EP1858678B1 - Method for producing wood-base materials - Google Patents

Abstract

The present invention relates to a process for the production of wood-base materials which have at least one thin veneer layer adhesively bonded over the surface to a substrate or to further veneer layers, which process comprises the following steps: i. impregnation of a veneer with an aqueous curable composition which comprises a) at least one curable urea compound selected from urea compounds H which have at least one N-bonded group of the formula CH2OR, where R is hydrogen or C1-C4-alkyl, and/or a 1,2-bishydroxyethane-1,2-diyl group bridging the two nitrogen atoms of the urea, precondensates of the urea compound H, and reaction products or mixtures of the urea compound H with at least one alcohol which is selected from C1-C6-alkanols, C2-C6-polyols and oligoethylene glycols, and b) at least one catalyst K effecting crosslinking of the urea compound; ii) gluing of the impregnated veneer and/or the substrate with a glue composition and iii) processing of the glued veneer to give a wood-base material at elevated temperature with curing of the crosslinkable urea compound, the impregnated veneer comprising the crosslinkable urea compound in substantially uncrosslinked form before the gluing in step ii).

Description

The present invention relates to a process for the production of wood-based materials which have at least one thin veneer layer adhesively bonded to a support or with further veneer layers.

Wood-based materials with veneer layers made of wood (veneer wood materials), including prefinished parquet, are characterized not only by their aesthetic properties but also by their more homogeneous properties compared to solid wood. On the other hand, their low dimensional stability with changing ambient humidities and their low biological resistance prove disadvantageous, so that these materials are generally not weather-resistant. In addition, the glue joint is heavily stressed by the swelling and shrinkage of the wood in changing weather conditions, so that they lose their mechanical properties after some time, peel the veneer layers from the carrier, or in the case of veneer composites dissolution of the composite occurs.

Although the risk of infestation with wood-discoloring and / or wood-destroying microorganisms can be reduced by treating the wood with biocidal equipment, this represents an additional cost factor and can be problematic for ecological reasons. However, the problems of lack of mechanical stability and deformation under the influence of moisture are not solved by such equipment. Therefore, the field of application of veneer materials remains largely limited to the interior.

In the case of engineered parquet, there is also the problem that an entry of moisture into the butt joints between the parquet slats, z. B. by wet cleaning or spilled liquids, leads to a swelling of the slats and thus to damage the parquet.

The DE 19925865 proposes to solve this problem an impregnation of the faces of parquet lamellae. Impregnating agents are conventional varnishes, varnishes, waxes, oils and the like. The EP-A 903451 describes the sealing of the edges of engineered parquet panels with a coating based on diphenylmethane diisocyanate. A durable resistance to moisture can not be achieved by these measures.

WO 20041033171 describes the impregnation of wood slats for the top layer of engineered parquet with a curable composition that acts as a hardenable component a modified with methanol and ethylene glycol 1,3-bis (hydroxymethyl) -4,5-dihydroxyimidazolidin-2-one. The lamellae are cured after drying at temperatures of 130 ° C and high pressure. Further processing of the wood slats is not described. The treatment leads to an improved surface hardness of the slats thus produced. A disadvantage is the reduced elasticity and flexibility of the slats thus produced, which can lead to problems in further processing and damage to the slats. In addition, the times required for further processing, in particular the pressing time, are extended in comparison to untreated veneers.

The present invention has for its object to provide a process for the production of veneer materials, d. H. of wood-based materials which have at least one surface-bonded thin veneer layer with a support, which leads to wood-based materials with improved weathering stability. In particular, the method should allow the production of the veneer materials in a simple manner.

These and other objects are achieved by the method described below.

The invention therefore relates to a method for producing a wood-based material according to claim 1.

The method according to the invention makes it possible to produce veneer materials in a simple manner. Damage to the veneers occurs in the method according to the invention not or only to a small extent. Another advantage is that the amount of sizing agent for producing a solid composite of the veneer with the carrier can be reduced. The method provides veneer materials with improved weathering stability, in particular a reduced shrinkage and swelling behavior with changing ambient humidity. If the impregnated veneer layer forms at least one surface of the veneer material, these surfaces of the resulting materials also have an increased hardness (Brinell hardness). In addition, the veneer materials according to the invention have an improved resistance to attack by wood-damaging organisms, without the need to use conventional biocides.

The term "veneer material" as used herein includes all wood-based materials that have at least one veneer layer. This veneer layer can be arranged on a support, which usually consists of a wood material, or form a composite together with further veneer layers. The veneer materials to be produced according to the invention include, for example, veneered panels, e.g. Veneered fiberboard, veneered blockboard, veneered chipboard including veneered OSL and PSL (oriented strand lumber), plywood, glued, plywood, laminated veneer lumber (eg Kerto plywood), multiplex panels, laminated veneer material (Laminated Veneer Lumber LVL), decorative veneer materials such as cladding, ceiling and Fertigparkett panels but also non-planar, three-dimensionally shaped components such as plywood moldings, plywood moldings and any other, coated with at least one veneer moldings. The inventive method is particularly suitable for the production of Holzwerkstofffen, where a plurality of modified veneer layers form a composite, for example for the production of plywood, glued wood, plywood, veneer plywood and moldings made therefrom. The method according to the invention is particularly suitable for the production of wood-based materials which have a veneer layer arranged on a support.

In principle, all conventional veneers made of wood such as knife, peel or saw veneers, including parquet slats, can be used as veneers. The thickness of the veneers is usually in the range of 20 microns to 10 mm, often 100 microns to 10 mm and in particular in the range of 0.6 mm to 6 mm. In a first preferred embodiment of the invention is comparatively thin veneers with thicknesses in the range of 100 microns to 3 mm, in particular in the range of 0.5 mm to 3 mm and especially in the range of 0.6 to 2.5 mm. In another embodiment of the invention is comparatively thick veneers with thicknesses in the range of 3 mm to 10 mm, in particular in the range of 3 mm to 8 mm.

Suitable types of wood for the veneers to be treated according to the invention are in principle all types of wood commonly used for veneer production, in particular those which can absorb at least 30%, in particular at least 50%, of their dry weight of water, and particularly preferably those which fall into the saturability classes 1 and 2 according to DIN EN 350-2. These include, for example, woods of conifers such as pine (Pinus spp.), Spruce, cedar, stone pine, Douglas fir, larch, pine, fir, coastal fir, and woods of deciduous trees, eg. Maple, hardmaple, acacia, ayons, birch, pear, beech, oak, alder, aspen, ash, dorsal, hazel, hornbeam, cherry, chestnut, linden, American walnut, poplar, olive, robinia, elm, walnut, rubber tree , Zebrano, willow and Turkey oak, but also mixed veneers, eg. B. Fine-line veneers of poplar and Ayons.

In a first step of the method according to the invention, the at least one wood veneer is impregnated with the aqueous, curable composition. The impregnation is generally carried out in such a way that the amount of crosslinkable urea compound taken up by the veneer is in the range from 1 to 100% by weight, frequently from 5 to 80% by weight, in particular from 10 to 70% by weight on the untreated veneer (calculated as Darrtrockenes veneer), lies.

The moisture of the veneer before impregnation is not critical and can be up to 100%. Often, for practical reasons, the veneer has a moisture content of not more than 80%, or 50%, e.g. 1 to 80%, or 5 to 80% or 5 to 50%. Optionally, the veneer may have been hydrophilized prior to impregnation, for example by dielectric discharge in an oxygen-containing atmosphere analogous to that described in U.S. Pat DE-C 199 57 775 described procedure.

Here and below, the terms used in connection with the veneer "moisture" or "moisture" synonymous with the term residual moisture content according to DIN 52183.

The aqueous compositions of crosslinkable urea compounds used for impregnating in step i) are known per se, for example from the cited above WO 2004/033171 , as well as out WO 2004/033170, K. Fisher et al , " Textile Auxiliaries - Finishing Agents "Chapter 7.2.2 in Ullmann's Encyclopaedia of Industrial Chemistry, 5th Ed. On CD-ROM, Wiley-VCH, Weinheim 1997 and literature cited there, e.g. B. US 2,731,364 . US 2,930,715 , and are commonly used as crosslinkers for textile finishing. Reaction products of urea compounds H with alcohols, eg. B. modified 1,3-bis (hydroxymethyl) -4,5-dihydroxyimidazolidin-2-one (mDMDHEU) are for example from US 4,396,391 and the WO 98/29393 known. Incidentally, urea compounds H and their reaction products and precondensates are commercially available, for example under the trade names Fixapret® CP and Fixapret® ECO from BASF Aktiengesellschaft.

The urea compounds contained in the aqueous compositions are low molecular weight compounds or oligomers of low molecular weight, which are generally completely dissolved in water. The molecular weight of the urea compounds is usually below 400 daltons. These compounds are thought to allow the compounds to penetrate into the cell walls of the wood and, upon hardening, improve the mechanical stability of the cell walls and reduce their swelling caused by water.

• 1,3-Bis(hydroxymethyl)-4,5-dihydroxyimidazolidin-2-on (DMDHEU),
• 1,3-Bis(hydroxymethyl)-4,5-dihydroxyimidazolidin-2-on, das mit einem C₁-C₆-Alkanol einem C₂-C₆-Polyol, einem Oligoethylenglykol modifiziert ist (modifiziertes DMDHEU bzw. mDMDHEU),
• 1,3-Bis(hydroxymethyl)harnstoff,
• 1,3-Bis(methoxymethyl)harnsfoff;
• 1-Hydroxymethyl-3-methylharnstoff,
• 1,3-Bis(hydroxymethyl)imidazolidin-2-on (Dimethylolethylenharnstoff),
• 1,3-Bis(hydroxymethyl)-1,3-hexahydropyrimidin-2-on (Dimethylolpropylenharnstoff)
• 1,3-Bis(methoxymethyl)4,5-dihydroxyimidazolidin-2-on (DMeDHEU) und
• Tetra(hydroxymethyl)acetylendiharnstoff.

Examples of crosslinkable urea compound of the curable, aqueous composition include, but are not limited to:

• 1,3-bis (hydroxymethyl) -4,5-dihydroxyimidazolidin-2-one (DMDHEU),
• 1,3-bis (hydroxymethyl) -4,5-dihydroxyimidazolidin-2-one modified with a C ₁ -C ₆ -alkanol, a C ₂ -C ₆ -polyol, an oligoethylene glycol (modified DMDHEU or mDMDHEU),
• 1,3-bis (hydroxymethyl) urea,
• 1,3-bis harnsfoff (methoxymethyl);
• 1-hydroxymethyl-3-methyl-urea,
• 1,3-bis (hydroxymethyl) imidazolidin-2-one (dimethylolethyleneurea),
• 1,3-bis (hydroxymethyl) -1,3-hexahydropyrimidin-2-one (dimethylolpropyleneurea)
• 1,3-bis (methoxymethyl) 4,5-dihydroxyimidazolidin-2-one (DMeDHEU) and
• Tetra (hydroxymethyl) acetylene diurea.

Among the crosslinkable urea compounds are the compounds which have at least two N-bonded groups of the formula CH ₂ OR and in particular those where R = H.

Particularly preferred is 3-bis (hydroxymethyl) -4,5-dihydroxyimidazolidin-2-one, 1,3-bis (hydroxymethyl) urea, 1,3-bis (hydroxymethyl) imidazolidin-2-one, tetra (hydroxymethyl) acetylenediurea and specifically 1,3-bis (hydroxymethyl-4,5-dihydroxyimidazolidin-2-one (DMDHEU).

In a very particularly preferred embodiment of the invention, the crosslinkable urea compound is 1,3-bis (hydroxymethyl) -4,5-dihydroxyimidazolidin-2-one and one having a C ₁ -C ₆ -alkanol a C ₂ -C ₆ -polyol , an oligoethylene glycol-modified 1,3-bis (hydroxymethyl) -4,5-dihydroxyimidazolidin-2-one selected.

MDMDHEU are reaction products of 1,3-bis (hydroxymethyl-4,5-dihydroxyimidazolidin-2-one with a C ₁ -C ₆ alkanol, a C ₂ -C ₆ polyol, an oligoethylene glycol or mixtures of these alcohols. Suitable C _1-6 -alkanols are, for example, methanol, ethanol, n-propanol, isopropanol, n-butanol and n-pentanol, preferably methanol .. Suitable polyols are ethylene glycol, diethylene glycol, 1,2- and 1,3-propylene glycol , 1,2-, 1,3-, and 1,4-butylene glycol, glycerol Suitable oligoethylene glycols are in particular those of the formula HO (CH ₂ CH ₂ O) _n H where n is from 2 to 20, of which diethylene glycol and triethylene glycol are preferred To produce mDMDHEU, DMDHEU are mixed with the alkanol, the polyol or the polyethylene glycol, wherein the monohydric alcohol, the polyol, or the oligo- or polyethylene glycol are usually in a ratio of 0.1 to 2.0, respectively 0.2 to 2 molar equivalents, based on DMDHEU, are used The mixture of DMDHE U, the polyol or polyethylene glycol is usually reacted in water at temperatures of preferably 20 to 70 ° C and a pH of preferably 1 to 2.5, wherein the pH after the reaction is usually in a range of 4 is set to 8.

The curable aqueous compositions may contain, in addition to the urea compounds H or their reaction products or precondensates (component a)), one or more of the abovementioned alcohols, C ₁ -C ₆ -alkanols, C ₂ -C ₆ -polyols, oligoethylene glycols or mixtures of these alcohols ( Component c)). Examples of suitable C _1-6 -alkanols are methanol, ethanol, n-propanol, isopropanol, n-butanol and n-pentanol, preference being given to methanol. Suitable polyols are ethylene glycol, diethylene glycol, 1,2- and 1,3-propylene glycol, 1,2-, 1,3-, and 1,4-butylene glycol, glycerol. Suitable oligoethylene glycols are, in particular, those of the formula HO (CH ₂ CH ₂ O) _n H where n is from 2 to 20, of which diethylene glycol and triethylene glycol are preferred.

The concentration of urea compound H or its reaction product or precondensate in the aqueous composition is usually in the range from 1 to 80 wt .-%, often in the range of 10 to 60 wt .-% and in particular in the range from 15 to 50% by weight, based on the total weight of the composition. If the curable, aqueous composition contains one of the abovementioned alcohols, its concentration is preferably in the range from 1 to 50% by weight, in particular in the range from 5 to 40% by weight. The total amount of component a) and component c) is usually from 10 to 80 wt .-%, often 10 to 60 wt .-% and in particular 20 to 50 wt .-% of the total weight of the aqueous composition.

In addition to the components a) and optionally c), the aqueous composition contains a catalyst K (component b)), which causes the crosslinking of the urea compound H, or its reaction product or precondensate. In general, as catalysts K metal salts from the group of metal halides, metal sulfates, metal nitrates, metal phosphates, Metalltetrafluoroborate; boron trifluoride; Ammonium salts from the group of ammonium halides, ammonium sulfate, ammonium oxalate and diammonium phosphate; and organic carboxylic acids, organic sulfonic acids, boric acid, sulfuric acid, phosphoric acid and hydrochloric acid.

Examples of metal salts suitable as catalysts K are, in particular, magnesium chloride, magnesium sulfate, zinc chloride, lithium chloride, lithium bromide, aluminum chloride, aluminum sulfate, zinc nitrate and sodium tetrafluoroborate.

Examples of suitable as catalysts K ammonium salts are in particular ammonium chloride, ammonium sulfate, ammonium oxalate and diammonium phosphate.

Particularly suitable as catalysts K are water-soluble organic carboxylic acids such as maleic acid, formic acid, citric acid, tartaric acid and oxalic acid, furthermore benzenesulfonic acids such as p-toluenesulfonic acid, but also inorganic acids such as hydrochloric acid, sulfuric acid, boric acid or mixtures thereof.

Preferably, the catalyst K is selected from magnesium chloride, zinc chloride, magnesium sulfate, aluminum sulfate or mixtures thereof, magnesium chloride being particularly preferred.

The catalyst K is usually added to the aqueous composition only shortly before the impregnation of the lignocellulosic material. It is usually used in an amount of 1 to 20 wt .-%, in particular 2 to 10 wt .-%, based on the total weight of the components contained in the curable aqueous composition a) and optionally c). The concentration of the catalyst, based on the total weight of the curable, aqueous composition, is usually in the range of 0.1 to 10 wt .-% and in particular in the range of 0.5 to 5 wt .-%.

Further, the aqueous composition used to impregnate the wood veneer may contain some or all of the binder components (sizing ingredients) of the sizing agent used in step ii) to sock the veneer, as further explained below. In a preferred embodiment of the invention, the composition used in step i) contains at least 50%, in particular at least 80%, and especially the total amount of glue components contained in the sizing composition, based on the total amount of sizing ingredients used in the method. The terms glue ingredients and binder components are used interchangeably herein and in the following and refer to the non-volatile, the bonding of the veneer with the carrier-causing constituents, including any excipients and preservatives contained in the sizing agent. In this case, the concentration of binder in the aqueous composition is usually in the range of 0.5 to 25 wt .-%, often in the range of 1 to 20 wt .-% and in particular in the range of 5 to 15 wt .-%, based on the total weight of the aqueous composition. It is assumed that the binder components, unlike the crosslinkable urea compounds, the catalyst K and the optionally present alcohols of component c), not or only partially absorbed by the cell walls of the wood, but largely remain on the surface of the wood veneer and therefore be available as sizing agent in the subsequent bonding process.

The impregnation can be done in a conventional manner, for. By immersion, by use of vacuum optionally in combination with pressure or by conventional application methods such as brushing, spraying and the like.

For dipping, the veneers, optionally after predrying, are immersed in a container containing the aqueous composition. The dipping is preferably carried out over a period of a few seconds to 24 h, in particular 1 min to 6 h. The temperatures are usually in the range of 15 ° C to 50 ° C. Here, the veneer absorbs the aqueous impregnating composition, whereby the amount of curable components taken up by the veneer can be controlled by the concentration of curable components (ie, components a) and c)) in the aqueous composition, temperature, and treatment time. The amount of curable components actually absorbed can be determined and controlled by the skilled person in a simple manner by means of the weight increase of the veneer and the concentration of the aqueous composition. The veneers can be pre-pressed by means of pressing rollers, so-called calenders, which are in the aqueous impregnating composition. The occurring when relaxing in the wood Vacuum then leads to an accelerated uptake of aqueous impregnating composition.

The impregnation can also be achieved by the use of reduced pressure, which may optionally be followed by an elevated pressure phase. For this purpose, veneer, which generally has a humidity in the range of 1% to 100%, under reduced pressure, which is often in the range of 10 to 500 mbar and in particular in the range of 40 to 100 mbar, in contact with the aqueous composition brought, for. By immersion in the curable aqueous composition. The time period is usually in the range of 1 minute to 1 hour. Optionally, a phase at elevated pressure, z. B. in the range of 1 to 20 bar, especially in the 5 to 15 bar and especially 10 to 12 bar, to. The duration of this phase is usually in the range of 1 min to 12 h. The temperatures are usually in the range of 15 to 50 ° C. Here, the veneer absorbs the aqueous impregnating composition, whereby the amount of curable components taken up by the veneer can be controlled by the concentration of hardenable components in the aqueous composition, by the applied pressure, by the temperature and the treatment time. The actual amount absorbed can also be calculated here by the weight gain of the veneer.

Furthermore, the impregnation can be carried out by conventional methods for applying liquids to surfaces, for. B. by spraying or rolling or brushing. For this purpose, advantageously a veneer with a humidity of not more than 50%, in particular not more than 30%, z. In the range of 12% to 30%. The application is usually carried out at temperatures in the range of 15 to 50 ° C. The concentration of curable ingredients in the aqueous composition, the amount applied, the temperature, and the duration of spraying, can control the amount of curable ingredients taken up by the veneer. The actual absorbed amount of curable components results directly from the applied amount of aqueous composition. The spraying can be carried out in a conventional manner in all suitable for spraying of flat bodies devices, for. B. by means of nozzle arrangements and the like. When brushing or rolling the desired amount of aqueous composition is applied with rollers or brushes on the veneer.

In a preferred embodiment of the impregnation, the veneer is first compressed, then it is brought into contact with the aqueous curable composition. The compression can be carried out in a simple manner by means of pressing or in particular by means of press rolls, so-called calenders, which are in the aqueous impregnating composition. But you can also do that Compress veneer in a chamber with a conventional, flat press, then flood the chamber with the impregnation solution and then reduce the pressure in the flooded state. The compression pressure applied during compression is typically in the range of 1 to 1000 N / cm ² , often in the range of 10 to 800 N / cm ² , in particular in the range of 50 to 500 N / cm ² . The vacuum occurring in the wood when relaxing then leads to an accelerated absorption of aqueous impregnating composition.

The method according to the invention furthermore comprises a gluing step ii). Here, a liquid sizing composition is applied to the veneer impregnated with the aqueous composition.

According to the invention, the curable constituents of the aqueous impregnating composition are in substantially uncrosslinked form during the gluing. As a rule, the gluing step ii) therefore takes place immediately after the impregnating step i) or simultaneously with it. Optionally, however, to remove moisture between the impregnation and the gluing, a drying step may be carried out under conditions in which curing of the constituents contained in the aqueous composition does not take place or only to a very limited extent. Preferably, a temperature of 100 ° C, especially 80 ° C is not exceeded during such a drying step. If drying is carried out, it will be preferable to fix the veneer in a way, e.g. B. in a press to counteract deformation of the veneer.

Preferably, after impregnation and before gluing, a moisture content of at least 5%, in particular at least 10%, based on the dry mass of the veneer, does not fall below in order to prevent premature curing of the aqueous constituents of the composition and to facilitate the further processing. Preferably, therefore, the gluing step ii) takes place immediately after the impregnation step i) or particularly preferably simultaneously with it. In the latter case, the impregnating solution will already contain the main amount or, in particular, the total amount of binder components of the sizing agent, and the sizing will take place in the manner described for the impregnation.

If the gluing is carried out separately from the impregnation, the method used in a conventional manner depends on the veneer material to be produced. Methods for this are known to the expert, for. B. off HH Nimz et al. Wood - Wood-based Products "2.2 Laminate Bonding, in particular 2.2.2.5 Production of Veneer Plywood in Ullmann's Encyclopaedia of Industrial Chemistry, 5th Edition on CD-Rom, Wiley-VCH (see also F. Kollmann (ed .) Veneers, storage wood and carpenter plates, Springer-Verlag, Berlin 1962 ). Examples of gluing methods are the application of the liquid sizing composition by means of rollers, z. B. by 2- or 4-roller assemblies, the infusion of the liquid sizing composition, for. Example by means of a gluing curtain or the melting of the glue composition.

If the veneer material to be produced according to the invention is a material which comprises a plurality of veneer layers glued together, not all veneer layers must be glued. As a rule, veneer layers glued on both sides will be glued together with non-glued veneer layers in a layer arrangement, the outer veneer layers generally being un-glued. If the veneer material to be produced according to the invention is a material which comprises a veneer layer glued to a carrier, both the veneer layer and the surface to be bonded of the carrier can be glued.

In principle, all sizing compositions customary for the production of veneer materials are suitable as sizing compositions. Preference is given to liquid sizing compositions and in particular to aqueous sizing compositions. Suitable size compositions are known in the art, for. B. off HH Nimz et al. "Wood - Wood-based Products" 2.2.2.4 Adhesives and Additives in Ullmann's Encyclopaedia of Industrial Chemistry, 5th Edition on CD-Rom, Wiley-VCH such as A. Pizzi (ed.): Wood Adhesives, Marcel Dekker, New York 1983 ,

• i) Flüssige, insbesondere wässrige Zubereitungen thermisch härtbarer Bindemittel (Reaktiv-Bindemittel) wie Aminoplastharze, Phenolharze, Isocyanatharze und Epoxidharze; und
• ii) wässrige Zubereitungen filmbildender Polymere, z. B. wässrige Polymerdispersionen auf Basis von Styrol-Acrylaten, Polyacrylaten (Acrylsäureester/Methacrylsäureester-Copolymere), Vinylacetat-Polymeren (Polyvinylacetat), StyrolButadien-Copolymeren und dergleichen.

Examples of sizing agents are:

• i) Liquid, in particular aqueous preparations of thermally curable binders (reactive binders) such as amino resins, phenolic resins, isocyanate resins and epoxy resins; and
• ii) aqueous preparations of film-forming polymers, e.g. Aqueous polymer dispersions based on styrene-acrylates, polyacrylates (acrylic esters / methacrylic acid ester copolymers), vinyl acetate polymers (polyvinyl acetate), styrene-butadiene copolymers and the like.

Preferred sizing agents are those based on the thermally curable binders mentioned in group i) and mixtures thereof with film-forming polymers of group ii). Preferred binders are aminoplast resins, phenolic resins, isocyanate resins and polyvinyl acetate.

As aminoplast resins in particular formaldehyde condensates of urea (urea-formaldehyde condensates) and melamine (melamine-formaldehyde condensates) are suitable. They are available as aqueous solutions or powders under the names Kaurit ^® and Kauramin ^® (Prod. BASF) and contain urea and / or melamine-formaldehyde precondensates. Typical phenolic resins are phenol-formaldehyde condensates, phenol-resorcinol-formaldehyde condensates and the like. Also suitable are mixed condensates of aminoplast resins and phenolic resins. Examples of mixed condensates of aminoplast resins and phenolic resins are urea-melamine-formaldehyde condensates, melamine-urea-formaldehyde-phenol condensates, and mixtures thereof. Their preparation and use for the production of moldings from finely divided lignocellulosic materials is well known. Preference is given to urea-formaldehyde resins and of these in particular those having a molar ratio of 1 mol of urea to 1.1 to 1.4 mol of formaldehyde.

In the processing of aminoplast resins and phenolic resins a transition of soluble and meltable precondensates occurs in infusible and insoluble products. In this process, known as curing, it is known that continuous cross-linking of the precondensates occurs, which is generally accelerated by hardeners. As curing agents, the hardener known to those skilled in the art for urea, phenol and / or melamine-formaldehyde resins can be used, such as acid-reacting and / or acid-releasing compounds, for. For example, ammonium or amine salts. In general, the proportion of hardener in a glue resin liquor is from 1 to 5% by weight, based on the liquid resin content.

As Isocyanatharze all common resins based on Methylendiphenylenisocyanaten (MDI) resins are suitable. They usually consist of a mixture of monomeric and oligomeric di- or polyisocyanates, the so-called precondensates, which are capable of reacting with the cellulose, the lignin and the moisture of the lignocellulosic particles. Suitable isocyanate resins are available, for example as Lupranat® ^® grades (from Elastogran) in the trade.

Suitable binders of group ii) are, in principle, all water-insoluble polymers which are film-forming and dispersible in water. These include, in particular, emulsion polymers and the powders produced therefrom, as described, for example, in US Pat. In WO 01/27198 be referred to as polymers A1. The polymers often have a glass transition temperature in the range of -20 to +150 ° C and in particular in the range of 0 to +100 ° C. In particular, these are polyvinyl acetates, copolymers based on styrene / butadiene, based on styrene / acrylic acid alkyl esters and those based on alkyl methacrylates / alkyl acrylates.

The application amount of sizing agent depends in a conventional manner on the veneer to be glued and on the type of veneer material to be produced and is typically in the range from 50 to 500 g / m ² , in particular from 60 to 300 g / m ² , each glued veneer or 1 to 30 wt .-%, in particular 5 to 25 wt .-%, based on the veneer material and calculated as dry glue (ie, less any solvents and diluents).

The processing of glued veneer to a wood material is carried out in a conventional manner, for example by surface bonding of the glued veneer with a carrier (or the veneer with the glued carrier), preferably a support made of wood or a wood material, or by gluing two Veneer layers to so-called rinds, or of several, usually 3 to 11, z. B. 3, 5, 7, 9 or 11 veneer layers to a wood material or by combined bonding with a carrier and other veneer layers.

If the veneer material to be produced in accordance with the invention is one in which the veneer is glued flat to a carrier, the carrier is preferably wood or a wood-based material, eg. B. to sawed layers and possibly glued together wood rods to plywood, chipboard, including OSB, LSL and PSL to fiberboard, z. As softboard, MDF or HDF, plasterboard, cardboard and the like. The carriers, if made of wood, may also be impregnated and cured with the curable aqueous compositions used to impregnate the veneer or not. The preparation of such impregnated wood support materials may be carried out according to the methods described in WO 2004/033170 and WO 2004/033171 described method. Wood fiberboard and chipboard used as a support may also be made from wood chip materials impregnated and cured with one (or more) of the curable aqueous composition (s) used to impregnate the veneer. A method of manufacturing such plates is the subject of a co-pending patent application.

If the veneer material to be produced according to the invention is a material which comprises a plurality of veneer layers glued together, at least one, preferably several and in particular all veneer layers are provided with an impregnation according to the invention.

The further processing is typically carried out at elevated temperature to achieve, on the one hand, effective gluing of the glued veneer and, on the other hand, to achieve hardening of the wood-absorbed hardenable constituents of the aqueous impregnating composition. The temperatures used are typically above 100 ° C and below the decomposition temperature of the wood and the glue components, preferably in the range of 110 ° C to 200 ° C and especially in the range of 120 ° C to 180 ° C. Advantageously, the further processing takes place by application of elevated pressure of generally at least 0.1 MPa, z. B. 0.1 to 10 MPa, preferably at least 0.2 MPa, z. B. 0.2 to 8 MPa and in particular at least 0.3 MPa, z. B. in the range of 0.3 MPa to 5 MPa, in particular in the range of 0.3 to 2 MPa or 0.5 to 1.6 MPa, to a uniform bonding of the glued veneer with the carrier or with the other veneer layers achieve. The times required for bonding depend on the nature of the material to be produced and are typically in the range of 1 minute to 60 minutes. per cm of veneer material thickness, often in the range of 2 min. up to 30 min. per cm veneer material thickness and in particular in the range of 5 to 15 min per cm veneer material thickness.

The inventive method is basically suitable for the production of all known veneer materials. Examples of suitable veneer materials are the aforementioned.

In a preferred embodiment, it is Fumierwerkstoffe in which at least one surface, in particular a decorative or weathered surface is formed by a veneer layer treated according to the invention. Examples of this are decorative panels for wall and ceiling coverings, forged chipboard, fibreboard and plywood panels for the furniture industry, and especially engineered parquet flooring.

Under parquet, the expert understands wood panels with a decorative decking layer of wood veneer lamellae and at least one support or base layer, which is usually made of a wood material, eg. B. a layer of sawn and optionally glued together wooden rods, plywood, chipboard, including OSB, fiberboard, z. As softboard, MDF or HDF, and the like. In addition, the Fertigparkettpaneele may also include intermediate layers, which are also typically made of wood or wood-based materials, as well as layers that cause impact sound insulation, as in EP1364774 described. In addition, such panels can also constructive devices that facilitate laying the panels have, for. B. tongue and groove or notches. Advantageously, in the engineered parquet panels according to the invention, in particular the wood lamellae or veneers of the cover layer, ie the wear layer of the parquet, have an impregnation according to the invention. Finished parquet panel designs are described, for example, in the article by A. Truscek and Z. Budrovic, "Manufacturing, characteristics and use of pre-finished engineered parquet" in Wood in construction industry: prospectives of reconstruction, International conference proceedings.

In a further preferred embodiment, the wood material is one of two or more, preferably one of an odd number, for. B. 3, 5, 7, 9 or 11, glued together veneer layers existing wood material, for example, a plywood or a plywood, as explained above. In these wood-based materials, the individual veneer layers may be identical or different, ie consist of different woods and / or have different thicknesses, and / or contain different amounts of crosslinked urea compound H. The preparation is usually carried out by alternately gluing both sides glued and unglued veneer layers in layers and glued together under the above conditions, the outer veneer layers, ie those which form the surface of the veneer material, are unglued.

The following examples serve to further illustrate the invention.

Example 1: Production of a Finished Parquet Board

A 50 wt% aqueous solution of diethylene glycol and methanol modified (mDMDHEU) was mixed with 1.5 wt% MgCl ₂ .6H ₂ O. Rough hay, lamellae made of beech wood, dried to about 12% wood moisture, with the dimensions 500 mm x 100 mm x 4 mm were placed in an impregnation system. The impregnation system was exposed for 30 minutes to a vacuum of 100 mbar and then flooded with the impregnating agent. Subsequently, a pressure of 10 bar was applied for one hour. The printing phase was stopped and the residual liquid was removed.

The impregnated lamellae of the cover layer were fixed in stacks so that warping was impossible. The slats were dried for about 4 days at a temperature of 50 ° C. The residual moisture was then at 20%.

Subsequently, the lamellae thus produced were glued on one side with an aqueous melamine resin preparation in an amount of 200 g / m ² , based on the non-aqueous portion of the preparation.

Subsequently, the wooden slat was glued with a fiberboard to a Fertigparkett floorboard. This was done in such a way that the lamella and the fiberboard were placed in a heatable press. The press was heated to 140 ° C and the blades pressed at 0.9 N / mm ^{2 for} about 30 min.

After cooling, the finished parquet floorboard was removed from the press.

Example 2: Production of a Multiplex Plate

A 50 wt% aqueous solution of diethylene glycol and methanol modified (mDMDHEU) was mixed with 1.5 wt% MgCl ₂ .6H ₂ O. Sawn rough, birch wood veneers dried to approx. 12% moisture content with the dimensions 300 mm x 300 mm x 1.5 mm were placed in an impregnation system. The impregnation system was exposed for 30 minutes to a vacuum of 100 mbar and then flooded with the impregnating agent. Subsequently, a pressure of 10 bar was applied for one hour. The printing phase was stopped and the residual liquid was removed.

The impregnated veneers were glued on both sides with an aqueous melamine resin preparation in an amount of 200 g / m ² , based on the non-aqueous portion of the preparation.

Subsequently, each 5 veneers were glued to a multiplex board. For this purpose, the veneers were placed in a heated press. The press was heated to 140 ° C and the veneers pressed with 0.8 N / mm ^{2 for} about 15 min.

After cooling, the plate was removed from the press.

Claims (14)

1. A process for the production of a wood-base material which has at least one veneer layer adhesively bonded over the surface to a substrate or to further veneer layers, comprising:

   i. impregnation of at least one veneer which has a thickness of from 20 µm to 10 mm with an aqueous curable composition which comprises

   a) at least one crosslinkable urea compound selected from urea compounds H which have at least one N-bonded group of the formula CH₂OR, where R is hydrogen or C₁-C₄-alkyl, and/or a 1,2-bishydroxyethane-1,2-diyl group bridging the two nitrogen atoms of the urea, precondensates of the urea compound H, and reaction products or mixtures of the urea compound H with at least one alcohol which is selected from C₁-C₆-alkanols, C₂-C₆-polyols and oligoethylene glycols, and

   b) at least one catalyst K effecting crosslinking of the urea compound;

   ii) gluing of the impregnated veneer and/or the substrate with a glue composition and

   iii) processing of the glued veneer to give a wood-base material at elevated temperature with curing of the crosslinkable urea compound,

   the crosslinkable urea compound being present in the impregnated veneer in substantially uncrosslinked form during the gluing in step ii.
2. The process according to claim 1, the aqueous composition being used in step i. in an amount such that the amount of crosslinkable urea compound taken up by the veneer is in the range from 1 to 100% by weight, based on the untreated veneer.
3. The process according to any of the preceding claims, the impregnated veneer having a moisture content of at least 5%, based on the dry mass of the veneer, before the gluing in step ii.
4. The process according to claim 3, the composition used in step i. comprising at least 50%, based on the total amount of the glue components used in the process, of the glue components which the glue composition comprises.
5. The process according to claim 4, the gluing and impregnation being effected in one step.
6. The process according to any of the preceding claims, the further processing in step iii. being effected at temperatures in the range from 100 to 200°C.
7. The process according to any of the preceding claims, the glue composition used in step ii. comprising at least one heat-curable binder.
8. The process according to claim 7, the glue composition being used in the form of an aqueous formulation of the heat-curable binder.
9. The process according to any of the preceding claims, the impregnated veneer forming at least one surface of the wood-base material.
10. The process according to claim 9, the wood-base material being a prefinished parquet.
11. The process according to claim 9, the wood-base material being a laminated wood or plywood.
12. The process according to any of the preceding claims, the crosslinkable urea compound being selected from

    - 1,3-bis(hydroxymethyl)-4,5-dihydroxyimidazolidin-2-one,

    - bis(hydroxymethyl)-4,5-dihydroxyimidazolidinone which is modified with a C₁-C₆-alkanol, a C₂-C₆-_Polyol or an oligo- or a polyethylene glycol,

    - 1,3-bis(hydroxymethyl)urea,

    - 1,3-bis(methoxymethyl)urea,

    - 1-hydroxymethyl-3-methylurea,

    - 1,3-bis(hydroxymethyl)imidazolidin-2-one,

    - 1,3-bis(hydroxymethyl)-1,3-hexahydropyrimidin-2-one,

    - 1,3-bis(methoxymethyl)-4,5-dihydroxyimidazolidin-2-one,

    - tetra(hydroxymethyl)acetylenediurea.
13. The process according to any of the preceding claims, the concentration of crosslinkable urea compound in the aqueous curable composition being in the range from 1 to 60% by weight, based on the total weight of the composition.
14. The process according to any of the preceding claims, the catalyst K being selected from metal salts from the group consisting of the metal halides, metal sulfates, metal nitrates, metal phosphates, metal tetrafluoroborates; boron trifluoride; ammonium salts from the group consisting of the ammonium halides, ammonium sulfate, ammonium oxalate and diammonium phosphate; organic carboxylic acids, organic sulfonic acids, boric acid, sulfuric acid and hydrochloric acid.