Method for controlling a press for pressing a substrate material having at least one resin layer disposed on the substrate material

Abstract

The present invention relates to a method for controlling a press for adjusting operating parameters of the press, wherein the press is suitable for pressing a substrate material having at least one resin layer disposed on the substrate material, wherein at least one NIR multi-measurement head is provided upstream of the press in the direction of travel of the substrate material to be pressed, and at least one NIR multi-measurement head is provided downstream of the press in the direction of travel of the substrate material to be pressed, wherein the NIR multi-measurement heads are connected to at least one control system for controlling the press, comprising at least one computer-controlled evaluation unit and a database for processing and, optionally, storing the recorded and evaluated NIR data, comprising the steps of: - determining the degree of cross-linking of the resin layer disposed on the substrate material as at least one first parameter, by recording at least one NIR spectrum of the resin layer applied to the substrate material, in a wavelength range between 500 nm and 2500 nm, preferably between 700 nm and 2000 nm, particularly preferably between 900 nm and 1700 nm and particularly advantageously between 1450 nm and 1550 nm, using the at least one NIR multi-measurement head disposed upstream of the press, and evaluating the recorded NIR spectrum in the evaluation unit by way of an automatic comparison of the recorded NIR spectrum with a calibration model created for the parameter of the resin layer; - determining the degree of curing of the resin layer disposed on the substrate material as at least one second parameter of the resin disposed on the substrate material, by recording at least one NIR spectrum of the resin layer applied to the substrate material in a wavelength range between 500 nm and 2500 nm, preferably between 700 nm and 2000 nm, particularly preferably between 900 nm and 1700 nm and particularly advantageously between 1450 nm and 1550 nm, using the at least one NIR multi-measurement head disposed downstream of the press, and evaluating the recorded NIR spectrum in the evaluation unit by way of an automatic comparison of the recorded NIR spectrum with a calibration model created for the degree of curing of the resin layer; - wherein the determined degree of cross-linking upstream of the press (actual value for the degree of cross-linking) is compared with a target value for the degree of cross-linking, and wherein the determined degree of curing downstream of the press (actual value for the degree of curing) is compared with a target value for the degree of curing, and wherein if the actual value for the degree of cross-linking and if the actual value for the degree of curing deviate from the respective target values, the operating parameters of the press are automatically adjusted by the control system, so that the target value of the degree of cross-linking and the target value of the degree of curing are achieved.

Description

[0001] Method for controlling a press for pressing a carrier material with at least one resin layer arranged on the carrier material

[0002] The present invention relates to a method for controlling a press for adjusting operating parameters of the press, wherein the press is suitable for pressing a carrier material with at least one resin layer arranged on the carrier material.

[0003] Description

[0004] In the production of industrial "prepregs" (impregnated materials, e.g. resin-impregnated paper layers) or surface coatings in the wood-based materials industry, carrier materials are impregnated or coated with resins.

[0005] For this purpose, decorative resin-impregnated papers can be pressed onto the surface of the material board, or laminates, which are first pressed together from several resin-impregnated papers to form a laminate, can be glued onto a wood-based panel. Decors can also be applied directly to the wood-based panel using direct printing, which is then sealed with a resin and pressed.

[0006] The resins used for impregnating paper layers or for directly coating other carrier boards undergo various polymerization and crosslinking states in these processes.

[0007] This will be illustrated below using the melamine-formaldehyde resin frequently used in the production of wood-based panels.

[0008] Melamine and formaldehyde initially react to form water-soluble products by forming methylol groups on the amino groups of melamine (see Scheme I).

[0009] Scheme I

[0010] These melamine-formaldehyde monomers undergo polycondensation after addition of a suitable catalyst, preferably an acid, whereby the monomers are linked via ether and methylene groups and higher molecular weight precondensates and polycondensates are formed (see Scheme II).

[0011] Scheme II

[0012] Precondensates and polycondensates differ in their molecular weight and solubility. For example, low-molecular-weight precondensates may still have limited water solubility, while higher-molecular-weight polycondensates are insoluble. The limited water solubility of precondensates is due, among other things, to the presence of free methylol groups and the low degree of crosslinking of the mostly linear oligomers. The precondensates are thus a polymerization intermediate.

[0013] When the polycondensates are fully cured, strong cross-linking occurs with the release of the remaining free methylol groups as formaldehyde, forming tightly cross-linked plastics via methylene groups (see Scheme III).

[0014] Scheme III

[0015] For synthetic resins that cure via condensation reactions, the following resin states are distinguished:

[0016] A-state: easily soluble in solvent, meltable, curable;

[0017] B-state: only partially soluble in solvent, meltable, curable;

[0018] C-state: insoluble, cured

[0019] During the hot pressing process, pressure and temperature trigger the polycondensation reaction, during which the resin, particularly melamine resin, hardens. This process involves converting the resin from state b (partially condensed, still meltable and hardenable) to state c (fully condensed and hardened).

[0020] The degree of curing of a melamine resin (C stage) and the degree of crosslinking (B stage), which influences the degree of curing, are important tools for determining the surface quality of wood-based products. Excessive curing leads to embrittlement, which can cause cracking during subsequent processing steps (sawing, drilling, milling, etc.). Insufficient curing can lead to poor surface properties with regard to resistance to chemicals and / or wear. This is all the more true if the surface is likely to be exposed to a specific stress on a frequent basis. Examples include a work surface in a laboratory that frequently comes into contact with aggressive chemicals or a floor surface that is subjected to heavy mechanical stress through walking. Conventionally, the degree of curing is determined using the so-called acid test.The surface is exposed to a diluted mineral acid (6 molar hydrochloric acid) for a defined period of time. The change in gloss and / or color is then assessed. The less gloss / color loss is observed, the greater the curing. However, this test also takes time, which means that products that do not meet the required quality are not manufactured until the test results are available. For example, a sample must first be cut from a larger board (format: up to 2800 x 2070 mm). The board from which the sample was cut must be sent to the second choice or rejected because of the cut-out. In addition, the result depends to a certain extent on the color of the decorative paper used or the embrittlement of the melamine resin surface. This complicates the assessment, especially with very light decors and matte surface finishes.However, this test is only a selective test. A reliable statement about the curing of the entire production batch cannot be made. Furthermore, working with concentrated hydrochloric acid is not without its risks.

[0021] Optimizing press times can therefore only be achieved very slowly, as testing the samples from production, including sampling, takes almost an hour. This means that by the time a result is available, the entire production batch may already be finished.

[0022] Conventional methods for determining the degree of cure of a resin applied to a material sheet therefore have a number of disadvantages. In particular, it is not possible to quickly adjust press operating parameters depending on the degree of cure to ensure optimal results and thus quality assurance.

[0023] The invention is therefore based on the technical problem of developing a method that enables rapid and repeatable statements about the curing of a polymer layer applied to a material plate, such as a melamine resin layer, and at the same time to control the operating parameters of the press to influence pressing parameters, such as pressure, temperature and pressing time.

[0024] This object is achieved by a method having the features of claim 1. Accordingly, a method for controlling a press for adjusting operating parameters of the press is provided, wherein the press is suitable for pressing a carrier material with at least one resin layer arranged on the carrier material, wherein at least one NIR multi-measuring head is provided in the running direction of the carrier material to be pressed before the press and at least one NIR multi-measuring head is provided in the running direction of the carrier material to be pressed after the press; wherein the NIR multi-measuring heads are connected to at least one control system for controlling the press with at least one computer-assisted evaluation unit and a database for processing and, if necessary, storing the recorded and evaluated NIR data, comprising the steps

[0025] - Determining the degree of crosslinking of the resin layer arranged on the carrier material as at least one first parameter by recording at least one NIR spectrum of the resin layer applied to the carrier material in a wavelength range between 500 nm and 2500 nm, preferably between 700 nm and 2000 nm, particularly preferably between 900 nm and 1700 nm and particularly advantageously between 1450 nm and 1550 nm, by the at least one NIR multi-measuring head arranged in front of the press, and evaluating the recorded NIR spectrum in the evaluation unit by an automated comparison of the recorded NIR spectrum with a calibration model created for the parameter of the resin layer,

[0026] - Determining the degree of curing of the resin layer arranged on the carrier material as at least a second parameter of the resin layer arranged on the carrier material by recording at least one NIR spectrum of the resin layer applied to the carrier material in a wavelength range between 500 nm and 2500 nm, preferably between 700 nm and 2000 nm, particularly preferably between 900 nm and 1700 nm and particularly advantageously between 1450 nm and 1550 nm, by the at least one NIR multi-measuring head arranged downstream of the press and evaluating the recorded NIR spectrum in the evaluation unit by an automated comparison of the recorded NIR spectrum with a calibration model created for the degree of curing of the resin layer;wherein the degree of crosslinking determined before the press (actual value of the degree of crosslinking) is compared with a target value of the degree of crosslinking, and wherein the degree of curing determined after the press (actual value of the degree of curing) is compared with a target value of the degree of curing, and wherein if the actual value of the degree of crosslinking and the actual value of the degree of curing deviate from the respective target values, the operating parameters of the press are automatically adjusted by the control system so that the target value of the degree of crosslinking and the target value of the degree of curing are met.;

[0027] This allows parameters of the resin layer applied to a substrate to be determined before and after pressing, compared with specified target values, and, in the event of any deviations, used to control the press. The resulting differences are then used to control or regulate the press arranged in a production line. The parameters of crosslinking degree and curing degree are used in combination to control the press. The press's operating parameters are automatically adjusted to ensure that the target values ​​are met.

[0028] The automatic feedback of the measured parameters, degree of crosslinking and degree of curing, to the press enables improved process reliability and reduced rejects due to defective products. Immediate feedback of deviations to the press increases production quality and helps reduce costs.

[0029] The combined use of the crosslinking degree and curing degree parameters to control a press in a production line for manufacturing wood-based panels is not known from the prior art. For example, EP 3 885 740 A1 does contain a reference to the use of various parameters of a resin-coated wood-based panel (such as the crosslinking degree) using NIR spectroscopy to control a production line. However, the parameters determined using NIR spectroscopy are generally used to control the production line for coating wood-based panels. This particularly applies to the control of application devices and drying devices. This document does not contain any reference to the use of the determined parameters to control a press.According to EP 3 238 934 B1, the degree of curing can also be determined using NIR spectroscopy in a production line, with at least one NIR detector being provided in the production line downstream of the application device and the pressing device. However, neither document provides any indication that a combination of the determined parameters of degree of crosslinking and degree of curing can be used to control the press.

[0030] The curing determined by NIR represents, alongside other parameters (such as a brilliantly visible decoration, a closed and optically flawless surface, no delamination of the carrier and coating), an important online determined parameter for the quality of the laminate. This is all the more so because the degree of curing after the press is not easily visible (with the naked eye), but, as described above, must first be determined through complex acid tests.

[0031] In one embodiment of the present method, the operating parameters of the press to be controlled are selected from press temperature, press pressure and / or press time, in particular press temperature and press time.

[0032] The degree of curing (C-stage) of a resin layer is determined primarily by the pressing temperature and pressing time. If the pressing time is too short, this can lead to insufficient curing (undercuring). If the pressing time is too long, it can cause overcuring and cracking. The pressing temperature has a similar influence: If the pressing temperature is too low, this can lead to insufficient curing (undercuring). If the pressing time is too long, it can lead to overcuring and cracking. Incorrectly setting the pressing pressure, in turn, can cause the substrate material to stick in the press.

[0033] The degree of crosslinking determined before the press (B-stage) also influences the degree of curing (C-stage) and can therefore be used to control the press's operating parameters. It is advisable to compare the values ​​determined for the degree of crosslinking with the values ​​determined for the degree of curing in order to set the optimal pressing conditions in the press for a specific batch of substrates to be pressed. For example, the degree of crosslinking of resin layers applied and dried to substrates can vary, which affects the curing. If the degree of crosslinking before the press is too high, this can lead, among other things, to poor adhesion of the impregnate to the substrate. If the degree of crosslinking is too low, this can lead to under-curing of the resin layer and thus to an overly soft surface. Excessive crosslinking can, for example,This can be caused by overdrying during the impregnation of the paper or by improper or excessively long storage of intermediately stored resin-coated substrates. In this case, the crosslinking of the resin layer continues, resulting in a higher degree of crosslinking. In this case, it is desirable and necessary to adjust the press's operating parameters accordingly.

[0034] Pressing time and temperature depend on the type of carrier material to be pressed, the layers arranged on the carrier material, and the desired product. On average, the pressing time is in a range between 6 and 40 seconds, preferably 8 and 36 seconds. If the resin layer to be pressed with the carrier material is in the form of a liquid resin layer (e.g., liquid overlay), the pressing time is between 6 and 10 seconds, preferably 8 and 9 seconds. If the carrier material is pressed with a resin-containing paper, the pressing time is 12 to 20 seconds, preferably 13 to 18 seconds, particularly preferably 14 to 16 seconds, e.g., 15 seconds.

[0035] The press temperature to be set at the feed line of the press to be controlled is between 180°C and 220°C, preferably between 190°C and 200°C. The surface temperature on the product is approximately 20°C lower than the feed line temperature and is therefore between 160°C and 200°C, preferably between 180°C and 190°C.

[0036] It should be noted that the press time and press temperature to be set or controlled are mutually inverse; that is, an extension of the press time is linked to a reduction in the press temperature. In one embodiment, using short-cycle presses, an extension of the press time by 1-2 seconds results in a reduction in the press temperature by 10°C. In the case of CPL presses, the feed rate is adjusted accordingly. Thus, a reduction in the feed rate by 1-2 m / min (i.e., a slower passage through the press) results in a reduction in the press temperature by 10°C. Press control

[0037] As mentioned, if there are deviations from the target values, the parameters for crosslinking and curing determined by NIR spectroscopy, the operating parameters of the press are adjusted so that the target values ​​are met and the quality of the products can be ensured.

[0038] To control and adjust the actual values ​​and the target values, classes or ranges are first determined that are assigned to the target values ​​and actual values.

[0039] As discussed in more detail below, to determine the curing parameter, NIR spectra are first recorded for calibration purposes on reference samples, which are then assigned to the results of a conventional acid test. The acid test results for a board are averaged and assigned to the spectrum of that board.

[0040] The results of the conventional acid test and the NIR measurements are divided into five classes. Table 1 shows the corresponding classifications.

[0041] Table 1

[0042] These curing classes can be used to control the press. If, for example, in an ongoing process downstream of the press for a resin-coated substrate, parameters are determined using NIR spectroscopy that correspond to curing class 1 (and thus deviate from the target value), the press's operating parameters will be automatically adjusted by the control system so that the target value for the degree of cure is met, whereby the target value here corresponds to curing class 3. This can be achieved, for example, by reducing the pressing temperature. To determine the crosslinking parameter (B-stage), NIR spectra are also recorded for the purpose of calibrating reference samples; these spectra are then assigned to the results of a VC (volatile compounds) test. An average value is calculated from the results of the VC test for a board and assigned to the spectrum of this board.

[0043] In conventional VC value determination, the residual moisture content of a reference sample is determined after drying in an oven, during which not only water but also formaldehyde (formed from the free methylol groups) is released. The proportion of free methylol groups is therefore a factor in determining the degree of crosslinking. The optimal moisture content (as the sum parameter of water and formaldehyde release) of impregnates is usually 5-7 wt.%, depending on the intended use. The methylol group content is optimal in this case.

[0044] Samples with a moisture content below 5 wt%, e.g., 3-4 wt%, have a methylol group content below the optimum and are considered overdried. Samples with a moisture content above 7 wt%, e.g., 8-9 wt%, have a methylol group content above the optimum and are considered underdried.

[0045] With this data, a calibration for the cross-linking of the various resin and paper systems can be carried out and a basic prediction about the state of the cross-linking can be made.

[0046] The results of the conventional VC test and the NIR measurements are also divided into five classes. Table 2 shows the corresponding classifications.

[0047] Table 2 The crosslinking classes can be used to control the press. For example, if parameters corresponding to crosslinking class 5 (and thus deviating from the target value) are determined using NIR spectroscopy in an ongoing process upstream of the press for a resin-coated substrate, the press's operating parameters will be automatically adjusted by the control system to ensure that the target crosslinking level is met, where the target value in this case corresponds to crosslinking class 3. This can be achieved, for example, by increasing the press temperature and / or the press time.

[0048] It should be noted that in an impregnate, part of the water is free water and part is chemically bound water. In a freshly produced impregnate, around 60-70% of the water is chemically bound in the methylol groups and 20-30% is free water, i.e. the ratio between bound and free water in freshly produced impregnates is approx. 3:1 to 2:1. However, this ratio can vary depending on the melamine resin (molar ratio of melamine to formaldehyde). In a stored impregnate, on the other hand, >70% is free water and approx. 30% is chemically bound water; i.e. the ratio between bound and free water in stored impregnates is approx. 1:3 to 1:2. This difference is due to the slow further reaction of the resins in the impregnate. This reaction is acid-catalyzed and proceeds even at room temperature.It is therefore possible to determine the degree of overlap of an impregnate by measuring the ratio of the water peak to the methylol group peak in the NIR spectrum. Determining the degree of overlap of an impregnate is advantageous because overlapped impregnates are not suitable, or only partially suitable, for further processing (e.g., pressing with wood-based panels).

[0049] When using the VC value to create a calibration model, the ratio of the water peak at 1950 nm and the methylol peak at 2050 nm (first harmonic) in the measured NIR spectrum can also be used - additionally or exclusively - to determine the degree of crosslinking of a resin layer. This means that an overlaid impregnate has more free water and thus a water peak that is more pronounced compared to the methylol peak, whereas in a non-overlaid impregnate the water peak is less pronounced compared to the methylol peak. Determining this ratio as a measure of the degree of crosslinking is particularly advantageous when using overlaid impregnates.Accordingly, in a further aspect, a method for determining the degree of overlay of a resin layer, in particular an impregnate, applied to a carrier material by means of NIR spectroscopy can be provided, wherein the method is carried out in a production line with at least one NIR measuring head, preferably an NIR measuring head arranged in front of a press, wherein the method comprises the following steps;.

[0050] - Recording of at least one NIR spectrum of the resin layer arranged on the carrier material in a wavelength range between 900 nm and 2500 nm, preferably between 1300 nm and 2300 nm, particularly preferably between 1500 nm and 2100 nm, even more preferably between 1800 nm and 2100 nm by the at least one NIR multi-measuring head,

[0051] - Determining the degree of crosslinking of the resin layer arranged on the carrier material by evaluating the recorded NIR spectrum by an automated comparison of the recorded NIR spectrum with a calibration model created for the degree of crosslinking of the resin layer, wherein (additionally) the ratio of the spectrum recorded in the wavelength range between 1900 nm and 2000 nm, preferably at 1950 nm (water peak) and the spectrum recorded in the wavelength range between 2000 nm and 2100 nm, preferably at 2050 nm (methylol peak) is used as a measure of the degree of superposition of a resin layer applied to a carrier material.

[0052] This involves comparing the ratio of the spectrum recorded in the wavelength range between 1900 nm and 2000 nm, preferably at 1950 nm (water peak) and the spectrum recorded in the wavelength range between 2000 nm and 2100 nm, preferably at 2050 nm (methylol peak) with a calibration model created for the degree of overlap. To create the calibration model, the ratio of the respective NIR wavelength ranges is determined for corresponding reference samples (resin-coated carrier material) before and after storage (at room temperature). Storage can take place for different periods of time. The ratios of the specified wavelength ranges determined for the reference samples stored for different lengths of time represent the degree of overlap.This information on the ratio of water peak to methylol group peak can therefore also be used, after calibration for the various resin and paper systems, to make a basic prediction about the state of crosslinking and to control the press.

[0053] Further parameters of the resin layer

[0054] In addition to the degree of crosslinking and curing, other parameters of the resin layer can be determined.

[0055] In one embodiment of the present method, in addition to the degree of crosslinking, the following parameters are determined before the press, in particular by means of NIR spectroscopy: moisture content of the applied resin layer (see EP 2 808 636 B1 ) and quantity of the applied resin layer (EP 3 428 619 B1 ).

[0056] These additional parameters, determined prior to the press, provide further information about the quality of the resin layer applied to the substrate and thus serve as quality assurance. In one embodiment, these additional parameters are not used to control the press, but rather are displayed to the operating personnel during the production process for quality control purposes (e.g., green light - optimal values; red light - inadequate values). This makes it possible to identify information about faulty values ​​in the resin layers applied to the substrate early in the production process.

[0057] If the moisture content of the resin layer is too low before pressing, this will result in poor flow of the resin layer, poor transparency, and / or poor adhesion when using impregnated materials. Excessive moisture content will adversely affect the surface quality. Suboptimal moisture levels in the resin layer can be compensated for in the press by adjusting the operating parameters. For example, if the moisture content is too high, the pressing temperature and, in parallel, the pressing pressure in the press can be increased. In particular, the pressure should be set to values ​​that are above the water vapor pressure. However, this is only possible within certain limits.

[0058] The amount of resin applied can also affect the surface quality of the pressed and cured resin layer. If the applied resin quantity deviates upwards from the optimal application quantity (i.e., is too high), the cured resin layer may have a gray, milky film. If the applied resin quantity is too small, this can lead to a damaged surface, delamination, and poor adhesion.

[0059] In a further embodiment of the present method, in addition to the degree of curing, the following parameter is determined after the press, in particular by means of NIR spectroscopy: resin penetration (or penetration height / penetration quantity of the resin) into at least one porous coating material arranged on the resin-coated carrier material.

[0060] This additional parameter, determined after the press, also provides further information on the quality of products, such as floor coverings finished with a porous coating material, in particular veneer layers. The porous coating material is applied to a substrate coated with a resin layer, in particular a substrate plate, before the press and then pressed in the press. During the pressing process, the resin penetrates or rises into the at least one porous coating material. The degree of resin penetration into the porous coating material, as a quality characteristic, can be measured using NIR spectroscopy (see WO 2022 / 179883 A1).

[0061] If resin penetration into the porous coating deviates, the press operating parameters, particularly the pressing temperature and / or pressing time, can be adjusted. Here, too, the aforementioned parameters are adjusted in the opposite direction. Reducing the pressing temperature increases the pressing time. For example, reducing the pressing temperature by 10°C increases the pressing time by 10 to 20 seconds.

[0062] press

[0063] The press to be controlled in the present process is a short-cycle press (KT press) or a continuous press.

[0064] Short-cycle presses (KT presses) are used to refine the surfaces of wood-based panels. KT presses are particularly suitable for pressing chipboard and MDF / HDF with liquid resin layers or resin-impregnated paper applied to them. This allows the resin layers to be permanently applied to the surfaces of wood-based panels. The resin penetrates the surface pores, ensuring adhesion. It also creates a surface that is resistant to various environmental influences.

[0065] Continuous presses (CPL presses) are used to compress impregnated materials in a continuous or continuous process. A continuously operating press features a heated roller belt press.

[0066] The pressing step in the press (CPL press) is carried out at an applied pressure between 50 - 70 kg / cm 2and a temperature between 150 and 200°C, preferably 180°C. The press line speed is 5-20 m / min, preferably 5 to 15 m / min, e.g., 9.5 m / min. The press zone in a CPL press is typically 3000-4000 mm long. This allows the press time to be determined with a known feed rate. 10 m / min for a length of 3 m corresponds to a press time of 18 seconds.

[0067] resin layer

[0068] In one embodiment of the present method, the at least one resin layer applied to the carrier material comprises a resin-impregnated paper layer, a resin-containing powder, or a resin-containing liquid. The applied resin layer can thus be present as a powder or liquid overlay or as a partial or full impregnation of a paper layer on the carrier material.

[0069] Resin-impregnated paper layer (overlay)

[0070] The resin-impregnated paper layer is typically based on a cellulose-containing layer with an average sheet weight of 18-50 g / m 2 , preferably 20-30 g / m 2 , e.g. 25 g / m 2 .

[0071] The paper layers are impregnated with thermosetting resins as binders, such as formaldehyde resins, especially melamine resin, phenolic resin, urea resin, or mixtures of these resins. Such paper layers are also known as overlays.

[0072] Aqueous resin solutions with a resin solids content between 40 and 80 wt%, preferably between 50 and 65 wt%, are used to impregnate the paper layers. The resin is applied in an amount of 200% to 600%, preferably 250% to 400% solids, based on the basis weight of the paper layer. The resin is used in an amount sufficient to allow the resin to penetrate at least some of the porous coating material during the pressing process.

[0073] After applying the resin to the paper layer, especially after impregnating the paper layer with the resin, the surface is only pre-dried and therefore still tacky. This tacky state is achieved at a volatile substance content with a residual moisture content (VC value) of 10-15%. The VC value is determined as the difference between the initial weight and the final weight after drying at 105 °C to constant weight.

[0074] The sticky surface of the resin-impregnated paper layer simplifies the application of additives for further finishing of the porous coating material, such as a veneer layer.

[0075] In one embodiment, overlay papers are used as paper layers. Overlay papers are thin papers that are typically already impregnated with a conventional melamine-formaldehyde resin. Overlay papers are also available in which abrasion-resistant particles, such as corundum particles, are mixed into the overlay resin or sprinkled onto the resin-wetted overlay to increase abrasion resistance. Resin coatings with up to 400 wt% melamine resin are used to impregnate overlay papers. For most applications (laminates for countertops or payment counters), overlays without corundum are sufficient.

[0076] Powdered resin (powder overlav)

[0077] In case of using powdered resin, the amount of powdered resin applied to the surface of the carrier plate is 50-150g / m 2 , preferably 60-100 g / m 2 , particularly preferably 70-80 g / m 2 .

[0078] The powdered resin used has a spreading density of 0.5 to 1.5 kg / l, preferably 0.8 to 1.0 kg / l, and an average particle size of 10 to 50 μm, preferably 20 to 30 μm, and particularly preferably 25 μm. The powdered resin used here contains only minimal traces of moisture. A moisture content of 0.5% should not be exceeded, as otherwise clumping will occur and spreading will no longer be possible.

[0079] In a further variant of the present method, the surface or side of the carrier plate to be sprinkled with the powdered resin is pretreated before sprinkling the powdered resin to improve the adhesion of the powdered resin to the surface of the carrier plate. This pretreatment can include applying moisture to the side or surface or electrostatically charging the side or surface of the carrier plate.

[0080] As powdered resin, a formaldehyde resin, preferably a urea resin, a melamine resin or a phenolic resin, particularly preferably a melamine-formaldehyde resin, a melamine-phenol-formaldehyde resin or a melamine-urea-formaldehyde resin is used.

[0081] The powdered resin is preferably applied using a spreading device. The spreading is preferably carried out in a continuous process. A suitable spreading device is the precision spreader "Oscillating Brushing System" from TPS. However, electrostatic application with a tribo-gun can also be used.

[0082] This additional layer to be applied can consist solely of a powdered resin, or it is also possible to use a mixture containing the resin, natural and / or synthetic fibers, and possibly other additives.

[0083] The powder consists of 30 to 65 wt%, preferably 40 to 60 wt% fibers, 20 to 45 wt%, preferably 30 to 40 wt% binder, and 0 to 8 wt%, preferably 0.5 to 6 wt% additive. The natural and / or synthetic fibers are preferably selected from a group consisting of bleached cellulose fibers or organic polymer fibers.

[0084] Liquid resin (liquid overlav)

[0085] In case of using liquid resin as the resin layer, the amount of liquid resin applied to the surface of the carrier plate is between 50 and 150 g / m 2 , preferably between 60 and 100 g / m 2 , particularly preferably between 70 and 80 g / m 2 , where the solids content of the resin is approximately 65% ​​by weight and contains the usual auxiliaries such as hardeners, wetting agents, etc.

[0086] As liquid resin, a formaldehyde resin, preferably a urea resin, a melamine resin or a phenolic resin, particularly preferably a melamine-formaldehyde resin, a melamine-phenol-formaldehyde resin or a melamine-urea-formaldehyde resin is used.

[0087] As in the case of the resin powder, the liquid resin can also be used in a mixture with natural and / or synthetic fibers, and possibly other additives.

[0088] Porous coating material

[0089] As indicated above, a porous coating material, such as a veneer layer, may be provided on the at least one resin layer.

[0090] If a veneer layer is used, in one embodiment this comprises at least one layer of real wood veneer. In a further embodiment, the at least one veneer comprises at least one real wood layer with a thickness between 0.2-10 mm, preferably 0.5-5 mm, particularly preferably 0.5-2 mm. The veneer can be produced in one piece from a log, for example by peeling. However, it can also be composed of individual pieces that are connected to one another, for example by binding agents or so-called glue threads. The veneer preferably has the dimensions of the carrier plate. The veneer has an underside facing the carrier plate and an upper side facing away from the carrier plate.

[0091] Carrier material

[0092] The carrier material used here is in the form of a carrier plate, paper layer or film layer.

[0093] If a carrier board is used as the carrier material, the at least one carrier board is a board made of a wood-based material, in particular a chipboard, medium-density fiberboard (MDF), high-density fiberboard (HDF), oriented strand board (OSB), or plywood board, a wood-plastic mixture, or a WPC (wood-plastic composite) board. The layer thickness of the resin layer applied to the carrier board is between 10 and 100 μm, preferably between 30 and 80 μm, particularly preferably between 30 and 60 μm.

[0094] The surface of the core board can be surface-treated. The surface of a wood-based core board can also be sanded (without a pressed skin) or unsanded (with a pressed skin).

[0095] It is also conceivable that at least one primer layer or at least one undercoat can be provided between the surface of the carrier plate and the resin layer. Isocyanate-based compounds are preferably used as primers, with non-aromatic, aliphatic isocyanates, such as hexamethylene diisocyanate, isophorone diisocyanate, or prepolymers containing these isocyanates being particularly preferred.

[0096] In a further embodiment, it can be provided that the at least one resin layer is provided on the upper side of the carrier plate (ie the side facing the user after installation of the carrier plate), and at least one sound-insulating layer is arranged on the rear side or underside of the carrier plate, in particular in the case of a wood-based panel as the carrier plate.

[0097] Such wood-based panels are preferably used as floor panels, wall panels, ceiling panels, furniture panels or as cutting boards.

[0098] CPL (Continuous Pressure Laminates)

[0099] In the case of a paper layer as the carrier material, a kraft paper layer is preferably used, which is pressed with at least one resin layer in a continuously operating press (CPL press).

[0100] Resin-impregnated paper layers, especially resin-impregnated decorative papers and / or resin-impregnated overlay papers and / or resin-impregnated backing papers, can be used as the resin layer. These layers are pressed with the kraft paper layer in a continuous press to form Continuous Pressure Laminates (CPL). CPL is usually available in roll form and is used, for example, for the production of worktops, wrapped profiles, and door panels. CPLs are pressed in a continuous or continuous process in roller belt presses heated on both sides. When producing CPL on double-belt presses, resin-impregnated soda kraft papers (NKP) are used in the core layer.

[0101] The kraft paper layers used here have a weight between 50 and 200 g / m 2 , preferably between 80 and 170 g / m 2 , particularly preferably between 80 and 160 g / m 2 , such as 80 g / m 2 , 120 g / m 2 or 160 g / m 2 As mentioned above, kraft papers are highly durable and consist of cellulose fibers to which starch, alum, and glue are added to create surface effects and increase strength.

[0102] At least one additional paper layer is placed on top of the kraft paper layer. Any number of paper layers can be applied, although two, three, or four additional paper layers are preferred.

[0103] The at least one additional paper layer to be applied can be a kraft paper layer, a decorative paper layer, or an overlay paper layer. Preferably, an additional kraft paper layer is applied, followed by a decorative paper layer and / or an overlay paper layer. The possible layer or cover structures are described in detail below.

[0104] The paper layers used can be completely saturated (impregnated) with a resin, preferably melamine-formaldehyde resin. In the case of fully impregnated paper, a resin quantity of 80-400 wt%, preferably 90-120 wt%, particularly preferably 100-110 wt%, based on the paper weight is applied.

[0105] In one variant, a material layer (e.g. glass fleece, aluminum foil) is placed on the kraft paper layer, followed by a second kraft paper layer, a decorative paper layer and / or overlay paper layer.

[0106] However, it is also possible to omit a second kraft paper layer and / or decorative paper layer and apply an overlay paper layer directly to the material layer. The type and order of the additional paper layers can be flexibly designed depending on the type of material layer. If the material layer is colored, for example, decorative paper can be omitted.

[0107] The at least one material layer can be selected from the following materials: graphite-containing papers to increase conductivity, plastic films, especially thermoplastic films (enabling tight postforming radii), aluminum foil, nonwoven material, and other fabric materials. The coating materials used can either be porous or nonporous, i.e., impermeable to liquids. In particular, materials are included that have a porosity through which liquid resin can rise during compression and that are at least partially plastically deformable.

[0108] The use of a glass fiber mat improves impact resistance. The use of aluminum foil, preferably primed with an isocyanate primer before application, reduces water vapor permeability. The thickness of the aluminum foil is 0.1–0.3 mm, preferably 0.2 mm.

[0109] In a further embodiment of the present method, the layered structure of kraft paper layer and at least one further paper layer is pressed with at least one structuring paper (placed on the at least one further paper layer on the upper side of the layering) and at least one transparent paper (on the underside of the layering).

[0110] A structuring paper is a paper that, after being applied and pressed, imparts a structure (e.g., a 3D structure) to the surface of the laminate. In addition to its structuring function, the structuring paper also serves a protective function, particularly during the pressing step. The structuring paper is removed after the layer or cover structure has been pressed and can be recycled.

[0111] The tracing paper used in this laminate is also known as glassine. Glassine is a tracing paper made from finely ground pulp that is largely greaseproof but not water-resistant. It achieves its high transparency through a very sharp calendering process.

[0112] NIR spectroscopy

[0113] In one embodiment of the present method, the calibration model applied for the respective parameters of the resin layer to be determined is determined using reference samples as follows:

[0114] - Recording of at least one NIR spectrum from several

[0115] Reference samples each having different values ​​of the desired parameters using at least one NIR multi-measuring head in a wavelength range between 500 nm and 2500 nm, preferably between 700 nm and 2000 nm, particularly preferably between 900 nm and 1700 nm, and particularly advantageously between 1450 nm and 1550 nm;

[0116] - Determination of the desired parameters of the measured reference samples using non-spectroscopic methods;

[0117] - Assignment of the determined parameters to the recorded NIR spectra of the measured reference samples.

[0118] Accordingly, reference samples of the resin-coated substrate are first prepared. It is essential that the reference sample be similar to the sample to be measured; in particular, the resin layer of the reference sample has the same composition as the resin layer to be measured. The similarity of the sample to be measured and the reference sample is particularly important when using liquid resin layers with additives such as flame retardants, fibers, and other additives.

[0119] At least one NIR spectrum of these reference samples is recorded in a wavelength range between 500 nm and 2500 nm, preferably between 700 nm and 2000 nm, particularly preferably between 900 nm and 1700 nm and particularly advantageously between 1450 nm and 1550 nm.

[0120] These reference samples are also subjected to non-spectroscopic analysis to determine the desired parameters, i.e., quantity, degree of cure, degree of crosslinking, moisture content of the resin applied to the substrate, and the quantity of applied particles and their abrasion resistance (or a selection of these parameters). The non-spectroscopic analyses are described in detail below for each of the parameters mentioned.

[0121] An average value is calculated from the parameters determined for the reference samples using non-spectroscopic analysis, which is then assigned to the 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 parameter values ​​using multivariate data analysis; that is, each parameter value of the reference sample corresponds to an NIR spectrum of the reference sample. The calibration models created for the various parameters are stored in a suitable data storage system.

[0122] Subsequently, at least one resin layer is applied to at least one side of the substrate, and at least one NIR spectrum of the resin layer applied to the substrate is recorded. The desired parameter of the resin layer applied to the substrate can then be determined by comparing the NIR spectrum recorded for the resin layer with the created calibration model.

[0123] It is thus possible to simultaneously determine several parameters of interest of the resin layer applied to a carrier material from a single NIR spectrum determined for the sample to be measured by means of an automated comparison or adjustment with the calibration models created for the respective parameters.

[0124] A comparison and interpretation of the NIR spectra is best performed across the entire recorded spectral range. This is best done using a well-known multivariate data analysis (MDA). Multivariate analysis methods typically examine several statistical variables simultaneously in a well-known manner. To achieve this, these methods typically reduce the number of variables contained in a data set without simultaneously diminishing the information contained therein.

[0125] In this case, the multivariate data analysis is performed using partial least squares regression (PLS), which allows for the creation of a suitable calibration model. The obtained data is preferably evaluated using suitable analysis software, such as SIMCA-P from Umetrics AB or The Unscrambler from CAMO.

[0126] In a further embodiment, spectral data from the NIR spectral range between 1450 and 1550 nm are used to create the calibration model, which data are pretreated using suitable mathematical methods and then fed to the multivariate data analysis.

[0127] The significance of a wavelength for predicting parameters of the resin layer, such as the amount of resin, from the NIR spectrum is illustrated using the regression coefficients. Regions with large coefficient values ​​have a strong influence on the regression model. The representation of the regression coefficients in a PLS regression model for determining the amount of resin or the resin content shows that the wavelength range between 1460 nm and 1530 nm, with a maximum at 1490 nm (absorption band of the amino groups of the resin), is the most important for calculating the model, as this is where the regression coefficient values ​​are largest. Although the other regions in the spectrum have less information with regard to the NIR measurement, they nevertheless help to take into account or eliminate other information or interfering factors (such as the transparency of the layer, the surface quality of the resin layer or the carrier material, etc.).to minimize.

[0128] To eliminate interfering influences (such as the nature of the surface of the substrate, the color of the samples, light scattering on solid particles or other additives, etc.), it is necessary to process the spectral data using mathematical pretreatment methods (e.g. derivative data pretreatment, standardization according to SNVT (Standard Normal Variate Transformation), multiplicative signal correction (EMSC, Extended Multiplicative Signal Correction, etc.). In this process, the baseline effects, which are mainly caused by the different colors of the samples, are removed from the spectra, overlapping bands are separated from one another, and the dependence of the light scattering on the substrate surface or on the solid particles in the coating is taken into account. If, for example, the resin application quantity on untreated surfaces of substrate materials, such asWhen measuring wood-based panels, data pretreatment is preferably carried out to reduce light scattering on the rough surface of the substrate. When measuring on decorative layers, the focus of calibration and data pretreatment is on removing the baseline shift.

[0129] From the pre-treated data, a calibration model is developed using multivariate data analysis, which includes all decors used in the calibration.

[0130] Accordingly, the comparison and interpretation of the NIR spectra are preferably carried out in the spectral range between 500 nm and 2500 nm, preferably between 700 nm and 2000 nm, particularly preferably between 900 nm and 1700 nm, and particularly advantageously between 1450 nm and 1550 nm using multivariate data analysis (MDA). Multivariate analysis methods typically examine several statistical variables simultaneously in a conventional manner. For this purpose, the number of variables contained in a data set is reduced without simultaneously diminishing the information contained therein. As already noted, the reference samples are measured or determined both spectroscopically and non-spectroscopically in order to assign the parameters to the recorded NIR spectra of the reference samples.

[0131] Depending on the parameter, different non-spectroscopic analysis methods are used.

[0132] Amount of resin layer applied:

[0133] A common method for determining application quantities is weighing. This involves coating the substrate with the coating medium in the application unit, and then determining the application quantity by determining the weight difference (see also EP 3 428 619 B1).

[0134] Moisture of the applied resin layer:

[0135] The kiln-dry method is the most accurate method for determining moisture content (especially wood moisture content). A sample is dried in a drying oven at 103±2°C for 24 hours. Moisture content is defined as the ratio of the weight of water contained in the material to the weight of the absolutely dry material (kiln weight). Moisture content is therefore the ratio between wet weight and dry weight (kiln weight); see EP 2 808 636 B1.

[0136] Degree of curing of the applied resin layer:

[0137] Curing is determined using the acid test. The surface is exposed to a diluted mineral acid (4 molar hydrochloric acid) for a defined period of time. The change in gloss and / or color is then assessed. The less gloss / color loss is observed, the greater the curing. An average value is calculated from the acid test results for a board and assigned to the spectrum of that board (see EP 3 238 934 B1).

[0138] Degree of crosslinking of the applied resin layer:

[0139] The degree of crosslinking of partially crosslinked precondensates or polycondensates (also known as partially crosslinked, still partially soluble B-stage) can be determined using the VC test (Volatile Compound Test), in which not only water but also a small amount of formaldehyde is released from the synthetic resins. For the VC test, a sample (usually 10 x 10 cm) is weighed and dried for 5 minutes at 105°C. After cooling, the sample is weighed again. The mass loss is then determined based on the final weight and expressed as a percentage. The previously determined paper weight serves as the basis for determining the resin application in percent ((final weight - paper weight / paper weight) x 100), see EP 3 327 424 B1.

[0140] In addition to determining the VC value, the ratio of the water peak at 1950 nm to the methylol peak at 2050 nm (first harmonic) in the measured NIR spectrum is used to determine the degree of crosslinking of a resin layer. Determining this ratio as a measure of the degree of crosslinking is particularly advantageous when using layered impregnates. The test for free and bound water is performed by combining a VC test with storage of an impregnate in a desiccator over desiccant. During calibration, the ratio between the water and methylol peaks is then considered.

[0141] Resin penetration into porous coating:

[0142] Resin penetration into a porous coating of the reference samples was determined using a Taber abrasor. The test was conducted in accordance with DIN EN 13329. The abrasive wheels of the Taber abrasor were covered with standard sandpaper and loaded with standard weights. After each 200 revolutions, a visual inspection was conducted to determine whether black discoloration was already visible in the veneer. A dial indicator was then used to measure the material removal in mm in the circular depression created by the sandpaper in the four circle segments formed by a coordinate system, and the average value was calculated. This average was then calculated from this average value together with the four other samples. The material removal was then subtracted from the veneer thickness, which was determined using a microscope, and then correlated with the spectra (see WO 2022 / 179883).

[0143] production line

[0144] The present method is carried out in a production line comprising at least one press, at least one NIR multi-measuring head, preferably at least two NIR multi-measuring heads, and at least one control system. Such a production line can be integrated into a line for producing resin-coated material panels or a CPL system for producing laminates (CPL). In particular, the production line comprises at least one first NIR multi-measuring head arranged upstream (before) of a press and at least one second NIR multi-measuring head arranged downstream (after) of this press.

[0145] The control system comprises at least one computer-based evaluation unit (or processor unit) and a database. The evaluation unit compares or compares the NIR spectrum measured for the product (i.e., the substrate with the applied resin layer) with the calibration models created for the individual parameters. The parameter data thus determined is stored in the database.

[0146] According to the invention, the data determined using this spectroscopic method can be used to control the press. The non-contact measured parameter values ​​of the NIR multi-measuring head ("actual values") can, as previously described, be used directly and in real time for the control or regulation of the press in question. For example, by storing the measured actual values ​​in a database, e.g., a relational database, and comparing them with the target values ​​of these parameters available there. The resulting differences are then used to control or regulate the press.

[0147] For the calibration and control of the press, a computer-implemented method and a computer program comprising instructions that, when executed by a computer, cause the computer to execute the computer-implemented method are provided. The computer program is stored in a memory unit of the press's control system. It is also possible for the press to be networked with at least one other production line as part of a production line.

[0148] As mentioned, the press to be controlled can be integrated into a production line for coating material panels.

[0149] In one embodiment, such a production line may have the following structure:

[0150] - at least one first application device for applying a first resin layer to the top and / or bottom of the material plate,

[0151] - at least one first drying device arranged downstream of the first application device in the processing direction for drying the first upper and / or lower resin layer; - at least one second application device arranged downstream of the first drying device in the processing direction for applying a second resin layer to the upper side and / or lower side of the material plate,

[0152] - at least one second drying device arranged downstream of the second application device in the processing direction for drying the second upper and / or lower resin layer;

[0153] - optionally at least one third application device arranged behind the second drying device in the processing direction for applying a third resin layer to the top and / or bottom of the material plate,

[0154] - optionally at least one third drying device arranged downstream of the third application device in the processing direction for drying the third upper and / or lower resin layer; and

[0155] - at least one first NIR measuring head, in particular an NIR multi-measuring head, arranged behind the second or optionally third drying device in the processing direction for online determination of the degree of crosslinking of the resin layer arranged on the upper side of the material plate;

[0156] - at least one pressing device, in particular a short-cycle press, for pressing the layer structure, and

[0157] - at least one second NIR measuring head, in particular an NIR multi-measuring head, arranged behind the pressing device in the processing direction for the online determination of the degree of curing of the pressed resin layer arranged on the upper side of the material plate.

[0158] A CPL system for producing laminates comprises a continuously operating press, wherein a first NIR measuring head, in particular an NIR multi-measuring head, is provided for online determination of the degree of crosslinking before the press (upstream) and a second NIR measuring head, in particular an NIR multi-measuring head, is provided for online determination of the degree of curing after the press (downstream).

[0159] The invention is explained in more detail below with reference to several embodiments. Determining the degree of curing of the

[0160] Resin layer applied to wood-based panel

[0161] Creating a reference sample and calibration: Calibration is performed by recording an NIR spectrum of a cured sample, which is then tested for curing using acid tests, and is carried out as follows.

[0162] HDF boards (207 cm x 280 cm) printed with various designs are coated from above with liquid melamine-formaldehyde (MF) resin or with an overlay paper impregnated with MF resin using a roller application system. They are then pressed in a short-cycle press at 190-210°C and approximately 40 bar for 8 to 36 seconds. This cures the protective layer. By varying the pressing time and temperature, samples with differently cured protective layers are produced.

[0163] During calibration for an online measurement, the NIR spectra are recorded directly on the production line a few seconds after the pressing process. The board is then tested for curing using an acid test at the locations where the NIR spectra were recorded. The acid test results for a board are averaged and assigned to the spectrum of that board.

[0164] In this way, several reference spectra of differently cured panels with different color decors are recorded (for calibration of the online measurement).

[0165] The acid test is performed as follows: Three drops of 6 M HCl are added to a panel cooled to room temperature. After 25 minutes of contact time, the acid is rinsed off with water. A statement about the curing quality is made based on the visual and tactile assessment of the surface at the contact site.

[0166] For calibration, the test results are correlated with spectral data. The calibration model is created using multivariate data analysis. This is done using suitable analysis software, e.g., The Unscrambler from CAMO. This program enables, among other things, special pretreatment techniques for the spectral data to minimize various interference factors on the measurement, such as the surface texture of the samples, infrared-inactive fillers in the coating, or different colors of the samples, among others. As previously described, the influence of color on the NIR measurement can also be resolved by forming decorative groups with similar color classifications. A calibration model is created from the reference spectra, which can be used to determine (predict) the curing of an unknown sample.

[0167] The online NIR measurement then directly predicts the result of the acid test or the quality of the curing.

[0168] Online measurement of the degree of curing of a resin coating:

[0169] With online determination of curing after the press, the NIR measurement or recording of the NIR spectra takes place directly on the production line, immediately after the resin coating has cured. After creating a calibration model, it is installed in the measuring device. As the samples pass under the measuring head, several NIR spectra of the coating are recorded. Using the calibration model, an average curing (acid test) of the coating is calculated from the recorded spectra. In this way, each board is tested for curing quality during production.

[0170] Behind the press is an NIR multi-measuring head that moves across the material web on a traverse. If deviations from the target specifications occur, an automatic control system adjusts the operating parameters in the press to the target values. 2 Determination of the degree of cross-linking a) Degree of cross-linking of impregnates

[0171] Creating a reference sample and calibration:

[0172] In the case of impregnated papers, the NIR measurement is calibrated by first measuring impregnated samples in various stages of drying using the NIR measuring head. For this purpose, impregnated samples are taken from an impregnation channel produced at different speeds. The speeds of the impregnation channel are varied up and down around the known optimum. The samples are then measured using the NIR measuring head, and the VC value is determined in an oven. After five minutes of drying, the final cured state (C stage) is reached. After drying in the oven, the samples are measured a second time using the NIR measuring head. This measurement provides the end point of the drying process.

[0173] After correcting the baseline shift, the spectra show changes in the absorption intensity of the NIR bands at approximately 1450 nm (water) and at approximately 1490 nm (NH groups).

[0174] A correlation can then be established between the VC values ​​and the NIR spectra. The calibration model, which describes the relationship between the NIR spectra and the corresponding VC values, is created using multivariate regression methods (e.g., MLR, PCR, or PLS regression methods, etc.). The evaluation is carried out across the entire spectrum. The longer the sample is dried in the oven, the higher the degree of crosslinking. This also allows samples with a higher VC value than typically desired to be measured. Testing these underdried samples can also improve the control of the impregnation channel (drying channel). Underdried samples have a methylol group content that is above the optimum, while overdried samples have a methylol group content that is below the optimum.Thus, by recording the NIR spectra in combination with visualization, it is possible to control the channel based on the methylol group content. With this data, after calibration, a basic prediction of the curing state can be made for the various resin and paper systems.

[0175] Measuring the degree of cross-linking:

[0176] In an impregnation channel, an overlay (paper weight: 25 g / m 2 ) impregnated with a mixture of melamine resin and corundum. The total application rate is approximately 75 g / m 2, of which approximately 55 g is melamine resin. The impregnation channel is operated at various speeds. Samples are taken from each speed variation in such a test and measured using the NIR measuring head. They are then tested for their VC value. VC values ​​of 3.0 to 8% were found. All samples were measured a second time with the NIR measuring head after drying.

[0177] A correlation was then created from the spectra and the VC values, which allowed a prediction of the degree of crosslinking on other overlay samples. b) Crosslinking of resin layers applied to carrier plates

[0178] This process can, of course, also be used for systems where the pre-cured resins are applied directly to printed or unprinted wood-based panels. These panels present the same problems as impregnated papers.

[0179] Here, too, it is important to know the degree of crosslinking of the synthetic resin on the board. This applies both to a linked production line, where resin application and drying are followed directly by further processing in a short-cycle (KT) or continuously running press (Continuous Press), and to a non-linked production line, where resin application and drying are followed by intermediate storage before the intermediate product is further processed at a later time. In the case described, determining the degree of crosslinking before the press is all the more important because, in contrast to impregnated papers, determining the quality of the parameters usually required after the press is otherwise virtually impossible.

[0180] By carrying out a measurement directly on the production line, the operating parameters of the press can be adjusted immediately in the event of deviations from the target condition.

[0181] In front of the press is an NIR multi-measuring head that moves across the web on a traverse. If deviations from the target values ​​occur, an automatic control system adjusts the operating parameters in the press to the target values.

[0182] Example 3: combined determination of degree of curing and degree of crosslinking to control the press

[0183] The crosslinking degree parameters determined before the press and the curing degree parameters determined after the press are considered together. If deviations from the target values ​​for both parameters occur, an automatic control system adjusts the operating parameters in the press to the combined target values. Example 4: Using the crosslinking degree to determine superimposed impregnates

[0184] A pallet with a remaining amount of overlays ( parameters of the impregnate: final weight 150 g / m 2, VC value: 5.8%) was used to produce laminate flooring. A high degree of crosslinking of the impregnated material was detected by an NIR measuring head before the press. A determination of the VC value resulted in 5.6%. A test press subsequently showed slightly poorer transparency and only a slight increase in the degree of crosslinking when measured with a second NIR measuring head. It was concluded that the pallet was outdated and no longer suitable for production.

Claims

Claims 1. A method for controlling a press for adjusting operating parameters of the press, wherein the press is suitable for pressing a carrier material with at least one resin layer arranged on the carrier material, wherein at least one NIR multi-measuring head is provided in the running direction of the carrier material to be pressed before the press and at least one NIR multi-measuring head is provided in the running direction of the carrier material to be pressed after the press; wherein the NIR multi-measuring heads are connected to at least one control system for controlling the press with at least one computer-assisted evaluation unit and a database for processing and, if necessary, storing the recorded and evaluated NIR data, comprising the steps Determining the degree of crosslinking of the resin layer arranged on the carrier material as at least one first parameter by recording at least one NIR spectrum of the resin layer applied to the carrier material in a wavelength range between 500 nm and 2500 nm, preferably between 700 nm and 2000 nm, particularly preferably between 900 nm and 1700 nm and particularly advantageously between 1450 nm and 1550 nm, by the at least one NIR multi-measuring head arranged in front of the press, and evaluating the recorded NIR spectrum in the evaluation unit by an automated comparison of the recorded NIR spectrum with a calibration model created for the parameter of the resin layer, - Determining the degree of curing of the resin layer arranged on the carrier material as at least one second parameter of the resin layer arranged on the carrier material by recording at least one NIR spectrum of the resin layer applied to the carrier material in a wavelength range between 500 nm and 2500 nm, preferably between 700 nm and 2000 nm, particularly preferably between 900 nm and 1700 nm and particularly advantageously between 1450 nm and 1550 nm, by the at least one NIR multi-measuring head arranged after the press and evaluating the recorded NIR spectrum in the evaluation unit by a Automated comparison of the recorded NIR spectrum with a calibration model created for the degree of curing of the resin layer; whereby the degree of crosslinking determined before the press (actual value of the degree of crosslinking) is compared with a target value of the degree of crosslinking, and whereby the degree of curing determined after the press (actual value of the degree of curing) is compared with a target value of the degree of curing, and whereby if the actual value of the degree of crosslinking and the actual value of the degree of curing deviate from the respective target values, the operating parameters of the press are automatically adjusted by the control system so that the target value of the degree of crosslinking and the target value of the degree of curing are met.

2. Method according to claim 1, characterized in that the operating parameters of the press to be controlled are selected from pressing temperature, pressing pressure and / or pressing time, in particular pressing temperature and pressing time.

3. Method according to claim 2, characterized in that the pressing time is in a range between 6 and 40 seconds, preferably 8 and 36 seconds.

4. Method according to claim 2, characterized in that the pressing temperature at the inlet of the press to be controlled is between 180°C and 220°C, preferably 190°C and 200°C.

5. Method according to one of the preceding claims, characterized in that in addition to the degree of crosslinking, the following parameters can be determined before the press, in particular by means of NIR spectroscopy: moisture content of the applied resin layer and amount of the applied resin layer.

6. Method according to one of the preceding claims, characterized in that in addition to the degree of curing, the following parameters can be determined after the press, in particular by means of NIR spectroscopy: resin penetration (or penetration height / penetration quantity of the resin) into at least one porous coating material arranged on the resin-coated carrier material.

7. Method according to one of the preceding claims, characterized in that the at least one press is a short-cycle press (KT press) or a continuous press.

8. Method according to one of the preceding claims, characterized in that the at least one resin layer comprises a resin-impregnated paper layer, a resin-containing powder or a resin-containing liquid.

9. Method according to one of the preceding claims, characterized in that the carrier material is in the form of a carrier plate, paper layer or film layer.

10. Method according to one of the preceding claims, characterized in that the calibration model used for the respective parameters of the resin layer to be determined is determined on the basis of reference samples as follows: - Recording at least one NIR spectrum of several reference samples, each with different values ​​of the desired parameters, using at least one NIR multi-measuring head in a wavelength range between 500 nm and 2500 nm, preferably between 700 nm and 2000 nm, particularly preferably between 900 nm and 1700 nm, and particularly advantageously between 1450 nm and 1550 nm; - Determination of the desired parameters of the measured reference samples using non-spectroscopic methods; - Assignment of the determined parameters to the recorded NIR spectra of the measured reference samples.

11. Production line for carrying out a method according to one of the preceding claims, comprising at least one press, at least one first NIR multi-measuring head arranged upstream (before) of the press, and at least one second NIR multi-measuring head arranged downstream (after) of the press, and at least one control system for controlling the press, wherein the The press control system comprises at least one computer-assisted evaluation unit and a database.

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