Production line with X-ray fluorescence measuring head for determining the quantity of at least one primer applied to at least one carrier material

Description

[0001] The present invention relates to a production line for applying a primer layer to a substrate, which is designed for a method of determining the quantity of at least one primer applied to at least one substrate using X-ray fluorescence analysis. The use of X-ray fluorescence analysis to determine the thickness of a primer layer on a substrate is known, for example, from EP0269590, which describes how to determine the thickness of a calcium carbonate-containing adhesive coating on a cardboard sample after drying by X-ray fluorescence measurement.

[0002] Decorative substrates, such as wood-based panels or paper layers, are mainly printed using gravure printing or digital printing processes.

[0003] Intaglio printing is a printing technique in which the elements to be reproduced are represented as recesses in a printing plate, which is inked before printing. The printing ink is primarily located in the recesses and is transferred to the substrate, such as a substrate, due to the pressure of the printing plate and adhesive forces.

[0004] In contrast, digital printing transfers the print image directly from a computer to a printing machine such as a laser printer or inkjet printer. This eliminates the need for a static printing form.

[0005] As printing technology for various substrates continues to advance, digital printing is increasingly being used. While digital printing processes were initially primarily used in the graphic arts industry, such as advertising agencies, promotional material manufacturers, and printing companies, they are now becoming more common in other sectors as well. There are many reasons for this, but two key arguments stand out. Digital printing enables the production of exceptionally high-quality printed images thanks to its higher resolution and also allows for a wider range of applications with greater flexibility. This is illustrated by the fact that there are no longer any limitations on the length of the printed image.

[0006] In all printing processes (in this case, paper, but also wood-based panels), it is crucial that the customer receives a uniform and repeatable print image; both the colors and the shapes must match the original sample in every print run. Deviations are undesirable and will not be accepted.

[0007] To print on paper with digital printing ink, it is therefore necessary to first coat the paper with an intermediate layer. A primer, or pre-coating, is used as this intermediate layer to minimize color variations between printed designs within a production batch, or even between identical printed designs from different production batches, caused by pigment transfer.

[0008] The primer has two functions: firstly, it forms a barrier layer between the ink and the paper; secondly, it contains a reactive component that reacts with the ink, ensuring that an ink droplet of a specific size remains unchanged on the paper. The primer reacts with the ink in such a way that the droplet immediately stops spreading.

[0009] Furthermore, using a primer reduces the amount of ink required for printing. Without a primer, the ink soaks into the paper, and a larger quantity of ink is needed to achieve the desired print result. Since primer is significantly cheaper than printing ink, its use results in considerable cost savings.

[0010] In the digital printing system, the paper to be printed is primed. This primer is applied in a defined volume to a rubber roller and then to the paper using a roller (anilox roller; a curtain or spray application would also be possible). The primer is then dried before the digital printing ink is applied and the paper is dried again.

[0011] This can result in various disadvantages.

[0012] The application of the primer can be uneven due to various factors. This can occur, for example, with (mechanical) damage to the anilox roller, (mechanical) damage to the rubber roller used for primer transfer, misaligned installation of one of the rollers, roller wear, wear and tear resulting in changes to the cell depth and thus the ink volume, insufficient cleaning of the rollers resulting in changes to the cell depth and thus the ink volume. Wrinkling of the paper can also be responsible for varying application amounts.

[0013] High costs arise from unusable rejects, from repeating production (materials, personnel), from complaints, from excessive material usage (ink, primer).

[0014] Production times increase due to repeating a production run and / or costly roller changes, because simple cleaning is no longer sufficient.

[0015] Furthermore, resources are wasted in the use of materials and personnel, through duplicate production and waste, and / or through excessive amounts of ink and primer.

[0016] The invention is therefore based on the technical problem of establishing a measuring method in a production line with which the primer application can be monitored both over time, i.e., the linear meters, and across the web width. Monitoring the primer application ensures that there are no deviations in the printed image.

[0017] This problem is solved according to the invention by a production line with the features of claim 1.

[0018] Accordingly, a production line for applying a primer layer to a support material is provided, which enables a method for determining a quantity of at least one primer applied to at least one support material using X-ray fluorescence analysis, wherein the production line comprises: at least one application unit for applying the primer to the at least one substrate material, at least one X-ray fluorescence measuring head for recording at least one X-ray fluorescence spectrum of the primer layer applied to the substrate material, wherein the emitted X-ray radiation comprises energy in a range between 2000 and 6000 eV, at least one control system for controlling the production line, wherein the control system of the production line comprises at least one computer-aided evaluation unit and a database, wherein the evaluation unit is configured to compare the X-ray fluorescence spectrum measured for the primer-coated substrate material with a created calibration model;wherein the database is configured to store the data thus determined, wherein the control system is configured to use the determined data to control the production line, and wherein the evaluation unit is configured to determine the calibration model using reference samples measured by the X-ray fluorescence measuring head.

[0019] The calibration model is created as follows: Providing several reference samples by applying at least one primer in different quantitatively defined amounts to the at least one support material; recording at least one X-ray fluorescence spectrum of each of the reference samples using at least one X-ray fluorescence measuring head in a position suitable for the element to be detected in the primer, preferably a divalent cation; assigning the different quantitatively defined amounts of primer of the reference samples to the recorded X-ray fluorescence spectra of said reference samples; and creating a calibration model for the relationship between the recorded X-ray fluorescence spectra of the reference samples and the corresponding quantitatively defined amounts of primer.

[0020] Using the calibration model, the measurement procedure is carried out as follows: Providing at least one sample to be measured by applying at least one layer of at least one primer to the at least one support material, recording at least one X-ray fluorescence spectrum of the sample to be measured using the at least one X-ray fluorescence measuring head, determining the quantitative amount of the primer applied to the support material in the sample to be measured by comparing the X-ray fluorescence spectrum of the sample to be measured with the calibration model created from the reference samples.

[0021] The X-ray fluorescence analysis used in the present procedure makes it possible to reliably determine even small application quantities of the primer.

[0022] X-ray fluorescence analysis (XRF) or X-ray fluorescence spectroscopy (XRF) is a method used in materials analysis and is one of the most frequently used methods for the qualitative and quantitative determination of the elemental composition of a sample, as the sample is not destroyed by the measurement and no digestion is required. X-ray fluorescence analysis (XRF) is particularly widely used in the metalworking industry, in the examination of glass, ceramics and building materials, as well as in the analysis of lubricants and petroleum products.

[0023] The major advantage of X-ray fluorescence over other measurement methods is that even the smallest application quantities (< 1 g / m²) can still be reliably determined. This is the case with primer application.

[0024] By irradiating the material sample with X-rays, the electrons of the element to be identified are first knocked out of the inner orbits of the electron shell. Subsequently, electrons from the outer shells fall back into these vacancies, emitting characteristic X-rays. These X-rays are specific to each element and allow for the determination of the element's quantity. The element-specific X-rays are detected by a suitable radiation detector.

[0025] This method enables continuous, non-contact, online determination of the applied primer quantity. This allows the applied primer quantity to be measured during ongoing production, both across the web width and along the web length. Only in this way can deviations that lead to printing problems be detected early.

[0026] Before the measurement technology can be used in the system, calibration will first be performed using reference samples. This involves first measuring an uncoated substrate (such as untreated raw paper) as the zero point, and then creating a calibration series with varying amounts of primer applied to the substrate. Different known quantities of primer are applied to the substrate and analyzed by XRF. Based on the data obtained, a regression line is generated, which is then used to determine the primer quantity for the samples to be measured.

[0027] In one embodiment, for calibration purposes, a primer with different amounts of divalent cations, such as Ca²⁺, is applied as a reference sample, the entire spectrum is recorded, and the emitted radiation is analyzed in the region specific to the divalent cation. It is also possible to examine the emitted radiation for other elements.

[0028] For the samples to be measured in a production plant, an X-ray fluorescence measuring head is installed downstream of the primer application unit and, if applicable, downstream of a dryer. The measured or detected X-ray radiation provides information about the primer concentration in the sample. Ideally, the measured value should be constant. Deviations indicate that the current primer application quantity does not meet the target and that this can lead to variations in the printed image.

[0029] The measuring head can traverse the web during measurement, or alternatively, several measuring heads can be installed side by side across the web width, so that the primer application can be checked across the web width.

[0030] All these methods share the common feature of continuously recording spectra to monitor the primer application over its entire duration. This allows deviations to be detected and corrected early on.

[0031] This procedure ensures that the current printed image corresponds to the stored master copy, i.e., the target printed image. It guarantees that the customer's requirements are met.

[0032] Cost savings result from the timely detection and replacement of roller wear, the avoidance of defective production runs, the optimal use of primer and ink, and time savings from preventing defective production runs and major downtime caused by defects in the application rollers. Furthermore, resources are conserved through the optimal use of primer and ink and the avoidance of defective or duplicate production runs.

[0033] The primer used here comprises, as the element to be detected, at least one salt with a divalent cation, in particular Mg²⁺, Ca²⁺, Sr²⁺, Ba²⁺, preferably Ca²⁺. X-ray fluorescence analysis is particularly effective for elements with higher atomic numbers, such as Ca²⁺, Sr²⁺, or Ba²⁺. The divalent cation thus serves as an indicator for the amount of primer applied.

[0034] Divalent cations are used as salts, particularly in the form of carbonates, sulfates, and formates. Suitable salts include calcium diformate, calcium carbonate, calcium chloride, magnesium carbonate, barium sulfate, and calcium sulfate.

[0035] The salts are preferably used in water-based dispersions that are completely miscible or partially soluble in water. The primer should have a low solvent content of less than 3 wt%, preferably less than 2 wt% or less than 1 wt%. Typical solvents are ethane-1,2-diol (glycol) or methanol.

[0036] The concentration of the divalent cation salts in the primer mixture or primer dispersion can be between 5 and 25 wt%, preferably between 10 and 20 wt%. For example, primer mixtures with 5-10 wt% calcium diformate and 5-10 wt% methanol or with 10-20 wt% calcium chloride and 0.1-1 wt% methanol are used.

[0037] Other components of the primer mixture may be polymeric binders, such as those from the group consisting of hydroxyethylcellulose; hydroxypropylcellulose; hydroxyethylmethylcellulose; hydroxypropylmethylcellulose; hydroxybutylmethylcellulose; methylcellulose; sodium carboxymethylcellulose; sodium carboxymethylhydroxyethyl cellulose; water-soluble ethylhydroxyethylcellulose; cellulose sulfate; polyvinyl alcohol; vinyl alcohol copolymers; polyvinyl acetate; polyvinyl acetal; polyvinylpyrrolidone; polyacrylamide; acrylamide / acrylic acid copolymer; polystyrene, styrene copolymers; acrylic or methacrylic polymers; styrene / acrylic copolymers; ethylene-vinyl acetate copolymer; vinylmethyl methyl vinyl acetate copolymer; vinyl methyl ether / maleic acid copolymer; poly(2-acrylamido-2-methylpropanesulfonic acid); poly(diethylenetriamine-coadipic acid); polyvinylpyridine; polyvinylimidazole; epichlorohydrin-modified polyethyleneimine; ethoxylated polyethyleneimine;Ether-containing polymers such as polyethylene oxide (PEO), polypropylene oxide (PPO), polyethylene glycol (PEG), and polyvinyl ether (PVE); polyurethane; melamine resins; gelatin; carrageenan; dextran. A preferred polymer for this is a polyvinyl alcohol (PVA), a vinyl alcohol copolymer, or a modified polyvinyl alcohol. The modified polyvinyl alcohol can be a cationic polyvinyl alcohol.

[0038] The primer mixture may contain further additives such as colorants (e.g., TiO2 as a white pigment), surfactants, biocides, antistatic agents, elastomers, UV absorbers, plasticizers, light stabilizers, pH adjusters, bleaching agents, matting agents, and the like. For example, 2-methyl-2H-isothiazol-3-one and / or 5-chloro-2-methyl-2H-isothiazol-3-one may be added as further components of primer mixtures, but these are preferably present in only small amounts of less than 0.005% by weight.

[0039] As described above, an X-ray fluorescence spectrum is recorded for each sample to be measured. Preferably, a complete spectrum is recorded so that, in addition to the selected divalent cation, other elements of the primer composition can also be determined. For example, it may be desirable to determine not only the divalent cation salt but also higher-valent salts or oxides such as TiO₂.

[0040] For this purpose, the sample to be measured is first excited (e.g., by electron impact) and the X-rays emitted by the excited element are determined. In the present method, the emitted X-rays have an energy in the range between 2000 and 6000 eV.

[0041] When determining the amount of Ca²⁺ as an indicator of the primer application quantity, an energy range between 3600 and 3800 eV, preferably 3620 and 3770 eV, is analyzed. In a preferred embodiment, the energy range for Ca²⁺ is at an initial energy of 3627 eV and a final energy of 3763 eV. In the case of TiO₂, for example, an energy range between 4200 and 4700 eV would be analyzed.

[0042] The element-specific X-ray radiation emitted is displayed in the form of pulses or counts. The intensity or amplitude of the emitted counts is proportional to the amount of primer applied. The counts detected by the detector correspond to the number of photons released after the sample has been irradiated with high-energy radiation.

[0043] In one embodiment of the present method, the at least one primer is applied to the at least one carrier material as a liquid suspension or solution with a solids content of 15 to 30 wt%, preferably 20 to 25 wt%. The primer can be applied using an anilox roller or by spraying.

[0044] In a further embodiment of the present method, the primer application is dried and then the X-ray fluorescence spectrum is recorded using the at least one X-ray fluorescence measuring head.

[0045] In one embodiment of the present method, the amount of primer applied to the at least one carrier material is more than 0.5 g solid / m², preferably more than 1 g solid / m². Thus, the amount of primer applied can be between 0.5 g solid / m² and 10 g solid / m², preferably between 1 g solid / m² and 8 g solid / m², and in particular between 1.5 g solid / m² and 5 g solid / m².

[0046] The at least one substrate material that is coated with the primer can be a paper layer or a wood-based panel.

[0047] Preferably, a paper layer is used, in particular a paper layer made of at least one raw paper or at least one pre-treated impregnated paper.

[0048] In one embodiment, at least one substrate material to be printed is a base paper. Base papers are defined as papers that have not undergone sizing in the bulk or surface impregnation with a resin or glue. Base papers consist essentially of pulp, pigments, fillers, and conventional additives. Softwood pulp, hardwood pulp, or mixtures of both can be used to produce base papers such as decorative papers. Inorganic pigments such as metal oxides, metal hydroxides and hydrates, metal sulfides, metal sulfates, metal chromates, and metal molybdates, as well as organic pigments and / or dyes such as carbonyl dyes, cyanine dyes, and others, can be used to color the base paper.

[0049] In a preferred embodiment, the raw paper to be printed is at least one paper web without impregnation.

[0050] In another embodiment, the at least one substrate material to be printed is at least one pretreated, impregnated paper. A pretreated paper (or cellulose layer) is understood to be a paper or paper web that is impregnated with a resin solution. The paper can be impregnated with a wide variety of resin solutions, for example, melamine resins and urea resins, polymer-acrylate compounds, or starch sizing. Mixtures of the resins are also possible. It is also possible to impregnate the paper using resin powder. The use of resin powder is described in detail below.

[0051] In a preferred embodiment, an impregnated paper is used, which is provided by the following process steps (see also EP 2 980 313 A1): a) complete impregnation of the cellulose layer with a curable resin, e.g. melamine-formaldehyde resin), b) removal of the excess resin forming on the surface (e.g. by peeling or scraping), c) drying of the impregnated cellulose layer such that, after the water has evaporated from the resin, the cellulose fibers on the surface from which the resin has been removed are at least partially exposed.

[0052] By peeling or scraping off the resin, the resin remaining on the surface of the cellulose layer seals against the fiber tips. During the drying process, the resin retracts into the fibers, so that the fibers are impregnated with the resin but not encased by it. Such a surface is suitable for printing with water-based digital printing inks.

[0053] The special device used for scraping or removing the resin works similarly to a spatula machine, where one or more rollers run backwards across the paper, collecting the excess resin. Different roller speeds allow for precise control of the amount applied and ensure repeatability.

[0054] Paper weights can vary between 30 and 250 g / m². For example, the paper weight of decorative papers can be between 30 and 150 g / m², preferably between 50 and 120 g / m², and particularly preferably between 80 and 100 g / m². In the case of raw paper or kraft paper, the paper weight can be between 50 and 250 g / m², preferably between 100 and 200 g / m², and particularly between 120 and 150 g / m².

[0055] As mentioned, it is also possible to use a wood-based panel as the substrate to be coated with a primer. In this case, the wood-based panel can be a particleboard, medium-density fiberboard (MDF), high-density fiberboard (HDF), oriented strand board (OSB), plywood, a wood-plastic composite, a wood-plastic composite, or a WPC (wood-plastic composite) panel.

[0056] The present process is carried out continuously and online in the production line, comprising at least one X-ray fluorescence measuring head and at least one control system. Two or three X-ray fluorescence measuring heads can also be provided at different points in the production line. Such a production line can be used for processing or finishing paper layers or material sheets.

[0057] The production line includes: at least one application unit for applying the primer to the at least one carrier material, at least one X-ray fluorescence measuring head provided after the application unit; and optionally also: at least one dryer arranged downstream of the coating unit, at least one X-ray fluorescence measuring head provided downstream of the dryer; at least one printing device for printing the primer-coated substrate material, further coating units with corresponding dryers for applying and drying at least one, preferably several, resin layers onto the printed substrate material.

[0058] In one embodiment, the production line comprises: at least one coating unit with an anilox roller for applying the primer to the at least one substrate material; optionally at least one X-ray fluorescence measuring head provided after the coating unit; at least one dryer arranged after the coating unit; at least one X-ray fluorescence measuring head provided after the dryer; at least one digital printer for printing the primer-coated substrate material; further coating units with corresponding dryers for applying and drying at least one, preferably several, resin layers on the printed substrate material.

[0059] According to the invention, the production line's control system comprises at least one computer-aided evaluation unit (or processor unit) and a database. In the evaluation unit, the X-ray fluorescence spectrum measured for the primer-coated substrate material is compared with the generated calibration model. The data thus determined are stored in the database.

[0060] The data determined using the present spectroscopic method can be used to control the production line. As previously described, the non-contact parameter values ​​measured by the X-ray fluorescence sensor can be used directly and in real time for controlling the relevant system. This is achieved, for example, by storing the measured actual values ​​in a database (e.g., a relational database) and comparing them with the target values ​​for these parameters. The resulting differences are then used to control the production line.

[0061] In one embodiment, the primer application unit and the subsequent dryer are controlled. If the values ​​determined by the X-ray fluorescence measuring head and in the evaluation unit indicate a fault in the primer application, process steps can be specifically influenced or defects rectified.

[0062] The contact pressure of the primer applicator's roller can be precisely controlled to compensate for irregularities in the substrate's surface. A faulty application can also result from damage to the applicator roller; the roller can be replaced and / or repaired accordingly. Another cause of a faulty primer application could be an empty primer container or a defective dryer. These defects can be easily and quickly rectified using this method.

[0063] For the alignment and control of the production line, a computer-implemented procedure and a computer program comprising instructions that, when executed by a computer, cause it to carry out the computer-implemented procedure, are provided. The computer program is stored in a memory unit of the production line's control system.

[0064] The invention is explained in more detail below with reference to the figures in the drawings, using an exemplary embodiment as an example. It shows: Figure 1 shows an X-ray fluorescence spectrum of a substrate coated with a primer and a substrate without a primer coating. calibration

[0065] From the diagram of Figure 1 A typical X-ray fluorescence spectrum of a primer layer applied to a layer of raw paper can be obtained. The primer used contains Ca²⁺ in the form of calcium formate.

[0066] The samples were irradiated with radiation in an energy range of 2 keV to 5.6 eV and the emitted X-ray radiation was determined as pulses or counts.

[0067] For recording the X-ray fluorescence spectra, an X-ray fluorescence measuring head from Spektro was used. The measuring head is a silicon drift or silicon PIN detector. The detector is selected according to the application. During the measurement, care must be taken to maintain a short distance between the measuring head and the sample being measured. Preferably, this distance should be only a few millimeters.

[0068] For calibration, various primer amounts (0 g / m²; 1.1 g / m²; 2.2 g / m²; 3.3 g / m²) were applied and measured. Three measurements were taken for each primer amount, at three different points on the primer-coated base paper layer: A-side (AS), B-side (BS), and center (Mitte). The reverse side (rueck) was also measured for verification.

[0069] The different measurements appear as peaks in the X-ray fluorescence spectrum of the Figure 1 The signal is shown in the graphs. The signal typical for the Ca²⁺ cation lies in the range between 3.6 and 3.8 keV. It is clearly evident that primer-coated paper exhibits significantly higher pulse counts compared to uncoated paper. For example, the peaks for the sample coated with 3.3 g / m² primer reach maximum values ​​of 4,000 pulses (on the x-axis), while the control samples show 700 pulses.

[0070] The integrals of the peaks are given as counts. Table 1 lists the individual and mean counts from the three respective measurements for each primer set. Table 1: Correlation of primer quantity and counts of detected X-ray fluorescence rays. A regression line is created from the mean values, on the basis of which the primer quantity of the samples to be measured can be determined. Primer quantity (g / m²< ) Sample designation Counts Counts (average) 0 Blind sample 2 front 25542 25149 0 Blind sample 1 front 24756 0 Blind sample 2 Back 24567 24557 0 Blind sample 1 back 24547 1,1 Run 1 AS 128501 124831 1,1 Run 1 BS 127764 1,1 Run 1 middle 118229 1,1 Cycle 1 BS return 72191 2,2 Run 2 AS 223821 224624 2,2 Run 2 BS 224051 2,2 Run 2 middle 226000 3,3 Run 3 AS 306453 310012 3,3 Run 3 BS 314678 3,3 Run 3 middle 308906 3,3 Cycle 3 AS return 140647 Example 1:

[0071] In a digital paper printing system, untreated raw paper is first coated with a primer to create a bond between the paper and the ink. The primer is applied to the paper using an anilox roller and then immediately dried. Behind the dryer is a traversing X-ray fluorescence measuring head that determines the amount of primer applied. It covers the entire web width of Y meters within X seconds. After maintenance on the primer application unit, the system is run for a test. After one minute, a warning tone sounds and a signal light flashes. The operators stop the system manually. The measurements show that the primer application on the left side is significantly below the target value. The primer application unit is then checked again. It is found that there were differences in the contact pressure between the pages. After the problem is rectified, the system continues to run without further issues. Example 2:

[0072] In a digital paper printing system, the raw paper is first primed to create a bond between the paper and the ink. The primer is applied to the paper using an anilox roller and then immediately dried. Behind the dryer, three X-ray fluorescence measuring heads are evenly spaced across the web width to determine the primer quantity. During the production of a decorative print, the system stops and a signal (audible and visual) is triggered. This is due to a faulty primer application on the right side. The X-ray fluorescence measuring head detects a 30% lower primer application at this point compared to the left and center. Upon inspection of the inking unit, damage is found on the right side of the primer roller. The doctor blade has damaged the cells, thus reducing the primer application. Example 3:

[0073] In a digital paper printing system, raw paper is first primed to create a bond between the paper and the ink. The primer is applied to the paper using an anilox roller and then immediately dried. A permanently installed X-ray fluorescence sensor is located behind the dryer. During a large print run exceeding 15 tons, the system emits an audible / visual signal. The system stops automatically. The X-ray fluorescence sensor detects a primer application of 0 g / m². The system operators then determine that the primer IBC is empty and no new container has been connected.

Claims

1. A production line for applying at least one primer layer as a printing primer to a substrate, wherein the production line comprises - at least one application unit for applying the primer to the at least one carrier material, - at least one X-ray fluorescence measuring head for recording at least one X-ray fluorescence spectrum of the primer layer applied to the carrier material, wherein the emitted X-ray radiation comprises energy in a range between 2000 and 6000 eV, - at least one control system for controlling the production line, wherein the control system of the production line comprises at least one computerized evaluation unit and a database, - wherein the evaluation unit is configured to compare the X-ray fluorescence spectrum measured for the primer-coated carrier material with a calibration model that has been created; - wherein the database is configured to store the data thus determined, - wherein the control system is configured to use the determined data to control the production line, wherein the evaluation unit is configured to determine the calibration model based on reference samples to be measured by the X-ray fluorescence measuring head as follows: - providing several reference samples by applying at least one primer in different quantitatively defined amounts to the at least one carrier material; - recording at least one X-ray fluorescence spectrum of each of the reference samples using at least one X-ray fluorescence measuring head in an energy range for the respective divalent cation to be detected contained in the primer, wherein the emitted X-rays comprise energy in a range between 2000 and 6000 eV, - assigning the different quantitatively defined amounts of primer of the reference samples to the recorded X-ray fluorescence spectra of said reference samples; and - creating a calibration model for the relationship between the recorded X-ray fluorescence spectra of the reference samples and the associated quantitatively defined amounts of primer.

2. Production line according to claim 1, characterized in that the production line further comprises - at least one dryer arranged downstream of the applicator, - wherein the at least one X-ray fluorescence measuring head is provided after the at least one dryer, - at least one printing device for printing the primer-coated carrier material, - further application units each with corresponding dryers for applying and drying at least one, preferably several, resin layers on the printed carrier material.

3. Production line according to claim 2, characterized in that the control system of the production line is configured to use the determined data to control the primer application unit and the subsequent dryer.

4. Production line according to one of the preceding claims, characterized in that the divalent cation to be detected comprises Mg2+, Ca2+, Sr2+, Ba2+, preferably Ca2+.

5. Production line according to one of the preceding claims, characterized in that the divalent cation is used in the primer in the form of calcium diformate, calcium carbonate or calcium sulfate.

6. Production line according to one of the preceding claims, characterized in that, in the case of determining the amount of Ca2+as divalent cation, an energy range of the X-ray fluorescence spectrum between 3600 and 3800 eV, preferably 3620 and 3770 eV, is analyzed.

7. Production line according to one of the preceding claims, characterized in that the at least one primer is applied to the at least one carrier material as a liquid suspension or solution with a solids content of 15 to 30% by weight, preferably 20 to 25% by weight.

8. Production line according to one of the preceding claims, characterized in that the amount of primer applied to the at least one carrier material is more than 0.5 g / m2, preferably more than 1 g / m2.

9. Production line according to one of the preceding claims, characterized in that the at least one carrier material comprises at least one paper layer, in particular at least one base paper or at least one pre-treated, impregnated paper.

10. Production line according to one of the preceding claims, characterized in that the at least one carrier material is a board made of a wood-based material, in particular a chipboard, medium-density fibre (MDF), high-density fibre (HDF), oriented strand board (OSB) or plywood board, a wood-based material / plastic mixture or a composite material, or a WPC board (wood plastic composites).

11. Production line according to one of the preceding claims, characterized in that the production line is configured so that the determination of the amount of primer applied takes place continuously and online.