EP3395520B1 - Method for the preparation of osb wood-base panels with reduced emission of volatile organic compounds (vocs) - Google Patents

Description

The present invention relates to a process for treating wood strands with water vapor according to claim 1, a process for producing OSB wood-based panels according to claim 7 and a production line for producing OSB wood-based panels according to claim 11.

description

Chipboard, also known as OSB (oriented strand boards), are wood-based panels made from long strands. OSB boards are increasingly being used in timber and prefabricated house construction, as OSB boards are lightweight and still meet the structural requirements imposed on building boards. For example, OSB boards are used as building boards and as wall or roof planking or in the floor area.

The production of OSB boards is carried out in a multi-stage process, wherein initially the chips or strands of debarked roundwood, preferably coniferous wood, are peeled off in the longitudinal direction by rotating blades. In the subsequent drying process, the natural moisture of the beach is reduced at high temperatures. The degree of moisture of the strands may vary depending on the adhesive used, and the humidity should be well below 10% in order to avoid breakers during later compression. Depending on the adhesive, wetting may be more favorable on rather wet beaches or on dry beaches. In addition, as little moisture as possible should be present in the strands during the pressing process, in order to reduce the vapor pressure generated during the pressing process as far as possible, as this could otherwise cause the raw plate to burst.

Following the drying of the strands they are introduced into a gluing device in which the glue or adhesive is applied finely distributed to the chips. For gluing predominantly PMDI (polymeric diphenylmethane diisocyanate) or MUPF glues (melamine-urea-phenol-formaldehyde) are used. The glues can also be mixed in the OSB boards. These glues are used because the OSB boards are often used for structural applications as mentioned above. Moisture or moisture-resistant glues must be used there.

After gluing the glued strands are scattered in scattering apparatuses alternately along and across the production direction, so that the strands are arranged crosswise in at least three layers (lower cover layer - middle layer - upper cover layer). The scattering direction of the lower and upper cover layer is the same, but deviate from the scattering direction of the middle layer. Also, the strands used in the top and middle layers differ from each other. Thus, the strands used in the outer layers are flat and the strands used in the middle layer are less flat up to span-shaped. Usually, two strands of material are used in the manufacture of the OSB boards: one with flat strands for the later cover layers and one with "chips" for the middle layer. Accordingly, the strands in the middle layer may be qualitatively inferior because the flexural strength is generated substantially by the cover layers. Therefore, fines produced during machining can also be used in the middle layer of OSB boards. The percentage distribution between middle and top layer is at least 70% to 30%. Following the scattering of the strands, continuous compression of the same under high pressure and temperature of e.g. 200 to 250 ° C.

Not least because of their sustainability, OSB boards are enjoying increasing popularity and diverse applications, for example as a construction element in house construction or as formwork in concrete construction. The inherent hygroscopic properties of wood-based materials, however, have a detrimental effect in some applications.

Especially when using indoor OSB, the escape of wood constituents is viewed critically. This is particularly problematic in OSB pine panels, as they show very high emission of volatile organic compounds.

In the course of the production of wood-based panels and in particular due to the production process of the wood strands arise or a variety of volatile organic compounds are released. Volatile organic compounds, also called VOCs, include volatile organic compounds which readily evaporate or are already present as gas at lower temperatures, for example at room temperature.

The volatile organic compounds (VOC) are either already present in the wood material and are released during workup from this or they are formed according to the current state of knowledge by the degradation of unsaturated fatty acids, which in turn are decomposition products of wood. Typical conversion products which occur during processing are, for example, pentanal and hexanal, but also octanal, 2-octenal or 1-heptenal. In particular, softwoods from which OSB boards are predominantly produced contain large amounts of resin and fats which lead to the formation of volatile organic terpene compounds and aldehydes. However, VOCs, such as the aldehydes mentioned, can also be formed or released when certain adhesives are used for the production of wood-based materials.

The emission of ingredients in OSB boards is critical mainly because this material is predominantly used uncoated. This allows the ingredients to exude unhindered. In addition, the OSB boards are often used for cladding / paneling of large areas, which usually results in a high space loading (m ² OSB / m ³ room air). This leads in addition to a concentration of certain substances in the room air.

To solve the problem of VOC emission, various approaches have been described in the past.

In the past, attempts have been made to at least reduce the emissions of aldehydes by adding reducing agents. However, many of these reductants were sulfur containing resulting in undesirable emissions of sulfur dioxide during plate production and later use.

One approach was in the EP 1 907 178 B1 tracked. Here wood chips or wood fibers are treated before gluing at a pressure of 6-12 bar in a saturated steam atmosphere or in a water vapor-saturated air over a period of 3-8 minutes with a bisulfite compound, such as sodium or ammonium bisulfite. The addition of bisulfite is believed to bind volatiles in shredded wood and suppress the buildup of volatiles. However, the used chemicals more expensive not only the process but also partly lead to odor nuisance in production.

The addition of activated carbon was also tested, but is technologically and in terms of cost unsatisfactory.

The addition of suitable VOC scavengers almost always takes place after the drying process of the strands, since this or also the temperature exposure in the press was considered to be the triggering reasons of the majority of the emission. The VOC scavengers were added in liquid form via the gluing system, solids were added at various points of the process (eg scattering). This required an additional installation of dosing stations to ensure a homogeneous distribution.

The invention is based on the technical object of improving the known method for the production of OSB material plates in order to produce OSB material plates with a significantly reduced emission of volatile organic compounds (VOCs) in a simple and safe manner. At least the emission of terpenes should be reduced. If possible, the manufacturing process should be changed as little as possible and the cost should not rise disproportionately. Furthermore, the solution should include the greatest possible flexibility. Ultimately, ecological aspects should also be taken into account, d. H. the solution should not cause additional energy consumption or generate additional waste.

Another technical task was to design a plant that would allow easy treatment of the beaches to reduce the emission of VOCs. This should be integrated into the production process and should not disturb or increase the cost of manufacturing the OSB. Also, the technical effort for the treatment should not lead to an increase in safety measures or involve a greater risk potential.

This object is achieved by a method for the treatment of wood strands with water vapor with the features of claim 1, a method for producing OSB wood-based panels with the features of claim 7, and a suitable production line according to claim 11.

Accordingly, there is provided a method of treating wood strands with water vapor to reduce the emission of volatile organic compounds (VOCs) from these wood strands, the wood strands, after being recovered, from suitable wood strands Wood treated without drying with steam over a period of 5 to 20 min, the steam is passed over the wooden strands at a temperature between 80 ° C and 120 ° C and a pressure between 0.5 bar and 2 bar. The water strands thus treated with steam are used to produce OSB boards with reduced emission of volatile organic compounds.

From the US 5,44,7,686 While a method of heat treating wood or wood products such as tree trunks or wood chips with steam or hot water is known, this serves to kill plant pests.

EP 0695609 A2 relates to a method for preheating grit to a predetermined preheat temperature during the manufacture of wood-based panels. Preheating here allows an increase in performance for the production of wood-based panels, since the pressing time can be shortened.

In one embodiment of the present method, the treatment of the wood strands with steam takes place in such a way that the steam at a temperature between 90 ° C and 110 ° C, particularly preferably of 100 ° C at a pressure between 0.7 bar and 1.5 bar, particularly preferably at 1 bar (atmospheric pressure) is passed over the wooden strands.

Thus, the steam treatment is carried out at the temperature-dependent pressure with which the steam is introduced into the treatment device. In particular, a steam treatment at atmospheric pressure (temperature of the introduced steam of 100 ° C) is preferred. Accordingly, the application of an additional (external) pressure (i.e., in addition to the pressure with the water vapor entering the system) can be dispensed with. This leads to a simplification of the apparatus since no pressure vessels (such as an autoclave or a pressure chamber) are necessary for the steam treatment.

Due to the preferably used saturated steam atmosphere, the steam treatment of the wood strands takes place in an oxygen-poor atmosphere or with the greatest possible exclusion of oxygen.

The present water vapor treatment of the wood strands is carried out in a separate steam treatment apparatus. The steam treatment takes place outside of a chipper (eg knife ring chipper or disc chipper) and is thus not part of the cutting or crushing process of wood for the production of wooden strips. It is also essential that the steam treatment can be carried out before the drying of the wood strands.

Also, no additives are added to the steam: In particular, no addition of bleaching agents, such as bisulfites or oxygen-releasing substances. But also on the addition of other VOC scavengers to the binder can be dispensed with.

In the present process, the steam treatment of the wood strands is carried out over a period of 5 to 20 minutes, preferably from 10 to 20 minutes, particularly preferably 15 minutes. The amount of steam is a maximum of 1 kg of steam / kg of beach (atro).

The duration of the steam treatment is determined primarily by the speed of the transport device on which the wood strands are continuously fed through the steam treatment device.

In a particularly preferred embodiment, the water vapor is trapped as condensate after passing the wood strands. It is advantageous that the loading of the condensate with organic compounds is relatively low. The COD (Chemical Oxygen Demand) was about 250 mg COD / l when one kilogram of steam was treated with one kilogram of steam.

The wood strands used herein may have a length of between 50 to 200 mm, preferably 70 to 180 mm, particularly preferably 90 to 150 mm; a width between 5 to 50 mm, preferably 10 to 30 mm, particularly preferably 15 to 20 mm; and a thickness between 0.1 and 2 mm, preferably between 0.3 and 1.5 mm, particularly preferably between 0.4 and 1 mm.

In one embodiment, the wooden strands have e.g. a length between 150 and 200 mm, a width between 15 and 20 mm, a thickness between 0.5 and 1 mm and a humidity of max. 50% up.

• mindestens ein Gehäuse, insbesondere ein rohrförmiges Gehäuse;
  • mindestens eine das Gehäuse durchlaufende Transportvorrichtung zum Transportieren der Holzstrands durch das Gehäuse; und
  • mindestens eine oberhalb der Transportvorrichtung Gehäuse vorgesehene Zuleitung für den Wasserdampf, wobei entlang der Zuleitung mindestens ein Sprühmittel zum Applizieren des Wasserdampfs auf die sich auf der Transportvorrichtung befindlichen Holzstrands angeordnet ist.

The steam treatment of the wooden strands is carried out in a device comprising the following elements or features:

• at least one housing, in particular a tubular housing;
  • at least one transport device passing through the housing for transporting the wooden strands through the housing; and
  • at least one above the transport device housing provided supply line for the water vapor, wherein along the supply line at least one spraying means for applying the water vapor is disposed on the located on the transport device wood strands.

In a variant, the at least one housing may be in the form of a metal tube or tubular body.

In one embodiment of the present device, the at least one transport device consists of at least one conveyor belt. The conveyor belt should have perforations or other openings so that the water vapor can be passed from the top of the conveyor belt past the wooden strands to the underside of the conveyor belt. The wooden strands are distributed on the conveyor belt so that a homogeneous flow through the wood strands with steam is possible.

In a further embodiment of the present device, more than one spraying means is provided on the steam supply line. The number of spray is particularly dependent on the total length of the housing. Also, the spray can be controlled individually, so that the required amount of water vapor is specifically adjustable. As a spray nozzle or other suitable injectors can be used, which allow a uniform spraying and a uniform distribution of water vapor on and between the wooden strands.

As already mentioned above, in a particularly preferred embodiment, the water vapor is collected after passing through the wood strands as condensate. For this purpose, at least one means for collecting the condensate is provided in the vaporization system below the conveyor belt (based on the flow direction of the water vapor). For example, the tubular body may be angled upwards in the feed direction.

The condensate thus collected contains wood components washed out of the wood strands, in particular aldehydes, organic acids and / or terpenes, in particular those which have a certain water solubility.

After leaving the steam treatment apparatus, the steam-treated strands have a temperature of 80 to 90 ° C. At this temperature, the wood strands from the steam treatment station enter a dryer (as part of the OSB board production line), resulting in an increase in dryer performance. This will continue to use the energy needed to remove wood constituents for the drying process. In a normal process, the inlet temperature of the strands into the dryer is about 25 ° C.

1. a) Herstellen von Holzstrands aus geeigneten Hölzern;
2. b) Behandeln von zumindest einem Teil der Holzstrands mit Wasserdampf gemäß dem oben beschriebenen Verfahren;
3. c) Trocknen der mit dem Wasserdampf behandelten Holzstrands;
4. d) Beleimen der mit Wasserdampf behandelten und getrockneten Holzstrands und optional Beleimen von nicht mit Wasserdampf behandelten Holzstrands mit mindestens einem Bindemittel;
5. e) Aufstreuen der beleimten Holzstrands auf ein Transportband; und
6. f) Verpressen der beleimten Holzstrands zu einer OSB-Holzwerkstoffplatte.

Also provided is a process for producing OSB wood-based panels having reduced emission of volatile organic compounds (VOCs) comprising the steps of:

1. a) making wooden strips of suitable woods;
2. b) treating at least a portion of the wood strands with water vapor according to the method described above;
3. c) drying the steamed wood strands;
4. d) gluing the steam-treated and dried wood strands and optionally gluing non-steamed wood strands with at least one binder;
5. e) sprinkling the glued wooden strands on a conveyor belt; and
6. f) pressing the glued wooden strands into an OSB wood-based panel.

The present method enables the production of OSB wood-based panels using steam-treated wooden strands which are introduced into a known manufacturing process in addition to or as an alternative to untreated wood strands. An OSB wood-based panel produced by the process according to the invention comprises steam-treated wood strands has a reduced emission of volatile organic compounds, in particular terpenes and aldehydes.

By providing the present method, there are several advantages. Thus, a simple production of OSB wood-based panels is possible without significantly influencing the usual process chain with significantly reduced emission of volatile organic compounds from the OSB. In addition, the energy requirement for drying the wood strands can be reduced because the wood strands already have an elevated temperature (e.g., about 90 ° C) when entering the dryer; i.e. The energy used in the steam treatment supports the drying process. Also, can be dispensed with the use of additional chemicals, whereby the overall process is ecologically and economically advantageous.

In the present process, the production of OSB is changed in comparison to the conventional OSB production processes in that at least part of the strands used after production are treated with steam before drying. The beaches can be those that act for the cover or middle class. After treatment, the strands are fed to the standard drying process. This is done z. B. immediately before gluing, whereby a complete substitution or even a partial substitution of the standard strands can take place.

In a further embodiment of the present process, steam-treated wood strands or a mixture of steam-treated wood strands and non-steam-treated wood strands are used as the middle layer and / or top layer of the OSB wood-based panel.

Accordingly, in one variant, a complete substitution of the wood strands is possible, wherein the steam-treated wood strands are used in the middle layer, and in one or both cover layers or in all layers.

In another variant, it is possible to form only the middle layer of steam-treated wood strands and to use non-steam-treated wood strands for one or both cover layers. Since steam-treated wooden strands have a lighter color, it may be correspondingly advantageous in the topcoat to use steam-treated wooden strands. These give the OSB a more appealing color.

In yet another variant, only one or both cover layers of steam-treated wood strands are formed, and for the middle layer, if necessary, dried and non-steam-treated wood strands are used.

In yet another variant, it is conceivable and possible to use for the middle and outer layers in each case a mixture with any ratio of steam-treated wood strands and non-steam-treated wood strands. In such a case, the mixture may comprise between 10 and 50% by weight, preferably between 20 and 30% by weight of untreated or non-steamed wood strands and between 50 and 90% by weight, preferably between 70 and 80% by weight of steam-treated wood strands.

In a further embodiment variant, the step of steam treatment of the wood strands can be carried out separately from the production process of the OSB wood-based panels. Accordingly, the steam treatment in this embodiment of the present method takes place outside the overall process or the process line. The wood strands are thereby discharged from the manufacturing process and introduced into the steam treatment apparatus (e.g., steaming equipment). Subsequently, the steam-treated wood strands may, if necessary after intermediate storage, e.g. be returned to the conventional manufacturing process immediately before gluing. This allows a high flexibility in the manufacturing process.

The steam treatment of the wood strands can be integrated into the manufacturing process of the OSB wood-based panels in an even further embodiment variant, i. The steam treatment step is integrated into the overall process or process line and takes place online.

In this case steam treatment may be carried out i) immediately after cutting and providing the strands of wood or ii) only after sifting and separating the strands of wood according to the use of the strands for the middle or top layer. In the latter case, a separate water vapor treatment of the wood strands can be made according to the requirements of the wood strands used in the middle and top layers.

In a further variant of the present process, the steam treatment of the wood strands is carried out in at least one vaporization plant, preferably in two vapor deposition plants. The vaporization system used in the present case can be present or function as a batch plant or as a continuously operated plant, wherein a continuously operated plant is preferred.

As already noted above, the steam treatment of wood strands used for the middle layer and the top layers of the OSB wood-based panel may each be carried out separately in at least two vapor deposition units. This makes it possible to adapt the degree of water vapor deposition of the steam-treated wood strands used in the middle and / or outer layer to the respective requirements and customer requirements. The two vapor deposition systems used are preferably connected in parallel or arranged in this case.

The contacting of the wood strands with the at least one binder in step d) is preferably carried out by spraying or atomizing the binder onto the wood strands. Many OSB systems work with rotating coils (drums with atomizer gluing). A mixer gluing would also be possible. The strands are intimately mixed with the glue in a mixer by rotating blades.

In one embodiment of the present method, a polymer adhesive selected from the group consisting of formaldehyde adhesives such as urea-formaldehyde resin adhesive (UF) and / or melamine-formaldehyde resin adhesive (MF), polyurethane adhesives is preferably used as a binder , Epoxy Adhesives, Polyester Adhesives. In the present case, the use of a polyurethane adhesive is preferred, wherein the polyurethane adhesive is based on aromatic polyisocyanates, in particular polydiphenylmethane diisocyanate (PMDI), tolylene diisocyanate (TDI) and / or diphenylmethane diisocyanate (MDI), with PMDI being particularly preferred.

In a variant of the present process, the steam-treated and non-steam-treated wood strands are glued with a binder amount of 1.0 to 5.0% by weight, preferably 2 to 4% by weight, in particular 3% by weight (based on the total amount of wood strands).

It is also possible to supply at least one flame retardant to the wood strands together or separately with the binder. The flame retardant may typically be added in an amount between 1 and 20% by weight, preferably between 5 and 15% by weight, particularly preferably ≥ 10% by weight, based on the total amount of wood strands. Typical flame retardants are selected from the group comprising phosphates, sulfates borates, in particular ammonium polyphosphate, tris (tri-bromneopentyl) phosphate, zinc borate or boric acid complexes of polyhydric alcohols.

The glued (steam-treated and / or non-steam-treated) wood strands are scattered on a conveyor belt to form a first cover layer along the transport direction, then forming a middle layer transversely to the transport direction and finally forming a second cover layer along the transport direction.

After sprinkling, the glued wooden strands are pressed at temperatures between 200 and 250 ° C., preferably 220 and 230 ° C., to form an OSB wood-based panel.

• Herstellen von Holzstrands aus geeigneten Hölzern, insbesondere mittels Zerspanen von geeigneten Hölzern,
• Behandeln von der Holzstrands mit Wasserdampf mit einer Temperatur zwischen 80°C und 120°C bei einem Druck zwischen 0,5 bar und 2 bar, in sauerstofffreier oder sauerstoffarmer Atmosphäre;
• Trocknen der mit dem Wasserdampf behandelten Holzstrands;
• Sichten und Separieren der wasserdampfbehandelten Holzstrands in Holzstrands geeignet zur Verwendung als Mittelschicht und Deckschicht;
• Beleimen der separierten Holzstrands;
• Aufstreuen der beleimten wasserdampfbehandelten Holzstrands auf ein Transportband in der Reihenfolge erste untere Deckschicht, Mittelschicht und zweite obere Deckschicht; und
• Verpressen der beleimten Holzstrands zu einer OSB-Holzwerkstoffplatte.

In a first preferred embodiment, the present process for producing an OSB wood-based panel with reduced VOC emission comprises the following steps:

• Making wooden strips of suitable woods, in particular by means of cutting suitable woods,
• Treating the wood strands with water vapor at a temperature between 80 ° C and 120 ° C at a pressure between 0.5 bar and 2 bar, in an oxygen-free or oxygen-poor atmosphere;
• Drying the steamed wood strands;
• Sifting and separating the steam-treated wooden strands in wooden strands suitable for use as a middle layer and topcoat;
• Gluing the separated wooden strips;
• Sprinkling the glued steam-treated wooden strands onto a conveyor belt in the order of first lower cover layer, middle layer and second upper cover layer; and
• Pressing the glued wooden strands into an OSB wood-based panel.

• Herstellen von Holzstrands aus geeigneten Hölzern, insbesondere mittels Zerspanen von geeigneten Hölzern;
• Sichten und Separieren der Holzstrands in Holzstrands geeignet zur Verwendung als Mittelschicht und Deckschicht;
• Behandeln der für die Mittelschicht vorgesehenen Holzstrands und/oder der für die Deckschicht(en) vorgesehenen Holzstrands mit Wasserdampf mit einer Temperatur zwischen 80°C und 120°C bei einem Druck zwischen 0,5 bar und 2 bar, in sauerstofffreier oder sauerstoffarmer Atmosphäre;
• Trocknen der mit dem Wasserdampf behandelten Holzstrands;
• Beleimen der separierten wasserdampfbehandelten Holzstrands und Beleimen von nicht-wasserdampfbehandelten Holzstrands;
• Aufstreuen der beleimten wasserdampfbehandelten und nicht-wasserdampfbehandelten Holzstrands auf ein Transportband in der Reihenfolge erste untere Deckschicht, Mittelschicht und zweite obere Deckschicht; und
• Verpressen der beleimten Holzstrands zu einer OSB-Holzwerkstoffplatte.

In a second preferred embodiment, the present process for producing an OSB wood-based panel with reduced VOC emission comprises the following steps:

• Manufacture of wooden strips of suitable woods, in particular by means of cutting of suitable woods;
• Sifting and separating the wooden strands in wooden strands suitable for use as a middle layer and topcoat;
• Treating the wood strands intended for the middle layer and / or the wood strands intended for the cover layer (s) with water vapor having a temperature between 80 ° C and 120 ° C at a pressure between 0.5 bar and 2 bar, in an oxygen-free or oxygen-poor atmosphere;
• Drying the steamed wood strands;
• Gluing the separated steam-treated wooden strips and gluing non-steam-treated wooden strips;
• Spreading the glued steam-treated and non-steam-treated wood strands onto a conveyor belt in the order of first lower cover layer, middle layer and second upper cover layer; and
• Pressing the glued wooden strands into an OSB wood-based panel.

Accordingly, the present method enables the production of an OSB wood-based panel with reduced emission of volatile organic compounds (VOCs) comprising water-treated wood strands.

The present OSB wood-based panel may consist entirely of steam-treated wood strands or of a mixture of steam-treated and non-steam-treated wood strands. In one embodiment, both cover layers and the middle layer of OSB consist of steam-treated wood strands, in another embodiment the two cover layers consist of non-steam-treated wood strands and the middle layer of steam-treated wood strands and in yet another embodiment, the two cover layers consist of steam-treated wood strands and the middle layer from non-steamed wooden strands.

The present OSB wood-based panel may have a bulk density between 300 and 1000 kg / m ³ , preferably between 500 and 800 kg / m ³ , particularly preferably between 500 and 600 kg / m ³ .

The thickness of the present OSB wood-based panel may be between 5 and 50 mm, preferably between 10 and 40 mm, wherein in particular a thickness between 15 and 25 mm is preferred.

The OSB wood-based panel produced by the present method has, in particular, a reduced emission of aldehydes released during wood pulping, in particular pentanal or hexanal, and / or terpenes, in particular carene and pinene.

The release of aldehydes takes place during the machining process and an associated aqueous workup and purification of the wood strands. In this case, specific aldehydes can be formed from the basic building blocks of cellulose or hemicellulose. For example, The aldehyde furfural is formed from mono- and disaccharides of cellulose or hemicellulose, while aromatic aldehydes can be liberated from lignin. The aliphatic aldehydes (saturated and unsaturated) are formed by the fragmentation of fatty acids with the participation of oxygen.

Due to the use of steam-treated wood strands is a reduction of the emission of C ₂ -C ₁₀ aldehydes, more preferably acetaldehyde, pentanal, hexanal or furfural, and a reduction of liberated terpenes, especially C ₁₀ monoterpenes and C ₁₅ sesquiterpenes, in particular preferably acyclic or cyclic monoterpenes in the OSB wood-based panels.

Typical acyclic terpenes are terpene hydrocarbons such as myrcene, terpene alcohols such as gerianol, linaool, ipsinol and terpene aldehydes such as citral. Typical representatives of the monocyclic terpenes are p-menthane, terpeninol, limonene or carvone, and typical representatives of the bicyclic terpenes are caran, pinane, bornan, in particular 3-carene and α-pinene being of importance. Terpenes are components of the tree resins and therefore especially in very resinous tree species such as pine or spruce.

Also, the emission of organic acids, in particular the emission of acetic acid from OSB wood-based panels can be reduced. Organic acids are obtained in particular as cleavage products of the wood components cellulose, hemicellulose and lignin, wherein preferably alkanoic acids, such as acetic acid and propionic acid or aromatic acids are formed.

In particular, the strong reduction of aldehydes was foreseeable in any way for the skilled person. Thus, it can be assumed that during the steam treatment water attaches to the double bonds of the unsaturated fatty acids and thus aldehyde formation is avoided. However, such additions are usually due to the low electrophilicity of water only in the presence of mineral acids (sulfuric acid, phosphoric acid, etc.) at higher temperatures.

• mindestens eine Vorrichtung zum Entrinden von geeigneten Holzstämmen;
• mindestens einen Zerspaner zum Zerspanen der entrindeten Holzstämmen in Holzstrands;
• mindestens eine oben beschriebene Vorrichtung zur Wasserdampfbehandlung von mindestens einem Teil der Holzstrands;
• mindestens einen Trockner zum Trocknen der wasserdampfbehandelten Holzstrands;
• mindestens eine Vorrichtung zum Sichten und Separieren der Holzstrands (wasserdampfbehandelt und nicht-wasserdampfbehandelt);
• mindestens eine Vorrichtung zum Beleimen der Holzstrands;
• mindestens eine Vorrichtung zum Streuen der beleimten Holzstrands auf ein Transportband, und
• mindestens eine Presse zum Verpressen der gestreuten Holzstrands zu OSB.

The present process is carried out in a production line for producing an OSB board and comprises the following elements:

• at least one device for debarking suitable logs;
• at least one chipper for cutting the debarked logs in strips of wood;
• at least one above-described device for steam treatment of at least a part of the wood strands;
• at least one dryer for drying the steam-treated wooden strips;
• at least one device for sifting and separating the strands of wood (steam-treated and non-steam-treated);
• at least one device for gluing the wooden strips;
• at least one device for spreading the glued wooden strands on a conveyor belt, and
• at least one press for pressing the scattered wooden strands to OSB.

As already noted above, the steamer can be designed continuously. For this purpose, the wooden strands are applied to a Tramsportband which leads the wood strands with a given speed through the steamer. During the passage through the vaporization system, the wood strands are sprayed evenly with steam, which is introduced from above the conveyor belt provided nozzles.

The steamer may be provided upstream (upstream) of the device for sifting and separating the strands of wood. In this case, all wooden strands are exposed to a steam treatment.

However, it is also possible for two steaming plants to be provided behind (downstream) the device for sifting and separating the wooden strips. In this case, a steam treatment of the steam treatment of the wood strands are provided for the middle layer, and the other steaming system of steam treatment of the wood strands are provided for the outer layers. This allows optional steam treatment of the strands for the middle layer or the strands of wood for the cover layers.

Figur 1

eine schematische Darstellung einer Ausführungsform einer Vorrichtung zur Wasserdampfbehandlung von Holzstrands;

Figur 2

eine schematische Darstellung einer ersten Ausführungsform des erfindungsgemäßen Verfahrens zur Herstellung von OSB-Platten, und

Figur 3

eine schematische Darstellung einer zweiten Ausführungsform des erfindungsgemäßen Verfahrens.

The invention will be explained in more detail with reference to the figure of the drawing of an embodiment. Show it:

FIG. 1

a schematic representation of an embodiment of a device for steam treatment of wooden strands;

FIG. 2

a schematic representation of a first embodiment of the method according to the invention for the production of OSB boards, and

FIG. 3

a schematic representation of a second embodiment of the method according to the invention.

FIG. 1 shows a variant of a device 10 for steam treatment of wooden strands. The device comprises a (thermally insulated) tubular body 11 with a perforated conveyor belt 12 passing through the tubular body 11. Above the conveyor belt 12 is a supply line 13 for the water vapor, wherein the supply line 13 a plurality of nozzles 14 for spraying the water vapor on the on the conveyor belt Has 12 wooden strands. Below the conveyor belt 12, a collecting means 15 is provided for the forming water vapor condensate.

The present apparatus 10 allows steaming of the strands prior to drying the strands in the tumble dryer. In this case, all or parts of the strands, which are intended for the later production of the OSB, can be treated. The treatment is carried out at normal pressure and achieved by the use of the conveyor belt 12 made of metal fabric, the homogeneous treatment of the beach with steam.

The band of the transport device is dimensioned so that the beaches can not fall through the gaps. The strands are transferred directly to the production of the conveyor belt 12, which passes through the tubular body 11. On the conveyor belt 12, the strands are distributed so that a homogeneous flow through the beach with steam is possible. Periodically positioned separation stations provide for the dissolution of existing or forming beach piles.

Since the conveyor belt 12 is cooled by condensate forming upon heating of the strands and has a relatively high mass compared to the strands, heating of the strip prior to spreading of the strands is to be provided. This speeds up the heating of the beaches and thus reduces the treatment time with steam. The heating can be done by resistance heating or by radiation.

From the top steam is then applied through nozzles 14 on the beaches. The steam has a temperature of about 100 ° C. The insulation of the metal tube 11 ensures that the heat losses are minimized. The forming condensate is collected under the transport device 12, freed of suspended matter and returned to the system after a cleaning step to remove dissolved substances.

The residence time of the beaches in the saturated steam atmosphere is 5 to 15 min. At regular intervals, the progress of the beach heating is detected by thermocouples. The temperature of the beaches should be near 90 ° C at the end of the treatment.

In the FIG. 2 shown first embodiment of the method according to the invention describes the individual process steps, starting with the provision of the wood output product to the finished OSB wood-based panel.

Accordingly, in step 1 suitable wood starting material for the production of the wood strands is first provided. As wood source material all conifers, hardwoods or mixtures thereof are suitable.

The debarking (step 2) and the cutting (step 3) of the wood starting material takes place in suitable chippers, wherein the size of the wood strands can be controlled accordingly. After shredding and providing the wooden strands they may become one Pre-drying process, wherein a humidity of 5-10% is adjusted with respect to the initial moisture content of the wood strands (not shown).

In the case of in FIG. 2 In the embodiment shown, the wooden strands are introduced into an evaporator (step 4). The steam treatment of the wood strands takes place in a temperature range between 80 ° and 120 ° C at a pressure between 0.5 bar and 2 bar. The resulting condensate can be collected and washed out of the wood strands substances (terpenes, aldehydes) can be supplied from the condensate for further use.

After completion of the steam treatment, which takes in the present case about 10-20 minutes, the steam-treated wood strands are dried (step 9), spotted and separated (step 5).

There is a separation in wooden strands for use as a middle layer (step 6a) or as a cover layer (step 6b) with respective gluing.

The glued steam-treated wooden strands are spread on a conveyor belt in the order of first lower cover layer, middle layer and second upper cover layer (step 7) and then pressed into an OSB wood-based panel (step 8).

In the in FIG. 3 As shown in the second embodiment, the wood starting material is analogous to FIG. 1 initially provided (step 1), debarked (step 2) and machined (step 3). The strands of wood may be subjected to a predrying process, with a humidity of 5-10% being adjusted in relation to the initial moisture content of the strands of wood (step 3a).

In contrast to the variant of the FIG. 2 a separation in wood strands is already carried out after the optional drying for use as a middle layer or as a cover layer (step 5).

This is followed by the steam treatment of the wood strands provided for the middle layer (step 4a) and / or steam treatment of the wood strands (step 4b) provided for the cover layer (s) in a suitable vapor deposition system. The steam treatment of the wood strands takes place in a temperature range between 80 ° and 120 ° C at a pressure between 0.5 bar and 2 bar. The resulting condensate can be collected and washed out of the wood strands substances (terpenes, aldehydes) can be supplied from the condensate for further use.

It is also possible that only the wood strands for the middle layer are subject to a steam treatment, while the wood strands for the cover layers remain untreated.

After completion of the steam treatment, which takes in the present case about 10-20 minutes, the steam-treated wooden strips are dried (step 9a, 9b) and glued (steps 6 a, b).

The glued water-treated wood strands are scattered onto a conveyor belt in the order of the first lower cover layer, middle layer and second upper cover layer (step 7) and then pressed into an OSB wood-based panel (step 8).

In the finishing, the obtained OSB wood-based panel is assembled in each case in a suitable manner.

Embodiment 1

Strands are produced from pine trunks (length: max 200 mm, width: 20 mm, thickness: max 1 mm, humidity max 50%) and treated in a continuous process with about 100 ° C hot water vapor. During treatment, the strands are loosely piled up on a conveyor belt which has perforations and thereby allows the passage of the steam after passing the beaches. The steam treatment was preferably from top to bottom. The conveyor belt is guided through a tubular body. Preferably, nozzles are attached above the conveyor belt with the loosely piled up strands, which distributes the steam evenly over the beach. The treatment with steam takes about 15 minutes. The steam treatment takes place with the greatest possible exclusion of oxygen, so that one can speak of a reductive process control.

The tube body has a diameter of 50 cm at a length of 3 m to achieve a residence time of about 15 minutes. The conveyor belt was moved through the pipe body at a speed of about 2 m / 10 minutes. In the feed direction was the tubular body slightly angled upwards (2 to 10 degrees) so that the condensate that formed could easily be collected. This is a pilot plant with which the effect should be demonstrated. For a production plant, this can be increased and easily optimized in terms of transport speed and quantity by the expert.

Thereafter, the strands are dried in a conventional drum dryer. The energy requirement of the tumble dryer is reduced significantly, since the beaches already have a temperature of about 90 ° C when entering the dryer. Then they are glued in a coil with glue, preferably with PMDI (about 3% by weight on atro wood).

The glued stands are sprinkled in a standard OSB plant as a top and middle layer. The percentage distribution between middle and top layer is preferably 70% to 30%. The strands are pressed into slabs with a density of about 570 kg / m3. After a storage period of one week, the test plate was tested together with a standard plate in the same thickness in a micro-chamber on the VOC delivery.

Chamber parameters: temperature: 23 ° C; Humidity: 0%; Air flow: 150 ml / min; Air exchange: 188 / h; Load: 48.8 m ² / m ³ ; Sample surface: 0, 003 m ² ; Chamber volume: 48 ml. The values of the quantitatively most important parameters are shown in Table 1. Table 1 parameter Experimental plate [μg / m2 xh] Standard plate [μg / m2 xh] hexanal 194 1474 3-Carene 208 626 α-Pinene 181 925 pentanal - 155 β-pinene - 285 2-octenal 60 115

As can be seen from the results, the emissions of the quantitatively most important parameters are significantly reduced. Some parameters could not be detected at all. Surprisingly, this also applies to the saturated and unsaturated aldehydes, which, according to the pathway assumed to be correct and plausible, should first form in the press at high temperatures. This means that either the previously assumed mechanism for the formation of aldehydes is wrong or in the Steam treatment, the precursors of aldehydes are chemically converted so that the formation of aldehydes is only possible to a limited extent. Originally it had been expected that the steam treatment would only reduce the terpene emission. These would be expelled in the process as in a steam distillation.

Embodiment 2:

Corresponds to Embodiment 1, except that only strands for the middle layer (about 70% of the OSB) were treated with steam, with the following result of the VOC test:
Chamber parameters: temperature: 23 ° C; Humidity: 0%; Air flow: 150 ml / min; Air exchange: 188 / h; Load: 48.8 m ² / m3; Sample surface: 0, 003 m ² ; Chamber volume: 48 ml. The values of the quantitatively most important parameters are shown in Table 2. Table 2 parameter Experimental plate [μg / m2 xh] Standard plate [μg / m2 xh] hexanal 243 1474 3-Carene 299 626 α-Pinene 178 925 pentanal - 155 β-pinene - 285 2-octenal 61 115

Here, too, a significant reduction of the emission can be observed, although the top layer consists of standard strands.

Claims (13)

1. A process for treating wood strands with steam to reduce the emission of volatile organic compounds from such wood strands,

   wherein the wood strands being treated with steam for a period of 5 to 20 minutes after their production without drying, the steam being passed over the wood strands at a temperature of between 80°C and 120°C and a pressure of between 0.5 bar and 2 bar, and

   wherein the steam treated wood strands are used to produce OSB boards with reduced emission of volatile organic compounds.
2. Process according to claim 1, characterized in that, for the treatment of the wood strands with steam, the steam is passed over the wood strand at a temperature between 90°C and 110°C, in particular preferably 100°C, at a pressure between 0.7 bar and 1.5 bar, in particular preferably 1 bar, i.e. at atmospheric pressure.
3. Process according to claim 1 or 2, characterized in that the steam treatment of the wood strands takes place over a period of 10 to 20 minutes, in particular preferably 15 minutes.
4. Process according to one of the preceding claims, characterized in that the steam treatment of the wood strands takes place in an atmosphere low in oxygen.
5. Process according to one of the preceding claims, characterized in that the wood strands for steam treatment are continuously guided on at least one transport device through a steam treatment device (4, 4a, 4b).
6. Process according to one of the preceding claims, characterized in that the water vapor is collected as condensate after passing through the wood strands.
7. A process for the production of OSB wood-based panels with reduced emission of volatile organic compounds (VOCs) comprising the steps:

   a) producing wood strands from suitable wood logs;

   b) treating at least part of the wood strands with steam by a process of Claims 1 to 6;

   c) drying the steam-treated wood strands;

   d) gluing the steam-treated and dried wood strands and optionally gluing the non-steam-treated wood strands with at least one binder;

   e) spreading the glued wood strands on a conveyor belt; and

   f) Pressing of the glued wood strands into an OSB wood-based panel.
8. Process according to claim 7, characterized in that steam-treated wood strands or a mixture of steam-treated wood strands and non-steam-treated wood strands are used as the middle layer and/or top layer of the OSB wood-based panel.
9. Process according to one of claims 7 to 8, characterized in that the steam-treated and non-steam-treated wood strands are glued with a binder in an amount of 1.0 to 5.0 % by weight, preferably 2 to 4 % by weight, in particular 3 % by weight, based on the total amount of the wood strands.
10. Process according to one of claims 7 to 9, characterized in that the glued wood strands are pressed at temperatures between 200 and 250°C, preferably 220 and 230°C, to form an OSB wood-based panel.
11. Production line for the production of an OSB board according to a process according to one of the preceding claims 7-10 comprising

    - at least one device (2) for debarking suitable logs (1);

    - at least one chipper (3) for chipping the debarked logs into wood strands;

    - at least one device (4, 4a, 4b) for steam treatment of at least a part of the wood strands, wherein the device for steam treatment (4, 4a, 4b) comprises at least one housing; at least one transport device running through the housing for transporting the wood strands through the housing; and at least one supply line for the steam provided above the transport device in the housing, wherein at least one spraying means for applying the steam to the wood strands located on the transport device is arranged along the supply line;

    - at least one dryer (9, 9a, 9b) for drying the steam-treated wood strands;

    - at least one device (5) for classifying and separating the steam-treated and non-steam-treated wood strands;

    - at least one device (6a, 6b) for gluing the wood strands; and

    - at least one device (7) for spreading the glued wood strands on a conveyor belt, and

    - at least one press (8) for pressing the scattered wood strands into OSB boards.
12. Production line according to claim 11, characterized in that the at least one transport device in the steam treatment device (4, 4a, 4b) comprises at least one transport belt with perforations.
13. Production line according to one of claims 11 to 12, characterized in that at least one means for collecting the condensate is provided below the at least transport device in the at least one housing of the steam treatment device (4, 4a, 4b).

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