Process for producing a material plate

Abstract

Shown and described is a method for producing a material board, in particular a wood-based board, from a material according to patent claim 1.

Description

The invention relates to a method for producing a material panel, in particular a wood-based material panel, from a material, comprising the following steps: a) providing at least one layer of a material, in particular a material which contains wood chips and / or wood fibers, b) providing a press, comprising: an upper pressing device and a lower pressing device, between which a gap for receiving the material forms, wherein the upper pressing device and / or the lower pressing device has hydraulic press cylinders, which can change the gap width between the upper pressing device and the lower pressing device and can transmit pressing forces to the material, and wherein the upper pressing device and / or the lower pressing device has a heating device, in particular a heating plate, which can transmit heat at least indirectly to the material, c) pressing the material in the gap between the upper pressing device and the lower pressing device, d) heating the material in the gap between the upper pressing device and the lower pressing device, wherein steps c) and d) take place at least partially simultaneously.Material panels, in particular wood material panels, are known in different configurations and are widely used-for example for the construction of furniture. Wood material boards are produced by the joining together of comminuted wood materials, wherein the size and the shape of the wood particles determine the properties of the wood material and of the wood material boards produced therefrom. The wood materials can be, for example, wood chips (fine chips and / or coarse chips) or wood fibers. Accordingly, the material boards made of these wood materials can also be classified as particle board, coarse particle board ("OSB board"), medium density fiber board ("MDF board") or high density fiber board ("HDF board").The comminuted wood materials are usually joined together under the action of pressure and / or temperature, for which reason presses are frequently used for the production process. The bonding of the chips or fibers achieved in the production is due in part to properties inherent in the chips or fibers (e.g., the properties of lignins, the natural "glues" in wood). In addition, the connection between the chips or fibers can be achieved or increased by a binder, which is mixed with the wood materials. For cost reasons and for reasons of health protection (e.g. reduction of emissions harmful to health), however, the aim is generally to minimize the use of binders.In addition to the wood-based materials used, the production processes can also be differentiated on the basis of other criteria, for example on the basis of the moisture content of the wood-based materials to be processed. Accordingly, a distinction is made between dry process and wet process. In the standard DIN EN 316, a sheet according to the wet process is defined as a "fibre sheet with a moisture content of more than 20% at the stage of sheet formation", while a sheet according to the dry process is defined as a "fibre sheet with a moisture content of less than 20% at the stage of sheet formation".The moisture content or moisture content (often also referred to as "wood moisture" or "wood moisture") is understood to mean a quantity which is defined by the ratio of the water mass contained in the wood to the dry mass of the wood in percent. It is to be distinguished from the water content of the wood, which represents the ratio of the water mass contained in the wood to the total mass of the (moist) wood in percent. The moisture content is expressed in percent (%) ATRO (absolute dry).In practice, the dry process is frequently carried out with moisture contents of around 10% and below, while the wet process is frequently carried out with significantly higher moisture contents than 20%, for example with about 100% (values above 100% are also possible because of the previously mentioned definition of the ATRO moisture). However, the initial moisture content is again significantly reduced in the wet process by mechanically pressing out the moisture in the first step and subsequently evaporating it. Therefore, in wet processes, a screen fabric is arranged on the underside of the chip or fiber mat, which facilitates the dewatering and the steam escape, but leaves behind a frequently undesirable grid-like impression on the underside of the plate.While in the wet process it is often possible to dispense with binders such as glue, in the dry process the use of binders is customary. In particular in dry processes, there is therefore the challenge of reducing the use of binders.Against this background, the object of the invention is to specify a method for producing a material panel, in particular a wood material panel, with which panels having good mechanical and optical properties can be produced even when binder is dispensed with partially or completely.This object is achieved in a method according to the preamble of claim 1 in that the contact pressure acting on the material is lowered during step c) to a contact pressure which is in the range between 10 N / cm 2 and 150 N / cm 2, in particular between 30 N / cm 2 and 100 N / cm 2.The method is a method for producing a material panel, in particular a wood material panel, from a material. The method comprises first step a), which comprises providing at least one layer of a material, in particular a material which contains wood chips and / or wood fibers. The (wood) material can be provided in different ways, for example the (wood) material-if it is a dry, free-flowing material-can be scattered in one layer or in a plurality of layers onto a conveyor belt in order to be fed to a press (usually in dry processes). As an alternative to scattering, the material can also be placed on a conveyor belt, for example in the form of a pulp (customary in wet processes). The method further comprises step b) providing a press. The press can be, for example, a continuously operating press or a cyclically operating press. In the case of the cycle press, presses having one "floor" or having a plurality of "floors" may be used. The press used in the method comprises first an upper pressing device and a lower pressing device, between which a gap for receiving the material is formed. In the gap ("press gap"), the material can be processed into a plate under the influence of pressure and / or heat. The upper pressing device and / or the lower pressing device has hydraulic press cylinders which can change (i.e. reduce and increase) the gap width between the upper pressing device and the lower pressing device and can transmit pressing forces to the material. In practice, it has proven advantageous to assign the hydraulic press cylinders to the upper press device. The upper pressing device and / or the lower pressing device additionally has (at least) one heating device, in particular (at least) one heating plate, which can transfer heat directly or indirectly to the material. Preferably, both the upper pressing device and the lower pressing device have a heating plate, so that the material can be heated from the upper side and from the lower side. The method further comprises step c), pressing the material in the gap between the upper pressing device and the lower pressing device, and step d), heating the material in the gap between the upper pressing device and the lower pressing device. Steps c) and d) can be partially or completely superimposed, i.e. take place at least partially simultaneously.According to the invention, it is provided that the contact pressure acting on the material is lowered during step c) to a contact pressure which is in the range between 10 N / cm 2 and 150 N / cm 2, in particular between 30 N / cm 2 and 100 N / cm 2. It is thus provided that the contact pressure is not completely released (i.e. lowered to ambient pressure) during step c), i.e. during the pressing process, but rather is lowered from a higher pressure level ("working level") to a lower pressure level ("holding level") and is held there for a while. Thus, pressure relief should take place already before the adhesive bonding.According to one embodiment of the method, it is provided that the pressure of the press cylinders is lowered during step c) from a working pressure to a holding pressure which is in the range between 5 bar and 40 bar, in particular between 10 bar and 30 bar. The above-described lowering of the contact pressure acting on the material during the pressing process from a "working level" to a "holding level" can be achieved, for example, by the pressure of the press cylinders being lowered and held in a corresponding manner.In a further embodiment of the method, it is provided that the lowered contact pressure and / or the lowered holding pressure is held for at least 10 seconds, in particular for at least 20 seconds. By the "holding level" continuing for a sufficiently long time, it is ensured that the still quite soft, unstable material plate is still "held in shape" and thus stabilized for a sufficiently long time before the pressing operation is ended and the material plate is released from the opening press.According to a further embodiment of the method, it is provided that the temperature is lowered from a maximum temperature to a holding temperature which lies in the range between 120° C. and 220° C., in particular between 140° C. and 180° C. As has already been described above with regard to the pressure, the temperature in the middle of the plate should also be lowered in a corresponding manner not yet completely (i.e. to ambient temperature), but rather should be lowered from a higher temperature level ("working level") to a lower temperature level ("holding level") and held there for a while.In a further embodiment of the method, it is provided that the holding temperature is held for at least 10 seconds, in particular for at least 20 seconds. This ensures that the thermal and / or chemical processes running in the material can run as completely as possible.According to a further embodiment of the method, it is provided that during step c) a lowering of the contact pressure acting on the material takes place, wherein the contact pressure is lowered by at least 50 N / cm 2, in particular by at least 100 N / cm 2, preferably by at least 200 N / cm 2. The pressure reduction should take place "during step c)", i.e. during the pressing process. A distinction is to be made between the (specific) pressure acting on the material (unit used here: N / cm 2) and the hydraulic pressure prevailing in the press cylinders of the press (unit used here: bar). The beginning and the end of the pressing process can be defined with respect to both of the stated pressures: the pressing process begins at a point in time at which the specific pressure acting on the material increases in a measurable manner for the first time and / or exceeds a value of 1N / cm 2. The pressing process ends at a point in time at which the specific pressure acting on the material falls below a value of 1N / cm 2 and / or falls below the measurable limit. Alternatively and / or additionally thereto, the pressing process begins at a point in time at which the pressure of the press cylinders increases in a measurable manner for the first time and / or exceeds a value of 1 bar. The pressing operation ends at a point in time at which the pressure of the press cylinders falls below a value of 1 bar.Since the pressure reduction takes place during this pressing operation, it differs from a (complete) pressure reduction which typically arises at the end or after the end of the pressing operation as a result of the complete opening of the press. The contact pressure acting on the material can be lowered, for example, by reducing the pressure in the press cylinders, wherein the contact pressure can differ quantitatively from the pressure in the press cylinders by a system-specific factor because of the active surfaces of different sizes.The pressure reduction takes place actively and takes place through the opening of the press gap, as a result of which the compressed material can expand slightly again and is thus geometrically relieved. The pressure drop thus also differs from the naturally occurring pressure drop during the pressing of wood materials. This known pressure drop occurs over time during the pressing process, while the distance of the press nip is kept substantially constant. The material plasticises as a result of the moisture and temperature present, so that the counterpressure which the compacted material applies against the press decreases. In fact, the restoring forces of the material still present at the time of the active pressure reduction can be used (i.e. in particular before the above-described plasticizing of the material, or before the hardening of binders that may be used) in order to allow the material to inhale and thus to enlarge the pores present between the particles.During the geometric relief period, the moisture flows very quickly out of the material as vapor through the pores now open. This has the consequence that the gas phase (steam-air mixture) expands. The escape of steam enables further water still in liquid form to evaporate. Both effects (expansion of the gas phase and evaporation of water) draw energy from the environment, which leads to a rapid cooling which occurs directly in the interior of the material plate. In addition, a rapid drying takes place, so that only a small residual amount of moisture is still present in the plate at the end of the pressing process. In conventional methods, the material vaporizes slowly over the entire pressing course and, if appropriate, a controlled, slow relief (and thus a slow cooling) takes place only at the end of the pressing method in order to prevent the plate which is still quite soft in this phase from bursting. However, it has been recognized that the rapid escape of steam is possible even without damage to the plate if it is already effected at an early stage of the pressing operation, i.e. if the pressing operation is continued during and after the strong steam escape (with reduced pressure) and the plate is thus still "held in shape" by the press during the steam escape. In this way, the plate can be "stabilized" in such a way that significantly fewer binders can be used or that even binders can be dispensed with completely.In principle, the pressure and the gap width are two variables which can be directly connected together during a pressing operation and can influence one another. In the event of a change in one of these two variables, the other of these two variables can therefore also change. If, for example, a "pressure reduction" takes place, this can entail a geometric opening of the press nip (=increase in the nip width); regardless of whether this process takes place in a pressure-controlled or distance-controlled manner by regulation technology.According to one embodiment of the method, it is provided that during step c) a lowering of the contact pressure acting on the material takes place at a speed of at least 100 N / cm 2 s, in particular at least 200 N / cm 2 s. According to this embodiment, it is provided that during step c), i.e. during the pressing process, a rapid lowering of the contact pressure acting on the material takes place. The minimum speeds of the pressure reduction to be maintained here ensures that very rapid cooling and drying takes place, which on the one hand triggers the processes described above and on the other hand can reduce the process duration and thus increase productivity.According to a further embodiment of the method, it is provided that during step c) the pressure of the press cylinders is lowered from a working pressure to a holding pressure, wherein the pressure of the press cylinders is lowered by at least 15 bar, in particular by at least 30 bar, preferably by at least 60 bar. As has already been explained above, the contact pressure acting on the material can be lowered, for example, by the pressure prevailing in the press cylinders being lowered in a corresponding manner, as a result of which the same effects--described above--occur.In a further embodiment, the method provides that during step c) the pressure of the press cylinders is reduced at a speed of at least 10 bar / s, in particular at least 15 bar / s. The aforementioned rapid lowering of the contact pressure acting on the material can be achieved, for example, by a correspondingly rapid lowering of the pressure in the press cylinders.According to a further embodiment of the method, it is provided that during step c) an increase of the gap width takes place which lies in the range between +2% and +20%, in particular between +4% and +15%, of the gap width. The gap width can increase during step c), i.e. during the pressing process, because the contact pressure acting on the material is reduced. The reduced pressure and the increased gap width result in the compressed material being able to expand somewhat again. Since the enlargement of the gap width is limited, even with an enlarged gap width, the contact between the material and the two pressing devices-i.e. the upper and the lower pressing device-is maintained, so that the pressing process can be continued or does not have to be interrupted.A further embodiment of the method provides that during step c) the temperature in the material is lowered by at least 20° C., in particular at least 30° C., preferably at least 40° C. The temperature present in the material is measured in the middle of the plate, i.e. it is measured at a plate thickness of 10 mm, for example at a "height" of 5 mm. This can be effected, for example, by a measuring wire introduced into the material for test purposes. Since a significant cooling and drying of the material takes place already in step c), that is to say already during the pressing operation, as a result of the emergence of steam, the time required after completion of the pressing operation is shortened in order to lower the temperature even further and to dry the material even further.In a further embodiment of the method, it is provided that during step c) a lowering of the temperature in the material takes place at a speed of at least 10° C. / s, in particular at least 20° C. / s, preferably at least 30° C. / s. According to this embodiment, it is provided that during step c), i.e. during the pressing process, a rapid lowering of the material temperature is achieved. The minimum cooling rates to be maintained here ensure that the process time can be reduced, which increases productivity.According to one embodiment of the method, it is provided that during step d) the temperature in the material is increased to at least 130° C., in particular at least 150° C., preferably at least 180° C. Due to the temperatures in the middle of the board that are unusually high-lying clearly above 100° C.-for the production of wood material boards, the natural constituents of the wood (e.g. lignin, starch, sugar) can be activated and utilized particularly effectively. The passage through a high-temperature phase can therefore make a substantial contribution to improving the mechanical properties of the sheets to be produced.A further embodiment of the method provides that during step d) the temperature in the material rises strictly monotonically for at least 20 seconds, in particular at least 30 seconds. As during step d), i.e. during the heating of the material, the temperature continues to rise over a minimum period of time, the thermal and / or chemical processes occurring in the material can proceed without interruptions and thus the desired results can be reliably achieved.According to a further embodiment of the method, it is provided that the temperature in the material is at least 10 seconds, in particular at least 20 seconds 150° C. or more, in particular 180° C. or more. By maintaining a minimum duration for the high-temperature phase, it is ensured that the thermal and / or chemical processes occurring in the material can proceed as completely as possible.With regard to the press used in the method, it is proposed that in step b) a cyclically operating press is provided, wherein the upper pressing device is formed by a plurality of press cylinders and an upper heating plate, and wherein the lower pressing device is formed by a lower heating plate. A cyclically operating press is understood to mean a press in which the material to be processed is not continuously moved, but rather is moved cyclically (i.e. is temporarily stationary). The cyclically operating press is first opened in order to introduce the material to be pressed into the press. Thereafter, the press is closed to press the material. The press is then opened again in order to remove the plate just produced from the press. The material for the next plate to be produced can then be placed in the press and the steps mentioned repeated. Cyclically operating presses with one "floor" or with several "floors" can be used. A cyclically operating press is illustrated by way of example in FIG. 2 and is described in conjunction with FIG. 2.With regard to the press used in the method, it is alternatively proposed that in step b) a continuously operating press is provided, wherein the upper pressing device is formed by a plurality of press cylinders, an upper heating plate, an upper steel strip and upper rolling rods, wherein the lower pressing device is formed by a lower heating plate, a plurality of pressure distribution plates, a lower steel strip and lower rolling rods, wherein the steel strips are mounted in a revolving manner around rollers in such a way that the gap for receiving the material is formed between the steel strips, and wherein the rolling rods are mounted in a revolving manner around rollers in such a way that they are arranged between the steel strips and the heating plates and allow a relative movement between the steel strips and the heating plates. A continuously operating press is understood to mean a press in which the material to be processed is continuously moved, i.e. does not rest in any method step-even during the pressing of the material. A continuous press is shown by way of example in FIG. 1 and is described in connection with FIG. 1.According to a further embodiment of the method, it is provided that in step a) the wood material is provided in multilayer form, in particular in 3-ply, 5-ply or 7-ply form, in particular with at least one middle layer, at least one lower cover layer and at least one upper cover layer. The different layers or layers of the material can differ, for example, by the constituents (chips, fibers), the size of the constituents (small chips, large chips), by the density and / or by the moisture. In this way, the mechanical properties of the plate to be produced can be optimized. For example, it can be provided that the middle layer (less relevant for the bending strength) is made less dense and thus "lighter" by the use of coarser chips than the cover layers (more relevant for the bending strength) which are made more dense by the use of finer chips. It can also be provided that the moisture of the outer layers (i.e. of the surfaces) is greater than the moisture of the middle layer.According to a further embodiment of the method, it is provided that in step a) a wood material with a moisture content in the range between 2% ATRO and 40% ATRO, in particular between 5% ATRO and 30% ATRO, particularly preferably between 10% ATRO and 25% ATRO, is provided. With a moisture content within the above-mentioned limits optimum results have been obtained.According to a further embodiment of the method, it is provided that in step a) a wood material with a binder content of less than 15%, in particular less than 10%, preferably in the range between 0% and 6%, is provided. By the procedure it is possible to produce wood material boards with a very low binder content ("low-glue" boards) or even free from binders (0% binder content: "glueless" boards). This is possible by the combination of several measures, in particular by the use of high temperatures (utilization of the properties of lignins, the natural "adhesives" in wood) and by the rapid cooling and by the stabilizing holding pressure. For this configuration, it is further proposed that glue and / or bio glue be used as binder. Glues and bio-glues are very well-proven and powerful binders in wood materials.A further embodiment of the method provides that in step a) fine wood chips for producing flat press boards and / or long chips for producing coarse particle boards or OSB boards are provided. By selecting the type of chips and their length, the type of plate to be produced and their mechanical properties can be determined.According to a further embodiment of the method, it is provided that in step a) wood fibers for producing wood fiber boards are provided, for example medium-density wood fiber boards or MDF boards or high-density wood fiber boards or HDF boards, wherein the wood fiber boards produced preferably have smooth surfaces on both sides. By selecting the type of fibers and their length, the type of plate to be produced and their mechanical properties can also be determined. The wood fibre boards produced in this way differ in the smooth surfaces on both sides from wood fibre boards produced according to a wet process, since such wood fibre boards do not have smooth surfaces but rather have a lattice-like impression caused by the screen fabric.The invention is explained in more detail below with reference to a drawing which represents only a preferred exemplary embodiment. In the drawing, the following are shown: FIG. 1 : shows a continuously operating press known from the prior art for producing a wood material board for carrying out the method according to the invention, FIG. 2 : shows a cyclically operating press known from the prior art for producing a wood material panel for carrying out the method according to the invention, and FIG. 3 : shows a diagram with the parameters of the method according to the invention.FIG. 1 shows a continuously operating press 1 known from the prior art for producing a wood material board for carrying out the method according to the invention. The press 1 is a continuous press which comprises two endless revolving steel belts 2, namely an upper steel belt 2A and a lower steel belt 2B. The steel strips 2 are guided around a plurality of rollers 3, at least one roller 3A of which has a drive 4 (for example an electric motor) per steel strip 2 in order to drive the rollers 3 and the steel strips 2 (the direction of movement of the steel strips 2 is marked with arrows in FIG. 1 ). The steel strips 2 are arranged in such a way that a gap 5 is formed between the upper steel strip 2A and the lower steel strip 2B, which gap extends from the inlet 6 of the press 1 to the outlet 7 of the press 1. The gap 5 has a variable gap width 8 and serves to receive the wood material to be processed and to guide it through the press 1 along a transport direction TR. The gap 5 can be divided along the transport direction TR into a narrowing section ("inlet" of the press, gap width 8 decreases), a parallel section (gap width 8 remains approximately constant) and an widening section ("outlet" of the press, gap width 8 increases).The press 1 has a plurality of vertically running frame elements 9, which are connected to one another via stiffening beams 10 running along the transport direction TR. The frame elements 9 have recesses 11 through which the steel strips 2 can be passed. The press 1 also has in its upper region a plurality of hydraulic press cylinders 12 which can transmit pressing forces via the steel belts 2 to the material. The press cylinders 12 are mounted on the frame elements 9, for example in the recesses 11 of the frame elements 9. numerous press cylinders 12 are provided along the transport direction TR, whereby the pressure can be set very precisely-and differently along the transport direction TR. In addition, it can be provided that a plurality of press cylinders 12 are arranged next to one another transversely to the transport direction TR (concealed in FIG. 1 ) in order to achieve a uniform pressure distribution in the transverse direction. In the press 1 shown in FIG. 1, press cylinders 12 are arranged only above the gap 5; in contrast, pressure distribution plates 13 are provided below the gap 5, which are likewise mounted on the frame elements 9, for example in the recesses 11 of the frame elements 9.In addition, the press 1 has heating plates 14, namely an upper heating plate 14A and a lower heating plate 14B. The upper heating plate 14A is disposed above the gap 5 (e.g., below the press cylinders 12), and the lower heating plate 14B is disposed below the gap 5 (e.g., above the pressure distribution plates 13). The heating plates 14 preferably have numerous bores or channels (not shown in FIG. 1 ), so that a heating or cooling medium (e.g. oil) can flow through the heating plates 14 in order to be able to set the desired temperature. The heating plates 14 also have sufficient flexibility, so that the width of the gap 5 along the transport direction TR can be variably adjusted by the press cylinders 12 elastically deforming the heating plates 14 (slightly). Between the steel belts 2 and the heating plates 14 there are arranged rolling bars 15 which are connected to one another and form an endless "rolling bar carpet" which rotates around rollers 16. The rolling rods 15 can be divided into upper rolling rods 15A and lower rolling rods 15B, the upper rolling rods 15A being disposed above the gap 5 and inside the upper steel strip 2A, and the lower rolling rods 15B being disposed below the gap 5 and inside the lower steel strip 2B. The rolling rods 15, like a needle bearing, allow a low-friction relative movement between the steel strips 2 (moving in the transport direction TR) and the heating plates 14 (not moving in the transport direction TR) and the components connected thereto (e.g. the press cylinders 12 or the pressure distribution plates 13). Preferably, the rolling rods 15 roll off in a driveless manner between the steel belts 2 and the heating plates 14, while they transfer the pressing pressure and the thermal energy.In the region of the inlet 6, the press 1 has a plurality of inlet rollers 17 which are mounted in an adjustable manner and can act on the steel strips 2 in order to change the geometry of the inlet 6 and to adapt it to different applications. Unlike the illustration in FIG. 1, frame elements 9 with press cylinders 12 can optionally also be arranged in the region of the inlet 6 of the press 1. A continuously operating press is known, for example, from DE 10 2017 110 882 B4.The press 1 shown in FIG. 1 has an upper pressing device 1A and a lower pressing device 1B, which are separated from one another by the gap 5, but are nevertheless connected to one another by the frame elements 9. The upper pressing device 1A includes the upper steel belt 2A, the upper rolling bars 15A, the upper heating plate 14A, and the press cylinders 12.FIG. 2 shows a cyclically operating press 1' known from the prior art for producing a wood material board for carrying out the method according to the invention. Those features of the press which have already been described in connection with FIG. 1 are provided with corresponding reference numerals in FIG. 2. The essential difference from the continuously operating press 1 shown in FIG. 1 is that the material to be processed by the press is not moved forward during the pressing operation in the case of the cyclically operating press 1' from FIG. 2, but rests. Therefore, the press 1' from FIG. 2 also has no revolving steel belts 2 and no revolving rolling rods 15. Nevertheless, it has also proved advantageous in a cyclically operating press 1' to introduce the material from one side (inlet 6) into the gap 5 of the press 1' and--after the pressing operation has taken place--to remove the produced material plate again from the gap 5 of the press 1' from the opposite side (outlet 7). Thus, also in the case of the cyclically operating press 1' there is a (preferred, although not obligatory) "transport direction" TR.Since neither steel strips 2 nor roll bars 15 are present, in the press 1' shown in FIG. 2, a direct contact is produced between the two heating plates 14 (i.e. the upper heating plate 14A and the lower heating plate 14B) and the material to be processed during the pressing process. As in the case of the press 1 in FIG. 1, the pressing forces are also generated in the case of the press 1' in FIG. 2 by press cylinders 12, which can also bring about a change in the gap width 8. The press 1' of FIG. 2 also has a plurality of vertically extending frame elements 9, which are connected to one another via stiffening beams 10. The frame elements 9 have recesses 11 which serve, for example, to be able to pass the two heating plates 14 through the frame elements 9. A cyclically operating press is known, for example, from DE 20 2012 104 004 U1.The press 1' shown in Fig. 2 also comprises an upper pressing device 1A' and a lower pressing device 1B', which are separated from each other by the gap 5, but are nevertheless connected to each other by the frame elements 9. The upper pressing device 1A' comprises the upper heating plate 14A and the pressing cylinders 12.FIG. 3 shows a diagram with selected parameters of the method according to the invention. The method can be carried out, for example, on the press 1 shown in FIG. 1 or on the press 1' shown in FIG. 2. The time t is shown on the first (horizontal) axis in FIG. 3 (unit: minutes, seconds). On the second (vertical) axis, several parameters are shown in FIG. 3 : First, the second axis shows the temperature T (unit: ° C.), by which the temperature T in the material (in the middle of the material plate) is meant. The temperature T can be measured, for example, by wires which are inserted into the material for measurement purposes. The second axis also shows the pressure P (unit: bar), by which is meant the pressure P prevailing in the press cylinders 12 of the press 1, 1'. The pressing force exerted by the press cylinders 12 corresponds approximately to the contact force acting on the material because of the third Newton's law ("force equal to counter force"). Nevertheless, the contact pressure differs from the pressure in the press cylinders, since the two pressures act on active surfaces of different sizes; the factor can be different from press to press. The third (vertical) axis finally shows the gap width 8 (unit: mm), that is to say the distance between the steel strips 2 (FIG. 1 ) or between the heating plates 14 (FIG. 2 ).The parameter profiles illustrated in FIG. 3 are explained below in chronological order. A first time t 1 denotes the time of the beginning of the pressing process. This point in time is defined as the point in time at which a pressure P (legend in FIG. 3 : "pressure") reaches or exceeds a value of 1 bar for the first time. The pressure P rises very rapidly and reaches or exceeds a pressure of 100 bar at a second time t 2. The increase in the pressure P has the immediate consequence that the gap width 8 (legend in FIG. 3 : "distance") decreases until the gap width 8 reaches a value of approximately 2.2 mm at a third point in time t 3. A working pressure P A is set, which lies approximately in the range between 100 bar and 115 bar, and is kept as constant as possible. Since the heating plates 14 are heated (legend in FIG. 3 : "heating plate temperature at the top" approximately 250° C.), the temperature T in the material (legend in FIG. 3 : "MT 2" and "MT 4") rises on contact with the heating plates 14 starting from an initial temperature T A( e.g. room temperature; here approximately 30° C.) and approaches the temperature of the heating plates 14 up to a maximum value T max of approximately 230° C. Due to temperature-induced effects, a variance occurs about the desired setpoint pressure value, which, however, rapidly decreases upon oscillation about the desired value.At a fourth time t 4 the pressure P is 100 bar and is rapidly lowered until the pressure P reaches a pressure P of 20 bar at a fifth time t 5. The rapid pressure drop between the fourth time t 4 and the fifth time t 5 results in the gap width 8 being slightly increased (to approximately 2.5 mm); nevertheless, the contact between the press and the material is maintained, since the gap width 8 is only slightly increased and the compressed and not yet fully consolidated material expands again as far as the gap width 8 permits as a result of the reduced pressure.The pressure and temperature drops take place in a controlled manner, wherein the pressure P is lowered from the working pressure P A to a holding pressure P H which is about 20 bar or below and wherein the temperature T drops from the maximum temperature T max to a holding temperature T H which is about in the range of 180° C. The pressing process is ended at a sixth point in time t 6, which (analogously to the first point in time t 1) defines as the point in time at which a pressure P reaches or falls below a value of 1 bar again.The pressing process thus begins at the first time t 1 and ends at the sixth time t 6. The pressing process can be divided simply into four phases: a pressure increase phase (first time t 1 to second time t 2), a high pressure phase (second time t 2 to fourth time t 4), a pressure decrease phase (fourth time t 4 to fifth time t 5) and a holding phase (fifth time t 5 to sixth time t 6). Of particular interest in this case is the pressure reduction phase, which, in the case of the sequence illustrated in FIG. 3, takes about 4 seconds (t 4 to t 5) for example, the pressure being reduced by about 80 bar. The pressure drop is accordingly about 20 bar per second. As a result of the rapid pressure reduction, the temperature in the material also falls rapidly (although slightly offset in time). The temperature drop takes about 1.5 seconds, with the temperature dropping by about 50°C (T max → T H). The temperature drop is thus about 33° C. per second.Alternatively, the method may be divided into the phases of "heating", "cooling by controlled pressure relief", and "consolidation". Referring to FIG. 3, the "heating" phase begins as the temperature T rises from the initial temperature T A and ends at the beginning of the pressure drop (fourth time t 4). The second phase "cooling by controlled pressure relief" follows immediately after this, i.e. it begins at the beginning of the pressure drop (fourth time t 4) and, for example when the holding temperature T H is reached or when the holding pressure P H( is reached, the fifth time t 5) passes over into the third phase "consolidation".List of reference numbers:1, 1' Press 1A, 1A' Upper press device 1B, 1B' Lower press device 2 Steel strip 2A Upper steel strip 2B Lower steel strip 3, 3A Roller (for steel strip 2) 4 Drive 5 Gap 6 Inlet 7 Outlet 8 Gap width 9 Frame element 10 Reinforcing carrier 11 Recess 12 Press cylinder 13 Pressure distribution plate 14 Heating plate 14A Upper heating plate 14B Lower heating plate 15 Rolling rod 15A Upper rolling rod 15B Lower rolling rod 16 Roller (for rolling rod carpet) 17 Inlet roller TR Transport direction t Time t 1- t 6 Time T Temperature T A Initial temperature T H Holding temperature T max Maximum temperature P Pressure P A Working pressure P H Holding pressure P K Contact pressureReferences included in the specificationThis list of documents cited by the applicant has been produced in an automated manner and is only included for the better information of the reader. The list is not part of the German patent application or utility model application. The DPMA does not take any adhesion for any faults or omissions.Patent Literature citedDE 10 2017 110 882 B4

[0041] DE 20 2012 104 004 U1

[0044]

Claims

Method for producing a material panel, in particular a wood material panel, from a material, comprising the following steps: a) providing at least one layer of a material, in particular a material which contains wood chips and / or wood fibres, b) providing a press (1, 1') comprising: - an upper pressing device (1A, 1A') and a lower pressing device (1B, 1B') between which a gap (5) for receiving the material is formed, - wherein the upper pressing device (1A, 1A') and / or the lower pressing device (1B, 1B') has hydraulic press cylinders (12) which have the gap width (8) between the upper pressing device (1A, 1A') and the lower pressing device (1B, 1b') and being able to change pressing forces and to transmit pressing forces to the material, and - wherein the upper pressing device (1A, 1A') and / or the lower pressing device (1B, 1B') has a heating device, in particular a heating plate (14A, 14B), which are able to transmit heat at least indirectly to the material, c) pressing the material in the gap (5) between the upper pressing device (1A, 1A') and the lower pressing device (1B, 1B'), d) heating the material in the gap (5) between the upper pressing device (1A, 1A') and the lower pressing device (1B, 1B'), - wherein steps c) and d) take place at least partially simultaneously, characterized in that, the contact pressure (P K) acting on the material is lowered during step c) to a contact pressure (P K) which is in the range between 10 N / cm 2 and 150 N / cm 2, in particular between 30 N / cm 2 and 100 N / cm 2.Method according to Claim 1, characterized in that the pressure (P) of the press cylinders (12) is lowered during step c) from a working pressure (P A) to a holding pressure (P H) which is in the range between 5 bar and 40 bar, in particular between 10 bar and 30 bar.Method according to claim 1 or claim 2, characterised in that the lowered contact pressure (P K) and / or the lowered holding pressure (P H) is held for at least 10 seconds, in particular for at least 20 seconds.Method according to one of Claims 1 to 3, characterized in that the temperature (T) is lowered from a maximum temperature (T max) to a holding temperature (T H) which is in the range between 120°C and 220°C, in particular between 140°C and 180°C.Method according to one of Claims 1 to 4, characterized in that the holding temperature (T H) is held for at least 10 seconds, in particular for at least 20 seconds.Method according to one of Claims 1 to 5, characterized in that during step c) the contact pressure (P K) acting on the material is lowered, the contact pressure (P K) being lowered by at least 50 N / cm 2, in particular by at least 100 N / cm 2, preferably by at least 200 N / cm 2.Method according to one of Claims 1 to 6, characterized in that during step c) the contact pressure (P K) acting on the material is lowered at a speed of at least 100 N / cm 2 s, in particular at least 200 N / cm 2 s.Method according to one of Claims 1 to 7, characterized in that during step c) the pressure (P) of the press cylinders (12) is lowered from a working pressure (P A) to a holding pressure (P H) wherein the pressure (P) of the press cylinders (12) is lowered by at least 20 bar, in particular by at least 40 bar, preferably by at least 60 bar.Method according to one of Claims 1 to 8, characterized in that during step c) the pressure (P) of the press cylinders (12) is lowered at a speed of at least 10 bar / s, in particular at least 15 bar / s.Method according to one of Claims 1 to 9, characterized in that during step c) the gap width (8) is increased, which is in the range between +2% and +20%, in particular between +4% and +15%, of the gap width (8).Method according to one of Claims 1 to 10, characterized in that during step c) the temperature (T) in the material is lowered by at least 20°C, in particular at least 30°C, preferably at least 40°C.Method according to one of Claims 1 to 11, characterized in that during step c) the temperature (T) in the material is lowered at a speed of at least 10°C / s, in particular at least 20°C / s, preferably at least 30°C / s.Method according to one of Claims 1 to 12, characterized in that during step d) the temperature (T) in the material is increased to at least 130°C, in particular at least 150°C, preferably at least 180°C.Method according to one of Claims 1 to 13, characterized in that during step d) the temperature (T) in the material rises strictly monotonically for at least 20 seconds, in particular at least 30 seconds.Method according to one of Claims 1 to 14, characterized in that the temperature (T) in the material is at least 10 seconds, in particular at least 20 seconds 150°C or more, in particular 180°C or more.Method according to one of Claims 1 to 15, characterized in that in step b) a cyclically operating press (1') is provided, - wherein the upper pressing device (1A') is formed by a plurality of press cylinders (12) and an upper heating plate (14A), and - wherein the lower pressing device (1B') is formed by a lower heating plate (14B).Method according to one of Claims 1 to 15, characterized in that in step b) a continuously operating press (1) is provided, - wherein the upper pressing device (1A) is formed by a plurality of press cylinders (12), an upper heating plate (14A), an upper steel strip (2A) and upper rolling rods (15A), - wherein the lower pressing device (1B') is formed by a lower heating plate (14B), a plurality of pressure distribution plates (13), a lower steel strip (2B) and lower rolling rods (15B), - wherein the steel strips (2A, 2B) are mounted in a manner such that they circulate around rollers (3, 3A) in such a way that the gap (5) for receiving the material forms between the steel strips (2A, 2B), and - wherein the rolling rods (15A, 15B) are mounted so as to be encircling rollers (16) in such a way that they are arranged between the steel strips (2A, 2B) and the heating plates (14A, 14B) and enable a relative movement between the steel strips (2A, 2B) and the heating plates (14A, 14B).The process according to any of claims 1 to 17, wherein in step a) the wood material is provided in multilayer form, in particular in 3-ply, 5-ply or 7-ply form, in particular having at least one middle layer, at least one lower outer layer and at least one upper outer layer.Method according to one of Claims 1 to 18, characterized in that in step a) a wood material having a moisture content in the range between 2% ATRO and 40% ATRO, in particular between 5% ATRO and 30% ATRO, particularly preferably between 10% ATRO and 25% ATRO, is provided.Method according to one of Claims 1 to 19, characterized in that in step a) a wood material is provided with a binder content of less than 15%, in particular less than 10%, preferably in the range between 0% and 6%.Method according to claim 20, characterised in that glue and / or bio glue are used as binder.Method according to one of Claims 1 to 21, characterized in that, in step a), fine wood chips for producing flat pressed boards and / or long chips for producing coarse particle boards or OSB boards are provided.Method according to one of Claims 1 to 22, characterized in that wood fibres for producing wood fibre boards, for example medium-density wood fibre boards or MDF boards or high-density wood fibre boards or HDF boards, are provided in step a), wherein the wood fibre boards produced preferably have smooth surfaces on both sides.

Images