EP3386699A1

EP3386699A1 - Wood material board with reduced emission of volatile organic compounds (vocs) and method for the production thereof

Info

Publication number: EP3386699A1
Application number: EP16794249.9A
Authority: EP
Inventors: Norbert Dr. Kalwa; Jens Siems
Original assignee: Swiss Krono Tec AG
Current assignee: Swiss Krono Tec AG
Priority date: 2015-12-07
Filing date: 2016-11-03
Publication date: 2018-10-17
Also published as: JP2020023195A; RU2766678C2; ES2687495T3; WO2017097506A1; ES2687495T8; JP6832411B2; US10399245B2; EP3178622B1; US20180345529A1; CA3007578A1; RU2019112232A3; US11148317B2; RU2689571C1; EP3178622A1; JP6622423B2; JP2018536568A; PT3178622T; RU2019112232A; PL3178622T3; US20190329445A1

Abstract

The present invention relates to a method for producing wood material boards, in particular chipboards and fibreboards, with reduced emission of volatile organic compounds (VOCs), comprising the steps: a) producing woodchips from suitable timbers; b) heat-treating at least one portion of the woodchips at a temperature between 150 °C and 300 °C for a period of 1 to 5 hours; c) crushing the wood chips that are not heat-treated and at least one portion of the heat-treated woodchips by machining in order to obtain wood shavings or by solubilising in order to obtain wood fibres; d) glueing the wood shavings or wood fibres with at least one binding agent; e) applying the glued wood shavings onto a transport belt while forming a multi-layered shavings cake or applying the glued wood fibres onto a transport belt while forming a single-layer fibre cake; and f) compressing the shavings cake or the fibre cake to form a wood material board. The present invention also relates to a chipboard and a fibreboard produced with said method.

Description

Wood-based panel with reduced emission of volatile organic compounds (VOCs) and process for their preparation

The present invention relates to a process for the production of wood-based panels, in particular chipboard or fiberboard according to the preamble of claim 1, with the process produced chipboard according to claim 10, produced by the method wood fiber boards according to claim 12, their use according to claim 14 and the use of heat-treated wood chips produced wood chips and wood fibers according to claim 15.

description

Wood-based panels, such as chipboard or wood fiber boards, which in the present case are always medium or high density wood fiber boards (MDF / HDF) are understood to be the basis of many everyday objects, such as furniture or coverings for wall, floor or ceiling. In addition to some technological parameters that affect the strength of the panels under mechanical stress, emission from the products is becoming an increasingly important quality criterion. Typically, emissions of volatile organic compounds (VOCs) from a particleboard or fiberboard are only a minor problem because many products have the surface refined with decorative coatings. However, there are also applications in which chipboard and wood fiber boards are used uncoated on a larger scale (eg as tongue and groove panels, interior fittings, etc.). The use of lightweight and super light wood fiber boards is often done without coating. It is a critical aspect that emissions are often referred to as the so-called AgBB scheme by assuming emissions of a space loading of 1 m ² / m ³ and a defined air change (0.5 / h). By wall and ceiling coverings, floor coverings and furniture made of MDF / HDF wood fiber boards, these room loads can be significantly exceeded. Also, the air exchange of 0.5 / h is often well below in modern low-energy houses. This, in combination, can lead to higher room concentrations of wood constituents. In the course of the production of wood-based panels and in particular due to the manufacturing process of the wood chips and wood fibers arise or a variety of volatile organic compounds are released. Volatile organic compounds, also called VOCs, include volatile organic compounds that readily evaporate or are already present as gas at lower temperatures, such as room temperature.

The volatile organic compounds VOC are either already present in the wood material and are released during workup from this or they are formed according to the current state of knowledge by the degradation of unsaturated fatty acids, which in turn are decomposition products of wood. Typical conversion products that occur during processing are, for example, higher aldehydes or organic acids. Organic acids are produced in particular as cleavage products of the wood constituents cellulose, hemicelluloses and lignin, alkanoic acids such as acetic acid, propionic acid, hexanoic acid or aromatic acids preferably being formed. Aldehydes will be formed during the hydrolytic workup 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 during the partial hydrolytic exclusion of lignin. Other released aldehydes include i.a. the higher aldehydes hexanal, pentanal or octanal.

In order to solve the problem of VOC emission, various approaches have been described in the past. On the one hand there is the possibility of wood fibers with other natural fibers such. Wool, hemp salmon, which behave more favorably with regard to their emission behavior, in order to obtain an ecological wood fiber board with improved emission characteristics. A disadvantage here, however, is the high costs associated with these fibers and limited availability, since in some cases higher-value applications exist for the corresponding fiber types, suggesting a different use.

Also, by adding alkaline substances, the pH in the wood matrix can be increased so as to prevent or reduce the acid catalyzed reactions taking place in the wood matrix (Roffael, E., et al, Holzzentralblatt 1990, 16: 1684-1 685). Further possibilities for reducing the emission of volatile organic compounds are the addition of zeolite (WO 2010/136166), bisulfites or pyrosulfites (US2009 / 0130474 A1) as aldehyde scavenger or in the addition of polyamines to reduce released during the aqueous wood pulping aldehydes and organic acids (EP 2 567 798). In EP 0639434 B2 a manufacturing method for MDF wood fiber boards is described, which differs from the conventional method in the field of fiber pulping. Here, a CTMP (chemo-thermo-mechanical-pulping) fiber pulping process is used to reduce the emission of volatile organic compounds in the finished wood fiber board. For this purpose, Na ₂ S0 ₃ or NaOH was added as the chemical component. However, this method has not yet prevailed on the market.

Accordingly, there is still a very large demand for low-emission wood-based panels as well as the simplest and safest production methods.

The present invention is therefore based on the technical object of providing a process for the production of wood-based panels, in particular of particle board or wood fiber boards, which allows the production of these wood-based panels with significantly improved VOC emissions. This should be done without any serious change to the usual manufacturing process and not lead to cost increases. In addition, the production itself should not generate higher emissions or place more pressure on the process waters that are usually generated. In addition, the resulting products should be processable without any problems in the subsequent value-added chain. This object is achieved by a process for the production of wood-based panels, in particular of particleboard and wood fiber boards with the features of claim 1 and produced by this method wood-based panels according to claims 1 0 and 1 2. Accordingly, there is provided a process for making wood-based panels, in particular chipboard panels and reduced-volatile-matter (VOC) emission wood fiber panels, comprising the steps of: a) making wood chips from suitable timbers, b) heat treatment of at least a portion of the woodchips at a temperature between 1 50 ° C and 300 ° C over a period of 1 h to 5 h; c) crushing the non-heat treated wood chips and at least a portion of the heat treated wood chips by machining to obtain wood chips or by digestion to obtain wood fibers; d) lining the wood chips or wood fibers with at least one binder; e) applying the glued wood chips to a conveyor belt to form a multi-layered chipboard or the glued wood fibers on a conveyor belt to form a single-layer fiber cake; and f) pressing the chip cake or the fiber cake into a wood-based panel.

The present method enables the production of wood-based panels such as chipboard and fiberboard using heat-treated wood, in particular heat-treated wood chips, which are introduced into a known manufacturing process in addition to or as an alternative to untreated, non-heat-treated wood chips.

A wood-based panel produced by the method according to the invention, in particular in the form of a chipboard or a fiberboard with a typical density of 400 to 1200 kg / m ³ comprising wood chips or wood fibers produced from heat-treated wood chips has a reduced emission of volatile organic compounds, especially higher aldehydes and of organic acids.

By providing the present method, there are further advantages. Thus, a simple production of wood-based panels, such as chipboard and wood fiber boards is possible without significantly affecting the usual process chain. In addition, the emission of volatile compounds into the air during the manufacturing process of the wood-based panels and the burden of process water is reduced. The presently applied heat treatment of the wood chips is preferably carried out in a saturated steam atmosphere, in particular under an elevated pressure, preferably above 5 bar. The present heat treatment can be understood both as torrefaction known per se and, at least with regard to the pressure conditions, as a modification of the torrefaction known per se. Torrefaction is a thermal treatment process in which the material to be torrefied is typically heated at atmospheric pressure in an oxygen-free gas atmosphere. The treatment of biomass without air access leads to a pyrolytic decomposition and drying. The process is carried out at relatively low temperatures of 250 to 300 ° C for pyrolysis. The aim is, as in the case of coking, to increase the mass and volume-related energy density and thus the calorific value of the raw material, to increase transportability or to reduce the expense of subsequent biomass milling.

The step of heat treating the woodchips may be provided in various ways in the present process.

Thus, according to one embodiment, it is possible to integrate the step of heat treatment of the woodchips into the manufacturing process of the wood-based panels, such as chipboard and fiberboard, i. the heat treatment step is integrated into the overall process or process line and takes place online.

In another embodiment variant, the step of heat treatment of the wood chips can be carried out separately from the production process of the wood-based panels, such as chipboard and wood fiber boards. Accordingly, the heat treatment step in this embodiment of the present method is outside the overall process or process line. The woodchips are thereby discharged from the manufacturing process and introduced into the heat treatment apparatus (e.g., heat treatment reactor). Subsequently, the heat-treated woodchips may possibly be introduced again into the conventional manufacturing process after an intermediate storage. This allows a high flexibility in the manufacturing process.

The wood chips used in the present case may have a length between 10 to 100 mm, preferably 20 to 90 mm, particularly preferably 30 to 80 mm; a width between 5 to 70 mm, preferably 1 0 to 50 mm, particularly preferably 15 to 20 mm; and a thickness between 1 and 30 mm, preferably between 2 and 25 mm, particularly preferably between 3 and 20 mm.

In a further embodiment of the present method, the wood chips are heat treated at temperatures between 200 ° C and 280 ° C, more preferably between 220 ° C and 260 ° C.

As stated above, the heat treatment process of the wood chips may be between 1 and 5 hours, preferably between 2 and 3 hours, with the duration of the process varying depending on the amount and type of starting material used. The process de heat treatment is preferably terminated at a mass loss of wood chips from 1 0 to 30%, preferably 1 5 to 20%.

As already mentioned above, in one embodiment variant of the present method, the wood chips are heat-treated by heating in a low-oxygen or oxygen-free atmosphere, in particular in a saturated steam atmosphere. This can be done under atmospheric pressure. In the case of the use of saturated steam, the heat treatment process preferably takes place at temperatures between 1 60 ° C and 220 ° C and pressures of 6 bar to 16 bar.

It is also preferred if at least a portion of the woodchips are heat treated at a moisture content of 20-50% by weight, i. no previous drying of the wood chips takes place here, but the wood chips are fed to the heat treatment device after further machining without further pretreatment.

The presently used heat treatment reactor can be present as a batch plant or as a continuously operated plant.

The pyrolysis gases released during the heat treatment process essentially from hemicelluloses and other low molecular weight compounds are used to generate process energy. The amount of gas mixture formed as gaseous fuel is sufficient to operate the process energetically self-sufficient.

The heat-treated woodchips are preferably cooled to room temperature and, if appropriate, temporarily stored or returned to the production process directly, if necessary after moistening. In a variant of the present method, the heat-treated woodchips are cooled and watered in a water bath, wherein at least one wetting agent is added to the water. The wetting agent, for example a conventional surfactant, facilitates the wetting of the hydrophobic surface of the woodchip chips produced by the heat treatment with water. The amount of wetting agent is in the water bath, in which the wood chips are transferred at 0, 1 to 1, 0% by weight. Watering positively influences the subsequent cutting or defibering process. The wetting of the chips or fibers with binders containing water as a solvent is thereby improved. As a result of the washing process, the moisture content of the heat-treated chips is adjusted to 5 to 20%, preferably 1 0 to 1 5%.

Likewise, the moisture content of the untreated, non-heat treated wood chips is adjusted accordingly. The woodchips are in this step e.g. washed and cooked. The water treatment is desirable so that the wood chips can be chipped or shredded. In addition, without water in the machining or defibration would be very unwanted dust.

This is followed by a machining process of the woodchips in a chipper or a defibration process of the wood chips in a refiner, wherein wood chips or the wood fibers during the fiberization process also a wetting agent for improving the water wetting of the heat-treated wood or wood chips can also be added. The wood chips produced in the cutting process are divided into fine and coarse chip material, wherein the larger wood chips are preferably used in the middle layer of the chipboard and the smaller wood chips are preferably used in the cover layers. It is preferred if the wood chips used in the middle layer were produced from heat-treated wood chips, since these typically have a dark color. When using the dark colored chips in the middle layer, the plate optics is thus not affected. In addition, since the middle layer is typically about 2/3 of a particle board, the effect on emission reduction is not adversely affected. The wood fibers produced by the defibration process have a length of between 1, 5 mm and 20 mm and a thickness of between 0.05 mm and 1 mm. In a further step of the present method, the wood chips after the machining process or the wood fibers after the defibration process are brought into contact with at least one binder suitable for crosslinking the wood chips or fibers, the contacting of the wood chips and wood fibers with the binder in each case in different ways can be done.

Thus, the wood fibers can be contacted with the at least one binder in step d) in a blow-line process in which the binder is injected into the stream of wood fibers. It is possible that the binders described below for wood fiber crosslinking in the blow-line are fed to a wood fiber-steam mixture.

By contrast, wood chips are preferably contacted with the binder in a mixing device.

The amount of binder added depends on the type of binder and the type of wood-based panel.

In the case of a formaldehyde-based binder for a wood fiber board, the amount of binder to be applied to the wood fibers is from 3 to 20% by weight, preferably from 5 to 15% by weight, more preferably from 8 to 12% by weight. If, on the other hand, polyurethane-containing binders, such as PMDI, are used for wood fiber boards, the necessary amount of binder is reduced to 1 to 10% by weight, preferably 2 to 8% by weight, particularly preferably 4 to 6% by weight.

Binders based on formaldehyde are preferably used in the case of wood chip boards, with binder amounts of from 5 to 8% by weight, preferably from 6 to 7% by weight, and from 6 to 10% by weight, preferably from 8 to 9% by weight, for the middle layer. be used. When using a polyurethane-based binder, such as PMD I, in chipboard, the amount of binder in the middle layer is between 2 and 5% by weight, preferably 3% by weight, and in the top layer between 4 and 8% by weight, preferably 5% by weight.

As already indicated, 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, polyurethane adhesives, epoxy adhesives, polyester adhesives, wherein mainly formaldehyde adhesives are used. As the formaldehyde adhesive, in particular, a phenol-formaldehyde resin adhesive (PF), a cresol / resorcinol-formaldehyde resin adhesive, urea-formaldehyde resin adhesive (UF), and / or melamine-formaldehyde resin adhesive (MF) can be used.

Polyurethane adhesives based on aromatic polyisocyanates, in particular polydiphenylmethane diisocyanate (PMDI), tolylene diisocyanate (TDI) and / or diphenylmethane diisocyanate (MDI), with PMDI being particularly preferred, are available to a lesser extent as an alternative to the formaldehyde adhesive.

It would also be conceivable and conceivable to use mixtures of two or more polymer adhesives, such as a formaldehyde adhesive (such as MUF, MF, UF) and a polyurethane adhesive (such as PMDI). Such hybrid adhesive systems are known from EP 2 447 332 B1.

It is also possible to supply at least one flame retardant to the wood chips or wood fibers together or separately with the binder.

The flame retardant may typically be added in an amount of between 1 and 20% by weight, preferably between 5 and 15% by weight, more preferably 10% by weight, of the wood fiber-binder mixture.

Typical flame retardants are selected from the group comprising phosphates, borates, in particular ammonium polyphosphate, tris (tri-bromneopentyl) phosphate, zinc borate or boric acid complexes of polyhydric alcohols.

In a next process step, the wood chips or wood fibers are dried to a degree of moisture of 1 to 1 0%, preferably 3 to 5%. In the case of wood chips, the drying process is preferably carried out in a one-step process, e.g. in a drum dryer, whereas wood fibers can be dried in a two-stage process.

The dried wood chips or wood fibers are then sorted according to their size or sighted and preferably stored, for example, in silos or bunkers. The screening of the chips or fibers after the drying process is typically associated with a post-cleaning. For this purpose, the fibers are placed in an air stream and freed either largely by vortex formation, sharp deflections, impact vision, Steigluftsichtung or a combination of several effects of heavy particles such as glue lumps. Subsequently, the fibers are again separated by cyclone from the air flow and fed to further use. In the case of sighting of wood chips, these are subdivided into coarser chips for the middle class and finer chips for the outer layers.

As stated above, the gluing of the wood fibers can be done before drying. The gluing of the wood chamfers can also be done after drying. In the case of the use of wood chips, however, the gluing is done after the screening, wherein the Beieimen done by mixing chips and glue.

After sifting, the glued wood chips or wood fibers are sprinkled on a conveyor belt to form a chip cake or fiber cake. The scattering station typically used in the case of wood fibers consists of a dosing bunker, a mat diffusion and a mat smoothing. In the case of wood shavings, it is customary to work with wind scattering, in which case firstly a first covering layer, followed by the middle layer and finally a second covering layer, is spread.

The chip cake or fiber cake is then first pre-pressed and then pressed hot at temperatures between 1 00 ° C and 250 ° C, preferably 130 ° C and 220 ° C, especially at 200 ° C. Here, the chip cake or the fiber cake is first weighed after spreading and measured the moisture. The chip or fiber cake then passes into the pre-press. Here, the cake is reduced in thickness during the cold pre-compaction, so that the subsequent hot presses can be charged more efficiently and the risk of damage to the cake is reduced. In the pre-compaction in the run is usually worked with tape pre-pressing, according to the principle of the conveyor belt (rarely with Plattenbandvorpressen, according to the principle of the tank chain, or with Walzenbandvorpressen, according to the principle of pyramid stone transport with round timbers).

After pre-pressing, the trimming of the compacted cake or mat follows. Here side strips are separated from the mat, so that the corresponding desired plate width can be produced. The side strips are in front of the spreader in the Process returned. Other measuring devices for density control or metal detection may follow. Also a Mattenbesprühung to improve the surface qualities or acceleration of the Mattwartwärmung can follow. This is followed by the hot pressing, which can be clocked or continuously performed. In the present case, continuous hot pressing is preferred. For this purpose, continuous presses are used, which work with a press belt or press plates, via which the pressure and the temperature are transmitted. The tape is supported either by a roll carpet, a rod carpet or an oil pad against the mostly with thermal oil (more rarely with steam) heated heating plates. This press system enables the production of plate thicknesses between 1, 5 mm and 60 mm. On calender presses only thin chipboard or fibreboard can be produced. The pressing takes place here with press rolls and an outer belt on a heated calender roll.

After hot pressing, the pressed plates are assembled. This is usually followed by a series of quality control measurements, in particular thickness control.

In a particularly preferred embodiment, the present method for producing a particle board with reduced VOC emission comprises the following steps: a1) producing wood chips from suitable woods, b1) if necessary pre-drying the wood chips, c1) heat treatment of at least part of the wood chips in a Temperature between 1 50 ° C and 300 ° C over a period of 1 h to 5 h, d1) water treatment of the heat-treated wood chips, e1) cutting of the non-heat-treated woodchips and at least part of the heat-treated woodchips into woodchips; f1) sifting of the wood chips; (gl) cladding wood chips produced from heat-treated woodchips or a mixture of wood shavings produced from non-heat-treated wood chips and wood shavings produced from heat-treated wood chips with at least one binder; h1) sprinkling the glued wood chips onto a conveyor belt to form a multi-layered chipboard, the wood chips being spread over one another as first cover layer, middle layer and second cover layer; i1) pressing the chipboard to a chipboard.

In a particularly preferred embodiment, the present method for producing a wood fiber board with reduced VOC emission comprises the following steps: a2) producing wood chips from suitable woods, b2) if necessary pre-drying the wood chips, c2) heat treatment of at least a portion of the wood chips in a Temperature between 1 50 ° C and 300 ° C over a period of 1 h to 5 h, d2) water treatment of the heat-treated wood chips, e2) fiber pulping of the non-heat-treated wood chips and at least part of the heat-treated wood chips to wood fibers; f2) mixing the wood fibers produced from heat-treated wood chips or a mixture of wood fibers produced from non-heat-treated wood chips and wood fibers produced from heat-treated wood chips with at least one binder; g2) sprinkling the glued wood fibers onto a conveyor belt to form a single-layered fiber cake, h2) pre-pressing the fiber cake, and i2) hot pressing the fiber cake to a fiberboard.

The use of heat-treated woodchips for the production of particle boards and fiberboard has a number of advantages. Thus, it is particularly advantageous that the wood chips and wood fibers produced from the heat-treated wood chips are particularly easy to dry, which is due in particular to the low hydrophilicity of the heat-treated wood. This is also advantageous for the use of the wood fiberboards produced, since the wood chips or wood fibers produced from the heat-treated wood chips have a lower equilibrium moisture content at defined temperatures and humidities than the non-heat-treated wood.

Another positive aspect of the use of heat-treated woodchips as starting material is that a homogenization of the starting raw material wood is achieved. This is of particular economic importance, since the use of wood chips for the production of chipboard, wood fiber boards or other wood materials, the seasonal variations of the raw material wood must be considered. Another advantage is that heat treated woodchips are not subject to biodegradation or other alterations due to storage, allowing storage of the heat treated woodchips for an extended period of time. Furthermore, no ingredients are washed out by contact with water, as they have been destroyed in the heat treatment process.

Accordingly, the present method enables the production of a particle board and fibrous board having reduced emission of volatile organic compounds (VOCs), which comprise wood chips or wood fibers produced from heat-treated wood chips, respectively. The present chipboard may consist entirely of wood chips produced from heat-treated wood chips or consist of a mixture of untreated (ie not heat-treated) wood chips and wood chips produced from heat-treated wood chips. Accordingly, the present fiberboard may be wholly made of wood fibers made of heat-treated wood chips or may consist of a mixture of wood fibers made from untreated (ie not heat-treated) wood chips and wood fibers made from heat-treated wood chips. In particular, the present chipboard or wood fiber board has a reduced emission of aldehydes released during the wood pulping, in particular pentanal, hexanal or octanal, and / or of organic acids, in particular acetic acid.

The present wood-based panel in the form of a chipboard or wood fiber board may have a bulk density between 400 and 1200 kg / m ³ , preferably between 500 and 1000 kg / m ³ , particularly preferably between 600 and 800 kg / m ³ .

The thickness of the present wood-based panel as chipboard or wood fiber board may be between 3 and 20 mm, preferably between 5 and 1 5 mm, in particular, a thickness of 1 0 mm is preferred.

The present chipboard consists of 60 to 90% by weight, preferably 70 to 80% by weight of wood chips and 5 to 20% by weight, preferably 10 to 15% by weight of binders. The present wood fiber board consists of a fiber mixture comprising 60 to 90% by weight, preferably 70 to 80% by weight of wood fibers and 5 to 20% by weight, preferably 1 0 to 1 5% by weight of binders. In this regard, reference is made to the above comments on the type of binders used. As stated above, both the present wood chip board and the present wood fiber board may consist of a mixture of wood shavings / wood fibers produced from non-heat treated wood chips and wood shavings / wood fibers made of heat treated wood chips. The mixture used in the chipboard and in the wood fiberboard may be between 10 and 50% by weight, preferably between 20 and 30% by weight, of chips / fibers produced from non-heat treated woodchips and between 50 and 90% by weight, preferably between 70 and 80% by weight. comprise chips / fibers produced from heat-treated wood chips. As already explained above, in the case of chipboard, the chips obtained from the heat-treated woodchips are preferably used in the middle layer.

Both the present chipboard and the present fiberboard can be used as a low-emission wood chip or wood fiber board for furniture and floor, wall or ceiling coverings. The object of the present invention is also achieved with the use of wood chips or wood fibers produced from heat-treated wood chips according to claim 15. Accordingly, wood chips and wood fibers produced from heat-treated woodchips are used to reduce the emission of volatile organic compounds (VOCs) from wood chip boards or wood fiber boards.

In a preferred variant, the wood chips and wood fibers produced from heat-treated woodchips are used to reduce aldehydes and / or organic acids released during wood pulping.

Accordingly, the wood chips / wood fibers produced from heat-treated woodchips are presently preferably used for reducing the emission of organic acids, in particular for reducing the emission of acetic acid and hexanoic acid. Organic acids are produced in particular as cleavage products of the wood constituents cellulose, hemicelluloses and lignin, alkanoic acids such as acetic acid, propionic acid, hexanoic acid or aromatic acids preferably being formed. It is also desirable to use wood shavings / wood fibers made from heat treated woodchips to reduce the emission of aldehydes. In this case, it is particularly preferred if the wood fibers are used to reduce aldehydes released during the aqueous wood pulping process. Accordingly, the wood chips or wood fibers produced from heat-treated wood chips are used to reduce the emission of C1-C10 aldehydes, particularly preferably pentanal, hexanal or octanal.

The invention will be explained in more detail below with reference to the figures of the drawing of several embodiments. Show it :

Figure 1 is a schematic representation of a first embodiment of the inventive method for producing a wood fiber board, and

Figure 2 is a schematic representation of a second embodiment of the method according to the invention for producing a wood fiber board. The first embodiment of the method according to the invention shown in FIG. 1 describes the individual method steps beginning with the provision of the wood starting product to the finished fibreboard. Accordingly, in step 1 suitable wood starting material for producing the woodchips is first provided. As wood source material all conifers, hardwoods or mixtures thereof are suitable. The roundwood is debarked and shredded in wood chippers or drum chippers (step 2), whereby the size of the wood chippings can be controlled accordingly.

After comminution and provision of the wood chips, they are possibly subjected to a predrying process, wherein a moisture content of 5-1 0% is set in relation to the initial moisture content of the woodchips. In the case of the first embodiment shown in FIG. 1, at least some of the optionally predried woodchips are removed from the conventional production process and introduced into a heat treatment reactor (step 3). The heat treatment of the discharged wood chips takes place in a temperature range between 220 ° and 260 ° C. The resulting pyrolysis gases are used to generate the energy required for the process plant.

After completion of the heat treatment, which takes in the present case about 2 hours, the heat-treated woodchips be reintroduced into the process and optionally together with the non-heat treated wood chips in a washing and cooking step 4 back to a humidity of 1 0-20 % brought.

Thereafter, the wood fibers are subjected to the pulping process in a refiner (step 5), whereby a suitable wetting agent is supplied to the wood fibers in the course of the pulping process.

The wood fibers can be mixed immediately after the fiber pulping with a liquid binder and optionally a flame retardant (step 6). The contacting of the wood fibers with the liquid binder can be carried out in this process stage, for example in a blow-Iine method. The gluing step 6 is followed by a drying process of the glued wood fibers (step 7), wherein this drying process can take place in two stages I, II. The dryer is designed as a 2-stage dryer, with the main drying in stage 1 being done by means of hot gases (air or superheated steam) and after-drying in stage 2, where it is also possible to use hot air or superheated steam. The mixture is separated in / after each stage by means of separation cyclone and capsule plants.

The dried wood fibers are sorted according to their size (step 8).

Subsequently, the glued wood fibers are scattered on a conveyor belt (step 9), the formed fiber cake initially fed to a pre-press (step 1 0) and finally pressed in the hot press (step 1 1) to a large-sized wood fiber board. In the finishing, the wood fiber board obtained is assembled in a suitable manner.

The second embodiment shown in Figure 2 differs from the first embodiment shown in Figure 1 in that the step of heat treatment of the woodchips (step 3) is integrated into the manufacturing process of the wood fiber boards, i. The heat treatment step is integrated into the overall process or process line and takes place online. Removal of wood chips from the process line for heat treatment is thus eliminated. This is particularly advantageous if the wood fiber board is made entirely from wood fibers obtained from heat-treated wood chips.

Embodiment 1: Wood fiber board, in particular MDF

Wood chips are kept undried (humidity: approx. 50%, format: approx. 5 x 5 cm, thickness: approx. 1 cm) in a continuous heat treatment device at 220 ° C under saturated steam for approx. 2 h. The device consists of a conveyor through which the wood chips are transported slowly by means of a screw conveyor.

Then the chips are cooled in the wood chips laundry and then led to the normal defibration. In the process, the wood chips washing contained 0.1% of a commercially available surfactant. This was added to improve the wetting of the hydrophobic chips. The water of the laundry showed a clear lower staining and exposure to organic compounds was reduced by about 90%.

The wood chips resulting after defibration were glued in the blowline with a commercially available urea-formaldehyde glue and dried. Subsequently, the fibers were scattered and processed into MDF having a density of 650 kg / m ³ and a thickness of 10 mm.

The resulting MDF is then tested for VOC emission according to the AgBB scheme along with a blank sample (from non-heat treated wood chips). For reasons of time, the 3-day value was determined.

Chamber parameters: temperature 23C ° C; Humidity 50% + - 5%; Air change 0.5 / h + - 0.1 / h; Loading 1 m ² / m ^3; Chamber volume 225 m ³

As shown in the table, the emissions of the quantitatively most important parameters from the test plate are at a significantly lower level. Embodiment 2: Chipboard

The production of particleboard is generally known. The heat treated wood chips analogous to Example 1 are fed to a chipper. After cutting, the wood chips are dried to a residual moisture content of approx. 2% in a drum dryer. After drying, the wood chips are sorted and separated into coarser chips for the middle layer and finer chips for the top layer.

After filling with urea-formaldehyde glue, the chips are scattered to multilayer chip cake, wherein the chips used in the middle layer of heat treated wood chips was obtained, and pressed at temperatures of about 200 ° C to plates.

The emission study carried out analogously to Example 1 showed similarly reduced VOC emission values for acetic acid and the higher aldehydes.

Claims

Process for the production of wood-based panels, in particular chipboard and fiberboard, with reduced emission of volatile organic compounds (VOCs) comprising the steps of: a) producing wood chips from suitable woods; b) heat-treating at least a portion of the woodchips at a temperature between 150 ° C and 300 ° C over a period of 1 hour to 5 hours; c) crushing the non-heat treated wood chips and at least part of the heat treated wood chips by chipping to obtain wood chips or by digestion to obtain wood fibers; d) lining the wood chips or wood fibers with at least one binder; e) applying the glued wood chips to a conveyor belt to form a multi-layered chipboard or the glued wood fibers on a conveyor belt to form a single-layer fiber cake; and f) pressing the chip cake or the fiber cake into a wood-based panel.

A method according to claim 1, characterized in that the step of heat treatment of wood chips is integrated into the manufacturing process of the wood-based panel.

A method according to claim 1, characterized in that the step of heat treatment of wood chips is performed separately from the manufacturing process of the wood-based panel.

4. The method according to any one of the preceding claims, characterized in that the wood chips are heat-treated at temperatures between 200 ° C and 280 ° C, more preferably between 220 ° C and 260 ° C.

5. The method according to any one of the preceding claims, characterized in that the wood chips are heat treated for a period of between 2 h and 3 h.

6. The method according to any one of the preceding claims, characterized in that the wood chips are heat-treated by heating in low-oxygen or oxygen-free atmosphere, in particular in a saturated steam atmosphere. 7. The method according to any one of the preceding claims, characterized in that at least a portion of the wood chips is heat treated with a humidity of 20-50% by weight.

8. The method according to any one of the preceding claims, characterized in that the heat-treated wood chips are cooled in a water bath, wherein the water at least one wetting agent is added.

9. The method according to any one of the preceding claims, characterized in that the moisture content of the heat-treated wood chips to 5 to 20%, preferably 1 0 to 1 5% is set.

10. A chipboard with reduced emission of volatile organic compounds (VOCs) preparable in a method according to one of the preceding claims comprising wood chips produced from heat-treated wood chips.

1 1. Chipboard according to claim 10, characterized in that it consists entirely of the wood chips produced from heat-treated wood chips or of a mixture of wood chips produced from non-heat-treated wood chips and wood chips produced from heat-treated wood chips.

12. Wood fiber board with reduced emission of volatile organic compounds (VOCs) preparable in a method according to one of claims 1 to 9 comprising wood fibers produced from heat-treated wood chips.

13. wood fiber board according to claim 12, characterized in that it consists entirely of the wood fibers produced from heat-treated wood chips or from a mixture of non-heat-treated wood chips produced wood fibers and wood fibers produced from heat-treated wood chips.

14. Use of a chipboard according to claim 10 or 1 1 or a wood fiber board according to claim 12 or 13 for furniture, wall, floor and ceiling coverings.

15. Use of wood chips and wood fibers derived from heat-treated wood chips to reduce the emission of volatile organic compounds (VOCs) from wood chip boards and wood fiber boards.