Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B27—WORKING OR PRESERVING WOOD OR SIMILAR MATERIAL; NAILING OR STAPLING MACHINES IN GENERAL
  • B27N—MANUFACTURE BY DRY PROCESSES OF ARTICLES, WITH OR WITHOUT ORGANIC BINDING AGENTS, MADE FROM PARTICLES OR FIBRES CONSISTING OF WOOD OR OTHER LIGNOCELLULOSIC OR LIKE ORGANIC MATERIAL
  • B27N7/00—After-treatment, e.g. reducing swelling or shrinkage, surfacing; Protecting the edges of boards against access of humidity
  • B27N7/005—Coating boards, e.g. with a finishing or decorating layer
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
  • B05D—PROCESSES FOR APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
  • B05D1/00—Processes for applying liquids or other fluent materials
  • B05D1/36—Successively applying liquids or other fluent materials, e.g. without intermediate treatment
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
  • B05D—PROCESSES FOR APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
  • B05D3/00—Pretreatment of surfaces to which liquids or other fluent materials are to be applied; After-treatment of applied coatings, e.g. intermediate treating of an applied coating preparatory to subsequent applications of liquids or other fluent materials
  • B05D3/12—Pretreatment of surfaces to which liquids or other fluent materials are to be applied; After-treatment of applied coatings, e.g. intermediate treating of an applied coating preparatory to subsequent applications of liquids or other fluent materials by mechanical means
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
  • B05D—PROCESSES FOR APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
  • B05D7/00—Processes, other than flocking, specially adapted for applying liquids or other fluent materials to particular surfaces or for applying particular liquids or other fluent materials
  • B05D7/06—Processes, other than flocking, specially adapted for applying liquids or other fluent materials to particular surfaces or for applying particular liquids or other fluent materials to wood
  • B05D7/08—Processes, other than flocking, specially adapted for applying liquids or other fluent materials to particular surfaces or for applying particular liquids or other fluent materials to wood using synthetic lacquers or varnishes

Definitions

• the present invention generally relates to the production of layered substrates and, in particular, to a method and system for monitoring or controlling resin application in the production of layered substrates including layered wood based products.
• Layered substrates such as layered wood based products are normally manufactured by coating a substrate such as a board with a layer.
• Suitable boards include e.g. particle boards, medium density fibre boards, plywood, waferboards, oriented strand boards (OSB) 1 hardboards.
• the layer can be applied on the board by means of veneering, flooring or foliating in order to produce, for example, paper laminated particleboard, laminate flooring, parquet flooring, medium density overlaid (MDO) plywood, shuttering board, veneered board and the like.
• MDO medium density overlaid
• shuttering board veneered board and the like.
• a number of different resin applicators including roll coaters, curtain coaters, extruders, sprayers etc. can be used.
• a problem encountered in the production of layered wood based products is the determination of the dosage of resin to be applied on a specific board and also the maintaining of the desired resin dosage.
• the required or proper dosage of resin may vary significantly between different boards, even within the same consignment, due to shifting properties or characteristics between different boards such as wood species in the board, moisture content, particle size in the surface layer, board density, amount of urea/formaldehyde resin in the surface layer, the varying degree of penetration of resin into the substrate, etc.
• Other factors may be connected to the production line including line speed of conveyor, hardener dosage, thickness of the board, etc.
• changes may occur in the resin itself.
• Such changing properties or characteristics of the boards and/or production line factors can result in non-uniform resin-application of the boards. Furthermore, they can entail over-dosage of resin, which, in turn, may lead to higher costs (due to the fact that an unnecessary large amount of resin is used), fibre aberrations such as erection of fibres in the surface layer of the substrate causing a rough surface of the board, which, in turn, may give rise to the so called "orange peel" effect. Moreover, over-dosage may result in, inter alia, discolouration of the applied surface and blisters in the substrate-layer interface. Under-dosage of resin is also a serious problem, which, for example, may lead to that the applied layer disengages from the board. Hence, it is essential that the resin dosage is accurately adjusted with respect to these varying properties of the specific board, changed characteristics of the production line and/or the resin itself etc.
• Another parameter of importance in production of layered substrates is the penetration of resin into the substrates, which is closely related to the presence of pores in the ' substrate.
• the phenomenon of penetration of resin is essential for the quality of the layered product. This is owing to the fact that the amount of applied resin penetrating into the substrates does not take part in the glue joint in the gluing process of the product, which of course depends on the penetration depth.
• Penetration into a substrate like a particleboard might be related to parameters such as moisture content, hydrophobic properties of the substrate surface, presence of pores on a macroscopic scale due to distance between sawdust particles forming the board surface but also on a microscopic scale due to presence of resin channels, bordered pits and lumens of the tracheids in the wood material.
• the presence of pores in a particleboard is closely related to the permeability of the particleboard. Permeability is measured by simply measuring the transport of air through the board.
• Other analytical tools which might have potential of measuring responses related to penetration is contact angle analysis in static and dynamic mode.
• WO 2004/094947 discloses a method for spectroscopically monitoring resin-application of veneer-wood sheets during travel in an assembly line.
• Spectroscopic instrumentation for monitoring applied resin is calibrated by measurements of predetermined resin applications to reference-test-samples so as to provide a predetermined relationship enabling monitoring of applied resin during commercial production of a veneer-wood product using the visible light spectrum and near infrared extending to 2500 nm.
• the spectroscopic measurement is performed directly after the resin applicator by means of a probe adapted to enable a selection of wavelengths of electromagnetic radiation within the above-mentioned range.
• the method according to WO 2004/094947, Mbachu et al. does not take into account effects such as, for example, the degree of penetration of resin into the substrate.
• moisture content of the substrate might vary between different substrates.
• the resin used for example, urea/formaldehyde (UF) or phenol/formaldehyde (PF) also contains water, there is an considerable risk of interference from the water (in the resin and in the substrate) in the NIR spectra when the resin application is measured using the methods disclosed in WO 2004/094947, Mbachu et al.
• the substrates may also contain amounts of UF resin load in the surface layer, which, in addition, may vary between different substrates. This can induce errors in the NIR spectra when the resin application is measured using the methods disclosed in WO 2004/094947, Mbachu et al.
• An object of the present invention is to provide an improved method and system for monitoring or controlling parameters, e.g. resin dosage or permeability of the substrates, in the production of layered substrates, such as layered wood based products.
• Another object of the present invention is to provide an improved method and system for monitoring or controlling resin application in the production of layered substrates, such as layered wood based products, with respect to accuracy of resin dosage.
• substrate refers to a panel such as a board including, inter alia, particle boards, medium density fibre boards, plywood boards, waferboards, oriented strand boards (OSB), and handboards.
• OSB oriented strand boards
• layered substrate refers to a substrate provided with a layer by means of, inter alia, veneering, flooring, or foliating.
• a method for controlling a process for producing a layered substrate the process involving the steps of applying a hardener on the substrate; applying a resin on the substrate; and conveying the substrate to a press by means of a conveying means where at least one layer is applied on the substrate in a pressing step in order to form a layered substrate.
• the method further comprises the steps of: collecting at least one first set of measurement data related to parameters of the substrate at a first process stage employing a first measurement means, the first process stage being localized upstream the pressing step in the translation direction of the conveying means; collecting at least one second set of measurement data related to parameters of the substrate at a second process stage employing a second measurement means, the second process stage being localized upstream the pressing step and downstream the first process stage in the translation direction of the conveying means; and controlling an amount of resin to be applied on a substrate in the step of applying resin during the process for producing layered substrates by using collected measurement data from the first and second process stage and a calculated calibration model, the model being based on collected measurement data of substrates at the first and/or second process stage.
• a system for controlling a process for producing a layered substrate such as a layered wood based substrate
• the system comprising means for applying a hardener on the substrate; means for applying a resin on the substrate; and conveying means adapted to translate the substrate to pressing means adapted to apply at least one layer on the substrate in order to form a layered substrate.
• the system further comprises a first measurement means adapted to collect at least one first set of measurement data related to parameters of the substrate at a first process stage, the first measurement means being arranged upstream the pressing means in the translation direction of the conveying means; a second measurement means adapted to collect at least one second set of measurement data related to parameters of the substrate at a second process stage, the second measurement means being arranged upstream the pressing means and downstream the first measurement means in the translation direction of the conveying means; and control means connected to the first and second measurement means being adapted to control the resin applying means in order to determine an amount of resin to be applied on a substrate during the process for producing a layered substrate by using collected measurement data from the first and second process stage and a calculated calibration model, the model being based on collected measurement data of substrates at the first and/or second process stage.
• a computer program for a system according to the second aspect of the present invention.
• the program comprises program instructions, which when run in a control means of the system, causes the control means to perform steps of the inventive method.
• a computer program product comprising computer readable medium and a computer program according to the third aspect, wherein the computer program is stored on the computer readable medium.
• the present invention is based on the insight that the effect of penetration of resin into the substrate is essential when determining the resin application (the resin dosage) due to the fact that the amount of resin penetrating into the substrate is not taking part in the glue joint in the gluing process of the product (depending on the penetration depth).
• the penetration of resin into a substrate such as a particleboard, might be related to parameters such as moisture content, hydrophobic properties of the substrate surface, etc.
• the invention is also based on the insight that these properties can be quantified by spectroscopy using measurement probes located at, at least two specific process stages along a production line for producing layered substrates.
• the present invention provides several advantages in comparison with the conventional technique disclosed in WO 2004/094947, Mbachu et al., in which effects such as, for example, the degree of penetration of resin into the substrate are not take into account.
• the present invention provides for a highly accurate and reliable control of the resin application since effects such as the penetration depth is taken into account in the calibration model.
• the first process stage i.e. the first measurement means
• the first measurement means is located upstream the hardener applier stage. It has been found in tests that this location of the first measurement means provides especially useful measurement data for the calibration model as well as for the control of the resin dosage during the production process.
• the second process stage is located downstream resin applier stage. It has been found in tests that this location of the second measurement means provides especially useful measurement data for the calibration model as well as for the control of the resin dosage during the production process.
• data related to the hardener dosage applied on the substrate is collected during production of the layered substrate, and the hardener dosage data is used in the control of the resin dosage.
• data related to related to the line speed of the conveyer during production of a layered substrate is collected and used in the control of the resin dosage.
• data related to process variables such as temperature and/or atmospheric humidity of the process premises, the temperature of the press, or the effect of the heater can be collected and used in the control of the resin dosage.
• the calibration model is calculated by means of multivariate analysis.
• PLS, PCA, or PCR are multivariate techniques that can be used in the invention.
• neural networks are also a technique that can be used for developing the calibration model.
• the calibration model is calculated in accordance with the following steps: the collected measurement data at the first process stage is arranged in at least one matrix; a first sub-model for the first process stage is calculated using multivariate analysis; and receiving, in the second process stage from at least a first process stage, information related to a multivariate sub-model calculated for at least the first process stage.
• a model having a higher degree of predictability can be obtained, i.e. the resin dosage predicted by means of the model shows a higher degree of accuracy and reliability.
• the measurement data may be collected by means of spectroscopic measurements made in the ultra-violet (UV), infrared (IR), near-infrared (NIR), or visible light (Vl) spectra, and preferably in the near-infrared (NIR) spectrum.
• the measurement data may be collected by means of ultra sound.
• the calibration model is used to control the permeability of the substrate.
• Fig. 1 is a schematic view of a production line for producing a layered substrate at which the present invention can be utilized.
• Fig. 2 is a schematic view of a system for monitoring resin-application during production of a layered substrate at the production line shown in Fig. 1 according to an embodiment of the present invention.
• Fig. 3 is a schematic view of a system for monitoring resin-application during production of a layered substrate at the production line shown in Fig. 1 according to another embodiment of the present invention.
• Fig. 4 shows the general principles of the method for monitoring resin-application during production of a layered substrate at the production line shown in Fig.
• the production line 10 comprises means for applying a hardener 16 adapted to apply a hardener on the substrate 12, for example, a spreader, means for applying a resin 18 on the substrate, for example, a resin spreader, and a pressing means 20, such as a hot roll press, adapted to apply at least one layer on the substrate in order to form a layered substrate.
• a hardener 16 adapted to apply a hardener on the substrate 12
• a spreader means for applying a resin 18 on the substrate, for example, a resin spreader
• a pressing means 20, such as a hot roll press adapted to apply at least one layer on the substrate in order to form a layered substrate.
• the layer may be applied on the substrate by means of, for example, flooring, veneering or foliation.
• the layer may be, for example, paper, veneer, or textile.
• suitable pressing means in addition to a hot roll press that are conceivable including a plane pressing machine, which however is not suitable in the case of foliation, or
• Substrates such as wood based products in form of boards, 12 are transported or conveyed by means of a conveyer means 14 between the different process stages of the production line 10 in a direction of the arrow indicated with an A.
• a heater 22 arranged between the hardener spreader 16 and the resin spreader 18 , which heater is adapted to heat the substrate in order to dry the applied hardener.
• the heater 22 is an IR-heater.
• a saw (not shown) is arranged downstream of the hot roll press 20 in order to saw the substrate in pieces having a desired dimension.
• a first measurement means 24 adapted to collect at least one first set of measurement data related to parameters of the substrate is arranged at a first process stage, which in this embodiment is located upstream the hot roll press 20.
• the first measurement means is located upstream hardener spreader 16.
• a second measurement means 26 adapted to collect at least one second set of measurement data related to parameters of the substrate is arranged at a second process stage.
• the second measurement means 26 is located upstream the hot roll press 20 and downstream the first measurement means 24.
• the second measurement means 26 is located between the resin spreader 18 and the hot roll press 20.
• the first and second measurement means 24 and 26 are spectroscopic probes adapted emit wavelengths of electromagnetic radiation in one or more ranges of peak absorbance by the applied resin, and by other constituents, such as moisture content of the substrate material and of the resin.
• the electromagnetic radiation is in form of ultra- violet, infrared, near-infrared, or visible light. If near infrared light is used, so called NIR probes may be utilized.
• control means 28 comprising processing means 27 connected to the first and second measurement means 24 and 26, respectively.
• the control means 28 controls whether the first and second measurement means 24 and 26, respectively, should be active or not, i.e. when measurements should be performed.
• the control means 28 comprises a storage means 29 communicating with the processing means 27 via a standard control/address bus (not shown).
• the storage means 29 may include a random access memory (RAM) and/or a non-volatile memory such as read-only memory (ROM).
• RAM random access memory
• ROM read-only memory
• storage means may include various types of physical devices for temporary and/or persistent storage of data which includes solid state, magnetic, optical and combination devices.
• the storage means may be implemented using one or more physical devices such as DRAM, PROMS, EPROMS, EEPROMS, flash memory, and the like.
• the storage means 29 may further comprise a computer program 21 comprising instructions for bringing a computer to perform method steps in accordance with the present invention.
• the control means 28 is also adapted to control the resin spreader 18 in order to determine an amount of resin to be applied on a substrate during the process for producing a layered substrate.
• This control of the resin spreader 18 is performed by using collected measurement data, which may be stored in the storage means 29, from the first and/or second measurement means 24 and 26, respectively, and a calculated calibration model, which may be stored in the storage means 29.
• the calibration model is based on collected measurement data of substrates at the first and/or the second process stage.
• measurement data regarding the applied hardener dosage and the line speed of the conveyer 14 can be used when calculating the calibration model.
• This measurement data can be obtained by means of a hardener dosage measurement device 30 and a line speed sensor 32.
• the use of integration of process signals in the invention is however not limited to hardener dosage and line speed as the skilled man within the art realizes and other relevant signals from the process can be used for this purpose.
• Such signals include temperature and/or atmospheric humidity of the process premises, the temperature of the press, or the effect of the heater.
• Fig. 3 an alternative embodiment of the present invention is shown. Parts or devices shown in Figs. 2 and 3 having similar or like function or functions will be denoted with the same reference numerals.
• the first measurement means 24 adapted to collect at least one first set of measurement data related to parameters of the substrate is arranged located downstream hardener spreader 16. Furthermore, the second measurement means 26 adapted to collect at least one second set of measurement data related to parameters of the substrate is located between the resin spreader 18 and the hot roll press 20.
• the function of and location of other devices and parts, such as the control means 28, are the same as in the embodiment shown in Fig. 2, and, therefore, description thereof are omitted in connection to this embodiment.
• a hardener is applied on the substrate by the hardener spreader 16.
• at step 32 at least one first set of measurement data related to parameters of the substrate is collected at a first process stage employing a first measurement means 24, which, as indicated above, preferably is a NIR probe adapted to operate with wavelengths within
• the measurement data is transferred to the control means 28 for use in determining the resin dosage on basis of the calibration model.
• the first NIR probe 24 is located upstream the hardener spreader 16.
• at least one second set of measurement data related to parameters of the substrate employing a second measurement means 26, which, as indicated above, preferably is a NIR probe adapted to operate with wavelengths within 400-2500 nm.
• the measurement data is transferred to the control means 28 for use in determining the resin dosage on basis of the calibration model.
• the second NIR probe 26 is located upstream the hot roll press 22 and downstream the resin spreader 19.
• an amount of resin to be applied on the substrate is controlled by using the collected measurement data from the first and second NIR probe 24 and 26 , respectively, and a calculated calibration model.
• the calibration model is, as indicated above and as will be described in greater detail below, based on collected measurement data of substrates by the first and second NIR probe 24 and 26, respectively.
• the collected measurement data from a substrate at the first process stage, i.e. by the first NIR probe 24, and at the second process stage, i.e. by the second NIR probe 26, during the production process is compared in the control means 28 with reference data of from the calculated calibration model during the production of a layered substrate in order to adjust the resin dosage to the properties of the specific substrate in process.
• the substrate is translated to the hot roll press 22, where at least one layer is applied on the substrate in order to form a layered substrate.
• data related to hardener dosage applied on substrate test-samples and data related to a line speed of the conveyer means 14 is used when calculating the calibration model.
• NIR spectroscopy technique has gained widespread acceptance in recent years as a powerful diagnostic tool, particularly for assurance and on-line process control purposes in harsh industrial environments (Antti et al. Journal of Chemometrics, 10, 591-603 (1996), Pope J. M. "Near-Infrared Spectroscopy of Wood Products” (1995), Conners T.E. and Banerjee S Ed., "Surface Analysis of Paper", 142-151).
• Normally, in NIR spectroscopy wavelengths between 400-2500 nm are used.
• the fundamental principles of NIR spectroscopy have been summarized in a large number of articles, for example, in Barton Spectroscopy Europe 14, no. 1 , 12-18 (2002).
• PCA principal component analysis
• PLS partial least square projection to latent structures
• PCA principal component analysis
• PLS partial least square projection to latent structures
• PCR principal components regression
• Partial least squares projection to latent structures PLS is a modelling and computational method by which quantitative relations can be established between blocks of variables, e.g. a block of descriptor data (spectra) for a series of samples and a block a response data measured on these samples.
• blocks of variables e.g. a block of descriptor data (spectra) for a series of samples and a block a response data measured on these samples.
• spectra a block of descriptor data
• spectral data for a new sample to the descriptor block and make predictions of the expected response.
• One great advantage of the method is that the results can be evaluated graphically by different plots. In most cases, visual interpretations of the plot are sufficient to obtain a good understanding of different relations between the variables.
• the method is based on projections, similar to PCA.
• the PLS method is disclosed in detail in Carlsson R, "Design and optimization in organic synthesis", and B.G.M. Vandeginste, O.M. Kvalheim,
• PCR is closely related to PCA and PLS.
• each object in the descriptor block is projected onto a lower dimensional space yielding in scores and ladings.
• the scores are then regressed against the response block in a least squares procedure leading to a regression model which can be used to predict unknown samples.
• the same model statistics as in PCA and PLS can be used to validate the model.
• Hierachical modelling is a method were scores and/or residuals from one model is used as variables in another model. The method is described by S Wold et al. in "Hierarchical multiblocks PLS and PC models for easier model interpretation and as an alternative to variable selection", Journal of Chemometrics, vol. 10, 463-482 (1996).
• ANNs Artificial Neural Networks
• the ANN can be used for forecasting and prediction of output values and for detection of trends.
• a first NIR instrument or probe 24 was placed upstream the hardener spreader 16 and a second NIR instrument or probe 26 was placed upstream the hot calendar roller 20 and downstream the resin spreader 20, as schematically shown in Fig. 2.
• both instruments were of diode array type operating at 900-1700 nm.
• instruments operating at, for example, 400-2500 nm can also be used.
• comparative tests between instruments operating at wavelengths between 900- 1700 nm and instruments operating at wavelength between 400-2500 nm have shown similar results.
• the operation of the instruments 24, 26 were synchronized in order to make it possible to collect spectra from the same test sample board at the two measurements points or process stages.
• R2 represents the cumulative sum of squares of the predicted resin dosage explained by the extracted components.
• Q2 represents the fraction of the total variation of the resin dosage, which can be predicted by the extracted components, as estimated by cross-validation. In cross-validation parts of the data are kept out of the model development and is then predicted by the model and compared with the actual values. Table 1
• the measurement data contains absorbance values from 128 wavelengths between 900 and 1700 nm from 44 test boards.
• the measurement data contains absorbance values from 128 wavelengths between 900 and 1700 nm from 44 test boards.
• the measurement data contains absorbance values from 128 wavelengths between 900 and 1700 nm from 44 test boards.
• the results in table 1 contain the spectral data from the NIR probe downstream the resin spreader and score values for each board from a two principal components PCA analysis of the spectral data from the NIR probe placed upstream the hardener spreader.
• model A including actual line speed and hardener dosage for each board.
• model C including actual line speed and hardener dosage for each board.
• Model C is superior to model A and B by comparison of RMSEP and model E is superior to model D.
• Model E shows the best overall predictive ability of the compared models.
• Particleboards with different characteristics were made according to an experimental design, where board density, relative amount of surface chips and molar ratio between formaldehyde and urea in the Urea/formaldehyde based resin were varied according to a 2 3 design.
• the boards were analyzed using NIR spectroscopy in the wavelength range of 410-2250 nm on rotating boards and the permeability of air through the boards were determined. Modelling of the spectroscopic data using PLS with permeability as the response gave an eight-component model describing 75.1 % of the variation in permeability.
• the above results indicate that an improved control of the permeability of the substrates can be obtained by using a calibration model in accordance with the present invention.

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• Engineering & Computer Science (AREA)
• Life Sciences & Earth Sciences (AREA)
• Wood Science & Technology (AREA)
• Mechanical Engineering (AREA)
• Manufacturing & Machinery (AREA)
• Forests & Forestry (AREA)
• Investigating Or Analysing Materials By Optical Means (AREA)
• Casting Or Compression Moulding Of Plastics Or The Like (AREA)
• Dry Formation Of Fiberboard And The Like (AREA)
• Laminated Bodies (AREA)
• Moulding By Coating Moulds (AREA)
• Veneer Processing And Manufacture Of Plywood (AREA)

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