EP3615288A1

EP3615288A1 - Method for producing osb wood boards with a reduced emission of volatile organic compounds (vocs)

Info

Publication number: EP3615288A1
Application number: EP18713575.1A
Authority: EP
Inventors: Norbert Kalwa
Original assignee: Swiss Krono Tec AG
Current assignee: Swiss Krono Tec AG
Priority date: 2017-04-25
Filing date: 2018-03-12
Publication date: 2020-03-04
Anticipated expiration: 2038-03-12
Also published as: HUE048530T2; US11904496B2; WO2018197094A1; ES2904805T3; PT3620282T; PT3395520T; PL3615288T3; ES2958617T3; PL3395520T3; EP3395520B1; CA3060986A1; ES2767090T3; CA3060986C; US11007668B2; US20210245391A1; EP3620282A1; CN110545971A; CN112476694A; PL3620282T3; UA127129C2

Abstract

The invention relates to a method for treating wood strands which are suitable for producing OSB boards. The wood strands are treated with steam without being dried after being obtained, and the steam is conducted over the wood strands at a temperature between 80 °C and 120 °C and at a pressure between 0.5 bar and 2 bar. The invention likewise relates to a method for producing OSB wood boards, in particular OSB wood boards with a reduced emission of volatile organic compounds (VOCs), having the steps of a) producing wood strands from suitable timbers; b) treating at least some of the wood strands with steam; c) drying the wood strands treated with the steam; d) gluing the wood strands which are treated with steam and dried and gluing wood strands not treated with steam using at least one binder; e) scattering the glued wood strands onto a transport belt; and f) compressing the glued wood strands in order to form an OSB wood board.

Description

Process for producing OSB wood-based panels with reduced emission of volatile organic compounds (VOCs)

The present invention relates to a process for treating wood strands with water vapor according to claim 1, a device for carrying out the steam treatment according to claim 7, a process for the production of OSB wood-based panels according to claim 10, a production line for the production of OSB wood-based panels according to claim 14, and the use of steam-treated wooden strands according to claim 15.

description

Coated boards, also known as OSB (Oriented Strand Boards), are wood-based panels made of long chips (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 as the OSB boards as mentioned above, are often used for constructive applications. 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. Typically, two strands of material are used in the manufacture of the OSB panels: 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 essentially due to the cover layers Therefore, fines produced during machining can also be used in the middle layer of OSB boards.The percentage distribution between the middle and top layers is at least 70% to 30%, followed by continuous spreading of the strands the same under high pressure and high temperature of eg 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 ^VOC's called, include volatile organic compounds which evaporate easily and at lower temperatures such as at room temperature are present as a gas. 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 predominantly OSB boards are produced contain large amounts of resin and fats leading 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 OS B boards is particularly critical 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 followed in EP 1 907 178 B1. 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 now the technical object of the invention to improve the known per se method for the production of OSB boards to the effect to produce easily and safely OSB boards with a significantly reduced emission 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 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 problem it was a system to design the ^'s will allow a simple treatment of the strands to reduce the emission of VOC. 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 device for steam treatment according to claim 7, a method for producing OSB wood-based panels with the features of claim 10, and a suitable production line according to claim 14 solved.

Accordingly, there is provided a method of treating wood strands suitable for producing OSB boards, in particular with the aim of reducing VOC emissions from these wood strands, the wood strands being made after being recovered suitable woods are treated without drying with steam, wherein the steam is passed with a temperature between 80 ° C and 120 ° C and a pressure between 0.5 bar and 2 bar on the wooden strands. In one embodiment of the present method, the treatment of the wood strands with steam takes place in such a way that the water vapor at a temperature between 90 ° C and 1 10 ° 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, it can be dispensed with the application of an additional (external) pressure (ie in addition to the pressure with the water vapor in the system). This leads to a simplification of the device, since no pressure vessel (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 is carried out outside of a chipper (e.g., knife ring chipper or disc chipper) and thus is not part of the cutting or crushing process of wood for making wooden strands. 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 one embodiment of the present process, the steam treatment of the wood strands takes place over a period of 5 to 30 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 guided by 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.

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 housing passing through the transport device for transporting the wood strands through the housing; and

- At least one provided above the transport device housing supply line for the water vapor, wherein along the supply line at least one spray means for applying the water vapor to the on the

Transport device located wooden strands is arranged.

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.

The water-treated wood strands are used according to the invention for the production of OSB wood-based panels with reduced emission of volatile organic compounds (VOCs). The production of OSB wood-based panels with reduced emission of volatile organic compounds (VOCs) is carried out in a process comprising the following steps: a) producing wood strands from suitable timbers; b) treating at least a portion of the wood strands with water vapor according to the method described above; c) drying the steamed wood strands; d) lining the steam-treated and dried wood strands and optionally lining non-steamed wood strands with at least one binder; e) sprinkling the glued wooden strands on a conveyor belt; and 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 comprising steam-treated wood strands has a reduced emission of volatile organic compounds, in particular of 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 wooden strands can be reduced, since the wood strands already have an elevated temperature (eg, about 90 ° C) when entering the dryer; ie the energy input during 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 wood strands have a lighter color, it may accordingly be advantageous to use steam-treated wood strands in the cover layer. 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 removed from the manufacturing process and introduced into the steam treatment device (eg, steaming system). Subsequently, the steam-treated wood strands may, if appropriate, be introduced into the conventional production process again after intermediate storage, for example immediately before gluing. This allows a high flexibility in the manufacturing process.

The steam treatment of the wood strands can be integrated in a still further embodiment variant in the manufacturing process of the OSB wood-based panels, 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 is preferably used as a binder, which is selected from the group consisting of 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 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 used with a binder amount of from 1.0 to 10% by weight, in particular from 1.0 to 5.0% by weight, preferably from 2 to 4% by weight, particularly preferably 3% by weight on the total amount of wooden strands). It is conceivable that the same binder or different binders are used for the top and middle layers.

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

In another alternative variant, the cover 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 cover 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 mentioned relate in each case to the gluing of the cover layers and the middle layer of a 3-layer OSB with a thickness of 19 to 22 mm. 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.

In a first 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,

- 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 treated with steam wood strands;

- sifting and separating the steam-treated wooden strands in wooden strips suitable for use as a middle layer and top layer;

- lining 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. 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 strips suitable for use as a middle layer and top layer;

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

- Drying treated with steam wood strands;

- lining the separated steam-treated wooden strips and lining 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 cutting process and an associated aqueous workup and cleaning 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 in the emission of C2-C10 aldehydes, particularly preferably acetaldehyde, pentanal, hexanal or furfural, and a reduction of liberated terpenes, especially Cio-monoterpenes and cis-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, 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.

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 device described above for the steam treatment of at least part of the wood strands;

- At least one dryer for drying the steam-treated

Wood strands;

- At least one device for sifting and separating the wooden strands

(steam-treated and non-steam-treated);

- At least one device for Beimimen 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 wood 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 serves a steaming the steam treatment of the wood strands which are provided for the middle class, and the other steaming system of the steam treatment of the wood strands which 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.

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

Figure 1 is a schematic representation of an embodiment of a device for

Steam treatment of wooden strips;

Figure 2 is a schematic representation of a first embodiment of the method according to the invention for the production of OSB boards, and

Figure 3 is 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 1 1 with the tubular body 1 1 continuous perforated conveyor belt 12 above the conveyor belt 12 is a supply line 13 for the steam provided, wherein the feed line 13 a plurality of nozzles 14 for spraying the water vapor on Having the conveyor belt 12 located 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 passed directly to the production of the conveyor belt 12, which passes through the tubular body 1 1. On the conveyor belt 12, the strands are distributed so that a homogeneous flow through the Strands 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 1 1 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.

The first embodiment of the method according to the invention shown in FIG. 2 describes the individual method steps beginning with the provision of the wood starting product up 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 comminution and provision of the wood strands, they may be subjected to a predrying process, with a humidity of 5-10% being adjusted with respect to the initial moisture content of the wood strands (not shown). In the case of the embodiment shown in FIG. 2, the strands of wood are introduced into an evaporator (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 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 second embodiment shown in FIG. 3, the wood starting material is initially provided (step 1), debarked (step 2) and machined (step 3) in analogy to FIG. 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 embodiment variant of FIG. 2, a separation into wood strands for use as a middle layer or as a cover layer takes place already after the optional drying (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 steam. 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 of the tube body was slightly angled upward (2 to 10 degrees), so that the forming condensate could be easily 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 drum dryer is reduced significantly, as the beaches when entering the Dryers already have a temperature of about 90 ° C. 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

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 forming the aldehydes is wrong or in the steam treatment, the precursors of the 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

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

Claims

claims

1 . Process for the treatment of suitable for the production of OSB boards wood strands, characterized in that the wood strands are treated after their extraction without drying with steam, the water vapor having a temperature between 80 ° C and 120 ° C and a pressure between 0.5 bar and 2 bar is passed over the wooden strands.

2. The method according to claim 1, characterized in that for the treatment of the wood strands with water vapor, the steam at a temperature between 90 ° C and 1 10 ° C, particularly preferably of 100 ° C at a pressure between 0.7 and 1, 5 bar, in particular preferably at 1 bar (atmospheric pressure) is passed over the wooden strands.

3. The method according to claim 1 or 2, characterized in that the steam treatment of the wood strands over a period of 5 to 30 minutes, preferably from 10 to 20 minutes, more preferably 15 minutes.

4. The method according to any one of the preceding claims, characterized in that the steam treatment of the wood strands takes place in an oxygen-poor atmosphere.

5. The method according to any one of the preceding claims, characterized in that the wood strands for steam treatment are performed on at least one transport device continuously through a device for steam treatment.

6. The method according to any one of the preceding claims, characterized in that the water vapor collected after passing the wood strands as condensate.

7. Apparatus for steam treatment of wooden strands comprising according to one of the preceding claims

- At least one housing; - At least one housing passing through the transport device for transporting the wood strands through the housing; and

- At least one provided above the transport device in the housing 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 wood strands located on the transport device.

8. Apparatus according to claim 7, characterized in that the at least transport device comprises at least one conveyor belt with perforations.

9. Device according to one of claims 7 to 8, 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.

10. A process for producing OSB wood-based panels, in particular OSB wood-based panels with reduced emission of volatile organic compounds (VOCs), comprising the steps of: a) producing wooden strips of suitable timbers; b) treating at least a portion of the wood strands with water vapor according to a method according to any one of claims 1 to 6; c) drying the steamed wood strands; d) lining the steam-treated and dried wood strands and optionally lining non-steamed wood strands with at least one binder; e) sprinkling the glued wooden strands on a conveyor belt; and f) pressing the glued wooden strands into an OSB wood-based panel.

1 1. A method according to claim 10, characterized in that steam-treated wood strands or a mixture of water-treated wood strands and non-treated steam-treated wood strands are used as a middle layer and / or top layer of OSB wood-based panel.

12. The method according to any one of claims 10 to 1 1, characterized in that the steam-treated and non-steam-treated wood strands with a

Binder amount of 1, 0 to 5.0 wt%, preferably 2 to 4 wt%, in particular 3 wt% (based on the total amount of wood strands) are glued.

13. The method according to any one of claims 10 to 12, characterized in that the glued wooden strands at temperatures between 200 and 250 ° C, preferably 220 and

230 ° C to an OSB wood-based panel to be pressed.

14. Production line for producing an OSB board according to a method according to one of the preceding claims comprising

- At least one device (2) for debarking suitable logs

(1 );

- at least one chipper (3) for cutting the debarked logs in strips of wood;

- At least one device (4, 4a, 4b) for the steam treatment of at least part of the wood strands according to one of claims 7 to 9; at least one dryer (9, 9a, 9b) for drying the steam-treated wooden strands;

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

- At least one device (6a, 6b) for lining the wooden strands; and

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

- At least one press (8) for pressing the scattered wood strands to OSB boards.

15. The use of steam-treated wood strands for the production of OSB boards with reduced emission of volatile organic compounds (VOCs), wherein The wood strands are treated after their extraction without drying with steam, wherein the steam is passed with a temperature between 80 ° C and 120 ° C and a pressure between 0.5 bar and 2 bar on the wood strands.

16. Use according to claim 15, characterized in that for the treatment of the wood strands with water vapor of the steam at a temperature between 90 ° C and 1 10 ° C, particularly preferably of 100 ° C at a pressure between 0.7 and 1, 5 bar, in particular preferably at 1 bar (atmospheric pressure) is passed over the wooden strands.

17. Use according to claim 15 or 16, characterized in that the steam treatment of the wood strands over a period of 5 to 30 minutes, preferably from 10 to 20 minutes, more preferably 15 minutes.

18. Use according to one of claims 15 to 17, characterized in that the steam treatment of the wood strands takes place in an oxygen-poor atmosphere.

19. Use according to one of claims 15 to 18, characterized in that the wood strands for steam treatment on at least one transport device are continuously passed through a device for steam treatment.

20. Use according to any one of claims 15 to 19, characterized in that the water vapor collected after passing through the wood strands as condensate.