EP3615288B1 - 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 method for producing OSB wood-based panels according to claim 1.

OSB (oriented strand boards), also known as oriented strand boards, are wood-based panels that are made from long chips (strands). OSB panels are increasingly being used in timber and prefabricated house construction, since OSB panels are light and still meet the static requirements placed on building panels. OSB panels are used as building panels and as wall or roof cladding or in the floor area.

The production of the OSB panels takes place in a multi-stage process, whereby first the chips or strands of debarked round wood, preferably softwood, are peeled off in the longitudinal direction by rotating knives. In the subsequent drying process, the natural moisture in the strands is reduced at high temperatures. The degree of moisture in the strands can vary depending on the adhesive used, although the moisture should be well below 10% to avoid splitting during later pressing. Depending on the adhesive, wetting on rather damp strands or on dry strands can be better. In addition, there should be as little moisture as possible in the strands during the pressing process in order to reduce the steam pressure that occurs during the pressing process as much as possible, since this could otherwise cause the raw panel to burst.

After the strands have dried, they are fed into a gluing device, in which the glue or adhesive is applied to the chips in a finely distributed manner. PMDI (polymeric diphenylmethane diisocyanate) or MUPF (melamine-urea-phenol-formaldehyde) glues are mainly used for gluing. The glues can also be used mixed in the OSB panels. These glues are used because, as mentioned above, the OSB boards are often used for constructive applications. Glues that are resistant to moisture or moisture must be used there.

After gluing, the glued strands are scattered alternately lengthwise and crosswise to the direction of production in scattering devices, so that the strands crosswise into at least three Layers are arranged (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. The strands used in the top layer and middle layer also differ from each other. The strands used in the top layers are flat and the strands used in the middle layer are less flat and even chip-shaped. Normally, two strands of material are used in the manufacture of the OSB panels: one with flat strands for the later top layers and one with "chips" for the middle layer. Accordingly, the strands in the middle layer can be of poorer quality, since the flexural strength is essentially generated by the top layers. For this reason, fines that are produced during machining can also be used in the middle layer of OSB panels. The percentage distribution between middle and top layer is at least 70% to 30%. Following the scattering of the strands, they are continuously pressed under high pressure and at a high temperature of, for example, 200 to 250°C.

Not least because of their sustainability, OSB panels are becoming increasingly popular and have a wide range of uses, for example as a construction element in house construction or as formwork in concrete construction. However, the inherent hygroscopic properties of wood-based materials have a disadvantageous effect in some applications.

Escaping wood ingredients is viewed critically, particularly when OSB is used indoors. This is particularly problematic with OSB panels made from pine wood, since these show particularly high emissions of volatile organic compounds.

In the course of the production of wood-based panels and in particular as a result of the production process of the wood strands, a large number of volatile organic compounds are created or released. Volatile organic compounds, also known as VOCs, include volatile organic substances that evaporate easily or are present as gases even at low temperatures, such as room temperature.

The volatile organic compounds (VOC) are either already present in the wood material and are released from it during processing or, according to the current state of knowledge, they are formed by the breakdown of unsaturated fatty acids, which in turn are decomposition products of the wood. Typical transformation products that occur during processing are for example pentanal and hexanal, but also octanal, 2-octenal or 1-heptenal. Softwoods in particular, from which OSB panels are mainly made, 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 arise or be released when using certain adhesives for the manufacture of wood-based materials.

The emission of ingredients from OSB material panels is critical above all because this material is used uncoated for the most part. This allows the ingredients to evaporate unhindered. In addition, the OSB panels are often used for cladding/cladding large areas, which usually results in a high room load (m ² OSB / m ³ room air). This also leads to a concentration of certain substances in the room air.

Various approaches have been described in the past to solve the problem of VOC emissions.

In the past, attempts were made to at least reduce the emissions of aldehydes by adding reducing agents. However, many of these reducing agents contained sulfur, which led to undesirable emissions of sulfur dioxide during board production and later use.

One approach was in the EP 1 907 178 B1 tracked. Here, before gluing, wood chips or wood fibers are treated with a bisulfite compound, eg sodium or ammonium bisulfite, at a pressure of 6-12 bar in a saturated steam atmosphere or in steam-saturated air for a period of 3-8 minutes. It is believed that the addition of bisulfite binds volatile substances in the crushed wood and suppresses the formation of new volatile substances. However, the chemicals used not only make the process more expensive, they also sometimes lead to unpleasant odors in production.

The addition of activated charcoal has also been tried, but is not satisfactory either technologically or in terms of costs.

The addition of suitable VOC scavengers almost always occurs after the drying process of the strands, as this and the temperature exposure in the press were considered to be the causes of the majority of emissions. The The VOC scavengers were added in liquid form via the gluing system, solids were added at various points in the process (e.g. spreading). This required an additional installation of dosing stations to ensure homogeneous distribution.

EP0695609A2 discloses a method for preheating grit to a predetermined preheating temperature during the manufacture of wood-based panels.

US5447686A discloses a method of treating wood strands with steam.

The invention is now based on the technical problem of improving the known method for producing OSB material panels to the effect that OSB material panels can be produced simply and safely with significantly reduced emissions of volatile organic compounds (VOCs). At least the emission of terpenes should be reduced. If possible, the manufacturing process should be changed as little as possible and the costs should not increase disproportionately. Furthermore, the solution should be as flexible as possible. Ultimately, ecological aspects should also be taken into account, i. H. the solution should not cause additional energy consumption or generate additional waste.

Another technical task was to design a system that would allow easy treatment of the strands to reduce VOC emissions. This should be integrated into the production process and not disrupt or make the production of the OSB more expensive. The technical effort for the treatment should not lead to an increase in safety measures or contain a greater risk potential. According to the invention, this object is achieved by a method for producing OSB wood-based panels having the features of claim 1 .

1. a) Herstellen von Holzstrands aus geeigneten Hölzern;
2. b) Behandeln von zumindest einem Teil der Holzstrands nach ihrer Gewinnung ohne Trocknung mit Wasserdampf, wobei der Wasserdampf mit einer Temperatur zwischen 80°C und 120°C und einem Druck zwischen 0,5 bar und 2 bar über die Holzstrands geleitet wird,
   wobei die Wasserdampfbehandlung unmittelbar nach der Zerspanung und Bereitstellung der Holzstrands erfolgt, oder die Wasserdampfbehandlung nach dem Sichten und Separieren der Holzstrands entsprechend der Verwendung der Holzstrands für Mittel- und Deckschicht erfolgt; wobei die Wasserdampfbehandlung der Holzstrands in den Gesamtprozess integriert online erfolgt,
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.

Accordingly, a method for producing OSB wood-based panels with reduced emissions of volatile organic compounds (VOCs) is provided, which comprises the following steps:

1. a) Manufacture of wooden strands from suitable woods;
2. b) treating at least some of the wooden strands after they have been obtained without drying them with steam, the steam being passed over the wooden strands at a temperature of between 80° C. and 120° C. and a pressure of between 0.5 bar and 2 bar,
   wherein the steam treatment takes place immediately after the chipping and provision of the wooden strands, or the steam treatment after the sifting and separating of the wooden strands is carried out according to the use of the wooden strands for the middle and top layer; whereby the steam treatment of the wooden strands is integrated online into the overall process,
3. c) drying the wooden strands treated with steam;
4. d) gluing the wooden strands treated with steam and dried and optionally gluing wooden strands not treated with steam with at least one binder;
5. e) spreading the glued wooden strands onto a conveyor belt; and
6. f) pressing the glued wood strands to form an OSB wood-based panel.

Correspondingly, wooden strands suitable for the production of OSB boards are provided, in particular with the aim of reducing VOC emissions from these wooden strands, the wooden strands being treated with water vapor after they have been obtained from suitable woods without drying, the water vapor having a temperature between 80°C and 120°C and a pressure between 0.5 bar and 2 bar over the wooden strands.

In one embodiment of the present method, the treatment of the wooden strands with steam takes place in such a way that the steam at a temperature between 90° C. and 110° C., particularly preferably 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.

The water vapor treatment thus takes place at the temperature-dependent pressure with which the water vapor is introduced into the treatment device. In particular, steam treatment at normal pressure (temperature of introduced steam of 100° C.) is preferred. Accordingly, there is no need to apply an additional (external) pressure (ie in addition to the pressure with which water vapor enters the system). This leads to a simplification of the device, since no pressure vessels (such as an autoclave or a pressure chamber) are necessary for the steam treatment.

Due to the preferably used saturated water vapor atmosphere, the water vapor treatment of the wooden strands takes place in a low-oxygen atmosphere or with the exclusion of oxygen as far as possible.

The present steam treatment of the wooden strands can be carried out in a separate steam treatment device (not according to the invention). The steam treatment takes place outside of a flaker (e.g. knife ring flaker or disc flaker) and is therefore not part of the chipping or shredding process of wood for the production of wooden strands. It is also important that the steam treatment can be carried out before the wooden strands are dried.

Also, no additives are added to the steam: in particular, no bleaching agents such as bisulfite or oxygen-releasing substances are added. But there is also no need to add other VOC scavengers to the binder.

In one embodiment of the present method, the steam treatment of the wooden strands takes place over a period of 5 to 30 minutes, preferably 10 to 20 minutes, particularly preferably 15 minutes. The amount of steam is at most 1 kg steam/kg strands (atro).

The duration of the steam treatment is primarily determined by the speed of the conveyor on which the wood strands are fed through the steam treatment device in a continuous manner.

In a particularly preferred embodiment, the water vapor is collected as condensate after it has passed the wooden strands. It is advantageous that the load of the condensate with organic compounds is relatively low. The COD (Chemical Oxygen Demand) was about 250 mg COD/I when treating one kilogram of water with one kilogram of steam.

The wooden strands used here can have a length 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 have 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 a length of between 150 and 200 mm, a width of between 15 and 20 mm, a thickness of between 0.5 and 1 mm and a maximum moisture content of 50%.

• 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 that includes the following elements and 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 supply line for the water vapor provided above the transport device housing, wherein at least one spray means for applying the water vapor to the strands of wood located on the transport device is arranged along the supply line.

In one variant, the at least one housing can 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 guided 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 in such a way that water vapor can flow through the wooden strands homogeneously.

In a further embodiment of the present device, more than one spray means is provided on the steam supply line. The number of spraying means is particularly dependent on the overall length of the housing. The spraying means can also be controlled individually, so that the required amount of water vapor can be set in a targeted manner. Nozzles or other suitable injectors can be used as spraying means, which enable uniform spraying and uniform distribution of the water vapor on and between the wooden strands.

As already mentioned above, in a particularly preferred embodiment, the water vapor is collected as condensate after it has passed the wooden strands. For this is in the At least one means for collecting the condensate is provided below the conveyor belt (relative to the direction of flow of the steam). For example, the tubular body can be angled upwards in the direction of advance.

The condensate collected in this way contains wood constituents 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 device, the steam-treated strands have a temperature of 80 to 90.degree. With this temperature, the wood strands from the steam treatment station enter a dryer (as part of the OSB board production line), which leads to an increase in dryer capacity. This means that the energy needed to remove wood ingredients can then be used for the drying process. In a normal process, the temperature at which the strands enter the dryer is around 25°C.

According to the invention, the wood strands treated with steam are used to produce OSB wood-based panels with reduced emissions of volatile organic compounds (VOCs).

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.

The production of OSB wood-based panels with reduced emissions of volatile organic compounds (VOCs) is generally carried out in a process that includes the following steps:

1. a) Manufacture of wooden strands from suitable woods;
2. b) treating at least part of the wooden strands with steam according to the method described above;
3. c) drying the wooden strands treated with steam;
4. d) gluing the wooden strands treated with steam and dried and optionally gluing wooden strands not treated with steam with at least one binder;
5. e) spreading the glued wooden strands onto a conveyor belt; and
6. f) pressing the glued wood strands to form an OSB wood-based panel.

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

Various advantages result from the provision of the present method. This means that the OSB wood-based panels can be produced easily without significantly influencing the usual process chain and with significantly reduced emissions of volatile organic compounds from the OSB. In addition, the energy requirement for drying the wooden strands can be reduced, since the wooden strands already have a higher temperature (e.g. approx. 90°C) when they enter the dryer; i.e. the use of energy during the steam treatment supports the drying process. The use of additional chemicals can also be dispensed with, which means that the overall process is ecologically and economically advantageous.

In the present process, the production of OSB is changed compared to the conventional OSB production process in that at least some of the strands used are treated with steam after production, before drying. The strands can be those intended for the top or middle layer. After treatment, the strands are sent to the standard drying process. This is done e.g. B. immediately before the gluing, with a complete substitution or only a partial substitution of the standard strands can be done.

According to the invention, steam-treated wooden strands or a mixture of steam-treated wooden strands and non-steam-treated wooden strands are used as the middle layer and/or top layer of the OSB wood-based panel.

Accordingly, a complete substitution of the wooden strands is possible in one variant, with the steam-treated wooden strands being used in the middle layer and in one or both top layers or in all layers.

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

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

In yet another variant, it is conceivable and possible to use a mixture with any ratio of steam-treated wood strands and non-water-vapour-treated wood strands for the middle and top layers. In such a case, the mixture can comprise between 10 and 50% by weight, preferably between 20 and 30% by weight, of untreated or non-steam-treated 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 manufacturing process of the OSB wood-based panels. Accordingly, in this embodiment variant of the present method, the steam treatment takes place outside of the overall process or the process line. The wooden strands are discharged from the manufacturing process and introduced into the steam treatment device (e.g. steaming system). The steam-treated wooden strands can then be fed back into the conventional manufacturing process, if necessary after intermediate storage, e.g. immediately before gluing. This enables a high degree of flexibility in the manufacturing process.

According to the invention, the water vapor treatment of the wooden strands is integrated into the production process of the OSB wood-based panels, i.e. the step of water vapor treatment is integrated into the overall process or process line and takes place online.

In this case, the steam treatment i) can be carried out immediately after the chipping and provision of the wooden strands or ii) only after the sifting and separating Wooden strands according to the use of wooden strands for middle or top layer. In the latter case, the wooden strands can be treated with steam separately according to the requirements for the wooden strands used in the middle and top layers.

In a further variant of the present method, the steam treatment of the wooden strands is carried out in at least one steaming system, preferably in two steaming systems. The vapor deposition system used here can exist or function as a batch system or as a continuously operated system, with a continuously operated system being 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 can be carried out separately in at least two steaming systems. This enables the degree of water vaporization of the water vapor-treated wood strands used in the middle and/or top layer to be adapted to the respective requirements and customer wishes. In this case, the two vapor deposition systems used are preferably connected or arranged in parallel.

The wooden strands are preferably brought into contact with the at least one binder in step d) by spraying or atomizing the binder onto the wooden strands. Many OSB plants work with rotating coils (drums with atomizer gluing). 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 is preferably used as the binder, which is selected from the group containing formaldehyde adhesives, such as urea-formaldehyde resin adhesive (UF), melamine-urea-phenol-formaldehyde adhesive (MUPF) and /or Melamine Formaldehyde Resin Adhesive (MF), Polyurethane Adhesives, Epoxy Resin Adhesives, Polyester Adhesives. The use of a polyurethane adhesive is preferred here, the polyurethane adhesive being based on aromatic polyisocyanates, in particular polydiphenylmethane diisocyanate (PMDI), tolylene diisocyanate (TDI) and/or diphenylmethane diisocyanate (MDI), PMDI being particularly preferred.

In a variant of the present method, the steam-treated and non-steam-treated wooden strands are treated with a binder quantity of 1.0 to 10% by weight, in particular 1.0 to 5.0% by weight, preferably 2 to 4% by weight, particularly preferably 3% by weight (based on the total amount of the wooden strands). It is conceivable that the same binder or also different binders are used for the top and middle layers.

In one variant, the top layers can each be provided with 2.6% by weight of PMDI on atro wood and the middle layer with 2.9% by weight of PMDI on atro wood.

In another alternative variant, the top layers can each be provided with 10% by weight MUPF on atro wood and the middle layer with 2.9% by weight PMDI on atro wood.

In yet another alternative variant, the top layers can each be provided with 10% by weight MUF on atro wood and the middle layer with 2.9% by weight PMDI on atro wood.

The alternatives listed relate to the gluing of the top layers and the middle layer of a 3-layer OSB with a thickness of 19 to 22 mm.

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

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

After scattering, 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 method for producing an OSB wood-based panel with reduced VOC emissions comprises the following steps:

• Manufacture of wooden strands from suitable woods, in particular by cutting suitable woods,
• Treating the wooden strands with steam 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 wooden strands treated with steam;
• Classifying and separating the steam-treated wooden strands into wooden strands suitable for use as a middle layer and top layer;
• gluing the separated wooden strands;
• Scattering the glued, steam-treated wooden strands onto a conveyor belt in the order of the 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 method for producing an OSB wood-based panel with reduced VOC emissions comprises the following steps:

• Manufacture of wooden strands from suitable woods, in particular by cutting suitable woods;
• Sifting and separating the wooden strands into wooden strands suitable for use as a middle layer and top layer;
• Treating the wooden strands intended for the middle layer and/or the wooden strands intended for the top layer(s) with steam at a temperature between 80°C and 120°C at a pressure between 0.5 bar and 2 bar in an oxygen-free or low-oxygen atmosphere;
• drying the wooden strands treated with steam;
• Gluing the separated steam-treated wooden strands and gluing non-steam-treated wooden strands;
• Scattering the glued steam-treated and non-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.

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

The present OSB wood-based panel can consist entirely of steam-treated wood strands or of a mixture of steam-treated and non-water-vapour-treated wood strands. In one embodiment, both top layers and the middle layer of the OSB consist of steam-treated wood strands, in another embodiment the two top layers consist of non-steam-treated wood strands and the middle layer consist of steam-treated wood strands and in yet another embodiment the two top layers consist of steam-treated wood strands and the middle layer made of non-steam treated wooden strands.

The present OSB wood-based material panel can have a bulk density of 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 material panel can be between 5 and 50 mm, preferably between 10 and 40 mm, with a thickness between 15 and 25 mm being particularly preferred.

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

Aldehydes are released during the machining process and the associated aqueous processing and cleaning of the wood strands. 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 released 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 wooden strands, there is a reduction in the emission of C ₂ -C ₁₀ aldehydes, particularly preferably acetaldehyde, pentanal, Hexanal or also furfural, and a reduction in terpenes released, in particular C ₁₀ monoterpenes and C ₁₅ sesquiterpenes, particularly 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, linalool, 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 carane, pinane, bornane, 3-carene and α-pinene being particularly important. Terpenes are components of tree resins and are therefore particularly present in very resinous tree species such as pine or spruce.

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

In particular, the sharp reduction in aldehydes was in no way foreseeable by the person skilled in the art. It can be assumed that during the steam treatment, water accumulates on the double bonds of the unsaturated fatty acids, thus avoiding aldehyde formation. Because of the low electrophilicity of water, however, such additions usually only take place in the presence of mineral acids (sulphuric 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 method is carried out in a production line for the production of an OSB panel and includes the present elements:

• at least one device for debarking suitable logs;
• at least one chipper for chipping the debarked logs into wooden strands;
• at least one device as described above for steam treatment of at least part of the wooden strands;
• at least one dryer for drying the steam-treated wooden strands;
• at least one device for sifting and separating the wooden strands (steam-treated and non-steam-treated);
• at least one device for gluing the wooden strands;
• at least one device for scattering the glued wooden strands conveyor belt, and
• at least one press for pressing the scattered wooden strands into OSB.

As noted above, the vapor deposition system can be designed to be continuous. For this purpose, the wooden strands are placed on a conveyor belt, which guides the wooden strands through the steaming system at a specified speed. During the passage through the steaming system, the wooden strands are sprayed evenly with steam, which is introduced from nozzles provided above the conveyor belt.

The steaming system can be provided before (upstream) the device for sifting and separating the wood strands. In this case, all wooden strands are subjected to a steam treatment.

However, it is also possible for two steaming systems to be provided behind (downstream) the device for sifting and separating the wooden strands. In this case, one steam treatment system is used for the steam treatment of the wooden strands that are intended for the middle layer, and the other steam treatment system is used for the steam treatment of the wooden strands that are intended for the top layers. This enables optional steam treatment of the wooden strands for the middle layer or the wooden strands for the top 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 is explained in more detail below with reference to the figure of the drawing using an exemplary embodiment. Show it:

figure 1

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

figure 2

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

figure 3

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

figure 1 shows a variant of a device 10 for the steam treatment of wooden strands. The device comprises a (thermally insulated) tubular body 11 with a above the conveyor belt 12 there is a feed line 13 for the water vapor, the feed line 13 having a plurality of nozzles 14 for spraying the water vapor onto the wood strands on the conveyor belt 12 . Below the conveyor belt 12 there is a collecting means 15 for the water vapor condensate which forms.

The present device 10 enables a steam treatment of the strands before the strands are dried in the drum dryer. All or parts of the strands that are intended for later production of the OSB can be treated. The treatment takes place at normal pressure and, through the use of the conveyor belt 12 made of metal fabric, achieves the homogeneous treatment of the strands with steam.

The belt of the transport device is dimensioned in such a way that the strands cannot fall through the gaps. The strands are transferred to the conveyor belt 12 which runs through the tubular body 11 directly after production. The strands are distributed on the conveyor belt 12 in such a way that water vapor can flow through the strands homogeneously. Separation stations positioned at regular intervals ensure that existing or emerging heaps of beach are cleared.

Since the conveyor belt 12 is cooled by condensate forming when the strands are heated and has a relatively high mass in comparison to the strands, the belt must be heated before the strands are spread on. This accelerates the heating of the strands and thus reduces the duration of the steam treatment. The heating can be done by resistance heating or by radiation.

Steam is then applied to the strands through nozzles 14 from above. The steam has a temperature of approx. 100 °C. The insulation of the metal tube 11 ensures that the heat losses are as small as possible. The condensate that forms is collected under the transport device 12, freed from suspended matter and, after a cleaning step to remove dissolved substances, returned to the system.

The dwell time of the strands in the saturated steam atmosphere is 5 to 15 minutes. The progress of the strand heating is determined by thermocouples at regular intervals. The temperature of the strands should be close to 90°C at the end of the treatment.

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

Accordingly, in step 1, suitable raw wood material is provided for the production of the wooden strands. All softwoods, hardwoods or mixtures thereof are suitable as the starting wood material.

The debarking (step 2) and chipping (step 3) of the wood starting material takes place in chippers suitable for this purpose, whereby the size of the wood strands can be controlled accordingly. After the wooden strands have been comminuted and made available, they may be subjected to a pre-drying process, with a moisture content of 5-10% being set in relation to the initial moisture content of the wooden strands (not shown).

In the case of the in figure 2 shown embodiment, the wood strands are introduced into a vaporization system (step 4). The steam treatment of the wooden 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 the substances washed out of the wood strands (terpenes, aldehydes) can be reused from the condensate.

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

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

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

in the in figure 3 shown second embodiment, the wood starting material in analogy to figure 1 first provided (step 1), debarked (step 2) and machined (step 3). If necessary, the wooden strands are subjected to a pre-drying process, with a moisture content of 5-10% being set in relation to the initial moisture content of the wooden strands (step 3a).

In contrast to the variant of the figure 2 Already after the optional drying, a separation into wooden strands for use as a middle layer or as a top layer takes place (step 5).

This is followed by the steam treatment of the wooden strands provided for the middle layer (step 4a) and/or the steam treatment of the wooden strands provided for the top layer(s) (step 4b) in a suitable steaming system. The steam treatment of the wooden 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 the substances washed out of the wood strands (terpenes, aldehydes) can be reused from the condensate.

It is also possible that only the wooden strands for the middle layer are subjected to a steam treatment, while the wooden strands for the top layers remain untreated.

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

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

In the final processing, the OSB wood-based panel obtained is suitably finished in each case.

Example 1:

Strands are produced from pine trunks (length: max. 200 mm, width: 20 mm, thickness: max. 1 mm, moisture max. 50%) and treated with steam at around 100°C in a continuous process. During treatment, the strands are loosely piled up on a conveyor belt that has perforations and thus allows the steam to pass through after passing the strands. Steaming was preferably done from top to bottom. The conveyor belt is guided through a tubular body. Nozzles, which distribute the steam evenly over the strands, are preferably fitted above the conveyor belt with the loosely piled-up strands. The treatment with steam takes about 15 minutes. The steam treatment takes place with the exclusion of oxygen as far as possible, so that one can speak of a reductive process control.

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

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

The glued stands are scattered in a standard OSB plant as a top and middle layer. The percentage distribution between middle and top layers is preferably 70% to 30%. The strands are pressed into boards with a bulk density of around 570 kg/m3. After a storage period of one week, the test panel was tested for VOC emissions together with a standard panel of the same thickness in a micro chamber.

Chamber parameters: temperature: 23°C; humidity: 0%; air flow: 150 ml/min; Air change: 188 / h; loading: 48.8 m ² /m ³ ; sample surface area: 0.003 m ² ; Chamber volume: 48 ml. The values of the quantitatively most important parameters are shown in Table 1. Table 1 parameter Test panel [µg/m2 × h] Standard plate [µg/m2 × h] hexanal 194 1474 3-Carene 208 626 α-pinenes 181 925 pentanal - 155 β-pinene - 285 2-octenal 60 115

As can be seen from the results, the emissions of the most important parameters in terms of quantity are significantly reduced. Some parameters could no longer be detected at all. Surprisingly, this also applies to the saturated and unsaturated aldehydes, which, according to the formation path assumed to be correct and plausible, should only form in the press at high temperatures. This means that either the previously assumed mechanism for the formation of the aldehydes is incorrect, or the precursors of the aldehydes are chemically converted during the steam treatment in such a way that the formation of the aldehydes is only possible to a limited extent. It was originally expected that the steam treatment would only reduce terpene emissions. These would be expelled in the process like in a steam distillation.

Example 2:

Corresponds to example 1, but only the 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 change: 188 / h; load: 48.8 m ² /m3; sample surface area: 0.003 m ² ; Chamber volume: 48 ml. The values of the quantitatively most important parameters are shown in Table 2. Table 2 parameter Test panel [µg/m2 × h] Standard plate [µg/m2 × h] hexanal 243 1474 3-carene 299 626 α-pinenes 178 925 pentanal - 155 β-pinene - 285 2-octenal 61 115

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

Claims (10)

1. A process for producing OSB wood-based panels with reduced emission of volatile organic compounds (VOCs), comprising the steps:

   a) Producing wood strands from suitable woods;

   b) Treating at least part of the wood strands after their production without drying with steam, wherein the steam is passed over the wood strands at a temperature between 80°C and 120°C and a pressure between 0.5 bar and 2 bar,
   wherein the steam treatment takes place immediately after the chipping and preparation of the wood strands, or the steam treatment takes place after the classification and separation of the wood strands according to the use of the wood strands for middle and top layer; wherein the steam treatment of the wood strands takes place integrated into the overall process online,

   c) Drying of the wood strands treated with the steam;

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

   e) Scattering the glued wood strands onto a conveyor belt; and

   f) Pressing of the glued wood strands into an OSB wood-based panel.
2. Process according to one of the preceding claims, characterized in that the steam treatment is carried out in at least one steam treatment device, preferably in at least two steam treatment devices.
3. Process according to claim 2, characterized in that the steam treatment device is operated as a batch system or continuously.
4. Process according to one of the preceding claims, characterized in that the steam treatment of the wood strands is carried out over a period of 5 to 30 min, preferably 10 to 20 min, in particular preferably 15 min.
5. Process according to one of the preceding claims, characterized in that the steam-treated and non-steam-treated wood strands are glued with a polymer adhesive as binder, which on the one hand is selected from the group comprising formaldehyde adhesives, such as urea-formaldehyde resin adhesive (UF), melamine-urea-phenolformaldehyde adhesive (MUPF) and/or melamine-formaldehyde resin adhesive (MF), or on the other hand polyurethane adhesives, epoxy resin adhesives, polyester adhesives.
6. Process according to one of the preceding claims, characterized in that identical binders or also different binders are used for the top and middle layers.
7. Process according to one of the preceding claims, characterized in that the steam-treated and non-steam-treated wood strands are glued with a binder amount of 1.0 to 10% by weight, preferably 1.0 to 5.0% by weight, in particular preferably 2 to 4% by weight, based on the total amount of wood strands.
8. Process according to one of the preceding claims, characterized in that the glued steam-treated and/or non-steam-treated wood strands are scattered onto the conveyor belt forming a first cover layer longitudinally to the transport direction, then forming a middle layer transversely to the transport direction and finally forming a second cover layer longitudinally to the transport direction.
9. Process according to one of the preceding claims, characterized by the following steps:

   - Producing of wood strands from suitable woods, in particular by means of chipping of suitable woods,

   - Treating the wood strands with steam at a temperature between 80°C and 120°C at a pressure between 0.5 bar and 2 bar, in oxygen-free or low-oxygen atmosphere;

   - Drying of the steam treated wood strands;

   - Classifying and separating the steam-treated wood strands into wood strands suitable for use as a middle layer and top layer;

   - Gluing the separated wood strands;

   - Scattering of the glued steam treated wood strands on a conveyor belt in the order of first lower top layer, middle layer and second upper top layer; and

   - Pressing of the glued wood strands into an OSB wood-based panel.
10. Process of one of claims 1-8, characterized by the following steps:

    - Producing of wood strands from suitable woods, in particular by means of chipping of suitable woods;

    - Classifying and separating the wood strands into wood strands suitable for use as a middle layer and top layer;

    - Treating of the wood strands intended for the middle layer and/or the wood strands intended for the the top layer(s) of wood provided with steam at a temperature between 80°C and 120°C at a pressure between 0.5 bar and 2 bar, in oxygen-free or oxygen-poor atmosphere;

    - Drying of the steam treated wood strands;

    - Gluing of the separated steam-treated wood strands and gluing of non-steam-treated wood strands;

    - Scattering of the glued steam treated and non steam-treated wood strand onto a conveyor belt in the order first lower top layer, middle layer and second upper top layer; and

    - Pressing of the glued wood strands into an OSB wood-based panel.

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