EP3470191A1 - Method and device for manufacturing a wood composite board - Google Patents

Abstract

The invention relates to a method for producing a wood-based panel (2), the method comprising the following steps:
(a) spreading a plurality of wood particles into a particle cake,
(b) applying adhesive to at least some of the wood particles during spreading and / or before spreading,
(c) pressing the particle cake under elevated pressure and elevated temperature,
wherein an amount of adhesive applied to the wood particles varies depending on their expected position in the particle cake.

Description

The invention relates to a method for producing a wood-based panel, the method comprising the following steps: (a) spreading a plurality of wood particles into a particle cake, (b) applying adhesive to at least some of the wood particles during spreading and / or before spreading, (c) pressing the particle cake under elevated pressure and elevated temperature. The invention also relates to an apparatus for carrying out such a method.

Wood-based panels are used in a wide variety of technological areas. For example, they are used for floors, wall coverings, furniture or in structural timber construction.

Wood materials and in particular wood-based panels have a core of wood particles and usually some glue. As wood particles in particular wood strands, wood chips and wood fibers are used. They are usually pressed in a continuous or in a clocked process under the action of heat and pressure, the so-called hot pressing, to plates or at least to the core.

Due to their diverse fields of application, wood-based panels must be able to withstand a wide variety of loads and stresses and meet these requirements. This applies, for example, to point loads or surface loads, for example when the panels are used as furniture panels, doors or floor elements.

Usually wood-based panels are made such that they over the entire size of the plate uniform and very constant properties, such as have bulk density or resistance to shock loads or deflections.

The bulk density is the ratio between mass and volume of the wood-based panel and is, inter alia, a parameter for the strength of a wood-based panel. The higher the bulk density, the greater is generally the strength of a wood-based panel. Today's wood-based panels have, for example, a density of 620 kg / m ³ to 650 kg / m ³ in particleboard, 600 kg / m ³ to 650 kg / m ³ in OSB and 700 kg / m ³ in MDF.

Depending on the intended use, wood-based panels must withstand very different loads. These loads are not constant over the entire surface of the wood-based panel, for example, when used as a furniture panel or door leaf. In the field of fishing, a door leaf must withstand significantly higher loads than in the remaining area of the door leaf. The same applies to cabinet doors or shelves, in which very high loads are to be expected, especially in the area of small contact surfaces.

If the use and in particular the orientation of the wood-based panel is known, the bulk density can be made lower in low-load areas, which leads to a lower board weight and a material saving. Such a method is for example from the EP 2 653 279 A1 known, in which particles are removed from a falling particle curtain. Also the WO 2005/046950 A1 describes a method and a corresponding device with which fewer particles are used in certain areas of the wood-based panel in order to reduce the bulk density in these areas. The reduction of the scattered particles in a range, however, limits are set, since a sufficient amount of particles is needed to produce no depression or dent in the wood-based panel to be produced.

The individual adjustment of certain properties of wood-based panels is also from the EP 2 623 282 A1 which describes a method for impregnating material plates, in which an impregnating medium is already pressed into an impregnating medium Wood material board is introduced. So the edge areas are to be impregnated and in the middle layers no impregnation medium can be used.

The object of the present invention is to provide a method for producing a wood-based panel which has a different density in different areas, wherein the method is less expensive and further reduces manufacturing costs.

The invention achieves the object by a method according to the preamble of claim 1, which is characterized in that an amount of adhesive which is applied to the wood particles varies depending on their expected position in the particle cake.

In this way, on the one hand, the amount of adhesive can be reduced, which for example reduces the emission of volatile adhesive constituents, and on the other hand, the bulk density in these areas can be further reduced, without the scattered amount of particles must be reduced. The amount of adhesive applied varies depending on the expected position of the particles to be glued with the adhesive. It can thus vary along the thickness of the wood-based panel and / or in a plane parallel to the surface of the wood-based panel.

Preferably, the wood particles are only provided during spreading with an adhesive. The particles leave a spreader or a conveyor and are glued in falling by the adhesive is sprayed by at least one Beleimdüse on the falling particles. The amount of adhesive applied is varied depending on the expected position within the particle cake. In the course of the production process of such a particle cake, therefore, the amount of adhesive discharged by the at least one Beleimdüsen also varies. This can be achieved by changing the application rate of at least one nozzle and / or by changing the number of spray nozzles.

Particularly preferably, some, in particular all wood particles are pre-glued prior to sprinkling with a preferably constant amount of adhesive. The pre-glued wood particles are then scattered to a particle cake. at The sprinkling of the pre-glued wood particles is then applied in varying amounts on all or only some wood particles. For this purpose, the already pre-glued and / or unembellished wood particles are conducted past, for example, in a stream of air at the at least one Beleimdüse, which apply, for example programmatically different amounts of adhesive.

The adhesives used are, in particular, urea-formaldehyde resins, melamine or phenolic resins. Preferably, they are isocyanates, such as polymeric diphenylmethane diisocyanate (PMDI), which is in particular formaldehyde-free.

Preferably, the method comprises introducing one or more additives into the particle cake during spreading. The addition of additives can in particular affect other properties of the wood-based panel. Such additives include, in particular, fire-retardant substances, biocidal substances, substances for swelling of wood, substances which influence the optical and / or haptic appearance of the later wood-based panel, the thermal conductivity or electrical conductivity-changing substances, as well as foaming agents and already foamed substances.

Preferably, the at least one additive contains at least one filler, such as chalk, talc, quartz powder, glass beads, expanded glass or expanded clay, at least one optical brightener, such as titanium dioxide, calcium carbonate or fluorescent organic substances, at least one fire-retardant substance, at least one biocidal substance, at least one substance for swelling of wood, at least one foaming agent and / or at least one substance which alters an optical and / or haptic and / or a physical property of the wood-based panel, for example its thermal conductivity.

In addition, the additives may be primers, for example based on silanes or other adhesion promoters. In particular, these improve the adhesion of different glue systems or different layers to one another. In addition, it is also possible to apply substances that are in themselves form an intermediate layer and thus avoid mixing of individual other layers. For example, it can be prevented or made more difficult for chipboard particles that relatively thin outer layers migrate into a coarser middle layer.

In addition to or instead of the introduction of additives, it is also possible to enter energy, for example in the form of heat or radiation energy. As a result, for example, adhesive reactions of multicomponent adhesives or reactions of or with additives can be specifically triggered or influenced. Furthermore, it is possible to introduce moisture, for example by treatment with steam, in the particle cake.

Preferably, different amounts of additives are introduced at different positions within the particle cake. In this way, the leg-fluent properties can be developed in different areas, or can develop or vary to different degrees. Preferably, different additives and / or different amounts of different additives are introduced to different positions within the particle cake.

The one or more additives are introduced in particular via separate introduction devices, such as nozzles. This happens in particular not only during the scattering, but can also happen if no wood particles are scattered.

At least one additive is preferably a further adhesive or an adhesive component. In the context of the present invention, the application of adhesive also means, for example, the application of one or more adhesive components, it being possible for this to occur in varying amounts or for other adhesive components to be applied in varying amounts.

Preferably, an amount of wood particles that are scattered to the particle cake, depending on their expected position in the particle cake varied. This makes it possible in particular, by the choice of different large scattered amounts of wood particles, further influence on the bulk density within the particle cake and thus in particular to take the strength.

The invention also achieves the object by a device for carrying out a method described here, which has an electrical control which is set up to vary an amount of adhesive to be applied to the wood particles as a function of their expected position in the particle cake.

The electrical control preferably has an electronic data processing device which is set up to access information stored in an electronic data memory and to vary the quantity of adhesive to be applied on the basis of this information. This can be done by controlling one of the at least one nozzle supplied amount of adhesive and / or can be achieved by opening and closing of nozzles.

Preferably, the device has at least one Beleimdüse, more preferably several Beleimdüsen. Preferably, the at least one Beleimdüse is movable, in particular transversely to a transport direction of a conveyor belt, on which the wood particles are scattered formed.

In a particularly preferred embodiment, the expected position of the wood particles is determined or determinable on the basis of a position of the scattering nozzle which scatters the wood particles. This is independent of whether such a scattering nozzle is designed to be movable or stationary relative to the particle cake. Whether the adhesive is applied to the wood particles before spreading or only during spreading is preferably dependent on the type of adhesive. For adhesives with a particularly low dripping time, for example, it is advantageous to apply them only during spreading.

It is also possible that the expected positions of the wood particles in the particle cake are determined or calculated during scattering. For this purpose, for example, a measuring device is arranged on the device. This can for example, a high-speed camera or the like. In this case, it is advantageous if the adhesive is applied during scattering.

Preferably, the device has a conveyor belt, which is movable in a transport direction, wherein the at least one scattering nozzle is arranged above the conveyor belt and is adapted to scatter the wood particles onto the conveyor belt. Advantage of such a conveyor belt is in particular that the wood-based panels or the particle cake can be made continuously. However, it is also possible by means of a conveyor belt, that the wood-based panels are made clocked, for example.

The expected position of the wood particles in the particle cake is preferably calculated on the basis of the position of the corresponding scattering nozzle, in particular with respect to the particle cake to be scattered, which scatters the wood particles. In this case, a transport speed of the conveyor belt is preferably included.

Preferably, the at least one Beleimdüse is arranged above the conveyor belt and adapted to apply adhesive to the wood particles during scattering. Preferably, in this case one, in particular a plurality of Beleimdüsen arranged in a Beleim-scattering head, so that this Beleim scattering head can be moved in particular as a whole, without changing an orientation or position of the Beleimdüsen and the scattering nozzles to each other.

Preferably, a plurality of scattering nozzles and / or a plurality of Beleimdüsen are arranged transversely to the transport direction. In particular, over the entire width of the particle cake or over the entire width of the conveyor belt are arranged. This is advantageous because in particular variable intervals wood particles and / or adhesive can be applied.

Preferably, several Beleimdüsen form a Beleimleiste. It is also possible that at least two such Beleimleisten are combined to form a Beleimkopf. More preferably, at least one Beleimleiste with at least one scattering nozzle, in particular at least one scattering bar from a plurality of scattering nozzles to one Scattering Beleimkopf summarized, of which the device preferably comprises a plurality.

Especially when using movable Beleimdüsen existing devices can be retrofitted and benefit from the advantages of the present invention. In addition, by the mobility, for example, an adaptation of the manufacturing apparatus to different wood-based panels to be produced without much additional effort possible.

Preferably, the electrical control is arranged to vary the amount of wood particles depending on their expected position in the particulate cake.

According to an embodiment of the present invention for producing a 19 mm chipboard, a urea-formaldehyde glue is used as the adhesive. For this purpose, a lower cover layer of wood particles is first scattered onto a conveyor belt by means of wind scattering. Subsequently, a thin layer of foamed urea-formaldehyde glue (20 g fl / m ² , solids content about 50%) is applied by means of a series of Beleimdüsen. With a throwing spread, a middle layer is then applied. In turn, an equal amount of foamed resin is applied to these with Beleimdüsen. By means of wind scattering, an upper cover layer is applied to this. The ratio between cover layer and middle layer is approximately 28 to 72%. The resulting particle cake in the form of a chip cake is pressed into a particle board in a chipboard, then cooled and ground.

In one test, a chipboard was made without the intermediate layers of glue. Both plates were then coated in a short-cycle press with a white decorative paper impregnated with a melamine resin. The paper weight was 65 g / m ² . The plates were then visually inspected in cross-section.

It showed that the chipboard with the glue between the layers had a much more symmetrical structure. Especially between the top Cover layer and the middle layer was observed significantly less surface layer migration into the middle layer than in the comparison plate. When processing the two plates on a router, the plate without glue additive showed more edge breakouts and a messier milling than the test plate.

According to an embodiment of the present invention for producing a 19 mm OSB, MUF size (melamine-urea-formaldehyde glue in the top layer and PMDI size in the middle layer are used.) The ratio between top layer and middle layer is about 30 70%.

First, glued cover layer strands are spread on a conveyor belt. With the aid of a strip of application equipment (nozzle application), a polyethylene glycol (molecular weight: 200 g / mol) is sprayed onto the beach cake in an amount of 5 g / m ² . Then the middle class is scattered. The same amount of polyethylene glycol is again applied to the scattered middle layer with nozzles. This is followed by the scattering of the second covering layer. The beach cake is then pressed in a Contipresse to the OSB.

For comparison, an OSB was co-produced with the same glue systems without polyglycol coating. The plates were tested for their transverse tensile strength after cooling in the laboratory. It showed that the comparison pattern did not tear in the middle, but between the top and middle layers. In addition, the test values were about 20% lower.

Figur 1

eine perspektivische und schematische Schnittdarstellung einer, nach einer Ausführungsform des erfindungsgemäßen Herstellungsverfahrens erhältlichen Holzwerkstoffplatte, und

Figur 2

eine schematische Ablauf-Darstellung des Herstellungsverfahrens.

An embodiment of the invention will be explained below with reference to drawings. Show it

FIG. 1

a perspective and schematic sectional view of a obtainable according to an embodiment of the manufacturing process of the invention wood-based panel, and

FIG. 2

a schematic flow diagram of the manufacturing process.

FIG. 1 is a perspective sectional view of a wood-based panel 2, as it is available according to an embodiment of the manufacturing method according to the invention. Such a wood-based panel has an extension in the x, y and z directions. In the case of the x-direction, this is the extent of the wood-based panel transverse to the longitudinal direction y. The height or thickness of the wood-based panel extends in the z-direction.

In FIG. 1 Sections 4.1 and 4.2 are described with different amounts of adhesive applied. The areas 4.1 are areas with a larger amount of glue. The areas 4.2 are adhesive areas.

FIG. 2 describes schematically the manufacturing process of a wood-based panel, here in particular a wood fiber board.

For this purpose, wood 10 is initially provided. This is preferably forest wood or residual wood, which in particular has been previously debarked. This is processed in a crushing device 12, for example a disc or drum chipper, to wood chips. These chips are fed to a digester 14. In this, the wood chips, possibly with the previous preheating of the wood chips, processed under the action of superheated steam and cleaned. For example, the chips are digested at a temperature of about 170 ° for about 3-4 minutes.

The digestion in the cooker 14 is followed, in particular when it is a fibreboard, by a pulping of the woodchips in the refiner 16. In this, the chips are ground, for example in a disc, cylinder or cone mill and processed into wood fibers.

Subsequently, the especially still wet wood fibers are pre-glued with an adhesive such as urea-formaldehyde resin (UF resins) in a pre-gluing. Preferably, the wood fibers are here, before or after, separated for the later scattering heads over which they are scattered in a later scattering device 24. This has the advantage that the later applied by means of Beleimdüsen adhesive amount, which may also be Nul, depending on an expected position of the wood fiber can be adjusted very easily.

The glued wood fibers are then dried in a dryer 20, for example by means of hot gas, which for example has a temperature of about 160 °, to a certain residual moisture of, for example, 10-15%.
The drying step is followed by a sifting in a sifter 22. As a result, the fibers are separated, for example, due to their particle size or fiber length, their mass or their inertia. This takes place, for example, in a gas stream in a so-called air classifier.

As a result, unsuitable fiber sizes can be sorted out, in particular for further processing. Too large fibers can in this case in particular be added to the comminution process again; too small fibers or pulverized wood particles can be removed from the further process. Alternatively, it is also possible that the sighting is carried out before gluing the wood fibers.

After sifting, the wood fibers are fed to the scattering device 24, which in particular has a plurality, for example at least three Beleimköpfe 26 with Beleimdüsen not shown. Preferably, the spreading device 24 has a conveyor belt, which can be moved in a transport direction. The Beleimdüsen the Beleimköpfe 26 are arranged in particular transversely to this transport direction. Preferably, these Beleimdüsen extend across the entire width of the conveyor belt transversely to the transport direction. Particularly preferably, these are pivotable in at least one, in particular in all spatial directions.

The glue heads 26 are connected to an electrical controller 28 which is adapted to set an amount of adhesive to be applied to the wood particles depending on their position in the particle cake, for example in a plane parallel to the longitudinal direction and the transverse direction.

Preferably, each Beleimkopf 26 a continuous and constant amount of wood particles is scattered, which optionally differs between the individual Beleimköpfen 26. It is also possible, for example, for a Beleimkopfes 26 more spaced apart Beleimdüsen transverse to the transport direction 26 eject larger amounts of adhesive per unit time than other Beleimdüsen this Beleimkopfes 26th

The particle cake resulting from the scattering is precompressed in one or more precompression steps in a supercharger 30. This can be done, for example, continuously or discontinuously, that is, in several separate steps.

To the supercharger is followed by a hot press 32, by means of which the wood-based panel 2 is formed from the precompacted particle cake under the action of temperature and pressure. In the present case, for example, a large-format high density (HDF) or medium density (MDF) wood fiber board is produced.

This can be generated for example by sawing the continuously formed wood-based panel 2 in the transverse direction to the transport direction. These large-format plates are further processed in particular by sawing in the transverse and / or longitudinal direction to a plurality of smaller plates.

LIST OF REFERENCE NUMBERS

2

Wood panel

4.1

Area with larger amount of glue

4.2

Area with reduced bulk density

10

Wood

12

comminution device

14

Stove

16

refiner

18

Vorbeleimungseinrichtung

20

dryer

22

sifter

24

scattering device

26

Beleimkopf

28

control device

30

supercharger

32

hot press

Claims (11)

Method for producing a wood-based panel (2), the method comprising the following steps: (a) spreading a plurality of wood particles into a particle cake, (b) applying adhesive to at least some of the wood particles during spreading and / or before spreading, (c) pressing the particle cake under elevated pressure and elevated temperature, characterized in that
an amount of adhesive applied to the wood particles varies depending on their expected position in the particle cake. A method according to claim 1, characterized in that at least one additive is introduced during the scattering in the particle cake. A method according to claim 2, characterized in that different amounts of additive are introduced to different positions within the particle cake. Method according to one of claims 2 and 3, characterized in that at least one additive is a further adhesive or an adhesive component. A method according to claim 2, 3 or 4, characterized in that the at least one additive At least one filler, such as chalk, talc, quartz powder, glass beads, expanded glass or expanded clay, At least one optical brightener, such as titanium dioxide, calcium carbonate or fluorescent organic substances, At least one fire-retardant substance, At least one biocidal substance, At least one material for the swelling treatment of wood, • at least one frother and / or Contains at least one substance which alters an optical and / or haptic and / or a physical property of the wood-based panel, for example its thermal conductivity. Method according to one of claims 2 to 5, characterized in that different additives and / or different amounts of different additives are introduced to different positions within the particle cake. Method according to one of the preceding claims, characterized in that an amount of wood particles which are scattered to the particle cake, depending on their expected position in the particle cake varies. Apparatus for carrying out a method according to any one of the preceding claims, comprising an electrical control, which is adapted to vary an amount of adhesive to be applied to the wood particles depending on their expected position in the particle cake. Apparatus according to claim 8, characterized in that the electrical control comprises an electronic data processing device which is adapted to access information stored in an electronic data memory and to vary the amount of adhesive to be applied based on this information. Apparatus according to claim 8 or 9, characterized in that it comprises at least one Beleimdüse by which adhesive can be applied to the wood particles, wherein the electrical control is adapted to vary a lot of adhesive that can be applied by the at least one Beleimdüse. Apparatus according to claim 10, characterized in that the at least one Beleimdüse movable, in particular transversely to a transport direction of a conveyor belt, on which the wood particles are scattered, is formed.

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