Method for determining the volume of at least one powdery binder in a mixture with wood particles

Description

[0001] The present invention relates to a method for controlling a production line for manufacturing wood-based panels from a mixture of wood particles and at least one biodegradable powdered binder. Description

[0002] Wood-based panels, such as particleboard or fiberboard (where fiberboard always refers to medium-density fiberboard or high-density fiberboard (MDF / HDF)), form the basis of many everyday objects, for example, furniture or wall, floor, or ceiling coverings. Oriented strand board (OSB) is used in timber frame and prefabricated house construction because it is lightweight yet meets the structural requirements for building panels. OSB is used as building panels, wall and roof sheathing, and flooring.

[0003] The wood-based panels mentioned are manufactured in multi-stage processes. Each of these processes begins with a step involving the mixing of the corresponding wood particles with a suitable binder, followed by spreading the mixture onto a conveyor belt and pressing the spread mixture into a wood particle mat or panel. The binders or adhesives typically used are usually based on urea-formaldehyde, phenol-formaldehyde, or PMDI (polymeric diphenylmethane diisocyanate) adhesives.

[0004] The wood-based materials industry is also increasingly facing the demand to replace these petroleum-based components with renewable raw materials. A wide variety of products are currently available when using adhesives based on renewable raw materials. To avoid competition between food production and adhesive use, more and more byproducts from food production are being utilized.

[0005] Residual materials from other industrial production processes are also used. These originate, for example, from the production of pulp (lignin) or from crop waste (rapeseed pomace, etc.). Products used as foodstuffs are also utilized (sugar, starch, soy flour). Lignin is a macromolecule based on phenolic compounds. Soy flour and rapeseed pomace contain proteins and oils as their main components. Sugar and starch are carbohydrates.

[0006] These glue alternatives are produced as powdered products and, with the exception of sugar, do not have good water solubility. If the existing technical equipment is to be used, they could only be used in production as a dispersion.

[0007] The petroleum-based adhesives described above are all liquids that can be homogeneously dosed onto the wood particles or fibers using spray systems in mixers or gluing drums. This dosing method has been used in production for decades and has been further optimized, for example, through nozzle optimization or high-pressure gluing, with regard to the distribution of the adhesive and the required quantity.

[0008] For adhesives based on renewable raw materials, dispersions are rather unsuitable, as they introduce a relatively large amount of water into the system, which is problematic for the process. Too much water in the chip or fiber cake can lead to steam splitting, which would have to be avoided by post-drying the chips / fiber.

[0009] For these reasons, dosing is a more suitable alternative to powder. This is achieved via dosing screws that apply the powder to the wood particles / fibers. Further distribution can then take place, for example, in mixers.

[0010] However, the distribution on the wood matrix can vary considerably depending on the powder. It is unclear whether the existing mixers can even achieve a homogeneous distribution. An assessment of the glue particle distribution on the wood particles can only be made visually. However, the powder particle sizes range from 1 to 200 µm, which complicates this assessment. Furthermore, the powders sometimes have a similar color to the wood particles, which also makes an objective evaluation of the powder distribution difficult. Neither continuous nor in-line assessment is possible during production. This means that, in order to achieve certain minimum values ​​for strength and swelling, a higher dosage of glue powder must be used. This leads to unnecessary raw material consumption and higher costs.

[0011] One possible solution to this problem would be to color the powder or use a UV-active substance, which would then allow for assessment of the distribution using a special lamp. However, this would first require a homogeneous distribution of the dye or UV-active compound within the powder and would incur additional costs. Furthermore, determining whether a change in dosage results in better distribution is only possible by examining the product itself and determining its technological properties. This can lead to defective production or scrap.

[0012] An example of a method for determining the amount of a powdered binder in a mixture with wood particles using NIR spectroscopy is given in patent US2007 / 131862 A1.

[0013] Current manufacturing processes have disadvantages. For example, production lines for wood-based panels are optimized for liquid adhesives. When using powdered adhesives or binders, the lack of analytical capabilities can lead to unnecessarily higher dosages, resulting in increased costs. Furthermore, unclear production conditions can arise.

[0014] The present invention therefore addresses the technical problem of providing an analytical method with which the powder distribution of biodegradable powdered binder on wood particles can be continuously determined during production. This method should be feasible at any point in the production process and, through a high measurement frequency, should quickly deliver a large amount of data. The measurements should be non-destructive and require minimal technical effort. No modifications to the equipment for installing the analytical measurement system should be necessary. The conditions present at the various possible measurement points in production should not interfere with the measurements.

[0015] This problem is solved according to the invention by a method having the features of claim 1.

[0016] Accordingly, a method for controlling a production line for manufacturing wood-based panels from a mixture of wood particles and at least one biodegradable powdered binder is provided. wherein the production line comprises at least: at least one NIR multi-sensor for recording at least one NIR spectrum of the mixture of the at least one powdered binder and wood particles using the at least one NIR sensor in a wavelength range between 900 nm and 1700 nm, at least one control system for controlling the production line, wherein the control system of the production line comprises at least one computer-aided evaluation unit and a database, wherein the evaluation unit is configured to compare the NIR spectrum recorded for the mixture of the at least one powdered binder and wood particles with NIR spectra recorded for reference samples and to determine the quantitative proportion of powdered binder in the mixture of powdered binder and wood particles;wherein the database is configured to store the parameter data thus determined, wherein the control system is configured to use the determined parameters to control the production line, wherein the NIR spectra of the reference samples are determined as follows: providing mixtures of at least one powdered binder and wood particles as reference samples, wherein the at least one powdered binder and wood particles are present in the mixtures in quantitatively defined mixing ratios, recording at least one NIR spectrum of the reference samples using at least one NIR measuring head in a wavelength range between 900 nm and 1700 nm.

[0017] The amount of at least one biodegradable powdered binder in a mixture with wood particles is determined using the reference samples with the following steps: Providing a mixture to be measured consisting of at least one powdered binder and wood particles, recording at least one NIR spectrum of the mixture of the at least one powdered binder with wood particles using the at least one NIR measuring head in a wavelength range between 900 nm and 1700 nm, and determining the quantitative proportion of powdered binder in the mixture of powdered binder and wood particles by comparison with the NIR spectra recorded for the reference samples.

[0018] According to the present method, the quantity of a powdered binder and, if applicable, the composition of a combination of two or more powdered binders in a mixture with wood particles is determined using NIR spectroscopy. The method can be used in the ongoing production of wood-based panels. The NIR measurement method can be carried out at various positions or process steps in the wood-based panel production, as will be explained in detail below. The NIR measuring head, in particular the NIR multi-measuring head, can not only measure a single position but can also be moved across a chip, strand, or fiber cake. This allows, for example, the detection of edge effects, which frequently occur in the production of wood-based panels. Individual layers (top layer / middle layer) can also be advantageously measured. Another advantage is that further parameters (e.g.,Moisture (see, for example, EP 2 915 658 B1, EP 2 808636 B1) can be analyzed. It is known that adhesives based on renewable raw materials require certain minimum amounts of moisture for curing. Furthermore, moisture also improves the adhesion of the adhesive to the wood particles or fibers. This can also help to avoid quality defects.

[0019] This method enables the rapid provision of measurement data (online, preferably without disruptive delays) compared to conventional (known) measurement methods. The measurement data can be used for quality assurance, research and development, process control, process regulation, process management, etc. The measurement process does not reduce production speed or other factors. In principle, this improves production monitoring. Furthermore, downtime due to quality control and equipment adjustments is also reduced.

[0020] The determination of the quantity of powdered binder or binder mixture possible with the present method is preferably carried out exclusively by means of NIR measurement. A combination with other spectroscopic methods, in particular using wavelengths other than the NIR range, is not intended.

[0021] This involves the use of a near-infrared (NIR) measuring head, preferably a multi-sensor NIR head, which allows the determination of the quantity of powdered binder by acquiring spectral data (spectra) in the near-infrared range (700–2000 nm). The NIR radiation interacts with the organic functional groups, such as OH, CH, and NH, present in the binder. During this interaction, the NIR radiation is scattered and reflected by the sample. A NIR spectrum is generated by receiving the reflected NIR radiation with an NIR detector. In this measurement, a large number of individual NIR measurements are performed per second, thus ensuring statistical reliability of the values. NIR spectroscopy offers a way to establish a direct correlation between the spectral information (NIR spectra) and the parameters of the binder to be determined.

[0022] The present method utilizes the fact that NIR radiation penetrates to some extent into the near-surface regions of the material, but that the majority of the NIR radiation is reflected or scattered at the surface of a wood particle mixture or wood particle cake. The reflected or scattered NIR radiation is detected by the NIR detector, and the resulting NIR spectrum is used to determine the desired parameters (in this case, the amount of powdered binder).

[0023] To determine the amount of powdered binder, spectral data from the entire recorded spectral range are preferably used; that is, not a single, discrete wavelength, but rather an entire range of several wavelengths is used.

[0024] According to the inventive method, mixtures of at least one powdered binder and wood particles are first provided as reference samples, wherein the at least one powdered binder and the wood particles are present in the mixtures in quantitatively defined mixing ratios. For the provision of the reference samples, different amounts of powdered binder are mixed with wood particles, e.g., 5 wt%, 7 wt%, 10 wt%, 15 wt% of powdered binder based on the total amount of the binder-wood particle mixture.

[0025] It is also important to note that the reference sample must be identical to the sample being measured; that is, in particular, the binder-wood particle mixture of the reference sample must have the same composition as the binder-wood particle mixture being measured. The similarity of the sample being measured and the reference sample is especially important when using additives such as flame retardants, fibers, or other additives.

[0026] At least one NIR spectrum is recorded from these reference samples in a wavelength range between 900 nm and 1700 nm, preferably between 1400 and 1700 nm, particularly between 1450 nm and 1650 nm, and especially preferably between 1500 nm and 1600 nm.

[0027] The different quantitative amounts of powdered binder in the reference samples are then assigned to the respective recorded NIR spectra of these reference samples, and a relationship is established between the spectral data of the NIR spectra of the reference samples and the corresponding amounts of binder as parameter values, i.e., each parameter value of the reference sample corresponds to an NIR spectrum of the reference sample.

[0028] Subsequently, at least one mixture of at least one powdered binder and wood particles is provided, and at least one NIR spectrum of the mixture is recorded using at least one NIR measuring head in a wavelength range between 900 nm and 1700 nm. The quantitative amount or proportion of the powdered binder in the mixture of powdered binder and wood particles can then be determined by comparison with the NIR spectra recorded for the reference samples.

[0029] As already mentioned, a comparison and interpretation of the NIR spectra is best performed across the entire recorded spectral range. For example, in one embodiment, spectral data from the NIR spectral range between 900 nm and 1700 nm are used to determine the quantity of at least one powdered binder in a mixture with wood particles. In another embodiment, spectral data from the NIR spectral range between 1400 nm and 1700 nm, preferably between 1450 nm and 1650 nm, and particularly preferably between 1500 nm and 1600 nm, are used to determine the quantity of at least one powdered binder in a mixture with wood particles. In yet another embodiment, spectral data from the NIR spectral range between 900 nm and 1100 nm, preferably between 900 nm and 1000 nm, are used to determine the quantity of at least one powdered binder in a mixture with wood particles.

[0030] In one embodiment of the present method, the proportion of powdered binder in the mixture with the wood particles is between 5 and 50 wt%, preferably between 7 and 40 wt%, particularly preferably between 10 and 30 wt%, and even more preferably between 15 and 20 wt%. In a preferred embodiment, the proportion of powdered binder in the mixture with the wood particles is 5 wt%, 7 wt%, 10 wt%, or 15 wt% (based on the total amount of the binder-wood particle mixture).

[0031] The present measurement method can be used to determine the quantity of any type of biodegradable powdered binder.

[0032] Biodegradable binders can be either naturally occurring binders or synthetic binders.

[0033] In the case of using a natural binder as a biodegradable binder, it is selected from the following group: starch, cellulose derivatives such as carboxymethyl cellulose, chitosan, gluten-containing binders such as hide glue, bone glue, leather glue; milk protein-containing binders, particularly from the casein group; and plant protein-containing binders, particularly from the soy binder group, agar-agar, alginate, gelatin, guar gum, gum arabic, xanthan gum, pectins, locust bean gum, polysaccharides such as carrageenan, lignin, or rapeseed pomace. The use of starch and soy flour is particularly preferred.

[0034] In one embodiment of the present wood fiber mat, the starch used as a binder is selected from the group consisting of potato starch, corn starch, wheat starch, and rice starch.

[0035] Starch is a polysaccharide with the formula (C₆H₁₀O₅)n, composed of α-D-glucose units. This macromolecule is therefore classified as a carbohydrate. When heated, starch can physically bind many times its own weight in water, causing it to swell and gelatinize. When heated with water, starch swells at 47–57 °C, the layers burst, and at 55–87 °C (potato starch at 62.5 °C, wheat starch at 67.5 °C) starch paste forms. Depending on the type of starch, this paste has varying degrees of stiffening power (corn starch paste greater than wheat starch paste, and wheat starch paste greater than potato starch paste) and decomposes more or less readily upon acidification.

[0036] Starch can be used as a binder in both its native and modified (derivatized) forms. Thus, at least one starch component can be present in the wood fiber mat in either its native or modified (derivatized) form. DuraBinders from Ecosynthetix is ​​preferably used as the starch-containing binder.

[0037] In the case of the use of modified or derivatized starch as a binder, it may be selected from a group containing cationic or anionic starch, carboxylated starch, carboxy-methylated starch, sulfated starch, phosphorylated starch, etherified starch such as hydroxyalkylated starch (e.g. hydroxyethylated starch, hydroxypropylated starch), oxidized starch containing carboxyl or dialdehyde groups and hydrophobic starches such as acetate, succinate, hemi- or phosphate esters.

[0038] It is also generally conceivable to use a mixture of a natural starch and a derivatized starch, or of several natural starches and / or several derivatized starches.

[0039] The particle size of the starch is between 20 and 100 µm, preferably between 30 and 80 µm, particularly preferably between 40 and 60 µm, e.g. at 50 µm.

[0040] In one embodiment of the present method, when using starch as a powdered binder, spectral data from the NIR spectral range between 900 nm and 1100 nm, preferably between 900 nm and 1000 nm, are used to determine the amount of starch in a mixture with wood particles.

[0041] The particle size of the soy flour used is between 30 and 300 µm, preferably between 50 and 200 µm, particularly preferably between 60 and 100 µm, e.g. at 70 µm.

[0042] In one embodiment of the present method, when using soy flour as a powdered binder, spectral data from the NIR spectral range between 1450 nm and 1650 nm, preferably between 1500 nm and 1600 nm, are used to determine the amount of soy flour in a mixture with wood particles.

[0043] The present spectroscopic method also enables the determination of the quantity and composition of a combination of at least two powdered binders in a mixture with wood particles. This is particularly evident from the fact that different spectral regions of the NIR spectrum can be used for evaluation.

[0044] In such a combination, for example, a first powdered binder and a second powdered binder can be present in a ratio of 10 wt% : 90 wt% and 90 wt% : 10 wt%, preferably between 25 wt% : 75 wt% and 75 wt% : 25 wt%, and particularly preferably between 55 wt% : 45 wt% and 45 wt% : 55 wt%, e.g., 50 wt% : 50 wt%. A preferred combination can, for example, consist of starch and soy flour. When using binder mixtures, it may be necessary to create a calibration model using multivariate data analysis (MDA) for the reference samples. In multivariate analysis methods, several statistical variables are typically examined simultaneously in a manner known per se. For this purpose, these methods usually reduce the number of variables contained in a dataset without simultaneously reducing the information it contains.In this case, multivariate data analysis is performed using partial least squares regression (PLS), which allows for the creation of a suitable calibration model. The evaluation of the obtained data is preferably carried out using appropriate analysis software, such as SIMCA-P from Umetrics AB or The Unscrambler from CAMO.

[0045] In the case of using a synthetic binder as a biodegradable binder, it is preferably selected from the group consisting of saponified polyvinyl alcohol, polycaprolactam polyamide, polylactate, aliphatic polyester resins, in particular polybutylene succinate, polybutylene succinate adipate, and polyethylene-polypropylene composite resin, with polylactates being particularly preferred. In a particularly preferred embodiment, polylactic acid fibers with a length of 38 mm ± 3 mm and a fineness of 1.7 dtex are used.

[0046] As already mentioned above, wood fibers, wood chips or wood strands are preferably used as wood particles.

[0047] Wood fibers or chips can be obtained by machining the wood chips in a chipper or by a fiberization process of the wood chips in a refiner.

[0048] The wood fibers typically used to manufacture wood fiberboards, especially dry wood fibers, have a length of 1.5 mm to 20 mm and a thickness of 0.05 mm to 1 mm.

[0049] The wood strands used for the production of OSB can have a length between 50 and 200 mm, preferably 70 to 180 mm, particularly preferably 90 to 150 mm; a width between 5 and 50 mm, preferably 10 to 30 mm, particularly preferably 15 to 20 mm; and a thickness between 0.1 and 2 mm, preferably between 0.3 and 1.5 mm, particularly preferably between 0.4 and 1 mm.

[0050] However, it is also generally conceivable that existing measurement methods could be used for other pre-products derived from renewable raw materials for the production of panels or molded parts (e.g. straw, hemp, bagasse, etc.).

[0051] As already indicated above, the inventive method for determining the amount of powdered binder in a wood particle mixture can be carried out continuously and online in a production line for the manufacture of wood-based panels. In particular, the method can be carried out in an automatically controlled system with alarm notification.

[0052] The determination of the amount of powdered binder in a wood particle mixture can be carried out at various process stations in the production line for the manufacture of wood-based panels.

[0053] A process for manufacturing wood-based panels using a powdered binder comprises the following steps: a) Production of wood particles from suitable woods, b) if necessary, temporary storage of the wood particles, in particular in silos or bunkers, c) drying of the wood particles, d) sorting or screening of the wood particles according to their size, e) mixing of the wood particles with at least one powdered binder, e.g. using metering screws; f) application of the mixture of wood particles and the at least one powdered binder onto a conveyor belt by means of wind and / or throw screening, and g) compaction of the mixture of wood particles and the at least one powdered binder arranged on the conveyor belt.

[0054] The determination of the quantity of the at least one powdered binder in the mixture with wood particles using the measuring method according to the invention can, for example, i) after mixing the wood particles with the at least one powdered binder but before applying the mixture of wood particles and the at least one powdered binder to a conveyor belt (i.e., after step e), and / or ii) after applying the mixture of wood particles and the at least one powdered binder to a conveyor belt by wind and / or throw classification, but before compressing the mixture of wood particles and the at least one powdered binder arranged on the conveyor belt (i.e., after step f), and / or iii) after compressing the mixture of wood particles and the at least one powdered binder arranged on the conveyor belt to form a wood particle cake (i.e., after step g).

[0055] It can also be advantageous to measure individual layers, such as the top layer / middle layer in the production of particleboard and OSB. Furthermore, NIR not only measures at the surface but also penetrates into near-surface areas. This is particularly useful for analyzing the effects of scattering (wind / throw scattering).

[0056] In particular, the measurement of the binder-wood particle mixture deposited on a conveyor belt and the resulting wood particle cake (i.e., chip, strand, or fiber cake) after pressing can be performed traversing the material. The at least one NIR measuring head moves transversely to the direction of travel of the deposited or pressed binder-wood particle mixture in the production line, across its entire width, to analyze specific problem areas, especially areas with insufficient material coverage at the edges or in the center of the deposited or pressed binder-wood particle mixture. This allows, for example, the detection of edge effects that frequently occur in the production of wood-based panels.

[0057] This provides a method in which the quantity of a powdered binder in a binder-wood particle mixture can be determined from a single NIR spectrum or from the reflection or scattering of NIR radiation using a non-contact measurement with an NIR measuring head. In an advantageous embodiment of the invention, the data obtained with the measuring head(s) are used directly for plant control or regulation.

[0058] Furthermore, in another advantageous embodiment of the invention, data storage enables improved quality control. The stored data can also advantageously contribute to the evaluation of plant trials, for example, during the commissioning of a new plant, after maintenance or repair, or for in-situ testing of new production or measurement processes. The immediate availability of the measured values ​​and the high measurement frequency allow for very close monitoring, control, and regulation of the plants.

[0059] The advantages of the present method are manifold: Non-contact multi-parameter determination ("real time" or "real-time" measurement) with significantly reduced time delay in the evaluation of the measured parameter values; improved plant control and regulation, reduction of scrap, improvement of the quality of the products manufactured on the plant, improvement of plant availability.

[0060] The control system of each production plant comprises at least one computer-aided evaluation unit (or processor unit) and a database. In the evaluation unit, the NIR spectrum measured for the product (i.e., coated substrate material) is compared with the calibration models created for each individual parameter. The parameter data determined in this way is stored in the database.

[0061] The data determined using the present spectroscopic method are used to control the respective production line. The non-contact measured parameter values ​​of the NIR multi-sensor head ("actual values") can, as previously described, be used directly and in real time for controlling the relevant system. This is achieved, for example, by storing the measured actual values ​​in a database (e.g., a relational database) and comparing them with the target values ​​for these parameters. The resulting differences are then used to control the production line.

[0062] For the alignment and control of the respective production line, a computer-implemented procedure and a computer program comprising instructions that, when executed by a computer, cause it to carry out the computer-implemented procedure, are provided. The computer program is stored in a memory unit of the control system of the respective production line.

[0063] The following describes in detail the processes for the production of wood fiberboard, wood particleboard and OSB in which the measuring method according to the invention can be used.

[0064] Fiberboard and particleboard are typically manufactured using a process with the following steps: a) Production of wood chips from suitable wood, b) Chipping the wood chips into wood shavings or wood fibers, c) Temporary storage of the wood shavings or wood fibers, in particular in silos or bunkers, d) Drying of the wood shavings or wood fibers, e) Sorting or screening of the wood shavings or wood fibers according to their size, f) If necessary, further shredding of the wood shavings or wood fibers and temporary storage, g) Mixing the wood shavings or wood fibers with at least one powdered binder, e.g. using metering screws; h) Applying the mixture of wood shavings or wood fibers and the at least one powdered binder to a conveyor belt by means of wind and / or throw screening, and i) Compacting the wood shavings or wood fibers arranged on the conveyor belt.

[0065] The determination of the quantity of the at least one powdered binder in the mixture with wood chips / wood fibers using the measuring method according to the invention can i) after mixing the wood chips / wood fibers with the at least one powdered binder but before applying the mixture of wood chips / wood fibers and the at least one powdered binder to a conveyor belt (i.e., after step g), and / or ii) after applying the mixture of wood chips / wood fibers and the at least one powdered binder to a conveyor belt by wind and / or throw screening, but before compressing the mixture of wood chips / wood fibers and the at least one powdered binder arranged on the conveyor belt (i.e., after step h), and / or iii) after compressing the mixture of wood chips / wood fibers and the at least one powdered binder arranged on the conveyor belt to form a wood particle cake (i.e., after step i).

[0066] The processes for manufacturing particleboard and fiberboard differ particularly with regard to the size and properties of the wood fibers or wood chips used, as well as the pressures and temperatures applied. However, the essential process flow and thus the sequence of process steps are similar for all boards and are known to those skilled in the art.

[0067] In the case of wood fiberboards, the mixture of wood fibers and binder is spread onto a conveyor belt to form a single-layer fiber cake, which is then pre-pressed before hot pressing. Accordingly, an (additional) NIR measurement according to the inventive method would also be conceivable between the pre-pressing and hot-pressing steps.

[0068] In the case of particleboard, the mixture of wood chips and binder is spread onto a conveyor belt to form a multi-layered chip cake, with the wood chips being spread on top of each other as a first top layer, middle layer, and second top layer. Accordingly, an (additional) NIR measurement according to the inventive method would be conceivable after each layer has been spread, i.e., after the first top layer, after the middle layer, and after the second top layer.

[0069] The production of OSB boards also involves a multi-stage process. First, the strands of debarked roundwood, preferably softwood, are peeled lengthwise using rotating knives. In the subsequent drying process, the natural moisture content of the strands is reduced at high temperatures. The moisture content of the strands can vary depending on the binder used, but it should be well below 10% to prevent splitting during later pressing. Depending on the binder, wetting the strands may be more advantageous on either moist or dry strands. Furthermore, as little moisture as possible should be present in the strands during the pressing process to minimize the steam pressure generated, which could otherwise cause the raw board to burst.

[0070] Following drying, the strands are mixed with a suitable binder. The mixture is then spread alternately lengthwise and crosswise to the production direction using spreading equipment, so that the strands are arranged crosswise in at least three layers (bottom face layer - middle layer - top face layer). The spreading direction of the bottom and top face layers is the same, but differs from that of the middle layer. The strands used in the face and middle layers also differ. The strands used in the face layers are flat, while those used in the middle layer are less flat, sometimes even chip-like. Typically, two material streams are used in the production of OSB boards: one with flat strands for the face layers and one with chips for the middle layer.Accordingly, the strands in the middle layer can be of lower quality, since the flexural strength is primarily generated by the surface layers. Therefore, fine material generated during machining can also be used in the middle layer of OSB boards.

[0071] Following the spreading of the strands, they are continuously compressed under high pressure and high temperature, e.g. 200 to 250°C.

[0072] Accordingly, an NIR measurement according to the measurement method according to the invention would be possible after mixing the strands with the at least one powdered binder, after spreading the individual layers, i.e. after the first top layer / after the middle layer / after the second top layer, and / or after pressing the mixture of wood strands and binder spread onto a conveyor belt.

[0073] The invention is explained in more detail below using exemplary embodiments with reference to the figures. The figures show: Figure 1: NIR spectra of wood chips, soy flour, and mixtures of soy flour and wood chips. Figure 2: NIR spectra of wood chips, starch, and mixtures of starch and wood chips. Figure 3: Section of NIR spectra of wood chips and mixtures of starch and wood chips. Example of implementation 1: Mixture of wood shavings and soy flour

[0074] Surface-layer wood chips for particleboard production were mixed with varying amounts of soy flour (Prolia) (5, 7, 10, and 15 wt%). The soy flour had a mean particle size of 70 µm (maximum particle size < 200 µm). The chips and flour were homogeneously blended using a laboratory mill. The mixtures were then analyzed on a plate using a NIR probe. A chip sample and a soy flour sample were also analyzed.

[0075] As it turned out, a clear gradation between the individual concentrations was noticeable. Calibration / evaluation is best performed at the peak at approximately 1550–1560 nm (see diagram of the Figure 1 ). Example 2: Mixture of wood chips and starch

[0076] Surface layer chips for particleboard production were mixed with varying amounts of cornstarch (5, 10, and 15 wt%). The cornstarch had an average particle size of 50 µm (maximum particle size < 100 µm). The chips and starch were homogeneously mixed using a laboratory mill. The mixtures were then analyzed on a plate using a NIR probe.

[0077] A wood chip sample and a starch sample were also measured. As it turned out, a significantly weaker gradation between the individual concentrations was noticeable in the range between 1550 and 1560 nm. This applies particularly to 5 and 10 wt% (see diagram of the Figure 2 )..

[0078] For this reason, the range between 950 and 995 nm is selected for calibration. In this range, the spectra are separated with increasing starch content (see diagram of the Figure 3 ).

[0079] As it turns out, it is possible to reliably determine the concentrations of various powdered adhesives. The determined concentrations fall within the concentration ranges that would also be used in the production of HWS (High-Performance Wood Adhesives). Using a NIR (near-infrared) measuring head, the concentrations of bio-powdered adhesives on particulate or fibrous wood, as well as their fluctuations, can be determined. Since the peaks used for evaluation lie in different regions of the NIR spectrum, combinations of different bio-adhesives can also be analyzed.

Claims

1. A method of controlling a production line for the manufacture of wood-based panels from a mixture of wood particles and at least one biodegradable powdery binder wherein the production line comprises at least: - at least one NIR multi-measuring head for recording at least one NIR spectrum of the mixture of the at least one powdery binder and wood particles using the at least one NIR measuring head in a wavelength range between 900 nm and 1700 nm, - at least one control system for controlling the production line, wherein the control system of the production line comprises at least one computerized evaluation unit and a database, - wherein the evaluation unit is configured to compare the NIR spectrum recorded for the mixture of the at least one powdery binder and wood particles with NIR spectra recorded for reference samples and to determine the quantitative proportion of powdery binder in the mixture of powdery binder and wood particles; - wherein the database is configured to store the parameter data so determined, - wherein the control system is configured to use the determined parameters to control the production line, wherein the NIR spectra of the reference samples are determined as follows: - providing mixtures of at least one powdery binder and wood particles as reference samples, wherein the at least one powdery binder and wood particles are present in the mixtures in quantitatively defined mixing ratios in each case, and - recording at least one NIR spectrum of the reference samples using at least one NIR measuring head in a wavelength range between 900 nm and 1700 nm.

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

3. Method according to one of the preceding claims, characterized in that the at least one NIR multi-measuring head is arranged such that the determination of the amount of the at least one powdery binder in the mixture with wood particles takes place after the wood particles have been mixed with the at least one powdery binder but before the mixture of wood particles and the at least one powdery binder is applied to a conveyor belt.

4. Method according to one of claims 1-2, characterized in that the at least one NIR multi-measuring head is arranged in such a way that the determination of the amount of the at least one powdery binder in the mixture with wood particles takes place after the mixture of wood particles and the at least one powdery binder has been applied to a conveyor belt by means of air and / or throw sifting, but before the mixture of wood particles and the at least one powdery binder arranged on the conveyor belt has been pressed.

5. Method according to claim 4, characterized in that the at least one NIR multi-measuring head is configured to traverse over the binder-wood particle mixture deposited on a conveyor belt.

6. Method according to one of claims 1-2, characterized in that the at least one NIR multi-measuring head is arranged such that the determination of the amount of the at least one powdery binder in the mixture with wood particles takes place after pressing the mixture of wood particles and the at least one powdery binder arranged on the conveyor belt into a wood particle cake.

7. Method according to claim 6, characterized in that the at least one NIR multi-measuring head is configured to traverse over the wood particle cake obtained after pressing.

8. Method according to one of the preceding claims, characterized in that spectral data from the NIR spectral range between 1450 nm and 1650 nm, preferably between 1500 nm and 1600 nm, are used to determine the amount of at least one powdery binder in a mixture with wood particles.

9. Method according to one of claims 1-5, characterized in that spectral data from the NIR spectral range between 900 nm and 1100 nm, preferably between 900 nm and 1000 nm, are used to determine the amount of at least one powdery binder in a mixture with wood particles.

10. Method according to one of the preceding claims, characterized in that the amount of the powdery binder in the mixture with the wood particles is between 5 and 50% by weight, preferably between 7 and 40% by weight, more preferably between 10 and 30% by weight, even more preferably between 15 and 20% by weight (based on the total amount of the binder-wood particle mixture).

11. Method according to one of the preceding claims, characterized in that a naturally occurring binder is used as a biodegradable binder, in particular selected from a group comprising starch, cellulose derivatives, such as carboxymethyl cellulose, chitosan, gluten-containing binders, such as hide glue, bone glue, leather glue; milk protein-containing binders, in particular from the group of caseins, and plant protein-containing binders, in particular from the group of soy binders, agar-agar, alginate, gelatin, guar gum, gum arabic, xanthan gum, starch, pectins, locust bean gum, polysaccharides, such as carrageenan, is used.

12. Method according to one of the preceding claims, characterized in that a synthetic binder is used as biodegradable binder, in particular selected from the group comprising saponified polyvinyl alcohol, polycaprolactam-polyamide, polylactate, aliphatic polyester resins, in particular polybutylene succinate, polybutylene succinate-adipate, polyethylene-polypropylene composite resin, preferably polylactates.

13. Method according to one of the preceding claims, characterized in that wood chips, wood fibres and / or wood strands are used as wood particles.

14. Method according to one of the preceding claims, characterized in that the determination of the amount of at least one powdery binder in a mixture with wood particles is carried out continuously online in the production line for wood-based panels.