TECHNICAL FIELD

The present invention relates to a wood chip board in accordance with the introductory portion of claim 1 and a method of manufacturing the wood chip board according to claim 13.

The invention relates to the manufacturing industry for wood chip boards and built up furniture, such as do-it-yourself-kits of wood chip boards. Such wood chip boards are thus used in the manufacturing of furniture. The wood chip board exhibits sections, such as edge areas, central portions etc., which constitute support for other objects in view of fastening or support at the wood chip board, such as shelves, legs, lists, handles, wheels, hinges, hooks, fasteners, screws, bolts, etc., or other structural furniture building parts. Other sections of the wood chip board exhibit portions that are without other objects, where such section of the wood chip board constitutes surface for temporarily stored items, such as clothings, books, paper, porcelain, etc.. Known wood chip boards which may today be used for manufacturing of furniture comprise an upper and a lower layer with wood chips of finer particle size and an intermediate layer with wood chips of coarser particle size. There may also be wood chip boards which are produced with more layers than three. There could be five layers, where a middle layer is produced with the lowest density with coarser wood chips, and the layers lying on the outside of the middle layer on the inside of the surface layers exhibit somewhat finer wood chips, for the sake of strength. The surface layers are produced with fine wood chips in order to achieve satisfactory surface smoothness. Said types of wood chip boards are produced under pressure and heat with glue as binding agent. The wood chips are of wood and can be constituted by, for example, knife-cut chippings from roundwood, sawdust, or chip shavings. An example of such a board is shown in WO 2005/023499 A1.

Today, the intermediate layer is produced with a density of about 650-700 kg/m ³ , and the wood chips in the intermediate layer are thus coarser than the wood chips in the upper and lower surface layers. These coarser wood chips are glued loosely to each other so that the intermediate layer exhibits relatively large air pockets. However, when cutting a board with such an intermediate layer, a "frayed" surface is exposed in the cut-surface to which it may be difficult to fasten an edging. This is an obvious problem with such an intermediate layer exhibiting wood chips which are glued loosely to each other, which layer exhibits, as it is, a relatively low density.

Also, it is desired to further reduce the use of wood chips for the manufacturing of wood chip boards for furniture. The costs of transportation and also the costs of chippings will be reduced. At the same time this is lenient on the environment.

It is also desired to reduce the costs of the manufacturing of such wood chip boards.

BACKGROUND

Today, in view of the stringent environmental requirements and desired cost- efficiency in the manufacturing, in terms of material consumption, pressing times, etc., it is sought to provide a wood chip board for the furniture industry which meets such requirements. That is to say, which, among other things, will be lightweight, but which still maintains its strength in the area of the board intended for fastening of other objects, such as spikes for shelves, legs, lists, handles, wheels, hinges, hooks, fasteners, screws, bolts, etc.

Swedish patent SE 526 784, granted 2005-1 1-01 , discloses a wood chip board with intermediate layer composed of coarser wood chips, and the intermediate layer exhibits varying density. The middle layer with coarser wood chips thus exhibits portions with higher density where the wood chip board is to be fastened to other objects, such as gables, legs, shelves, etc.. This wood chip board is commercially very useful in the furniture industry, but is now the object of further development. SUMMARY OF THE INVENTION

Problems that remain are how to further reduce the material consumption and pressing time for the manufacturing of a wood chip board used for the production of furniture. In this application, the term wood chip board is used for the present invention, although the intermediate layer consists of defibrated wood fibres. The reason for this is that the lower and the upper layers exhibit wood chips, which lower and upper layers are readily visible for a viewer.

The object is to reduce the material consumption of wood fibres of a wood chip board for furniture, while at the same time maintaining its strength.

It is also the object to facilitate the edge processing of the wood chip board so that a smooth edge surface can be accomplished for smooth and good adherence of edge foil or other edge covering protecting against moisture penetration into the wood chip board via the edges. It is important that good adherence of the edge covering to the edge surface can be achieved.

It is also the object to reduce the energy used for transporting wood chip boards.

Likewise, it is the object to make the production of wood chip boards cost- efficient.

It is also the object how to achieve a piece of furniture made of wood chip boards with as low weight as possible. Wood chip boards for building a piece of furniture are arranged side against side in a flat package and are sold to the consumer. Fasteners, screws and nuts, hooks, etc., are enclosed with the package. It is desirable for such a package to be as light as possible.

DESCRIPTION OF THE INVENTION

The above objects have been solved by means of the wood chip board defined in the preamble exhibiting the features set forth in the characterizing portion of claim 1. In this way, a very light wood chip board for furniture has been achieved. At the same time it has been achieved that the material consumption of wood fibres is reduced, while the strength can be maintained. Due to the lightweight wood chip board obtained, the energy consumption for transportation of wood chip boards can be reduced. A piece of furniture can thus be manufactured of wood chip boards with as low weight as possible. These lightweight wood chip boards for building a piece of furniture can be arranged side against side in a flat package and sold to the consumer. Enclosed with the package are fasteners, screws and nuts, hooks, etc. It is desirable for such a package to be as light as possible. Fastening advantageously take place in the area of the second volume of defibrated wood chips. Suitably, the varying density of the second quantity has been achieved in that the at least one first volume exhibits defibrated wood chips that are less densely packed than defibrated wood chips of the at least one second volume. In this way, a wood chip board can be achieved as the same fraction of defibrated wood chips can be used both for the first and the second volume.

Preferably, the varying density of the second quantity is achieved in that the at least one first volume exhibits defibrated wood chips with a larger chip size than defibrated wood chips of the at least one second volume.

Thus, the wood chip board can be made rigid, which is advantageous in view of the wood chip board comprising a substantial amount of air. The larger defibrated wood chips of the first volume thus serve at the same time as reinforcement.

Alternatively, the respective interface between said first and second volumes being inclined relative to the plane of the wood chip board. In this way, the wood chip board can be made more rigid, which is advantageous as first volume is made of defibrated wood chips with as low density as possible. It has surprisingly been found that the inclined interface between the first and the second volumes of defibrated wood chips greatly influences the strength in positive direction. Suitably, the intermediate layer of the wood chip board in the area of the second volume is adapted for fastening of a structural furniture building part.

In this way, the wood chip board can be used as a part or a furniture component for a lightweight piece of furniture in a flat package. The second volume exhibits such density that the fastening is not compromised, while satisfactory strength for the fastening is maintained.

Preferably, the first volume of defibrated wood chips exhibits a density of 200-360 kg/m ³ , preferably 260-300 kg/m ³ , and the second volume of defibrated wood chips exhibits a density of 520-580 kg/m ³ , preferably 540-

560 kg/m ³ .

Thus, a lightweight wood chip board for furniture has been achieved. In that defibrated wood chips are used in the intermediate layer, and a first volume with defibrated wood chips in the intermediate layer has as low density as possible, a very light wood chip board for furniture can been achieved. It has surprisingly turned out that defibrated wood chips in the intermediate layer in a first volume can be made with low density, while simultaneously the strength becomes satisfactory for the wood chip board of a piece of furniture. It has turned out by way of experiments that the upper and lower layers with coarser chip size facilitate the rigidity of the wood chip board. Preferably, the defibrated wood chips in the first volume exhibit such quantity of adhesive (glued defibrated wood chips), which provides satisfactory co-curing with the glued wood chips in the upper and lower layers, and, after the compression with heat and cooling, build a rigid wood chip board. It has turned out to be possible to achieve the low density of the wood chip board by arranging the first volume of defibrated wood chips with a lower density than the second volume. The second volume with the more dense assembly of defibrated wood chips, such as strings, has proved to support the first volume with defibrated wood chips of lower density. It has been found that despite the low density (which precisely defibrated wood chips voluminously packed for the first volume provide) good strength of the finished wood chip board can be guaranteed by said inclined interface, so that the contact surface gets as large as possible, between the first and the second volumes with defibrated wood chips. This combined with the finer defibrated wood chips in the intermediate layer (to provide a fine cut-surface so as to facilitate edge processing and application of edge foil) provides an optimal, cost-effective, lightweight and environmentally friendly wood chip board for furniture. The inclined interface provides satisfactory fastening as opposed to a surface extending perpendicularly across the plane of the board.

Alternatively, the second volume of defibrated wood chips is constituted by a string-like portion oriented parallel to the longitudinal direction of the wood chip board and in its plane.

In this way, a lightweight wood chip board can be achieved which can be cut along the string-like portions in a modular system. The string-like portions fall within the areas of the wood chip board where fastening to another furniture component takes place. Thereby wood chip boards for building a piece of furniture can be transported together in a do-it-yourself-kit in an accomplished lightweight, flat, furniture package, which is environmentally friendly.

Suitably, the expanse of the first volume, parallel to the plane of the wood chip board, viewed transversely to the longitudinal direction of the wood chip board, is at least three times as large as the expanse of the second volume in said plane transversely to said direction.

Thereby, the wood chip board can be accomplished light. It has turned out that the interface where the defibrated wood chips change properties in the first volume (lower density) and in the second volume (higher density) is important. Suitably, the interface is sprayed with atomized water to raise the moisture content in the interface. Upon compression of the defibrated wood chips under heat, steam will thus, in that the water evaporates, expand in the interface between the first and the second volumes of defibrated wood chips. A larger amount of heat can thus be supplied to the interface, and thus satisfactory curing can take place, which further increases the flexural strength.

Preferably, the second volume of defibrated wood chips is constituted by a string-like portion oriented transversely to the longitudinal direction of the wood chip board and in plane.

In this way, a wood chip board can be achieved with areas where also arranged transverse furniture components in the wood chip board can be attached. A furniture component can be provided by cutting the wood chip board along the centrelines of the string-like portions, both in the longitudinal direction and in the transverse direction, where a lightweight piece of furniture can be built with, for example, fastening around the periphery of the wood chip board.

Alternatively, a fourth quantity of wood chips constitutes an additional layer between said lower and intermediate layers.

In this way, the wood chip board can be made more rigid, which is important for a wood chip board this light, where a voluminous intermediate layer with defibrated wood chips exhibits low density.

Suitably, the wood chips of the lower and upper surface layers exhibit in majority larger wood chip size than the defibrated wood chips of the intermediate layer.

In this way, the lower and upper surface layers exhibit a larger degree of air pockets due to the larger wood chip size. Preferably, the wood chips in the upper and lower layers are arranged such that the finer wood chips in these layers end up in the surface layer to provide a smooth surface. In that the intermediate layer exhibits a finer fraction of defibrated wood chips, the exhibited cross-section of strings of this intermediate layer (or volumes of different density) will not exhibit a rough surface. This is advantageous at the application of an edge foil which serves to cover the cut wood chip board in its cut transversely to the strings. The intermediate layer with the finer fraction of defibrated wood chips, where the intermediate layer exhibits a first volume with lower density than a second volume with defibrated wood chips, thus exhibits a finer chip size of defibrated wood chips, and the cross-section of the first volume with lower density does not get as "frayed", which facilitates the application of edge foil or other covering of the cut surface. A furniture component, such as a gable of a book shelf, where there are arranged longitudinal strings in the intermediate layer with defibrated wood chips of higher density, in the area of which strings fastening of shelves (or other fastenings) takes place, thus exhibits, in a cut edge surface transversely to the longitudinal direction of the strings, both defibrated wood chips of lower density and defibrated wood chips of higher density. Since the first volume of defibrated wood chips with the lower density exhibits defibrated wood chips of a small chip size (smaller chip size than the chip size of the wood chips in the upper and lower layers), the cut surface does not get "frayed", and good adherence can be achieved between the cut edge surface of the wood chip board and an edge covering, such as a foil or edge veneer etc.. The edge becomes smooth, which is advantageous for a piece of furniture and aesthetically pleasing.

The above objects have also been solved by the method according to claim 13 defined in the preamble.

In this way, the production of wood chip boards can be accomplished cost- effectively as a smaller quantity of wood chips is used for the manufacture of a wood chip board. Preferably, the compression takes place by means of a lower and an upper press band, which successively approach each other during the compressing. A predetermined final distance between the lower and the upper press bands determines the thickness of the finished wood chip board. Thus, it is also possible to reduce the pressing time for the compression of chip mats (building the various layers) in the manufacturing of the wood chip boards as the quantity of moisture in the defibrated wood chips is lower than in traditional intermediate chip mats with coarser particle size. The lower quantity of moisture is due to the defibrated wood chips exhibiting a lower density than traditional wood chips and entails that a smaller amount of water vapour needs to be pressed away, thus reducing the pressing time. The first volume of defibrated wood chips of lower density thus entails further reduced pressing time, which is cost-effective. Suitably, the distribution of defibrated wood chips is effected by means of the distributing means by take up of defibrated wood chips from defibrated wood chips distributed uniformly on the first chip mat in a previous step, which taken up defibrated wood chips are subsequently returned to said uniform distribution of defibrated wood chips.

In this way, application of defibrated wood chips in the middle layer can be controlled to exhibit different density after the compression, as the first volume is constituted by the troughs (smaller quantity of defibrated wood chips), and the second volume is constituted by the peaks (larger quantity of defibrated wood chips), and when the compression is completed, the first volume will exhibit a lower density than the second volume. Preferably, the first volume is distributed relative to the second volume such that the interface between the two volumes is inclined relative to the plane of the wood chip board.

In this way, an optimally large interface is achieved between the first volume and the second volume, which after compressing, cooling and finishing gives a stable wood chip board. The fact that strings with defibrated wood chips are provided by means of the distribution means, where the strings automatically exhibit sloping screes in their edge regions, does itself facilitate the achievement of said inclined interface.

It has surprisingly been found by way of experiments which the applicant has carried out that suitably the intermediate layer with defibrated wood chips has fractions in the following ranges: Chip size larger than 0.5 mm and smaller than 4.0 mm. Advantageously, use is made of large splints/splinters in mixture with finer chippings. Single splinters have reinforcing effect.. The object of the defibrated material is to build up air, and in that it has surprisingly been found to reduce the quantity of defibrated material between the strings to such a degree that almost only air is left, the board becomes extremely light without its strength being affected. The technical effect of this is that a board that can be manufactured with a small quantity of wood material has been achieved.

It has also been found that suitably the lower and upper layers with wood chips have fractions in the following ranges: The thickness of the fibre structure (single fibre) may be more than or equal to 0.2 mm up to 1.0 mm, the width larger than .0 mm and smaller than 3.0 mm. The length of the fibre structure (single fibre) may be larger than 0.5 mm and smaller than 2,00 mm.

In this way, a board has been achieved which is light and can be accomplished with a second quantity of defibrated wood chips, where this second quantity of defibrated wood chips exhibits at least a first volume which has a lower density than at least a second volume, without the fibre structure in the lower and upper layers having to be adapted, while existing production lines can be used.

Preferably the "scree", or the angle which the strings exhibit (seen in the direction transversely to the longitudinal direction of the strings), is such that the angle is between 7-50 degrees to the normal as defined relative to the plane of the board, preferably 20-35 degrees at the laying out of the intermediate mat. As regards compressed and finalized board, this angle is defined in a flatter angle range.

The density in the various layers and volumes is thus accomplished different. For the intermediate layer, wood chips can be used with bulk density of about 80-120 kg/m ³ . For finished board, the density of the strings can be about 520-680 kg/m ³ , preferably 550-650 kg/m ³ , and in the area between the strings about 380-540 kg/m ³ , preferably 400-520 kg/m ³ . Preferably, the upper and lower outer layers exhibit a density of about 650-950 kg/m ³ , preferably 700-900 kg/m ³ , or 850 kg/m ³ . A wood chip board of standard model with the thickness 18 mm will preferably have an intermediate layer with a thickness of approximately 13 mm, and the outer layers with thicknesses of approximately 2.5 mm each. Preferably, use is made of grinders in the manufacturing of the defibrated wood chip material. Suitably, grinders are coupled in series where the "fluffy" properties of the wood chip material are maintained. Alternatively, more than two grinders (called fibre grinders) are connected in series. Using grinders in series saves energy in comparison to using a refiner. Grinding with grinder (hammer mill or rotary cutter) also provides the advantage that the fibres are kept intact, which from a strength point of view is advantageous. At the end of the process of preparing the defibrated wood chip material it is sieved in a by-pass-sieve. Preferably, 40 % of the material are then fibres going directly to the production line. The remaining 60 % are returned and are mixed with chippings which again pass the grinders (may be granulators) in series.

BRIEF DESCRIPTION OF FIGURES

The invention will now be explained with reference to the drawing, which schematically shows:

Figure 1 a a cross-section of a wood chip board according to a first embodiment with defibrated wood chips in an intermediate layer with volumes of different densities;

Figure 1 b a cross-section of a wood chip board according to a second embodiment with an enlarged section representing an interface between different volumes of defibrated wood chips;

Figure 2 a piece of furniture comprising fastening elements for supporting other furniture components in the form of shelves;

Figure 3a shows a cross-section of a wood chip board where a string with defibrated wood chips of higher density is illustrated;

Figure 3b shows a cross-section where the interface between defibrated wood chips of higher or lower density, respectively, exhibits the largest possible expanse;

4a shows an example of a method of distributing defibrated wood chips at the manufacturing of a wood chip board of the type shown in Figure 1a;

Figure 4b shows the second chip mat with defibrated wood chips laid out in "strings" with screes;

Figure 4c shows the intermediate layer compressed with a first and a second volume with defibrated wood chips, the volumes having different density; Figure 4d shows an embodiment for distributing the defibrated wood chips; Figure 4e shows an additional embodiment using adjustable nozzles; Figure 5 shows a variant of expanses in plane of different volumes with different density for the defibrated wood chips in the intermediate layer, adapted in expanse according to subsequent cutting of the wood chip board for manufacturing of furniture components;

Figure 6a shows a cross-section of the fastening elements of a piece of furniture arranged in the area of the second volumes with defibrated wood chips;

Figure 6b shows the section A-A in Figure 6a where a cover foil is shown, which by the smaller chip size of the defibrated wood chips can be applied uniformly and obtain good adherence to the cut edge of the wood chip board exposing the first volume, and

Figure 7 grinders in series for the production of "fluffy" wood chip material . DETAILED DESCRIPTION OF EMBODIMENTS

The invention will now be explained by means of embodiments. Details on the schematic drawing may represent the same type of detail, but in different figures with the same reference numeral. The drawing should not be construed strictly, and details that are of no importance to the invention have been excluded from the drawing, for the sake of clarity.

Figure 1 a shows schematically a cross-section of a wood chip board 1 according to a first embodiment. The wood chip board 1 includes three layers S1 , S2, S3 with different fractions of wood chips. There is a lower layer S1 of a first quantity M1 of wood chips 3 of different chip size, an intermediate S2 layer comprising a second quantity M2 of defibrated wood chips 5, and an upper layer S3 comprising a third quantity M3 of wood chips of different chip size. The second quantity M2 is constituted by a mixture of defibrated wood chips 5 and is composed of a first volume V1 of defibrated wood chips 5' having a lower density than a second volume V2 of defibrated wood chips 5".

The varying density (that is, lower density of the first volume V1 of defibrated wood chips 5' than of the second volume V2 of defibrated wood chips 5") of the second quantity M2 is achieved in that the first volume V1 is arranged with defibrated wood chips 5' of the first volume V1 which are less densely packed than the defibrated wood chips 5" of the second volume V2. The wood chips 3 of the lower S1 and upper S3 layers exhibit in majority a larger wood chip size than the wood chip size of the defibrated wood chips 5 of the intermediate layer S2.

Figure 1 b shows schematically a cross-section of a wood chip board 1 according to a second embodiment. The wood chip board 1 comprises five layers with different wood chip fractions; a lower S1 and an upper S3 layer, an intermediate layer S2, and between these outer layers and the intermediate layer additional layers S4, S5. A fourth M4 and fifth M5 quantity of wood chips thus constitute the additional layers S4, S5, between the lower S1 (outer) and intermediate S2 layers and the upper S3 (outer) and intermediate S2 layers, respectively. The outer S1 , S3 layers constituted by a first and a third quantity, respectively, M1 , M3 of wood chips 3 of different chip sizes. The fourth and the fifth quantity M4, M5 are constituted by coarser wood chips 3, and the intermediate S2 layer comprising the second quantity M2 of defibrated wood chips 5 exhibits varying density. The second quantity

M2 is constituted by a mixture of defibrated wood chips 5. The second quantity M2 of defibrated wood chips 5 exhibits a first volume V1 with defibrated wood chips 5' having a lower density than a second volume V2 with defibrated wood chips 5". The defibrated wood chips 5 in the intermediate layer S2 thus exhibit volumes V1 , V2 with different density. The size of the defibrated wood chips 5', 5" is smaller than a largest chip size of the first M1 and the third M3 quantity, respectively, of wood chips 3. The defibrated woodchips 5', 5" are constituted partly of exposed wood fibres. In this way, a voluminous "fluffy" intermediate layer S2 is provided which builds volume and which is light. By providing a volume (the first V1 ) with defibrated wood chips 5' in volume with extra low density in the areas of the wood chip board 1 where no fastening elements are applied, the wood chip board 1 can be made extremely light, and at the same time the defibrated finer exposed wood fibres 5"' provide a fine edge surface 7 after cutting the wood chip board 1 in this area. Thus, an edge foil 9 (only a portion shown) can be applied with satisfactory adherence, which is desirable for manufacturing of furniture. The defibrated finer wood chips 5', 5" are achieved by utilizing wood materials (not shown), such as wood chippings, that are torn to wood chips, which wood chips are then defibrated in a grinder (not shown) once or twice. In this way, exposed wood fibres can be achieved without it being necessary to boil or heat the wood material. The varying density of the second quantity M2 is achieved in that the first volume V1 exhibits defibrated wood chips 5' which are less densely packed than the defibrated wood chips 5" of the second volume V2. The first volume V1 of defibrated wood chips 5' exhibits a density of 200-360 kg/m ³ , preferably 260-300 kg/m ³ , and the second volume V2 of defibrated wood chips 5" exhibits a density of 520-580 kg/m ³ , preferably 540-560 kg/m ³ . Figure 1 b also shows schematically an enlargement representing a section of an interface 1 1 between the first V1 and the second V2 volumes. The first V1 volume of defibrated wood chips 5' exhibits a lower density than the second V2 volume of defibrated wood chips 5". The interface 1 1 is inclined relative to the plane P of the wood chip board

1. In this way, the wood chip board 1 can be made more rigid, which is advantageous as the first volume V1 is made of defibrated wood chips 5' in volume with as low density as possible. It has surprisingly been found that the inclined interface 11 between the first V1 and the second V2 volumes of defibrated wood chips 5', 5" greatly influences the strength in positive direction as a larger binding area for the interface 11 between the two volumes V1 , V2 is accomplished.

Figure 2 shows schematically in perspective a piece of furniture 13 in the form of a book shelf 3'. The gables 15 of the book shelf 13' include fastening elements 17 (spikes 17') for the support of other furniture components 19, here in the form of shelves 19'. The gables 15 are made of a wood chip board 1 shown in cross-section in Figure 3a, which is cut in a suitable manner. The intermediate layer S2 (not shown in Figure 2) of the gables 5 with defibrated chips 5 is divided into a central first volume V1 of defibrated wood chips 5' and peripheral second volumes V2 of defibrated wood chips 5' adjacent the first volume V1. The first volume V1 of defibrated wood chips 5' is provided with as low density as possible to make the furniture 3 light. At the same time, the chip size of the first volume V1 can be kept smaller than the chip size of the first M1 and third M3 quantity of wood chips 3 in the outer layers (not shown in Figure 2) as defibrated wood chips are used in the intermediate layer S2. This facilitates the application of an edge foil 9 to the cut end of the gable 15, because the finer defibrated wood chips 5', 5" allow a smooth surface and good adherence. The prior art more frayed edge of heavier wood chip boards for furniture complicates such application.

Experiments made by the applicant have shown that it is indeed possible to reduce the density of the first volume V1 of defibrated wood chips 5' to make the wood chip board 1 light without compromising its strength. The intermediate layer S2 of the wood chip board 1 is thus in the area of the second volume V2 arranged for fastening of another structural furniture building part or furniture component 19; here eight spikes 17' and two shelves 19'.

Figure 3a shows schematically a cross-section of a wood chip board 1. There is shown a cross-section of a string 25 with defibrated wood chips of higher density in the second volume V2. In that the interface 1 1 between the first V1 and the second V2 volumes is inclined relative to the plane P and expanse of the wood chip board 1 (inclined at the angle a = 15 degrees to the normal N relative to the plane P, an optimal interface area can be obtained, which improves the strength. It is important that in areas with changes in material composition not to create preconditions for fracturing. Fig. 3b shows another example of a cross-section where the interface between volumes V1 and V2 with defibrated wood chips, V1 and V2 exhibit lower and higher density, respectively, and the interface 1 1 exhibits as large expanse as possible through relatively flat inclination (a = 45 degrees to the normal N) of the interface 1 1 relative to the plane P of the wood chip board 1. A lead-through

22' extends all the way through the board in the transverse direction (i.e. transversely to the expanse of the board), both through the intermediate layer S2 and through the outer layers S1 , S3. The lead-through 22' is arranged in the area of the second volume V2.

The adjacent volume V1 makes the board light, and at the same time strong fastening of a pin bolt (not shown) can be made in the board.

Figure 4a shows schematically an example of a method of distributing defibrated wood chips 5', 5" in the manufacturing of a wood chip board 1 according to any of the embodiments. The method is provided for producing the wood chip board 1 comprising layers S1 , S2, S3 with different fractions of wood chips, the lower layer S1 with a first quantity M1 of wood chips 3 of different chip size, the intermediate layer S2 with a second quantity M2 of defibrated wood chips 5', 5", the upper layer S3 with a third quantity M3 of wood chips 3 of different chip size. The second quantity M2 of defibrated wood chips 5 exhibits the first volume V1 , which has a lower density than the second volume V2. The method includes the steps of uniform distribution by means of a first sprinkling equipment 20' of a first quantity M1 of glued wood chips 3, building a first wood chip mat 21 ; distribution of defibrated wood chips 5, building the second quantity M2, such as a second chip mat 22, on top of the first quantity M1 of wood chips by means of distribution means, such as a second sprinkling equipment 20". This is done such that the second quantity M2 (for first volumes V1) will be thinner laid out than the strings 25 (for second volumes V2), both volumes V1 , V2 being applied to the first chips mat 21. Thereafter, a uniform distribution of a third quantity M3 of glued wood chips 3 takes place, building a third chip mat 23, on top of the defibrated wood chips 5 by means of a third sprinkling equipment 20"'. Finally, by means of pressing equipment 28 simultaneous compression takes place with heat of the first 21 , second 22, and third 23 chip mats for co- curing, so that the thickness of the intermediate layer S2 becomes uniform, and thus the second volume V2 exhibits higher density than the first volume V1. The thickness of the intermediate layer S2 is accomplished uniform in that an upper and a lower press band, in the direction of the conveyance of the chip mats, are set with a distance (measured along the band normal) from each other corresponding to the desired thickness of the finished wood chip board, where the intermediate layer S2 obtains uniform thickness. Since the second chip mat has varying thickness, the intermediate layer S2 will, after the compression to uniform thickness, exhibit varying density. The distribution of defibrated wood chips 5 by means of the second sprinkling equipment 20" is effected by take-up of defibrated wood chips 5 from defibrated wood chips 3 distributed uniformly on the first chip mat 21 in a previous step, which taken up defibrated chips 5 are subsequently returned to said uniform distribution of defibrated wood chips 5. The second volumes V2 with defibrated wood chips 5 are thus accomplished by string-like portions 25 oriented parallel to the longitudinal direction of the wood chip board 1 and in its the plane P. The first volume V1 is distributed relative to the second volume V2 such that the interface 11 between the two volumes V1 , V2 is inclined relative to the plane P of the wood chip board. It has surprisingly turned out that the natural scree R, which the sides of the string-like portions 25 exhibit at said distribution by the distributing means, very satisfactorily after compression and curing provides satisfactory sloping of the interface 1 1 for the finished wood chip board. Thus, the strength can be guaranteed for the lightweight wood chip board 1 for furniture. The use of defibrated wood chip/wood fibres also the for the first volume (very voluminous) provides a more uniform and strong edge covering over a cut wood chip edge exposing the intermediate layer S2. The wood chip board 1 , which is produced according to the method set out in Figure 4, is achieved in that the expanse of the first volume V1 , parallel to the plane P of the wood chip board 1 , viewed transversely to the longitudinal direction of the wood chip board 1 , is at least three times as large as the expanse of the second volume V2 in said plane P transversely to said direction.

Figure 4b shows the second chip mat 22 with defibrated wood chips laid out in "strings" 25 with screes R. The second chip mat 22 is laid out on the first chip mat 21 , which in turn is distributed uniformly on a lower press band 30. The third chip mat 23 is applied to the second chip mat 22 with defibrated wood chips. At the compression with heat, the screes R will naturally, as shown in Fig. 4c, provide (sloping relative to the plane P of the wood chip board) satisfactorily inclined interface 1 1 between the first V1 and the second volume V2 for the finished wood chip board.

Compression is effected in that the lower press band 30 is moved towards an upper press band 31 , as schematically shown in Figure 4c, so that the chip mats 21 , 22, 23 are compressed under heat and pressure and cure such that the finer defibrated wood chips in the intermediate layer S2 are bonded together in the first V1 and the second V2 volumes, and the defibrated wood chips in the respective volumes V1 , V2. Thus, Figure 4c shows the intermediate layer S2 compressed with the first V1 and the second V2 volumes with defibrated wood chips, and the volumes have different density. Another variant of distributing the defibrated wood chips for building the intermediate second chip mat is to use variable plough elements 38', shown schematically in Figure 4d.

Another variant is to use adjustable nozzles 38", shown schematically in Figure 4e, for application of the correct quantity of defibrated wood chips to achieve variation in density of the first and the second volumes of defibrated wood chips.

It has surprisingly been found by way of experiments carried out by the applicant that suitably the intermediate layer with defibrated wood chips has fractions in the following ranges: Chip size larger than 0.5 mm and smaller than 4.0 mm. Advantageously, use is made of large splints/splinters in mixture with finer chippings. Single splinters have reinforcing effect. The object of the defibrated material is to build up air and in that it has surprisingly been found to reduce the quantity of defibrated material between the strings to such a degree that almost only air remains, the board becomes incredibly light, without its strength being affected.

The technical effect hereof is that a board that can be manufactured with a small quantity of wood material has been achieved.

It has also been found that suitably the lower and upper layers with wood chips have fractions in the following ranges: The thickness of the fibre structure (single fibre) is larger than or equal to 0.2 mm up to 1.0 mm, the width is larger than 1.0 mm and smaller than 3.0 mm. The length of the fibre structure (single fibre) is larger than 0.5 mm and smaller than 2.00 mm.

In this way, a board has been achieved which is light and can be accomplished with a second quantity of defibrated wood chips, where this second quantity of defibrated wood chips exhibits at least a first volume which has a lower density than at least a second volume, without the fibre structure in the lower and upper layers having to be adjusted, while existing production lines can be used. Preferably, the "scree", or the angle which the strings exhibit (seen in the direction transversely to the longitudinal direction of the strings) is such that the angle is between 7-50 degrees to the normal defined relative to the plane of the board, preferably 20-35 degrees at the laying out of the intermediate mat. As regards compressed and finished board, this angle is defined in a flatter angle range. The density in the various layers and volumes is thus accomplished different. For the intermediate layer, wood chips can be used with bulk density of about 80-120 kg/m ³ . As regards finished board, the density of the strings is about 520-680 kg/m ³ , preferably 550-650 kg/m ³ , and the area between the strings is about 380-540 kg/m ³ , preferably 400-520 kg/m ³ . Preferably, the upper and lower outer layers have a density of about 650-950 kg/m ³ , preferably 700- 900 kg/m ³ , or 850 kg/m ³ . A wood chip board of standard model with the thickness 8 mm will preferably have an intermediate layer with a thickness of approximately 13 mm, and the outer layers with thicknesses of approximately 2.5 mm each.

Figure 5 shows schematically a variant of expanses in plane of different volumes V2 with different density for the defibrated wood chips 5', 5" in the intermediate layer. The strings 25 (or second volumes V2) are adapted in expanse according to the subsequent cutting of the wood chip board 1 for manufacturing of furniture components K. The furniture component K includes vertical and horizontal strings 25 so that the fastening of horizontal rails (not shown) and vertical hinges (not shown) may be achieved in the area of the strings with defibrated wood chips. The edge surface 7 of the cut wood chip board 1 becomes smooth as fine defibrated wood chips 5', 5" are used for the intermediate layer. The fine defibrated wood chips 5', 5" have smaller chip size than the wood chips in the upper and lower layers. The defibrated wood chips 5', 5' build, despite the finer wood fibres and wood chips of the defibrated wood chips, a voluminous volume, and it has turned out that the first volume V2 can be accomplished extra "fluffy" without the strength of the wood chip board being compromised, a smooth and fine edge surface 7 at the same time being achievable.

Figure 6a shows schematically in cross-section fastening elements 40 of a piece of furniture 13. The fastening elements 40, in the form of a screw 41 and a pin bolt 42, and backstop 43, are arranged in the area of the second volumes V2 with defibrated wood chips 5" in the intermediate layer S2 of the wood chip board . In this way, the fastening becomes strong while at the same time the wood chip board 1 can be accomplished light with smooth edge surface 7. Support hole 44' extends through the second volume V2 for receiving the screw 41. The adjacent volume V1 makes the board light, while at the same time fastening of the screw 41 can be made strong.

Figure 6b schematically shows the section A-A in Figure 6a. A cover foil 9' is glued on the edge surface 7. Thanks to the smaller chip size of the defibrated wood chips, the cover foil 9' can be applied uniformly to the edge surface 7. The cover foil 9' thereby obtains good adherence to the cut edge surface 7 of the wood chip board 1 exposing the first V1 and second V2 volumes. Figure 7 shows grinders in the manufacturing of the defibrated wood chip material. Suitably, grinders 40 are coupled in series, where the "fluffy" properties of the wood chip material are obtained. Three grinders (so-called fibre grinders) are coupled in series. Using grinders in series saves energy in comparison to using a refiner. Grinding with grinder also provides the advantage that the fibres are kept intact, which from a point of view of strength is advantageous. At the end of the process of preparing the defibrated wood chips material it is sieved in a by-pass-sieve 42. Preferably, 40 % of the material are then fibres going directly to the production line. The remaining 60 % are returned and are mixed with chippings which again pass the grinders (may be granulators) in series. Thus, in the series about half the ground wood splinters becomes "fluffy" material, and half is returned to the material with wood splinters to be ground and ground again together therewith. The invention is not to be seen as limited by the above described embodiments, but within the scope of the invention there are also other embodiments which likewise describe the inventive idea or combinations of the embodiments described. By the term "fluffy" is meant defibrated wood chip material. Naturally, there may be other types of edge covering. This may be cover foil of plastic, veneer, tape, adhesive layer, paint, etc.. The wood chip board can be used for other types of furniture than the abovementioned. These could be beds, tables, cabinets, chairs, kitchen furniture, etc.. The number of strings may be more than one, for example two, three, four, or five, or more, all according to the use of the wood chip board.