Method for controlling a press for pressing a substrate material with at least one resin layer arranged thereon

Abstract

The invention relates to a method for controlling a press for adjusting operating parameters of the press, the press being suitable for pressing a carrier material together with at least one resin layer arranged on the carrier material, wherein at least one NIR multi-measuring head is arranged upstream of the press in the running direction of the carrier material to be pressed and at least one NIR multi-measuring head is arranged downstream of the press in the running direction of the carrier material to be pressed; wherein the NIR multi-measuring head is connected to at least one control system for controlling the press, which control system has at least one computer-aided evaluation unit and a database for processing and optionally storing recorded and evaluated NIR data, the method comprises the following steps: recording at least one NIR spectrum of a resin layer applied to a carrier material in the wavelength range of between 500 nm and 2500 nm, preferably between 700 nm and 2000 nm, especially preferably between 900 nm and 1700 nm and especially advantageously between 1450 nm and 1550 nm by means of at least one NIR multi-measuring head arranged upstream of a press, a degree of cross-linking of a resin layer arranged on the carrier material is determined as at least one first parameter, and the recorded NIR spectrum is evaluated in the evaluation unit by automatically comparing the recorded NIR spectrum with a calibration model created for the parameters of the resin layer, at least one NIR spectrum of the resin layer applied to the carrier material in the wavelength range of between 500 nm and 2500 nm, preferably between 700 nm and 2000 nm, especially preferably between 900 nm and 1700 nm and especially advantageously between 1450 nm and 1550 nm is recorded by means of at least one NIR multi-measuring head arranged downstream of the press, determining a 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, and evaluating the recorded NIR spectrum in the evaluation unit by automatically comparing the recorded NIR spectrum with a calibration model created for the degree of curing of the resin layer; wherein a degree of crosslinking (an actual value of degree of crosslinking) determined upstream of the press is compared with a desired value of degree of crosslinking, and wherein a degree of curing (an actual value of degree of curing) determined downstream of the press is compared with a desired value of degree of curing, when the actual value of the degree of crosslinking deviates from the corresponding desired value and the actual value of the degree of curing deviates from the corresponding desired value, the operating parameters of the press are automatically adjusted by the control system in such a way that the desired value of the degree of crosslinking and the desired value of the degree of curing are satisfied.

Description

Technical Field

[0001] The invention relates to a method for controlling a press to adjust operating parameters of the press, wherein the press is suitable for pressing a carrier material and at least one resin layer arranged on the carrier material. Background Art

[0002] In the production of industrial "prepregs" (impregnations, for example resin-impregnated paper layers) or surface coverings in the artificial wood industry, a carrier material is impregnated with resin or coated.

[0003] For this purpose, a decorative resin-impregnated paper can be pressed onto the surface of the material panel, or a layer material can be attached to the artificial wood, the layer material first being pressed into a laminate from a plurality of resin-impregnated papers. Alternatively, the decoration can be applied directly to the artificial wood panel by printing, which is then sealed with resin and pressed.

[0004] The resins used for impregnation of paper layers or also for direct coating of other carrier sheets undergo different polymerization and crosslinking states in the process.

[0005] This is described below based on the melamine formaldehyde resins commonly used in the manufacture of artificial wood.

[0006] Melamine and formaldehyde initially react with the formation of methylol groups at the amino groups of melamine to give water-soluble products (see Scheme I).

[0007]

[0008] After addition of a suitable catalyst, preferably an acid, the melamine formaldehyde monomers are subjected to polycondensation, wherein linkage of the monomers via ether groups and methylene groups and the formation of high molecular weight precondensates and polycondensates occur (see Scheme II).

[0009]

[0010] Precondensates and polycondensates differ in their molar mass and solubility. Thus, low-molecular-weight precondensates can still have limited water solubility, while high-molecular-weight polycondensates are insoluble. The limited water solubility of precondensates is caused, in particular, by the low degree of crosslinking of the still free methylol groups and the generally still linear oligomers. Precondensates are therefore polymeric intermediates.

[0011] During the complete curing of the polycondensate, intense crosslinking occurs due to the splitting of the methylol groups still present to formaldehyde, with a tightly crosslinked plastic forming via the methylene groups (see variant III).

[0012]

[0013] Therefore, among synthetic resins that cure via condensation reactions, the following resin states are distinguished:

[0014] -A state: easily soluble in solvent, meltable and solidifiable;

[0015] -B state: only partially soluble in solvent, meltable, and solidifiable;

[0016] -C state: insoluble, solidified.

[0017] During pressing (hot pressing), the pressure and temperature cause a polycondensation reaction during which the resin, especially the melamine resin, solidifies. This transfers the resin from state b (partially condensed, still molten and solidified) to state c (completely condensed and solidified).

[0018] The degree of cure (C-state) of the melamine resin and the degree of crosslinking (B-state), which influences the degree of cure, are important tools for determining the surface quality of artificial wood products. Excessive curing leads to embrittlement, which can cause tearing during further processing steps (sawing, drilling, milling, etc.). Excessive curing can lead to poor surface properties in terms of chemical resistance and / or wear. This is particularly true when the likelihood of a surface being subjected to specific loads is high. As examples, one can mention a single work surface in a laboratory that frequently comes into contact with corrosive chemicals, or a floor surface that is subject to high mechanical loads due to walking.

[0019] The degree of cure is typically determined using the so-called acid test. Here, a dilute mineral acid (6 molar hydrochloric acid) is applied to the surface over a defined period of time. The gloss and / or color changes are then assessed. It has been observed that the less loss of gloss / color, the stronger the cure. However, this test also takes time, which means that products that meet quality requirements are not produced until the test results are available. Therefore, samples must first be cut from larger boards (sizes up to 2800 x 2070 mm). Due to the gaps, the boards cut from the samples must be sent to secondary production or scrap. Furthermore, a certain correlation between the results and the color of the decorative paper used or the embrittlement of the melamine resin surface has been shown. This makes assessment difficult, especially with very bright decorations and matte surface designs. However, this test is only a point test. Reliable conclusions about the cure of the entire production batch cannot be drawn. Furthermore, working with concentrated hydrochloric acid is not without risks.

[0020] Therefore, the optimization of the pressing time in the press can only be carried out very slowly, because the inspection of the sample from the production together with the sampling takes almost an hour. This has the result that the product batch may have been produced before the results are available.

[0021] Therefore, the conventional method for determining the degree of curing of the resin applied to the material sheet has a series of disadvantages. In particular, it is not possible to adjust the operating parameters of the press according to the degree of curing in a short time in order to ensure the best results and thus ensure quality reliability. Summary of the Invention

[0022] The technical object underlying the present invention is therefore to develop a method which enables rapid and reproducible description of the curing of a polymer layer, such as a melamine resin layer, applied to a material sheet, and at the same time controls the operating parameters of the press to influence the pressing parameters, such as pressure, temperature and pressing time.

[0023] This object is achieved by a method having the features of claim 1 .

[0024] Correspondingly, a method for controlling a press to adjust operating parameters of the press is provided.

[0025] wherein the press is suitable for pressing the carrier material and at least one resin layer provided on the carrier material,

[0026] wherein at least one NIR multi-measuring head is provided upstream of the press in the running direction of the carrier material to be pressed, and at least one NIR multi-measuring head is provided downstream of the press in the running direction of the carrier material to be pressed;

[0027] wherein the NIR multi-measuring head is connected to at least one control system for controlling the press, said control system having at least one computer-assisted evaluation unit and a database for processing and optionally storing the recorded and evaluated NIR data,

[0028] The method comprises the following steps:

[0029] - determining the degree of crosslinking of the resin layer applied to 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 means of at least one NIR multi-measuring head arranged upstream of the press, and evaluating the recorded NIR spectrum in an evaluation unit by automatically comparing the recorded NIR spectrum with a calibration model created for the parameters of the resin layer,

[0030] - determining the degree of curing of the resin layer applied to the carrier material as at least one second parameter of the resin layer applied to 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 means of at least one NIR multi-measuring head arranged downstream of the press, and evaluating the recorded NIR spectrum in an evaluation unit by automatically comparing the recorded NIR spectrum with a calibration model created for the degree of curing of the resin layer;

[0031] wherein the degree of crosslinking determined upstream of the press (actual value of the degree of crosslinking) is compared with the expected value of the degree of crosslinking, and

[0032] wherein the degree of solidification determined downstream of the press (actual value of the degree of solidification) is compared with the expected value of the degree of solidification, and

[0033] When the actual value of the degree of crosslinking deviates from the corresponding expected value and when the actual value of the degree of curing deviates from the corresponding expected value, the operating parameters of the press are automatically adjusted by the control system so that the expected values ​​of the degree of crosslinking and the degree of curing are met.

[0034] Thus, the parameters of the resin layer applied to the carrier material before and after pressing are determined, compared with predetermined desired values, and used to control the press in the event of deviations. The resulting differences are then used for open-loop or closed-loop control of the press installed in the production line. The parameters, namely the degree of crosslinking and the degree of curing, are used in combination for press control. The operating parameters of the press are automatically adjusted to meet the desired values.

[0035] Automatically feeding back the measured parameters, namely the degree of crosslinking and curing, to the press improves process safety and reduces rejects due to defective products. Feeding back deviations directly to the press improves production quality and serves to reduce costs.

[0036] In the prior art, unknown parameters, namely the degree of crosslinking and the degree of cure, are used in combination to control presses in production lines for producing artificial wood panels. Thus, while EP 3 885 740 A1 suggests using NIR spectroscopy to control production lines using various parameters of resin-coated artificial wood panels (e.g., the degree of crosslinking), the parameters determined using NIR spectroscopy are generally used to control production lines for coating artificial wood panels. This particularly relates to the control of coating and drying equipment. The document does not provide any information on using specific parameters to control presses. According to EP 3 238 934 B1, the degree of cure can also be determined in production lines using NIR spectroscopy, wherein at least one NIR detector is provided downstream of the coating and pressing equipment in the process direction. However, neither document provides any information on combining specific parameters, namely the degree of crosslinking and the degree of cure, to control presses.

[0037] Along with other parameters such as brightly visible decoration, a closed and optically interference-free surface, and the absence of delamination between carrier and cover, curing determined using NIR is also an important parameter for determining the quality of the laminate online. This is all the more important because the degree of curing downstream of the press cannot be easily detected (visually) but, as mentioned above, must first be determined using a complex acid test.

[0038] In one embodiment of the method, the operating parameter of the press to be controlled is selected from the group consisting of pressing temperature, pressing pressure and / or pressing time, in particular pressing temperature and pressing time.

[0039] The degree of curing (C state) of the resin layer is therefore determined in particular by the pressing temperature and the pressing time. If the pressing time is too short, this may lead to insufficient curing (undercuring). Conversely, if the pressing time is too long, this may lead to overcuring associated with cracks. The pressing temperature has a similar effect: if the pressing temperature is too low, this may lead to insufficient curing (undercuring). Conversely, if the pressing time is too long, this may lead to overcuring associated with cracks. Incorrect setting of the pressing pressure may in turn lead to sticking of the carrier material in the press.

[0040] The degree of crosslinking (state B) determined upstream of the press also influences the degree of solidification (state C) and can therefore be used to control the operating parameters of the press. It is useful to compare the values ​​determined for the degree of crosslinking with the values ​​determined for the degree of solidification in order to thereby set the optimal pressing conditions in the press for a particular batch of carrier material to be pressed.

[0041] Therefore, the degree of crosslinking of the resin layer applied to the carrier material and dried can vary, which influences curing. If the crosslinking is too high upstream of the press, this can also lead to poor adhesion of the impregnant to the carrier material. Conversely, if the crosslinking is too low, this can lead to undercuring of the resin layer, resulting in an overly soft surface. Excessive crosslinking can be caused, for example, by overdrying during impregnation of the paper or by improper or prolonged storage of the resin-coated carrier material during intermediate storage. In this case, crosslinking of the resin layer proceeds further, leading to even higher crosslinking. In this case, it is desirable and necessary to adjust the operating parameters of the press accordingly.

[0042] The pressing time and pressing temperature depend on the carrier material to be pressed, the layers arranged on the carrier material, and the type of desired product. On average, the pressing time is between 6 and 40 seconds, preferably between 8 and 36 seconds. If the resin layer to be pressed together with the carrier material is a liquid resin layer (e.g., a liquid cover layer), the pressing time is between 6 and 10 seconds, preferably between 8 and 9 seconds. If the carrier material is pressed together with resin-containing paper, the pressing time is between 12 and 20 seconds, preferably between 13 and 18 seconds, particularly preferably between 14 and 16 seconds, for example, 15 seconds.

[0043] The pressing temperature to be set at the inlet 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 inlet temperature, so that the temperature is between 160° C. and 200° C., preferably between 180° C. and 190° C.

[0044] It should be noted that the press time and press temperature to be set or controlled are mutually exclusive; that is, an increase in press time is associated with a decrease in press temperature. In one embodiment, when using a short-cycle press, an increase in press time of 1 to 2 seconds results in a 10°C decrease in press temperature. In the case of a CPL press, the feed is adjusted accordingly. Thus, a decrease in feed of 1 to 2 m / min (i.e., a slower feed through the press) results in a 10°C decrease in press temperature.

[0045] Press control

[0046] As mentioned, in the event of deviations from the desired values, the parameters of crosslinking and curing determined by means of NIR spectroscopy adjust the operating parameters of the press so that the desired values ​​are met and the quality of the product can be guaranteed.

[0047] In order to control and adjust actual values ​​to desired values, first determine the levels or ranges associated with desired and actual values.

[0048] Therefore, as will be discussed in more detail below, to determine the parameters of the curing, an NIR spectrum is first recorded for the purpose of calibrating a reference sample, which is then correlated with the results of a conventional acid test. An average value is formed from the results of the acid test for the board and correlated with the spectrum of the board.

[0049] The results of the conventional acid test and the NIR measurement are divided into 5 levels. Table 1 shows the corresponding correlation.

[0050] Curing grade Quality of curing 1 Overcuring 2 Slightly overcured 3 (expected value) Optimal curing 4 Slightly undercured 5 Under-cured

[0051] Table 1

[0052] The curing levels can be used to control the press. For example, if, during the ongoing process, NIR spectroscopy is used to determine parameters for the resin-coated carrier material downstream of the press that correspond to a curing level of 1 (thus deviating from the desired value), the operating parameters of the press are automatically adjusted by the control system so that the desired value for the degree of curing is achieved, which in this case corresponds to a curing level of 3. This can be achieved, for example, by reducing the pressing temperature.

[0053] To determine the parameters of the crosslinking (B state), NIR spectra were also recorded for the purpose of calibration of reference samples, which were then correlated with the results of the VC (volatile compounds) test. An average value was formed from the results of the VC test for the board and correlated with the spectrum of the board.

[0054] In conventional VC value determination, the residual moisture content of a reference sample is determined after drying in an oven. In addition to water, formaldehyde (formed from free methylol groups) is also broken down. Therefore, the proportion of free methylol groups is a factor used to determine the degree of crosslinking. Depending on the intended use, the optimal moisture content of the impregnated material (as a summation of water and formaldehyde release) is typically between 5% and 7% by weight. In this case, the methylol group content is optimal.

[0055] Samples with a moisture content below 5 wt%, such as 3 wt% to 4 wt%, have a lower than optimal hydroxymethyl content and are considered over-dried. Samples with a moisture content above 7 wt%, such as 8 wt% to 9 wt%, have a higher than optimal hydroxymethyl content and are considered under-dried.

[0056] Based on this, a calibration of the crosslinking for different resin and paper systems can be carried out with the aid of the data, and the state of the crosslinking can essentially be predicted.

[0057] The results of conventional VC test and NIR measurement are also divided into 5 levels. Table 2 shows the corresponding correlation.

[0058] Cross-linking grade Humidity (weight %) Quality of cross-linking 1 3 Overdrying 2 4 Slightly over-dry 3 5-7 wt% (desired value) Optimal drying 4 8 Slightly less dry 5 9 Underdrying

[0059] Table 2

[0060] The crosslinking level can be used to control the press. For example, if, during the ongoing process, NIR spectroscopy is used upstream of the press to determine parameters corresponding to a crosslinking level of 5 (thus deviating from the desired value) for the resin-coated carrier material, the operating parameters of the press are automatically adjusted by the control system so that the desired value for the degree of crosslinking is achieved, which in this case corresponds to a crosslinking level of 3. This can be achieved, for example, by increasing the pressing temperature and / or pressing time.

[0061] It should be noted that in impregnations, some water is present as free water and some as chemically bound water. In freshly prepared (fresh) impregnations, approximately 60% to 70% of the water is chemically bound in the methylol groups, while 20% to 30% is free water. This means that in freshly prepared impregnations, the ratio of bound water to free water is approximately 3:1 to 2:1. However, this ratio can vary depending on the melamine resin (mol ratio melamine:formaldehyde). In contrast, in superimposed impregnations, >70% is free water and approximately 30% is chemically bound water; in superimposed impregnations, the ratio of bound water to free water is approximately 1:3 to 1:2. This difference is due to the slow further reaction of the resin in the impregnation. This reaction is acid-catalyzed and occurs even at room temperature. Therefore, it is possible to determine the degree of superposition of the impregnations by the ratio of the water peak to the methylol group peak in the NIR spectrum. It is advantageous to determine the degree of superposition of the impregnation, since superimposed impregnations are unsuitable or only conditionally suitable for further processing (for example pressing together with artificial wood panels).

[0062] Therefore, when using the VC value to establish a calibration model, the ratio of the water peak at 1950 nm to the methanol peak at 2050 nm in the measured NIR spectrum (first harmonic) can also be used to determine the degree of crosslinking of the resin layer. In other words, a superimposed impregnation material has more free water and thus has a water peak that is more intense relative to the methanol peak, while in the case of an unsuperimposed impregnation material, the water peak is less intense relative to the methanol peak. Determining this ratio as a measure of the degree of crosslinking is particularly advantageous when using superimposed impregnation materials.

[0063] Correspondingly, in another aspect, a method for determining the degree of overlap of resin layers, in particular impregnations, applied to a carrier material by means of NIR spectroscopy can be provided, wherein the method is carried out on a production line by means of at least one NIR measuring head, preferably an NIR measuring head arranged upstream of a press, wherein the method comprises the following steps;

[0064] - recording 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, more preferably between 1800 nm and 2100 nm, by means of at least one NIR multi-measuring head,

[0065] - by evaluating the recorded NIR spectrum, determining the degree of crosslinking of the resin layer provided on the carrier material by means of an automated comparison of the recorded NIR spectrum with a calibration model created for the degree of crosslinking of the resin layer, wherein (additionally)

[0066] - The ratio of the spectrum recorded in the wavelength range between 1900 nm and 2000 nm, preferably 1950 nm (water peak) to the spectrum recorded in the wavelength range between 2000 nm and 2100 nm, preferably 2050 nm (hydroxymethyl peak) is used as a measure of the degree of overlap of the resin layer applied to the carrier material.

[0067] In this case, the ratio of the spectrum recorded in the wavelength range between 1900 nm and 2000 nm, preferably 1950 nm (water peak) to the spectrum recorded in the wavelength range between 2000 nm and 2100 nm, preferably 2050 nm (hydroxymethyl peak) is compared with a calibration model created for the degree of overlap. To create the calibration model, the ratio of the corresponding NIR wavelength ranges is determined for a corresponding reference sample (resin-coated support material) before and after storage (at room temperature). The storage can be carried out for periods of varying lengths. The ratios of the wavelength ranges determined for the reference samples stored for each of the different lengths represent the degree of overlap.

[0068] This means that the stated information on the ratio of the water peak to the methylol peak can also be used, after calibration for different resin and paper systems, to essentially predict the crosslinking state and to control the press.

[0069] Other parameters of the resin layer

[0070] In addition to the degree of crosslinking and the degree of curing, further parameters of the resin layer can also be determined.

[0071] In one embodiment of the method, in addition to the degree of crosslinking, the following parameters are determined upstream of the press, in particular by means of NIR spectroscopy: the water content of the applied resin layer (see EP 2 808 636 B1) and the amount of the applied resin layer (EP 3 428 619 B1).

[0072] The additional parameters determined upstream of the press provide further information on the quality of the resin layer applied to the carrier material and thus serve for quality assurance. In one embodiment, the additional parameters are not used to control the press, but rather are displayed to the operator during the production process for quality control (e.g., green light for optimal value; red light for defective value). This makes it possible to promptly identify incorrect values ​​of the resin layer applied to the carrier material during the production process.

[0073] If the resin layer has too low humidity before pressing, this causes poor fluidity, poor transparency and / or poor adhesion of the resin layer when using the impregnation. When the humidity is too high, the surface quality is adversely affected. The non-optimal humidity level of the resin layer can be balanced in the press by adjusting the operating parameters. Therefore, when the humidity is too high, the pressing temperature in the press can be increased and the pressing pressure in the press can be increased in parallel. In particular, the pressure should be set to a value higher than the water vapor pressure. However, this is only feasible within a specific range.

[0074] The amount of resin applied can also affect the surface quality of the pressed and cured resin layer. If the amount of resin applied deviates upward from the optimal coating amount (i.e., too high), the cured resin layer will have a gray, milky haze. If the amount of resin applied is too low, this can result in a defective surface, delamination, and poor adhesion.

[0075] In another embodiment of the method, in addition to the degree of curing, the following parameter is determined downstream of the press, in particular by means of NIR spectroscopy: resin penetration (or resin penetration height / amount) into at least one porous coating material arranged on the resin-coated carrier material.

[0076] The additional parameters determined downstream of the press also provide further information on the quality of products, such as floor coverings, which are finished with a porous covering material, in particular a veneer layer. In this case, the porous covering material is applied upstream of the press onto a carrier material, in particular a carrier plate, provided with a resin layer, and then pressed in the press. During the pressing process, the resin penetrates or rises into at least one porous covering material. The degree of resin penetration into the porous covering material, which serves as a quality characteristic, can be measured using NIR spectroscopy (see WO 2022 / 179883 A1).

[0077] If the resin penetration into the porous coating deviates, the operating parameters of the press, particularly the pressing temperature and / or pressing time, can be adjusted. This also involves adjusting these parameters in opposite directions. When the pressing temperature is lowered, the pressing time is increased. For example, when the pressing temperature is lowered by 10°C, the pressing time is increased by 10 to 20 seconds.

[0078] press

[0079] The press to be controlled in the process is a short-cycle press (KT press) or a continuous press.

[0080] Short-cycle presses (KT presses) are used to refine the surfaces of boards made of artificial wood. KT presses are particularly suitable for pressing particleboard and MDF / HDF with a liquid resin layer or resin-impregnated paper applied thereto. This results in a durable application of the resin layer to the surface of the artificial wood board. The resin penetrates the pores of the surface, ensuring adhesion. Furthermore, it creates a surface that is insensitive to various environmental influences.

[0081] Continuous presses (CPL presses) are used to press impregnates in a continuous or circulating process. Continuously operating presses have heated roller belt presses.

[0082] The pressing step in the press (CPL press) was carried out at a pressing pressure of 50 kg / cm 2 Up to 70kg / cm 2 The press is carried out at a temperature between 150°C and 200°C, preferably 180°C. The press speed is 5 to 20 m / min, preferably 5 to 15 m / min, for example 9.5 m / min. The press zone in a CPL press typically has a length of 3000 to 4000 mm. This allows the press time to be determined given a known feed rate. Thus, at a length of 3 m, 10 m / min corresponds to a press time of 18 seconds.

[0083] Resin layer

[0084] In one embodiment of the 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. Thus, the applied resin layer can be present as a powder or liquid covering of the paper layer on the carrier material or as a partial or complete impregnation.

[0085] Resin-saturated paper layer (cover layer)

[0086] The resin-impregnated paper layer is usually based on an average paper basis weight of 18 g / m 2 Up to 50g / m 2 , preferably 20g / m 2 Up to 30g / m 2 , such as 25g / m 2 of a cellulose-containing layer.

[0087] The paper layer is impregnated with a thermosetting resin as a binder, such as a formaldehyde resin, in particular a melamine resin, a phenolic resin, a urea resin or a mixture of the resins. This paper layer is also referred to as a covering layer.

[0088] For impregnation of the paper layer, an aqueous resin solution is used having a resin solids content of between 40% and 80% by weight, preferably between 50% and 65% by weight.

[0089] The resin is applied in an amount of 200% to 600%, preferably 250% to 400%, solids content, based on the grammage of the paper layer. The resin is used in an amount sufficient to penetrate the porous cover material at least partially during the pressing process.

[0090] After applying the resin to the paper layer, in particular after impregnating it with the resin, the surface is only pre-dried and thus still tacky. This tacky state is achieved with a volatile matter content of 10% to 15% with a residual moisture (VC value). The VC value is determined as the difference between the initial weight and the final weight after drying at 105°C until the weight is constant.

[0091] The adhesive surface of the resin-saturated paper layer simplifies the application of additives for further refinement of porous covering materials, such as overlays.

[0092] In one embodiment, overlay paper is used as the paper layer. Overlay paper is typically a thin paper that has been impregnated with conventional melamine-formaldehyde resin. Overlay paper is also commercially available in which wear-resistant particles, such as corundum particles, are already mixed into the resin of the overlay layer or are sprinkled onto the resin-moistened overlay layer to increase wear resistance. To impregnate the overlay paper, a resin coating containing up to 400% by weight of melamine resin is used. For most applications (laminates for worktops or cashier counters), an overlay layer without corundum is sufficient.

[0093] Powdered resin (powder coating)

[0094] In the case of using powdered resin, the amount of the powdered resin applied to the surface of the carrier plate was 50 g / m 2 Up to 150g / m 2 , preferably 60g / m 2 Up to 100g / m 2 , especially preferably 70g / m 2 Up to 80g / m 2 .

[0095] The powdered resin to be used has a dusting 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, particularly preferably 25 μm.

[0096] The powdered resins currently used have only traces of moisture. Therefore, a moisture content of 0.5% should not be exceeded, as otherwise lumps will form and spreading is no longer possible.

[0097] In an improved variant of the method, the surface or side of the carrier plate to be sprinkled with the powdered resin is pretreated before the powdered resin is sprinkled to improve the adhesion of the powdered resin to the surface of the carrier plate. The pretreatment can include applying moisture to the side or surface or electrostatically charging the side or surface of the carrier plate.

[0098] As powdered resins, formaldehyde resins are used, preferably urea resins, melamine resins or phenolic resins, particularly preferably melamine formaldehyde resins, melamine phenol formaldehyde resins or melamine urea formaldehyde resins.

[0099] The powdered resin is preferably applied using a spreading device. Spreading is preferably carried out in a continuous process. A suitable spreading device is the "Resonance Brush System" precision spreader from TPS. However, electrostatic application using a tribospray gun is also possible.

[0100] The further layer to be applied can consist solely of powdered resin, or it is also possible to use a mixture comprising resin, natural and / or synthetic fibers and optionally further additives.

[0101] The powder consists of 30% to 65% by weight, preferably 40% to 60% by weight, of fibers, 20% to 45% by weight, preferably 30% to 40% by weight, of binder, and 0% to 8% by weight, preferably 0.5% to 6% by weight, of additives. The natural and / or synthetic fibers are preferably selected from bleached cellulose fibers or organic polymer fibers.

[0102] Liquid resin (liquid cover)

[0103] In the case of using liquid resin as the resin layer, the amount of the liquid resin coated on the surface of the carrier plate is 50 g / m 2 and 150g / m 2 Between, preferably 60g / m 2 and 100g / m 2 between, especially preferably between 70g / m 2 and 80g / m 2The solid content of the resin is about 65% by weight, and it contains common additives such as curing agents, wetting agents, etc.

[0104] As liquid resin, formaldehyde resin is used, preferably urea resin, melamine resin or phenolic resin, particularly preferably melamine formaldehyde resin, melamine phenol formaldehyde resin or melamine urea formaldehyde resin.

[0105] As in the case of resin powders, liquid resins can also be used in admixture with natural and / or synthetic fibers and optionally further additives.

[0106] Porous cladding materials

[0107] As mentioned above, a porous covering material, such as a veneer layer, can be provided on at least one resin layer.

[0108] When using a veneer layer, the veneer layer comprises in one embodiment at least one layer consisting of solid wood veneer panels. In a further embodiment, at least one veneer panel comprises at least one solid wood layer with a thickness between 0.2 mm and 10 mm, preferably between 0.5 mm and 5 mm, and particularly preferably between 0.5 mm and 2 mm. The veneer panel can be manufactured in one piece from a tree trunk, for example by stripping. However, the veneer panel can also be assembled from a single piece, which is connected to each other, for example, by an adhesive or so-called glue line. The veneer panel preferably has the size of a carrier board. The veneer panel has a lower side facing the carrier board and an upper side facing away from the carrier board.

[0109] Carrier material

[0110] The carrier materials currently used are in the form of carrier sheets, paper layers or film layers.

[0111] Carrier board

[0112] If a carrier board is used as the carrier material, at least one carrier board is a board made of artificial wood, in particular a particle board, a medium-density fiberboard (MDF), a high-density fiberboard (HDF), an oriented strand board (OSB) or a plywood, an artificial wood-plastic mixture or a WPC board (wood-plastic composite). The layer thickness of the resin layer applied to the carrier board is between 10 μm and 100 μm, preferably between 30 μm and 80 μm, particularly preferably between 30 μm and 60 μm.

[0113] The surface of the carrier board can be surface treated. The surface of the artificial wood carrier board can also be ground (without a pressed surface) or unground (with a pressed surface).

[0114] It is also conceivable that at least one primer layer or at least one primer layer 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.

[0115] In another embodiment, it can be provided that at least one resin layer is arranged on the upper side of the carrier plate (i.e. the side facing the user after the carrier plate is installed), and at least one sound-absorbing layer is arranged on the back side or underside of the carrier plate, in particular in the case of an artificial wood board as a carrier plate.

[0116] Such artificial wood panels are preferably used as floor panels, wall panels, ceiling panels, furniture panels or as cutting boards.

[0117] CPL (Continuous Pressure Laminate)

[0118] In the case of a paper layer as carrier material, preference is given to using a kraft paper layer which is pressed together with at least one resin layer in a continuously operating press (CPL press).

[0119] The resin layer can be a resin-impregnated paper layer, in particular a resin-impregnated decorative paper and / or a resin-impregnated overlay paper and / or a resin-impregnated balancing paper. These paper layers are pressed with kraft paper in a continuous press to form a continuous press laminate (CPL). This continuous press laminate is usually obtained as a roll and is used, for example, to produce work panels, clad profiles, and door panels. The CPL is pressed in a continuous or circulating process in a web press heated on both sides.

[0120] When manufacturing CPL on a double belt press, resin-impregnated sodium hydroxide kraft paper (NKP) is used in the core layer.

[0121] The kraft paper currently used has a 2 and 200g / m 2 Between, preferably 80g / m 2 and 170g / m 2 between, particularly preferably between 80g / m 2 and 160g / m 2 Between, for example 80g / m 2 , 120g / m 2 or 160g / m 2 As already mentioned above, kraft paper has high strength and consists of cellulose fibers to which starch, alum and glue are added in order to achieve surface effects and increased strength.

[0122] At least one further paper layer is laid onto the kraft paper layer. Any number of paper layers can be laid, with two, three or four further paper layers being preferred.

[0123] At least one further paper layer to be laid can be a kraft paper layer, a decorative paper layer or a covering paper layer. Preferably, another kraft paper layer is laid, followed by a decorative paper layer and / or a covering paper layer. Possible layer configurations or covering configurations will be described in further detail below.

[0124] The paper layer used can be completely saturated (impregnated) with a resin, preferably melamine-formaldehyde resin. In the case of completely impregnated paper, the resin is applied in an amount of 80% to 400% by weight, preferably 90% to 120% by weight, particularly preferably 100% to 110% by weight, based on the paper weight.

[0125] In one variant, it is provided that a material layer (eg glass fiber fleece, aluminum foil) is placed on the kraft paper layer, followed by a second kraft paper layer, a decorative paper layer and / or a cover paper layer.

[0126] However, it is also possible to omit the second kraft paper layer and / or the decorative paper layer and apply the cover paper layer directly to the material layer. The type and order of the applied additional paper layers can be flexibly designed depending on the type of material layer. If the material layer is colored, for example, the decorative paper can be omitted.

[0127] The at least one material layer can be selected from the following materials: graphite-containing paper to increase electrical conductivity; plastic films, particularly thermoplastic films (to achieve narrow post-forming radii); aluminum foil; fleece materials and other textile materials. The coating material used can be either porous or non-porous, i.e., liquid-impermeable. This particularly includes materials with a porous structure in which the liquid resin can rise during pressing and which can be at least partially plastically deformed.

[0128] Glass fiber fleece is used to improve impact resistance. Aluminum foil, preferably primed with a primer such as an isocyanate primer before laying, is used to reduce water vapor permeability. The thickness of the aluminum foil is 0.1 mm to 0.3 mm, preferably 0.2 mm.

[0129] In another embodiment of the method, the layer construction consisting of a kraft paper layer and at least one further paper layer is pressed together with at least one structure-providing paper (laid onto the at least one further paper layer on the upper side of the layer stack) and at least one transparent paper (on the lower side of the layer construction).

[0130] Here, a structure-providing paper is understood to be a paper that imparts structure (e.g., a 3D structure) to the surface of the laminate after laying and pressing. In addition to its structuring function, the structure-providing paper also has a protective function, particularly during the pressing step. After pressing the layer or cover structure, the structure-providing paper is removed again and can be reused.

[0131] The transparent papers currently used in laminates are also known by the term "glass paper". Glass paper is a transparent paper made from finely ground pulp that is largely resin-tight but not moisture-resistant. Its high transparency gives it a very vivid satin effect.

[0132] NIR spectroscopy

[0133] In one embodiment of the method, the calibration model for the respective parameter to be determined for the resin layer is determined based on a reference sample as follows:

[0134] recording, with at least one NIR multi-measuring head, at least one NIR spectrum of a plurality of reference samples having respectively different values ​​of the desired parameter 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;

[0135] - determining the desired parameters of the measured reference sample by means of non-spectral methods;

[0136] - Correlating the determined parameters with the respectively recorded NIR spectra of the measured reference samples.

[0137] For this purpose, a reference sample of a carrier material coated with resin is first provided. It is important that the reference sample is of the same type as the sample to be measured; that is, in particular, the resin mixture of the reference sample has the same composition as the resin mixture to be measured. The identical type of sample to be measured and reference sample is particularly important when using a liquid resin layer with additional materials such as flame retardants, fibers, and other additives.

[0138] At least one NIR spectrum is recorded from the reference sample 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.

[0139] The reference sample is also provided for non-spectral analysis to determine the desired parameters, namely the amount of resin applied to the carrier material, the degree of cure, the degree of cross-linking, the moisture content, the amount of particles applied and their abrasion resistance (or a selection of said parameters). The non-spectral analysis will be described in detail below for each of the mentioned parameters.

[0140] From the parameters determined for the reference samples using the non-spectroscopy analysis, a mean value is formed. This mean value is then correlated with the respectively recorded NIR spectrum of the reference sample. Using multivariate data analysis, a calibration model is created for the correlation between the spectral data of the NIR spectrum of the reference sample and the associated parameter values; i.e., the NIR spectrum of the reference sample is associated with each parameter value of the reference sample. The calibration models created for the different parameters are stored in a suitable data memory.

[0141] Subsequently, at least one resin layer is applied to at least one side of the carrier material, and at least one NIR spectrum of the resin layer applied to the carrier material is recorded. The desired parameters of the resin layer applied to the carrier material can then be determined by comparing the recorded NIR spectrum of the resin layer with the created calibration model.

[0142] It is thus possible to simultaneously determine a plurality of interesting parameters of the resin layer applied to the carrier material from an NIR spectrum determined uniquely for the sample to be measured by automated comparison or adjustment with a calibration model created for the corresponding parameters.

[0143] The comparison and interpretation of NIR spectra is meaningfully performed over the entire recorded spectral range. This is advantageously performed using multivariate data analysis (MDA), which is known per se. In multivariate analysis methods, a plurality of statistical variables are usually investigated simultaneously in a manner known per se. To this end, the number of variables included in the data set is usually reduced in these methods without reducing the information contained therein.

[0144] In the present case, the multivariate data analysis is performed via the Partial Least Squares Regression (PLS) method, which allows the creation of a suitable calibration model. The acquired data are preferably evaluated with the aid of suitable analysis software, for example, the analysis software SIMCA-P from Umetrics AB or The Unscrambler from CAMO.

[0145] In another embodiment, it is provided that spectral data from the NIR spectral range between 1450 nm and 1550 nm are used to create the calibration model, said spectral data being preprocessed by means of suitable mathematical methods and subsequently being provided to a multivariate data analysis.

[0146] The importance of wavelength for predicting parameters of the resin layer from the NIR spectrum, such as the amount of resin, is shown with the aid of regression coefficients. Regions with large coefficient values ​​have a strong influence on the regression model. Thus, the regression coefficients shown in the PLS regression model for determining the amount of resin or resin content indicate 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 the calculation of the model, since the value of the regression coefficient is the largest here. Although other ranges in the spectrum have less information content with respect to the NIR measurement, they still help to take into account or minimize other information or interfering influencing variables (such as the transparency of the layer, the surface properties of the resin layer or the carrier material, etc.).

[0147] In order to eliminate interfering influences (such as the surface properties of the carrier material, the color of the sample, light scattering from solid particles or other additives, etc.), the spectral data must be processed using mathematical preprocessing methods (such as derivative data preprocessing, standardization according to SNVT (Standard Normal Variable Transformation), multiplicative signal correction (EMSC, extended multiplicative signal correction), etc.). Baseline effects caused primarily by the different colors of the samples are removed from the spectrum, overlapping bands are separated from one another, and correlations with light scattering from the substrate surface or from solid particles in the coating are taken into account. If, for example, the resin coating amount is to be determined on the untreated surface of a carrier material such as an artificial wood board, data preprocessing is preferably performed to reduce light scattering from the rough surface of the substrate. When measuring on decorative layers, the focus of calibration and data preprocessing is on removing baseline offsets.

[0148] From the pre-processed data, a calibration model is developed by means of multivariate data analysis, which calibration model includes all decorations used in the calibration.

[0149] Accordingly, the NIR spectra are preferably compared and interpreted using multivariate data analysis (MDA) 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. In multivariate analysis methods, a plurality of statistical variables are usually examined simultaneously in a manner known per se. To this end, the number of variables contained in the data set is reduced without reducing the information simultaneously contained therein.

[0150] As already indicated, the reference sample is measured or determined either spectroscopically or non-spectrally in order to thus correlate the parameters with the recorded NIR spectrum of the reference sample.

[0151] Different non-spectral analysis methods are used depending on the parameters.

[0152] Amount of resin layer applied:

[0153] A common method for determining the coating weight is gravimetric weighing. In this case, the carrier material is coated with the coating medium in a coating device and the coating weight is subsequently determined by determining the weight difference (see also EP 3 428 619 B1).

[0154] Humidity of the applied resin layer:

[0155] The most accurate method for determining moisture content, particularly in wood, is the kiln drying method, in which a sample is dried in a drying oven at 103°C + / - 2°C for 24 hours. Moisture content is defined as the ratio of the weight of the water contained in the material to the weight of the absolutely dry material (dry wood weight). Thus, moisture content is the ratio of wet weight to dry weight (dry wood weight); see EP 2 808 636 B1.

[0156] Degree of curing of the applied resin layer:

[0157] The curing is determined via the so-called acid test. Here, a dilute mineral acid (4 molar hydrochloric acid) is applied to the surface over a defined period of time. The gloss change and / or color change are then evaluated. The less gloss loss / color loss observed, the stronger the curing. From the results of the acid test on the board, an average value is formed and the average value is correlated with the spectrum of the board, see EP 3 238 934 B1.

[0158] Degree of cross-linking of the applied resin layer:

[0159] The degree of crosslinking of partially crosslinked precondensates or polycondensates (also referred to as partially crosslinked, still partially soluble B state) can be determined via a VC test (volatile compound test), in which not only water but also a small proportion of formaldehyde is split off from the synthetic resin.

[0160] For the VC test, a sample (typically 10 x 10 cm) is weighed and dried at 105°C for 5 minutes. After cooling, the sample is reweighed. The mass loss is then determined based on the final weight and reported as a percentage. The previously determined paper weight serves as the basis for determining the resin coating in percentage ((final weight - paper weight / paper weight) x 100), see EP 3 327 424 B1.

[0161] In addition to determining the VC value, the ratio of the water peak at 1950 nm and the methylol peak (first harmonic) at 2050 nm in the measured NIR spectrum is also considered to determine the degree of crosslinking of the resin layer. Determining this ratio as a measure of the degree of crosslinking is particularly advantageous when using superimposed impregnations. The balance between free and bound water is checked by a combination of the VC test and storage of the impregnation in a desiccant over a desiccant. The ratio between the water peak and the methylol peak is then taken into account during calibration.

[0162] Resin penetration into porous cladding:

[0163] The resin penetration into the porous covering layer of the reference sample was determined using a Taber abrader. The test was carried out in accordance with DIN EN 13329. The friction wheel of the Taber abrader was fitted with conventional sandpaper and also loaded with conventional counterweights. A visual check was then carried out after 200 revolutions to determine whether black staining was observed in the veneer. The peeling in mm was then determined using a measuring table in the circular recess created by the sandpaper in the four circular segments formed by the intersection of the coordinates, thereby forming an average value. This average value was combined with the other four samples to form an overall average value. The peeling was then subtracted from the veneer thickness determined using a microscope and then correlated with the spectrum, see WO 2022 / 179883.

[0164] production line

[0165] The 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 facility for producing laminates (CPL).

[0166] In particular, the production line comprises at least one first NIR multi-measuring head arranged upstream (before) the press and at least one second NIR multi-measuring head arranged downstream (after) the press.

[0167] The control system includes at least one computer-assisted evaluation unit (or processor unit) and a database. The evaluation unit aligns or compares the NIR spectrum measured for the product (i.e., the carrier material and the applied resin layer) with calibration models created for the respective parameters. The parameter data thus determined are stored in the database.

[0168] According to the present invention, the data determined using the current spectroscopic method can be used to control a press. As already described above, the parameter values ​​("actual values") measured contactlessly by the NIR multi-measuring head can be used directly and in real time for the open-loop or closed-loop control of the relevant press. This can be done, for example, by measuring the actual values, storing them in a database, such as a relational database, and comparing them with the desired values ​​of the parameters present there. The resulting differences are then used for the open-loop or closed-loop control of the press.

[0169] For adjusting and controlling a press, a computer-implemented method and a computer program comprising instructions are provided, which, when executed by a computer, cause the computer to perform the computer-implemented method. The computer program is stored in a memory unit of a control system of the press. It is also possible for the press to be interconnected as part of a production line with at least one other production line.

[0170] As mentioned, the press to be controlled can be integrated into a production line for coating material panels.

[0171] In one embodiment, such a production line can have the following configuration:

[0172] at least one first coating device for applying a first resin layer to the upper side and / or the lower side of the material sheet,

[0173] at least one first drying device arranged after the first coating device in the machine direction, for drying the first upper resin layer and / or the lower resin layer;

[0174] at least one second coating device, arranged downstream of the first drying device in the machine direction, for applying a second resin layer to the upper side and / or the lower side of the material sheet,

[0175] at least one second drying device arranged after the second coating device in the machine direction, for drying the second upper resin layer and / or the lower resin layer;

[0176] - optionally at least one third coating device, arranged downstream of the second drying device in the machine direction, for applying a third resin layer to the upper side and / or lower side of the material sheet,

[0177] - optionally at least one third drying device arranged after the third coating device in the machine direction, for drying the third upper resin layer and / or the lower resin layer; and

[0178] at least one first NIR measuring head, in particular an NIR multi-measuring head, arranged downstream of the second or optionally third drying device in the process direction for online determination of the degree of crosslinking of the resin layer provided on the upper side of the material panel;

[0179] at least one pressing device for pressing the layer structure, in particular a short-cycle press, and

[0180] At least one second NIR measuring head, in particular an NIR multi-measuring head, arranged downstream of the pressing device in the processing direction for online determination of the degree of curing of the pressed resin layer arranged on the upper side of the material panel.

[0181] A CPL facility for producing laminates comprises a continuously operating press, wherein a first NIR measuring head, in particular an NIR multi-measuring head, is arranged 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 arranged for online determination of the degree of curing after the press (downstream). DETAILED DESCRIPTION

[0182] The present invention is described in detail below with reference to a number of embodiments.

[0183] Example 1 : Determine the degree of cure of the resin layer applied to the artificial wood panel

[0184] Constructing reference samples and calibration:

[0185] Calibration is performed by recording the NIR spectrum of a cured sample which is then checked for cure by means of an acid test and is carried out as follows.

[0186] HDF boards (207 cm x 280 cm) printed with different decorations were coated from above with liquid melamine formaldehyde (MF) resin or with cover paper impregnated with MF resin using an applicator roller in a coating facility. The coating was then pressed in a short-cycle press at 190°C to 210°C and approximately 40 bar for 8 to 36 seconds. The protective layer cured during this process. By varying the pressing time and temperature, samples with differently cured protective layers were created.

[0187] During calibration for in-line measurement, an NIR spectrum is recorded for a few seconds directly on the production line after the pressing process. Subsequently, the curing of the panels is checked using an acid test at the location where the NIR spectrum was recorded. An average value is formed from the results of the acid test on the panels and correlated with the panel's spectrum.

[0188] In this way, a plurality of reference spectra of differently cured panels with different color decorations (for calibration of the in-line measurement) are recorded.

[0189] The acid test is carried out as follows. 3 drops of 6M HCl are added to a room temperature cooled plate. After a 25 minute exposure time, the acid is rinsed off with water. Based on a visual and tactile assessment of the surface at the exposure site, conclusions about the quality of the cure are drawn.

[0190] For calibration, the test results are correlated with the spectral data. The calibration model is created using multivariate data analysis. This is performed using suitable analysis software, such as The Unscrambler from CAMO. This program, in particular, minimizes various interfering factors affecting the measurement, such as the surface properties of the sample, infrared-inactive fillers in the coating, or different sample colors, through specialized preprocessing techniques for the spectral data. As already described, color influences on the NIR measurement can also be mitigated by creating groups of decorations with similar color divisions.

[0191] From the reference spectra, a calibration model is created, which can be used to determine (predict) the curing of an unknown sample.

[0192] In an online NIR measurement, the result of the acid test or the quality of the curing is then directly predicted.

[0193] Online measurement of the degree of curing of resin coatings:

[0194] For in-line determination of post-press curing, NIR measurements or recording of the NIR spectrum are performed directly at the production facility after the resin coating has cured. After creating a calibration model, it is installed in the measuring device. As the sample passes under the measuring head, multiple NIR spectra of the coating are recorded. The average cure of the coating is calculated from the recorded spectra using the calibration model (acid test). In this way, each panel can be checked for curing quality during production.

[0195] Behind the press there is an NIR multi-measuring head which moves on a transverse member over the product web. In the event of deviations from the desired pre-set values, the operating parameters in the press are adapted to the desired values ​​by automatic open-loop or closed-loop control.

[0196] Example 2 : Determination of cross-linking degree

[0197] a) Degree of cross-linking of the impregnated material

[0198] Create reference samples and calibration:

[0199] In the case of impregnated paper, to calibrate the NIR measurement, the impregnated paper is first measured in different drying states using the NIR measuring head. To do this, the impregnated paper, produced at different speeds, is removed from the impregnation tunnel. The speed of the impregnation tunnel is varied upwards and downwards at a known optimal value. The sample is then measured using the NIR measuring head and the VC value is subsequently determined in an oven. After 5 minutes of drying, the final state of curing (C state) is reached. After drying in the oven, the sample is measured a second time using the NIR measuring head. This measurement provides the end point of drying.

[0200] After correction for baseline shifts, spectral changes in the absorption intensity of the NIR bands at approximately 1450 nm (water) and at approximately 1490 nm (NH groups) are shown.

[0201] A correlation between the VC value and the NIR spectrum can then be established. A calibration model describing the relationship between the NIR spectrum and the associated VC value is created using multivariate regression methods (e.g., using MLR, PCR, or PLS regression methods). The evaluation is performed over the entire spectrum. The longer the sample is dried in the oven, the higher the degree of crosslinking. Samples with higher VC values ​​than those typically sought to be achieved can also be measured. By examining the underdried samples, improved control of the impregnation channel (drying channel) can also be achieved. Underdried samples have a methylol content that is higher than the optimal value, while overdried samples have a methylol content that is lower than the optimal value. Therefore, by recording the NIR spectrum in combination with visualization, it is possible to control the channel based on the methylol content. In other words, these data can be used to make basic predictions about the curing state for different resins and paper systems after calibration.

[0202] Measuring the degree of crosslinking:

[0203] In the impregnation channel, the cover layer (paper weight: 25 g / m 2 ). The total coating amount is about 75g / m 2 , of which approximately 55g was melamine resin. The impregnation channel was run at different speeds. In this test, samples were pulled at various speed variations and measured using an NIR measuring head. The VC values ​​of these samples were then investigated. VC values ​​ranging from 3.0% to 8% were found. After drying, all samples were measured a second time using the NIR measuring head.

[0204] Correlations were then created from the spectra and the VC values, which allowed the prediction of the degree of cross-linking at other covering patterns.

[0205] b) Crosslinking of the resin layer applied to the carrier plate

[0206] Of course, this method can also be used in systems in which the precured resin is applied directly to printed or unprinted artificial wood panels. The same problems arise in these panels as in the case of impregnated paper.

[0207] It is important to know the degree of crosslinking of the synthetic resin present on the board. This applies both to inline production lines, where further processing takes place directly after resin coating and drying in a short-cycle (KT) press or a continuously operating press (continuous press), and to non-inline production lines, where the intermediate product is initially stored after resin coating and drying until further processing at a later point in time. In this case, determining the crosslinking state upstream of the press is even more important because, unlike with impregnated paper, quality determination of the parameters that are typically determined downstream of the press is rarely possible otherwise.

[0208] By means of measurements carried out directly at the production line, adjustments to the operating parameters of the press can be made immediately in the event of deviations from the desired state.

[0209] Upstream of the press is an NIR multi-measuring head that moves on a transverse member over the product web. In the event of deviations from the desired settings, the operating parameters in the press are adapted to the desired values ​​via an automatic open-loop or closed-loop control.

[0210] Example 3: Combined determination of the degree of curing and crosslinking to control the press

[0211] The parameters of the degree of crosslinking determined upstream of the press and the parameters of the degree of curing determined downstream of the press are considered in combination. In the event of deviations from the desired defaults of these two parameters, the operating parameters in the press are adapted to the combined desired values ​​by automatic open-loop or closed-loop control.

[0212] Example 4: Using the degree of cross-linking to determine superimposed impregnations

[0213] Cover with residual amount (parameters of impregnation: final weight 150 g / m 2 A pallet with a VC value of 5.8% (a VC value of 5.8%) was used to produce laminate flooring. Here, an NIR measuring head upstream of the press determined the high degree of crosslinking in the impregnant. The VC value was determined to be 5.6%. Subsequently, measurements with a second NIR measuring head revealed slightly lower transparency and only a slight increase in the degree of crosslinking. This led to the conclusion that the pallet was superimposed and no longer suitable for production.

Claims

1. A method for controlling a press to adjust operating parameters of the press, wherein the press is suitable for pressing together a carrier material and at least one resin layer provided on the carrier material, wherein at least one NIR multi-measuring head is provided upstream of the press in the running direction of the carrier material to be pressed, and at least one NIR multi-measuring head is provided downstream of the press in the running direction of the carrier material to be pressed; wherein the NIR multi-measuring head is connected to at least one control system for controlling the press, the control system having at least one computer-assisted evaluation unit and a database for processing and optionally storing the recorded and evaluated NIR data, The method comprises the following steps: - determining the degree of crosslinking of the resin layer applied to 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 means of the at least one NIR multi-measuring head arranged upstream of the press, and evaluating the recorded NIR spectrum in the evaluation unit by automatically comparing the recorded NIR spectrum with a calibration model created for the parameters of the resin layer, - determining the degree of curing of the resin layer applied to the carrier material as at least one second parameter of the resin layer applied to 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 means of at least one NIR multi-measuring head arranged downstream of the press, and evaluating the recorded NIR spectrum in the evaluation unit by automatically comparing the recorded NIR spectrum with a calibration model created for the degree of curing of the resin layer; wherein the degree of crosslinking determined upstream of the press (the actual value of the degree of crosslinking) is compared with a desired value of the degree of crosslinking, and wherein the degree of solidification determined downstream of the press (the actual value of the degree of solidification) is compared with a desired value of the degree of solidification, and When the actual value of the degree of crosslinking deviates from the corresponding expected value and when the actual value of the degree of curing deviates from the corresponding expected value, the operating parameters of the press are automatically adjusted by the control system so that the expected value of the degree of crosslinking and the expected value of the degree of curing are met.

2. The method according to claim 1, characterized in that The operating parameter of the press to be controlled is selected from the group consisting of pressing temperature, pressing pressure and / or pressing time, in particular from the group consisting of pressing temperature and pressing time.

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

4. The 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 between 190°C and 200°C.

5. The method according to any one of the preceding claims, characterized in that In addition to the degree of crosslinking, the following parameters can be determined upstream of the press, in particular by means of NIR spectroscopy: the water content of the applied resin layer; and the amount of the applied resin layer.

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

7. The method according to any 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. The method according to any one of the preceding claims, characterized in that The at least one resin layer comprises a resin-saturated paper layer, a resin-containing powder, or a resin-containing liquid.

9. The method according to any one of the preceding claims, characterized in that The carrier material is present in the form of a carrier sheet, a paper layer or a film layer.

10. The method according to any one of the preceding claims, characterized in that The calibration model for the parameters to be determined, respectively, applied to the resin layer is determined based on a reference sample as follows: recording at least one NIR spectrum of a plurality of reference samples having respectively different values ​​of a desired parameter 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 at least one NIR multi-measuring head; - determining the desired parameters of the measured reference sample by means of non-spectral methods; - Correlating the determined parameters with the respectively recorded NIR spectra of the measured reference samples.

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

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