ES2663007T3 - Procedure for the production of a composite material derived from wood and composite material derived from wood - Google Patents

Abstract

Composite material derived from wood with a density of 200-550 kg / m3 and a stiffness measured in the 4-point bending test according to EN 789 of 4,000-12,000 MPa, comprising macrofibers with a slenderness ratio of more than 20 and a binder, the slenderness ratio being understood as the ratio of the length with respect to the thickness of the fibers, the binder having a mainly fine-pored foam structure such that 90-95% of the pores have a size of 30-500 μm pore, and that the binder in the case of free foaming forms a foam with a density of 30-300 kg / m3

Description

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DESCRIPTION

Procedure for the production of a composite material derived from wood and composite material derived from wood

Technical field

The present invention relates to a composite material derived from wood that is suitable for the production of bearing elements, and to a process for its production.

Background

In the case of bearing elements that are requested by bending, the material's own weight represents an important parameter of the material. Materials with reduced density and despite this a sufficiently high strength and stiffness offer, due to their lower buckling caused by their own weight, advantages over derived materials with the same mechanical properties, but a higher density.

A reduction in density and associated with it a reduction in the weight of derived materials (while maintaining rigidity and resistance) entails many advantages in ergonomics and logistics. The advantages and savings associated with the lower weight start during the first processing (for example during the handling by people, the dimensioning and the energy consumption of means of transport and lifting) and continue at each stage of handling or processing additional until the final use (for example the assembly of constructive pieces) if necessary, even until the elimination.

Many efforts have been made in recent years to reduce the density of wood-derived materials. The basic idea of almost all wood-derived materials for light construction is a multilayer sandwich structure. In this respect, resistant, rigid, or solid wood elements derived from the edge areas absorb pressure and tensile forces, while the central layer transmits mainly thrust and normal forces.

Thus, for example, honeycomb paper boards that have been on the market for decades are currently experiencing a revival in the wood-derived materials industry through innovations and optimizations in the production process. Although these materials are characterized by very low densities, due to their mechanical properties and the absence of water resistance, these materials cannot be used for carrying purposes.

Better properties can be achieved by lightweight materials with sandwich structure and foam core. However, due to the high thrust load of the low density central layer, the absence of stiffness against the thrust in the case of flexural loads leads to high deformations. In most cases, the resistance properties are also insufficient for use as a bearing element.

Currently, during the production of wood-derived composite materials that are composed of macropiles and a binder, binder is applied to the strands, particles or fibers and then compacted by a compression pressing operation, making the heat acting from the Press plates harden the binder. In particular, on the surfaces that limit with the press plates, this procedure leads to significant compaction. Conventional board materials such as chipboard and fiber board, OSB, etc. as well as special wood-derived materials such as crushing wood, Scrimber (pressed bamboo), TimTek, Srimtec, SST, etc. they therefore have a more or less marked density profile by means of the thickness of the board. In the case of a mostly absent density profile, all the material is very compressed or it is derived from materials for boards with a very low density (for example light wood wool boards, low density fiber boards, etc.), which cannot be compared in terms of their reduced resistance values with derived materials for carrying purposes.

As previously stated, the wood components of conventional board materials as well as special wood-derived materials such as crushing wood, Scrimber, TimTek, Srimtec, SST, etc. they are compacted significantly during production. In addition to the increase in density, this pressing operation is also accompanied by a compaction of the cellular structure of the wood (cellular collapse). In the case of water absorption, a deformation of this type due to the highly hygroscopic properties of the wood and due to the swelling of the cell walls can be partially reversed. However, this is accompanied by strong swelling phenomena of the compressed parts and with it all the board material.

In addition, in these procedures, due to compaction, the introduction of heat for the hardening of the board materials inside the board is difficult. Therefore, these procedures generally depend on the effect of steam blow, to ensure sufficient heat transport. However, to take advantage of the steam blow effect, the macro fibers and / or the binder must have sufficient (residual) moisture.

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Without the so-called steam blow effect (in particular in the case of materials for low density boards), a technological implementation of board production is only possible with difficulty.

EP-A1-1588814 discloses a composite material derived from wood with a density of 300 kg / m3 up to 800 kg / m3 and with an elastic modulus of 3000 MPa up to 14100 MPa.

In spite of numerous attempts, to date there is no composite material derived from wood on the market that combines a reduced density with a rigidity very suitable for supporting elements and in whose production the disadvantages of compaction can be avoided. Therefore, the objective is to provide a composite material derived from wood of this type.

Description of the invention

This objective is achieved according to the invention by a composite material derived from wood according to claim 1 and by a method according to claim 8.

The composite material derived from wood according to the invention has a density of 200-550 kg / m3, preferably 300-550 kg / m3. The stiffness measured as module E in the 4-point bending test according to EN 789 is 4,000-12,000 MPa, preferably 5,000-12,000 MPa, especially preferably 6,000-12,000 MPa. In a particularly preferred embodiment, the wood-derived composite material has a density of 300-550 kg / m3 and a stiffness (module E) of 6,000-12,000 MPa.

The composite material derived from wood according to the invention comprises wood macrofibers with a slenderness ratio (ratio of length to fiber thickness) of more than 20.

Preferably, the macro fibers used are 100-400 mm long, especially preferably 150-300 mm. In this regard, it is clear to the person skilled in the art that from the point of view of the production technique it cannot be excluded that the fibers used also always comprise a certain percentage of shorter fibers.

The composite material derived from the wood according to the invention further comprises a binder which in the hardened state has a foam structure mainly of a fine pore such that 90-95% of the pores have a pore size in the range of 30 -500 | im, preferably 50-300 | im, measured by means of a microscope in a cut through the material, and which in the case of free foaming forms a foam with a density of 30-300 kg / m3, preferably of 80-200 kg / m3.

To determine the density in the case of free foaming, the binder that has not yet reacted is poured into an open container at the top. Due to the chemical reaction, the binder foams and can expand freely through the opening. After hardening, the foam that has overflowed with a blade is cleanly removed. The density of the freely foamed binder can be calculated from the volume and weight of the previously determined container and the weight of the container filled with foam.

Preferably, a binder that forms a closed pore foam structure is used in the present invention. Since the fibers in the composite material derived from the wood according to the invention are almost completely surrounded by the foam and almost all the hollow spaces between the fibers are filled with foam, by means of a closed pore structure of the foam is reduced or even completely prevents moisture penetration, which leads to an advantageous behavior of the wood-derived composite material in the case of moisture action, such as reduced swelling.

The composite material derived from wood according to the invention thus has, in comparison with conventional wood-derived materials, a clearly smaller swelling in the case of moisture action. This is in the range of solid wood or even below, while conventional wood-derived materials generally have a clearly greater swelling compared to the swelling of the raw wood used. For example, in the case of using macrofibers of pine wood, thickness swelling rates can be achieved according to DIN 52364 of between 2.7% and 6%, according to EN 317 of between 1.5 and 5%. The swelling rate for solid pine according to DIN 52364, in comparison with this, also amounts to approximately 4 to 6%. In contrast, the corresponding chipboard or OSB boards show swelling rates from 7% to 30%.

To further reduce the swelling of the wood-derived composite material, the used macro fibers can be modified before further processing by appropriate measures. Such measures are, for example, acetylation or impregnation with suitable resins or chemicals such as, for example, melanin resin or DMDHEU, thermal modification or other known compensating swelling measures. In this way the swelling of the fibers is reduced in the case of moisture absorption and the total swelling of the composite material derived from the wood becomes especially reduced. In this way, swelling values of up to 2% to 4% can be achieved. Due to their reduced thicknesses, the macro fibers used

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in the composite material derived from wood according to the invention they can be impregnated very easily. On the contrary, the modification of solid wood fails in many cases due to the lack of impregnability of the wood.

In chemical procedures it is also necessary, after impregnation of the wood, often a heat treatment. In this case, the reduced dimensions of the macrofibers used according to the invention with respect to solid wood also prove to be advantageous, since in this way the heat encompasses all the wood more quickly. The heat treatment necessary for such a modification can be advantageously partially or even totally integrated in the post-production process of the wood-derived composite material according to the invention.

As the binder according to the invention, preferably a polymer based binder is used. For example, epoxy resin, isocyanate (including polyurethane), melanin, urea, phenolic resin foams or mixtures thereof can be used. Especially preferably a polyurethane system is used, such as a one or more component polyurethane system, in particular a two component polyurethane system. However, thermoplastic foams such as polystyrene (for example EPS or EPX) can also be used.

In a further preferred embodiment, the wood-derived composite material according to the invention further contains particles that can be excited by fields, such as iron oxide particles. In the case of using such particles, the foaming and hardening operation of the binder can be initiated (started) and / or accelerated by applying a field (for example by induction, microwave, high frequency, radiation, etc.). The particles can be conveniently incorporated before the production of the wood-derived composite material into the binder, but can also be used separately.

Alternatively, heat, hot air or steam can also be used to initiate or accelerate the foaming and hardening operation of the binder.

The composite material derived from wood according to the invention may also contain suitable additives, for example foaming agents, fillers, pigments, (nano-, micro- or macro-) reinforcing fibers, fireproofing or wood protection agents as well as agents to compensate for swelling, etc. These additives can either be added to the binder or incorporated separately into the material. Such additives may, in a manner known to the person skilled in the art, confer special properties on the wood-derived composite, such as increased hardness or resistance to thrust, durability, moisture resistance, etc.

The composite material derived from wood according to the invention can be obtained by means of a process comprising the following steps:

a) produce macro fibers;

b) orient the macro fibers;

c) apply the binder;

d) close a press; Y

e) cause foaming of the binder.

In the process according to the invention, the binder is applied on the oriented macrophares (sequence of steps: a, b, c, d and e). Alternatively, the binder can also be applied before the orientation of the macro fibers (sequence of steps: a, c, b, d and e).

The process can be advantageously carried out continuously, for example by means of a band press.

For the production of the wood-derived composite material according to the invention, the macro fibers are dried and oriented in press plates or pressing molds for the most part uniaxially (ie parallel). The binder is applied between and / or on the oriented macro fibers. The application of the binder can take place by procedures established in the wood industry, such as spraying or by gluing or chip mixing facilities.

In a preferred embodiment of the process according to the invention, the foaming time of the binder is adjusted such that the foaming operation especially does not begin until the press is closed. That is, the binder system is chemically adjusted in such a way that the start time for foaming is delayed so that the press or pressing mold can be closed, before significant foaming occurs.

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When closing the press or pressing mold, the macro fibers are preferably compacted only minimally, so that the density of the composite material derived from the wood produced does not differ essentially from the density of the wood used. Since the macro fibers in the process according to the invention are only compacted insignificantly, swelling that occurs in the event of subsequent contact with water or in the case of water accumulation can be minimized or avoided. In this way, swelling values can be achieved that are in the swelling range of the wood used or even below. This is an essential advantage with respect to conventional wood-derived materials, which have a mostly high compaction of the wood and thus in contact with water have a clearly greater swelling than the wood used.

In the pressing mold or the closed press, the compression pressure applied from the outside acts on the one hand, on the other hand, by means of foaming the binder, a compression pressure is generated from within, so that the binder penetrates essentially completely in the macro fiber net and moisturizes its surface for the most part completely. The macro fibers are thus surrounded by a matrix of binder and thus are well protected against moisture absorption.

Since the binder is incorporated into the macro fiber net by expanding the binder, a very homogeneous material with a uniform density is produced, in which almost all the hollow spaces are filled with the foam structure and the fibers are surrounded ( coated) almost completely by foam.

Furthermore, the process according to the invention, in particular in the case of using a two-component polyurethane system as a binder, has the advantage that only insignificant heat has to be supplied to begin hardening. The necessary heat can already be incorporated by a slight preheating of the macro fibers (for example up to 30-90 ° C, preferably 50 ° C).

Since the binder is only combined with the macro fibers directly before hardening, essentially 100% of the binder is available for adhesion and "coating" of the chips.

When the binder system is adjusted so that it hardens completely in the press, then the press can immediately open again. However, even in the case of non-hardened boards completely of the wood-derived composite material according to the invention, the boards are not destroyed, unlike conventional wood-derived material boards, due to so-called cleavages. By a subsequent hardening, only a subsequent thrust occurs in the composite material derived from the wood according to the invention.

The wood-derived composite material according to the invention is suitable for all products that are produced from solid wood or wood-derived materials, such as chipboard or OSB boards, etc. Due to the low density, the use of the wood-derived composite material according to the invention leads to a smaller weight of the products thus produced.

It is especially advantageous to use the composite material derived from wood according to the invention for products, in which, in addition to the weight, dimensional stability is also important in the case of moisture action and the maintenance of resistance or stiffness. Such products include, due to use without outdoor protection:

- formwork products, such as formwork supports, or parts thereof, such as strip or core,

- coated or uncoated formwork boards or parts thereof, such as intermediate layers or coating layers,

- platforms for work and protection scaffolding,

- formwork products in the form of a bar or flat in a mono-, bi- or three-dimensional form for the formation or reinforcement of the formwork liner, and

- lost formwork or parts thereof that remain in the construction.

Additional products that can be advantageously produced from the wood-derived composite material according to the invention, include:

- supports of construction of wood of solid material or with hollow spaces or parts thereof, such as bands or souls (advantage: reduced weight, homogeneous properties without weak points such as knots in solid wood; possibility of producing a profile (profile in I or other cross-section optimized similar to metal supports)),

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wood construction boards and furniture construction boards (advantage: properties such as plywood with respect to static, swelling, moisture resistance with at the same time a very low weight and economic production capacity) ,

wooden construction board parts (cladding layers, intermediate layers),

intermediate layers with fixed fiber direction for the most part that are produced from blocks with a parallel fiber direction by a transverse cut to the fibers (advantage: reduced weight, virtually no thickness swelling, economical production (eg replacement balsam assembled wood)),

sandwich boards of a particularly light macro-fiber central layer with supporting coating layers of suitable materials such as wood veneer, plywood or also plastic boards with a vertical or horizontal central layer,

"Multilayer solid wood panels" - materials for homogeneous panels for walls and ceilings with thicknesses from 5 cm to> 20 cm. (advantage: weight, thermal insulation, static, moisture resistance),

multilayer solid wood board with hollow spaces (advantage: see above, even smaller weight, material savings)

profiles of solid material or with hollow spaces of the most diverse types for construction pieces, windows, doors and furniture (advantage: profile that can be produced without loss of material, static, weight)

panels, supports and profiles for vehicle construction (advantage: weight, static, moisture resistance)

two-dimensional and flat-shaped bar-shaped and flat-shaped molded parts for wood-vehicle construction, interior design and furniture construction (advantage: production capacity of almost any shape, static, weight)

Example

The macro fibers are dried by a stream of hot air (50 ° C) and stored for several days at ambient conditions of 20 ° C and 65% relative humidity, which adjusts a wood moisture of approximately The 12%. 210 g of the macro fibers are oriented in parallel as closely as possible. 50% of the fibers are disposed in an aluminum mold heated to 50 ° C (30 x 12 cm) and moisturized evenly with 60 g of two-component polyurethane (RAMPF company No. 80 L86 / 4-1 ). The remaining 50% of the fibers are then placed in the mold and the mold is closed, so that the arranged macrophares are compressed to a height of 16 mm. Through the chemical reaction of the two components of the polyurethane with the water available in the wood, it is foamed with intensity. After 30 min the foam has completely hardened and the composite material derived from the wood can be removed from the mold.

Claims (13)

10 2. 3. 15 Four. 20 5. 6. 25 7. 30 8. 35 40 Four. Five 9. 50 10. eleven. 55 12. 13. 60 14. 65 15. Composite material derived from wood with a density of 200-550 kg / m3 and a stiffness measured in the 4-point bending test according to the EN 789 standard of 4,000-12,000 MPa, comprising macro fibers with a slenderness ratio of more than 20 and a binder, the relationship of slenderness being understood as the ratio of the length to the thickness of the fibers, the binder having a foam structure mainly of fine pore such that 90-95% of the pores have a size of pore of 30-500 | im, and that the binder in the case of free foaming forms a foam with a density of 30-300 kg / m3. Composite material derived from wood according to claim 1, the composite material derived from wood having a density of 300-550 kg / m3 and a stiffness of 6,000-12,000 MPa. Composite material derived from wood according to claim 1 or 2, 90-95% of the pores having a pore size of 50-300 | im. Composite material derived from wood according to one of claims 1-3, using as a binder a polyurethane system. Composite material derived from wood according to one of claims 1-4, further containing particles that can be excited by fields, preferably iron oxide particles. Composite material derived from wood according to one 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%, especially preferably less than or equal to 3% . Composite material derived from wood according to one of claims 1-6, the macro fibers being modified by acetylation, impregnation with suitable resins or chemicals or thermal modification. Process for the production of a composite material derived from wood according to one of claims 1-7, comprising the following steps: - produce macro fibers; - target macro fiber; - apply the binder; - close a press; Y - cause foaming of the binder, adjusting the binder system in such a way that, above all, the foaming operation mainly does not begin until after the press is closed, and when the press or the pressing mold is closed, the macro fibers are preferably only minimally compacted. Method according to claim 8, the foaming and hardening process being initiated and / or accelerated by means of a field. Method according to claim 9, in addition to the binder particles that can be excited by fields. Process according to claim 10, the particles being contained in the binder. Method according to claim 8, the foaming and hardening process being initiated and / or accelerated by heat, hot air or steam. Method according to one of claims 8-12, which is carried out as a continuous process, for example, by means of a belt press. Composite material derived from wood according to one of claims 1-7, which can be obtained by a process according to one of claims 8-13. Product comprising the composite material derived from wood according to one of claims 17 or 14, the particular product being selected from formwork products and parts thereof; coated or uncoated formwork boards and parts thereof; work and protection scaffolding platforms; bar-shaped or flat-shaped mono-, bi- or three-dimensional formwork products for the formation or reinforcement of the formwork liner; lost formwork and parts thereof that remain in the construction; wooden building stands or parts thereof; 5 wooden construction boards; building boards for furniture; coating layers and intermediate layers of construction boards (of wood); sandwich boards; multilayer solid wood boards; profiles; panels, supports and profiles for the construction of vehicles; and molded parts.