Procedure for determining the quantity and / or composition of a powder resin layer applied to a support material

Abstract

The invention relates to a method for determining the quantity and / or composition of at least one layer of at least one powdered resin from a resin mixture, said layer being applied onto at least one support material. The method comprises the steps of: applying at least one powdered resin or a powdered mixture of at least two resins in a defined mixing ratio onto a respective support material in quantitatively defined quantities as reference samples; recording at least one NIR spectrum of each reference sample in a wavelength range of 700 nm to 2000 nm, preferably from 900 nm to 1700 nm, particularly from 1400 nm to 1600 nm, and particularly advantageously from 1450 nm to 1550 nm, using at least one NIR measuring head;assign the different quantitative amounts of the powdered resin or resin mixture from the reference samples to the recorded NIR spectra of the aforementioned reference samples; generate a calibration model for the relationship between the spectral data of the NIR spectra and the corresponding quantitative amounts of the powdered resin or resin mixture from the reference samples using multivariate data analysis; apply at least one layer of at least one powdered resin or resin mixture onto a support material; record at least one NIR spectrum of the support material coated with the powdered resin or resin mixture in a wavelength range of 700 nm to 2000 nm, preferably 900 nm to 1700 nm, in particular 1400 nm to 1600 nm, particularly advantageously 1450 to 1550 nm, using at least one NIR measuring head;and determine the quantitative amount of powdered resin or resin mixture applied to the support material by comparing the NIR spectrum recorded for the coated support material with the generated calibration model.

Description

[0001] The present invention relates to a method for controlling a production line for manufacturing a coated substrate material, wherein at least one layer of at least one powdered resin or resin mixture is applied to the at least one substrate material. Description

[0002] The use of engineered wood panels in the furniture industry, as flooring, or for cladding walls and ceilings requires surface treatment and finishing. Typically, in these applications, the panels are coated with an impregnated decorative paper. There are virtually no limits to the variety of decorative papers available, allowing engineered wood panels to be produced with a multitude of different decors, such as stone or wood finishes. To increase wear resistance, overlays are applied to the decorative paper. These overlays are typically thin papers already impregnated with melamine resin. Overlays are also available that incorporate abrasion-resistant particles, such as corundum particles, into the resin to further enhance the abrasion resistance of the laminate or engineered wood panel.

[0003] As an alternative to using decorative papers on wood-based panels, direct printing on wood-based panels has developed in the past, as this eliminates the need for printing on paper and subsequently laminating or directly coating the wood-based panel. Several layers of liquid, thermosetting resin are then applied to the directly printed decorative layer. These layers may contain abrasion-resistant particles to increase wear resistance. Such a thermosetting resin layer is also known as a liquid overlay.

[0004] The resins or adhesives used in these applications are usually liquid, often aqueous, formulations for impregnating paper layers or coating substrates. These are applied to paper via a saturation process in an impregnation channel or to sheet-like substrates by roller application. The solvent is then evaporated by heated air or radiation. This is a relatively energy-intensive process and also results in emissions that must be eliminated via thermal afterburning or an exhaust air purification system. Furthermore, this process is also considered critical from an environmental perspective.

[0005] The application rates onto paper or substrates are adjusted using roller gaps, doctor blades, etc., and then usually checked by weighing. This technology was also used when working with resin mixtures.

[0006] An alternative to liquid resins or adhesives is the use of powdered resins. These can be applied to paper or substrates via spreading devices or spray nozzles. Since these applications are contactless, the amount applied per unit area can only be determined by the quantity consumed per unit of time. However, inhomogeneities due to turbulence or static influences are possible with powdered applications. This can be particularly problematic at the edges and boundaries of the system. Furthermore, determining the amount applied to paper or substrates often requires waiting until the end of the production line, after the powder has been fixed by compression or curing. Otherwise, powder may fall off during sampling. This is especially critical when multiple applications are made consecutively, as only the total amount applied can be determined at the end.For many products, however, the product quality depends crucially on the precise application of the individual layers. Cost disadvantages can also arise if certain functional layers are not applied in the desired manner.

[0007] Disadvantages include the lack of in-line monitoring and the need for readjustment, which can only be carried out with a time delay. Furthermore, variations in the composition of the applied resin powder or resin powder mixtures are not detectable.

[0008] The invention is therefore based on the technical problem of developing a non-destructive method that can determine the application quantity and composition of a powdered resin or adhesive application. The method is intended to be installed in-line in production lines and to provide as many measurements as possible per unit of time in and across the production direction. The measurements should not disrupt the production process.

[0009] This problem is solved by a method having the features of claim 1.

[0010] Accordingly, a method for controlling a production line for manufacturing a coated substrate material is provided, wherein at least one layer of at least one powdered resin or resin mixture is applied to the at least one substrate material. wherein the production line comprises at least one NIR multi-sensor head for recording at least one NIR spectrum of the substrate material coated with the powdered resin or resin mixture using the at least one NIR sensor head in a wavelength range between 1400 nm and 1600 nm, preferably between 1450 nm and 1550 nm; 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 NIR spectrum recorded for the substrate material coated with the powdered resin or resin mixture with a created calibration model in order to determine the quantitative amount of powdered resin or resin mixture applied to the substrate material, wherein the database is configuredto store the parameter data thus determined regarding the application quantity of powdered resin, wherein the control system is configured to use the determined parameters to control the production line, wherein the calibration model is determined using reference samples as follows: application of at least one powdered resin or a powdered mixture of at least two resins in a defined mixing ratio in different quantitatively defined quantities onto a carrier material as reference samples; recording of at least one NIR spectrum of each of the reference samples using at least one NIR measuring head in a wavelength range between 700 nm and 2000 nm, preferably between 900 nm and 1700 nm, particularly preferably between 1400 nm and 1600 nm,and particularly advantageously between 1450 nm and 1550 nm; assignment of the different quantitative amounts of powdered resin or resin mixture of the reference samples to the recorded NIR spectra of said reference samples; and creation of a calibration model for the relationship between the spectral data of the NIR spectra and the corresponding quantitative amounts of powdered resin or resin mixture of the reference samples by means of a multivariate data analysis.

[0011] The quantity and / or composition of at least one layer of at least one powdered resin or resin mixture applied to at least one carrier material is determined using the calibration model with the following steps: Applying at least one layer of at least one powdered resin of the resin mixture onto a substrate material; recording at least one NIR spectrum of the substrate material coated with the powdered resin or resin mixture using the at least one NIR measuring head in a wavelength range between 700 nm and 2000 nm, preferably between 900 nm and 1700 nm, particularly preferably between 1400 nm and 1600 nm and particularly advantageously between 1450 nm and 1550 nm; and determining the quantitative amount of the powdered resin or resin mixture applied to the substrate material by comparing the NIR spectrum recorded for the coated substrate material with the created calibration model.

[0012] According to the present method, a NIR spectrum of the powdered resin applied to a substrate, such as a backing board or paper, is recorded. This allows not only the determination of the application quantity but also the analysis of the composition of a powdered resin or adhesive mixture. To this end, NIR spectra of various application quantities of powdered resins or resin mixtures on different substrates were first recorded. This was intended to examine the influence of the substrate on the spectrum. Surprisingly, it was found that even application quantities of up to 600 g resin powder / m² could be determined. The same procedure was then carried out with resin mixtures. Calibration models were subsequently created, which can then be used to infer unknown quantities and compositions. A further advantage is that other parameters (e.g., moisture content, see, for example, [reference]) can also be determined from the NIR spectra.EP 2 915 658 B1, EP 2 808636 B1) can be analyzed. This can also help to avoid quality defects.

[0013] While US Patent 2007 / 131862A1 discloses the use of NIR spectroscopy to determine the composition of samples made from mixtures of wood particles and other components such as resin, wax, polyols, and inorganic hardeners, this method requires the samples to be crushed, ground, and mixed before measurement. The aim is to monitor and improve process variables for the production of wood-based composites, such as mixing efficiency, rotational speed, resin temperature, etc.

[0014] In contrast, the inventive method is used after the finished substrate material, in particular after a pressed wood-based panel (e.g., HDF panel), has been provided, during the surface finishing process of the wood-based panel. According to the inventive method, the quantity and composition of a resin powder sprinkled onto a substrate material (such as a pre-pressed wood-based panel) are determined; that is, it is not necessary to grind the sample to be measured before measurement using NIR spectroscopy. This allows for continuous measurement.

[0015] As explained further below, NIR spectroscopy can be used to determine the composition of a wide variety of resins and adhesives. These can include, among others, powdered melamine-formaldehyde resins, urea-formaldehyde resins, phenol-formaldehyde resins, or mixtures thereof. Other resins may be based on powdered polyester, epoxy resin, etc. The powdered resins may also contain additives such as hardeners, pigments, antistatic agents, etc. Additives to improve application properties may also have been used.

[0016] This method can be used on a production line both in the direction of production and perpendicular to it. Visualization allows changes in order quantities or distribution to be shown in a timely manner.

[0017] This method enables the rapid provision of measurement data (online, preferably without disruptive delays) compared to conventional (known) measurement methods. The measurement data can be used for quality assurance, research and development, process control, process regulation, process management, etc. The measurement process does not reduce production speed or other factors. In principle, this improves production monitoring. Furthermore, downtime due to quality control and equipment adjustments is also reduced.

[0018] The determination of the application quantity of powdered resin or resin mixture possible with the present method is preferably carried out exclusively by means of NIR measurement. A combination with other spectroscopic methods, in particular using wavelengths other than the NIR range, is not intended.

[0019] This method employs a near-infrared (NIR) measuring head, preferably a multi-sensor NIR measuring head, which allows for the determination of the quantity of powdered resin by acquiring spectral data (spectra) in the near-infrared range (700–2000 nm). The NIR radiation interacts with organic functional groups, such as OH, CH, and NH, which are present in both urea and melamine resins. During this interaction, the NIR radiation is scattered and reflected by the sample. The reception of the reflected NIR radiation by the NIR detector generates an NIR spectrum. In this measurement process, numerous individual NIR measurements are performed per second, thus ensuring statistical reliability of the values.NIR spectroscopy, together with the (listed below) multivariate data analysis, offers a way to establish a direct link between the spectral information (NIR spectra) and the parameters of the applied resin layer to be determined.

[0020] The present method utilizes the fact that NIR radiation does not penetrate the substrate material but is reflected or scattered at its surface. The reflected or scattered NIR radiation is detected by the NIR detector, and the resulting NIR spectrum is used to determine the desired parameters (in this case, the amount of powdered resin applied).

[0021] To determine the amount of powdered resin applied, spectral data from the entire recorded spectral range are preferably used; that is, not a single, discrete wavelength, but rather an entire range of several wavelengths is used.

[0022] According to the inventive method, reference samples of the substrate material coated with a resin or resin mixture are first provided. For the provision of the reference samples, various quantities of powdered resin or a powdered resin mixture, e.g., 10 g / m², 20 g / m², 40 g / m², 60 g / m², 80 g / m² and / or 100 g / m², are applied to the substrate material to be coated.

[0023] In the case of a powdered resin mixture, a defined mixture of a first powdered resin and a second powdered resin, e.g., a defined mixture of urea resin and melamine resin, was applied to the substrate material to be coated. Mixtures with a ratio of 25 wt% : 75 wt%, 50 wt% : 50 wt%, and 75 wt% : 25 wt% were applied as reference samples. At the endpoints of this series, 100% of both the first and second powdered resins were determined as reference samples.

[0024] It is also important to note that the reference sample must be identical to the sample being measured; that is, in particular, the resin layer of the reference sample must have the same composition as the resin layer being measured. The similarity of the sample being measured and the reference sample is especially important when using powdered resin layers with additives such as flame retardants, fibers, or other additives.

[0025] At least one NIR spectrum is recorded from these reference samples in a wavelength range between 700 nm and 2000 nm, preferably between 900 nm and 1700 nm, particularly preferably between 1400 nm and 1600 nm, and most advantageously between 1450 nm and 1550 nm.

[0026] The varying quantities of powdered resin in the reference samples are then assigned to the respective recorded NIR spectra of these reference samples. A calibration model is created for the relationship between the spectral data of the NIR spectra of the reference samples and the corresponding resin quantities as parameter values ​​using multivariate data analysis; that is, each parameter value of the reference sample corresponds to a specific NIR spectrum of the reference sample. The calibration models created for the various parameters are stored in a suitable data repository.

[0027] Subsequently, at least one layer of at least one powdered resin or resin mixture is applied to a substrate, and at least one NIR spectrum of the powdered resin layer applied to the substrate is recorded. The quantitative amount of powdered resin or resin mixture applied to the substrate can be determined by comparing the NIR spectrum recorded for the coated substrate with the established calibration model.

[0028] A comparison and interpretation of the NIR spectra is best performed across the entire recorded spectral range. This is advantageously carried out using a well-established multivariate data analysis (MDA). Multivariate analysis methods typically examine several statistical variables simultaneously in a well-established manner. These methods usually reduce the number of variables contained in a dataset without diminishing the information it provides.

[0029] In this case, multivariate data analysis is performed using partial least squares regression (PLS), which allows for the creation of a suitable calibration model. The evaluation of the obtained data is preferably carried out using appropriate analysis software, such as SIMCA-P from Umetrics AB or The Unscrambler from CAMO.

[0030] In another embodiment, it is provided that spectral data from the NIR spectral range between 1450 and 1550 nm are used for the creation of the calibration model, which are pretreated using suitable mathematical methods and then subjected to multivariate data analysis.

[0031] The significance of a wavelength for predicting resin layer parameters, such as the amount of resin, from the NIR spectrum is illustrated using regression coefficients. Regions with large coefficient values ​​have a strong influence on the regression model. For example, the representation of regression coefficients in a PLS regression model for determining the amount or content of resin shows that the wavelength range between 1460 nm and 1530 nm, with a maximum at 1490 nm (absorption band of the resin's amino groups), is most important for the model calculation, as the regression coefficient values ​​are highest in this range. While other regions of the spectrum contain less information regarding the NIR measurement, they nevertheless contribute to incorporating additional information and interfering factors (such as layer transparency, surface properties of the resin layer or the substrate, etc.).to minimize.

[0032] To eliminate interfering influences (such as the surface properties of the support material, the color of the samples, light scattering by solid particles or other additives, etc.), it is necessary to pretreat the spectral data using mathematical methods (e.g., derivative data pretreatment, standardization according to SNVT ( S standard N normal V ariate T transformation), multiplicative signal correction (EMSC, E extended M ultimate S signal C(correction, etc.). This involves removing baseline effects, primarily caused by the different sample colors, from the spectra, separating overlapping bands, and taking into account the dependence of light scattering at the substrate surface or on the solid particles in the coating. For example, if the resin application rate is to be determined on untreated surfaces of substrate materials such as wood-based panels, data pretreatment is preferably performed to reduce light scattering at the rough surface of the substrate. When measuring on a decorative layer, the focus of calibration and data pretreatment is on removing baseline shifts.

[0033] In one embodiment of the present method, the powdered resin to be applied is a formaldehyde resin, preferably a urea resin, a melamine resin, or a phenolic resin, and in particular preferably a melamine-formaldehyde resin or a urea-formaldehyde resin. Other resins based on powdered polyester, epoxy resin, etc., can also be used.

[0034] The particle size of the powdered resin is between 20 and 100 µm, preferably between 40 and 89 µm.

[0035] In one embodiment of the present method, at least one mixture of at least two powdered resins is applied to the at least one carrier material. A mixture of urea and melamine resin is preferred. Urea and melamine resins exhibit very similar NIR spectra, with the urea resin peak lying in the shoulder of the melamine resin peak.

[0036] The at least one mixture can contain a first powdered resin and a second powdered resin in a ratio between 10 wt% : 90 wt% and 90 wt% : 10 wt%, preferably between 25 wt% : 75 wt% and 75 wt% : 25 wt%, particularly preferably between 55 wt% : 45 wt% and 45 wt% : 55 wt%, e.g. 50 : 50 wt%.

[0037] In one embodiment of the present method, the powdered resin or the mixture of at least two powdered resins is applied to the at least one carrier material in an amount of up to 600 g / m², preferably up to 400 g / m², and particularly preferably up to 200 g / m². Alternatively, the powdered resin or the mixture of at least two powdered resins can be applied to the at least one carrier material in an amount between 10 and 150 g / m², preferably between 20 and 100 g / m², and particularly preferably between 40 and 80 g / m².

[0038] Other substances can also be added to the resin powder. A particular advantage is that substances that are poorly compatible with liquid melamine resin, such as those that affect salting out, thickening, settling, or curing, can be used. These substances can include salts to increase conductivity, organic or inorganic flame retardants, cellulose derivatives, radical scavengers, pigments, UV absorbers, etc.

[0039] Accordingly, the powdered resin used may contain additives such as pigments, conductive substances and cellulose.

[0040] By adding color pigments, the resin powder layer can simultaneously serve as a white primer layer for a decorative layer that may be subsequently printed on. White pigments such as titanium dioxide (TiO₂) can be used as color pigments. Other color pigments include calcium carbonate, barium sulfate, or barium carbonate. The proportion of color pigments can be up to 50% by weight of the total powder quantity.

[0041] The addition of color pigments to the first layer of resin powder increases the opacity, so that it can be used as the (sole) base or primer for the subsequent decorative layer.

[0042] The amount of cellulose fibers applied with the resin powder can be between 0.1 and 1 wt%, preferably between 0.5 and 0.8 wt% (based on the amount of resin to be applied), or between 0.1–0.5 g / m², preferably 0.2–0.4 g / m², and particularly preferably 0.25 g / m². The cellulose fibers preferably used are colorless and in the form of a fine or granular, slightly hygroscopic powder.

[0043] The conductive substances can be selected from the group containing carbon black, carbon fibers, metal powders, and nanoparticles, especially carbon nanotubes. Combinations of these substances can also be used.

[0044] The resins used preferably contain additives such as hardeners, wetting agents (surfactants or mixtures thereof), release agents and / or other components.

[0045] In one embodiment, a paper layer is used as the substrate. Examples of paper layers include overlay papers, decorative papers, or kraft papers. Overlay papers are thin papers that are typically already impregnated with a conventional melamine resin. Overlay papers are also available in which abrasion-resistant particles, such as corundum particles, are already mixed into the resin to increase abrasion resistance. Decorative papers are specialty papers for surface finishing of wood-based materials, allowing for a wide variety of decorative designs. In addition to the typical prints of various wood textures, more extensive prints of geometric shapes or artistic designs are available. There are virtually no limitations on the choice of motif.Kraft papers have high strength and consist of cellulose fibers to which starch, alum and glue are added to achieve surface effects and increase strength.

[0046] In another embodiment, a support panel is used as the support material. In this case, this support panel is preferably a panel made of a wood-based material, plastic, a wood-based material-plastic mixture or a composite material, in particular a particleboard, medium-density fiberboard (MDF), high-density fiberboard (HDF), oriented strand board (OSB) or plywood panel, a cement fiberboard, gypsum fiberboard or a WPC panel (wood plastic composite) or an SPC panel (stone plastic composite).

[0047] As already indicated above, the inventive method for determining the amount of powdered resin or resin mixture applied to the substrate can be carried out continuously and online in a production line, in particular in a production line for manufacturing wood-based panels or in a production line for impregnating paper layers. In particular, the method can be carried out in an automatically controlled system with alarm notification.

[0048] The determination of the amount of powdered resin applied to at least one carrier material can be carried out several times in the production line, in particular after each time the material leaves a device for applying a layer of powdered resin.

[0049] In one embodiment of the present measuring method, it is provided that the at least one NIR measuring head moves transversely to the direction of travel of the carrier material containing the powdered resin in the production line and traverses the entire width of the carrier material in order to analyze certain problem areas, in particular under-deposition in the edge or middle area of ​​the carrier material.

[0050] In a further embodiment of the present measuring method, the at least one NIR measuring head moves in the direction of travel of the carrier material containing the powdered resin in the production line; i.e., in this embodiment, the measuring head can remain stationary in a position that is considered, for example, particularly critical.

[0051] This provides a method in which the quantity and composition of an applied resin powder or resin mixture can be determined from a single NIR spectrum or the reflection or scattering of NIR radiation using a non-contact measurement with an NIR measuring head. In an advantageous embodiment of the invention, the data obtained with the measuring head(s) are used directly for system control or regulation.

[0052] Furthermore, in another advantageous embodiment of the invention, data storage enables improved quality control. The stored data can also advantageously contribute to the evaluation of plant trials, for example, during the commissioning of a new plant, after maintenance or repair, or for in-situ testing of new production or measurement processes. The immediate availability of the measured values ​​and the high measurement frequency allow for very close monitoring, control, and regulation of the plants.

[0053] The advantages of the present method are manifold: Non-contact multi-parameter determination ("real time" or "real-time" measurement) with significantly reduced time delay in the evaluation of the measured parameter values; improved plant control and regulation, reduction of scrap, improvement of the quality of the products manufactured on the plant, improvement of plant availability.

[0054] The control system of each production plant comprises at least one computer-aided evaluation unit (or processor unit) and a database. In the evaluation unit, the NIR spectrum measured for the product (i.e., coated substrate material) is compared with the calibration models created for each individual parameter. The parameter data determined in this way is stored in the database.

[0055] The data determined using the present spectroscopic method can be used to control the respective production line. The non-contact measured parameter values ​​of the NIR multi-sensor head ("actual values") can, as previously described, be used directly and in real time for the control of 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.

[0056] For the alignment and control of the respective 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 control system of the respective production line.

[0057] The following section describes in detail two processes and production lines in which the measurement method according to the invention can be used.

[0058] Thus, a first process for manufacturing a wood-based panel with a decorative finish comprises the following steps: a) Applying at least one first layer of at least one powdered resin or resin mixture to at least one side of a wood-based panel and melting the at least one applied layer of powdered resin; b) Applying at least one decorative layer by means of a direct printing process; and c) Applying at least one further (second) layer of at least one powdered resin or resin mixture to the at least one printed decorative layer and melting the at least one layer of powdered resin sprinkled onto the decorative layer.

[0059] The measuring method according to the invention for determining the application quantity of the powdered resin (or powdered resin mixture) is preferably carried out following the respective step of applying the first and / or second and / or each further layer of powdered resin.

[0060] "Action melting" or "gelling" within the meaning of the present application means that the resin layer is not yet fully polymerized, but rather the polymerization is stopped at an intermediate stage in which further crosslinking or polymerization is still possible at a later processing stage. The purpose of "gelling" is therefore usually to allow for the application of further functional layers to the already applied protective layer at a later stage, or to complete the product only in further processing steps.

[0061] In a preferred embodiment, the resin powder is applied by means of electrostatic charging. Application can also be carried out by powder coating using the tribological process. In this case, the powder to be applied is charged by friction.

[0062] The melting of the applied layer of powdered resin or resin mixture can be carried out using an IR emitter, microwave systems, or similar devices. The use of IR emitters is particularly preferred.

[0063] The surface of the substrate can be surface-treated; for example, in the case of a wood-based substrate, the surface can be sanded or unsanded and have a pressed-on skin. In the case of a plastic substrate, the surface can be corona-treated.

[0064] In a preferred embodiment, in a next step at least one primer is applied to the (first) melted resin powder layer to increase the opacity.

[0065] The primer preferably comprises casein, cornstarch or soy protein and may contain inorganic color pigments, thus serving as a primer layer for the decorative layer to be printed on subsequently.

[0066] White pigments such as titanium dioxide (TiO₂) can be used as color pigments. Other color pigments include calcium carbonate, barium sulfate, or barium carbonate, as well as iron oxide pigments (for a brownish base coat). In addition to the color pigments and casein, cornstarch, or soy protein, the base coat may also contain water as a solvent.

[0067] The amount of liquid primer applied can be between 10 and 50 g / m², preferably between 15 and 30 g / m², and particularly preferably between 20 and 25 g / m².

[0068] It is also conceivable that the primer consists of at least one, preferably at least two or more successively applied layers or coats (e.g. up to five coats), wherein the amount of coating applied between the layers or coats is the same or different, i.e. the amount of coating applied to each individual layer can vary.

[0069] The primer can be applied to the wood-based substrate using a roller, followed by drying. Alternatively, it can be applied to the plastic substrate using digital printing. The digital printing inks used for this purpose are preferably UV-based or water-based inks enriched with white pigments. However, water-based or hybrid inks can also be used. Digital printing is advantageous because the printing system is significantly shorter than a roller application, thus saving space, energy, and costs.

[0070] In another embodiment of the present process, a primer layer is applied to the primer, preferably as a single application followed by drying. The primer layer is particularly useful in the case of a subsequent gravure printing process (with rollers), whereas it is not strictly necessary when using a digital printing process.

[0071] The amount of liquid primer applied is between 10 and 30 g / m², preferably between 15 and 20 g / m². Polyurethane-based compounds are preferably used as primers.

[0072] For direct printing on wood-based panels, gravure and digital printing processes are advantageously used. Gravure printing is a printing technique in which the elements to be reproduced are recesses in a printing plate, which is inked before printing. The 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. Indirect gravure printing uses multiple printing rollers.

[0073] In a particularly preferred embodiment, the at least one decorative element is applied to the (surface-treated and pre-coated) substrate using a digital printing process. In digital printing, the print image is transferred directly from a computer to a printing machine, such as a laser printer or inkjet printer. This eliminates the need for a static printing plate. The decorative printing is carried out according to the inkjet principle in a single pass, where the entire width of the surface to be printed is covered, with the plates moving under the printer. However, it is also possible for the substrate to be held under the printer, which then passes over the surface at least once during printing.

[0074] The printing inks are grouped in separate printhead rows, with one or two rows of printheads available for each color. Digital printing inks include, for example, black, blue, red, reddish yellow, and greenish yellow; CMYK is also optional. These digital printing inks are optionally based on the same pigments used for analog and / or digital printing with water-based inks. UV-based digital printing inks are preferred, but water-based or hybrid inks are also possible. After printing, the decorative print undergoes drying and / or irradiation.

[0075] The printing inks are applied in an amount between 1 and 30 g / m², preferably between 3 and 20 g / m², and particularly preferably between 3 and 15 g / m².

[0076] Along with the decoration, the markings required for alignment in the press are also printed on the surface.

[0077] It is possible to temporarily store the printed plate after this process step. In this case, the applied and partially melted resin powder layer serves as a protective layer, which on the one hand protects the printed surface during temporary storage and on the other hand (due to the resin layer not yet being fully cured) enables further processing. Particularly in complex processing operations, decoupling certain work steps is necessary for reasons of cost, technology, etc. For example, linked production lines can vary significantly in their productivity. In such cases, buffer storage must be established where materials are stacked on top of each other. Furthermore, multiple passes may be necessary in a production line because order quantities, etc., cannot be processed in a single pass. In all these cases, partially dried or...Hardened surfaces are advantageous because they both protect the printed surface in case of intermediate storage and allow for further processing.

[0078] In a further embodiment, abrasion-resistant particles are evenly sprinkled onto the decorative layer or the resin powder layer applied in step c) (step d).

[0079] Abrasion-resistant particles such as corundum (aluminum oxides), boron carbides, silicon dioxides, and silicon carbides can be used. Corundum particles are particularly preferred. Ideally, these are high-quality (white) corundum with high transparency to minimize any adverse effect on the underlying decorative layer. Corundum has an irregular shape.

[0080] The amount of abrasion-resistant particles applied is 7 to 50 g / m², preferably 10 to 30 g / m², and particularly preferably 15 to 25 g / m². The amount of abrasion-resistant particles applied depends on the desired abrasion class and the particle size. For example, the amount of abrasion-resistant particles for abrasion class AC3 is in the range of 10 to 15 g / m², for abrasion class AC4 it is in the range of 15 to 20 g / m², and for abrasion class AC5 it is in the range of 20 to 35 g / m² when using F200 grain size. In the present case, the finished panels preferably have abrasion class AC4.

[0081] Abrasion-resistant particles with grain sizes in classes F180 to F240, preferably F200, are used. The grain size of class F180 covers a range of 53–90 µm, F220 45–75 µm, F230 34–82 µm, and F240 28–70 µm (FEPA standard). In one variant, white corundum F180 to F240, preferably with a main grain size range of 53–90 µm, is used as the abrasion-resistant particles. In a particularly preferred embodiment, corundum particles of classes F180–220 are used. The abrasion-resistant particles must not be too fine (risk of dust formation) but also not too coarse. The size of the abrasion-resistant particles thus represents a compromise. In a further embodiment, silanized corundum particles can be used. Typical silanizing agents are aminosilanes.

[0082] In a further embodiment of the present method, at least a third layer of at least one powdered resin (step e) is applied, in particular to the layer of abrasion-resistant particles, and melted. This layer serves as a separating layer to seal off the abrasion-resistant particles.

[0083] In a further embodiment of the present method, glass spheres are sprinkled, in particular onto the at least one third molten resin powder layer (step f). The glass spheres serve as spacers between abrasion-resistant particles and the subsequent press sheet. This allows sheet wear to be at least partially reduced.

[0084] The glass beads preferably used have a diameter of 60–120 µm, preferably 80–90 µm. The diameter of the glass beads is matched to the average particle size of the abrasion-resistant particles used to ensure optimal sealing against the subsequent press plate. Thus, in the case of corundum F220, glass beads with a diameter between 70–90 µm are used, and in the case of corundum F180, glass beads with a diameter between 80–120 µm are used. The amount of glass beads is 5 to 30 g / m², preferably 8 to 20 g / m², and particularly preferably 8 to 15 g / m². The glass beads can also be in silanized form. Silanization of the glass beads improves their embedding in the resin matrix.

[0085] In a further embodiment of the present method, at least a fourth layer of at least one powdered resin (step f) is applied, in particular to the layer of glass beads, and fused. This layer serves to seal the glass beads and as a finishing layer.

[0086] In a further embodiment of the present method, the layer structure is pressed in a short-cycle press (CT press) (step h). The pressing step takes place under pressure and temperature at temperatures between 180 and 250°C, preferably between 200 and 230°C, particularly preferably at 200°C, and a pressure between 30 and 60 kg / cm², particularly preferably between 40 and 50 kg / cm². The pressing time is between 8 and 30 seconds, preferably between 10 and 25 seconds.

[0087] Preferably, the coated wood-based panel is aligned in the short-cycle press with a structured press plate located in the short-cycle press using markings on the wood-based panel, so that an alignment is achieved between the decor on the wood-based panel and the structure to be embossed on the press plate.

[0088] This enables the production of a decor-synchronous structure. During pressing, the melamine resin layers melt and a laminate is formed through a condensation reaction, encapsulating the components corundum / glass / fibers.

[0089] A counter-layer, such as several layers of resin without additives or a counter-layer paper, can be applied to the underside of the wood-based panel. This ensures that the tensile forces exerted on the wood-based panel by the applied layers during pressing cancel each other out. The counter-layer applied to the underside corresponds approximately in its layer structure and thickness to the layer sequence applied to the top side, but without the addition of abrasion-resistant particles or glass beads. An impregnating agent can also be used as a counter-layer.

[0090] The production line for manufacturing a substrate panel with a decorative finish, in particular a wood-based panel, can therefore include the following elements: at least one application device for applying a first layer of resin powder, which may contain fibers, to the top surface of the wood-based panel and at least one device for melting the first layer of resin powder, in particular an IR emitter; optionally at least one application device for applying at least one primer layer; optionally at least one application device for applying at least one primer layer; at least one printing device; optionally at least one application device for applying a further layer of resin powder and at least one device for melting the resin powder layer, in particular an IR emitter; optionally at least one device for sprinkling a predetermined quantity of abrasion-resistant particles; at least one application device for applying a further layer of resin powder and at least one device for melting the resin powder layer, in particular an IR emitter; optionally.at least one device for sprinkling a predetermined quantity of glass beads; optionally at least one application device for applying a further layer of resin powder and at least one device for melting the first layer of resin powder, in particular an IR emitter; and optionally at least one short-cycle press arranged downstream of the last drying device in the processing direction; wherein, downstream of the application device for applying a first layer of resin powder and / or downstream of the application devices for applying each further layer of resin powder, at least one NIR measuring head, preferably at least one NIR multi-measuring head, is provided for recording at least one NIR spectrum of the wood-based panel coated with the powdered resin.

[0091] As mentioned, the NIR measurement method according to the invention can also be used for coating paper layers with resin powder.

[0092] A process for coating a layer of paper as a substrate material comprises the following steps: Applying at least one layer of at least one powdered resin (or powdered resin mixture) to at least one side of a paper layer and melting the at least one applied layer of powdered resin or resin mixture; and drying and hardening the layer structure.

[0093] The measuring method according to the invention for determining the application quantity of the powdered resin (or powdered resin mixture) is preferably carried out following the step of applying the layer of powdered resin or resin mixture.

[0094] A production line used for coating paper layers with a powdered resin comprises at least one application device for applying at least one layer of resin powder, in particular by means of triboguns, at least one device for melting the resin powder layer, preferably using an IR emitter, and at least one device for drying and hardening the coated paper layer.

[0095] At least one NIR measuring head is provided after the application device for applying a resin powder layer to record at least one NIR spectrum of the paper layer coated with the powdered resin.

[0096] In both versions of the production lines (wood-based panel, impregnated), the NIR measuring heads are each connected to a control system with an evaluation unit and database for processing and storing the acquired NIR data. If the measured actual values ​​deviate from the target values, the system control automatically adjusts them. Essentially, all NIR measuring heads used in a production line transmit their measured actual values ​​to the central control and evaluation unit. If the measured actual values ​​of, for example, a single NIR measuring head deviate from the corresponding target values, this unit adjusts the production process accordingly or proactively controls it.

[0097] The invention is explained in more detail below using exemplary embodiments with reference to the figures. The figures show: Figure 1: NIR spectra of different amounts of melamine powder resin. Figure 2: NIR spectra of different amounts of urea resin. Figure 3: NIR spectra of urea and melamine powder resins and of mixtures of both powder resins. Example 1:

[0098] Different amounts of powdered melamine resin (20, 40, 80, and 100 g / m²) were applied to a decorative paper in a medium shade. Spectra were recorded from the different application amounts using a NIR measuring head. A calibration model was then created from these spectra using software. The peak at approximately 1500 nm proved particularly suitable (see [reference]). Fig. 1 Subsequently, unknown application quantities of melamine resin were determined on various substrate materials with different color tones. Example 2:

[0099] The same procedure was used for powdered urea resin. The same application quantities were analyzed. Here too, the peak around 1500 nm could be used to create a calibration model (see Fig. 2 ). Example 3:

[0100] Subsequently, mixtures of urea and melamine resin were prepared. The total quantity was 40 g / m² in each case. The concentrations were varied between 100%, 25% / 75%, 50% / 50%, 25% / 75%, and 100%. Here, too, analysis proved possible. The spectra of the mixtures lay between those of urea powder resin and melamine powder resin. With increasing melamine content, they approached the melamine spectrum. Again, the peak around 1500 nm is suitable for creating a calibration (see [reference]). Fig. 3 ). After creating a calibration, the homogeneity of the mixture can be checked or application quantities can be determined for powder mixtures.

Claims

1. A method of controlling a production line for the manufacture of a coated carrier material, wherein at least one layer of at least one powdered resin or resin mixture is applied to the at least one carrier material, wherein the production line comprises at least - at least one NIR multi-measuring head for recording at least one NIR spectrum of the carrier material coated with the powdered resin or resin mixture using the at least one NIR measuring head in a wavelength range between 1400 nm and 1600 nm, preferably between 1450 nm and 1550 nm; - 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 NIR spectrum recorded for the carrier material coated with the powdered resin or resin mixture with a created calibration model to determine the quantitative amount of the powdered resin or resin mixture applied to the carrier material, - wherein the database is configured to store the thus determined parameter data on the amount of powdered resin applied, - wherein the control system is configured to use the determined parameters to control the production line, wherein the calibration model is determined based on reference samples as follows: - applying at least one powdered resin or a powdered mixture of at least two resins in a defined mixing ratio in respectively different quantitatively defined amounts to respectively one carrier material as reference samples; - recording at least one NIR spectrum of each of the reference samples using at least one NIR measuring head in a wavelength range between 1400 nm and 1600 nm, preferably between 1450 nm and 1550 nm; - correlating the different quantitative amounts of powdered resin or resin mixture of the reference samples to the recorded NIR spectra of said reference samples; and - creating the calibration model for the relationship between the spectral data of the NIR spectra and the corresponding quantitative amounts of powdered resin or resin mixture of the reference samples by means of multivariate data analysis.

2. Method according to claim 1, characterized in that the NIR multi-measuring head is configured to supply the measured parameters (actual values) to the evaluation unit, which controls the production process accordingly if the measured parameters (actual values) deviate from the corresponding target values of these parameters.

3. Method according to one of the preceding claims, characterized in that the powdered resin is a formaldehyde resin, preferably a urea resin, a melamine resin or a phenolic resin, in particular preferably a melamine-formaldehyde resin or a urea resin.

4. Method according to one of the preceding claims, characterized in that at least one mixture of a first powdered resin and a second powdered resin is applied to the at least one carrier material.

5. Method according to claim 4, characterized in that the at least one mixture comprises a first powdered resin and a second powdered resin in a ratio between 10% by weight: 90% by weight and 90% by weight : 10% by weight, preferably between 25% by weight : 75% by weight and 75% by weight : 25% by weight, more preferably between 55% by weight : 45% by weight and 45% by weight : 55% by weight, e.g. 50 : 50% by weight.

6. Method according to one of the preceding claims, characterized in that the powdered resin or the mixture of at least two powdered resins is applied in an amount of between 10 and 150 g / m2, preferably between 20 and 100 g / m2, more preferably between 40 and 80 g / m2.

7. Method 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 pretreated, impregnated paper.

8. Method according to claim 7, characterized in that the production line is a production line for impregnating paper layers, comprising at least one application device for applying at least one resin powder layer, in particular by means of tribo-guns, at least one device for melting the resin powder layer, preferably using an IR emitter, and at least one device for drying and curing the coated paper layer.

9. Method according to one of claims 7-8, characterized in that at least one NIR measuring head is provided after the application device for applying a resin powder layer for recording at least one NIR spectrum of the paper layer coated with the powdered resin.

10. Method 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 fibreboard (MDF), high-density fibreboard (HDF), oriented strand board (OSB) or plywood board, made of plastic, a wood-based material / plastic mixture or a composite material, a cement fibreboard, gypsum fibreboard or a wood plastic composites (WPC) board or a stone plastic composites (SPC) board.

11. Method according to claim 10, characterized in that the production line is a production line for manufacturing a wood-based panel provided with a decor, comprising - at least one application device for applying a first resin powder layer, which may contain fibers, to the top surface of the wood-based panel and at least one device for melting the first resin powder layer, in particular an IR emitter; - opt. at least one application device for applying at least one primer layer; - opt. at least one application device for applying at least one primer layer; - at least one printing device, - opt. at least one application device for applying a further resin powder layer and at least one device for melting the resin powder layer, in particular an IR emitter; - opt. at least one device for scattering a predetermined quantity of abrasion-resistant particles; - at least one application device for applying a further resin powder layer and at least one device for melting the resin powder layer, in particular an IR emitter; - opt. at least one device for scattering a predetermined quantity of glass beads; - opt. at least one application device for applying a further resin powder layer and at least one device for melting the first resin powder layer, in particular an IR emitter; and - opt. at least one short-cycle press arranged downstream of the last drying device in the processing direction; - wherein at least one NIR measuring head, preferably at least one NIR multi-measuring head, is provided after the application device for applying a first resin powder layer and / or after the application devices for applying in each case a further resin powder layer, for recording at least one NIR spectrum of the wood-based panel coated with the powdered resin.

12. Method according to one of the preceding claims, characterized in that the determination of the amount of powdered resin or resin mixture applied to the carrier material is carried out continuously and online in the production line.

13. Method according to one of the preceding claims, characterized in that the at least one NIR measuring head moves transversely to the running direction of the carrier material provided with the powdered resin in the production line and traverses over the entire width of the carrier material in order to analyze certain problem areas, in particular shortfall orders in the edge or middle area of the carrier material.

14. Method according to one of the preceding claims, in that the at least one NIR measuring head moves in the running direction of the carrier material provided with the powdered resin in the production line.

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