Method for producing a top sheet for an osb panel

Abstract

The invention relates to methods for producing a cover layer for an OSB board.In order to use more recycled wood in an OSB board than before, it is provided that by means of a first production line for recycled or fresh wood strands and with at least one second production line for recycled wood strands, wherein an OSB board is produced with the steps - producing first recycled or fresh wood strands from recycled or fresh wood in a first production line, - producing second recycled strands from recycled wood in a second production line, - spreading a first, outer layer of strands from a first spreading device, then spreading at least a second, inner layer of strands from a second spreading device, and wherein - the spreading of the first recycled or fresh wood strands and the second recycled strands is controlled by the control device, wherein the control takes place as a function of the properties of the recycled strands and / or the fresh wood strands.

Description

[0001] The invention relates to a method for producing a cover layer for an OSB board, an OSB board and a device for producing a cover layer for an OSB board.

[0002] OSB (oriented strandboard) boards are high-strength wood-based panels manufactured primarily from strands, i.e., large-area wood particles. OSB boards are typically multi-layered, comprising at least two outer layers surrounding a middle layer. The middle layer can be multi-layered, usually with an odd number of layers. Fresh wood is predominantly used to manufacture OSB boards because it is easier to process and has better strength properties. However, fresh wood is not available in unlimited quantities. Furthermore, sustainability considerations must be taken into account in the production of wood-based panels, so efforts are being made to increasingly use recycled wood in the production of OSB boards.

[0003] The invention is therefore based on the object of proposing an OSB board that uses more recycled wood than before.

[0004] This object is achieved with a method according to claim 1, an OSB board according to claim 9 and a device according to claim 15.

[0005] The method according to the invention for producing a cover layer for an OSB board uses a first production line for recycled and / or fresh wood strands and at least one second production line for recycled wood strands as well as a control device, wherein the first and the second production line each have at least one cutting device, a drying device and a gluing device and comprises the steps: Producing first recycled or fresh wood strands from recycled and / or fresh wood in a first production line, Producing second recycled strands from recycled wood in a second production line, Drying and gluing the first recycled and / or fresh wood strands and the second recycled strands, Feeding the first recycled and / or fresh wood strands and the second recycled strands to a first or second production line, respectively.second spreading device of the first and second production lines, wherein the spreading devices are arranged one behind the other in a production direction, and wherein after drying, gluing and feeding the first recycled and / or fresh wood strands and the second recycled strands, the first and second production lines are designed to spread a first, outer layer of strands from the first spreading device, then spread at least a second, inner layer of strands from the second spreading device, and wherein the spreading of the first recycled and / or fresh wood strands and the second recycled strands is controlled by the control device, wherein the control takes place as a function of the properties of the recycled strands and / or the fresh wood strands.

[0006] The method according to the invention assumes that fresh wood strands and recycled wood strands are preferably produced in separate production lines, dried if necessary, and then glued and spread in at least two layers. With the strands produced separately in this way, a particularly uniform quality of the first, outer layer and the at least one second, inner layer of a top layer of an OSB board can be ensured, so that OSB boards of particularly homogeneous quality can be produced.

[0007] The cover layers produced according to the invention can be scattered with one or more middle layers of any material to form chip cakes and produced by pressing, but preferably with a middle layer made predominantly or entirely of recycled wood particles. An OSB board with a high proportion of recycled wood strands or chips or flakes can be advantageously used in applications where the OSB board cannot be subsequently recycled or reused, e.g., in permanent formwork, on construction sites, or for packaging, especially when no special requirements are placed on the strength of the OSB board.

[0008] For the fresh wood or recycled wood used, a maximum and, if applicable, a desired size of the strands (length, width, thickness) is specified depending on the raw material used, in particular its dimensions. The desired size, if applicable, is lower than the maximum size that can be produced from the respective raw material. Typical average lengths for strands are approximately 30 mm to 250 mm, typical average widths are 1 mm to 50 mm, and typical average thicknesses are 0.25 mm to 3 mm. Fresh wood often results in larger strands than recycled wood. Typical average dimensions for recycled wood strands are 15 mm to 150 mm long, 0.25 mm to 15 mm wide, and 0.25 mm to 3 mm thick. These specifications are usually stored in the control device, which then passes these specifications on in the form of signals to machining and, if applicable, sorting equipment.

[0009] The moisture content of the fresh wood or recycled wood is also recorded. With, for example, 100% water content based on dry wood, fresh wood has on average a higher moisture content than recycled wood, which typically has a moisture content of 5% to 15%. Therefore, fresh wood must generally always be dried before gluing. Recycled wood, on the other hand, has often already been dried and can or must be processed in a dry state. The moisture content is recorded by sensors and is usually processed in a control device, e.g. converted into signals to drying devices. The control device switches the various drying devices on and off accordingly and, if necessary, adjusts the drying output to ensure that strands with the desired moisture content of, for example, between 4% and 8% are transferred to the gluing device.The extreme difference in the water content of the fresh wood and recycled wood strands demonstrates the particular advantage of maximizing the use of recycled wood for OSB boards. Avoiding or limiting the use of fresh wood saves significant amounts of energy that would otherwise be required to dry fresh wood. At the same time, the exhaust air from the fresh wood drying process is complex to clean, which is also energy-intensive. Thus, maximizing the use of recycled wood saves energy and emissions.

[0010] The adhesive to be used is specified for the respective gluing equipment – ​​typically melamine-formaldehyde resin (MF), melamine-urea-formaldehyde resin (MUF), melamine-urea-phenol-formaldehyde resin (MUPF), or PMDI or eMDI – and the amount of adhesive to be used is typically between 5% and 15% by weight, based on the amount of absolutely dry wood (dry wood) used. These parameters are usually stored in the control unit, which converts these specifications into signals to the gluing equipment. If necessary, the control unit specifies the addition of further additives based on the stored specifications, such as hardeners for the adhesive, hydrophobic agents such as wax or paraffin, fire retardants, antifungals, or other additives. The addition of additives can also be controlled separately for each production line, which leads to more targeted and usually more economical use of the additives.This allows the different properties of fresh wood and recycled wood to be taken into account.

[0011] The control device controls the respective spreading devices of the first and the at least one second production line individually. Depending on the strength properties of the various raw materials for the strands, which are produced by the first and second and possibly further production lines and then fed to a spreading device after drying and gluing if necessary, the control device specifies the quantity of strands a spreading unit spreads per inner or outer layer of a cover layer and in which direction the strands are aligned, relative to a production direction. The quantity of strands per inner or outer layer of a cover layer is calculated in particular according to the strength properties of the respective strands, whereby the aim is to use the highest possible proportion of strands made from recycled wood.

[0012] It has been shown that a homogeneous quality of OSB boards can be achieved in particular by processing fresh wood and recycled wood in separate layers rather than mixing them in one layer. Accordingly, the various strands or flakes made from fresh or recycled wood can, for example, be coated with different binding agents and / or with different amounts of binding agent in order to achieve optimal strength properties of the various layers of the top layer with minimal effort and cost. In the same way, the use of additives can be adapted to the requirements of each layer of the top layer. For the individually and therefore optimally produced strands or flakes coated with binding agent, the top layer is then manufactured as described below.

[0013] The optimally produced strands, which have been coated with binder, are then fed to a spreading device, each of which is assigned to a production line. According to an advantageous embodiment, the strands of the first production line can each be fed to a first spreading device for a lower cover layer and to a second production line for an upper cover layer. Correspondingly, the strands of a second production line can each be fed to a first spreading device for a lower second layer and to a second spreading device for an upper second layer. Since the cover layers according to the invention are generally constructed symmetrically, two spreading devices are preferably connected to each production line for strands of a layer of the cover layer.This means that one of the two spreading devices can be used to spread the respective layer of the lower covering layer and the other of the two spreading devices can be used to spread the respective upper layer of the covering layer of an OSB board.

[0014] To produce an OSB board having a covering layer according to the method according to the invention, a lower covering layer is first spread, with the first, outer layer being spread first, followed by at least a second, inner layer of the lower covering layer. A single- or multi-layer middle layer is spread onto the second, inner layer of this first, lower covering layer. An upper covering layer is spread onto the middle layer in the reverse order of the layers to the lower covering layer, i.e. the second, inner layer is spread first, followed by the first, outer layer of strands or flakes. The OSB board spread in this way is then fed to a press in which the covering layers and the middle layer are pressed together.The sequence of layers means that the second, inner layer is adjacent to the middle layer, while the first, outer layer of the top layer is adjacent to the second, inner layer and, with its other surface, forms the outer side of the OSB board. The second, inner layer, in particular, can be constructed from two or more layers, with each layer of a top layer advantageously being manufactured using a separate production line.

[0015] In order to produce a differentiated and optimized structure of a multi-layer top layer for an OSB board, at least a third, preferably also a fourth, production line is advantageously used in addition to the first and second production lines. Strands of each production line preferably each have their own profile with regard to the average size of the strands, moisture content, and the type and quantity of the applied adhesive. The third and, if applicable, fourth production lines are arranged before, between, or after the first or second production line, so that a top layer consisting of an outer and one, two, or three inner layers is spread.

[0016] It is preferred that strands or flakes made from recycled wood or from a mixture of recycled wood and fresh wood are used for the second layer of the cover layer. It is particularly preferred if the second layer of the cover layer is made up of several layers, with individual layers being made from fresh wood strands or flakes or from recycled wood strands or flakes. Further preferably, recycled wood strands or flakes are used in the inner layers of the second layer, arranged towards the middle layer. In this way, the individual layers can be used in a controlled and thus optimized manner, and an OSB board is produced which, using the cover layers according to the invention, has optimal strength properties, which generally enable the production of an OSB 3 board in accordance with DIN EN 300: 2006-09.

[0017] According to a preferred embodiment of the invention, a cover layer is produced which has at least a first, outer layer and a second, inner layer, which are scattered in such a way that the cover layer has an inhomogeneous distribution of recycled wood strands and fresh wood strands across its thickness. In this way, optimal production of OSB boards with high strength can be ensured. It is preferred that the proportion of recycled wood strands is greater towards the middle layer. It is further preferred that the proportion of fresh wood strands or flakes is limited to the first, outer layer of the cover layer. This has advantages with regard to the color of the OSB board, which is usually lighter when fresh wood is used, as well as advantages with regard to strength and, at the same time, low costs.

[0018] The proportion of recycled wood strands or flakes should be as high as possible. Depending on the strength requirements of the OSB board, the proportion of recycled wood strands is at least 5 wt.%, advantageously at least 20 wt.%, preferably at least 45 wt.%, particularly preferably at least 65 wt.%, in each case based on the weight of the top layer. The upper limit for use is usually 90 wt.%, with the aim of making the proportion of recycled wood strands as high as possible. This leads to the desired maximum use of available recycled wood quantities for a high-quality purpose, the conservation of fresh wood resources, the saving of drying energy, and thus overall lower costs for the production of an OSB board while simultaneously maintaining the good strength properties.

[0019] It has been found that OSB boards with good strength properties can be produced when recycled wood strands are manufactured with dimensions that are smaller than fresh wood strands, as explained above. It has also been found that it is advantageous to use smaller strands for the production of the second inner layer of the cover layer according to the invention than for the production of the first, outer layer. Selecting larger strands for the production of the first, outer layer has advantages, both in terms of the appearance of an OSB board and in terms of strength properties.

[0020] In principle, it is preferable to produce and spread the strands from recycled and fresh wood separately. This can optimize quality within a production line. However, if the available material does not allow for any other method, it is preferable to use a mix of recycled and fresh wood strands in the first, outer layer of the top layer if the use of recycled wood strands is to be maximized.

[0021] The invention further relates to an OSB board comprising two outer cover layers and a middle layer arranged between the cover layers, wherein the cover layers each comprise strands of recycled wood. It is preferred that the middle layer comprise strands of recycled wood.

[0022] According to a preferred embodiment, the cover layers of the OSB board each comprise a first, outer layer and a second, inner layer. Further preferably, the first, outer and second, inner layers of the cover layer differ in their composition of strands of fresh wood and / or recycled wood. Advantageously, the cover layer comprises at least 5 wt.% and a maximum of 90 wt.% recycled wood, based in each case on the weight of the cover layer.

[0023] The first outer layer of the top layer, which typically has the highest content of fresh wood strands, makes up a maximum of 40%, preferably a maximum of 30%, of the top layer thickness. A typical proportion of the top layer thickness is 15% to 25%.

[0024] The invention further relates to a device for spreading a cover layer of an OSB board, wherein the device comprises a first production line for recycled and / or fresh wood strands and at least one second production line for recycled wood strands, wherein the first and second production lines each have at least one machining device, a drying device, and a gluing device, as well as at least one spreading device per production line and a control device for controlling the first and at least second production lines and the spreading devices. The separate production lines, which ensure that individual layers of the cover layer are processed with a defined composition of the raw material, ensure, according to the invention, the production of homogeneous cover layers and, consequently, OSB boards with good strength properties.

[0025] A production line can advantageously be operated with fresh wood or recycled wood. This promotes a homogeneous quality of the individual layers. Alternatively, a mixture of fresh wood and recycled wood can be used. It is preferred that the mixture of the starting material be as consistent as possible in order to create a homogeneous layer within the top layer. Layers with strands made from a mixture of fresh and recycled wood are preferably used as the first layer of a top layer, but alternatively, they can be used in a second layer of the top layer.

[0026] The individual devices of the apparatus for spreading a facing layer are known per se. They can be arranged in any way; only the spreading devices of the first and second production lines are arranged one behind the other in the production direction of the OSB board. The spreading device of a production line usually has two outlets, one for producing the lower facing layer and one for producing the upper facing layer. In this case, the first layer of a facing layer in the overall sequence of all layers of an OSB board (face layers and middle layer) is spread from a first outlet of the spreading device of the first production line as the first layer of the lower facing layer and from a second outlet of the spreading device of the first production line as the last layer of the upper facing layer.Accordingly, the spreading device of the first production line forms the beginning of the series of spreading devices with its first outlet and the end of the series of spreading devices with its second outlet, each seen in the direction of production.

[0027] The spreading device(s) of the second and, if applicable, each subsequent production line for the second layer of the facing layer are arranged between the spreading device of the first production line. For the lower second layers, first outlets are arranged downstream of the first outlet of the first production line for spreading the second layers of the lower facing layer. Second outlets of the spreading device of the second production lines are arranged in the reverse order in production direction to that for spreading the lower facing layer, namely upstream of the second outlet of the spreading device of the first production line. The spreading device(s) of the middle layer are arranged between the spreading devices or outlets for spreading the lower and upper facing layers of an OSB board.

[0028] The equipment of a production line is controlled by a control unit depending on the raw material used - fresh wood, recycled wood, or a mixture thereof - and, if applicable, the requirements for each layer of the facing layer and / or the requirements for the OSB board. The control unit stores data on the raw material and, if applicable, the requirements for the individual layers of the facing layer and the OSB board. Raw material data includes, for example, moisture content, type of raw material (fresh or recycled wood), dimensions of the strands to be produced or the suitable size of the strands for each layer, as well as specifications for gluing the strands. The data relating to the requirements of each layer includes, in particular, the thickness of the respective layer and the orientation of the strands in relation to the direction of production.The data relating to the overall requirements for the surface layer include, for example, the total thickness of the surface layer(s) and the number and sequence of the individual layers of a surface layer.

[0029] According to a preferred embodiment of the method for producing a cover layer, the control device receives signals from sensors that record the aforementioned parameters such as the moisture content of the strands, the size, quantity and type of gluing, the thickness of the spread layers, and other influencing variables. The sensors are arranged on the devices or assigned to the devices that produce, dry, apply glue, and / or spread strands or flakes. Alternatively, the corresponding parameters can also be input into the control device as information without the involvement of a sensor, e.g., when the moisture content of a batch of raw material is determined, here by drying at 105°C to constant weight, and the recorded moisture content is then fed into the control device.

[0030] The control device optionally also processes other information, either from sensors or through other, e.g. manual or automatic input, which otherwise relate to the production of the OSB board and which is relevant for the production of the top layer, in particular the speed of the conveyor belt onto which the strands are scattered, the pressing conditions (in particular temperature, pressure, duration of the pressing process) and the specified properties of the OSB board such as the thickness of the entire OSB board and strength properties of the OSB board. Furthermore, information on the composition of one or more layers, the raw material and the thickness of the middle layer can be included, whereby the middle layer is preferably made from strands or flakes of recycled wood.

[0031] Once all the information required to produce a top layer for an OSB board is available, the control unit controls the cutting unit, whereby the average thickness, length, and width of the strands can be specified. The control unit also controls the drying unit, based on the moisture content of the strands, with regard to, for example, the temperature and duration of drying. The gluing unit is controlled with regard to the amount and type or composition of the adhesive. If necessary, the addition of additives such as hardeners, hydrophobic agents, conductivity adjusters, biocides, or the like is controlled, whereby the addition of the additives does not have to take place at the same time as or in the gluing unit. Additives can, for example, also be added before or after gluing or after spreading the respective layer and before spreading the next layer. The spreading unit is controlled so that, for example,the specified quantity of strands for the respective layer and, if applicable, the specified orientation of the strands in relation to the production direction of the OSB board is maintained, e.g. parallel or perpendicular to the conveying direction, alternatively at another, defined angle to the production direction or without any special orientation relative to the production direction.

[0032] Details of the invention are presented below using exemplary embodiments. Fig. 1 is a schematic representation of an OSB board having cover layers according to the invention; Fig. 2 is a schematic representation of an apparatus for producing a cover layer according to the invention

[0033] Fig. 1shows an OSB board 1, which is constructed from two cover layers, a lower, first cover layer 2a and a second, upper cover layer 2b, wherein the cover layers 2a, 2b enclose a middle layer 3. The middle layer 3 can be single-layer or multi-layered. The OSB board 1 is therefore preferably constructed in a mirror-image or symmetrical manner with respect to the middle layer. The cover layers 2a, 2b each have a first, outer layer 4 and a second, inner layer 5. The first, outer layer 4 of the cover layer 2a, 2b forms the surface of the OSB board 1, either the underside 6 or the top side 7 of the OSB board 1. The first, outer layer 4 of the cover layer 2a, 2b further borders on the second, inner layer 5 of the cover layer at the interface 8. The inner layer 5 borders on the middle layer 3 with its other interface 9.

[0034] The first, outer layer 4 of the cover layer 2a, 2b according to the invention is made from strands of fresh wood, but can also be made from a mixture of fresh wood and recycled wood strands, or exclusively from recycled wood strands. The second, inner layer 5 of the cover layer 2a, 2b according to the invention is preferably made from recycled wood, but can also be made from a mixture of fresh wood and recycled wood strands. The first and second layers 4, 5 of the cover layer 2a, 2b are Fig. 1 shown as having the same thickness. Advantageously, the first, outer layer 4 can be spread more thinly than the second, inner layer 5, so that the first, outer layer 4 amounts to a maximum of 40%, preferably a maximum of 30%, particularly preferably between 15% and 25% of the thickness of the entire cover layer.

[0035] The inner layer 5 has at least one, advantageously several layers, which differ from one another at least in their composition or orientation. For example, inner layers 5 can differ from one another in the size of the strands or their orientation; however, differences can also exist in the adhesive or the amount of adhesive, just as individual inner layers 5 can differ in the composition of the raw material. For example, one inner layer can be made exclusively from recycled wood strands, while another inner layer is scattered from a mixture of recycled and fresh wood strands. From the above, it follows that the cover layers 2a, 2b each have an inhomogeneous structure across the thickness of the cover layer.

[0036] The proportion of recycled wood strands increases preferentially from the first, outer layer 4 in the second, inner layer 5, i.e. in the direction from the bottom 6 or the top 7 to the middle layer 3.

[0037] With regard to the size of the strands, an inhomogeneous distribution from the bottom side 6 or top side 7 to the middle layer 3 is also preferred, with larger strands preferably being found on the bottom or top side 6, 7, while smaller strands are found in the second, inner layer 5 towards the middle layer 3. Typical average lengths for strands are from approximately 30 mm to 250 mm, typical average widths from 1 mm to 50 mm, and typical average thicknesses from 0.25 mm to 3 mm. Fresh wood often results in larger strands than recycled wood, usually up to the dimensions mentioned above. Typical average dimensions for recycled wood strands, which are used for both the first, outer layer 4 and the second inner layer 5, are a length of 15 mm to 150 mm, a width of 0.25 mm to 15 mm, and a thickness of 0.25 mm to 3 mm.It is also advantageous to use larger recycled wood strands in the first, outer layer 4 and smaller recycled wood strands in the second, inner layer 5.

[0038] With the cover layer 2a, 2b according to the invention, conventional OSB boards 1 can be produced with a thickness of, for example, 6 mm to 80 mm. These OSB boards 1 produced according to the invention meet all the technical requirements for an OSB-3 board after testing in accordance with DIN EN 300: 2006-09.

[0039] OSB boards 1 with at least one cover layer 2 according to the invention as described above can advantageously be produced in a device according to Fig. 2 be manufactured. Fig. 2shows two production lines 10, 15, each designed to produce strands with different properties, in particular a different average length. Typically, the first and second production lines are also designed to process different raw materials, with the first production line advantageously being used to process fresh wood and / or recycled material, and the second production line to process recycled material.

[0040] The first production line 10 is according to Fig. 2designed for processing fresh wood 11, but can also be used for processing recycled wood or a mixture of recycled and fresh wood. The first production line 10 includes a chipping device 12 for producing strands, e.g. a ring chipper, a drying device 13, e.g. a drum dryer, and a gluing device 14, in which glue is added to the strands, which ensures the bond between the strands during the subsequent pressing of the OSB board 1. The second production line 15 for strands of the face layer is designed for processing recycled wood. The recycled raw material, typically e.g. offcuts from panel blanks, packaging material such as boxes or pallets, but also used construction material that is not contaminated with other materials, is collected in a container 16 and fed to the chipping device 17, e.g. a ring chipper.After machining, the drying device 18 can be activated if necessary to adjust the strand moisture content to the desired level. Since the recycled material is usually already sufficiently dry, the drying device can be omitted, at least temporarily. Otherwise, the conditions (temperature, air velocity, residence time in the dryer) can usually be much milder than in the first production line, if fresh wood is processed there. Accordingly, energy and emissions are saved. The drying device 18 is followed by a gluing device 19, in which the strands of the second production line 15 are coated with adhesive. The gluing device 19 can be technically designed in the same way as the gluing device 14 of the first production line 10. However, the gluing in the second gluing device 19 will usually take place under different parameters than in the first production line 10.A different adhesive or adhesive mixture, a different amount of adhesive or a different adhesive application can be selected and additives or other additives can be added.

[0041] The finished glued strands are transferred from a first distribution container 20 of the first production line 10 or from a second distribution container 21 of the second production line 15 to first and second spreading devices 22 and 23, respectively, which each have two outlets, 22a, 22b and 23a, 23b. Optionally, chips produced in the second chipping device 16, but which have average dimensions too small to be used as strands, can be sorted out and, after drying and gluing, fed to a separate, third spreading device 24. These chips can be used to spread the middle layer. Alternatively, the chips of the middle layer 3 can be produced in a separate production line, not shown here. In the present exemplary embodiment, a single-layer middle layer is spread; the spreading device 24 therefore has only one outlet.

[0042] Below the first and second production lines 10, 15 and the associated outlets 22a, 22b, 23a, 23b of the two spreading devices 22, 23 and optionally 24, runs a circulating conveyor belt 25, which extends from the spreading devices 22a, 22b, 23a, 23b and optionally 24 to a press (not shown here), and which moves in the production direction P relative to the outlets 22a, 22b, 23a, 23b and optionally to the spreading device 24 towards the press. The following outlets are arranged one after the other in the production direction P: Outlet 22a spreads the first, lower layer 4 of fresh wood strands onto the conveyor belt. This first lower layer 4 forms the underside of the OSB board to be produced. Next, the outlet 23a is arranged, which spreads the second lower layer 5 of the inventive lower cover layer 2a made of recycled wood strands. The middle layer 3 made of chips, preferably recycled wood chips, is spread onto this second lower layer 5.For this purpose, the spreading device 24 is arranged downstream of the outlet 23a in the production direction. To ensure a symmetrical construction of the OSB board 1 starting from the middle layer 3, downstream of the spreading device 24 in the production direction P are first the outlet 23b for producing the second, upper layer 5 from recycled wood strands and then the outlet 22b for producing the first, upper layer 4. The outlets 22a and 23a thus spread the lower cover layer 2a, which is composed of the lower layers 4 and 5; the outlets 23b and 22b spread the upper cover layer 2b, which is composed of the upper layers 4 and 5. If the cover layer 2a, 2b according to the invention is to have more than two layers, a third production line is preferably constructed according to the scheme of the production lines 10, 15.However, at least one further scattering device must be provided, which preferably also has two outlets and with which a further layer can be produced for each of the lower and upper cover layers 2a, 2b, e.g. by scattering otherwise identical strands, relative to the production direction P, in directions (perpendicular, parallel or at any angle to the production direction or scattered without orientation) that deviate from the direction of adjacent layers of the cover layer 2.

[0043] The individual devices of the first and second production lines 10, 15 are connected by a Fig. 2The drying process is coordinated or controlled by a control device (not shown). This control device preferably interacts with sensors that record parameters important for producing optimal facings for an OSB board. These include, in particular, the moisture content of the strands before and, if applicable, after drying, the type and amount of gluing, and the quantity of strands spread per facing layer.

[0044] Possible compositions of the cover layer 2a, 2b according to the invention are explained below using exemplary embodiments. The information regarding the amount of adhesive used refers to 100% adhesive. Example 1:

[0045] In a first production line 10, strands of fresh forest wood (coniferous wood) with an average length of 230 mm, an average width of 45 mm, and an average thickness of 2 mm are first produced in a first machining device 12. These strands are dried in a first drying device 13 from a water content of approximately 100% to a moisture content of 6%. The thus dried strands are coated with PMDI (polymeric diphenylmethane diisocyanate) in a first coating device 14 (coating: 2.5-3.0 wt.% based on dry strands). The thus coated fresh wood strands are coated by a first coating device 22 as the first, outer layer 5 of the lower cover layer 2a from the first outlet 22a longitudinally, i.e., parallel to the production direction P. The thickness of the first layer 4 of the lower cover layer 2a accounts for approximately 30% of the thickness of the entire cover layer.

[0046] Subsequently, 15 strands of recycled wood are produced in the second production line. These strands have an average length of 145 mm, an average width of 12 mm, and an average thickness of 2 mm. The recycled wood strands produced in the second machining device 17 are also dried in the second drying device 18 to a moisture content of 6% based on dry wood. However, since the recycled raw material is significantly drier than fresh wood, the second drying device is operated at a much lower temperature than the first drying device. The recycled wood strands dried to a moisture content of 6% are coated with PMDI in a second gluing device 19 in the same amount as the strands of the first production line 10.From the distribution container 21, the strands of the second production line are fed to the second spreading device 23, which spreads the second layer 5 of the lower cover layer 2a from the first outlet 23a. The second, inner layer is also spread parallel to the production direction P. The second, inner layer 5 accounts for 70% of the thickness of the lower cover layer 2a according to the invention. The strands of the lower cover layer 2a thus originate predominantly, in particular more than 50%, preferably more than two-thirds, from recycled wood.

[0047] As described above, the control device controls the cutting devices 12, 17, the drying and gluing devices 13, 14 and 18, 19 as well as the spreading devices used to produce the upper and lower cover layers 2a, 2b.

[0048] The chips or strands of middle layer 3 are produced in a separate production line. Their dimensions are smaller than those of the strands of the outer layer. After drying and gluing, the chips of the middle layer are fed into a separate spreading device. The strands or chips of middle layer 3 are also glued with PMDI (2.0–2.5 wt.% based on dry strands). The middle layer, which consists of 70% recycled strands or chips, is then spread across the production direction.

[0049] After the middle layer 3 has been spread, the second inner layer 5 is spread from the second outlet 23b in reverse order to the lower cover layer 2a, followed by the first outer layer 5 of the upper cover layer 2b from the second outlet 22b. The two upper layers 4, 5 of the upper cover layer 2b are again spread longitudinally, i.e., parallel to the production direction P. The production of the middle layer 3 is also controlled by the control device.

[0050] The resulting cake of strands forming the lower and upper face layers 2a, 2b, and the strands or chips of the middle layer 3, was pressed into an 18 mm OSB in a continuous press. After cooling, the board was tested according to DIN EN 300: 2006-09. All technical requirements for an OSB 3 board were met. Example 2:

[0051] The cover layers 2a, 2b according to the invention are produced in the same way as in Example 1.

[0052] The middle layer, which consists of 100% recycled strands, is otherwise manufactured in the same way as in Example 1.

[0053] The cake consisting of the above-described inventive cover layers 2a, 2b with the intermediate middle layer 3 was pressed in a continuous press to form an 18 mm OSB board 1. After cooling, the OSB board 1 was tested according to DIN EN 300: 2006-09. All technical requirements for an OSB 3 board were met.

[0054] OSB board 1 was then subjected to an emissions test according to 16516 (October 2020) and the AGBB scheme. A blank sample of the same thickness, made from fresh forest wood (pine), was tested in parallel. It was found that OSB board 1 made with recycled wood met all the requirements of the AGBB scheme after just seven days. The OSB board made with fresh forest wood only met the requirements of the AgBB scheme after 28 days. This clearly demonstrates the advantages of using recycled wood, which emits significantly lower emissions. Example 3:

[0055] In a first production line 10, strands of recycled wood are initially produced, which are dried as in exemplary embodiment 1, but under milder conditions and glued with 3 wt.% PMDI. The strands are the same size as the recycled strands of exemplary embodiment 1. These recycled wood strands are spread lengthwise, i.e. parallel to the production direction P, as the first covering layer. These recycled wood strands, spread as the first, outer layer 4 of the lower covering layer 2a, make up approximately 50% of the thickness of the covering layer 2a, based on the entire covering layer. Then, equally sized recycled wood strands, which are also glued with 2.5 wt.% PMDI at 6% moisture, are spread as the second, inner layer 5 of the lower covering layer 2a, also parallel to the production direction P. Subsequently, the middle layer 3, which consists 100% of recycled strands, is spread transversely to the covering layer. The strands orChips of middle layer 3 are also glued with 2.0 wt.% to 2.5 wt.% PMDI (based on dry wood).

[0056] Then, as in Example 1, the two inner and outer layers 5 and 4 of the upper facing layer 2b are spread lengthwise in reverse order. They have the same composition as the outer and inner layers 4, 5 of the lower facing layer 2a. The spread cake was pressed in a continuous press to form an 18 mm OSB board 1. After cooling, the OSB board was tested according to DIN EN 300: 2006-09. All technical requirements for an OSB 3 board were met. List of reference symbols

[0057] 1 OSB board 2a First, lower cover layer 2b Second, upper cover layer 3 Middle layer 4 First, outer layer of the cover layer 5 Second, inner layer of the cover layer 6 Bottom of the OSB board 7 Top of the OSB board 8 Interface between the first, outer layer and the second, inner layer of the cover layer 9 Interface between the second, inner layer of the cover layer and the middle layer 10 First production line 11 Raw material 12 First machining device 13 First drying device 14 First gluing device 15 Second production line 16 Recycling material 17 Second machining device 18 Second drying device 19 Second gluing device 20 First feed container 21 Second feed container 22 Spreading device of the first production line 22a, 22b Outlets of the spreading device 22 23 Spreading device of the second Production line 23a, 23bOutlets of the spreading device 23 24Spreading device for the middle layer 25Conveyor belt PProduction direction

Claims

1. A method for producing a cover layer (2) for an OSB board (1) by means of a first production line (10) for recycled or fresh wood strands and with at least one second production line (15) for recycled wood strands, wherein the first and the second production lines (10, 15) each have at least one machining device (12, 17), a drying device (13, 18) and a gluing device (14, 19), and by means of a control device with the steps - producing first recycled or fresh wood strands from recycled or fresh wood in a first production line (10), - producing second recycled strands from recycled wood in a second production line (15), - drying and gluing the first recycled or fresh wood strands and the second recycled strands, - feeding the first recycled or fresh wood strands and the second recycled strands each to the spreading device (22,23) of the first and second production lines (10, 15), wherein the spreading devices (22, 23) are arranged one behind the other in a production direction (P), and wherein, after drying and gluing the first recycled or fresh wood strands and the second recycled strands, the first and second production lines (10, 15) are designed to feed the strands to a spreading device with subsequent - spreading of a first, outer layer (4) of strands from a first spreading device (22), subsequent spreading of at least a second, inner layer (5) of strands from a second spreading device (23), and wherein - the spreading of the first recycled or fresh wood strands and the second recycled strands is controlled by the control device, wherein the control takes place depending on the properties of the recycled strands and / or the fresh wood strands.

2. Method according to claim 1, characterized in thatat least one further production line for recycled or fresh wood strands of the surface layer is provided, with a further spreading device which is arranged before, between or after the first or the second spreading device.

3. Method according to claim 1 or 2, characterized in that at least the second, inner layer (5) of the covering layer (2) is scattered using strands of recycled wood.

4. Method according to one of claims 1 to 3, characterized in that the cover layer (2), which has at least a first, outer layer (4) and a second, inner layer (5), is scattered in such a way that it has an inhomogeneous distribution of recycled wood strands and fresh wood strands over its thickness.

5. Method according to one of claims 1 to 4, characterized in that more recycled wood chips are used to produce the second, inner layer (5) of the cover layer (2) than to produce the first, outer layer (4).

6. Method according to one of claims 1 to 5, characterized in that to produce the second, inner layer (5) of the cover layer (2) smaller strands are used than to produce the first, outer layer (4).

7. Method according to one of claims 1 to 6, characterized in that a covering layer (2) has two or more layers (4, 5), wherein the layers (4, 5) are each spread from strands of recycled wood, fresh wood or a mixture thereof.

8. Method according to one of claims 1 to 7, characterized in thatthe scattering device (22) has a first outlet (22a) for scattering the first layer (4) of the lower cover layer (2a) and a second outlet (22b) for scattering the first layer (4) of the upper cover layer (2b), wherein the scattering device (22) is connected to the first production line (10), and that the scattering device (23) for scattering the second, inner layer (5) has a first outlet (23a) for scattering the second layer (5) of the lower cover layer (2a) and a second outlet (23b) for scattering the second layer (5) of the upper cover layer (2b), wherein the scattering device (23) is connected to the second production line (15).

9. OSB board, comprising two outer cover layers (2a, 2b) and a middle layer (3) arranged between the cover layers, characterized in that the cover layers (2a, 2b) each have strands of recycled wood.

10. OSB board according to claim 9, characterized in thatthe cover layers (2a, 2b) of the OSB board (1) each have a first, outer layer (4) and a second, inner layer (5) which differ in their composition from strands of fresh wood and / or recycled wood.

11. OSB board according to claim 9 or 10, characterized in that the second, inner layer (5) of the cover layer (2) has a larger proportion of recycled wood strands than the first, outer layer (4).

12. OSB board according to claim 9 or 10, characterized in that the first outer layer (4) and the second inner layer (5) of a cover layer (2) each have strands of different sizes.

13. OSB board according to one of claims 9 to 12, characterized in that the first, outer layer (4) is a maximum of 40%, preferably a maximum of 30% of the thickness of the cover layer (2).

14. OSB board according to one of claims 9 to 13, characterized in that the covering layer (2) contains at least 5 wt.% to a maximum of 90 wt.% strands of recycled wood.

15. Device for producing a covering layer (2) of an OSB board (1), comprising a first production line (10) for recycled or fresh wood strands and at least one second production line (15) for recycled wood strands, wherein the first and the second production line (10, 15) each have at least one machining device (12, 17), a drying device (13, 18) and a gluing device (14, 19), and wherein the device has at least a first and a second spreading device (22, 23) and a control device for controlling the first and the at least second production line (10, 15) and the first and the second spreading device (22, 23) for recycled or fresh wood strands.

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