detected. Correction data was printed during the next gap, as calculations and replacements required this time.

[0071] Because the printing data for wooden decorations is adjusted and replaced automatically in a timely manner, production can meet the similarity index specifications within a certain gap.

[0072] Example 3 - Paper Digital Printing Decoration

[0073] In a paper-based digital printing system, wooden decorations are printed onto paper. In a specific embodiment, the working width is 2070 mm. The speed in this embodiment is 135 m / min. The surface weight used is 65 g / m². 2 White decorative paper and water-based CRYK ink with approximately 3 g / m 2The inline primer was applied. The wood trim's grain specifications were 1400 mm long and 2070 mm wide. In the production system, Ipac's online monitoring system was installed across the entire width (2070 mm). A digital template of the trim was saved. During production, print measurement data records for each repeating pattern (i.e., each printed trim) were detected and stored. Based on these print measurement data, a similarity index with reference measurement data was calculated. Before production began, a predetermined standard was set at 95%. Therefore, if the deviation in this case was less than 95%, the digital template had to be modified. For the generated repeating pattern 4.587, a similarity index of 63% was calculated. The measurement data indicated that the deviation was essentially on the L-axis > light to dark (e.g., 30% to dark). Because the deviation exceeded the specified tolerance, the measurement data was automatically transferred to Colorgate software, and a corrected digital template for the wood trim was calculated and saved. After automatic transfer to the output device, the print file (digital template) previously used for the print job was automatically replaced with the corrected digital template for the wood trim and used as the print file for subsequent repeating patterns. After outputting the corrected digital template of the wooden decoration, a similarity index of 75% was calculated based on the first printing measurement data.

[0074] The cause of this deviation is the incorrect type of paper used for printing. The software cannot correct this significant deviation.

[0075] An alarm sounds to alert the machine operator to any deviation. The production system stops, the dryer is adjusted to lower settings, and production resumes.

[0076] Example 4 - Digital Printed Decorative Panel - Unable to Correct - Panel Too Cold - Then Signal is Issued

[0077] Wood decoration was produced on a digital printing system (working width 2070mm, board size 2070mm x 2800mm, speed 80 m / min, 8mm thick HDF board, white primer, CRYK water-based ink, approximately 3 g / m). 2(Inline primer application rate). The wood trim's grain specifications are 2800 mm long and 2070 mm wide. The gap between boards is 140 cm. In the production system, ipac's online monitoring system is installed across the entire width (2070 mm). During production, printing measurement data for each repeating pattern (i.e., each printed trim) is detected and stored. Based on these printing measurement data, a similarity index with reference measurement data is calculated. Before production begins, a predetermined standard is set at 90%. Therefore, if the deviation is below 90% in this case, it is preferable to modify the digital template. For the generated repeating pattern 1123, a similarity index of 58% was calculated. The measurement data indicates that the deviation is essentially > light to dark (e.g., 35% to dark) on the L-axis. Since the deviation is higher than the specified tolerance, the measurement data is automatically transmitted to Colorgate, and a corrected digital template for the wood trim is calculated and saved. After automatic transmission to the output device, the printing file (digital template) previously used for the printing job is automatically replaced with the corrected digital template for the wood trim and used as the printing file for subsequent repeating patterns. After outputting the corrected digital template of the wooden decoration, a similarity index of 74% was calculated based on the first printing measurement data.

[0078] In this case, the deviation is caused by an excessively low board temperature, which results in the applied ink drying too slowly and sinking too deeply into the board surface. The software cannot correct this significant deviation.

[0079] An alarm sounds to alert the machine operator to any deviations, and the production line stops automatically. The operator can then check, correct, and generate further parameters for the printing system.

Claims

1. A method for printing a decorative workpiece surface using a digital printing system, wherein the printing system has at least one coating tool for applying a liquid to the workpiece and at least one drying unit for drying the workpiece, wherein the method includes the following steps: a. Provide information about the expected humidity of the workpiece to be dried in the electronic controller of the printing system. b. Based on the provided information, drying parameters are determined, and the at least one drying unit can be operated using these drying parameters. c. Based on the determined drying parameters, the workpiece is dried using the at least one drying unit. After drying by at least one drying unit, the humidity of the workpiece surface is measured by at least one humidity sensor and compared with a predetermined target value, wherein the degree of deviation between the measured humidity and the predetermined target value is incorporated into the future determination of drying parameters.

2. The method according to claim 1, characterized in that, Providing the information includes the following steps: a1. The humidity of the workpiece surface is measured using at least one humidity sensor. a2. The measured humidity is provided in the electronic controller.

3. The method according to claim 2, characterized in that, The humidity is determined by one or more of the following methods: infrared (IR) measurement method, microwave measurement method, and L-value determination.

4. The method according to claim 1, 2 or 3, characterized in that, The expected humidity is calculated based on the following information. - At least one amount of liquid applied to the workpiece before drying. - At least one temperature, or - The humidity of the workpiece.

5. The method according to claim 1, characterized in that, The information provided regarding the expected humidity and the determined drying parameters are functions of the position on the surface of the workpiece.

6. The method according to claim 1, characterized in that, The workpiece is dried multiple times, and method steps a and b are performed before each drying.

7. The method according to claim 1, characterized in that, The workpiece is dried before and / or after applying at least one liquid to it.

8. The method according to claim 1, characterized in that, The printing system includes multiple coating tools for applying at least one liquid to the workpiece, and for drying the workpiece before and / or after each application of at least one liquid.

9. The method according to claim 1, characterized in that, The workpiece is paper pulp, and in the printing system, the degree of wrinkling of the paper pulp is detected by means of a laser scanner through 2D and / or 3D contour measurement.

10. The method according to claim 9, characterized in that, The degree of detected wrinkles is compared with a predetermined target value, and when the deviation between the detected degree and the target value exceeds a predetermined limit, the tension applied to the workpiece is changed.

11. A digital printing system, comprising: At least one coating tool for applying liquid to the workpiece and at least one drying unit for drying the workpiece, and an electronic controller, characterized in that the digital printing system is configured to perform the method according to any one of the preceding claims.