WO2005039845A1

WO2005039845A1 - Postformable derived timber product sheet and method for production thereof

Info

Publication number: WO2005039845A1
Application number: PCT/EP2004/008738
Authority: WO
Inventors: Kerstin Schmidt; Andreas Weber; Dirk Grunwald; Steffen Tobisch; Björn LILIE
Original assignee: Fraunhofer-Gesellschaft Zur Förderung Der Angewandten Forschung E.V:; Institut für Holztechnologie Dresden gGmbH
Priority date: 2003-09-25
Filing date: 2004-08-04
Publication date: 2005-05-06
Also published as: DE10344598B3

Abstract

The invention relates to a method for production of postformable derived timber product sheets with at least one layer of thin, long, preferably aligned cuttings, coated with a glue and combined in a press unit under the action of pressure and thermal energy and a postformable derived timber product sheet. The aim of the invention is the production of postformable derived timber product sheets with at least one layer of thin, long, preferably aligned cuttings, exhibiting an improved moisture-resistance, transverse tensile strength and a good thermal resistance after shaping. Said aim is achieved, whereby a thermoplastic and a duroplastic glue are used as glue and the cuttings are combined only after activation of the thermoplastically-hardened glue, or the cuttings are coated with glue components of the glue which may be activated and hardened duroplastically which are not yet duroplastically hardened.

Description

Patent application: Postformable wood-based panel and process for its production

description

The invention relates to a process for the production of re-formable wood-based panels with at least one layer of slender, long, preferably aligned chips, which are wetted with an adhesive and bonded to one another under the action of pressure and thermal energy, and to a re-formable wood-based panel with at least one layer longer , slender, preferably aligned chips, which are wetted with an adhesive and were connected to one another under the influence of pressure and thermal energy in a press system.

Boards are produced from long, slim, preferably aligned chips, so-called strands, by cutting the wood in drum barkers after debarking the starting material. Knife ring chippers are used almost exclusively, whereby the dimensions of the strands have increased to lengths of 120 to 145 mm in recent years. The production of longer beaches is basically possible. After drying in drum dryers, the strands are fractionated in drum sieves.

Wetting with binder or gluing takes place mechanically in glue drums into which the binder or adhesive is finely divided and introduced via spray heads or so-called atomizers. The fine distribution of the adhesive and the friction of the beaches against each other creates a wiping effect and a large part of the beach surface is thinly glued. After glueing or wetting with adhesive, the wood materials or strands are bonded to one another in discontinuous one- or multiple-day hot presses or continuously working hot presses after the nonwoven formation, which can be done either in one layer without orientation or in three layers with a blocked middle layer. The wood-based panel, the so-called OSB (Oriented Strand Board), is usually given its final shape, which can be further processed by grinding, trimming or coating.

Technologies are known from the prior art with which it is possible to bring wood materials into their final shape by shaping, that is to say the subsequent shaping of wood or semi-finished products from wood chips and fibers. A distinction is to be made between forming and forming, in which molded parts made from chip and fiber masses are obtained in one operation, the molded part not receiving its final shape through subsequent processing. In order to be called a malleable wood-based material, a product must have the following properties:

- the wood components of the material must be recognizable in the material,

- The adhesive content (solid) must be less than 25% based on dry wood and

- The wood-adhesive mixture must not be able to climb, so it must not flow under pressure when softened.

Several processes have been developed for producing molded parts from wood particles by means of primary shaping, for example the thermodynamic process in which a molded part is made from wood fiber material by activating the inherent adhesive power of certain wood components. Furthermore, the Collipress process for the production of packaging containers from wood chips and the Werzalit process according to DE-OS 2 035 053 known. A large number of molded parts are produced in a two-step process from a chipboard mass in the primary molding process.

From the . ^DD 20 1 1 20 a forming process for wood-based materials is known, in which the suitability of thermoplastic-bonded wood particle materials for the production of two- and three-way deformed components, primarily for the furniture industry, was investigated. Both wood-based materials from MDF production and various chip fractions were used as wood particles. Since the adhesives used were purely thermoplastic, the plate-shaped semi-finished product was formed after prior heating to soften the

Adhesive in press and bending dies without further crosslinking or condensation. The disadvantage here is the lack of moisture resistance of the bond and the thermoplasticity of the connection when using such adhesive systems.

The object of the present invention is to provide post-formable wood-based panels with at least one layer of long, slender, preferably aligned chips which, after being formed, have improved moisture resistance, transverse tensile strength and good heat resistance.

According to the invention this object is achieved by a method with the features of claim 1 and a wood-based panel with the features of claim 8. Advantageous refinements and developments of the invention are described in the subclaims.

The use of both thermoplastic and thermosetting curing adhesives as an adhesive means that both properties of a wood-based panel, which initially appear to be contradictory, are achieved, namely, on the one hand, the formability, on the other hand the high heat resistance as well as low thickness swelling and high transverse tensile strength of the formed Wood panel. This is achieved in that the chips are only connected to one another by activating the thermoplastic curing adhesives, so that the thermosetting curing adhesives have not yet been crosslinked, that is to say have not yet been activated.

Surprisingly, in the case of wood-based panels, in which the chips have only been connected to one another by activating the thermoplastic curing adhesives, board properties have been determined which permit an industrially customary, continuous production of wood-based panels or OSB which can be subsequently reformed without major restrictions. The reshaping of the correspondingly produced wood-based panels, which serve as semi-finished products, at molded part manufacturers can be carried out at different pressing temperatures and, unlike the destructive shaping of conventional OSB, is unproblematic and possible without a reduction in properties. The pressing temperatures depend on the adhesives or adhesive mixture used and are between 100 ° and 240 ° C.

An advantageous embodiment of the invention provides that the crosslinking temperature for thermosetting is above a setting temperature for thermoplastic adhesives, with the chips below the crosslinking temperature for thermosetting, but above the setting temperature for thermoplastic curing, so that a wood-based panel is joined together arises, which still has the potential for thermoset curing, but due to the thermoplastic curing of the adhesives it already has sufficient stability to be stored, transported and processed without any problems.

In order to enable precise setting of the press temperature, in particular in the end area of the press system, it is provided that individual segments, especially the last press segments of a press system that are not heated or actively recooled.

Alternatively, in discontinuously operating press systems, recooling under pressure is provided, whereby thermal activation of the thermosetting adhesives due to the cooling of the press is avoided.

The wood-based panel can be coated before the reshaping and activation of the thermosetting adhesives, in particular with veneers, furniture foils or flexible laminates.

A mixture of MUPF adhesive and acrylate is preferably used as the adhesive. The thermoplastic and thermosetting adhesives can either be applied together as a mixture to the chips or applied individually, if necessary in layers and one after the other. Due to the high metal stickiness, PMDI adhesives are preferably used in the interior of the wood-based material fleece.

The reshapable wood-based panel according to the invention provides that the chips are connected to one another via thermoplastic hardening adhesive portions of the adhesive and are wetted with activatable, thermosetting adhesive portions of the adhesive that have not yet hardened, in order to enable non-destructive reshaping of the wood-based panel.

The adhesive advantageously has portions of MUPF adhesive and acrylate.

The wood-based panel can be composed of a single-layer layer of long, slender, possibly aligned beaches. Alternatively, the long, slim beaches can be arranged as cover layers that enclose a middle layer, the chips or the wood-based materials being unoriented in contrast to the cover layers. The top layers enclose the middle layer, whereby the middle layer can be wetted with PMDI adhesive.

Exemplary embodiments of the method are described below.

The inventive production of re-formable wood-based panels with long, slim chips, at least as a top layer, so-called OSB, using an adhesive combination of thermoplastic and thermosetting components takes place under conditions customary in industry, whereby conventional softwood and possibly hardwood beaches or their mixtures with a beach length of up to 145 mm can be mechanically glued with the adhesive mixture in drum mixers. In addition, the use of other property-improving additives, such as. B. water repellant possible. The material moisture should be between 6 and 12% after gluing and before pressing.

After the formation of the fleece, which can take place either in one layer or in three layers with a blocked middle layer, the wood-based panels are produced as semi-finished products in discontinuously working single or multi-day hot presses or continuously working hot presses. During pressing, the pressing time factor, the pressing temperature and the pressure regime depend on the adhesive combinations used in the adhesive. The last segments of a continuous press system should not be heated or actively recooled in order to avoid thermoset curing of the corresponding adhesive components. When manufacturing in discontinuous press systems, recooling and pressure reduction may be required. After pressing, the boards can be treated like conventional boards, in particular trimming, grinding, cutting or storage is possible. After storage for 3 to 5 days in a ripening stack at room temperature and, if necessary, transport to a processor, the previously thermoplastic-bonded wood-based panels are re-crosslinked as semi-finished products at a temperature of 100 to 240 ° C on single-day or molded presses. The duroplastic component of the adhesive hardens completely. Both the processing of pure OSB and a coating with solid coating materials such as veneers, furniture foils or flexible laminates is possible. The reshaping or the deformations can be carried out both in the two-dimensional and in the three-dimensional range. The molded parts are similar in their possibilities for further processing and the strength properties of conventionally manufactured, flat OSB panels.

In a first embodiment, 100% pine beaches with a thickness of 0.8 mm and a length of 145 mm were used. The raw plate thickness was 1 1, 5 mm with a single-layer plate structure and a target bulk density of 650 kg / m ³ . 70% MUPF adhesive and 30% acrylate were used as the adhesive, the adhesive content being 10% solid resin based on atro strands. 1% solid paraffin, based on atro strands, was added as the hydrophobizing agent, and at a moisture content of 10% after the gluing, the semi-finished product was produced at a hot plate temperature of 95 ° C. with a press time factor of 20 sec / mm. The bulk density achieved was 620 kg / m ³ , the transverse tensile strength (dry) was 0.26 N / mm ² , the bending strength was 17.1 N / mm ² with a flexural modulus of 3000 N / mm ² and one Thickness swelling after 24 h WL of 70.8%.

The post-forming was carried out in the form of a plate and gave a plate thickness of 11 mm, the heating plate temperature being 180 ° C. and the pressing being carried out with a pressing time factor of 20 sec / mm. The bulk density of the postformed plate was 645 kg / m ³ with a transverse tensile strength (dry) of 0.60 N / mm ² , a bending strength of 25.5 N / mm ² , a flexural modulus of 3500 N / mm ² and a thickness swelling of only 17.8% after 24 hours of water storage. The result shows that the transverse tensile strength tripled, the flexural strength increased by more than 50% and the thickness swell was reduced to a quarter of the semi-finished product, which shows that the mechanical properties of the re-formed plate are essential due to the final thermosetting of the materials be improved.

In the second exemplary embodiment, 100% beech beaches with a length of 90 mm to 120 mm and a thickness of 0.5 mm were used. The raw board thickness was 11.5 mm with a single-layer board structure with a target bulk density of 680 kg / m ³ . 70% MUPF adhesive and 30% ethylene-modified polyvinyl acetate were used as adhesives, with an adhesive content of 12% solid resin based on atro strands. 1% solid paraffin based on atro strands was used for the hydrophobization. The heating plate temperature was 95 ° C with a moisture content of 0% after gluing and a pressing time factor of 15 s / mm. The post-deformation was three-dimensionally curved to form a chair seat. The material thickness was 1 1 mm and the hot plate temperature during post-forming was 100 ° C. The pressing time for post-forming was 6 minutes. Due to the deformation of the finished workpiece in the form of a three-dimensional chair seat, no standardized product properties could be determined, but the reshaped product was usable.

Due to the initially only thermoplastic-based binding of the chips of the wood-based panel, it is possible to enable two-dimensional or three-dimensional post-forming without mechanical destruction of the wood-adhesive connection already formed. Mechanical destruction would preclude further material use due to the loss of strength. The adhesive mixture according to the invention and the wood-based panels surprisingly achieve this Even at comparatively low press temperatures, sheet properties that allow further processing and in particular forming.

Acrylates and polyvinyl acetates are particularly suitable for thermoplastic curing, while urea-formaldehyde (UF), melamine-urea-formaldehyde (MUF) and melamine-urea-phenol-formaldehyde (MUPF) adhesives are mainly used for thermosetting in question.

The setting temperature of thermoplastic adhesives is generally below the crosslinking temperature of thermosetting systems. The post-deformation temperature selected in exemplary embodiment 2 was below the setting temperature of the thermoplastic adhesive due to the technological conditions in the production of molded parts. Cross-linking of the thermoset was achieved by a correspondingly longer pressing time. A post-crosslinking of the molded part at 180 ° C to 210 ° C would have been desirable in terms of a faster reaction time.

Claims

claims

1 . Process for the production of re-formable wood-based panels with at least one layer of slender, long, preferably aligned chips, which are wetted with an adhesive and bonded together in a press system under the influence of pressure and thermal energy, characterized in that thermoplastic and thermosetting adhesive is used as the adhesive and that the chips are connected to one another by activating only the thermoplastic curing adhesives.

2. The method according to claim 1, characterized in that the crosslinking temperature for thermosetting is above a setting temperature for thermoplastic curing, and that the chips below the crosslinking temperature for thermosetting and above the setting temperature for thermoplastic curing are connected to one another ,

3. The method according to claim 1 or 2, characterized in that individual segments of the press system are not heated or actively recooled.

4. The method according to any one of the preceding claims, characterized in that in the case of discontinuously operating press systems, recooling takes place under pressure which is kept away.

Method according to one of the preceding claims, characterized in that the wood-based panel is coated, in particular with veneers, furniture foils or flexible laminates.

6. The method according to any one of the preceding claims, characterized in that a mixture of MUPF adhesive and acrylate is used as the adhesive.

7. The method according to any one of the preceding claims, characterized in that the thermoplastic and thermosetting adhesives are applied as a mixture together on the chips, in particular sprayed and then mixed.

8. Post-deformable wood-based panel with at least one layer of long, slender, preferably aligned chips, which are wetted with an adhesive and were connected to one another under the influence of pressure and thermal energy in a press system, characterized in that the chips have parts of the adhesive that are thermosetting adhesive connected to one another and wetted with activatable, thermosetting adhesive portions of the adhesive which are not yet thermosetting.

9. Wood-based panel according to claim 8, characterized in that the adhesive has proportions of MUPF adhesive and acrylate.

0. Wood-based panel according to claim 8 or 9, characterized in that the long, slender chips are arranged as cover layers which enclose a middle layer, the middle layer being wetted with PMDI adhesive.