Patent Application
20080246177
The present invention relates to a process for the production of moldings from finely divided materials based on lignocellulose, and the moldings obtainable thereby. The invention also relates to the use of aqueous compositions which comprise at least one crosslinkable urea compound for the preparation of finely divided materials treated with this composition and based on lignocellulose for the production of moldings.
Moldings based on finely divided materials based on lignocellulose (also referred to below as moldings based on lignocellulose particles), such as, for example, based on wood particles, are widely used as construction materials in the construction and furniture sectors. They are produced, as a rule, by glue-coating of the lignocellulose particles with a liquid, usually aqueous composition of binder polymers, shaping of the materials thus glue-coated and curing. During the curing, adhesive bonding of the finely divided materials takes place, if appropriate with crosslinking of the binder, with the result that the molding retains its stability. In the case of wood-plastic composites (WPC), the finely divided materials are embedded in a plastic matrix. An overview of the customary types of moldings based on lignocellulose particles and the processes for their production is given by H. H. Nimz et al, “Wood—Wood-based Materials”, in Ullmann's Encyclopedia of Industrial Chemistry, 5th Ed. on CD-ROM, Wiley-VCH, Weinheim 1997. As mass-produced goods, moldings based on finely divided lignocellulose particles are subject to immense cost pressure.
A key problem in the case of moldings based on lignocellulose particles is their frequently only moderate to low stability to water. This results from the property of the lignocellulose particles to incorporate water, for example into the cell walls, on contact with water or in a humid atmosphere. As a result, the moldings swell and their mechanical strength is reduced. Moreover, moldings based on lignocellulose particles, in particular in the moist state, are attacked by wood-degrading or wood-discoloring organisms, in particular microorganisms, necessitating the treatment of the moldings with corresponding fungicides and biocides. This in turn is a not inconsiderable cost factor and is also disadvantageous from environmental points of view.
For improving the stability, wood and comparable lignocellulose-based materials are frequently rendered water repellent, for example by treatment with wax-containing impregnating agents. This makes it more difficult for water to penetrate into the pores of the material.
It was proposed to improve the dimensional stability of wood-base materials, such as particle boards and fiberboards, and their stability to wood-destroying organisms by acetylating the wood particles with the aid of anhydrides, such as acetic anhydride (cf. EP-A 213252 and literature cited therein and Rowell et al., Wood and Fiber Science, 21 (1), pages 67-79). The high costs of the treatment and the unpleasant intrinsic odor of the material thus treated are disadvantageous, so that these measures have not become established on the market.
Other chemicals too, such as isocyanates, siloxanes and acrylamide, were proposed for the modification of lignocellulose fibers (J. Appl. Polym Sci., 73 (1999) 2493-2505). However, these measures too are as a whole unsatisfactory.
WO 2004/033170 and WO 2004/033171 describe the use of impregnating agents based on hydroxymethyl- or alkoxymethyl-modified urea derivatives, such as 1,3-bis(hydroxymethyl)-4,5-dihydroxyimidazolidin-2-one, bis(hydroxymethyl)-4,5-dihydroxyimidazolidinone modified with alkanols, 1,3-bis(hydroxymethyl)urea, 1,3-bis(methoxymethyl)urea, 1-hydroxymethyl-3-methylurea, 1,3-bis(hydroxymethyl)-imidazolidin-2-one, 1,3-dimethyl-4,5-dihydroxyimidazolidin-2-one or tetra(hydroxy-methyl)acetylenediurea, for improving the durability, dimensional stability and surface hardness of wood bodies comprising solid wood. The problem of the dimensional stability of moldings based on finely divided lignocellulose materials is not discussed.
Accordingly, it is the object of the present invention to provide a finely divided material based on lignocellulose, from which material moldings having improved dimensional stability under the action of moisture can be produced. The finely divided material should moreover be economical to produce with regard to the use in the production of mass-produced products, such as fiberboards and particle boards.
It was surprisingly found that this and further objects can be achieved by finely divided materials based on lignocellulose which were treated with an aqueous composition which comprises at least one crosslinkable urea compound, the crosslinkable urea compound being 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.
Below, finely divided materials based on lignocellulose are also referred to as finely divided lignocellulose materials or lignocellulose particles for short. Accordingly, finely divided materials treated according to the invention and based on lignocellulose are also referred to as treated lignocellulose materials or finely divided lignocellulose materials according to the invention or as treated lignocellulose particles or lignocellulose particles according to the invention, and untreated finely divided materials based on lignocellulose are also referred to as untreated finely divided lignocellulose materials or untreated lignocellulose particles.
Treatment is understood as meaning impregnation or soaking of the untreated finely divided lignocellulose materials with the aqueous composition and, if appropriate, drying and/or curing of the impregnated material or the curable components absorbed by the impregnated material.
Finely divided lignocellulose materials which were impregnated with the aqueous composition of the crosslinkable urea compounds and which were treated in a manner such that the crosslinking of the urea compounds (curing) has taken place give, on customary further processing, moldings which are distinguished by superior mechanical properties, in particular by improved shape stability or dimensional stability, i.e. less swelling on contact with moisture, and by a higher surface hardness. Moreover, the moldings are less susceptible to attack by wood-destroying microorganisms, such as harmful wood-destroying fungi and wood-destroying bacteria, with the result that the application of corresponding fungicides and biocides can be reduced and frequently even avoided. The crosslinking of the crosslinkable urea compounds of the aqueous composition is effected after the impregnation, optionally in a separate drying/curing step at elevated temperature and/or during the subsequent shaping process after the glue-coating with a binder customary for the production of moldings, if appropriate by addition of a catalyst promoting the curing of the urea compounds.
Accordingly, the present invention firstly relates to the use of an aqueous composition, comprising at least one crosslinkable urea compound from the group consisting of the 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, for the preparation of finely divided materials treated with this composition and based on lignocellulose for the production of moldings.
The invention furthermore relates to the treated lignocellulose materials thus obtainable and their use for the production of moldings. The invention also relates to the moldings produced using such impregnated lignocellulose materials.
Aqueous compositions of crosslinkable urea compounds of the type under discussion are disclosed, for example, in WO 2004/033170 and WO 2004/033171 cited at the outset and in K. Fisher et al. “Textile Auxiliaries—Finishing Agents” Section 7.2.2 in Ullmann's Encyclopedia of Industrial Chemistry, 5th Ed. on CD-ROM, Wiley-VCH, Weinheim 1997, and literature cited there, e.g. U.S. Pat. No. 2,731,364 and U.S. Pat. No. 2,930,715, and are usually used as crosslinking agents for textile finishing. Reaction products of urea compounds with alcohols, for example modified 1,3-bis(hydroxymethyl)-4,5-dihydroxy-imidazolidin-2-one (mDMDHEU), are disclosed, for example, in U.S. Pat. No. 4,396,391 and WO 98/29393. In addition, 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 present in the aqueous compositions are low molecular weight compounds or oligomers having a low molecular weight which as a rule are present completely dissolved in water. The molecular weight of the urea compounds is usually below 400 dalton. It is assumed that, owing to these properties, the compounds can penetrate into the cell walls of the lignocellulose particles and, on curing, improve the mechanical stability of the cell walls and reduce their swelling caused by water.
Examples of a crosslinkable urea compound of the curable, aqueous composition are the following, without being restricted thereto:
In a preferred embodiment of the invention, the crosslinkable urea compound is selected from 1,3-bis(hydroxymethyl)-4,5-dihydroxyimidazolidin-2-one and a 1,3-bis(hydroxymethyl)-4,5-dihydroxyimidazolidin-2-one modified with a C1-C6-alkanol, a C2-C6-polyol or an oligoethylene glycol.
mDMDHEU are reaction products of 1,3-bis(hydroxymethyl)-4,5-dihydroxyimidazolidin-2-one with a C1-C6-alkanol, a C2-C6-polyol, an oligoethylene glycol or mixtures of these alcohols. Suitable C1-6-alkanols are, for example, methanol, ethanol, n-propanol, isopropanol, n-butanol and n-pentanol, methanol being preferred. Suitable polyols are ethylene glycol, diethylene glycol, 1,2- and 1,3-propylene glycol, 1,2-, 1,3- and 1,4-butylene glycol and glycerol. Suitable oligoethylene glycols are in particular those of the formula HO(CH2CH2O)nH, where n is from 2 to 20, among which diethylene glycol and triethylene glycol are preferred. For the preparation of mDMDHEU, DMDHEU are mixed with the alkanol, the polyol or the polyethylene glycol. Here, the monohydric alcohol, the polyol or oligo- or polyethylene glycol is usually used in a ratio of from 0.1 to 2.0, in particular from 0.2 to 2, mole equivalents each, based on DMDHEU. The mixture of DMDHEU and the polyol or the polyethylene glycol is usually reacted in water at temperatures of, preferably, from 20 to 70° C. and a pH of, preferably, from 1 to 2.5, the pH being adjusted as a rule to a range of from 4 to 8 after the reaction.
In addition to the urea compounds H or the reaction products or precondensates thereof (component A), the curable aqueous compositions may also comprise one or more of the abovementioned alcohols, C1-C6-alkanols, C2-C6-polyols, oligoethylene glycols or mixtures of these alcohols (component C). Suitable C1-6-alkanols are, for example, methanol, ethanol, n-propanol, isopropanol, n-butanol and n-pentanol, methanol being preferred. Suitable polyols are ethylene glycol, diethylene glycol, 1,2- and 1,3-propylene glycol, 1,2-, 1,3- and 1,4-butylene glycol and glycerol. Suitable oligoethylene glycols are in particular those of the formula HO(CH2CH2O)nH, where n is from 2 to 20, among which diethylene glycol and triethylene glycol are preferred.
The concentration of urea compound H or the reaction product or precondensate thereof in the aqueous composition is usually in the range from 1 to 60% by weight, frequently in the range from 10 to 60% by weight 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 comprises one of the abovementioned alcohols, the concentration thereof 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) usually accounts for from 10 to 60% by weight and in particular from 20 to 50% by weight of the total weight of the aqueous composition.
In addition to the components A) and, if appropriate, C), the aqueous composition may also comprise a catalyst K which effects crosslinking of the urea compound H or of its reaction product or precondensate. As a rule, metal salts from the group consisting of the metal halides, metal sulfates, metal nitrates, metal phosphates and metal tetrafluoroborates; boron trifluoride, ammonium salts from the group consisting of the ammonium halides, ammonium sulfate, ammonium oxalate and diammonium phosphate; and organic carboxylic acids, organic sulfonic acids, boric acid, sulfuric acid and hydrochloric acid are suitable as catalyst K.
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 ammonium salts suitable as catalysts K are in particular ammonium chloride, ammonium sulfate, ammonium oxalate and diammonium phosphate.
Water-soluble organic carboxylic acids, such as maleic acid, formic acid, citric acid, tartaric acid and oxalic acid, and furthermore benzenesulfonic acid and p-toluene-sulfonic acid, but also inorganic acids, such as hydrochloric acid, sulfuric acid, boric acid or mixtures thereof, are in particular also suitable as catalysts K.
The catalyst K is preferably chosen from magnesium chloride, zinc chloride, magnesium sulfate, aluminum sulfate and mixtures thereof, magnesium chloride being particularly preferred.
The catalyst K is usually added to the aqueous composition only shortly before the impregnation of the lignocellulose material. It is usually used in an amount of from 1 to 20% by weight, in particular from 2 to 10% by weight, based on the total weight of the components A) and, if appropriate, C) present in the curable, aqueous composition. The concentration of the catalyst is usually in the range from 0.1 to 10% by weight and in particular in the range from 0.5 to 5% by weight, based on the total weight of the curable, aqueous composition.
Furthermore, the aqueous composition used for the impregnation may comprise a part or the total amount of the binders which are required for the production of the moldings and which are explained in more detail further below. If desired, the concentration of the binder in the aqueous composition is usually in the range from 0.5 to 25% by weight, frequently in the range from 1 to 20% by weight and in particular in the range from 5 to 15% by weight, based on the total weight of the aqueous composition and calculated as dry glue components (i.e. without any solvent or diluent components of the binder).
It is assumed that the binder components of the glue composition, in contrast to crosslinkable urea compounds, the catalyst K and any alcohols of component C) which are present are not absorbed or are absorbed only to a small extent by the cell walls of the lignocellulose particles and remain substantially on the surface of the particles and they are therefore available as binder in the subsequent shaping process of the production of the moldings.
The preparation of the finely divided materials impregnated with the aqueous composition and based on lignocellulose can in principle be effected by two different methods.
Thus, according to a first embodiment of the invention, a coarse-particled, untreated material based on lignocellulose, e.g. wood blocks, can be treated with the aqueous compositions which comprise a catalyst K in the manner described in WO 2004/033170 or WO 2004/033171 and then comminuted, for example by conversion into chips, defibering or milling, or the treated wood chips or wood fibers obtained on processing or recycling of the materials thus obtained can be recovered.
Preferably, however, an untreated, finely divided material based on lignocellulose is impregnated with the curable aqueous composition and the catalyst K and then exposed to conditions which effect crosslinking of the urea compounds present in the composition and hence curing of the composition. The aqueous composition and the catalyst K can be applied together in one composition or in two separate compositions to the untreated finely divided material based on lignocellulose. Usually, however, the catalyst K is incorporated into the aqueous composition before the application. However, it is also conceivable to impregnate the finely divided material based on lignocellulose simultaneously or in succession with a first aqueous formulation which comprises the catalyst K in dissolved form, and a second aqueous composition which comprises the crosslinkable urea compound and, if appropriate, the alcohol component C).
The type of untreated finely divided lignocellulose material depends in a known manner on the molding to be produced. Examples of suitable finely divided lignocellulose materials comprise, without being restricted thereto, finely divided materials comprising wood, such as, for example, wood chips, for example from chipped round wood and logs, chipped industrial wood and residual industrial wood, sawmill and veneer wastes, chips from thermomechanically digested wood, shavings from planing and peeling, wood chips and wood shreds, and furthermore lignocellulose-containing raw materials differing from wood, such as bamboo, bagasse, cotton stalks, jute, sisal, straw, flax, coconut fibers, banana fibers, reeds, e.g. Chinese silvergrass, ramie, hemp, Manila hemp, esparto (alfa grass), rice husks and cork.
The untreated finely divided lignocellulose materials may be present in the form of granules, powder or preferably chips, including sawdust and planing shavings, fibers and/or shreds. Among these, materials comprising wood and bamboo, such as wood fibers, wood chips and wood shreds or bamboo fibers, bamboo shreds and bamboo chips and mixtures thereof, are particularly preferred. These are in particular finely divided materials comprising wood. The wood species of which the finely divided materials consist comprise, for example, softwood, such as douglas fir, spruce, pine, larch, stone pine, fir, cedar and Swiss stone pine, and hardwood, such as maple, acacia, birch, beech, oak, alder, ash, aspen, hazel, hornbeam, cherry, lime, poplar, locust, elm, walnut, willow, adriatic oak and the like.
The dimensions, i.e. the measurements (length, thickness), which at least 90% of the finely divided lignocellulose materials have is usually in the range from 0.1 to 20 mm, in particular from 0.5 to 10 mm, and especially from 1 to 5 mm, it being possible for the length which at least 90% of the particles have also to exceed 10 mm and be up to 200 mm in the case of elongated finely divided materials having a length/width ratio>5. The average width or thickness of elongated particles is typically in the range from 0.1 to 10, in particular in the range from 0.2 to 5, mm and especially in the range from 0.3 to 3 mm.
The impregnation or soaking, respectively, of the untreated finely divided materials based on lignocellulose can be carried out, for example, by immersing the fibers in the aqueous composition, by applying reduced pressure, if appropriate in combination with pressure, or by spraying. The conditions are as a rule chosen so that the amount of curable components of the aqueous composition which are absorbed is at least 1% by weight, based on the dry matter of the untreated material. The amount of curable components which is absorbed may be up to 100% by weight, based on the dry matter of the untreated lignocellulose materials and is frequently in the range from 1 to 60% by weight, preferably in the range from 5 to 50% by weight and in particular in the range from 10 to 30% by weight, based on the dry matter of the untreated material used. Usually, the impregnation is effected at ambient temperature, typically in the range from 15 to 40° C.
The moisture of the untreated lignocellulose materials used for the impregnation is not critical and may be, for example, up to 100% by weight. Here and below, the term “moisture” is synonymous with the term residual moisture content according to DIN 52183. Frequently, it is in the range from 1 to 80% and in particular from 5 to 50%.
On immersion, the untreated finely divided lignocellulose materials, which advantageously have a moisture content in the range from 1% to 100%, are immersed for a period of from a few seconds to 12 h, in particular from 1 min to 60 min, in the aqueous composition in a container or are suspended therein. The finely divided lignocellulose material absorbs the aqueous impregnating composition during this, it being possible for the amount of curable components which is absorbed by the finely divided lignocellulose material to be controlled by the concentration of curable components (i.e. components A) and C)) in the aqueous composition, by the temperature and by the duration of treatment. The amount of curable components which is actually absorbed can be determined by the person skilled in the art in a simple manner from the weight increase of the finely divided lignocellulose material and the concentration of the aqueous composition.
The impregnation can also be achieved by applying reduced pressure, it being possible, if appropriate, for a phase of elevated pressure to follow. For this purpose, the finely divided lignocellulose material is brought into contact with the aqueous composition under reduced pressure, which is frequently in the range from 10 to 500 mbar and in particular in the range from 50 to 100 mbar, for example by immersion or suspension in the curable aqueous composition. The time span is usually in the range from 1 min to 1 h. If appropriate, a phase at elevated pressure, for example in the range from 1 bar to 20 bar, follows. The duration of this phase is usually in the range from 1 min to 6 h, in particular from 5 min to 1 h. During this, the finely divided lignocellulose material absorbs the aqueous impregnating composition, it being possible for the amount of curable components which is absorbed by the finely divided lignocellulose material to be controlled by the concentration of curable components in the aqueous composition, by the pressure applied, by the temperature and by the duration of treatment. Here too, the amount actually absorbed can be calculated from the weight increase of the finely divided lignocellulose material.
In a further embodiment of the invention, the impregnation is effected by spraying the untreated lignocellulose particles with the aqueous composition. The lignocellulose particles advantageously have a moisture content of not more than 50%, for example in the range from 1% to 30%. The spraying is usually effected at temperatures in the range from 15 to 50° C. The amount of curable components which is absorbed by the finely divided lignocellulose material can be controlled by the concentration of curable components in the aqueous composition, by the amount applied, by the temperature and by the duration of spraying. The amount of curable components which is actually absorbed results directly from the amount of aqueous composition sprayed on. The spraying can be carried out in a conventional manner in all apparatuses suitable for the spraying of solids, for example in spray towers, fluidized-bed apparatuses and the like.
The impregnation can also be effected by means of ultrasound.
The impregnated finely divided lignocellulose particles thus obtained are further processed to give moldings, if appropriate after a drying step and/or a curing step.
In many cases, the further processing comprises glue-coating of the treated finely divided material with a liquid or pulverulent formulation of a binder and shaping and curing of the treated material to give a molding. In other cases, for example in the production of WPCs, the further processing comprises mixing of the material obtained in step i) with a thermoplastic polymer and shaping of the mixture. In this case, the production in step i) usually comprises an impregnation and a drying or curing step.
The invention therefore also relates to a process for the production of moldings from finely divided lignocellulose-based materials, comprising
The invention also relates to the moldings obtainable by the process.
If the provision of the treated finely divided lignocellulose materials comprises the impregnation of untreated lignocellulose materials, a drying step, also predrying step below, can be carried out after the impregnation in step i) and before the glue-coating in step ii). During this, the volatile components of the aqueous composition, in particular the water and excess organic solvents which do not react in the curing/crosslinking of the urea compounds, are partly or completely removed. In addition, depending on the chosen drying temperature, partial or complete curing/crosslinking of the curable components present in the formulation may take place. The predrying/curing of the impregnated materials is usually effected at temperatures of from 50° C. to 220° C., in particular in the range from 80 to 200° C. If curing is desired, the drying is preferably effected at above 100° C. The curing/drying can be carried out in a conventional fresh air/exhaust air system, for example a drum drier. The predrying is preferably effected in a manner such that the moisture content of the finely divided lignocellulose materials after the predrying is not more than 30%, in particular not more than 20%, based on the dry matter. It may be advantageous to carry out the drying/curing to a moisture content of <10% and in particular <5%, based on the dry matter. The moisture content can be controlled in a simple manner by the temperature, the duration and the pressure chosen in the predrying.
However, a predrying step is in principle not necessary, and removal of volatile components and crosslinking of the curable components of the aqueous composition can also be effected after the glue-coating in step ii) or can be carried out in the shaping and curing step iii). Such a procedure not only has the advantage of simplifying the process but permits shorter glue-coating and shaping times. In a preferred embodiment, therefore, preferably no separate drying step is carried out and the glue-coating is effected immediately after the impregnation or simultaneously therewith.
If the aqueous composition already comprises an amount of binder which is sufficient for the production of the molding, treatment step i) and glue-coating ii) take place at the same time, and the removal of the volatile components and the crosslinking of the curable components of the aqueous composition are carried out in the shaping and curing step iii).
If the aqueous composition used for the impregnation in step i) does not comprise an amount of binder which is sufficient for the production of the moldings, the impregnated and, if appropriate, predried and cured lignocellulose particles are then glue-coated in a conventional manner with the binder required for the production of the moldings.
The glue-coating can be effected in a conventional manner. If appropriate, further finely divided materials forming the molding, additives, catalysts or assistants are added at this stage.
The type of binder depends in a known manner on the type of molding to be produced. Suitable binders are described, for example, in A. Pizzi (editor): Wood Adhesives, Marcel Dekker, New York 1983. Examples of binders are:
Preferred binders are the heat-curable binders mentioned in group i) and mixtures thereof with film-forming polymers of group iii), the heat-curable binders preferably being used in the form of aqueous formulations.
Preferred binders are aminoplast resins, phenol resins, isocyanate resins, polyvinyl acetate and polycarboxylic acid resins.
Particularly suitable aminoplast resins are formaldehyde condensates of urea (urea-formaldehyde condensates) and of melamine (melamine-formaldehyde condensates). They are commercially available as aqueous solutions or powders with the names Kaurit® and Kauramin® (produced by BASF) and comprise urea- and/or melamine-formaldehyde precondensates. Typical phenol resins are phenol-formaldehyde condensates, phenol-resorcinol-formaldehyde condensates and the like. Cocondensates of aminoplast resins and phenol resins are also suitable. Examples of cocondensates of aminoplast resins and phenol resins are urea-melamine-formaldehyde condensates, melamine-urea-formaldehyde-phenol condensates and their mixtures. Their preparation and use for the production of moldings from finely divided lignocellulose materials are generally known. Urea-formaldehyde resins are preferred, and among 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 phenol resins, there is a transition from the soluble and fusible precondensates to infusible and insoluble products. In this process designated as curing, complete crosslinking of the precondensates is known to occur, which as a rule is accelerated by curing agents. Curing agents which may be used are the curing agents known to the person skilled in the art for urea-, phenol- and/or melamine-formaldehyde resins, such as acidic and/or acid-eliminating compounds, e.g. ammonium or amine salts. As a rule, the proportion of curing agent in an adhesive resin liquor is from 1 to 5% by weight, based on the proportion of liquid resin.
Suitable isocyanate resins are all conventional resins based on methylenediphenylene isocyanates (MDI). As a rule, they consist of a mixture of monomers and oligomeric di- or polyisocyanates, the so-called precondensates, which are capable of reacting with the cellulose, the lignin and the moisture content of the lignocellulose particles. Suitable isocyanate resins are commercially available, for example, as Lupranate brands (Elastogran).
Examples of reactive polycarboxylic acid resins are compositions comprising
Reactive polycarboxylic acid resins are known to the person skilled in the art and are described in, for example, EP-A-882 093, WO 97/45461, WO 99/09100, WO 99/02591, WO 01/27163 and WO 01/27198.
Polymers P which comprise maleic acid and/or maleic anhydride as monomers a) are particularly preferred.
Preferred monomers b) are ethylenically unsaturated C3-C6-monocarboxylic acids, such as acrylic acid or methacrylic acid, olefins, such as ethene, propene, butene, isobutene, cyclopentene or diisobutene, vinylaromatics, such as styrene, alkyl vinyl ethers, e.g. methyl vinyl ether or ethyl vinyl ether, acrylamide, 2-acrylamido-2-methylpropanesulfonic acid, vinyl acetate, butadiene, acrylonitrile or mixtures thereof. Particularly preferred monomers b) are acrylic acid, methacrylic acid, ethene, acrylamide, styrene and acrylonitrile or mixtures thereof.
Polymers P in which the monomer b) comprises at least one C3-C6-monocarboxylic acid, preferably acrylic acid, as comonomer b) are particularly preferred.
Alkanolamines having at least two OH groups, such as diethanolamine, triethanolamine, diisopropanolamine, triisopropanolamine, methyldiethanolamine, butyldiethanolamine and methyldiisopropanolamine, are mentioned as component A-(OH)2. Triethanolamine is preferred. Component A-(OH)2 furthermore includes alkoxylated, in particular ethoxylated, polyamines, as described in WO 97/45461, for example compounds of the formulae I and in particular Ia, Ie and If described there.
All water-insoluble polymers which are film-forming and are dispersible in water are in principle suitable as component P′ and as a binder of group iii). These include in particular emulsion polymers and the powders prepared therefrom, such as those referred to as polymers A1, for example, in WO 01/27198. The polymers P′ frequently have a glass transition temperature in the range from −10 to +150° C. and in particular in the range from +20 to +120° C. They are in particular copolymers based on styrene/butadiene, based on styrene/alkyl acrylate and those based on alkyl methacrylate/alkyl acrylate.
For the preparation of the polycarboxylic acid resins, the polymer P and the alkanolamine A-(OH)2 are preferably used in a ratio relative to one another such that the molar ratio of carboxyl groups of the component P and of the hydroxyl groups of the component A-(OH)2 is from 20:1 to 1:1, preferably from 8:1 to 5:1 and particularly preferably from 5:1 to 1.7:1 (the anhydride groups are calculated here as 2 carboxyl groups).
The binder is usually used in amounts of from 0.5 to 30% by weight, frequently from 1 to 20% by weight, in particular in amounts from 5 to 15% by weight, based on the treated lignocellulose materials.
Preferred binders of group i) can of course also be used as mixtures with one another or as mixtures with binders of groups ii) and in particular iii).
In addition, conventional assistants and additives can be used for the production of the moldings, such as the abovementioned curing agents, i.e. catalysts, which result in more rapid crosslinking of the binder.
The assistants include, for example, bactericides or fungicides and water repellents for increasing the water resistance of the moldings. Suitable water repellents are conventional aqueous paraffin dispersions or silicones. Furthermore, wetting agents, thickeners, plasticizing agents and retention aids can be used in the production. These are frequently added to the binder composition. The binder compositions frequently also comprise coupling reagents, such as alkoxysilanes, for example 3-aminopropyltriethoxysilane, soluble or emulsifiable oils as lubricants and dust-binding agents and wetting assistants.
Conventional additives comprise inert fillers, such as aluminum silicates, quartz, precipitated or pyrogenic silica, gypsum and barytes, talc, dolomite or calcium carbonate; color-imparting pigments, such as titanium white, zinc white, iron oxide black, etc.
Finally, conventional fireproofing agents, such as, for example, aluminum silicates, aluminum hydroxides, borates and/or phosphates, can be used in the production of the moldings.
The glue-coating is effected by the methods customary for this purpose, for example by mixing the finely divided, impregnated lignocellulose materials with the binder in conventional mixing apparatuses for mixing liquid with solid materials, by fluidizing the lignocellulose materials in an air stream and spraying the binder, preferably in the form of a liquid binder composition, into the fiber stream thus produced (“blow-line” method).
The glue-coated mixture of lignocellulose-containing materials and the binder composition can be predried at elevated temperature, for example at temperatures of from 10 to 200° C., for removal of volatile components prior to shaping. Depending on the type of binder composition, however, the removal of volatile components can also be dispensed with or can be carried out during the shaping step.
After the glue-coating and, if appropriate, predrying, a shaping step is effected, which is carried out in a manner known per se, as a rule at elevated temperature, for example at temperatures of from 50 to 300° C., preferably from 100 to 250° C. and particularly preferably from 140 to 225° C., and usually at elevated pressures of, in general, from 2 to 200 bar, preferably from 5 to 100 bar, particularly preferably from 20 to 50 bar.
Suitable methods of shaping are familiar to the person skilled in the art and comprise, for example, extrusion methods, thermoforming and in particular hot pressing, it being possible for these methods to be batchwise or continuous, for example as roller pressing, gliding film pressing, calender pressing, extrusion pressing or steam injection pressing. An overview of conventional methods is to be found, for example, in Ullmann's Encyclopedia of Industrial Chemistry, “Wood—Wood based Materials”, Sections 2.3.1, 2.3.2 and 2.3.3, 5th Edition on CD-ROM, Wiley-Verlag-Chemie, Weinheim 1997.
At the temperatures prevailing during the shaping and the pressure, adhesion of the lignocellulose particles and, depending on the type of binder, melting and/or crosslinking of the binder components takes place so that a stable molding forms on cooling and removal of the mold.
The moldings may be shaped in any desired manner and comprise sheet-like moldings, such as boards or mats, or have a 3-dimensional form, for example specially shaped articles. Examples of sheet-like moldings comprise OSB boards (oriented structural board), particle boards, wafer boards, insulating panels, medium density fiberboards (MDF) and high density fiberboards (HDF). The moldings according to the invention also include OSL boards and OSL shaped articles (oriented strand lumber) and PSL boards and PSL shaped articles (parallel strand lumber). The moldings also include shaped articles comprising WPC (wood-plastic composites).
The process according to the invention is particularly suitable for the production of moldings wherein the lignocellulose material is wood. Here, depending on the size of the lignocellulose-containing particles used, a distinction is made between OSB boards (oriented structural boards), particle boards, wafer boards, OSL boards and OSL shaped articles (oriented strand lumber), PSL boards and PSL shaped articles (parallel strand lumber), insulating panels and medium density fiberboards (MDF) and high density fiberboards (HDF) and the like.
The process according to the invention is also particularly suitable for the production of so-called WPC (wood-plastic composites), as described, for example, in WO 96/34045, and the literature cited there and in a general manner in Öster. Kunststoffzeitschrift 35, 2004, 10-13 and in Klauditzforum 5th Edition 6/2004. The processes known for the production of WPC can be carried out in an analogous manner with the lignocellulose materials treated according to the invention.
For the production of the WPCs, the finely divided lignocellulose material treated according to the invention, after a drying/curing step has been carried out beforehand, is mixed with at least one thermoplastic material, for example thermoplastic polymers based on poly-C2-C6-olefins, such as polyethylene, polypropylene and the like, or based on poly-C2-C4-haloolefins, such as polyvinyl chloride, polyvinylidene chloride or copolymers of vinyl chloride with vinylidene chloride, vinyl acetate and/or C2-C6-olefins, and then subjected to a shaping process, as a rule an injection molding or extrusion process. The amount of thermoplastic polymer generally accounts for from 20 to 90% by weight and in particular from 30 to 80% by weight, based on the total mass. Accordingly, the proportion of finely divided lignocellulose material treated according to the invention is in the range from 10 to 80% by weight and in particular from 20 to 70% by weight, based on the total weight of the WPC. In addition, conventional additives, such as adhesion promoters (e.g. organosilanes, maleic anhydride, isocyanates), pigments, light stabilizers, lubricants or fire-retardant components, can be added to the WPCs. The addition of biocides is on the other hand not required.
The finely divided lignocellulose materials treated according to the invention are particularly suitable for the production of wood-base materials, such as wood particle boards and wood fiberboards, including HDF, MDF, OSB, OSL and PSL (cf. Ullmann's Encyclopedia of Industrial Chemistry, loc. cit.), which are produced by gluing of comminuted wood, such as, for example, wood chips, wood shreds and/or wood fibers.
The production of particle boards is generally known and is described, for example, in H. J. Deppe, K. Ernst Taschenbuch der Spanplattentechnik, 2nd Edition, Verlag Leinfelden 1982, and can be used analogously in the process according to the invention.
In the production of particle board, the glue-coating of the previously dried chips is effected in continuous mixers. In general, different chip fractions are differently glue-coated in separate mixers and then poured separately (multilayer boards) or together. Chips whose average chip thickness is from 0.1 to 2 mm, in particular from 0.2 to 0.5 mm, and which comprise less than 6% by weight of water are preferably used. The binder composition is applied as uniformly as possible to the wood chips, for example by spraying the binder composition in finely divided form onto the chips. The glue-coated wood chips are then scattered to form a layer having a surface which is as uniform as possible, the thickness of the layer depending on the desired thickness of the final particle board. The scattered layer is, if appropriate, precompressed while cold and pressed to give a dimensionally accurate board at a temperature of, for example, from 100 to 250° C., preferably from 140 to 225° C. by application of pressures of, usually, from 10 to 750 bar. The required pressing times may vary within a wide range and are in general from 15 second to 30 minutes.
The wood fibers of suitable quality which are required for the production of medium density wood fiberboards (MDF) can be produced from bark-free wood shreds by grinding in special mills or so-called refiners at temperatures of about 180° C. In the case of MDF and HDF board production, the fibers are glue-coated in the blow-line after the refiner. For glue-coating, the wood fibers are generally fluidized in an air stream, and the binder composition is sprayed into the fiber stream thus produced (“blow-line” method). The glue-coated fibers then pass through a drier in which they are dried to moisture contents of from 1 to 20% by weight. In a few cases, the fibers are also first dried and subsequently glue-coated in special continuous mixers. A combination of blow-line and mixer glue-coating is also possible. The ratio of wood fibers to binder composition, based on the dry content or solids content, is usually from 40:1 to 3:1, preferably from 20:1 to 4:1. The glue-coated fibers are dried in the fiber stream at temperatures, of, for example, from 130 to 180° C., scattered to give a fiber mat, if appropriate precompressed while cold and compressed at pressures of from 20 to 40 bar to give boards or moldings.
In the case of OSB production, the wood chips (strands), if appropriate after drying, are separated into middle and outer layer material and glue-coated separately in continuous mixers. For completion of the boards, the glue-coated wood chips are then poured to give mats, if appropriate precompressed while cold and pressed with heated presses at temperatures of from 170 to 240° C. to give boards.
The glue-coated wood fibers can also be processed to give a transportable fiber mat, as described, for example, in DE-A 2 417 243. This semifinished product can then be further processed in a second spatially separate step carried out at a different time to give boards or shaped articles, such as, for example, interior trims of doors of motor vehicles.
Other lignocellulose materials, for example natural fibers, such as sisal, jute, hemp, ramie, straw, flax, coconut fibers, banana fibers and other natural fibers, can also be processed with the use of binders known per se to give boards and moldings. The natural fibers can also be used as mixtures with plastics fibers, for example polypropylene, polyethylene, polyester, polyamides or polyacrylonitrile. These plastics fibers may also act as cobinders in addition to the abovementioned binder composition. The proportion of the plastics fibers is preferably less than 50% by weight, in particular less than 30% by weight and very particularly preferably less than 10% by weight, based on all chips, shreds or fibers. The processing of the fibers can be effected by methods practiced in the case of the wood fiberboards. However, preformed natural fiber mats can also be impregnated with the binders according to the invention, if appropriate with addition of a wetting assistant. The impregnated mats are then pressed in the binder-moist or predried state, for example at temperatures of from 100 to 250° C. and pressures of from 10 to 100 bar, to give boards or shaped articles.
Owing to their high stability, the moldings according to the invention are suitable for a multiplicity of different applications, in particular for applications in which they are exposed to weathering and moisture, for example as a base for structural components in house building and in shipbuilding, for example for interior and exterior walls, floor construction, for the production of claddings in house building, shipbuilding and automotive construction, for example as exterior trims, interior trims, trunk and engine space linings, as a substrate for decorative panels, such as ceiling, wall and prefabricted parquet panels, as components and boards in the furniture industry and for the do-it-yourself sector, etc.
The following examples are intended merely to explain the examples according to the invention and are not to be understood as being limiting.
The stated moisture contents were determined according to DIN 52183.
The impregnating agent used was a 50% strength aqueous solution of a DMDHEU modified with diethylene glycol and methanol (mDMDHEU), which solution was mixed with 1.5% of MgCl2.6H2O.
Thermomechanically digested spruce wood chips having an average fiber length (90% value) and a moisture content of 11% were introduced into an impregnating unit by means of a metal basket. The impregnating unit was subjected to a reduced pressure of 100 mbar absolute for 30 minutes and then flooded with the impregnating agent. A pressure of 10 bar was then applied for one hour. The pressure phase was terminated and the residual liquid was removed. The chips thus obtained were then dried in a drier for 4 h at 50° C.
In a manner analogous to example 1, planing shavings of pinewood having average dimensions of 0.5 mm×5 mm×100 mm were impregnated and then dried.
The impregnated pinewood shavings obtained in example 2 were heated to 130° C. in a drying oven for 1 h, cured pinewood shavings being obtained.
5400 g of dried chips from example 1 were sprayed with 1628 g of the composition stated in table 1, and 3370 g thereof were poured into a mold (56.5 cm×44 cm). The material was pressed in a press at 190° C. up to a thickness of 18 mm in 230 s to give a particle board.
The particle board comprised 14% of solid resin/absolutely dry chips, 0.5% of solid wax/absolutely dry chips (absolutely dry=% by weight, based on dry chips).
1000 g of absolutely dry fibers from example 3 were sprayed with the glue batch stated in table 2 and dried to a moisture content of 8%. 920 g thereof were poured into a mold (30 cm×30 cm). The material was pressed in a press at 190° C. to a thickness of 12 mm in 300 s to give an MDF board.
The MDF board comprised 14% of solid resin/absolutely dry fibers and 0.5% of solid wax/absolutely dry fibers.
In each case 70 g of wood fibers from example 3 were thoroughly mixed with 13.2 g of a pulveruient composition according to example P2 to P6 of WO 01/27198.14 g of water were then also sprayed onto this fiber-binder mixture with continued mixing. The glue-coated fibers were dried at 70° C. to a residual moisture content of 10% (absolutely dry) and scattered to give a 19×19 cm fiber mat.
These fiber mats were compressed using a hydraulic press (manufacturer Wickert Maschinenbau GmbH, Landau, model WKP 600/3.5/3) at a pressing temperature of 220° C. for 120 sec between two metal plates with 2 mm spacers. For this purpose, a press pressure of 50 bar was first established. After the pressure had been relieved for 10 sec, a pressure of 200 bar was then maintained for a further 90 sec.
The fiberboards obtained were stored for 24 h under standard temperature and humidity conditions at 23° C. and 65% relative humidity and then tested. The water absorption was determined from the weight increase (in %, based on the original weight). The swelling, based on thickness, of the wood fiberboards was determined as a relative increase in the thickness of 2×2 cm test specimens after storage for 24 h in demineralized water analogously to DIN 52351.
Shavings, prepared by chipping pine panels modified with DMDHEU, prepared according to WO 2004/033170, by analogy to example 2, were pressed with the glues given in Table 3 by analogy to example 4 at 190° C. for 230 s to give particle boards (density 650 kg/m3). Likewise, non-modified pinewood shavings were pressed under similar conditions to give particle boards. The thus prepared particle boards were stored in demineralised water at ambient temperature for 24 h and the swelling was determined as a relative increase in the thickness.
1),4),5)aqueous urea resin glues, brands of BASF AG, Ludwigshafen
2)resin components, based on shavings (absolute dry)
3)aqueous melamine resin glue, brand of BASF AG, Ludwigshafen
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2005 010 042.2 | Mar 2005 | DE | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP2006/001979 | 3/3/2006 | WO | 00 | 8/31/2007 |
