FORM-2
THE PATENTS ACT, 1970
(39 of 1970)
&
THE PATENTS RULES, 2003
COMPLETE SPECIFICATION
(See section 10 and rule 13)
WOOD COMPOSITE MATERIAL
DOKA INDUSTRIE GmbH
an Austrian Company of Josef Umdasch Platz 1 A-3300 Amstetten, Austria Inventors:
1. GRATER, Peter
2. FRYBORT, Stephan
3. MULLER, Ulrich
4. MAURITZ, Raimund
The following specification particularly describes the invention and the manner in
which it is to be performed,

Technical field
The present invention relates to a wood composite material, which is suitable for the production of bearing elements, and a method for its production,
Background
The tare weight of the material represents an important material parameter in bearing elements which are subjected to bending. Due to their lower warpage caused by the tare weight, materials with low.density and yet sufficiently high strength and stiffness offer advantages compared to materials with identical mechanical properties but higher density.
A reduction in density with an associated reduction in the weight of the materials -while simultaneously maintaining stiffness and strength - brings with it many advantages in ergonomics and logistics. The advantages and savings associated with the lower weight begin with the initial handling (e.g. handling by personnel, design and energy consumption of transport and lifting devices) and continue at every stage of handling or further processing through to end use (e.g. assembly of structural parts) and even, if applicable, to disposal.
In recent years, numerous efforts have been made to reduce the density of wood composite materials. The basic idea behind almost all wood light-frame construction materials is a multi-layer sandwich structure. In this way, strong, stiff materials or solid wood elements absorb pressure and tensile forces in the marginal zones while the middle layer transmits mainly shear and normal forces.
Thus, paper honeycomb panels, for example, which have been on the market for decades, are currently experiencing a renaissance in the wood material industry through new developments and improvements. Although these materials are characterised by very low densities, they cannot be used for bearing purposes due to their mechanical properties and lack of water resistance.

Improved properties can be achieved by lightweight materials with sandwich structure and foam-like core. However, due to the high shear load on the low-density middle layer, the lack of shear strength during bending load results in severe deformations. In addition, the strength properties are mostly inadequate for use as a bearing element.
Currently in the production of wood composite materials consisting of macrofibres and a binder, the strands, particles or fibres are embedded with binder and subsequently compressed through a compressing press process, the binder being cured by the heat acting on the pressing plates. This procedure results in a significant compression particularly in the marginal areas of the pressing plates. Conventional panel materials such as chipboard and fibreboard, OSB, etc. and the special wood materials such as Quetschholz, scrimber, TimTek, Srimtec, SST, etc. thus have a more or less distinctive density profile across the panel thickness. In the case of a largely absent density profile, all the material is strongly compressed or these are panel materials with very low density (e.g. lightweight wood wool panel, low density fibreboards, etc.), which cannot be compared with materials for bearing purposes due to their low strength values.
As explained above, the wood components of conventional panel materials and of the special wood materials such as Quetschholz, scrimber, TimTek, Srimtec, SST. etc. are significantly compressed during production. Besides the increase in density, this press process is also associated with a compression of the cell structure of the wood (cell collapse). If water is absorbed, such deformation can be partly reversed due to the strong hygroscopic properties of the wood and the swelling of the cell walls. However, this is associated with strong swelling of the compressed parts and thus of the entire panel material.
Moreover, due to the compression, it is difficult with this method to introduce heat into the inside of the panel for curing the panel materials. For this reason, these methods generally rely on steam shock in order to ensure adequate heat transport. However, in order to exploit the steam shock, the macrofibres and/or the binder must have sufficient (residual) moisture. Without the so-called steam shock, technological

implementation of panel production is possible only with difficulty (particularly in the case of low density panel materials).
Despite numerous trials, there is no commercially available wood composite material which combines a low density with stiffness well suited for bearing elements and where the disadvantages of compression can be avoided in its production. The object is therefore presented to make such a wood composite material available.
Description of the invention
This object is achieved according to the invention by a wood composite material, which has a density of 200-550 kg/m and a stiffness measured in the 4-point bending test according to EN 789 of 4,000-12,000 MPa, the wood composite material comprising macrofibres with a slenderness ratio (ratio of length to thickness of fibres) exceeding 20 and a binder, and the binder having a foam structure.
The wood composite material according to the invention has a density of 200-550 kg/m , preferably 300-550 kg/m . The stiffness measured in the 4-point bending test according to EN 789 is 4,000-12,000 MPa, preferably 5,000-12,000 MPa, particularly preferably 6,000-12,000 MPa. In a particularly preferred embodiment, the wood composite material has a density of 300-550 kg/m3 and a stiffness of 6,000-12,000 MPa.
The wood composite material according to the invention comprises macrofibres made of wood with a slenderness ratio (ratio of length to thickness of fibres) exceeding 20.
The macrofibres used preferably have a length of 100-400 mm, particularly preferably 150-300 mm. Yet, it is obvious to the person skilled in the art that for production reasons it cannot be excluded that the fibres used will still comprise a certain quantity of shorter fibres.
The wood composite material according to the invention further comprises a binder that has a foam structure in the cured state. The binder preferably has a predominantly fine-pore foam structure. The binder particularly preferably has a foam structure in such a way that 90-95 % of the pores have a pore size in the range 30-500 (im,

preferably 50-300 µm, measured by means of a microscope on a section through the material.
In a preferred embodiment, a binder is used for the wood composite material according to the invention which forms a foam with a density of 30-300 kg/m3, preferably 80-200 kg/m3, when freely foaming.
To obtain the density when freely foaming, the binder which has not yet reacted is poured into an open-topped container. The binder foams up due to the chemical reaction and can freely expand through the opening. After curing, the overspill foam is stripped off cleanly with a knife. The density of the freely foamed binder can be calculated from the previously obtained volume and tare weight of the container and from the weight of the foam-filled container.
In the present invention, a binder is preferably used which forms a closed-pore foam structure. As the fibres in the wood composite material according to the invention are virtually fully enveloped by the foam and virtually all void spaces between the fibres are filled with foam, a closed-pore structure of the foam reduces or even completely prevents the ingress of moisture, which results in the wood composite material exhibiting advantageous behaviour when exposed to moisture such as, e.g., slight . swelling.
The wood composite material according to the invention thus exhibits markedly less swelling when exposed to moisture compared to conventional wood materials. This lies within or even below the range for solid wood whereas conventional wood materials generally have marked increased swelling compared to the swelling of the roundwood used. For example, when using macrofibres from spruce, measurements of thickness swelling according to DIN 52364 of between 2.7 % and 6 % can be attained, and according to EN 317 of between 1.5 and 5 %. In comparison, the measurement of swelling for solid spruce according to DIN 52364 is also approximately 4 to 6 %. In contrast to that, corresponding chipboard or OSB reveals swelling measurements from 7 % to 30 %.

In order to reduce the swelling of the wood composite material even further, the macrofibres used can be modified by appropriate measures before further processing. Such measures are, for example, acetylation or impregnation with suitable resins or chemicals such as, e.g., melamine resin or DMDHEU, thermal modification or other known swelling-improvement measures. The swelling of fibres from moisture absorption is thus reduced and the total swelling of the wood composite material is particularly low. Swelling values of less than 2 % to 4 % can thus be achieved. Due to their low thicknesses, the macrofibres used in the wood composite material according to the invention can be very easily impregnated. In contrast to that, the modification of solid wood often fails due to the lack of impregnability of the wood.
Furthermore, in the chemical method, a heat treatment is often still required after impregnation of the wood. Here, the small dimensions of the macrofibres used according to the invention also prove advantageous compared to solid wood as the heat thus encompasses the whole wood more rapidly. The heat treatment required for such a modification can be integrated advantageously partly or even Hilly into the following procedure of the production of the wood composite material according to the invention.
A polymer-based binder is preferably used as binder according to the invention. For example, epoxy resin, isocyanate (including polyurethane), melamine, urea, phenol resin foams or mixtures thereof can be used. A polyurethane system is particularly preferably used such as, e.g., a one- or multi-component polyurethane system, particularly a two-component polyurethane system. However, thermoplastic foams such as polystyrene (e.g. EPS or EPX) can also be used.
In a further preferred embodiment, the wood composite material according to the invention additionally contains particles such as, e.g., iron oxide particles that can be excited by fields. When using such particles, the foam and curing process of the binder can be initiated (started) and/or accelerated by applying a field (e.g. by induction, microwave, high frequency, radiation, etc.). The particles can be usefully incorporated into the binder before the production of the wood composite material but they can also be inserted separately.

Alternatively, heat, hot air or steam can also be used to initiate and/or accelerate the foaming and curing process of the binder.
Furthermore, the wood composite material according to the invention can contain suitable additives, e.g. foaming agents, fillers, pigments, reinforcement fibres (nano, micro or macro), fire or wood protection agents, and agents for improvement of swelling, etc. These additives can either be added to the binder or incorporated separately into the material. In a manner known to the person skilled in the art, such additives can impart special properties to the wood composite material, such as greater hardness or shear strength, durability, moisture resistance, etc.
The wood composite material according to the invention can be obtained by means of a method which comprises the following steps:
a) production of macrofibres;
b) alignment of the macrofibres;
c) application of the binder;
d) closing of a press; and
e) foaming up of the binder.
In the method according to the invention, the binder is applied to the aligned macrofibres (sequence of steps: a, b, c, d and e). Alternatively, the binder can also be applied before aligning the macrofibres (sequence of steps: a, c, b, d and e).
The method can be advantageously carried out continuously, e.g., by means of a coil press.
To produce the wood composite material according to the invention, macrofibres are dried and aligned largely uniaxially (i.e. parallel) on pressing plates or press moulds. The binder is applied between and/or on the aligned macrofibres. The application of the binder can be carried out by methods established in the timber industry such as spraying on or by glueing machines or chip blenders.

In a preferred embodiment of the method according to the invention, the foaming up time of the binder is controlled so that the foaming up Procedure starts predominantly only after the press has been closed. That means that the binder system is chemically controlled so that the start time for foaming up is delayed such that the press or press mould can be closed before the foam has expanded significantly.
When closing the press or the press mould, the macrofibres are preferably only minimally compressed so that the density of the wood composite material produced does not deviate greatly from the density of the wood Used. As the macrofibres in the method according to the invention are only negligibly compressed, the swelling that occurs with subsequent water contact or water immersion can be minimised or avoided. Thus, swell values can be achieved which lie within or even below the swelling range of the wood used. This is an important advantage compared to conventional wood materials, which have a predominancy high wood compaction and thereby a markedly higher swelling in contact with water than the wood used.
In the closed press mould or press, on the one hand the mould pressure applied from the outside has an effect, while on the other hand a mould pressure develops from the inside through the binder foaming up so that the binder largely fully penetrates the network of macrofibres and largely completely wets the surface of said macrofibres. The macrofibres are thus surrounded by a binder matrix and are thereby well protected from moisture absorption.
As the binder is introduced into the network of macrofibres through the expansion of the binder, a very homogeneous material with uniform density is formed, in which virtually all void spaces are filled up with the foam structure and the fibres are virtually completely surrounded (encapsulated) by foam.
Moreover, the method according to the invention, particularly when using a two-component polyurethane system as the binder, has the Advantage that only negligible heat has to be supplied to initiate curing. The required heat can be introduced by mild preheating of the macrofibres (e.g. to 30-90 °C, preferably 50 °C).

As the binder is only brought into contact with the macrofibres immediately before its curing, essentially 100 % of the binder is available for glueing and "encapsulating" the chips.
If the binder system can be controlled so that it fully cures in the press, then the press can be immediately opened again. Even if the panels of the wood composite material according to the invention are not fully hardened, in contrast to conventional wood material panels, the panels are not destroyed by so-called splitters. If there is any post-curing, this merely results in some post-expanding of the wood composite material according to the invention.
The wood composite material according to the invention is suitable for all products that are produced from solid wood or wood materials such as chipboard or OSB, etc. Due to the lower density, the use of the wood composite material according to the invention results in a lower weight in products produced in this way.
The use of the wood composite material according to the invention is particularly advantageous for products where dimensional stability during exposure to moisture and retention of strength and stiffness are also important besides weight. By virtue of their unprotected use in the open air, such products include:
— formwork products such as formwork girders and parts thereof such as flange or web,
— coated or uncoated formwork panels and parts thereof such as middle layers or top layers,
— platform facings for working and protection scaffolding,
— round or flat-shaped formwork products in 1-, 2- or 3-dimensional shape for creating or supporting the formwork facing, and
— lost formwork or parts thereof which remain in the structure.
Other products which can be advantageously produced from the wood composite material according to the invention include:

— wood construction girders made of solid material or with cavities or parts thereof such as flanges or webs (advantage: low weight, homogeneous properties without weak spots such as knots in solid wood; option for production of a beam (I-beam or other optimised cross-section similar to metal .girders)),,
— wood structural panels and structural panels for furniture (advantage: properties like plywood with regard to statics, swelling, moisture resistance together with very low weight and economic production capacity),
— parts of wood structural panels (top layers, middle layers),
— middle layers with largely vertical fibre direction, which are produced from blocks with parallel fibre direction by cutting perpendicular to the fibre (advantage: low weight, practically no thickness swelling, economic production (e.g. balsa endgrain substitute)),
— sandwich panels made of particularly light macrofibre middle layer with bearing top layers made of suitable materials such as veneer, plywood or even acrylic panels with vertical or flat-grain middle layer,
— "thick wood panels" - homogeneous panel materials for walls and ceilings with thicknesses of 5 cm to > 20 cm (advantage; weight, heat insulation, statics, moisture resistance),
— thick wood panel with cavities (advantage: see above, even lower weight, saving on material)
— a plurality of sections made of solid material or with cavities for structural components, windows, doors and furniture (advantage: section can be produced without loss of material, statics, weight)
— panels, beams and sections for vehicle construction (advantage: weight, statics, moisture resistance)

— round and flat-shaped 2D and 3D moulded parts for wood structure in vehicle construction , interior trims and furniture (advantage: virtually any shape can be produced, statics, weight)
Example
Macrofibres are dried by a warm (50 °C) airflow and stored for several days in an ambient temperature of 20 °C and 65 % relative air humidity, thus producing a timber humidity of approximately 12 %. 210 g of macrofibres are aligned parallel to each other as precisely as possible. 50 % of the fibres are placed into an aluminium mould (30 x 12 cm) heated to 50 °C and uniformly wetted with 60 g two-component polyurethane (RAMPF no. 80L86/4-1). Then, the remaining 50% of the fibres are placed in the mould and the mould is closed so that the macrofibres inserted are compressed to a height of 16 mm. The water foams up strongly due to the chemical reaction of the two components of the polyurethane with the water available in the wood. After 30 min. the foam is fully cured and the wood composite material can be taken out of the mould.

We Claim;
1. Wood composite material with a density of 200-550 kg/m3, preferably 300-550 kg/m3, and a stiffness measured in the 4-point bending test according to EN 789 of 4,000-12,000 MPa, preferably 5,000-12,000 MPa, particularly preferably 6,000-12,000 MPa, the wood composite material comprising macrofibres with a slenderness ratio (ratio of length to thickness of fibres) exceeding 20 and a binder characterised in that the binder has a foam structure.
2. Wood composite material according to claim 1, the binder having a predominantly fine-pore foam structure, preferably such that 90-95 % of the pores have a pore size of 30-500 urn, preferably 50-300 (am.
3. Wood composite material according to claim 1 or 2, a binder being used which forms a foam with a density of 30-300 kg/m3, preferably 80-200 kg/m3, when freely foaming.
4. Wood composite material according to any of claims 1-3, a polyurethane system being used as binder.
5. Wood composite material according to any of claims 1-4 which further contains particles, preferably iron oxide particles, that can be excited by fields.
6. Wood composite material according to any of claims 1-5, the thickness swelling according to EN 317 being less than or equal to 5 %, preferably less than or equal to 4 %, particularly preferably less than or equal to 3 %.

7. Wood composite material according to any of claims 1-6, the macrofibres being modified.
8. Method for the production of a wood composite material according to any of claims 1-7 comprising the following steps:

— production of macrofibres;
— alignment of the macrofibres;
— application of the binder;
— closing of a press; and
— foaming up of the binder.

9. Method according to claim 8, the binder system being controlled so that the foaming up process starts predominantly only after the press has been closed.
10. Method according to any of claims 8-9, the foam and curing process being initiated and/or accelerated by a field.
11. Method according to claim 10, with particles which are able to be excited by fields being applied in addition to the binder.
12. Method according to claim 11, the particles being contained in the binder.
13. Method according to any of claims 8-9, the foam and curing process being initiated and/or accelerated by heat, hot air or steam.

14. Method according to any of claims 8-13 which is carried out as a continuous
process for example by means of a coil press.
15. Wood composite material according to any of claims 1-7 obtainable by a method
according to any of claims 8-14.
16. Product comprising the wood composite material according to any of claims 1-7 or
15, the product being particularly selected from formwork products and parts
thereof; coated or uncoated formwork panels and parts thereof; platform facings
for working and protection scaffolding, round or flat-shaped formwork products in
1-, 2- or 3-dimensional shape for creating or supporting the formwork facing; lost
formwork or parts thereof which remain in the structure; wood construction girders
or parts thereof; wood structural panels; furniture structural panels; top layers and
middle layers of (wood) structural panels; sandwich panels; thick wood panels;
sections; panels, beams and sections for vehicle construction; and moulded parts.